Journal of Bridge Engineering

Moment redistribution is important in the ductile design of concrete structures, but moment redistribution in externally prestressed concrete (EPC) continuous curved beams has not yet been studied. Neutral axis depth approaches to moment redistribution in current design codes are based on the test results of straight beams, which are not applicable to continuous curved beams. This paper presents experimental results for three three-span EPC curved box beam specimens, including their failure processes and modes, the strains in the reinforcement and concrete, and the full-range behavior of the neutral axis depth. The test results show that moment redistribution occurred from cracking of the specimens to their failure. The test results also reveal a significant difference in the mechanical behavior of the inner and outer sides of the specimens. A method for conversion of the neutral axis depth is proposed, and the calculated results, which are typically conservative, are compared with the test results. The test results show that flexural yielding in curved beam specimens did not induce a sudden increase in torsion before moment redistribution as the European standard would predict.

This paper presents experimental and analytical studies on the punching shear behavior of concrete-filled steel-tube (CFT) bridge column to pile-foundation connections. Five CFT bridge column to reinforced-concrete (RC) four-pile cap connections were constructed and tested under monotonic downward vertical loads to the columns, and the effects of the connection details, including embedment depths of CFT columns, shear studs, face annular rings, and headed shear reinforcement, on punching shear behavior were evaluated. Test results indicate that the connection details significantly affected the cracking patterns of pile caps and the failure modes of connections. The use of shear studs, face annular rings, headed shear reinforcement, and reduced embedment depths of CFT columns can substantially enhance the punching shear strength of CFT column to RC-pile cap connections. The tested specimen with a face annular ring welded onto the CFT column base showed the most favorable punching shear behavior with the highest loading capacity and the most ductile failure mode. On the basis of the experimental observations, the effective depths of pile caps for CFT columns under punching were proposed, and then the punching shear strength of the tested connections was predicted using current design codes for the design of RC footings. A modified empirical strength model was also developed on the basis of experimental and finite-element analysis results.

Corrosion of girder ends is a prevalent problem that significantly reduces the bearing capacity of bridges. Current repair methods are expensive and difficult to implement. A novel repair method was developed for steel girder ends with corrosion damage using ultrahigh-performance concrete (UHPC) to encase the corrosion. For this repair, UHPC panels were attached to girders with shear studs welded to the web and flange surrounding the corroded area. This allowed shear and bearing forces to transfer from the girder to the UHPC panels. The UHPC panels provided a new load path, thereby increasing the bearing capacity of the girder. Half-scale experiments were conducted on undamaged, damaged, and repaired rolled steel girder specimens. The test results were used to (1) determine the decrease in bearing capacity attributable to section loss, (2) demonstrate the ability of the UHPC repair to restore lost girder capacity, and (3) investigate the constructability of the repair method. The experimental results show that the UHPC repair was easily implemented and succeeded in restoring bearing capacity lost as a result of corrosion damage.

Current bridge provisions limit the contribution of the reinforcing steel in concrete shear interface design to a yield strength of 420 MPa (60 ksi). Because of this, the higher yield strength of high-strength steel (HSS) reinforcing bars cannot currently be used in design. Only a limited number of tests have been performed to characterize the shear friction resistance of members containing HSS, and results from these tests indicate that using the full HSS reinforcing bar yield stress capacity could overestimate the shear interface capacity of the specimens. However, shear friction design using HSS reinforcement at its yield strength, if shown viable, could provide constructability benefits. In this work, the effect of HSS reinforcement on concrete–concrete shear interface capacity is investigated. The specimens had varying reinforcing steel ratios (0.42 and 0.64%), bar sizes [#13M (#4) and #16M (#5)], and steel grades [Grade 420 (60 ksi) and Grade 550 (80 ksi)]. Four sets of five push-off test specimen types were tested for a total of 20 specimens. All push-off specimens were designed to have similar interface shear resistance using current design equations. Testing results indicate that although the peak strength capacity of the specimens reinforced with Grade 550 #16M (#5) bars was greater than that of the Grade 420 #16M (#5) bars, a similar increase was not observed in the #13M (#4) specimens in which negligible differences were observed in the peak strength. However, the use of HSS reinforcement increased the postpeak sustained loads.

