Temperature cracks are the most common in walls, which exist at the junction of different materials, such as horizontal cracks at the junction of ring beams and brick masonry. The thermal expansion and contraction of materials, the deformation of building structures due to the change of surrounding temperature, and the different expansion coefficients of different materials lead to temperature cracks.
(b) Cracks caused by uneven settlement of foundation
After the building is completed, the foundation exists in settlement. If the foundation settlement is uneven, the large settlement part and the small settlement part will be relatively displaced, resulting in shear and tension of the wall. When this additional internal force exceeds the tensile and shear strength of the wall itself, cracks will occur, and these cracks will increase with the increase of uneven settlement of the foundation. An oblique crack is formed, and the crack hits the depression. This kind of crack is obvious in the lower part of the building, developing from bottom to top, showing the shape of "eight", inverted "eight", horizontal and vertical. When the settlement in the middle of a long building is too large, it will crack in a figure of eight at both ends of the building from bottom to top, and break through the window angle first; On the other hand, when the settlement at both ends is too large, it will form a splayed crack with both ends inverted from bottom to top, and it will also break through the window angle first, or break through the window sill in the middle of the bottom floor to form a vertical joint from top to bottom. When one end sinks too much, one end forms an inclined crack with high settlement end; When the settlement at the junction of vertical and horizontal walls is too large, a vertical seam with a wide top and a narrow bottom is formed just at the lower corner of the window sill, and sometimes there is a horizontal seam along the lower corner of the window sill; When the vertical and horizontal walls are designed to be concave and convex, due to uneven settlement on one side, horizontal thrust can be generated to form a couple, resulting in vertical joints at the joints.
(3) Structural cracks
Structural cracks are cracks caused by the upper load, indicating that the bearing capacity of the wall is insufficient or there is a big problem. Cracks caused by building structures are mainly as follows: structural design is wrong, load calculation is omitted, and the structure is unreasonable; The quality of masonry construction is poor, and the ash is not full when building walls; Uneven thickness; The assembly method does not meet the requirements; When building a brick wall, the brick is not wet, and the dry brick is used on the wall, which will reduce the bearing capacity of the masonry and cause the wall to crack in the future; In real life, all kinds of pipelines are often buried through the wall after the building is completed, which destroys the integrity of the wall, reduces the bearing area of the wall and weakens the bearing capacity of the wall, thus causing the wall to crack.