Editor’s Note

The January 2010 issue of the ASCE Journal of Bridge Engineering begins with three papers on field behavior and numerical investigations of integral abutment bridges. “Field Behavior of an Integral Abutment Bridge Supported on Drilled Shafts,” by Ooi, Lin, and Hamada, discusses the monitoring of a drilled-shaft-supported integral-abutment bridge from foundation installation to in-service behavior phases. Field data show that, after becoming integral, the upright members of the longitudinal bridge frame were not vertical because the excavation and backfilling process caused deep seated movements of the underlying clay resulting in the drilled shafts bellying out toward the stream. The drilled shaft axial loads from strain gages are larger than expected. This study indicates the importance and need for staged construction analysis in design of integral bridges in highly plastic clays.

“Numerical Study of an Integral Abutment Bridge Supported on Drilled Shafts” by Ooi, Lin, and Hamada investigates the integral abutment bridge, monitored over a period of $45\text{months}$ before and after construction, using the finite-element method (FEM) in both two (2D) and three (3D) dimensions. Three-dimensional FEM yields larger overall pile curvature and moments than 2D because in 3D the high-plasticity soil is able to displace in between the drilled shafts, thereby “dragging” the shafts to a more highly curved profile while soil flow is restricted by plane strain beam elements in 2D.

“Field-Measured Response of an Integral Abutment Bridge with Short Steel H-Piles” by Davids, Sandford, Ashley (née Hartt), Delano, and Lyons discusses the response of an integral abutment bridge with short H-piles supported foundations and no special pile tip details such as drilling and socketing based on instrumentation of a single-span integral abutment bridge with $4\text{-}\mathrm{m}$ -long piles at one abutment and $6.2\mathrm{m}\text{to}8.7\mathrm{m}$ -long piles at the second abutment. Abutment and pile head rotations due to self-weight, live load, and seasonal movements were all found to be significant. Measured abutment movements were likely affected by both temperature changes and deck creep and shrinkage. Based on the field study results, the paper recommends that moderately short H-piles be driven to bedrock.

The next three papers discuss design issues related to the behavior of concrete and steel girders. “Shear Performance of RC Bridge Girders Reinforced with Carbon FRP Stirrups” by Ahmed, El-Salakawy, and Benmokrane presents experimental data on the behavior and shear strength of concrete bridge girders reinforced with carbon-fiber-reinforced polymer (CFRP) stirrups. A comparison of tests results with different codes and design guidelines shows that the current ACI 440.1R-06 design method provides conservative predictions; however, the CAN/CSA S6-06 and JSCE 1997 underestimate the contribution of the FRP stirrups due to low strain limits.

“Rotation Compatibility Approach to Moment Redistribution for Design and Rating of Steel I-Girder Bridges” by McConnell, Barth, and Barker discusses key aspects of the rotation-compatibility method along with resulting series of simple equations that may be used for both design and rating of straight continuous-span steel I-girders. Advantages of this procedure include a rational basis for removing the current restrictions on girder geometries permissible for use with moment redistribution provisions and greater design economy because of computation of maximum allowable redistribution moments, which justifies the use of higher levels of moment redistribution.

“Structural Reliability of Prestressed UHPC Flexure Models for Bridge Girders” by Steinberg examines three analytical approaches to evaluate the ultimate flexural strength of UHPC girders. The analysis results show that an acceptable level of reliability can be achieved by using typical AASHTO procedures while allowing the use of familiar and noncomplex equations.

The next five papers address various aspects of bridge engineering. “Directional Effects of Shear Combined with Compression on Bridge Elastomeric Bearings” by Nguyen and Tassoulas discusses large-deformation rubber hyperelasticity and a theoretical model for the steel-reinforced bearing subjected to compression in the direction through the thickness followed by shear in various lateral directions, including bridge longitudinal and transverse directions. The results indicate that the shear direction affects the pad stiffness in 50% shear very little. At directions other than the longitudinal direction for the rectangular elastomeric bearing, or the longitudinal and transverse directions for the square bearing, the rubber strains are reduced by as much as 12% while the stress levels are either reduced considerably or increased slightly. The maximum Mises (equivalent uniaxial) stress in the steel shims is reduced by as much as 42% in the case of the rectangular elastomeric bearing subjected to shear in the transverse direction, or is affected very little in the case of the square elastomeric bearing.

“Active Confinement of Reinforced Concrete Bridge Columns Using Shape Memory Alloys” by Andrawes, Shin, and Wierschem discusses experimental and analytical work to explore the feasibility of using an innovative technique for seismic retrofitting of reinforced concrete (RC) bridge columns using shape memory alloy (SMA) spirals. Uniaxial compression tests of concrete cylinders confined with SMA spirals show a significant improvement in the concrete strength and ductility even under small confining pressure. The analytical results show the superiority of the proposed technique using SMA spirals to CFRP sheets in terms of enhancing the strength and effective stiffness and reducing the concrete damage and residual drifts of retrofitted columns.

“Testing the Response of Box-Type Soil-Steel Structures under Static Service Loads” by Flener presents the static loading of four long-span deep-corrugated steel box culverts with spans of 14 and $8\mathrm{m}$ . Two of the culverts were stiffened at the crown. The test results showed that the stiffening applied on the culverts is quite effective and that plain structure is more sensitive to cover depth compared to stiffened structure. The crown stiffening is more effective under shallow soil covers. Results show that the Swedish and Canadian design methods are conservative when estimating live load moments but they underestimate live load thrusts.

“Time-Dependent Behavior of Concrete-Filled Steel Tubular Arch Bridge” by Shao, Peng, Li, Yan, and Hu presents a simplified method to calculate the time-dependent behavior of a concrete-filled steel tubular (CFST) arch bridge based on the geometric compatibility principle, a step-by-step time-incremental process, and self-equilibrium equations. Through an experimental test on a scaled (1:5) segmental model of the main arch ribs of the Maocaojie Bridge, they show that the numerical results are in good agreement with the experimental results. The stresses in the steel tubes increase, and the compressive stresses in the concrete decrease due to the effects of concrete creep and shrinkage.

Finally, the paper “Influence of Early Temperature Rise on Movements and Stress Development in Concrete Decks” by Subramaniam, Kunin, Curtis, and Streeter develops an understanding of temperature changes introduced by hydration heat release in the first few hours after casting in the thermal movements and stresses of the concrete deck and girders by measuring temperature and strain measurements from a simply supported, single-span, steel-girder bridge with a composite concrete deck. It is shown that setting occurs during the temperature rise and partial strain compatibility between steel girder and concrete deck is initiated at the end of the concrete temperature rise, whereas full strain compatibility between concrete deck and steel girder is achieved at the end of the cooling period following the initial temperature rise.

In the discussion and closure for “Flexural Strengthening of Steel Bridges with High Modulus CFRP Strips” by Schnerch and Rizkalla, Sallam disputes the argument made by the authors pertaining to negligible shear lag for the epoxy in conjunction with the high modulus CFRP strips during the study to examine the behavior of strengthened steel-concrete composite beams with high modulus CFRP materials. The discusser attributes this discrepancy to the locations and the different types of strain gauges. In their closure to the discusser’s comments, the authors thank the discusser and attribute this discrepancy to the possibility that the shear lag effect could become apparent with adhesives with different material properties and/or with the use of thicker FRP strips.