Journal of Bridge Engineering

The fatigue performance of a new type of butt-welded tensile-plate cable-girder anchorage that requires higher load-bearing capacity and lower stress concentration compared with normal tensile-plate anchorages for a long-span cable-stayed railway bridge was evaluated using a finite-element analysis and full-scale laboratory model. The test results show that the stresses remained constant over the first 2 million fatigue cycles, stress redistribution occurred at the end of the butt weld after 2.75 million cycles, and no surface cracks were observed after 3 million cycles. Anatomical milling tests found a fatigue crack originating from a microscopic welding defect in the end of the butt weld. The fatigue properties of butt welds of the anchor plate combined effect of tensile and shear forces are lower than the common butt welds. The fatigue details at two ends of the butt weld are crack vulnerable for the relative weak weldability of 40-mm-thick anchor plate. However, the measured minimum fatigue life of 2.75 million cycles (or 137.5 years) for the butt weld is larger than the bridge design requirement of 2 million cycles (or 100 years), indicating satisfied fatigue performance of the anchorage. The addition of leading and blowout plates is suggested to reduce butt weld residual stresses and defects, improving the fatigue performance of the anchorage.

A short-span highway bridge system composed of steel tee sections embedded in a concrete deck slab during fabrication of the member was developed for the Pennsylvania Department of Transportation. The connection between the concrete deck slab and steel tee sections consists of transverse reinforcing bars passing through drilled holes located near the top of the steel tee stems and cast into the deck slab. This paper presents the design and fabrication approach for the composite steel tee concrete deck bridge system. A full-scale prototype is fabricated in accordance with the design and fabrication approach, and the approach is verified through monitoring and destructive testing of the prototype. The prototype is load tested to examine its performance relative to AASHTO service and strength requirements. The full-scale prototype results indicate that the design and fabrication approach produces a composite steel tee concrete deck bridge system that satisfies AASHTO limit state criteria.

The most common type of bridge on South Dakota local roads is a precast prestressed double-tee (DT) girder bridge. For old and/or deteriorated bridges, the estimation of the bridge safe live load is necessary to ensure the safety of the traveling public and to prevent excessive bridge damage and collapse. Nevertheless, load rating of damaged bridges is challenging mainly because of a lack of information regarding the capacity and distribution of the live load between damaged components. The main goal of the present work is to propose a systematic analytical load rating methodology for precast bridges, specifically those with DT girders when girders are damaged with different damage levels. First, quantitative definitions in-line with those from AASHTO were modified and proposed to identify all damage types and condition states specific to DT girders. Subsequently, a statistical analysis was performed on the South Dakota DT bridge inventory to comment on the most frequent observed damages. Then, two DT bridges, which had a significant girder-to-girder joint damage, were field tested, and the measured data was used to recommend girder distribution factors and dynamic load allowance specific to DT bridges with deteriorated longitudinal joints. Furthermore, two 45-year-old DT girders, each with significant damage, were used in a strength test, and the measured data from these tests and others collected from the literature was used to validate the capacity estimation method for old and/or damaged DT girders. The verified methods were then utilized to calculate the shear and moment capacities of 23 different DT sections, which have been used in South Dakota. Based on the statistical, experimental, and analytical studies, a new methodology was proposed for load rating of typical damaged DT bridges.

In this paper, ultrahigh-performance concrete (UHPC) combined with fiber-reinforced polymer (FRP) composites is proposed for the shear strengthening of corroded reinforced concrete (RC) beams. The UHPC–FRP composites are utilized to replace the spalled concrete cover in corroded RC beams. UHPC helps controlling the crack width and preventing the corrosive substances in the environment from invading the internal steel stirrups, whereas the carbon FRP (CFRP) meshes are embedded in UHPC to increase its tensile strength. The experimental study shows that the UHPC­–­FRP shear strengthening significantly increased the shear capacity of the RC beams and suppressed the formation of shear cracks. The introduction of thin CFRP meshes in UHPC greatly decreased the crack width in concrete. No debonding was observed between FRP and UHPC. The shear capacity contribution between the steel stirrups and UHPC–FRP composites was affected by the corrosion level in the existing internal shear stirrups. An analytical model is proposed for the prediction of shear capacity contributions of all materials to the strengthened RC beams, which shows satisfactory precision as compared to the experimental data.

