CUP AND TRAINING WORKS
Formwork and scaffolding have material and labor costs that account for about 40-60% of the cost of concrete.
1.1. The effects of formwork, momentum
Formwork is used as a mold to shape and size the structure, to protect the concrete mixture when pouring and compacted against cement splatter or water loss and to protect the concrete structure during freezing.
The scaffolding is a formwork support system, ensuring the formwork is in position, stable and stable throughout the process of pouring, compacting, curing concrete and slipping when the formwork is removed.
Classification of formwork
Formwork can be classified in the following ways:
According to the subdivision material
Bamboo ratters or bamboo sticks are used to make formwork for vortex staircases, small rolls, round columns, floor boards where there is a lot of bamboo. Bamboo is cheap and is available in all rural areas. However, the processing and erection of bamboo formwork is costly, with low circulation, and poor concrete surface quality. Plywood bamboo is a new material used for flooring and formwork.
Wood formwork has many types: formwork made by sawn wood, plywood formwork, plywood.
Formwork of sawn wood (raw wood)
Usually made from wood of group VII (oval, pink color), group VIII (bamboo shoots), pillars use group VI wood (oval, oak, crocodile, …). The width of the plank for formwork should not be more than 20cm, the thickness must be at least 2cm.
Lumber formwork is often used for small constructions. ! Low quality wood, irregular size, unable to create large standard boards; concrete is often pockmarked with high moisture absorption of wood, less smooth and smooth concrete surface; ability to use from 3 to 5 times; After a period of use, the wood is susceptible to warping and cracking.
b) Plywood formwork:
Plywood is produced into 1.22 × 2.44cm centers. thickness of 5 to 25mm. To make the plywood sheet hard, people use wooden ribs or metal ribs. For quick and convenient disassembly work, some metal binding details are also made.
Laminate is now used more because it creates high quality concrete surface tank, does not warp, is light, is easier to install and dismantle than metal formwork, lower cost. the rotation rate from 5 to 40 times; It is also used as a portable formwork.
In the US, plywood formwork is manufactured as coated panels. The main phenolic coating is the kraft paper impregnated with phenolic resin to saturation level. Coatings increase the surface properties of plywood. Coating panels come in a variety of types, the choice of which depends on: the quality of the concrete finish and the return on the investment.
Different brands of panel coatings of each style will provide a wide range of concrete trim styles and different gloss grades. For example, concrete poured with an M-coated formwork will have a surface finish, adhere to paint, and is susceptible to adhesives and coatings.
In order to increase investment efficiency in formwork, attention should be paid to:
Choose the type of coated mold panel that is appropriate for the type of base mix used, the high test container mix is more destructive and requires better control of the coating panels.
Requirements for concrete surface tanks when using.
Structural and strength requirements.
How many times is the formwork required to do this (or that thing).
Costs for potential use.
Advantages of the coated mold panel: Reducing finishing costs (finishing costs range from 25% to 55% of total labor costs).
High quality concrete.
Made from iron, alloy, heavy iron formwork so transport, erection and dismantling is difficult; light alloys but higher cost. The advantage of the metal formwork is easy to disassemble and less laborious, long side. for smooth and flat concrete surface tanks.
Metal formwork is typical panels with ribs made of flat steel, 2.5mm cross-section welded to a black steel face plate 1 to 2mm thick: each plate size: 20x120cm, 30x150cm, 30xl80cm … Along the ribs In addition to the sheet metal large holes were created. small for bonding the formwork together with pins and nails. Weight of each plate is from 20-40kg.
Metal formwork used as formwork for all types of structures: foundations, square columns, round columns, floors, … for smooth and flat concrete surfaces, standard structure sizes.
Wood and steel formwork combined:
Usually with steel ribs, plywood panels. The advantage of this type of formwork is easy to replace face plate, many times of reuse, low cost.
Reinforced concrete formwork
Both function as formwork and part of the structure, it can bear the loads that must be born in construction and compressive and flexural loads of the structure. The outer surface is finished to make the surface of the concrete, the inside has steel beard and roughness for bonding.
Using synthetic resin formwork for a flat concrete surface with small edges increases the adhesion of the plastering, lightweight, compact transport, erection, dismantling and storage; Resistant to rain, sun and impact is quite high, tightly sealed, difficult to lose cement water, the number of uses is over 50 times. However, the formwork has less stiffness, so it costs a lot of momentum (1.2 to 1.3 times compared to the metal formwork).
