seismic design of rc structures using ubc_aci provisions
TRANSCRIPT
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Ports, Customs & Free Zone Corporation TRAKHEES ‐ ‐ تــــراخيص مؤسســة الموانــئ و الجمارك والمنطقــة الحــرة
Seismic Design of RC Structures Using
UBC / ACI Provisions
By Dr. S. K. Ghosh
Organised by
TRAKHEES
CIVIL ENGINEERING DEPARTMENT – WHITBY & BIRD
Dubai – November 2008
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1. AN OVERVIEW OF CODES AND STANDARDS
2. COMPUTATION OF GRAVITY LOAD EFFECTS AND
DESIGN LOAD COMBINATIONS
3. COMPUTATION OF DESIGN WIND FORCES
4. AN OVERVIEW OF THE DESIGN LOAD COMBINATIONS AND THE SEISMIC DESIGN PROVISIONS OF THE 1997 UBC
5. EASY, STEP-BY-STEP DETERMINATION OF DESIGN BASE
SHEAR
6. 1997 UBC COMPUTATION OF DESIGN SEISMIC FORCES
7. SEISMIC DETAILS FOR REINFORCED CONCRETE BUILDINGS IN MODERATE SEISMIC APPLICATIONS
8. DESIGN OF TYPICAL STRUCTURAL MEMBERS
9. CODE SUPPORT SERVICES, CODE CHANGE PROCESS,
AND PLAN REVIEW
10. OVERVIEW OF THE SEISMIC DESIGN PROVISIONS OF THE 2006 INTERNATIONAL BUILDING CODE
11. DESIGN OF REINFORCED CONCRETE BUILDINGS UNDER
THE 1997 UBC
12. EARTHQUAKE DESIGN - EXAMPLE
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AN OVERVIEW OF CODES AND STANDARDS
S. K. Ghosh Associates Inc.Palatine, IL
www.skghoshassociates.com
CONSTRUCTION PERMIT
Plans and Specs approved for code compliance?
Permit issued
Redesign and resubmit
Appeal
No
Yes
Win
Lose
Application for permit for proposed construction
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CERTIFICATE OF OCCUPANCY
Construction inspections approved for code
compliance?
Certificate of occupancy issued
Reconstruct and correct
Appeal
No
YesWin
Lose
BUILDING CODE - AUTHORITY
• State legislature has sole authority to enact and enforce building codes.
• State may choose to delegate a portion of this power to constituent local government units, such as cities.
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BUILDING CODE
• Enacted by a state or local government’s legislative body to regulate construction within its jurisdiction.
• Minimum acceptable requirements necessary to preserve public health, safety, and welfare in the built environment.
• Primary application to new or proposed construction.
APPLICABILITY OF STATEWIDE BUILDING CODE
• Buildings based on construction methods such as factory-manufactured buildings,
• All construction except single-family dwellings,
• A single or narrow aspect of building construction such as fire safety,
• All construction.
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ADMINISTRATION AND ENFORCEMENT
• Local government responsibility, subject to varying degrees of state agency supervision and oversight.
MODEL BUILDING CODES
• State and local governments adopt model building codes, rather than relying on custom-drafted building codes.
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MODEL CODES
• Originally promulgated by:
the National Board of Fire Underwriters, later to become American Insurance Association
• New editions at approximately 10-year intervals.
• Withdrawn in 1984.
MODEL CODES AND THEIR AREAS OF INFLUENCE
LocallyWritten Code
UBC BOCA
StandardUBC &Standard
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MODEL CODES
• A new edition every three years, with annual supplements.
• Annual code change cycle.
A REBIRTH OF THE MODEL BUILDING CODE SYSTEM IN THE UNITED STATES
The International Code Council:
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FORMATION OF ORGANIZATIONS
Model Code Organizations:
• BOCA – 1915
• CABO – 1972
• ICBO – 1923
• ICC – 1994
• SBCCI - 1940
INTERNATIONAL CODE COUNCIL
• The International Code Council (ICC) was formed in December 1994 with the purpose of developing a single set of comprehensive and technical codes.
• The International Codes provide a complete set of construction codes without regional limitations.
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IBC 2006
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NFPA 5000 BUILDING CODE
from
National Fire Protection Association
Quincy, MA
First (2003) Edition Published in 2002
NFPA 5000
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FORMATION OF ORGANIZATIONS
National Standards:
• ACI - 1905
• AFPA - 1993 (NFoPA 1902)
• ASCE - 1892
• ANSI - 1918
• ASHRAE - 1895
• ASTM - 1898
FORMATION OF ORGANIZATIONS
National Standards:
• AWS - 1919
• Factory Mutual - 1835
• Gypsum Asscn. - 1930
• NFPA - 1896
• UL - 1894
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ASCE 7
ACI 318
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STANDARDS
• Standards reference other standards. For instance, ACI 318 references a whole host of ASTM standards.
RESOURCE DOCUMENTS
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ICC EVALUATION SERVICE
A nonprofit, public-benefit corporation, ICC-ES does technical evaluations of building products, components, methods, and materials.
The evaluation process culminates with the issuance of reports on code compliance, which are made available free of charge to code officials, contractors, specifiers, architects, engineers, and anyone else with an interest in the building industry and construction.
ICC-ES evaluation reports provide evidence that products and systems meet code requirements.
For more information…
www.skghoshassociates.com
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Computation of Gravity Load Effects and Design Load
Combinations
S. K. Ghosh Associates Inc.
Palatine, IL
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Dead Loads
• 1997 UBC Section 1606 – Movable
partition loads of 0.96 kN/m2 included
in dead loads for floors in office
buildings
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Live Loads
• 1997 UBC Section 1607Table 16-A: Uniform and Concentrated LoadsTable 16-B: Special LoadsTable 16-C: Minimum Roof Live Loads
UBC 1607.5 Reduction of Live Loads
• Applies to live loads set forth in Table 16-A for floors and Table 16-C, Method 2, for roofs
1. Reduction not permitted in Group A (assembly) occupancies
2. Reduction not permitted when live load exceeds 4.79 kN/m2, except design live load from storage for columns may be reduced by 20%
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UBC 1607.5 Reduction of Live Loads
• Applies to live loads set forth in Table 16-A for floors and Table 16-C, Method 2, for roofs3. The live load reduction shall not
exceed 40 percent in garages for the storage of private pleasure cars having a capacity of not more than nine passengers per vehicle
UBC 1607.5 Reduction of Live Loads
For live loads not exceeding 100 psf, design live loads for any member supporting 13.94 m2 or more may be reduced by
R (%) = r (A − 13.64)where r = 0.861 percent for floors, given in Table
16-C for roofs
Such reduction shall not exceed 40% for horizontal members, 60% for vertical members, nor R (%) = 23.1 (1 + D/Lo)
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Floor Live Load Reduction
18.6 55.8 74.4 93.037.2
100
60
40
Floor Members
Tributary Area, A, m2
Per
cent
of L
ive
Load
UBC 1607.6 Alternate Floor Live Load Reduction
• ASCE 7For KLL AT > 37.16 m2
L shall not be less than 0.50Lo for members supporting one floor nor than 0.40Lo for members supporting two or more floors
⎟⎟⎠
⎞⎜⎜⎝
⎛+=
TLL0 AK
57.40.25LL
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Influence Areas
Interior supporting member
Edge supporting member
Corner supporting member
Influence and Tributary Areas
Limits of Influence Area
Limits of Tributary Area
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Live Load Element Factor, KLL
1
All other members not identified above including:
- Edge beams with cantilever slabs
- Cantilever beams
- Two-way slabs
- Members without provisions for continuous shear transfer
normal to their span
2
2
2
Corner columns with cantilever slabs
Edge beams without cantilever slabs
Interior beams
3Edge columns with cantilever slabs
4
4
Interior Columns
Exterior columns without cantilever slabs
KLLElement
Limitations on Live Load Reductions
• ASCE 7-054.8.2 – Live loads that exceed 4.79 kN/m2 shall not
be reduced, except live loads for members supporting two or more floors may be reduced by 20%
4.8.3 – Live loads shall not be reduced in passenger car garages, except live loads for members supporting two or more floors may be reduced by 20%
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Limitations on Live Load Reductions
• ASCE 7-05
4.8.4 – Live loads of 4.79 kN/m2 or less shall not be
reduced in public assembly occupancies
4.8.5 – Live loads shall not be reduced for one-way
slabs except as permitted in 4.8.2. Live loads of
4.79 kN/m2 or less shall not be reduced for roof
members except as specified in 4.9
Snow Loads
• UBC left it to local jurisdictions
(sections 1908, 1914)
• ASCE 7 has detailed provisions
• Of little interest in Dubai
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Wind Loads
• 1997 UBC Section 1609. Refers to
Sections 1615 – 1625.
• Simplified version of wind design
provisions from ASCE 7-88
• Wind design in Dubai by ASCE 7-05
Typical Plan of Example Building
A
B
C
D
1 2 3 4 5 6
N
7 87.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m
6.71
m6.
71 m
6.71
m
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Typical Elevation of Example Building
11@
3.66
m=
40.2
6 m
10
11
12
7
8
9
4
5
6
1
2
3
4.88
m
Design Data
• Building Location Dubai, UAE
• Material PropertiesConcrete: fc
’ = 30 N/mm2, wc = 23.55 kN/m3
Reinforcement: fy = 415 N/mm2
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Design Data• Service Loads
Live loads: roof = 957.6 N/m2
floor = 2394 N/m2
Superimposed dead loads:
roof = 478.8 N/m2 + 889.64 kN for penthouse
floor = 1436.4 N/m2 (957.6 N/m2 permanent partitions + 478.8 N/m2 ceiling, etc.)
Design Data
• Member Dimensions
Slab: 205 mm
Beams: 560 × 560 mm
Interior columns: 660 × 660 mm
Edge columns: 610 × 610 mm
Wall thickness: 305 mm
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Beam C4 – C5
Tributary area = 2 ×(0.5 × 3.35 × 3.35 × 2 + 1.22 × 3.35) = 30.62 m2
C
54
7.92 m
6.71 m
3.35m 1.22 m
3.35m
3.35m
6.71 m
Beam C4 – C5
• Dead load:Beam self weight:
23.55 × 0.560 × 0.355 = 4.68 kN/m
Slab self weight within the tributary area: 23.55 × 0.205 = 4.78 kN/m2
4.78 × 30.62 m2 = 146.39 kN146.39 KN / 7.92 m = 18.48 kN/m
Superimposed dead load:1436.4 N/m2 × 30.62 m2 × 1/1000 = 43.98 kN43.98 KN / 7.92 m = 5.55 kN/m
wD = 4.68 + 18.48 + 5.55 = 28.71 kN/m
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Beam C4 – C5Bending moments and shear forces:
From ACI 318 Section 8.3.3:
Negative moment at the supports:
(wD × ln2) / 11 = (28.71 × 7.262) / 11 = 137.63 m-kN
Positive moment at midspan:
(wD × ln2) / 16 = (28.71 × 7.262) / 16 = 94.62 m-kN
Shear force = (wD × ln) / 2 = (28.71 × 7.26) / 2
= 104.27 kN
ln is clear span length (7.92 × 1000– 660 = 7260 mm = 7.26 m)
Beam C4 – C5
• Live load:
Lo = 2.394 kN/m2
kLL = 2, AT = 30.62 m2 kLLAT = 61.24 m2 > 37.16 m2
Therefore, live load reduction is permitted.L = Lo (0.25 + 4.57 / (61.24)0.5 ) = 2.394 × 0.834
= 1.997 kN/m2 > 0.5 Lo
wL = (1.997 × 30.62) / 7.92 = 7.721 kN/m
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Beam C4 – C5Bending moments and shear forces:
From ACI 318 Section 8.3.3:
Negative moment at the supports:
(wL × ln2) / 11 = (7.721 × 7.262) / 11 = 37.0 m-kN
Positive moment at midspan:
(wL × ln2) / 16 = (7.721 × 7.262) / 16 = 25.43 m-kN
Shear force = (wL × ln) / 2 = (7.721 × 7.26) / 2
= 28.03 kN
ln is clear span length (7.92 ×1000 – 660 = 7260 mm = 7.26 m)
Beam C4 – C5Summary of Design Bending Moments and Shear Forces for
Beam C4-C5 at the Second Floor Level
Live (L)
Dead (D)
Load Case
25.4Midspan28.0 –37.0Support
94.6Midspan104.3–137.6 Support
Shear Force (kN)
Bending Moment (m-kN)
Location
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1612.2.1 Strength Design or LRFD Load Combinations (1997 UBC)
1.4D (Equation 12-1) 1.2D + 1.6L + 0.5(Lr or S) (Equation 12-2)1.2D +1.6(Lr or S) + (f1L or 0.8W) (Equation 12-3) 1.2D + 1.3W + f1L + 0.5(Lr or S) (Equation 12-4) 1.2D + 1.0E + (f1L + f2S) (Equation 12-5) 0.9D ± (1.0E or 1.3W) (Equation 12-6)
f1 = 0.5 except in special circumstancesf2 = 0.2 except in special situations
Note exceptions for concrete structures
1612.2.2 Other Loads. Where F, H, P or
T are to be considered in design, each
applicable load shall be added to the
above load combinations factored as
follows: 1.3F, 1.6H, 1.2P and 1.2T
1612.2.1 Strength Design or LRFD Load Combinations (1997 UBC)
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2.3.2 Strength Design or LRFD Load Combinations
(ASCE 7-05)1. 1.4(D + F)
2. 1.2(D + F + T) +1.6(L + H) + 0.5(Lr or S or R)
3. 1.2D +1.6(Lr or S or R) + (L or 0.8W)
4. 1.2D + 1.6W + [1.0]L + 0.5(Lr or S or R)
5. 1.2D + 1.0E + L + 0.2S
6. 0.9D + 1.6W + 1.6H
7. 0.9D + 1.0E + 1.6H
2.3.2 Strength Design or LRFD Load Combinations (ASCE 7-05)
Exceptions:
• Now: Identify directionality effect explicitly in Kd. Round load factor from 1.53 to 1.6.
1. The load factor on L in combinations (3), (4), and (5) is permitted to equal 0.5 for all occupancies in which L0 is less than or equal to 100 psf, with the exception of garages or areas occupied as places of public assembly.
2. The load factor on H shall be set equal to zero in combinations (6) and (7) if the structural action due to H counteracts that due to W or E.
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ASCE 7-05 6.5 Analytical Procedure
• Directionality factor Kd introduced in 1998– Added to velocity pressure equation
•qz = 0.613 Kz Kzt Kd V2 I– Separate out effect of wind load factor– Requires adjustment to wind load factor ( 1.3 → 1.6 )– Table 6-4
Reason: Explicitly identify directionality effect in future editions.
ASCE 7-05 2.3.2 Strength Design Load Combinations
Wind load factor:• Old (1995): LF = 1.3 → included
directionality effect
0.85 (directionality) x 1.53 (LF w/o directionality) = 1.3
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Seismic Strength Design Load Combinations (1997 UBC)
• 1.2D + 1.0E + (f1L + f2S) Equation (12-5)
• 0.9D ± 1.0E Equation (12-6)
• E = ρEh + 0.5CaID in Equation (12-5)
• E = ρEh - 0.5CaID in Equation (12-6)
• ρ = 1 in Seismic Zones 1 and 2
Seismic Strength Design Load Combinations (2006 IBC, ASCE 7-05)
• 1.2D + 1.0E + f1L + f2S Equation (16-5)
• 0.9D + 1.0E Equation (16-7)
• E = ρQE + 0.2SDSD in Equation (16-5)
• E = ρQE - 0.2SDSD in Equation (16-7)
• ρ = 1 in Seismic Design Category (SDC) A, B and C
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Δs (UBC)
V
Eh (UBC)QE (IBC) δxe (IBC)
Effect of Vertical Earthquake Ground Motion (1997 UBC)
• Gravity and Earthquake Effects Additive
U = 1.2D + 1.0E + 0.5L +0.2S
= 1.2D + (ρEh + 0.5CaID) + 0.5L + 0.2S
= (1.2 + 0.5CaI)D + ρEh + 0.5L + 0.2S
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Effect of Vertical Earthquake Ground Motion (ASCE 7-05)
• Gravity and Earthquake Effects Additive
U = 1.2D + 1.0E + 0.5L +0.2S
= 1.2D + (ρQE + 0.2SDSD) + 0.5L + 0.2S
= (1.2 + 0.2SDS)D + ρQE + 0.5L + 0.2S
Effect of Vertical Earthquake Ground Motion (1997 UBC)
• Gravity and Earthquake Effects Counteractive
U = 0.9D - 1.0E
= 0.9D - (ρEh + 0.5CaID)
= (0.9 - 0.5CaI)D - ρEh
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Effect of Vertical Earthquake Ground Motion (ASCE 7-05)
• Gravity and Earthquake Effects Counteractive
U = 0.9D - 1.0E
= 0.9D - (ρQE + 0.2SDSD)
= (0.9 - 0.2SDS)D - ρQE
Beam C4 – C5Summary of Design Bending Moments and Shear Forces for Beam C4-C5
at the Second Floor Level
Shear Force (KN)
Bending Moment (m –KN)
LocationLoad combination
154.2Midspan167.0-224.3Support1.2D + 1.6L
132.4Midspan146.0-192.6Support1.4D
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Column C4
Tributary area = 7.92 × 6.71 = 53.14 m2
C
43
7.92 m
6.71 m
6.71 m
7.92 m
6.71 m
7.92 m
5
Column C4• Dead load:
Column self weight:0.66 × 0.66 × 11 × (3.66 – 0.560) × 23.55 = 349.92 kN
Slab self weight within the tributary area:4.781 ×53.14 × 11 = 2794.69 kN
Beam self weight within the tributary area:(0.560×0.355 ×7.92+0.560×0.355×(6.71-0.560))×23.55= 65.94 kN11 × 65.94 = 725.34 kN
Superimposed dead load:Roof: 0.479 + 889.64 / (20.73×56.08)* = 1.244 kN/m2
Floor: 1.436 kN/m2
1.244 × 53.14 + 1.436 × 53.14 × 10 = 829.20 kN*Done this way only because location of penthouse is notincluded
D = 349.92 + 2794.69 + 725.34 + 829.20 = 4699.15 kN
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Column C4
• Live load:
Story supporting roof:
R1 = 1.2 – 0.011 At = 1.2 – 0.011 × 53.14 = 0.615
R2 = 1.0
957.6 N/m2 × 0.615 × 1.0 = 588.92 N/m2
0.589 × 53.14 = 31.3 kN
Column C4
Story supporting floor 11:
AT = 53.14 + 53.14 = 106.28 m2
kLL = 4kLLAT = 425.12 m2 > 37.16 m2, therefore live load reduction is permitted.
