Investigating the seismic performance of MRF-CBF (X Brace) dual system under the effects of staged construction

Nowadays, with the advances in welding technology and increased use of steel structures in the construction of buildings, especially high-rises, the necessity of matching the construction procedure with the structure analysis procedure has become more evident. In steel structures with moment-resisting frame-concentrically braced frame (MRF-CBF) 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 on MRF-CBF dual systems with X brace. In this regard, 3D models with 5, 10, 15, 20, and 25 stories incorporating MRF-CBF dual system were first generated and subjected to pushover analysis under cyclic loading protocols. Subsequently, parameters such as column shortening and column axial forces under dead load, displacement and base shear corresponding to the first plastic hinge formation, effective lateral stiffness, ultimate lateral strength, and energy dissipation of the structure under cyclic loading protocols were investigated. From the obtained results, it was concluded that staged construction could lead to maximum increases of 17.9% in the axial forces in internal columns due to dead load, 3.8% in the displacement corresponding to the first plastic hinge formation, 8.3% in the base shear corresponding to the first plastic hinge formation, 18.4% in the ultimate lateral strength, and 4.3% 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.