Static and Fatigue Tests on Ductal® UHPFRC Footbridge Sections

Abstract

This paper describes how static and fatigue flexural tests were performed on transverse sections of a 33.6 m (110.2 ft) Ductal® ultra-high performance fiber-reinforced concrete (UHPFRC) girder for a single-span, 53 m (173.9 ft) pedestrian overpass to be built in the City of Calgary, Canada. Load tests were performed on three 1 m long, full-width and full-depth slab sections. In the first and second tests, the concrete was reinforced with, 13 mm (0.51 in.) long steel fibers (2% by volume). The sections were also reinforced with glass fiber reinforced polymer (GFRP) bars and tested to failure under monotonic loading. The specimens cracked and failed at similar loads. The third specimen had no reinforcement other than the steel fibers. Initially, the specimen was loaded until it cracked. Subsequently the specimen was subjected to 1 million cycles between 20 and 80% of the design service load, followed by a second million load cycles over a load range of 20 to 80% of the observed first-crack load. As the specimen did not fail under this loading regimen, nor was there any observed degradation of stiffness, a third million load cycles were applied to 20 to 80% of the failure load of the sections with GFRP reinforcement. Static tests were performed to evaluate the specimen stiffness several times during the fatigue test. The service load range was not observed to cause damage to the specimen. Some stiffness degradation was noted during the beginning of the third million cycles of loading, but stabilized at about two thirds of the original stiffness. Subsequent to fatigue testing, the specimen was loaded to failure, with collapse occurring at a load higher than predicted. The compressive strength of the Ductal® concrete used in these tests was over 200 MPa (29,008 psi) and the tensile strength at first crack was over 8 MPa (1,160 psi).