A, template installation and construction process of quality control
1, template installation
"Formwork and support should have sufficient bearing capacity, rigidity and stability, and can reliably bear the weight, lateral pressure and construction load of concrete", which is the most basic requirement for formwork installation and the necessary guarantee for construction safety and quality. The main body must be shaped steel formwork and large formwork.
2, template cleaning
Mortar on the formwork shall be cleaned and evenly coated with release agent, but no release agent shall be used that affects the structural performance or hinders the decoration.
3, the removal of the template
(1) The formwork is dismantled prematurely, and the concrete strength is not enough, which may easily lead to structural settlement, deformation, cracking and even collapse. The formwork must be dismantled according to the strength requirements specified in the specification;
(2) The concentrated load of formwork stacked on the floor shall not be overweight.
4, beam and plate shuttering standard practice:
(1) When the formwork span at the bottom of the beam is greater than or equal to 4m, arch camber shall be carried out. The springing height should be11000 ~ 3/1000 of the beam span. The main beam should arch first, and the secondary beam should arch. The arching line shall be straight, and there shall be no broken line. When the beam height is greater than 75cm, it should be considered to fix it with the opposite bolt;
(2) The position, axis, verticality, height and width of the formwork shall meet the design requirements. It is best to make the formwork support less than half a centimeter, so as not to violate the requirements of the specification, but also to ensure that the cross-sectional size of concrete does not exceed the standard and to save concrete materials.
(3) The joint of beam and column should be flat-fell seam neatly with neat edges and corners. If the beam-column joint can't keep up with the modulus, a small template should be added. It cannot be added to the beam-column joint, but should be added to the middle part of the beam to avoid the common quality problem of expanding die and shrinking diameter at the beam-column joint.
(4) For the slab joints of cast-in-place slabs, the method of sticking sponge strips should be adopted to avoid the common quality defects of concrete slurry leakage.
(5) Before pouring concrete, clean the garbage in the front beam with a vacuum cleaner, and water and wet the wooden formwork.
(6) setting prefabricated positioning bars to control the spacing between main bars of frame columns;
(7) For slab joints of cast-in-place slabs, the method of pasting sponge strips with a thickness of 2cm and a width of 5cm should be adopted to avoid the common quality defects of concrete leakage at the root of frame columns.
(8) the standard practice of roof shuttering:
① Template installation: it is required to be flat, without slurry leakage, formwork erection and formwork running. The sponge strip and foam plastic used for caulking shall not protrude from the surface of the formwork, and the formwork support shall be provided with a cushion block in contact with the foundation soil to prevent sinking.
② Elevation control of slab bottom: After the main body construction, 50 or 1m elevation control line will pop up on the wall. When looking at the drawings, we must make clear the dimensions of building elevation and structural elevation, and make clear the correct elevation dimensions of the bottom of the plate after formwork support. When checking, check whether the elevation of the bottom of the plate is correct according to line 50.
The gap in the board should have been taped, because it affected the decoration. Now some areas have cancelled this requirement, which can be solved by clamping sponge strips.
5, column shuttering standard practice:
(1) "The uprights of the upper and lower supports should be aligned, and the bottom plate should be laid", which is stipulated in the specification, which is mainly beneficial to the transfer of the concrete's own weight and construction load, and is also an effective measure to ensure the construction safety and quality;
(2) When shuttering at the corner of the column, sponge bars should be clamped to prevent slurry leakage and straightness at the corner.
(3) In order to control the occurrence of common quality defects of expanding formwork, the spacing between reinforcement belts of frame columns and the spacing between bracing bolts of formwork should not exceed 50cm. For frame columns with a diameter greater than 90cm, we should consider increasing the number of opposite bolts. The following reinforcement spacing is relatively dense, which plays a role in pre-control.
6, shear wall shuttering standard practice:
(1) The spacing between horizontal and vertical reinforcing bars and the spacing between opposite bolts of shear wall formwork should not exceed 50cm, so as to avoid the common quality defects of formwork expansion;
(2) Arrangement of opposite bolts: The spacing arrangement should be uniform, neat and beautiful. The exposed parts of bolt holes should be neat and clear;
(3) Bolt hole plugging: It should be dense, flat and uniform in depth, and the hole should be plugged with the same batch of cement, and the color should be the same as that of the wall.
(4) the intersection of the lower wall and the column is butted with a customized heterosexual template;
(5) Before formwork support, the lower part of the shear wall is pasted with sponge strips, and then the formwork is buckled, which effectively controls the slurry leakage at the lower opening of the shear wall.
