Post-Fire Mechanical Properties of High Strength Grade 8.8 Steel Bolts

Abstract

In order to understand the post-fire performance of bolted connections, it is essential to have a deep knowledge of the material behavior of all the components, including bolts, after fire conditions. Very limited research has been carried out on the behavior of high-strength steel bolts during and after fire conditions. This paper presents experimental investigations of the residual mechanical properties of Grade 8.8 bolts after exposed to elevated temperatures up to 900°C. The post-fire stressstrain curves, residual elastic modulus, yield and ultimate strengths as well as tensile failure modes of bolts were investigated. Also, the effect of factors including target temperature level, chemical composition of feedstock steels (SAE 10B21 and 10B38) and heat treatment characteristics in production process of Grade 8.8 bolts were studied. It was observed that, the bolts exhibited drastic reduction in strength after cooling down from temperatures beyond 400°C, as they lost about 50% of their ultimate strength after experiencing 800°C. Furthermore, a set of predictive equations are proposed for evaluating the residual mechanical properties of Grade 8.8 bolts after fire.