The principle of retention of concrete construction joints and the key points of construction joint

The position of the construction joint should be determined before the concrete is poured, and it should be left in the structure with less shear force.

and a part that is convenient for construction. The retention position of the construction joint shall comply with the following provisions:

First, the column should be left on the top surface of the foundation, below the corbel of the beam or crane beam, and the crane.

the top of the car beam and the bottom of the column cap of the beamless floor slab;

2. The large cross-sectional beam that is connected with the plate as a whole is left at 20 30mm below the bottom surface of the plate. When there is a beam bracket under the plate, it is left in the lower part of the beam bracket;

3. One-way plate, which is left at any position parallel to the short side of the plate;

Fourth, the floor slab with primary and secondary beams should be poured in the direction of the secondary beam, and the construction joints should be retained.

The middle of the secondary beam span is within 1 stew 3 (Fig. 4-4-18);

Fifth, the wall, left in the door opening beam span 1 stew 3 range, can also be left in the vertical and horizontal.

the junction of the wall;

6. Two-way stressed floor slabs, large-volume concrete structures, arches, dome arches, thin shells, and storage.

Pools, bucket silos, multi-layer rigid frames and other projects with complex structures, the location of construction joints should be.

Retention according to design requirements.

When continuing to pour concrete at the construction joint, the following provisions should be met:

1. The compressive strength of the poured concrete should not be less than 1 2n mm2;

2. On the hardened concrete surface, the cement film and loose stones should be removed.

and a layer of weak concrete, which shall be fully moistened and rinsed clean, and shall not accumulate water;

3. Before pouring concrete, it is advisable to lay a layer of cement slurry or mix with the construction joint.

cement mortar of the same composition in the concrete;

Fourth, the concrete should be carefully tamped, so that the old and new concrete are closely combined.

The foundation of the equipment bearing the action of power should not be left in the construction joints;

When it is necessary to retain lien, the consent of the design unit shall be obtained.

Retention of construction joints within the scope of anchor bolts of the equipment foundation.

location, which should meet the following requirements:

1. The horizontal construction joint must be lower than the bottom end of the anchor bolt, which is the same as the bottom of the anchor bolt.

The distance between the ends should be greater than 150mm;

When the diameter of the anchor bolt is less than 30mm, the horizontal construction joint can be left at no less than.

Three-quarters of the total length of the concrete part where the anchor bolt is buried;

Second, the distance between the vertical construction joint and the center line of the anchor bolt shall not be less.

250mm, and not less than 5 times the diameter of the bolt.

Article 4 4 22 The construction joint treatment of the equipment foundation that bears the power action shall be complied with.

Comply with the following provisions:

1. Two horizontal construction joints with different elevations should be left as steps at the junctions of their high and low levels.

shape, the height-to-width ratio of the step shall not be greater than 1 0;

Second, before continuing to pour concrete on the horizontal construction joint, the anchor bolts should be carried out.

Calibration of one observation;

3. Reinforcements should be inserted at the vertical construction joints, with a diameter of 12 16mm and a length.

500 600mm, the spacing is 500mm, and the vertical plane of the stepped construction joint should also be filled.

insert reinforcement; Fourth, the concrete surface of the construction joint should be chiseled, before continuing to pour concrete, it should.

Rinse with water, moisten and apply a layer of cement mortar with a thickness of 10 to 15mm and the same composition as the concrete.

Principle: Stay in the part of the structure that is less stressed and easy to construct.

Specific parts: 1) Column construction joints: the top surface of the foundation, under the beam or corbel.

2) The large cross-section beam connected with the plate as a whole is left 20-30mm under the bottom of the plate.

3) the floor slab with the main and secondary beams, the concrete is poured in the direction of the secondary beam, and the construction joint is left in the middle 1 3 range of the secondary beam span.

4) Construction joints of other complex parts shall be retained according to the design requirements.

5) The foundation of the equipment bearing the power effect, the basement with impermeability requirements, should not leave construction joints.

Treatment of concrete construction joints.

1. First of all, it is necessary to determine the reserved position of the construction joint, under normal circumstances, the wall can not reserve the vertical construction joint, the roof, the floor can not reserve the construction joint, etc. The wall construction joints can be reserved to smash the horizontal and longitudinal wall junctions and so on.

2. When the concrete is initially set, the surface needs to be chiseled at the position where the construction joint is set, and the excavation depth is about 20 to 30 mm, and the concrete coarse aggregate needs to be exposed.

3. After the concrete is chiseled, it needs to be rinsed with a water gun and other tools, and the plain cement slurry should be painted.

4. Pour concrete again according to the requirements.

The position of the construction joint should be set in the part where the shear force of the structure is small and convenient for construction, and the following provisions should be met: Horizontal joints should be left in columns and walls, and the concrete of beams and slabs should be poured at one time without leaving construction joints.

The construction joint should be left on the top surface of the foundation, below the corbel of the beam or crane beam, above the crane beam, and below the column cap of the beamless floor slab.

For the large-section beam that is connected with the floor slab, the construction joint should be left 20mm 30 mm below the bottom surface of the slab. When there is a beam bracket under the plate, it is left in the lower part of the beam bracket;

For one-way slabs, the construction joints should be left anywhere parallel to the short side of the slab.

