February 27, 1997
DEVELOPMENT OF A DYNAMIC
LOAD FACTOR MODEL FOR THROUGH TRUSS TYPE BRIDGES
by:
Department of Civil & Environmental Engineering
The Pennsylvania State
University
The objective of this study is to develop a model for dynamic load factors (DLF) of steel through truss bridges as a function of bridge component location, truck locations, and truck type. Three steel through truss bridges with similar characteristics were investigated in this study. Each bridge was instrumented with six to eight linear voltage displacement transducers (LVDT) placed on different bridge components (truss members, stringers and floorbeams). The microstrain time history files recorded by these LVDTs were then processed to obtain the bridge component’s static and dynamic responses. Maximum static and dynamic microstrain values were selected from each processed file. These maximum values were then divided to give a dynamic load factor for each of the instrumented bridge components. These calculated DLFs were scatter plotted as a function of maximum static microstrain reading for each bridge. Each plot represented the DLF according to channel location, truck location, truck type (2, 3, 4 or five axle semi) and truck direction. These plots showed that the DLF is dependent upon truck location and GVW. A curve was then fitted to these plots to allow for the approximation of the DLF as a function of different stress levels in the stringer and floorbeam members.