AASHTO BSG-1:2011 Bridge Security Guidelines.
This article presents a broad view of the issues that need to be considered during the planning and design of bridge projects to address bridge security. Bridge owners should establish criteria for the size and location of the threats to be considered when analyzing bridges fbr security as specified in Article 1.2. These criteria should take into account the type, geometry, and importance of the structure being considered.
Bridge owners are responsible for establishing the procedures by which bridge importance is assessed and by which tbrmal vulnerability studies are conducted. This work can be carried out by bridge owners with appropriate experience or by retaining the services of a qualified security consultant.
Currently, there are no uniform procedures for assessing the importance of a bridge. Accordingly, it is up to the discretion of the bridge owner to establish the procedures required to assess the importance of a bridge. Factors common to many of the proposed procedures include the following:
• Social and economic impact of bridge loss,
• Role played by bridge in defense or security of region. state, and nation,
• Average daily traffic,
• Average daily truck traffic,
• Distance to nearest detour, and
• Symbolic importance.
Work is being done to produce a uniform procedure to prioritize bridges for security. In the absence of uniform procedures, some states have developed their own, incorporating security prioritization methods that, while similar, differ in the details. In addition, state procedures to assess bridge importance have been developed by departments of transportation to assist in prioritizing seismic rehabilitation. These procedures also may be used in conjunction with security considerations.
Protecting a bridge from every conceivable threat is not possible. The most likely threat scenarios should be determined based on the bridge structural system and geometry as well as identified vulnerabilities. The most likely attack scenarios will minimize the attacker’s required time on target, possess simplicity in planning and execution, and have a high probability of achieving maximum damage.
The level of acceptable damage should be proportionate to the size of the attack. For example, linear behavior, local damage. or both, should be expected in a small-sized attack; while significant permanent deformations, significant damage, partial failure of some components. or some combination thereof should be acceptable under larger-sized attacks.
The level of threat and the importance of the bridge should be taken into account when determining the level of analysis to be used in determining the demands. Approximate methods may be used for low-force, low- importance bridges whereas more sophisticated analyses should be used for high-force threats to important bridges.
Type of threat, vulnerability, and method of mitigation vary depending on the type, geometry, location, and importance of the structure. The following arc examples for each of the factors:
• Type of threat:
o Vehicle-borne or hand-emplaced explosives,
o Impact from motor vehicles,
o Intentionally derailed trains, or watercraft.AASHTO BSG-1 pdf download.