Construction method for replacing partial frame beams of existing building

Abstract

The application discloses a construction method for replacing part of frame beams of existing buildings, and relates to the technical field of existing building reconstruction. The method comprises the following steps: multiple support points are arranged below frame beams around a beam to be replaced, each support point comprises a support column and a tool column, a jacking mechanism is arranged on the top of the tool column, and a jacking force is applied by a jack in stages to actively unload; a steel wedge is arranged between the support column and the frame beam, and concrete is poured to transfer the upper load to the support column; a full-floor steel pipe scaffold is erected; the concrete of the beam to be replaced is chipped off, the original concrete joint surface is chipped and then a steel bar is planted, tied and bound, a formwork is supported and new concrete is poured; the formwork is removed after maintenance; and the tool column, the support column and the scaffold are removed after the jack is unloaded in stages and synchronously. By means of the active unloading in stages and reliable load transmission, the method realizes safe replacement of part of frame beams of existing buildings under a load-bearing state, has high construction safety, and has little influence on the surrounding structure.

Description

Technical Field

[0001] This invention relates to the field of existing building renovation technology, specifically a construction method for replacing part of the frame beams in an existing building. Background Technology

[0002] In existing building renovation projects, changes in the use of space often necessitate modifications to existing frame beams. For example, to meet clearance requirements, the height of already constructed frame beams needs to be reduced (especially at the support locations). However, since the upper load (such as the soil covering the basement roof) has already been applied, it is not possible to reduce the beam height by removing the structural floor slabs. Instead, beam replacement must be carried out without unloading the upper load, which presents significant construction challenges and safety risks.

[0003] Currently, the commonly used methods for renovating existing building frame beams mainly include the following: (a) Traditional support replacement method. Existing beam-column replacement methods are basically support replacement methods, that is, without unloading the components to be replaced, temporary supports are directly erected at the bottom of the beam before chiseling away and recasting. Although this method is simple to construct, directly chiseling away the original concrete under load can easily lead to a sudden release of stress in the beam, causing structural collapse and making it difficult to guarantee safety.

[0004] (II) Concrete Replacement Reinforcement Method. The conventional replacement reinforcement construction sequence is: support → removal of the original concrete component → re-pouring of concrete → removal of support. When this method is used for replacement construction in the beam-column joint area of ​​a frame, there are often problems such as an imperfect support system and unclear load transfer path, which can easily lead to additional stress and deformation in the surrounding components.

[0005] (III) Overall Replacement Method. Some existing technologies use the method of replacing the entire beam as a whole. However, for cases where only a local area of ​​the beam needs to be replaced, overall replacement will cause unnecessary waste of engineering work and have a greater impact on the surrounding structure. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a construction method for replacing part of the frame beams of an existing building, which aims to solve the technical problem of safely replacing part of the frame beams of an existing building under load.

[0007] The technical solution adopted by this invention to solve its technical problem is a construction method for replacing part of the frame beam in an existing building, comprising the following steps: S1: Multiple support points are set under the frame beams around the beam to be replaced. Each support point includes a support column and a tool column arranged on one side of the support column. A lifting mechanism is set on the top of the tool column. The fixed end of the lifting mechanism is set on the upper surface of the tool column, and the output end abuts against the frame beam. Active unloading is performed by applying lifting force in stages with jacks, with each stage increasing by 10kN and holding the load for 5 minutes. S2: Set steel wedges between the support column and the frame beam, and pour concrete in the gap between the support column and the frame beam. After the concrete has cured, transfer the upper load of the frame beam to the support column. S3: Erect full-span steel pipe scaffolding around the area to be replaced. The full-span steel pipe scaffolding has a vertical pole spacing of 1.2m and a horizontal pole step spacing of 1.5m. Vertical and horizontal scissor bracing is also provided. S4: Remove the concrete of the beam to be replaced, chip the original concrete interface to a depth of not less than 6mm, then install and tie the reinforcing bars, set up the formwork and pour new concrete. S5: New concrete shall be cured for no less than 7 days. When the strength of the test block cured under the same conditions reaches 75% of the design strength, the side formwork shall be removed. When it reaches 100%, the bottom formwork and support shall be removed. S6: Unload the jacks in stages, reducing the load by 20kN at each stage and holding the load for 10 minutes. After stabilization, remove the tool column, support column, and scaffolding.

