Zum Verbund- und Querkrafttragverhalten von Spannbetonträgern aus ultra-hochfestem Beton
Within the priority program SPP 1182 of the German Research Foundation (DFG), the bond behavior of strands in ultra-high performance concrete (UHPC) as well as the shear bearing behavior of pretensioned girders were investigated at the Institute of Structural Concrete at the RWTH Aachen University. This thesis deals with both of these topics. The experimental program includes 72 pull-out tests and 14 small scale beam tests to investigate the transfer length. Furthermore, 60 shear tests on pretensioned girders were carried out. Additionally, nonlinear methods were applied to derive calculation models for the bond as well as the shear behavior. The bond behavior of strands in UHPC is described with a bond model consisting of three contributions: a constant base value, a slip depending and a stress depending part of the bond strength. Similar to normal and high strength concrete, a minimum specific concrete cover c/dp = 2.5 is required to transfer the prestressing force without splitting cracks. Using 0.5’’ strands the measured transfer lengths ranged approximately between 20 and 22 cm (7.9 and 8.7 in.). When several layers of strands were arranged in girders, the transfer lengths were increased by about 20%. The test results can be determined by the derived bond model very adequately. Altogether, 60 shear tests on pretensioned girders with and without openings in the web were carried out. The main aspects were the contributions of the steel fibers and the additional shear reinforcement to the shear capacity as well as the influences of the openings and size effects. The shear capacity of beams with steel fibers was approximately doubled or tripled compared to beams without fibers. The influence of the position and the number of openings was investigated systematically. Openings with a diameter 0.5d lead to a reduced shear capacity of about 75%. Additional shear reinforcement beside the openings was adequate to nearly reach the shear capacity of beams without openings. The shear capacity of beams with several openings was similar to beams with single openings, when the distance between the openings was at least 1.5d. Size effects were primarily observed affecting the fiber action. While the fibers were activated favorably by a slow crack growth in beams with a small height, the sudden crack growth in higher beams leads to significantly decreased fiber efficiency. The shear capacity was described with a model based on additive terms: a contribution of the strut-and-tie model consisting of a fiber as well as a rebar part and a concrete contribution. The results of the calculation model adequately coincide with the experimental data including the own tests and further tests from literature.
info:eu-repo/classification/ddc/620, Verbundverhalten, Querkraft, Ultrahochfester Beton, Vorspannung mit sofortigem Verbund, Stahlfaserbeton, Ingenieurwissenschaften, bond behavior, shear, ultra high performance concrete, pretensioning, fiber reinforced concrete
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Lehrstuhl und Institut für Massivbau der RWTH Aachen