Local Stress Behavior of Post-Tensioned Prestressed Anchorage Zones in Continuous Rigid Frame Arch Railway Bridge

The concrete stress behavior and cause of cracking at the anchorage zones of top and bottom slabs of a post-tensioned prestressed concrete box beam were studied. Based on the complex stress distribution under local anchor problem for the Yichang Yangtze River Bridge, which is the longest continuous rigid frame arch railway bridge in the world, model tests were conducted. Two full-scale specimens of top and bottom slabs were fabricated and gradually loaded based on principle of equivalent stress. The goal was to analyze the longitudinal and transverse stress distributions of cross sections of specimens at various loading cases during the experiment. From the experimental results, it can be concluded that the mechanical behavior of the concrete and steel bars were in good agreement when prestressed tendons were loaded. Tensile stress of concrete in prestressed anchorage zone gradually increased and surpassed the ultimate tensile strength of concrete with the increasing load. Consequently, local longitudinal cracking was formed at the anchorage block. Some recommendations to avoid the concrete at the anchorage zone continuing to crack are summarized in this paper

In-Situ Test and Dynamic Response of a Double-Deck Tied-Arch Bridge

In this study, in-situ dynamic tests of the world\u27s longest steel box tied-arch bridge over the Yangtze River, China, are reported. The double deck bridge supports highway and monorail systems at upper and lower levels, respectively. Strain, displacement, and acceleration responses were measured and used to investigate the vibration characteristics of the bridge when excited by running trains and/or trucks at a speed of 5-60 km/h, train braking, and truck bouncing. Impact factors were correlated with the running speed of trains and trucks. A three-dimensional finite element model of the coupled monorail-train-bridge vibration system accounting for track irregularities was established to understand the system behavior and validated by the experimental results. Truck bouncing was the dominant impact factor on bridge responses. The running speed of vehicles determined the riding comfort of traveling trains

Dynamic Behavior of Hybrid Framed Arch Railway Bridge under Moving Trains

In this study, the dynamic behavior of a concrete-filled steel tube (CFST) hybrid framed arch railway bridge under moving trains are investigated through an in-site dynamic test. The bridge was tested under train loadings in different scenarios and at different speeds of the trains. The free vibration characteristics, strain, displacement, and acceleration of the bridge structure were measured to evaluate the dynamic responses of the train-bridge coupling system. A three-dimensional finite element model, which took into account the train-bridge coupling and track irregularities, was established to analyze the behaviors of the train-bridge system. The model was validated against the in situ test results. The impact effect on the girder was greater than that of the arch frame. The acceleration responses of the trains on the bridge increased with the train\u27s speed. The riding comfort of the trains was evaluated based on the measured dynamic responses of trains

Thermo-Hydro-Mechanical Combined Effect Analysis Model for Early-Age Concrete Bridges and Its Application

The early cracking of concrete beam bridges remains a concern in civil engineering. An analytical model considering the combined effect of thermo-hydro-mechanical processes forms the basis for assessing the cracking risk of girders during construction. Based on the equivalent hydration theory, the temperature and moisture conduction processes and the evolution of the mechanical properties of concrete were modeled as a function of the equivalent age. A coupling model for the temperature and moisture fields was established, and a theoretical framework for analyzing the thermo-hydro-mechanical combined effect was presented. Based on this, a numerical analysis method was proposed and implemented into ABAQUS; the results were validated with some typical tests. Finally, a long-span prestressed concrete (PC) box girder bridge with balanced cantilever construction was taken as an example, and the causes of web cracking and its impact degree were analyzed. The results show that the rate of moisture conduction is significantly lower than the rate of temperature conduction; even for thin-walled components, there exists a significant humidity gradient on the surface layer. The humidity-induced shrinkage and restraint of the precast members are the main causes of web cracking

Experimental Study on Dynamic Effects of a Long-span Railway Continuous Beam Bridge

Studies on impact effects of trains on the railway bridge are important for ensuring the reliability of bridge and the safety of train operation. This paper presents an experimental study on the dynamic effects of moving trains on a long-span railway continuous beam bridge. The dynamic responses of the bridge under the moving trains were measured through in-situ testing and finite element analysis. The influences of the moving trains and track irregularity are considered. The investigated influencing factors include the weight and speed of the train and the irregularity of the track on the bridge. The results indicate that the train’s speed does not have obvious influence on the impact factor, while train’s weight and track irregularity have notable effects on the impact factor. But from the overall development law, with the increase of train speed, the impact factor increases. The impact factors obtained in this study are larger than the values provided by the China bridge design codes, which indicates that the bridge code underestimates the impact effect of the train on the bridge. The design value of the impact factor should be properly improved in the bridge design

