Load testing of 30-year-old AASHTO Type III highway bridge girders

Abstract

As part of a bridge reconstruction project in Florida, American Association of State Highway and Transportation Officials (AASHTO) Type III girders were salvaged from an almost 30-year-old bridge. This paper reports on load tests that were conducted on these girders. Specimens were tested in three-point bending at shear span–to–depth ratios (a/d) ranging from 1.2 to 5.4. The age of the structure, lack of confinement steel, performance of horizontal and vertical mild steel in the end region, presence of end diaphragms, and the combination precast/cast-in-place concrete bridge deck were considered in the testing. The results gave no indication of reduced capacity or performance due to age or exposure. Girders tested with short shear spans (a/d < 3.1) exhibited a bond-shear failure mode categorized by cracks in the strand development zone, slipping of the strands, and failure to reach moment capacity. Mild steel reinforcement in the end region improved the capacity by 25% beyond the point where strand slip was detected. The single girder tested with an a/d of 5.4 failed in flexure. One of the two girders tested with an a/d of 4.2 exhibited abrupt bond-shear failure, while the other exhibited abrupt shear-compression failure. Experimental capacities were compared with sectional models, strut-and-tie models, and the end-region requirement for longitudinal reinforcement in the AASHTO Load and Resistance Factor Design specifications. The sectional models predicted generally conservative shear capacities. No adverse effects from the bridge deck system were observed.