Journal of Bridge Engineering

Dynamic distributed fiber optic strain sensors were used, for the first time, to monitor the behavior of an in-service corrugated steel culvert with a span of 2.75 m and a skew angle of 45° under static and dynamic vehicle loading. These sensors enabled thrust and moment distributions to be measured around the circumference of the culvert. The peak thrusts were not found at the springlines as assumed by North American design codes. Additionally, the flexural stresses were of a similar magnitude to the hoop stresses, contrary to the assumption of ring compression used in many design codes. Dynamic truck loading resulted in higher thrusts and lower moments than did static loading. For this culvert, the deteriorated asphalt pavement had little influence on thrusts but did reduce the magnitude of the moments. Maximum thrust envelopes were developed using the distributed data, and demonstrated that positions near the crown experienced thrusts higher than those at the springlines. The peak measured strain was 9.3% of the yield strain, suggesting that the culvert had adequate live load capacity.

Numerous bridges with piers over 40 m are constructed in Southwest China, which is known as a region of high seismicity. In current research, this type of bridge is commonly simplified as a single-column system, and researchers mainly focused on how seismic performance is affected by the higher modes of columns. This study aims to investigate the seismic behavior of the entire system of tall-pier bridges subjected to near-fault ground motions, using probability-based fragility analysis. A numerical model of the entire bridge system is constructed incorporating the effects of higher-order modes of pier columns and the influence of various structural components as bearings, shear keys, and end abutments. Both pier columns and rubber bearings are considered as vulnerable components during fragility analysis. With probability seismic demand models (PSDMs) developed from extensive nonlinear time history analyses, both component-level and system-level fragility curves of the prototype bridge are constructed and compared. The results show that bridge performance is usually dominated by rubber bearings, rather than pier columns, and the relative vulnerability of components might change with the intensity of input motions. This fact implies that only focusing on the seismic demands of pier columns, as is usual in current investigations, is insufficient in estimating the damage states of tall-pier bridges; failure of bearings should be carefully considered in engineering practice as well. Furthermore, compared with fragility curves of individual components, higher seismic vulnerability is observed in those corresponding to the entire system, indicating that the seismic fragility of tall-pier bridges should be assessed at the system level rather than component level.

Several connection details have been developed for connecting precast cap beams to precast columns in accelerated bridge construction (ABC) applications. Currently, the suggested details involve either reinforcement or penetration of a portion of the precast column inside the cap beam. Such details present several challenges in the field. To overcome these challenges, a new connection detail was envisioned. In this detail, the cap beam and the column are spliced in the column and joined with a closure joint of ultrahigh-performance concrete (UHPC). The primary goals of this research were to describe the proposed detail and verify its structural performance through an experimental program. The results showed that the detail is applicable in both seismic and nonseismic regions and is capable of achieving adequate levels of ductility. The proposed detail, with the current detail, requires a temporary bracing or shoring tower to support the precast column and pier cap during construction, which may not be favorable for accelerated bridge construction. Additionally, the test specimens in this study do not represent current methods in the construction industry. Further research is needed to evaluate the performance of the proposed detail considering construction means and methods.

To study the structural response of a long-span cable-stayed bridge to cable loss during construction, the static performance of the Chishi Bridge subjected to multiple-cable loss caused by a fire accident was investigated in detail by field inspection and finite-element simulation. Nine cables on the same cable plane ruptured successively during the fire accident. As a result, the cantilever end of the girder dropped by 2.08 m, and the girder cracked severely. The cable tension, the displacements, and the damage state in the girder and pylon were measured to verify the nonlinear finite-element model. A comprehensive numerical study was then conducted to analyze the structural behavior of the bridge throughout the process of cable loss and subsequent restoration. The results from the field inspection and simulation showed that (1) the obvious change in cable tension and concrete cracking occurred in only the remaining cables and part of the girder within and around the cable loss area; (2) the loss of nine cables in the local area caused the combined action of torsion and biaxial bending in the girder, and resulted in dense distribution of diagonal cracks in the top slab and box girder webs; (3) after the accident, the maximum tensile stresses in the remaining cables and prestressed tendons reached 1,495 and 1,546 MPa, or 89.3% and 92.3% of the yield strength of steel strands, respectively, while the maximum principal compressive stress in the box girder reached 29.8 MPa, or 83.9% of the concrete compressive strength; and (4) the global structural performance of the damaged bridge recovered very well when the temporary cables that were added to replace the broken cables were jacked to the original design tension, indicating that the global behavior of the cable-stayed bridge was mostly controlled by the cables.

This paper presents an efficient framework for the fatigue reliability assessment of typical long-span steel-truss suspension bridges under the combined action of random traffic and wind loads based on a stress analysis approach. The Aizhai Bridge in China was selected as an example to demonstrate the numerical procedure for this framework. In the numerical analysis, the critical locations of the bridge were first determined by refined finite-element analyses, and 30,000 samples of random input parameters (random wind field and traffic flow) were generated. Subsequently, the corresponding dynamic stress responses at the critical locations of the bridge were obtained via a stress analysis approach under the combined action of random traffic and wind loads. Finally, the fatigue reliability of the bridge was assessed considering the influence of the wind load, traffic growth, and vehicle axle load growth. The results show that both the wind and traffic loads have certain effects on the fatigue reliability of the bridge. The upper and lower chords of the main truss at one-fourth of the span, which is sensitive to both the wind and vehicle loads, should be given more attention.

