Journal of Bridge Engineering

In the design of new composite steel and concrete bridge beams, the shear connectors are assumed to transmit all of the longitudinal shear forces at the interface between the concrete slab and the steel beam. However, in practice, the forces on the shear connectors are modified by friction resistances at the interface. The effect of friction on the fatigue endurance of shear connectors is first illustrated through a specially developed finite-element analysis procedure. Then a simple mathematical assessment model is proposed that allows for the beneficial effect of friction on the fatigue endurance of shear connectors in composite steel and concrete bridge beams. This procedure can extend the design life of the shear connectors in existing composite bridge beams, as it can be used to estimate their remaining endurance and their remaining strength and, if necessary, to determine the effect of remedial work on increasing the endurance of the shear connectors.

In recent bridge construction in Connecticut involving heavy sections, galvanized coating thicknesses were in excess of 12 mils. The current American Association of State Highway and Transportation Officials specification is based on research conducted with coating thicknesses not greater than 6 mils. Since thicker coatings on steel can reduce shear capacity in high-strength bolted connections, there was concern that the thick galvanized coating could compromise the performance. In this research, tests were conducted to study the relaxation and the shear capacity of high-strength bolted connections with galvanized coating thicknesses up to 20 mils. Both normal and oversize holes were studied. The research shows that the shear capacity of connections with thick galvanized coatings is reduced due to the loss in the clamping force. The test results have been used to develop design guidelines.

Many reinforced concrete bridges throughout the United States on county and state highway systems are deteriorated and/or distressed to such a degree that structural strengthening of the bridge or reducing the allowable truck loading on the bridge by load posting is necessary to extend the service life of the bridge. The structural performance of many of these bridges can be improved through external bonding of fiber-reinforced plastic (FRP) laminates or plates. This paper describes the rehabilitation of an existing concrete bridge in Alabama through external bonding of FRP plates to the bridge girders. Field load tests were conducted before and after application of the FRP plates, and the response of the bridge to test vehicle loadings was recorded. Results of the field tests are reported, and the effects of the FRP plates on the bridge response are identified. The repaired bridge structure exhibited a decrease in steel reinforcing bar stresses and vertical midspan deflections. These decreases ranged from 4 to 12% for various static and dynamic loading cases.

External dampers have been utilized in a number of cable-stayed bridges to suppress transverse cable vibrations. However, simple and accurate damper design recommendations that concurrently consider all important cable parameters are lacking. Previous efforts have been based on the idealization of cables as taut strings. In this paper, the governing differential equation for vibration of cables containing a viscous damper was first converted to a complex eigenvalue problem containing nondimensional cable parameters. Then, a parametric study was conducted involving repeated solutions of the eigenvalue problem for a wide range of nondimensional parameters. Based on the results of the parametric study, the effects of dampers on first mode vibration frequencies and first mode cable damping ratios were presented in nondimensional format. It is shown that for the range of parameters involved in most stay cables, the influence of cable sag is insignificant, whereas the cable bending stiffness can have a significant influence on the resulting cable damping ratios. Simplified nondimensional relationships are proposed for calculating damper-induced changes in the first mode cable damping ratios. Results of laboratory tests on a scaled model cable are compared with the estimated values using the formulation presented. Finally, example problems are presented for comparison with other relationships, and for the design of mechanical viscous dampers for suppression of cable vibrations including rain-wind induced vibrations.

The study of the dynamic response of the elevated railway for the high-speed train in the Taiwan area at the preliminary design stage is presented. Two types of the elevated reinforced concrete railway, they being the simple-span and the three-equal-span box girders supported on piers; three types of the high-speed train, namely, the French T.G.V., the German I.C.E., and the Japanese S.K.S.; and the maximum operation speed 350 km/h are under investigation. The general dynamic stiffness matrix of a damped Timoshenko beam is employed for the structural analysis. The influence line of any dynamic response (also called the dynamic influence line) of the elevated railway subjected to the high-speed train, considered as a series of the moving loads, is calculated by the mode-superposition method. A preliminary design of the section of the railway is proposed for this study.

