A review of code and performance based seismic design procedures of reinforcedconcrete high-rise building structures

摘要

Reinforced concrete is commonly used in high-rise building construction. Performance basedseismic approaches are necessary for sound design for such buildings but these present significantchallenges due to reinforced concrete's (RC) complex behavior. It is intrinsically non-linear even inthe elastic range due to cracking, and its ductility in flexure is strongly affected by the axial andshear loads supported concurrently.The paper discusses the influence of modeling assumptions and analysis methods on the predictedperformance of an idealized tall building, the 40 story tall RC building defined by the Los AngelesTall Buildings Structural Design Council (LATBSDC)[1] as a case study for application of its 2005draft provisions. This is a 126.5 meter tall reinforced concrete residential building 36 meter by 29.3meter in plan. The lateral load carrying comprises bearing core walls coupled with 0.813 to 1.524meter deep spandrel beams. The gravity system consists of 0.203 meter (8") thick post-tensionedconcrete flat slabs supported on reinforced concrete gravity columns and bearing walls.The paper presents the results of analysis of the building by nonlinear response history proceduresin 475 and 2,475 year return period seismic events using Perform3D[2] and LS-DYNA[3] software.The significance of modelling assumptions – including the influence of the flexural stiffness of thefloor slabs, and the way in which the core is modelled- are also discussed.A key finding is that the Code approach underestimates the shear demand on the building by asubstantial factor. This may invalidate the plastic rotation demand at the base of the core as thesystem behavior will be most likely dominated by shear. Hence, it is suspected that significantlyreduced base shear response in Code design base earthquake (DBE) analysis may lead to designswhich would likely fall short of satisfying 'Life Safety' objective for DBE even in cases where adual system is utilized since stiffness of the rigid core and flexible moment frame systems willdiffer significantly.