Journal of Bridge Engineering

The Florida Slab Beam (FSB) has been developed by the Florida Department of Transportation (FDOT) to be used for short-span bridges [less than about 19.8 m (65 ft) long]. The FSB system consists of shallow precast, prestressed concrete inverted-tee beams that are placed adjacent to each other and then involve reinforcement and concrete being placed in the inner joints and deck all in one single cast. Ultra-high-performance concrete (UHPC) is becoming more widely used in bridge construction applications as a result of its remarkable structural performance. Many departments of transportation have tested and deployed the use of UHPC in bridges around the United States. Most of these applications have been to connect precast members (e.g., slabs to beams and slabs, adjacent beams, caps to columns, etc.). A modified FSB design is desired to eliminate the cast-in-place (CIP) deck and allow for UHPC to be used in the joint region, which will allow for accelerated construction and decrease the impact of construction on traffic. Different joint details and cross-section geometries were analyzed and experimentally evaluated to determine feasible joint details with UHPC for slab beam bridges used in accelerated construction. Results from numerical modeling, strength, and fatigue experimental testing of the transverse joint performance of four different UHPC joints in two different depth slab beam bridges are presented. Straight-side and shear-key UHPC joint details were found to behave similar to or better than the current FSB joint detail.

This paper presents ground-coupled ground penetrating radar (GPR) data-processing procedures for concrete bridge deck evaluation. GPR signals are analyzed in the depth range from the concrete surface to top reinforcement mat. Although most ground-coupled GPR analysis methods focus on the attenuation of signals from rebar reflections only, the proposed algorithms extract three types of parameters from GPR scans: Direct coupling amplitude, wave velocity in concrete cover depth, and normalized, depth-corrected GPR signal amplitude from rebar reflections. These parameters provide information about bridge deck deterioration conditions at different depths. First, the signal amplitude of the direct coupling wave on the concrete surface is analyzed over the entire bridge. Second, the wave velocity in cover concrete is obtained through migration of rebar reflections, and then the rebar depth can be calculated. Third, signal attenuation in concrete is calculated from the rebar reflection and further corrected by the rebar depth. In addition, the true time zero for GPR signal analysis is validated by numerical simulation and experimental data. Finally, this algorithm is demonstrated on field testing data, and the final results are presented in the forms of direct coupling wave amplitude, wave velocity, and attenuation maps.

Design of reinforced concrete (RC) bridge members with fiber-reinforced polymer (FRP) bars as internal reinforcement are usually governed by their serviceability parameters, such as crack width and deflection. This study investigates the effect of structural fibers on the shear behavior of RC beams with glass fiber-reinforced polymer (GFRP) rebar as longitudinal reinforcement. The objective of this study is to understand the efficiency of macrosynthetic polyolefin (PO) polymer and a hybrid combination of steel and PO fibers in improving the shear behavior of GFRP-reinforced beams. In total, 13 full-scale RC beams are cast with GFRP rebars as internal reinforcement and varying PO and hybrid fiber dosages. Three different fiber dosages by volume of concrete (v_f), namely 0.35%, 0.70%, and 1.0% are considered. The beams are tested under three-point bending configuration with a shear span (a) to effective depth (d) ratio of 2.2 to simulate shear dominant behavior. Experimental results revealed that the addition of fibers increased the postcracking stiffness, peak load, and ductility when compared with control beams with no fibers. Soon after cracking, an excessive load drop in the control specimen is observed due to the low elastic modulus of GFRP rebars. The addition of PO and hybrid fibers reduced the load drop significantly and enhanced the postcracking performance by improving the aggregate interlock and through reduction of residual tensile stresses at the crack tip. The angle of the crack increased with an increase in fiber dosages, indicating the change of the failure mode from brittle shear tension to ductile flexure at higher fiber dosages (0.7% and 1.0%). The shear strength predictions obtained from ACI and RILEM recommendations are found to be very conservative when compared with the test results.

