PEER/ATC-72-1 Modeling and Acceptance Criteria for Tall Buildings Jon A. Heintz Director of Projects Applied Technology Council Redwood City, California SEAONC April 19, 2011 Overview Introduce the PEER/ATC-72-1 Report Describe nonlinear analysis modeling issues Present modeling recommendations 1
Who and What? Project Participants PEER Task 7 Project Core Group Jim Malley (Technical Director) Greg Deierlein i Helmut Krawinkler Joe Maffei Mehran Pourzanjani John Wallace Jon Heintz 2
Workshop Conducted a workshop on tall building seismic design and analysis issues (2007) 35 practitioners, researchers, and building officials Identified and prioritized about 30 issues (large and small) used to seed the work Quantification i of inelastic i properties Recommendations for acceptance criteria Guidance on damping, P-Delta effects Modeling of podiums and diaphragms Report Contents Ch.1 Introduction Ch. 2 General Nonlinear Modeling Ch. 3 Modeling of Frame Components Ch. 4 Modeling of Shear Wall and Slab- Column Frame Systems App. A Modeling of Podium Effects 3
Review Expert Review Panel Larry Griffis Mike Mehrain Bob Hanson Jose Restreppo Leonard Joseph Charles Roeder Ron Klemencic Michael Willford Graham Powell Nabih Youssef Farzad Naeim General Nonlinear Modeling 4
Types of Nonlinear Models Continuum nonlinear material behavior Phenomenological observed forcedeformation behavior (e.g., from tests) Types of Nonlinear Models Continuum Advantages Ability to simulate material cracking and yielding behaviors Disadvantages Limited ability to capture degradation Concentrated Hinge Ability to capture degradation Consistent with force/deformation limit state checks in codes and standards Behavioral relationships are empirical rather than theoretical 5
Inelastic Component Attributes M y Ke Cap,pl p K pc rce (kn) Shear For 300 200 100 0-100 Exp. Results Model Prediction -200 y Inelastic hinge model -300-0.1-0.05 0 0.05 0.1 Column Drift (displacement/height) (a) (b) (c) Initial (monotonic) backbone curve Hardening/softening response Cyclic response model Strength/stiffness deterioration response Modes of Cyclic Deterioration 1 3 3 2 1. Basic strength deterioration 2. Post-capping strength deterioration 3. Unloading stiffness deterioration 6
Modeling of Hysteretic Behavior Modeling of cyclic deterioration is based on: A backbone curve, or reference ence force-deformation relationship defining the capacity boundary, A set of rules that define the basic characteristics of the hysteretic behavior, and FEMA P-440A (ATC-62) A set of rules that define various modes of deterioration with respect to the backbone curve. FEMA P-440A (ATC-62) Modeling of Hysteretic Behavior FEMA P-440A (ATC-62) Capacity boundary is often taken as the initial monotonic backbone curve Cyclic Envelope is different from the initial (monotonic) backbone curve Cyclic Envelope is load-path dependent ASCE 41 curves are Cyclic Envelopes 7
Modeling Options Four options based on what you know and how accurate you need to be Option 1 explicit it incorporation of cyclic deterioration in model Option 2 use of cyclic envelope Option 3 use of modified (factored) initial backbone curve Option 4 - no deterioration in model Explicit Modeling of Deterioration Monotonic backbone curve Initial backbone and cyclic deterioration known No limitations on use 8
Use of Cyclic Envelope Modified backbone curve u Cyclic envelope known from tests No further deterioration modeled Deformations cannot exceed the envelope established by test Modified (factored) Backbone Modified backbone bac bo e cu curve e u Fp.9 Fp mono p 0.7 p mono u 0.5 u mono Cyclic envelope based on empirical factors No further deterioration modeled Deformations cannot exceed the modified backbone parameters 9
No Deterioration in Model F c Modified backbone curve 0.8F c u Deterioration parameters not known or not considered Maximum deformations cannot exceed deformation at 0.8F u-mono Component Acceptance Criteria Two performance states considered: Onset of Structural Damage Forces and deformations beyond the yield point, with some permanent deformation (yielding, cracking) Onset of Significant Degradation Deformations beyond the capping point, but before the ultimate deformation capacity F F c F y F r K e y c r u p pc 10
