Extreme strength criterion and design of RC elements

V. P. Mitrofanov, Poltava National Technical University, Ukraine 

This paper presents an improved design of reinforced concrete elements (RCE) subjected to flexure and eccentric compression or tension. The disadvantages of the traditional deformational strength criterion of concrete as confirmed by experimental data are noted. Emphasis is put on the difficulties in determining ultimate concrete strain experimentally, as well as in accounting for the influence of many conditions and factors. To remove these disadvantages, the extreme strength criterion (ESC) is proposed and used. The ESC expresses the determination of the maximum load parameter as a function of the extreme fibre compression compressive strain ecu in a RCE section at failure. On the basis of the ESC, a new general design method is developed for RCEs under bending and eccentric compression/tension. In addition to the constitutive relations for concrete and steel, the plane sections hypothesis and the balance equations, the proposed method includes the ESC, which replaces the traditionally used concrete strength criterion. The advantages of the proposed method are demonstrated to be generality, completeness, exactness, reliability and systematic accounting of a large number of factors. The proposed method does not require the experimental determination of the ultimate concrete strain, because the ecu is found during solution of the RCE strength problem as one of the unknowns of the equation system.