How to identify load cracks and non-load cracks

Structural cracks caused by different types of loads are as follows:

1, structural cracking caused by construction load

After the concrete construction and pouring is completed, it gradually produces strength after setting and hardening, but the early concrete strength is too low to bear the load; It is very important that all kinds of supports of the formwork also need to be stabilized in the original position. The strength of early concrete has not been fully exerted, and if it is loaded, it will inevitably cause cracking.

2. Cracking caused by long-term load

Cracks in reinforced concrete structures under long-term load can be considered to be caused by low structural resistance during design. The long-term load acting on structural members includes the weight of the structure itself and the live load acting on the structure.

3. Shear cracking

Some cast-in-place reinforced concrete structures have concrete beams supported on concrete walls. Because the load of beam is too large, the concrete grade of wall is low, and the shear reinforcement is insufficient, the wall under the beam pad will appear shear cracking.

4. Cracking caused by overstretching the plate.

Too low design datum and too large deflection are the main reasons for cracks. The crack width of the upper surface of the floor slab can be observed on the surface of the facing mortar with a width exceeding 1 mm. There are many cracks below 0.3mm outside the surface width of floor concrete. This is because there is tensile stress above the floor and compressive stress below; Under the action of this bending stress, due to the lack of steel bars at the upper end of the floor, there are large cracks in the floor facing mortar. Because the end of the floor support is cracked, the bending moment is redistributed, the bending moment in the middle of the span is increased, and the deflection deformation is further increased.

5. Cracking under fatigue load

When reinforced concrete members are subjected to repeated loads, compared with static tests, the members are destroyed under lower loads. That is to say, due to repeated fatigue, even if the load is lower than the cracking load, bending cracks will occur under the plate. And with the increase of cracks, the width of cracks also gradually expands. This is due to fatigue caused by repeated loads, which reduces the strength of concrete. The bond degradation between steel bars and concrete is also one of the reasons.

Exclude the above load cracks as non-load cracks.