Curved Steel Box Girder Bridges Research Articles

Effects of external bracing on horizontally curved box girder bridges during construction

In horizontally curved steel box girder bridges, large relative displacements between box girders and individual girder rotations may occur during the deck pouring operation. Installing intermediate external cross-frames between box girders is perceived to be an effective means to control these displacements. However, it is imperative to minimize the number of such cross-frames, as these external cross-frames are not only expensive but also have adverse consequences for the fatigue characteristics of the steel box girders. A new parameter, deck unevenness ratio, was defined in this study to quantify the degree of uneven deck caused by relative deflections and rotations. In order to assess the effects of external cross-frames on the deck unevenness ratio that affect deck slab construction, a number of hypothetical twin-box girder bridges were analyzed for this study using a commercial finite element program, ABAQUS. The conventional method and Wisconsin DOT deck pouring sequences were compared for three-span continuous curved bridges.

Spacing of intermediate diaphragms in horizontally curved steel box girder bridges

Horizontally curved box girder bridges inherently exhibit complex torsional and distortional behavior as well as bending due to the initial curvature. Distortional warping and transverse bending normal stresses, two major stress components resulting from distortion, are generally limited to a specific level for efficient use of the cross section by installing adequate intermediate diaphragms. The objectives of the present study are to develop a curved box beam finite element and to propose tentative design charts for adequate maximum spacing of intermediate diaphragms. The validity of the developed box beam element having nine degrees of freedom per node including two distortional degrees of freedom is verified from a series of thorough comparative studies using conventional shell element models. Extensive parametric studies using the box beam elements are performed and the design charts for the maximum spacing of the intermediate diaphragms are presented. Bridges taken into account are single-span, two-span, and three-span continuous horizontally curved box girder bridges. The design parameters considered are the central angle, the number of spans, the span length, the aspect ratio of the box section, the spacing of the intermediate diaphragms, and the desired ratio of the distortional warping normal stress to the bending normal stress. Unlike the current practice where the ratio of the distortional warping normal stress to the bending stress is fixed to a specific value, the proposed design charts facilitate the determination of the maximum spacing of intermediate diaphragm for various desired stress ratios.

Dynamic Test and Analysis of Curved Steel Box Girder Bridges

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...

Dynamic Test and Analysis of Curved Steel Box Girder Bridges

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.

Field Test and Rating of Arlington Curved-Steel Box-Girder Bridge: Jacksonville, Florida

A load capacity rating procedure and the results of field tests conducted on the Arlington curved-steel box-girder bridge are presented. Two Florida Department of Transportation (FDOT) test trucks with a total weight of up to 117 tons provided the static loading. One FDOT test truck with a total weight of 52.7 tons applied the dynamic loading. The actual behavior of the bridge was ascertained by comparing the field test results with those obtained from three different theoretical mechanical models. Analysis demonstrates how the actual mechanical behavior and load capacity of a curved-steel box-girder bridge can be well predicted by a proper finite element method based on as-built bridge plans. Some important parameters, such as impact factors, the effective width of the concrete slab, and the structural effect of barriers, are discussed. Finally, the load rating factors for a variety of Florida's rating vehicles were determined on the basis of a finite element model generated from field test results and analytical modeling of the bridge. The current capacity ratings are approximately 17% to 27% higher than those determined in 1988 using a conventional analytical method. The capacity increase is due mostly to the conservativeness of traditional methods and codes. The research results are instructive and applicable to bridge design and bridge load rating.

Application of EBEF Method for the Distortional Analysis of Steel Box Girder Bridge Superstructures during Construction

For curved steel box girder bridges, loads applied away from the shear center of the box can be separated into bending and torsional components. Associated with these flexural and torsional loads are three normal stresses, four shear stresses, and one bending stress. The least understood stresses are stresses (normal distortional warping stress, distortional warping shear stress and distortional transverse bending stress) associated with distorsion of the box cross section. By the addition of steel diaphragms, distortional stresses can be decreased. A practical approach to the distortional analysis of steel box girder bridge superstructures during construction is presented in this paper. The EBEF (equivalent beam on elastic foundation) method is an enhancement of the BEF (beam on elastic foundation) method, which has been widely used in design practice. Also presented herein are methodologies and results of numerical examples in comparison with the finite strip method.

Seismic Response of Curved Steel Box Girder Bridges

The results of a comprehensive study of the seismic response of curved steel box girder bridges are presented. Multiple‐span bridges with up to five spans are analyzed. The bridge is modeled using 3‐D space frame elements and El Centro earthquake accelerogram is used as a dynamic input to calculate the maximum responses at the bridge deck and columns. Different elements of the bridge model and the seismic loading are examined, and a comparison between the response history and the response spectrum methods for analyzing curved bridges, using El Centro earthquake accelerogram, shows that the latter technique fails when vibration modes with relatively high frequencies are considered. The simultaneous application of the earthquake loadings in the three global directions is also discussed. Parametric studies are performed and the effect of the span length, radius of curvature, bridge weight, and column geometry are presented.