Use of CFRP/CFCC Reinforcement in Prestressed Concrete Box-Beam Bridges

Abstract

This paper presents the results of an experimental investigation on the flexural response of two identical box-beam bridge models reinforced and prestressed with different types of carbon fiber reinforced polymer (CFRP) tendons/strands. The first box-beam bridge model BBD-I was reinforced and prestressed using CFRP-DCI tendons, while the second bridge model BBC-I was reinforced and prestressed using carbon fiber composite cable (CFCC) strands. Each box-beam bridge model consisted of two precast prestressed box beams placed adjacent to each other and a CFRP/CFCC reinforced deck slab. The two box beams of each bridge model were prestressed using seven pretensioning tendons/ strands and consisted of four transverse diaphragms for transverse post-tensioning. Each box-beam bridge model was also prestressed using 12 longitudinal and four transverse unbonded post-tensioning tendons/strands. The changes in pretensioning forces during and after casting the box beams, ultimate loads and modes of failure, deflections, post-tensioning forces, strains, and energy ratios of both bridge models are presented in this paper. The average values of the measured transfer lengths of 9.5 mm (0.37 in.) diameter CFRP-DCI tendons and 12.5 mm (0.49 in.) diameter CFCC strands were measured as 27.4 times and 22.4 times the nominal strand diameter, respectively. As expected, both bridge models experienced similar failure modes, that is, the failure was initiated by the crushing of concrete in the compression zone followed by the immediate rupture of prestres'sing tendons/strands. Moreover, it was observed that the ultimate strength of Bridge Model BBD-I was higher and the energy ratio for the same was lower than that of Bridge Model BBC-I. However, the longitudinal unbonded post-tensioning tendons/strands of the two bridge models remained intact even after the complete collapse of the bridge models. In general, both Bridge Models BBD-I and BBC-I experienced identical flexural behavior, especially the cracking load, mode of failure, and variation in post-tensioning forces.