Project Objective:

The main focus of NCHRP 12-72 project is to develop guidelines for design and detailing of bridge components during blast events based on existing seismic guidelines. Although the effect of blast loading is usually localized compared with that of an earthquake, the ability to sustain local damage without total collapse is a key similarity between seismic and blast resistant design approaches. Unlike during seismic loading, bridge bents and piers may be subjected to large lateral forces, possibly resulting in large deformations, shear or flexural failures due to an explosion under the bridge deck. Extensive local damage to bridge bents and piers may result in loss of their load-carrying capacity which, in turn, may trigger a cascade of failure resulting in progressive collapse of the bridge. This aspect can be simply exemplified through multi-hazard design of bridge piers for seismic and blast loads. For seismic loading, a simplified SDOF model may be sufficient for preliminary design and analysis model. On the other hand, a higher precision FEM model is required for analysis and design for blast load cases [Ettouney, Alampalli and Agrawal (2005)]. High-precision FEM tools will facilitate better understanding of capability of bridge components to resist blast loads and help evaluate the effectiveness of different hardening techniques realistically. Proposed three tasks will investigate all aspects of this problem in detail and propose a comprehensive knowledgebase and approach that can be used by major stakeholders in the transportation community.

Project Abstract:

According to the Blue Ribbon Panel set up to study the issue of blast attacks [BRP (2003)], substantial causalities, economic disruptions and other societal ramifications would result from isolated attacks on 1000 of 600,000 bridges in the country. This clearly shows that the highway system in the country has vulnerabilities to blast damages that must be addressed urgently. Although some work on blast resistant design and detailing guidelines is being carried out through different initiatives [e.g., NCHRP 12-72], there is an urgent need to develop high-precision finite element analysis tools to realistically model the behavior of different bridge components, including uncertainties involved in modeling structural parameters during high strain loading encountered during blast loads, interaction between blast wave and bridge components and effectiveness of different mitigation strategies. This project proposes to address this crucial need through the following tasks: (i) Development of high-precision finite element models of bridge components based on current state of the art in high strain behavior of bridge component materials, (ii) Verification of high-precision FEM model through available experimental data on blast loads (experimental, intentional, unintentional and visual), and (iii) simulation of behavior of bridge components during various blast event scenarios (under deck, above deck, proximity to columns, etc.). This research will be carried out by the PI, Professor Anil K. Agrawal and his doctoral student, Mr. Zhihua, Yi. Dr. Mohammed Ettouney, Principal of Applied Research at Weidlinder Associates, New York, and Dr. Sreenivas Alampalli, Director of Bridge Program and Evaluation Services Bureau at the New York State Department of Transportation will be members of advisory committee to evaluate research work, progress and reports. The outcome of this project will be necessary tools on blast effects on highway bridges that engineers and DOT decision makers across the country can use.