Discussion on construction control measures of high formwork in building engineering?

Because the construction of high formwork is very difficult, in the actual construction process of high formwork, the construction must be carried out in strict accordance with the design requirements and relevant specifications to ensure the construction quality of high formwork. According to the general situation of a project, this paper discusses the construction control measures of high formwork.

First, the definition of high modulus

The so-called high formwork is the general name of steel pipe erection and formwork construction with a height of more than 5m used in the construction of large frame buildings. Generally, it will be implemented after case analysis by relevant designers and staff during construction. This formwork support system is a relatively independent and related concrete formwork project whose height exceeds the horizontal projection and width. In the current engineering project, the construction of high formwork is dangerous, which is one of the links with great danger in the whole engineering project. Therefore, it is necessary to equip special construction technicians and safety personnel to be responsible for monitoring and design.

Second, the project overview

A three-story beam slab of a factory building (within the range of 1-5 axis /D-J axis) has a structural height of1.17m, a floor thickness of 120mm, and a maximum frame beam section size of 400mm×1000.

Three, the template preparation control points before construction

1. Expert argumentation to improve the scheme.

This formwork system is divided into plate formwork support system and beam formwork support system, which is a tall formwork support system. According to the Measures for Safety Management of Dangerous Sub-projects (J.Z. [2009] No.87), the concrete formwork support project with a height of more than 8m must be implemented only after the construction scheme is prepared and experts are organized to demonstrate it.

2. Strictly control materials.

(1) steel pipe: The steel pipe for formwork support in this project adopts No.3 ordinary steel pipe specified in the current national standard "Straight Welded Steel Pipe" (GB/T 13793), and its material shall meet the requirements of Q235-A grade steel in Carbon Structural Steel (GB/T700). The size of steel pipe shall be steel pipe with an outer diameter of 48 mm and a wall thickness of not less than 3.0 mm. The new steel pipe shall have product quality certificate and quality inspection report, and the inspection method of steel pipe material shall conform to the relevant provisions of the current national standard "Metal Tensile Test Method" (GB/T228). The surface of steel pipe should be straight and smooth, and there should be no cracks, scars, delamination, dislocation, hard bending, burr, indentation and deep scratches. The deviation of outer diameter, wall thickness and end face of steel pipe shall meet the requirements of Safety Technical Specification for Fastening Steel Pipe Scaffolding in Building Construction. It is forbidden to use old steel pipes with obvious deformation, cracks, flattening and serious corrosion.

(2) Fasteners: malleable cast iron fasteners are used for the erection of steel pipe scaffolding in this project. The specifications of the fasteners should match the outer diameter of the steel pipe, the joint surface should be smooth, the movable parts should be flexible, and the material should conform to the current national standard "steel tube scaffold couplers" (GB 1583 1). When the torque of bolt tightening reaches 65N? M, shall not be damaged.

The new fastener shall have the manufacturer's production license, the inspection report of the statutory inspection unit and the product quality certificate. When the quality of fasteners is in doubt, sampling inspection shall be conducted according to the current national standard steel tube scaffold couplers (GB 1583 1). Old fasteners should be checked for quality before use. Cracks and deformation are strictly prohibited. Bolts with slippery threads must be replaced, and the surface of fasteners should be coated with antirust paint.

(3) Jacking: the standard adjustable jacking is adopted. When there is a gap between the bracket and the beam, the U-shaped bracket (steel plate thickness ≥4mm, width ≥ 100mm, length ≥ 100mm and height ≥60mm) must be wedged tightly, and its screw (L≥600mm) must not protrude from the top of the steel pipe.

(4) Square timber: The square timber section of the battens meets the size requirements of 50mm× 100mm and 100mm× 100mm, and non-standard and irregular sizes (such as logs and bark) are not used.

3. Foundation

Ground backfill soil. Backfill soil shall be compacted by layers with sandy clay, and the compactness shall be ≥94%, and 100mm thick concrete cushion shall be adopted.

Four, the main points of structural control

1 column formwork installation sequence and construction technology

1. 1 template installation sequence

Template installation sequence: scaffolding → template preparation and template release agent brushing → template installation in place → template installation → bracket installation → template reinforcement and fixation → concrete pouring → scaffolding and template removal → template cleaning and stacking.

1.2 technical points

Before installing the wall column template, the summer-planting place of the wall column should be chiseled away, the sundries in the wall should be removed by air compressor, and the measuring and setting-out work should be done well. In order to prevent slurry leakage and "root rot" at the root of the wall column template, before installing the wall column template, stick sponge strips on the bottom plate according to the setting-out size or leveling with cement mortar to make it smooth, accurate and firmly bonded, and pay attention to the installation quality of the wall bolts, and then add column hoop and support system to fix the column.

