Journal of Bridge Engineering

Recognizing the limitations of the generic truck weight data and conservative assumptions made during the calibration of live load factors for bridge rating, the AASHTO load and resistance factor rating (LRFR) manual for bridge evaluation provides sufficient flexibility and allows state agencies to adjust the live load factors based on their individual conditions and site-specific or state-specific information. This paper describes a reliability-based process that can be followed to perform such adjustments and illustrates its application using an example in which the procedure was followed during the calibration of a LRFR methodology for New York State bridges. This methodology is applied to the rating of existing bridges, posting of understrength bridges, and checking of permit trucks. The live load models used during the calibration are based on weigh-in-motion data collected from several representative sites. The LRFR live load factors developed using the proposed calibration process would provide uniform and consistent levels of bridge safety and reliability for the bridge classes and configurations targeted. The target reliability levels used during the calibration should reflect the experience gained by state bridge engineers from evaluation of existing bridges under current loading conditions.

A multihazard reliability-based framework is developed through this study to evaluate the structural response of RC bridges under the combined effects of pier scour and earthquake events. This framework is used to calibrate the scour load-modification factors for the design of bridges located in high seismic areas. Toward this goal, a series of case study bridges are investigated. For each bridge case, the joint probability of failure owing to scour and earthquake hazards is determined for a range of expected combinations of these two extreme events. The occurrence probability of each scour-earthquake scenario is identified by taking into account all of the major sources of load uncertainty through scour risk and seismic hazard curves. Furthermore, the uncertainties inherent in the structural response of bridges are included in the framework to improve the accuracy of estimated failure probabilities. The calculated probabilities are then compared with the maximum acceptable probability of failure (or its equivalent target reliability index) given by current design codes to obtain scour load-modification factors. The developed framework provides a reliable approach for the calibration of code specifications in the extreme event situations and can be extended to other combinations of natural hazards.

This paper focuses on the development of a strut-and-tie model (STM) that can be used in the design of previously developed longitudinal joints with accelerated construction features. Four joint specimens reinforced with tight bend diameter U-bars and previously tested under bending are summarized here to validate the STM. The validated STM is proposed to calculate the ultimate moments of the joints, which is capable of identifying the most critical parameters and yields safe and consistent predictions. It shows that the joint capacity increases with increasing of the concrete strength and overlap length, and the capacity reaches the maximum value when the U-bar spacing is twice the overlap length. Design recommendations to U-bar spacing, overlap length, diameter of lacer bars, as well as concrete strength of the closure pour material are developed for full-strength joints.

After the collapse of the Interstate 35W Bridge in Minneapolis, Minnesota, in 2007, transportation agencies began evaluating and rating their inventories of gusset plate connections. Connection evaluations require accurate drawings that detail the plate, member, and fastener geometries. These structural details should also accurately reflect the as-built conditions. For some connections, as-built information may not be available, or the available drawings may not represent the actual field conditions. To fill this gap, a new methodology was developed that enables rapid and accurate collection of field measurements for connection plate geometry. The method uses close-range photogrammetry techniques to rectify images taken with consumer-grade cameras using flat-field and fish-eye lenses. The technique has been demonstrated on full-scale gusset plates in the laboratory and in the field. Dimensional measurements from the processed images provided results that are as good as or better than conventional field measurements and with tolerances below what most engineers require for calculation of gusset plate connection capacity. This technique provides a new tool for bridge engineers to quickly collect gusset plate geometry that can be used in connection evaluations and rating and can further enhance bridge-management tasks.

Horizontally curved I-girders are subjected to combined vertical bending and torsion under gravity loads alone. The torsional behavior of open I-shaped girders is commonly and conveniently transformed to self-equilibrating lateral bending of flanges. The interaction of vertical bending and lateral flange bending reduces the vertical moment–carrying capacity of the section. The interaction equations for predicting the nominal bending strength of horizontally curved I-girders of compact-flange sections subjected to vertical moment and torsion have been derived. Singly symmetric composite and noncomposite I-shaped cross sections in the positive and negative moment zones, respectively, are considered. These strength criteria are based purely on the static equilibrium of the cross section with no secondary amplification considered. The limitations and applicability of the derived equations toward the design use are demonstrated and analyzed.

Crowding is a critical condition for footbridges that are prone to vibration problems from pedestrian loads. Synchronization of pedestrian movements has been identified as the cause of the excessive lateral vibration in some footbridges. Two conditions have been named as the cause of synchronization: increase in crowd density and pedestrian-structure interaction. The former would be related to the onset of the phenomenon; the latter takes place after structural vibration reaches a certain level. This paper focuses on the former condition. A test program to investigate whether this condition occurs was carried out for a range of pedestrian densities, complementing data previously published on this subject. The head movement of pedestrians walking both in groups and in a flow was recorded by a video camera, and the examination of the video indicated no synchronization from densification. However, it was observed that the lateral sway of the pedestrians’ bodies increased with the increase of density. By using an existing model of an inverted pendulum to estimate lateral forces applied by a pedestrian and using the collected data as input to the model, a steady increase of lateral force from the rise in density was observed: it reached a 104% increase for a density of 1.8 pedestrians/m² compared with the force applied for an unrestricted walking condition.

