The Control Of Non-load Factor Cracking Of Reinforced Concrete Basement Outer-wall Structure

This paper aims to control the cracking and the crack development of reinforcement concrete basement outer-wall. Firstly the base constraint coefficient of the concrete wall was studied when non-load deformation occurred. A simple formula was achieved by computing lots of reinforcement concrete walls with different length/height ratio and different length, and then regressing these resulting data. With this formula, to compute the volume change and the corresponding stress is rather simplified because the calculation results accord well with the FEM program.After the non-load deformation of concrete wall and the corresponding stresses fully studied, the main factors inducing to crack are found out. The non-load deformation of wall constrained by base mainly includes the thermal deformation and the shrinkage deformation of concrete. Studies show that the cracking stress mainly induced by the seasonal change of temperature, the shrinkage of concrete and the residual stress caused by hydrate temperature.The volume change of concrete wall and the corresponding stresses are closely related to the nonlinear properties of concrete. A program considering the nonlinear properties of concrete was developed. With the program the design of crack control conform to procedures planned in flow chart.Reinforcing concrete wall, grooving a stress-release slot in basement wall and adopting tiny expansive concrete are good measures to control the cracking. Analyzing the base constraint coefficient along the length shows that the efficient of reinforcement can be discussed by analyzing the fully constrained reinforced members. So based on this conclusion this paper followed discussed the relationship of concrete strain and stress to the steel ratio, the relationship of crack width to steel ratio, quantitative relationship of crack width to crack number and the rational steel ratio, all of which can be regarded as theoretic basement for design.This article emphasize particularly on the stress development by contrasting before grooving a stress-release slot in the basement wall with after doing so. The results prove setting stress-release slot is a effective design if the length of reinforcement concrete basement slab-wall is limited in reason. The simplifying formulas and design suggestion are proposed.Basing the most disadvantageous weather data of the Hunan province, thelast part of paper discusses how to control cracking by controlling the temperature of tiny extended concrete. Calculation results can be used to guide the practical engineering design.