Journal of Bridge Engineering

Influence line (IL)–based damage indices for long-span bridges are investigated in this study. Their effectiveness is experimentally validated for the first time through the scaled physical model of the Tsing Ma Bridge (TMB). First, the IL mechanism for damage detection and its corresponding damage indices are briefly introduced. Subsequently, the scaled TMB model instrumented with different types of sensors, including displacement sensors, strain gauges, and accelerometers, is introduced. The IL characteristics of different bridge components are compared. Two different damage cases with single- and double-damage locations at the bottom chord were tested. In the single-damage case, different ILs extracted from the nearby components were used for damage identification. These ILs can successfully locate damage visually. The strain IL (SIL) is more sensitive to local damage than deflection IL, but its detection performance degrades rapidly with the increasing distance between sensor and force locations. In the double-damage case, the SIL extracted from a single sensor cannot identify both damage cases because of the limited detectable range of each SIL; therefore, using multiple sensor information becomes necessary. For comparison, the modal parameters were also employed for damage detection. These experimental results validated the merits of the IL–based methods proposed for long-span bridges, indicating that IL–based damage indices are good indicators of local damage detection in long-span bridges. This finding contributes to the development of real-time techniques for damage localization in long-span bridges equipped with a structural health monitoring system.

As a widely used deck system of long-span bridges, the U rib–diaphragm connection in orthotropic steel bridge deck (OSBD) is prone to fatigue cracking under repeated vehicle loads, and the corrosion medium will accelerate the fatigue cracking. To study the influence of corrosion on the fatigue properties of bridges and the fatigue crack propagation law, the three-dimensional (3D) corrosion morphologies of typical OBSD components under different mass loss rates (w) were obtained by the cellular automata (CA) corrosion model. The, the CA model could reflect the electrochemical metal (M_e) corrosion. Then, based on AutoCAD, Rhinoceros, and ABAQUS, the solid model of a U rib–diaphragm connection with surface pits was obtained in ABAQUS. Finally, a multiscale finite-element (FE) model of a long-span bridge with millimeter-scale corrosion pits and cracks was established. The stress intensity factors at crack tips and dynamic fatigue crack propagation at the U rib–diaphragm connection were studied by the extended finite-element method (XFEM), and the difference in fatigue crack propagation life and cumulative energy release rate under different wwere investigated. The results showed that compared with the method of uniform thickness reduction to characterize corrosion effects, the ultimate bearing capacity that was obtained by the CA corrosion model was more consistent with the experimental results. Compared with when the corrosion effects were not considered, when the wof the U rib was 6%, 8%, and 10%, the peak stress intensity factor (K_I) of the crack initiation at the weld toe of the U rib increased by 32%, 49%, and 86% and the fatigue growth life of the U rib–diaphragm was reduced by 6.5%, 18.9%, and 50%, respectively. According to the cumulative energy release rate of the crack initiation at the weld toe of the U rib, the crack was a composite crack that was dominated by the opening model crack, supplemented by the in-plane shear model crack and the antiplane shear model crack.

This paper presented an assembly scheme that was based on bundled bars–grouted corrugated duct connections. The scheme was used for the connection between the bridge column with bundled bars and the cap beam in an elevated subway station. Two 1/3-scale bridge column–cap beam joint specimens were designed and fabricated to verify the scheme. The test specimens included a precast assembly specimen and a cast-in-place (CIP) specimen. Pseudostatic cyclic loading tests were performed to investigate the flexural capacity, failure mode, and hysteretic behavior of the CIP and precast assembly specimens. The test results showed that: (1) the flexural capacity of the precast assembly specimen was close to that of the CIP specimen; (2) the energy dissipation capacity of the precast assembly specimen was weaker compared with that of the CIP specimen; and (3) the assembly scheme that was based on bundled bars–grouted corrugated duct connections was reliable. Finally, the finite-element model for the test specimens was established by calling the PQ-FIBER user subroutine developed by Tsinghua University with ABAQUS to study the seismic performance of the test specimens. Compared with the test results, the finite-element models could simulate the failure mode and hysteretic behavior of the reinforced-concrete specimens.

