formwork will play an important role in ensuring the flat appearance of concrete structures and components of concrete and steel bars, as well as the strength and stiffness of the structure. Project quality problems occur frequently due to incorrect template size and poor support, which attracts great attention.
1. The joints are not strict
1. Presentation:
Because the joints in the formwork are not strict and there are gaps, slurry leaks during concrete pouring, honeycombs appear on the concrete surface, and serious holes and exposed tendons appear.
2. Cause analysis:
(1) sample is not serious or wrong, the template is made carelessly, and the seams are too large when assembling.
(2) wooden template installation cycle is too long, and cracks are caused by the dry shrinkage of the template. The axis measurement and the amplitude error occurs.
(3) The wooden formwork is roughly made, and the joints are not tight
(4) When pouring concrete, the wooden formwork is not watered in advance to moisten it, causing it to swell.
(5) The joint size of the beam and column junction is inaccurate and misaligned.
3. Prevention and control measures:
(1) Sampling must be carefully translated, and the parts must be translated into detailed drawings strictly at the ratio of 1/10 to 1/50, and detailed notes. After review, the operators must be given a briefing to strengthen the workers' quality awareness, and carefully produce the molding templates and assemble them.
(2) Strictly control the moisture content of the template, and the joints must be tight when making.
(3) The installation cycle of wooden formwork should not be too long. When pouring concrete, the wooden boards should be watered in advance to make them expand and tightly seamed.
(4) The support at the intersection of beams and columns should be firm, the joints should be tight, and the misalignment should be corrected.
2. The template has not been cleaned
1. Present:
(1) Remaining wooden blocks, floating slurry residues, gravel and other construction waste in the template. After dismantling the mold, there are gaps in the concrete and garbage inclusions.
(2) Remaining wooden blocks, floating slurry residues, gravel and other construction waste in the formwork. After dismantling the formwork, there are gaps in the concrete and garbage and debris.
2. Cause analysis:
(1) The steel bars have been tied up, the template has not been rinsed with pressure water, and the mold has not been cleaned before sealing.
(2) wall column root, no cleaning holes are left at the lowest point of the beam and column joint, or the position left is inappropriate and cannot be cleaned.
3. Prevention and control measures:
(1) After the steel bars are tied, rinse the template with high-pressure water to remove garbage in the mold.
(2) Before sealing the model, send a special person to clean the garbage inside the model.
(3) Cleaning holes are reserved at the root of the wall column and at the joints of beams and columns. The reserved hole size is ≥100mm*100mm. After the garbage in the mold is removed, seal the cleaning port in time.
3. Column template defects
1. Phenomenon
(1) The mold blows up, resulting in inaccurate cross-sectional size, bulging out, leaking slurry, not dense concrete or honeycomb truncated surface .
(2) deflection, a row of columns is not on the same axis, and the column body is twisted, and the beam and column joints are large.
2. Cause analysis
(1) The spacing between column stirrups is too large or not firm, the steel bar frame is reduced, or the wooden mold nails are pulled out by concrete pressure.
(2) The axis of measurement and playback is not serious, and the beam and column joints are not installed according to the large sample diagram.
(3) The column support molds do not follow the lines or find squares. If the steel bars are offset and the column molds are installed, they are installed without being straightened.
(4) The two sides of the template are tight and there is no design of template column hoops and wall bolts.
3. Preventive measures
(1) Before supporting molds in rows of columns, the line should be popped out at the bottom and the column position should be squarely located.
(2) The position of the steel bar must be corrected before the column supports the mold.
(3) When supporting the column molds at both ends should be upright first. After the alignment and review positions are correct, the long line is pulled on the top and then the column molds in the middle should be upright.
(4) According to the size and height of the column section, a firm column hoop should be added every 500 to 800mm outside the column mold, and pull bolts should be added if necessary to prevent mold explosion.
4. Defects of the board formwork
1. The middle part of the board is deflected; the concrete surface at the bottom of the board is uneven; when using wooden formwork, the beam edge formwork is embedded in the beam and is not easy to remove.
2. Cause analysis
(1) The material used in the template keel is small or the spacing is too large, and it cannot provide sufficient stiffness and strength. The base mold does not arch according to the design or specification requirements, resulting in excessive deflection.
(2) The bottom of the support under the slab is not firm, and the load continues to increase during the concrete pouring process, the support sinks and the plate form is deflected.
