the international conference on earthquake engineering...

Naveed AnwarICEES 2011

25 - 26 April 2011

NUST, Islamabad Pakistan

The International Conference on Earthquake Engineering and Seismology

CE 72.32 - Design of Tall Buildings - January 2011, Dr. Naveed Anwar 2

• The why, the how and the what of Performance Based Design and Review of Tall Buildings

• Application of recent research and development to real world problems within the associated cost and time constraints

• Demonstrated outcome for the client/owners/public

CE 72.32 - Design of Tall Buildings - January 2011, Dr. Naveed Anwar

• Naveed Anwar

Faculty, SEC, AIT

CEO, AIT Consulting

• Thaung Htut Aung

Projects Coordinator, AIT Consulting

• Rojit Shahi

Project Specialist, AIT Consulting

• Amelia Kusuma

Project Specialist, AIT Consulting

• Deepak Rayamajhi

External Consultant, AIT Consulting

• Pennung Warnitchai

Associate Prof., SEC, AIT

• Keerati Tunthasuwattana

Manager, ACECOMS, AIT

3

• Why do we need to carryout Performance Based Design/ Evaluation when we have the building and design codes

5

Building Officials

Structural Designer

Architect Structural Design Codes

General Building Codes

Legal and Justice System

Public/ Users/ Occupants

Client/Owner

Law Makers

Builder/Contractor

Peer Reviewer

Geotech Consultants


• Traditional codes govern design of general, normal buildings– Over 95% buildings are covered, which are less than about 50 m

• Not specifically developed for tall buildings > 50 m tall

• Prescriptive in nature, no explicit check on outcome

• Permit a limited number of structural systems

• Do not include framing systems appropriate for high rise

• Based on elastic methods of analysis

• Enforce uniform detailing rules on all members

• Enforce unreasonable demand distribution rules

• Do not take advantage of recent computing tools


• Applied Technology Council (ATC-72)

• Pacific Earthquake Engineering Research Center (PEER)

• Building Seismic Safety Council Research Center (BSSCR)

• Federal Emergency Management Agency (FEMA 356)

• Basic ASCE Documents (ASCE 7, ASCE 3, ASCE 4)

• Structural Engineering Association of California (Blue Book and SEAOC PBD Framework)

• Guidelines from National Earthquake Hazard Reduction Program (NEHRP)

• Los Angeles Tall Buildings Structural Design Council (LATBSDC)

• Council on Tall Buildings and Urban Habitat (CTBUH)

• What is needed and needs to be done to carry out an effective Performance Based Design and Evaluation


• To enhance the structural performance– Improved serviceability, safety and reliability

– Explicit check on various performance indicators

• To improve cost effectiveness – Achieve efficient use of materials, resources and time

– Direct reduction cost through reduction of structural material quantities

• Objectives to be achieved through– Better structural system selection and its proportions

– Use of advanced design methodologies and tools


• Enhancement of Performance– Dynamic response

parameters

– Lateral load response

– Vertical load response

– Demand and capacity ratios

– Response irregularity, discontinuity

– Explicit Performance Evaluation at Service, DBE and MCE

• Cost Effectiveness– Capacity utilization ratio

– Reinforcement ratios

– Reinforcement volume ratios

– Concrete strength and quantity

– Rebar quantity

– Constructability, time and accommodation of other constraints

10

11

Level of Earthquake Seismic Performance Objective

Frequent/Service: 50% probability of exceedance in 30 years (43-year return period)

Serviceability: Structure to remain essentially elastic with minor damage to structural and non-structural elements

Design Basis Earthquake (DBE): 10% probability of exceedance in 50 years (475-year return period)

Code Level: Moderate structural damage; extensive repairs may be required

Maximum Considered Earthquake (MCE): 2% probability of exceedance in 50 years (2475-year return period)

Collapse Prevention: Extensive structural damage; repairs are required and may not be economically feasible


• Seven site specific ground motions records are used.

• Determined by qualified geotechnical and geological consultant, for the site located near by building.

• For the evaluations, “Average of 7 pairs of ground motions” approach is used to determine the overall response and vulnerability of the building.

15

Service Level

MCE Level


Element Action Type Classification ExpectedBehavior

RC column Axial-flexureShear

DuctileBrittle

LinearLinear

RC shear wall FlexureShear

DuctileBrittle

NonlinearLinear

RC coupling beams (Deep beam, ln/d<4.0)

Shear Ductile Nonlinear

RC coupling beams (slender beam, ln/d≥4.0)

FlexureShear

DuctileBrittle

NonlinearLinear


Item Limit

Story Drift 0.5 percent

Coupling Beams Shear strength to remain essentially elastic

Core Wall Flexure Remain essentially elastic

Core Wall Shear Remain essentially elastic

Columns Remain essentially elastic

BRB Remain elastic (no yielding permitted)

• Essentially elastic behavior is defined as no more than 20% of the elements with ductile actions having a D/C between 1.0 and 1.5. No elements will be allowed to have a D/C >1.5

