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What problems might arise during construction when using formwork?

Release time:

2020-05-19 17:16

Source:

http://www.gxbml.com

　　We all know that nothing in this world is perfect. For example, even construction formwork can encounter various problems during the building process. So, when different issues arise, how should they be addressed? The preventive measures for common quality problems in formwork engineering mainly include measures to address and prevent axial displacement of formwork axes, deviations in formwork elevation, and structural deformation of formwork. Let’s take a closer look at these together with a Guangxi formwork manufacturer.

　　1. Axial displacement of building formwork

　　1. The phenomenon of axial displacement in architectural formwork

　　When the formwork was removed after concrete pouring, it was discovered that the actual positions of the columns and walls were offset from the building’s axis lines.

　　2. Analysis of the Causes of Axial Displacement in Construction Formwork

　　(1) The template design was not thorough, or the technical briefing was unclear, resulting in component parts not being properly positioned during the assembly of construction formwork.

　　(2) Errors arise from the layout of the axis lines.

　　(3) The wall and column formwork lacks adequate positioning measures at the base and top, or the positioning is unstable. Once displacement occurs, it is not corrected promptly, leading to cumulative errors.

　　(4) During formwork support, horizontal and vertical reference lines were not established, and no measures were in place to control verticality.

　　(5) The formwork has poor rigidity and lacks horizontal tie rods or has excessively large spacing between horizontal tie rods.

　　(6) During concrete placement, the material was not evenly and symmetrically fed, or the pouring height was too high at one time, resulting in significant lateral pressure that caused the formwork to shift out of position.

　　(7) Improper use or loosening of tie rods, props, and wooden wedges can cause axial misalignment.

　　3. Prevention and Control Measures for Axial Displacement of Building Formwork Axes

　　(1) Strictly prepare detailed drawings of each sub-division and sub-item at a scale of 1/10 to 1/15, clearly indicating the part numbers, axis positions, geometric dimensions, sectional shapes, reserved openings, embedded parts, and other relevant details. After careful verification to ensure accuracy, thoroughly conduct technical briefings for production teams and operating workers, using these drawings as the basis for the fabrication and installation of construction formwork.

　　(2) After the axis layout of the formwork is completed, assign dedicated personnel to conduct a technical review and acceptance check. Formwork may only be erected after confirming that all measurements are accurate.

　　(3) Reliable limiting measures must be provided at the base and precast sections of wall and column formwork, such as using short reinforcing bars embedded in the cast-in-place floor concrete to secure steel supports, thereby ensuring accurate positioning of the bottom section.

　　(4) During formwork installation, use horizontal and vertical reference lines, and set up vertical plumb control lines to ensure the accurate horizontal and vertical positioning of the building formwork.

　　(5) Based on the characteristics of concrete structures, specialized designs are developed for construction formwork to ensure that the formwork and its supporting systems possess sufficient strength, rigidity, and stability.

　　(6) Before concrete pouring, carefully inspect and verify the building formwork’s axis lines, supports, shoring, and bolts. Address any issues found promptly.

　　(7) During concrete placement, the material should be fed evenly and symmetrically, and the pouring height must be strictly controlled within the range permitted by the construction specifications.

　　II. Elevation Deviation of Construction Formwork

　　1. Phenomenon of elevation deviation in construction formwork

　　During measurement, it was found that the elevation of the concrete structural layer, as well as the elevations of embedded parts and reserved openings, did not match the elevations specified in the construction drawings.

　　There are occasional deviations.

　　2. Analysis of the Causes of Elevation Deviations in Construction Formwork

　　(1) There are no elevation control points on the floor or too few control points, making it impossible to close the control network; the bases of the vertical construction formwork have not been leveled.

　　(2) The top of the formwork lacks elevation markings, or construction was not carried out according to the markings.

　　(3) The high-rise building’s elevation control lines have been transferred too many times, resulting in excessive cumulative errors.

　　(4) The embedded parts and reserved openings were not securely fixed, and the construction methods were not given sufficient attention during construction.

　　(5) The architectural formwork for stair treads did not take into account the thickness of the finishing layer.

　　3. Measures for Preventing and Controlling Elevation Deviations in Construction Formwork

　　(1) Each floor shall be equipped with sufficient elevation control points, and the base of the vertical formwork must be leveled.

