Journal of Bridge Engineering

The technique for extracting bridge frequencies from a moving vehicle was proposed only recently. However, its efficacy may be reduced by road-surface roughness. To this end, the stochastic subspace identification (SSI) is modified to deal with the present time-variant coupled noisy vehicle–bridge interaction system. First, the governing equations for the vehicle and bridge are expressed in state space, including the effects of road roughness and multiple vehicles. Then, they are discretized and transformed to a form suitable for SSI by separating the known from the unknown parameters. Using the Hankel matrix along with the orthogonal projection theorem and singular value decomposition, the observability matrix derived with the vehicle effect suppressed can be used to identify the bridge dynamic properties. It is demonstrated that (1) the proposed SSI approach is more effective for identifying bridge frequencies below 20 Hz for the cases studied, compared with conventional approaches; (2) adding a little damping to the test vehicle can help suppress the vehicle frequency using the proposed approach; and (3) the ongoing traffic is beneficial for amplifying the frequencies of bridges with rough surface.

Cover plates are often added to built-up steel columns as an effective retrofit method for increasing strength. For retrofitted columns, the original member carries all loads, whereas the added cover plates resist only the loads applied after their addition. As a result, the original member may yield before the added cover plates. Although some specifications provide guidance for evaluating the capacity of retrofitted columns, the approaches are conservative and do not address the behavior of retrofitted columns if portions of the original cross section yield first because of preload. In this paper, the behavior and strength of retrofitted built-up columns, as well as the influence of the cover plates, are evaluated using two analysis approaches: (1) three-dimensional finite-element analysis and (2) nonlinear inelastic column buckling analysis. Both approaches include the effects of geometric imperfections, column slenderness, cyclic loading, and temperature gradient on the behavior and strength of retrofitted columns. The failure modes of the retrofitted columns depend on the column slenderness ratio ($KL/r$). For short columns, the failure mode consists of compression yielding of the entire cross section, where the existing section yields first, followed by the cover plates. For slender columns, the failure mode consists of inelastic flexural buckling about the weak axis. The existing section yields first, significantly reducing the flexural stiffness of the retrofitted section.

Infrared thermography (IRT) is a promising nondestructive evaluation technique that has been widely used for bridge deck inspection. It is a quick and fairly simple method for providing preliminary information about defected areas in bridge decks. However, detection capabilities and sensitivity to environmental conditions and material properties impose certain challenges for the application of IRT. In this paper, the effect of various concrete mixtures on passive IRT was investigated. Four concrete mixtures (i.e., conventional, high-strength, self-consolidated, and lightweight concrete) were considered in the evaluation. Various defects with relatively small sizes placed at different depths were simulated and planted in cast-in-place slabs. The casting and testing took place in the United Arab Emirates (UAE), which is considered a hot-weather region. The defected slabs were imaged, and the existence of defects was judged visually. A minimum of 0.8°C was used for successful detection to make a more confident judgment for the existence of a defect. In addition, the images were compared with those of nondefected slabs to enhance the judgment of defect detection. Thermal conductivity of each mix was estimated using the Maxwell–Eucken two-phase composite-material model, and rapid chloride penetration was tested and used as an indication of concrete density. The slabs were imaged during the cooling cycle. Results showed that mix variation had a significant effect on IRT. High-strength concrete provided the highest detection possible among the mixes. Results also showed that the higher the density and thermal-conductivity coefficient, the better the defect detection using IRT under ideal imaging conditions. For the UAE, ambient conditions are favorable for passive IRT because the results indicated minimal sensitivity to wind, relative humidity, and temperature, as opposed to other locations in the world where passive IRT would not be applicable. Nevertheless, because of its limitations, IRT would better serve as a health-monitoring technique using baseline comparisons rather than as an independent inspection tool for bridges.

