by When the shaped steel formwork is adopted, the internal corner formwork is not used, and the large corners are often not closely connected, there are gaps, and the formwork expansion occurs from time to time.
1.2 prevention measures for common problems of construction formwork expansion formwork is an important tool for concrete structure engineering construction, especially the formwork technology of cast-in-situ structure.
(3) The external formwork of the beam should be steel formwork.
(4) After the formwork is used, it shall be cured and repaired to ensure that the formwork is clean and intact.
3.
Drainage facilities shall be provided.
10.
Determine the formwork installation sequence to ensure the overall installation quality.
Internal formwork of beam floats upward 1.
7.
(2) When pouring the roof concrete, the internal formwork of the beam begins to float upward, resulting in the elevation of the beam top surface and cracking cracks.
When there is no external scaffold, it is difficult to install the external formwork of the surrounding beam, the quality cannot be guaranteed, the external formwork support is not smooth and straight, and the support is not firm, resulting in formwork expansion.
Design the door and window opening formwork, and reserve the support form and installation and positioning method of the opening formwork.
3.
After the formwork on both sides of the beam is removed, it is found that there are horizontal cracks, corners and rough surface bubbles on the side.
Prevention measures (1) for the internal formwork of the rubber airbag, the fixed reinforcement shall be set and welded to the main reinforcement of the beam.
Support shall be adopted to reinforce the parts where split bolts or tie tabs are improperly set, and the lower opening of the formwork shall be fixed with 518-525 reinforcement feet.
At the same time, considering the concentrated reaction force at both ends during tensioning, the foundation at both ends must be reinforced to meet the needs.
4.
1.2.2 quality control measures for formwork installation 1.2.2.1 formwork construction scheme 1.
For the support of the floor slab, the beam slab support frame shall be calculated respectively on the basis of structural calculation, and the large head column shall be supported according to the actual situation.
The lateral pressure of concrete at the lower opening of formwork is the largest.
Cause analysis: the positioning and fixing measures of the internal formwork are not effective.
Temporary fixed facilities against overturning shall be set during installation.
5.
The formwork used shall ensure correct shape, size and relative position, and have sufficient strength, stiffness and stability.
The door and window openings and reserved openings with wooden formwork are difficult to support and locate, which is a frequent area of formwork expansion.
8.
(2) The internal formwork of hollow wood formwork shall be supported against the top plate.
The expansion of concrete formwork will cause the change of component size and irregular appearance.
6.
1.2.2.2 the installation of formwork shall be carried out in strict accordance with the formwork construction scheme.
The formwork shall be pre arranged according to the actual situation of the building structure, and the non-standard formwork shall be placed at the position convenient for treatment in the middle of the span.
1.1.2.
When the U-shaped clamp at the external corner is not in place or the cantilever end of the large formwork is too long, die expansion is easy to occur.
The combination type of formwork shall be reasonable, the support calculation shall be accurate, and the layout of split bolts and tie pieces shall be reliable and effective.
Eliminate the quality hidden dangers of formwork expansion caused by lax splicing, non vertical plate surface, gap between the lower opening of the formwork and the components, failure to screw the split bolt in place, loose tie piece, missing U-shaped clamp on the formwork splicing, failure to support the formwork according to the calculation, suspension of the support, etc.
3.
Formwork expansion is easy to occur when one-time pouring is too high and too fast.
Cause analysis (1) the formwork is not straight in the longitudinal direction.
In addition to lateral pressure, other loads that may occur such as concrete pouring method and stacking method shall be considered in load combination calculation.
2.
If necessary, a detailed formwork drawing shall be drawn to assist the construction.
1.2.2.3 in addition to checking whether the component size meets the design requirements, the formwork installation acceptance shall also check the implementation of the formwork construction scheme, and the support, camber, side formwork support and node formwork installation of beams and floors; For the wall column formwork, the splicing, internal and external corner connection and formwork lower opening support shall be checked and accepted.
Finally, we should also deal with the following problems: the form and size of corner formwork and the connection mode with wall and slab formwork; Splicing method between formwork, splicing method between formwork and corner formwork, beam column joint, internal and external formwork support method at the junction with wall and column.
(4) No camber is set for the bottom formwork.
Due to the residual slurry left on the surface, the secondary joint can not ensure the tight splicing between the formwork and the wall, and the cylindrical surface, so it is also easy to expand the formwork.
Lax splicing of formwork at beam column joints and the junction of floor slab, shear wall and column is also easy to cause membrane expansion.
7.
2.
1.2.1 ＾ analysis on the position and cause of formwork expansion 1.
Generally, it is necessary to chisel the surface for shaping, which seriously affects the appearance quality of concrete.
2.
Because it directly affects the quality, cost and economic benefits of engineering construction, it is an important content to promote the progress of construction technology in China.
3.
Finally, whether the overall installation is reasonable shall be checked and accepted..
Phenomenon: the beam body is uneven along the longitudinal direction, the beam bottom is uneven, and there are exposed reinforcement.
(6) The bottom formwork of post tensioned prestressed concrete beam shall be set on the pedestal.
5.
When the mid span of the beam is not arched as required, the beam is easy to sink.
(2) The stiffness of the side formwork shall be checked, and the section form with large stiffness shall be adopted as far as possible.
Arbitrarily cancel the tie piece to cause die expansion.
Phenomenon (1) when pouring web concrete, the internal formwork of beam starts to float upward, which is the thinning of beam roof concrete.
4.
Defects in the formwork outside the beam 1.
9.
It also affects the normal progress of the next process of concrete surface.
6.
(2) The garbage on the beam bottom plate was not removed.
Prevention measures (1) the form of covering the bottom with the help should be adopted between the side formwork and the bottom formwork of the beam.
The number of supports at the cantilever is not enough, and the elevation is not allowed to cause formwork expansion.
(5) For the beam cast-in-situ on the support, the support must be installed on a solid foundation and have sufficient support area to ensure that it does not sink.
2.
(3) The quality of the formwork itself is poor and the deformation is large after concrete pouring.
Prefabricated component formwork 1.1.1.
1.1.
Now, according to the construction technology and construction environment in northern China, this paper summarizes some common problems of formwork expansion, analyzes the causes, and puts forward some prevention methods through the cause analysis, so as to provide reference for construction.