This study investigated damage detection of cable structures in bridge engineering using the virtual distortion method (VDM). The main theory of damage detection based on the VDM, including the influence matrix, the stiffness reduction, and an optimized algorithm, was applied to damage detection in hangers in a real three-dimensional finite-element model (FEM) of an existing arch bridge. Two damage-detection methods for hangers were used. One method is based on the static VDM, which has high precision but requires more sensors. The other method is based on the dynamic VDM, which does not require many sensors but has a lower precision. The effectiveness of damage detection in hangers was investigated through a numerical simulation. The steps of damage detection that can be combined with practical engineering were determined. The anti-interference ability of the wind load, the optimal placement of sensors, and the antinoise capability were considered in the case study. It was verified that the proposed methods can rapidly and accurately identify the damage location and degree of damage.

Although prestressed concrete (PC) bridges with corrugated steel webs have become a promising form of bridge, their long-term behavior is not well understood. A study of their long-term behavior is reported. A numerical model to account for the creep and shrinkage of concrete and tendon relaxation was formulated and verified by test. Because the assumption that plane sections remain plane, commonly adopted in Euler-Bernoulli and Timoshenko beam theories, is not valid, an extended sandwich beam theory was used considering the presence of diaphragms and external tendons. The long-term behavior of a typical bridge of this type was studied and compared with that of conventional PC bridges with flat steel and concrete webs. The effects of diaphragm and interaction between web shear deformation and local flange bending of the bridge were found to relieve with time. Moreover, the long-term deflection of this type of bridge was larger than that of the counterpart bridges.

This paper proposes two new models for the simplified seismic analysis of seismically isolated highway bridges with massive piers. Both models include two components, one of which includes the superstructure mass, the isolators, and massless pier, and the other one the pier with its distributed mass and stiffness properties. In one model, the isolator stiffness is added at the top of the pier in the second component. The total seismic response is obtained from the square root of the sum of squares (SRSS) of the two individual component results. Applicability and accuracy of the models were assessed by considering bridges with wide ranges of stiffness and mass properties of piers (M_p) and superstructures (M_ss). Multimode spectral analysis (MMSA) and nonlinear time-history analysis (NLTHA) were used to define reference solutions for the superstructure displacements, vibration periods, and shears and moments at pier bases. Results from four currently available models, including the model prescribed in American and Canadian bridge codes, were also examined. The study shows that current models for the simplified analysis method yield good estimates of superstructure displacements and vibration periods; however, they generally underestimate the shear and moment demands at pier bases. The errors are more significant for more massive piers or when the stiffness of the piers is high compared to that of the isolators. In contrast, for all bridges studied, the seismic responses from the proposed models show very good agreement with those from the MMSA. Better predictions are obtained when considering the isolator stiffness in the second component of the model. The NLTHA results also show that the proposed models give overall satisfactory predictions for pier base shears and moments. The proposed models extend the range of application of the American and Canadian code simplified method to isolated bridges with massive piers while preserving its simplicity with limited extra computational effort.

This paper presents the results of the first shake-table tests of a large-scale rubberized concrete column. The rubberized column was formed by replacing 20% of the volume of fine aggregate with crumb rubber. The response of the rubberized column was compared to that of a conventional bridge column. Both columns had the same construction details, and the only difference was the material used. Both columns were subjected to a sequence of scaled historical ground motion recorded in the Northridge-01 1994 earthquake with near-fault pulse-like characteristics. The conventional column formed a flexural plastic hinge with rebar fracture after 14 scaled test runs, corresponding to 140% of the design earthquake. The rubberized column experienced the rebar fracture after 19 test runs, corresponding to 190% of the design earthquake. The rubberized column achieved a strength that was only 3% lower than that of the conventional column. Moreover, the rubberized column displayed a 12.5% increase in the lateral drift capacity. The dissipated energy of the rubberized column increased by 16.5% compared with the conventional column.

Recent research on ultrahigh-performance concrete (UHPC) for connection elements in highway bridges indicates an improvement in the performance of the overall bridge superstructure. However, there is limited information on the effect of the material and bond strength of the UHPC on the load transfer mechanism between adjacent box girders. A three-dimensional finite-element (FE) model was developed to study the interface between UHPC and high-strength concrete (HSC) highway bridge connections. The UHPC-HSC interface was modeled using traction-separation, damage initiation criteria, and damage evolution while taking into account adhesion, friction, and the nonlinear material behavior. Material properties were determined directly from laboratory testing, and the interface parameters were identified through model calibration using direct tension test results and friction coefficients reported in the previous work. The model was validated by simulating the laboratory tests conducted at the Federal Highway Administration (FHWA) Turner-Fairbank Highway Research Center (TFHRC), and good agreement between numerical and experimental results was obtained. Finally, numerical simulations of two adjacent box-girder models using the proposed interface parameters and other interface models from past research were compared, and the results highlight the importance of using a high-fidelity model to accurately represent the system behavior.