Lo = 2.394 × 53.14 = 127.22 kNL = Lo (0.25 + 4.57 / (4 ×106.28)0.5)
= 127.22 × 0.472 > 0.40 Lo
L = 60.05 kN
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Column C4
Story supporting floor 10:AT = 53.14 × 3 = 159.42 m2
kLL = 4L = Lo (0.25 + 4.57 / (4 ×159.42)0.5)
= 127.22 × 0.431 = 54.83 > 0.40 Lo
Story supporting floor 9:AT = 53.14 × 4 = 212.56 m2
kLL = 4L = Lo (0.25 + 4.57 / (4 ×212.56)0.5)
= 127.22 × 0.407 = 51.78 > 0.40 Lo
Column C4
Story supporting floor 8:AT = 53.14 × 5 = 265.7 m2
kLL = 4L = Lo (0.25 + 4.57 / (4 ×265.7)0.5)
= 127.22 × 0.39 < 0.40 Lo
= 0.4 × 127.22 = 50.89 kN
Total live load:L = 31.3 + 60.05 + 54.83 + 51.78 + 7 × 50.89
= 554.19 kN
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Column C4Summary of Design Axial Forces, Bending Moments, and Shear Forces on
Column C4 Supporting the Second Floor Level
00554Live (L)004699Dead (D)
Shear Force (KN)
Bending Moment (m-KN)
Axial Force (KN)
Load Case
Column C4Summary of Design Axial Forces, Bending Moments, and Shear
Forces on Column C4 Supporting the Second Floor Level
0065251.2D + 1.6L
0065791.4D
Shear Forces
(KN)
Bending Moment (m-KN)
Axial Force (KN)Load combination
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Shear wall B7 – C7
Tributary Area = 7.92 × 13.42 = 106.29 m2
B
76
7.92 m
6.71 m
6.71 m
7.92 m
8
6.71 m
A
C
D
7.92 m
13.42 m
Shear wall B7 – C7• Dead load:
shear wall self weight (base):(2×0.66×0.66+0.305×6.05)×(45.14-0.560×12)×23.55 = 2458.59 kN
Slab self weight within the tributary area:4.781 × 106.29 × 12 = 6098.07 kN
Beam self weight within the tributary area:(0.560×0.355×13.42+2×0.560×0.355×(7.92-0.560))×23.55 = 131.89 kN12 × 131.89 = 1582.68 kN
Superimposed dead load:Roof: 0.479 + 889.64 / (20.73×56.08)* = 1.244 kN/m2
Floor: 1.436 kN/m2
1.244 × 106.29 + 1.436 × 106.29 × 11 = 1811.18 kN* Done this way only because location of penthouse is notincluded
D = 2458.59 + 6098.07 + 1582.68 + 1811.18 = 11,950.5 kN
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Shear wall B7 – C7
• Live load:
Story supporting roof:
R1 = 0.6 (At > 55.74 m2)
R2 = 1.0
957.6 N/m2 × 0.6 × 1.0 = 574.56 N/m2
0.575 × 106.29 = 61.12 kN
Shear wall B7 – C7
Story supporting floor 11:
AT = 106.29 + 106.29 = 212.58 m2
kLL = 3kLLAT = 637.74 m2 > 37.16 m2, therefore live load reduction is permitted.Lo = 2.394 × 106.29 = 254.46 kNL = Lo (0.25 + 4.57 / (3 ×212.58)0.5)
= 254.46 × 0.431 > 0.40 Lo
L = 109.67 kN
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Shear wall B7 – C7
Story supporting floor 10:AT = 106.29 × 3 = 318.87 m2
kLL = 3L = Lo (0.25 + 4.57 / (3 ×318.87)0.5)
= 254.46 × 0.398 < 0.40 Lo
= 0.4 × 254.46 = 101.78 kN
Total live load L = 61.12 + 109.67 + 101.78 ×10 = 1188.59 kN
Shear wall B7 – C7Summary of Design Axial Forces, Bending Moments, and
Shear Forces at Base of Shear Wall on Line 7 (SDC C)
001189Live (L)0011,951Dead (D)
Shear Forces (kN)
Bending Moment (m-kN)
Axial Force (kN)
Load Case
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Shear wall B7 – C7Summary of Design Axial Forces, Bending Moments, and
Shear Forces at Base of Shear Wall on Line 7 (SDC C)
0016,2441.2D + 1.6L
0016,7311.4D
Shear Force (kN)
Bending Moment (m-kN)
Axial Force (kN)
Load combination
For more information…
www.skghoshassociates.com
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Computation of Design Wind Forces
S. K. GhoshS. K. Ghosh Associates Inc.
Palatine, IL
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Wind Flow Around Building
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External Pressure due to Wind
External Pressure due to Wind
ps = pressure at stagnation point, psf (N/m2)pa = ambient pressure, psf (N/m2)ρ = air density, lb-sec2/ft4 (kg-sec2/m4)V = ambient wind speed, ft/sec (m/sec)
2
2
2
2
Vρppp
Vρpp
as's
as
=−=
+=
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Velocity Pressure (ASCE 7-05)
• ASCE 7 includes two factors:– Topographic Factor - Kzt
• Hills and Escarpments• Complex Equations
– Directionality Factor - Kd
• 0.85 for all building structures
( )m/sec in VN/m inq
IKKKV613.0q
,2 z
dztz2
z =
Fastest-mile WindInstantaneous velocity of wind at a point as a function of time:
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Fastest-mile Wind
• VT = max. wind speed based on averaging time of T sec• VH = max. wind speed based on averaging time of 1 hour
Fastest-mile Wind
• Max. wind speed averaged over one mile of
wind passing through anemometer.
• Averaging time of fastest-mile wind: T(sec)
3600/Vf
Vf – fastest-mile wind speed in mph
For Vf = 60 mph, T = 3600/60 = 60 sec
For Vf = 120 mph, T = 3600/120 = 30 sec
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Return Period
• Also known as mean recurrence interval (MRI). • Used for the statistical determination of the
predicted wind speed. • Most U.S. inland locations, MRI of 50 years is used
for normal use structures. • MRI for critical use facilities such as hospitals is
100 years.• MRI for low risk buildings such as barns is 25
years.
Importance Factor• For MRI of 25, 50 , and 100 years -
• 3 Maps???? - No!
• MRI is adjusted by using importance factor, I.
• Ratio of difference in velocity pressure from one
MRI to another is a fairly consistent ratio for non-
hurricane locations.
• Inclusion of “I” in the wind pressure equation has
the mathematical effect of adjusting the wind
speed up or down.
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Variation of Wind Velocity with Height for a Steady Wind
Gust
• Rapid fluctuation of wind• Ordinary structures sensitive to peak gusts of
about 1 sec duration.• Use of fastest-mile wind in design inadequate
Gust speed, Vg = Gv V• Pressure generated by gust, pg = Gp p
p ∝V 2 ∴ Gp = Gv2
• Flexible structures more sensitive to gust.
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Gust Effect Factor
• Accounts for the loading effects in the along-wind
direction (parallel to the direction of the wind) due to
wind turbulence-structure interaction.
• Also accounts for along-wind loading effects due to
dynamic amplification for flexible structures.
• Does not account for other dynamic effects such as
across-wind Loads.
Dimensionless Pressure or Pressure Coefficient
221
'
221
ap V)(
pV)(ppC
ρρ=
−= p = actual pressure at any
arbitrary point on building, psf
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Internal Pressure
Basic Wind Equation
• For buildings with External and Internal
Pressure:
qi = Velocity pressure calculated for
internal pressure.
piiGCqqGCp p −=
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ASCE 7-056.2 Definitions
• Basic Wind Speed V : 3-second gust speed at 10 m above the ground in Exposure C.
– Removed reference to “50-yr mean recurrence
interval”
– Loads calculated from the wind speed map, when
multiplied by the wind load factor, represent an
“ultimate load” having approximately a 500 year
return period.
– Map contours include hurricane importance factor
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ASCE 7-05Mean Roof Height
ASCE 7-056.5 Method 2: Analytical Procedure
• Design Pressure – MWFRS –Rigid Buildings of All Height (6.5.12.2.1):
p = q GCp - qi (GCpi)Velocity Pressure (6.5.10):
qz = 0.613KzKztKdV2I N/m2, V in m/sec
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ASCE 7-05 6.5 Analytical Procedure
• Design Pressure – MWFRS – Rigid Buildings of All Height (6.5.12.2.1):
qi = qh for windward walls, side walls, leeward walls, and roofs of enclosed buildings and for negative pressure evaluation in partially enclosed buildings
qi = qz for positive pressure evaluation in partially enclosed buildings at height z from the ground. Can be conservatively taken as qh
Wind-resistant Design
• Wind Pressures on a Building
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ASCE 7-05 6.5 Analytical Procedure
• Design Procedure (6.5.3):1. Wind Speed V (Figure 6-1 map), Wind Directionality Factor Kd (6.5.4.4, Table 6-4)2. Importance Factor I (6.5.5, Table 6-1)3. For each wind direction:
Exposure Category (6.5.6)
Velocity Pressure Exposure Coefficient Kh, Kz (6.5.6.6, Table 6-3)
ASCE 7-05 Fig. 6-1 Basic Wind Speed
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Basic Wind Speed
Dubai
45 m/sec
(100 mph)
ASCE 7-05 Table 6-4 Wind Directionality Factor, Kd
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ASCE 7-05 Table 6-1 Importance Factor, I
100 mph = 45 m/sec
ASCE 7-056.5.6.2 Surface Roughness Categories
• A ground surface roughness within
each 45-degree sector shall be
determined for a distance upwind of
the site as defined ….
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ASCE 7-056.5.6.2 Surface Roughness Categories
• Surface Roughness B:
Urban and suburban areas, wooded areas
or other terrain with numerous closely
spaced obstructions having the size of
single-family dwellings or larger.
ASCE 7-056.5.6.2 Surface Roughness Categories
• Surface Roughness C:Open terrain with scattered obstructions having heights generally less than 9.1 m. This category includes flat open country, grasslands, and all water surfaces in hurricane-prone regions
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ASCE 7-056.5.6.2 Roughness Categories
• Surface roughness D:
Flat, unobstructed areas and water
surfaces outside hurricane-prone regions.
This category includes smooth mud flats,
salt flats, and unbroken ice
ASCE 7-056.5.6.3 Exposure Categories
• Exposure B:Shall apply where Surface Roughness B prevails in the upwind direction for at least 792 m or 20 times the building height, whichever is greaterException. For buildings with h ≤ 9.1 m, the upwind distance may be reduced to 457 m.
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ASCE 7-056.5.6.3 Exposure Categories
• Exposure C:
Shall apply for all cases where
Exposure B or D does not apply
ASCE 7-056.5.6.3 Exposure Categories
• Exposure D:shall apply where Surface Roughness D prevails in the upwind direction for at least 1524 m or 20 times the building height, whichever is greater. Exposure D shall extend into downwind areas of Surface Roughness B or C for a distance of 200 m or 20 times the building height, whichever is greater.
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ASCE 7-05 Table 6-3Velocity Pressure Exposure
Coefficients, Kh and Kz
ASCE 7-05 Table 6-3 Velocity Pressure Exposure Coefficients, Kh and Kz
Table 6-2 Terrain Exposure ConstantsThe velocity pressure exposure coefficient
may be determined from the following formulas:For 4.6 m ≤ z ≤ zg, Kz = 2.01(z/zg)2/α
For z < 4.6 m, Kz = 2.01(4.6/zg)2/α
Note: z shall not be taken less than 9.1 m for Case 1 in Exp. B
21311.5D
2749.0C
3667.0B
Zg, mαExposure
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ASCE 7-05 6.5 Analytical Procedure
(Continued from Slide 23)
• Design Procedure (6.5.3):4. Topographic Factor, Kzt (6.5.7, Figure 6-4)5. Gust Effect Factor G or Gf (6.5.8)6. Enclosure Classification (6.5.9)7. Internal Pressure Coefficient GCpi (6.5.11.1, Figure 6-5)8. External Pressure Coefficients Cp, GCpf (6.5.11.2) or force coefficients Cf (6.5.11.3)
ASCE 7-05 Fig. 6-4 Topographic Factors, Kzt
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ASCE 7-05 Fig. 6-4 Topographic Factors, Kzt
ASCE 7-05 6.5.8 Gust Effect Factor, G or Gf
• For rigid structures as defined in Section 6.2, G shall be taken as 0.85 or calculated by Eqs. 6-4, 6-5, 6-6 and 6-7, using Table 6-2.
• For flexible or dynamically sensitive structures as defined in Section 6.2, Gf shall be calculated by Eqs. 6-8, 6-9, 6-10, 6-11, 6-12, 6-13a, 6-13b and 6-14, using Table 6-2.
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ASCE 7-05 6.2 Definition-Enclosure Classification
• Buildings, Open:A building having each wall at least 80% open.Mathematically, Ao > 0.8Ag where:Ao = Total area of openings in a wall that receives positive external pressure, in m2
Ag= Gross area of that wall in which Ao is identified, in m2
ASCE 7-05 6.2 Definition-Enclosure ClassificationBuildings, Partially Enclosed:If the following two conditions are satisfied:1. Ao > 1.1Aoi
2. Ao > 0.37 m2 or >0.01Ag, whichever is smaller, & Aoi < 0.2Agi
where:Aoi = The sum of the areas of openings in the building envelope (walls & roof) not including Ao, in m2
Agi = The sum of the gross surface areas of the building envelope (walls & roof) not including Ao, in m2
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ASCE 7-05 6.2 Definition-Enclosure Classification
• Buildings, Enclosed:
A building that does not comply with
the requirements for open or partially
enclosed buildings.
ASCE 7-05 6.5.9.3 Wind Borne Debris Regions
– Glazing in lower 18.3 m or within
9.2 m above aggregate surface
roofs located within 458 m of a
Category II, III, IV building requires
impact resistant glazing or
covering
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ASCE 7-05Figure 6-5 Internal Pressure Coefficients,
GCpi
ASCE 7-05External Pressure Coefficients
Cp for main wind force resisting systems –Fig. 6-6
GCpf for low-rise buildings – Fig. 6-10GCp for components & cladding – Fig. 6-11
through 6-17CN for main wind force resisting systems – Fig. 6-18
for components & cladding – Fig. 6-19Cf - Figs. 6-20 through 6-23
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ASCE 7-05 Fig. 6-6External Pressure
Coefficient, Cp for
MWFRS
ASCE 7-05 Fig. 6-6 Cp for MWFRS: Walls
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ASCE 7-05 Fig. 6-6 Cp for MWFRS: Roofs
ASCE 7-05 Fig. 6-6 Cp for MWFRS
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ASCE 7-05 6.5 Analytical Procedure
(Continued from Slide 37)
• Design Procedure (6.5.3)
9. Velocity Pressure qz, qh (6.5.10)
qz = 0.613 Kz Kzt Kd V2 I Eq. 6-15
ASCE 7-05 6.5 Analytical Procedure
• Design Procedure (6.5.3)10. Design wind pressure p (6.5.12, 6.5.13)
Enclosed or Partially Enclosed Buildings, MWFRS:
Rigid, All heights: p = q GCp - qi(GCpi) Eq. 6-17
Parapets: pp = qp GCpn Eq. 6-20
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ASCE 7-05 6.5 Analytical Procedure• Design Procedure (6.5.3)
10.Enclosed and Partially Enclosed Buildings - C & C
(6.5.12.4):
– Low rise and buildings with h ≤ 18.3 m
p = qh[(GCp) - (GCpi)] Eq. 6-22
– Buildings with h > 18.3 m
p = q(GCp) - qi(GCpi) Eq. 6-23
– Parapets
p = qp(GCp - GCpi) Eq. 6-24
Typical Plan of Example Building
A
B
C
D
1 2 3 4 5 6
N
7 87.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m
6.71
m6.
