Journal of Bridge Engineering

This study reports on experimental test results of reinforced concrete pier caps with different shear spans to effective depth ratios (a/d) of 0.5, 1, and 1.5. Each test specimen is then designed theoretically using both shear friction (SF) and strut-and-tie modeling (STM) approaches, according to Section 16.5 and Chapter 23 of ACI 318-14, respectively, and the results are compared with the pier caps experimental test results. The cracking load, failure load, deflection, crack pattern, crack width, steel reinforcement strains, concrete surface average strains, and failure modes are observed, recorded, and discussed. The experimental load capacities are compared with the theoretical load capacities of SF and STM. Experimental test results indicate that both STM and SF are conservative approaches and STM is more conservative than SF. The reason for this is because they do not take secondary reinforcement into direct consideration. That is why, a model is proposed, modifying STM, for estimating the ultimate capacity of pier caps based on calculating the strength of concrete and secondary reinforcement separately that gave more realistic results.

Collision of overheight vehicles into bridge superstructures often leads to structural damage, posing an immediate risk to the safety of motorists and the functionality of bridges. Considering the proven vulnerability of current high-strength concrete (HSC) girders to impact-induced forces, the use of ultrahigh-performance concrete (UHPC) (to fully or partially replace HSC) is expected to improve the impact resistance of bridge superstructures. However, despite the growing attention that UHPC has received for various bridge applications, this important application has remained largely unexplored. This motivated the current study to perform a holistic investigation to (1) quantify how the performance of bridge girders subjected to overheight collision can be improved by a one-to-one replacement of HSC with UHPC; (2) assess how UHPC can be considered as a material of choice for repairing existing bridge girders impacted by overheight vehicles; and (3) examine how equivalent UHPC girders designed for a performance similar to HSC girders under service loads can introduce advantages when subjected to overheight collision. For this purpose, upon validating a set of finite-element models with experimental test results, numerical simulations are performed on two types of AASHTO girders. The simulations cover two impacting objects, i.e., a concrete conduit pipe and a cylindrical steel tank, in addition to a tractor–semitrailer. The structural performance measures of the bridge girders made of HSC (entirely), UHPC (entirely), HSC repaired with UHPC, and equivalent UHPC are then evaluated and compared based on the recorded damage patterns, impact forces, internal shears, and lateral displacements. The outcome of this study provides the necessary details to shed light on how a transition from HSC to UHPC can contribute to improving the overall safety and performance of new and retrofitted bridges, especially when subjected to overheight collision.

In this study, field testing is conducted on two full-scale guideway reinforced concrete (RC) beams, one reinforced entirely by glass fiber–reinforced polymer (GFRP) and the other by conventional steel, under 450 passes of two-car monorail trains at various speeds and vehicle loads. The two beams were part of a 1.86-km test track traveled by trains for 4.5 months. The objective of the study was to evaluate GFRP bars as a sustainable reinforcement for transit infrastructure, particularly for monorail trains. The study showed that cracking and stiffness degradation in both beams occurred during train loading with one-loaded and one-empty cars, after 79–132 cumulative train passes. Cracks stabilized after 149 accumulative passes. Deflection in the GFRP-RC beam, measured during train passes at fully loaded cars, was 36%–47% higher than that in the steel-RC beam. After 200 accumulative passes, stiffness was reduced to approximately 43% and 57% of the original uncracked value for GFRP- and steel-RC beams, respectively. By the end of 450 passes, stiffness in the same beams appeared to have stabilized at 38%, and 50% of the uncracked value. The GFRP-RC beam satisfied all serviceability limits imposed in national codes. A two-dimensional finite-element analysis was also performed on the test beams, showing good correlations with test results of deflections and cracking patterns. Of the six analytical equations that were used to estimate the effective moment of inertia and subsequently beam’s deflection, only those by Branson and Bischoff seemed to yield acceptable predictions.

The recent development of automated operational modal analysis (OMA) has enabled the modal tracking of environmental and operational conditions. Variations in these conditions have prevented investigations into the long-term characteristics of the damping ratio due to its inherently high degree of scattering. In this study, the long-term damping characteristics of a twin cable-stayed bridge under environmental and operational variations were investigated. A displacement reconstruction algorithm was applied to resolve the model-order dependency in OMA-based damping estimates. In order to automatically establish groups of modal estimates, optimal parameters for a density-based unsupervised clustering algorithm were proposed on the basis of gaps between target modal frequencies. The proposed clustering parameters were first validated by comparing the clustering results with those of manually determined ground truth classes. Next, the applicability of the clustering parameters for long-term damping estimation was demonstrated by quantifying the dispersion of modal estimates in each cluster. Subsequently, the framework was applied to 2.5 years of monitoring data to evaluate the long-term damping characteristics of the twin cable-stayed bridge that is often subjected to high variations in environmental and operational conditions. The following aspects are mainly discussed: (1) seasonal fluctuation in long-term damping ratios; (2) the effect that aerodynamic interference exerts on variations in the dynamic characteristics; and (3) the amplitude dependency of the damping ratio. The probability distribution of the modal damping ratio is provided based on the statistical analysis of reliable modal damping ratios.

