Journal of Bridge Engineering

The majority of railway lines in Sweden are designed to support axle loads of up to 250 kN. Because of increased transport needs on some lines, an axle load limit of at least 300 kN would be beneficial. To upgrade the Haparanda line in northern Sweden to 300 kN, the slabs in existing concrete trough bridges require a higher transverse shear resistance. Methods for in situ strengthening of bridge slabs in this way have not been fully developed, and this paper discusses the possibility of increasing the load capacity by horizontal prestressing. Internal, unbonded posttensioning was performed on one bridge on the Haparanda line, and the strengthening effects were investigated. The strengthening was designed according to the European Eurocode design regulations, and testing was conducted before and after the implementation. Strains in the main transverse reinforcement, caused by a train with an axle load of 215 kN, were completely counteracted by eight prestressing bars, stressed with 430 kN/bar. The results indicate that the actual strengthening effect is larger than what is predicted by the design equations. The Haparanda project showed that unbonded posttensioning can be implemented relatively fast and does not obstruct the ongoing railway traffic during installation.

The conventional design process of the launching nose of an incrementally launched bridge is usually based on parametric models with great limitations and the use of a trial and error technique to improve the design. Facing the disadvantages of traditional approaches, the use of numerical optimization techniques permits the development of objective, rigorous, and complete formulations. This work solves the design optimization problem of an incrementally launched prestressed concrete bridge during construction, searching simultaneously for the optimum cross section dimensions and the prestressing forces of the concrete deck, as well as the most adequate characteristics of the launching nose for the best economic solution. A computer code that allows the generation of a deck was developed, under real design constraints similar to those a bridge designer may encounter in practice. This code is very useful for preliminary phases of a project. The results obtained with this innovative formulation show the benefit of considering numerical optimization tools.

An updated version of the ASCE benchmark on controlled cable-stayed bridges has been recently developed in the ANSYS framework. It includes new aspects in the relative transversal motion of the main girder with respect to the towers in the simulation of the stay cable dynamics with respect to the coupled motion of the main girder in the soil-structure interaction and the numerical formulation by assuming full geometric nonlinearities. Analyses are carried out in a multiple support framework in a time domain by using the earthquake records as collected from the benchmark original statement. The original benchmark configuration considered earthquake restrainers in the transverse direction. The proposed updated bridge model first reproduces this kinematic arrangement, and a new configuration with transversal releases is subsequently implemented. The control strategies consist of passive and decentralized semiactive systems working in the horizontal plane and are also those studied in a previous investigation for the original statement. When the devices are implemented in the transversal direction, the proposed schemes distinctively mitigate the transversal structural response of the bridge with reasonable efficiency.

This paper presents a preliminary design approach for tuned particle dampers for continuous viaducts. A series of shaking table tests of a $1/10$-scale model bridge with and without tuned particle dampers was carried out to evaluate the performance of the system and verify the analysis method. An analytical energy method was established to simulate the behavior of the damper using a finite-element model. The experimental and computational results show that the preliminary design method proposed for tuned particle dampers can be a valuable tool in the application of particle damping in controlling the seismic response of bridges. A tuned particle damper can effectively reduce the seismic response of a continuous viaduct. One of the keys to the performance of a tuned particle damper is the excitation intensity. A tuned particle damper has a wider control frequency band than a single tuned mass damper or a single tuned liquid damper. The simplified method is effective in simulating the behavior of the damper using a finite-element model.

The accuracy and precision of low-frequency (center frequency of approximately 55 kHz) ultrasonic testing for detection and characterization of delamination in concrete bridge decks were evaluated. A multiprobe ultrasonic testing system (with horizontally polarized shear-wave transducers) was used to detect built-in delamination defects of various size, depth, and severity (i.e., thickness) in a test specimen—a $6.1\hspace{0.17em}\mathrm{m}\times 2.4\hspace{0.17em}\mathrm{m}\times 216\hspace{0.17em}\text{mm}\hspace{0.17em}(20\hspace{0.17em}\text{ft}\times 8\hspace{0.17em}\text{ft}\times 8.5\hspace{0.17em}\text{in.})$ reinforced concrete slab-built to simulate a concrete bridge deck. The collected data sets were reconstructed applying synthetic aperture focusing technique (SAFT). The reconstructed measurement results were then used to assess the condition of the concrete slab at individual points [point-by-point data collection and two-dimensional (2D) reconstruction] as well as along lines, where data were collected at smaller steps and reconstructed in a three-dimensional (3D) format. The local-phase information was also calculated, superimposed on the reconstructed images and used as complementary information in condition assessment. The precision and accuracy of condition assessments were evaluated. The results indicated that, using the multiprobe ultrasonic array, delamination defects as small as $30\hspace{0.17em}{\text{cm}}^2\hspace{0.17em}(1\hspace{0.17em}{\text{ft}}^2)$ could be reliably detected. Deep delaminations [i.e., those deeper than 150 mm (6 in.)] were directly detected and characterized, whereas shallow delaminations [shallower than 65 mm (2.5 in.)] were detected only indirectly. The precision of the measurements was demonstrated by comparing repeated measurements at several test points. Similar measurement results obtained on a delaminated portion of a real bridge deck support the conclusions of the validation study.