71 m
6.71
m
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Typical Elevation of Example Building
11@
3.66
m=
40.2
6 m
10
11
12
7
8
9
4
5
6
1
2
3
4.88
m
Design Data
• Building LocationDubai, UAE
• Material PropertiesConcrete: fc
’ = 30 MPa, wc = 23.55 KN/m3
Reinforcement: fy = 415 MPa
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Design Data
• Service LoadsLive loads: roof = 957.6 N/m2
floor = 2394 N/m2
Superimposed dead loads:
roof = 478.8 N/m2 + 889.64 KN for penthouse
floor = 1436.4 N/m2 (957.6 N/m2 permanent partitions + 478.8 N/m2 ceiling, etc.)
Design Data
• Wind Design DataBasic wind speed V = 45 m/sec for DubaiExposure B (IBC 1609.4, ASCE 6.5.6.3)For Occupancy Category II, I = 1.0 (IBC Table 1604.5, ASCE Table 6-1)
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Design Data
• Member Dimensions
Slab: 205 mm
Beams: 560 × 560 mm
Interior columns: 660 × 660 mm
Edge columns: 610 × 610 mm
Wall thickness: 305 mm
Wind Load Analysis
1. Basic wind speed, V, and wind directionality factor, Kd
V = 45 m/sec at location of structure per IBC Figure 1609 or ASCE Figure 6-1.
The wind directionality factor, Kd = 0.85 for main wind-force-resisting systems of buildings per ASCE Table 6-4.
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Wind Load Analysis
2. Importance factor, I
I = 1.0 per ASCE Table 6-1 for Occupancy
Category II
Wind Load Analysis3. Exposure category and velocity
pressure exposure coefficient, Kz
Values of Kz are to be determined from ASCE Table 6-3. In lieu of linear interpolation, Kz may be calculated at any height z ft above ground level by the following equations:
m 4.6 for 01.2
m 4.6 for 1501.2
/2
/2
⎪⎪⎪
⎩
⎪⎪⎪
⎨
⎧
≤≤⎟⎟⎠
⎞⎜⎜⎝
⎛
<⎟⎟⎠
⎞⎜⎜⎝
⎛
=
gg
g
z
zzzz
zz
Kα
α4.6
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Wind Load Analysis
α = 3-second gust speed power law exponentfrom ASCE Table 6-2
= 7.0 for Exposure B
Zg = nominal height of the atmosphericboundary layer from ASCE Table 6-2
= 366 m for Exposure B
Wind Load AnalysisVelocity Pressure Exposure Coefficient Kz
0.5864.8810.6878.5420.76112.2030.82015.8640.87019.5250.91423.1860.95326.8470.98930.5081.02134.1691.05137.82101.07941.48111.10645.1412
KzHeight above ground level, z (m)
Level
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Wind Load Analysis
4. Topographic factor, Kzt
Assuming the example building is situated on level ground and not on a hill, ridge, or escarpment, Kzt is equal to 1.
Wind Load Analysis
5. Gust effect factors, G and Gf
Gust effect factor depends on whether a building is rigid or flexible (ASCE 6.5.8). A rigid building has a fundamental natural frequency n1 greater than or equal to 1 Hz, while a flexible building has a fundamental natural frequency less than 1 Hz (ASCE 6.2).
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Wind Load Analysis
N-S direction:
Ta = 1/n1 = 0.0488 (hn)3/4 = 0.0488 (45.14)3/4
= 0.85 sec < 1 sec
So building is rigid and G = 0.85
See ASCE 7-05 Commentary Section C6.5.8
Wind Load Analysis
E-W direction:
Ta = 1/n1 = 0.0466 (hn)0.9 = 1.44 sec > 1 sec
So building is flexible.
Extensive calculation using n1 = 1/1.44 = 0.7Hz yields Gf = 0.93
See ASCE 7-05 Commentary Section C6.5.8
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6. Enclosure classification
It is assumed in this example that the building is enclosed per IBC 1609.2, ASCE 6.5.9.
Wind Load Analysis
Wind Load Analysis
7. Internal pressure coefficient, GCpi
For an enclosed building, GCpi = ± 0.18.
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Wind Load Analysis8. External pressure coefficients, Cp
For wind in the N-S direction (ASCE Figure 6-6) :Windward wall: Cp = 0.8
Leeward wall (L/B = 20.7/56.1 = 0.37): Cp = -0.5
Side wall: Cp = - 0.7
Roof (h/L = 45.1/20.7 = 2.18):
Cp = -1.3 over entire roof (20.7 m < h/2 = 22.6 m).
May be reduced to 0.80 × -1.3 = -1.04 for area
greater than 93 m2 per Figure 6-6.
Wind Load Analysis
For wind in the E-W direction:Windward wall: Cp = 0.8Leeward wall (L/B = 56.1/20.7 = 2.70):
Cp = -0.26Side wall: Cp = -0.7Roof (h/L = 45.1/56.1 = 0.80):
Cp = -1.14 from windward edge to h/2 = 22.6 mCp = -0.78 from 22.6 m to h = 45.1 mCp = -0.62 from 45.1 m to 56.1 m
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Wind Load Analysis
9. Velocity pressure, qz
The velocity pressure at height z is determined by Eq. 6-15 in ASCE 6.5.10:
qz = 0.613 Kz Kzt Kd V2 I N/m2, V in m/sec
where all terms have been defined previously.
Wind Load AnalysisVelocity Pressure qz (V = 45 m/sec)
6180.5864.8817250.6878.5428030.76112.2038650.82015.8649180.87019.5259640.91423.186
10060.95326.84710440.98930.50810771.02134.16911101.05137.821011381.07941.481111671.10645.1412
qz(N/m2)
KzHeight above ground level, z (m)Level
where q = qz for windward walls at height z above groundq = qh for leeward walls, side walls, and roof, evaluated at height hqi = qh for all walls and roofs of enclosed buildings
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Wind Load Analysis
10. Design wind pressure, p
For rigid buildings of all heights, design wind pressures on the main wind-force-resisting system are calculated by Eq. 6-17:
p = q GCp – qi (GCpi)
Wind Load AnalysisDesign Wind Pressure in N-S Direction (V = 45 m/sec)
± 210± 0.181167-1032-1.040.85116745.14---Roof± 210± 0.181167-694-0.70.851167All---Side± 210± 0.181167-496-0.50.851167All---Leeward± 210± 0.1811674200.800.856184.881± 210± 0.1811674930.800.857258.542± 210± 0.1811675460.800.8580312.203± 210± 0.1811675880.800.8586515.864± 210± 0.1811676240.800.8591819.525± 210± 0.1811676560.800.8596423.186± 210± 0.1811676840.800.85100626.847± 210± 0.1811677100.800.85104430.508± 210± 0.1811677320.800.85107734.169± 210± 0.1811677550.800.85111037.8210± 210± 0.1811677740.800.85113841.4811± 210± 0.1811677940.800.85116745.1412
Windward
qiGCpi(N/m2)
GCpiqi(N/m2)
qGCp(N/m2)
CpGq(N/m2)
Internal PressureExternal PressureHeight above ground level,z(m)
LevelLocation
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Wind Load AnalysisDesign Wind Pressure in N-S Direction (V = 45 m/sec)
205.0118.8-49686.24204.274.881203.0101.8-496101.24933.668.542213.9101.8-496112.15463.6612.203222.5101.8-496120.75883.6615.864229.9101.8-496128.16243.6619.525236.5101.8-496134.76563.6623.186242.2101.8-496140.46843.6626.847247.6101.8-496145.87103.6630.508252.1101.8-496150.37323.6634.169256.8101.8-496155.07553.6637.8210260.7101.8-496158.97743.6641.4811132.450.9-49681.57941.8345.1412
Design Wind
Force, P* (kN)
External Design Wind
Pressure, qhGfCp(N/m2)
Design Wind
Force, P* (kN)
External Design Wind
Pressure,qzGfCp(N/m2)
Total Design Wind Force (kN)
LeewardWindwardTributary Height
(m)
Height above
ground level, z
(m)Level
*P = qGCp × Tributary height × 56.1 m Σ 2702.6
Wind Load Analysis
For flexible buildings, Eq. 6-19 is to be used:
p = q GfCp – qi (GCpi)
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Wind Load AnalysisDesign Wind Pressure in E-W Direction (V = 110 mph)
± 210± 0.181167-1237-1.140.93116745.14*---± 210± 0.181167-847-0.780.93116745.14†---± 210± 0.181167-673-0.620.93116745.14‡---
Roof± 210± 0.181167-760-0.700.931167All---Side± 210± 0.181167-282-0.260.931167All---Leeward± 210± 0.1811674590.800.936184.881± 210± 0.1811675390.800.937258.542± 210± 0.1811675970.800.9380312.203± 210± 0.1811676430.800.9386515.864± 210± 0.1811676830.800.9391819.525± 210± 0.1811677180.800.9396423.186± 210± 0.1811677480.800.93100626.847± 210± 0.1811677770.800.93104430.508± 210± 0.1811678010.800.93107734.169± 210± 0.1811678260.800.93111037.8210± 210± 0.1811678470.800.93113841.4811± 210± 0.1811678680.800.93116745.1412
Windward
qiGCpi(N/m2)
GCpiqi(N/m2)
qGCp(N/m2)
CpGq(N/m2)
Internal PressureExternal PressureHeight above
ground level,z(m)
LevelLocation
* from windward edge to 22.6 m, † from 22.6 m to 45.1 m, ‡ from 45.1 m to 56.1 m
Wind Load AnalysisDesign Wind Pressure in E-W Direction (V = 110 mph)
65.524.9-28240.64594.274.88162.221.4-28240.85393.668.54266.621.4-28245.25973.6612.20370.121.4-28248.76433.6615.86473.121.4-28251.76833.6619.52575.821.4-28254.47183.6623.18678.121.4-28256.77483.6626.84780.321.4-28258.97773.6630.50882.121.4-28260.78013.6634.16984.021.4-28262.68263.6637.821085.621.4-28264.28473.6641.481143.610.7-28232.98681.8345.1412
Design Wind Force, P* (kN)
External Design Wind
Pressure, qhGfCp(N/m2)
Design Wind Force, P* (kN)
External Design Wind
Pressure,qzGfCp(N/m2)
Total Design Wind Force (kN)
LeewardWindwardTributary Height
(m)
Height above
ground level, z
(m)Level
Σ 867.0*P = qGCp × Tributary height × 20.7 m
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Wind Load AnalysisDesign Wind Force in N-S and E-W Direction (V = 45 m/sec)
65.5205.04.88162.2203.08.54266.6213.912.20370.1222.515.86473.1229.919.52575.8236.523.18678.1242.226.84780.3247.630.50882.1252.134.16984.0256.837.821085.6260.741.481143.6132.445.1412
Total Design Wind
Force E-W (kN)
Total Design Wind
Force N-S (kN)
Height above ground
Level, z (m)
Level
Σ 2702.6 867.0
Wind Load Analysis
The stiffness properties of the members were input assuming cracked sections. The following cracked section properties were used:
Beam: Ieff = 0.5 IgColumn: Ieff = 0.7 IgShear walls: Ieff = 0.5 Ig
where Ig is the gross moment of inertia of section.
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Wind Load Analysis
According to ASCE 6.5.12.3, the main wind-force-resisting systems of buildings of all heights, whose wind loads have been determined according to ASCE 6.5.12.2.1 and 6.5.12.2.3, must be designed for the full and partial wind load cases of Figure 6-9 (Cases 1 through 4). These four cases were considered in the three-dimensional analyses.
Wind Load AnalysisResults of 3-D Analysis under Wind Force in E-W Direction for
Frame C (V = 45 m/sec)
33-3333-3333-34351
33-3333-3333-33342
31-3131-3131-31313
28-2828-2828-28284
25-2525-2525-24255
22-2222-2221-21216
19-1919-1919-18187
15-1515-1515-14158
12-1212-1212-10119
8-88-88-7710
5-55-55-4411
2-22-22-1112
-2.8-2.8-2.8-2.91
-2.8-2.8-2.8-2.82
-2.6-2.6-2.6-2.63
-2.4-2.4-2.4-2.44
-2.1-2.1-2.1-2.15
-1.9-1.9-1.9-1.86
-1.6-1.6-1.6-1.57
-1.3-1.3-1.3-1.28
-1.0-1.0-1.0-0.99
-0.7-0.7-0.7-0.610
-0.4-0.4-0.4-0.311
-0.2-0.2-0.2-0.112
Bending Moments in Beams (m-kN) Shear Forces in Beams (kN)
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Wind Load AnalysisResults of 3-D Analysis under Wind Force in E-W Direction for Frame C
(V = 45 m/sec)
69695064-27-27-21-17133332614-33-33-26-17227272215-32-32-25-18325252011-30-30-24-17421211810-27-27-21-1551919158-25-25-20-1461515136-21-21-17-1371212104-19-19-15-1189972-16-16-12-1095551-12-12-9-810222-1-9-9-6-611000-2-4-4-3-212
6.46.44.85.41
6.66.65.33.02
5.95.94.83.23
5.55.54.42.74
4.94.93.92.55
4.34.33.42.16
3.73.72.91.97
3.13.12.41.58
2.42.41.91.29
1.81.81.40.810
1.11.10.80.511
0.50.50.3-0.112
0.00.10.219.31
0.00.10.216.42
0.00.10.313.53
0.00.00.310.94
0.00.00.38.55
0.00.00.36.46
0.00.00.24.67
0.00.00.23.18
0.00.00.21.99
0.00.00.11.010
0.00.00.10.411
0.00.00.00.112
Bending Moments in Columns (m-kN)
Shear Forces in Columns (kN)
Axial Forces in Columns (kN)
Wind Load AnalysisResults of 3-D Analysis under Wind Force in N-S Direction for
Frame 4 (V = 45 m/sec)
30-30321
39-38392
44-43443
47-45464
47-45475
47-44466
45-42437
43-39408
39-36379
36-323310
35-303111
25-222312
-3.1-3.11
-3.9-3.92
-4.4-4.43
-4.8-4.74
-4.8-4.75
-4.8-4.66
-4.6-4.37
-4.3-4.08
-4.0-3.79
-3.7-3.310
-3.5-3.111
-2.6-2.312
Bending Moments in Beams (m-kN)
Shear Forces in Beams (kN)
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Wind Load AnalysisResults of 3-D Analysis under Wind Force in N-S Direction for Frame 4
(V = 45 m/sec)
4641-15-614123-28-1124326-35-1634524-41-2044423-43-2254321-44-2364120-43-2373818-41-2283416-39-2193114-36-19102812-30-16113012-45-2312
4.13.21
6.93.32
7.84.23
8.64.44
8.84.55
8.74.46
8.44.27
7.93.98
7.33.69
6.83.210
5.82.811
7.43.512
2.646.21
2.743.12
2.639.23
2.634.74
2.430.15
2.325.46
2.020.77
1.816.68
1.412.59
1.18.810
0.75.511
0.22.312
Bending Moments in Columns (m-kN)
Shear Forces in Columns (kN)
Axial Forces in Columns (kN)
Wind Load AnalysisResults of 3-D Analysis under Wind Forces in N-S Direction for
Wall on Column Line 7 (V = 45 m/sec)
-143820,045-1305501-120613,360-896602-10219376-566003-5876143-302204-7093545-96305-572149958206-442-52166207-318-1153230808-196-1829235909-68-2093253901043-19291772011
285-1383343012BottomTop
Shear Force(kN)
Bending Moment (m-kN)Axial Forces(kN)Level
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An Overview of the Design Load Combinations and the Seismic Design
Provisions of the 1997 UBC
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Referenced Standards
Design Loads and Load Combinations ASCE 7-95Concrete ACI 318-95Masonry NoneSteel MultipleWood AF&PA NDS - 91
Referenced Steel Standards
None
AISI LRFD 1991AISI ASD 1986 (with 1989 addendum)
AISC Seismic 1992
AISC ASD 1989
AISC LRFD 1993
1997 UBC
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Structural Design Requirements1997 UBC
Chapter 16 – Design Loads Chapter 17 – Inspections / Testing Chapter 18 – FoundationsChapter 19 – ConcreteChapter 20 – AluminumChapter 21 – MasonryChapter 22 – SteelChapter 23 – Wood
1612.2.1 Strength Design or LRFD Load Combinations (1997 UBC)
E = Design earthquake force (strength-level)
(12-6)0.9D ± (1.0E or 1.3W)U =
(12-5)1.2D + 1.0E + (f1L + f2S)U =
(12-4)1.2D + 1.3W + f1L + 0.5(Lr or S)U =
(12-3)1.2D + 1.6(Lr or S) + (f1L or 0.8W)U =
(12-2)1.2D + 1.6L + 0.5 (Lr or S)U =
(12-1)1.4DU =
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1612.2.1 Strength Design or LRFD Load Combinations (1997 UBC)
U = 1.2D + 1.0E + (f1L + f2S) (12-5)U = 0.9D ± (1.0E or 1.3W) (12-6)E = ρEh + Ev in (12-5), (12-6)Ev = 0.5CaID• ρ = 1 in Seismic Zones 0,1,2
EhΔs
V
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Effect of Vertical Earthquake Ground Motion
• Gravity and Earthquake Effects AdditiveU = 1.2D + 1.0E + 0.5L +0.2S
= 1.2D + (ρEh + 0.5CaID) + 0.5L + 0.2S= (1.2 + 0.5CaI)D + ρEh + 0.5L + 0.2S
Effect of Vertical Earthquake Ground Motion
• Gravity and Earthquake Effects CounteractiveU = 0.9D - 1.0E
= 0.9D - (ρ Eh + 0.5CaID)= (0.9 - 0.5CaI)D - ρEh
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Strength Design or LRFD Load Combinations - Exceptions
UBC Exceptions for concrete structures
1612.3.1 ASD Load Combinations -Basic (1997 UBC, from ASCE 7-95)
D (12-7)
D + L + (Lr or S) (12-8)
D + (W or E/1.4) (12-9)
0.9D + E/1.4 (12-10)
D + 0.75[L + (Lr or S) + (W or E/1.4)] (12-12)
E = ρEh + 0
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ASD Load Combinations - Basic (ASCE 7-95) – Allowable Stress Increase
• 1/3 stress increase not permitted• Load duration increase permitted
1612.3.2 ASD Load Combinations -Alternate Basic (1997 UBC)
D + L + (Lr or S) (12-12) D + L + (W or E/1.4) (12-13) D + L + W + S/2 (12-14) D + L + S + W/2 (12-15) D + L + S + E/1.4 (12-16) 0.9D + E/1.4 (?)
