An Empirical Study on Seismic Load Reduction Factors for SDOF and MDOF systems

Abstract

For the purpose of safety and economy the plastic deformations of buildings are allowed to reduce seismic loads When the ductility design is applied the domestic building seismic design code provides formulas to estimate the seismic load reduction factor by the ductility capacity and then the seismic load is reduced from the elastic design spectrum The relationship of the seismic load reduction factor on the ductility capacity depends on the ground motions so it is necessary to investigate the code formulas or propose a new one on the basis of the elastic design spectrum This paper proposes an improved Kaul’s method to efficiently generate artificial earthquakes compatible with the design spectra The original ground accelerograms come from seismic records of TSMIP operated by CWB and are modified as less as possible in our method Over than one thousand artificial ground accelerograms are generated and then are classified by different site conditions and design spectra Through the nonlinear response history analysis on SDOF systems a lot of seismic load reduction factors corresponding to different parameters such as natural vibration period ductility capacity and stiffness ratio are obtained for further study Through the sensitivity analysis on parameters it is found that the seismic load reduction factor is highly correlated to system properties On the basis of regression results a tri-linear relationship of the mean seismic load reduction factor on the normalized natural vibration period is proposed and the two transition periods locate exactly at both ends of the platform in the elastic response spectra The code formula generally underestimates the seismic load reduction factor on the short-period region but our formula considers a compromise between safety and economy On the other hand it is observed that the response results of MDOF systems by the static analysis and the response spectrum analysis are more conservative than those by the nonlinear response history analysis It is also found in the nonlinear response history analysis that only the ductility capacities of the lower stories are well used if the building is designed with uniform story shear yield strength This paper provides an optimum design procedure to calculate the story shear yield strength in order for achieving the same ductility capacity in each story Finally for uniform shear buildings a formula of optimal distribution of the story shear yield strength ratio is proposed

Date of Award	2014 Jan 24
Original language	English
Supervisor	Li-Ling Hong (Supervisor)