Performance Evaluation of Dual-eccentrically Braced Frames

Abstract

The later force resistance in dual-eccentrically braced frames is provided by two structural system: eccentrically braced frames (the primary sub-system) and moment-resisting frames (the secondary sub-system). Eccentrically braced frames dissipates most of the seismic energy through plastic deformations in links, while moment-resisting frames represent a back-up system, increases the redundancy of the overall system. This paper presents the modelling approach of steel dual-eccentrically braced frames using the OpenSees software framework. Ten different structural configurations were used to evaluate their performance given two levels of seismic hazard. The analyses of the frames is part of the ongoing European pre-QUALified steel JOINTS project, concerned with the pre-qualification of all-steel Beam-to-Column joints in steel structures. The designed frames were evaluated in terms of seismic performance by means of non-linear static (pushover) analyses, with a modal and uniform distribution of forces, time history and incremental dynamic analyses. The eccentrically braced frame contains short links, for which the shear force - shear deformation (V-γ) curve was calibrated based on experimental results. The physical theory models were used for columns and braces in the numerical model. The model was built in a 3D environment and extra nodes were added at each column and brace midpoint to account for initial imperfections. The midpoints were without restraints so that buckling could occur about the weak axis.