This paper aimed to determine safety levels involved in bridge pier design when the fatigue nature of traffic load is included. Reliability analysis was used to estimate values of reliability index for the ultimate limit state (pier’s capacity). The analysis was performed in two steps. In the first step, reliability indexes were calculated using statistical information on traffic load and resistance of piers, as it was used during the AASHTO, Load and Resistance Factor Design (AASHTO LRFD) code calibration. The purpose was to estimate design safety according to code provisions. The second step also involved estimating reliability indexes, but with different statistical parameters for live load and resistance. A new, recent live load model with new statistics was used. Statistical parameters of pier resistance were established, including different statistics for concrete strength when fatigue of material is considered. The study was performed for a range of design cases, including different span lengths, sizes of a pier’s cross section, three typical strengths of concrete, and three reinforcement ratios. In the resistance analysis, piers were considered as short columns under biaxial bending. The results did not show a drastic drop in piers’ capacity when the fatigue nature of the traffic load is considered. The resulting reliability indexes when fatigue was included were, on average, 12% smaller compared with the values of the index associated with the current code design.

This paper proposes an equivalent suspension bridge model for the preliminary design of support towers of suspension bridges. In this simplified model, the bridge is composed of its support towers, with equivalent springs replacing suspension cables and girders. An explicit formula for the spring stiffness was derived for the horizontal stiffness at the end of an inclined main cable and compared with Ernst’s formula as well as finite-element analysis results. For the analysis of the model, dead and live loads acting on the girders of each span were replaced with horizontal and vertical forces calculated using the deflection theory and placed on the tops of the support towers. Equilibrium equations were derived from free-body diagrams for each tower and their solutions were obtained from boundary conditions at the ends of the towers. This resulted in the formulation of nonlinear load-displacement equations in matrix form for the simplified bridge model. An example four-span suspension bridge was analyzed for displacements at the tops of the towers and moment reactions at the bottoms of the towers under six live-load cases. A comparison of the model predictions with a FEM analysis showed excellent agreement. The results prove that the proposed analysis method can be a useful alternative for the preliminary analysis and design of suspension bridge towers.

A modified two-dimensional (2D) Moses algorithm for acquiring the field-calibrated influence line (IL) of an existing bridge is presented, based on strain data acquired continuously at a high scanning rate with calibration vehicles of known axle weights and axle spacings crossing an instrumented bridge. Considering the transverse distribution of the wheel loads on each girder attributable to the 2D behavior of the slab-girder bridge, the IL of each of the girders can be calculated, which does not require the girders to possess identical material and geometric properties. By using the calculated IL of each girder as a reference, a modified 2D Moses algorithm was derived to identify axle weights of moving vehicles, taking into consideration the transverse distribution of the wheel loads on each girder. Mathematical equations to calculate ILs and axle weights were derived, and the proposed algorithms were implemented by a computer program. The accuracy of the IL calculation and axle weight identification was verified through a field test of a bridge on U.S. Route 78 in Alabama. The identified axle weights showed agreement with the static measurements from weighing pads and with results from the bending-plate weigh-in-motion (BPWIM) system near the instrumented bridge.

Traditionally, the impacts of traffic and earthquake loading have been considered independently when assessing bridge reliability. This paper presents a framework for joint seismic and live-load fragility assessment of highway bridges. Full probabilistic analyses accounting for variation in bridge parameters, ground motion, and truck load and position are proposed to develop bridge system fragility curves and to identify the critical truck position that renders the bridge most vulnerable to earthquakes. A fragility surface is derived for the critical truck position at which the failure probability is conditioned on the governing vehicle weight in addition to ground motion intensity, thus depicting the impact of truck load on bridge seismic fragility. This fragility surface is convolved with the governing vehicle weight distribution (obtained from weigh-in-motion data) and probability of truck occurrence (function of truck flow rate) to determine traffic-informed conditional seismic reliability estimates. The proposed methodology is demonstrated on a case study of a multispan continuous steel girder bridge in the central and southeastern United States. The framework can find ready extensions to assess the joint impact of earthquake and live loads for other bridges and hazard conditions and can offer a basis for deriving reliability-based load combinations consistent with emerging trends in bridge design.

