Concrete cantilever structure upward pulling formwork construction method

Abstract

The application discloses a concrete overhanging structure upward pulling formwork construction method, which is characterized by comprising the following steps: load calculation and component selection, U-shaped bolt pre-burying, upper section pull rod pre-burying, I-shaped steel end connecting plate welding, double-layer angle steel connecting plate welding at the I-shaped steel overhanging end, I-shaped steel overhanging main beam installation, pull rod system assembly, pull rod fastening and system leveling, two pull rods being fastened synchronously, the double rods being ensured to advance and retreat simultaneously by an adjusting device, leveling being observed by a level after initial adjustment, formwork frame and safety enclosure installation, pull rod pre-tensioning and deflection monitoring, pre-tension being applied by the adjusting device, overhanging end deflection being detected, monitoring points being set and a deformation early warning mechanism being established, concrete pouring regulation and control, formwork dismantling and recovery. The application has strong overturning resistance, is suitable for large-span and special-shaped overhanging structures, and safety is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of formwork support construction for high-altitude cantilever structures, and more specifically, to a method for constructing a concrete cantilever structure with upward-pulling formwork. Background Technology

[0002] With the continuous development of construction technology, the design of modern buildings is becoming increasingly complex and challenging, with special structural forms such as large-span cantilever structures and irregularly shaped facades frequently appearing in architectural designs. On-site construction of such structures presents problems such as complex processes and lengthy construction periods, and traditional ground-supported scaffolding systems are no longer sufficient to meet construction requirements.

[0003] When traditional ground-supported scaffolding supports cantilever structures, it is necessary to erect the scaffolding layer by layer from the ground. This not only consumes a large amount of materials such as steel pipes and fasteners, resulting in high material costs, but also significantly extends the construction period due to the complicated erection process. At the same time, the cantilever end is prone to large deflection under load, which is difficult to control and can easily affect the dimensional accuracy of the concrete structure, leading to potential structural quality problems. In addition, for complex facade structures such as irregular curved surfaces and large-span cantilever structures, traditional ground-supported scaffolding has poor stability and low safety for construction workers, posing significant safety risks. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a method for constructing cantilever concrete structures with top-supported formwork, which has strong anti-overturning ability, is suitable for large-span and irregularly shaped cantilever structures, and significantly improves safety.

[0005] The present invention adopts the following technical solution:

[0006] A method for constructing a cantilevered concrete structure with formwork support includes the following steps:

[0007] S1. Load Calculation and Component Selection

[0008] Based on the cantilever structure parameters, calculate the total construction load and select the I-beam cantilever main beam and diagonal tie rods;

[0009] S2, U-bolt pre-embedding

[0010] Before pouring concrete for the cantilever support layer, U-bolts are pre-embedded to control positioning errors and the exposed length of the bolts. After pre-embedding, the coordinates are checked and fixed.

[0011] S3, Upper tie rod pre-embedded

[0012] Before pouring the upper frame beam of the cantilever support layer, pre-embed the upper section of the round steel tie rod, control the horizontal projection position of the tie rod and the length of the exposed end thread, and inspect the verticality after pre-embedding.

[0013] S4, Welding of end connecting plates of I-beams

[0014] Weld double-layer angle steel connecting plates to the cantilevered ends of the I-beams;

[0015] S5, I-beam cantilever main beam installation

[0016] Once the concrete strength of the cantilever support layer reaches ≥75% of the design value, the tower crane will hoist the I-beam to the design position and fix it with U-bolts and double pads. The gap between the I-beam and the structure will be filled with wooden blocks, and the bolt tightening torque will be controlled.

[0017] S6, tie rod system assembly

[0018] Two round steel tie rods are used to tie the I-beam. Each tie rod is divided into upper and lower sections. One end of the lower tie rod passes through the anchor hole of the connecting plate and is locked with double nuts. The other end is connected to the upper tie rod through an adjustment device. Double nuts are provided at all nodes.

[0019] S7. Tie rod fastening and system leveling

[0020] Simultaneously tighten the two tie rods, and ensure that the two rods move forward and backward together when adjusting the adjustment device. After the initial adjustment, use a level to observe and find the level.

