Journal of Bridge Engineering

In this study, two column and pile-footing models consisting of concrete-filled steel tube (CFT) columns, reinforced concrete footings, and steel H-piles were designed and constructed at approximately one-fifth scale. The experimental differences between the two models were in the design details of the CFT column-to-footing connections. One connection consisted of welded studs, and the other used a base plate and stiffeners. The two models were tested in a vertical cantilever condition with cyclic horizontal forces and a constant axial load applied to the top of the column. The model footings were supported on 16 model steel H-piles simulating the pile foundation. Under imposed horizontal displacement, the 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 show the force-resisting mechanism in the reinforced concrete footing. The study also validated a new design detail for the anchorage of steel H-piles to pile caps.

Pipe-pin two-way hinge details were recently developed by California Department of Transportation (Caltrans) to eliminate moments while transferring shear and axial loads from integral bridge bent caps to reinforced concrete bridge columns. The hinges consist of a steel pipe that is anchored in the column with an extended segment into the cap beam. There is no specific design guideline for these hinges, and the current design method is primeval and only controls shear failure of the steel pipe. In this study, a rational method is proposed on the basis of the possible limit states to obtain the 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; for this purpose, a macro model was developed for pipe-pin hinges in this study. The experimental results confirmed that the hinges designed on the basis of the proposed guideline remain elastic with no damage. The good correlation between the analytical and experimental data indicated that the macro model and other modeling assumptions were appropriate.

This paper 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 are 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.

This paper discusses the variation of the $P$-multiplier ($P_m$) used with the $p\mathrm{\text{-}}y$ curve to assess the response of a pile group under lateral loads, which is a crucial topic for the design of bridge pile foundations. $P_m$ is influenced by the site geotechnical conditions (i.e., soil profile, type and properties), pile front and side spacings, and pile-group deflection. The presented study shows the needs to incorporate these factors with the recommended sets of $P_m$ to avoid any compromise or uncertainty when $P_m$ is treated as a single (unique) value based only on pile spacings. The current study 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 must be assessed based on the site geotechnical conditions along with the pile-row front and side spacings. Because the employed $P_m$ values must be a function of these influential factors, additional full- and model-scale load tests with different pile spacings and soil types might be required. 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 the U.S. bridge design practice, an approach slab is commonly provided to facilitate a smooth transition from the highway pavement to the bridge deck. Maintenance of bridge approaches often necessitates the repair or replacement of approach slabs owing to damage from heavy traffic loads, washout of fill materials, and settlement of the approach embankment. Approach slab damage because of embankment settlement is considered a more common problem and has been extensively investigated in the literature. In this paper, performance of the approach slab degraded by void formation underneath the slab is examined by load testing. Full-size approach-slab specimens were tested under increasing magnitude up to four times AASHTO HS20-44 design truck loads. The test matrix 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 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 and end rotation among the four slabs.

A new type of steel-concrete composite cable anchorage system is conceived and investigated preliminarily for self-anchored suspension bridges with steel box girders to optimize the mechanical behavior of the conventional cable anchorage systems. Model tests and 3D elaborate finite-element analysis (FEA) of the pure steel and steel-concrete composite cable anchorage systems are carried out for the Qingdao Bay Bridge Project, which is under construction in China. For the pure steel anchorage system, a complex stress distribution with obvious stress concentration is observed in the test. The 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 a sufficient safety margin. In the contrast test of the composite anchorage system, owing to the composite effect between the steel and concrete, the stress level is reduced significantly and the stress distribution becomes more uniform in comparison with the pure steel anchorage system. The measured stress reduction rate of the composite anchorage averages approximately 40%, which is slightly smaller than the FEA results, and indicates the partial composite effect between the steel and concrete. The proposed composite anchorage system can effectively reduce the thickness and consumption of the steel plates, improve the mechanical behavior of the anchorage system, and simplify the fabrication and construction procedures.

An energy damage detection strategy through disposing strain responses has been developed. First, the strain-based energy dynamic indexes for a system with multiple degrees of freedom were derived from the frequency response function (FRF) of strain responses and energy spectra density. Then, the traditional mode-shape curvature strategy and the proposed strain-based energy damage detection strategy were both used to analyze a long-span cable-stayed bridge, and it was found through comparison that the proposed strain-based energy damage detection strategy solved the shortcomings of the traditional mode-shape curvature strategy. Finally, damage location, damage quantification, and noise pollution resistance analysis for a long-span cable-stayed bridge with different degrees of damage were carried out to verify the effectiveness of the proposed strain-based energy damage detection strategy. The numerical analysis showed that the proposed strain-based energy damage detection strategy can locate damage positions accurately, and it also has good damage quantification and noise pollution resistance abilities.

Investigation of the background of the 610 mm (24 in.) spacing of stud shear connectors showed that this limit was set on the basis of a small amount of testing of beams with spacing greater than this limit. The literature search showed that some attempts have been recently made to extend this limit. 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 cluster 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 covers the second part of the experimental investigation, which is fatigue and ultimate testing of full-scale composite beams. The full-scale testing has proven 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.).

An investigation was conducted on noncomposite prestressed precast concrete adjacent-box-beam bridges that suffered catastrophic failures resulting from the corrosion of the prestressing steel. These failures highlight the need to improve the methods used to detect corrosion damage and, subsequently, to 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 were examined through the destructive evaluation and material characterization of seven box-beam segments. The research results indicate that the fabrication techniques used for box-beam construction in the 1950–1960 time period allowed for large variations in construction tolerance. Half-cell methods were shown not to provide an accurate or reliable method of identifying the corrosion of prestressing strands. Longitudinal cracking was shown to be an accurate and reliable indicator of the underlying corrosion of prestressing strands. The probability of corrosion on strands adjacent to longitudinal cracks was determined and quantified. On the basis of the results, a new recommendation for determining the residual flexural strength of corroded prestressed beams is provided.

A loading test can provide valuable insight into the behavior and fundamental characteristics of an existing or new bridge. The full-bridge deflected shape in long-span bridges is an important parameter that evaluates the safety state of a structure. To improve efficiency and reduce labor costs of bridge deflection measurements in a loading test, a measurement system established on hydraulic head principles and optoelectronic liquid-level sensors has been developed. With this system, the deflection of the bridge is converted into an electrical signal through optoelectronic liquid-level sensors, and the liquid-level values of all the sensors can be collected synchronously by a host computer. As a result, the multipoint deflection can be measured so that the full-bridge deflected shape is obtained. The method has been applied to the Caiyuanba Yangtze River Bridge in Chongqing, China, and the results show that the proposed method has apparent advantages in time efficiency and labor costs.

Cables with intermediate elastic supports are widely used in bridge engineering, but there is a lack of effective methods for estimating the tensions in these cables. In this paper, 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 has been developed in which the bending stiffness of the cable, the stiffness of the end restraints, and the stiffness of the intermediate supports are taken into account by using this element and MATLAB. The program has been verified by comparison of the results from laboratory experiments. The method has been applied to compute the tension in the tie bars of a concrete-filled steel tube arch bridge. This demonstrates that the cable tension estimated by the present method is suitably accurate.