The floor slab with the main and secondary beams should be poured along the direction of the secondary beam, and the construction joint should be left in the range of the middle of the secondary beam span 1 3.

The construction joint on the wall should be left in the range of the lintel span 1 3 of the door opening, and can also be left at the junction of the longitudinal and horizontal walls.

The construction joints on the stairs should be left in 1 3 places of the tread board. The concrete of the staircase should be poured continuously. If it is a multi-storey staircase, and the upper floor is a cast-in-place floor slab and has not been poured, the construction joint can be retained; It should be left in the middle of the staircase 1 3 parts, but it should be noted that the joint surface should be diagonally perpendicular to the direction of the stair axis.

The reason for the dispute in the construction is that the old specification stipulates that the staircase construction joint must be left in the middle 1 3 section, and the traditional construction is left in the upper and lower 3 steps, and when it is left in the middle of the staircase, theoretically the shear force is smaller, but the quality of the construction joint is not well controlled during construction, and it is easy to produce the short-term "cantilever" of the poured part when the secondary formwork is supported, which is not conducive to the quality control of the component. ）

The construction joints of the pool wall should be left on the vertical wall 200 mm and 500 mm above the surface of the bottom plate.

For two-way stressed floor slabs, large-volume concrete, arches, shells, silos, equipment foundations, multi-layer rigid frames and other complex structures, the location of construction joints should be set up according to the design requirements.

Answer]: A construction joint Qingbi refers to the joints formed between the concrete poured first and later due to the design requirements or construction needs to be poured in sections during the concrete pouring process. The position of the construction joint should be set in the part where the shear force of the structure is small and convenient for construction, and the following provisions should be met:

The construction joint should be left on the top surface of the foundation, below the corbel of the beam or crane beam, above the crane beam, and below the column cap of the beamless floor slab. The construction joint of the large-section beam connected with the floor slab as a whole should be left at 20mm 30mm below the bottom surface of the slab, and when there is a beam bracket under the slab, it should be retained in the lower part of the beam bracket; For one-way slabs, the construction joints should be left anywhere parallel to the short side of the slab. The floor slab with the main and secondary beams should be poured along the direction of the secondary beam, and the construction joint should be left in the range of the middle of the secondary beam span 1 3. The construction joint on the wall should be left in the range of the lintel span 1 3 of the door opening, and can also be left at the junction of the longitudinal and horizontal walls. The construction joints on the stairs should be left in 1 3 places of the tread board. The construction joints of the pool wall should be left on the vertical wall 200 mm and 500 mm above the surface of the bottom plate. Two-way stressed floor slabs, general socks dry concrete, arches, shells, silos, equipment reputational foundations, multi-layer rigid frames and other complex structures, the location of construction joints should be left according to the design requirements; Horizontal joints should be left for columns, and vertical joints should be left for beams, plates, and walls.

Answer]: Bumper slip a, d, e

The construction seam of one-way plate is left at any position parallel to the short side of the plate; The floor slab with the main and secondary beams is funny, and the construction joints are left in the range of 1 3 in the middle of the secondary beam span.

Answers]: a, d, e

2021 new textbook p69 page.

The main investigation of this question is: the requirements for the retention of construction joints, see option A, the horizontal construction joints of the column and the wall can be left on the top surface of the foundation and floor structure, the distance between the column construction joints and the upper surface of the structure should be 0-100mm, the distance between the wall construction joints and the upper surface of the structure should be seen as an option, and the one-way plate construction joints should be left in any position parallel to the short side of the plate. C option sees, the vertical application of the floor slab with the primary and secondary beams should be left in the range of 1 3 in the middle of the span of the secondary beam; D, E option see, the vertical construction joint of the wall should be arranged in the door opening lintel span 1 3 range, can also be left at the vertical and horizontal junction;

The concrete construction joint is retained in the correct position, and the construction joint with columns is retained on the top surface of the foundation.

1. The construction joint should be left on the top surface of the foundation, below the corbel of the beam or crane beam, above the crane beam, and below the silver column cap of the beamless floor.

2. For the large cross-sectional beam connected with the floor slab, the construction joint should be left at 20mm 30mm below the bottom surface of the slab. When there is a beam bracket under the plate, it is left in the lower part of the beam bracket;

3. For one-way plates, the construction joints should be left at any position parallel to the short side of the plate trace.

4. The floor slab with the main and secondary beams should be poured in the direction of the secondary beam, and the construction joint should be left in the range of 1 3 in the middle of the secondary beam span.

5. The construction joint on the wall should be left in the range of 1 3 in the lintel span of the door opening, and can also be left at the junction of the vertical and horizontal walls.

Features of concrete:

1. Concrete is one of the most important civil engineering materials in contemporary times. It is an artificial stone made of cementitious materials, granular aggregates (also known as aggregates), water, and admixtures and admixtures added if necessary in a certain proportion, evenly stirred, densely molded, cured and hardened.

2. Concrete also has the characteristics of abundant raw materials, low quality and simple production process, so that the amount of concrete is getting larger and larger. At the same time, concrete also has the characteristics of high compressive strength, good durability and wide range of strength grades. These characteristics make it widely used, not only in various civil engineering projects, but also in shipbuilding, machinery industry, marine development, geothermal engineering, etc., concrete is also an important material.