According to the structure and construction method divided
Specially engineered for the special structural types of the program. After disassembling, if you want to use it for other projects, you must reprocess. Therefore, this type of formwork is usually made of wood such as formwork of vortex staircases, rolling arches; sometimes with large construction parts such as ring-shaped overpass, it is machined with metal: shaped hard ribs, faceted steel plate. In these cases, there is no economic effect.
Forming formwork (penalty shootout)
Manufactured available in the factory or the machining workshop according to a number of standard sizes suitable for the majority of the size of structural components, when going to the gate, it is usually only necessary to arrange and assemble at the location of the culverts. . When removed, it remains in shape.
Shootout formwork has two types, small plate formwork and large plate formwork. The small formwork is presented in section 1.2. Classification of formwork. The flying formwork is a large sheet formwork that is designed, fabricated and organized at a high level. Formwork used for construction of high-rise floor panels.
Structure of flying formwork includes: flooring can be made of metal or plywood which is firmly fixed to the rafting system, the unloading system is a fixed space frame; The horizontal movement and adjustment system is mounted under the pillars. After the reinforced concrete slab has strengthened to dismantle the formwork, the entire formwork system will be lowered by the lifting mechanism; The wheel system or the sliding device will help the crane pull the formwork system out of the cell and room easily and bring them upstairs for installation. is a schematic diagram of the flight formwork horizontal movement and adjustment system.
c) Mobile formwork
A set of fixed formwork that is moved gradually during pouring by a jacking system (usually head size). The working cycle time of the formwork is calculated by calculation. According to the direction of movement, people divide; The formwork moves vertically, the formwork moves horizontally.
The formwork moves in the correct direction:
According to the displacement, it is divided into: Sliding formwork: is a type of formwork that moves continuously up during the pouring process thanks to special structures and jacking systems.
Sliding formwork is used for construction of works such as silos, chimneys, water towers, … In the construction of today’s high-rise buildings-, people started to apply the method of sliding formwork and pre-engineered pre-stressed floors to speed up construction progress, improve work quality and save formwork.
The height of the formwork is sliding from 1 to
5m, it surrounds the entire wall to be poured with concrete (high-rise buildings) or the entire cross-section of the structure (chimney …). The structure of the sliding formwork is shown in figure II.6.
The hydraulic jack is responsible for the sun for the entire household of the formwork to slide continuously up. Lifting capacity of a hydraulic jack is 3-5 tons.
Cling to the structure to climb from site to site using the crane.
The structure of climbing formwork is very special, can be 1 row (Fig. II.7 a,
or 2 to 3 rows (Figure II.7 c), each row from 0.6 to l, 2m in height, the rows linked together and linked to the bearing structure.
Climbing formwork is used when need to pour concrete walls, walls. After the section has been poured to the required strength, the formwork is removed and moved to another piece.
The climbing formwork is used to pour structures with variable cross-sections such as chimneys. Hanging formwork:
Slab steel slabs, welded with angular steel ribs, with upper working platforms (for moving and storing materials), and lower (for finishing and inspection) suspended to the central pillar. (3) by wiring and increasing dirt (4). The wiring household is equipped with a check chain to move the formwork system up.
Formwork moves horizontally:
The entire formwork can be moved on rails or wheels through a jacking or winch system.
This type of formwork is used for the construction of reinforced concrete structures with constant cross-section and large length such as: tunneling underground tunnels (e.g. tunnels at Ngang Pass), or slopes, simple book, … Construction of tunnels is often done first, while ceilings and walls are constructed together by the method of formwork moving horizontally.
rubber formwork. formwork to draw water in concrete, …
Sequence of construction of formwork and momentum
Including the following parts: Fabrication and erection of formwork and momentum; inspect and accept the formwork gate and the spearhead before placing the reinforcement; monitoring, checking, adjusting (if necessary) formwork and momentum during concrete pouring; disassembly and repair work.
The processing of formwork and momentum is carried out in the production workshop or the processing workshop by line construction method, utilizing modern machinery and equipment to improve labor productivity.
The erection of formwork and scaffolding must comply with the order of magic and construction drawings to ensure safety during erection and dismantling.
Check and accept the formwork and scaffolding according to the requirements of TCVN 4453: 1995.
The monitoring and inspection of formwork and scaffolding must be strictly implemented to promptly repair and correct construction problems with formwork and scaffolding during the pouring of concrete.
Formwork removal and scaffolding: Allowable time and sequence to remove formwork and scaffolding must comply with the design requirements and TCVN 4453: 1995.
