Journal of Bridge Engineering

This paper reviews the derivation of the fundamental equations of suspension bridge analysis based on the deflection theory. A method is presented for the practical solution of these equations that can be implemented in commercially available mathematical analysis programs or for simpler cases in spreadsheet programs. The method takes advantage of the analogy between a suspended girder and a beam under tension. A table with analytical solutions to the beam-under-tension problem is presented for load cases applicable to suspension bridge analysis. Previous presentations of this method are expanded to address the effects of pylon stiffness and of continuity of the stiffening girder.

A stress ribbon bridge is a very slender structure in which the deck hangs in a suspended cablelike form. The structural response of this kind of structure is complex because of the combined effects of geometric nonlinearity, prestressing, and time-dependent materials behavior, and it has not been fully presented yet. However, since the introduction of this new structural type in the 1960s, a considerable number of stress ribbon bridges have been built. The structural behavior of prestressed concrete stress ribbon bridges is presented emphasizing the geometrical nonlinear character of the equations and the effects of creep and shrinkage of concrete. Analytical equations are integrated for the particular case of a built-in stress ribbon bridge, allowing for the determination of the effects of posttensioning, evenly distributed live load, and temperature variation. Expressions are given for the calculation of the vibration frequencies. A preliminary design of an 80-m built-in stress ribbon bridge is finally worked out based on the presented formulation.

A severe maintenance penalty exists for composite multibeam highway bridges in areas where the use of deicing chemicals is prevalent. This maintenance concern is largely due to the corrosion of embedded steel reinforcing bars and the attendant concrete degradation in the deck slab. Transverse steel straps, placed below the concrete slab, eliminate the deleterious effects of corrosion on the concrete. Further, the straps can be designed to provide the restraint necessary to promote the development of internal arching in the concrete slab in response to a concentrated load. A design procedure is presented for an externally restrained highway bridge deck. The method has been developed, based on the Canadian Limit States design philosophy, considering both the strength and serviceability requirements. It is demonstrated that the ultimate strength requirements dictate the external restraint requirements, and a numerical example of the design procedure is given.

The general advantages and disadvantages of steel single box-girder bridges, as well as their particular use in single-lane ramps, are discussed. Comparisons between steel single box girders and twin box girders are presented in regards to cost, adaptability to site restrictions, aesthetics, erection, and maintenance. It was concluded that for single-lane bridge ramps, if the economy (cost) is satisfied, a single box-girder bridge, produced by a competent steel workshop satisfying the requirements for fabrication of fracture critical members, is a viable, and often favorable, alternative.

Field testing is valuable for evaluating existing bridges. It allows the owner to reduce the conservatism of analytical rating methods and safely rate the bridge for higher loads. Many factors not considered in design contribute to the response of a tested bridge. Several of these, like actual load distribution and additional stiffness from curbs and railings, are welcome benefits that can be used to increase load ratings. However, there are also contributions from bearing restraint forces and unintended composite action that may not be reliable during the bridge's service life. These factors tending to increase the load capacity need to be separated and quantified so that the bridge owner can: (1) confirm the origin of the useable benefit; and (2) remove the unwanted contributions. Presented are procedures for load rating steel girder bridges through field testing. A systematic approach is presented to separate and quantify the contributions from various effects. Therefore, the responsible engineer can remove the unwanted contributions and justify an experimental load rating. The procedures are demonstrated for a three-span steel girder bridge.

As part of an ongoing program into the noninvasive geometrical characterization of masonry arch bridges, a laboratory study of radar propagation through masonry has been undertaken. A 2.4 m long × 1 m wide × 1.5 m high experimental test rig was built in the laboratory with brick walls on three sides and a wooden gate on the fourth narrow side. The objective was to construct a composite test rig that would replicate certain of the environments that ground-penetrating radar might encounter when being used to test a masonry arch bridge. Tests were undertaken using 500, 900, and 1,000 MHz bow-tie antennas with the masonry box filled with fresh water and then saline water with different concentrations of sodium chloride. Further tests were undertaken with the masonry box filled with dry sand and wet sand. Finally the test rig was modified to simulate a composite masonry structure and tests were performed both on the hollow- and sand-filled models. The results from this work are reported herein indicating the reliability and ease of identifying various targets. It was found that radar signals were severely attenuated when the saline concentration exceeded 0.05% by mass. Better penetration of the radar signals was obtained when the masonry box was filled with dry sand rather than wet sand. In the case of the hollow cellular masonry structure, refraction effects were more evident.

This paper deals with the jacking procedure for the replacement of prestressed concrete I-girder bearings, without damaging the superstructure. The finite-element method-based analysis procedure to compute the jacking force and overall jacking sequence for the girders is proposed. The proposed method takes into account the stress concentration at the loaded area on the girder and the behavior of superstructure due to the jacking force. An analytical equation is proposed to compute the allowable jacking force considering the bursting stress induced at the loaded area on the girder. On the other hand, the overall jacking sequence to lift the superstructure for the bearing replacement is determined by considering the response of the superstructure being jacked. This paper also includes an illustrative example of a jacking procedure for a prototype prestressed concrete I-girder bridge.

This paper presents a procedure to improve the accuracy of the classical grillage method for the nonlinear analysis of concrete girder bridges. The procedure uses equivalent element plastic hinge lengths that account for the actual mesh size instead of using a mesh-independent global plastic hinge length. A thorough review of the results of tests conducted on two 1/3-model prestressed concrete girders and a 1/3-model prestressed concrete girder bridge is undertaken in order to model the nonlinear properties of prestressed concrete girder bridges. The purpose of this review is to study the extent of plastification and plastic hinge length development as well as the evaluation of the validity of the grillage method for the nonlinear analysis of girder bridges. An L_p transfer model is used to calculate the plastic hinge length for every beam element of the grillage based on the results from the experiments and other empirical models. The L_p transfer model allows the use of empirical data obtained from tests on individual girders to model the response of a variety of bridge configurations subjected to different loading conditions. The equivalent grillage element plastic hinge length L_gp is calculated as a function of the grillage mesh size. A number of examples are presented to demonstrate the validity of the proposed method by comparing the analytical results of grillage analysis using the L_p transfer model with those of laboratory and in situ tests on full-scale and model-scale prestressed concrete bridges. The proposed approach has a high potential for use in engineering practice because of the simple input requirement and improved accuracy.

This paper presents the implementation of the finite-element model updating for the Kap Shui Mun Bridge, a 430 m main span double-deck cable-stayed bridge in Hong Kong. The dynamic characteristics of the bridge have been studied through both three-dimensional finite-element prediction and field vibration measurement previously. In this paper, the developed finite-element model is updated based on the field measured dynamic properties. A comprehensive sensitivity study to demonstrate the effects of various structural parameters (including the connections and boundary conditions) on the modes of concern is first performed, according to which a set of structural parameters are then selected for adjustment. The finite-element model is updated in an iterative fashion so as to minimize the differences between the predicted and the measured natural frequencies. The final updated finite-element model for the Kap Shui Mun Bridge is able to produce natural frequencies in good agreement with the measured ones, and can be helpful for a more precise dynamic response prediction.