A partial connection–prestressing (PCP) method is proposed in this paper to decrease the prestress that was transferred to steel girders in the negative moment region of steel–concrete composite bridges. The partial connection is achieved by the application of rubber-sleeved studs (RSS) in the prestressed concrete slab in the negative moment region. Since there is no experimental research on the PCP method in continuous composite girders, to the best of the authors’ knowledge, two continuous composite girders were tested under a four-point static load to evaluate their mechanical performance. The test results showed that without decreasing the ultimate strength and overall stiffness of the steel–concrete composite girders, the PCP method enhanced the cracking load (P_cr) 3.1 times. In addition, 12.5% of the prestressing force was transferred into the steel girder at the internal support section with the PCP method, and the girder without the PCP reached 25.9%. Then, to elucidate the partial interaction effect and prestressing effect on continuous girders’ mechanical behavior, numerical models were developed and calibrated with the test results. From the numerical analysis, compared with normal composite girders, the application of RSS or prestressing could improve P_cr by 11.8% and 157.0%, respectively, and the value increases to 234.3% when RSS and prestressing are applied at the same time. The results indicate that the application of RSS in the negative moment region could effectively increase the prestressing efficiency in the concrete slab and enhance the bridge's durability.

The recent trend of increasing global terrorist attacks and identified vulnerabilities associated with critical bridges highlights the necessity to protect cable-stayed bridges from terrorist assaults. The cables are the most crucial load-carrying components within the envelope of a cable-stayed bridge, whose failure could result in the progressive collapse of the whole bridge structure with disastrous consequences. However, there is a very limited understanding of the blast effects on cables. This paper presents an experimental and numerical investigation of the blast performance of parallel wire cables under close-in explosions. Field blast tests were conducted on three identical parallel wire cable specimens with varying explosive charge weights. An equivalent beam–shell model was developed in LS-DYNA to reproduce the dynamic response of parallel wire cables subjected to close-in explosions and was comprehensively validated against the experimental results. With the validated numerical modeling techniques, the dynamic behavior of parallel wire cables in a realistic blast scenario of vehicle-borne improvise explosive devices (VBIEDs) detonated on the bridge deck was investigated. The results showed that high bending stress was induced in the cable end near the deck, indicating that the cable-to-girder anchorage zone is the most vulnerable position under the close-in blast scenario. Parametric analyses were carried out to further investigate the effects of cable dimension, prestressing force, cable length, and anchorage angle on the dynamic response of the parallel wire cables. It was found that the cables with smaller dimensions and higher prestressing force are more vulnerable, while the cable length and anchorage angle have limited effects on the performance. The results could be used in the safety evaluation and preliminary protective design of cable-stayed bridges under potential blast threats.

The use of lightweight self-consolidating concrete (LWSCC) has significantly increased due to enhanced mix designs and its projected lower overall costs than normal-weight concrete. Accelerated bridge construction (ABC) has become a common alternative to conventional construction techniques. The use of LWSCC in ABC will reduce structural loads and expedite transportation and installation of precast bridge elements. Limited research, however, has investigated LWSCC bridge elements reinforced with glass fiber–reinforced polymer (GFRP) bars. This paper reports on the performance of full-scale edge-restrained bridge deck slabs (simulating slab-on-girder bridges) fabricated with LWSCC reinforced with GFRP bars. The test specimens included three edge-restrained slabs and one unrestrained slab for comparison. The test specimens were 3,000 mm long × 2,500 mm wide × 200 mm thick and were tested up to failure under a concentrated load simulating the footprint of a standard CL-625 truck wheel load (87.5 kN) defined in current design codes. The investigated parameters were (1) reinforcement ratio; (2) top reinforcement; and (3) effect of edge-restraining. The cracking behavior, ultimate capacity, deflection, and concrete and reinforcement strains of the specimens were presented and discussed. In addition, the punching-shear capacity of the tested specimens was assessed with the currently recommended design equations. The test results indicate that the overall performance of LWSCC deck slabs reinforced with GFRP bars is similar to such structures made with normal-weight concrete.