• Brittle actions are limited to D/C of 1.0


Element Action Type Classification ExpectedBehaviour

Acceptance Limit

Beams

Plastic hinge rotation

Ductile Nonlinear Hinge rotation ≤ ASCE limit

Shear Brittle Linear D/C for strength capacity

Columns

Axial-Flexural interaction

Ductile Nonlinear Hinge rotation ≤ ASCE limit


Shear Walls

Axial-Flexural interaction

Ductile NonlinearTensile strain in rebar rotation ≤ 0.050Compressive strain in concrete ≤ 0.004



Item Limit

Story Drift 3 percent

Coupling Beam Rotation (Diagonal Reinforcement)

0.06 radian rotation limit

Coupling Beam Rotation (Conventional reinforcement)

0.025 radian rotation limit

Core Wall Reinforcement Axial StrainRebar strain = 0.05 in tension and 0.02 in compression

Core Wall Concrete Axial StrainConcrete Compression Strain = 0.004 + 0.1 ρ(fy / f’c)

BRB 9 times yield strain

• Brittle actions are checked against 1.3 times the average MCE demand using expected material strength and code specified strength reduction factors.

• How to carry out an effective Performance Based Design and Evaluation so that it can provide useful outcome

21

Clie

nt/

Ow

ner

Carryout Code Based Design

Develop Site Specific Ground Motions and Demand Spectrums

Carry out explicit Performance Evaluation for • Service Level for frequent earthquakes

• Design Basis Level for once-in-lifetime event

• MCE Basis for extreme earthquake

Review the PBE carried out by

Engineer in Record (Sy^2)

Specialist Geotech Consultant (Fugro) or ASCE 7

PBD/ PBE Reviewers (AIT Consulting)

PBD/ PBE Peer Reviewers (MKA)


Design/ Evaluation Stage Analysis Type Software Used

Code based design and preliminary evaluation

Response spectrum analysis ETABS V9.5SAP 2000 V 14.2

Serviceability check Response spectrum analysis ETABS V9.5SAP 2000 V 14.2

Collapse prevention check Nonlinear time history analysis Perform3D V4.0.4SAP 2000 V 14.2


• Concrete– Confinement effect is considered

– Mander’s confinement model is used

– Tensile strength is neglected

– Use tri-linear backbone curve

– Takeda hysteresis model

• Reinforcing Steel– Use tri-linear backbone curve

– 1% of strain hardening

– Kinematic Hysteresis model


• Fiber modeling– Two parallel fiber sections are

used

– Shear behavior is modeled as elastic

• Nonlinear Shell Element– 7 layer NL shell with explicit

cover, mid portion, vertical and horizontal bars

24


• Use rigid diaphragm

• Equivalent slab outrigger beams connected the core and columns

• Moment curvature hinges are used

25


• Located in Philippines

• 50-story building with 3½ -story below grade parking

• Total height of 166.8 m above ground level

• 34.5 x 26 meters plan dimension

27

Designer : Sy^2 + Associates Inc

Performance reviewer : AIT Consulting

Peer reviewer for Performance Based Design: Magnusson Klemencic Associates

28Tower 1

BRBs (43rd – 47th floor)

BRBs (19th – 23rd floor)

Principal Major Direction

Principal Minor Direction


BRB in Plan

Principal Major Direction

Principal Minor Direction


• Type of Building : Residential Building

• Number of stories :19-story building (plus 3 basements)– Comprised of three towers

(19-, 14-, and 7-story)

• Total area : 49,000 m2

• Structural System : Reinforced Concrete Moment Resisting System with Shear Walls

30

Designer : Sy^2 + Associates Inc

Performance reviewer : AIT

Consulting


• Part 1 is the tallest part and has irregularity in plan, with 19 floors.

• Part 2 is the second tallest part of the building with few irregularities in plan and 14 floors.

• Part 3 is the lowest part and generally regular in geometry and stiffness with 7 floors.

31

Layout Plan of Each Part of the

Building

Part 1

Part 2

Part 3

32

Part 1 Part 2 Part 3


• Reinforced concrete residential building

• 70-Story building plus 5 basements

• Total height of 242m height

• Approximate floor area of 100,000 m2

• Structural system: Moment resisting frames with shear walls

• Mega-truss wall (MTW) panels to control the lateral deformation

• Designer : R.S Caparros Associates

• Sy^2 + Associates Inc.

• Performance Reviewer : AIT Consulting

34

Typical tower framing plan Sectional elevation of MTW panel

`


• Modeled using ETABS for DBE Response Spectrum

• Member stiffness properties are adjusted in accordance with effective stiffness values given in Table 6-5 of FEMA 356 provisions

Typical Floor Plan Full 3D Finite Element Model


• 3D nonlinear model using PERFORM-3D

• Seven pairs of site ground motions used

• Shear wall modeling

• Inelastic wall element is used.

