Experimental Investigation on the Creep Effect of Shear Tab Connections Subjected to Fire Temperatures

Abstract

The aim of this research is to study the effect of thermal creep on the strength capacities and failure modes of shear tab connections at elevated temperatures. Thirteen bolted lap joints (representing shear tab connections) are experimentally tested under different loading rates: fast rate (10 mm/min) and two slow rates (1 mm/min and 0.3 mm/min) for temperatures ranging from 450°C to 700°C. The temperature- and the time-dependent behavior of the lap joints are examined. The results show a change in failure mode from tear-out failure when using fast loading rates to net section fracture when using slow loading rates at temperatures 450°C and 500°C. The results show that the failure mode of the lap joints changed from plate failure to bolt shear failure at temperatures larger than 500°C. The slow loading rate tests resulted in a reduction in the bolt shear capacities as compared to the fast rate.

Finite element (FE) simulations are performed to validate the performed experimental program and previous experiments on isolated shear tab connections. The study aims at understanding the behavior, strength, and failure modes of shear tab connections with and without the thermal creep effect. The results show that the thermal creep effect causes change in failure mode and reduction of shear bolt strength capacities at elevated temperatures.

Finally, a step-by-step fire design procedure and an example of an isolated shear tab connection re developed. The design example is controlled by bolt shear failure, and thus the thermal creep effect is added in the bolt materials only. The fire design example shows that adding the effect of thermal creep decreases the strength capacity of the connection by 40% at 500°C.

This research shows the importance of considering the effect of thermal creep when studying shear tab connections during fire. Studying thermal creep effect in bolted connections is of great importance for structural fire engineering applications.