2. Technical requirements for formwork and scaffolding (TCVN 4453: 1995) 2.1. General requirements
Formwork and scaffolding should be designed and constructed to ensure rigidity, stability, ease of assembly, and no difficulty in the installation of reinforcement, pouring and compacting of concrete.
Formwork must be sealed and tight so as not to lose the water of the cement when pouring and concrete beams, and at the same time protect the new concrete poured from the impact of the weather.
Formwork and momentum should be machined and erect to ensure the correct shape and size of the structure according to the design regulations.
Materials for formwork and spear
Formwork, beam can be made of wood, diaphragm, steel, precast concrete or plastic. Da spears can use bamboo, luong and luong.
Choosing materials for formwork, spear beam must be based on specific conditions and economic efficiency.
Wood for formwork, momentum wood is used in accordance with the Vietnamese standard of building wood TCVN l075: 1971 and current standards, and can also use indifferent types of wood.
Metal formwork, spear should be used so that it is suitable for the ability to rotate many times for different types of structures.
Erection of formwork and momentum
Installation of formwork and scaffolding must meet the following requirements:
Formwork tanks in contact with concrete should be non-sticking; the door-side formwork of walls, floors, beams and columns should be installed in such a way that it is suitable for early dismantling without affecting the remaining formwork and scaffolding that remains to support (such as bottom formwork beams, floors and pillars); erection of scaffolding formwork of floor panels and other parts of multi-storey buildings should ensure that each part can be dismantled and moved gradually according to the pouring and solidifying process of concrete; support pillar of the scaffolding must be firmly placed on a hard foundation, not slipping and deformed under load and impact during construction.
When erecting the formwork, it is necessary to have calibration markers or appropriate measures to facilitate checking of the axial center and elevation of structures.
During the installation of the formwork, it is necessary to construct some suitable holes at the bottom so that when cleaning the surface of the water, there is room to escape. Before pouring concrete, these holes are sealed.
3. Formwork anti-unloading system
Formwork anti-unloading system has many types from single scaffold to combinational scaffolding depending on the type of construction and the nature of the work that are used accordingly.
3.l. Single spear
Single spear can be made of bamboo, wood or metal. Wooden trusses used as pillars for construction of low-rise buildings. With high-rise buildings, people often use metal single-metal spears, which are stronger and safer.
Made of log or sawn timber.
Scaffolding pillars can only use wood from group VI and below and use non-bent wood, which is heavily bent (with scarring, lumpy eyes, rotting), which may affect construction safety and quality. the building is not used. The cross-section of the pillar is calculated by calculation, usually using sawn timber with minimum cross-section 8.locm, log timber with a diameter of 80 – 120, length of 3 to 4m. The beam formwork supports are usually machined into a T-shape.
The support post is stored flat to place it firmly on the wedge. Wood pillar wedge is usually made of wood, or sand box.
The wedge has the effect of making height adjustment and column removal easy. The pillars are spaced 700 – 800mm apart and are tied diagonally in both vertical and horizontal directions. Cross bracing is arranged according to the project’s perimeter, inside there is a bracing system for every two rows of columns. Wooden bracing bar with section 25.lo0mm.
Single mast with adjustable height:
Made of tube steel, available in the following forms:
Single mast adjusts the height by connecting segments. This type has many different size segments, depending on the working height that choose them accordingly. Bolted between pipe sections to connect flanges
Stacked column, adjustable in screw thread height:
Consists of 2 interlocking pipes, linked by horizontal and tough latches; used to fight against formwork of beams, floors with small size under 5m; Simple structure, easy to transport and store. Simple disassembly, height adjustment mechanism (adjustable rotation), rotates many times. The screw-threaded height-adjusting guard can, when used, be fitted with a combination column, or an additional column with a fixed length.
To ensure stability for column-support, cross bracing is required. The brace can be a steel tube (spear tube) when it is linked to the support by a spear; when the bracing is made of wood it is linked to the column
anti with arc lock.
The pipe ends of the screw thread assembly, and the screw thread, must be carefully painted against impact, and regularly covered with rust.
Work to keep the formwork stable, vertical or oblique at a certain angle a during concrete pouring and compacting until the total concrete strength reaches the required strength and can remove the wall. The lower end of the anti-slant rests against the foundation or the work floor, the other end is connected to the edge of the wall.
For ease of filling and adjustment, it is recommended to use adjustable slant struts or a combination of adjustable length bevel supports with wooden skewers.
Pa1 is used in wide form of interest in many countries, with the advantage of being a universal support, safe and economical, used for all projects with large structures, high floor height. Made of mild steel, simple structure, convenient transportation, erection and dismantling.