3. Prevention and control measures
(1) The keel and pulling bar wood under the cast-in-place plate template should be designed and calculated to ensure sufficient stiffness and strength, and the support surface should be flat.
(2) The support material should have sufficient strength, and the front, back, left and right are firmly matched to increase stability; if the support is supported, the ground should be compacted first, and a long mattress should be laid. If necessary, the mattress should be placed under the wood and then the horizontal plate should be added to increase the contact surface of the support and the ground to ensure that there is no sinking under the weight of the concrete. The
(3) board template should be arched according to the regulations.
5. Wall template defects
1. In reality,
(1) mold blowing, tilting deformation, wall not vertical
(2) wall thickness and thickness, and wall surface uneven.
(3) The wall slurry is slurry and exposed ribs are carried out, and the bottom of the formwork is wrapped in concrete and mortar, making it difficult to dismantle the formwork.
(4) The corner template cannot be removed.
2. Cause analysis
(1) The template is made unevenly, the thickness is inconsistent, the two adjacent wall forms are not spliced strictly, unevenly, and the support is not firm. pair pull bolts are not used to withstand the side pressure of concrete on the formwork, resulting in the formwork being exploded during concrete pouring.
(2) The support method between the formwork is improper, such as only horizontal support, when the concrete is vibrated, the wall mold will be squeezed out to both sides under the pressure of the concrete side, and there is an oblique support on the outside of the wall, so the formwork is not easy to tilt out; while there is only horizontal support between the wall and the wall. The side pressure causes the wall form to bulge out, and the horizontal support is pushed towards the wall form, which makes the formwork concave and the wall loses straightness; when the concrete is poured on the wall, its side pressure pushes to the wall ○3, causing the position of the wall to shift larger.
(3) The corner mold and the wall panel are not spliced tightly, the cement slurry leaks out, and the lower part of the template is wrapped. The mold removal time is too late, and the bonding force between the formwork and concrete is too large.
(4) Not coated with isolator .
3. Prevention and control measures
(1) The wall template should be assembled and flat to meet the quality inspection and evaluation standards.
(2) The middle of the wall body should be equipped with pulling bolts according to the formwork design book. The connecting rods are used to strengthen the strength on both sides of the formwork to bear the side pressure of the concrete to ensure that the mold is not exploded. Between the two formworks, steel pipes or hard plastic support should be used according to the thickness of the wall to ensure the consistency of the thickness of the wall.
(3) The template surface should be coated with isolating agent.
(4) The top-pull support set on the exterior wall should be firm and reliable, and the spacing and position of the support should be determined by the template design.
6. Axial displacement
1. Phenomenon
When the formwork was removed after concrete pouring, it was found that the actual location of the columns and walls were offset from the axis of the building.
2. Cause analysis
(1) Inadequate sampling or unclear technical briefing, and the assembly failed to be in place as required during the template assembly.
(2) Axial measurement and release errors are generated.
(3) Unlimited positioning measures or the limits at the roots and tops of the wall and column formwork are not firm, and they are not corrected in time after the deviation occurs, resulting in cumulative errors. When
(4) supports the mold, horizontal or vertical lines are not pulled, and there is no vertical verticality control measure.
(5) The stiffness of the template is poor, and there is no horizontal pull rod or the spacing between the horizontal pull rods is too large.
(6) The concrete is not uniformly and symmetrically discharged during pouring, or the one-time pouring height is too high, causing the side pressure to extrude the formwork.
(7) Improper use of pull bolts, top braces, and wooden wedges causes the axis to deviate.
3. Prevention and control measures
(1) Strictly translate each section and item into detailed drawings in the ratio of 1/10-1/15 and indicate the number of each part, axis position, geometric dimensions, section shape, reserved holes, embedded parts, etc. After verification, the production team and operators will be carefully explained as the basis for template production and installation. After the template axis is measured and placed, a special person will be organized to conduct technical review and acceptance, and the mold can only be supported after confirming that it is correct.
(3) Reliable limiting measures must be set up at the roots and prefabricated parts of the wall, column formwork, such as the fixed steel support of short steel bars embedded on cast-in-place floor concrete to ensure the accurate position of the bottom. When supporting the mold, horizontal and vertical lines should be pulled, and vertical verticality control lines should be set to ensure the accurate horizontal and vertical position of the template.
