Journal of Bridge Engineering

The objective of the present study was to experimentally evaluate the statistics of dynamically induced stress levels in steel through-truss bridges as a function of bridge component type, component peak static stress, vehicle type, and vehicle speed. Better understanding of critical bridge rating parameters will enable more accurate bridge evaluations of this type of structure. Three 60-year-old, steel through-truss bridges with similar characteristics were investigated in the present study. Several bridge components on each of the three bridges were instrumented (truss members, stringers, and floor beams), and dynamic strain data were collected under controlled and normal traffic conditions. The dynamic strain histories were processed to obtain bridge component peak static response and peak dynamic response, resulting in the determination of the dynamic load allowance (DLA) for each of the instrumented bridge components for each of several truck crossings. The calculated DLA value are plotted as a function of member peak static stress for each bridge member instrumented. The DLA data are examined as a function of component type, component location, truck type, number of axles, truck speed, and truck direction. This study has demonstrated that the DLA is dependent on truck location, component location, component type, and component peak static stress but appears to be nearly independent of vehicle speed.

Cables instead of interval piers support cable-stayed bridges, and the bridge deck is subjected to strong axial forces due to the horizontal components of cable reactions. The structural behavior of a bridge deck becomes nonlinear because of the axial forces, large deflection, and nonlinear behavior of the cables and the large deformation of the pylons as well as their interactions. The locations and amplitude of axial forces acting on the bridge deck may depend on the number of cables. Agrawal indicated that the maximum cable tension decreases rapidly with the increase in the number of cables. This paper investigates the stability analysis of cable-stayed bridges and considers cable-stayed bridges with geometry similar to those proposed in Agrawal's paper. A digital computer and numerical analysis are used to examine 2D finite element models of these bridges. The eigen buckling analysis has been applied to find the minimum critical loads of the cable-stayed bridges. The numerical results indicate that the total cumulative axial forces acting on the bridge girder increase as the number of cables increases, yet because the bridge deck is subjected to strong axial forces, the critical load of the bridges decreases. Increasing the number of cables may not increase the critical load on buckling analysis of this type of bridge. The fundamental critical loads increase if the ratio of I_p/I_b increases until the ratio reaches the optimum ratio. If the ratio of I_p/I_b is greater than the optimum ratio, depending on the geometry of an individual bridge, the fundamental critical load decreases for all the types of bridges considered in this paper. In order to make the results useful, they have been normalized and represented in graphical form.

Construction of cable-stayed bridges involves major changes in configuration of the structure with the addition and removal of structural components to the partially constructed structure. At every stage of construction, it is necessary to have sufficient information about the existing partial structure as-built, to verify the requirements called for in the construction guidelines and to investigate the effects of possible modifications in the construction procedures. The final stresses and deformations in the completed structure are strongly dependent on the sequence of events during the construction and the erection procedure used. Therefore, analysis of the actual construction sequence is an important first step in any analysis of the performance of the bridge under external loads. In this paper a general methodology for construction sequence simulation of cable-stayed bridges is presented, and stage-by-stage construction of an actual bridge is simulated. The objective of the simulation is to evaluate short-term and long-term influences of the construction sequence on the structural integrity of the cable-stayed bridge. Comparisons are presented between results from the present analysis, conventional procedures, and the actual field measurements.

Bridge management systems have a common need for a well-established inspection data acquisition system. Inspection data management requirements have expanded after establishment of new Federal Highway Administration regulations that require bridge inspection to be performed on an element-level basis. Currently, paper forms are the typical media used to record field-generated bridge inspection data. Better methods of data recording are needed to improve the accuracy and speed of the bridge inspection process. This paper discusses pen-based data acquisition technology and its potential in automating bridge inspection. The pen-based technology was utilized to develop an Automated Bridge Inspection System for the South Carolina DOT. As illustrated herein, the use of an automated inspection system simplifies the data processing effort, improves inspection data accuracy, and permits bridge inspectors to devote more time to the actual inspection process.

This study is in response to the dramatic increase in railway car axle loads that has occurred over the last 50 years. The paper presents the results of an experimental program undertaken to evaluate the structural performance of treated timber bridge ties under different railway car load levels. A portion of a prototype bridge deck, consisting of eight prototype timber bridge ties, was tested under various loading and support configurations to determine the axle load distribution. The serviceability of the treated bridge timber ties was evaluated based on the fatigue strength of eight prototype timber ties under different load levels. A theoretical model, based on energy principles, was developed to predict the axle load distribution to the ties for different span configurations. The model compares well with the measured test results and it complies with the American Railway Engineering Association requirements.

A 5-year program to monitor the performance of a red oak longitudinal girder, transverse deck glued-laminated (glulam) highway bridge is presented. The bridge design details, including preservative treatment results, are described. The live loading results indicate that the predicted and observed live load beam deflections agree to within 7% when the stiffness of the individual beam laminations is used as a predictor and a 10% increase in beam stiffness due to composite action between the deck panel and logitudinal girders is incorporated into the design. The dimensional stability of the deck panels over 3 years has been monitored and analyzed. Significant reflexive cracking of the asphaltic wearing surface has been observed at the interface between each red oak deck panel. This has been attributed to the gap provided between each panel during construction, to the placement of the waterproof membrane directly over the creosote-treated deck panels, and to improper mating of the deck panels to the beams during installation of the lag bolts. Long-term (3-year) dead load deflection measurements indicate that after approximately 1 year, dead load deflections remain nearly constant for the interior beams. Elevations of the lower surface of the two exterior beams fluctuate considerably and vary seasonally. There is no evidence of delamination of the girders or deck panels after 4 years. However, there is some evidence of delamination of the curbs and the tops of rail posts.

Three southern pine stress-laminated deck bridges were constructed in late 1991 in Leon County, Fla. The bridges consisted of approximately 7.32 m (24 ft) simple spans and were 10.97 m (36 ft) wide. They were constructed with #2 and better lumber treated with chromated copper arsenate and redried to moisture contents of <12%. A monitoring program for the bridges was undertaken to investigate the use of southern pine lumber treated with waterborne preservatives in stress-laminated bridges. The program began with static load testing in January 1992. The performance monitoring involved gathering data on the moisture content of the decks, force levels in stressing bars, deck deflection, and the behavior of the bridges under static load conditions. In addition, comprehensive visual inspections were conducted to assess the overall condition of the bridges. Based on almost 3 years of field evaluations, the bridges performed well with no major structural or serviceability deficiencies.