(6) Cast-in-place doors and windows openings and internal corners shall be prefabricated and shaped templates: wooden fang, wooden templates and internal corner connectors shall be used to process the shaped templates.
(7) Effective control measures should be taken in advance to ensure the correct position of the shear wall, such as welding angle steel under the foot of the wall to fix it. The construction method is simple and reliable, and the effect will be better if the fixed angle template is used.
7, stair shuttering standard practice:
It's best to use the shaped formwork to support the formwork, so as to ensure that the height and width of the stair tread are consistent, as shown below: shaped steel formwork and shaped wood formwork.
8, water, electricity, fire protection reserved hole shuttering requirements:
The reserved holes fixed on the formwork shall not be omitted, and the position and size shall be accurate, especially for the cast-in-place floor slab. It is not allowed to drill holes to cut off the steel bars afterwards.
Second, the template support system collapse case analysis
(a) template support system collapse case 1
1. When the roof concrete was poured in the studio center of Nanjing TV Station, the formwork support system collapsed, resulting in 6 deaths and 35 injuries.
2. The direct cause of the accident is that there are serious defects in the erection of the formwork support system frame, insufficient horizontal connecting rods and lack of connection between the formwork support and the structure, which leads to the local instability and collapse of the main bar of the frame.
(II) Case II of formwork support system collapse
1. The accident happened in Chen Hang Economic Development Zone, Minhang District. Factory building expansion of Shanghai Tiqiao Textile Dyeing & Yarn Co., Ltd. 14 When workers poured concrete on the roof of a 20-meter-high boiler room, the bent frame of the formwork platform collapsed, resulting in 1 1 death, 2 serious injuries and 1 minor injuries.
2. The direct causes of the accident are: unreasonable erection of formwork support system, excessive horizontal spacing of vertical poles, failure of continuous vertical bracing and horizontal diagonal bracing, instability of frame poles and collapse of support system.
(3) The formwork support system is a simple stress structure. As a stressed structure, it must abide by the mechanical principles. Whoever is subjective and reckless will be punished by law and science. Quality accidents in formwork construction are often closely related to safety accidents.
(4) In order to avoid major quality and safety accidents in formwork construction, the following problems should be paid attention to in formwork construction:
1. calculation control: the technicians of the project department must calculate the strength, stiffness and stability of the formwork support system.
2. Control through reinforcement: Although the requirements are met after calculation, I am still not sure about 100%, so it is also an effective method to reinforce the structure according to relevant regulations, such as taking the following measures:
(1) Add a horizontal link;
(2) The bottom is provided with a vertical and horizontal sweeping rod;
(3) setting continuous bracing;
(4) According to the construction experience, double bent frame is adopted.
3. Strengthen the supervision and management of the examination and approval system: professional technicians prepare plans, which are reviewed by the chief technical engineer of the project department, approved by the chief engineer of the branch company, and reported to the construction engineering safety supervision station for the record.
Chapter 2: Practice of quality standards for steel bar construction.
A, steel molding standard practice
1. Stacking and marking of formed steel bars: The formed steel bars shall be stacked in categories, and identification plates shall be set up to indicate the forming size, diameter, use position, etc. To avoid misuse.
2. Lifting rings of prefabricated members: round steel bars shall be used, and cold drawing is strictly prohibited. The depth of embedded concrete should not be less than 30 days.
3, steel substitution, must go through the design unit, there is a checklist, which is also the content of the mandatory provisions.
Second, the foundation steel binding standard practice
1, when the bottom plate adopts double-layer steel mesh, a reinforced horse stool should be set between the two layers, and the horse stool should be placed on the lower steel mesh, and a horse stool should be placed every1m.
2. When the independent foundation is reinforced in two directions, the short-term reinforcement at the bottom should be placed on the long-term reinforcement. This joint should be knotted at three points.
3. On the basis of directly bearing dynamic load, it is not advisable to weld the joint. Because high temperature will affect the material of steel, destroy the original impact toughness and ductility, and the fatigue performance will be greatly affected, which can not adapt to the periodic change of dynamic load and directly affect the structural safety. Therefore, high-strength bolt connection or other flexible measures should be adopted according to the situation.
4. When the diameter of foundation reinforcement is greater than 16mm, welded joints should be adopted, which is the requirement in the process standard. Some requirements in the process standard are higher than those specified in the specification.
5, the foundation slab adopts reinforced horse stool to support the upper reinforcement, so as to control the concrete thickness of the slab.