Stress-laminated timber (SLT) bridge decks are generally designed using either linear hand calculation methods or linear finite-element models. Several studies have shown, however, that the behavior of SLT decks is nonlinear when loaded until failure. In this paper, several linear design methods are compared with one another and with an ultimate load test of a full-scale SLT deck subjected to an eccentric load. Some of the linear hand calculation methods show significant discrepancies in results, depending on the load position. There are also variations in the results from finite-element models, depending on the material properties assigned to the deck. All the design methods failed to predict the deflection of the tested deck when loaded to failure. A larger deflection was observed in the full-scale test than that predicted by the design methods. As a result, the linear design method could underestimate the bending stresses in the deck. Several hand calculation methods are also unable to calculate the transverse forces and moments necessary for design according to Eurocode 5.

Fatigue damage in a conventional orthotropic steel bridge deck system poses a formidable challenge to bridge engineers all over the world because of ever-increasing heavy traffic volumes and higher wheel loads over the past decade. An effective solution may be to enhance the stiffness of the bridge deck to reduce the fatigue stress amplitude of its components. This paper proposes an innovative composite bridge deck system that consists of an orthotropic steel deck stiffened with a 45-mm reactive powder concrete (RPC) layer. Based on the analysis of HuMen Bridge in China (a suspension bridge with a conventional orthotropic steel bridge deck system with span length of 888 m) and two types of full-scale model tests, a comparison investigation is conducted between a conventional orthotropic deck system where the asphalt wearing course has been ignored and the proposed orthotropic deck system that includes an integral concrete wearing course, and the proposed composite bridge deck system proves to be considerably effective in reducing the stress range caused by service vehicle loads when applied to long-span steel suspension bridges. The thin RPC layer can be reliably integrated with the deck plate through stud shear connectors, and no shrinkage cracking occurs on the surface of the RPC layer that is cast on the deck plate. The fact that the tensile stress of the RPC layer is up to 42.7 MPa before cracking occurs demonstrates that cracking will not appear in the RPC layer under service vehicle loads. The analysis, which is investigated on the premise that the dead load weight of the bridge deck of HuMen Bridge is approximately the same for the two different deck systems, demonstrates that the stress of the orthotropic steel deck is significantly reduced with the application of the proposed composite deck system. Analysis with a three-dimensional finite-element model indicates that the transverse tensile stress of the deck plate is reduced by 71%, while that of the connection between the deck plate and the longitudinal troughs is reduced by 72%. This indicates that the risk of causing fatigue cracks in the steel bridge deck system can be considerably reduced during the entire life cycle of the bridge.

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) were initially developed without any internal steel reinforcement as viable alternatives to conventional RC columns in nonseismic regions. Studies have shown that extending CFFT application to seismic regions requires a moderate amount of internal steel reinforcement. To date, cyclic performance of CFFTs as part of a structural frame has not been assessed. This paper describes testing of four one-sixth-scale two-column bents: a control RC, a glass FRP-concrete frame (GFF), a carbon FRP-concrete frame (CFF), and a hybrid glass/carbon FRP-concrete frame (HFF). Each frame was tested under reverse cyclic lateral loading with a constant axial load. Specimen HFF with hybrid FRP tubes demonstrated the highest moment capacity and initial stiffness, with an increase of 200 and 70%, respectively, over the control specimen. Specimen GFF showed no sign of cracking up to a drift ratio of 15% with considerable residual strength, whereas specimen CFF had the least ductility. Glass FRP tubes extended the plastic hinge length of the pier columns to twice that of the control RC frame.

Bridge load rating is traditionally done based on the load-carrying capacity of the superstructure components. Only in some rare instances does the bridge load rating consider the load-carrying capacity of the substructure. However, the authors believe that for bridges over waterways, which are susceptible to scour, the load-carrying capacity of the substructure must be evaluated to assess the need for reduced load rating and posting limits. The results in this paper attempt to address the importance of assessing the substructure load rating. Case histories for bridges susceptible to scour are analyzed. The analysis and evaluation of the actual bridges presented demonstrate that the bridge load rating is limited by the substructure load-carrying capacity and the tolerable deformation. The examples clearly illustrate that reduced load rating is experienced when scour occurs. Thus, bridges impacted by scour need to be judged based on both the super- and substructure components. The findings suggest the need to augment the current bridge load rating procedures to include the substructure load rating in a quantitative manner.