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.

FHWA's multi-year infrastructure security research program is the context for this project. The major goal is to significantly increase the resistance of suspension bridges and their components to destruction by specified attack methods, removing targets on which to plan an attack. This could be achieved in two ways. The first is strengthening existing bridge components. The second would involve replacing existing bridge components with newly developed ones. The latter will also apply to new bridge construction. The aim of this particular project is to achieve the major goal, stated above, on three components: 1) Towers; 2) Main Cables; 3) Suspenders. The proposed program is based on the availability of a suspension bridge to be demolished: The Waldo-Hancock Bridge, near Bucksport, Maine. A limited on-site study, outlined in a prior FHWA funding request, was conducted under DHS sponsorship. A more extensive off-site study, following the demolition of the structure and removal from its present site, is the subject of this request. 1. Verify and calibrate analytical predictions of the behavior of steel towers, main cables, and suspender ropes, and individual components, subjected to attack under specific methods and magnitudes. 2. Verify the predicted performance of currently-used or proposed mitigation measures. 3. Analyze and evaluate new concepts and materials for mitigation. 4. Develop new retrofits and bridge component designs and verify their performance.

The study shall consist of physical, full-scale testing of steel suspension bridge elements, their connections, and, where practical, assembled groups of bridge elements, subjected to simulated attack. Attack methods include the use of vehicle bombs or other standoff charges; hand-emplaced breaching charges, cutting charges, and mechanical cutting. Direct impact by airplane, vessel, or truck is beyond the scope of this study. The full-scale explosive demolition testing will be conducted in a secure environment at a USACE test facility. The Off-site study will be influenced by the available specimens¿ condition. The areas now being examined for inclusion in physical testing include: Suspender Cutting Charges; Tower Section Standoff Attack; Main Cable Shear; Main Cable Standoff Attack; and Main Cable Cutting Attack. If sections of main cable remain, a fire heat transmission study will also be conducted. After the behavior of the unprotected structure has been calibrated, the effects of retrofits will be studied. These will include: Main cable wrapping; External and internal tower reinforcement and energy routing; Suspender replacement materials; Energy-absorbing suspender sockets; and any other retrofit identified as suitable for inclusion in this study. Research into both retrofit materials and retrofit designs are within the scope. This includes material combinations beyond those previously considered. 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.

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