Ten Key Points of Formwork Support Systems (Reposted)

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Ten key points of formwork support systems (reposted) Formwork engineering (forwork) refers to the formwork used to give shape to freshly poured concrete, as well as the entire structural system that supports this formwork. The components that come into contact with the concrete and are responsible for controlling its dimensions, shape, and position are known as the formwork itself. The members, trusses, connectors, metal accessories, and temporary work bridges that serve to support and fix the formwork constitute the support system. For sliding formworks or self-elevating formworks, additional elements such as lifting mechanisms, elevators, and platforms are required. Formwork works are a type of temporary structure in concrete construction. The structure of formwork work includes the panel system and the support system; today I will mainly share with you information about the support system. The support system includes vertical and horizontal enclosures, bearing beams, bearing trusses, cantilever beams, cantilever trusses, columns, diagonal braces, and tie rods. In the early days, wooden forms were commonly used. After the 1950s, it gradually evolved to use materials such as steel, plywood, reinforced concrete, or a combination of steel, wood, and concrete. Table of Contents for the Safety Manual on Formwork Scaffolding 1. Construction Plan 2. Scaffold Foundation 3. Scaffold Structure 4. Scaffold Stability 5. Construction Loads 6. Instruction and Inspection 7. Member Connections 8. Base and Braces 9. Material of Components 10. Dismantling of the Scaffold I. Construction Plan ★ A specialized construction plan must be prepared for formwork scaffolding, and the structural design must be based on calculations. ★ Special construction plans must be reviewed and approved in accordance with the established procedures. ★ A special construction plan for super-scale formwork supports must be subject to expert review in accordance with regulations. Requirements: 1. The construction unit shall prepare a special plan before carrying out the construction of sub-projects with high risks ； In construction projects where general contracting is employed, the specialized plans shall be prepared by the general contracting company ； 2. The special plan shall be reviewed by professional technicians from the construction company’s technical, safety, and quality departments, as organized by the company’s technical department. Once approved, it must be signed by the company’s technical director and stamped with the company’s official seal before being submitted to the supervision company. There, it shall be reviewed and signed by the project’s chief supervision engineer, who will also stamp it with his professional registration seal ； 3. For special plans for sub-projects with a certain scale and high risk, the construction enterprise shall organize expert review meetings. In the case of a general construction contract, the general construction contractor shall organize an expert review meeting. II. Support Foundation ★ The foundation must be solid and level; its load-bearing capacity must meet the design requirements, and it must be able to support all the loads applied to the upper part of the support. ★ Shims must be placed at the bottom of the support in accordance with the specifications; the dimensions of these shims must also comply with the relevant standards. ★ The longitudinal and transverse diagonal braces at the bottom of the support must be installed as required by the specifications. ★ Drainage measures must be implemented for the foundation to ensure proper drainage. ★ When the support is installed on a floor structure, the strength of that floor structure must be checked, and reinforcement measures may be necessary if required. Installation requirements: 1. When the vertical formwork and the supporting columns of the support are installed on the underlying soil, shims must be used. These shims must have sufficient strength and support area, and they must bear the load at their center. The subgrade should be firm and there should be drainage measures. 2. The wooden shims should have a length of not less than 2 spans, a thickness of not less than 50 mm, and a width of not less than 200 mm. 3. When the scaffold is erected on the concrete base of a permanent building structure, the base or pad under the vertical poles may not be installed, depending on the circumstances. 4. At a height of 200 mm from the bottom of the column, sweepers should be installed in the horizontal directions, following the pattern of vertical ones downward and horizontal ones upward. 5. The lower floor slab should be capable of bearing the loads from construction above; otherwise, support brackets should be added. 6. When the lower floor slab is unable to bear the loading from construction above it, the formwork support structure for the lower floor slab should not be removed. Instead, additional columns should be added at the positions of the vertical posts beneath the beams in the areas where high-formwork support is required on the upper level, as a means of reinforcement; or the design team should propose a solution for dealing with this situation. III. Scaffold Construction
★ The spacing between vertical posts shall comply with design and specification requirements.
★ The step distance between horizontal members shall comply with design and specification requirements.
★ Horizontal members shall be installed continuously as required by the specifications.
