Journal of Bridge Engineering

Skewed steel I-girder bridges experience complex load distribution under live load that is not thoroughly understood, while standard design practice for such bridges consists of simplifications that should be further evaluated and verified. Commonly used line girder analysis (LGA) can estimate strong-axis bending stress through the application of a live load distribution factor (LLDF) that considers the skew effect from 30° to 60°, and it accounts for skew-related lateral response by simply adding a flange lateral bending stress for skew exceeding 20°. Since LGA calculations related to skew do not account for bridge width, and because girder lateral bending response is considered in a simplified fashion, further refinement may be possible. In addition, the widely used practices of designing exterior and interior girders with the same demand and analyzing stub and integral abutment bridges in a similar way need to be further assessed. This paper evaluates the effect of bridge geometric parameters—including skew of 0°–70°, bridge width ranging from 8 to 26 m (27–84 ft), and abutment type (stub versus integral)—on skewed steel I-girder bridge response through a numerical parametric study (using field-validated models), considering live load positioning across the width of a bridge. The distribution of girder strong-axis and lateral bending stress was analyzed, with peak stress compared to LGA calculations. Exterior girders were generally observed with larger strong-axis bending stress but smaller lateral bending stress (versus interior girders) when directly loaded; estimating girder strong-axis bending stress using LGA with a controlling LLDF for all girders can be overly conservative for interior girders. The distribution of strong-axis and lateral bending stress on a skewed bridge with either stub or integral abutments was also found to be dependent on live load positioning, with peak stress closer to bridge obtuse corners (away from bridge midspan) as skew increases. The standard practice of providing a minimum distance between the bridge end and the first intermediate cross-frame was confirmed to be important to avoid lateral bending stress concentration near bridge obtuse corners. Girder response near the bridge pier was generally less significant than that along bridge spans under live loading, except for exterior girder flange lateral bending stress. Near the pier, bottom flange lateral bending stress increases with increasing skew, while interior and exterior girders behave differently under the skew effect for strong-axis bending stress.

An increasing number of arch and suspension bridges have been built in railway networks. Suspender cables serve as the critical load-transmitting component in these cable-supported bridges, which are subjected to a combination of the adverse impacts of train-induced fatigue stress and a corrosive environment. However, little research effort has been made on the corrosion fatigue performance of railway bridge suspender cables. This paper proposes an approach for the corrosion fatigue evaluation of the suspenders that integrates a sophisticated fatigue stress computational model and an enhanced corrosion fatigue model. The dynamic stresses of the suspenders are computed using a three-dimensional (3D) train–bridge interaction (TBI) model, which is established to consider the train-induced flexural vibrations on the suspender. Then, the corrosion fatigue damage of steel wires is characterized by a continuum damage mechanics-based model. The condition for the transition from pitting to fatigue crack is derived. Based on this, the corrosion fatigue assessment framework for suspenders is formulated, which can describe the time-dependent damage evolution that considers significant effects. A tied-arch railway bridge is investigated to showcase the effectiveness of the proposed approach and gain insights into the corrosion fatigue performance of the suspender cables in railway bridges. The field test data are employed to validate the stress computational model. In addition, the time-dependent corrosion fatigue evolution and service life of the suspenders are obtained. The results show that the suspender flexural vibrations cause considerable variations in the equivalent stress range and number of stress cycles. The corrosion fatigue life (CFL) of the critical suspender is reduced by 25% on average due to train-induced flexural vibrations.