6, the standard practice of foundation beam slab steel binding:
(1) When there are bent steel bars in the beam, the distance from the joint to the starting point of bending should not be less than 10 times the diameter of the steel bar;
(2) The openings of beam stirrups should be staggered.
Three, shear wall steel binding standard practice
1, shear wall reinforcement should be bound point by point, and the binding between double rows of reinforcement should be one model larger than the vertical reinforcement of the wall, and trapezoidal positioning reinforcement should be made, with vertical and horizontal spacing not greater than 60cm.
2. Fabrication of horizontal trapezoidal ribs: The trapezoidal ribs are placed according to the mold spacing and fixed by spot welding with arc welding.
3. Initial reinforcement position of horizontal distribution reinforcement of shear wall: After the first initial reinforcement is bound from 5cm, it shall be bound according to the drawing spacing.
4.f fixture can also be used to control the width of horizontal distribution bars on both sides of shear wall.
5. Vertically distributed steel bars can be overlapped at the same height, and the overlapping length should not be less than 1.2 times of the anchorage length of longitudinal tensile steel bars.
6. When the shear wall opens a hole, edge members should be set on both sides of the hole, and the upper and lower edges of the hole should be equipped with structural longitudinal bars.
7, waterproof requirements, steel plate water stop treatment.
Four, column steel binding standard practice
1, when the steel bar diameter in the column is greater than 25mm, two stirrups should be added on each side of the joint with a spacing of 5cm.
2, stirrup hook lap should be staggered along the column vertical reinforcement.
3. The angle of stirrup hook in the seismic zone is 135, and the length of straight part of hook is not less than 10 times of stirrup diameter.
4. Control method of column main reinforcement: place precast positioning stirrups to prevent the common quality problem that the main reinforcement is easy to displace.
5, steel plate water stop through the column processing: local broken into open stirrups for binding.
6, the location of the longitudinal reinforcement connection joint should avoid the beam end, column end encryption area, when can't avoid, should use high quality mechanical connection joint, joint area percentage should not exceed 50%.
7. The corner columns of the first and second seismic grade frame columns should all be encrypted with stirrups, that is, the spacing between each stirrup is 5cm.
8. Requirements for stirrup encryption zone of constructional column: The length of the encryption zone at the bottom column root should not be less than 1/3 of the column clear height. When there is a rigid ground, stirrups should be densified within 500mm from top to bottom of the ground.
9. Principles to be observed: If the drawing requirements are higher than the specification requirements, the construction shall be carried out according to the drawing requirements; When the drawing requirements are lower than the specifications, the construction shall be carried out according to the specifications.
Five, the frame beam steel binding
1, if the tension zone is the end of the round steel binding joint, it should be hooked, but the steel bar should not be hooked.
2, the joint should be staggered, in any case, the binding lap length of compression reinforcement should not be less than 20cm, and the lap length of tension reinforcement should not be less than 30cm.
3. This beam is a cantilever beam, and the main reinforcement is not in the lower part, but in the upper part, and the vertical reinforcement is in the lower part. This is right, and the cushion block is also padded, but the stirrup below is bound incorrectly, and the stirrup openings at the lower part of the beam should be staggered.
Six, site casting steel binding
1, the intersection of two steel bars at the periphery should be fully tied, and other points can be staggered.
2. The floor adopts reinforced horse stool to support the upper reinforcement, which is used to control the thickness of concrete.
Seven, steel bar connection
1, tensile steel bar diameter d >；; 28mm (process standard is 22mm), and the diameter of compressed steel bar is d >；; When it is 32mm, it is not appropriate to use binding joints, but to use welding or mechanical connection, and the joints should be staggered. This is a specification requirement and an effective measure to save steel.
2. Straight thread connection of steel bar: appearance quality of processing: full tooth profile of thread head, no broken or bald tooth defect, smooth tooth surface.
3, ribbed steel radial extrusion joint connection:
(1) The two steel bars connected can have the same diameter or different diameters, but the diameter difference shall not exceed 9mm.
(2) Appearance quality: the length of the extruded casing shall be1.10 ~1.15 times of the original casing length, and there shall be no cracks in the extruded casing. If the indentation depth is not enough, make up the pressure; if it is too deep, remove the joint and reconnect it.
4. Electroslag pressure welding connection: the axial deviation of the joint should not be greater than 0. 1 times the diameter of the steel bar, and should not be greater than 2mm. If the appearance inspection is unqualified, it should be dismantled and welded again.
