Experimental and Finite Element Investigation of Tension-loaded ASTM A325 Bolts Under Simulated Fire Loading

Abstract

Nuts and bolts have been used in a wide range of steel structures for many years. However, these structures remain susceptible to fire damage. Conducting fire experiments on steel structures is costly and requires specialized equipment. The main objective of this research is to test, analyze and predict the behavior of ASTM A325 bolts in tension under simulated fire conditions and develop a reliable finite element model that can predict the response of similar bolts without the need for repeated testing. The experimental work was conducted at the University of Wisconsin-Milwaukee; a furnace was custom-built to test a bolted specimen under tension loading. The tests were divided into two groups, the first one was used to calibrate the equipment and choose a final testing arrangement; the second group, consisting of four identical tests, was used to validate the finite element model. The temperature-displacement and load-displacement response was recorded. The tested bolts exhibited a ductile fracture in which a cup-and-cone shaped failure surface forms in the threaded section, at the root of the nut. A parametric three dimensional finite element model simulating the tested specimen and attachments was constructed in the ANSYS Workbench environment. The model included the intricate details of the bolt and nut threads, as well as all the other components of the tested specimen. A pretension load, a tension force and a heat profile were applied to the model and a nonlinear analysis was performed to simulate the experiments. The results of the FE model were in good agreement with the experimental results, deviations of results between experimental and FE results were within acceptable range.