[0021] S8. Installation of formwork and safety enclosure

[0022] Install uprights, horizontal bars, formwork and steel bars on the cantilever platform. Cover the upper part of the I-beams with safety netting and fix it. Arrange timber on the upper part of the safety netting. Set anti-slip limit blocks, safety mesh netting and kickboards on the frame.

[0023] S9, Tie rod pretensioning and deflection monitoring

[0024] Pre-tension is applied by adjusting the device, the deflection of the cantilever end is detected, monitoring points are set up and a deformation early warning mechanism is established.

[0025] S10, Concrete Pouring Control

[0026] Concrete was poured symmetrically in layers, and deflection was monitored once after every 1m³ of concrete was poured.

[0027] S11. Demolding and Recycling

[0028] Once the concrete strength reaches ≥100% of the design value, dismantle the formwork in the following order: "formwork frame → tie rods and adjustment devices → I-beams". Set up an isolation area on the ground to hoist the I-beams. After the components pass inspection, they can be reused.

[0029] Furthermore, the total construction load is calculated using the formula S=1.2Q1+1.4Q2, and the maximum axial force and maximum bending moment are obtained through mechanical analysis. Based on the "Steel Structure Design Standard GB 50017", the I-beam cantilever main beam is selected, and the tie rod is selected using the formula N / A≤[σ].

[0030] In the formula, Q1 is the dead load, including the self-weight of the structure and the formwork frame; Q2 is the live load, including the construction live load, and the maximum axial force Nmax and the maximum bending moment Mmax are obtained by mechanical analysis from the load S value.

[0031] In the formula, N is the design value of the axial tensile force of the tie rod; A is the cross-sectional area of ​​the tie rod; and σ is the design value of the tensile strength of the tie rod.

[0032] Furthermore, in step S2, Φ20mm U-bolts are pre-embedded, with a positioning error ≤5mm and an exposed bolt length ≥100mm. After pre-embedding, the coordinates are checked and the bolts are fixed to prevent displacement.

[0033] Furthermore, in step S3, the upper section of the HPB300 grade round steel tie rod is pre-embedded, with a diameter ≥20mm; the horizontal projection is aligned with the lower I-beam, and the center point is 28±8mm from the edge of the I-beam; the exposed end of the tie rod has a thread length ≥50mm, and the verticality is inspected after pre-embedding, with a verticality deviation ≤2°.

[0034] Furthermore, in step S5, each I-beam cantilever main beam has at least two fixing points, and the bolt torque is ≥100 N·m.

[0035] Furthermore, in step S8, a safety net is fully laid on the upper part of the cantilevered main beam of the I-beam, and the net is connected to each other with iron wire of not less than 18# and then tied tightly to the I-beam; timber is arranged on the upper part of the safety net perpendicular to the direction of the I-beam, with a spacing of not more than 200mm between the timbers, and the timbers are tied tightly to the I-beam with iron wire of not less than 18#; template is arranged on the upper part of the timbers and connected to the timbers with iron nails; anti-slip limit blocks are welded to the bottom of the uprights of the frame; the uprights on the outer side of the template frame are connected to the inner template frame, extending 1.5m beyond the working surface; the spacing between the uprights is the same as that of the template frame; the step distance is the same as that of the template frame; two additional horizontal crossbars are added to each step distance of the frame; a safety mesh net is set on the outer side; and a kick plate is set at the bottom.

[0036] Furthermore, in step S9, the deflection at the cantilever end is detected using a level and adjusted to ≤L / 500. A prefabricated leveling rod label is installed at the cantilever end, with one monitoring point every 5m. The initial elevation is recorded, and a deformation early warning mechanism is established with a warning value of L / 400.

