Journal of Bridge Engineering

This study evaluated the potential benefits of using buckling-restrained braces (BRBs) to seismically rehabilitate straight bridges. For this purpose, a three-span RC box girder bridge was used as a case study. A three-dimensional model was developed using software to incorporate BRBs between bent columns. The BRB inelastic behavior was represented using the Menegotto–Pinto model to reproduce its isotropic and kinematic strain-hardening properties. Nonlinear time-history analyses were performed to assess the seismic performance of the BRBs and the existing RC bridge. The structure was evaluated under several performance limit states using far-field records, which were scaled to the maximum considered earthquake level at the site using an average interval scaling method. The results show that BRB components improve the seismic performance of bridges under serviceability and ultimate limit states by decreasing drifts in the bents and by reducing the steel and concrete strains of the original RC columns. The retrofit BRBs redistribute and dissipate energy in the transverse direction of the bridge, and reduce the potential failure in the concrete columns and abutment shear keys.

An innovative bridge that includes prefabricated folded-plate girders (FPGs), precast-posttensioned lower sections of the integral abutments, and a precast T-wall gravity wingwall system is studied. Some results are specific to the girder system, but others can be generalized to single-span integral-abutment bridges and to the durability of prefabricated elements. Data were collected during construction, static live-load testing, and long-term monitoring and were compared to finite-element modeling. Stresses in concrete and steel components remained low throughout construction, long-term data collection, and truck-load testing. Live-load test data indicate that the elastic neutral axis of the FPG is higher than that calculated and that positive shear lag (nonuniform girder flange stress) is observed under localized point loads. Limiting the movement of the wingwall and directing attention to the curing of cast-in-place elements would further improve the quality of future bridges. Observations on the daily thermal gradient are applicable to other single-span integral abutment bridges and show that reversed thermal gradient (superimposing day strains from a warmer deck than girder on cold days and night strains from a cooler deck on warm days) can lead to higher girder stresses than those observed on the hottest or coldest days.

This paper presents an application of the embedded data collector (EDC) approach using strain and acceleration measurements at the top and bottom of a pile (drilled shaft) during dynamic loading (Statnamic) for estimation of static side and tip resistance. For assessment of the skin friction, wave propagation along the pile was modeled as a one-dimensional (1D) wave equation with nonlinear static skin friction and viscous damping. The soil–pile system was divided into segments, and each segment was characterized with independent multilinear skin friction. The skin friction of each segment was determined by least-squares fitting of computed particle velocities to the measured data at the top and bottom of the pile. For assessment of the tip resistance, the pile tip was modeled as a single—degree-of-freedom nonlinear system. A nonlinear stiffness–displacement relationship was determined by balancing force and energy from inertia, damping, and stiffness against the measured tip data. The technique was applied to a side- and tip-grouted drilled shaft 7.8 m in length with various cross sections (1.05-m diameter for top segment and 1.20-m diameter for bottom segment). The estimated static resistance was compared to results from top-down static compression loading and the segmental unloading point approach during Statnamic testing.

A new system for framing curved bridges using precast prestressed concrete girders is introduced. The main feature of the new system is the use of relatively short [6–12 m (20–40 ft)] straight girder segments that are joined and posttensioned to form a full-length curved girder. The visual impact of the deviation of these chords from a true curve is indistinguishable by a casual observer. However, it greatly simplifies production of precast curved girders, which are currently produced in full-span piece lengths. Another feature of the new system is utilization of two of the most commonly used precast concrete girder shapes: I-girder and U-girder. The straight-line bridge girder forms and prestressing bed can be used for the proposed curved girder system, saving considerable initial capital and allowing more precasters to compete for this type of bridge. The result is a better value of the cost-effective precast concrete stringer system compared to curved steel, cast-in-place concrete, and segmental precast systems. This paper presents the components of the new system and proposed construction stages. It also presents an overview of the analytical and experimental investigations conducted to evaluate the constructability and structural performance of the proposed system. Preliminary design aids are presented to assist in determining suitable girder size for different span lengths and radii of curvature.

