Journal of Bridge Engineering

There is an increasing demand for rapidly deployable causeways that can provide access from ship-to-shore for military and disaster relief operations. Existing systems have major limitations including only being transportable and emplaceable by large strategic sealift vessels, having high weight and packaged volumes, and requiring intensive on-site assembly. In response to the demand for a lightweight, air-liftable, quickly emplaceable causeway, the Engineer Research and Development Center (Vicksburg, Mississippi) developed a prototype comprised of aluminum modules joined by compliant connections and supported by pneumatic floats. As research and development progressed and experience was gained, eliminating the heavy and complex compliant connections was identified as a potential improvement. To eliminate these compliant connections, this paper shows how this design can be reconceptualized so a desired superstructure flexibility (that takes advantage of buoyancy while meeting deflection limits) is achieved. The superstructure has been designed for a target stiffness to permit a desired curvature under a design moment. This paper will review existing causeways, present this reconceptualization, and discuss the optimization implemented to achieve this new design.

A new type of bamboo composite I-shaped beam, which consists of bamboo laminate as its upper and down flange plates and bamboo curtain plywood as its web, was introduced in the paper. In this new type of beam, a connection between the flange plates and the web was enabled with a combined action of epoxy resin adhesive and a bolting joint. A model test on the bending mechanical properties (e.g., bending failure mode and bending capacity) and the factors influencing the flexural rigidity of the bamboo composite I-shaped beam was conducted. The preliminary results showed that the bamboo composite I-shaped beam has excellent mechanical properties that could offer high bending capacity and bending rigidity, as well as excellent ductility of the structure. Therefore, the bamboo composite I-shaped beam is potentially interesting for application in small- to medium-span bridges as a new type of structure. Moreover, this experimental research could help with a design method for bamboo composite I-shaped beams in the future.

Seismic fragility analysis is a complex process involving different sources of uncertainties. In this paper, an alternative procedure for seismic fragility analysis based on the uniform design method (UD) is proposed. UD is used to generate a reasonable sample to build probabilistic seismic demand models (PSDMs), which are used to generate the fragility curves of a cable-stayed bridge. Sensitivity analyses of different uncertainties are carried out by comparison of the fragility curves for different components. It is concluded that (1) the UD method can consider different sources of uncertainties in fragility analysis with reasonable accuracy; (2) the bridge system is more fragile than any component of bridges; and (3) the damage probability of fragility considering uncertainty in the ground motion, geometry, and material is larger than that considering only the uncertainty in the ground motion.

Four full-scale exterior bent cap connections utilizing plain pile embedment were evaluated for suitability in seismic regions. A self-reacting test setup was used to investigate the special case of reverse axial tension and compressive loading expected to occur in the exterior portions of bridge bents. The current state of practice design detail was first evaluated and performed unsatisfactorily. Three additional specimens were then specially designed and evaluated. Specimen variables include embedment depth of the prestessed pile, bent cap reinforcement design, and bent cap dimensions. Specimens were evaluated in terms of moment capacity, plastic hinge length, ductility, and damage to the bent cap. Design alternatives include an idealized hinge connection and two moment transfer connections. The results indicate that the use of plain pile embedment is feasible for regions similar in level of seismicity to South Carolina, provided that the embedment depth is sufficient.

Warping restraining devices can result in substantial improvements in the girder elastic buckling capacity; however, calculating this increase can be complex. This paper presents a simplified method to evaluate the increase in elastic buckling strength and corresponding unbraced length due to improved warping restraint provided by split pipe stiffeners located at the ends of doubly symmetric W-shapes. The solution is based on analytical studies and results from a finite-element parametric study validated using large-scale laboratory tests. The laboratory tests include specimens exposed to concentrated loads with split pipe warp-restraining devices and others with standard plate stiffeners. The proposed analytic method is based on uniform moment and shows that warping restraint can increase the elastic buckling capacity of a girder by 30–100%. The improved warping stiffness can result in increases in the unbraced length in the range of 20–35% compared with systems with plate stiffeners.

