What are the causes of the failure of reinforced concrete beams? 30

There are three types of suitable reinforcement failure, super reinforcement failure, and less reinforcement failure.

1. Failure of suitable reinforcement: the beam should bear the bending resistance, and the beam bending resistance depends on the tensile strength of the steel bar.

to achieve it. If the reinforcement in the beam is appropriate, the bearing capacity will reach the most economical capacity in theory, and there is a warning when the beam is disconnected by load, and there is a certain time delay.

2. Over-reinforcement failure: the beam has to bear the bending resistance, and the beam bending resistance is achieved by the tensile strength of the steel bar. If there is too much reinforcement in the beam, the bearing capacity will be very large, but there is no warning when the beam is disconnected by load.

We generally do not use it because it is uneconomical and unpredictable (it will cause accidents).

3. Less reinforcement failure: the beam should bear the bending resistance, and the beam bending resistance is achieved by the tensile strength of the steel bar. If there is too little reinforcement in the beam, the bearing capacity will be very small, and the beam will be easily disconnected under load.

Premature demoulding; The load on it is too large; Less gluten.

1. The failure of the positive section of the reinforced concrete beam mainly has the following forms:

1) Suitable reinforcement failure: The beam has a normal reinforcement ratio.

The tensile steel bar yields first, and with the development of the plastic deformation of the tensile steel bar, the edge fibers of the compressed concrete reach the ultimate compressive strain, and the concrete is crushed. This failure form has obvious signs before failure, and cracks and deformation develop rapidly before failure, so it is also called ductile failure.

2) Over-reinforcement failure: When the amount of reinforcement in the tensile area of the component is very high, the tensile reinforcement will not yield during failure, and the failure is caused by the compressive edge of the concrete reaching the ultimate compressive strain and the concrete being crushed. When this kind of failure occurs, the concrete crack in the tension zone is not obvious, and there is no obvious warning before the failure, which is a brittle failure.

Because the failure of the over-reinforced beam belongs to the brittle failure, there is no warning before the failure, and the strength of the tensile steel bar is not fully utilized and is not economical, so it should not be used.

3) Failure of less reinforcement: when the amount of reinforcement in the tensile zone of the beam is very small, its bending capacity and failure characteristics are similar to those of plain concrete without reinforcement.

Similarly, once the concrete in the tensile zone is cracked, the tensile stress of the reinforcement in the crack zone quickly reaches the yield strength.

And into the strengthening section, even the reinforcement is pulled off. The concrete cracks in the tension zone are wide and the structural disturbance is large, while the compressive concrete does not reach the ultimate compressive strain. This kind of destruction is the "crack and break" type, breaking the bending moment.

It is often lower than the bending moment when the component is cracked, which belongs to brittle failure, so it is not allowed to design a beam with less reinforcement.

2. Reinforced concrete structure.

The main failure patterns of the oblique cross-section:

1) Cable-stayed failure: when shear-span ratio.

Larger and stirrups.

When the configuration is less and the spacing is too large, once the oblique crack appears, the crack often becomes a critical oblique crack, which quickly extends to the concentrated load application point, splitting the beam into two parts along the oblique section, resulting in the failure of the beam. The deformation of the failure front beam is very small, and there is often only one oblique crack, and the failure has obvious brittleness.

2) Shear compression failure: When the shear-span ratio is moderate or the stirrup amount is appropriate, and the stirrup spacing is not too large, the failure is called shear compression failure. There is a certain omen of shear failure.

3) Baroclinic failure: This failure occurs on T-beams or I-beams with a very small shear-span ratio or a very narrow web width. When this kind of failure occurs, the load load is very high, but the deformation is very small, and the stirrups will not yield, which is a brittle failure.

What are the characteristics of reinforced concrete beams when they fail?

The tensile steel bar yields, the concrete in the compression zone is crushed, and the deformation before failure is large, and there is an obvious omen, which belongs to the ductile failure type.

In the reinforced concrete structure, utilize the characteristics that the compressive capacity of concrete is strong and the tensile capacity is very weak, and the tensile capacity of the steel bar is very strong, the concrete mainly bears the pressure of the Bila pressure zone above the beam and the shaft, and the steel bar mainly bears the tensile force of the tension zone below the middle and shaft, even if the concrete crack of the tension zone can continue to bear considerable load, until the tensile steel bar reaches the yield collision imitation strength, the load increases slightly, and the concrete in the compression zone is crushed, and the beam is destroyed.

Because the concrete hardening produces a good adhesion between the steel bar and the concrete, and the temperature line expansion coefficient of the two materials of the steel bar and the concrete is very close to each other, when the temperature changes, the bond between the two will not be destroyed due to the large temperature stress, so as to ensure the coordinated work of the steel bar and the concrete.

It can be treated with concrete admixtures to change the adsorption state of the cement particle surface. After adding an admixture to the concrete, it is adsorbed on the surface of the cement particles to form an adsorption film, which changes the potential and produces different suction or repulsion forces; It will destroy the flocculation structure, improve the stability of the cement diffusion system, and improve the conditions for cement hydration. It can form a macromolecular structure and change the adsorption state of the surface of cement particles; It will reduce the surface tension and surface energy of water, etc.

Thanks to the retarder, the setting time of the cement can be extended, which makes it possible to reduce slump losses and extend the construction operation time.

Active cracks in the beam and surrounding structures, as well as unstable cracks due to continued expansion, can be repaired with functional mortar. The recommended materials are: RMO joint repair mortar, BUS flexible cement caulking, ECM epoxy repair mortar, EC2000 polymer anti-crack mortar, RC polymer reinforcement mortar, etc.