Natural time period equations for moment resisting reinforced concrete structures comprising hollow sections

A precise estimation of the natural time period of buildings improves design quality, causes a significant reduction of the buildings' weight, and eventually leads to a cost-effective design. In this study, in order to optimise the reinforced concrete frames design, some symmetrical and unsymmetrical buildings composed of solid and hollow members have been simulated using finite element software SAP 2000. In numerical models, different parameters such as overturning moment, story drift, deflection, base reactions, and stiffness of the buildings were investigated and the results have been compared with strength and serviceability limit criteria proposed by Australian Standard (AS 3600 2018). Comparing the results of the numerical modelling with existing standards and performing a cost analysis proved the merits of hollow box sections compared to solid sections. Finally, based on numerical simulation results, two equations for natural time period of moment resisting reinforced concrete buildings have been presented. Both derived equations reflected higher degree of correlation and reliability with different complexities of building when compared with existing standards and relationships provided by other scholars. Therefore, these equations will assist practicing engineers to predict elastic behaivour of structures more precisely.