The composite rigid-frame bridge presented in this study is a new type of structural solution that combines the steel–concrete composite box girder and the concrete-filled double-skin steel tube (CFDST) piers with rigid connecting joints. Compared with the conventional prestressed concrete rigid-frame bridge, it shows superior static and dynamic performances. This study performs shake table tests of a 1:10-scaled three-span steel–concrete composite rigid-frame bridge (SCCRFB) to explore its seismic characteristics and damage modes. The details of the bridge model design, construction, measurements, and testing process are presented. The seismic responses of the bridge under one typical near-fault and one far-field ground motions were experimentally investigated. Testing results revealed that the damage to the bridge is mainly located at the upper and lower ends of the CFDST piers, with yielding of the outer steel box and separation between the steel skins and infilled concrete. The testing results also indicated that the near-fault ground motions containing strong velocity pulse could significantly amplify the structural responses compared with the far-field ground motions. Furthermore, a detailed finite element (FE) model of the SCCRFB with CFDST piers is developed and validated by the experimental results, and numerical studies are then carried out to compare the seismic performances of this bridge type and the one supported by the conventional reinforced concrete (RC) piers. The numerical results show that the SCCRFB with CFDST piers exhibits superior seismic performances compared with the traditional bridge, especially when subjected to the near-fault ground motions. This study can provide useful references for the engineering solution and seismic design of long-span, high-pier composite rigid-frame bridges.

Exposed to the challenging coastal environment, slender bridges could experience significant dynamic responses and complex stress states resulting from the coupled dynamic impacts of wind, wave, and vehicle loads. Cracks could gradually initiate and propagate at structural details that might trigger failures of the structural members or the entire structural system. To predict the remaining fatigue life of slender coastal bridges, stochastic fatigue damage for structural details is quantified using machine learning (ML)-based methods, such as support vector machines (SVM), Gaussian process (GP), neural network (NN), and random forest (RF). Parametric probabilistic models for vehicles, defined based on long-term field measurements, and stochastic loadings from wind and waves, parameterized for various loading scenarios, serve as the input parameters. As for the output of ML models, equivalent fatigue damage accumulation is obtained based on the coupled vehicle-bridge-wind-wave (VBWW) system and stress analysis for complex structural details using multiscale finite-element analysis (FEA). With different training strategies, fatigue life for critical local details is obtained considering the ever-changing coastal environmental conditions. Training and testing results show that the GP algorithm outperforms other algorithms even though all algorithms exhibit the reasonable capability of predicting the fatigue damage accumulation.

Aerodynamic flutter instability could lead to the catastrophic collapse of flexible long-span bridges and needs to be prevented. This study investigated the variability of eight experimentally measured flutter derivatives (FDs) for a commonly used a Pasco–Kennewick (PK) section girder using a free vibration technique in a wind tunnel, which provided some new insights into the identification of FDs and supplemented the reliability analysis for buffeting and flutter performance. The aerodynamic uncertainties in terms of the dispersion of flutter coefficients were studied and two implications behind the extraction of FDs were discussed. The statistical and probabilistic behaviors of FDs at different reduced wind speeds were examined before generating sufficient independent random samples using the Monte Carlo (MC) approach. The intercorrelations between experimental FDs quantified by correlation coefficients were also examined and were employed to randomly sample the correlated FDs. The probabilistic flutter solutions in terms of critical wind speed propagated from the FDs uncertainties were studied utilizing step-by-step analysis, which resulted in several multimodal probability distributions of flutter onset. In addition, the role played by each FD on the variation of critical wind speed was discussed.

In January 2016, the FHWA and AASHTO announced a joint agreement that only bridge railing and longitudinal barriers evaluated using the 2016 edition of Manual for Assessing Safety Hardware (MASH) will be allowed for new permanent installations after December 31, 2019. However, in the current AASHTO-LRFD, railing design forces and their applications for concrete barriers have not been updated to MASH requirements, and the detailed impact process of the MASH truck on concrete barriers has not been systematically investigated. In most of the previous studies on MASH truck impacts, the concrete barrier had been assumed to be a rigid structure capable of sustaining a vehicular impact without any significant damage. This assumption neglects the deformation of the barrier and does not improve our understanding on the barrier's failure mechanisms. In this study, high-fidelity finite-element simulations have been carried out to investigate the demands imposed upon, and damage modes of, MASH TL-4 and TL-5 concrete barriers. An inelastic pushover analysis approach is proposed for the evaluation of the capacity of these concrete barriers. Based on the damage mode observed from the pushover analysis, a modified yielding line method (MYLM) is proposed for estimating the capacity of concrete barriers. It is observed that the capacity of concrete barriers estimated by the proposed MYLM matches with that from the pushover analysis quite well and it is generally much higher than from the current AASHTO-LRFD specifications.

