Design of reinforced concrete slabs subject to the construction joints

Abstract

Introduction. When erecting monolithic reinforced concrete floor slabs, a necessity of construction joints arises. The construction joints are the areas of structural weakening. The construction practice shows that the compliance with the correct technology of the construction joint arrangement is not a sufficient condition to ensure the strength balance of reinforced concrete floor slabs. As a result, the stress-deformation state calculated on the assumption of the concrete slab solidity deviates from the actual state. The relevance of the task is determined by the fact that the conformity of design and actual characteristics of the in-situ reinforced concrete structures as a whole depends on the correct calculations of construction joints. Materials and methods. The problem of implementing the construction joints in the monolithic floor slabs was considered by way of example of a residential building under construction. In the course of construction, pre-construction land surveys were carried out at the areas of the construction joint arrangement. Calculations of reinforced concrete structures using finite element method (FEM) were also performed. Results. As a result of the study, the actual deflections of the floor slabs were measured at the areas of the construction joints and FEM calculations were made on the same floor slabs, both those erected at once and those erected in stages subject to the construction joints. The difference between the calculated and actual deflections is conditioned upon the inaccurate conformity between the mathematical model and the real reinforced concrete structure, its erection and maintenance conditions. It should be noted that the deflection of horizontal reinforced concrete structures is only one of the stress-deformation state parameters that can be measured better than the others. It is shown that if the deflection of a real reinforced concrete structure does not correspond with the design estimation, the other stress-deformation state parameters will differ from the design estimation as well. Conclusions. The influence of joints can be taken into account in the scope of FEM computer-aided calculations with the explicit reproduction of the structure erection by pouring concrete, using engineering approach to the consideration of nonlinearity on the basis of the introducing reduction coefficients to the reinforced concrete effective modulus of elasticity. Solid composition modeling of reinforced concrete provides the best possibilities on taking all sorts of nonlinearity manifestations into consideration.