Primary Creep in ASTM A325 Bolts Under Simulated Fire Loading

Abstract

At room temperature, small creep effects are present on steel structures. This is not the case at fire condition where the temperature is much higher than room temperature; in this case creep can be significant, and should be taken into consideration. Since fire hazard can happen in any building, creep effect must be taken into consideration when designing a building. Creep strain behaves as a function of time, temperature and stress. As the temperature increases, the creep strain increases. Similarly, the longer the temperature at a given stress on the structure, the more the creep strain present. The smallest component of steel connection is the steel bolt. Being the smallest component, and most likely highly stressed, it can have significant creep. The ASTM A325 bolt was chosen in this study because it is widely used in steel structures and in the construction industry. In previous work by Shrih (2013), tensile tests under high temperature on ASTM A325 bolts were performed. A finite element model was developed to simulate his experiments. Temperature-Displacement plots were generated; F.E. results showed good agreement with the experimental investigations at lower temperatures. At higher temperatures, the F.E. model had shown deviation from experimental results. Creep effects were not considered in the F.E. model in Shrih's work. In this Thesis it is hypothesized that creep effects are the reason why FE and experimental curves did not match. Further experimental investigations were proposed and performed to account for creep effects. Computational models were developed to predict the creep strain. The models were functions of stress, temperature and time. Since creep was not taken into consideration in the work done by Shrih, the work in this thesis will modify the F.E. result to include the creep effect. The adjusted F.E. results had shown significant agreement compared with the experimental results. Experimental work that was done during this research to predict creep was simulated using ANSYS software. Finite element results were compared to the experimental results and found to graphically match.