“Bonded composite-to-concrete joints have been investigated previously, but only in the context of strengthening existing concrete beams where thin composite strips are attached to cracked concrete,” says Sebastian. “In our project, the entire structure is new, the flanges of the composite units are thick and the prestressing should strongly inhibit cracking of the concrete.”
A team of practitioners serves as advisors on the project, including structural engineers, a contractor, bridge owners and composite materials suppliers (Fiberline Composites in Denmark and Weber Saint-Gobain in France). They are interested in how the test bridge reacts when subjected to millions of cycles of realistic car loading.
“By using high cycling rates, millions of car passages can be simulated in reasonable time frames in the lab,” says Sebastian. “Also, the external actions on the bridge can be carefully monitored and quantified, enabling reliable assessment of both the actions on the bridge and the response of the bridge to those actions.” Using the prototype is a great alternative to testing a real road bridge (which would require considerable time for the passage of millions of cars) or testing individual joints (which lack the interface between the joints and the remaining structure). In addition, testing full-scale decking and beams is advantageous. “Scaled-down specimens notoriously introduce unrealistic factors into the resilience of materials such as concrete, which fail in a brittle manner,” says Sebastian.
The university lab relies on state-of-the-art strain, pressure and load sensors to quantify the response of the bridge to the applied loads. It uses vertical servo-hydraulic actuators to simulate loads from the tires of cars rolling along the composite deck. Researchers are performing tests with and without anti-skid surfacing on the deck. Future work includes simulating the combined effects of weathering and car loads. Sebastian says results will be incorporated into design guidelines for the composites and engineering communities.