Ultrahigh-performance concrete (UHPC), with its enhanced strength and durability, has been proposed as the joint material in adjacent box-beam bridges to address the issue of longitudinal cracking. Recently, the Federal Highway Administration (FHWA) performed laboratory testing of two adjacent box beams connected by a UHPC shear key containing transverse shear reinforcement bars (SRBs), and the results suggest that an improvement in the overall performance of adjacent box-beam bridges may be achieved by using the new shear key design. However, there is no information about the load transfer mechanism within the new connection. The aim of this research is to perform finite-element (FE) analysis of the two adjacent box-beam models to investigate the load transfer mechanism in, and ultimate load capacity of, the new FHWA shear key design. The three-dimensional FE model used in the study was validated based on the FHWA laboratory test results. The model is used to identify the roles of the UHPC material, the transverse SRBs, and the shear key surface roughness on the load transfer mechanism between adjacent box beams at different load levels, and to investigate the suitability of widely accepted criteria for shear key condition/performance for the new shear key design. The results of the analysis show that a shear key with a smooth surface and minimum transverse SRBs is sufficient for load transfer between adjacent box beams for the load level used in the FHWA testing and that a shear key with a sandblasted surface and minimum transverse SRBs is capable of transferring load up to failure of the box-beam system. The results of the analysis provide valuable useful insight into the shear key behavior, which can be used to optimize the design of future UHPC shear keys.

This paper presents a parametric study that identifies the relevance of soil-structure interaction (SSI) on the static stiffness matrix of bridge piers founded on caissons. Bridge piers and caissons with different geometric features and foundation soils characterized by low or high shear wave velocity are encompassed. A discrete model for the foundation-soil system (lumped-spring approach) and a single-degree-of-freedom (SDOF) scheme for the superstructure are adopted to analyze the coupled system of pier, caisson, and soil. The SSI is introduced in the structural model by concentrated springs and masses taking into account the embedment of the caisson. For each case of the parametric study, the ratio between the overall stiffness of the soil-caisson-pier system and the stiffness of the pier in its fixed-base configuration is evaluated by defining the geometrical and mechanical parameters that play the primary role. Last, a closed-form equation combining the key parameters is developed for providing a unique parameter that allows engineers to quickly assess the relevance of SSI in bridge pier design before performing cumbersome and time-consuming interaction analyses.

For concrete box girders with wide flanges, a ribbed slab can increase the cantilever length and transverse stiffness while reducing the dead weight of the deck. For single box girder bridges with a large width-to-span ratio, the traditional cross section of a single-cell box girder (the two-web box section) can lose efficiency because of the effect of shear lag, cross-section distortion, and transverse bending moments. A literature search revealed that the prestressed concrete box girder with transverse ribs is already used in certain countries to meet the requirements of wide bridge decks of single-cell concrete box girders. However, little research has been conducted on the mechanical properties of this spine-like box girder, although it has been used in many applications. In this paper, the structural forms and dimensions of a concrete box girder with wide flanges and a ribbed slab are introduced on the basis of design experience. A significant difference in the mechanical performance of ribbed box girders and conventional box girders was observed in the influence of the stiffened ribs. Therefore, on the basis of engineering practices, three representative three-dimensional (3D) finite-element models (i.e., ribbed box girder, equivalent box girder, and ordinary box girder) were established to quantitatively investigate the influence of stiffened ribs on transverse stress under the action of gravity and vehicle loads. The results of this investigation can be used as a reference for designing and constructing similar projects.

