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Project Title: Dynamic Load Allowance For Truss Bridges
Investigators: Dr. Jeffrey Laman, Dr. Thomas Boothby
Research Assistants: Timothy Schank, James Bintrim
Project Duration: May 1996 to December 1998
   
References: Schenck*, T.S., J.A. Laman, and T.E. Boothby. "Comparison of Experimental and Analytical Load Rating Methodologies for a Pony-Truss Bridge," Journal of the Transportation Research Board No. 1688, TRB, National Research Council, Washington, D.C., December 1999, pp. 68-75.
  Laman, J.A. and T.E. Boothby. "Truss Bridge Dynamic Load Allowance and Distribution Factors," Proceedings of the 7th International Conference on Structural Faults and Repair - 1997, Vol. 1, Edinburgh, Scotland, July 1997, pp. 487-493.
  Laman, J.A., J.S. Pechar, and T.E. Boothby. "Dynamic Impact Factors for Through-Truss Bridges," Journal of Bridge Engineering, American Society of Civil Engineers, Vol. 4, No. 4, November 1999, pp. 231-241.
   
   

The objective of the present study was to experimentally evaluate the statistics of dynamically induced stress levels in steel through-truss bridges as a function of bridge component type, component peak static stress, vehicle type, and vehicle speed. Better understanding of critical bridge rating parameters will enable more accurate bridge evaluations of this type of structure. Three 60-year old steel through-truss bridges with similar characteristics were investigated in the present study. Several bridge components on each of the 3 bridges were instrumented (truss members, stringers, and floor beams) and dynamic strain data collected under controlled and normal traffic conditions. The dynamic strain histories were processed to obtain bridge component peak static response and peak dynamic response, resulting in the determination of the dynamic load allowance (DLA) for each of the instrumented bridge components for each of several truck crossings. The calculated DLA values are plotted as a function of member peak static stress for each bridge member instrumented. The DLA data is examined as a function of component type, component location, truck type, number of axles, truck speed, and truck direction. This study has demonstrated that the DLA is dependent on truck location, component location, component type, and component peak static stress, but appears to be nearly independent of vehicle speed.

 
     




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