★ The installation of vertical and horizontal diagonal braces (for fastener-type steel tube scaffolds) or special diagonal and horizontal members (for modular steel tube scaffolds and plug-in type coupler steel tube scaffolds) shall also conform to the specified requirements.

Installation requirements:
1. The longitudinal and transverse spacing between vertical posts shall meet the requirements of the construction plan and relevant specifications:
① When using fastener-type steel tubes as scaffolding components, the longitudinal and transverse spacing between vertical posts must not exceed 1.5 meters ； ②When using fastened steel pipes as supports for tall formwork, the longitudinal and transverse spacing of the vertical poles should not exceed 1.2 m ； 2. The spacing between supports should meet the requirements of the construction plan and relevant specifications: ① When using fastened steel pipes as supports, the spacing between these supports should not exceed 2.0 m ； ②When using fastened steel pipes as supports for tall formwork, the spacing between the supports should not exceed 1.8 m ； ③A horizontal tie rod should be installed along the longitudinal and transverse directions at the top of the column supporting the bottom of the adjustable support. The spacing between the sweeping rod and the horizontal tie rods at the top is determined by evenly distributing the spacing as required by the template design; one horizontal tie rod is installed in each direction at each such spacing point. When the floor height is between 8-20m, an additional horizontal tie rod should be installed between the two horizontal tie rods at the topmost step spacing ； When the floor height is greater than 20m, an additional horizontal tie rod should be added between the horizontal tie rods at the top two levels. The ends of all horizontal tie rods should be firmly pressed against the roofs of the surrounding buildings. When there is no other option, continuous diagonal bracing should be installed vertically at the ends and in the middle of the horizontal tie rods. 3. For the formwork support system, continuous diagonal bracing from bottom to top should be provided along the outer perimeter ； For bolted steel tube full-house support frames, diagonal bracing should be installed according to the type of frame: ① Ordinary type: Inside the frame, vertical and horizontal diagonal bracing should be provided every 5m–8m, from the bottom to the top, and even in a continuous vertical pattern; the width of such diagonal bracing should be 5m–8m ； Horizontal diagonal bracing should be installed in the plane of the intersection of the vertical diagonal bracings. For oversized formwork supports, horizontal diagonal braces shall be installed at the layers where the sole plates are placed. The distance from the horizontal diagonal braces to the bottom plane of the scaffold and the spacing between horizontal diagonal braces should not exceed 8 meters ； ②Enhanced version: When the longitudinal and transverse spacing between uprights is 0.9m × 0.9m to 1.2m × 1.2m, continuous vertical diagonal braces shall be installed from bottom to top every 4 spans (both longitudinally and transversely) within the structure, with a width equivalent to 4 spans ； When the longitudinal and transverse spacing of the vertical poles is 0.6m×0.6m to 0.9m×0.9m, continuous vertical diagonal bracing should be installed from bottom to top every 5 spans internally in both longitudinal and transverse directions (with a minimum span of 3m), and the width of such diagonal bracing should be equal to 5 spans ； When the longitudinal and transverse spacing of the vertical poles is 0.4m×0.4m to 0.6m×0.6m, continuous vertical bracing should be installed from bottom to top at intervals of 3m to 3.2m in both the longitudinal and transverse directions inside; the width of such bracing should be 3m to 3.2m ； Horizontal diagonal bracing should be installed in the plane of the intersection at the top of the vertical diagonal bracings, and horizontal diagonal bracing should also be installed at the level where the ground-clearing bars are placed. The distance from the horizontal diagonal braces to the bottom surface of the scaffold and the spacing between such braces should not exceed 6 meters; the width of the diagonal braces should be 3 to 5 meters ； ③Diagonal braces shall be fixed to the intersecting horizontal or vertical members using swivel couplers; the distance from the centerline of the swivel coupler to the main joint should not exceed 150 mm. 4. The installation construction of support columns for beams and slabs shall comply with the following provisions: ① For the columns supporting beams and slabs, the longitudinal and transverse spacing shall be equal or in a multiple relationship. ②The bottom of wooden columns should be fitted with shims, while the top should be equipped with support heads. At the bottom of the steel pipe column, shims and a base should be installed, while at the top, adjustable supports should be used. If there is any gap between the U-shaped support and the sides of the ribbed beam, it must be filled tightly. The