Journal of Bridge Engineering

The stability of stiffened plates has always been an important research issue in bridge engineering. The application of stiffened curved plates (SCPs) in the field of bridge engineering is gradually increasing, but the corresponding research needs to be more comprehensive. Guidelines have yet to be established in bridge design codes for the stability design of SCPs. To study the failure mode and ultimate resistance of SCPs with trapezoidal longitudinal stiffeners under uniaxial compression, six test specimens with a scale ratio of 1:2 were designed in this work, and static loading tests were conducted on three kinds of SCPs with different curvatures. The influence of curvature on the ultimate resistance and failure mode of SCPs was analyzed, and a calculation method for the ultimate resistance of SCPs was discussed. Results showed that the SCPs with trapezoidal longitudinal stiffeners have sufficient overall and local stability. The failure of the SCPs occurred locally in the subpanels between stiffeners, and the ultimate resistance of specimens with different bending radii was insignificantly different. The ultimate compressive resistance calculated following the effective section of the main plate was close to the test results. When the subpanels are locally buckled, the stiffened flat plate calculation method can be used to analyze the ultimate resistance of SCPs, and the calculated results deviate conservatively.

Connections between precast bridge deck panels (PBDPs) have the risks of cracking and leaking during service life, influencing the performance and durability of PBDPs. High-performance materials offer the possibility for simplifying joint configurations and increasing serviceability performance. Traffic causes the bridge deck panels to bear the action of fatigue load inevitably. Therefore, this paper conducted validation tests and fatigue bending tests to investigate the fatigue behaviors of PBDPs with the proposed high-performance connections. Ultrahigh-performance concrete and carbon fiber–reinforced polymer tendons were adopted in the proposed connection. The validation tests proved the reliability of connections in the longitudinal and transverse directions under Vehicle mode-III in the Chinese code. The fatigue bending tests analyzed the performance parameter development of PBDPs with the proposed connection during the whole fatigue process, including crack pattern, deflection, strain, stiffness, and energy dissipation. Then, empirical models used to predict fatigue deflection and fatigue damage quantity were put forward based on the test results. The results show that the capacity of the static test after fatigue is 2.17 and 13.63 times the upper fatigue limit when the connection is along the support direction and perpendicular to the support direction, respectively. The proposed high-performance connection has enough safe reserves irrespective of which direction it is arranged. The fatigue damage of PBDPs with the proposed connection under moment develops in three stages: rapid development of fatigue damage stage, stable accumulation of damage stage, and imminent failure stage. The maximum midspan deflection and logarithmic cycle numbers present linear relationships. These empirical models have ideal accuracy for predicting flexural fatigue deflection and accumulative damage.

A high-resolution digital image correlation (DIC) system was developed for monitoring bridge deformations under load testing. Significant advantages of the new system compared with contact-instrument based systems include its relative low cost, ease of operation, speed of setup, ability to monitor any point over a large field of view in a single setup, and its relatively high accuracy. The civil infrastructure vision (CIV) system consists of two high-resolution low-noise digital cameras and a DIC software coded by the authors. It can track the three-dimensional (3D) spatial movement of any visible target on the surface of a bridge to a resolution on the order of 1/40th of a millimeter (1/1,000th of an inch), even when the cameras are over 30 m (100 ft) away from the bridge. The accuracy of the CIV system is quantified using certified gage blocks over the full measurement volume encompassing sight distances between 12.2 m (40 ft) and 33.5 m (110 ft). System accuracy is further validated through two field studies by comparing deflection measurements obtained using the system with those obtained by displacement transducers attached to the underside of bridges. In Field Study 1, a multigirder steel bridge was monitored during applied truck loading using traditional instrumentation and the CIV system. In Field Study 2, a multicell concrete culvert was monitored under truck loading. In both field studies, the deflection readings obtained by the CIV system were comparable to those obtained from traditional instruments.