E = ρEh + 0
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ASD Load Combinations -Alternate Basic (1997 UBC) – Allowable
Stress Increase
• When using these alternate basic load combinations that include wind or seismic loads, allowable stresses are permitted to be increased or load combinations reduced, where permitted by the material chapter of this code or referenced standard.
1612.4 Special Seismic Load Combinations (1997 UBC)
• 1.2D + f1L + 1.0Em (12-17)• 0.9D + 1.0Em (12-18)
Em = Ω0Eh, whileE = ρEh + Ev
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1997 UBC Seismic Design Provisions
Introduction andBasic Principles
1997 UBC Seismic Design Provisions
Based on 1996 SEAOC Blue Book,
influenced by the1994 NEHRP Provisions
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1626.1 Purpose
The purpose of the earthquake provisions herein is primarily to safeguard against major structural failures and loss of life…not to limit damage or maintain function.
Purpose
SEAOC “Blue Book” Commentary…
• Resist minor ground motion without damage
• Resist moderate ground motion without structural damage but with some nonstructural damage
• Resist major ground motion without collapse but with possible structural / nonstructural damage
• Provisions will not prevent damage from earth faulting, slides or similar movements, nor soil liquefaction
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1997 UBC Design Earthquake Ground Motion
• Approximately 90% probability of non-exceedance in 50 years (approx. 475 yr. return period)
Idealized Force-Displacement
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Idealized Relationship between Base Shear and Drift
Earthquake-Induced Forces
• FM ≈ ΩoFS» FM = Maximum inelastic response force» FS = Code-prescribed force» Ωo = Seismic force amplification factor
Ωo gives a reasonable approximation of actual forces acting in an inelasticallyresponding structure
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EQ Design Considerations• Seismic Zone• Proximity to known Faults• Site Geology and soil characteristics• Building Occupancy• Structural framing system• Structural configuration… regular or
irregular• System redundancy• Building height• Lateral force procedure• Framing system limitations• Special strength and detailing
1626.3 Earthquake vs. Wind
1. Code-Prescribed Forces2. Exposed Area vs. Mass3. Design for Larger Force4. Provide Seismic Detailing
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EQ Design Procedure• Step 1 – Select basic structural system• Step 2 – Identify lateral force-resisting
system• Step 3 – Identify structural
irregularities and any framing system limitations
• Step 4 – Select lateral force procedure• Step 5 – Calculate total design base
shear and distribute over height of structure
EQ Design Procedure
• Step 6 – Elastically analyze building, including torsional effects. Include P-Δeffects, if necessary
• Step 7 – Check story drift limitations• Step 8 – Calculate redundancy (ρ) of lateral
force-resisting system and increase earthquake forces as necessary
• Step 9 – Design elements of lateral force-resisting system for required strength and do special detailing
• Step 10 – Confirm complete load path to resist earthquake forces
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Sec 1702Structural Observation
Required for:
1. Essential facilities, hazardous facilities and special occupancy structures (Table 16-K)
2. “High-rise” office building, hotels and apartments (Section 403)
3. Seismic Zone 4… Near-Source Factor (Na) greater than 1.0
Sec 1702Structural Observation
4. When designated by A/E of record or building official
• Seismic Zones 3 and 4 only• Structural system only• Performed by A/E of record or designated A/E• Periodic site visits• Compliance with plans and specifications• Final report to building official
Note: Structural Observations does not waive inspections by Section 108 and 1701
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1997 UBC Seismic Design Provisions
Structural Systems
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1997 UBC Fig. 16-3Design Response Spectra
1997 UBC Sec. 1630.2 Static Force Procedure
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Response Modification Factor, R
8.5 > R > 2.2
IBC vs. UBC Response Modification Factor, R• 1997 UBC (Strength-level
earthquake forces)Table 16-N
Bearing wall systemR = 4.5
Special moment resisting frame system
R = 8.5
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Table 16-N – Structural Systems1
Footnote for Table 16-NN.L. – no limit1 See Section 1630.4 for combination of structural systems.2 Basic structural systems are defined in Section 1629.6.3 Prohibited in Seismic Zones 3 and 4.4 Includes precast concrete conforming to Section
1921.2.7.5 Prohibited in Seismic Zones 3 and 4, except as permitted
in Section 1634.2.6 Ordinary moment-resisting frames in Seismic Zone 1
meeting the requirements of Section 2211.6 may use a Rvalue of 8.
7 Total height of the building including cantilevered columns.
8 Prohibited in Seismic Zones 2A, 2B, 3 and 4. See Section 1633.2.7.
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Sec 1630.4.2Vertical Combinations
Sec 1630.4.2Vertical Combinations
1. Design structure for lowest (R) for structural systems used… or
2. Two-stage analysis permitted for structures with flexible upper portion supported by rigid lower portion (Sec 1629.8.3 Item 4)
3. In Seismic Zones 3 & 4, dynamic analysis required for structures > 5 stories or 19.8 m in height with vertical combinations (Sec 1629.8.4 Item 3)
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Sec 1630.4.3Combinations Along Different Axes
• With bearing wall system in only one direction, (R) not greater in orthogonal direction (Zones 3 and 4 only)
Sec 1630.4.3Combinations Along Different Axes
• Structures < 48 m» Bearing wall system» Building frame system» Moment-resisting frame system» Dual system
• Structures > 48 m (Zones 3 and 4 only)» Special moment-resisting frames» Dual systems
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Sec 1630.4.4Combinations Along Same Axes
• With different structural systems in same direction, value of (R) in that direction to be taken as least (R) for structural systems utilized
• Dual systems…and shear wall-frame interactive systems in Seismic Zones 0 & 1…excluded
Sec 1630.4.4Combinations Along Same Axes
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1997 UBC Seismic Design Provisions
Static Force Procedure
1997 UBC Fig. 16-3Design Response Spectra
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1997 UBC Sec. 1630.2 Static Force Procedure
Terms to Calculate Earthquake Load
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UBC Seismic Zones
Table 16-I Seismic Zone Factor
0.0751
0.152A
0.22B
0.33
0.44
ZSeismic Zone
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Table 16-1 Seismic Zone Factor
• Accounts for geographical variations in expected levels of earthquake ground shaking
• Seismic zone map (Fig 16-2) estimates effective peak horizontal acceleration on rock with a 10 percent probability of being exceeded in a 50-year period
• See Appendix 1A – Seismic Zone Coefficient… in 1996 SEAOC “Blue Book”
Soil Profile Types / Site Classes
FSoil Requiring Site-Specific
EvaluationSF
ESoft Soil ProfileSE
DStiff Soil ProfileSD
CVery Dense Soil and Soft RockSC
BRock (west coast rock)SB
AHard Rock (east coast rock)SA
Site ClassSoil Profile DescriptionSoil Profile Type
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Table 16-J – Soil Profile Types
< 50< 15< 180Soft Soil ProfileSE1
Soil Requiring Site-specific Evaluation. See Section 1629.3.1.SF
50 to 10015 to 50180 to 360Stiff Soil ProfileSD
> 100> 50360 to 760Very Dense Soil and Soft Rock
SC
760 to 1,500
RockSB
> 1,500Hard RockSA
UndrainedShear
Strength (kPa)
Standard Penetration Test, N [or NCH for cohesionless soil
layers] (blows/foot)
Shear Wave velocity (m/sec)
Average Soil Properties for Top 30,480 mm of Soil Profile
Soil Profile Name/
Generic Description
Soil Profile Type
Default Soil Profile Type
• Soil Profile Type SD must be used when the soil properties are not known in sufficient detail, unless the building official determines that Soil Profile Type SE or SF is likely to be present at the site
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Soil-Modification of Short-Period Ground Motion (1997 UBC)
Soil-Modification of Long-Period Ground Motion (1997 UBC)
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SEISMIC GROUND MOTION AMPLIFICATION DUE TO SOIL, Ca / Z (1997 UBC)
*****SF
0.9Na2.21.72.02.5SE
1.1Na1.21.41.51.6SD
1.0Na1.11.21.21.2SC
1.0Na1.01.01.01.0SB
0.8Na0.80.80.80.8SA
Z = 0.40Z = 0.30Z = 0.20Z = 0.15Z = 0.075
SEISMIC ZONE FACTOR - ZSOIL PROFILE
TYPE
* Site specific geotechnical investigation and dynamic site response analysis required
SEISMIC GROUND MOTION AMPLIFICATION DUE TO SOIL, Cv / Z (1997 UBC)
*****SF
2.4Nv2.83.23.33.5SE
1.6Nv1.82.02.12.4SD
1.4Nv1.51.61.71.7SC
1.0Nv1.01.01.01.0SB
0.8Nv0.80.80.80.8SA
Z = 0.40Z = 0.30Z = 0.20Z = 0.15Z = 0.075
SEISMIC ZONE FACTOR - ZSOIL PROFILE
TYPE
* Site specific geotechnical investigation and dynamic site response analysis required
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TABLE 16-S NEAR-SOURCE FACTOR Na(1997 UBC)
1.01.01.0C
1.01.01.3B
1.01.21.5A
≥ 10 km5 km≤ 2 km
Closest Distance to Known Seismic Source
Seismic Source Type
TABLE 16-T NEAR-SOURCE FACTOR Nv(1997 UBC)
1.0
1.0
1.0
≥ 15 km
1.01.01.0C
1.01.21.6B
1.21.62.0A
10 km5 km≤ 2 km
Closest Distance to Known Seismic SourceSeismic Source Type
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Design Spectrum
1997 UBC Sec. 1630.2 Static Force Procedure
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63
Table 16-K Occupancy Category
1.001.00Factories; Private Garages; Carports/Sheds
5. Miscellaneous structures
1.001.00Hotels; Apartments; Dwellings; Wholesale/Retail; Office Bldgs
4. Standard occupancy structures
1.001.00Public Assembly; Schools; Day-Care Centers; Nurseries; Nursing Homes; Jails
3. Special occupancy structures
1.501.25Dangerous Toxic or Explosive Substances
2. Hazardous facilities
1.501.25Hospitals; Fire/Police Stations; Emergency Shelters
1. Essential facilities
Seismic Importance
Factor Ip
Seismic Importance
Factor I
Occupancy or Function of Structure
Occupancy Category
Seismic Importance Factor, I
• Used to amplify….design forces as a means of controlling damage and producing “enhanced”performance in Occupancy Categories 1 and 2
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Minimum Design Base Shear• All Seismic Zones
Vmin = 0.11 Ca I W 1997 UBC
Minimum Design Base Shear
• Seismic Zone 4
UBC 1997 R
I0.8ZNV WV
min =
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Structure Period
Calculated by……1) Approximate Formulae
2) Rational Analysis using structural properties and deformational characteristics of resisting elements in a properly substantiated analysis
Approximate Period Formulae
Ta = CT (hn)3/4 1997 UBC (30-8)
0.0853Steel Moment Frames
0.0488All other buildings
0.0731Concrete Moment FramesEccentrically Braced Steel
Frames
CTLateral Force Resisting System
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Approximate Period Formula(Optional – 1997 UBC )
For structures with concrete or masonry shear walls,
Ct = 0.0743/√Ac
Ac = ΣAe[0.2 + (De/hn)2]
Replaced by a different formula in ASCE 7-05
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Rayleigh Formula
(30-10)
)(2
2
ΔΣ+ΔΔΣ
π=FtFtg
wT)(
22
ΔΣ+ΔΔΣ
π=FtFtg
wT)(
22
ΔΣ+ΔΔΣ
π=FtFtg
wT
)(2
2
ΔΣ+ΔΔΣ
π=FtFtg
wT
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Upper Limit on T by "Rational Analysis"
1997 UBCT ≤ 1.3 Ta, Zone 4≤ 1.4 Ta, Zones 1,2,3
1997 UBC 1630.1.1 Effective Seismic Weight
V = CSWW = total dead load + ……
• Warehouses………………..…………..25% live• Buildings with partitions……………….0.48 kN/m2
• Design snow load > 1.44 kN/m2………… ≥ 25% design snow load **• Permanent equipment…………………100% dead
** UBC leaves this up to local jurisdictions
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IBC vs. UBCVertical Force Distribution
07TV.0sec....F 0.7T0sec....F 0.7T
where
)F-(VwhhwF
t
t
txx
x
=>=≤
=∑
1997 UBC
≤ 0.25V
Vertical Force Distribution1997 UBC
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1997 UBC 1630.6 Horizontal Distribution of Forces
• Rigid diaphragms» Seismic story shear is to be distributed to
elements of seismic-force-resisting system based on stiffness of vertical-resisting elements
• Flexible diaphragms» Seismic story shear is to be distributed to
elements of seismic-force-resisting system based on tributary areas
Sec 1630.6Diaphragm Flexibility
• Diaphragm considered flexible if… Max.diaphragm deflection Δ > 2 (Averagestory drift)
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Sec 1630.6Diaphragm Flexibility
• Compare midpoint in-plane deflection of diaphragm (Δ) with average story drift of adjoining vertical resisting elements
• Torsion» Torsional moment due to difference in location
of center of mass and center of resistancemust be considered for rigid diaphragms
• Accidental torsion» For rigid diaphragms, must be included in
addition to the torsional moment• Displacement of center of mass = 5% building dimension
perpendicular to direction of applied forces
1997 UBC 1630.6 Horizontal Distribution of Forces
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Sec 1630.1.2Modeling Requirements
“Accuracy of Results”Mathematical model of physical structure to
include…• All elements of lateral-force-resisting system• All stiffness and strength significant to force
distribution…representation of spatial distribution of mass and stiffness of structure
• Effects of “cracked sections” for concrete and masonry
• Contribution of panel zone deformation to story drift for steel moment frames
Even with new guidelines for structure modeling…structure period (T) calculated by “rational analysis” still RESTRICTED
1997 UBC 1630.9 Story Drift Determination (Δ)
Lateral displacement of one level relative to the next level above or below
x
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EhΔS
V
1997 UBC 1630.10 Story Drift Limitation
1997 UBCΔx = ΔM,x - ΔM,x-1 ≤ Δa
where….ΔM,x = 0.7R Δs,x
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Allowable Story Drift (Δa ) 1997 UBC
Δa = 0.020 hsx for T ≥ 0.7 sec.= 0.025 hsx for T < 0.7 sec.
hsx = Story height below level x
REDUNDANCY
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Redundancy
ρ = 1 in Seismic Zones 1 and 2
ANALYSIS PROCEDURES
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Static vs. Dynamic Analysis (1997 UBC)
WhatSeismicZone?
Is No. ofStories ≤ 5 and
Ht. ≤ 19.8 m?
Is Bldg.Irregular
Table 16-L1, 2, 3?
WhatOccupancyTable 16-K
?Is
Bldg. Height< 73 m
Use Dynamic Analysis
Use Static Analysis
1, 2, 3
3 or 4
Yes
No
Yes
4, 5
1
No
Yes
No
2
Building Configuration
• Plan Structural Irregularities (1997 UBC Table 16-M)» Torsional irregularity» Re-entrant corners» Diaphragm discontinuity» Out-of-plane offsets» Nonparallel systems
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Building Configuration• Vertical Structural Irregularities (1997 UBC
Table 16-L)» Stiffness irregularity – soft story» Weight (mass) irregularity» Vertical geometric irregularity» In-plane discontinuity in vertical lateral-force-resisting
elements» Discontinuity in lateral strength – weak story
EXEMPTIONS FROM SEISMIC DESIGN
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1997 UBC Exemption from Seismic Design
1629.1 … One- and two-family dwellings in Seismic Zone 1 need not conform to the provisions of this section.
