Journal of Bridge Engineering

A masonry arch bridge can be analyzed by frame analysis methods by considering a unit width of the arch ring and the overlying fill. The arch ring is divided into at least 10 segments, each of which is given cross-sectional properties corresponding to the properties of the material in the arch ring. The dead load of the arch ring and the overlying fill are considered as nodal loads, and the axle loads are applied to the frame as linearly varying pressures, based on a simplified distribution of pressures through the fill. The supports are considered to be rigid in the vertical direction and elastic springs in the horizontal direction. The elastic spring constant varies depending on the type of foundation and the condition of the springings. Based on this application of dead and live loads to the structure, the axial thrust and moment can be found throughout the arch ring, and compared to an estimate of the capacity of the arch ring. This procedure can be used to find an appropriate load rating for the structure service level. An example rating of a bridge in Adams County, Pa., is provided, along with the results of a validation field test of the structure.

This paper focuses on improving bridge substructures by developing attractive and rapidly constructed substructure systems for short- and moderate-span bridges. The importance of improved substructure design is discussed. A review of current cast-in-place and precast concrete substructure systems is presented. A specific proposal for a precast segmental substructure system is described including methods of fabrication and erection. The goal of this system is to improve aesthetics and reduce construction time for standard bridges. Reduced construction time leads to important safety and economic advantages when traffic disruption or rerouting is necessary. Precasting would result in an increased use of high performance concrete and will bring improved substructure durability. Recommendations are made for standardization of precast substructure systems.

The goal of this study was twofold: (1) To demonstrate that engineered heat straightening is a viable alternative for the repair of damaged steel bridge girders; and (2) to illustrate how the latest results of research and development can be implemented for heat-straightening repairs. The bridge chosen for repair crosses over I-10 in Louisiana, just east of Lake Charles. Working with personnel from the Louisiana Department of Transportation and Development, the bridge was repaired during August 1998. A fascia noncomposite beam had been impacted, and the bottom flange was displaced 0.43 m (17 in.). The repair was designed by the writers and implemented in conjunction with Louisiana Department of Transportation and Development personnel. Described in this paper are the design of the repair, including assessment of damage, selection of heating patterns, development of jacking restraint locations and magnitudes, and heating sequences; the step-by-step implementation; a cost comparison; and a discussion of lessons learned. It is concluded that heat straightening is an effective alternative for repairing damaged steel bridges, when implemented with proper engineering design.

Several functional problems have been reported on pin and hanger system truss bridges, such as frozen pins, stress spikes in hangers, lack of expansion joint movements, etc. It has been difficult to develop a pin and hanger retrofit strategy because the cause for the observed problems is usually unknown. This paper presents a study performed on the pin and hanger system of one such bridge—the Newburgh Beacon bridge. Extensive field testing performed so far has failed to identify the cause for the observed stress spikes. The concept of misalignment loading is developed in this article to explain the observed behavior. Stress spikes predicted using this concept matched very well with the observed stress spikes. Finally, the use of misalignment loading to evaluate other truss members is also discussed.

Rectangular columns constructed from steel plates are widely used to support highway bridges in Japan. Columns of this type, designed without special consideration for ductility, sustained damage during the 1995 Hyogo-ken Nanbu earthquake. This paper describes tests of 24 large-scale models of hollow and concrete-filled stiffened rectangular columns in order to investigate their seismic performance. Testing under constant axial loading and cyclic bending as well as on the shaking table was carried out. It was found that columns partially filled with concrete had a larger strength than did hollow columns, but their displacement capacity was sometimes smaller. Bridge column models tested on the shaking table tended to sustain increasing displacements in only one direction, and columns tested by reverse cyclic loading possessed member displacement ductility capacities between 2.6 and 6.1, even though the columns had not been designed specifically for ductility. A rational and simple empirical method for estimating the deformation capacity of hollow columns subjected to reverse cyclic loading that considers the different modes of buckling is proposed and a design example is provided.

Foundation compliance appears to be one of the key features of the lateral load response of bridges, but it has not been seen so far as a possible solution to the problem of regularizing the response of bridges with piers of unequal height in such a way that a reasonably uniform ductility demand is achieved. The present study focuses on the effect of pile foundation stiffness on the lateral displacements and flexibility of the bridge as a whole as well as on the ductility demand of the pier itself. Conventional lumped plasticity beam models and 2D finite-element models are used for carrying out nonlinear static (pushover) analyses of alternative bridge superstructure systems. The results clearly indicate that the foundation type, the number of piles and their arrangement, and the adopted design approach affect the distribution of ductility demand. It is confirmed that control of the foundation stiffness may be a useful tool for improving the distribution of ductility demand and hence the overall performance of a bridge during strong ground motions.

Accurate modeling of support conditions is important in the analysis of bridges for seismic loading. To address the problem of modeling the soil-structure interface of bridges supported by piles driven in loess in West Tennessee, a series of quick-release (“pluck”) tests were performed. In the process of performing the pluck tests, sufficient static lateral load was applied to a large mass supported by a single pile to achieve a prechosen lateral displacement. This load was released; dynamic response was monitored; dynamic stiffness coefficients were calculated. A static stiffness was also calculated as simply the applied load divided by the prechosen deflection. The “secant” stiffness values thus obtained were compared to the dynamic stiffness values, and the two stiffness values were found in all cases to be essentially equal. This fact suggests the use of static lateral load tests to determine appropriate values of stiffness to use in modeling the pier-pile interface for purposes of dynamic analysis of a bridge.

In modern approaches, the target and design values for traffic effects on bridges are obtained through suitable stochastic traffic models processing recorded traffic data. To this aim, several theoretical and numerical stochastic models have recently been proposed. Despite their elegance, theoretical models often have limited fields of application, while numerical models, particularly efficient when single-lane traffic flow is considered, turn out to be unsatisfactory when traffic in several lanes, or a combination of traffic actions with those from other sources must be dealt with. This paper presents a more general theoretical stochastic traffic model, which is able, not only to reproduce actual traffic, but to account for such traffic interactions as well. The model, based on an equilibrium renewal process of vehicle arrivals, can be used in all cases where sophisticated evaluation of real traffic effects is required, such as calibration of conventional load models in bridge codes, assessment of existing bridges, as well as the design and analysis of bridges with less traditional schemes or subjected to particular traffic conditions. The efficiency of the model is illustrated through meaningful applications.

Stress-laminated timber bridge decks have gained increasing popularity in the United States in recent years. As with all wood exposed to the environment, wood for these decks must be treated with preservatives. There has been reluctance to build chromated-copper-arsenate (CCA) –treated wood bridges due to concerns about dimensional stability. Because no research has been undertaken to investigate the use of CCA-treated southern pine in stress-laminated bridge decks, a good resource for economic rural bridges has remained untapped. The objective of this study was to evaluate the performance of various wood preservatives on stress-laminated southern pine bridge decks. A total of nine decks with seven different preservatives were built and exposed to the environment for more than 2 years. Force levels in prestressing bars and wood moisture contents from each deck were continuously monitored. It was found that the short-term variations in the bar stress levels are less for decks with oil-type preservatives, as compared to CCA preservatives. The long-term performance for decks with both preservative types was found to be similar. The anchorage effect on the deck performance was found to be negligible.