The complex mechanical behavior of a steel–concrete joint (SCJ) in a bidirectional curved pylon of a cable-stayed bridge is investigated using finite-element analysis (FEA) and a 1:4 scaled full-section model test. Formulas for the stress distribution and stress nonuniformity coefficients of the concrete in the SCJ are proposed to evaluate the force transmission characteristic of the SCJ. The FEA results indicate that variations in the section stiffness at both the bearing plate and the end of the steel structure result in abrupt stress changes and distinct spatial force characteristics of the SCJ. The experimental results reveal that the SCJ exhibits better force resistance than the concrete and steel transition segments, and the force transfer is dominant through the bearing plate. The proposed formulas are validated by using the measured results, which reveal significant nonuniformity in the stress distribution. The stiffness variation at the bearing plate, nonuniform concrete stress distribution, and spatial force characteristics should be considered during the design of similar SCJs in spatial pylons.

To avoid fatigue cracking of K-joints in concrete-filled steel-tube (CFST) truss arch bridges, fatigue performance tests and finite-element analysis were conducted to investigate the hot spot stress distribution, fatigue performance evolution, and final fatigue failure pattern of the CFST K-joints. The results of a CFST K-joint were compared with those of a steel tube (ST) K-joint, to reveal the influence of concrete filled in a chord on the fatigue performance of the CFST K-joint. The results show that the hot spot stress of a CFST K-joint can be obtained by quadratic extrapolation. The stress concentration factor (SCF) on the chord side of the intersecting weld of CFST K-joints is larger than those on the brace side, and the maximum SCF is located at the crown point on the chord side of the intersecting weld connecting the tensioned brace to the chord. Because the constraint action of the core concrete improves the radial stiffness of the chord, making the section radial deformation of the CFST K-joint much smaller than that of the ST K-joint, the in-chord concrete could relieve the SCF of CFST K-joints by 19.5%–49.7%. Since the existing SCF calculation methods of ST K-joints and CFST K-joints do not consider the effect of in-chord concrete or the coupling effect of geometric parameters, they are not applicable to the SCF calculation of CFST K-joints. The fatigue crack growth process of a CFST K-joint can be divided into four stages: crack initiation, slow propagation, rapid propagation, and sharp fracture. The fatigue crack propagation speed of the CFST K-joint is obviously slower than that of the ST K-joint due to the effect of the in-chord concrete. The number of cycles corresponding to the 15% change of the peak dynamic strain is recommended as the fatigue life of the CFST K-joint. An S-N curve for fatigue life evaluation of CFST K-joints is proposed. Comparing with the fatigue test in this paper and existing fatigue test of other CFST joints, the proposed S-N curve for CFST K-joints has high precision and safety.

Abstract

Potentially unfavorable stress redistributions could occur in post-tensioned concrete box-girder bridges upon deck rehabilitation by an ultrahigh-performance concrete (UHPC) overlay. The reason for such redistributions is that the deck forms an integral part of the load-resisting mechanism so that deck rehabilitation, namely, the process of removing the deteriorated deck and casting a fresh UHPC overlay, may cause large stress redistributions in the box girder. In addition, the significantly different shrinkage behavior between the freshly cast UHPC deck overlay and the old existing concrete deck below would result in restrained stress in the UHPC–old concrete interface. Therefore, how to evaluate the stress redistributions and the potentially unfavorable stresses in the box girder resulting from construction operations and the incompatible shrinkage is a crucial issue. Here, we propose an analytical model to assess the short- and long-term performances of the concrete box girder during and after deck rehabilitation. The analytical model was verified by using finite-element models incorporating the staged construction simulation and time-dependent behavior of materials. The model can be easily established and calculated with a great amount of time-saving compared with finite-element modeling, and it applies to different types of post-tensioned concrete box-girder bridges. The analytical model involves the balancing-load concept and the age-adjusted effective modulus method (AEMM). The balancing-load concept in the short-term analysis is to account for the prestressing force, and the AEMM in the time-dependent analysis is an effective tool to determine how stresses and strains vary with time due to the creep and shrinkage of a UHPC deck overlay. A parametric study was then conducted based on the analytical model, which involved the thickness of the deck layer to be rehabilitated and the addition of steel reinforcement in the new UHPC deck overlay. Analysis results indicated that pronounced tensile stresses developed in the UHPC deck overlay, which resulted from the restraint of the free shrinkage of the UHPC overlay by the subjacent concrete deck. An increase in the thickness of the newly cast UHPC deck overlay resulted in a decrease of the tensile stress in the UHPC deck overlay, and a rehabilitation thickness of 3.8–5.1 cm (1.5–2.0 in.) was deemed appropriate for the selected bridge according to the analysis.

