selection of optimal intensity measure for seismic assessment of steel buckling restrained braced frames under near-fault ground motions

Buckling restrained braces (brbs) have a similar behavior under compression and tension loadings. therefore, they can be applied as a favorable lateral load resisting system for structures. in the performancebased earthquake engineering (pbee) framework, an intermediate variable called intensity measure (im) links the seismic hazard analysis with the structural response analyses. an optimal im has desirable features including efficiency, sufficiency and predictability. in this paper, the efficiency and sufficiency of some traditional, cumulativebased, and advanced scalar ims to predict maximum interstory drift ratio (midr) demand on low to midrise steel structures with brbs, under nearfault ground motion records having forward directivity, are investigated. the results indicate that most of the ims contemplated are not sufficient with respect to sourcetosite distance (r), for predicting midr. it is also demonstrated that decreasing the strain hardening ratio decreases the efficiency of the ims. in addition, imm(λ=0.5) and saavg are more efficient and also sufficient with respect to pulse period (tp), for predicting midr demand on the lowrise steel brb frames under nearfault ground motions, when compared with the other ims. in the case of midrise structures, pgv and imm(λ=0.33) are selected as optimal ims. as a result of the higher efficiency and sufficiency of the selected optimal ims, the obtained fragility curves calculated applying these ims, are more reliable in comparison with the fragility curves calculated using other ims.