(5) According to the characteristics of the concrete structure, the formwork is specially designed to ensure that the formwork and its support have sufficient strength, stiffness and stability.
(6) Before pouring concrete, carefully check and review the formwork axis, bracket, top brace, and bolts, and deal with problems in a timely manner if they are found.
(7) When pouring concrete, the feeding should be evenly and symmetrically, and the pouring height should be strictly controlled within the scope permitted by the construction specifications.
7. Elevation deviation
1. When measuring phenomenon
, it was found that there was a deviation between the concrete structure layer height, the elevation of embedded parts and reserved holes and the construction drawing design elevation.
2. Cause analysis
(1) There is no elevation control point on the floor or there are few control points, so the control network cannot be closed; the root of the vertical template is not leveled.
(2) There is no elevation mark on the top of the template, or it is not constructed according to the mark.
(3) The number of times the elevation control line of high-rise buildings is transferred is too large, and the cumulative error is too large.
(4) The embedded parts and reserved holes are not firmly fixed, and construction methods are not paid attention to during construction.
(5) The stair step template does not consider the thickness of the decoration layer.
3. Prevention and control measures
(1) Each floor has sufficient elevation control points, and the roots of the vertical template must be leveled.
(2) Set elevation marks on the top of the template and strictly follow the marks to construct.
(3) Building floor elevation is controlled by the first floor ±0.000 elevation. It is strictly forbidden to induce upwards one layer to prevent cumulative errors. When the building height exceeds 30m, another elevation control line should be set up, and there should be no less than 2 elevation measurement points on each floor for review.
(4) Embedded parts and reserved holes should be compared with the drawings before installation, and after confirming that they are correct, they should be fixed in the design position. If necessary, they should be fixed by welding or frames. When pouring concrete, they should be poured evenly along the surroundings. It is strictly forbidden to hit or vibrate the embedded parts formwork.
(5) The thickness of the decoration layer should be considered when installing the stair step template.
8. Structural deformation
1. Phenomenon
After removing the mold, it was found that the concrete columns, beams and walls were convex, necked or warped.
2. Cause analysis
(1) The distance between the support and purlins is too large, and the stiffness of the template is poor.
(2) A small steel mold was assembled, and the connecting parts were not set according to regulations, resulting in poor integrity of the template.
(3) There are no pull bolts on the wall formwork or the bolt spacing is too large, and the bolt specifications are too small.
(4) The vertical load-bearing support is not compacted on the foundation soil, has not been padded with flat plates, and has no drainage measures, causing the branches to sink with part of the foundation.
(5) The support between the inner molds in the door and window openings is not firm, and the formwork is easily squeezed out when the concrete in is vibrating .
(6) The spacing between beam and column formwork clamps is large, or the formwork is not clamped, or the number of tension bolts is insufficient, so that the local formwork cannot withstand the lateral pressure generated by concrete vibration, resulting in local formwork explosion.
(7) The wall and column concrete is poured too fast, the pouring height is too high at one time, and the vibration is too high.
(8) is constructed using wooden formwork or plywood . After passing the acceptance, the concrete is not poured in time, and the surface is deformed after long-term sun and rain.
3. Prevention and control measures
(1) When designing formwork and support systems, the self-weight, construction load, concrete self-sufficiency and lateral pressure generated during pouring should be fully considered to ensure that the formwork and support have sufficient load-bearing capacity, stiffness and stability.
(2) The support spacing at the bottom of the beam should be able to ensure that there is no deformation under the action of concrete weight and construction load. If the bottom of the support is a soil foundation, it should be carefully compacted, drainage ditches should be installed, and long mattresses or steel should be laid to ensure that the support does not subside.
(3) When assembling a small steel mold, the connectors should be placed in accordance with regulations, and the spacing and specifications of the purlins and pulling bolts should be set according to design requirements.
(4) If the beam and column formwork is clamped, the spacing should be set as specified and the template should be clamped, and the width should be slightly smaller than the cross-sectional size.
(5) There must be temporary support on the upper part of the beam and wall formwork to ensure the width of the upper mouth of the beam and wall when concrete is poured.
(6) When pouring concrete, it is necessary to be uniformly symmetrical and not to cut the material. The pouring height must be strictly controlled, especially on both sides of the door and window formwork. It is necessary to ensure that the concrete is vibrated and compact, and to prevent excessive vibration from causing deformation of the formwork.
