Journal of Bridge Engineering

This paper investigates the flexural behavior of steel–UHPC composite beams with waffle slabs (SUCBWS) under hogging moment. A three-point, reduced-scale flexural test was performed to investigate the effect of reinforcement ratio and partially filled UHPC in the compressive flange of the steel beam. The parameters, including the force ratio R, the laying length L_pfu, and thickness H_pfu of partially filled UHPC, were analyzed. A theoretical formulation was proposed to calculate the flexural capacity of SUCBWS under the hogging moment. The results show that the increase of reinforcement ratio and partially filled UHPC in the compressive flange of steel beam can improve the crack resistance and the flexural capacity of SUCBWS under the hogging moment. Force ratios of 0.22 and 0.48 are recommended for SUCBWS and partially filled steel–UHPC composite beams with waffle slabs (PFSUCBWS), respectively. It was also found that the reasonable laying length and thickness of partially filled UHPC should not be less than 0.5 times the clear span of the specimen (0.5l₀) and 0.2 times the web height of the steel beam (0.2h_w), respectively. The theoretical predictions based on the proposed formulas are in good agreement with the test results and numerical results.

Inerter-based dynamic vibration absorbers (IDVAs) have been theoretically studied in the vibration control of civil structures. However, experimental studies, especially studies on the nonlinearity of this mechanical device and its influence on the control efficiency of civil structures, are limited. In the present study, a ball-screw inerter aimed to control the vortex-induced vibration (VIV) of a scaled bridge model is designed and manufactured. The dynamic property of this device is examined through experiments. A nonlinear physical model is proposed to simulate this device and is incorporated into the governing equations of the bridge-TMDI (tuned mass damper inerter) system to investigate its influence on VIV control efficiency. Design suggestions on how to mitigate the influence of inerter nonlinearity are also proposed. The results indicate that the dynamic property of the ball-screw inerter depends on the magnitude of driving acceleration. With the increment of acceleration magnitude, the ball-screw inerter approaches an ideal linear inerter. Due to this acceleration-dependent property, the control efficiency of the TMDI when considering the inerter nonlinearity is worse than that of an ideal linear TMDI. By retuning the optimum design parameters of a TMDI obtained based on linear assumption, the influence of inerter nonlinearity can be compensated to some extent. In addition, for a certain designed inertance, one can choose a larger diameter of a ball screw and a larger value of lead to further reduce the influence of inerter nonlinearity. Even though this design option will reduce the mass amplification ratio of the inerter, the actual physical mass of the inerter is still ignorable as compared with the mass of the TMDI mass block.

A mechanical bar splice, which is known as a bar coupler, is an alternative to traditional lap splicing to connect bars in reinforced-concrete (RC) structures. Although it is feasible to incorporate mechanical bar splices in bridge bents as a precast detailing to expedite construction, the use of bar couplers in the plastic hinge region of bridge columns is prohibited in current US codes. This ban was mainly because the coupler performance and the effects of couplers on the seismic behavior of columns were not fully understood. Further, the test data regarding the performance of mechanically spliced bridge columns are scarce, and the available data are for columns with different geometries, confinements, and testing procedures. An experimental investigation was performed to systematically determine the seismic performance of mechanically spliced bridge columns and to develop the most comprehensive test database for these columns. Seven half-scale bridge columns were constructed and tested. One column was cast-in-place (CIP) to serve as the reference model and six were precast and incorporating different couplers at the column base with a coupler product per specimen. Two grouted, one threaded, and three hybrid couplers were included. To minimize the effects of other test parameters, all columns had the same geometry, were longitudinally reinforced with steel bars from a single batch, and were tested under the same loading. The test results showed that seismic couplers, which had a consistent failure mode of bar fracture, reduced the precast column displacement capacities from 3% to 45% compared with CIP and the lateral strength of the precast columns was slightly higher than that of CIP. All precast columns that were tested in this study met the current code seismic requirements; therefore, they might be used in any seismic region of the United States. However, only seismic couplers must be utilized in bridge bents. Finally, a simple design method for mechanically spliced bridge columns was evaluated using a database that consisted of 10 specimens and was viable for practice.

In this study, an experimental program was conducted to explore the feasibility of using aluminum alloy (AA) bars in the flexural strengthening of reinforced-concrete (RC) beams that are subjected to fully reversible cyclic loads. A total of seven RC beam specimens including one control beam and six RC beams strengthened with near-surface mounted (NSM) 7075 AA bars were fabricated and tested under incrementally increasing reversed cyclic loading. The effects of the NSM reinforcement ratio, anchorage system, groove filling material, and surface treatment of the AA bar on the performance of the strengthened beams were studied. The results were analyzed in terms of failure mechanisms, crack propagation, hysteresis response, skeleton curves, degradation in stiffness and load-carrying capacity, and the energy dissipation capacity of tested beams. It was revealed that application of the NSM AA strengthening technique can enhance the flexural response of RC beams by increasing the strength and energy dissipation capacity and decreasing the stiffness degradation.

