Papers in This Issue

This September 2011 issue of the Journal features nine technical papers and two technical notes. The issue begins with three papers on seismic aspects of bridges. “Seismic Behavior of CFT Column and Steel Pile Footings” by Xiao et al. discusses two column-and-pile footing models consisting of concrete-filled steel tube (CFT) columns, reinforced concrete footings, and steel H-piles designed and constructed at approximately one-fifth scale. The focus of the study is on the comparison between two types of connections between CFT columns and footings: connections consisting of welded studs and connections between base-plate and stiffeners. The two models were tested in a vertical cantilever condition with cyclic horizontal and constant axial loads applied at the top of the column. The model footings were supported on 16 model steel H-piles simulating the pile foundation. Under imposed horizontal displacement, two models with different CFT-to-pile-cap connection details demonstrated satisfactory cyclic behavior with the development of full plastic hinges at the bottom of the columns. Strut and tie modeling analysis was carried out to demonstrate the force-resisting mechanism in the reinforced concrete footing. The study also validated a new design detail for the steel H-pile to pile-cap anchorage.

“Shake Table Studies of a Concrete Bridge Pier Utilizing Pipe-Pin Two-Way Hinges” by Zaghi et al. investigates pipe-pin two-way hinge connections to eliminate moments while transferring shear and axial loads from integral bridge bent caps to reinforced concrete bridge columns. In this study, a rational method is proposed on the basis of the possible limit states to obtain lateral capacity of these hinges. To validate the proposed method, a large-scale two-column bridge pier model utilizing pipe-pin hinges was tested on a shake table. The model was subjected to increasing levels of one of the Sylmar-Northridge 1994 earthquake records. A comprehensive analytical modeling of the pier was also performed using OpenSees on the basis of a macromodel developed for pipe-pin hinges. The experimental results confirm that the hinges designed using the proposed guideline remain elastic with no damage. A good correlation between the analytical and experimental data indicates the appropriateness of the macromodel and other modeling assumptions.

“Performance Evaluation of Deteriorating Highway Bridges Located in High Seismic Areas” by Alipour et al. studies the life-cycle performance and cost of reinforced concrete highway bridges subjected to earthquake ground motions while they are continuously exposed to the attack of chloride ions. The penetration of chloride ions into the concrete is simulated through a finite-difference approach that takes into account all the parameters that can affect the corrosion process. From simulation results, the corrosion initiation time is predicted and the extent of structural degradation is calculated over the entire life of the bridge. A group of detailed bridge models with various structural attributes is developed to evaluate the changes in the structural capacity and seismic response of corroded bridges. For the purpose of the probabilistic seismic risk assessment of bridges, the seismic fragility curves are generated and updated at regular time intervals. The time-dependent fragility parameters are employed to investigate the life-cycle cost of bridges by introducing a performance index that combines the effects of probable seismic events and chloride-induced corrosion. The proposed approach provides a multihazard framework that leads to more realistic performance and cost estimates.

The next two papers relate to geotechnical aspects of bridges. In “Employment of the $P$-multiplier in Pile Group Analysis,” authors Ashour and Ardalan discuss the variation of the $P$-multiplier ($P_m$) used with the $p$-$y$ curve to assess the response of pile group under lateral loads. The $P$-multiplier is influenced by the site geotechnical conditions (i.e., soil profile, type, and properties), pile front and side spacings, and pile group deflection. This study shows the need to incorporate these factors with the recommended sets of $P$-multiplier to avoid any compromise or uncertainty when the $P$-multiplier is treated as a single (unique) value on the basis of pile spacings only. This paper addresses these influential elements using the strain wedge (SW) model technique, suggested $P_m$ values, and data collected from full-scale pile group load tests. The experimental results show that $P_m$ is not unique and should be assessed on the basis of the site geotechnical conditions along with the pile row front and side spacings. The paper also emphasizes that using other techniques such as the SW model, in addition to the $P$-multiplier, could increase the confidence in the predicted pile group lateral response. In “Experimental Study on the Performance of Approach Slabs under Deteriorating Soil Washout Conditions,” Chen and Chai investigate the performance of the approach slab degraded by void formation underneath the slab by load testing. Full-size approach slab specimens were tested under increasing magnitude up to four times AASHTO HS20-44 design truck loads. These tests included four slab specimens with the following details: (1) conventional steel reinforcement representative of current California design, (2) steel reinforcement replaced by a double-layer pultruded fiber-reinforced polymer grating, (3) steel reinforcement replaced by glass fiber-reinforced polymer rebars, and (4) incorporation of steel and polyvinyl alcohol fibers in the concrete mix and removal of top longitudinal and transverse steel. Results indicated that the slabs show satisfactory performance under standard HS20-44 design truck load. Tests also revealed that these slabs exhibited similar performance in terms of stiffness, deformation, and crack pattern when fully supported, but they registered noticeable difference in performance under deteriorating soil washout conditions. The fiber-reinforced concrete slab, in general, showed the best crack control and the smallest deflection, as well as end rotation among the four slabs.

