Assessment of Seismic Design Coefficients for Different Structural Systems of Buildings

Abstract eng:
The verification of the approaches and coefficients used for the seismic design of the diverse structural systems of multi-story buildings represents a priority, particularly with the unprecedented escalation in the number of buildings in earthquake-prone regions. The seismic design modification factors of modern multi-story buildings with three different structural systems are verified in this paper using a systematic assessment approach. Ten reference structures of low, medium and high-rise buildings are selected to represent the contemporary building inventory in metropolitan areas. The selected structures are reinforced concrete (RC) buildings of 2, 8, 18, 26, 40, 50, 56, 66, 80 and 100-story. The benchmark buildings have six various layouts and three different lateral force resisting systems, namely flat slab-columns (FSC), shear walls (SW) and tube in tube (TIT) structural systems. The ten reference buildings are fully designed and detailed according to the latest U.S. building codes. The seismic design response parameters, namely overstrength (Ω), force reduction (R) and deflection amplification (Cd) factors, are estimated through a large number of inelastic pushover analyses (IPAs) and dynamic time history analyses (THAs) using detailed fiber-based analytical models and a large set of earthquake records. The effective stiffness of different structural systems is also compared with the code recommended values and realistic stiffness values are proposed for design to reflect the anticipated cracking at the life safety performance level. The large inelastic analysis results obtained from the seismic assessment of ten multi-story buildings at different performance levels up to collapse reflect the urgent need to decrease the design Ω factor by 10% and increase the Cd factor by 10% for the low-rise FSC system. For the SW and TIT systems, the R factor can be safely increased by 10% to arrive at more cost effective design, with the potential of increasing it further after a thorough assessment of the proposed changes in seismic loads.

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