[0008] Furthermore, in S2, monitoring points for stress and deformation are arranged on the support points and frame beams. When the measured stress or deformation exceeds 10% of the theoretical value, an early warning is issued, and construction is suspended when it exceeds 15%. Furthermore, the support column is made of seamless steel pipe with diameter 203mm×8mm and stiffening plate with thickness 10mm. The steel material is Q235B. The bottom of the steel column is equipped with an adjustable base or a fixed base.

[0009] Furthermore, the bottom of the uprights of the full-span steel pipe scaffold is provided with wooden pads or channel steel with a thickness of not less than 50mm and a width of not less than 200mm; a vertical scissor brace is provided every 6m along the perimeter and inside the scaffold, and a horizontal scissor brace is provided every two steps at the top, bottom and middle.

[0010] Furthermore, in the S4 rebar installation, the main bars are HRB500 grade steel bars, the stirrups are HRB400 grade steel bars, and the stirrup spacing is 100mm; the installation depth of the main bars is not less than 22 times the diameter of the main bars, the drilling diameter is determined according to the rebar adhesive instructions as d+4~8mm, the rebar adhesive is Grade A pre-made rebar adhesive, with a splitting tensile strength ≥8.5MPa, a bending strength ≥50MPa, and a tensile shear strength ≥16MPa.

[0011] Furthermore, after the rebar installation step is completed, a pull-out test is conducted. During the non-destructive test, the measured load value is not less than 1.15 times the design value. During the destructive test, the rebar yielding or the interface between the rebar adhesive and the concrete is considered as qualified. The sampling ratio is not less than 3 pieces per specification.

[0012] Furthermore, the new concrete uses C35 micro-expansion fine aggregate concrete with a slump of 160~200mm and contains 6%~8% UEA expansion agent.

[0013] The beneficial effects of this invention are as follows: By setting up a lifting mechanism for graded active unloading, the stress level of the beam to be replaced is gradually reduced, avoiding the collapse of the beam caused by directly chiseling away concrete under load, thus effectively ensuring construction safety. By setting steel wedges between the support columns and the frame beams and pouring concrete, reliable transfer of the upper load from the frame beams to the support columns is achieved, ensuring that the load is fully borne by the support columns after unloading. This method is designed for situations where only a portion of the frame beam needs to be replaced. Through precise unloading support and localized chiseling, unnecessary engineering work and excessive impact on the surrounding structure caused by overall replacement are avoided. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a structural diagram of the support point; Figure 3 This is a schematic diagram of the monitoring point layout; Figure 4 This is a schematic diagram of scaffolding erection; Figure 5 This is a schematic diagram of the frame beams and the new concrete; Figure 6 yes Figure 5 Sectional view of AA.

[0015] Attached diagram labels: 1-Beam to be replaced; 2-Frame beam; 3-Support point; 4-Support column; 5-Tool column; 6-Lifting mechanism; 7-Steel wedge; 8-Monitoring point; 9-Ground-supported full-span steel pipe scaffold; 10-Main reinforcement; 11-Stirrup; 12-New concrete. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0017] like Figure 1As shown, this embodiment of the present invention is aimed at a renovation project of an existing building. The project is a concrete frame structure. Due to space requirements, the height of the already constructed frame beam 2 needs to be reduced, but the upper load cannot be removed and needs to be replaced with the load on.