While application of full-depth precast bridge deck panels may be appealing because of an accelerated construction schedule and improved safety conditions, corrosion of steel reinforcement is a major factor affecting the structural durability of precast panels and overall serviceability of a bridge deck. Herein, the concept of using aramid fiber reinforced polymer (AFRP) bars as a substitute for conventional steel reinforcement to overcome corrosion issues is verified. For this purpose, a full-scale bridge deck slab consisting of full-depth precast panels reinforced and prestressed with AFRP bars is constructed and experimentally evaluated in terms of load capacity, deformation, crack pattern, and failure mode. The precast panels are reinforced and prestressed in parallel and perpendicular to the traffic directions, respectively, and supported by reinforced concrete beams. Realistic dimensions, boundary conditions, and structural details are physically modeled to represent an actual bridge deck condition, and different concentrated load configurations including wheel and tandem axle loads are applied on both the slab interior span and overhang. The experimental results show the average failure load of the interior spans and overhangs, respectively equal to 3.9 and 1.4 times the maximum factored wheel load, where the deflection serviceability criteria are met and satisfactory deformability performance is achieved.

Concrete-filled steel tubular (CFST) arch bridges have gained popularity over the last decades for use in long-span applications. At service conditions, these bridges are influenced significantly by the time-dependent behavior of the concrete. This paper presents a finite-element model that was developed using commercial finite-element software and is capable of describing the time-dependent behavior. The proposed approach can account for the construction process, time effects, and geometric nonlinearity. The time-dependent behavior of the core concrete in the arch ribs was modeled using European guidelines and the integral-type creep law, implemented with the finite-element model with a user-defined subroutine. The accuracy of the proposed method was validated against real site measurements recorded for a representative arch bridge. As part of this work, the necessity of considering the variation of the time of first loading and the geometric nonlinearity has been discussed. Finally, a simplified method was developed based on the results of the refined finite-element model and is recommended for possible use in day-to-day routine design.

This paper outlines a general methodology used to design digital data streams of electronic sensors attached to critical components of a structure to be processed by a structural impairment detection system (SIDS). The methodology begins by evaluating a specific structure, establishing a baseline behavior profile, and identifying specific structural impairments that are likely to occur. Finite-element modeling of a specific test bed is presented as a tool with which to design and create diagnostic data streams. Establishing a list probable impairments is critical to designing diagnostic data streams with which to implement a SIDS capable of indicating and, more importantly, identifying digital data signatures that may indicate specific structural impairments. Once a set of impairment scenarios is defined, finite-element models representing those impairments are created and several locations sensitive to modeled impairments are identified. A matrix of different locations and measurement types determines the instrumentation schedule. Through experimental observation and iterative structural analysis, diagnostic data streams are created that serve as (1) patterns for training neural diagnostic algorithms and (2) patterns to be interrogated to evaluate a testbed structure.

This paper discusses the effect of agricultural live-loads on lateral load distribution characteristics of girder bridges on rural roadways in the United States. In this study, load distribution factors for bridges subjected to agricultural vehicles frequently used on rural roads are calculated based upon codified processes, field test results, and simulations. As part of this work, five simply supported steel girder bridges in Iowa were selected for field tests with four agricultural vehicles and a highway-type truck. Strain sensors were mounted on the bottom flanges of girders at midspan of all five bridges. Strain data resulting from the test vehicles were measured and used to determine girder distribution factors for each bridge. These strain data were also used to calibrate analytical models of the bridges. Over 120 agricultural vehicles were identified and used to analytically load the models. Girder distribution factors were then computed using responses from the vehicle-induced model simulations. Findings revealed that the analytical and field distribution factors were in most cases smaller than code-specified values, as has been observed by others. In some cases, however, these factors exceeded code values. Furthermore, the variability in agricultural vehicles’ characteristics had a significant impact on the live-load distribution factors for each bridge.

