tall building initiative response evaluation

Tall Building Initiative

Response EvaluationHelmut KrawinklerProfessor EmeritusStanford University

On behalf of the Guidelines writers:Y. Bozorgnia, C.B. Crouse, R.O. Hamburger, R. Klemencic, H. Krawinkler, J.O Malley, J.P. Moehle, F. Naeim, J.P. Stewart Quake Summit 2010, October 8, 2010

Quake Summit 2010, October 8, 2010

Performance ObjectivesDemonstrate that structure will be capable of essentially elastic response and limited damage under Service-level Earthquake shaking (mean RP = 43 years = 50/30)

Demonstrate, with high confidence, that structure will respond to Maximum Considered Earthquake (MCE) shaking without loss of gravity-load-carrying capacity without inelastic straining of important lateral-force resisting elements to a level that will severely degrade their strength; and without experiencing excessive permanent lateral drift or development of global structural instability.


MCE Level EvaluationObjective: provide, implicitly, adequate life safety protection Protection against collapseProtection against life threatening falling hazardsProtection against aftershocks & condemnationUse 3-D nonlinear response history analysis for at least 7 ground motion pairsUse a realistic model of the structural systemFollow capacity design principles (enforced in acceptance criteria)Minimum base shear not required


Acceptance Criteria at Component LevelForce-controlled actions with severe consequences:

Fu fFn,e

Fu = smaller of1.5 times meanMean + 1.3s but 1.2 times meanFn,e = nominal strength based on expected material propertiesf = resistance factor


Acceptance Criteria at Component LevelDeformation controlled actions:No specific limitations, but use realistic model of component behavior, including deterioration, or limit maximum deformation to a conservative (low) value du.

If d > du in any one analysis:Strength in this action should drop to zeroEffect on related strength properties should be evaluated


Mean of max. transient drift in every story 3.0%Max. transient drift in every story 4.5%Mean of max. residual drift in every story 1.0%Max. residual drift in every story 1.5%Loss in story strength at max. drift should not be more than 20%Acceptance Criteria at System Level


System Modeling IssuesIncorporate all components and all behavior modes (e.g., shear in RC) that significantly affect prediction of seismic responseMight require post-analysis review and re-analysisFlexibility of floor diaphragms should be modeled if deemed importantAnalysis should provide information needed to quantify diaphragm forcesPodium and backstay effects must be represented realisticallyP-Delta effects must be includedInclude real torsion, but no requirement for accidental torsion


Wall Hinging at the BaseLoadingStory Sheargy=Vy/WStory OTM


NRHA force demands may be very different from elastic expectationsMaximum moment in shear wall


NRHA force demands may be very different from elastic expectationsMaximum shear force in shear wall


Component ModelingDeterioration in strength and stiffness must be considered if it significantly affects the response of the structure to the MCE ground motions Or conservative estimates must be made of strength and deformation capacities


Modes of Deterioration


Basic ObservationThe cyclic envelope curve is different from the monotonic backbone curve


Resource DocumentATC-72-1Interim Guidelines on Modeling and Acceptance Criteria for Seismic Design and Analysis of Tall Buildings


GENERAL MODELING ISSUESTypes of ModelsDeteriorationP-Delta effectsDampingUncertainties

PROPERTIES OF NONLINEAR STRUCTURAL COMPONENTSSteel beams and columnsSteel panel zonesAxially loaded steel bracesRC beams, columns, and joints

PLANAR AND CORE WALL SYSTEMS AND COMPONENTSPlanar walls, flanged walls, core wallsCoupling beamsSlab-columns and connections

FLOOR DIAPHRAGMS, COLLECTORS, AND PODIUM AND BACKSTAY EFFECTSRigid, semi-rigid, and flexible diaphragmsPodium and backstay effects Resource DocumentATC-72-1


Source: G. Deierlein


Use of Strain-based Models (Fiber & Curvature Models)Argument for their use:

whenever lumped plasticity models are not available

Columns subjected to biaxial bending and large axial forceShear walls with (and without?) openingsSpandrel beams?


Use of Strain-based Models (Fiber & Curvature Models)Arguments against their use:RC:Rebar buckling?Rebar fracture?Bond slippage and pullout?Shear?Steel:Local instabilities?Fracture?Joint panel zones?

Need to account for cyclic deterioration


Use of Concentrated Plasticity (Spring) ModelsRotational spring models if inelastic behavior mode is bending

Translational spring models if inelastic behavior mode is shear

Arguments for their useCan capture deterioration characteristics if good calibrations are available from experimental dataAre relatively simple

Arguments against their useAre approximate Not available for many important failure modes


ASCE 41 models may be used if deemed appropriateThey were intended to be used in conjunction with pushover analysisThey were not intended to be used for hysteresis modelingThe sharp drop from C to D is not representative of reality except for brittle failure modesThey may not be applicable to many new components


Component Models with Deterioration (see ATC-72) Q-HYST Degrading Stiffness Flag-Shaped Bi-Linear Hysteresis1. Monotonic (initial) backbone curve:Cyclic deterioration parameterDescription of hysteresis loopsFd


Modeling Option #1 ATC-72Use of monotonic backbone curve and explicit incorporation of cyclic deterioration


Modeling Option #2 ATC-72Use of cyclic envelope curve as modified backbone curve, and no incorporation of cyclic deterioration limit du to max. observed in test


Modeling Option #3 ATC-72Use of factors to generate modified backbone curve from monotonic backbone curve, and no incorporation of cyclic deterioration

- capping strength Fc* = 0.9 Fc- plastic deformation capacity dp* = 0.7dp- post-capping deformation capacity dpc* = 0.5dp- residual strength Fr* = 0.7Fr- ultimate deformation capacity du* = 1.2dc


Modeling Option #3


Modeling Option #4 ATC-72 No deterioration at all in analytical model

ultimate deformation capacity du* corresponding to 80% of capping strength on descending branch of Options 2 or 3


Comparison of ATC-72 Modeling Options


qyqcqp0.5qpcqpcqcqp=0.7qp1.5qcMc0.8McInitial backbone curveModified backbone curve, Option 3Ultimate rotation, Option 4qpuUltimate rotation, Option 3Penalties for Options 3 and 4


What is new?No radical changesExplicit formulation of performance objective and acceptance criteria at two levels of ground motions (SLE & MCE)Consideration of deterioration in component properties if it is importantOr acceptance of penalty in component modelingConsistent design and performance evaluation process


I think we are making progress

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tall building initiative response evaluation

Documents

requiredquake summit

evaluatedquake summit

shear wallquake summit

story strength

stewart quake summit

system levelquake summit

resistance factorquake

vywstory otmquake summit