The determination of a suitable strut-and-tie model (STM) of a number of disturbed three-dimensional (3D) domains is a challenging task. To overcome this problem, this paper presents a performance-based ground structure optimization method for automatically generating optimal STMs in 3D concrete structures. In this method, first, a new microtruss element in which each internal node provides equal opportunities for transferring loads is proposed. Then, an equivalence mode between the microtruss element and the continuum element is introduced to ensure a realistic and precise simulation of actual structures. Finally, several examples are used to demonstrate the capability of the proposed approach for revealing the true mechanisms of the load transfer in 3D concrete structures. The numerical results indicate that the developed algorithm can generate optimal STMs that are supported by design specifications and previously existing solutions and can be used in practice, especially in complex disturbed concrete structures for which STMs cannot be obtained by general optimization methods. Generally, the procedure presented in this paper is limited to homogeneous material with linear constitutive laws.

The nonlinear flutter featured by the limit cycle oscillation (LCO) is a typical aeroelastic phenomenon for bluff decks and/or streamlined decks at large incidence angles. In this study, the flutter characteristics of a streamlined deck were investigated by using comprehensive wind-tunnel tests, and a nonlinear mathematical model was introduced to model the aeroelastic behavior of the nonlinear torsional flutter oscillation. The nonlinear aerodynamic force is the major source of the nonlinear flutter. The nonlinear flutter LCO corresponds to a state in which the energy absorbed by the linear damping and the energy dissipated by the nonlinear damping are balanced within an oscillation period. On the basis of the instantaneous amplitude and instantaneous frequency calculated by using the normalized Hilbert transform, a system identification method was developed to simultaneously extract the linear and nonlinear aerodynamic parameters. The efficacy of the nonlinear mathematical model and the identification accuracy of aerodynamic parameters were validated by two examples. The sensitivities of aerodynamic parameters to the signal length were studied, and the corresponding causes were revealed. The linear aerodynamic damping parameter and structural damping ratio are the dominant parameters for determining the critical flutter wind speed. For the nonlinear torsional flutter, a practical approach was proposed to predict the critical reduced wind speeds and the LCO amplitudes with different structural damping ratios, and its accuracy was verified by comparing the experimental results.

Structural identification (St-Id) is an effective structural evaluation approach for health monitoring and performance-based engineering. However, various uncertainties may significantly influence the reliability of St-Id. This paper presents ambient vibration measurements to develop a baseline model for a newly constructed arch bridge over Hongshui River in Guangxi, China. In this study, modal parameter identification was performed using the random decrement (RD) technique together with the complex mode indicator function (CMIF) algorithm, and the results were compared with those from stochastic subspace identification (SSI). First, a three-dimensional (3D) finite-element (FE) model was constructed to obtain the analytical frequencies and mode shapes. Then, the FE model of the arch bridge was tuned to minimize the difference between the analytical and experimental modal properties. Three artificial intelligence algorithms were used to calibrate uncertain parameters: the simple genetic algorithm (SGA), the simulated annealing algorithm (SAA), and the genetic annealing hybrid algorithm (GAHA). The simulation results showed that GAHA exhibited the best performance in mathematic function tests among the three methods and that the large-scale arch bridge could be efficiently calibrated using a hybrid strategy that combines SGA and SAA. To verify the admissibility of the calibration procedure, a sensitivity analysis was performed for the Young’s modulus of the steel members, and the relative error for the static deformation of the bridge deck was determined. Finally, to verify the accuracy of the results, a multimodel updating method based on Bayesian statistical detection was analyzed for further validation. Through a detailed St-Id study using precise modeling, operational modal analysis (OMA), and the artificial intelligence algorithms, the authors confirmed the accuracy of the updated FE model for further structural performance prediction.

Among components of a suspension bridge, suspenders transmit wind or live loads on the deck to the main cable, which are then transmitted to the pylons, and finally to the earth. Suspenders are vulnerable to corrosion caused by harsh environments and fatigue due to live loads, and they often have a shorter life span than that of other components. In this paper, premature failure of short suspenders in a suspension bridge is investigated with monitoring data and finite-element (FE) simulation, and a replacement method is proposed and implemented on the bridge. The investigation and discussion in the paper is fourfold. First, premature failure of the short suspenders in a suspension bridge is investigated, with the most severe damage found to be in the cylindrical bushing of the pin connection between the suspenders and the deck. Second, monitoring data analysis and FE simulation are conducted to find out the reasons for the premature damage of the short suspenders. Third, a replacement method using temporary suspenders was proposed, and field implementation of suspender replacement was performed. Finally, conclusions are drawn that could shed light on the maintenance and replacement of short suspenders in suspension bridges.