Seismic Performance of Steel Moment Resisting … · Fundamentals of Structural Dynamics and Application to Earthquake Engineering ... (sti soil), building

One Week FDPFundamentals of Structural Dynamics and Application to

Earthquake Engineeringin Sanjay Ghodawat Group of Institute

Seismic Performance of Steel Moment Resisting FramesDesigned with: Displacement-Based and Strength-Based

Approaches

Dr. Swapnil B. Kharmale

Assistant Professor, Applied MechanicsGovernment College of Engineering and Research, Avasari

[email protected] 12, 2013

Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering

Introduction

Moment Resisting Frames (MRF)

Offers substantial ductilityand significant inelasticdeformation capacity

Hence, MRF is

Most efficient and favoredsystem among new as wellas conventional lateralload resisting systems

Widely used in high tomedium seismic regions ofglobe

Design Approaches

Strength/Force-Basedapproach in most of seismicdesign codes like

ASCE 7 (ASCE, 2005)and AISC SeismicProvision (AISC,2005)IS: 1893 (Part I) and IS:800 (BIS, 2007).....

Performance-Basedapproach

Emerged as promising andefficient in last decadeExplicitly accounts theinelastic behaviour ofstructural system


Introduction: Objective of Work

Objective

To compare the seismic performance of steel MRF designed withforce/strength based approach of existing standards anddisplacement-based design approach of PBSD

Scope of Work

Typical nine-storey steel MRF located in high seismic region:designed for the same seismic hazard

Strength-Based Approach: AISC Seismic Provision (AISC, 2005)

Displacement-Based Approach: PBPD method (Lee and Goel,2001)

Evaluation seismic performances of these designs using:

Nonlinear Static Pushover Analysis (NSPA)

Nonlinear Response History Analysis (NLRHA)

Nonlinear incremental dynamic analysis (NIDA)


Introduction: Objective of Work

Objective

To compare the seismic performance of steel MRF designed withforce/strength based approach of existing standards anddisplacement-based design approach of PBSD

Scope of Work

Typical nine-storey steel MRF located in high seismic region:designed for the same seismic hazard

Strength-Based Approach: AISC Seismic Provision (AISC, 2005)

Displacement-Based Approach: PBPD method (Lee and Goel,2001)

Evaluation seismic performances of these designs using:

Nonlinear Static Pushover Analysis (NSPA)

Nonlinear Response History Analysis (NLRHA)

Nonlinear incremental dynamic analysis (NIDA)Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering

Strength-Based Seismic Design Method for MRF

Strength-Based Approach: AISCSeismic Provision (AISC, 2005)

Seismic force calculationsare based on ASCE 7

Inelasticity is only implicitlyaccounted for throughresponse modification factor,R

ASCE 7 specifies a responsemodification factor, R = 8and a system overstrengthfactor, Ωo = 3

Implicitly design is fordisplacement ductility ratio,µ = R/Ωo = 2.67

Seismic force calculations

As per ASCE 7 (ASCE, 2005)

The seismic responsecoefficient, Cs is

Cs =SDS

R/I

where SDS is design spectralacceleration parameter, I isimportance factor

The design base shear, Vb is

Vb = CsW

where W is seismic weight

IBC (ICC, 2006) lateral forcedistribution


Strength-Based Approach: AISC Design Flow Chart


Displacement-Based Seismic Design Method for MRF

Performance-based plastic design(PBPD) method(Lee and Goel, 2001)

Considers pre-selected yieldmechanism and uniformtarget drift as performanceobjectives

Based on modified energybalance concept

Inelastic energy demand ona structural system isequated with the inelasticwork done through theplastic deformations resultedfrom pre-selected yieldmechanism

Pre-selcted yield mechanism dueto monotonic uni-directionalloading up to target drift


Displacement-Based Seismic Design Method for MRF


As per displacement-based designapproach (Lee and Goel, 2001)the design base shear, Vb forMRF system is

V

W=

−α +√α2 + 4γC 2

e

2

where

α =

(n∑

i=1

Cvihi

)8θpπ

2

T 21 g

Cvi =FiVb


where,

Ce(= Sa/g) is normalizeddesign pseudo-acceleration

γ is energy modificationfactor

T1 is fundamental timeperiod

hi is the height of ith floormeasured from ground

Cvi is the lateral forcedistribution factor

θp is the plastic drift


Displacement-Based Approach: PBPD Design Flow Chart


Design of Nine-Storey MRF with Strength-Based andDisplacement-Based Approach

Nine-storey MRF

Located in high seismic zone(Downtown San Francisco)

Site Class D (stiff soil), buildingoccupancy category I

Spectral accelerationSs = 1.75g at 0.2 s andS1 = 0.870g at 1.0 s.

