On direct determination of shear force taken up by concrete in oblique cross-sections of reinforced concrete structures

Aleksei N Morozov

doi:10.5377/nexo.v34i02.11629

Abstract

A method has been presented for the direct determination of shear force in oblique cross-sections of reinforced concrete structures using a classic formula Q=bzτ, when the main problems of determining the shear force in oblique cross-sections are related to finding cleaving stresses in concrete and the shape of a stress-block of normal stresses in the design section, with no principles of practical division between the forms of failure in oblique sections due to concrete compression or shear. This work incorporates a criterion for dividing the forms of failure due to concrete compression or shear, based on the assumed shape of a compression stress-block with a segment cut away in a normal section, passing through the top of an inclined crack. The height of the compressed area in this normal section is defined from simultaneous solution of the equations of equilibrium in the moments in normal and oblique sections, from testing the experimental beams made of concrete and gas-concrete. This work deals with seeking the approaches for solving the above-mentioned problems in practice. The data of testing beams from gas-concrete and heavy-weight concrete have been used. Strain gauges were used to measure concrete and reinforcement deformities, computer processed thereafter. The studies have been considered on determination of cleaving stresses in oblique sections, further verified according to this method on certain alternative schemes of their application. A practical method for finding the shear force depending on the value of a shear span has been proposed. The work can encourage active discussion of this computation method.

Highlights

The known formula, Qb = bzτ (1)for determining the shear force in oblique cross-sections, taken up by concrete, was derived about 100 years ago, it has not found any direct application so far, except for a constraint on its value
Mersch (1927) suggested that the concrete shear value should be determined by formula Rsh = √RbRbt
The direct determination of shear force is made through simultaneous solution of the equations of equilibrium in the moments in normal and oblique sections for both compressed and tensile zone of normal section, passing through the top of an inclined crack, what, in the last case provides a way of estimating stresses in tensile reinforcement

Summary

Introduction

If compression and tensile strength are defined by standard tests, cleaving strength is very difficult to determine due to a complex strain-stress state (SSS) of heterogenous concrete in oblique cross-sections. Behind the experimental data to develop this method for direct determination of the shear force in oblique sections were the results of testing beams made of gas-concrete (Morozov, 2018; 2019a, 2019b) without coarse aggregate, that makes SSS substantially heterogeneous and has low plasticity, what allows more accurate estimates of stresses to be made. The problem of using this section in practice as a design one is constrained by the shape of a stress-block for normal stresses therein. The simplest triangular shape of a stress-block of normal stresses in concrete is assumed in formula (1) and other works, devoted to the studies of the concrete SSS in oblique cross-sections

Methods

Results

Conclusion