| Bridges are critical to the transportation system especially at the time of crises. They are essential for rescue missions, evacuations, and rapid distribution of aid and medical supplies. Bridges are highly visible and accessible structures which make them valued potential targets for terrorist attacks as their destruction could have significant impact on the nation. An efficient security system can minimize the potential of terrorism, yet it will not completely eliminate the threat. Consequently, critical bridges should be protected and designed to mitigate probable blast hazards.;The primary objective of this investigation is to analyze the effect of blast loads on critical bridge components and bridge global response, and propose protection measures for mitigating blast hazards. This investigation presents an overview of the characteristics of blast loads, pressure distributions, wave propagation and reflection, energy dissipation, and the factors affecting the behavior of structural elements subjected to blast loading.;To simplify the analysis of structural elements subjected to blast loads, blast load response spectra were developed. These spectra are used to transform the dynamic blast loads into equivalent static loads. Blast response spectra can be used to analyze and design individual structural components subjected to blast loads, estimate the required ductility, and estimate the minimum standoff distance for the probable blast hazards.;The global behavior of a typical highway bridge was evaluated using computer simulation. The bridge model was subjected to various blast scenarios applied above or below the bridge deck. The results from these computer simulations were used to identify the vulnerable components in the bridge during a blast hazard as well as estimating the magnitudes and locations of maximum shear forces and bending moments. The results from the computer simulations were compared to those from the response spectral analysis. Thus, protection measures were proposed and evaluated. Protection measures include preventive measures such as standoff distance and added security. They also include improved redundancy through utilizing multiple column bents with double and triple edge columns, using highly ductile materials, longer seat widths, doubly reinforced decks, hold-down devices, and the use of cable auxiliary systems. |
