Structural Behavior of Short Span Precast Channel Beam Bridges without Shear Reinforcement

This paper presents findings of a research study conducted by the writers for the Arkansas State Highway and Transportation Department. The study investigated precast nonprestressed concrete channel beam sections cast without shear reinforcement used in short, multispan bridges. The original objective of the study was to establish a correlation for inspection purposes between the beam’s visual deteriorated state and its corresponding approximate structural capacity. However, during four-point load testing of 33 beams, it was found that beam strength was more a function of a beam’s concrete compression strength rather than deterioration state. A national survey of state transportation departments within the contiguous states was conducted by the authors and found that 13 states currently use precast channel beam bridges. The particular section considered in this paper is a $5.79\mathrm{m}$ $\left(19\mathrm{ft}\right)$ precast channel beam section used to cross small streams and depressions; however constructed without shear reinforcing steel. Bridges using these sections were constructed in the 1950s through to the early 1970s and were designed for H15 loading. Thirty-three formally in-service beams, in various states of deterioration, were load tested. The writers found that the majority of the beams exhibited load capacity greater than the initially required H15 design strength. Second, member strength was a function of concrete compressive strength. Of the 33 beams load tested, 28 beams showed ductile behavior; conversely, the other five beams failed without exhibiting a yield plateau.