Practical Applications

Post-tensioned concrete box-girder bridges are one of the most common bridges worldwide. The concrete bridge deck, the surface of a bridge that carries the roadway, is most prone to damage in a bridge due to years of exposure to unfavorable environmental conditions and direct impact loadings from vehicles. The deck rehabilitation for deteriorated post-tensioned concrete box-girder bridges has become an urgent maintenance issue. However, potentially unfavorable mechanical behavior could occur in the bridge during a series of deck rehabilitation operations, that is, the process of deck removal and construction of a new deck. A careful evaluation of the bridge’s mechanical behavior during the entire deck rehabilitation construction process is essential to ensure a safe and feasible deck rehabilitation strategy. Here, we propose an analytical model to evaluate the bridge behavior during and after the deck rehabilitation, which offers an effective and time-saving tool for bridge engineers and researchers to rapidly assess the short- and long-term responses of post-tensioned concrete box-girder bridges. In addition, how rehabilitation thickness affects the bridge behavior during the construction was studied based on the analytical model, and then the appropriate rehabilitation thickness of the deck was recommended according to the analysis.

A number of coastal bridges faced significant damage due to recent natural hazards, inducing extreme waves. The fragility function is the basic step for assessing the resilience of a structure, thereby allowing the designers to alleviate post-event structural disasters and develop improved design methods for new structures. The majority of the focus of fragility functions developed in literature are concentrated on superstructure components and wave load on bridge decks. This paper presents a simplified methodology for the definition of damage states of the substructure component (pier drift) due to wave loads acting on piers as well as the bridge deck. The hazard intensity parameters representing the extreme wave loads chosen for this study are wave period, wave height, and still water depth. The Latin hypercube sampling technique is applied to consider the uncertainties in the intensity parameters as well as the material properties for the finite-element bridge models. Results indicate that the wave period is the most dominant factor affecting the wave-load intensity. The deck-level loading caused a higher probability of failure compared with the pier-level wave loading scenario. In both loading scenarios considered, the elastomeric bearing and shear keys are found to be one of the most vulnerable components in the system-level fragility curves developed. The system-fragility curves generated in this paper can be used to assess the resiliency of coastal bridges subjected to extreme wave-induced loads. The findings of this paper will also add to the risk mitigation and reliability assessment of coastal structures under multi-hazard conditions.

The two support bearings of an elastically supported (ES) bridge may be unequal in stiffness due to aging or other factors. This paper proposed an effective technique of using the contact residual response (CRR) generated by a two-axle test vehicle in its round-trip movement to detect the weak end and frequencies of the bridge. First, the round-trip CRR is presented in closed form. It is featured by three facts: (1) the CRR is given in terms of the vehicle–bridge “contact” response and thus is free of the annoying vehicle’s frequency; (2) being created as the “residual” of the responses of the two axles, the CRR is immune to the disturbance of the surface roughness; and (3) by letting the vehicle move in “round trip,” the weak end of the bridge can be detected, while all the bridge frequencies are enhanced. A procedure is presented for calculating the CRR considering the discrete nature of field measured data recorded by the test vehicle. In the numerical study, the closed-form solution is validated using the finite-element method (FEM). The results from a realistic example demonstrated that weak-end amplification can be clearly recognized for the CRR (both temporal and spectral) for the vehicle moving in a round trip. Such a feature enables the weak end of the bridge to be easily detected. The other advantage is that more bridge frequencies of higher orders can be identified using the CRR generated by the vehicle moving from the weak end.