Trag- und Nachbruchverhalten von Stützen aus ultrahochfestem Beton mit hochfester Längsbewehrung: Fid-Bau Portal

Trag- und Nachbruchverhalten von Stützen aus ultrahochfestem Beton mit hochfester Längsbewehrung

Steven, Guido

UHPC allows reinforced concrete columns with a bearing capacity which are comparable to steel and composite columns. But when no specific mechanical measures were applied, the post-peak behaviour of UHPC-columns is significantly more brittle than conventional columns made of normal-strength concrete. The post-peak behaviour can be enhanced by a combination of steel fibres and in comparison to conventional rc-columns higher strength and reinforcement ratio of longitudinal bars and stirrups. In order to adjust this measurements on the requirements of the particular application a model for the numerical determination of the load-bearing behaviour including the post-peak zone is necessary. The literature reports about different models for the numerical determination of the load-bearing capacity of re-cross-sections and columns. There was no model available to accurately foresee fully load-deformation curve of UHPFRC-columns with high-strength longitudinal reinforcement and confining lateral reinforcement. This knowledge gap should be closed for practical application of UHPRC-columns. The experimental and numerical investigations focused on the load-bearing capacity and post-peak behaviour of UHPRC-columns with a slenderness λ ≤ 70. As experimental basis a test programme with all in all 17 large scale column tests were carried out and analysed in detail. As a result it was determined that the load bearing capacity of cross section and system of UHPFRC-columns subjected to centrically and eccentrically axial thrust can be well estimated by the nonlinear computation methods used for conventional rc-constructions.. Derived from the experimental results an engineering model for UHPFRC-columns subjected to centrically axial thrust and a three-dimensional numerical model for centrically and eccentrically axial thrust has been developed. These models allow the realistic determination of the fully load-deformation curve of short and slender UHPFRC-columns with high-strength longitudinal reinforcement and confining lateral reinforcement. With these tools validated on own tests and tests given in literature a parametric study was carried out. The parameter steel fibres dosage and strength and reinforcement ratio of longitudinal bars and stirrups has been varied with the aim to give a recommendation on the measures which are optimal to achieve a higher load bearing capacity and/or robustness of UHPFRC-columns. On this basis proposals for the dimensioning and structural design could be formulated, which allow a reliable determination of the load-bearing capacity and a optimum adaption of the post-peak behaviour to the requirements of the specific application.