Structural health monitoring (SHM) enables bridge owners to evaluate bridge conditions efficiently and accurately. When implementing SHM, a popular method to detect the abnormal response of a structure is statistical pattern recognition. This often involves unsupervised statistical analysis due to a lack of measured SHM data from abnormal conditions. In this study, a novel methodology to calculate strain threshold indices (STIs) and establish decision boundaries (DBs) was used to detect the abnormal responses of the Indian River Inlet Bridge (IRIB), Sussex County, Delaware. First, a series of statistical models were applied and compared. Gaussian three mixture distributions were the optimal statistical models for the heavy vehicle-induced strain peaks. Threshold values for the strain gauges were selected using 99% uppers limits (USLs), and these limits were used to detect the abnormal response of the IRIB. The outlier ratios (R) for the sensors were calculated based on the threshold values. Corresponding STIs were defined by analyzing R, and DBs were determined using a t-distribution. The abnormal responses of the IRIB were detected by comparing the STI and DBs. The validity and sensitivity of the proposed methodology were demonstrated through simulated data that was created by perturbing the actual collected SHM data. Varying degrees of simulated damage were successfully detected using the proposed DBs. The proposed methodology showed promise when short and long-term abnormal responses and could provide practical guidance for bridge owners when using SHM data in their decision-making process.

To ensure the flutter stability of long-span suspension bridges during deck erection under normal and skew winds, by taking the Runyang suspension bridge as example, the evolution of flutter stability of the bridge under normal and skew winds during the symmetric deck erection from the midspan to towers is investigated numerically by the computational procedure of three-dimensional refined flutter analysis of long-span bridges under skew wind, and the erection stages with weak flutter stability are pointed out. To improve the flutter stability of suspension bridges during deck erection under normal and skew winds, two schemes of symmetric towers-to-midspan erection and nonsymmetric erection scheme from middle part to the towers are investigated numerically, and the favorable deck erection schemes of suspension bridges are obtained. The results show that the flutter stability of suspension bridges during erection is significantly reduced by the skew wind effect; when the deck is erected as the symmetric midspan-to-towers scheme, both the early period (the erection ratio is below 20%) and the middle-later period (the erection ratio is between 40% and 80%) have weak flutter stability; following the symmetric towers-to-midspan erection scheme, the flutter stability at the early stages is significantly improved, and basically the whole erection period has good flutter stability, and the flutter critical wind speed has an overall average increase of 34.2% as compared with the symmetric midspan-to-towers erection scheme; in the case of nonsymmetric erection from middle part to towers, the flutter critical wind speed does not increase monotonically with the eccentricity, showing a trend of increasing first and then decreasing, and reaches the peak at the eccentricity of 8.6%. Under the optimal eccentricity, the flutter stability throughout the erection process is significantly improved compared with the symmetric erection scheme, and the overall average increase is 14.5%; from the viewpoint of flutter stability, the symmetric towers-to-midspan erection scheme is the best, followed by the nonsymmetric erection scheme from middle part to towers, and the traditional symmetric midspan-to-towers erection scheme is the worst.

An analysis method to quantify the alternate load paths (ALPs), inspired by the concept of ALP for progressive analysis of buildings, is proposed for steel truss bridges subject to the loss of a critical member. Quantification of ALP in bridges is defined as the spectra of the surrounding members undergoing load redistribution to prevent collapse following the sudden damage to member(s) of a bridge. Two indicators – demand to capacity ratio for linear elastic analysis and strain ratio for nonlinear dynamic analysis – were incorporated into the analysis method and applied to a representative long-span truss bridge. The results of the ALP analysis showed that the three-dimensionality of truss bridges, stemming from the upper and lower braces, sides trusses, floor beam trusses, and the reinforced-concrete deck, played a primary role in protecting the bridge from collapse following the sudden removal of a member(s).

The success of detecting damage robustly relies on the availability of long periods of past data covering multiple weather scenarios and on the information contained in the data used during the learning process. Thus, the innovation of this paper is to apply a hybrid data set to train a Gaussian process regression, assuming a practically plausible range of environmental conditions. The proposed model presents a satisfactory performance to detect damage when structural changes caused by damage are blurred with changes caused by temperature. Rather than relying exclusively on experimental data, this strategy use finite-element models to generate complementary data when the structure is undamaged under a broad spectrum of temperature variations that are not measured. Once the stochastic interpolation is defined, the damage detection model is tested using experimental data considering different damage levels and temperature conditions. Induced settlements of a bridge pier are used as realistic damage scenarios. The Z24 prestressed concrete highway bridge in Switzerland is used to demonstrate the applicability of the proposed strategy.

