1. Make sure the coordinate system and control points are accurate.

2, column construction lofting

Using total station and level meter, the plane position and elevation of the column are measured according to each control point or encryption point. If the control point (or encryption point) is found to be damaged or displaced, it must be jointly measured from the control network immediately. The vertical elevation error of the column is controlled as follows: z ≤ 5 mm; The horizontal position error of the column is controlled as follows: X ≤ 10mm, Y ≤ 10mm. ..

Second, the column construction scheme

1, construction process

2, construction joint treatment

Before column construction, pumice and concrete should be chiseled away from the surface of the joint between pile cap and column until stones are exposed. Then clean the concrete surface with a wire brush to remove rust spots and cement slurry on the steel bars. After the construction joint treatment, leveling layer construction should be carried out, that is, a 3cm thick fine stone concrete guide wall should be made along the root of the formwork, and two layers of carpets should be laid. After the installation of column formwork is completed, foaming agent should be embedded to ensure that the concrete at the root of column does not leak slurry. Before the concrete of the column is cast, the slump of the concrete is 12 ~ 14 cm, and the column is fully grouted. After the construction joint treatment and leveling layer construction on the column surface are completed, the template and interconnection line will pop up on the column surface according to the cross control line, and then the large template spacing bar will be welded on the column steel dowel according to the template control line, and the position will be about 50mm on the column surface. After the concrete is chiseled, it shall be washed with water to remove accumulated water, which shall be accepted by the supervisor.

3, steel bar installation

Clean the rust and cement slurry on the embedded reinforcement, and the concrete at the top of the bearing platform and tie beam should be roughened and cleaned. Align the vertical line with the center of the column, hoist the vertical rod in place with a crane, mark the welding parts, and weld them on the embedded steel bar in turn. At the same time, stirrups are installed according to the vertical line to ensure that the position of the steel skeleton does not deviate from the center of the column. Before rebar welding, steel wire brush shall be used to remove oil stain, rust and double-sided weld for 5d, with a width of ≥0.7d and a depth of ≥ 0.3d, and the surface shall be free of undercut, crack, full welding, flash and incomplete welding. After the fabrication of the reinforcing cage is completed, cement pads should be uniformly bound around to ensure the thickness of the protective layer. Please ask the supervision engineer for acceptance before formwork erection.

(1) column main reinforcement insertion control

Because the column rebar is pre-inserted in the pile cap before concrete is poured and poured, and the column rebar is inserted in place at one time, it is required to set aside the rebar insertion position in advance when binding the pile cap rebar, and fix the column rebar before concrete is poured and poured to ensure the verticality of the column rebar. When binding the reinforcement of the pile cap, firstly, the size of the pier column outsourcing is popped up on the cushion, and the distribution line of the reinforcement of the pile cap is drawn with chalk, and the position of the inserted column iron is staggered in advance. When binding the skin iron on the pile cap, use a wire hammer to cast points to guide the placement of the skin iron and avoid inserting the iron into the column.

(2) Control of protective layer of column reinforcement

Correctly controlling the thickness of the protective layer of the column is to meet the stress requirements of the main reinforcement, meet the protection requirements of the reinforcement itself, and prevent hidden reinforcement from appearing on the concrete surface of the column due to too small protection. The thickness of the protective layer is controlled at 46 mm ... The qualified rate of the first protective layer inspection of the column is 92%. The vertical steel bar connection shall be butted by sleeve or pressure welding, and the vertical steel bar joints shall be staggered in advance; Steel bar intersection shall be fastened with iron wire, and all the two-way reinforced bars shall be fastened. Stirrups shall be in the form of welded closed hoops. Before binding, the cement slurry on the surface of steel bar must be removed, and corroded steel bar is strictly prohibited.

4, template installation

Template requirements surface smooth, verticality conform to the requirements of the specification. Joints should be glued tightly with rubber sheets to ensure no slurry leakage when pouring concrete, and release agent should be evenly applied on the formwork to avoid affecting the quality of concrete joints after formwork erection. After the formwork is erected, adjust the formwork to ensure the verticality of the column. According to the geographical environment and height of the site, at least 4 wind cables shall be set, and the column formwork shall be ensured by adjusting the flange screw or hoist. In order to ensure that the bottom of the column formwork does not leak slurry and the appearance image after formwork removal, mortar with no less than column concrete label should be filled around the bottom.

(1) The formwork surface shall be smooth, with tight joints and no slurry leakage, so as to ensure the beautiful exposed surface of the structure and smooth lines, and chamfers can be set.

(2) simple structure and convenient manufacture, installation and disassembly.

(3) Before pouring concrete, the formwork shall be coated with release agent, and the release agent for exposed concrete formwork shall be of the same variety, and shall not pollute the construction joints of steel bars and concrete.

(4) After the formwork is installed, check its plane position, top elevation, node connection and vertical and horizontal stability, and then pour concrete after signing. When casting, it is found that the formwork may exceed the allowable deviation deformation value, and it must be corrected in time.

(5) Non-load-bearing side formwork can only be removed when the strength of concrete can ensure that its surface and edges and corners are not damaged by formwork removal. Generally, when the compressive strength of concrete reaches 2.5MPa, the side formwork can be removed.

(6) The bearing formwork and support of reinforced concrete structure can only be removed when the concrete strength can bear its own gravity and other possible superimposed loads. When the span of members is not more than 4m, the strength of concrete can meet the requirement of 50% of the standard value of design strength. When the member span is more than 4m, it can only be removed after the concrete strength reaches 75% of the design strength standard value.

