Journal of Bridge Engineering

The terrorist attack on September 11, 2001, and subsequent potential threats to the United States transportation systems have presented an urgent need to elevate the security of the transportation infrastructure and to develop emergency response plans to quickly react to the possible consequences of an extreme event. Highway bridges, as critical components of the nation’s transportation network, have been brought to closer attention by government agencies. A research project was conducted to identify strategies and technologies to restore the use of a damaged bridge quickly. One of the tasks associated with the research was to perform several case studies of previous bridge replacements following extreme events. These events include explosion and fire caused by vehicle impact, vessel collision with a bridge, and damage caused by flood and earthquake. By studying the cases, the research team seeks to identify and expand on lessons learned and address which actions did and did not work well given the circumstances of the incident. These lessons have great value to the people who need to develop and implement an emergency response plan.

Vehicular overloads are essential for economic activities, but the circulation of very heavy vehicles involves serious concerns regarding the structural safety of bridges. In most countries, the necessary permit process is time and cost consuming and the evaluation criteria sometimes do not lead to safe situations. This paper presents a new methodology for permit checking of vehicular overloads, based on an initial statistical study performed to characterize these vehicles. The method includes software that performs a simplified structural safety analysis of the bridges crossed by a vehicular overload, computing safety factors that compare code design load effects with those due to vehicular overload. The software also connects the vehicular overload database with a geographic information system representation of the highway network, allowing for the definition of several functionalities that support the permit decision. This new methodology allows for prompt, economical, and safe decision making on permit checking of vehicular overloads and is presently applied by the Portuguese national major expressway authority.

The paper presents a method for comparing the mechanical effects of overweight and design load vehicles on bridges. There is no restriction on the arrangement of the axles and on the size of the axle loads. The bridge may be a simple span bridge, a continuous girder, a truss girder, or an arch. Even for a very complex bridge structure the only required parameter of the bridge is the span length. The presented method is a robust and reliable tool for the permitting process of overweight vehicles, which is verified by several thousand comparisons.

Large-amplitude vibrations are known to occur in the main stays of cable-stayed bridges in the presence of rain and wind. Although this problem first surfaced in many bridges around the world in the mid-1980s, it was not until 1996 when the Texas Department of Transportation began to investigate this problem in the United States. Both wind-tunnel and full-scale tests were conducted simultaneously to better understand this phenomenon and devise mitigation methods to reduce the vibrations. Full-scale tests were conducted on four cable stays of the Veterans’ Memorial Bridge near Port Arthur, Tex., over a period of three years. This paper presents observations from selected full-scale data and compares them to wind-tunnel test results as well as results found in past literature. Some observations regarding assessment of a distributed passive mitigation device that was installed on one of the cable stays in the field to control vibrations in the presence of rain and wind are also presented. Wind-tunnel tests show that this device is very effective. Limited data collected from the field after the installation of the device gives some evidence of its effectiveness in reducing the vibrations.

A probabilistic approach is proposed to help select the most suitable nondestructive inspection (NDI) technique and associated optimal schedule for fracture-critical member/detail fatigue inspections on a specific steel bridge. The probability of detection (POD) function for the NDI technique, which is a measure of the detection accuracy, is employed. By combining probability calculations based on use of the POD function together with numerical Monte Carlo simulations of the crack propagation of the fracture-critical detail, a cost function is formulated that includes the expected cost of inspections and failure resulting from the chosen NDI technique and alternative inspection schedules. In summary, the selection of an NDI technique with an associated inspection schedule for fracture-critical inspections is formulated as an optimization problem that can guarantee minimum total cost. The inspection frequency is determined as part of the optimization that utilizes appropriate constraints on inspection intervals and a minimum acceptable (target) structural safety level. A case study for a box girder bridge is presented to demonstrate the application of the proposed probabilistic method.

This paper focuses on the fatigue damage caused in steel bridge girders by the dynamic tire forces that occur during the crossing of heavy transport vehicles. This work quantifies the difference in fatigue life of a short-span and a medium-span bridge due to successive passages of either a steel-sprung or an air-sprung vehicle. The bridges are modeled as beams to obtain their modal properties, and air-sprung and nonlinear steel-sprung vehicle models are used. Bridge responses are predicted using a convolution method by combining bridge modal properties with vehicle wheel forces. A linear elastic fracture mechanics model is employed to predict crack growth. For the short-span bridge, the steel-sprung vehicle caused fatigue failure up to 6.5 times faster than the air-sprung vehicle. For the medium-span bridge, the steel-sprung vehicle caused fatigue failure up to 277 times faster than the air-sprung vehicle.

