Large scale fire resistance tests of prestressed continuous steel-concrete composite beams to evaluate the effects of geometric imperfections

Little attention has been devoted to exploring the effect of geometric imperfections under fire conditions. To bridge this knowledge gap, this paper presents findings from five large scale fire tests on prestressed continuous steel-concrete composite beams (PCCBs) designed to investigate the effect of initial geometric imperfection (IGI) on the fire resistance of PCCBs. The examined parameters include several IGI modes, load levels, and prestress levels. Various fire responses were monitored and recorded during these tests, such as cross-sectional temperature rise, mid-span deflection, prestress in the cable strands, and side-support reactions. The results of these fire tests indicate that PCCBs with the initial mode of flexural-torsional buckling at the middle support applied as an IGI had larger mid-span deflection and lower critical temperature relative to that of the beams without IGI. The same beams also underwent a larger degree of relaxation in prestress levels, thus reaching failure at a faster pace. Our findings also indicate that while the end-support reactions were redistributed when exposed to fire, the side-support reactions decreased at the first stage of fire exposure and then gradually increased toward the final stage of the fire exposure. Evidently, for PCCBs with IGI, the side-support reaction towards the end of the fire tests is larger than the initial reaction. To complement the conducted fire tests, a series of finite element (FE) models were developed to further study the effect of IGIs in terms of the fire response of PCCBs.

Automated summary

Little attention has been given to the effect of geometric imperfections on the fire resistance of prestressed continuous steel-concrete composite beams (PCCBs). Therefore, this paper presents findings from fire tests on PCCBs with initial geometric imperfections (IGIs), investigating their impact on fire response. The results show that PCCBs with flexural-torsional buckling as an IGI have increased mid-span deflection and decreased critical temperature, leading to faster failure. In addition, the side-support reactions decrease initially and then gradually increase during fire exposure. Finite element models were also developed to further study the effect of IGIs on the fire response of PCCBs.