SIMPLIFIED STATIC LATERAL FORCE PROCEDURE
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1997 UBC Sec. 1629.8.2
• Applicable to following structures in Occupancy Category 4 or 5:» Buildings not more than 3 stories in
height excluding basements, that use light-frame construction
» Other buildings not more than 2 stories in height excluding basements
1997 UBC Sec. 1630.2.3.2
• Seismic Base Shear, V (Eq. 30-11):
V = 3.0 Ca W / R
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1997 UBC Sec. 1630.2.3.3
• Vertical Distribution (Eq. 30-12)
Fx = 3.0 Ca wx / R
1997 UBC Sec. 1630.2.3.4
• Where used, ΔM shall be taken equal to 0.01 times the story height of all stories
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For more information…
www.skghoshassociates.com
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Easy, Step-by-Step Determination of
Design Base Shear1997 UBC
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1997 UBC Division IV: Earthquake DesignSection Title Page
1626 General 2-91627 Definitions 2-91628 Symbols and Notation 2-101629 Criteria Selection 2-111630 Minimum Design Lateral Forces and Related
Effects2-13
1631 Dynamic Analysis Procedures 2-161632 Lateral Forces on Elements of Structures,
Nonstructural Components and Equipment Supported by Structures
2-18
1633 Detailed Systems Design Requirements 2-191634 Nonbuilding Structures 2-21
What is Design Base Shear?
FR
F2
F1
"Base"
V(Design Base Shear)
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STEP 1:DETERMINE SEISMIC ZONE FACTOR,
Z
Dubai: Seismic Zone 2A
UBC Seismic Zones
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UBC Seismic Zones
Appendix Chapter 16
Division III: Seismic Zone Tabulation
Section 1653 – FOR AREAS OUTSIDE THE
U.S.
United Arab Emirates
Abu Dhabi…..Zone 0
Dubai……..…Zone 07
STEP 1:DETERMINE SEISMIC ZONE FACTOR,
Z
Seismic Zone Z1 0.075
2A 0.152B 0.203 0.304 0.40
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STEP 2:DETERMINE IMPORTANCE
FACTOR, I (Table 16-K)Occupancy Category Seismic Importance
Factor, IEssential Facilities 1.25
Hazardous Facilities 1.25
Special Occupancy Structures 1.00
Standard Occupancy Structures
1.00
Miscellaneous Structures 1.00
STEP 3:DETERMINE IF STATIC FORCE
PROCEDURE is OK
CED – Structural Design Guidelines
VS.
1997 UBC
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STEP 3:DETERMINE IF STATIC FORCE
PROCEDURE is OK
• CED Section 3.2
All structures and buildings exceeding 12
stories in height shall be analyzed by
employing Response Spectrum Analysis
STEP 3:DETERMINE IF STATIC FORCE
PROCEDURE is OK (97 UBC Section 1629.8)
What SeismicZone ? Does building have
an irregularity asdescribed in Item 1, 2or 3 of Table 16-L ?
WhatOccupancy ?
Table 16-K
IsBuilding Height
< 73.2 m ?
Is No. ofStories ≤ 5
and Ht ≤ 19.8 m ?USE DYNAMIC ANALYSIS
USE STATIC ANALYSIS
What SeismicZone ? Does building have
an irregularity asdescribed in Item 1, 2or 3 of Table 16-L ?
WhatOccupancy ?
Table 16-K
IsBuilding Height
< 73.2 m ?
Is No. ofStories ≤ 5
and Ht ≤ 19.8 m ?USE DYNAMIC ANALYSIS
USE STATIC ANALYSIS
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STEP 3:DETERMINE IF STATIC FORCE
PROCEDURE is OK1. Stiffness Irregularity
- Soft Story2. Weight (Mass)
Irregularity3. Vertical Geometric
Irregularity
Stiff Resisting Elements
Soft
Heavy Mass
“Soft Story” Stiffness< 70% Story Stiffness
Above or< 80% (Avg. Stiffness
of 3 Stories above)
Story Mass > 150% Adjacent Story Mass
Exception: Lighter Roof is Acceptable
Story Dimension > 130% Adjacent Story Dimension
Exception: One-Story Penthouse Acceptable
Irregularities in Items 1, 2 and 3
STEP 4:DETERMINE SOIL PROFILE TYPE
Section 1636 and Table 16-J
Soil Profile Type Soil Profile DescriptionSA Hard rockSB RockSC Very dense soil and soft rockSD Stiff soil profile SE Soft soil profileSF Soil requiring site-specific evaluation.
See UBC Section 1629.3.1.
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STEP 4:DETERMINE SOIL PROFILE TYPE
Section 1629.3
EXCEPTION: When the soil properties
are not known in sufficient detail to
determine the soil profile type, Type
SD shall be used….
STEP 5:DETERMINE Ca and Cv
Ca• Function of Z and Soil Profile Type
• Represents site-dependent effective
peak acceleration at grade.
• Used in base shear equation
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STEP 5:DETERMINE Ca and Cv
Spec
tral
Acc
eler
atio
n
Period (T)
Ca
Response Spectrum
STEP 5:DETERMINE Ca and Cv
Soil ProfileType
Seismic Zone Factor, ZZ = 0.075 Z = 0.15 Z = 0.2 Z = 0.3 Z = 0.4
SA 0.06 0.12 0.16 0.24 0.32Na
SB 0.08 0.15 0.20 0.30 0.40Na
SC 0.09 0.18 0.24 0.33 0.40Na
SD 0.12 0.22 0.28 0.36 0.44Na
SE 0.19 0.30 0.34 0.36 0.36Na
SF See Footnote 11 Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine seismic coefficients for Soil Profile Type SF.
SEISMIC COEFFICIENT Ca
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STEP 5:DETERMINE Ca and Cv
Cv• Function of Z and Soil Profile Type
• Represents the value of acceleration
response at a 1.0 second period.
• Cv is significantly > Z for soft soil
sites.
STEP 5:DETERMINE Ca and Cv
Spec
tral
Acc
eler
atio
n
Period (T)
Cv
T = 1.0 second
RESPONSE SPECTRUM
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STEP 5:DETERMINE Ca and Cv
SEISMIC COEFFICIENT CV
Soil ProfileType
Seismic Zone Factor, ZZ = 0.075 Z = 0.15 Z = 0.2 Z = 0.3 Z = 0.4
SA 0.06 0.12 0.16 0.24 0.32Na
SB 0.08 0.15 0.20 0.30 0.40Na
SC 0.13 0.25 0.32 0.45 0.56Na
SD 0.18 0.32 0.40 0.54 0.64Na
SE 0.26 0.50 0.64 0.84 0.96Na
SF See Footnote 11 Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine seismic coefficients for Soil Profile Type SF.
STEP 6:DETERMINE BUILDING PERIOD, T
Section 1630.2.2:
T = Ct (hn) ¾
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STEP 6:DETERMINE BUILDING PERIOD, T
*Ct for structures with concrete or masonry shear walls may alternatively be computed using UBC formula (30-9).
Alternative methods for calculating the period of a structure are found in UBC Section 1630.2.2. Periods may be computed by any rationalprocedure that is in conformance with the principles of mechanics. Rationally computed period may not be taken any larger than 1.3 times the period given by the above formula in Zone 4, or 1.4 times the period obtained from the above formula in Zones 1, 2 and 3.
Structural System CtSteel moment resisting frames 0.0835
Reinforced concrete moment resisting frame and eccentrically braced frames
0.0731
All other systems 0.0488*
STEP 7:DETERMINE SYSTEM RESPONSE
FACTOR, R
Table 16-N: STRUCTURAL SYSTEMS1. Bearing Wall System2. Building Frame System3. Moment-Resisting Frame System4. Dual System5. Cantilevered Column Building System6. Shear Wall-Frame Interaction System7. Undefined System
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STEP 7:DETERMINE SYSTEM RESPONSE
FACTOR, RBearing Wall
SystemBuilding Frame
SystemMoment-Resisting
Frame System
LateralForces
Gravity Loads LateralForces
LateralForces
Gravity Loads Gravity Loads
Stiff Resisting Elements…Shearwalls or Braced Frames
Stiff Resisting Elements…Shearwalls or Braced Frames
STEP 7:DETERMINE SYSTEM RESPONSE
FACTOR, RDual System Cantilevered Column
Building SystemShear Wall-FrameInteraction System
LateralForces
LateralForcesGravity Loads
Gravity Loads
Stiff Resisting Elements…Shearwalls or BracedFrames (See Section
1629.6.5 for requirements)
Zero MomentRestraint
FixedBase
Concrete only
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STEP 8:Calculate W
Seismic Dead Load, W, per Section 1630.1.1:
Description LoadWarehouses 25% Live LoadBuildings with Partitions
Min. 0.48 kN/m2
Snow Load > 1.44 kN/m2, includePermanent Equipment 100% Dead Load
STEP 9:Calculate Design Base Shear
Section 1630.2…Description and Equation Equation No.“Long Period” Structures: 30-4
“Short Period” Structures: 30-5
Design Base Shear Minimum: 30-6
WTRIC
V v=
WR
IC.V a52=
WIC.V a110=
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STEP 9:Calculate Design Base Shear
Design Response SpectrumD
esig
n B
ase
shea
r
Period (T)Ts
“Short period”structures
“Long period”structures
WR
IC.V a52=
WTRIC
V v=
minV
a
vs C.
CT
52=
STEP 10:Distribute Design Base Shear
Section 1630.5( )
∑−=
iixx
tx hwhwFVF When T ≤ 0.7 sec, Ft = 0
When T > 0.7 sec, Ft = 0.07TV ≤ 0.25V
Ft = 0.07TV n
hn
hx
Fx x wx
V
i i
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EXAMPLE
SKGA California Office Relocated
to Dubai, “Regular”
Plan Dimension of Example Building
9.14 m
7.62 m
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Elevation of Office
2.74 m
2.74 m
2.74 m
1
2
3
Design Data
• Building Location
Dubai (Seismic Zone: 2A)
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EXAMPLE: Step 1
Step 1: Determine Seismic Zone Factor
Z = 0.15 (Seismic Zone: 2A)
EXAMPLE: Step 2
Step 2: Determine Importance Factor
I = 1.0 (Standard Occupancy Structure in Table 16-K)
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EXAMPLE: Step 3Step 3: Determine If Static Procedure is OK
What SeismicZone ? Does building have
an irregularity asdescribed in Item 1, 2or 3 of Table 16-L ?
WhatOccupancy ?
Table 16-K
IsBuilding Height
< 73.2 m ?
Is No. ofStories ≤ 5
and Ht ≤ 19.8 m ?USE DYNAMIC ANALYSIS
USE STATIC ANALYSIS
What SeismicZone ? Does building have
an irregularity asdescribed in Item 1, 2or 3 of Table 16-L ?
WhatOccupancy ?
Table 16-K
IsBuilding Height
< 73.2 m ?
Is No. ofStories ≤ 5
and Ht ≤ 19.8 m ?USE DYNAMIC ANALYSIS
USE STATIC ANALYSIS
EXAMPLE: Step 4
Step 4: Determine Soil Profile Type
Assume SD Soil (Stiff Soil Profile)
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EXAMPLE: Step 5
Step 5: Determine Ca and Cv
Soil Profile
Type
Seismic Zone Factor, Z
Z = 0.075 Z = 0.15 Z = 0.2 Z = 0.3 Z = 0.4
SA 0.06 0.12 0.16 0.24 0.32Na
SB 0.08 0.15 0.20 0.30 0.40Na
SC 0.09 0.18 0.24 0.33 0.40Na
SD 0.12 0.22 0.28 0.36 0.44Na
SE 0.19 0.30 0.34 0.36 0.36Na
SF See Footnote 1
SEISMIC COEFFICIENT Ca
EXAMPLE: Step 5
Step 5: Determine Ca and Cv
SEISMIC COEFFICIENT CV
Soil Profile
Type
Seismic Zone Factor, Z
Z = 0.075 Z = 0.15 Z = 0.2 Z = 0.3 Z = 0.4
SA 0.06 0.12 0.16 0.24 0.32Na
SB 0.08 0.15 0.20 0.30 0.40Na
SC 0.13 0.25 0.32 0.45 0.56Na
SD 0.18 0.32 0.40 0.54 0.64Na
SE 0.26 0.50 0.64 0.84 0.96Na
SF See Footnote 1
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EXAMPLE: Step 6
Step 6: Determine Building Period T
0.2 m
9.14 m
7.62 m 0.2 m
EXAMPLE: Step 6
Direction 1:Direction of lateral seismic load is parallel to the longer
dimension of the shear wall (9.14 m)
ΣAe = 9.14 × 0.2 × 2 + (7.62-0.4) ×0.2 ×2 = 6.54 m2
De = 9.14 (the length of a shear wall in loading direction)
De/hn = 9.14 / 8.22 = 1.11 > 0.9, therefore De/hn = 0.9
Ac = ΣAe [0.2 + (De/hn)2] = 6.54 × [0.2+0.92] = 6.61 m2
Ct = 0.0743 / Ac0.5 = 0.0743 / (6.61)0.5 = 0.0289
T = Ct (hn)0.75 = 0.0289 × (8.22)0.75 = 0.14 sec
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EXAMPLE: Step 6
Direction 2:Direction of lateral seismic load is parallel to the shorter
dimension of the shear wall (7.62 m)
ΣAe = 9.14 × 0.2 × 2 + (7.62-0.4) ×0.2 ×2 = 6.54 m2
De = 7.62 (the length of a shear wall in loading direction)De/hn = 7.62 / 8.22 = 0.927 > 0.9, therefore De/hn = 0.9Ac = ΣAe [0.2 + (De/hn)2] = 6.54 × [0.2+0.92] = 6.61 m2
Ct = 0.0743 / Ac0.5 = 0.0743 / (6.61)0.5 = 0.0289
T = Ct (hn)0.75 = 0.0289 × (8.22)0.75 = 0.14 sec
Therefore, T = 0.14 sec in both directions
EXAMPLE: Step 7
Step 7: Determine System Response FactorBasic Structural
SystemsLateral-Force-Resisting System Description R
1. Bearing Wall System 1. Light-framed walls with shear panels
a. Wood Structural panel walls for structures three stories or less 5.5
b. All other light-framed walls 4.5
2. Shear walls
a. Concrete 4.5
b. Masonry 4.5
3. Light steel-framed bearing walls with tension-only bracing 2.8
4. Braced frames where bracing carries gravity load
a. Steel 4.4
b. Concrete 2.8
c. Heavy timber 2.8
Gravity LoadLateralForces
Stiff Resisting Elements…Shearwalls or Braced Frames
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EXAMPLE: Step 8
Step 8: Calculate W
Level Story weight, wx (kN)3 (Roof) 510
2 6811 681Σ 1872
EXAMPLE: Step 9
Step 9: Calculate design base shear
Ts = Cv/(2.5 × Ca) = 0.32/(2.5 × 0.22) = 0.582 sec > T (= 0.14 sec)
Vmin = 0.11 ×Ca × I × W = 0.11 × 0.22 ×1.0 × 1872 = 45.3 kN
V = (2.5 × Ca × I)/R × W = (2.5 × 0.22 ×1.0)/4.5 × 1872 = 228.8 kN > Vmin
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Seismic Design Forces
Step 10: Distribute design base shear
Story hx (m) wx (kN) hxwx(m-kN)
Fx (kN)
3 (Roof) 8.22 510.0 4192.2 97.97
2 5.48 681.0 3731.9 87.22
1 2.74 681.0 1865.9 43.61
Σ 1872.0 9790.0 228.8
Fx = (wxhx)/(Σwihi) × V when T ≤ 0.7 sec
EXAMPLE: Step 10
97.97 kN
87.22 kN
43.61 kN 1
2
3
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Computation of Design Seismic Forces
S. K. Ghosh Associates Inc.Palatine, IL
www.skghoshassociates.com
Typical Plan of Example Building
A
B
C
D
1 2 3 4 5 6
N
7 87.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m
6.71
m6.
71 m
6.71
m
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Typical Elevation of Example Building
11@
3.66
m=
40.2
6 m
10
11
12
7
8
9
4
5
6
1
2
3
4.88
m
Design Data
• Building LocationDubai (Seismic Zone 2A)
• Material PropertiesConcrete: fc
’ = 30 MPa, wc = 23.55 KN/m3
Reinforcement: fy = 420 MPa
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Design Data
• Service LoadsLive loads: roof = 957.6 N/m2
floor = 2394 N/m2
Superimposed dead loads:
roof = 478.8 N/m2 + 889.64 KN for penthouse
floor = 1436.4 N/m2 (957.6 N/m2 permanent partitions + 478.8 N/m2 ceiling, etc.)
Design Data
• Seismic Design DataZone 2A: Z = 0.15
Soil Profile Type: SD (stiff soil profile; UBC Table 16-J)
For Occupancy Category 4, I = 1.0 (UBC Table 16-K)
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Design Data
• Member Dimensions
Slab: 205 mm
Beams: 560 × 560 mm
Interior columns: 660 × 660 mm
Edge columns: 610 × 610 mm
Wall thickness: 305 mm
Values of Ca as Function of Soil Profile Type and Z (Table 16-Q)
1: Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine seismic coefficients for Soil Profile Type SF.
