Behavior of slip-critical bolted connections subjected to impulsive loads

Bolted structural steel connections are one of the most common connection types in structures due to their low cost and efficient installation. However, experimental research on the behavior of bolted connections subjected to impulsive loads (e.g., blast, shock, impact) and their residual load carrying capability after the impulse is limited. Most prior research is focused on quantifying the capacity of the bolt material at high rates and less on the energy dissipation of the connection system. In most connections, the bolts are pretensioned to varying levels, which creates a clamping force on the connected members. The friction associated with this clamping force significantly contributes to the overall impulse-resisting force of the system. An experimental program was developed using an impulsive shear apparatus with two loading phases to investigate the effects of friction in slip-critical connections. The objectives of this test series were to collect data to begin to quantify the energy dissipation of an impulsive load through friction, to quantify the residual clamping force, and to determine the force required to initiate slip after such an event. A total of twelve experiments were conducted using the experimental method. This article describes the materials and methods used in the test series, presents the significant findings and observations from the experiments, and discusses key conclusions and recommendations. These initial experiments support the recommendation that structural bolts in relevant structures, including those in bearing-type connections, be installed with the minimum bolt tension required in slip-critical connections, providing a low cost, effective safety measure for protection against extreme loads.