[0037] Beneficial effects

[0038] Cost and schedule optimization: The use of an adjustable top-pull support system to replace traditional ground-supported scaffolding reduces the amount of steel pipes used, shortens the construction period, and significantly reduces overall construction costs;

[0039] Structural accuracy assurance: By dynamically compensating for the tension of the tie rod through the adjustment device, the deflection of the cantilever end is actively controlled, ensuring that the concrete structure dimensions achieve a very high pass rate;

[0040] Enhanced safety: The I-beam main beam is double-anchored with U-bolts, which has strong anti-overturning ability and is suitable for large-span and irregular cantilever structures, significantly improving construction safety;

[0041] High versatility: The support system is lightweight and adjustable, adaptable to cantilever structures with different parameters, and is especially suitable for construction scenarios with complex facades (such as irregular curved surfaces). Attached Figure Description

[0042] Figure 1 This is a schematic diagram of a U-bolt pre-embedded according to an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of an embodiment of the present invention showing the pre-embedded upper tie rod in a frame beam;

[0044] Figure 3 This is a schematic diagram of welding angle steel to the cantilevered end of an I-beam according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of the installation of an I-beam cantilever main beam according to an embodiment of the present invention;

[0046] Figure 5 for Figure 4 Sectional view;

[0047] Figure 6 This is a schematic diagram of the connection between the upper and lower sections of the tie rod according to an embodiment of the present invention;

[0048] Figure 7 This is a schematic diagram of the support frame erection according to an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0050] As shown in the figure, this invention discloses a method for constructing a cantilever concrete structure using top-support formwork, comprising the following steps:

[0051] Step S1: Based on the cantilever structure, first calculate the construction load using the formula S = 1.2Q1 + 1.4Q2 (where Q1 is the dead load, including the self-weight of the structure and formwork; Q2 is the live load, including construction live load). The maximum axial force Nmax and maximum bending moment Mmax can then be obtained from the load S value through mechanical analysis.

[0052] Then, the horizontal cantilever I-beam main beam is calculated and selected according to the "Steel Structure Design Standard GB 50017". The cross-section of the tie rod is selected by calculating N / A≤[σ] (where N is the design value of the axial tensile force of the tie rod; A is the cross-sectional area of ​​the tie rod; σ is the design value of the tensile strength of the tie rod), and a tie rod of appropriate size is selected.

[0053] Step S2, as follows Figure 1 As shown, U-bolt 1 is pre-embedded in the cantilever support layer. Before the concrete is poured for the cantilever support layer, Φ20mm U-bolt 1 is pre-embedded according to the design drawings, with a positioning error ≤5mm. The exposed length of the bolt is ≥100mm. After pre-embedding, the coordinates are checked and fixed to prevent displacement.

[0054] Step S3, as follows Figure 2 As shown, before the upper frame beam of the cantilever support layer is poured, four upper tie rods of HPB300 grade round steel (Φ≥20mm) are pre-embedded; the horizontal projection is aligned with the lower I-beam, and the center point is 28±8mm from the edge of the I-beam; the exposed end of the tie rod has a thread length ≥50mm, and the verticality is inspected after pre-embedding (deviation ≤2°).

[0055] Step S4, as follows Figure 3 As shown, the connecting plate at the cantilever end of the I-beam 2 is welded, and the double-layer angle steel 3 with dimensions of 100×80×10mm is welded to the cantilever end of the I-beam. The opening diameter is 2mm larger than that of the tie rod, and it is used to connect the cantilever main beam of the I-beam and the tie rod.

[0056] Step S5, as follows Figure 4 and Figure 5 As shown, the I-beam cantilever main beam is installed, and the concrete strength of the cantilever support layer is ≥75% of the design value (verified by test blocks under the same conditions). The tower crane hoists the I-beam to the design position, and the U-bolts 1 are tightened with double washers (≥2 fixing points per beam); the gap between the I-beam 2 and the structure is filled with wooden blocks 5, and the bolt torque is ≥100 N·m (tested with a torque wrench).

[0057] Step S6, as follows Figure 6 As shown, the tie rod system is assembled. The I-beam cantilever main beam is connected by two round steel tie rods, each of which is divided into upper and lower sections. When installing the lower tie rod 6 (threaded at both ends), one end should pass through the anchoring hole of the angle steel connecting plate welded on the I-beam cantilever main beam and be locked with double nuts (exposed threads ≥ 2). The other end is connected to the upper tie rod 4 through an adjustment device. All connections are bolted connections with double nuts.

