What are the basic assumptions for the calculation of the bearing capacity of the positive section o

3 basic assumptions:

1. The average strain of the cross-section conforms to the assumption of the flat cross-section;

2. The tensile strength of the uncracked concrete in the tensile zone is not considered;

3. The relationship between the stress and strain of the concrete in the compression zone is shown in the following figure

There are three phases of stress on the cross-section of flexural members:

1. The first stage - the stage before the cracking of the cross-section: when the load is very small, the internal force on the cross-section is very small, the stress and strain are proportional, and the stress distribution on the cross-section is a straight line.

2. The second stage - from the cross-section cracking to the longitudinal tensile reinforcement begins to yield: the concrete cracks, the stress redistribution occurs on the cross-section, the concrete at the crack no longer bears the tensile stress, the tensile stress of the reinforcement increases suddenly, the concrete in the compression area appears obvious plastic deformation, and the stress pattern is curved.

3. The third stage - failure stage: after the yield of the reinforcement in the tension zone, the bearing capacity of the section does not increase significantly, but the plastic deformation develops rapidly, and the cracks develop rapidly and extend to the compression zone. The area of the compression zone decreases, and the compressive stress of the concrete in the compression zone increases rapidly.

The compressive stress-strain relationship curve of concrete was used as the basis for calculation.

cross-sectional strain retention plane;

The tensile strength of the concrete is not considered, and the full tensile force is borne by the longitudinal tensile steel bar;

The idealized reinforcement stress-strain curve is used to determine the reinforcement stress.

The basic assumption is that the strain of the 1st section is maintained in a plane.

2. The tensile strength of concrete is not considered.

3. Assumption of the relationship curve between compressive stress and strain of concrete.

In the design, suitable reinforcement failure should be selected, because both over-reinforcement and less reinforcement belong to brittle failure, and suitable reinforcement failure belongs to ductile failure. The yield of the tensile reinforcement means that the well-reinforced beam has been destroyed, and the bearing capacity has reached the limit, if the load is increasing, do you want to break the beam or how to drop?

The basic formula of the bearing capacity of the positive section of the double-reinforced rectangular cross-section bending member: Applicable conditions: (1) is to ensure the yield of the tensile reinforcement, the brittle failure of the over-reinforced beam does not occur, and to ensure that the compression reinforcement reaches the yield strength before the component is broken and concealed; (2) In order to make the compressive reinforcement reach the design value of compressive strength, it should be satisfied, which means that the position of the compression reinforcement is not lower than the center of gravity of the compressive stress rectangular figure.

When the conditions are not satisfied, it indicates that the position of the compression reinforcement is too close to the neutralization axis, and the orange roller strain of the compression reinforcement is too small, so that the stress cannot reach the design value of compressive strength.

2.What are the applicable conditions for calculating the bearing capacity of the normal section of the bending structure of the double-reinforced rectangular section? What does that mean?

There are two basic formulas for the bearing capacity of the positive section of the bending member of the double-reinforced rectangular section: Applicable conditions: (1) It is to ensure the yield of the tensile reinforcement, and the brittle breakage of the slag super-reinforced beam does not occur, and the compression is guaranteed.

Based on the state of stress.

For the three failure modes of beam oblique cross-section, the "Specification" uses the minimum size of the restricted cross-section to accompany the buried void and the minimum clamping ratio to prevent and avoid baroclinic and tensile failure, and to prevent shear failure through calculation. Therefore, the Code for the Design of Concrete Structures

The basic formula specified in is established according to the stress state of shear compression.

The oblique cross-section at the edge of the support because of the shear force of the cross-section here.

Utmost. Bend the rebar.

The oblique cross-section at the bending point cannot be included in the calculation because the resistance of the cross-section is reduced.

The number of stirrups and the spacing change of the blind surface of the reed are obliquely cut, because the resistance of the cross-section here is reduced, and the shear capacity of the coupling is reduced due to the reduction of the coupling.

The diagonal cross-section where the width of the web changes, because the resistance of the cross-section here is reduced, and the shear capacity of the concrete is reduced during the calculation.

For example, the cross-section of the beam is 200mm and 450mm.

Beam concrete self-weight: .

Beam plastering: (.

Beam Load: .

Total Liquid Banquet: .

Live Load: .

Bending moment in the beam span.

Design value: m=(.

Beam shear design value: v=(.

The formula for calculating the bearing capacity of the oblique section of the flexural member is as follows

The formula for calculating the bearing capacity of the inclined section of a flexural member is the shear-span ratio.

The compressive strength and longitudinal reinforcement ratio of the concrete covered by the bucket.

The stirrup ratio and stirrup strength are based on the aggregate bite bench pin force of oblique cracks, the pin action of the rebar and the loading mode. (1) Under the influence of shear-span ratio, the shear bearing capacity gradually decreases with the increase of shear-span ratio;

The basic formula for calculating the bearing capacity of the positive section of a single-rib rectangular section is as follows.

The conditions of use are divided into two categories, one is to prevent ultra-gluten brittle failure, and the other is to prevent febrile brittle failure, as follows.

Dear, I am glad to answer the basis for the calculation of the bearing capacity of the positive section of the flexural member as follows: 1. The average strain of the cross-section conforms to the assumption of the flat section. 2. The tensile strength of the uncracked concrete in the tensile zone is not considered.

3. Set the stress and strain relationship diagram of concrete in the compression zone Failure of suitable reinforcement beam - there are three types of failure modes of the Zhengqing section of the shaped broken and broken bending member: suitable reinforcement beam failure, over-reinforced beam failure, and less reinforced beam failure. The latter two are brittle failures.