Most major long span bridges in the United States are vulnerable to terrorism. They are high visibility structures, with a potential for extensive media exposure and public reaction if an incident were to occur. As a result of the long spans, complicated designs, site locations, etc., these bridges have very high replacement costs, and multi-year replacement construction periods. The potential for impacting regional and national economy is also greater because of the increased time for reconstruction. Many of these bridges serve as transportation arteries critical for emergency evacuation and for carrying lifelines besides vehicular traffic. Depending on the location, there is potential for mass casualties because of the volume of traffic it can carry at any given time. Most if not all of these long span bridges cross rivers, bays or other navigational channels. Damage resulting from an attack could impede navigation in addition to disrupting vehicular or other lifeline traffic flows.

The objectives of this study are to develop better analytical modeling and numerical analysis capabilities of steel bridge towers subjected to airblast, and to develop retrofit schemes for the towers. The numerical analysis, both with and without retrofits are to be verified through large scale experimental testing.

The scope consists of analytical and controlled explosive tests on large-scale steel tower sections representative of typical towers in both their as-built and retrofitted configurations to determine performance under various blast scenarios and for verification of numerical analysis techniques. Section sizes and detailing will be carefully determined to insure realistic boundary conditions and applicability to actual towers. It is envisioned that this work will consist of, at the minimum, following tasks done in several phases: Ø Phase I - Selection of Steel Bridge Towers and Numerical Analysis of As-Built Towers Task 1 - Select steel bridge towers from existing population of bridges for computer modeling and numerical analysis Task 2 - Develop drawings for the selected towers to be used in Task 3 Task 3 - Utilizing various levels of tools developed by the military from low resolution prediction code (CONWEP), to medium resolution code (BlastX), to high resolution hydrodynamic code (SHAMRC and FEFLO), and one suitable commercial program, develop models and analyze selected towers to determine behavior in response to a large explosion both in close proximity and with stand-off distances. Ø Phase II - Experimental Testing of As-Built Towers Task 1 - Develop experimental test plans, to include determination of representative tower sections, model designs, testbed layout, required bomb sizes, instrumentation plan, etc. Task 2 - Conduct experimental tests of as built towers for validation of numerical analysis with towers subjected to both close in detonation and with stand-offs Task 3 - Analyze the experimental results and refine numerical modeling and analytical procedures as necessary Task 4 - Prepare Report I that summarizes the work from phases I and II including the numerical modeling, test results and correlation of these results to the numerical models. Ø Phase III - Numerical Analysis and Experimental Testing of Retrofitted Towers Task 1 - Select blast resistant retrofit schemes for the bridge towers tested in phase II, Task 2 - Conduct computer modeling and analysis of the retrofit schemes using programs from Phase I Task 3 - Develop experimental test plans, to include determination of representative tower sections, model designs, testbed layout, required bomb sizes, instrumentation plan, etc. Task 4 - Conduct experimental tests of retrofitted towers subjected to close in detonation and with stand-offs for verification of the retrofit schemes and validation of numerical analysis. Task 5 - Analyze experimental results and refine modeling and analytical procedures as necessary Task 6 - Prepare Report II that summarizes the work under Phase II, including the test results and correlation of these results to the numerical models. The report should provide an analysis of the effectiveness of the tested retrofits and should discuss possible improved retrofit schemes. Ø Phase IV - Final Report and Executive Summary Task 1 - Prepare a final report synthesizing the findings of all phases Task 2 - Prepare an executive summary

Funds are still being solicited from potential partners. The commitments received to date is $915,000 while the projected amount for fully funding the study is $1,500,000. The requested minimum contribution is $50K per fiscal year.