Investigating the bond strength in box beam bridges

What is it about?

Box beam bridges are a type of bridge in which the main beams consist of girders in the form of a hollow box. Shear keys are essential parts that connect these box beams. They contribute to the stability of bridges against various forces. In this study, the authors examine the bond strength between high strength concrete (HSC) box beams and ultrahigh performance concrete (UHPC) shear keys in box beam bridges. They investigated how temperature cycles and the cracks formed by loading and unloading affect this connection. To mimic real conditions, test pieces were put through 60, 120, and 180 freezing and thawing (FT) cycles, which correspond to one to three years of exposure with each year taken as having 60 FT cycles. The FT process was simulated in a controlled environment. The temperature inside the chamber was adjusted at a rate of 4 °C per hour from –20 °C to 20 °C, and the specimens were exposed to these extreme temperatures for two hours. Specimens that experienced 180 FT cycles were also subjected to further testing involving repetitive loading and stress reversals.

Featured Image

Photo by Chris Briggs on Unsplash

Photo by Chris Briggs on Unsplash

Why is it important?

The impact of temperature cycles on the bond between HSC and UHPC remains a concern. Understanding this bond's performance is vital for the safety of box beam bridges. This study finds that the number of FT cycles does not significantly impact the bond's strength or its failure mechanism. In addition, typical guidelines underestimate the cohesion and friction when concrete is applied to rough surfaces. Furthermore, exposing test pieces to repetitive loading and stress reversals does not weaken the direct tensile bond strength. KEY TAKEAWAY: The bond between HSC box beams and UHPC shear keys remains strong, even with temperature changes and repeated loading. This insight is crucial for designing safe and durable box beam bridges. This research relates to the following Sustainable Development Goals: • SDG 9: Industry, Innovation, and Infrastructure • SDG 11: Sustainable Cities and Communities • SDG 13: Climate Action