In twin-girder crossbeam composite (TGCBC) bridges, the concrete slab supported only by steel plate girders is typically regarded as a one-way slab, and its transverse bending moments are essential for structural optimization and evaluation. However, little research has been conducted on the transverse-moment distribution of the slab in TGCBC bridges and the slab moment prediction method capable of considering the effects of actual configurations and dimensions is not available in the current TGCBC bridge design practice. Recommendations by design codes for continuous slabs in steel or concrete bridges have not considered the structural characteristics of TGCBC bridges, which may result in an uneconomical or unsafe slab design for TGCBC bridges. In this paper, finite-element analyses were conducted on an existing TGCBC bridge to investigate the transverse-moment distribution of its concrete slab under external loads. A simplified method based on a frame model for predicting the transverse-moment distribution coefficients was then proposed. The effects of geometric parameters and cracking of concrete slabs on the transverse-moment distribution coefficients were also examined through a parametric analysis. The analysis results show that the transverse bending stiffness of steel plate girders, which is mainly determined by the layouts of web transverse stiffeners and crossbeams, has a significant influence on the transverse-moment distribution of the slab. Additionally, the distribution coefficients are also dependent on the geometric parameters of TGCBC bridges as well as the magnitude of external loads. The results also show that the transverse-moment distribution coefficients could be precisely estimated by the proposed simplified method.

Transverse post-tensioning is commonly introduced in top slabs of concrete box girders to control transverse tensile stresses induced by dead and live wheel loads. However, longitudinal cracks with a definite pattern have occurred time and again on the bottom of top slabs. This unexpected cracking distress urges a reevaluation of the structural effect of transverse prestressing. First, a step-by-step three-dimensional (3D) modeling was employed to simulate the balanced cantilever construction of box-girder bridges. It was found that the stressing sequence of transverse tendons has a significant influence on the slab prestress distribution along the bridge. The commonly adopted immediate tensioning method (referring to stressing transverse tendons in segment $i$ immediately after the casting and hardening of segment $i$) yields a $\pm 40\%$ fluctuation of slab prestress within each segment, resulting in much lower prestress near the segment’s rear joint, where cracks are easily occurred. In contrast, the delayed tensioning method (referring to stressing transverse tendons in segment $i$ after the casting and hardening of segment $i+1$) will greatly alleviate the nonuniform distribution. Second, an explicit equation based on an analytical model is proposed for calculating the slab transverse prestress. To overcome the problem of large friction losses in the current flat anchorage (FA) system, an alternative single-large-strand (SLS) system was designed and its performance verified by full-scale comparative tests. The test results show that the friction loss of the SLS system is only one-third of the FA system, and the overall structural efficiency can be increased by 20%.

The use of timber–concrete composite (TCC) bridges in the United States dates back to approximately 1924 when the first bridge was constructed. Since then a large number of bridges have been built, of which more than 1,400 remain in service. The oldest bridges still in service are now more than 84 years old and predominately consist of two different TCC systems. The first system is a slab-type system that includes a longitudinal nail-laminated deck composite with a concrete deck top layer. The second system is a stringer system that includes either sawn timber or glulam stringers supporting a concrete deck top layer. The records indicate that most of the TCC highway bridges were constructed during the period of 1930–1960. The study presented in this paper discusses the experience and performance of these bridge systems in the US. The analysis is based on a review of the relevant literature and databases complemented with field inspections conducted within various research projects. Along with this review, a historical overview of the codes and guidelines available for the design of TCC bridges in the US is also included. The analysis undertaken showed that TCC bridges are an effective and durable design alternative for highway bridges once they have shown a high performance level, in some situations after more than 80 years in service with a low maintenance level.

Estimation of the time that a bridge or bridge component stays in a specific condition can guide decision-making on bridge maintenance and preservation. Statistical models of the time-in-condition rating (TICR) for bridges or bridge components are good candidates for this purpose. Typically, these models are calibrated using existing inspection data. Current practice tends to trim a large portion of the data that are deemed incomplete. However, there is actually a lot of useful information in these data (e.g., lower bounds for TICR), which should also be incorporated to establish better estimation of TICR. To address this, within the Bayesian framework, this paper proposes the adoption of a modified likelihood function to explicitly incorporate both complete and incomplete inspection data for model calibration. In addition, Bayesian model class selection is used to select the most appropriate models out of several candidate statistical models. The proposed approach is applied to establish TICR models for different types of bridges and bridge components in Colorado using National Bridge Inventory (NBI) data. The results and comparisons show the importance and necessity of explicitly incorporating incomplete inspection data in the model calibration and class selection for bridge condition deterioration models.