Journal of Bridge Engineering

The first modern metal cantilever bridge in the United States, using erection methods that were to be utilized in most future cantilever bridges, was by C. C. Schneider across the Niagara Gorge in 1883. The Niagara, saw in order, John Roebling’s Railroad Suspension Bridge, Samuel Keefer’s Honeymoon Suspension Bridge, Edward Serrell’s Lewiston-Queenston Suspension Bridge, Schneider’s cantilever, Leffert Buck’s arch bridge at the falls as well as Buck’s arch built under Roebling’s suspension bridge. Schneider’s bridge had a useful life of over 40 years during a period when rolling stock on the railroads was increasing rapidly. The speed of erection of a new style bridge coupled with its performance makes it one of the most innovative and significant bridges built in the world at the time.

Bridges expand and contract due to temperature changes. These movements are estimated in design, and expansion joints and bridge bearings are designed to accommodate the movements. Integral construction is another means of adapting to thermal movements. If the design movements are too small, the bridge may be damaged during extreme conditions. If the movements are too large, less economical joint and bearing systems may be selected, and higher long-term maintenance costs will be incurred. An improved thermal movement design procedure is developed and compared to existing AASHTO Specifications and field observations. The recommended design temperatures are developed from more than 60 continuous years of weather data after considering the relationship between bridge temperature and climatic conditions for different bridge types. The recommended temperatures provide a realistic indication of actual bridge performance and eliminate the ambiguity of present design methods. Strategies for defining design movements and design installation temperatures for different joint and bearing systems are also developed. The design recommendations result in significant changes in predicted movement for some bridges, and the recommendations are compared with field measurements of bridge temperatures and movements to verify the proposed limits. The proposed design provisions are presently under consideration by AASHTO Committees for adoption into the AASHTO Specifications.

Due to the orthogonal elastic properties and significant two-way bending action, orthotropic plate theory may best be used to describe the behavior of concrete filled grid bridge decks. The current AASHTO LRFD specification employs an orthotropic plate model with a single patch load to predict live load moment in concrete filled grid bridge decks, which may not be conservative. This paper presents alternative equations to predict maximum moments, based on classical orthotropic plate theory, which include multiple patch loads, both the LRFD design truck and tandem load cases, and the two most common deck orientations. The predicted moments are verified through finite-element analyses.

The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum.

Reinforced concrete arch bridges are ideal to span over river valleys or deep ravines. However, the construction of the arch rib is very often the most crucial aspect that may influence the feasibility of the bridge. Casting concrete in situ on formwork and falsework supported directly on the valley is often out of the question. One method that is gaining popularity in recent years is to use precast concrete segments erected by the cantilever construction method with tiebacks. As the tiebacks are temporary and therefore recoverable, the method is considered to be very economical. This paper describes a method for construction control. It uses the concept of influence matrix in the adjustment of cable forces to keep the stresses in the arch rib within acceptable limits as well as to ensure that the arch rib is constructed to line and level. It is observed that the required minimum tieback forces vary during the progress of cantilever erection. Various strategies of tensioning the tiebacks have been studied, and it is found that a two-stage tensioning method gives acceptable results. The recent application of the proposed method and the results are also described.

A framework is presented for predicting the dynamic response of long suspension bridges to high winds and running trains. A three-dimensional finite-element model is used to represent a suspension bridge. Wind forces acting on the bridge, including both buffeting and self-excited forces, are generated in the time domain using a fast spectral representation method and measured aerodynamic coefficients and flutter derivatives. Each 4-axle vehicle in a train is modeled by a 27-degrees-of-freedom dynamic system. The dynamic interaction between the bridge and train is realized through the contact forces between the wheels and track. By applying a mode superposition technique to the bridge only and taking the measured track irregularities as known quantities, the number of degrees of freedom of the bridge-train system is significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation is then applied to a real wind-excited long suspension bridge carrying a railway inside the bridge deck of a closed cross section. The results show that the formulation presented in this paper can predict the dynamic response of the coupled bridge-train systems under fluctuating winds. The extent of interaction between the bridge and train depends on wind speed and train speed.