Refined transverse shear strains in thick plate-shell elements.

摘要

High transverse shear force regions in concrete plates and shells have always been a controversial subject in structural design and analysis. Punching shear in the slab-column connections is a case in point. Existing building codes all over the world do not have a common approach to handle this phenomenon and could be unduly conservative. Offshore structures and highly pressurized concrete containments are other examples in which the presence of high transverse shear forces makes it hard to determine the failure mode, ductility and thus reliability of the design in the analysis process.; Numerical analysis of structure by finite element method offers a substitute to expensive experimental investigations in such cases. Nevertheless, the available finite element models for concrete plates or shells are not accurate in the regions of high transverse shear force. Inaccuracy in finite element analysis of concrete shells and plates stems from the strain field approximation and material model idealization. To address the former a new plate-shell element with a refined strain field is developed in this work. This element which is called "Refined Degenerated Shell Element", is capable of adjusting its strain field approximation to the actual situation of strain in the structure more closely than that of other shell elements. This unique characteristic is especially important in the case of concrete plates and shells which are subjected to diffuse material failure across the thickness. The concrete material model is another issue which needs special consideration. In this work a three dimensional material model based on the fracture energy and plasticity approaches for concrete is integrated into the finite element model of plate and shells to remove the problems associated with inclined cracking in zones of high transverse shear force. Tension stiffening is also addressed and its implementation in the finite element modeling of these problems discussed.; Examples to verify the new shell element are presented. The material model is also verified in special cases that are pertinent to ordinary stress fields in thin plates and shells. Lastly, the results of numerical analysis of different thick plate and beam type structures in the presence of high transverse shear forces are attempted and discussed.