(7) For cast-in-place reinforced concrete beams with spans not less than 4m, the formwork should be arched according to the design requirements; when there are no specific requirements in the design, the arch height should be 1/1000-3/1000 of the span.
(8) When using wooden formwork and plywood formwork, concrete should be poured in time after passing the acceptance inspection to prevent the wooden formwork from deforming after long-term exposure to sunlight and rain.
9. The seams are not tight
1. Phenomenon
Because the joints in the formwork are not tight and there are gaps, slurry leaks during concrete pouring, honeycombs appear on the surface of the concrete, and serious holes and exposed tendons appear.
2. Cause analysis
(1) The sample is not serious or correct, the template is made carelessly, and the seams are too large when assembling.
(2) The installation cycle of the wooden formwork is too long and cracks are caused by the shrinkage of the wooden formwork.
(3) The wooden template is roughly made and the seams are not tightly patched.
(4) When pouring concrete, the wooden formwork is not watered in advance to moisten it, causing it to swell.
(5) The steel formwork is not trimmed in time.
(6) steel template seam measures are improper.
(7) The joint sizes of the beam and column are inaccurate and misaligned.
3. Prevention and control measures
(1) The samples must be carefully translated, and the details of each sub-item are strictly translated into detailed drawings according to the ratio of 1/10-1/50, and detailed notes will be compiled and noted. After review, the operators will be given a careful briefing, strengthen the workers' quality awareness, and carefully produce the molding templates and assemble them.
(2) Strictly control the moisture content of wooden templates and tight joints when making.
(3) The installation cycle of wooden formwork should not be too long. When pouring concrete, the wooden formwork should be watered in advance to make it expand and tightly seamed.
(4) The steel formwork deformation, especially the outer deformation of the edge bar, should be trimmed and straightened in time.
(5) The caulking measures between steel formwork must be controlled, and linoleum, plastic cloth, cement bags, etc. should not be used to remove caulking and blocking leakage.
(6) The support should be firm at the intersection of beams and columns, and the joints should be tight (add double-sided tape to the joints if necessary), and correct the misalignment.
0, mold release agent improper use
1. Phenomenon
The surface of the formwork is painted with waste engine oil, causing concrete pollution, or the residual concrete slurry is not removed and the release agent is brushed, causing defects such as lump surface on the concrete surface.
2. Cause analysis
(1) After removing the mold, the mold release agent will be brushed if the concrete residue is not cleaned.
(2) The release agent is unevenly applied or missed, or the coating is too thick.
(3) uses waste engine oil release agent, which not only contaminates steel bars and concrete, but also affects the decorative quality of concrete performance.
3. Prevention and control measures
(1) After removing the mold, the residual concrete slurry left on the template must be removed before brushing the mold release agent.
(2) It is strictly forbidden to use waste engine oil as a mold release agent. The principle of selecting mold release agent materials should be: it is both convenient for mold release and concrete surface decoration. The selected materials include soap liquid, talc powder , lime water and its mixture, and various special chemical mold release agents.
(3) The release agent material should be mixed into a thick shape, and should be applied evenly and should not flow. Generally, it is advisable to brush twice to prevent missed brushing, and it is not advisable to apply too thick brushing. After the release agent is applied, the concrete should be poured in a timely manner in the short term to prevent damage to the isolation layer.
1. The template has not been cleaned up
1. Phenomenon: There are residual wood blocks, floating slurry residues, gravel, etc. in the
formwork to construction waste. After dismantling the mold, there are gaps in the concrete and garbage inclusions.
2. Cause analysis
(1) The steel bars were tied up and the template position was not cleaned with compressed air or pressure water.
(2) No cleaning was performed before sealing the mold.
(3) No cleaning holes are left at the root of the wall column and at the lowest point of the beam and column joint, or the location left is inappropriate and cannot be cleaned.
3. Prevention and control measures
(1) After the steel bars are tied, use compressed air or pressure water to remove the garbage in the template. Before sealing the mold in
(2), a special person will be sent to remove the garbage in the mold.
(3) No cleaning holes are left at the root of the wall column and at the joints of beams and columns. The reserved hole size is ≥100mm×100mm. After the garbage in the mold is removed, the cleaning hole will be sealed in time.