[0018] S1. Unloading and Support Construction

[0019] Multiple support points 3 are set below the frame beams 2 surrounding the beam to be replaced 1. Each support point 3 includes a support column 4 and a tool column 5 arranged on one side of the support column 4. See also Figure 1 In this embodiment, a total of 7 support points 3 are set. The support points 3 are first estimated according to the planar load and the beam and slab layout in the construction drawings, and then the structural stress analysis calculation software (such as PKPM, MIDAS, etc.) is used for calculation simulation and adjustment to ensure that the stress distribution at the support points 3 is uniform. The support column 4 is made of seamless steel pipe with diameter 203mm×8mm and stiffening plate with thickness of 10mm. The steel material is Q235B. The support column 4 is equipped with an adjustable base at the bottom.

[0020] A lifting mechanism 6 is installed at the top of the tool column 5. The lifting mechanism 6 uses a 30-ton hydraulic jack. The fixed end of the lifting mechanism 6 is located on the upper surface of the tool column 5, and the output end abuts against the frame beam 2. Active unloading is achieved by applying lifting force in stages with the jack, each stage increasing by 10kN and holding the load for 5 minutes. The target unloading force at each support point 3 is 100kN, and the initial lifting force of the jack is 10kN.

[0021] S2, Load Transfer

[0022] See Figure 2 Steel wedges 7 are installed between the support column 4 and the frame beam 2, and C40 non-shrink grout is poured into the gap between the support column 4 and the frame beam 2 to fill it. After the grout has cured, the upper load is entirely borne by the support column 4. (See also...) Figure 3 Monitoring points 8 are arranged on support point 3 and frame beam 2. The monitoring points 8 can be located above support column 4, above lifting mechanism 6, or above tool column 5. Monitoring points 8 are equipped with strain gauges, displacement gauges, shielded wires, strain gauges, etc. The stress change of support column 4 is calculated by monitoring the strain of support point 3 itself, and at the same time, it is observed whether deformation or cracks occur on the beam 1 to be replaced. When the measured stress or deformation exceeds 10% of the theoretical value, an early warning is issued, and when it exceeds 15%, construction is suspended and the emergency plan is activated.

[0023] The monitoring steps are as follows: (1) Before unloading, set up the instrument at monitoring point 8 and zero the instrument; (2) During unloading, the stress and deformation changes at monitoring point 8 are monitored simultaneously. When the stress and deformation reach the unloading calculation value, the jack stops applying force and the steel wedge block 7 is used to wedge the support column 4 tightly. The gap is filled with grout. (3) After unloading is completed, concrete replacement treatment shall be carried out; (4) During concrete replacement treatment, observe the stress and deformation changes of support column 4 and tool column 5; (5) After removing the support column 4 and the tool column 5, continue to monitor the changes in stress and deformation at monitoring point 8.

[0024] S3, scaffolding erection

[0025] See Figure 4 A full-span steel pipe scaffold 9 was erected around the area surrounding the beam to be replaced (1), with uprights spaced 1.2m apart and horizontal bars spaced 1.5m apart. Wooden pads at least 50mm thick and 200mm wide were installed along the entire length of the bottom of each upright. Vertical scissor bracing was installed every 6m along the perimeter and interior of the scaffold, and horizontal scissor bracing was installed every two steps at the top, bottom, and middle.

[0026] The erection process for full-span steel pipe scaffolding (Type 9) is as follows: site leveling and obstacle removal → positioning and setting up continuous upright base plates → laying longitudinal ground bracing → erecting uprights → connecting longitudinal ground bracing to uprights → installing transverse ground bracing → installing longitudinal horizontal bracing → installing transverse horizontal bracing → installing vertical and horizontal scissor bracing → laying scaffold boards. The erection requirements for full-span steel pipe scaffolding (Type 9) shall be implemented in accordance with the "Safety Technical Specification for Construction Coupler-Type Steel Pipe Scaffolding" (JGJ130-2011).

[0027] S4, Concrete Beam Replacement

[0028] (a) Measurement and layout. Based on the original design drawings and the actual measured dimensions of the concrete components, mark the rebar placement lines on the beam to be replaced (1) and mark them with a marker.