See Footnote 1SF
0.36Na0.360.340.300.19SE
0.44Na0.360.280.220.12SD
0.40Na0.330.240.180.09SC
0.40Na0.300.200.150.08SB
0.32Na0.240.160.120.06SA
Z = 0.4Z = 0.3Z = 0.2Z = 0.15Z = 0.075Seismic Zone Factor, ZSoil
Profile Type
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Values of Cv as Function of Soil Profile Type and Z (Table 16-R)
1: Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine seismic coefficients for Soil Profile Type SF.
See Footnote 1SF
0.96Nv0.840.640.500.26SE
0.64Nv0.540.400.320.18SD
0.56Nv0.450.320.250.13SC
0.40Nv0.300.200.150.08SB
0.32Nv0.240.160.120.06SA
Z = 0.4Z = 0.3Z = 0.2Z = 0.15Z = 0.075Seismic Zone Factor, ZSoil
Profile Type
Seismic ForcesThe equivalent lateral force procedure of 1997 UBC Section 1630.2 is used to compute the seismic base shear. In a given direction, V is determined by UBC Eqs. 30-4 – 30-7:
V = Cs W
where Cs is the seismic response coefficient determined in accordance with UBC 1630.2.1 and W is the total dead load of the structure and applicable portions of other loads as indicated in UBC 1630.1.1. For the member sizes and superimposed dead loads, W = 121,107 kN.
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Seismic Forces in N-S Direction
In the N-S direction, a dual system is utilized.
As a minimum, the dual system must have
intermediate reinforced concrete moment
frames and ordinary reinforced concrete shear
walls in a building in Zone 2A. For this system,
the response modification coefficient R = 6.5
(see UBC Table 16-N).
Seismic Forces in N-S Direction• Approximate period (Ta)
The fundamental period of the building T is determined in accordance with UBC 1630.2.2. In lieu of a more exact analysis, an approximate fundamental period Ta is computed by UBC Eq. 30-8 for the dual system:
Building height hn = 45.14 m Approximate period parameter Ct = 0.0488 (1630.2.2 Method A)Period Ta = Cthn
3/4 = 0.0488 × (45.14)3/4 = 0.85 sec
No further refinement of the period is made in this example.
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Seismic Forces in N-S Direction
• Seismic base shear (V)
The seismic response coefficient Cs is determined by UBC Eq. 30-4:
Cs = CvI / RT= 0.32x1 / (6.5x0.85)= 0.058
Seismic Forces in N-S Direction
The value of Cs need not exceed that from UBC Eq. 30-5:
Cs = 2.5CaI / R = 2.5x0.22 / 6.5 = 0.085
Also, Cs shall not be less than the value given by UBC Eq. 30-6:
Cs = 0.11CaI = 0.024
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Seismic Forces in N-S Direction
Thus, the value of Cs from UBC Eq. 30-4 governs and the base shear in the N-S direction is:
V = 0.058 W = 0.058 × 121,107 = 7024 kN
Seismic Forces in N-S Direction• Vertical distribution of seismic forces
The total base shear is distributed over the height of the building in conformance with UBC Eqs. 30-14 and 30-15:
where Fx is the lateral force induced at level x, wx and wi are the portions of W assigned to levels x or i.
∑=
−= n
iii
xxtx
hw
hwFVF
1
)(
sec 0.7 T for 25.007.0 >≤= VTVFt
Concentrated force Ft is applied at the top floor and accounts for
the higher mode effects in tall buildings
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Seismic Forces in N-S Direction
• Vertical distribution of seismic forces
For T = 0.85 sec, Ft = 0.07x0.85x7024.2 = 418 kN
V – Ft = 7024 - 418 = 6606 kN
Seismic Forces in N-S DirectionSeismic Forces and Story Shears in N-S Direction
Story Shear, Vx (kN)
Lateral Force, Fx+Ft (kN)wxhx
Height, hx (m)
Story Weights, wx
(kN)Level
70243,004,357121107Σ
702411150,6314.8810382.151.00691219086,5938.5310146.392.006722272123,70412.1910146.393.006450353160,81615.8510146.394.006096435197,92719.5110146.395.005661516235,03923.1610146.396.005144598272,15026.8210146.397.004546680309,26230.4810146.398.003866761346,37334.1410146.399.003104843383,48537.8010146.3910.002261924420,59641.4510146.3911.0013361336417,77645.149261.2012.00
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In the E-W direction, a moment-resisting frame system is utilized. As a minimum, this must be an intermediate reinforced concrete moment frame in a building in Zone 2A. For this system, the response modification coefficient R = 5.5 (UBC Table 16-N).
Seismic Forces in E-W Direction
Seismic Forces in E-W Direction
• Approximate period (Ta)The fundamental period of the building T is determined in accordance with UBC 1630.2.2. In lieu of a more exact analysis, an approximate fundamental period Ta is computed by UBC Eq. 30-8 for the intermediate RC moment frame:
Building height hn = 45.14 mApproximate period parameter Ct = 0.0731Period Ta = Cthn
3/4 = 0.0731 × (45.14)3/4 = 1.27 sec
No further refinement of the period is made in this example.
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Seismic Forces in E-W Direction
• Seismic base shear (V)
The seismic response coefficient Cs is determined by UBC Eq. 30-4:
Cs = CvI / RT= 0.32x1 / (5.5x1.27) = 0.05
Seismic Forces in E-W Direction
The value of Cs need not exceed that from UBC Eq. 30-5:
Cs = 2.5CaI / R = 2.5x0.22 / 5.5 = 0.10
Also, Cs shall not be less than the value given by UBC Eq. 30-6:
Cs = 0.11CaI = 0.024
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Seismic Forces in E-W Direction
Thus, the value of Cs from UBC Eq. 30-4 governs and the base shear in the E-Wdirection is:
V = 0.05 W = 0.05 × 121107 = 6055 kN
Seismic Forces in E-W Direction• Vertical distribution of seismic forces
The total base shear is distributed over the height of the building in conformance with UBC Eqs. 30-14 and 30-15:
where Fx is the lateral force induced at level x, wx and wi are the portions of W assigned to levels x or i.
∑=
−= n
iii
xxtx
hw
hwFVF
1
)(
sec 0.7 T for 25.007.0 >≤= VTVFt
Concentrated force Ft is applied at the top floor and accounts for
the higher mode effects in tall buildings
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Seismic Forces in E-W Direction
• Vertical distribution of seismic forces
For T = 1.27 sec, Ft = 0.07x1.27x6055.35 = 538 kN
V – Ft = 6055 – 538 = 5517 kN
Seismic Forces in E-W DirectionSeismic Forces and Story Shears in E-W Direction
Story Shear, Vx (kN)
Lateral Force, Fx+Ft (kN)wxhx
Height, hx
(m)
Story Weights, wx (kN)
Level
60553,004,357121107Σ
60559250,6314.8810382.151.00596215986,5938.5310146.392.005803227123,70412.1910146.393.005576295160,81615.8510146.394.005280363197,92719.5110146.395.004917431235,03923.1610146.396.004485499272,15026.8210146.397.003986567309,26230.4810146.398.003418636346,37334.1410146.399.002782704383,48537.8010146.3910.002077772420,59641.4510146.3911.0013051305417,77645.149261.2012.00
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Method of AnalysisA three-dimensional analysis of the building was performed in the N-S and E-W directions for the seismic forces using SAP2000. In the model, rigid diaphragms were assigned at each floor level, and rigid-end offsets were defined at the ends of the horizontal members so that results were automatically obtained at the faces of the supports. The stiffness properties of the members were input assuming cracked sections. The following cracked section properties were used:
Beams: Ieff = 0.5 IgColumns: Ieff = 0.7 IgShear walls: Ieff = 0.5 Ig
where Ig is the gross moment of inertia of the section. P-delta effect were also considered in the analysis.
Method of Analysis
In accordance with UBC 1630.6, the center of mass was displaced each way from its actual location a distance equal to 5 percent of the building dimension perpendicular to the applied forces to account for accidental torsion in seismic design.
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Method of Analysis
In a dual system, an additional safeguard is provided by requiring that moment-resisting frames be capable of resisting at least 25% of the design forces without the benefit of shear walls (UBC 1629.6.5). Thus, the building was also analyzed in the N-S direction using 25% of the design forces without the shear walls present, including torsional effects.
Method of AnalysisResults of 3-D Analysis under Seismic Force in E-W Direction for
Frame C
347-347347-348348-3473551
356-356356-357357-3483532
349-348349-350351-3393453
335-335335-337337-3233284
315-315315-317317-3013065
291-291291-294294-2762806
263-263263-265266-2462507
231-229231-233233-2132178
194-194194-196197-1761799
153-153153-156156-13513710
110-110110-112112-909111
65-6464-6768-485112
959596961
989898962
969697943
929293894
878787835
808081766
727273687
636464598
535354499
4242433710
3030312511
1818191412
Bending Moment in Beams (m-kN) Shear Forces in Beams (kN)
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Method of AnalysisResults of 3-D Analysis under Seismic Force in E-W Direction for Frame C
747747537517-286-286-207-1581351351256157-333-333-246-1592326326243165-340-340-252-1713307308227144-335-336-247-1674285287210134-324-325-238-1625261262192118-308-309-225-1546232233170103-288-289-210-144720020114685-264-265-191-133816416511865-236-237-170-12091241258843-204-205-145-1031078815622-166-167-118-9011383922-6-127-129-84-5112
2252251621471
2212211621022
2152151601093
2072081531004
197197145955
184184135886
168169123807
150150109708
12913093609
106107754710
7980563611
5354341512
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
-7-2117861
-6-1546892
-6-1145933
-6-794994
-5-504105
-5-253276
-4-62507
-391828
-3181249
-2237510
-1223811
0.0-1111312
Bending Moment in Columns (m-kN)
Shear Forces in Columns (kN)
Axial Forces in Columns (kN)
Method of AnalysisResults of 3-D Analysis under Seismic Force in N-S Direction for
Frame 4
84
118
142
159
170
175
176
173
168
161
160
118
122
122
119
114
107
98
88
76
63
48
33
18
-81
-113
-135
-150
-159
-162
-162
-158
-152
-144
-142
-104
120-119841
125-1211152
123-1171383
118-1121534
112-1051625
104-961666
95-861657
84-751618
71-621559
56-4714710
42-3314511
26-1710912
412841271
433941382
424740453
415338504
385636535
365833546
325829547
295726538
245621519
1953164810
1453114711
93963512
Bending Moment in Beams (m-kN) Shear Forces in Beams (kN)
Italic denotes results with 25% of design base shear applied to the frame.
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Method of AnalysisResults of 3-D Analysis under Seismic Force in N-S Direction for
Frame 4
21712014981-91-27-50-911211305470-112-74-53-2921061435477-110-104-55-4731031564981-110-128-54-594951624582-106-144-53-695871644082-100-155-50-756781623579-94-156-47-797671572976-861-61-43-798551502371-76-158-39-779421431667-65-156-34-761027131961-51-132-28-651115147167-42-214-18-10512
693245201
826638322
768038403
749236454
719934495
6610332506
6010429517
5410326508
469922489
3896174610
2785134111
2011795612
24
24
23
21
19
17
15
13
10
7
5
453395551
442985282
432574903
412174454
381793955
341433426
301102887
26802348
21551819
153413110
10178311
2463512
Bending Moment in Columns (m-kN)
Shear Forces in Columns (kN)
Axial Forces in Columns (kN)
360563,925-46,34501315947,057-35,50202287336,538-26,02903257627,309-17,88604228719,335-10,97005199212,523-52360616866841-67207136222862694081016-1103481809617-32735530010277-40475060011632-36111296012
BottomTopShear Force
(kN)Bending Moment (m – kN)Axial Forces
(kips)Level
Results of 3-D Analysis under Seismic Forces in N-S Direction for Wall on Column Line 7
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Story Drift and P-Delta Effects
• Story drift determination
ΔM = 0.7RΔs
Story Drift = ΔM(x) - ΔM(x-1)
Story Drift and P-Delta EffectsLateral Displacements and Interstory Drifts due to Seismic Forces
in N-S and E-W Directions
64.764.716.813.713.73163.1127.833.218.231.97263.6191.449.723.755.512.2361.2252.665.627.382.818.2458.2310.880.729.6112.424.7554.2365.094.831.4143.831.6649.7414.7107.731.9175.638.6744.2458.9119.231.4207.045.5838.2497.1129.130.9238.052.3931.1528.2137.230.0268.058.91023.5551.8143.328.7296.765.21115.4567.2147.326.8323.571.112
Story Drift (mm)
ΔM
(mm)
Δs
(mm)
Story Drift (mm)
ΔM
(mm)
Δs
(mm)
E-W DirectionN-S DirectionStory
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Story Drift and P-Delta Effects
The design story drifts must not exceed the
allowable story drift from 1997 UBC 1630.10.2 -
for Occupancy Category II, Δa = 0.020hsx where
hsx is the story height below level x. Thus, for
the 12-ft story heights, Δa = 0.020 × 3.66 × 1000 =
73.2 mm, and for the 4.88-m story height at the
first level, Δa = 97.5 mm. It is evident the limits
are satisfied in both directions.
Story Drift and P-Delta Effects
• P-delta effects
As noted above, P-delta effects were automatically considered in the analysis using SAP2000. The provisions of P-delta effects are given in 1997 UBC 1630.1.3.
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Seismic Details for Reinforced Concrete Buildings
in Moderate Seismic Applications
S. K. Ghosh Associates Inc.Palatine, IL
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Applicability of Requirements
ACI 318-05 Chapter 21
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Flexural Members
Beams of Intermediate Moment Frames –Longitudinal Reinforcement
(10.3.5, 10.5.1, 21.12.4.1)
M-n,l
M+n,l ≥ M-
n,l/3
M-n,r
M+n,r ≥ M-
n,r/3
M-n or M+
n ≥ (max. Mn at either joint)/5
ρmin = 0.25√f’c/fy, 1.4/fy
εt ≥ 0.004
Sect. 7.13
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Beams of Intermediate Moment Frames–Transverse Reinforcement
(21.12.3, 21.12.4.2, 21.12.4.3)
≤ 50mm Stirrups
Trans. reinf. based on Mnand factored tributary gravity load
s ≤ d/2≥ 2h
h
s ≤
d/48 × smallest long. bar dia.24 × hoop bar dia.300 mm
Hoops
Hoop Reinforcement
(21.3.3.6)
(≥ 75 mm)
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Intermediate Moment Frames –Two-way Slabs
(21.12.6)
c2 c2 + 3h
½ Middle strip
½ Middle strip
Column stripAll reinforcement necessaryto resist Ms to be placed incolumn strip
h = slab thickness
Note: Applies to both top and bottom reinforcement
As ≥Reinforcement necessary to resist γfMs
Reinforcement in column strip/2
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Banded Column Strip Reinforcement
21.10.6.5, 21.10.6.7 -Longitudinal Reinforcement in
Column Strip of Slab
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Longitudinal Reinforcement in Middle Strip of Slab
21.12.6.8 – Shear Strength of Two-Way Slabs without Beams in Intermediate Moment Frames
• Slab-column frames are susceptible to punching-shear failures during earthquakes if the shear stresses due to gravity loads are high
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• At the critical sections for columns defined in 11.12.1.2, two-way shear caused by factored gravity loads shall not exceed 0.4φVc, where Vc shall be calculated as defined in 11.12.2.1 for nonprestressed slabs and 11.12.2.2 for prestressed slabs
21.12.6.8 – Shear Strength of Two-Way Slabs without Beams in Intermediate Moment Frames
• It shall be permitted to waive this requirements if the contribution of the earthquake-induced factored two-way shear stress transferred by eccentricity of shear in accordance with 11.12.6.1 and 11.12.6.2 at the point of maximum stress does not exceed one-half of the stress φVn
permitted by 11.12.6.2
21.12.6.8 – Shear Strength of Two-Way Slabs without Beams in Intermediate Moment Frames
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Members Subjected to Bending and Axial Load
Columns of Intermediate Moment Frames– Transverse Reinforcement
(21.12.3, 21.12.5)
s to conform to 7.10 and 11.5.5.1
h2
h1
≤ so/2Joint reinf.per 11.11.2
Trans. reinf. based on Mn and factored tributary gravity load
so ≤
8 × smallest long. bar dia.24 × hoop bar dia.0.5 × min. (h1 or h2)300 mm
lo
lo ≥
Larger of h1 or h2
Clear span/6450 mm
Hoops
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Design of Typical Structural Members
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Typical Plan of Example Building
A
B
C
D
1 2 3 4 5 6
N
7 87.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m 7.92 m
6.71
m6.
71 m
6.71
m
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Typical Elevation of Example Building
11@
3.66
m=
40.2
6 m
10
11
12
7
8
9
4
5
6
1
2
3
4.88
m
Design Data
• Building LocationDubai (Seismic Zone 2A)
• Material PropertiesConcrete: fc
’ = 30 MPa, wc = 23.55 KN/m3
Reinforcement: fy = 420 MPa
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Design Data
• Service LoadsLive loads: roof = 957.6 N/m2
floor = 2394 N/m2
Superimposed dead loads:
roof = 478.8 N/m2 + 889.64 KN for penthouse
floor = 1436.4 N/m2 (957.6 N/m2 permanent partitions + 478.8 N/m2 ceiling, etc.)