12. Closed or vertical templates have no exhaust holes, pouring holes
1. Phenomenon
Because the closed or vertical formwork has no exhaust holes, the concrete surface is prone to defects such as pores, and the high column and high wall formwork have no holes left, making it easy to cause the concrete to be imperfect or hollow.
2. Cause analysis
(1) There is no exhaust hole in the bottom mold of the large top hole in the wall, which can easily cause airbags to occur when the concrete is discharged symmetrically, resulting in unfilthy concrete.
(2) There is no pouring hole on the side molds of high columns and high walls, resulting in too large free drop of concrete pouring, easy separation or the vibrating rod cannot be inserted in place, resulting in poor vibration.
3. Prevention and control measures
(1) The bottom mold of the large reserved holes (doors and windows, etc.) of the wall should have air exhaust holes to allow bubbles to be discharged in time during concrete pouring to ensure that the concrete pouring is dense.
(2) The side molds of high columns and high walls (more than 3m) should be opened to make pouring holes to facilitate concrete pouring and vibration.
13. The template support is improperly selected
1. Phenomenon
Due to the improper selection and support methods of formwork support, structural concrete will be deformed during pouring.
2. Cause analysis
(1) Support optional sloppy, has not been checked for safety, does not have sufficient load-bearing capacity and stiffness, and the formwork is deformed after concrete pouring.
(2) The support stability is poor and there is no guaranteed measure. The support itself is unstable after pouring, causing the formwork to deform.
3. Prevention and control measures
(1) The template support system is selected according to different structural types and template types so that it can coordinate and cooperate with each other. When in use, the support system should be checked and reviewed, especially the pillar spacing should be determined by calculation to ensure that the template support system has sufficient load-bearing capacity, stiffness and stability.
(2) If the wooden support system is coordinated with the wooden formwork, the wooden support must be nailed firmly and wedged tightly, and the stretching bonds must be strengthened between the pillars. The elevation and fixing of the wooden support system with a large load can be operated by the sleeper tower pile method and nailed to fix it.
(3) The steel support system has a steel corrugated and support arrangement form that meets the formwork design requirements and can ensure safely withstand construction loads. The steel pipe support system should generally be buckled into an integral frame type, and the vertical and horizontal spacing of the columns is generally about 1m (there should be a tight-distance form when the load is large), and diagonal braces and scissors support should be added.
(4) The substrate with the support body must be solid and reliable. When the vertical support base is added to the soil layer, it should be placed on the support base, the support base is laid steel or hard materials such as scaffolding board .
(5) In multi-layer or high-rise construction, attention should be paid to adding support layer by layer to disperse the construction load in layers. The lateral support must be firmly supported, and the tie and reinforcement are reliable. If necessary, the ground anchor should be inserted or the iron parts and short steel heads should be embedded in the concrete to serve as support.
14. Top board template defects
1. The phenomenon is that the middle part of the
plate is deflected; the concrete surface at the bottom of the slab is uneven; and when using wooden formwork, the beam edge formwork is embedded in the beam and is not easy to remove.
2. Cause analysis
(1) The material used for the template keel is small or the spacing is too large, and it cannot provide sufficient strength and stiffness. The bottom mold does not arch according to the design or specification requirements, resulting in excessive bottom tamping.
(2) The bottom of the support under the slab is not firm, and the load continues to increase during the concrete pouring process, the support sinks and the plate form is deflected.
(3) The bottom formwork of the plate is uneven, and the flatness of the concrete contact surface exceeds the allowable deviation.
(4) Lay the plate formwork on the side form of the beam, and even slightly extend into the beam formwork. After pouring the concrete, the plate formwork absorbs water and expands, and the beam formwork also slightly expands externally, causing a formwork on the edge to be embedded in the concrete.
3. Prevention and control measures
(1) The keel and pull-bar wood under the floor formwork should be calculated and determined by the template design to ensure sufficient strength and stiffness, and the support surface should be flat.
(2) The support material should have sufficient strength, and be firmly matched to each other in the front, back, left and right to increase stability; if the support is supported on a soft soil foundation, the ground must be pre-tamped and a long cushion wood must be laid. If necessary, the cushioning board will be added to increase the contact surface of the support on the ground and ensure that there is no sinking under the weight of concrete (Measures must be taken to eliminate the possible sinking after the mud is damp).
