Maintaining aging infrastructure is critical for governments and engineers to ensure public safety. Repairing bridges to extend their lifetime and enhance their seismic strength is often less expensive than replacing the entire bridge. Concrete frequently used in bridge construction is widely available and durable, but it does crack and deteriorate over time.
A recent case study in the Journal of Composites for Construction by authors Enrique del Rey Castillo, Ph.D. A.M.ASCE; Rhys Rogers, Ph.D.; Natalia Uran; and Marc Stewart, examines the Mohaka Township Bridge in New Zealand, which measures almost 784 feet in length, and consists of two abutments and 13 piers, made entirely of reinforced concrete. Engineers were battling stress cracking and corrosion, which compromised the durability of the structure.
“Seismic Strengthening of the Mohaka Township Concrete Bridge with FRP Fabric and FRP Spike Anchors: Case Study in New Zealand” outlines the process of inspections and assessments to identify the key areas of concern, and steps taken to repair and strengthen the bridge. Learn more about this study, and how it can help for future concrete bridge maintenance. To see the results, read the full paper in the ASCE Library: https://doi.org/10.1061/(ASCE)CC.1943-5614.0001144
The Mohaka Township, New Zealand, reinforced concrete bridge was designed in 1958, measuring 239 m long and divided into 14 spans, each 17.1 m long. The piers are doubly reinforced concrete walls over a pile cap with 12 piles. Four prestressed T-beams and a singly reinforced deck form the superstructure. All individual structural members were deemed to comply with current standards, with the main issue being the connection between substructure and superstructure. The integral connection did not have enough reinforcement bars to resist lateral and rotational movement of the girders, resulting in significant cracking at the beams’ ends. A solution was devised to release those movements by physically separating the beams and the pier cap and installing an elastomeric bearing. However, the new detailing required an enlarged pier cap, which in turn increased the lever arm and the moment demand on the pier cap—from both traffic loads and seismic loads. Vertical layers of fiber-reinforced polymer (FRP) were bonded on the face of the wall piers, anchored at the top and bottom using FRP spike anchors. The capacity of the new pier was calculated using section analysis, but no method was available at the time to design the anchors, which were grossly oversized. More current research enables this design, which would result in significant savings in materials and labor. An innovative method using metallic U-tubes was used to try to minimize drilling through concrete members, but it was not satisfactory, owing to constructability.
Read the full paper in the ASCE Library: https://doi.org/10.1061/(ASCE)CC.1943-5614.0001144