5, arc welding connection:
(1) covered electrode must have a product certificate.
(2) One-sided welding of 2)HPB235 (rebar): ≥8d, and double-sided welding: ≥ 4d; One-sided welding of HRB335, HRB400 and RRB400 (round steel): ≥ 10d, and double-sided welding: ≥5d.
(3) The weld thickness should not be less than 0.3 times the diameter of the main reinforcement; The weld width should not be less than 0.8 times the diameter of the main reinforcement.
(4) There shall be no sag, flash and crack, and the residual height of weld shall not be greater than 3mm.
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Eight, reinforced protective layer control
1, the importance of reinforced protective layer
(1) A reasonable protective layer of steel bars is relatively safe. However, if the thickness of the protective layer is too small, it is easy to expose the steel bar, or the surface concrete will fall off when the steel bar is stressed, and the surface concrete will gradually carbonize. It won't be long before it loses its protective effect. Steel bars are easy to oxidize at room temperature, which will lead to corrosion of steel bars, reduction of cross section and strength, loss of bonding force between steel bars and concrete, and destruction of the integrity of reinforced concrete.
(2) The displacement of the steel bars on the upper part of the beam slab will seriously affect the bearing capacity and crack resistance of the structure, so the code stipulates that the qualified rate of the protective layer thickness of the beam slab must reach more than 90% to be qualified;
(3) In the process of construction, the position of reinforcement is always correct when binding, but it is different when pouring concrete. People step on it and tools press on it. As a result, the horse stool supporting the steel bar was trampled down, the upper steel bar was bent and deformed, and the thickness of the protective layer could not be guaranteed. Therefore, the operation should be standardized, and finished product protection measures should be taken. It is forbidden for operators to walk on steel bars at will to prevent the above phenomenon. According to statistics, about 70% of residential floor cracks are caused by the incorrect position of reinforced protective layer, and the harm caused cannot be ignored. Therefore, we should fully realize the importance of reasonable protective layer thickness of steel bars to engineering structures. Whether the foreman or the quality inspector, we should pay attention to whether the thickness of the mortar pad prefabricated on site is correct. Before pouring concrete, deformed steel bars must be repaired.
2, wall, plate reinforced pad:
(1) Foundation slab reinforced cushion block: precast concrete cushion block is adopted, and the thickness of reinforced protective layer under longitudinal stress is not less than 4cm, and it is not less than 7cm without cushion block.
(2) The spacing of the pads is 80cm, and they are arranged in a plum blossom shape.
3. Strengthening pad of cantilever structure
In building structures, the usual beam-slab structure is supported at both ends, either on the beam or on the wall. Under the vertical load, a positive bending moment is generated in the beam, and the bottom of the beam or slab is in tension, so the main reinforcement in tension is arranged below. This is the most basic mechanical knowledge that your teacher said at school.
However, cantilever structure is different. Under the vertical load, the cantilever beam produces negative bending moment, and the upper side is in tension, so the main reinforcement in tension is arranged on the upper side. If the protective layer of the upper reinforcement is too large, the bearing capacity of the cantilever part will be reduced. Everyone should know the calculation method of the protective layer of cantilever plate, which needs special attention. Then the steel stripper must calculate the lower side of the steel bar, how high the cushion block should be or how high the steel bar stool should be to ensure the correct size of the protective layer after the steel bar is bound. If you don't understand the principle, putting steel bars below will inevitably lead to quality accidents of balconies, awnings and overhangs.
Chapter III, Concrete Construction
I. Mass concrete
1. The concrete structure with the smallest cross-sectional dimension exceeding 80cm in any direction is mass concrete.
2. In mass concrete construction, corresponding technical measures must be taken to reduce temperature and control temperature stress and cracks.
3. Mass concrete should have two records: temperature measurement record and crack inspection record.
4. Allowable deviation value of concrete crack width (mm)
(1) Chimneys and silos: 0.2;
(2) Weight under normal conditions: 0.3;
(3) Underground and roofing works with seepage control requirements: 0. 1.
Second, the frame column, beam and slab concrete construction quality requirements
1, cement has been on the scene for more than three months, and quick-hardening cement has been on the scene for more than one month. Re-examination is required.
2, pumping concrete should be continuous pouring, pause time can't exceed+/-0.5 ~ 2 hours.
3. Appearance quality requirements of concrete: the concrete should be solid inside and light outside, without honeycomb pits, exposed tendons, holes, slag inclusion, rotten roots, staggered platforms and cracks. There is no common quality problem of shrinkage and expansion of beam-column joints.