Accurate prediction of optimum damper size and its corresponding maximum attainable modal damping ratio is essential for the design of a linear viscous damper to control cable vibrations on cable-stayed bridges. The stiffness within the damper and the damper support would affect both the required damper size and the resulting equivalent modal damping ratio of the damped cable and thus influence the damper efficiency. An experimental study on a cable-damper system is conducted to investigate the individual and the combined effects of damper stiffness and damper support stiffness on the performance of a linear viscous damper. A finite-element model of the corresponding cable-damper system is developed to verify the experimental results and further study these two parameters within the typical ranges of cable and damper properties used on real bridges. Results show that higher damper stiffness and/or lower damper support stiffness would have an adverse impact on damper performance. Increasing the stiffness of a damper and/or its support would result in a larger optimum damper size. However, the maximum attainable damping ratio would decrease with larger damper stiffness but increase if the support is more rigid. To facilitate practical design, a set of asymptotic relationships has been proposed, of which the optimum damper size and the maximum achievable damping ratio are expressed concisely as functions of nondimensional damper properties in terms of its location, stiffness, and support stiffness. Design examples are given to illustrate the various applications of the proposed refined damper design tool.

Numerous terrorist events during the last decade, including the 2001 attack on the World Trade Center, have heightened concern about the safety of bridges during intentional/unintentional blast load effects. Analysis of highway bridges under blast loads requires accurate generation and application of blast loads and good understanding of the behavior of components of a bridge during high strain rate loading encountered during blast loads. In this paper, a new approach for the application of blast loads on bridge components has been presented. This approach can apply realistic loads and can simulate both reflection and diffraction of blast loads. Using this approach, verification of simulation of blast loads in LS-DYNA has been carried out by using available blast tests on two types of beams. A high fidelity model of a typical three-span highway bridge has been developed for investigation of blast load effects on a three-span reinforced concrete bridge. It is observed that the range of demands imposed on bridge components during blast loads may be significantly higher than those during other extreme hazards, e.g., seismic, for which bridge components may have been designed. Detailed results on various failure modes of this bridge and seismic blast correlations using this model of the bridge are presented in the companion paper.

Bridges with different seismic design levels and concrete compressive strengths have been analyzed for three levels of underdeck blast loads. It is observed that there are several other damage modes besides failure of bridge columns that may contribute to a complete collapse of the bridge. In general, it is demonstrated that an increased seismic resistance leads to improved performance during blast loads. Both concrete strength and seismic capacity are equally effective for bridges designed with higher seismic resistance. Extensive simulations have been performed to establish a correlation between the ratio of ductility and strength reduction factor, $\mu \text{/}R$, and pier top displacement for concrete with different compressive strengths. It has been observed that the pier top displacement decreases drastically for $\mu \text{/}R>6$. Moreover, it is observed from results of 27 simulations that bridge piers with $\mu \text{/}R>6$ survive high levels of blast loads (without failure of piers).

A double-cable system has wide application prospects in multispan suspension bridges. Longitudinal restraint stiffness of a double-cable system to the tower was studied in this paper. Two formulas were derived to calculate the longitudinal restraint stiffness of a double-cable system to the tower and the load distribution between the cables, respectively. A mathematical model of a two-span double-cable suspension bridge was created to verify the formulas. The tower-top displacement and the cable force were obtained by formulas, and the results are in good agreement with the results calculated by the FEM. The effects of some important design parameters on longitudinal restraint were studied. Analysis shows that the restraint stiffness increases with the increasing of unit weight of the bridge, dead load distribution to the top cable, sag ratio of the bottom cable, and elastic stiffness of the cables. Effects of tower-top displacement and span length were also analyzed, and some suggestions were given to design a double-cable suspension bridge.

Differential settlement between the bridge approach embankment and bridge abutment is a major issue in bridge engineering. To mitigate the differential settlement, a new ground-improvement technique, a fixed-geogrid-reinforced and pile-supported embankment (referred to as a FGT embankment) was proposed. To investigate the performance of the FGT embankment, a numerical analysis was performed for a trial bridge approach embankment in Changzhi, China. The numerical model was carefully calibrated to ensure good representation of the realistic conditions. The comparison analyses and parametric study were conducted to evaluate the effects of the traffic load, long-term tensile stiffness of the geogrid, and long-term elastic modulus of the soil. The results show that the FGT embankment can reduce the settlement, enhance the stability, and offer a better performance measure for the construction of a high embankment at the bridge approach.