Journal of Bridge Engineering

Precast bent caps offer the opportunity to reduce onsite labor and materials and to accelerate the speed of construction. For many bridges, the weight is manageable for shipping and placement without the need for large cranes. For large bent caps, the weight can become a significant challenge for construction. Internal voids can be effective in reducing the weight but introduce the potential for the formation of shear cracks at service loads, because the shear width is smaller than in a solid bent cap. Internal voids are an attractive option when bent caps are pretensioned, because pretensioning delays the formation of cracks. This paper presents the results of a full-scale experimental test program that investigated the progression of damage and the failure mechanisms of pretensioned bent caps with internal voids. Test specimens were subassemblies of a portion of a multicolumn bent that included an overhang, a negative bending region at the connection to a column, and a positive bending region. The variables investigated were the presence of a void, the amount of prestressing, and the void termination location. Results indicated that voided caps had similar flexural behavior to solid caps, but were more prone to shear cracking and had more brittle failures. The use of a higher prestressing force was found to significantly delay flexural cracking but to have a minor effect on delaying the formation of shear cracks. The location of void termination adjacent to the connection region influenced the extent of the damage at failure.

Temperature profiles for bridge design were developed and introduced into current bridge design specifications after soffit cracking in prestressed concrete bridges was attributed to nonlinear temperature distribution through the superstructure depth. The profiles in the specifications are based on average conditions over wide geographical areas of the United States. As a consequence, the desert climate of the southwestern portion of the United States, with high solar radiation and extreme daily temperature differentials, could be expected to cause larger thermal gradients than those recommended in the specifications. In this study, thermal gradients in representative concrete box girder and composite steel bridge superstructures were calculated by heat flow analysis using long-term meteorological data recorded at two weather stations in Reno and Las Vegas, Nevada. This study is believed to be the first to use continuously collected weather data to allow analysis of temperature variation at any point in the season. For both types of superstructures, the calculated temperature difference between the top surface and an internal layer was typically 10°C larger than the corresponding value in the current design temperature profile, suggesting that the current profile is unconservative. Furthermore, for concrete superstructures, the shape of the calculated temperature profile was better represented by a fifth-order curve than the current multilinear thermal gradient. For composite superstructures, the temperature in the steel girder (which was almost uniform over its depth) was significantly higher than that given in the design profile.

In composite structures, the shear keys, that is, the headed studs or the perfobond rib shear connectors (PBL shear connectors), are typically subjected to external pressure, owing to the self-weight of the pavement and safeguards, for example. These loads may exert some influence on the shear behavior of such shear keys. To investigate the shear behavior of the headed studs and PBL shear connectors under external pressure, eight specimens were tested, and the slip-load curve and crack developments were obtained. According to the test results, the external pressure significantly contributed to the stiffness and strength of the headed studs owing to the friction effect. The relative improvement for the PBL shear connectors was not very obvious owing to its huge basic capacity. For the PBL shear connectors, the external pressure resulted in the slight relative enhancement of the load-carrying capacity regardless of the friction force. Employing the confining concrete strength improved the prediction of the PBL shear connectors, and the estimation error was reduced to less than 0.3%.

A study on the shear properties of tapered box girders with steel trapezoidally corrugated webs (STCWs) considering the Resal effect was carried out based on theoretical analysis, experimental testing, and numerical simulation. This study verifies the Resal effect in tapered box girders with STCWs, which is the dominant factor that contributes to the significant differences in mechanical properties between prismatic and tapered box girders with STCWs. This paper points out that it is too conservative to accept that STCWs carry the entire vertical shear force in tapered box girders because a considerable percentage of the shear force is resisted by the inclined concrete slabs, which cannot be ignored especially in regions of large bending moments. Through analysis of a linearly tapered cantilever box girder with a single vertical force acting at the unrestrained end, the study found that the average shear stress of the STCWs decreases from the unrestrained end to the cantilever’s supported end, which is different from the case of prismatic members. Also, it was found that the root section near the support is not the most unfavorable position for the shear design of STCWs. Accordingly, the traditional method and assumptions for determining the shear stress of a prismatic beam with STCWs will cause considerable errors when applied to tapered members. Thus, a simple and effective equation for determining the shear stress of tapered girders with STCWs is suggested that considers the Resal effect. The correctness of the proposed equation was verified by comparing the theoretical predictions with both experimental data and finite-element simulation.