4, the roof should be flat, no exposure phenomenon, the main reason for the exposure is that the reinforced protective layer on the cast-in-place slab is not well padded.
5. The section size meets the allowable deviation requirements of the specification: +8 and -5.
Third, the post-cast strip, construction joints, reinforcing strip
1. concrete construction of post-cast strip: if the design does not require retention time, it should be retained for more than 42 days, mainly to make the concrete fully shrink and deform. And maintain water retention for at least 28 days. Shrinkage compensating concrete should be used in post-cast strip.
2, high-rise buildings should be retained every 30 ~ 40 meters post-cast strip, the bandwidth is 700 ~ 1000 mm, reinforced by lap, post-cast strip should be supported and protected by steel mesh or steel wire mesh, before pouring concrete, post-cast strip should be covered with abandoned formwork to protect the finished product, and the concrete had better be kept for two months.
4. Manufacture and installation of precast concrete members
1, prefabricated components should be made on a hard plane, with neat appearance and no corner drop.
2. The overlapping length of precast concrete lintels at the openings of doors and windows and the switch box is 24cm.
3, lintel side should be marked with the date of production, model, inspection results, the upper and lower position of reinforced arrows and other signs. Only after the strength reaches 100% can it be used.
4. Why should I mark the direction of the stress bar? It is to prevent the lintel from breaking and affect the safe use function.
5. The concrete test block must be retained according to the requirements of mandatory standards, and the strength shall not be lower than C 15. The test block can be made together with the main concrete structure, but the name of the precast member should be indicated in the test block report.
Five, slab stairs construction joint lien practice
In order to ensure the accurate position of reinforcement at the foot of stair tread plate and prevent slag inclusion caused by unclean foot of stair tread plate and formwork, the specification stipulates that the concrete construction joint of stair tread plate shall be retained in the middle of slab span 1/3.
The concrete method is to leave construction joints at the upper or lower three steps of stairs.
Six, deformation cracks in the cleaning of debris
1. The deformation joints below the natural ground shall be filled with loose materials with the construction.
2. A debris skateboard with a slope greater than 30 should be set at the deformation joint above the natural ground, and the debris should be cleaned once a day.
Seven, to prevent the cast-in-place concrete floor crack control counter method.
1. When laying the conduit, place a steel mesh on the upper surface of the conduit, and the mesh diameter of the steel mesh is 40mm. When laying the conduit, the conduit shall be arranged in parallel or cross with the stressed steel bars, and shall not be arranged vertically.
2. The conduit in the cast-in-place floor must be laid between the bottom reinforcement and the cover reinforcement, and the construction should be completed at the bottom reinforcement and laid before the cover reinforcement construction. When laying conduit, it must be bound with cushion blocks and steel bars. The fixed spacing between conduit and steel bars should not be greater than 1m, so as to ensure the position of conduit in the plate. The spacing between embedded pipes in the same direction should not be less than 10cm.
3, it is forbidden to trample negative bending reinforcement.
4. In order to improve the surface density of concrete, strengthen the closure of water-collecting cracks and reduce the occurrence of plastic shrinkage cracks, effective measures should be taken before initial setting, such as rolling with iron pipes and rubbing with wooden trowels for more than two times. If plastic shrinkage cracks appear after the concrete is hardened, it can be leveled by pouring mud.
5, the water on the surface of the concrete should be timely guide centralized discharge.
6, when the surface laitance is thick, can add stone slurry before initial setting, evenly spread on the surface.
Eight, concrete curing
1. Covering with water and curing: covering with straw curtains or sacks for water and curing. At room temperature, the concrete shall be cured within 12 hours after pouring. The concrete with portland cement, ordinary portland cement or slag portland cement shall not be less than 7 days, and the concrete with retarding admixture or impermeability requirements shall not be less than 14 days.
2. Plastic sheeting curing: Cover with plastic sheeting to ensure that the concrete is fully cured in case of water loss, and keep the condensed water in the plastic sheeting to prevent shrinkage cracks on the concrete surface.
3. Curing with film curing liquid: When concrete is inconvenient to water or covered with plastic film cloth, film curing liquid can be coated to prevent water evaporation inside concrete.
The average temperature today is below 5 degrees Celsius. Water conservation is not allowed, and heat preservation measures should be taken in winter construction.
5. Cure the test block in the same place and under the same conditions (used for structural entity detection and formwork removal with strength requirements).
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