Fhwa / in / Jhrp - 88 / 6 - 1 Structural Behavior of High Strength Concrete Prestressed I - Beams

This report deals with the evaluation of the ultimate behavior of AASHTO I-beams with concrete strengths up to 9000 psi. The relevant AASHTO and IDOH design specifications are thoroughly evaluated based on the results of this research. The findings of this study remark the many beneficial implications of the use of higher strength concrete in precast prestressed AASHTO I-beams. Higher strength concrete's with comparatively greater compressive strength per unit weight and unit volume would result in reductions in dead load allowing lighter more slender bridges. The increased stiffness of higher strength concrete is advantageous in the stability and control of deflections in these longer more slender structures. The larger tensile and compressive strength is also helpful in the service load design of these members. Furthermore, the inherent relationship between higher strength concrete and higher quality concrete should result in an improved long-term preformance under service loads. This study also points out the increased importance of adequate detailing of higher strength concrete members to insure ductile behavior under ultimate load. At simple supports of typical bridge structures the support centerline is usually between six and twelve inches from the end of the beam, and twelve inches from the end of the beam, and as a result, the transfer length of the strand extends into the shear span. Three tests conducted during this study, using this standard detailing, resulted in a premature strand anchorage failure as a web-shear crack penetrated into the transfer length of the strand. Although the specimens tested in this study had minimum amounts of shear reinforcement at the end