seismic performance of steel moment resisting … · fundamentals of structural dynamics and...
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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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Strength-Based Approach: AISC Design Flow Chart
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Displacement-Based Seismic Design Method for MRF
Seismic force calculations
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
Seismic force calculations
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Displacement-Based Approach: PBPD Design Flow Chart
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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)
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Design Summary for Nine-Storey MRF
AISC Design PBPD Design
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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)
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Seismic Performance of Strength-Based andDisplacement-Based Designs of MRF
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Seismic Performance of Strength-Based andDisplacement-Based Designs of MRF
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Seismic Performance of Strength-Based andDisplacement-Based Designs of MRF
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
Seismic Performance of Strength-Based andDisplacement-Based Designs of MRF
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
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering
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.
Dr. Swapnil B. Kharmale Fundamentals of Structural Dynamics and Application to Earthquake Engineering