Doctor's Theses (authored and supervised):

G. Hofstetter:
"Physikalisch und geometrisch nichtlineare Traglastanalysen von Spannbetonscheiben, -platten und -schalen mittels der Methode der Finiten Elemente";
Supervisor, Reviewer: H.A. Mang, H. Reiffenstuhl; Vienna University of Technology, Vienna, Austria, 1990.

English abstract:
This treatise refers to ultimate load analysis of thin prestressed concrete panels, slabs and shells by the Finite Element Method. The method proposed for determination of work-equivalent node forces from prestress is characterized by the analytic representation of the middle surface of the shell and of the course of the axes of the tendons as space or surface curves. A curved, triangular, C^1-conforming, thin-shell finite element serves as the analysis tool. Pretensioned as well as bonded und unbonded posttensioned tendons are considered. The mathematical formulation is based on the expression for the virtual work of the forces exerted by the tendons on the remeining part of the shell, treated as a free body. Prestress losses during the tensioning operation as well as changes of the prestress forces resulting from loads applied after prestressing are taken into account. Long-time deformations of concrete and relaxation of the prestressing steel are not considered in this work. The efficiency of the method regarding the analytic treatment of prestress follows from automatic determination of the numbers of all elements passed through by a tendon and of the coordinates of the points of intersection of the tendon with the interfaces of these elements. Within the framework of a total Lagrange formulation geometric nonlinearity is considered by a shell theory of small displacements but moderately large rotations, proposed by Koiter, which is based on the Love-Kirchhoff assumptions. Physical nonlinearity models for concrete, reinforcing steel and prestressing steel. In order to model the material behaviour of concrete, the shell is subdivided into sufficiently many thin layers, such that a state of plane stess many be assumed for each layer. This permits the use of constitutive equations for plane stress, developed by Liu, Nilson and Slate, based on experiments carried out by Kupfer. Cracking and crushing of concrete and the capacity to carry tensile stresses between neighbouring cracks, normal to these cracks, transferred from the reinforcement to the concrete by means of bond slip are considered by a concept developed by Floegl and Mang. The steel reinforcement is smeared to thin layers of equivalent stiffness. Its material behaviour is modeled by a bilinear stress-strain relationship including strain hardening. The material behaviour of the prestressing steel is modeled by a nonlinear stress-strain relationship. Based on these assumptions a computer program was written in FORTRAN V. It serves as the tool of a detailed numerical study consisting of ultimate load analysis and convergence as well as parameter studies of a plate with unbonded posttensioned tendons, a cylindrical barrel vault with edge beams with bonded posttensioned tendons in the middle surface of the shell and in the edge beams and a prestressed concrete secondary containment structure. The results obtained from these ultimate load analyses are compared to corresponding results obtained from experiments, reported in the literature.

Keywords: @dissertation

Created from the Publication Database of the Vienna University of Technology.