Bridge inspections performed by the response of the moving vehicle have been widely studied because of its mobility and efficiency, whereas mode shapes extracted by the moving vehicle have low order and limited accuracy in existing studies. In this study, experimental studies are conducted in which a stationary shaker is used to excite the steady-state-forced vibration of the bridge, and the bridge vibration is collected by an accelerometer installed on a moving vehicle. Accurate multiorder mode shapes are obtained by extracting the vehicle acceleration envelope. First, a theoretical derivation of the method is provided, and an extraction process for field tests is proposed. Then, a model test of a three-span continuous beam bridge and a field test of a two-span continuous girder bridge are conducted. To verify the accuracy of the mode shapes extracted by the moving vehicle, reference data are obtained by finite-element modal analysis and by using the hammer test. Through a difference analysis of accelerations between the parked vehicle and the bridge deck under the test vehicle, the ability of the designed test vehicle to collect bridge vibration in different frequency bands is evaluated. Finally, the first five mode shapes of the bridge model and the first six mode shapes of the field bridge are extracted by a moving test vehicle, and the effects of vehicle speed and excitation amplitude on mode shape extraction are analyzed. The results show that multiorder mode shapes can be accurately extracted by a moving test vehicle.

This study explored extending the performance-based seismic design method to three case study arch bridges with geometry and loading conditions representative of the long-span concrete deck arch bridge class. The force-based design method was first utilized to develop preliminary seismic designs of the three bridges and validate the assumption that bridges designed following the force-based design are protected against collapse under rare seismic events. The preliminary designs of the short spandrel columns failed to achieve code-specified performance objectives under longitudinal seismic loads and were thus revised. The three bridges with the revised details were analyzed using nonlinear time history analysis considering three suites of ground motions scaled to the code-specified hazard levels at the site of interest. The three suites of ground motions represented crustal, subcrustal, and subduction earthquakes. Under individual records associated with the subduction earthquakes, the revised designs of two bridges failed to achieve the code-specified performance objectives. Seismic fragility curves were generated for the bridges considering details based on force-based and performance-based design methods. The probabilities of the collapse of bridges designed following the force-based design method were near zero under rare events. The assumption that bridges designed following the force-based design method meet the collapse prevention limit state was thus found to hold true when extended to the special case of long-span concrete deck arch bridges. Such bridges, however, were found to be unlikely to meet low to intermediate levels of damage and performance criteria corresponding to low to moderate levels of seismicity. Despite being designed to achieve code-specified performance objectives, performance-based designed piers were also characterized by some probability of not meeting the damage levels and performance criteria, albeit to a much lesser extent than force-based designed piers. Considering demands associated with individual records with particular emphasis on those representatives of the dominating seismic hazard at the site of interest is thus recommended for performance evaluation of long-span concrete deck arch bridges.

Aerodynamic admittance functions (AAFs) of twin-box decks are particularly complex due to the presence of a central gap, so require the performance of dedicated studies to determine them. Two main approaches are available for this purpose, which consist of studying the aerodynamic forces produced by the section when impinged by sinusoidal gusts or continuous turbulence, respectively. However, owing to the difficulty in the generation of large-scale turbulence in traditional wind tunnel tests, the two aforementioned approaches often provide remarkably different results. To address this problem, this study aims to systematically investigate the admittance function of twin-box decks by comparing three approaches: active wind tunnel tests, and large eddy simulations (LESs) using both sinusoidal gusts and continuous synthetic turbulence. In particular, wind tunnel tests equipped with an active gust generator are conducted to generate a series of single-frequency vertical sinusoidal gusts. The effects of gust amplitudes and gap widths on the AAFs are experimentally investigated. In addition, LESs are performed aiming to provide valuable insights regarding the discrepancy between AAFs obtained in the two inflow conditions. Results obtained adopting all the aforementioned methodologies are compared, showing good agreement among the three approaches and values sometimes higher than the Sears function. It is also shown that buffeting forces are mainly produced by the upstream deck, so explaining the good agreement obtained between sinusoidal gust and continuous turbulent inflows.

This paper studies a dynamic testing method called dynamic displacement testing (DDT). Similar procedures to this method have been used in the past to perform experimental testing; however, the procedure was never acknowledged as a specific testing method, and therefore, its errors have never been investigated. The method analyzes the finite-element (FE) model of a structure under dynamic base excitation and applies the obtained displacement time history to the specimen in the laboratory. Sensitivity analyses using 3D continuum (representing the actual specimen) and 2D macro FE models are performed on steel and reinforced concrete bridge pier case studies to detect and quantify significant sources of error associated with this method. Furthermore, 500 Monte Carlo simulations are performed for each case study to assess the variability of the responses. It is shown that the method could apply 30% and 18% errors into displacement and energy dissipation responses, respectively. However, calibrating the FE models at material and element levels could significantly increase the accuracy and precision of the method.

