The concern over bridge vulnerability in the US has grown at an accelerated rate over the past ten years. This distress is caused by more than just accumulated wear and tear on infrastructure. The rise in domestic and international terrorist threats and activities has motivated significant interest in bridge-specific protective design.
Doctoral student Eric Sammarco has honed in on the multifaceted area of blast-resistant design as his area of study and is involved in developing technology to protect bridges. His research for the department’s Mechanics, Uncertainty, and Simulation in Engineering (MUSE) program is focused on the development of vulnerability assessment software for blast-loaded bridge components.
Because the security of the nation’s highway bridge inventory has been identified as an urgent national security issue, the American Association of State Highway and Transportation Officials (AASHTO) and the National Cooperative Highway Research Program (NCHRP) have recently developed an objective and logical procedure for identifying infrastructure in need of immediate security enhancement and for prioritizing threat mitigation for bridges. NCHRP and other organizations have also funded research to cultivate bridge-specific protective design provisions and engineering tools for implementation into practice.
Researchers from the Department of Civil, Architectural and Environmental Engineering helped develop a national standard for the blast-resistant design of highway bridge columns, which are critical to the structural integrity of a typical highway bridge. The work of professors Eric Williamson and Oguzhan Bayrak and graduate research assistants Carrie Davis (BSArE 2006, MSCE 2009) and Daniel Williams (MSCE 2005, PhD 2009) involved large-scale blast tests in two phases. The team first focused on characterizing the behavior of shock waves in the vicinity of slender structural elements, such as bridge columns. They then focused on the response of half-scale reinforced concrete column specimens subjected to small standoff and near-contact bulk explosives. The latter tests yielded information for developing design criteria for blast-resistant columns.
UT-Austin researchers also conducted a computational study to characterize shock wave behavior. The computed results aligned with the observations from the experimental blast tests – more detailed information is available in NCHRP Report 645. Research has also commenced on other critical bridge components.
Together, the experimental and computational research efforts have provided sufficient information to begin the development of bridge-specific engineering tools and protective design provisions. Sammarco is developing PC-based software capable of characterizing blast loads on critical bridge components, predicting dynamic response, and providing an estimate of incurred damage. His proposed software, Anti-Terrorist Planner for Bridges (ATP-Bridge), will eventually be used to facilitate rapid vulnerability assessments in the field, anti-terrorist/force protection retrofits of existing bridges, and safer designs of new bridges.
ATP-Bridge is an interactive, menu-driven software program designed to operate efficiently on a PC, maximizing user-friendliness and expedience without compromising the accuracy of analysis results. In the program, a “project” is associated with an entire bridge structure and multiple components are defined by the user for a given project. Multiple threat scenarios may also be defined for each bridge component.
Version 3 of the software contains component response models for reinforced concrete bridge columns, steel suspension bridge tower panels, reinforced concrete cable-stayed bridge tower panels, and various high-strength steel cable components. With regard to attack scenarios, ATP-Bridge is capable of considering bulk explosive detonations, both far-field and close-in configurations, and various man-portable threats.
“This area of research is of great interest to me because it offers complex engineering challenges, is a relatively new ‘public domain’ field of study, and has the potential to positively impact the entire nation,” says Sammarco.
In an effort to validate the software, results gathered from the previously -mentioned NCHRP experimental test program were used. The predicted results from ATP-Bridge showed good agreement with those observed during the reinforced concrete column blast tests. Results of a U.S. Army Engineer Research and Development Center (ERDC) experimental test program were used to validate the ATP-Bridge steel tower component response model. The ERDC program focused on characterizing the response of a 3-cell portion of a steel suspension bridge tower to standoff detonations. Additional experimental data were obtained to validate the concrete tower panel and steel cable components. Gaps in experimental data were filled with synthetic data resulting from high-fidelity computational simulations.
Response to Sammarco’s ATP-Bridge program is also positive. A preliminary version of the software has already been utilized by the U.S. military in a wartime theater situation. It will be owned and maintained by the U.S. Army Corps of Engineers and will soon be available for distribution to government agencies and qualified government contractors.
“The ATP-Bridge software has been surprisingly successful even throughout its development,” says Sammarco. “It has been well-received by the sponsor and other government agencies, and the engineering community has been very receptive to the research topic during presentations at national conferences,” says Sammarco. “The idea behind the
ATP-Bridge software is for it to be continually updated and enhanced as new test data become available. There is certainly a need to incorporate additional bridge components and threats into ATP-Bridge. The current version of the software has essentially exhausted most of the available test data. Thus, the next step in future research is to create more data through experimental testing.”
The project team recently conducted a day-long workshop in New York City for various state transportation engineers as well as the New York Port Authority to demonstrate the software. The workshop prompted invitations to hold additional workshops in various states around the country.
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Sammarco holds a B.S. and M.S. in Civil Engineering from the University of Kansas. He has over three years of work experience as a Structural Engineer in Black & Veatch’s Commercial Nuclear Energy Division. While at Black & Veatch, his interest in seismic and blast design motivated him to lead several advanced analysis efforts pertaining to structural dynamics, earthquake engineering, and soil-structure interaction. During his doctoral studies, he also worked part-time for Protection Engineering Consultants, a specialty protective design consulting firm located in Austin.
He is a registered Professional Engineer in the state of Texas and an active member of the American Concrete Institute as well as the American Society of Civil Engineers. In his free time, Sammarco enjoys exercising and spending time with his wife, son, and three dogs. Upon completing his Ph.D., he plans to return to industry and start a career in applied research, although teaching is not out of the question.
Sammarco reflects, “I consider myself extremely fortunate to have been given the opportunity to work on this challenging and rewarding project with Professor Williamson and the rest of the research team. Interacting with him and graduate student peers has enabled me to grow exponentially, both professionally and personally, over the past four years. I am excited to see what the future holds as I use the knowledge and wisdom acquired through my tenure at UT Austin to springboard into an exciting and successful career and a new life chapter for the Sammarco family.”
Sammarco is also featured in the January issue of Structural Engineer.
