Effect of elevated temperatures on the compressive behavior of timber filled steel and pultruded GFRP tubes

This study examines the use of timber as a filler material for steel and pultruded GFRP tube elements and the performance of these sections is compared to solid timber columns, hollow steel and hollow pultruded GFRP tube element after exposure to elevated temperature. In total, 102 specimens were fabricated and exposure to elevated temperature ranging from 20 to 700 degrees C was evaluated. It was found out that filled tubes using timber could improve the compressive strength and stiffness of tubular section specimens up to 73 and 212 percent, respectively. Timber filled steel tube (TFST) and hollow steel tube specimens had a better performance at elevated temperature in comparison to other specimens such that they were able to maintain 28 and 44 percent of their compressive strength and axial stiffness at 700 degrees C. In contrast, timber filled pultruded GFRP tube (TFGT) and hollow pultruded GFRP tube lost more than 25 and 93 percent of their strength and initial stiffness at temperature beyond the glass transition temperature of the resin, 95 degrees C, and resin decomposition temperature, 288 degrees C, respectively. Two novel empirical models were developed which accurately predicted the compressive strength and axial stiffness of TFST and TFGT specimens at room and elevated temperature.

Automated summary

The study explored the use of timber as a filler material for steel and pultruded GFRP tube elements, finding that timber-filled tubes could significantly improve compressive strength and stiffness. Timber-filled steel tubes and hollow steel tubes exhibited better performance at elevated temperatures, while timber-filled pultruded GFRP tubes experienced significant strength and stiffness loss beyond resin transition and decomposition temperatures. Novel empirical models accurately predicted compressive strength and stiffness of filled tubes under various temperature conditions.