In this study, an optimized anchor system to enhance the anchor performance of multiple-tendon fiber-reinforced polymer (FRP) cables was proposed and evaluated. The manufacture of the cables comprised 37 basalt FRP (BFRP) tendons with nominal diameters of 4 mm. Their anchor system was first studied by solving the bonding problem for each tendon. Furthermore, a novel winding device was designed to realize a variable elastic modulus for the load transfer component (LTC) with different fibers. The experimental process included evaluating the tensile properties of the cable, the strain distributions in the anchor zone and central part, and the stress-strain relationship of the cables. The optimizing effect of the anchor was evaluated by comparing the results with those of previous studies. The results showed that the anchor could effectively bear the tension behavior of the cable and avoid shear stress concentration at the loading end. It was also shown that an LTC with three slits could maintain a higher elastic modulus than one with four slits. The losses in the tensile strain of the BFRP tendons at different locations under equal loads exhibited slight differences. The inner and outer BFRP tendons experienced almost no shear lag effect. Moreover, the tensile strain of the BFRP cables in the anchor zone decreased gradually from the loading end to the free end and no evident correlation between tensile strain and the location of the BFRP tendons for equal cross sections of the anchor zone was observed. The mean axial tensile strain–fitting curve of the BFRP cables in the anchor zone exhibited good agreement with the simulated curve for a variable stiffness.

Visual inspection is the primary means of ensuring the safety and functionality of in-service bridges in the United States and owners spend considerable resources on such inspections. While the Federal Highway Administration (FHWA) and many state departments of transportation have guidelines related to inspector qualification, training, and certification, an inspector’s actual capability to identify defects in the field under these guidelines is unknown. This paper describes the results from 30 hands-on, visual inspections performed on bridge specimens with known fatigue cracks. Background information was collected on each inspector and correlated with inspection performance. Field temperature, duration, experience, and training were significantly correlated with detection rate. Probability of detection (POD) curves were fit to the inspection results and the 50% and 90% detection rate crack lengths were determined. This POD study was conducted to provide a benchmark measure of visual inspection capability for detecting fatigue cracks in steel bridge components under controlled conditions. It is believed to be the first study in which a statistically significant set of data focused on visual detection of fatigue cracks in steel bridge components has been collected.

A large number of steel–concrete composite twin I-girder bridges have been built in both Europe and Japan, but the lack of redundancy has always been a concern in the US and many other countries. In addition, very few experimental studies have been performed on mechanical performance of such bridges, particularly for the intact twin I-girder bridges. On this background, a steel–concrete composite twin I-girder bridge specimen was designed according to the current highway bridge design specification in Japan. Static loading tests were performed, and two loading conditions including both symmetric loading and asymmetric loading were applied. The load versus deflection relationship and strain development on the steel main girders and concrete slab at key sections were measured. The flexural strains on the lateral beam were also measured and reported in this paper to confirm the load transfer between two main girders. In addition, the shear strain of shear connectors (stud, in this study) was also measured to investigate the shear force transmission on the steel–concrete interface. The theoretical values were also provided to compare with the test results from the twin girder specimen under symmetric loading condition. The experimental results indicate that the theoretical analysis can predict the behavior of the twin girders very well in the elastic stage by considering the effective width of the slab. The performances of each structural component and load transfer path in such bridges were also discussed.