Abstract

Fatigue tests were performed on a full-scale deck slab (15,240 × 3,890 × 210 mm) supported by steel girders spaced at 3.05 m using a rolling load simulator for up to 6 million equivalent cycles under two half axle moving loads of 90 kN each, spaced at 1.2 m. The loads were designed to produce the equivalent effect of the CL625 design truck of the Canadian Highway Bridge Design Code (CHBDC). The deck had several sections featuring three different reinforcement designs; namely, steel rebar, glass fiber–reinforced polymer (GFRP) rebar, and GFRP structural permanent form. The steel rebar was designed in accordance to the empirical method in Section 8 of the CHBDC. This paper focuses primarily on the performance of the 3,810 × 3,890 mm steel-reinforced section and compares it to the two adjacent GFRP-reinforced sections. It also introduces a method to define the loading cycle based on vertical deflection and recovery at the center of a section, which could differ from the vehicle travel cycles. As a result, it was shown that the middle steel-reinforced section experienced 6 million cycles, double that of the two end sections. It experienced a 71% reduction in stiffness and its live-load deflection increased by 2.36 times. The live-load strain of its bottom transverse reinforcement reduced from 384 to 264 με, while the strain of the top transverse reinforcement over the support increased from 20 to 301 με after 6 million cycles. The deflection limit of L/800 was satisfied up to 4.47 million cycles. A dense grid-pattern of cracks occurred at the bottom. Few transverse cracks occurred on top and longitudinal cracks developed above the girders.

Practical Application

The empirical design methods in bridge codes provide a convenient way for engineers to design bridge decks with steel or glass fiber–reinforced polymer (GFRP) reinforcement. This paper verifies the fatigue performance of such deck designs under realistic rolling load that simulates the full life of a bridge. The study quantified changes in deflection, stiffness, and strains over time throughout the life of the bridge deck along with the development of cracking patterns. The study is also the first to compare the performance of a GFRP-reinforced deck to that of the traditional steel-reinforced deck under rolling load cycles. A method to quantify the number of cycles the deck experiences is also proposed.

Using composite precast concrete bridge girders supporting cast-in-place bridge-deck slabs is a cost-efficient method because it merges precast and cast-in-place elements while maintaining the monolithic construction’s integrity and continuity. In terms of horizontal shear transfer in composite girders, there is a lack of experimental data on the performance of full-scale fiber-reinforced polymer (FRP)-reinforced composite girders. This study explored an innovative and sustainable approach using noncorroding basalt fiber–reinforced polymer (BFRP) as shear transfer reinforcement in precast concrete bridge girders supporting cast-in-place concrete bridge-deck slabs. Five full-scale composite reinforced concrete T-beams measuring 4,200 mm in length, 420 mm in depth, and 250 mm in width were designed, cast, and tested until failure. The main experimental variables evaluated were the interface shear reinforcement type (BFRP versus steel stirrups), the interface shear reinforcement ratio (0.32% versus 0.48%), and the interface shear reinforcement shape (stirrups versus bent bars). The test results were analyzed in terms of ultimate horizontal shear stress, deflection, slippage, and shear reinforcement strain. The experimental results indicated that the BFRP shear reinforcement provided reasonable shear transfer capacities compared to steel when provided across rough concrete interfaces. In addition, the existing equations in North American bridge design guidelines yielded overly cautious predictions of the BFRP bars’ interface shear strength. The study conclusively demonstrates the viability and potential of using BFRP bars as shear connectors in composite precast concrete girders supporting cast-in-place bridge-deck slab applications.

This study investigates the modification in the seismic response of a base-isolated bridge that is exposed to low temperatures. The isolation system is assumed to be composed of lead rubber bearings (LRBs). The parameters considered in this study (experimental and analytical) are the temperature (0°C, −10°C, and −20°C) and exposure time (3, 6, and 24 h). In the experimental section, a large-sized LRB was subjected to displacement-controlled cyclic motions once it had been conditioned at the desired low temperatures and exposure times. The recorded force–deformation relationships were used to construct deteriorating hysteretic bilinear representations for each loading condition. Then, in the analytical section, several bidirectional nonlinear response history analyses were conducted using the idealized bilinear representations. In the analyses, two sets of ground motion records that were representative of different seismicity levels were selected and scaled in accordance with the codified procedures. The exposure time is a key parameter that needs to be considered in the estimation of the maximum isolator forces (MIFs) that are transmitted to the bridge piers. For the selected parameters, the MIFs of the analyzed bridge model could increase up to 30% with a trend to increase with the increasing exposure time.