5, column concrete construction

The column concrete adopts commercial concrete, which is transported to the site by truck and pumped to the pouring position by pump truck. The column with height less than 12m is poured once, and the column with height greater than 12m is poured twice.

(1) Before concrete pouring, the formwork flat-fell seam shall be specially inspected. And do a good job of connecting new and old concrete.

(2) When pouring concrete, set a string tube or equivalent device to feed vertically downward. Considering the high pouring height of the column at one time, the tandem cylinder distribution operation is adopted when pouring concrete. Feeding and vibration are carried out in layers, and the thickness of layers is about 30cm. Plug-in vibrators are distributed according to the effective diameter of 60cm, and are constructed synchronously. Every time you pour a layer, lift a layer. When vibrating the upper layer, insert the lower layer 5- 10cm. Operation requires fast insertion and slow pulling, and try to avoid collision with steel formwork. The concrete shall be vibrated until it stops sinking, no obvious bubbles emerge, and the surface is flat and consistent, showing a thin layer of cement slurry.

(3) In order to ensure that the color difference of column concrete is basically the same, it is required to do a good job in material selection and measurement of concrete:

Column concrete materials must be yellow sand and stones from the same origin, and the same variety of cement from the same manufacturer.

Optimize the mixture ratio, add an appropriate amount of air entraining agent, reduce the water cement ratio and reduce bubbles.

When mixing concrete, it is required to strictly control the amount of materials, and the special person is responsible for starting the machine and adding additives to ensure accurate measurement.

(4) Form removal, decoration and maintenance

According to the temperature conditions at that time, the time of form removal after natural curing can generally be 24~36 hours, and it should be extended to more than 48 hours when the temperature is lower than 65438 00℃. When the formwork is removed, the upper formwork at the top of the column shall be removed in blocks, the formwork shall be removed in blocks, and it shall be lifted out block by block by car crane. If the cylinder surface is found to be pitted or sticky after form removal, after the approval of the supervision engineer, the decorator will be organized, and cement with the same manufacturer's label will be used, and white cement will be properly mixed to make cement slurry for repair, so that the repaired part will be consistent with the color of the nearby surface. Please ask the supervisor to go to the site for inspection when ripping. After being approved by the supervisor, the pier body is sealed and wrapped with plastic film, the top surface of the pier is covered with geotextile, and it is watered and maintained.

Third, technical guarantee measures

1, template production and installation quality assurance measures

The formwork shall have sufficient rigidity and strength to ensure its stress requirements and repeated turnover without deformation. The splicing place of the formwork shall be tight, flat, leakproof and easy to dismantle. In order to ensure the appearance quality of concrete, the joints between formwork should be lined with suitable plastic paper, and the formwork must be flat.

Before installation, the formwork shall be coated with enough isolation oil or release agent, but the steel bars shall not be polluted. After each use, the residual concrete on the formwork shall be removed, and the isolation oil or release agent shall not pollute the steel bar.

2, steel production and installation quality assurance measures

The steel bars entering the site shall be accepted in batches according to regulations, and can only be used after passing the mechanical performance test. In addition to the welder's certificate, the welded steel bars shall be bound after passing the mechanical test as required. Steel bar construction personnel should strictly follow the design drawings and bend the steel bar according to the sample drawing to ensure the accuracy of each steel bar size. Binding shall be carried out in strict accordance with the construction drawings, and the spacing error shall be controlled within the allowable range. Steel binding must be firm, especially at the intersection of stirrup corner and steel bar, which should be strengthened by electric welding when necessary. When binding steel bars, the steel bars should be directly placed on the foundation cushion, and the embedded steel bars should be welded firmly with the bottom steel bars and the upper steel bars of the foundation. The exposed foundation reinforcement shall be fixed firmly with two stirrups (stirrups of the same pile) to ensure the accuracy of the main reinforcement position.

3, concrete construction quality assurance measures

(1) concrete mixture ratio

The mixture ratio required for column construction has been verified according to relevant regulations.

(2) Transportation

Negotiate with the mixing station to determine enough vehicles, reasonably arrange the transportation and feeding time of the mixer, and set up a main transportation route and a standby transportation route to avoid accidental blockage of concrete transportation on the road. After the concrete is transported to the site, its slump should be tested one by one.

(3) Vibration

Strictly control the height and thickness of each blanking to ensure that the layered thickness does not exceed 30cm. Vibrating method should be correct, and no vibration leakage or excessive vibration is allowed. The secondary vibration method can be used to reduce surface bubbles, that is, the first vibration is carried out when pouring, and the second vibration is carried out after the concrete is allowed to stand for a period of time, usually before the second layer is poured, while the top layer is usually vibrated for the second time after half an hour. Strictly control the vibrating time and the depth of the vibrating rod inserted into the lower concrete to ensure that the depth is 5 ~ 10 cm. The vibrating time is about 15 seconds until the concrete stops sinking and bubbles appear on the surface.

(4) Health care

After the completion of concrete pouring, the slurry should be covered and watered as soon as possible. In the column construction of this project, the concrete curing on the top surface of the column is carried out by sprinkling water and covering geotextile, and the water for concrete curing should be clean and meet the requirements. The number of times of sprinkling water every day is to keep the concrete surface in a wet state. The pier shaft is sealed and wrapped with plastic film to reduce water evaporation, and heat preservation measures are taken.

(5) Hydration heat treatment of concrete

After pouring mass column concrete, the cement will release a lot of hydration heat during solidification, thus forming a large temperature difference between inside and outside, which is easy to cause concrete cracks. In order to effectively control the temperature stress of concrete and avoid cracks in concrete.

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