Damage states and fragility functions for link beams in eccentrically braced frames

Abstract

Steel Eccentrically Braced Frames (EBFs) are used in seismic force-resisting systems of buildings and infrastructure constructed in regions of moderate and high seismic hazard. Future performance assessment of such structures, which will focus on repair cost and business interruption rather than component checking per ASCE 41, will utilize fragility functions that relate the probability of exceeding one or more damage thresholds to an efficient response (demand) parameter. Fragility functions are developed for link beams of EBFs to enable future performance assessment of buildings and other structures incorporating these structural components. Data are presented for shear- and flexure-critical link beams. The functions are developed by review and statistical evaluation of data from tests. Link plastic rotation is used as the demand parameter. Experimental data are interpreted using damage states and methods of repairs. Observations from experimental programs are used to identify the most appropriate damage states and their corresponding methods of repair. Damage states are characterized in most instances by direct indicators of damage to steel components such as web and flange local buckling, and fracture. Each of these damage states is linked with one of four methods of repair in increasing order of repair cost, namely, cosmetic repair, concrete replacement, heat straightening, and link replacement. An ordered sequence of fragility functions is provided for EBF link beams.