This article presents a comparative study of 55 concrete arch bridges built over the last century. For each bridge considered in the study, section properties and geometrical ratios were determined and compiled into a database. These data were used to identify empirical trends related to important attributes such as proportions, stiffness, slenderness, and efficiency. These trends were then expressed as functions of span length. The database and empirical trends together provide a unique and comprehensive quantitative characterization of the state of the art of concrete arch bridges. By situating new design concepts within the trends compiled by this study, designers of arch bridges can gain insight into the implications of specific design decisions with regard to structural behavior and efficiency and will have a quick and reliable means of estimating the nature and extent of the effort required for validation.

The collision of barge flotillas against bridge piers is a design scenario that often controls the design of bridges that span navigable waterways. Current design approaches vary significantly in their assumptions and mostly rely on design code guidelines. The influence of adjacent barge columns on multicolumn flotilla impacts is not well established in the literature; some design codes ignore the effects of adjacent barge columns, assuming they break away upon impact, whereas others assume full contribution. The actual contribution of adjacent barge columns has a major influence on the amount of energy absorbed by the impacted structure and, therefore, on the load history attributable to the impact. The behavior of barge flotillas during impact depends upon several factors, such as configuration of flotilla, impact speed, barge bow-crushing behavior, and dynamic response of pier. This paper presents a simplified procedure that allows the estimation of the impulse delivered by the adjacent barge columns for head-on impacts. The proposed simplified procedure is based on a parametric study performed by means of a multidegree-of-freedom, two-dimensional model described in this paper. The proposed model is able to account for nonlinear interaction between barges, nonlinear barge bow behavior, and dynamic structural response. The proposed procedure allows for an improved estimation of impact load histories attributable to the collision of barge flotillas.

The South Carolina DOT employs a detail in which piles are plainly embedded into bent caps without the use of any special detailing to the pile. The behavior of these connections is of special concern in areas where seismic activity poses a threat to infrastructure. This paper discusses the experimental results of a full-scale three-pile bent specimen subjected to a modified earthquake displacement history. This study is significant in the type of loading applied, the scale of the specimen, the inclusion of multiple piles, and the evaluation of differing bent cap reinforcement designs. The specimen was the culmination of an experimental research effort that included eight full-scale single-pile specimens. Results of the full-scale experiment and a numerical model are used for evaluation of the connection as well as comparison between differing reinforcement designs at exterior ends of the bent cap. These results include concrete cracking and spalling, strand slippage, ductility, and the amount of confinement at each connection.

A method for measuring longitudinal strains with the height at a section, and thus the curvature, using a technique based on digital image correlation (DIC), is presented. The background to this technique is introduced as well as previous work in this area. The accuracy of DIC under ideal conditions is established using artificially generated images that represent beams with various curvatures. The practical accuracy of DIC is established by comparing the strains measured using DIC to those predicted by elastic theory and measured using strain gauges for a steel beam. The correlation between these results is found to be excellent. DIC is then used to measure curvatures in RC beams and these results are compared with analytically predicted results with good agreement. The choice of an appropriate gauge length for RC is discussed and is shown to be one of the significant advantages of using DIC as opposed to strain gauges in both laboratory testing and field monitoring of bridge structures.

As the span of conventional cable-stayed bridges reaches 1,200 m or longer, accumulated horizontal force components of the stay cables cause huge axial pressure in the girder, leading to sharp increases of girder dimension and weight, which makes it difficult to compete with suspension bridges in terms of economic consideration. In this paper, a new type of cable-stayed bridge is proposed, namely the partial ground-anchored cable-stayed bridge with crossing stay cables. In this new cable-stayed bridge system, long stay cables cross with each other in the midspan zone of the main span while the other ends of the long cables are anchored to the ground in the side spans. By this design, the long cables result in no additional horizontal pressure to the main girder, and the ratio of pylon height to span length can be reduced. A comparative analysis of this new bridge system with a conventional self-anchored cable-stayed bridge with a main span of 1,408 m is carried out. Results show that by using the new bridge system, the horizontal pressure in the main girder can be reduced by 29.6%, and the total cost can be reduced by 11.8%. Furthermore, the size of ground anchors for this new bridge system is only about 30% of that of a suspension bridge with the same span length. Finally, a cantilever construction method for the new bridge system is introduced as well.