Abstract

After the terrorist attacks of September 11th, 2001, blast load resistance of infrastructure has been of great concern to structural engineers, and government institutions in the United States have provided guidelines to mitigate these risks. The focus of these guidelines has been on buildings, and measures to protect infrastructure such as bridges have not received similar
attention. However, data on terrorist attacks show that bridges are often targeted, and the majority of these attacks are on non-landmark bridges, such as highway bridges.

With the threat of global terrorism, it is required to understand the behavior of bridges in Canada under blast loads. Specifically, bridge columns are often targeted and they represent a critical structural function as their failure can lead to collapse of the entire bridge. Transverse reinforcement is the key element in design of reinforced concrete (RC) bridge columns against blast, and it is also the key element in design for seismic loads. A generic two-span bridge located in Toronto, Ontario; Vancouver, British Columbia; and Victoria, British Columbia, is designed using the Canadian Highway Bridge Design Code (CHBDC). The three cities are chosen to represent low, high, and extremely high seismic hazard levels, respectively. The bridge columns are designed according to the required seismic detailing of the different hazard levels with a focus on spacing, bar size, and type of transverse reinforcement. The finite element software LS-DYNA is used to model the bridge columns and simulate the application of blast loads at different charge heights for various charge weights and standoff distances.

Analysis of the simulation results concentrates on the performance of columns with respect to concrete failure mechanisms, behavior and stress patterns of steel reinforcement, and displacement curves. The results of this study indicate that for equivalent blast loads, a charge
closer to the base of the column is more critical than a charge at mid-height. Moreover, charge weight has more of an impact than standoff distance in a columns ability to resist blast. The results also indicate that seismic detailing is extremely important in blast load resistance of columns. Specifically, columns with smaller spacing of transverse reinforcement, as well as bigger bar size, demonstrate an ability to successfully resist blast and allow a column to carry the required structural loads. Moreover, columns with spiral transverse reinforcement perform better than columns with tied transverse reinforcement.