Abstracts Category : Other

Fatigue Performance of Orthogonally Reinforced Concrete Slabs

by Christian A Spathelf

This thesis aims at contributing to a better understanding of the fatigue performance of orthogonally reinforced concrete slabs, focusing on the influence of a deviation between the principal moment and reinforcement directions with regards to fatigue strength. A new physical-mechanical model is presented that allows (i) a realistic assessment of the load-deformation behaviour of cyclically loaded slabs under various combinations of bending and torsional moments, (ii) the characterisation of changes in the response upon rupture of individual reinforcing bars, and (iii) a realistic prediction of fatigue life to supplement the current provisions for the design and evaluation of concrete structures.In the first part of this thesis, a brief overview of the fatigue phenomenon is provided, previous work on fatigue in reinforced concrete is reviewed and the relevant material properties of concrete, reinforcing steel and their interaction through bond are examined. The second part comprises the theoretical modelling of the response of reinforced concrete slabs to cyclic loading. Relevant kinematic and static relationships governing the load-deformation behaviour are outlined. The proposed model, based on a layered plate element formulation, is introduced. Herein, compressive stresses resulting from bending are assigned to an assemblage of plane stress concrete layers distributed over the element height. Tensile stresses in the reinforcement are considered in fictitious cracked membrane cover elements at the outer surfaces. Tension stiffening effects are considered in the cover elements, resulting in a realistic calculation of maximum reinforcing steel stresses at the cracks. A stochastic distribution of fatigue strengths is assigned to the reinforcement such as to allow an evaluation of the response after rupture of individual bars. In the third part, details of an experimental campaign carried out at the Institute of Structural Engineering of ETH Zurich are described. The testing program comprised two series of four large-scale tests on concrete slabs exhibiting differently orientated orthogonal reinforcement layouts with respect to the direction of applied moment. Specimens were tested under constant force-amplitude cyclic loading until failure.The fourth part of this thesis relates to the validation of the proposed new model through the comparison of calculations to own experimental results. The accuracy of the model assessment of fatigue performance is highlighted and the limitations are discussed.Advisors/Committee Members: Vogel, Thomas, Brhwiler, Eugen.