Accelerated bridge construction (ABC) is a feature incorporating new technologies, advanced planning, and new detailing to expedite bridge construction. Accelerated bridge construction offers many benefits, the most important of which is faster onsite construction. Precast systems and members are the key components of ABC. Even though the application of precast systems is common in low and moderate seismic regions, implementation of precast columns in high seismic zones has been scarce because of uncertainty in the seismic performance of precast member connections. Three low-damage materials, ultrahigh-performance concrete (UHPC), engineered cementitious composite (ECC), and nickel–titanium shape memory alloy (NiTi SMA), were incorporated in this study, in either the connection or the plastic hinge of a half-scale bridge column test model to develop a precast column that exhibits improved seismic performance over columns built cast-in-place with conventional materials. The column damage was significantly lower than in a reference cast-in-place column (CIP) in which the precast column damage was limited to only ECC cover spalling after 12% drift-ratio cycles. The precast column average residual displacement was 79% lower than that in the CIP, ensuring postearthquake functionality of bridges built with the proposed system. A UHPC-filled duct connection used in the column-to-footing connection showed no damage even after 12% drift-ratio cycles. A simple finite-element model was developed to simulate the column test responses. Good correlation between the measured and calculated local and global responses was achieved.

Development of the long-gauge fiber-optic sensor provides an excellent opportunity for structural-change localization, because it measures averaged strains over a long gauge length. A practical structural-change localization, procedure using long-gauge dynamic strains in the modal space is proposed to process the ambient vibration data of a steel-stringer bridge. The proposed procedure is easy to execute by general bridge engineers; meanwhile, it has a solid theoretical basis, thus guaranteeing its effectiveness. By theoretically deriving the magnitude ratios between the analytical strain frequency response functions (FRFs) and the estimated strain FRFs from ambient vibration data, it is proved that the proposed procedure is the same as using long-gauge strain mode shapes for change location; therefore, it is effective and much simpler for general bridge engineers to use. An ambient vibration test of a steel-stringer bridge using long-gauge fiber-optic sensors has been performed. The results of applying the proposed method to the measured and simulated data of the bridge have successfully verified its effectiveness for structural-change localization.

Because of the influence of the stochastic nature of structural properties and field measurements, the identification result of damage extent is, in essence, uncertain, causing possible deviations and affecting the reliability of the identification result. To give a probabilistic measure on the identification result of damage extent, a reliability-based damage identification method based on dynamic signatures is proposed in this study. The Monte Carlo simulation in conjunction with the response surface method is used to perform the reliability analysis of damage identification with given accuracy, and a trial-and-error procedure is proposed for conducting damage identification with acceptable reliability. The influence of both structural uncertainties and measurement noises on damage identification can be taken into account in the present approach. Meanwhile, the proposed method is capable of assessing the robustness of different types of dynamic signatures against noise and the sensitivity of various random parameters involved in structural damage identification. The present approach is applied to the probabilistic damage identification of a simply supported beam and a long-span arch bridge, indicating the feasibility and effectiveness of the proposed method for both simple structural components and complex structural systems.

Because the deterioration rate of bridge decks is higher than that of other bridge components, intermittent replacement of bridge decks stands to be a viable approach to extending bridge service life without replacing entire bridge components. A lack of understanding of the effects of concrete removal on the horizontal shear capacity of existing shear connectors led to a question being raised about the necessity of removing all of the concrete during a deck replacement. The purpose of this study is to investigate the influence of the remaining concrete around the shear connectors on the horizontal shear capacity of the shear connection. An experimental program consisting of push-out testing was implemented. Twenty-seven small-scale specimens were fabricated using three different concrete removal levels (50%, 75%, and 100% concrete removal) and three types of shear connectors (shear stud, channel, and angle plus bar). Push-out testing was conducted for all the fabricated specimens until the specimens failed. During testing, the ultimate horizontal shear load of each shear connection and the slip between the concrete deck and the steel girder were recorded. The failure modes of all specimens were also documented. Subsequently, simplified analysis and finite-element (FE) analysis were conducted to assist understanding and interpreting the test results. On the basis of the experimental and analytical results, it was found that the horizontal shear strengths of the three types of shear connections were not sensitive to the quantity of concrete removed.

Relatively slight bracing of steel girders can significantly reduce the risk of buckling failures before the composite action between steel and concrete occurs. This paper aims at both experimentally and numerically, studying the torsional bracing performance of a typical type of scaffoldings that are commonly used in bridge construction. Minor improvements in the structure of the scaffoldings and in their connections with steel girders were needed for this purpose and are discussed in this paper. In the numerical investigations, the effects of different initial imperfections on bracing properties of the scaffoldings were also investigated. The study was extended to different bridge lateral-torsional buckling slenderness ratios and geometries. Results showed that the proposed system greatly increased the load-carrying capacity of the studied bridges with consideration of lateral-torsional buckling during the construction phase. Brace forces created in the scaffolding trusses were also measured in both the experimental and numerical investigations. Finally, indications of the brace moment versus in-plane moment values for different magnitudes of initial imperfections and lateral-torsional buckling slenderness ratios are given.

