Analysis of Axial Stiffness Reduction Factors in Thermal Analysis of Multistorey Buildings

Abstract

  This study is aimed at the assessment of realistic values for the modification factors of beams’ axial stiffness, applied in finite element analysis of structures under thermal effect. In a previous study, the authors developed an algorithm and software package to determine the relationship between the axial force acting on a specific beam, and the axial stiffness modification factor which takes into consideration the flexural cracking of the beam. In this study, these relationship curves are utilized using a newly developed analytical algorithm for the iterative analysis of RC multistorey frames under the effect of thermal expansion/contraction. A new Excel/Visual Basic software package is developed , and used to control and perform iterative analysis runs on ETABS program, while continually modifying the axial stiffness modification factors of the beams, to reach the accurate value of the modification factors at convergence. A group of building frames designed according to the Code of Practice Software are used for application of the newly developed algorithm and software package and the effect of different numbers of floors on the axial forces developed in thermal analysis is investigated, with emphasis on estimation of the applicable modification factors in each case. The practical values obtained for these modification factors are compared to the common code specifications, and the common practice in design offices in the markets. Several geometric and section properties of the beam elements in the studied buildings are varied to widen the range of the study, and develop useful recommendations for designers in this field.