Large bridges can be demolished by explosives. Although this has long been useful, it presents an opportunity for a large terrorist attack as well. The first steps to eliminate this deficiency were taken in a FHWA National Pooled-Fund study on steel multi-cell towers conducted by the Engineer Research and Development Center of the Army Corps of Engineers. Next, work on suspender cables and on cable-stay bridge elements, was started under DHS sponsorship. Examination of suspension bridge countermeasures was also done - although on a limited basis - under DHS sponsorship. Limited work on concrete bridge piers was conducted under an NCHRP study. Despite these encouraging starts, bridges are still under-represented in counterterrorism research, and remain vulnerable. The experience of the early stage of research, as well as the feedback from field evaluations, countermeasure design, and construction projects, have provided a more detailed picture of the needs to be addressed in the next phase of research. Physical testing, to date, has employed specimens built specifically for the study, that is, specimens constructed with modern steel alloys and bolted or welded connections. The specimens, because they are new, are also in pristine condition at the time of testing. A useful extension of this test program would encompass early 20th Century alloys, riveted connections, gusset plates, built-up cross-sections, and decades of environmental and traffic loading (In particular, irregular effects of corrosion and uneven live load stresses). Modeling the behavior of bridge towers, main cables, and suspender ropes is still done on a case-by-case basis. Developing this area would also increase our ability to implement countermeasures on other bridges in the field and be a useful step in developing countermeasures for the most vulnerable components on other types of bridges as well.

1] To increase the resistance of suspension bridges to an attack on any of their three major components: Towers; Main Cables; Suspenders. 2] To extend the testing started in Pooled Fund Project 888, Validation of Numerical Modeling and Analysis of Steel Bridge Towers Subjected to Blast Loadings, to include older types of materials and connection details, and varying material conditions. 3] To develop high performance/lower intrusion countermeasure designs. The low intrusion is significant to bridge owners because the retrofit must not produce material degradation (e.g., corrosion), interfere with the operation of previously-installed mitigation measures for other hazards (e.g., seismic), or obstruct normal maintenance/inspection operations.

Experimental and analytical work will verify and calibrate: 1) Predictions of member behavior; 2) Performance of current mitigation measures; and, 3) Performance of new design concepts and materials subjected to the loads outlined below. The test loads will replicate vehicle bombs or other standoff charges; hand-emplaced breaching charges, cutting charges, and mechanical cutting, as required. Explosive tests are to be conducted in a secure environment at a USACE test facility. The study will include both small- and large-scale testing of steel suspension bridge elements, their connections, and, where practical, assembled groups of bridge elements. The response of early 20th century steel members to these loadings will be determined. Specimens for this portion will be obtained from bridges to be demolished: The Waldo-Hancock Bridge (Maine), the Crown Point Bridge (NY-Vt), and the Ft. Stueben Bridge (Ohio-WV). A limited on-site study, outlined in a prior FHWA funding request, was conducted under DHS sponsorship, and will be continued under this study. The study of both retrofit designs and retrofit materials are within the scope. Retrofit methods include: External and internal tower reinforcement and energy routing; Main cable wrapping; Suspender replacement materials; and energy-absorbing suspender sockets. Design issues to be considered include the typically severe size and weight limitations found on existing structures, as well as the need to address practical construction- and maintenance-imposed restrictions. The performance of advanced materials will be specifically assessed. This includes material combinations beyond those considered under Pooled Fund Project 888.

Recommended Funding: $2,500,000 Task 1: $1,200,000 Task 2: 750,000 Task 3: 500,000 Task 4: 50,000 Suggested minimum contribution: $50,000 per year