Three-dimensional (3D) finite-element analysis of a 106 × 200 × 106-m concrete box girder was conducted to study the effect of solar temperature gradients on long-span bridges during construction. Segments over the internal piers and at midspan were investigated to obtain temperature distributions and thermal stresses during critical times of the day. On the basis of results of the thermal analysis, temperature gradients were developed for 0600 and 1500 hrs. to be used on the entire bridge. The maximum longitudinal tensile stress in the girder was 2.67 MPa, whereas lateral tensile stress could reach 4.41 MPa. Therefore, appropriate measures must be taken during construction to avoid cracking of the box girder. A 3D model of half the entire bridge was analyzed to obtain the effects of thermal loads on the bridge in its longest cantilever construction stage. The maximum vertical deflection at the cantilever end reached 46.0 mm at 1500 hrs., when the effect of temperature was highest. It was concluded that the deflection as a result of temperature gradients should be accounted for when determining the formwork elevations in the segmental cantilever construction process.

A better understanding of the relationships among girder stresses, cross-frame design, and skew angle of two steel I-girder bridges, which have moderate and high levels of skew and differing cross-frame designs, was revealed via field testing under various load passes of a weighed load vehicle. Strains were measured at approximately 100 points on the two structures, and the majority of the instrumentation was located on the cross-frames. The data were analyzed in terms of vertical bending, lateral bending, and warping in the girders, and in the magnitudes and distribution of stresses in the cross-frames of the two structures. These metrics were compared between the two bridges and in relation to the assumptions typically used in contemporary bridge analysis. This comparison revealed the following: the magnitudes of lateral stresses were higher than current design guidance suggests in some cases when staggered cross-frames were used; significant magnitudes of warping stresses in the girder webs, which state-of-the-art analysis methods generally fail to consider; and cross-frame stresses that exceeded the values typically considered in design.

The performance of two real-life California bridges is assessed under a possible regional multihazard condition involving floods and earthquakes. For flood events with varied frequency, expected scour depths at bridge piers are calculated and incorporated in finite-element analyses (FEAs) of the bridges under earthquakes that represent regional seismic hazards. Based on FEA results, fragility curves of bridges are developed at component and system levels. Fragility surfaces are generated to acquire comprehensive knowledge on bridge failure probability for the combined effect of earthquake and flood events of varying frequency. Quantified bridge vulnerability is applied to a risk evaluation framework that combines hazard probability with bridge failure consequences. Obtained results depict that the occurrence of flood events can increase the seismic vulnerability and risk of bridges, although the amount of increase depends on bridge attributes. Bigger (large-diameter) foundations tend to reduce the impact of flood hazard on bridge seismic performance. Moreover, the multihazard response of the bridges indicates that the seismic design philosophy used for bridges can play a role in attaining the seismic safety of bridges with flood-induced scour at the foundations.

Several methods are used to increase the lateral displacement capacity of the piles supporting jointless bridges, the most effective of which are predrilled holes and a flexible pile-cap connection. Depending on soil type and required displacement capacity, these two methods can be combined. This paper discusses a simple study carried out to demonstrate the efficiency of the flexible-head condition, and a finite-element analysis conducted on a prestressed pile. The model was first calibrated with the test results, and then a flexible detail was applied to the model. The results of this part of the study show that a flexible connection can increase the displacement capacity of embedded piles. Finally, nonlinear analyses were conducted using simulation software for compact HP piles. The results of these analyses revealed that strong axis bending results in larger displacement capacity compared to weak axis bending, although the stiffness is smaller in the latter case. Provisions are also developed to account for partial fixity. The paper concludes by providing design provisions for H-piles for the application of a pinned head detail that will allow the use of jointless bridges in conjunction with longer bridge lengths.