Design Data
• Seismic Design DataZone 2A: Z = 0.15
Soil Profile Type: SD (stiff soil profile; UBC Table 16-J)
For Occupancy Category 4, I = 1.0 (UBC Table 16-K)
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Design Data
• Member Dimensions
Slab: 205 mm
Beams: 560 × 560 mm
Interior columns: 660 × 660 mm
Edge columns: 610 × 610 mm
Wall thickness: 305 mm
Load CombinationThe seismic load effect E for use in the basic strength design load combinations is the combined effect of horizontal and vertical earthquake-induced forces. The E for use in Eq. (9-5) is computed by UBC Eq. 30-1:
E = ρEh + Ev
where Eh = effect of horizontal seismic forcesEv = effect of vertical seismic forcesρ = redundancy factor
= 1.0 for structures in Seismic Zones 1 and 2
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Load Combination
where the effects of gravity and seismic ground motion are additive:
E = ρ Eh + 0.5 Ca I D
Load Combination
Similarly, where the effects of gravity and seismic ground motion counteract:
E = Eh - Ev = ρ Eh - 0.5 Ca I D
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Load Combination
Substituting Ca = 0.22 and ρ = 1.0 into the equations for E, and then substituting E into Eqs. (12-5) and (12-6) above results in the following:
U = 1.2D + 0.5L + 1.0Eh + (0.5 × 0.22)D= 1.31D + 0.5L + Eh
U = 0.9D +1.0 Eh - (0.5 × 0.22)D = 0.79D + Eh
Beam C4 – C5
Summary of Design Bending Moments and Shear Forces for Beam C4-C5 at the Second Floor Level (SDC C)
Wind (W)
Seismic (QE)
Live (L)
Dead (D)
Load Case
± 98.0± 356support± 2.8± 33Support
25.4Midspan
28.0-37.0Support
94.6Midspan
104.3-137.6Support
Shear Force (kN)
Bending Moment (m-kN)Location
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Beam C4 – C5Summary of Design Bending Moments and Shear Forces for Beam C4-C5
at the Second Floor Level (SDC C)
Shear Force (KN)
Bending Moment (m –KN)
LocationLoad combination
-16247Support0.79D - QE
249-555Support1.31D + 0.5L + QE
89-71Support0.9D – 1.6W144-236Support1.2D + 0.5L + 1.6W172-251Support1.2D + 1.6L + 0.8W
154.2Midspan167.0-224.3Support1.2D + 1.6L
132.4Midspan146.0-192.6Support1.4D
Beam C4 – C5
1. Flexural designThe factored axial load on the member, which is negligible, is less than Agfc
’/10; thus, the provisions of ACI 21.12.4 for beams must be satisfied. All other applicable provisions in Chapters 1 through 18 of ACI 318-05 are to be satisfied as well.
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Beam C4 – C5
Minimum flexural reinforcement:
(governs) mm935415
4955604.1
f
db4.1
mm914 415
4955603025.0
f
dbf25.0A
2
y
w
2
y
wcmins,
=××
==
=××
=′
=
Beam C4 – C5
Maximum flexural reinforcement:
2
y
c1maxs,
mm 6204
0.0070.003
415495560300.850.85
0.0040.0030.003
f
dwbf0.85βA
=
×××××
=
+
′=
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Beam C4 – C5Required Flexural Reinforcement for Beam C4-C5 at the
Second Floor Level (SDC C)
2073 - No 221161154.2Midspan
2073 - No 221161
5415 – No 293235- 461.4Support
φ Mn(m-kN)
ReinforcementAs (mm2)Mu(m-kN)
Location
Beam C4 – C5
ACI 21.12.4.1: the positive moment
strength at the face of the joint be greater
than or equal to 33% of the negative
moment strength at that location. This is
satisfied, since 207 m-KN > 541/3 = 180.3
m-KN.
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Beam C4 – C5
The negative or positive moment strength at any section along the length of the member must be greater than or equal to 20% of the maximum moment strength provided at the face of either joint.
541/5 = 108.2 m-KNProviding 2- No. 29 bars ( = 230 m-KN) or 2- No. 22 bars ( = 140 m-KN) satisfies this provision.
Minimum of 2 – No. 29 bars (= 1294 mm2) or 3 – No. 22 bars (= 1161 mm2) must be provided to satisfy minimum reinforcement requirement of ACI 10.5
Beam C4 – C5
2. Shear designShear demand from nominal flexural capacity
Vu = (541 + 207) / 7.26 = 103.03 kNShear demand from gravity load
Wu =1.31wD + 0.5wL
= 1.31 × 28.724 + 0.5 × 7.721 = 41.49 kN/mVu = wuln / 2 = (41.49 × 7.26) / 2 = 150.61 kN
Vu = 103.03 + 150.61 = 253.64 kN
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Beam C4 – C5
The nominal shear strength provided by
concrete (Vc)
Vc = 0.17 × (fc’)0.5 × bw × d Eq. (11-3)
= 0.17 × (30)0.5 × 560 × 495 / 1000 = 258.1 kN
Beam C4 – C5Vu (= 253.6 KN) > φVc (0.75 ×258.1 = 193.6 kN)
Provide shear reinforcement in accordance with ACI 11.5.6. Assuming No. 10 hoops, the required spacing s is determined by Eq. (11-15):
s = (Av × fy × d) / Vs
= (142 ×415 ×495) / (253,600/0.75 –258,100)= 364.5 mm
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Beam C4 – C5ACI 21.12.4.2: the maximum spacing of hoops over the length 2h = 2 × 560 = 1120 mm from the face of the support at each end of the member is the smallest of the following:
(1) d / 4 = 495 / 4 = 123.8 mm (governs)(2) 8 (diameter of smallest longitudinal bar)
= 8 × 22.2 = 177.6 mm(3) 24 (diameter of hoop bar) = 24 × 9.5 = 228 mm(4) 305 mm
Beam C4 – C5
Use 10-No. 10 hoops at each end of the beam spaced at 120 mm on center with the first stirrup located 50 mm from the face of the support.
For the remainder of the beam, the maximum stirrup spacing is d / 2 = 247.5 (ACI 21.12.4.3). Use No. 10 stirrups @ 240 mm for the remainder of the beam.
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Beam C4 – C5
660 mm
5-No.29
10-No.10 hoops @ 120mm
1830 mm 5-No.29 5-No.29
660 mm
560 mm
50 mm
7264 mm
3-No.22No.10 hoops @ 240mm
Design of Column C4 at 2nd Floor
-221-35137120.79D – Eh
221 35164331.31D + 0.5L + Eh
-11-664224N-S-11-534229E-W
0.9D – 1.6W
11665921N-S11535916E-W
1.2D + 0.5L + 1.6W
6336528N-S5266525E-W
1.2D + 1.6L + 0.8W
0065251.2D + 1.6L0065791.4D
Load Combination± 221± 351± 0.1E-WSeismic (QE)± 6.9± 41± 3.0N-S± 6.6± 330E-W
Wind (W)
00554Live (L) (reduced)004699Dead (D)
Shear Force(kips)
Bending Moment(ft-kips)
Axial Force(kips)Load Case
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Design of Column C4Design for Axial Force and BendingBased on the governing load combinations in the table, a 660 × 660 mm column with 12-No. 32 bars (ρg = 2.25%) is adequate for column C4 supporting the second floor level. The interaction diagram for this column is given below. Slenderness effects need not be considered, since P-delta effects were included in the analysis. Also, the provided reinforcement ratio is within the allowable range of 1% and 8% (ACI 10.9.1).
Design of Column C4
0
2000
4000
6000
8000
10000
12000
14000
16000
0 250 500 750 1000 1250 1500 1750 2000
Bending Moment (m-kN)
Axi
al F
orce
(kN
)
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ACI 7.6.3 requires that the clear distance between longitudinal bars shall not be less than
1.5db = 1.5 × 32.3 = 48.5 mm
nor 40mm. In this case, assuming No. 10 hoops and ties, the clear distance is equal to the following:
Design of Column C4
O.K.mm 5.48mm 9.1433.323
23.325.9402660
>=−⎟⎠⎞
⎜⎝⎛ ++−
Design of Column C4
Design for Shear
Columns in intermediate moment frames must satisfy the shear requirements in ACI 21.12.3. The first of the two options in that section is utilized here to determine the design shear strength:
The sum of the shear associated with development of nominal moment strengths of the member at each restrained end of the clear span and the shear calculated for the factored gravity loads
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Design of Column C4
Design for Shear
Because the column is at the 2nd floor, and the moment at any column end cannot exceed the average of the nominal moment strengths of the beams framing into that end, shear demand from the seismic forces is calculated from the nominal flexural strengths of the beams.
Design of Column C4
Design for Shear
Vu = (541+207)/3.1 + 0 = 241.3 kN > 221 kN
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Design of Column C4
Design for Shear
kN 531.9 1000/5386603066014
3712000117.0
dbfA14
N117.0V
2
wcg
uc
=××⎟⎟⎠
⎞⎜⎜⎝
⎛
×+=
′⎟⎟⎠
⎞⎜⎜⎝
⎛+=
The shear capacity of the column will be checked in accordance with ACI Eq. (11-4) for members subjected to axial compression:
where Nu = 3712 kN is the smallest axial force corresponding to the largest shear force on the section (see Table) and d = 538 mm was obtained from a strain compatibility analysis.
Design of Column C4
Design for Shear
Since Vu > ΦVc/2 = 0.75x531.9/2 = 199.5 kN, by ACI 318-05 Section 11.5.6.1, minimum transverse reinforcement would be required.
yt
wcmin,v f
sbf062.0A
′=
With No. 10 hoops with one cross-tie, Av = 213 mm2
=> s = 394.4 mm > d/2 = 269 mm (ACI 318 11.5.5.1)
Thus, srequired = 269 mm
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Design of Column C4
Design for Shear
For intermediate moment frames, the requirements in ACI 21.12.5.1 aims primarily to confine the concrete within the core and provide lateral support for the longitudinal reinforcement.
For No. 10 rectangular hoops, the vertical spacing s0
must not exceed the smallest of the following :
Design of Column C4
ACI 21.12.5.1:
• 8 (smallest longitudinal bar diameter) = 8 × 32.3 = 258.4 mm• 24 (hoop bar diameter) = 24 × 9.5 = 228 mm (governs)• Least column dimension/2 = 660/2 = 330 mm• 300 mm
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The governing s0 = 228mm must be provided over a length l0 measured from the joint face, where l0 is the largest of the following:
Design of Column C4
ACI 21.12.5.1:
• Clear span/6 = [3657 - 560]/6 = 516.2 mm• Maximum cross-sectional dimension of member = 660 mm (governs)
• 450 mm
Use 4-No. 10 hoops and crossties @ 220 mm with the first hoop located at 100 mm (< s0/2 = 114 mm; ACI 21.12.5.3) from the joint face above the first floor level and below the second floor level.
For the remainder of the column, tie spacing shall conform to ACI 7.10 and 11.5.5.1. In this case, ACI 11.5.5.1 governs. Use a tie spacing of 250 mm in this region of the column.
Design of Column C4
ACI 21.12.5.1:
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ACI 21.12.5.5 requires that joint reinforcement in intermediate moment frames conform to ACI 11.11.2. Since this beam-column joint is part of the primary seismic-force-resisting system, lateral reinforcement in the joint must not be less than that computed by Eq. (11-13). For No. 10 hoops with one crosstie, the required spacing is:
Design of Column C4
Joint Reinforcement:
mm 394.466030062.0
415)713(bf062.0
fAs
wc
ytv =×
××=
′=
For simpler detailing, continue the 220 mm spacing at the column ends through the joint.
Design of Column C4
Joint Reinforcement:
210
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Design of Column C4
Shear wall B7 – C7Summary of Design Axial Forces, Bending Moments, and
Shear Forces at Base of Shear Wall on Line 7 (SDC C)
Wind (W)
± 3604± 63,9250
± 1438± 20,0450
Seismic (QE)
001189Live (L)
0011,951Dead (D)
Shear Forces (kN)
Bending Moment (m-kN)
Axial Force (kN)Load Case
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Shear wall B7 – C7Summary of Design Axial Forces, Bending Moments, and
Shear Forces at Base of Shear Wall on Line 7 (SDC C)
-3604-63,92594410.79D - QE
360463,92516,2501.31D + 0.5L + QE
- 2301-32,07210,7560.9D – 1.6W
230132,07214,9361.2D +0.5L + 1.6W
115016,03616,2441.2D + 1.6L + 0.8W
0016,2441.2D + 1.6L
0016,7311.4D
Shear Force (kN)
Bending Moment (m-kN)
Axial Force (kN)
Load combination
Shear wall B7 – C7
1. Shear design
The shear strength of the concrete for wall subjected to axial compression (ACI 11.10.5)
Vc = 0.17 (fc’)0.5 h d
= 0.17 × (30)0.5 × 305 × 5892.8 /1000 = 1673.5 kN
where d = 0.8 lw (= 0.8 × 7366 = 5892.8 mm)
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Shear wall B7 – C7Since φVc (0.75 × 1673.5 = 1255.1 kN) < Vu (= 3604 kN), horizontal shear reinforcement shall be provided in accordance with ACI 11.10.9.
Required bar spacing with 2 layers of No. 13:s = (Av fy d) / Vs = (254 × 415 × 5892.8) / (3,604,000 / 0.75-1,673,500) = 198.3 mm
Note: ACI 14.3.4 requires two layers of reinforcement for walls more than 250 mm thick
Shear wall B7 – C7ACI 11.10.9.3: spacing of horizontal reinforcement shall not exceed (1) lw/5 = 7336/5 =1473.2 mm, (2) 3h = 3 × 305 = 915 mm, or (3) 450 mm.
ACI 11.10.9.2: ratio of horizontal shear reinforcement shall not be less than 0.0025
For 2-No.13 horizontal bar spaced at 450 mm:ρt = (2 ×127) / (305 ×200) = 0.0042 > 0.0025 O.K.
Therefore, use 2-No.13 horizontal bar @ 200 mm
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Shear wall B7 – C7
ACI 11.10.3: Shear strength Vn at any horizontal section must be less than or equal to 0.83 (fc
’)0.5 h d (= 8170.7 kN). In this case,
Vn = Vc + Vs
= 1673.5 + (254 × 415 × 5892.8) / 330= 1883.9 kN < 8170.7 kN O.K.
Shear wall B7 – C7
ACI 11.10.9.4: The ratio of vertical shear reinforcement area to gross concrete area of horizontal section shall not be less than 0.0025 not the value obtained by Eq. (11-32).
ρl = 0.0025 + 0.5 (2.5 – hw / lw) (ρt - 0.0025)= 0.0025 + 0.5 (2.5 – 45 / 7.366) (0.0042 – 0.0025)< 0.0025
Thus, ρl = 0.0025
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Shear wall B7 – C7
ACI 11.10.9.5: spacing of vertical shear reinforcement shall not exceed (1) lw/3 (= 7366/3 = 2455.3 mm), (2) 3h (= 3 × 305 = 915 mm), or (3) 450 mm (governs).
For 2 – No. 13 vertical bar spaced at 330 mm,ρl = (2 ×127) / (305 ×330) = 0.00252 > 0.0025 O.K.
Use 2-No.13 vertical bars @ 330 mm
Shear wall B7 – C7
The provided vertical and horizontal
reinforcement satisfy the requirements of
ACI 14.3.2 and 14.3.3 for minimum ratio of
vertical and horizontal reinforcement to gross
concrete area, respectively, and ACI 14.3.5 for
maximum bar spacing.
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Shear wall B7 – C7
2. Axial force and bending designACI 14.4 requires that walls subjected to axial load or combined flexure and axial load shall be designed as compression members in accordance with ACI 10.2, 10.3, 10.10 through 10.14, 10.17, 14.2, and 14.3 unless the empirical design method of ACI 14.5 or the alternative design method of ACI 14.8 can be used. Clearly, both of these methods cannot be applied in this case, and the wall is designed in accordance with ACI 14.4.