Pal spear is designed based on the principle of triangular frame system, forming solid pieces of continuous triangles, highly flexible and solid. You can create a square stand with side 120.120cm, or a foot for a triangle with side 120cm.
Spear Pal consists of parts:
Click on the column blanket and the jack at the top of the top column. The cross and cross ties (SN-12 and SD-12).
Standard triangular frame (S-1215).
Fasteners for coupling (SA-02).
Attention when erection:
horizontal in 2 directions
perpendicular and cross braces against horizontal displacement. Do not replace the stand parts and accessories with other objects during erection.
The entire stand system must be firmly linked together and controlled high and low by the nuts of the jacks.
The coupling must be adjusted to the correct position in order to install the coupling pin. In case the triangular frame is under compressive load, the coupling pin is not required.
3.3. The price of the charge
Used to support formwork in small outward concrete structures such as: eaves, support wall formwork and working floor (Figure II.17) titer bracket is linked to brick wall, concrete wall by anchors . With brick wall using flat steel anchors, it is more convenient to penetrate the mortar circuit than using round steel anchors.
Note: The heart of the column in two directions must be perpendicular, fix the column leg firmly in the positioning frame (the column footer), then place the slant and adjust the straightness of the column formwork.
The erection order is as follows:
Check all of the columns on a section of the house, conduct the heart line (in both directions) with red paint on the foundation or floor.
Fix the spherical bracket in the correct position and the center of the two directions (Figure 11.23).
Erection of column formwork. Column steel reinforcement is usually installed before pouring, if you install the column form by hand, you should assemble the 3 outside boards, then build up and place, fix the remaining board, then insert the column and use adjustable wedge; pay attention to the electric column must be square. It is possible to combine the column formwork into a mold box and then use the crane to install.
Place the skewer, drop the beam in two directions (or use a water bottle) and adjust the skewer to bring the column back to a firm vertical position.
Round column formwork
Made of wood or steel. Wooden formwork is made of thahh lati and rings, linked between them by palace. Depending on the diameter of the column to be molded, one can process 2 or 4 separate sheets. then put together into a round mold. The link between the loose formwork panels is made by wood panels or bolts. Wood formwork is used when the mass of the column needs to be cast is low or when the column is of special size.
Steel formwork is made of steel plates and steel ribs, welded together to form (Figure 11.25). The steel formwork for the round column is usually made up of 2 separate plates, fixed together by pins.
Steel formwork for the concrete tank is smooth and round. Steel formwork is used when the column mass is high and the column size is common.
Round column formwork is similar to that of square columns or rectangular columns.
When adjusting the verticality of the traverse column, three plumb strings are often used.
Polygonal column formwork
Polygonal columns often have hexagonal or hexagonal cross-sections.
The polygonal column formwork is usually made of wood. Formwork panels should be machined in an edge-to-edge manner so that the contact line between the formwork is on the road
radius through the polygon center, the column angles will be beautiful.
Beam formwork (Figure 11.27)
The beams have small electrical properties, large radios, and are placed on high so the formwork structure is relatively complicated. The main parts of the outside formwork
wall boards, anti-skewers also have planks, braces to keep the legs of the boards and T-pillars.
The bottom board and the pillar, in addition to the self-load, also withstand the re-weight of the concrete, reinforcement, load of people and means of transport, the thickness of the board and the cross-section of the support column are calculated according to the calculation. ensure the permissible strength and deflection of the stone board and the allowed thinness of the pillar. For beams with a height greater than 60cm, there must be internal bracing bolts to prevent bulging for the wall.
Plank into girder outside the bottom board so that the bottom of the box is sealed, the positioning of the footboard is sure and also makes it easy to remove the wall in the future. Veneer and beam wall boards are shaped panels made of lumber or plywood with 25-30mm thickness.
The order of erection of compact formwork is as follows:
Check, the main regulator then line the core of the beam on all the girder locations in the part of the house.
Based on the position of the marked foot of the column on the plywood, erect the T-pillars, adjust the vertical supports, then brace the pillars against, insert the column wedge.
Place the girder bottom board, and attach the girder bedboard to the top, bottom and middle 3 column support. Adjust the wedge under the foot of the pillar for the two ends of the board to use the column, stretch the rope over the two ends of the board, follow the wedge-shaped main line under the pillar to make the stone plank level. If the span is larger than 4m, the construction rainbow must be created.
Put 2 planks into beams, beam 2 braces to hold the foot of the wall to position.
Place the stick temporarily, place the anti-skewers, the main pipe for the board upright.