[0029] (II) Reinforcing bar processing. Main reinforcement bar 10 uses HRB500 grade steel bars, and stirrups 11 use HRB400 grade steel bars. The steel bars are ground and rust-removed, and then wiped clean with cotton yarn.

[0030] (III) Removal of concrete from beam 1 to be replaced and surface treatment of concrete base. Remove the concrete from beam 1 to be replaced. Chisel away the old and new interface of the original concrete component to a depth of not less than 6mm to expose fresh aggregate. Then remove dust with oil-free compressed air or rinse with clean water.

[0031] (iv) Drilling and rebar installation. See also Figure 5 and Figure 6After locating the newly added longitudinal reinforcement bars, drill holes, avoiding the main reinforcement bars of frame beam 2. If the main reinforcement bars of frame beam 2 are encountered, the position should be adjusted and the hole re-drilled. After drilling, clean the holes with cotton yarn to ensure the ducts are dry, inject the anchoring adhesive, and then insert the main reinforcement bar 10. The anchoring depth of the main reinforcement bar 10 should not be less than 22 times the diameter of the main reinforcement bar 10. The drilling diameter should be determined according to the anchoring adhesive instructions as d+4~8mm. The newly added stirrups 11 are spaced at 100mm intervals.

[0032] The rebar adhesive used must be a Grade A pre-finished rebar adhesive, which must meet the requirements of good seismic resistance, fire resistance, weldability, long-term performance, and fatigue resistance, and relevant product testing reports and durability guarantees must be provided. Specific performance indicators are: splitting tensile strength ≥ 8.5 MPa, flexural strength ≥ 50 MPa, and steel-to-steel tensile shear strength ≥ 16 MPa.

[0033] After the rebar installation is completed, a pull-out test is conducted. For non-destructive testing, the measured load value should not be less than 1.15 times the design value. For destructive testing, rebar yielding or failure of the interface between the rebar adhesive and concrete is considered acceptable. A minimum of three rebars of each specification should be sampled. After meeting the requirements, the rebar is tied.

[0034] (V) Formwork Erection. The horizontal joists for the beam side formwork are made of 50×100mm timber spaced 250mm apart, and the horizontal joists for the beam bottom formwork are also made of 50×100mm timber spaced 250mm apart. The timber and formwork should be pre-processed to ensure straight edges. The formwork should be constructed in a form where the side formwork covers the bottom formwork, with the joints between the side formwork made into a tongue-and-groove joint and sealed with a 1×5mm sealing strip. At the joints, the bottom formwork should extend 10cm beyond the timber. Two short timbers, each at least 1000mm long, should be added during formwork splicing.

[0035] (vi) Pouring new concrete 12. Pouring new concrete 12 (C35 micro-expansion fine aggregate concrete) with a slump of 160~200mm, and adding 6%~8% UEA expansion agent. Taking samples on site to make test blocks to test the 28-day strength of new concrete 12.

[0036] S5, Maintenance and Demolding

[0037] After pouring, promptly cover exposed parts with a film or spray water for curing. If it is inconvenient to water the surface of the component, a curing agent can be sprayed. Keep the new concrete moist for at least 7 days.

[0038] When the strength of the test blocks cured under the same conditions reaches 75% of the design strength, the side formwork is removed; when it reaches 100%, the bottom formwork and supports are removed. The demolding sequence follows the order of first removing the supports and connectors, and then removing them piece by piece. After removal, the connectors and supports are stacked separately, and the formwork is cleaned and painted.

[0039] S6, Remove support system

[0040] After the overall strength of the replacement beam 1 reaches C35 (i.e., the new concrete 12 reaches the design strength), the jacks are unloaded in stages, with each stage reducing the load by 20kN and holding the load for 10 minutes. At the same time, the stress and deformation changes at monitoring point 8 are observed. After confirming that there are no abnormalities, the tool column 5, support column 4, and the full-span steel pipe scaffolding 9 are completely removed.

