Dynamic Test and Analysis of Curved Steel Box Girder Bridges

Abstract

This paper presents experimental and analytical impact factors for two existing curved steel box girder bridges. A Florida Department of Transportation test truck with a total weight of 468.8 kN applied the dynamic loading. The truck speed was incrementally increased from crawl to design speed. To evaluate the test results, the truck was simulated as a nonlinear vehicle model with 15 degrees of freedom. The bridge deck surface was assumed to be good and was simulated as a random process. Test and analytical results show that the impact factors of torsion are normally less than 30%, as are the impact factors of bending moment for bridges with span lengths less than 39 m. The impact factors of vertical shear are generally less than 15%, as are the impact factors of bending moment for bridges with span lengths greater than 50 m. The current AASHTO Guide Specifications for Horizontally Curved Highway Bridges appears to overestimate the dynamic loading of curved steel box girder bridges, especially for bridges with span lengths greater than 50 m. The research results are instructive and applicable to both bridge design and bridge load rating.

Impact Factors of Curved Steel Multibox Girder Bridges

“…The bridge consists of two sections: a straight continuous three-span section and a curved continuous span with an average radius of 187.15 m. The spacing of internal cross-frames is 3.09 m except that the end spacing of the cross-frame is 2.71 m. Both bridges have no external lateral bracing between box girders, except at sections over supports. The detailed test procedures and results were reported in Huang (5,8). A comparison between test and analytical impact factors is given in Table 1.…”

“…The main role of the imaginary girders is to distribute the wheel loads to the related joints. This model can provide good results for the internal force analysis of this type of bridge (5,8,9).…”

“…The curved multibox girder bridge is treated as a curved grillage system (see Figure 1) and is divided into two types of finite elements: plane grid elements and curved grillage elements (5,8). The transverse action of the bridge deck is simulated by plane grid elements, and the curved box girder is modeled with curved grillage beam elements.…”

“…The Newmark method ( 19) is used to solve the equations of motion of vehicles and bridges. It is also assumed that the bridge deck and approaches have a road surface class of good (3)(4)(5). The detailed solution procedure can be found in Huang (4).…”