To Calculation Of Bended Elements Working Under The Conditions Of Exposure To High And High Temperatures On The Lateral Force By A New Method

The article presents a new method for calculating bending reinforced concrete elements made of conventional and heat-resistant concrete operating under conditions of high and high technological temperatures on the action of transverse forces. The advantage of the proposed calculation method over the method adopted in the current design standards based on a comparison of the calculation results of the experimental data is shown.


INTRODUCTION
When designing bending reinforced concrete structures of thermal units, special attention is paid to their calculation for the effect of transverse forces, since these structures often have short lengths and large transverse forces arise during operation. The design of bending reinforced concrete elements operating under conditions of high and high technological temperatures on the shear force is being improved as experimental and theoretical research is accumulating. For this purpose, complex studies of the resistance of bending

To Calculation Of Bended Elements Working Under The Conditions Of Exposure To High And High Temperatures On The Lateral Force By A New Method
The American Journal of Applied sciences (ISSN -2689-0992) Published: May 31, 2021 | Pages: 210-218 Doi: https://doi.org/10.37547/tajas/Volume03Issue05-33 IMPACT FACTOR 2021: 5. 634 OCLC -1121105553 reinforced concrete elements made of ordinary and heat-resistant concrete to the action of transverse forces under the influence of high and high temperatures were carried out, and proposals were developed for calculating the strength of inclined sections [1]. For this, the accumulated experimental material of both the authors and other researchers was analyzed [1][2][3][4][5][6][7][8][9][10]. The essence of the analysis was to compare the results of calculations by the KMC method [11,12] and the proposed method.

RESEARCH METHODOLOGY
When developing a new calculation method, simple methods of statistical processing were used. As a result of comparing the experimental data with the calculation results using the new method, the following data were obtained. Analysis of the strength of inclined sections of beams tested with onesided heating showed that the method of calculating the shear force, developed for elements operating at normal temperatures, can be applied to elements operating at elevated and high temperatures. At the same time, it was revealed the need to take into account the change in the strength and deformative properties of concrete and reinforcement during heating and the features of the stress-strain state of a bent element under conditions of one-sided heating.
A system of longitudinal and transverse forces is introduced into the design scheme of the forces of an inclined section of a bent reinforced concrete element operating under unilateral heating: in concrete above an inclined crack -Nb1 and Qb1, under an inclined crack Nb2 and Qb2, engagement forces in an inclined crack Νз and Qз, in a longitudinal reinforcement -Ns and Qs and axial forces in transverse reinforcement crossing an inclined crack -Qw ( Figure 1).
The forces in the longitudinal reinforcement and the forces of engagement in an inclined crack are considered in the form of the total values Νsз= Ns -Nз and Qsз = Qs + Qз, applied at the point of intersection of the inclined crack by the longitudinal reinforcement.
The design condition for the strength of inclined sections of bent reinforced concrete elements operating with one-sided heating is as follows:

Q=Qx+Qb1+Qb2
(1) The transverse force Qx is determined taking into account the maximum heating temperature of the clamps according to the formula: The transverse force Qb1, perceived by the concrete in the compressed zone above the inclined crack, is determined by the formula: The transverse force Qb2, which characterizes the thrust force in the longitudinal reinforcement and the engagement forces in the inclined crack, is determined by the formula: The value of concrete shear resistance during heating Rsht is determined depending on the concrete temperature at a distance of 0.2h0 from the most compressed edge of the section by the expression: The American Journal of Applied sciences (ISSN -2689-0992) where σy -vertical stresses from the local action of the load or the support reaction.
The values of the height of the compressed concrete zone above the normal X0 and inclined X cracks are determined by the formulas: Where ν=1,5•Est ⁄Ebt , for ordinary concrete elements Z1=0,7h0, from heat-resistant concrete Z1=0,6h0.
The length of the projection of the inclined crack "C" on the longitudinal axis of the element is determined from the equation of equilibrium of the moments in the lower block under the inclined crack.
If the height of the compressed zone of concrete X above an inclined crack, determined by formula (7), turns out to be negative, then the bending moment and shear force that can be perceived by the section are calculated taking the calculated stress diagram in concrete over normal triangular with a maximum on the most compressed face of the section Rbtem .
In this case, the height of the compressed zone X0 above normal cracks is determined as when calculating the strength of normal sections. For small values of the relative shear span (0.5≤a ⁄ h0≤1.5), the design shear force is determined from the condition of the strength of short elements: for elements without transverse reinforcement: for elements with transverse reinforcement: Where kbt=0,7, kst=0,9 -coefficients that take into account the deviation of pleasant calculation schemes from the actual; γb and γscoefficients that take into account the effect of surrounding concrete and reinforcement on the strength of an inclined strip, are determined according to the rules for calculating local shear according to KMK 2.03.04-98; μw is the transverse reinforcement coefficient; α is the angle of inclination of the calculated strip to the horizontal; β -angle of inclination of transverse reinforcement; lр is the calculated width of the inclined strip.  Before the destruction of reinforced concrete beams along an inclined section with one-sided heating, the total transverse force is perceived:

Comparison
In beams without clamps: -compressed concrete over an inclined crack -16-44%; -the total value of the thrust forces in the longitudinal reinforcement and the forces of engagement in an inclined crack -56-84%;