Finite element of composite behaviour of wall-beam structure

Abstract

It is a common practice in Bangladesh to design buildings in reinforced concrete frame ignoring the composite actions of wall-beam. Due to the ignorance of this composite action of wall-beam a considerable waste of materials result in building through under-utilazation. Although the concept is used extensively in many countries of the world, its optimum utilazation has been restrained to some extent due to the lack of proper investigations in the area. The previous investigations were mainly confined in the laboratory and very limited theoretical investigation based on finite element method was performed considering the brickwork as homogeneous material. This type of macro level model is suitable for the macro study but incapable of modeling local behaviour at the region of beam and wall ends where the stress gradients are very high and the fracture process is complex. , A project therefore has been undertaken in the Dept. of Civil Engineering ,which involves both experimental and theoretical investigations of the problem. The present study is a part of this on-going study which involves the development of linear elastic finite element model to study the composite action of wall-beam structures. Isoparametric elements have been used to model the bricks, mortar joints, supporting beams, and the interface elements in between the wall and the beam. The brickwork has been modeled both as a homogeneous material or nonhomogeneous material (Bricks and joints as different materials).The model is very useful in predicting. the local behaviour of the regions where the stress gradients are very high. A series of analyses of a number of wall-beam structures with different height to span ratios, sizes of the beam, different stiffness parameters and different modular ratios have been made in this study. Particular emphasis has been given to the variation of shear stress, vertical stress, and the bending moment in the beam of the wall-beam structures. From this parametric study it has been found that the maximum moment in the beam occurs at about 1/15th of the span from the supports rather than at midspan. Whereas the tension attains its maximum value at or near the midspan. It was also found that the shear stress along the wall-beam interface is parabolic for lower values of relative stiffness parameter and the spread of the shear stress along the length of the beam is twice that of the vertical stress.