CASE STUDY: PERFORMANCE-BASED SEISMIC DESIGN OF REINFORCED CONCRETE

DUAL SYSTEM BUILDINGNaveed Anwar, Thaung Htut Aung, Pramin Norachan, Ahmad Muneeb Badar

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23 September 2016 | Cebu, Philippines

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PERFORMANCE-BASED SEISMIC DESIGN

Performance-based Seismic Design

• Provides an alternative, as well a progression to more explicit evaluation of the safety and reliability of structures for different levels of earthquakes

• Provides opportunity to clearly define the levels of hazards to be designed against, with the corresponding performance to be achieved

• Assessing the performance capability of a building, system or component, considering the uncertainties in the post-yielding response and behavior of the building

• Detailed local acceptance criteria indicates element-by-element checking, rather than application of seismic response modification factor, R for entire system and structural overstrength factor, Ω0, in the conventional design of new buildings

Explicit Performance Objective in PBD

• Whereas traditional code procedures attempt to satisfy implicitly all three objectives by designing to prescriptive rules for a single (design) level of seismic hazard, performance based design of high-rise buildings investigates at least two performance objectives explicitly

• 1) Service-level Assessment• Negligible damage in once-in-a-lifetime earthquake having a return period of 43

years (50% of probability exceedance in 30 years)

• 2) Collapse-level Assessment• Collapse prevention under the largest earthquake with a return period of 2475

years (2% of probability exceedance in 50 years)

Seismic Performance ObjectivesLevel of Earthquake Seismic Performance Objective

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

Serviceability: Limited structuraldamage, should not affect the ability ofthe structure to survive future MaximumConsidered Earthquake shaking even ifnot repaired.

Maximum Considered Earthquake(MCE): 2% probability of exceedance in50 years (2475-year return period)

Collapse Prevention: Building may be onthe verge of partial or total collapse,extensive structural damage; repairs arerequired and may not be economicallyfeasible.

Overall Design Procedure

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Preliminary Design

(Code based design approach)

Service Level Evaluation

(43-year return period)

Collapse Prevention Level Evaluation

(2475-year return period)

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CASE STUDY BUILDING

Building Configuration

• 56-story residential building• 186-meter tall• 7-level podium with 3

basements for amenity area and car park

• Dual system (Reinforced concrete special moment resisting fame with special reinforced concrete shear walls)

• Mat foundation and isolated footings

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MODELING AND ANALYSIS PROCEDURES

Modeling and Analysis Procedures

Elastic models (ETABS)• Analyze

• Wind (Linear static analysis)• SLE (Response spectrum analysis)• DBE (Response spectrum analysis)

• Includes shear walls, columns, coupling beams, girders, beams, slabs, and foundation

• Shell elements were used to model the floor slabs, considering the diaphragm flexibility

Nonlinear model (Perform 3D)• Nonlinear response verification for

MCE (Nonlinear time history analysis)

• Includes inelastic member properties for elements that were anticipated to be loaded beyond their elastic limits (flexural response of shear walls, coupling beams, girders, and slab-outrigger beams)

• Elements that were assumed to remain elastic were modeled with elastic member properties.

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Response Spectrum Curves

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0

0.5

1

1.5

2

2.5

0 1 2 3 4 5 6 7 8 9 10

SpectralAcceleration(g)

NaturalPeriod (sec)

ResponseSpectra

SLE MCE

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ACCEPTANCE CRITERIA

Service Level Earthquake

Item LimitStory drift 0.5%Coupling beam Remain elasticShear wall Remain elasticGirder Remain elasticColumn Remain elastic

• Demand to capacity of the primary structural members shall not exceed 1.5, in which the capacity is computed by nominal strength multiplied by the corresponding strength reduction factor in accordance with ACI 318.

• It is anticipated that the demand to capacity ratio of 1.5 based on design strengths can be expected to result in only minor inelastic response.

Acceptance Criteria (MCE)Item Limit

Peak transient drift Mean value shall not exceed 3%.Maximum drift shall not exceed 4.5%.

Residual drift Mean value shall not exceed 1%.Maximum drift shall not exceed 1.5%.

Column Remain elasticCoupling beam rotation ≤ 0.05 radians

Girder rotation ≤ASCE 41limits

Shear wall reinforcement strain ≤ 0.05 in tension≤ 0.02 in compression

Shear wall concrete strain Intermediately confined concrete ≤ 0.004 + 0.1 ρ (fy / f'c)Fully confined concrete ≤ 0.015

Force-controlled action demand shall be 1.5 times the mean if it is not limited by well defined yieldmechanism. If it is limited by well-defined yield mechanism, use the mean plus 1.3 times standarddeviation but not less than 1.2 times the mean. The capacity is determined based on expectedmaterial properties with corresponding strength reduction factor.

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OVERALL RESPONSE

Modal Analysis

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Mode Period (sec)

Modal Participating Mass Ratio

X (%) Y (%)

1 8.81 0.1 54.3

2 8.08 53.1 0.1

3 6.96 1.3 0

Mode1Mode2

Mode3

Base Shear

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0.02.04.06.08.0

10.012.014.016.0

X Y

BaseSh

ear(%)

AlongDirection

BaseShearintermsofPercentageofWeightofBuildingatGroundLevel

SLE(Elastic) DBE(Elastic) MCE(Elastic) MCE(Inelastic)

Weightof thebuilding =2,255,500kN

Transient Drift

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-10

0

10

20

30

40

50

60

-0.04 -0.02 0.00 0.02 0.04

Stor

y

Transient drift

Transient drift (X-direction)

Drift-ADrift-BDrift-C

-10

0

10

20

30

40

50

60

-0.04 -0.02 0.00 0.02 0.04

Stor

y

Transient drift

Transient drift (Y-direction)

Drift-ADrift-BDrift-CAvg Limit

Residual Drift

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-10

0

10

20

30

40

50

60

0.000 0.005 0.010 0.015

Stor

y

Residual drift

Residual drift (X-direction)

Drift-ADrift-BDrift-CAvg Limit

-10

0

10

20

30

40

50

60

0.000 0.005 0.010 0.015

Stor

y

Residual drift

Residual drift (Y-direction)

Drift-ADrift-BDrift-CAvg Limit

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Evaluation of Components at MCE Level

Shear Wall

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Columns and Girders

• Columns• Axial• Axial-flexural interaction capacity• Shear capacity

• Girders• Flexural rotation

• Immediate Occupancy – 70% of total girders• Life Safety – 30% of total girders

• Shear capacity• Probable shear demand based on moment capacity of the girders

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Diaphragms

• Designed to transfer in-plane forces, comprising of inertial forces and transfer forces to vertical members of seismic forces-resisting system.• Diaphragm design forces were checked from ETABS model• Response spectrum analysis was conducted in ETABS, using

MCE level response spectrum• Scale factors for response spectrum analysis was determined,

based on demand forces from nonlinear time history analysis

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Diaphragms

• Designed according to stress fields determined by finite element analysis• Reinforcement• Chord

• Collector

• Distributor

• Shear reinforcement

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Diaphragms

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4-DB28 4-DB254-DB25

4-DB28 4-DB28

Diaphragm chord reinforcement In-plane forces

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Conclusion

Conclusion

• Global and component responses of reinforced concrete dual system building were checked against the acceptance criteria for multiple seismic events explicitly rather than application of modification factors under single code specified seismic demand level.• Floor diaphragms were designed to resist the in-plane

forces developed due to irregular T-shaped floor plan of the building.

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Thank You!