• Fiber modelling technique is used to model the flexural behaviour.

• Out-of-plane bending and shear is kept elastic.

• Out of plane stiffness of the wall is reduced to 1/4 value to account the effect of concrete cracking. Full 3D Finite Element Model


• Floor area: 56,000 m2

• Type of building: Residential Building

• Structural system: Reinforced concrete moment resisting building with shear walls

Mode Natural Period (s) Mode Shape

1 5.75 Translation in minor dir.

2 4.86 Translation in major dir.

3 3.77 Torsion

41

Minor

Major

Mode 1 Mode 2 Mode 3

Tran

slat

ion

in M

ino

r d

ire

ctio

nTr

ansl

atio

nin

Maj

or

dir

ect

ion

Tors

ion

al

42

• T1=5.32 sec

• 60% in Minor

direction

• T6=1.28 sec

• 18% in Minor

direction

• T9=5.32 sec

• 6.5% in Minor

direction

• T2=4.96 sec

• 66% in Major

direction

• T7=0.81 sec

• 5.2% in Major

direction

• T4=1.56 sec

• 15% in Major

direction

T3=4.12 sec T8=0.65secT5=1.30 sec

43

• Design base shear is larger than minimum limit of 3% set by LATBSDC-2008

• Nonlinear dynamic base shear is approximately 2 times higher than design base shear

Load CasesBase Shear

(KN) % of Seismic Weight

DBE level (In major dir.) 21,012 3.56

DBE level (In minor dir.) 22,691 3.84

MCE level (In major dir.) 47,892 7.76

MCE level (In minor dir.) 46,462 7.53


Weak Direction

(Y)

Strong Direction

(X)

46

Story Drift in Principal Major Direction

Story Drift in Principal Minor Direction

47

Story Shear in Principal Major Direction

Story Shear in Principal Minor Direction

48

Story Moment about Principal Minor Axis

Story Moment about Principal Major Axis

49

Wall Compressive Axial Strain Wall Tensile Axial Strain

-10

0

10

20

30

40

50

60

-0.005 -0.004 -0.003 -0.002 -0.001 0

Sto

ry

Axial Strain

Wall Compressive Axial Strain at Location 1-2Compressive Strain=2 times MCE strain

TAB MIN

ARC MIN

CHY MIN

DAY MIN

ERZ MIN

LCN MIN

ROS MIN

Average MIN-10

0

10

20

30

40

50

60

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007S

to

ry

Axial Strain

Wall Tensile Axial Strain at Location 1-2Compressive Strain=2 times MCE strain

TAB MAX

ARC MAX

CHY MAX

DAY MAX

ERZ MAX

LCN MAX

ROS MAX

Average MAX

51

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

PART 1 PART 2 PART 3

Summary of Beams Flexural Deformation

Beyond CP

Between LS and CP

Between IO and LS

Before IO

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Girder Shear Design Check Summary

Under demand

Just enough

Good

52

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%


Summary of Column Flexural Deformation

Beyond CP

Between LS and CP

Between IO and LS

Before IO

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%


Column Shear Design Check Summary

Under demand

Just enough

Good


Percentage of Total Base Shear Distributed to Shear Walls and MomentResisting Frame from Equivalent Static Analysis

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% (X-dir) % (Y-dir) % (X-dir) % (Y-dir) % (X-dir) % (Y-dir)

Part 1 Part 2 Part 3

93 9282 79

30

86

7 818 21

70

14

Frame

Shear Wall


Part Level Maximum Displacement Check

12

1489.3 mm82.6 mm

(89.3 + 82.6) mm = 171.9 mm < 250 mm

23

762.1 mm59.8 mm

(62.1 + 59.8) mm = 121.9 mm < 250 mm

Seismic gap size : 250 mm

56

Items Performance Overview

Shear Walls -Good Flexural Response

Flexure deformation-100% within acceptable limit

-Fair Response in Shear

Shear Capacity-Some shear walls may be overstressed in Part 1 and Part 2

Girders -Good Flexural Response

Flexure deformation-Only 1% beyond acceptable limit in Part 2

-Fair Response in Shear

Shear capacity – Approximately 6%, 8% and 3% seems to be overstressed

in Part 1, 2, and 3 respectively

Columns -Good Flexural Response

Flexure deformation– nearly 100% within acceptable limit

-– Fair Response in Shear

Shear capacity – Approximately 8% in Part 1 and 3% in Part 2 seem to be

overstressed.


• This is an attempt to explicitly check that the Building – Is serviceable under Frequent Earthquakes

– Has limited damage during Design Basis Earthquake

– Does not collapse in Maximum Credible earthquake

• This is done by– Avoiding the uncertainties that are inherent in traditional code based.

– Avoiding the uncertainties in the use of global force reduction/over strength factor R

– Considering the higher mode effects

– Considering the nonlinearities and dynamics in appropriate manner

• Use the state of the art knowledge and techniques for tall building design