Journal of Bridge Engineering

This paper describes different dynamic tests carried out on three bridges, B14, B15, and B13, over highway E19, which connects Brussels and Antwerpen in Belgium. Different excitation types are considered: a drop weight, a heavy truck on the bridge, and ambient vibrations mainly due to the traffic under the bridge. Finite-element models are constructed to support and verify the dynamic measurements. The modal parameters are extracted from the response time series using the data dependent system approach. A vector autoregressive model is developed and successfully applied to the measured responses in time domain. Good correlation between the finite-element simulations and the experiments is obtained.

In the incremental launch of a prestressed concrete (PC) bridge, the deck is a continuous beam that moves over fixed bearings. Their vertical misplacement causes secondary stresses that sometimes can be resisted by the deck, but that other times require expensive compensating devices. An original theoretical model permits an analysis of this phenomenon and the optimization of the interaction between torsion and distortion. This results in a more agile, faster analysis than finite-element analysis, which requires sophisticated, laborious models and does not distinguish between the two phenomena.

Precast concrete is increasingly being used for bridge construction. One useful modular bridge system consists of precast box deck units on precast concrete cap beams connected to exposed steel piles. This creates the difficult problem of a connection between the cap beam and the piles. A convenient design, favored by the Ministry of Transportation and Highways of British Columbia (MoTH), consists of a steel anchorage plate embedded in the concrete. The plate is then welded to the pile top after placement in the field. This research is an investigation of the performance of the MoTH design. A simple behavior model was devised that is suitable for preliminary design calculations, and a related finite element analysis was performed. The MoTH design was modified on the basis of the preliminary design. The connection was then fabricated and tested under cyclic loading to evaluate strength and ductility. The connection behaved as predicted, and plastic hinging in the pile was achieved. The principle of “capacity design,” in which the failure mode is controlled to ensure a favorable ductile response (e.g., pile yielding), was found to be difficult to implement due to numerous sources of overstrength of the materials, such as the pipe pile steel strength.

Two analytical methods capable of evaluating stresses at the curved polytetrafluoroethylene (PTFE) metal sliding interface in a cylindrical bearing subjected to combined vertical and horizontal loads are described. One method is based on a finite-element approach incorporating contact elements to model the sliding PTFE/metal interface, while the other, referred to as the displacement method, is based on an approach that assumes all displacement in the bearing under load is confined to the PTFE. Both methods are shown to give similar results. Basic equations for the displacement method are derived assuming a bilinear stress-displacement relationship for the PTFE, and this method is used to produce design curves for cylindrical bearings, based on criteria relating to prevention of separation of the interface and limitation of maximum stress level in the PTFE under service load. The displacement model shows that the common design practice of assuming linear elastic material behavior and a plane surface is conservative. The design charts presented in this paper provide an effective tool for taking advantage of the extra horizontal load resistance resulting from the bilinear behavior of the PTFE and the curved interface of the bearing.

This paper presents both free and forced vibration analyses of inclined cables, including the effects of cable sag, equipped with oil dampers in cable-stayed bridges by using a hybrid method recently developed by the writers. The hybrid method readily takes into account cable sag and inclination, damper stiffness and direction, and other parameters. The obtained results confirm that the installation of an oil damper to a stayed cable near the support can increase cable modal damping ratio and thus reduce cable vibration in most cases if the parameters of the damper are properly selected. However, it is found that if the sag parameter λ² (the ratio of the elastic-to-catenary stiffness) of an inclined cable falls in a certain range around one of the frequency avoidances of inclined sag cables, the cable modal damping ratios provided by the damper in the corresponding symmetric or antisymmetric or two hybrid modes can be significantly reduced. To facilitate the design of oil dampers for inclined sag cables in cable-stayed bridges, two sets of graphs are provided with respect to the achievable maximum modal damping ratio, the optimum damper size, and their relations with cable sag and inclination. One typical example is presented to demonstrate how to use these graphs.

Reinforced concrete frame corners were analyzed using the nonlinear finite-element method and fracture mechanics. The objective of the study was to determine whether the reinforcement detailing in frame bridges could be simplified, with preserved structural safety, by splicing the reinforcement within the frame corner. A constitutive model for concrete, based on nonlinear fracture mechanics and plasticity, was used. An interface model was used to account for slip between the reinforcement and surrounding concrete. Analysis of previously tested frame specimens, with both spliced and unspliced corner reinforcement, was used to study the overall behavior of the frames; more detailed analysis of only the frame corner regions was used to study the influence of the reinforcement splices. The analyses were found to reflect the mechanical behavior of the specimens, and are in good agreement with the test results. The analysis results support, together with the test results, the idea that it would be feasible to splice all reinforcement in a portal frame bridge within the corner regions.