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Thoughts on minimum strength & stiffness requirements for seismic design

Thoughts on minimum strength & stiffness requirements for seismic design. Greg Deierlein Stanford University. PEER/SF-AB Tall Building Discussion Feb. 23, 2007. 20 Story RC SMF Perimeter Frame (Haselton et al., 2006). Design Information (ASCE 7-02) V d /W = 0.044 V u /W = 0.086 (pushover)

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Thoughts on minimum strength & stiffness requirements for seismic design

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  1. Thoughts on minimum strength & stiffness requirements for seismic design Greg Deierlein Stanford University PEER/SF-AB Tall Building Discussion Feb. 23, 2007

  2. 20 Story RC SMF Perimeter Frame (Haselton et al., 2006) • Design Information (ASCE 7-02) • Vd/W = 0.044 • Vu/W = 0.086 (pushover) • T = 2.6 sec • _________________________________________________________________________________________________________________ • IDA Collapse (median quantities) • Sa(T1) = 0.48g (median intensity at collapse) • IDRmax = 0.051 (about = ¾ x Vu/W = 0.057) • RDRmax = 0.013 • ________________________________________________________________________________________________________________ • Observations: • IDRmax = 0.051 = about ¾ x Vu/W = 0.057 • Sd(T1) = (T/2pi)2 Sa(T1) = 32 in. • System Collapse Drift = 0.051 x 4 stories = 32 in. • Additional Study: ASCE 7-05 design with Vd/W = 0.022 has about one-half the collapse margin of ASCE 7-02. IDA collapse mechanism

  3. Building Code Criteria (SEI/ASCE 7-02) • Minimum Strength:Vd = Cs W • Minimum Stiffness: • Drift: • Stability: • Mechanism Controls:SCWB, capacity design, … • Toughness:component detailing, …

  4. Minimum Stiffness & Stability • Strength:Vd = Cs W Stiffness: • Identities: & • Combine & Rearrange: Observation: Based on conventional drift (stiffness) requirements, the 0.1 limit on the stability coefficient becomes significant at Cs < 0.04 to 0.05. Cd=5.5 Cd=8 Cs

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