The terrorist attacks of September 11, 2001 on the World Trade Center and the Pentagon focused the attention of the transportation industry on the vulnerability of existing state owned facilities to similar attacks. Science Applications International Corporation (SAIC) was contracted by the American Association of State Highway and Transportation Officials (AASHTO) and the Transportation Research Board to create a Vulnerability Assessment process to be used by the states to identify their most vulnerable facilities. Each state is expected to identify 15 to 20 of the most vulnerable facilities and than develop mitigation procedures for each identified facility. The mitigation can be anywhere from access denial and/or increased standoff distance, to structural hardening. All these mitigations are meant to stop or, at the very least, minimize the damage due to a terrorism attack on the facility. Most states DOT's, including the Washington State Department of Transportation (WSDOT), are not trained to make vulnerability assessments from attacks by terrorists. As a result, WSDOT enlisted the aid of FHWA to make these assessments. FHWA assembled a team of experts from New Jersey, Boston, and Washington DC as well as an explosives expert from the U.S. Army Corps of Engineers Engineer Research and Development Center (ERDC), Vicksburg, Mississippi and a faculty member from the University of New Mexico. The team spent an entire week discussing details of some of the bridges identified in Washington as vulnerable, field visiting a number of these bridges, and preparing an assessment presentation. Nationally, research and analysis procedures need to be developed to help all states implement proven bridge details addressing terrorism concerns. During the recent AASHTO Subcommittee on Bridges and Structures Meeting, a research project was initiated to create "hazard standard details." This study is intended to produce standard minimum details to be used nationally and it appears these details will be very similar to the minimum details now used for seismic force mitigation such as, column confinement, large beam seat widths, and elimination of rebar splices in columns. As a result of the vulnerability assessment exercise, we discovered that there has been very little research conducted on blast effects on bridges. During our discussions, it was identified that there was a need to conduct real life-size blast experiments on prestressed girder bridges. Based on past experience, the blast experts have a very good idea of what damage to expect from a blast originating on top of a prestressed girder bridge. It is assumed (note assumed, not known) that the deck will be blown out and it is most likely one of two girders would be damaged depending on the exact location of the detonated device. The big question is what will happen if the detonation occurs under the prestressed girder bridge. It is very well understood by engineers that, if one exerts an upward force on a prestressed girder, it will self-destruct due to the extreme bottom fiber compression with the application of a relatively small load. Therefore, the big question is will the deck be blown out and relieve the upward blast pressure before the girders fail due to the blast uplift force.

The objective of this research is: (1) to assess the damage done to precast, prestressed girder bridges from a blast generated below the girders, (2) to compare this damage with a blast generated on top of the bridge deck, and (3) to develop recommendations for possible mitigation measures that would harden this type of bridge blast damage.

The scope of work has been broken down into three phases: design, construction, and experiment. Currently, we are in the design phase and have determined the design of the bridges and blast test approach. Design Four blast tests are planned. Two tests will be performed on single-girder specimens, one with the blast above the girder and the other with the blast below the girder. These single-girder specimens will be 75 ft long, bulb tee precast prestressed girders, and they will be simply-supported on each end. The remaining two tests will be performed on bridge structures consisting of 4 precast prestressed girders, simply-supported on each end, and with a typical cast-in-place concrete deck. One of the bridge structures will be constructed of 150 ft long, BT72 prestressed girders. The other bridge structure will be constructed of 79 ft long prestressed girders of mixed (but similar) sizes (2 @ W50G; 1 @ 4¿-2 ½¿ deep; 1 @W58G). The 150 ft bridge structure will be subjected to a blast above the deck; the 79 ft bridge structure will be subjected to a blast below the deck. These bridges are similar to commonly constructed bridges in the United States. The girders will be set on timber bunking and a trench dug under the bridges so the test will be reasonably close to actual highway conditions. The test blasts will be fully instrumented and video taped. The collected data will be analyzed and used to formulate mathematical reproductions of the experienced forces and pressures for use in terrorism hardening of future designs and possible existing bridge retrofit schemes. The U.S. Army, Corps of Engineers, Engineer and Research Development Center (ERDC) will provide the expertise in sizing the appropriate detonation device. Construction The U.S. Army's Yakima Firing Range, located near Yakima, Washington, is scheduled to be the test site. The current agenda is in flux due to demands at the Yakima Firing Range because of training exercises, but WSDOT and the U.S. Army is looking for a suitable site. If another site on the Yakima Firing Range is located and funding is available, the bridges would be built in the fall of 2005 and blast testing would occur in the spring of 2006.

This study is open to all states; however, a minimum contribution of $10,000 will be required to be a member of the Technical Advisory Committee (TAC). The TAC will provide guidance for the study and review and comment on all documents produced by the research team.