Numerous fatigue cracks have been observed in many orthotropic bridge decks that have been in service for a long time. The cracks around rib-to-deck (RD) joints might affect traffic safety. In most current design specifications, the asphalt surfacing is treated merely as a layer dispersing wheel loads. To investigate critical transversal load cases for RD joints and to assess the influence of temperature and dynamic loads on stresses around RD joints, a full-size orthotropic bridge-deck specimen with asphalt surfacing was subjected to wheel loads under different thermal and dynamic conditions. Experimental results show that the most critical transversal load cases occurred when dual wheels traveled over the RD joint and also around adjacent RD joints. Stresses around RD joints were found to be extremely sensitive to asphalt temperature and dynamic loads. Hence, the asphalt’s temperature, vehicle speeds, and the number of heavy axles of trucks should be considered when evaluating RD joint fatigue life.

Many county highway agencies have explored different options for economical replacement of existing deteriorating bridges. Using retired railroad flatcars (RRFCs) as the bridge superstructure is an attractive and sustainable option for some owners with very limited budgets and where traffic volumes are low. Using RRFCs is also environmentally attractive because they are 100% recyclable. Previous research focused on the development of guidelines to address the uncertainty that exists when load rating these types of structures. Those guidelines were based on field testing conducted on existing RRFC bridges. However, questions remain about the response under loads higher than could be easily achieved during the field testing. Further, although most RRFC bridges utilize timber decks or thin plate decks covered in bituminous material, there is evidence suggesting that installing a traditional composite RC deck is actually more economical and greatly improves load distribution. This paper presents the results of laboratory testing of a RRFC bridge and the revision of previously proposed load-rating guidelines for RRFC bridges constructed with composite concrete decks, using experimental data and finite-element analysis.

Cover plates are often added to existing (loaded) steel columns as an effective retrofit method for increasing their compressive design strength. Current bridge design specifications provide equations for calculating the compressive design strength of steel columns. However, these equations cannot be extended to calculate the design strength of retrofitted columns because they do not account for the effects of cover plates added to the existing loaded members. The authors previously investigated the fundamental behavior of retrofitted built-up steel double-box columns using the finite-element analysis approach and also developed and benchmarked a nonlinear inelastic column buckling (NICB) analysis approach that accounts for the mechanics of existing (loaded) built-up steel columns retrofitted by added cover plates. This paper presents the results of comprehensive parametric studies conducted using the benchmarked NICB analysis approach to evaluate the behavior and strength of retrofitted steel columns. The parameters included are the geometric imperfection magnitude, locked-in dead-load ratio, cover-plate properties (yield stress, width, and thickness), and column-slenderness ratio (KL/r). Results from the parametric studies are used to propose revisions to the existing design equation. The proposed equation can conservatively estimate the axial compressive strength of retrofitted steel columns with (i) doubly symmetric sections and (ii) singly symmetric sections bending about the axis of symmetry. This is confirmed by using the equation to predict the axial compressive strength of retrofitted steel columns with different cross-sectional shapes. Finally, a design example is presented to illustrate the implementation of the proposed design equation.

This study focuses on the shear-friction behavior of a groove interface with transverse reinforcement between existing concrete and newly poured concrete, which has been adopted in the rehabilitation project of three prestressed concrete box girder bridges in China. A series of push-off specimens with groove interfaces was tested with parameters of concrete strength, groove geometry, and reinforcement ratio. For comparison purposes, monolithic specimens and roughened specimens with or without transverse reinforcement were also tested to failure. Cracking loads, ultimate loads, residual strengths, cracking patterns, and failure modes were recorded. Load-slip curves, load-dilation behaviors, and load-strain relationships in steel reinforcement have been investigated. The groove on the surface of the existing concrete can significantly enhance shear-friction capacity of the interface between new and existing concrete. The transverse reinforcement can improve deformation capacity and residual resistance. The nonsimultaneous failure of concrete and steel reinforcement is revealed. Based on the shear-friction mechanism, the test results are compared with the existing design provisions. Design details on applying the proposed groove interface in the actual bridge rehabilitation are suggested.