Load distribution factor for truck loads is a key parameter in evaluating the load-carrying capacity of existing bridges. This study aimed to investigate load rating procedures for reinforced concrete bridges using the tools of numerical analysis. In this study, three-dimensional finite-element modeling was used to estimate shear and bending moment demands and capacities for a sample of 10 (five flat slab and five T-beam) reinforced concrete bridges. The results were compared with those obtained using current rating procedures in accordance with AASHTO specifications. This comparison showed that the current two-dimensional analysis with the distribution factor approach resulted in lower estimates of the bridge rating, mainly due to the simplified representation of structural members and lack of consideration of the contribution of nonstructural elements. To further explore the impact of this observation, a focused parametric study was conducted to investigate the effect of geometrical features such as edge elements on moment and shear estimates. The findings confirmed the sensitivity of calculated demand considering superstructure edge elements primarily, railings, curbs, and sidewalks found in these bridges.

Buffeting-induced oscillations of hangers at a suspension bridge have been addressed in this work. The buffeting is obtained by a dynamic finite-element analysis procedure in the time domain, with simulated turbulent wind fields and experimentally obtained load parameters. Wind loadings inherent to the hangers are neglected intentionally to exclude potential interference. Dynamic properties of hangers are simulated by discretizing them into a number of elements. The numerical results show that a number of long hangers can experience large-amplitude oscillations due to the main structure’s buffeting at a moderate wind speed. Motions of the hangers are mainly contributed by their first-order modal shapes. The hangers oscillate in both directions in the horizontal plane, with motions in the longitudinal direction being more violent than in the lateral direction. Moreover, it is found that the dominant frequency of a single hanger in one direction differs slightly from that in the other, thereby causing an ever-changing phase angle between the two motions. Fourier transforms of the time series indicate that excitations resulting in the resonances are from the main cables. The functional motion component at cable-hanger intersections can be as small as a couple of millimeters, which can result in hangers’ motions as large as 300 mm. Replacement of steel wire hangers with carbon fiber-reinforced polymer (CFRP) ones can restrain effectively the resonance. However, replacements over an insufficient range of hangers may result in transferring of the resonance to neighboring ones, and a comprehensive mitigation necessitates replacements over quite a wide range along the bridge deck.

Stainless steel strands are a new technology and option available for the bridge industry. They have high corrosion resistance, which will result in more durable and low-maintenance concrete bridges. However, stainless steel strands have lower ductility and different stress–strain behavior than carbon steel strands, affecting the design criteria for prestressed concrete girders. Stainless steel strands have already been deployed in substructure components (piles) in many projects around the United States. However, due to their low ductility and lack of full-scale research studies and structural design approaches, they have not yet been deployed in flexural members. This study investigates the flexural behavior of stainless steel strand prestressed concrete girders. Five full-scale 12.8-m (42-ft)-long AASHTO Type II girders prestressed with 15.2-mm (0.6-in.)-diameter duplex high-strength stainless steel (HSSS) strands were designed, fabricated, and tested in flexure. The prestressing reinforcement ratio was varied in this experimental program. The transfer length and prestress losses of 15.2-mm (0.6-in.)-diameter HSSS strands were measured. The flexural behavior of the girders was assessed by the evaluation of cracking load, ultimate load-carrying capacity, load-deflection response, and failure mode. As designed, all girders failed due to rupture of the HSSS strands. Experimental results showed that, although the HSSS strand has low ductility and it may control the capacity of the girders, adequate warning (noticeable deflection and many cracks before failure) can be achieved in HSSS strand prestressed concrete girders. The predicted analytical and numerical moment strengths of the five girders were in close agreement with those measured experimentally. Although the analytical model gave better predictions, the numerical approach is easier to use for design. A flexural design approach for HSSS strand prestressed concrete I-girders is proposed where rupture of strands is an acceptable failure mode. The findings from this experimental program will be useful for the development of new design specifications for concrete girders prestressed with stainless steel strands.