Scoured pile-group foundations in bridges are likely to undergo inelastic deformation during earthquakes, which can be utilized to dissipate seismic energy and withstand seismic loads by the post-yield hardening strength of the foundation. However, limit states and associated ductility indices and post-yield strength indices are yet to be well documented. This study develops a surrogate model, namely, the classification–regression combination model (CRCM), for the efficient, interpretable, and high-confidence quantification of displacement ductility factor $({\mu }_{\mathrm{\Delta }}^{\mathrm{ER}})$ and associated strength hardening factor $(R_F^{\mathrm{ER}})$ of scoured bridge pile-group foundations at the easy-to-repair limit state, where the damage of piles is limited to the aboveground region (thereby being relatively easy to repair). To this end, a proper pushover method from those with different load patterns is first identified for efficient nonlinear analyses of scoured bridge pile groups. A large number of bridge samples are then analyzed to prepare a comprehensive database for the development of CRCM, which first classifies the failure process of scoured bridge pile-group foundations and then regresses ${\mu }_{\mathrm{\Delta }}^{\mathrm{ER}}$ and $R_F^{\mathrm{ER}}$ with variables characterizing the soil–bridge systems. It is found that the pushover method with a two-node load pattern (i.e., load at the superstructure and pile-cap centroids) can very well capture ${\mu }_{\mathrm{\Delta }}^{\mathrm{ER}}$ and $R_F^{\mathrm{ER}}$ and the failure process of bridge pile groups. The data-driven CRCM can efficiently provide reasonable predictions of ${\mu }_{\mathrm{\Delta }}^{\mathrm{ER}}$ and $R_F^{\mathrm{ER}}$ with errors mostly within 20%; it is specifically compared with a regression-only model to demonstrate the necessity of incorporating a classifier in advance of the regression model.

Concrete encasements are usually utilized to protect bridge above-ground piles from corrosion. These concrete encasements are usually square or round shapes reinforced by longitudinal rebars. However, the contributions of concrete encasements are not considered in traditional pile design procedures. On the other hand, rating engineers need to have realistic evaluations of the piles to estimate the capacity of the foundation for scour-critical bridges. Underestimation and overestimation of pile capacity can result in either potential bridge failure or uneconomical assessment. The objective of this paper is to investigate the effect of concrete encasement on pile buckling behavior subject to concentric load. To achieve this objective, four full-scale concrete encased pile specimens with various pile and concrete encasement lengths were fabricated and tested with concentric axial loading to measure the specimen ultimate capacity. In addition, the finite-element (FE) approach was utilized to simulate the buckling behavior and predict the ultimate capacities of the lab-tested specimens. The developed FE models were validated against the laboratory test data. Finally, the validated FE models were utilized in the parametric study to investigate the effect of the length and shape of the concrete encasement on the ultimate capacities of the steel H-piles. The results indicated that the concrete encasement could increase the buckling load of the pile, and ignoring the effect of the concrete encasement, as with the use of the equations suggested by the AISC, could result in a significantly underestimated prediction. It was also found that the concrete encasement increases the initial axial stiffness of the pile before the buckling load is achieved.

A lightweight glass fiber–reinforced polymer (GFRP)–ultrahigh performance concrete (UHPC) composite slab of high strength is proposed in this paper, having a reduced weight with respect to a composite slab with GFRP and normal concrete (GFRP–NC), and improved corrosion resistance compared to the steel–UHPC. Experiments are conducted on GFRP–UHPC composite slabs subjected to hogging moment. Their behavior is compared to that of a steel–UHPC composite slab. The effect of the steel fiber content and reinforcement ratio on their flexural performance is discussed. The cracking load and ultimate bearing capacity of the composite slabs are investigated. Their failure modes and failure mechanisms are analyzed. The results indicate that there are 1–3 primary cracks, with the majority of cracks distributed in the pure bending region. An increase in the reinforcement ratio causes significant bending stiffness, ultimate bearing capacity, and smaller maximum crack width, restraining the development of cracks. The effect of steel fiber content on their flexural performance is minimal, and lesser than the reinforcement ratio. Under the same condition, the self-weight of GFRP–UHPC composite slab is reduced by 26.4% compared to the steel–UHPC composite slab. However, the ultimate bearing capacity of the GFRP–UHPC composite slab is only reduced by 15.9%. The cross-sectional stress method is introduced to calculate the cracking load and achieve good agreement with experimental results. The proposed method gives more accurate results than the transformed section method. In addition, the calculation method for the ultimate flexural bearing capacity of the composite specimens is suggested and validated by the experimental results, presenting satisfactory accuracy.