[0058] Step S7: After the tie rods are connected, begin tightening and adjusting. When tightening the tie rods, ensure that both tie rods are tightened simultaneously. When adjusting the adjustment device, ensure that both tie rods move forward and backward together to ensure that the force on both tie rods is even. After the initial adjustment of the cantilever system is completed, use a level to observe and level the entire cantilever system, and adjust any parts with deviations to ensure that the entire system is under balanced force.

[0059] Step S8, as follows Figure 7 As shown, after the tie rods are adjusted, uprights and horizontal bars can be installed on the cantilever platform according to a general formwork support system, followed by the installation of formwork and reinforcing bars. A safety net is fully laid on the upper part of the I-beam cantilever main beam, and the netting is connected to the I-beams using wire of at least #18 (diameter greater than 1.2mm). Wooden beams are arranged perpendicular to the I-beams above the safety nets, with a spacing of no more than 200mm between beams, and these beams are secured to the I-beams with wire of at least #18. Formwork is then placed on top of the wooden beams and connected to the beams with nails. Anti-slip limit blocks are welded to the bottom of the uprights. The outer uprights of the formwork frame are connected to the inner formwork frame, extending 1.5m beyond the working surface. The upright spacing and step distance are the same as the formwork frame. Two additional horizontal crossbars are added to each step distance of the frame. A dense safety net is installed on the outer side, and a kickboard is installed at the bottom to prevent items from slipping.

[0060] Step S9: Pre-tension the tie rod by symmetrically tightening the nuts using the adjusting device to achieve a pre-tension force of 80% of the design value. Use a level to check the deflection at the cantilever end and adjust it to ≤L / 500 (e.g., 7.2mm for a 3.6m cantilever). Install prefabricated leveling rod labels at the cantilever end, with one monitoring point every 5m. Record the initial elevation and establish a deformation early warning mechanism (warning value = L / 400).

[0061] Step S10: Concrete pouring and dynamic control. Pour concrete symmetrically in layers, monitor and adjust in real time. Monitor the deflection once for every 1m³ of concrete poured. Stop pouring when the deviation reaches 90% of the warning value, and tighten the adjusting nut to compensate for the tension (adjustment amount ≤2mm / time). The maximum allowable deflection ≤L / 400 (final control value).

[0062] Step S11: Demolding and Recycling. The concrete strength must be ≥100% of the design value (verified using test blocks under the same conditions). Dismantle the scaffolding first, then loosen the adjusting device nuts, and finally remove the I-beams. A 6m isolation zone should be set up on the ground. The I-beams should be transported by tower crane (work should be suspended in winds exceeding level 6). The I-beams, tie rods, and adjusting devices can be reused after testing (deformation ≤ L / 1000).

