Investigating the seismic performance of MRF-CBF dual systems under the effects of staged construction

Abstract

In steel structures with moment-resisting frame-concentrically braced frame dual systems, as the moment-resisting frame can individually withstand gravity and seismic loads during construction, the braces can be installed on a story-by-story basis simultaneous with the installation of the moment frame or after its complete construction. This issue cannot be investigated and studied using ordinary analysis, where it is assumed that the entire structure is built at once, and then all the involved loads are applied to the completed structure. Accordingly, this research investigated the effects of staged construction in the mentioned dual systems with V, inverted-V (Chevron), and split-X braces. In this regard, three-dimensional models with 5, 10, 15, 20, and 25 stories incorporating these systems were generated and subjected to pushover analysis under cyclic loading protocols. From the results, it was concluded that staged construction could lead to maximum increases of 19.6% in the axial forces in internal columns due to dead load, 9.3% in the displacement corresponding to the first plastic hinge formation, 13.3% in the base shear corresponding to the first plastic hinge formation, 22.9% in the ultimate lateral strength, and 4.6% in the effective lateral stiffness. Also, staged construction was not found to significantly affect the axial forces in corner and braced-bay columns due to dead load and the energy dissipation under cyclic loading protocols.