The live load distribution factors contained in the AASHTO-LRFD Bridge Design Specification present a major change to the AASHTO-LFD specifications that have been in effect for more than 50 years. This change has generated some interest in the bridge engineering community and has raised some questions. The AASHTO-LFD formulas are based on the girder spacing only and are usually presented as S/D, where S is the spacing and D is a constant based on the bridge type. This method is applicable to straight and right (i.e., nonskewed) bridges only. The new formulas are more complex and consider more parameters, such as bridge length and slab thickness. It may not be obvious to the engineers what added accuracy and flexibility (e.g., skewed bridges) is gained by the increased complexity. This paper will present the background on the development of the formulas and compare their accuracy with the S/D method. A discussion on the extension of the single girder design (using formulas) to the skewed bridges is also presented.

Extensive research conducted over the past eight years in Canada has led to a concrete deck slab of girder bridges that can be entirely free of any tensile reinforcement. This slab, known as the steel-free deck slab, derives its strength from its internal arching action, which is harnessed longitudinally by making the slab composite with the girders, and transversely by restraining the relative transverse movement of the top flanges of adjacent girders. Two steel-free deck slabs have already been built, in which the transverse confinement is provided by welding steel straps to the girders. This paper presents test results on two other kinds of transverse confining systems, which are applicable to both steel and concrete girders. It is shown that the steel-free deck slab, in addition to being more durable than slabs with steel reinforcement, can also prove to be more economical.

A three-tenths-scale model of a posttensioned slab bridge is constructed in a laboratory and tested in the overload and ultimate load ranges. Dimensions of the slab are 16.9 × 5.33 × 0.23 m. In addition to uniformly distributed longitudinal posttensioning, a band of tendons is located in a narrow region directly above the supporting columns. A large array of strain gauges, linear variable differential transformers, and load cells serve to gather data for each loading configuration. Results are presented for a series of overloads that are placed on the slab in a variety of critical locations. Ultimate positive bending moment is imposed on one span and an ultimate negative moment is applied to the slab in the region of the supporting columns. Complementary nonlinear finite-element analyses of the overload and ultimate loadings are also presented. Results show that the posttensioned slab bridge supported a load-causing moment equivalent to 4.8 times the factored moment of an AASHTO MS 18 loading.

This paper focuses on the determination of section properties of latticed members for seismic retrofit of the San Francisco–Oakland Bay Bridge. To consider actual section integrity for a latticed member, the concept of reduction factors β_m for moment of inertia and β_t for torsional constant is introduced to account for the shear flow transferring capacity of lacing bars or battens and their connections. A set of formulas is proposed for calculating section properties required for seismic analysis and capacity determination. The validity of the proposed section properties is confirmed by a finite-element analysis of a latticed member. It is found that the proposed simple procedure closely resembles the finite-element analysis results. The proposed method is also supported by the recent 1/2 scale model test of the SFOBB laced member at UNR.

Two previous papers by the writers described the buckling and finite-displacement behavior of curved I-girder web panels subjected to pure bending, presented a theoretically pure analytical model, and presented equations that describe the reduction in strength due to curvature. This paper describes the buckling and finite-displacement behavior of curved web panels under combined bending and shear. Unlike straight girder web panels, the addition of shear in curved panels is shown to increase the transverse “bulging” displacement of the web prior to buckling. The accompanying decrease in moment carrying capacity is analyzed in a manner similar to that used for the combined bending and shear nominal strength interaction for straight girder design. Preliminary recommendations are made toward forming design criteria for curved webs.

Two previous papers by the writers described the buckling and finite-displacement behavior of curved I-girder web panels without longitudinal stiffeners subjected to pure bending, presented a theoretically pure analytical model, and presented equations that describe the reduction in strength due to curvature. This paper describes the optimum location and strength effects of one and two longitudinal stiffeners attached to curved I-shaped plate girders. Using lateral load and lateral pressure analogies similar to that described in the earlier papers, strength reduction equations are formulated for curved plate girders with longitudinal stiffeners. A comprehensive comparison is made between the equations developed in this investigation and design equations used in Japanese and American design guides, and the applicability and superiority of the method is demonstrated.