The response of structural connections during and after an impulsive load is often vital to the global stability of a structure. Post-impulse, structural connections must redistribute load around local failures such that progressive collapse does not occur. To do so, connections must have sufficient residual strength and deformation capacity even if damaged by the blast, impact, or other dynamic load. Therefore, understanding the dynamic behavior of steel structural connections is vital to preventing collapse due to an impulsive event. Previous research on steel connections and bolts suggests that a decrease in bolt ductility occurs in response to impulsive loads, both experimentally and in situ. Experimentation on the residual capacity of steel structures is limited, especially research involving the residual capacity of impulsively-damaged steel connections.To address this lack of data, an experimental method has been developed to determine the dynamic and residual behavior of A325 high-strength structural steel bolts in single-shear.&nbsp;The response of full-scale structures to blast load typically involves live explosive tests, however, the use of actual explosives in experimentation presents challenges in repeatability, financial expense, and response monitoring. Therefore, to investigate the dynamic behavior of A325 bolts, a high-speed hydraulic actuator is employed for structure-scale experimentation. Impact energies varied from 750J – 1400J and strain rates from between 75 s-1&nbsp;– 150 s-1.&nbsp;Then, surviving bolts were statically loaded to failure to evaluate their residual capacity properties.Results demonstrate that, below a critical impact energy, A325 steel structural bolts have residual strength and residual stiffness commensurate to undamaged bolts. However, though the strength capacity is comparable to undamaged bolts, there is a consistent negative correlation between impact energy and ductility.&nbsp;&nbsp;Further, above a critical impact energy, sudden bolt fracture with a significant loss of ductility has been observed.&nbsp;This loss of ductility, and thus capacity to absorb energy, may increase the susceptibility of a structure to progressive collapse. Therefore, these results prompted further investigation into the dynamic behavior of A325 bolt material to identify the driving factors of ductility loss. Specifically, the sensitivity of material behavior to strain rate is studied using a Split-Hopkinson Pressure Bar (SHPB) testing apparatus. Machined samples of A325 bolt steel were subjected to compression at intermediate strain rates, ranging from&nbsp;150s-1 -&nbsp;1000s-1.&nbsp;These results, in tandem with the single-shear bolt impulsive test data, are used to evaluate the role of strain hardening in the loss of ductility&nbsp;in impulsively-loaded&nbsp;bolts.

Characterization of A325 Structural Bolts Subjected to Impulsive Loads

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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