A new steel orthotropic deck was installed on the Bronx–Whitestone Bridge (BWB) between 2005 and 2006. In May 2007, longitudinal cracks were found by visual inspections underneath the deck plate in the rib-to-deck welds and have continued to occur. As of 2014, these rib-to-deck weld cracks have required weld repair of approximately 305 m (1,000 ft) of the 65,374 m (214,480 ft) of rib welds in the new orthotropic deck. Detectable cracks have occurred randomly in 66 of the 408 shop-fabricated deck panels. This paper’s focus is on modeling the crack propagation of the defective welds with fabrication-related hot cracks so that estimates of the possible cracking from these fabrication defects can be predicted. Creation of this model also involved considering truck traffic using the structure and the wheel paths along with the supporting ribs most likely to experience stress cycles during service.

This article presents the results of an investigation of the wind-induced resonance of hangers on a long-span suspension bridge. The data from field observations, numerical simulations, and wind tunnel experiments presented in this article show that the hangers experience buffeting-induced resonance oscillations and that the source of the excitation is the buffeting of the main cables to which the hangers are attached. Because of the dense natural frequencies of the main cables and the broad-spectrum structural buffeting that takes place, it appears that these oscillations occur as energy is transferred from the main cables to the hangers. Hence, it is the main cables rather than the hangers that trap energy from the oncoming turbulent wind field. The numerical results presented indicate that the resonance of the hangers could be sensitive to positions along the bridge deck, wind speeds, and damping ratios. This article also includes the results of simplified wind tunnel experiments that verified this kind of resonance, disregarding whether the wind loads developed directly on the hanger.

As a structural optimization technique, topology optimization is an important tool for helping designers to determine the most suitable shape of a structure. With this powerful tool, designers can define families of candidate solutions by modifying the input volume reduction (VR) ratio, reducing the structural weight as much as possible. However, finding the best compromise between material savings and structural performance among these candidate solutions is a critical issue for designers. To deal with this issue, an optimization index (OI) is presented in this paper. It provides a mathematical procedure that highlights the best choice among several candidate solutions obtained by the optimization procedure. The index was originally defined in a previous study on the structural optimization of composite steel-concrete bridges. In this paper, a generalized version of the original optimization index is introduced and used to investigate a particular aspect related to concrete shell-supported bridges. Starting from three shell-supported footbridges, the shapes of which are the final result of form-finding optimization procedures, different starting models are defined, and each is characterized by different edge-stiffening conditions. Despite using an anticlastic shell shape, unavoidable tensile stresses occur because of the thickness of the shell, variations in the material, the loading of the deck, and other factors. For each starting model, a finite-element topological optimization conducted with the solid isotropic material with penalization (SIMP) method is performed to minimize the weight (i.e., volume) of the shell by a certain percentage. According to the results obtained from topology optimization, the proposed generalized optimization index (OI*) analytical formulation is discussed in detail, and its effectiveness is validated.

This paper provides a very efficient, integrated framework for seismic analyses of long-span cable-stayed bridges. The efficiency comes from the dramatic reduction in formation time and the degrees of freedom (DOF) associated with the structure, using the integrated finite strip method (IFSM) along with the application of a very robust and efficient time history method (THM) using the Newmark scheme for dynamic analysis of the bridge structure. The previous versions of the finite strip method are limited to modeling the bridge deck only, whereas other structural components are replaced by assumed boundary conditions. Using the IFSM, all components of the long-span cable-stayed bridge can be modeled in a unified system, and consequently, the real dynamic behavior including the interactions between deck, piers, and cables can be perfectly considered. To verify the solution, the geometric and dynamic properties of the Kap Shui Mun (KSM) Bridge, as a real example of a long-span cable-stayed bridge, are derived by the proposed finite strip method. Then, the seismic response of KSM Bridge under uniform and nonuniform earthquake loadings is investigated by using the THM. The results show that the IFSM can be applied successfully for seismic analysis of long-span cable-stayed bridges, and the analysis can be performed in a minimal amount of time.

This paper presents the findings of an experimental and analytical research study that was conducted to evaluate the buckling behavior of steel bridge piles with localized severe section loss. Seven full-scale H-piles with different degrees of simulated corrosion were tested under axial compression. A nonlinear, three-dimensional (3D), finite-element model was developed to predict the inelastic buckling behavior of corroded piles under axial compression loading. The model was validated by comparison with the experimental results. The validated model was used to conduct a parametric study. Six parameters were investigated: (1) pile slenderness, (2) reduction of the flange thickness, (3) reduction of the web thickness, (4) location of the corroded region, (5) extent of the corroded region, and (6) magnitude of the residual stresses. The results indicate that the reduction of the flange thickness is the most significant factor affecting the inelastic buckling behavior. The pile slenderness and the magnitude of the residual stresses affected only the capacity of piles for which global buckling was the dominant failure mode. The experimental and numerical results were compared to three existing design methods to evaluate the suitability of the current design specifications for predicting the axial capacity of steel compression members with localized corrosion.

