11.46: The design of suspended zipper braced frames in the framework of eurocode 8

Abstract

To counteract the tendency of chevron-braced structures to form soft storey mechanisms during earthquakes, some researchers have proposed the addition of zipper columns between brace locations at midspan of floor beams and the design of an elastic hat truss system. In this paper, the design procedure proposed by Yang et al. for suspended zipper braced frames is first slightly modified to conform to the design approach and capacity design rules stipulated in Eurocode 8 (EC8) for concentrically braced frames. The procedure is applied to a set of structures with different number of storeys and founded on either soft or rock soil and the structural response is analysed to highlight qualities and deficiencies of the above design procedure. Some improvements are then proposed to the design procedure proposed by Yang et al. to achieve a better seismic performance of the suspended zipper braced frames. Compared with this latter design procedure, the proposed procedure allows a more accurate evaluation of the internal forces -axial forces and bending moments -and a direct control of the inelastic response of chevron-braces of all storeys. The effectiveness of the design proposal is evaluated by incremental dynamic analysis on structures characterised by a different number of storeys and soil of foundation.