The effects of elevated temperatures on the performance of concrete-filled pultruded GFRP tubular columns

Usage of concrete-filled pultruded glass fiber-reinforced polymer (GFRP) tubes (CFPGT) as columns can increase the service life of structures. However, marine structures such as oil platforms are always prone to fire because of the low resistance to the elevated temperatures. The purpose of this investigation is to evaluate the effects of concrete core strength (30 and 60 MPa), and exposure temperature (25, 100, 200, 300, and 400 degrees C) and time (60 and 120 min) on the compressive and bond behavior of CFPGTs. The properties of unexposed and exposed concrete core, pultruded GFRP hollow tubes, and CFPGTs were determined via compressive and disk-split tests. Also, the push-out test was used to measure bond-slip strength of partially-filled samples. The results showed that the maximum load-bearing capacity of the exposed stub columns at temperatures 100, 200, 300, and 400 degrees C was 8%, 22%, 34%, and 51% lower than that of the unexposed columns, respectively. Regardless of exposure conditions and the core strength, the pultruded GFRP tubes resisted about one fourth of the total load-bearing capacity. Moreover, it was observed that the ultimate axial strain (the strain corresponding to tube rupture) of column specimens was reduced with increase in concrete core strength and exposure temperature; however, the exposure time had insignificant effect on the ultimate axial strain. Dilation and load-bearing capacity of CFPGTs were considered to propose new models for predicting the experimental results. Concerning the bond strength tests, it was concluded that the exposure temperature increment led to the interlocking and coefficient of kinetic friction increase, resulting in higher bond strength. Finally, expressions were presented to estimate the bond strength of CFPGTs after exposure to elevated temperatures.