Strength and Deformation Problems in Cracked Concrete

The strength and deformation properties of concrete and reinforced concrete is strongly dependent on the internal crack system. This crack system may be characterized either as microcracks or macrocracks. Microcracks are present even before loading. They are mainly due to the shrinkage of the cement paste. Loading may further increase the number and width of microcracks and gives rise to a so-called load induced anisotropy. Macrocracks are in most cases visible on the surface of the structure. When stressed reinforcement passes a macrocrack a further increase of internal cracking takes place. In the project the Jin-Ping Zhang model for non shear reinforced elements is further developed. Structural elements as conventional beams, prestressed beams and hollow-core slabs including both statically determinate and statically indeterminate elements are treated. The first results are very promising.
The model is extended to disks, i.e. plane elements loaded in their own plane. A theory based on a model material fully cracked in all directions in the plane as a limiting case is developed. This part of the project has important bearings on the numerous rehabilitation projects on all kinds of reinforced structures which are carried out throughout the world in these years.
In a second part of the project the micro-mechanical model formulated by Jin-Ping Zhang for failure in concrete is further developed. The influence of fiber reinforcement on the compressive strength is studied and an extension to predict the descending branch of the compression stress strain relation of concrete will be made.
The models will be incorporated in some standard commercial programs which are used in rehabilitation projects.
One or more bridges suffering severe cracking will be investigated using the theory developed.