Displacement profile for displacement based seismic design of concentric braced frames

Abstract

The direct displacement based design (DDBD) procedure is well developed and used for designing reinforced concrete and steel moment resisting frame structures, wall structures and bridges. However, a limited number of studies is available on designing steel concentric braced frame (CBF) structures using DDBD approach. Moreover, those studies use the design displacement profile proposed for the reinforced concrete moment resisting frame structures by Priestley et al. (2007). Furthermore, Wijesundara et al. (2018) have highlighted that higher interstorey drifts can be observed in CBFs during the inelastic response due to the effects of higher mode amplifications. Therefore, the main objective of this study is to propose a new design displacement profile that is capable of predicting the effects of higher mode amplifications on the displacement profile for designing steel CBFs.In this regard, an attempt is made to develop a design displacement profile based on the median maximum storey displacements obtained from the nonlinear time-history analysis for a set of real ground accelerations. For this purpose, twelve different steel CBF structures with varying brace configuration, braces slenderness over the height of building, and different heights are selected. Nonlinear timehistory analyses are performed for the 3-D nonlinear finite element models of the selected frames using OpenSEES software. The developed models are capable of simulating the out-of-plane buckling. The models are subjected to a set of 30 real ground motion records with varying levels of spectral acceleration at the first modal period of the structures. The maximum storey displacement at each storey levels is recorded for all the ground motion records. On the basis of the observed storey displacement and interstorey drift, the appropriate design displacement profile for CBFs is proposed. The proposed equations show a high correlation with the observed behaviour of the suggested CBFs.