Transparency and structural lightness are inspiring ideas in the design of footbridges. Glass is the most performing transparent material to be used for structural purposes because of its high compressive strength, chemical stability, and absence of fatigue and viscosity phenomena at room temperature. However, its fragility constitutes a challenging limit in structural applications. This research provides and discusses a specific concept named TVTδ (Travi Vitree Tensegrity) for lightweight long-span beam-like footbridges made of structural glass. Hence, two design approaches of fail-safe design (FSD) and damage avoidance design (DAD) are applied to guarantee adequate safety levels and postcracking serviceability, respectively, with low damages on the main components. FSD provides the adoption of structural collaboration between glass and steel. Following DAD, glass is segmented into triangular panels, and reciprocal diffuse prestress is performed by steel tendons. This strategy assures low rehabilitation costs because only collapsed elements should be replaced once failed. At ultimate limit state (ULS), the TVTδ footbridge attains a global ductile behavior in which the yielding of steel tendons occurs before any fragile failure. Such result is achieved through a hierarchic calibration of the chain of failures. In glass panels, which are mostly precompressed, the buckling failure, representing the main risk, is delayed by the mutual stabilization of the panels’ compressed edges with steel clamping. However, because an accidental event may cause a localized or diffuse brittle failure of glass components, the system is designed to maintain a residual load bearing capacity in this scenario. At the serviceability limit state (SLS), the TVTδ footbridge is highly stiffened by the presence of glass panes, partially encased in metallic frames. Crack initiation is delayed by precompression.

Empirical single-peak wave spectra have been widely applied in current practice for the stochastic analysis of sea-crossing bridges under random waves. However, single-peak wave spectra may not be appropriate for evaluating the wave responses of bridges located in the nearshore site under tropical cyclones. In this study, typhoon wave spectra at an actual bridge site were measured and analyzed during Typhoon Dujuan in 2015. The stochastic structural responses of an example sea-crossing cable-stayed bridge under random waves were assessed by employing measured and empirical wave spectra. A frequency-domain approach was developed and validated with time-domain results as an efficient alternative for structural response analysis. The effect of wave directionality on the structural response was investigated and discussed as well. The main conclusions are: (1) the measured wave spectrum at the bridge site presents a double-peak shape and can be well described by the Ochi-Hubble spectrum; (2) the empirical Joint North Sea Wave Project (JONSWAP) spectrum may overestimate the internal force responses of the bridge towers and underestimate the displacement responses of the midspan; (3) the incident wave direction has remarkable impacts on the structural responses of the sea-crossing bridge and requires careful investigation; and (4) the proposed frequency-domain approach is an efficient as well as an accurate alternative for the long-duration evaluation of bridge responses.

Highway bridges are the key element of a transportation system and are essential for transportation of goods, services, and people. They are, however, vulnerable to extreme geologic and hydraulic events such as earthquakes, scour, and hurricanes. It is imperative to collect key perishable data during and after extreme hazard events for engineering evaluation and improving the current and future bridge design and maintenance practices. The objective of the posthazard damage assessment is to collect engineering data related to global structural behavior of different components of a highway bridge such as decks and piers. This paper studies the feasibility of using unmanned aerial systems (UASs) for posthazard damage assessment of highway bridges subjected to extreme geologic and hydraulic hazards through a mock-up test setup. For this purpose, a model bridge was developed to simulate movements of the key components of a highway bridge. Three types of structural movements in bridges have been studied: translation, rotation, and settlement. The results show the capability of the UAS and ground-based tripod assembly with high-resolution camera to detect these movements with high accuracy. The average absolute differences observed between the measured and estimated values were 0.7 cm (0.28 in.), 1 cm (0.39 in.), and 1.4 cm (0.55 in.) in the translation, rotation, and settlement movement experiments, respectively.

