Effects of Blast Loading on Seismically Detailed Reinforced Concrete Columns

Abstract

The rise in the number of terrorist attacks over the past few decades has led to growing concerns about the performance of buildings designed by well-established conventional design methods under blast loading. The concerns arise from the response of buildings and loss of lives in some of the more popular terrorist attacks such as those involving the Alfred P. Murrah Building, the Khobar Towers, and Marriott Hotel in Islamabad. Whereas most damage during these attacks was to non-structural elements such as infill wall systems and window glass, the collapse of the Alfred P. Murrah Building revealed that failure of load-bearing members can lead to widespread buildings failure. Thus, it has become imperative to investigate the performance of load-bearing building members to blast loading. More specifically, to quantify the blast resistance offered by buildings designed and detailed for other load types such as wind and earthquake.The effect of seismically detailed reinforced concrete columns on their blast resistance was investigated. Reinforced concrete columns not forming part of the seismic force resisting system were detailed according to CSA A23.3-04 -Design of Concrete Structures. The detailed reinforced concrete columns were subjected to blast loading in a numerical study using the high fidelity physics based finite element code (LS-DYNA). The numerical study was undertaken to investigate the effects of columns designed for different levels of seismicity in the National Building Code of Canada (NBCC) on their blast resistance.The results of the numerical study show that the lateral reinforcement detailing has a significant effect on the behaviour of columns under blast loading. When the reinforced concrete columns were detailed for high levels of seismicity by reducing the lateral reinforcement spacing in the plastic hinge region, the maximum lateral displacement was observed to reduce significantly in comparison with columns detailed with lateral reinforcement spaced for conventional design.ii Also, reducing the lateral reinforcement spacing at mid-height of the column, where plastic hinge formations is expected under blast loading, further reduced the maximum lateral displacement.The closely spaced lateral reinforcement in the seismically-detailed columns was observed to increase the blast resistance, especially to close-in blast loading.The effect of axial loading was also investigated in the numerical study. As the axial load ratio increased, the blast resistance of the concrete columns increased. However, at high, axial load ratios, the columns suffered concrete crushing in the compression zone leading to higher lateral displacements and instability. At higher scaled distances, increasing axial load ratios resulted in reduced maximum lateral displacements; with the seismically-detailed columns not offering any significant advantage over the conventionally-detailed columns.iii

Effect of Blast Loading on Seismically Detailed RC Columns and Buildings

“…As expected, the lateral displacements increased with increasing the charge mass at constant scaled distance. Similar observations were reported by Kyei [11]. Comparison of failure modes for conventional and seismically column, shown in Figure 13, indicates that the failure shape of seismically detailed column is better than that of the conventional column, showing only crushing and spalling of the concrete cover while the internal concrete core was confined enough without any crushing.…”

“…It is therefore essential to direct research to improve the resistance of columns to blast so as to provide protection to the structure [7,8]. Several researchers investigating experimentally the behavior of RC columns under near-field explosion showed that seismic detailing of RC columns has noticeable effect on the blast behavior [9][10][11]. Abladey and Braimah [10] investigated the effects of near-field explosions on RC columns and showed that RC columns designed and detailed for areas of high seismicity detailed reinforcement have a high blast resistance.…”

Performance Assessment of Concrete and Steel Material Models in LS-DYNA for Enhanced Numerical Simulation, A State of the Art Review

“…The examples presented here illustrate important differences between the various models in addition to illustrating some key concrete behaviours that the models should be able to capture. Kyei [90] was validated numerical simulation with experimental work conducted by Farouk [91].…”

Analysis of the Response of a One-Storey One-Bay Steel Frame to Blast

“…Kyei [26] investigated the responses of RC columns originally designed and detailed with sufficient ductility for a given magnitude of earthquake in a specific zone. The columns were modelled using various seismic detailing rules as well as conventional details and a comparison of the responses was investigated.…”