The Texas Department of Transportation (TxDOT) uses precast prestressed concrete slab beams in a side-by-side configuration for short-span bridges in low-clearance areas. To reduce costs, a new bridge type called a spread slab beam bridge was recently developed using the same concept as spread box beam bridges in which the beams are spaced apart. A full-scale spread slab beam bridge was constructed and tested under static and dynamic vehicular loads to evaluate constructability and structural performance. The load-distribution behavior was investigated through field testing, and experimental live-load distribution factors (LLDFs) were evaluated using alignments that provided the most adverse loading cases. The measured response provides detailed experimental data to validate computational modeling techniques for this new class of bridge systems. Research findings show that spread slab beam systems provide a viable construction method for short-span bridges, and that the desired performance was achieved for in-service loading. During field testing, the beam live-load deflections were within the design limits, and no significant cracking or reduction in the overall stiffness of the bridge was observed.

Because a large longitudinal force exists in hybrid girder cable-stayed bridges due to the cable tension, its transfer mechanisms on the steel-concrete combination segment would be an important issue. In this study, experiments and theoretical analysis were conducted to characterize the longitudinal force transfer mechanisms of the steel-concrete combination segment in hybrid girder cable-stayed bridges. Five full-scale local structure specimens were designed and manufactured based on the original design of the steel-to-concrete transition zone according to a completed cable-stayed bridge in China. The specimens were subjected to monotonic loading and tested up to complete failure. The load-slip curves; stress distribution and failure modes, which varied with the thickness of the bearing plate; and the shear connector distribution were obtained. To simulate the test properly, calculation methods for predicting the shear connector capacity and corresponding load-slip curves were proposed based on the analysis and experimental results including headed studs and perfobond strip connectors. Thus, a finite-element model using a nonlinear spring to simulate the shear connectors was proposed and validated by the test. Force transfer mechanisms were analyzed, and load distributing between different components of this composite system were revealed. As a result, the load distributing mode could be used to instruct preliminary engineering design and the modeling method could be used to verify it.

Three important issues related to vibration serviceability were investigated in this study using a slender steel footbridge: (1) the evaluation of footbridge vibrations by passive people (standing still on the footbridge) and active people (pedestrians); (2) the increase in vibrations when a group of people walk/run on a footbridge compared with a single pedestrian crossing the structure; and (3) the modal damping ratios for vibration analysis of footbridges. Using the results of a number of dynamic tests, relationships between various evaluation parameters were established, and more reliable and consistent limits based on the vibration dose values (VDVs) are proposed. In addition, a simplified method of computing the acceptable level of peak acceleration based on average number of footbridge crossings per day for the performance-based (usage-based) serviceability design of footbridges is suggested. The investigation on the group effects showed results consistent with those of past studies when the pedestrians crossed the footbridge at the average normal speed of 2 steps/sec. However, the footbridge vibrations resulting from a group of people increased less than the reported value in the literature when people walked randomly and more than the reported value when they moved at the first-mode resonance frequency of the structure. Based on the results of the dynamic field testing of the footbridge, a modal damping ratio of 0.6–0.8% for steel footbridges with timber decking is recommended.

Dry joints represent locations of discontinuity in precast concrete segmental bridges (PCSBs) through which compressive and shear stresses must be transmitted. Cracks in dry joints occur more easily than those in epoxy joints during the construction period or in service. Steel fiber-reinforced concrete (SFRC) with high rupture strength might be beneficial to the shear resistance of dry joints. In this study, shear behavior of various types of dry joints in PCSBs was investigated by experiments, especially focusing on shear strength of keyed dry joints of SFRC. The experimental parameters were joint types, concrete types, key numbers, contacting portions in the sliding plane, and horizontal confining stress levels. Cracking loads, cracking patterns, failure modes, and ultimate loads were recorded. Normalized shear stress-vertical slip curves and load-horizontal dilation relationships have been investigated. It can be concluded that the use of SFRC can improve shear strength and ductility of dry joints in PCSBs. The experimental results obtained from tests were compared with other design provisions. These provisions underestimate the shear capacity of single-keyed dry joint specimens of conventional concrete and SFRC and overestimate those of three-keyed dry joints of conventional concrete, whereas the design formula can accurately predict the shear strength of three-keyed dry joints of SFRC.

