structural vulnerability in ecuadorares.tu.chiba-u.jp/peru/pdf/meeting/110309/chiba 2nd ws...2nd...
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2nd Chiba Workshop on Enhancement of Earthquake and Tsunami Disaster Mitigation Technology
Chiba University, Japan, March 9-10, 2011
STRUCTURAL VULNERABILITY IN ECUADOR
Ing. Patricio Placencia Andrade, M.Sc.Professor Escuela Politécnica Nacional, EPN
Director of the Structural Engineering Laboratory, EPN
ACI 318 L committee member
Ecuadorian code R/C Buildings Chapter Coordinator
PAHO-WHO Structural Consulting Engineer
Buildings
Code
Research
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Zona Sismica
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TO REDUCE SEISMIC RISK
WE MUST REDUCE
STRUCTURAL VULNERABILITY
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1. Adequate Architectural seismic configuration
2. Proper structural analysis and design
3. Revision and approval of structural design.
4. Proper construction of structure - seismic detailing
5. Revision of construction – mainly seismic detailing
KEY ASPECTS TOWARDS SEISMIC SAFETY
ECUADORIAN CODE
CODIGO ECUATORIANO DE LA CONSTRUCCION CEC - 2000
EFFECTIVE SINCE MAY 2002
CURRENTLY REWRITEN
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1.We are updating the code.
There are several committees that deal withdifferent structural systems or materials.
CURRENT SITUATION
1.R/C Buildings Committee.
The committee for R/C buildings, recommendedthe adoption of ACI 318-08 S plus an additionalsection with local recommendations in order toget safer shear design of 5 important elementsof frame buildings:
1.Slab – column joints
2.Beam - column joints,
3.shear walls ,
4.Beams
5.columns.
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• Chapter 21 is clarified:
•It includes Flat plate systems, in addition to• Frame buildings• Frame with Shear Wall buildings• Frame with diagonal bracing buildings
•It states, for each building system, which elements should yield under a severe earthquake, and how to design for
• General seismic design objective is set in the following graph:
ELASTIC RESPONSE
INELASTIC RESPONSE
DESIGNEARTHQUAKE
0.14 W
CODE FORCES
DISPLACEMENT
SEISMIC DESIGN - SIMPLIFIED GRAPH
FORCE
Phase I
Phase II
0.4 - 06 W
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FLAT PLATE BUILDINGS
( without shear walls )
•ACI 318-08 does not give provisions for seismic design of this type of buildings in zone 3 or 4
•Most codes restrict its use to zone 2 at most
•Very poor behavior in past earthquakes
•Despite these facts, more than 50 % of buildings use this system
BUILDING CHARACTERISTICS
• 4 to 12 stories• Columns + Waffle slabs• Rather small columns• Integral beams between columns• No shear walls• Partitions made of non industrial concrete
blocks, and located arbitrarily
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•Use higher forces•CEC 2000: R= 8 •(R = 10 Special Moment Frame)
•Use effective width of 1/3 L
•Limit Inter story drift to 0.002
ANALYSIS
TRANSVERSE REINFORCEMENT
• Stirrups shall be designed for the most critical case of 1D or 2D shear.
• In 1D shear, the acting shear Vu shall be computed using the beam probable Flexure capacity Mn pr
• In 2D shear, the resultant punching stress shall be computed using the probable flexural capacity when finding M unbalanced.
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INELASTIC RESPONSE
• Objective :• Yielding of slab bars within the
effective width
• Strategy :1. Strong Column - Weak Beam2. Strong slab for punching -
Weak slab in flexion
1. Strong Column - Weak Beam
Sum M cols > 1.4 Sum M “Beams”
c2
c2 + 3h
h
As for M “Beams”
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2. Strong slab for punching - Weak slab in flexion
ACI 318 - 08 + CAPACITY CRITERIAvu punch < φ φ φ φ vn punch
vu punch = Vu / Ac + γγγγv Muub c / J Muub from flexural capacity
vn = vc + vs < 1.59 Kg/cm2
If vu punch [[[[ φ 1.59φ 1.59φ 1.59φ 1.59 √√√√ f´c Design the stirrups
If not, redesign the structure
f´c
STIRRUPS DESIGN FOR PUNCHING
• Av / # legs of stirrups • Legs in tension from shear = n• Legs in tension from torsion = 2
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FRAME BUILDINGS
H beam > 3 h slab
•Beams:
•When computing Design shear force:
Mpr= 1.2 (Mpr 318)
1.2 due to slab reinforcement
Columns:•Design shear force for the 1st floor:
Mc top and Mc bot are Mc max = Mc balanced
INELASTIC RESPONSE
• Objective :• Yielding of beam bars at column
faces
• Strategy :1. Strong Column - Weak Beam2. Strong Joint - Weak Beam
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1. Strong Column - Weak Beam
Sum M cols > 1.4 Sum M beams
h
A steel for M Beams
hc
hb
hc
hb
2. Strong joint - Weak Beam
SHEARhb / hc = 1 hb / hc = 0.5
Vn = Vc
Vs = 0
Vn = Vc
Vs = 0
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1 < hb / hc < 1.5 hb / hc > 1.5
hchc
hb
hb
Vn = Vc + Vs
hb/hc= 1 Vc = Vc 318
hb/hc= 1.5 Vc = 0
Vn = Vs
Vc = 0
Hcol > 20 d beam
H beam > 20 d col
2. Strong joint - Weak Beam
Bar passing through the joint
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SHEAR WALL BUILDINGS( + Frames )
• Individual
• Coupled
SHEAR WALL BUILDINGS( + Frames )
INELASTIC RESPONSE
• Objective :• Yielding of vertical wall bars at
base of wall
• Strategy :1. Strong wall in shear -
Weak wall in flexion
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Design shear force at base Vu
Vu = Vu analysis ( Mn / Mu )
Mn/ Mu //// 1.43
Where Mn = Wall flexural capacity from a P-Minteraction diagram
Mu = Factored design moment
STRUCTURAL SYSTEMS RECOMMENDED
• Concrete structural walls
• Frame + shear walls
• Frames
• Avoid flat plate systems w/o shear walls
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HOUSING RESEARCH CENTER
ESCUELA POLITECNICA NACIONAL - QUITO
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RESULTADOS MEDICION DE PERIODOS - PUNTO 10
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Muchas gracias
• .