This article presents the results of a study of the efficiency of post-tensioned bridges. It is an initial step toward a broader goal of providing designers with a simple and rational basis for assessing the efficiency of bridge design concepts. The approach consisted first of establishing a set of parameters defining the primary characteristics of the bridge type considered, simply supported multiple-T systems. Within a defined range of parameter values, designs were generated and checked by computer against applicable safety and serviceability criteria. A subset of valid cases was extracted with the lowest value of reference depth, defined as the ratio of the cross-sectional area and deck width. Reference depth was used as the primary measure of efficiency because it measures concrete quantity, independent of span or width. The study shows that cross sections with three webs minimize reference depth. For each span length, the range of values for span-to-depth ratio for efficient cross sections is well defined and limited. Minimizing reference depth does not require large quantities of prestressing steel.

Reinforced concrete (RC) deck slabs without transverse reinforcement are commonly used in bridge structures. The ability of RC slabs to distribute concentrated loads due to the pressure of wheels in a transverse direction is an important property for their verification. The main goal of this paper is to investigate the effect of the redistribution of shear forces on the load-carrying capacity of RC slabs subjected to a concentrated load. Several methods and design models for the assessment of one-way shear capacity were tested and statistically evaluated according to the results of 43 experiments carried out in the last two decades. The analyses showed that the effective shear width method provides unsafe results for higher values of the clear shear span to effective depth ratio unless the same limits are not imposed. Limiting the distance of the critical section from the inner edge of the loaded area significantly improved the accuracy of the method. The best results were obtained for the ACI 318-14 and AASHTO LRFD models in combination with a French approach when the CoV reached values of 0.091 and 0.097, respectively. A comparable degree of accuracy was provided also by a method that is based on a combination of a linear FEM analysis and Critical Shear Crack Theory with a CoV equal to 0.102.

Prefabricated bridge deck panels are a popular option for new construction and bridge rehabilitation. Further, ultra-high-performance concrete (UHPC) has become a common option for closure pours between adjacent prefabricated deck elements and between deck elements and the supporting girders. This study presents experimental research on the ultimate behavior of two new and simplified deck-to-girder composite connections that use UHPC and innovative detailing. The proposed systems were developed to simplify fabrication procedures and enhance on-site constructability. The two connections investigated in this study rely on short shear connectors on the supporting girders and either rebar dowels protruding from the underside of the deck panels or shear pockets that pass through the deck. These concepts were evaluated using a combination of small-scale direct shear tests and large-scale, double shear push-off tests. Experimental variables included pocket geometry, shear stud configuration, rebar dowel configuration, and dowel length. Results indicate that these novel connection details are ductile and have the potential to meet the existing strength limit state requirements in the AASHTO Bridge Design Specification (BDS) for horizontal shear.

Various local governments have developed state-specific vehicular live-load factors for bridge rating. However, a significant computational demand is often associated with such an effort. This is due to the large size of the weigh-in-motion (WIM) databases frequently used in the procedure. In this study, a method is proposed that can significantly reduce the computational cost of the analysis, while still maintaining reasonable accuracy. The proposed approach develops approximate live-load random-variable statistics by truncating the WIM database based on gross vehicle weight, and then a complete reliability analysis is conducted to develop new live-load factors that meet AASHTO-specified rating standards. Two WIM databases, one based on typically legal vehicles and another based on unusually heavy vehicles, are considered for evaluation. Results of the proposed approach are compared with an exact assessment as well as to a simplified method suggested by AASHTO. It was found that the proposed approach may provide very large reductions in computational cost with minimal loss of accuracy, whereas significant inaccuracies were found with the existing simplified approach.