Because of a lack of research on torsion, the Canadian design codes and AASHTO design specifications do not provide torsion provisions for the design of concrete bridge members reinforced with fiber-reinforced polymer (FRP) bars and stirrups. This paper reports on eight full-scale RC beams tested under pure torsional loading. The beams measured 4,000 mm long, 250 mm wide, and 600 mm deep. The test variables were the type and ratio of torsional reinforcement. Sand-coated glass-FRP (GFRP) and carbon-FRP (CFRP) bars and stirrups were used. The test beams included three beams totally reinforced with GFRP, three beams totally reinforced with CFRP, and two control beams reinforced with conventional steel. One beam for each of the three types was built without stirrups to determine the concrete contribution to torsional resistance. The test results indicate that all specimens failed as a result of diagonal torsional cracking. The test results were analyzed and compared with the corresponding predicted values using the new design provisions in recent standards. In addition, the cracking torsional strengths were compared to the available design equations in the literature (elastic theory, skew-bending theory, codes, and standards). The results of this study can be used as a fundamental step toward code provisions for using GFRP or CFRP stirrups as transverse torsional reinforcement in RC bridge and parking-garage applications.

The present paper deals with optimum performance of the shape memory–alloy-based rubber bearing (SMARB) compared with the conventionally adopted lead rubber bearing (LRB) for isolating the bridge deck against a random earthquake. Specifically, a systematic study on the optimum performance of SMARB is conducted and compared with the LRB to minimize the acceleration of the isolated deck subjected to a stochastic earthquake by addressing the limitation on the excessive isolator displacements. The optimal characteristic strength of the bearing and respective responses are obtained by solving a bi-objective optimization problem. The responses required for this are obtained by nonlinear random vibration analysis via stochastic linearization of the cyclic nonlinear force-deformation behavior of the shape memory?alloy restrainers. The robustness of the improved performances of the SMARB was studied through extensive parametric studies with respect to the variation of the system parameters and the scenario of earthquake loading. The results clearly indicate facilitation of the trade-off among the isolation efficiency and the bearing displacement in the SMARB over the conventional LRB. The approximate closed-form expressions for obtaining the proposed optimal parameters and system responses might be helpful in establishing an initial design.

The design and verification of built structures requires structural engineers to consider accidental loading situations. The accidental loading situation investigated in this paper is heavy-goods vehicle (HGV) collisions with roadside structures; focus is on the design of bridge-supporting structures. The impact loads were determined from Monte Carlo simulations of a probabilistic model in which highway traffic measurements and accident statistics in Sweden are input. These loads were calculated for structures adjacent to straight roads as well as roads with curvature, and include considerations of the directional load components. Comparisons were made between the simulation results and approaches given in design codes, with focus on the Eurocode. The simplified approaches provided in the code were inadequate in their treatment of these design situations. Alternative equations for calculating impact forces and energies are presented. These equations can be used for determining design values for impact forces or for conducting probability/risk-based assessments of bridge supports subjected to HGV impacts. In this way, a more consistent treatment of HGV impacts in the design of bridge structures is achieved.

The Sarah Mildred Long Bridge, an 854-m (2,804-ft) double-deck truss bridge in Portsmouth, New Hampshire, was struck by a 144-m (473-ft) cargo ship on April 1, 2013. After days of visual inspection and assessment, it was found that the main damage, significant bending of a vertical and a diagonal truss member, required replacement of the impacted members. According to the New Hampshire Department of Transportation, the repair cost $2.5 million. Before and after repairs, the authors collected vibration data on the bridge. This was a rare, valuable data set of a major structure at its damaged (prerepair) and healthy (postrepair) states. In this paper, the authors detail the data analyses and results and compare data collected before and after repairs at the Sarah Mildred Long Bridge. A finite-element model (FEM) of the damaged bridge span was created to compare the field data. By studying the frequency responses of the vibration data and the FEM, the authors were able to identify and explain noticeable changes between the bridge’s healthy and damaged states.