Effects of detailing on the blast and post-blast resilience of high-strength steel reinforced concrete (HSS-RC) beams

Abstract

This paper examines the influence of reinforcement detailing and fibers on the static and blast performance of beams built with high-strength concrete (HSC) and high-strength (HS) steel reinforcement. The beams in this study had dimensions of 125 mm × 250 mm × 2440 mm (b × d × L), and were built with HSC and Grade 690 MPa ASTM A1035 reinforcement. Longitudinal reinforcement in tension consisted of either 2-No.4 or 2-No.5 high-strength bars (ρ = 1% or 1.5%), while transverse reinforcement consisted of closed ties or open-stirrups made from 6 mm wire arranged at various spacing (s). Group A beams (6 specimens) were designed according to modern blast standards, with top continuity bars and closely spaced ties at s = 50 mm (d/4) throughout the beam span, while Group B beams (2 specimens) were designed with high-strength fiber-reinforced concrete (HSFRC) and a larger tie spacing of s = 100 mm (d/2). The performance of the beams is compared to that of a control set of singly-reinforced beams with “nominal detailing” consisting of open-stirrups spaced at s = 100 mm (d/2) in the shear spans only - Group C. Blast tests were conducted using a shock-tube with companion beams tested under quasi-static four-point bending. The use of blast detailing in Group A is found to significantly enhance the ductility of the high-strength steel reinforced concrete beams under static loading, allowing for full utilization of the high-strength bars in tension. Improved detailing also leads to important enhancements in blast behavior, including better control of displacements, increased blast capacity and high damage tolerance when compared to the Group C control specimens. Moreover, the results from Group B demonstrate that fibers can be used to relax transverse steel detailing without compromising ductility or performance under both static and blasts loads. The ability of high-strength steel to reduce steel requirements is also demonstrated. Moreover, the post-blast performance of the beams is assessed through residual static testing of the blast-damaged beams. The results show that blast detailing and fibers allow for significant residual post-blast resistance and energy-absorption capacity. As part of the analytical study the blast response of the test beams is predicted using 2D finite element (FE) modelling. The results show that the FE procedure which employed the Disturbed Stress Field Model was able to accurately capture the peak load and failure mode of the beams under static conditions. Under blast loading, the model also captured the displacement response of the beams up to first peak, however the accuracy reduced at subsequent cycles, with the results found to be sensitive to the choice of damping coefficients.