P-Delta Effects in Tall Buildings Recommendations for modeling P-Delta effects are provided Clear difference between frame versus shear wall systems Static pushover can be useful for identifying sensitivity to P-Delta P-Delta effects increase when components deteriorate into the post-capping range P-Delta causes the collapse potential of tall frame systems to increase with period Normaliz ed Base Shear (V/W) 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 ROOF DRIFT ANGLE vs. NORMALIZED BASE SHEAR Pushover (NEHRP '94 k=2 pattern); LA 20-Story P-Delta effect included P-Delta effect excluded 0 0.01 0.02 0.03 0.04 0.05 Roof Drift Angle Damping Includes hysteretic and viscous damping Damping due to structural components is implicit through h hysteretic response Damping from gravity framing, SFSI, and nonstructural components can be captured through viscous damping Issues related to Tall Buildings: Potential to overestimate viscous damping and double count hysteretic damping Potential for spurious damping effects and large force imbalances 11
Damping Stiffness-proportional over-damps Mass-proportional under-damps Powell (2008) Damping Recommendations D = /30 (for N < 30) D = /N (for N > 30) = 60 steel bldgs. = 120 concrete bldgs. Equivalent viscous damping ranges from 2%-4% for 30-story buildings 1%-2% for 70-story buildings 12
Component Modeling Recommendations Component Modeling Recommendations Four systems covered: Steel Frame Components Concrete Frame Components Concrete Shear Wall Components Slab-Column Frame Components 13
Component Modeling Recommendations Four systems covered: Steel Frame Components Concrete Steel Beams Frame Components Steel Columns Concrete Shear Wall Components Steel Panel Zones Slab-Column Frame Components Component Modeling Recommendations Four systems covered: Steel Frame Components Concrete Frame Components Concrete Shear BeamsWall Components Concrete Columns Slab-Column Frame Components Concrete Beam-Column Joints 14
Component Modeling Recommendations Four systems covered: Steel Frame Components Concrete Frame Components Concrete Shear Wall Components Slab-Column Planar Walls Frame Components Flanged Walls Core Walls Coupling Beams Component Modeling Recommendations Four systems covered: Steel Frame Components Concrete Frame Components Concrete Shear Wall Components Slab-Column Frame Components Effective Beam Width Slab-Column Connections Slab-Core Wall Connections 15
Component Modeling Recommendations For Each Component: Parameters of interest Behavioral considerations i Available experimental data Quantification of component properties Analytical versus experimental results Comparisons with ASCE 41 Summary recommendations Acceptance criteria (keyed to Guidelines) Steel Frame Components Recent research (Lignos and Krawinkler, 2009) has collected a large database of steel beam test data Data were studied for dependence on steel section properties: d, L/d, b f /2t f, h/t w Regression equations were developed to quantify nonlinear properties in the absence of test data 16
Steel Frame Regression Equations Concrete Frame Components Recent research (Haselton et al., 2008) has collected a large database of concrete column test data Data were studied for dependence on concrete material and section properties: f c, F y, A g, L s /H, sh Regression equations were developed to quantify nonlinear properties in the absence of test data 17
Concrete Frame Regression Equations Effective Stiffness: Pre-capping Plastic Rotation: Post-capping Plastic Rotation: Podium Diaphragms, Collectors, and Backstay Effects 18
Podium Backstay Effects tower core wall main backstay diaphragm Similar to backspan of a cantilever beam Caused by interaction between the tower, podium, foundation, and soil Relative rigidity problem Load path and force transfer problem Force path 2: backstay Force path 1: foundation overturning underneath tower core wall V M Elevation podium levels foundation Force Transfer Guidance on collector design and consideration of eccentricities Shear resistance at wall-to-slab interface Wall Collector reinforcement eccentric to vertical element Collector reinforcement in line with vertical element 19
Backstay Modeling Recommendations Backstay Modeling Recommendations 20
The End Thanks! 21