This study focused on evaluating the confinement requirements for glass fiber–reinforced polymer (GFRP) reinforcement in circular reinforced concrete (RC) columns subjected to seismic forces, including torsional effects. Seven large-scale GFRP-RC columns were tested under axial and quasi-static cyclic lateral loading. The test parameters included torsion-to-bending moment ratio (t_m) and transverse reinforcement spacing and configuration (spiral and hoops). The experimental results revealed that introducing torsion to the loading scheme reduced the lateral load resistance and drift capacity of the columns. The study recommends adopting a spiral pitch equal to one-sixth of the effective core diameter, as per the Canadian provisions for FRP-RC structures. This spiral pitch significantly enhanced peak lateral load, torque, drift, and twist capacities while ensuring column stability at high drift ratios and preventing complex modes of failure under seismic loading, including torsion. The GFRP spirally reinforced columns consistently surpassed the drift threshold requirements specified by the Canadian provisions for FRP-RC structures. In contrast, hoop-reinforced columns failed at lower drifts, with a notable lap-splice failure observed in columns under t_m of 0.4. It was concluded that using GFRP hoops with a lap splice length of 40 times the bar diameter is inadequate for columns subjected to seismic conditions with torsional effects.

Reinforced concrete (RC) single-column piers (SCPs) and double-column piers (DCPs) are widely used in highway girder bridges. However, the seismic behavior of conventional RC DCPs has not received sufficient attention. This study aimed to investigate the seismic behavior of DCPs, especially the comparison of the failure mechanism, hysteretic behavior, and dynamic response between SCPs and DCPs. To this end, the critical performance parameters between SCPs and DCPs in the elastic phase were first calculated according to the simplified calculation formulas. Eight 1/3 scaled SCPs and DCPs were then fabricated and tested under quasi-static cyclic loading, and the effective height of the DCPs was twice that of the SCPs. The test results showed that the failure modes and damage mechanisms between the SCPs and DCPs are obviously different. In particular, the plastic damage states at the top and bottom of each column in the DCP were asymmetric, and this behavior was also observed on both sides of each plastic hinge region. Subsequently, the relationship between the performance parameters of SCP and DCP in the plastic phase differed from that of the elastic phase and was not proportional. Existing formulas for calculating the plastic hinge length of SCPs cannot effectively predict DCPs and may even underestimate it. Furthermore, numerical simulations were analyzed to investigate the effects of various design parameters and ground motions on the seismic behavior of the SCPs and DCPs.

Progressive and sudden deteriorations are the main reasons affecting the functionality of a transportation network. This paper presents a general probabilistic approach in which the ensembles of regression trees (ERT) are innovatively adopted to predict the life-cycle system reliability of asphalt pavements using Monte Carlo simulations, and pavement segments are considered with bridges in the analysis, prediction, and management of the functionality of transportation networks under both progressive and sudden deterioration due to multiple hazards. Four performance indicators of asphalt pavement subjected to multiple hazards were modeled using ERT trained with the Long-Term Pavement Performance database. The specific hazard types corresponding to each pavement performance indicator for the associated ERT model training were identified. The structural performance associated with bridge superstructures and substructures was analyzed by considering corrosion, traffic loading, and seismic hazards. The proposed approach is illustrated on an existing transportation network in Pennsylvania. The essential retrofitting timing, importance measure, and retrofitting priority associated with the individual component were investigated utilizing the calculated time-variant connectivity-based functionality and resilience associated with the network. The results demonstrate that asphalt pavements have a significant impact on the network functionality and should be considered in the postevent decision-making process of retrofitting strategies.