1.3 formwork support

Formwork support engineering bars cannot be connected with external steel pipe racks and unloading platforms, and the rack body should be provided with vertical and horizontal sweeping bars, multi-channel horizontal tie bars and scissors to make the support system a solid whole. See figure 1 for column elevation and column section supported by formwork.

Figure 1 Column Elevation and Template Support Column Section

2. Installation sequence and technical control points of beam-slab formwork

2. 1 template installation sequence

"Mantang" steel pipe scaffold → main keel → secondary keel → stigma formwork keel → stigma formwork and roof formwork → assembly → roof and external wall stigma formwork keel → formwork adjustment and acceptance → proceed to the next process.

2.2 technical points

1 vertical pole bracket

At the bottom of each vertical pole, a wooden pad with a length of not less than 2 spans, a width of not less than 150mm and a thickness of not less than 50mm should be set; The extension of the vertical pole must be butted, and it is forbidden to lap. Strictly control the step distance of the vertical rod according to the plan, and the jacking of the free section screw shall not exceed 200mm；; The verticality deviation of the vertical pole shall be no greater than 1/500H(H is the total height of the frame), and the maximum deviation shall be no greater than 50mm；; It is forbidden to stagger the upper steel pipe column and the lower steel pipe column and fix them on the horizontal tie rod. The frame body must be continuously provided with vertical and horizontal sweeping bars and horizontal bars. The vertical sweeping pole should be fixed on the vertical pole with a right-angle fastener no more than 200mm away from the basic epithelium, and the horizontal sweeping pole should be fixed on the vertical pole near the bottom of the vertical sweeping pole.

2.2.2 bracing, horizontal bar

(1) A horizontal tie rod should be set at the top of the vertical pole along the vertical and horizontal direction, and the bottom of the vertical pole is 200mm high from the ground with an adjustable bracket. The spacing between the sweeping bar and the top horizontal tie rod should be evenly distributed, and the spacing should be determined under the condition of meeting the requirements of the horizontal tie rod spacing determined by the template design, and one horizontal tie rod should be set at intervals in the vertical and horizontal directions.

⑵ The outer ring shall be decorated with vertical continuous bracing from bottom to top, and the vertical continuous bracing shall be arranged from bottom to top at intervals of about 10m between the vertical and horizontal directions, with a width of 6m. Horizontal bracing shall be arranged at the top of the bracing part and the sweeping bar, and the bottom of the bracing piece shall be close to the ground with an included angle of 45 ~ 60. Each intersection of diagonal bar and vertical or horizontal bar shall be fixed with rotary fasteners. (3) In the middle of the top step distance between the beam and the plate bracket, vertical and horizontal tie rods are respectively added, and the ends of all horizontal tie rods should be fastened with the building structural columns or plates, and vertical continuous bracing is added along both sides of the beam bracket.

(4) When the building height is 8 ~ 20m, diagonal bracing should be added between adjacent vertical continuous bracing in vertical and horizontal directions, and horizontal bracing should be added where there is horizontal bracing in the middle of each bracing. When it is more than 20m, the diagonal bracing is changed to continuous bracing.

5] frame body and surrounding buildings should form a reliable connection, in order to reduce the adverse effects of frame body erection height on stability. Vertical direction according to each floor or along the column height 2m set a wall piece, horizontal direction according to 6m set a wall piece.

[6] The joints of vertical rods, horizontal rods and bracing diagonal rods should be staggered in different grid layers, and the joints of two adjacent vertical rods should not be set synchronously. The distance between two joints of a vertical rod set synchronously should not be less than 500mm in the height direction; The distance from the center of each joint to the main node is not more than 1/3 step; The formwork support system rod shall not be connected with external scaffolding, unloading platform, etc.

Once all nodes must be connected with fasteners, and no omission is allowed. The tightening torque of fasteners should be controlled at 45 ~ 60N? Between m.

2.3 template installation

For cast-in-place reinforced concrete beams and slabs with a span of not less than 4m, the formwork shall be arched according to the design requirements; When the design has no specific requirements, the springing height should be1l/1000 ~ 3l/1000 of the span. When the main beam and the secondary beam are handed over, the main beam will arch first, and then the secondary beam will arch. According to the design requirements, the main girder of the super-long-span part should be arched 3L/ 1000 in advance. After the bottom die is installed, install the side die, pedal and diagonal brace.

Five, concrete is poured concrete management control points

(1) On-site technicians, quality inspectors and supervisors check whether the formwork support conforms to the demonstrated construction scheme, whether the fasteners and steel pipes are firm and whether the steel pipes are deformed.