The spanwise coherence of aerodynamic forces on a strip section is vital to evaluate the buffeting response of large-span bridges. However, when employing the commonly used pressure measurement technique, it is difficult to obtain the buffeting force coherence of bridge decks with complex configurations. This paper aims to propose an approach to determining the buffeting force coherence of a strip section using the force measurement technique. The key to this approach is the transformation of the coherence of buffeting forces from segment models to strip sections. Based on the two-wavenumber buffeting analysis theory, the relationship between the coherence of a strip section and a segment model is elaborated theoretically. The influences of the aspect ratio (δ) and the ratio of the integral scale to half the model’s width (L_w/b) on buffeting lift coherence were investigated. Force and pressure measurement tests are conducted on a typical streamlined bridge deck to validate the proposed approach. The results show that the buffeting lift coherence of a segment model is much stronger than that on a strip section. An increase in δ or L_w/b can, respectively, enhance the buffeting lift coherence at low wavenumbers or high wavenumbers. The wind tunnel test results demonstrate that the proposed approach is feasible and reliable and can be easily utilized to identify the buffeting force coherence of a bridge deck with a complex configuration.

Abstract

The stiffness of suspension bridges, which are flexible systems composed of main cables and stiffening beams, is frequently increased by adding one or more pairs of central buckles in the midspan. This study examined a suspension bridge with flexible central buckles, proposing a set of analytical calculation methods for the shape-finding of the main cable under dead load and the structural deformation and internal forces under any uniform live loads. The proposed method is based on the known bridge design parameters. First, the suspender and central buckle tension of each hanging point of the stiffening beam was determined by the multipoint rigid support continuous beam method. After assigning these tensions to the suspenders and the central buckles, the multisegment catenary theory was used to derive the equation for each main cable segment in turn. The constraint equation was established through the closure condition of the height difference within the span. The equation was then transformed into an objective function to be programmatically solved, determining the completed bridge state. To determine the live load response of the bridge, the deformation and position relationships of the main cable, main beam, and bridge towers were analyzed in sequence, with known live load parameters. Five types of constraint equations were established through the conservation of the unstrained length of each main cable segment, the coordination of the force and deformation of each suspender, the coordination of the force and deformation of each central buckle, the closure of span length and height difference in each span, and the force balance of the main beam. Then, they were converted into an objective function to be programmatically solved, leading to the live load response of the structure. Finally, a case study of a suspension bridge with a main span of 1,050 m was used to verify the feasibility and effectiveness of the proposed method. The structural deformation and internal forces provided by the analytical solution for the live load action had good accuracy, which is in good agreement with the finite-element method results.

Practical Applications

Long-span suspension bridges, compared with traditional small- and medium-span bridges, have greater flexibility, and they are more prone to large deflection and deformation under live loads such as vehicles. To improve the structural stiffness of suspension bridges, engineers often set central buckles connecting the cable and stiffening beam in the middle of the span. The current method of calculating the live load response of suspension bridges depends on finite-element modeling. However, when purchasing and using finite-element software, it is often expensive. At the same time, the finite-element method (FEM) modeling process is relatively complex and exhibits low efficiency. In addition, Link10 element in the current commercial finite-element software ANSYS (version 16.0) cannot consider its geometric nonlinearity, which will produce deviation to the results. Therefore, this paper proposes a set of accurate live load analytical algorithms for suspension bridges with central buckles, which are solved by the same number of basic unknowns and constraint equations. It is helpful to reduce the dependence of practitioners on finite-element software and can also be used as the verification and supplement of finite-element results.