(3) At the connection between the wooden formwork and the beam form, the plate form should be laid flush to the outer opening of the side form to avoid the formwork being embedded in the beam concrete for easy removal. The
(4) board template should be arched according to the regulations. When mixing steel and wood formwork, the gaps must be embedded and maintained horizontally.
15. Wall template defects
1. Phenomenon
(1) mold blowing, tilting and deformation, and the wall is not perpendicular.
(2) The wall thickness is different, and the wall surface is uneven.
(3) The wall slurry is slurry and exposed ribs are carried out, and the bottom of the formwork is wrapped in concrete and mortar, making it difficult to dismantle the formwork.
(4) corner template cannot be removed.
2. Cause analysis
(1) The steel formwork has not been typed in advance and the arrangement is not drawn; the adjacent formwork has not been set up in purlins or the spacing is too large, the pulling bolts are too small or not tightened; there is no guide wall at the base of the wall, the root of the formwork is uneven and the gap is too large.
(2) The formwork is made unevenly and has inconsistent thickness. The two adjacent wall formwork is not spliced tightly or flatly, and the support is not firm. The pulling bolts are not used to withstand the side pressure of concrete on the formwork, which causes the mold to explode during concrete pouring; or it is pulled out because the diameter of the selected pulling bolts is too small or the spacing is too large to withstand the side pressure of the concrete.
(3) The concrete pouring layer is too thick, the vibration is not dense, the formwork is under too much pressure on the side, and the support is deformed.
(4) The corner mold and the wall template are not spliced tightly, the cement slurry leaks out, and the lower part of the template is wrapped. The mold removal time is too late, and the bonding force between the formwork and concrete is too large.
(5) Unpainted isolation agent, or washed away by rainwater after applying.
3. Prevention and control measures
(1) The wall formwork should be assembled and flat to meet the quality inspection and evaluation standards.
(2) When there are several concrete walls, except for the length of the top connecting the wooden square positioning, scissors are used to support each other.
(3) The middle of the wall body should be equipped with pulling bolts according to the formwork design book. The connecting rods on both sides of the formwork should bear the side pressure of the concrete to ensure that the mold is not exploded (generally Φ12-Φ16mm bolts are used). Between the two forms, steel pipes or hard plastic support should be used according to the thickness of the wall to ensure that the thickness of the wall is consistent. When there are waterproofing requirements, bolts with water stop plates should be used.
(4) The pouring thickness of each layer of concrete should be controlled within the allowable range of construction specifications.
(5) The template surface should be coated with isolating agent.
(6) The wall base is first poured into a 150-200mm high guide wall as the root template support according to the wall thickness. The upper part of the template is sealed with flat steel . When assembling
, two notches must be processed with the upper edge rib of the steel template. Align the notches of the two templates, place the slats into the notches, and clamp them with a U-shaped card.
(7) The keel should not be made of steel-flowered beams. The junction of the wall beams and the upper opening of the wall top should be tied. The support of the garbage roof set on the exterior wall should be firm and reliable, and the spacing and position of the support should be determined by the template design.
16. Stair template defects
1. The phenomenon is that the stairs are exposed and the slurry surface is exposed on the sides, and the bottom is uneven.
2. Cause analysis
(1) The bottom mold of the stairs uses steel formwork. When the module cannot be fully equipped, the wooden formwork is used, and the side mold of the stairs is also made of wooden formwork, which can easily lead to a tight joint, causing slurry to run away.
(2) The flatness deviation of the base plate is too large, and the support is not reliable
3. Prevention and control measures
(1) The side grip can be used to form a steel form at the ladder section, and the 2mm thick steel plate form and the 8th channel steel point welding connection. The two side grips must be symmetrical and not used in each step, and the side grips are connected with the staircase culture grips with U-shaped cards.
(2) The base mold should be flat, the joints should be tight, and meet the construction specifications. If the supporting rod is too slender, shear force should be used to support it firmly.
(3) When using plywood diaphragm formwork, the spacing between wooden keel of the stair support base plate should be 300-500mm, the spacing between the support and the cross-bracket is 800-1000mm, the two ends of the cradle are obliquely supported, and the lower one is tightened with single wedges, and pull the lever between the oblique supports tightly. The outer side plate is nailed on the outer side plate, and the high bottom is aligned with the stepping mouth, and a small support is nailed at the lower end of the stepping side plate to ensure the stability of the stepping side plate.
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