A modified equivalent frame method for lateral load analysis

Abstract

The equivalent frame method (EFM) was developed for two-way slabs as a simple approximate method. Current design codes (ACI 318-05, Eurocode 2 and BS 8110) permit the EFM for the analysis of two-way slab systems under gravity loads, as well as lateral loads such as seismic loads. The EFM, however, was developed based on a semi-empirical formula, derived from the behaviour of two-way slab systems under gravity loads. This study shows that the EFM is not appropriate in accurately predicting the response of two-way slab systems under lateral loads. To improve the EFM under lateral loads, this study proposes a modified equivalent frame method (MEFM). To verify the MEFM, an idealised two-storey flat plate frame is considered and analysed by both the MEFM and elastic finite-element (FE) analysis for estimating slab moments and lateral drifts. Analysis results obtained from the conventional EFM and effective beam width method (EBWM) are also compared. The lateral stiffness, based on the proposed MEFM, was also compared with experimental data.