To date, various monitoring techniques have been developed to alert authorities of potentially precarious scour depths at bridge foundations. The adoption of such techniques, however, is worthwhile only if sufficient warning time is offered to allow for preventative actions. This is true for any structural health monitoring system. The framework presented in this study is a simple and practical tool for predicting warning times given detected scour depths. The framework incorporates a probabilistic analysis of scour progression such that the uncertainty in warning times can also be determined and used for risk-based decision making. A detailed example was considered for demonstration. The resulting framework is useful in three stages of scour monitoring and management: first, in selecting optimum sensor configurations; second, in encoding the actions required at any detected level of scour depth; and third, in selecting appropriate countermeasures based on warning time.

This paper presents a crowdsensing framework employing smartphones in monitoring populations of bridges in future smart cities. In this regard, because there are a variety of vehicles with different features traveling over the bridge at different speeds, it is critical to investigate the robustness of indirect monitoring methods against vehicle features. Therefore, an experimental study was performed, including two lab-scale bridges with different boundary conditions and a robot car that was capable of maintaining a variety of speeds and suspension systems. The proposed framework focuses on the identification of frequencies of the bridge using acceleration signals recorded on the car. It was demonstrated that by using a large set of passing cars with different features, the fundamental frequency of the bridge was captured. Successful identification of the deviation of fundamental frequencies between two bridges with relatively close frequency values proved that the framework is capable of detecting damage induced frequency changes of the bridge. Since this framework relies on the use of smartphones, it provides the opportunity to efficiently monitor a plethora of bridges in a metropolitan area with minimum cost.

This paper describes the first application of Electrically Isolated Tendon (EIT) technology in the United States. These systems have been developed to provide a level of quality assurance for post-tensioned strand systems in bridge applications. The EIT system is intended to provide electrical isolation between the strand inside the post-tensioning duct and the reinforcement outside of the duct system thus reducing the potential for corrosion to occur. This is achieved using plastic tendon ducts, additional protection of the ducts, modified tendon trumpets, electrical isolation plates at the tendon anchorages, and encapsulation of the strand anchors. A demonstration was conducted with support of the FHWA and Pennsylvania Department of Transportation. The system consists of a three-span continuous bridge composed of pretensioned Pennsylvania Bulb tees spliced and post-tensioned. The bridge system was monitored during beam fabrication, erection, and bridge construction and an overview of the EIT installation methodology is presented. The performance of the EIT system is compared with standard recommendations on acceptable performance and was found to meet the requirements. Installation of the EIT system was not significantly different than that of a conventional post-tensioning tendon. The system provided additional assurance of the electrical isolation in the bridge and appears to be a viable approach for long-term monitoring of the performance of post-tensioned grouted tendons.

This paper addresses the dynamic behavior of the La Scarpe viaduct, which consists of a continuous nine-span steel–concrete composite bridge belonging to the French HSR line TGV Nord. The main objective of the paper is to compare the responses of the existing viaduct with an alternative solution using a double composite action deck with a lower concrete slab in support regions. This slab stabilizes the compression flange, resulting in a reduction in the weight of steel and, consequently, a cost reduction of the global price of the structure. The model of the existing solution is validated with numerical and experimental results presented in the literature. The dynamic analyses performed in this work have been carried out with moving load models using the modal superposition method. The results permit us to draw conclusions between the advantages and disadvantages of the two studied solutions, mostly in terms of the global response of the bridge and in terms of the requirements proposed by the European standards in terms of traffic safety.

The reliability of stay cables is critical to the safety of cable-stayed bridges. This paper investigates and compares reliability assessments of stay cables by using identified cable tension forces and monitored bridge loads. One-year monitoring data from a cable-stayed bridge was used to characterize the probability distributions of cable forces and pertinent bridges loads including temperature of the cable, wind load, and vehicle load. The results show that, for the bridge under study, the cable temperature, the wind load, and the vehicle weight obey the Beta distribution, whereas the axle weight obeys the lognormal distribution, indicating deviations from the design codes. Subsequently, two performance functions are proposed to compute the cable reliability index, where one directly uses the monitored cable forces and the other is based on the monitored loads and the finite element method simulation of the bridge. The computed index based on the monitored cable forces and the performance function I is larger than that based on the monitored loads and the performance function II. The reasonings attributed to the differences and the implication of the present findings in structural design and optimization are discussed.