Collisions between overheight semitrailer trucks with low-clearance railroad bridges are one of the leading causes for railroad traffic interruptions on bridges in the United States. Current sensing efforts to inform drivers to avoid low-clearance bridges are not effective, and the number of bridge impacts is not decreasing over time. Railroad bridge owners are interested in attenuating the impact by adding crash beams. Furthermore, crash beams can establish safer transportation operations for railroads, roadways, drivers, and pedestrians, especially in congested cities and communities with several transportation modes. Additionally, crash beams can reduce the damage caused by highway strike incidents and can be easily replaced in those low-clearance bridges that are frequently impacted. This paper presents an experimental study for assessing the effectiveness of various crash beams in attenuating the impact consequences of overheight vehicle collisions against railroad bridges. The experimental test setup includes a 1:5 scaled model of a ballast deck through plate girder (TPG) steel bridge. TPG is a common bridge type utilized frequently in the North American rail transportation system, and this study is the first experiment of this size for railroad bridges impact attenuation. The testing setup consists of a pendulum mass impacting the TPG. A realistic collision event is simulated when the steel block attached to the tip of the pendulum swings and hits the bridge girder. The drop height is adjusted to vary the velocity of the collision and the input force to the TPG. Researchers tested three different crash beam configurations under various impact loads to evaluate their ability in attenuating the consequences of collisions compared with a no-crash beam configuration. To achieve this objective, researchers measured total and permanent displacements of the impacted girder, also known as the outside girder, and permanent crash beam displacements. In general, all crash beams attenuate permanent displacements efficiently, which protects the bridge and its ability to carry railroad traffic after impact. This study designs and validates experimentally three different types of crash beams to protect the bridge serviceability and railroad operations after impacts. Further analysis shows that weak crash beams perform better in reducing outside girder permanent displacements for a low-intensity impact compared to strong beams. Conversely, strong crash beams can sustain high-intensity impacts where weak beams are unable to resist. Overall, there is a trade-off between the ability of the crash beam to dissipate impact energy and to sustain impact loads. Thus, engineers should consider the intensity of the expected impact and design crash beams accordingly. In conclusion, this research experimentally quantifies the efficiency of different crash beam configurations, which establishes new methods to inform different designs for the impact attenuation of overheight vehicle–railroad bridge collisions. Future research includes the experimental testing of larger forces and a larger pool of crash beams toward design recommendations.

On March 15, 2018, a pedestrian concrete truss bridge in Miami, Florida, collapsed during construction. The failure of this bridge caused multiple casualties and raised many serious concerns regarding the design and construction of the bridge, including the emerging concept of accelerated bridge construction (ABC). The causes of failure of this bridge have not yet been comprehensively investigated. This paper used high-fidelity computational simulation to investigate the behavior of critical structural members of the bridge during construction. Four important construction stages (prestressing, transportation, relocation, and retensioning) were simulated to identify dominant factors that could have contributed to the failure of the bridge. A recent investigation report from the National Transportation Safety Board (NTSB) attributed the collapse to flawed design at the failed joint at the northern end of the bridge, but the specific sequence of mechanisms that led to collapse was not identified. Based on simulation and demand/capacity analysis, this work shows that the horizontal component of the retensioning force overcame the resistance of the joint and caused it to slide with respect to the deck. As sliding progressed, dowel action between the deck and joint became fully mobilized, crushing and damaging concrete locally within the joint and the deck. The evolving damage (to the cold joint and adjacent joint and deck concrete) prompted more sliding and led to a vicious cycle that culminated in the collapse of the entire bridge. Parametric studies investigated the effects of the coefficient of friction at the cold joint, prestressing forces in the deck, and retensioning forces applied to the northern diagonal member on the collapse behavior of the bridge. The results from the analysis and simulations provide important insights into the collapse mechanism and highlight lessons that could be learned for preventing similar catastrophic failures in the future.

Both aerostatic torsional divergence and flutter are challenging for the wind-resistant performance of long-span cable-stayed bridges. Aiming at a cable-stayed bridge with double main spans of 1,500 m each and a typical twin-box bridge girder, a combination of wind tunnel tests and nonlinear aerostatic analysis was used to investigate the wind-induced stability of the bridge as well as the effects of central grids with 0% installed on the upper surface of the bridge girder for the wind-induced stability of the bridge. Aerostatic torsional divergence was observed both at initial attack angles of $+3°$ and 0° for the twin-box section and the initial attack angle of 0° for the revised section with central grids with 0%, whereas flutter was observed at the initial attack angle of $+3°$. Therefore, there are clear competitive relationships between aerostatic torsional divergence and flutter for a revised section with central grids with 0%, depending on the initial attack angle. Furthermore, the addition of central grids with 0% led to deteriorated wind-induced stability, including aerostatic torsional divergence and flutter. Then synchronous evolutionary relationships between structural stiffness and displacements in the instability process are presented. It was found that the downstream cable stress at the center node of the main span decreased prior to the twin-box section when central grids with 0% were added, and the upstream cable stress decreased faster than that of the twin-box section, resulting in the deterioration of aerostatic stability at the initial attack angles of $+3°$ and 0°.