The perceived and observed differences in the dynamic behavior between wheeled and tracked military vehicles should be considered when applying appropriate dynamic load effect values for bridge design and assessment. Based on available test data, tracked military vehicles appear to impose less severe dynamic load effects when compared with wheeled vehicles under similar crossing conditions. In exploring a range of crossing conditions, a review of test data was used to make a general comparison of the dynamic loading amplification between tracked and wheeled military vehicles. To expand the range of crossing conditions tested for an instrumented bridge, additional data were collected for an artificially induced roughness of the bridge surface. By combining the test results from previous studies with the results from this testing program, the relative dynamic loading amplification between tracked and wheeled military vehicles can be quantified for situations with similar crossing conditions. Given this comparison, it may be appropriate to use a dynamic load allowance (DLA) of as low as 70% of the code-specified DLA for wheeled vehicles when evaluating the capacity of bridges subjected to military tracked traffic. This is especially relevant when considering maneuver options for main battle tanks during military combat operations.

A new connection joint between precast concrete bridge slabs, headed bar joints in high-performance fiber-reinforced mortar (HPFRM), is proposed to reduce the lap length and simplify the construction process of the traditional slab joint configurations. To investigate the tensile behavior of the proposed headed bar joints in HPFRM between precast concrete bridge slabs, four groups of 12-headed bar joint specimens were tested in different loading rules. Contributing factors to the joint tensile strength, including anchor plate configurations and loading rules, were investigated. A three-dimensional refined rib-scale finite-element (FE) modeling method was further proposed and verified against the experimental results. The working mechanism of mechanical anchorage and indirect lap splice was analyzed based on the FE analysis. This research shows that with the reinforcing bar spacing and lap length used in this paper, the joint specimens having 60 mm or less anchor plate length encountered conical shear failure before the rebars reached the characteristic tensile strength. At the peak load, with the degradation of the bond between reinforcement and mortar, the coworking mechanism of the mechanical anchorage and bond was switched to mechanical anchorage alone carrying most of the applied load. Increasing the anchor plate thickness can effectively improve the tensile stiffness and strength of the joint and hence avoid conical shear failure, while the influence of loading rules is very limited. The proposed refined rib-scale model can accurately predict the failure mode and tensile strength of the headed bar joints without artificially assuming the bond–slip constitutive relationship.

Suspenders of long-span suspension bridges are thin structural components that are easily accessible to the public and in proximity to fast moving traffic. Their vulnerability and exposure to hazards make them especially prone to the risk of malicious or accidental damage. Albeit, the effect of suspender loss on the behavior and performance of long-span suspension bridges has not yet been thoroughly investigated. In this paper, therefore, using computational simulation, member removal analysis is undertaken to shed light on how a typical long-span suspension bridge responds to sudden loss of a single suspender. Two factors, the location of the lost suspender and live load cases, are addressed in the study. Simulation results show that only structural members in the immediate vicinity of the lost suspender are significantly affected by sudden suspender loss, while the rest of the bridge is hardly affected. The study suggests that single suspender loss scenarios in long-span suspension bridges like the prototype bridge investigated in this work do not trigger appreciable nonlinearity in the system or even cause the main cables to overcome friction at the saddles. As such, single suspender loss scenarios in bridges like the prototype system can generally be assessed using common analysis and design software.

This paper presents the technical causes of the collapse of the Annone overpass, a reinforced concrete half-joint bridge built in the early 1960s in northern Italy, occurred in October 2016. This work provides a detailed description of the geometry of the bridge and its conceptual design, highlighting the differences between the original design and the as-built situation. The condition of the bridge before the collapse and the event that triggered the collapse are also described. The paper highlights the critical issues occurring concurrently with the passage of a heavy truck. After a brief presentation concerning the characterization of the materials (concrete and steel), the work presents strut-and-tie models for the estimation of the ultimate capacity of the half-joints, which are considered to be the critical point of the entire structure. The strut-and-tie models are validated through comparison with experimental data obtained by testing a half-joint extracted directly from the bridge after collapse. The structural behavior of the bridge, the assessment of its safety, and the reasons that led to the collapse of the structure are also discussed through the use of simplified linear elastic and nonlinear finite-element models. Some weak points of the national infrastructural managing system, mainly referring to exceptional transports, are also discussed. The study highlights the methods that could be used to prevent future accidents in the absence of macrodesign mistakes and the main lessons learnt.