length of the screw protruding from the top of the steel pipe should not exceed 200 mm, and the gap between the outer diameter of the screw and the inner diameter of the column’s steel pipe should not be greater than 3 mm. During installation, it is necessary to ensure that the column is aligned vertically. ③At a height of 200 mm above the ground from the bottom of the column, sweepers shall be installed in the longitudinal and transverse horizontal directions, following the sequence of longitudinal first and then transverse. A horizontal tie rod should be installed along the longitudinal and transverse directions at the top of the column supporting the bottom of the adjustable support. The spacing between the sweeping rod and the top horizontal tie rods should be evenly distributed to determine the step distance, provided that this distance meets the requirements for the spacing of horizontal tie rods as specified in the formwork design. At each step distance, one horizontal tie rod should be installed both longitudinally and transversely. When the floor height is between 8 and 20 meters, an additional horizontal tie rod should be installed between the two horizontal tie rods at the topmost step spacing ； When the story height exceeds 20 m, an additional horizontal tie rod should be added between the top two spacing intervals of horizontal tie rods. The ends of all horizontal tie rods should be firmly pressed against the roofs of the surrounding buildings. When there is nowhere to brace against, continuous diagonal braces should be installed vertically at the ends and middle of the horizontal tie rods. ④The sweeping bars, horizontal tie rods, and diagonal braces for wooden columns should be made of 40mm×50mm wooden strips or 25mm×80mm wooden planks, which must be nailed securely to the wooden columns. The sweeping bars, horizontal tie rods, and diagonal braces for steel pipe columns shall be made of Φ48mm×3.5mm steel pipes, which must be securely fastened to the steel pipe columns using couplers. Wooden sweeping rods, horizontal tie rods, and diagonal braces shall be lapped and secured with nails. The steel pipe floor sweepers and horizontal tie rods should be connected by butt joints, while the diagonal bracing should be connected by lap joints; the lap length must be no less than 500 mm. These connections should be secured using two rotational fasteners, placed at a distance of not less than 100 mm from the ends of the rods. 5. When fastener-type steel pipes are used as column supports, their installation details shall comply with the following requirements: ① The specifications of the steel pipes, the spacing between them, and the fasteners shall meet the design requirements. At the bottom of each column, a base and underlay plate shall be provided; the thickness of the underlay plate must not be less than 50 mm. ②The spacing between the columns of the steel pipe scaffold, as well as the installation of the ground-level bars, horizontal tie rods, and diagonal bracing, shall comply with the provisions of Article 6.1.9 of these specifications. When the bottoms of the columns are not at the same height, the longitudinal sweepers on the higher side should be extended downward by at least two spans; the height difference shall not exceed 1 m, and the distance between the columns and the upper edge of the slope shall not be less than 0.5 m. ③It is strictly prohibited to overlap when extending the columns; joint fasteners must be used for connection. The joint surfaces of adjacent columns should not be aligned with each other, and the vertical offset between such joint surfaces should be no less than 500 mm. The distance between the center of each joint and the main node should not exceed 1/3 of the step distance. ④It is strictly prohibited to fix the upper section of steel pipe columns and the lower section of steel pipe columns at the horizontal tie rods out of alignment with each other. ⑤On the outer perimeter of the columns supporting the formwork for full-house templates and shared space templates, vertical continuous diagonal bracing should be installed from bottom to top ； Vertical continuous diagonal bracing should be installed every 10 meters or so in both the longitudinal and transverse directions, running from bottom to top; their width should be between 4 and 6 meters. Horizontal diagonal bracing should also be placed at the top of these diagonal bracing members as well as at the ground-level members (see diagram). The bottom end of the diagonal bracing members should be pressed tightly against the ground, with an angle of 45° to 60° being preferred. When the building height is between 8 and 20 meters, in addition to meeting the above requirements, zigzag diagonal bracing should be added between two adjacent vertical continuous diagonal bracings in both the longitudinal and transverse directions. At the locations where horizontal diagonal bracings are present, an additional horizontal diagonal brace should be installed in the middle of each such brace (see figure). When the building height exceeds 20m, in addition to meeting the above requirements, all zigzag