To investigate the seismic response characteristics of low-gravity-center cable-stayed bridges with twin towers, a simplified mechanics model was established based on the transmission path of the horizontal seismic inertial forces of the girder under earthquake excitation. The definition of a low-gravity-center cable-stayed bridge with twin towers was proposed. Two 1:75 scale models, a floating system (FS) cable-stayed bridge and a fixed-hinge system (HS) cable-stayed bridge, were fabricated, and shaking table tests were conducted. The results of these tests showed: (1) horizontal cracks appeared at the bottom and middle areas of the main tower in the Test Model FS, whereas diagonal cracks together with concrete spalling formed at the bottom area of the main tower and the bottom crossbeam in the Test Model HS; (2) the Test Model FS experienced a larger displacement response but a smaller acceleration response compared to the Test Model HS; and (3) the reinforcement strain response at the bottom of the main tower of the Test Model HS is smaller than those of the Test Model FS, which is in good agreement with the theoretical analysis of the low-gravity-center cable-stayed bridges. In general, the fixed-hinge system cable-stayed bridge can reduce the overall structural damage under strong earthquakes and is therefore suggested to be used in low-gravity-center cable-stayed bridges. The research results help to understand the failure characteristics of the cable-stayed bridges and to provide a reference for the seismic design of low-gravity-center cable-stayed bridges in practical engineering applications.

Accurately obtaining the stress of steel components is of great importance for the condition assessment of civil structures. Currently, methods for structure stress detection have some drawbacks such as the capability of obtaining structural stress increment rather than the total stress, causing structural damage, and high cost. To overcome these drawbacks, a deep learning framework for total stress detection of steel components is proposed and its feasibility is illustrated with an example. First, the adopted deep neural network is briefly introduced, followed by the introduction of the dataset preparation. In order to maximize the stress detection accuracy, parameter analysis was conducted and the mean average precision achieved by the well-trained model for detection of the stresses under consideration is 89.67%. The robustness of the trained model was further examined and the procedures for application of the proposed approach were summarized. The presented method provides a new idea to detect the total stress of structure components that is difficult to obtain with a traditional sensor-based method.

Twenty-five years ago, a bridge live-load model was developed along with the calibration of the AASHTO LRFD Specifications. The statistical parameters of truck loads were based on the Ontario, Canada, truck survey performed in the 1970s. The objective of this paper is to review the available weigh-in-motion (WIM) data and update the live-load model accordingly. The considered WIM database includes over 200 million records, from 44 WIM locations around the USA, with about 1–2 million vehicles per year for each location. The actual number of records depends on traffic volume expressed in terms of an average annual daily truck traffic (AADTT) and local conditions, such as type of road, local facilities, seasonal factors. The cumulative distribution functions of load effect are extrapolated to predict the maximum expected live load for extended time periods. The statistical parameters of live load are determined for the static component of the live-load effect for one lane in simple-span bridges based on the actual WIM data. The analysis showed that there is a 15%–20% increase in live load in comparison to Ontario data. An updated design tandem is proposed to adequately represent the traffic load for short simply supported spans.

Static load tests are currently essential to assess the actual response of prestressed concrete bridges: the bending stiffness is indirectly estimated from deflection measurements under loading. In this paper, to overcome the time-consuming and economic limits of static tests, an alternative testing procedure is developed based on the use of an instrumented vehicle. The vehicle hosts a swinging pendulum equipped with a laser sensor. Road irregularities and the beam detection due to the moving load excite the measurement device. The natural frequency of the pendulum is tuned to amplify low frequencies (f ≈ 2 Hz), i.e., the excitation due to the moving load, being practically insensitive to the high-frequency excitation due to the pavement roughness. The displacement response of the pendulum yields an estimate of the bending stiffness of each bridge span by optimizing the correlation function between the displacement time history recorded by the pendulum and the time history generated by numerical simulation. The optimization parameters are the bending stiffness itself and the initial conditions of the pendulum response. The feasibility of the procedure is tested on a set of real-case bridges. Preliminary outcomes give confidence for further development of the procedure and prelude an adequate validation of the method by comparing the results with static load tests. Covariance-based sensitivity analysis gives final matter for discussion, enlightening the effect of the uncertainties of the parameters on the results.

A new glass fiber-reinforced-polymer (GFRP)–metal box-truss composite girder was developed for use in lightweight deployable vehicular bridges with favorable torsional resistance for large spans. This paper describes the experimental characterization of the static behavior of the latest structure characterized by a closed cross section, with a comparative study on an early version having an open cross section. The structural form of the new structure differed considerably from that of the early version. Nondestructive tests with symmetrical and unsymmetrical static loadings were conducted on a newly fabricated prototype to identify the characteristic flexural and torsional performances of the new structure. Additionally, a comparative evaluation of the experimental behavior in terms of load–displacement and load–strain responses was conducted between the new structure and the early version. Favorable results demonstrated that the new structure enabled satisfactory static performances in terms of deployable bridge applications. The resulting comparisons indicated that the new structure featured a flexural resistance identical to that of the early version. However, the addition of lower plane-truss transverse braces in the new design significantly increased the torsional resistance of the space truss system. The overall torsional rigidity of the new structure approximately corresponded to 2.36 times that of the early version. Moreover, the stress state in the extrusion-type GFRP tubular elements of the space truss system was significantly improved. Compared to the early version, the latest structure is more appropriate for use in the primary load-carrying superstructures of large-span deployable bridges under critical unsymmetrical service loading conditions.