Limit state of collapse in flexure

Reinforced concrete beams and slabs carry loads primarily by bending. They are, therefore, designed on the basis of limit state of collapse in flexure. The beams are also to be checked for other limit states of shear and torsion. Slabs under normal design loadings (except in bridge decks etc.) need not be provided with shear reinforcement. However, adequate torsional reinforcement must be provided wherever needed.

This  topic explains the basic governing equations and the computation of parameters required for the design of beams and one way slabs employing limit state of collapse in flexure. There are three types of reinforced concrete beams:
(i) Singly or doubly reinforced rectangular beams
(ii) Singly or doubly reinforced T beams
(iii) Singly or doubly reinforced L beams

considered as rectangular for the negative moment and T for the positive moment. While for the intermediate spans of slabs the beam under positive moment is considered as T, the end span edge beam is considered as L beam if the slab is not projected on both the sides of the beam. It is worth mentioning that the effective width of flange of these T or L-beams is to be determined which
depends on:

(a) if it is an isolated or continuous beam
(b) the distance between points of zero moments in the beam
(c) the width of the web
(d) the thickness of the flange Stress Strain relationship for concrete, Stress Strain relationship for steel,Design Strength Values for Steel Design Stresses at Specified Strains.

## Stress Strain relationship for concrete and Stress Strain relationship for steel

Learn : Stress Strain relationship for concrete, Stress Strain relationship for steel,Design Strength Values for Steel Design Stresses at Specified Strains. fe 415 and fe 500 Stress Strain relationship for concrete and Stress Strain relationship for steel Stress Strain relationship for concrete Stress Strain relationship for concrete : The experimental or actual stress strain curve for concrete is very difficult to use in design Therefore, IS code 456:2000 has simplified or idealized it as shown in Fig. 4.1. For design purpose, the compressive strength of concrete in the structure in taken as 0.67 times the characteristic strength. The 0.67 factor is introduced to account for the difference in the strength indicated by a cube test and the strength of concrete in actual structure. The partial safety factor (rmc), equal to 1.5 is applied in addition to this 0.67 factor. The initial portion of the curve is parabolic. After a strain of…

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## Assumptions in limit state of collapse in flexure (Bending)

Learn Assumptions in limit state of collapse in flexure (Bending),relationship between the stress strain distribution in concrete,stresses in the reinforcement are taken from the stress-strain curve Assumptions in limit state of collapse in flexure (Bending) (REFER CL. 38, IS 456) The design of reinforced concrete sections for limit state of collapse in bending, is based on the following assumptions : (a)       Plane sections normal to the axis remain plane after bending. It means that the strain at any point in the cross-section is proportional to the distance from the neutral axis. (b)       The maximum strain in concrete at the outermost compression fibre is taken as 0.0035 in bending. (c)       The relationship between the stress-strain distribution in concrete is assumed to be parabolic, as shown in Fig. 4.1. For design purpose, the compressive strength of concrete is assumed to be parabolic, as shown in Fig. 4.1. For design purpose, the compressive…

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## Analysis of a singly Reinforced beam

Content of this article:Learn In singly Reinforced beam Strain distribution,Stress distribution,Stress block parameters,Neutral axis depth,Limiting depth of neutral axis Analysis of a singly Reinforced beam singly Reinforced beam The beam that is longitudinally reinforced only in tension zone, it is known as singly reinforced beam. In Such beams, the ultimate bending moment and the tension due to bending are carried by the reinforcement, while the compression is carried by the concrete. Practically, it is not possible to provide reinforcement only in the tension zone, because we need to tie the stirrups. Therefore two rebars are utilized in the compression zone to tie the stirrups and the rebars act as false members just for holding the stirrups. Consider a singly reinforced beam section subjected to bending as shown in fig 1.Strain Distribution: The assumption (1) of the limit state theory gives a linear strain distribution across the cross section as shown…

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