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THE SECOND KOREA - JAPAN JOINT SEMINAR ON STEEL BRIDGES / DYNAMIC BEHAVIOR OF BRIDGES DUE TO MOVING TRUCK
Eui Seung Hwang, Sung Pil Chang, Jeong In Suh, Young Hwan Park
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Abstract
Dynamic behavior of the bridge is one of the most important aspects in bridge analysis and design. Bridges vibrate mainly due to moving vehicle, wind or earthquake. This study deals with the dynamic behavior of bridges due to moving vehicle. Of the several types of vehicles running on the bridge, trucks are considered in this study. In the design, the effect of moving truck is included as the dynamic or impact load. From many analytical studies and actual measurements, it has been recognized that the dynamic behavior of bridges due to moving truck is affected by dynamic characteristics of the bridge and truck and surface roughness. The purpose of this study is to analyze the dynamic behavior of bridge due to moving truck using the actual model of trucks, bridges and surface roughness. Truck model representing 5 axle semi tractor-trailer, is composed of masses and springs. A multi-leaf type springs which show nonlinear hysteretic behavior are used for truck suspension systems. Vertical displacements and pitching rotations are considered for truck body masses. Bridges are modeled by the finite element method using three-dimensional frame elements. Surface roughness is considered as a vertical deviation from the reference line connecting the bridge entrance and exit. Road profiles representing vertical deviation are generated using inverse Fourier transform of measured power spectral density function. A computer program is developed to analyze the dynamic interaction between the bridge and the truck. It solves the equations of motion from truck and bridge models. To find the maximum dynamic response, direct integration scheme is used. Three bridges are selected in the analysis : one-dimensional simple span bridge, two-dimensional (grid) simple span bridge and one-dimensional two span continuous bridge. From the analysis, the dynamic load factors are calculated from maximum static and dynamic response. The dynamic load factors of each girder are compared for various transverse truck positions. Effects of truck weight and speed are examined. Results also are compared with the case when the truck is assumed as constant forces.