P-Δ Effects on Seismic Force Modification Factors for Modified-Clough and EPP Hysteretic Models

Abstract

Based on the elastic-plastic time-history analysis of SDOF(single degree of freedom) systems for the Modified-Clough(MC) model and the elastic perfectly-plastic (EPP) model, this paper carried out a study of the seismic force modification factors R_μ (SFMF) both when the P-Δ effects are not allowed for (R_μ) and when they are allowed for (R'_μ). 370 earthquake records from 4 site & soil conditions, 74 to 106 records for each site, were used to calculate the structural response. The structural periods varied from 0.1 to 6sec and the ductilities were taken to be 2,3,4,5 and 6. The stability index θ were varied from 0.025 to 0.1. The ratio spectra S of R_μ to R'_μ were constructed to analyze the influence of P-Δ effects on the SFMF. It is found that the spectral values of S depend on the ductility, the stability index and the normalized period T / T_gR. The results indicate that the influence of P-Δ effect is different for the two hysteretic models. The increase in strength demand to maintain constant ductility in the presence of P-Δ effects using the EPP model is greater than that given by the modified- Clough model.

Keywords

seismic design seismic force modification factor hysteretic models ductility

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