Three-pylon suspension bridges with unequal main-span lengths are terrain-adaptive, and this feature makes them suitable for broad applications. However, the design and construction control of such bridges requires an accurate assessment of the main cable shape. In this study, an analytical approach for shape finding of the main cable is proposed within the framework of multisegment catenary theory. For the determination of the $\mathrm{sag}:\mathrm{span}$ ratio of the secondary main span and the height of its side pylon, the basic principles were formulated. These imply that the elevation of the lowest hanging point of the main cable in the secondary main span should be equal to the main cable elevation at the midspan point in the main span. An analytical algorithm for estimating the thermal effect on the shape of the main cable was presented. Given the intermediary role of pylon top displacement and rotation angle of the splay saddle, a set of simultaneous equations was established and solved for all spans under three conditions: closure of elevation difference, moment equilibrium of splay saddle, and conservation of the unstressed length of the main cable. The proposed method was applied to a three-pylon suspension bridge with unequal spans of $248+\mathrm{1,060}+\mathrm{1,360}+380\mathrm{m}$. The results obtained proved the feasibility and efficacy of the proposed approach. The application of these principles made it possible to reduce the height of the side pylon on the side of the secondary main span. This not only reduced the material consumption of hangers in the secondary main span but also improved the overall appearance of the bridge. Further analysis of the thermal effects revealed a linear correlation between the structural deformation and temperature variation. Span length variation caused by the bending deformation of pylons was shown to have a significant impact on the temperature sensitivity coefficient of the main cable elevation. This impact can be counteracted by the thermal contraction/expansion in the left and right side spans, whereas the superposition of both effects occurs in the main and secondary main spans.

Chongqi Bridge is part of an important route over the Yangtze River connecting Chongming City in Shanghai with Qidong City in Jiangsu. The steel box-girder bridge consists of separate but adjacent twin six-span bridges, and each is 16 m wide and 944 m long. During construction of the bridge, vortex-induced vibration (VIV) was observed, which caused concern about the performance of the bridge. A vibration test was conducted and an eigensystem realization algorithm (ERA) was performed to identify mode properties of the bridge. A wind tunnel test showed that VIV could occur in the first vertical mode, and tuned mass dampers (TMDs) were installed in the four middle spans of the bridge to control large vibrations. A structural health monitoring (SHM) system was also deployed on the bridge and the TMDs, which includes anemometers, accelerometers, displacement transducers, and so on. On July 10–12, 2015, Typhoon Chan-hom passed through the area near Chongqi Bridge. Wind characteristics were calculated with monitoring data, and the response of the bridges and the TMDs were evaluated under Typhoon Chan-hom. The results indicate effectiveness of the TMDs and their functioning under different wind conditions. An effectiveness factor is proposed to describe the functioning of TMD to mitigate deck vibration, which is illustrated with the acceleration measurements of the deck and the TMDs.

In previous research, the authors numerically investigated 212 finite-element (FE) models of concrete-filled steel tubular (CFST) T-joints under axial force in the brace to derive formulae for stress concentration factors (SCFs). The formulations involve four nondimensional parameters: diameter ratio $\beta$, diameter-to-thickness ratio of chord $2\gamma$, thickness ratio $\tau$, and relative chord length $\alpha$. In the current study, the earlier formulation was extended to include four additional loading conditions: in-plane bending (IPB) in the brace, out-of-plane bending (OPB) in the brace, axial compression in the chord, and IPB in the chord. The validity of the new SCF formulae was demonstrated by comparing the SCFs obtained using the formulae with the results of numerical analysis.