The worldwide occurrence of numerous ship–bridge collisions has prompted a substantial concern regarding the safety of sea-crossing bridges. The majority of conventional risk models for ship–bridge collisions assume that collisions occur in inland waterways instead of sea waterways. Therefore, a new probability model should be established to assess the risks of ship–bridge collisions in sea waterways, considering the harsh navigation conditions such as strong wind and turbulent current in sea waterways. This study proposed a new risk assessment method to evaluate the collision probability of a ship with a sea-crossing bridge. Additionally, the motion state of a ship under the coupling effect of wind and current was analyzed to optimize the new probability model, and the drift trajectory of an aberrant ship was obtained. Moreover, the proposed model was applied to analyze the annual frequency of ship collisions at the Zhoushan-Daishan Sea-crossing Bridge in the East China Sea. For large tonnage ships, the annual frequency of ship collision was higher when calculated using the probability model based on the AASHTO Guide than that evaluated using the current model, whereas a significantly larger collision frequency was computed by the proposed model for small tonnage ships. Furthermore, we analyzed the relationship between navigation circumstances and the annual frequency of ship collision. The findings of this study will assist in appropriately assessing the risks of ship–bridge collisions for ships navigating through sea-crossing bridges under the influence of wind and current and provide a feasible method for improving the design and management of sea-crossing bridges.

Abstract

Triple-cable design of suspension bridges with an ultrawide main girder can improve their mechanical properties, making it lucrative for numerous engineering scenarios. However, its realization requires assigning an appropriate share of the dead load of the main girder supported by three main cables to avoid the middle main cable overload by the main girder’s dead load since the latter would impair the mechanical behavior of the upper transverse beams in the towers and deteriorate the whole bridge’s torsional stiffness. Therefore, this study proposes an analytical approach for dead load allocation to the suspension bridge with three main cables, which adjusts the share of the main girder’s dead load supported by three main cables via changing the unstrained lengths of the hangers. The main advantage of the proposed approach is that it can consider both uniform and nonuniform allocations. The spatial model for the suspension bridge with three cable planes is first converted into a plane model. The relationship between unstrained lengths of the three hangers in the same cross section is determined via the deformation compatibility conditions and one of the following options: (1) equality of stiffness of the two side hangers in the case of a symmetrical plane model; or (2) energy conservation conditions in case of an asymmetrical one. The proposed method was applied to an example of a triple-cable suspension bridge with a main span of 2,100 m and a width of 75 m, and its analytical solutions were compared against finite-element method calculation results. An increase in the share of the main girder’s dead load supported by the two side main cables increased the torsional stiffness of the whole bridge and reduced the vertical load exerted by the middle main cable on the top transverse beam of each tower. Meanwhile, variation of the share of the main girder’s dead load supported by the side and middle main cables only slightly influenced the whole bridge’s vertical and lateral stiffness values. The aforementioned adjustment by the proposed method could be accomplished without increasing the steel consumption of the bridge cables. The results could provide references for the design, static, and dynamic response analysis of similar triple-cable ultrawide suspension bridges.

Practical Applications

Installation of an ultrawide deck in a conventional two-cable suspension bridge requires resolving the following two major problems: (1) the main girder has a significant spatial effect, which considerably adds to the difficulty of design and analysis; and (2) at the midpoint of the main girder section, the deflection may be excessively large. The height of the main girder has to be increased to improve the stiffness, leading to high steel consumption and high construction cost. These problems may be solved by adding a cable plane (one more main cable and the corresponding hangers). Based on the findings and the major contributions of this paper, we can achieve random dead load allocation ratios by just adjusting the unstrained lengths of hangers. The application of triple-cable systems may be a great potential approach to increase the overall torsional stiffness. Meanwhile, changing the share of the dead load supported by the side and middle main cables has a slight effect on the total cable-steel consumption. It shows that the method presented in this paper will not increase the construction cost.