Floor beam formwork
The floor formwork uses eight plywood profiles or pre-machined lumber chutes, each piece should not weigh more than 50kg for easy transport. These planks are placed on wooden purlin system. Under wooden beams are a system of wooden or metal supports.
After installing the beam formwork, erect the floor board in the following order:
Place purlins and fillers.
Set the purlin system and support column for the floor after pouring using the adjustment wedge to make the board vertical.
Place frill planks, use water pipes to adjust the level of the fringes.
Place each piece of floor board to fasten the floor board with purlins.
Stretch through the fringed boards and adjust to level and level flooring.
Figure 11.29 shows L-shaped compacted formwork.
The form of the stairs has a cone
It is a form of continuous-slab formwork, but stage-1 floor and second-stage slab are tilted at a certain angle compared to the horizontal. Projection, the next beam should also be carefully paid attention otherwise the construction of the stairs will be difficult.
Stair formwork is usually wood plank, plywood; Stump supports using wood, sawn timber or single metal pillars to change the height.
Installation of stair formwork is similar to that of floor beam formwork, firstly the installation of formwork and scaffolding for forward beams, landing beams and stair beams; adjust them to the correct heart, core, design size and then install formwork and floor scaffolding and phase 2 staircase, phase 1 floor and staircase. figure 11.30.
Checking and accepting the erection of formwork and scaffolding (TCVN 4453: 1995-3.5)
Formwork and spears, once applied, are checked according to the requirements in Table II. 1, Deviations shall not exceed the values shown in Table II.2.
Board: The requirements to check formwork, spear
The requirements should be checked
The formwork has been installed
Shape and size
Visually, measure with a ruler of the appropriate length
In accordance with the structure of the design
Comply with the provisions of TCVN4453: 1995-3.3.3
Spread between coupling plates
The degree of lumber between panels is 3mm
Tightness, tightness between the formwork, between the film and the background
The formwork is sealed and tight, ensuring no loss of cement water when pouring and compacting the concrete
Details buried and placed papules
Determine the size, location and quantity by suitable means
Make sure the size, position and quantity as prescribed
The anti-adhesive layer covered all the exposed face of the concrete
Clean inside the formwork
No trash, mud and other contaminants left inside the formwork
The inclination, height and size of the formwork
Visually, surveyors and suitable equipment
Do not exceed the values shown in Table 2
Moisture of wood formwork
Wood formwork was watered before inspection
Daism has been installed
Visually, contrasting with the lance design
The scaffolding is installed to ensure the size, number and location according to the design
By losing, use your hand to shake vigorously the pillars, the wedges in each pillar
Pillars are supported, cushioned and placed on a hard foundation, ensuring stability
Hardness and stability
Visually, contrasting with the lance design
The mast is cross-braced and horizontal with sufficient quantity, size and position according to the design
The pre-acceptance test of the construction of formwork, momentum and scaffolding was carried out in the field, combined with the evaluation and consideration of the test results as prescribed in Table II. 1 and deviations shall not exceed the values shown in the table
Name is wrong
Acceptable level (mm)
1. The distance between the pillars to support the formwork and the supporting structure
bending and the distance between the unloading posts is stable. nco and
pillar against design distance:
a) Per meter length
b) On the entire stage
2. Formwork plane deviation and junction of
them relative to the design vertical or inclination:
a) Per meter length
b) On the entire shaving direction of the structure:
– Wall and column unloading the whole block with a height of 5m
– Walls and columns for unloading floor panels of the whole block are over 5m high
– Column column is linked by beam
– Beams and arches
3. Deviation of formwork shaft compared to design:
b) Walls and columns
c) Beams and arches
d) Foundations of steel structures
According to the law
of the design
4. Deviation of sliding formwork, climbing formwork and di-formwork
work compared to the construction axis
Formwork release agent
The formwork release agent enables quick formwork removal, keeping the concrete surface and formwork from damage during removal. People often use the marks of the waste machine to lubricate the inside of the formwork, after removing the gray concrete surface. dirty. Nowadays, open-pit constructions such as bridges, silos, water towers and works with high artistic requirements all need clean and beautiful surfaces for easy decoration. Some formwork release agents are used in Vietnam (such as separol) for a clean concrete surface. pretty.
Quality separol is 0.83kg / liter. The consumption on a wooden formwork is 1 liter for 2lm2. on plastic and steel formwork is 42m. The coating surface before spraying, rolling or applying the degreaser must be clean and free from grease. Before the release is dry, cover the formwork surface to insulate the water.