Performance based design approach for multi-storey concentrically braced steel frames

In this paper, a Performance Based Design (PBD) approach is validated for multi-storey concentrically braced frame (CBF) systems. Direct Displacement Based Design (DDBD) procedure is used and validated by designing 4- and 12-storey CBF buildings. Nonlinear time history analysis (NLTHA) is used to check the performance of the design methodology by employing different accelerograms having displacement spectra matching the design displacement spectrum. Displacements and drifts obtained from NLTHA are found to fall within the design displacement limits used in the DDBD procedure. In NLTHA, both tension and compression members are found to be resisting the base shear, F_b, not only the tension members as assumed in the design methodology and suggested by Eurocode 8. This is the reason that the total F_b in NLTHA is found to be greater than the design shear forces. Furthermore, it is found that the average of the maximum ductility values recorded from the time history analyses for the 4-and 12-storey buildings are close to the design ductility obtained from the DDBD methodology and ductility expressions established by several researchers. Moreover, the DDBD is compared to the Forced Based Design (FBD) methodology for CBFs. The comparison is carried out by designing 4 and 12-storey CBF buildings using both DDBD and FBD methodologies. The performance for both methodologies is verified using NLTHA. It is found that the F_b from FBD is larger than F_b obtained from DDBD. This leads to the use of larger sections for the structure designed by FBD to resist the lateral forces.