The next two papers in this issue are related to long-span bridges. In “Research on Cable Anchorage Systems for Self-Anchored Suspension Bridges with Steel Box Girders,” authors Nie et al. investigate a new type of steel-concrete composite cable anchorage system for self-anchored suspension bridges with steel box girders. Model tests and three-dimensional (3D) finite-element analysis of the pure steel and steel-concrete composite cable anchorage systems have been carried out for the Qingdao Bay Bridge Project under construction in China. For the pure steel anchorage system, a complex stress distribution with obvious stress concentration is observed in the test. Finite-element analysis (FEA) results of the stress distribution correlate well with the experimental measurements. The pure steel anchorage system adopted in the final design of the Qingdao Bay Bridge Project is reliable with sufficient safety margin. Conversely, test results of the composite anchorage system show that the stress level is reduced significantly and the stress distribution becomes more uniform in comparison with the pure steel anchorage system. The average measured stress reduction rate for the composite anchorage system is approximately 40%. This value is slightly smaller than FEA results, indicating a partial composite effect between the steel and concrete. It is shown that the proposed composite anchorage system can effectively reduce the thickness of the steel plates, improve the mechanical behavior of the anchorage system, and simplify fabrication and construction procedures. In “Energy Damage Detection Strategy Based on Strain Responses for Long-Span Bridge Structures,” Xu et al. present a damage detection strategy based on strain responses. For this, strain-based energy dynamic indexes for a multiple-degree-of-freedom system have been derived from the frequency response function (FRF) of strain responses and energy spectra density. Then the traditional mode shape curvature strategy has been used to analyze a long-span cable-stayed bridge. It has been observed that the proposed strain-based energy damage detection strategy resolved the shortcomings of traditional mode shape curvature strategy. It is shown through numerical results that the proposed strain-based energy damage detection strategy can locate damage positions accurately. The method also has good damage quantification and antinoise pollution abilities.

The next two papers are related to bridge decks and girders. In “Full-Scale Testing for Composite Slab/Beam Systems Made with Extended Stud Spacing,” Badie et al. investigate the limit on the 610-mm (24-in.) spacing of stud shear connectors in composite slab/steel beam systems. This paper presents experimental research carried out as part of the National Cooperative Highway Research Program (NCHRP) 12-65 project on this issue. One of the objectives of the NCHRP 12-65 research project was to investigate the possibility of extending this limit to 1,220 mm (48 in.) for clusters of studs used for precast concrete panels made composite with steel I-beams. The experimental investigation included testing of push-off specimens and full-scale composite beams. Results of the push-off specimens have shown that the fatigue loading has no detrimental effect on the load-slip relationship when the number of studs is doubled per cluster. This paper presents the second part of the experimental investigation, which focuses on fatigue and ultimate testing of full-scale composite beams. Test results have demonstrated that full composite action between precast concrete panels and steel girders can be achieved when the spacing between the stud clusters is extended up to 1,220 mm (48 in.).

In “Development of Flexural Strength Rating Procedures for Adjacent Prestressed Concrete Box Girder Bridges,” authors Naito et al. present an investigation on noncomposite prestressed precast concrete adjacent box-beam bridges. Recent catastrophic failure of prestressing steel because of corrosion has highlighted the need to improve methods used to detect corrosion damage and subsequently load rate the damaged members. Currently, the inspection of concrete box girder sections relies on visual methods that correlate longitudinal and transverse cracking, spalling, and exposed strands with the rated level of performance of the member. To improve the current inspection techniques, visual assessment methods are examined through destructive evaluation and material characterization of seven box-beam sections. The research results indicate that fabrication techniques used for box-beam construction in the 1950–1960 time period allowed for large variations in construction tolerance. Half-cell methods have not been found reliable in identifying corrosion of prestressing strands. Longitudinal cracking has been shown to be an accurate and reliable indicator of underlying corrosion of prestressing strands. A new recommendation for determining the residual flexural strength of corroded prestressed beams is presented in this paper.

The remaining two papers in this issue are technical notes. “Full-Bridge Deflected Shape Synchronous Measurement in Bridge Loading Test” by Zhang et al. presents a measurement system based on hydraulic head principles and optoelectronic liquid level sensors. With this system, the deflection of the bridge is converted into an electrical signal through optoelectronic liquid level sensors. Liquid level values of all the sensors can be collected synchronously by a host computer. As a result, the multipoint deflection can be measured to obtain the full-bridge deflected shape. The method has been applied to the Caiyuanba Yangtze River Bridge in Chongqing, China. Test results show that the proposed method has advantages in time efficiency and labor costs. “Estimation of Tension in Cables with Intermediate Elastic Supports Using Finite-Element Method” by Wang et al. presents a method for estimating the tensions in cables with intermediate elastic supports. An analytical form of the equilibrium equation for a tension bar has been used to provide a shape function to develop a suitable finite-element model for a cable. A program for estimating the tension in cables with intermediate elastic supports where the bending stiffness of the cable, the stiffness of the end restraints, and the stiffness of the intermediate supports are taken into account has been developed using this element and MATLAB. The program has been verified by comparison of the results from laboratory experiments. Application of the method to estimate tension in the tie bars of a concrete-filled steel tube arch bridge has been demonstrated.