Tensile and shear strength of 10.9 grade bolts in heating and cooling fire

Abstract

In this paper, an experimental study is presented to evaluate the tensile and shear capacity of 10.9 grade bolts in heating and cooling fire with an emphasis in the cooling phase properties. In total 44 specimens are tested and results are presented for the steady state tensile and shear tests conducted at room temperature, growth, cooling and postfire phases with peak temperature of heating from 600 to 800 °C. Based on the study, it has been seen that the growth phase data (as the temperature increases) follows an inverted S pattern while in cooling phase (as the temperature decrease from peak temperature) the strength is regained linearly upto ~400 °C, without much strength enhancement as the specimens cools farther to the postfire phase. The strength drop in tensile tests is higher than the shear tests when the temperature increases from 500 °C to 600 °C in growth phase. Based on the present and previous experimental data, different reduction factors are proposed for tensile and shear behavior at growth phase on contrary to the single material proposed in EN1993-1-2. The strength regain in cooling phase is higher in shear tests than tensile tests. The tensile and shear strength reduces by ~46–67% and ~ 67–79% respectively (as compared to strength in room temperature) at postfire phase when the specimens are heated to 600-800 °C. Based on present experimental study, tensile and shear reduction factors are proposed in cooling phase.