Bridge Structures - Volume 19, issue 4

Authors: Mahmoud, Khaled M.

Article Type: Editorial

DOI: 10.3233/BRS-230219

Citation: Bridge Structures, vol. 19, no. 4, pp. 133-134, 2023

Authors: Daly, Gavin | Zoli, Ted | Stoyanoff, Stoyan

Article Type: Research Article

Abstract: The Bronx-Whitestone Bridge was designed during the 1930s in an era of suspension bridges with decks stiffened by shallow plate girders, many of which were subsequently found to be vulnerable to aerodynamic instabilities such as vortex shedding and flutter. Following the occurrence of mild and benign wind-induced oscillations in the first several years after opening in 1939, the bridge has undergone a series of retrofits, from structural solutions such as stay cables, stiffening trusses, and a steel orthotropic deck, to aerodynamic enhancements such as a tuned mass damper and wind fairings. Wind tunnel studies in 2015 confirmed the improved aerodynamic …performance due to the recently installed wind fairing system and stiffer orthotropic deck. A subsequent rehabilitation project gave the opportunity to assess measures to further improve the aerodynamic performance of the bridge. A 3 ft (0.91 m) tall solid screen added on top of the median barrier was found to act as an above-deck vertical baffle plate, disrupting the alternating pattern of vortices, reducing the susceptibility of the bridge to instabilities. This led to the conceptual design of a Median Barrier Extension (MBE) comprised of 3 ft (0.91 m) solid transparent acrylic panels fixed to the top of the existing median barrier posts, supported by a tubular steel frame. To ensure this unique barrier modification met current industry safety standards, the MBE design was iterated through a crash analysis study using non-linear finite element models before the final design proceeded to a full-scale physical crash testing program to MASH Test Level 4. This paper presents the full timeline of this innovative retrofit project, from conception during wind tunnel testing, through to design, crashworthiness studies and final construction in 2020. This project has demonstrated that a vertical extension to a median barrier can act as a simple and cost-effective enhancement to the aerodynamic performance of existing bridges. Show more

Keywords: Long span bridges, aerodynamics, flutter, barrier, retrofit, vortex-induced oscillation, cable-supported, suspension, crashworthiness, wind tunnel

DOI: 10.3233/BRS-230216

Citation: Bridge Structures, vol. 19, no. 4, pp. 135-148, 2023

Authors: Malla, Pranit | Khedmatgozar Dolati, Seyed Saman | Mehrabi, Armin | Ortiz Polanco, Jesus | Nanni, Antonio | Dinh, Kien

Article Type: Research Article

Abstract: The application of Fiber Reinforced Polymer (FRP) materials in concrete structures has been rising due to their several advantages, including lightweight, high tensile strength, ease of installation, and corrosion resistance. They have been mostly implemented for strengthening and repairing existing structures in the form of an externally bonded system, i.e., sheet, jacket, near surface mounted. Furthermore, they have been recently utilized as internal reinforcement of concrete elements in the form of strands, bars, tendons, etc. Although higher durability and performance are associated with the FRP material in some aspects compared to steel, concerns remain regarding damages and defects in this …material, many of which are related to their unique features. Importantly, debonding of FRP materials from a concrete surface or within a concrete element has always been an issue resulting in the premature failure of the structure. To this end, concrete elements strengthened or reinforced with FRP materials has to be inspected periodically to detect potential issues and hence prevent any premature failures. This study first determines all possible or potential damages and anomalies attributed to FRP reinforced/strengthened concrete (FRP-RSC) elements. It then investigates Non-Destructive Testing (NDT) methods that can be applicable to the inspection of FRP-RSC elements from a literature survey of past studies, applications, and research projects. Furthermore, this study evaluates the ability of two of the most commonly used NDT methods, Ground Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU), in detecting FRP bars/strands embedded in concrete elements. GPR and PAU tests were performed on two slab specimens reinforced with GFRP (Glass-FRP) bars, the most commonly used FRP bar, with variations in their depth, size and configuration, and a slab specimen with different types of available FRP reinforcements. The results of this study propose the most applicable methods for detecting FRP and their damage/defects in FRP-RSC elements. This study further investigates the feasibility of two new methods for improving the detectability of embedded FRP bars. By providing the inspection community with more clarity in the application of NDT to FRP, this study offers means for verifying the performance and, therefore, help the proliferation of FRP materials in concrete structures. Show more

Keywords: Non-Destructive Testing (NDT), damage detection, Fiber-Reinforced Polymers (FRP), composites, concrete elements, FRP-reinforced, FRP-strengthened, bridges, GPR, PAU, improving detection

DOI: 10.3233/BRS-230217

Citation: Bridge Structures, vol. 19, no. 4, pp. 149-164, 2023

Authors: Huang, Jianwei

Article Type: Research Article

Abstract: The minimum flexural reinforcement requirement has been used in the current bridge design specifications to protect the member from brittle failure after the formation of the first flexural cracks. Several variables have been reported to affect this requirement, such as concrete strength, amount of prestressing in the member, and type of cross section. Recently, the Precast/Prestressed Concrete Institute (PCI) developed a new type of beam section (NEXT beam) to accelerate bridge construction and enhance the sustainability of bridges. As a newly developed beam section, no research on the minimum flexural reinforcement has been reported for NEXT beam bridges. This paper …aimed to examine the minimum flexural reinforcement requirements in the current AASHTO LRFD Bridge Design Specifications for NEXT beam bridges. A comprehensive parametric study was analytically conducted with various parameters, including bridge section, beam section, concrete strength, and span length. The results from this study showed that the current minimum flexural reinforcement requirements were met for all bridges examined herein; the concrete strength, beam cross section, and span length could affect the levels of safety against brittle failure after first flexural cracks for NEXT beam bridges. Show more

Keywords: Accelerated bridge construction, minimum flexural reinforcement, NEXT beam, prestressed concrete

DOI: 10.3233/BRS-230218

Citation: Bridge Structures, vol. 19, no. 4, pp. 165-173, 2023

Authors: Gao, Xiaoni | Ren, Hongwei | Liu, Rufei | Chen, Min | Lai, Ruixin

Article Type: Research Article

Abstract: How to quickly and accurately identify the bridge rubber bearing deterioration plays an important role in ensuring the bridge structure and road safety. This paper selects the common rubber bearings of domestic bridges as the research object, and proposes an improved YOLOv4-based bridge rubber bearing deterioration detection algorithm to address the reasons for the difficulty in detecting bridge rubber bearing deterioration due to large scale variations and small sample data sets. An image dataset (named HRBD) with annotations is constructed from real inspection scenarios, and the data is expanded by image processing means such as rotation, translation and brightness transformation, …so that this dataset has sufficient data complexity and solves the problem of overfitting due to insufficient samples for network training. The anchor applicable to this dataset was regained by the K-means++ clustering algorithm, and then the CA module was inserted into the YOLOv4 backbone network for more accurate anchor localization. The improved YOLOv4 network was used for migration learning to train the dataset, and finally the trained network model was used for detection on the test set. The experimental results show that the improved YOLOv4 bridge rubber bearing deterioration detection and identification network can effectively identify and locate bridge rubber bearings and their deterioration types (crack damage, shear deformation, bearing void). Show more

Keywords: Bridge engineering, deep learning, image recognition, rubber bearing, deterioration detection

DOI: 10.3233/BRS-230209

Citation: Bridge Structures, vol. 19, no. 4, pp. 175-188, 2023