International Concrete Abstracts Portal

Concrete bridges play an important role in the efficiency and reliability of transportation civil infrastructure. Significant advancements have been made over the last decades to enhance the performance and durability of bridge elements at affordable costs. From an application perspective, novel analysis techniques and construction methods are particularly notable, which have led to the realization of more sustainable built-environments. As far as the evaluation and rehabilitation of constructed bridges are concerned, new nondestructive testing approaches provide accurate diagnosis and advanced composites, such as carbon fiber reinforced polymer (CFRP), have become an alternative to conventional materials. This Special Publication (SP) contains nine papers selected from two technical sessions held at The ACI Concrete Convention and Exposition – Spring 2018, in Salt Lake City, UT. The objective of the SP is to present technical contributions aimed to understand the state of the art of concrete bridges, identify and discuss challenges, and suggest effective solutions for both practitioners and government engineers. All manuscripts were reviewed in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance in the development of the SP.

A significant number of in-service bridges have been subjected to loads above their original design capacities due to the increase in traffic and transported freight in the past decades. Externally bonded fiber-reinforced polymers (FRP) is a non-destructive retrofit technique that has become common for the strengthening of overloaded cap beams of bridges. However, there is a lack of analysis methods for the retrofitted cap beams that can accurately predict the retrofitted structural response while accounting for the critical material behaviors such as bond-slip relationships, confinement effects, and redistribution of stresses. In this study, an analysis methodology using nonlinear finite element models is proposed for cap beams retrofitted with externally bonded FRP fabrics. A two-stage verification of the proposed methodology was employed: a constitutive modeling and critical behavior of materials verification using experimental results available in the literature; and a system-level load capacity determination using a large, in-situ structure. The proposed methodology was able to capture the FRP-concrete composite structural behavior and the experimentally observed failure modes. The FRP retrofit layout created using the results of this study increased the capacity of the initially overloaded cap beam in 27%, granting it a 6% extra capacity under its ultimate loading condition.

This paper investigates the effects of material constituents on fresh and hardened properties of Self-Consolidating Concrete (SCC) mixture necessary for efficient prestressed bridge girder fabrication using a surrogate modeling technique. Response surface methodology (RSM)-based surrogate models consisting of input parameterssuch as density of coarse and fine aggregate were created based upon the past laboratory testing results for differentSCC mixture trials. These models were used to estimate various SCC material characteristics, including slump flow, J-ring flow, passing ability, filling capacity, Visual Stability Index (VSI), T50 (concrete spread time to reach the 50.8 cm [20 in] mark), column segregation, 16-hour compressive strength, and 28-days compressive strength, while examining the correlation between the input parameters on each material characteristic. To observe the effect of core input parameters in an efficient manner, 2D contour plot and 3D surface plot for material characteristics were also created. Then, statistical analyses with the testing results were performed to determine the accuracy of the surrogate models in terms of coefficient of regression (R2). Most of the R2 values are higher than 90%, indicating a higher degree of correlation among the testing and surrogate data. Average predicted-to-measure ratios of the surrogate models were almost equal to or slightly greater than 1.00, showing good agreement with the testing results, and specifically, the surrogate and testing values for J-ring flow and 28-days compressive strength were nearly identical. Key findings indicate that the coarse aggregate content significantly affected the characteristics of the SCC mixtures.

Basalt-Fiber Reinforced Polymer (BFRP) bars have been recently proposed to be used to prestress precast concrete elements. Mechanical properties, potential low production cost, low carbon footprint, and enhanced durability make the application of BFRP to prestressed concrete promising. Nevertheless, some issues related to anchorage and sustained stress still need to be fully addressed. Applications are so far limited to few laboratory tests. This paper discusses how the Serviceability Limit State (SLS) and Ultimate Limit State (ULS) checks of prestressed elements employing this technology vary with respect to elements pre-stressed with steel tendons. Furthermore, an attempt is made to investigate the potential application into the precast concrete industry, by analyzing several typical roof and floor slab elements with different cross-sections. This investigation highlights which type of element could be more advantageously switched to the use of pre-stressed BFRP bars, and at which cost in terms of structural performance.

On the morning of 23 May 2016, a traffic accident happened in the Middle Ring Road between the ramps of Zhenhua Road and Wanrong Road Shanghai, China. A series of on-the-spot tests are carried out and a real-time wireless sensor system is deployed in the bridge. The beam state is reasonably estimated according to the monitoring measurements and the rehabilitation is carried out through 28 steps. Health monitoring measurements show that the beam inclination is below 0.2°, and the beam stays in a stable state after traffic is resumed, which indicates that the repair has met the expected requirements.