[0041] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A construction method for replacing a portion of the frame beams in an existing building, characterized in that, Includes the following steps: S1: Multiple support points (3) are set below the frame beam (2) around the beam to be replaced (1). Each support point (3) includes a support column (4) and a tool column (5) arranged on one side of the support column (4). A lifting mechanism (6) is set on the top of the tool column (5). The fixed end of the lifting mechanism (6) is set on the upper surface of the tool column (5), and the output end abuts against the frame beam (2). Active unloading is carried out by applying lifting force in stages with jacks, each stage increasing by 10kN and holding the load for 5 minutes. S2: Set steel wedges (7) between the support column (4) and the frame beam (2), and pour concrete in the gap between the support column (4) and the frame beam (2). After the concrete is cured, transfer the upper load of the frame beam (2) to the support column (4). S3: Erect a full-span steel pipe scaffold (9) around the beam to be replaced (1). The spacing between the uprights of the full-span steel pipe scaffold (9) is 1.2m, the step distance of the horizontal bars is 1.5m, and vertical and horizontal scissor bracing is provided. S4: Remove the concrete of the beam to be replaced (1), chisel the original concrete interface to a depth of not less than 6mm, then install and tie the reinforcing bars, set up the formwork and pour new concrete (12). S5: New concrete (12) shall be cured for no less than 7 days. When the strength of the test block cured under the same conditions reaches 75% of the design strength, the side formwork shall be removed. When it reaches 100%, the bottom formwork and support shall be removed. S6: Unload the jacks in stages, reducing the load by 20kN at each stage and holding the load for 10 minutes. After stabilization, remove the tool column (5), support column (4), and the full-span steel pipe scaffold (9).

2. The construction method for replacing a portion of the frame beam in an existing building according to claim 1, characterized in that: In S2, monitoring points (8) for monitoring stress and deformation are arranged on the support point (3) and frame beam (2). When the measured stress or deformation exceeds 10% of the theoretical value, an early warning is issued, and construction is suspended when it exceeds 15%.

3. The construction method for replacing a portion of the frame beam in an existing building according to claim 1, characterized in that: The support column (4) is made of seamless steel pipe with diameter 203mm×8mm and stiffening plate with thickness 10mm. The steel material is Q235B. The bottom of the support column (4) is equipped with an adjustable base or a fixed base.

4. The construction method for replacing a portion of the frame beam in an existing building according to claim 1, characterized in that: The bottom of the uprights of the full-span steel pipe scaffold (9) is provided with wooden pads or channel steel with a thickness of not less than 50mm and a width of not less than 200mm; a vertical scissor brace is provided every 6m along the perimeter and inside of the scaffold, and a horizontal scissor brace is provided every two steps at the top, bottom and middle.

5. The construction method for replacing a portion of the frame beam in an existing building according to claim 1, characterized in that: In the S4 rebar installation, the main bar (10) is made of HRB500 grade steel bar, the stirrup (11) is made of HRB400 grade steel bar, and the stirrup (11) spacing is 100mm; the installation depth of the main bar (10) is not less than 22 times the diameter of the main bar, the drilling diameter is determined according to the rebar adhesive instruction manual as d+4~8mm, the rebar adhesive is Grade A pre-made rebar adhesive, the splitting tensile strength is ≥8.5MPa, the bending strength is ≥50MPa, and the tensile shear strength is ≥16MPa.

6. The construction method for replacing a portion of the frame beam in an existing building according to claim 5, characterized in that: After the rebar installation step is completed, a pull-out test is conducted. During the non-destructive test, the measured load value is not less than 1.15 times the design value. During the destructive test, the rebar yielding or the interface between the rebar adhesive and the concrete is considered as qualified. The sampling ratio is not less than 3 pieces per specification.

7. The construction method for replacing a portion of the frame beam in an existing building according to claim 1, characterized in that: The new concrete (12) uses C35 micro-expansion fine stone concrete with a slump of 160~200mm and 6%~8% UEA expansion agent.

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