The present doctoral thesis was developed within the framework of the research project "Deformation Capacity of Structural Concrete". This project aims at developing a consistent and experimentally verified theory of the deformation capacity of structural concrete. Previous work included the development of a theoretical model, the so-called Tension Chord Model, which allows a comprehensive description of the load-deforma- tion behaviour of tension members in non-prestressed and prestressed concrete struc- tures. The present work focuses on a new theoretical model, the so-called Cracked Mem- brane Model. For members subjected to in-plane forces this new model combines the ba- sic concepts of the modified compression field theory and the tension chord model. Crack spacings and tension stiffening effects in cracked membranes are determined from first principles and the link to plasticity theory methods is maintained since equilibrium conditions are formulated in terms of stresses at the cracks rather than average stresses between the cracks. The research project "Deformation Capacity of Structural Concrete" has been funded by the Swiss National Science Foundation and the Association of the Swiss Cement Pro- ducers. This support is gratefully acknowledged. Zurich, July 1998 Prof. Dr. Peter Marti Abstract This thesis aims at contributing to a better understanding of the load-carrying and defor- mational behaviour of structural concrete subjected to in-plane shear and normal forces.