Abstract

Structural connections must maintain strength and ductility during and after impulsive loading to prevent widespread failure of a structure. However, a decrease in ductility in response to impulsive loads has been observed both experimentally and in situ. Further, experimental data on the residual capacity of steel structures is limited, especially the residual capacity of impulsively-damaged steel connections. To ensure the safe design of structures, it is necessary to characterize the dynamic and residual capacity of steel connections. To address the lack of data in this realm, an experimental method has been developed to determine the dynamic and residual behavior of A325 high-strength structural steel bolts in single-shear. A high-speed hydraulic actuator is employed for structure-scale experimentation, with impact energies varied from 760 J – 1370 J. Then, surviving bolts are quasi-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 commensurate to undamaged bolts, but lessened residual ductility and energy absorption capacity. These data suggest that metrics other than residual strength should be explicitly included in residual capacity analyses. Further, above a critical impact energy, dynamic bolt fracture with a significant loss of ductility has been observed. A loss of deformation capacity at high impact energies (and thus, capacity to absorb energy through plasticity) may increase the susceptibility of a structure to progressive collapse. Therefore, these results prompted further investigation into the dynamic behavior of A325 bolts. Specifically, the sensitivity of material behavior to strain rate is studied using a Split-Hopkinson Pressure Bar (SHPB) testing apparatus. 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 observed in A325 bolts at high impact energies.

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