　　(2) Set elevation markers at the top of the formwork, and strictly follow these markers during construction.

　　(3) The elevation of each building floor shall be controlled by the elevation of the ground floor, which is set at ±0.000. It is strictly prohibited to measure elevations upward from one floor to the next, as this could lead to cumulative errors. When the building height exceeds 30 meters, an additional elevation control line should be established. Each floor must have no fewer than two elevation measurement points for verification purposes.

　　(4) Embedded parts and reserved openings shall be checked against the drawings before installation. After confirming their accuracy, they must be securely fixed in their designed positions. If necessary, they can be stabilized by methods such as electric welding or using frame supports. During concrete pouring, the concrete should be poured evenly in layers around these embedded parts. It is strictly prohibited to strike or vibrate the formwork adjacent to the embedded parts.

　　(5) When installing formwork for stair treads, the thickness of the finishing layer should be taken into account.

　　3. Structural Deformation of Construction Formwork

　　1. Phenomena of structural deformation in construction formwork

　　After form removal, it was found that the concrete columns, beams, and walls exhibited bulging, necking, or warping.

　　2. Analysis of the Causes of Structural Deformation in Construction Formwork

　　(1) The spacing between supports and waler beams is too large, resulting in poor rigidity of the formwork.

　　(2) The small steel formwork was assembled without the connecting components being installed according to regulations, resulting in poor overall integrity of the construction formwork.

　　(3) The wall formwork lacks tie rods, or the spacing between the bolts is too large, and the bolt specifications are too small.

　　(4) The vertical load-bearing supports were placed on foundation soil that had not been compacted, lacked a leveling slab, and had no drainage measures, resulting in settlement of part of the foundation beneath the supports.

　　(5) The internal formwork supports between door and window openings are not securely braced, making the formwork prone to being displaced during concrete vibration.

　　(6) The spacing between clamps for beam and column formwork is too large, or the formwork is not clamped tightly enough, or the number of tie rods provided is insufficient, causing certain sections of the formwork to fail to withstand the lateral pressure generated during concrete vibration, thus resulting in localized formwork failure.

　　(7) The concrete for walls and columns was poured too quickly, with excessive pouring height in a single lift and over-vibration.

　　(8) When wooden formwork or plywood is used for construction, and after passing inspection but before concrete is poured in a timely manner, prolonged exposure to sunlight and rain can cause the formwork to warp and deform.

　　3. How to address the issue of structural deformation in construction formwork

　　(1) When designing formwork and supporting systems for construction, full consideration should be given to their own self-weight, construction loads, the self-weight of concrete, and the lateral pressure generated during concrete placement and vibration, in order to ensure that the formwork and supports have sufficient load-bearing capacity, rigidity, and stability.

　　(2) The spacing of supports under the beam should be such that no deformation occurs under the combined action of the concrete weight and construction loads. If the base of the supports rests on a soil foundation, the soil should first be thoroughly compacted, drainage ditches should be provided, and continuous wooden pads or structural steel sections should be laid down to ensure that the supports do not settle.

　　(3) When assembling combined small steel formwork, connecting components shall be placed according to regulations, and the spacing and specifications of waler beams and tie rods shall be set in accordance with design requirements.

　　(4) When using clamps for formwork of beams and columns, the spacing between clamps must be specified and the formwork must be securely clamped. The width of the clamps should be slightly smaller than the dimensions of the cross-section.

　　(5) The upper part of beam and wall formwork must be equipped with temporary supports to ensure the width of the beam and wall openings during concrete pouring.

　　(6) When pouring and compacting concrete, ensure that the concrete is fed in evenly and symmetrically. Strictly control the pouring height, especially on both sides of formwork around door and window openings. It is essential to ensure that the concrete is thoroughly vibrated and compacted while also preventing over-vibration that could cause deformation of the formwork.

　　(7) For cast-in-place reinforced concrete beams and slabs with a span of not less than 4 meters, the formwork shall be cambered according to design requirements. When the design does not specify particular requirements, the camber height should preferably be between 1/1000 and 3/1000 of the span.

　　(8) When using wooden formwork or plywood formwork for construction, concrete should be poured promptly after acceptance inspection to prevent the wooden formwork from deforming due to prolonged exposure to sunlight and rain.

　　If any of the issues with construction formwork mentioned above arise during construction, do you know how to resolve them?

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