bracing members should be replaced with continuous scissor braces (see figure). IV. Scaffold Stability ★ When the height-to-width ratio of the scaffold exceeds the specified value, wall connectors should be installed as required, or reinforcement measures should be taken to increase the width of the scaffold structure ； ★ The length of the vertical pole extending from the center line of the top horizontal bar to the support point shall meet the requirements of the specifications ； ★ When pouring concrete, it is necessary to monitor the settlement of the scaffold foundation and the deformation of the scaffold; such settlement and deformation should remain within the specified allowable limits. Requirements for installation: 1. When the height-to-width ratio of the full-house support frame is greater than 2, the frame must be rigidly connected to the structural columns around its perimeter and in the middle; the horizontal spacing between the connecting elements should be 6m–9m, while the vertical spacing should be 2m–3m. In areas without structural columns, measures such as embedding steel pipes should be taken to establish a rigid connection with the building structure; in areas where space is available, the full-scale support frame should extend beyond the projection of the top loading area by (2-3) spans ； 2. When using fastened steel pipes as supports, the length of the screw protruding from the steel pipe should not exceed 200 mm, and the cantilever length of the adjustable bracket extending beyond the top horizontal bar should not exceed 500 mm ； 3. When steel pipes of the bowl-fastened, disc-fastened, or disc-pin type are used as supports, the cantilever length of the adjustable bracket for the vertical pole extending beyond the top horizontal bar should not exceed 650 mm ； 4. When pouring concrete, it is necessary to monitor the settlement of the scaffold foundation and the deformation of the scaffold; such settlement and deformation should remain within the specified allowable limits. V. Construction loads ★ The uniformly distributed loads and concentrated loads during construction should be within the limits permitted by the design ； ★ When pouring concrete, it is necessary to control the height at which the concrete is piled up. The following requirements apply: 1. Strictly control the construction load; it must not exceed the design values, and concentrated stacking of materials or standing of people in one area should be avoided ； When using a concrete distributor for pouring concrete, the support system beneath the distributor should be reinforced ； 2. During pouring, the stacking height of the concrete must not exceed the limit specified in the construction organization plan. VI. Instruction and Acceptance ★ Instructions should be provided before the erection and dismantling of the scaffolding, and records of these instructions must be kept ； ★ Once the scaffold has been erected, it shall be inspected in accordance with relevant regulations; the inspection must include quantitative criteria and be signed off by the responsible person. Requirements for setup: 1. Before the implementation of the specific plan, the person responsible for preparing it or the project’s technical supervisor shall provide safety and technical instructions to the relevant personnel in the project team, full-time safety officers, as well as other on-site managers and workers. The technical supervisor of the construction enterprise or the technical supervisor of its branch shall conduct regular inspections of the implementation of the specific plans, keep records of these inspections, propose corrective actions for any issues identified, and maintain inspection archives. 2. For sub-projects with high risks that require inspection in accordance with regulations, the construction company and the supervision company shall organize relevant personnel such as the project manager, the person who prepared the special plan, the project’s technical supervisor, the chief supervision engineer, and the professional supervision engineers to carry out the inspection. Only those that pass the acceptance inspection may proceed to the next stage of work, after being signed off by the project’s technical supervisor and the chief supervision engineer. VII. Connection of members ★ The connection of vertical members shall meet the requirements of the specifications ； ★ The connection of horizontal bars shall meet the requirements of the specifications ； ★ The extension of the diagonal bracing rods shall comply with the specification requirements ； ★ The tightening of all connection points of the members shall meet the requirements of the specifications. Requirements for installation: 1. It is strictly prohibited to overlap the columns when extending them; joint fasteners must be used for connection. The joints between adjacent columns should not be aligned with each other, and the vertical offset between such joints should be at least 500 mm. The distance from the center of each joint to the main node should not exceed 1/3 of the step length ； (Article 6.2.4 of JGJ162-2008) 2. The floor-scraping rods and