Designs : Strength-Based andDisplacement-Based

Strength-Based approach(AISC Design): R = 8 andΩo = 3 implicitly design is forµ = R/Ωo = 2.67

Displacement-BasedApproach (PBPDDesign): For µt = 2.67(design with sameseismic hazard)


Design Summary for Nine-Storey MRF

AISC Design PBPD Design


Seismic Performance of Strength-Based andDisplacement-Based Designs of MRF

Analytical Model of Nine-StoreySteel MRF

A centerline lumped massmodel in DRAIN-2DX

Material: Elastic perfectlyplastic steel with yieldFy = 344.74 MPa without anyoverstrength factor

Geometric nonlinearity and thenominal lateral stiffness fromgravity frames are neglected

Stable hysteresis behaviourwithout strength and stiffnessdegradation

Nonlinear Static Pushover Analysis(NSPA)

IBC 2006 (ICC, 2006)recommended lateral forcedistribution

Assessment of importantperformance parameters,including global drift, interstorydrift, and inelastic elementdeformations.

Roof displacement versus baseshear plot is bilinearized toobtain yield point (yielddisplacement, Dy ; yield baseshear,Vb)


NSPA: Pushover plots with Yielding Hierarchy

Observations

(a) AISC Design :- Yielding is not at all gradual, soft storey collapseat 6th storey

(b) PBPD Design :- Yielding is more gradual and as perpre-selected yield mechanism



Nonlinear Response History Analysis(NLRHA)

Four ground motion records ofhigh to medium seismicity

5% Rayleigh damping in thefirst two modes of vibration

Scaled acceleration time history

Ground motion records



For AISC and PBPD Designs from each NLRHA

Ultimate roof displacement, Dm is obtained

Achieved displacement ductility ratio µa = Dm/Dy is obtained

Statistics of achieved ductility with target ductility is studied

Displacement profile at the instant of peak roof drift is ploted

Result summary from NLRHA



Displacement profiles: (a) Northridge (b) El Centro (c) NW Himalaya

Observations

ASCE Design: Drift is not uniform across the height of MRF.Higher inter-storey drift at 5th and 6th storey

PBPD Design: Displacement profile resembles nearly same profile asassumed initially in design process and thus follow assumed plasticmechanism.



Nonlinear Incremental DynamicAnalysis (NIDA)

Thorough estimation ofstructural performance bysubjecting a structural modelsof MRF (both designs) toNorthridge earthquake scaledto multiple levels of intensity,and thus producing singlerecord NIDA.

Maximum inter-storey drift isas a damage measure

NIDA is carried out till themaximum inter-storey driftreaches to 5%.

NIDA under Northridge Earthquake

For 4% inter-storey drift

ASCE Design: 1.75Sa/g

PBPD Design: 3.00Sa/g


Concluding Remarks

Strength-based approach lacks in including the actual inelasticdeformation capacity of MRF in design seismic force calculation andhence unable to achieve the specified displacement ductility ratioR/Ωo

Displacement-based approach include actual inelastic target driftand an energy-based formulation in the design procedure thus, it isfound to be very effective in achieving a certain inelasticdisplacement for a given earthquake scenario.

Use of plastic design method in PBPD approach leads structures tomeet a pre-selected performance objective in terms of yieldmechanism and target drift.

PBPD approach prevents structures from developing undesirablecollapse mechanism even under action of strong motion record.

PBPD approach approach of design offer very simplistic designsolution while satisfying an advanced earthquake resisting designcriterion hence this approach should be treated as prospectivecandidate for design codes.


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Seismic Performance of Steel Moment Resisting … · Fundamentals of Structural Dynamics and Application to Earthquake Engineering ... (sti soil), building