Effect of Dead, Live and Blast Loads on a Suspension Bridge

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Kunal N. Suthar, Master of Science, 2007

Thesis directed by : Dr. Chung C. Fu

Department of Civil and Environmental Engineering

Bridges in America are of special importance. The analysis of these bridges should be carried out for different loading conditions. Bridges are normally designed for dead load, live load and other occasional loads. American Association of State Highways and Transportation Officials (AASHTO) have specified for the ship impact, seismic vulnerability and also against vehicular collisions. But there are no definite structural design criteria for the bridges under typical blast loadings.

This thesis is intended to provide a basic guideline for using the blast load analysis on the suspension bridge. Further research may be carried out in this field to develop some standards for the bridge resistance against explosions. Also, the AASHTO loading was applied to study the effect of live load on the bridge. The results obtained from live loading on the same suspension bridge were implemented to allocate costs depending upon the effect of particular vehicle on the bridge deck.

To study the non-linear analysis, a three-dimensional finite analysis model under dynamic load has been established for the Suspension bridge part (West-bound side) of the Chesapeake Bay Bridge for determining the effect of live load, which was used for cost allocation studies. This vehicle-bridge interaction modeling was done using a Finite Element Software known as "Visual Bridge Design System" (VBDS). Development and interaction of a detailed truck using proper design standards were applied to realistically represent the actual loading conditions. The results obtained were in close proximity when compared with the data available through the State Road Commission, State of Maryland. Results presented in this thesis hence demonstrate a significant potential for using the VBDS and for thorough investigation of the vehicle-bridge interaction and dynamic loading on bridges.

For carrying out the impact of blast loading, the bridge was modeled in parallel using the SAP2000 system. The whole modeling of the suspension part of the bay bridge was done on the SAP2000 for carrying out the non-linear analysis of the blast loads. The behaviors of each element under the effect of the blasts were studied from the output generated by the SAP2000. The output of the software presents results including moments, axial loads and displacements Moreover, moments and axial load at each node and at any point within the element, can be easily obtained from the software output. The "progressive collapse" approach of the bridge was also carried out to know the exact behavior with the formation of the plastic hinges under the impact of blast loadings. Also the comparisons of the blast loads with and without the application of initial stress were carried out. This shows the importance of using initial stress in the analysis of a suspension bridge.