Shear wall B7 – C7
0
10000
20000
30000
40000
50000
60000
70000
80000
0 20000 40000 60000 80000 100000 120000
Bending Moment (m-kN)
Axi
al F
orce
(kN
)
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Shear wall B7 – C7
For more information…
www.skghoshassociates.com
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Code Support Services, Code Change Process, and Plan
Review
Code Support Services
Publications
Seminars
Interpretations
Plan Review Services
Evaluation Services
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Code Support Services: Publications
Code Support Services: Publications
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Code Support Services: Publications
1999 Recommended Lateral Force Requirements / Commentary (SEAOC Blue Book)
This book reviews recommended provisions for earthquake-resistant design of structures. Highlights include design requirements, structural tests and inspections, foundations, and recommended modifications to the 1997 UBC for reinforced concrete, reinforced masonry, structural steel, and wood.
http://www.iccsafe.org/dyn/prod/9006S99.html
Code Support Services: Publications
Handbook to the 1997 Uniform Building Code
The handbook is a completely detailed and illustrated commentary on the 1997 Uniform Building Code, tracing historical background and rationale of the codes through the 1997 edition. The book contains numerous drawings and figures to clarify the application and intent of the code provisions. It is an essential reference for every building official, fire marshal, architect and engineer.
http://www.iccsafe.org/dyn/prod/6074S97.html
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Code Support Services: Publications
Code Support Services: Publications
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Code Support Services: Publications
Code Support Services: Seminars
Company/Organization WebsiteS.K. Ghosh Associates Inc www.skghoshassociates.comAmerican Society of Civil Engineers/ Structural Engineering Institute
www.seinstitute.com
International Code Council www.iccsafe.orgNational Council of Structural Engineers Associations
www.ncsea.com
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Code Support Services: Interpretations
ICC Technical Assistance
• Staff Opinions
• Committee Interpretations (not for time-sensitive issues)
www.iccsafe.org/cs/questions/index.html
Code Support Services: Interpretations
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Code Support Services:Plan Review Services
www.iccsafe.org/cs/techservices/#pr
The Code Official’s Technical Source for Approving New
and Innovative Building Products
Code Support Services: Evaluation Services
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Code Support Services: Evaluation Services
Find the Most Current Reports Online: http://www/icc-es.org
Code Support Services: Evaluation Services
• Click on the Evaluation Reports tab
• Search by » Product » Manufacturer » Report » Number
• No cost to access
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Code Change Process
1997 UBC
2000 IBC2001 Supplement2002 Accumulative Supplement
2003 IBC
Code Change Process
2003 IBC (18 month cycle began)2004 Supplement
2006 IBC2007 Supplement
2009 IBC (expected release date: 2/1/09)
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Code ChangesSubmitted
Code Development Hearing
Public Hearing ResultsPrinted & Distributed
Code ChangesPrinted & Distributed
Public CommentsSought on PublicHearing Results
Public CommentsPrinted & Distributed
Final ActionHearing
Supplement Or NewEdition Published
I-CODE DEVELOPMENTCYCLE
ICC Code Change Process
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Code Change Process
• All aspects of the ICC Code Development Process regulated by published procedures
• Council Policy (CP) 28 – Code Development
• Website link: » http://www.iccsafe.org/news/about/bylaws
.html
Code Change ProcessSteps in a Typical 18 month cycle
• Code changes due. Announcement posted on the website and other media. Anyone can submit a code change
• Staff review» Form and format: Legislative format» Proposals must be based on current text
• Publish» Website: Approx. 90 days prior to Code Development
Hearing» Published: Approx. 60 days prior to Code Development
Hearing
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Code Change Process
WEBCASTING:• Debut at 2002 Code Development
Hearings
• Followed up in all subsequent hearings
• Streaming video and audio
• Internet access on your PC
Code Change Process
• Adopted by reference in the IBC.
• Developed through ANSI-accredited consensus process
• Committee balanced and composed of producers, consumers and regulators.
• Committee ballots revisions.
• Public comment period.
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Code Change Process
• Next edition is ASCE 7-10 which will be adopted in 2012 IBC.
• 2009 IBC will adopt ASCE 7-05.
• ASCE 7-05 has two supplements
» Supplement No. 1» Supplement No. 2
• www.seinstitute.org
Structural Plan Review
Chapter 16: Structural Design Requirements
Chapter 17: Structural Tests and Inspections
Chapter 18: Foundations and Retaining Walls
Chapter 19: Concrete
Chapter 20: Lightweight Metals
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Structural Plan Review
Chapter 21: Masonry
Chapter 22: Steel
Chapter 23: Wood
Chapter 24: Glass and Glazing
Chapter 25: Gypsum Board and Plaster
Structural Plan Review
Step 1: Become familiar with project.
Step 2: Complete structural review.
Step 3: Write review.
Step 4: Critique review.
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Structural Plan Review
Step 1: Become familiar with project.
• Specifications
• Calculations
• Soils Report
• Plans
Structural Plan ReviewStep 2: Complete structural review.
• Identify structural systems and load paths
• Determine loads.
• Check structural members for load effects.
• Check plans and details for clarity and conformity with detailed code requirements based on material of construction.
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Structural Plan Review
Step 3: Write review
• Use checklist.
• Organize comments.
• Provide references: code sections, plan details, sections, grid lines, calculations pages, etc.
Structural Plan Review
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Structural Plan Review
Step 4: Critique review.
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Overview of the Seismic Design Provisions of the 2006 International
Building Code
S. K. Ghosh Associates Inc.Palatine, IL
www.skghoshassociates.com
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Seismic Design ProvisionsIBC Section 1613,
ASCE 7 Chapters 11-23excluding Chapter 14 and Appendix
11A
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ASCE 7-05 Chapters 11-23: Seismic Design
• ASCE 7-02 seismic provisions have been completely reformatted and reorganized.
• Much improved document that should be easier to use and result in more correct and uniform application of seismic requirements.
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ASCE 7-05 Figure 11.4-1: Design Response Spectrum
IBC Design Ground Motion• SS = mapped (MCE) spectral response
acceleration at short periods for Site Class B• S1 = mapped (MCE) spectral response acceleration
at 1.0-second period for Site Class B• ASCE 7 Figs. 22-1 through 22-20/ IBC Figs.
1613.5(1) through 1613.5(14) give contour maps for SS and S1, based on the latest version of USGS seismic hazard maps
• SS and S1 also available at http://eqhazmaps.usgs.gov
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Soil Classification
A. Hard RockB. RockC. Very dense soil or soft rockD. Stiff soilE. Soft soilF. Soils requiring site-specific
evaluations
Soil Classification
• Site Class D must be used when the
soil properties are not known in
sufficient detail, unless the building
official determines that Site Class E or
F is likely to be present at the site
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Values of Fa as Function of Site Conditions and Shaking Intensity
aaaaaF
0.90.91.21.72.5E
1.01.11.21.41.6D
1.01.01.11.21.2C
1.01.01.01.01.0B
0.80.80.80.80.8A
SS ≥
1.25
SS =
1.00
SS =
0.75
SS =
0.50
SS ≤
0.25
SHAKING INTENSITYSOIL
PROFILE
TYPE
Values of Fv as Function of Site Conditions and Shaking Intensity
aaaaaF
2.42.42.83.23.5E
1.51.61.82.02.4D
1.31.41.51.61.7C
1.01.01.01.01.0B
0.80.80.80.80.8A
S1 ≥
0.5
S1 =
0.4
S1 =
0.3
S1 =
0.2S1 ≤ 0.1
SHAKING INTENSITYSOIL
PROFILE
TYPE
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IBC Design Ground Motion
• SMS = soil-modified MCE spectral response
acceleration at short periods
= FaSS
• SM1 = soil-modified MCE spectral response
acceleration at 1.0-second period
= FvS1
IBC Ground Motion
• SDS = design spectral response
acceleration at short periods
= (2/3) SMS
• SD1 = design spectral response
acceleration at 1.0-second period
= (2/3) SM1
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IBC Ground Motion
• Maximum Considered Earthquake
(MCE)– Maximum level of earthquake ground
shaking that is considered reasonable to
design buildings to resist
IBC Ground Motion
• Maximum Considered Earthquake (MCE):» Deterministic earthquakes (in coastal
California)- best estimate of ground motion
from maximum magnitude earthquakes on
seismic faults with high probabilities of
occurrence.
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IBC Ground Motion
• Maximum Considered Earthquake (MCE)– 2% probability of exceedance in 50 years
(approximately 2,500 year return period) where
deterministic approach is not used
ASCE 7-05 Figure 11.4-1: Design Response Spectrum
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TL Map of Contiguous USA
Design Basis: IBC vs. UBC
• Design to avoid collapse in the
Maximum Considered Earthquake,
rather than to provide life safety in
the 500-year return period
earthquake
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1997 UBC Fig. 16-3Design Response Spectra
Correspondence between Ground Motion Parameters of the UBC and the IBC
Ca/Z of 1997 UBC = Fa of NEHRP/IBC
Cv/Z of 1997 UBC = Fv of NEHRP/IBC
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Correlation of Ground Motion Parameters
SDS = 2.5Ca
(2/3)FaSS = 2.5ZNaFa
SS = (1.5)ZNa(2.5)
Z ≥ 0.4gSDS = 1.00NaFa
(1.00Na for Site Class B)SS = 1.50Nag
SD1 = Cv
(2/3)FvS1 = ZNvFv
S1 = (1.5)ZNv
Z ≥ 0.4gSD1 = 0.4NvFv
(0.4Nv for Site Class B)S1 = 0.6Nvg
Design Spectrum
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UBC Seismic Zones
SDC Based on Short Period Response Acceleration – IBC
DCC0.33g < SDS < 0.50g
DaDaDa0.50g < SDS
CBB0.167g < SDS < 0.33g
AAASDS < 0.167 g
IVIIII or II
OCCUPANCY CATEGORYValues of SDS
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SDC Based on 1 sec. Period Response Acceleration – IBC
DaDaDa0.20g < SD1
DCC0.133g < SD1 < 0.20g
CBB0.067g < SD1 < 0.133g
AAASD1 < 0.067g
IVIIII or II
OCCUPANCY CATEGORYValues of SD1
SDC of IBC (Note a)
FEES1 ≥ 0.75g
IVIIII or II
OCCUPANCY
CATEGORYValue of S1
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ASCE 7-05 Section 11.6 Determination of Seismic Design Category
Can be based on SDS alone, provided• S1 < 0.75• Ta < 0.8Ts• T used to calculate story drift < Ts • Upper-bound design base shear is used in
design• Diaphragms are rigid, or for diaphragms
that are flexible, vertical elements of seismic-force-resisting system spaced at < 40 ft
Areas with S1 > 0.75g
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Ts = SD1/SDSTs = SD1/SDS
SDC of 2006 IBC vs. Seismic Zone of 1997 UBC
C (B)C (B)B (A)AA1Indianapolis, INBB (A)AAA1Wichita, KS
2006 IBC97 UBC
C (B)B (A)AAA2AKansas City, MO
DDCC (C)B2AHonolulu, HIDDD (C)CB3Sacramento, CADD (C)D (C)CB3Fresno, CADDD (C)CB3Chico, CADD (C)CC (C)B1Little Rock, AKCBBB (B)A2BTucson, AZEDCBA
ZoneLOCATION SITE CLASS
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SS ≤ 0.15g and S1 ≤ 0.04g
ASCE 7-05 11.7 Design Requirements for SDC A
11.7.2 Minimum Lateral Force
Fx = 0.01wx
w1
w2
w3
wr
0.01w1
0.01w2
0.01w3
0.01wr
V = 0.01(w1 + w2 + w3 + wr)
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ASCE 7-05 11.7 Design Requirements for SDC A
11.7.3 Load Path Connections
11.7.4 Connection to Supports
11.7.5 Anchorage of Concrete or
Masonry Walls
ASCE 7-05 12.8.1 Design Base Shear
0.6gSwhere(R/I)0.5S
0.01
TTfor(R/I)T
TS
TTfor(R/I)S
(R/I)TSC
WCV
11
L2LD1
LDSD1
S
S
≥≥
≥
>=
≤≤=
=
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ASCE 7-05 12.8 Equivalent Lateral Force Procedure
I/RWSV DS=
T)I/R(WSV D1=
g0.6Swhere,I/RWS0.5V ≥= 1
1
21
T)I/R(WTSV LD=
W0.01V =
LTDSD1s /SST = T,Period
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Concrete Structural Systems in ASCE 7-05 - SDC D, E, F
NLNLNL5 ½38MOMENT RESISTING FRAME SYSTEM using
Special Moment Frames of RC (SMF)
16016016052 ½5 BEARING WALL SYSTEM using
Special RC Shear Walls
10016016052 ½6BUILDING FRAME SYSTEM WITH OMF OF RC using
Special RC Shear walls
NL100
NL100
NL160
5 ½5
2 ½2 ½
76 ½
DUAL SYSTEM usingSpecial RC Shear Walls w/ SMFSpecial RC Shear Walls w/ IMF
FED
Height limitCdΩ0RCONCRETE STRUCTURAL
SYSTEMS - SDC D, E, and F
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Structure Period
Calculated by……1) Approximate Formulae
2) Rational Analysis using structural properties and deformational characteristics of resisting elements in a properly substantiated analysis
ASCE 7-05 12.8.2.1 Approximate Fundamental Period
Ta = Cr hnx
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ASCE 7-05 Table 12.8-2 Values of Approximate Period
Parameters Ct and x
0.90.016
(For SI: 0.044)
Moment resisting frame systems of reinforced concrete in which the frames resist 100 percent of the required seismic force and are not enclosed or adjoined by more rigid components that will prevent the frames from deflecting when subjected to seismic forces
0.80.028
(For SI: 0.068)
Moment resisting frame systems of steel in which the frames resist 100 percent of the required seismic force and are not enclosed or adjoined by more rigid components that will prevent the frames from deflecting when subjected to seismic forces
xCtStructure Type
ASCE 7-05 Table 12.8-2 Values of Approximate Period Parameters Ct and x (cont’d)
0.750.02
(For SI: 0.055)
All other structural systems
0.750.03
(For SI: 0.07)
Eccentrically braced steel frames
xCtStructure Type
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Upper Limit on T by "Rational Analysis"
Note: For drift analysis, upper limit on calculated T does
not apply (Section 12.8.6.2)
1.4
1.4
1.5
1.6
1.7
1.7
≥ 0.4
0.3
0.2
0.15
0.1
≤ 0.05
Coefficient Cu
Design Spectral Response
Acceleration (SD1)
Table 12.8-1 (ASCE 7-05)
Coefficient for Upper Limit on Calculated Period
ASCE 7-05 12.8.3 Vertical Distribution of Seismic Forces
wxhxk
Fx =Σ wihi
kV
k = 1 for T ≤ 0.5 sec
k = 2 for T ≥ 2.5 sec
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Horizontal Shear Distribution
For rigid diaphragms, the seismic design story shear shall be distributed to the various vertical elements of the seismic-force-resisting system in the story under consideration based on the relative lateral stiffnesses of the vertical resisting elements and the diaphragm.
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Accidental Torsion
Where diaphragms are not flexible, in addition to the torsional moment, the design also shall include accidental torsional moments caused by assumed displacement of the center of mass each way from the actual location by a distance equal to 5 percent of the dimension in the direction of applied forces.
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Story Drift
• Δ = δx − δx-1 < Δa
δx = Cd δxe / I
Cd = deflection amplification factor
Allowable Story Drift (Δa ) ASCE 7-05 Table 12.12-1
0.010hsx0.015hsx
0.007hsx0.007hsx
0.010hsx0.010hsx
0.015hsx0.020hsx
IVIII
Occupancy CategoryBuilding
I or II
0.025hsx
Buildings ≤ 4 stories in
height;other than masonry;
Non-structural elements
designed to accommodate
story drift
0.010hsxMasonry cantilever shear wall
buildings
0.007hsxOther masonry shear walls
buildings
0.020hsxAll other buildingshsx = Story height below level x
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Load Combinations
• Basic Load
E = ρQE + 0.2SDSD• Special Load
Em = Ω0QE +
0.2SDSD
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Load Combinations
• Basic LRFD
1.2D + 1.0E + f1L + f2S
0.9D + 1.0E
• Special
1.2D + f1L + Em
0.9D + Em
• Basic ASD
0.6D + 0.7E
D + 0.7E + L + (Lr or S or
R)
• Alternate Basic ASD
D + L + S + E/1.4
0.9D + E/1.4
Section 12.3.4.2Redundancy Factor, ρ, for Seismic
Design Categories D through F
• New redundancy provisions adopted into ASCE 7-05.
• Lack of redundancy is….. when failure of a component is failure of entire system.
• Logical way to determine lack of redundancy is to check whether a component’s failure results in an unacceptable amount of story strength loss or in the development of extreme torsional irregularity.
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Section 12.3.4.2Redundancy Factor, ρ, for Seismic
Design Categories D through F
In ASCE 7-05, ρ = 1.0 or 1.3, depending on whether or not an individual element can be removed from the lateral-force-resisting-system without:
• Causing the remaining structure to suffer a reduction of story strength of more than 33%, or
• Creating an extreme torsional irregularity.
Section 12.3.4.2Redundancy Factor, ρ, for Seismic
Design Categories D through F
2nd condition for which ρ = 1.0:
If structure is regular in plan and there are at least 2 bays of seismic force-resisting perimeter framing on each side of the structure in each orthogonal direction at each story resisting > 35% of the base shear.
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Section 12.3.4.2Redundancy Factor, ρ, for Seismic
Design Categories D through F
ρ = 1.0 for the following:
1. Structures assigned to SDC B and C.
2. Drift calculation and P-delta effects.
3. Design of nonstructural components.
4. Design of nonbuilding structures, not similar to buildings.
Section 12.3.4.2Redundancy Factor, ρ, for Seismic
Design Categories D through F(cont.)ρ = 1.0 for the following:
5. Design of collector elements, splices and their connections for which load combinations with overstrength are used.
6. Design of members or connections where load combinations with overstrength are required for design.
7. Diaphragm loads determined using Eq. 12.10-1.
8. Structures with damping systems designed in accordance with Chapter 18.
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