[0063] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concepts, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a cantilevered concrete structure using top-supported formwork, characterized in that, Includes the following steps: S1. Load Calculation and Component Selection Based on the cantilever structure parameters, calculate the total construction load and select the I-beam cantilever main beam and diagonal tie rods; S2, U-bolt pre-embedding Before pouring concrete for the cantilever support layer, U-bolts are pre-embedded to control positioning errors and the exposed length of the bolts. After pre-embedding, the coordinates are checked and fixed. S3, Upper tie rod pre-embedded Before pouring the upper frame beam of the cantilever support layer, pre-embed the upper section of the round steel tie rod, control the horizontal projection position of the tie rod and the length of the exposed end thread, and inspect the verticality after pre-embedding. S4, Welding of end connecting plates of I-beams Weld double-layer angle steel connecting plates to the cantilevered ends of the I-beams; S5, I-beam cantilever main beam installation Once the concrete strength of the cantilever support layer reaches ≥75% of the design value, the tower crane will hoist the I-beam to the design position and fix it with U-bolts and double pads. The gap between the I-beam and the structure will be filled with wooden blocks, and the bolt tightening torque will be controlled. S6, tie rod system assembly Two round steel tie rods are used to tie the I-beam. Each tie rod is divided into upper and lower sections. One end of the lower tie rod passes through the anchor hole of the connecting plate and is locked with double nuts. The other end is connected to the upper tie rod through an adjustment device. Double nuts are provided at all nodes. S7. Tie rod fastening and system leveling Simultaneously tighten the two tie rods, and ensure that the two rods move forward and backward together when adjusting the adjustment device. After the initial adjustment, use a level to observe and find the level. S8. Installation of formwork and safety enclosure Install uprights, horizontal bars, formwork and steel bars on the cantilever platform. Cover the upper part of the I-beams with safety netting and fix it. Arrange timber on the upper part of the safety netting. Set anti-slip limit blocks, safety mesh netting and kickboards on the frame. S9, Tie rod pretensioning and deflection monitoring Pre-tension is applied by adjusting the device, the deflection of the cantilever end is detected, monitoring points are set up and a deformation early warning mechanism is established. S10, Concrete Pouring Control Concrete is poured symmetrically in layers, with real-time monitoring and adjustment. Deflection is monitored once for every 1m³ of concrete poured. When the deviation reaches 90% of the warning value, stop pouring, tighten the adjusting nut to compensate for the tension, and adjust by ≤2mm / time; the maximum allowable deflection is ≤L / 400; S11. Demolding and Recycling Once the concrete strength reaches ≥100% of the design value, dismantle the formwork in the following order: "formwork frame → tie rods and adjustment devices → I-beams". Set up an isolation area on the ground to hoist the I-beams. After the components pass inspection, they can be reused.

2. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, The total construction load is calculated using the formula S=1.2Q1+1.4Q2. The maximum axial force and maximum bending moment are obtained through mechanical analysis. I-beam cantilever beams are selected according to the "Steel Structure Design Standard GB 50017". Diagonal tie rods are selected using the formula N / A≤[σ]. In the formula, Q1 is the dead load, including the self-weight of the structure and the formwork frame; Q2 is the live load, including the construction live load, and the maximum axial force Nmax and the maximum bending moment Mmax are obtained by mechanical analysis from the load S value. In the formula, N is the design value of the axial tensile force of the tie rod; A is the cross-sectional area of ​​the tie rod; and σ is the design value of the tensile strength of the tie rod.

3. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, In step S2, Φ20mm U-bolts are pre-embedded with a positioning error of ≤5mm and an exposed bolt length of ≥100mm. After pre-embedding, the coordinates are checked and the bolts are fixed to prevent displacement.

4. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, In step S3, the upper section of the HPB300 grade round steel tie rod is pre-embedded, with a diameter ≥20mm; the horizontal projection is aligned with the lower I-beam, and the center point is 28±8mm from the edge of the I-beam; the exposed end of the tie rod has a thread length ≥50mm, and the verticality is inspected after pre-embedding, with a verticality deviation ≤2°.

5. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, In step S5, each I-beam cantilever main beam has at least 2 fixing points, and the bolt torque is ≥100 N·m.

6. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, In step S8, a safety net is fully laid on the upper part of the cantilevered main beam of the I-beam, and the net is connected to each other with iron wire of not less than 18# and then tied tightly to the I-beam; timber is arranged on the upper part of the safety net perpendicular to the direction of the I-beam, with a spacing of not more than 200mm between the timbers, and the timbers are tied tightly to the I-beam with iron wire of not less than 18#; template is arranged on the upper part of the timbers and connected to the timbers with iron nails; anti-slip limit blocks are welded to the bottom of the uprights of the frame; the uprights on the outer side of the template frame are connected to the inner template frame, extending 1.5m beyond the working surface; the spacing between the uprights is the same as that of the template frame; the step distance is the same as that of the template frame; two additional horizontal crossbars are added to each step distance of the frame; a safety net is set on the outer side; and a kickboard is set at the bottom.

7. The method for constructing a cantilevered concrete structure with formwork support according to claim 1, characterized in that, In step S9, the deflection at the cantilever end is detected using a level and adjusted to ≤L / 500. A prefabricated leveling rod label is installed at the cantilever end, with one monitoring point every 5m. Record the initial elevation, establish a deformation early warning mechanism, and set the warning value to L / 400.

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