Journal of Bridge Engineering

Composite steel-concrete multicell box girder bridges are quite often used in modern bridge superstructures with curved alignments. They provide excellent torsional resistance as well as elegant appearance. While current design practices in North America recommend few analytical methods for the design of curved multicell box bridges, practical requirements in the design process require a need for a simplified design method. This paper summarizes the results from an extensive parametric study, using a finite-element model, in which 120 simply-supported curved bridge prototypes are analyzed to evaluate the shear distribution in the webs due to truck loading as well as dead load. Results from tests on four 1/12 linear-scale simply-supported curved composite concrete deck-steel three-cell bridge models are used to substantiate the analytical modeling. The parameters considered in the study are: cross-bracing system, aspect ratio, number of lanes, number of cells, and degree of curvature. Based on the data generated from the parametric study, expressions for the shear distribution factors for truck loadings as well as dead load are deduced. An illustrative design example is presented.

Many multigirder steel bridges built before 1985 are experiencing distortion-induced fatigue cracking at diaphragm-girder connections. Fatigue cracks in the welds and base metal in hundreds of diaphragm-girder connections in bridges in the Birmingham, Ala. area have been discovered. Many of the welded connections have been replaced with angles bolted to the diaphragm and girder web. The replacement angles have not performed satisfactorily due to fatigue cracking in the connection angle. Laboratory tests of three existing and one proposed replacement angle were conducted to determine the fatigue limit for the replacement angles and the most appropriate replacement angle to use on future repairs. Primarily, surface strain measurements and vertical girder deflections due to fatigue loading were recorded during fatigue tests of the laboratory model to evaluate the performance of the connections. Results indicate that the appropriate bending stress fatigue limit is 165 MPa and the proposed new replacement angle should be used for future repairs.

This paper is the first of two companion papers that cover the results of corrosion and structural testing of eight large-scale stay cable specimens. Four of the specimens had the traditional stay-cable corrosion protection system of portland cement (PC) grout and high-density polyethylene (HDPE) sheathing, whereas the second four specimens used improved protection systems such as epoxy-coated, galvanized, greased, and sheathed strand or an improved grout with silica fume in the grout. A unique accelerated corrosion testing technique developed for bridge stay cables is also described. Among other critical findings, it was found that the PC grout would crack within 2–3 days after the exterior sheathing was cut to simulate accidental breaks in the field. It was also found that precompressing the grout was not effective in reducing the amount and size of cracks in grout. In addition, it was found that the presence of grout did not significantly increase the axial or flexural stiffness of the test specimens.

This paper is the second of two companion papers that cover the results of corrosion and structural testing of eight large-scale stay cable specimens. Four of the specimens had the traditional system of portland cement (PC) grout and high-density polyethylene (HDPE) sheathing, while the other four specimens used improved protection systems such as epoxy-coated, galvanized, greased, and sheathed strands, or a grout improved with silica fume. A unique accelerated corrosion testing technique developed for bridge stay cables is also described. The traditional system of corrosion protection broke down almost immediately after the initiation of the accelerated corrosion test, while the improved corrosion protection systems provided far better corrosion protection than the traditional system. However, some problems were encountered with the improved corrosion protection systems that are of interest.

Proof load tests were carried out on three deteriorated steel girder bridges with simple supports. Selected bridges are more than 60 years old, and their span lengths range from 11.0 to 15.5 m. Two military tanks were used to load the bridges up to a predetermined proof load level, which depended on the maximum allowable legal load. The midspan moment was increased in several steps by gradually moving the tanks closer to the midspan. Each tank weighed over 530 kN. Stresses and deflections in steel girders were measured at selected locations. Small stresses and a linear response were considered as the indication of a safety reserve. All bridges were able to sustain the applied proof load. Observed stresses and displacements were considerably smaller compared with those from analytical models. The composite action between concrete slab and steel girders was observed even at the maximum load level, although no shear connectors were provided. Nonstructural members such as parapets, railings, and concrete facade were also contributing to the flexural stiffness. For all bridges, the bearings provided partial restraint to the rotation at supports.