(2) After the formwork and reinforcement works are accepted, fill in the commercial concrete entrustment form correctly, including the project name, construction site, strength grade, admixture, slump and other related information to ensure the normal concrete pouring.

(3) Before construction, check the concrete mixture ratio report, and measure the slump of concrete on site, and pouring can be carried out only after it meets the requirements.

(4) Before pouring commercial concrete, the layout of the conveying pipeline shall meet the requirements of the scheme. The pump pipe cannot be directly placed on the template or fixed on the bracket. Tire skin or welded stirrups should be placed under the pump pipe to avoid horizontal vibration load and excessive concrete accumulation during pouring.

(5) The wall, column and beam slab are poured separately, and the vertical structure can be used as the binding end of formwork support after reaching a certain strength.

(6) Carefully design the concrete pouring scheme to ensure the load balance during formwork support construction, and it is best to adopt the pouring method extending from the middle to both sides; Strictly control the actual construction load not to exceed the design load, take corresponding control measures for the maximum load, and do not pile up materials such as steel bars above the support; In the process of pouring, send someone to check the support and bearing, and find that sinking, looseness and deformation should be solved in time.

Six, template removal technology control measures

(1) Remove the tall formwork. After the strength of the concrete block with the same conditions retained on site meets the specification requirements, it can be removed only after it is reviewed by the technical director and submitted for inspection in time and signed by the personnel of the supervision company. The formwork can only be removed when the span is more than 8m and the strength of the cantilever balcony reaches 100%.

(2) Warning signs and formwork removal signs should be set around the dismantling area of tall formwork and its supports, and there should be modes for supervision.

(3) The order of dismantling templates is contrary to the order of installing templates, and the order of dismantling templates should follow the principles of first supporting and then dismantling, first supporting and then dismantling, and top-down. (1) wall column formwork removal The wall column formwork can only be removed when the concrete strength reaches 1.2MPa, so as to ensure that its surface and edges and corners are not damaged by removal. The order of template removal is opposite to the order of template installation, that is, the outer wall is followed by the inner wall, and the outer wall template is removed first; (2) When dismantling scaffolding, it shall be carried out in the order of bracing → main rail → small rail → vertical rod → diagonal support. Steel pipes and fasteners should be transported to the floor in time, and it is forbidden to throw them directly to the floor to produce impact load.

(4) After the formwork is dismantled, the steel pipes and fasteners shall be shipped out in time and cleaned up.

Maintain and stack according to specifications.

(5) Other technical requirements: ① Before dismantling the formwork, conduct targeted safety technical disclosure, and both parties shall perform the signing procedures; (2) When the formwork is dismantled, you should wear a safety belt when working at a height of more than 2m, set a reliable foothold and take corresponding safety protection measures; (3) Dismantle the wall column template, first dismantle the wall bolts, then dismantle the horizontal braces and braces, then gently pry the template with a crowbar to make the template leave the wall, and then pass it down one by one, and it is not allowed to throw it down directly; (4) The fixed parts shall be dismantled step by step with the scaffold. When the last riser is removed, temporary supports should be set for reinforcement, and then the fixing pieces and supports can be removed. (5) Safety personnel and technicians should check the safety of the scaffold before coming off work every day, and analyze it in combination with the surrounding environment and weather conditions. If there is any abnormality, it should be handled in time.

Seven. Monitoring and control measures

1. Monitoring control

Using theodolite and level to monitor the support system, mainly to monitor whether the horizontal and vertical positions of the system are offset. Or before concrete pouring, set two hanging vertical lines (both sides) at both ends and in the middle of the beam bottom, and hang them from the beam bottom to the column supporting bottom plate (foundation), control the tip of the hanging vertical line to be within 20mm from the ground and make records, make a cross mark with a red and blue pen directly below the tip of the hanging vertical line, and measure the relative distance between the vertical line and the column at the same time, and assign special personnel to monitor when concrete pouring.

2. Monitoring point settings

The observation points can be buried in the supporting foundation surface (beam or slab), column and wall in the adjacent position by using the inverted L-shaped steel bar head with the diameter of 12mm. When using the hanging vertical line method, the observation points are set at the two ends and the middle of the beam bottom.

3. Monitoring measures

In the process of concrete pouring, assign special personnel to check the supports and supports, and solve the sinking, looseness, deformation and horizontal displacement in time. When the hanging vertical line method is used for detection, the distance between the hanging vertical line and the ground and the distance between the hanging vertical line and the upright post should be controlled according to the allowable deformation requirements of the design. If abnormal conditions are found, the construction shall be stopped immediately, and the construction can be continued only after treatment.

I believe that after the above introduction, everyone has a certain understanding of the construction control measures of high formwork in building engineering. Welcome to Zhong Da for more information.

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