Why should the horizontal construction joints of the exterior wall be reversed by 300 on the raft bo

The main reason is that the specification has made a unified provision, which is located at a height of not less than 300 from the bottom plate surface, so that it is economical and can meet the requirements.

GB50666-2011 Code for Construction of Concrete Structure Engineering

There is no specific provision on the raft foundation.

of the construction joints are left in place.

It can be determined in accordance with the spirit of the norms and relevant provisions. Understand that the principle of standardizing the retention construction joint is that the horizontal member retains the vertical construction joint; Horizontal construction joints are left for vertical members.

Spirit: The raft is a horizontal member, and the vertical construction joints should be retained, and there is no provision for the raft to leave horizontal construction joints in the specification and article;

Therefore, the raft can not be left with horizontal construction joints, or determined by the design unit.

The construction joint is set according to the less stressed, and the smaller stress of the wall, wall and other components is not at the junction of the bottom plate and the wall, but is about half of its height, and it is a little difficult to set it at the less stressed place. It is not easy to construct if it is set high. If it is set low, the maximum force will be stressed, which is not good for the durability of the structure.

In order to co-ordinate such pros and cons. The norms are uniformly regulated. It is located at a height of not less than 300 from the bottom plate surface, so that it is economical and can meet the requirements. And stipulate the type of steel plate waterstop. Follow in the construction.

Under normal circumstances, if the shear wall can be formed at one time, it will be poured at one time, if not, it is necessary to reverse 300 horizontal construction joints and pre-embed water-stopping materials. The specifics may not be too detailed, but many general descriptions will make it clear.

According to the construction needs, for example, in the basement, you first construct the basement raft, and then you should leave horizontal construction joints at a 300mm level around the retaining wall.

Expand the bearing area of the foundation under the foundation to ensure that the stress of the foundation is not greater than the characteristic value of the bearing capacity of the bearing layer, fa;

The stress concentration value of the foundation under the corner of the wall is very large, which often exceeds the characteristic value of the bearing capacity of the bearing layer fa, and the stress concentration of the foundation under the bottom plate is significantly improved after a certain size is picked out, and the adjustment tends to be more uniform, which is important.

The bottom plate of the raft foundation is picked out 500mm from the edge of the outer wall, mainly to facilitate construction and increase the bottom area.

When the raft is thinned, a certain length can reduce the bending moment in the plate, and when the raft is thicker, the bearing area can be expanded, and the position of the center of gravity and the load center can be adjusted to make the structure more stable.

This is normal, just like we do the road, the width is 26, but we do 30-50cm on both sides of the roadbed to ensure the compaction of the most edge. You do a few tens of centimeters more, and it's the same to ensure the local load at the very edge.

Take into account the angle of force and the diffusion of force.

Facility joints are because you can't complete the construction of the exterior wall at one time, no matter what you do, it is impossible to pour the bottom plate with the exterior wall and the roof at the current level without leaving construction joints!

Therefore, there are generally two horizontal construction joints on the outer wall of the basement!

See GB 506666-2011 "Coagulation.

Construction of earth structure engineering.

Specification》 The retention position of the construction joint and the post-pouring belt should be determined before the concrete back-pouring answer, and the construction joint and the post-pouring belt should be left in the position where the structural shear force is small and convenient for construction. For structural components with complex stress or structural components with waterproof and impermeability requirements, the location of construction joints should be approved by the design unit.

The retention position of the horizontal construction joint shall comply with the following provisions:

1. The construction joints of columns and walls can be left on the top surface of the foundation and floor structures, and the distance between the column construction joints and the upper surface of the structure should be 0mm 100mm, and the distance between the wall construction joints and the upper surface of the structure should be 0mm 300mm;

2. The construction joints of columns and walls can also be left on the bottom surface of the floor structure, and the distance between the construction joints and the lower surface of the structure should be 0mm 50mm; When there is a beam bracket under the plate, it can be left under the beam bracket 0mm 20mm;

The Code for the Construction of Concrete Structure Engineering does not specifically stipulate the retention of construction joints of raft foundations. It can be determined according to the actual engineering situation.

The basement of high-rise buildings is usually used as an underground parking garage, and too many interior walls are not allowed on the building, thus limiting the use of box-shaped foundations; The raft foundation can not only give full play to the bearing capacity of the foundation, adjust the uneven settlement, but also meet the space use requirements of the parking garage, so it becomes a more ideal foundation type. The main structural types of raft foundation are flat raft foundation and beam plate raft foundation, and flat raft foundation is widely used in high-rise buildings due to its simple construction.

Not to stay.

But some protruding parts can be left. For example, the junction between the cushion cap and the plate should be approved by the design.

Oh, meter thick, this should be a pure plate raft without piles and cushion caps, this can leave horizontal construction joints, the treatment of this construction joints is very simple, and it can be washed down with water at the joint.

This plate generally does not leave horizontal construction joints, continuous pouring, if the area is too large, it is okay to stay.

Upstairs, there is a raft in Shenyang, which is a counterweight type, the plate is thick and meters, and the construction is at most 10 o'clock at night, which does not leave a horizontal seam? The area is more than 6,000, according to you, you don't have to do this job, hehe.