The displacement-based design methods for bridge abutments, essentially cantilever retaining walls, require an input of expected ground motion on-site. For major projects, these motions are obtained based on site-specific response studies. In other projects, it is merely a guess based on the PGA values prescribed in the design codes. Further, the seismic displacements in retaining walls are usually estimated using simplified rigid–plastic analytical models. These models do not account for the effect of soil nonlinearity, alteration of input signal due to soil–structure interaction, amplification effects, or material damping. The currently followed seismic load factor of 1 on the prescribed PGA does not account for the induced uncertainties for the reasons given here, which can often be unconservative and lead to failure. This study statistically quantifies the effect of these uncertainties and proposes scaling factors on the design PGA of the input motion to estimate more reliable seismic displacements accounting for the assumptions in the simplified rigid–plastic model. The nonlinear finite-element analysis of retaining wall in OpenSees has been compared with the analytical double-wedge model considering a realistic V-shaped mechanism in backfill. It includes analysis for 83 different cases of earthquake motions scaled to four different PGAs. Finally, the scaling factors are proposed to estimate residual as well as peak sliding and in-plane rotational displacements of cantilever retaining walls with and without shear key.

In this research, a low-damage posttensioned rocking solution referred to as dissipative controlled rocking (DCR) connection is proposed for bridge columns supported on monopile foundations. The DCR connection is a low-damage system that replaces the plastic hinge mechanism in a column and aims to minimize and potentially eliminate the repair time and costs after an earthquake. A DCR bridge system combines unbonded posttensioning and replaceable dissipaters to provide self-centering and energy absorption capabilities, respectively. Current research on DCR column systems has focused on the performance of bridge bents founded on a fixed foundation, neglecting soil damping effects. In this research, a one-third scaled bent supported on a monopile with passive soil resistance was tested under quasi-static cyclic loading to validate the lateral seismic response of a DCR bridge bent with the contribution of the soil–foundation–structure interaction. When developing the details for the DCR connection, particular emphasis was made on utilizing conventional construction materials and forms for a low-damage bent that yields a similar construction cost to a monolithic joint. Nevertheless, the proposed DCR connection can be easily and quickly repaired or replaced after a significant seismic event. The performance of the bent was compared against a benchmark structure with an emulative connection type that resembles a monolithic cast-in-place joint. Results from testing suggest a greater performance of the low-damage DCR column. The dynamic response of the DCR column built on a flexible foundation differed from that of a fixed-base structure, which is primarily due to the energy dissipation capability of the flexibly supported structure. Flexibility in the soil foundation increased the structural period of the structure and reduced the seismic response of the DCR column. Damage to the DCR bent was limited to concrete crushing at the rocking interface, which proved to be easily repairable. In contrast, the bent with an emulative connection developed plastic hinging at the bottom of the column, which was nonrepairable.

Design factors in load and resistance factor design (LRFD) codes are determined using structural reliability theory to account for the uncertainties in loads and resistance. The calibration of load factors for strength limit states has been investigated during the development of AASHTO LRFD bridge design specifications (BDS). In comparison, sparse efforts can be found for calibrating service limit state load factors. Temperature variations affect all types of bridges and cause additional stresses, deformations, and moments in different bridge components. Calibration of load factors for vertical temperature gradients appear to be lacking for both strength and service limit states. This paper focuses on calibrating positive vertical temperature gradient load factors for the Service III limit state. A design space consisting of 70 two-span continuous bridges with different bridge configurations is established and designed for severe corrosive exposure conditions. Design stresses for various load cases are first calculated. Using the first-order reliability method (FORM) and considering the sources of uncertainties due to materials, fabrication, and load effects, temperature gradient load factors were then calibrated for different risk levels. The results show that vertical temperature gradient load factors between 1.00 and 1.40 should be used for the Service III limit state.

Under strong wind actions, some long-span flexible deck bridges have been observed to exhibit significant lateral vibrations. Accurate quantification of the self-excited forces induced by lateral vibration is of great significance for the evaluation of the wind-resistant performance of bridges. Three typical deck sections, including a 5:1 rectangular section, a streamlined section, and a central-slotted section, are used to comprehensively address this issue using the unsteady Reynolds-averaged Navier–Stokes simulations. The applicability of the linear analysis method for quantifying the self-excited forces is reexamined for different lateral vibration amplitudes and reduced wind speeds. The results show that the self-excited drag force induced by lateral vibration agrees well with the linear theory for the three sections. However, the self-excited lift force and torsional moment induced by lateral vibration cannot be quantified by the linear formulations. For the rectangular section, the self-excited lift force and torsional moments are much smaller than the vortex-induced counterparts. For the streamlined and central-slotted sections, the ratios of the self-excited components to the vortex-induced components are closely related to the reduced wind speed and vibration amplitude. The ratios increase with an increase in vibration amplitude and a decrease in reduced wind speed. Thus, particular attention should be paid to the self-excited lift force and torsional moment induced by lateral motions for bridge decks.