To ensure bridge safety under vehicular traffic, the owners must systematically verify the adequacy of bridge live load-carrying capacity. Bridges are evaluated for design, legal, and permit loading. The legal load rating uses AASHTO legal trucks, which meet the Federal Bridge Formula requirements. However, each state has a federal law exemption for truck weight and size. The state-specific grandfather provisions allow the operation of legally overloaded vehicles. Thus, the objective of this study is to determine whether the current live load factors provide adequate safety for exempted vehicles because there are no provisions for overloaded vehicles under grandfather provisions. This study presents a reliability-based analysis to determine state-specific live load factor for bridge rating on an example of Montana’s 20% overload allowance for agricultural vehicles. This approach does not require a reanalysis of the state bridge inventory. Linear scaling of existing rating results from bridge records can be used to determine ratings for agricultural vehicles. The study provides a calibration method to maintain the required minimum safety level with the minimum cost and effort.

Beams that are strengthened with a plate at a soffit are susceptible to premature failure (peeling and debonding). Internationally available design standards provide varied recommendations that need to be compared. In addition, the models are too simplified (ACI440) or complex (FIB14), which miss some key parameters. This study will attempt to extend the design recommendations by proposing theoretical solutions based on the design codes (BS:5400 and IS:456). Ten different cases of possible modes of failure will be specified that specifically categorize peeling and debonding. Experiments will be conducted to identify the reasons why peeling failure is different from shear failure, which is an important criterion for the selection of appropriate models. The selected predictive models will be compared using a database of 507 beams to identify safety zones. Experiments from the literature will be selected to cover a wide range of geometrical and material properties and will be used to conduct parametric studies, which will lead to the design recommendations. ACI440 and FIB14 deviated significantly from the experimental observations. The results (with practical significance) and Chi-squared test (χ²) demonstrate that the proposed design formulations and recommendations are suitable to predict the moment capacity and failure mode.

Bearing displacement is a necessary monitoring index for a long-span bridge because abnormal bearing displacements could result from structural deterioration or damage. Therefore, an early warning method is established for bearing displacement of long-span bridges. In this study, a novel time-varying temperature–displacement nonlinear model, which can eliminate the model error induced by temperature field simplification, is first proposed to accurately estimate bearing displacement. Then, early warning methods for abnormal displacement and out-of-bounds displacement of bearings are established using estimation errors, and different warning levels are delineated depending on combinations of the two types of early warning, followed by an implementation procedure for the early warning method. Finally, the long-term monitoring data of a large-span bridge are utilized to validate the advantage of the proposed time-varying model and the effectiveness of the early warning method. The results show that the modeling and prediction errors of the time-varying model are smaller than that of the linear model. Additionally, attention needs to be paid to the changes in the warning information for bearings with large modeling errors, which will correspond to a relatively high warning level.

Due to its complex geometry and mechanical behavior, the prestress design of the cable–pylon anchorage zone is difficult to achieve but critical. In this paper, the use of the strut-and-tie model (STM) is evaluated to simplify the cable–pylon anchorage zone design. The traditional Evolutionary Structural Optimization (ESO) method is first used to generate the STM of a common one-box two-cell cable–pylon anchorage zone. However, the resulting STM is shown to be irrational by comparison with the real distribution of principal stress in the cable–pylon anchorage zone. Therefore, this paper proposes a tailored ESO method using a modified algorithm for the removal criterion based on the strain energy of the element. The proposed method is shown to overcome the drawback of the classical ESO method that some elements playing key roles in the distribution of principal stress, but having small von Mises stresses, may be deleted mistakenly. The prestress design of the Cao’e River Bridge is then presented using the correct STM generated by the tailored ESO method as a practical example. Finally, the rationality of the resulting prestress design of the cable–pylon anchorage zone is substantiated using the results of a full-scale model test.

In comparison with the short-term behavior of bridges in the early stages of their service life, predicting the long-term behavior of the concrete due to their shrinkage and creep effects is a more complex and difficult task. Curved steel–concrete composite box bridge girders have been widely used in urban highway interchanges and ramp bridges due to their lightness in weight, long spanning capacity, and high torsional stiffness. Presently, there are a few experimental studies on the long-term behavior of steel–concrete composite beams, but none of them focus on curved composite box beams. This paper reports the long-term test results of 5 scaled curved composite box beams, including 4 simply supported beams and 1 continuous beam. The span length of the 4 simply supported beams is 6.2 m and the span length of the 2-span continuous beam is 6.8 m. The beams are tested under sustained uniformly distributed loading for 222 days. In the test, the vertical deflection, interfacial slip between the concrete and the steel beam, rotational angle, and normal strain of the concrete slabs, rebars, and steel beams are measured. In addition, a concrete prism specimen is tested under uniaxial compression to measure the shrinkage and creep effects under the same environmental conditions as the beams. The research shows that shrinkage and creep of the concrete have significant effects on the long-term mechanical performance of composite beams. This experimental study contributes to the literature on the long-term behavior of composite beams and provides data for subsequent studies on the development of theoretical and numerical models of curved composite box beams.