horizontal tie rods made of steel pipes shall be joined by butt welding ； (Article 6.1.9 of JGJ162-2008) 3. The overlap length of the diagonal bracing must be at least 1000 mm, and two swivel fasteners should be used to secure it at points that are at least 100 mm away from the end of the rod ； (Article 6.3.6 of JGJ130-2011) 4. The tightening torque of the fastener bolts shall not be less than 40 N·m, nor shall it exceed 65 N·m ； (Article 4.4.7 of GB50666-2011) 5. The tightening torque of the fastener bolts after installation shall be checked using a torque wrench, and the sampling method shall follow the principle of random distribution during installation. The number of samples to be inspected and the quality judgment criteria shall be determined as specified in the table below. Those that do not meet the standards should be tightened again until they meet the requirements. (JGJ130-2011 Article 8.2.5) VIII. Base and Brackets ★ The diameter of the adjustable base and bracket screws should match the inner diameter of the vertical posts, and the clearance between them should meet the requirements specified in the standards. ★ The length of the screw inserted into the nut should be no less than 5 times the diameter of the screw. Requirements for installation: 1. The gap between the outer diameter of the screw and the inner diameter of the vertical steel pipe must not be greater than 3 mm (Article 6.1.9 of JGJ162-2008). 2. The outer diameter of the screw used in the adjustable support must be no less than 36 mm (Article 4.4.8 of GB50666-2011). 3. When adjustable supports are used for the frame, the protruding length of the adjustment screw must not exceed 150 mm (Article 5.1.8.4 of JGJ162-2008). IX. Material of components ★ The specifications, models, and materials of steel pipes and other components must comply with the requirements specified in the standards. ★ The members must not be bent, deformed, or severely rusted. Requirements for setup: 1. It is advisable to use steel pipes with a diameter of Φ48.3×3.6. The maximum mass of each steel pipe should not exceed 25.8 kg ； (Article 1.2 of JGJ130-2011) 2. The new steel pipes shall be accompanied by a product certificate and a quality inspection report; the surface of the pipes must be smooth, without any cracks, scars, delamination, misalignment, hard bends, burrs, dents, or deep scratches ； (Article 8.1.1 of JGJ130-2011) 3. For old steel pipes, the depth of surface rust and bending deformation should be checked. The corrosion degree should be checked once a year. During the inspection, three steel pipes with severe corrosion should be selected, and samples should be taken by making transverse cuts at the most corroded parts of each pipe; such pipes shall not be used if the corrosion depth exceeds the specified value ； (Article 8.1.2 of JGJ130-2011) 4. When fasteners arrive at the construction site, their product certificates must be checked, and sampling tests shall be conducted for reevaluation ； (Article 8.1.4 of JGJ130-2011) 5. When plug-in disc-type steel pipes are used as supports, the outer surface of the pin shall fit against the surface of the joint at the ends of the horizontal and diagonal bars; the pin connection must ensure that it does not come loose even after being locked in place by hammering, and the pull-out resistance shall be no less than 3 kN. (JGJ231-2010 Article 3.1.2) X. Removal of formwork ★ The concrete strength of the structure must reach the design requirements before the formwork is removed ； ★ A warning sign should be placed before the scaffold is removed, and a dedicated person should be assigned to supervise it. Requirements: 1. The measures for removing the template must be approved by the project’s technical supervisor ； The timing for removing formwork shall be in accordance with the relevant provisions of the current **standard, the ‘Code for Acceptance of Construction Quality of Concrete Structures’ GB50204 ； (Article 7.1.1 of JGJ162-2008) 2. The concrete strength at the time of removing the formwork and its supports shall meet the design requirements ； When there are no specific requirements in the design, the concrete strength shall meet the provisions of Table 4.3.1. (Article 4.3.1 of GB50204-2002). 3. For post-tensioned prestressed concrete structural members, the formwork on the sides should be removed before prestressing is applied ； The removal of the formwork supports shall be carried out in accordance with the construction technical plan; in the absence of specific requirements, they should not be removed before prestressing of the structural members is applied. (Article 4.3.2 of GB50204-2002) 4. The removal and support of formwork for post-cast strips shall be carried out in accordance with the construction technical plan (Article 4.3.3 of GB50204-2002). 5. When installing and removing formwork at heights, safety nets or scaffolding should be installed around the area, along with protective railings. Warning signs should also be installed on the street-facing sides and in areas with heavy traffic, along with dedicated personnel to oversee them. (Article 8.0.6 of JGJ162-2008)