This study investigates the behavior of ultrahigh-performance fiber-reinforced concrete (UHPFRC) joints between precast concrete panels reinforced with glass-fiber-reinforced polymer (GFRP) bars that are being used in the first cable-stayed bridge in northwest Ontario, Canada (Nipigon, Nipigon River Bridge). The test panels, which simulated the deck panels of the Nipigon River Bridge, were fabricated at the same precast facility in Ontario and delivered to the University of Sherbrooke for flexural testing until failure. The test matrix included eight panels measuring 3,000 mm long × 1,000 mm wide × 220 mm thick. The tests included three reference specimens without structural joints (one reinforced with steel bars and two reinforced with GFRP bars) and five jointed specimens (one reinforced with steel bars and four reinforced with GFRP bars). The structural joint width was a constant 220 mm for all jointed specimens. The specimens were tested in a cantilever-panel setup with the UHPFRC joint subjected to the maximum negative moment and shear load. The experimental results are presented and analyzed considering the cracking pattern, reinforcement strains, and the load–deflection response to investigate the performance of UHPFRC joints. The experimental shear strength was compared with the predicted values using the available bridge code provisions. The tested joints showed adequate strength and performance, and the failure occurred in the spliced concrete panels. The tested UHPFRC joints maintained the continuity and made the adjoining panels act monolithically.

Premature fatigue cracking in the tube-gusset plate connection of longitudinal diaphragms has been observed in long-span cable-stayed bridges, resulting in undesirable stress distribution of the decks and costly repair efforts. Based on field inspection and finite-element (FE) simulation, this paper presents a diagnosis of the fatigue damage, and it is found that under the vehicle loads the connections are subjected to large stress cycles and significant stress concentration exists around the cope holes. The secondary stresses caused by bending result in different degrees of cracking among the eight locations of the diaphragm within a chamber. To mitigate such damage, several retrofit measures, including plug welding at the slot end, crack-stop holes, welded plates, and bolted channels, were applied. According to field observation and FE simulation, it is found that although the plug welding, crack-stop holes, and welded plates may slightly mitigate the cracking, they cannot significantly elongate fatigue lives. The bolted steel channel connections, however, have an acceptable life without decreasing the stiffness of the diaphragms.

Vessel collisions with bridges occur frequently worldwide and have the potential to cause enormous casualties, substantial property loss, and environmental destruction. Physical protection systems designed for bridge piers against vessel collisions are viable solutions to alleviate/prevent those disruption costs. This paper introduces a floating steel fender system for bridge pier protection and evaluates the performance using an explicit dynamic finite-element analysis code. The analysis method is validated against available drop-weight impact tests of a steel box module, because the steel fender system is constructed by repeatedly stacking and aligning a similar subassembly. The introduced fender system noticeably reduced the peak impact force applied on a bridge pier by approximately 55.3% and on the colliding vessel by approximately 56.2% while extending the impact duration approximately 273.1% as compared to the head-on collision without any protection. It was also shown that the initial kinematic energy of the barge before impact was mainly dissipated by plastic deformation of the steel module (57.5%) and colliding barge (16.5%), as well as the damage of the rubber dampers after impact. The results indicate that the floating steel fender system has excellent energy-absorbing capabilities.

The nonobjective disadvantages of the force-based frame element, such as the nonobjective curvature prediction, have been discussed by many researchers. The trial-and-error method is commonly used to determine element size, but it could cost tremendous computational efforts. This paper proposes and analytically studies the optimal element size for reinforced-concrete piles for bridges when using force-based beam elements. In this study, the relationship between the optimum element size and integration point number is investigated, and the equivalent plastic hinge length is used and correlated to the optimal element size, on the basis of which the moment-curvature and force-displacement responses are objective and the soil effects on the pile response could be simulated sufficiently as required. The results of a case study show that both the local and global responses can be very well predicted, and the nonobjective disadvantage of the force-based element could be eliminated using the proposed optimal element size. Additionally, the optimal element size with more than two integration points is suggested for modeling the plastic hinge in the pile above the ground.