Hybrid concrete box-girder bridges that include prestressed slabs and corrugated steel webs provide a major improvement over traditional prestressed concrete box-girder bridges. To reduce the self-weight, high strength concrete is used for the top and bottom slabs and corrugated steel webs are employed for the webs. Because the weight of the girders has been reduced, the span length can be increased for more cost-effective design. A series of systematic tests on hybrid concrete box girders subjected to torsion has been performed. According to the test results, an analytical model was developed. Using the developed analytical model, a step-by-step procedure for torsional design of such bridges is presented in this article. Based on the design procedure proposed, a girder is designed by the analytical model and checked to satisfy structural codes.

An investigation is conducted to quantify long-term effects on a family of four precast segmental bridges. Segments are prefabricated, transported, and set into place with an appropriate lifting device and a launching gantry. Attention has been paid to the effects of long-term deformations of concrete, to avoid noticeable geometrical variations in its shape but also to account for redistribution of stresses, which creates a difficult analytical problem to solve. An attempt is made to provide a practical treatment of serviceability analyses of this type of concrete structure, having an evolutive process of erection, presenting: (1) an “exact” incremental step-by-step time approach; (2) a simplified approach for the inclusion of time dependent effects of creep and shrinkage; and (3) a comparison of both approaches, in order to treat these kinds of problems by means of a simplified approach.

An experimental study is presented of the behavior of eight reinforced concrete bridge girders taken from a decommissioned Interstate bridge and retrofitted with three different carbon-fiber-reinforced polymer (CFRP) systems. Specimens were subjected to monotonic loading to failure with and without significant fatigue conditioning. Experimental observations indicated that intermediate crack-induced debonding was the dominant failure mode for monotonically loaded beams and that degradation of the CFRP-to-concrete interface was caused by fatigue conditioning. Conventional adhesive applied and near-surface mounted (NSM) CFRP systems behaved well under monotonic loads, with the NSM system exhibiting significantly greater ductility. Powder actuated fastener applied retrofit was observed to be less efficient, requiring a relative slip of the CFRP in order to engage the shear transfer mechanism of the fasteners. The application of current accepted design guidelines for FRP retrofit indicated that guidelines aimed at mitigating debonding failure appear to be appropriately conservative under monotonic loading conditions; however, a significant additional reduction in CFRP strain limits is required to account for even small levels of fatigue loading.

A set of column-footing subassemblies were prepared to investigate construction feasibility and seismic performance of structural joints for concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) as bridge substructure. Based on the common practices of the precast industry and previous research on CFFT, the test matrix included a control reinforced concrete (RC) column and three CFFT columns, all with similar RC footings. The three CFFT columns included a cast-in-place CFFT column with starter bars, a precast CFFT column with grouted starter bars, and a precast CFFT column with unbonded posttensioned rods. The columns were subjected to a constant axial load and a pseudostatic lateral load. All proposed joints proved feasible in construction and robust under extreme load conditions. FRP tube, when secured properly in the footing, showed great influence on the seismic performance of the column by providing both longitudinal reinforcement and hoop confinement to the core concrete. The CFFT columns exhibited significant improvement over traditional RC columns in both ultimate strength and ductility. The study also showed that practices of the precast concrete industry can be easily and effectively implemented for the CFFT column construction.

An analytical study investigating how changes in the mechanical properties of individual seismic isolators affect the response of isolated bridge structures subjected to earthquake excitation is summarized. Nonlinear response-history analyses are conducted utilizing bins of recorded earthquake ground motion pairs. Twenty bilinear isolation systems are considered so that the results of this study are broadly applicable to the design of seismic isolation systems in the United States. Variations in the mechanical properties are considered using a property modification factor, $\lambda$ , to modify the appropriate bilinear isolator parameter. The results of analyses considering nominal and modified isolation systems are used to systematically identify changes in system response as a function of the property modification factor. These results are used to determine threshold values of the property modification factor that should aid engineers in the preliminary design and assessment of an isolation system prior to performing the bounding analysis now required by bridge and building design codes.