Fatigue Behavior of Prestressed Concrete Beam for Straddle-Type Monorail Tracks

Monorail transportation systems are widely built in medium and small cities, as well as hilly cities, because of their excellent performance. A prestressed concrete track beam is a key load-carrying structural component and guideway subjected to repeated traffic load. The fatigue behavior of the prestressed concrete beam is critical for the safety of the transportation system. This paper presents the results of an experimental study on the fatigue behavior of a prestressed concrete beam in terms of stiffness degradation and strain change. The displacement and rotation of the beam of concrete and reinforcement were examined, respectively. A three-dimensional finite element model was established to help understand the development of the mechanical behavior. No crack was observed throughout the test. Both concrete and bars behaved in their linear-elastic stage throughout the test, and the bond between them performed well

Dynamic Response of a Long-Span Concrete-Filled Steel Tube Tied Arch Bridge and the Riding Comfort of Monorail Trains

In this study, a dynamic response analysis procedure is proposed and applied to investigate the dynamic responses of a straddle-type concrete-filled steel tube tied arch bridge under train and truck loadings. A numerical model of the coupled monorail train–bridge system is established to investigate the dynamic behaviors of the bridge under moving trains. A refined three-dimensional finite element model is built for the bridge and a 15 degrees-of-freedom vehicle model is presented for the train. The numerical model is validated using in-situ test results and then used to analyze the dynamic displacement and acceleration of the bridge and the trains on the bridge. Based on the simulation results, the impact factor of the bridge is investigated and the riding comfort of the trains is evaluated. The investigation results show that the impact factor of vehicle loads reaches the maximum value when the resonance of the bridge is induced by the moving vehicles. The effect of train braking predominates the longitudinal vibration of the bridge but is negligible in the transverse and vertical directions. The vehicle speed is the dominating factor for the riding comfort of the train

Stress Distributions in Girder-Arch-Pier Connections of Long-Span Continuous Rigid Frame Arch Railway Bridges

Because of their large stiffness and spanning capability, continuous rigid frame arch bridges are attracting increasing interest in the development of high-speed railway networks in China. The internal loadings are associated with both the continuous rigid frame and arch substructural systems. Thus, the bridges are subjected to complex stresses, in particular, at the girder-arch-pier connections. The evaluation of the mechanical performance and understanding of the stress distribution of the girder-arch-pier connection are critical for ensuring the effective design and condition assessment of the bridges. This paper investigates the stress distributions in the girder-arch-pier connections of the world\u27s longest continuous rigid frame arch railway bridge, the Yichang Yangtze River Bridge. Two models with a length scale of 1/10 were prepared and tested for the side-span and midspan girder-arch-pier connections, respectively. Detailed stress distributions in the connection models were measured, and three-dimensional finite-element models were established to help understand the measured stress distributions. The side-span and midspan connections are primarily in compression and have similar stress distributions

Dietary Curcumin Ameliorates Aging-Related Cerebrovascular Dysfunction through the AMPK/Uncoupling Protein 2 Pathway

Background/Aims: Age-related cerebrovascular dysfunction contributes to stroke, cerebral amyloid angiopathy, cognitive decline and neurodegenerative diseases. One pathogenic mechanism underlying this effect is increased oxidative stress. Up-regulation of mitochondrial uncoupling protein 2 (UCP2) plays a crucial role in regulating reactive oxygen species (ROS) production. Dietary patterns are widely recognized as contributors to cardiovascular and cerebrovascular disease. In this study, we tested the hypothesis that dietary curcumin, which has an antioxidant effect, can improve aging-related cerebrovascular dysfunction via UCP2 up-regulation. Methods: The 24-month-old male rodents used in this study, including male Sprague Dawley (SD) rats and UCP2 knockout (UCP2-/-) and matched wild type mice, were given dietary curcumin (0.2%). The young control rodents were 6-month-old. Rodent cerebral artery vasorelaxation was detected by wire myograph. The AMPK/UCP2 pathway and p-eNOS in cerebrovascular and endothelial cells were observed by immunoblotting. Results: Dietary curcumin administration for one month remarkably restored the impaired cerebrovascular endothelium-dependent vasorelaxation in aging SD rats. In cerebral arteries from aging SD rats and cultured endothelial cells, curcumin promoted eNOS and AMPK phosphorylation, up-regulated UCP2 and reduced ROS production. These effects of curcumin were abolished by either AMPK or UCP2 inhibition. Chronic dietary curcumin significantly reduced ROS production and improved cerebrovascular endothelium-dependent relaxation in aging wild type mice but not in aging UCP2-/- mice. Conclusions: Curcumin improves aging-related cerebrovascular dysfunction via the AMPK/UCP2 pathway