A circular reinforced concrete (RC) bridge column with two layers of longitudinal and spiral reinforcements is becoming a common structural form in high-seismic regions because they are expected to have improved seismic performance compared to conventional bridge piers. In seismic hazard zones, a large amount of transverse reinforcement is commonly required to satisfy the so-called antibuckling requirements. Accordingly, the double-confined steel (DCS) RC bridge pier is a simple and effective way to achieve high ductility levels and postyield stiffness for bridge piers in seismic regions. In DCS, the longitudinal steel rebars are well distributed inside the cross section; at the same time, the two layers of transverse reinforcement outline different levels of confinement for concrete, including unconfined (cover), singly confined (positioned between two spiral layers), and doubly confined (found inside the inner spiral layer or the core). The adopted reinforcement details, layout, and scale were unprecedented for lateral testing of large-scale DCS. Therefore, this experimental program investigated the effectiveness of DCS as an alternative to typical RC bridge piers. The behavior of large-scale DCS was compared with the performance of conventional RC bridge pier. During the quasi-static cyclic lateral displacement-controlled loading, the onset of cracking, concrete cover spalling, damage progression, plastic hinge length development, lateral load–displacement relationship, and strain in the steel reinforcements were observed. Overall, the curvature, stiffness degradation, and energy dissipation capacity all revealed that the DCS could significantly enhance the seismic performance of a bridge pier. A fiber-based finite-element model was generated to predict the experimental response of the piers under cyclic loading. Charts depicting the relationship between the ratio of elastic stiffness and axial load were developed to serve as a valuable design resource for bridge piers. The charts were created by conducting moment–curvature (M−Φ) analyses on DCS sections. These analyses involved varying the longitudinal reinforcement ratios, reinforcement layouts, and other parameters while also considering different axial load ratios. Subsequently, the performance-based design (PBD) approach was employed to assess the extent of damage relative to engineering demand parameters. Furthermore, a comprehensive example was provided to showcase the design of DCS within the framework of PBD. The findings revealed that DCS successfully met the performance objectives outlined in the PBD guidelines, making it an attractive design option for conventional RC bridge piers.

Bridge bending stiffness, related to bridge material and geometric properties, is considered an important indicator of bridge performance. Accurately identifying bridge bending stiffness is essential for evaluating the condition of the bridge. The bridge influence line (IL), which can reflect the bending stiffness, is widely used for bending stiffness identification. The most frequently employed IL is deflection IL, which is typically extracted from the deflection response of the midspan section. In practice, a fixed reference point below the midspan section is usually unavailable, thus limiting the application of deflection measurements. Furthermore, existing methods primarily focus on simply supported girder bridges, which are not applicable to continuous girder bridges. This paper proposes a method for identifying the bending stiffness of continuous girder bridges by using multiple rotation influence lines (RILs) of the section near the bearing. The rotation responses of the section near the bearing are measured for RIL extraction since the bearing has a platform for sensor fixation and overcomes the limitation of deflection measurements. The distribution functions are introduced for simulating bending stiffness, and their parameters are estimated by an optimization algorithm using multiple RILs. This approach leverages multiple measurement points and is more accurate than the method using a single RIL. The effectiveness of the proposed method for identifying bridge bending stiffness is verified by both numerical simulations and laboratory experiments. A comparison between the identified bending stiffness using multiple RILs and that using a single RIL assesses the applicability of the proposed method.

Tapered beams are characterized by varying moments of inertia along their span, commonly the pier cap configuration used in bridge construction. This study presents the shear behavior of tapered beams reinforced with basalt fiber–reinforced polymer (BFRP) bars through experiments and analyses. Eight BFRP beams were tested to explore the influence of changing inclination angles and the presence of BFRP stirrups. These beams were divided into two groups, each consisting of four beams: one control straight beam and three tapered beams with different tapered angles. The first group was without shear reinforcement, while the second group was reinforced with BFRP stirrups. Results revealed that increasing tapered angles decreased the shear strength of BFRP tapered beams without stirrups but increased it in beams with BFRP stirrups. The analytical part proposed equations to estimate the shear strength of BFRP tapered beams, with findings indicating conservative estimations consistent with experimental data trends.