Hole opening and reinforcing method for adding elevator shaft on concrete floor

Abstract

The invention provides a holing and reinforcing method for adding an elevator shaft to a concrete floor, and belongs to the technical field of building transformation construction. The method is realized through the systematic steps of determining a punching position, accurately cutting concrete, retaining and bending original steel bars, optimally arranging section steel beams based on a minimum spanning tree algorithm, injecting structural adhesive, calculating distance fusion welding studs according to a stud distribution equation, pouring concrete and the like. The core of the method is that a clear structure stress model is established by applying a structure optimization equation set, so that a load transmission path after holing is clear and controllable and comprises a stud distribution equation, a shearing force distribution equation, a concrete strength equation and a stress analysis equation; by means of the method, the technical problem that in the prior art, when an elevator shaft is formed in a concrete floor, structural stress redistribution is not clear is solved, and the safety and reliability of the reinforced structure are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of building renovation construction. Specifically, it relates to a method for opening holes and strengthening an elevator shaft in a concrete floor slab. Background Art

[0002] During the renovation of existing buildings, it is a common requirement to open holes in the concrete floor slab for adding elevator shafts. Traditional concrete floor slab hole-opening and strengthening techniques mainly adopt the method of surrounding steel bar implantation combined with cast-in-place concrete frame beams, or the method of combining steel plate strengthening and angle steel support. These methods are widely used in renovation projects of residential, commercial buildings, and public facilities, especially in the installation of elevators in old residential areas and the functional upgrading of existing buildings.

[0003] However, the traditional techniques have significant defects: after the holes are opened in the floor slab, the original stress path of the structure is damaged, resulting in unclear stress redistribution; the traditional strengthening methods lack theoretical guidance and cannot accurately grasp the load transfer path, so there may be potential safety hazards in the stress concentration areas. The determination of the hole-opening position is usually based on experience rather than structural force analysis, making it difficult to accurately identify and specifically strengthen the weak points of the structure. In addition, it is difficult to quantitatively evaluate the change of the load transfer path by traditional strengthening techniques, and it is impossible to accurately predict the overall performance of the structure after the holes are opened.

[0004] With the increasing demand for the renovation of existing buildings, how to accurately analyze and control the structural force redistribution when opening an elevator shaft in a concrete floor slab, and optimize the strengthening plan while ensuring structural safety, has become a technical problem to be solved urgently. Especially the lack of systematic structural force analysis and optimization design methods makes there often be risks of over-strengthening or under-strengthening in engineering practice. Summary of the Invention

[0005] In view of this, the present invention provides a method for opening holes and strengthening an elevator shaft in a concrete floor slab, which can solve the technical problem of unclear structural force redistribution when opening an elevator shaft in a concrete floor slab in the prior art.

[0006] The present invention is implemented as follows: The present invention provides a method for opening and strengthening an elevator shaft in a concrete floor slab, including: determining the opening position; performing concrete cutting; removing the concrete in the opening area while retaining the original floor slab steel bars; installing steel beams around the opening, and determining the optimal layout scheme of the steel beams based on the minimum spanning tree algorithm; pouring structural adhesive between the steel beams and the bottom surface of the floor slab; welding studs on the upper surface of the steel beams based on the stud spacing distribution function calculated by the stud distribution equation; pouring concrete in the area around the steel beams; curing the newly poured concrete to the design strength; the stud distribution equation is used to calculate the optimal spacing distribution of the studs on the steel beams, the inputs include the length of the steel beam, the design shear force value, the single shear bearing capacity of the stud, the floor slab thickness, and the material safety factor, and the output is the spacing distribution function of the studs along the steel beam; the minimum spanning tree algorithm is used to optimize the layout of the steel beams to make the total length of the steel beams the shortest while meeting the structural requirements.

[0007] Among them, in the step of determining the opening position, the opening position is determined on the concrete floor slab according to the designed elevator shaft dimensions, and an additional distance equal to the cross-sectional width of the steel beam is reserved in each direction at the outer edge of the opening, marking the final opening range, and at the same time ensuring that a certain length of the original floor slab steel bars is retained.

[0008] Among them, in the step of performing concrete cutting, cutting is carried out on the concrete floor slab along the marked line, and a concrete cutting machine is used to accurately cut to the designed depth. During the cutting process, the original floor slab steel bars are protected to ensure that the cutting surface is flat.

[0009] Among them, in the step of removing the concrete in the opening area while retaining the original floor slab steel bars, after cutting is completed, the concrete in the opening area is carefully removed, the retained original floor slab steel bars are cleaned and bent upwards, and the bending height meets the requirements of subsequent construction.

[0010] Among them, in the step of installing steel beams around the opening, the cross-sectional dimensions of the steel beams are determined according to structural calculations, and during installation, it is ensured that the steel beams are in close contact with the bottom surface of the floor slab.

[0011] Among them, in the step of welding studs on the upper surface of the steel beams based on the stud spacing distribution function calculated by the stud distribution equation, the studs are M19-100 studs, and the stud arrangement should avoid the positions of the retained steel bars of the original floor slab.

[0012] Among them, in the step of pouring concrete in the area around the steel beams, it includes formwork installation and positioning of bent steel bars to ensure that the top surface of the poured concrete is at the same elevation as the top surface of the original floor slab.

[0013] Among them, in the step of pouring concrete in the area around the steel beams, the concrete of the concrete strength grade calculated by the concrete strength equation is used for pouring, and the pouring range includes the projection area of the cross-sectional width of the steel beam, forming the edge of the new opening sealing floor slab.

[0014] Among them, the shear force distribution equation is used to analyze the shear force distribution at the interface between the steel beam and the concrete floor slab. The inputs include the applied load, the cross-sectional properties of the steel beam, the concrete strength grade, the stud spacing distribution function, and the interface contact area, and the output is the interface shear stress distribution function; the concrete strength equation is used to determine the optimal strength grade of the newly cast concrete. The inputs include the strength of the original floor slab concrete, the design load, the interface characteristics between the new and old concretes, the cross-sectional properties of the steel beam, and the environmental conditions, and the output is the minimum strength grade of the newly cast concrete; the stress analysis equation is used to calculate the stress distribution state of the reinforced structural system. The inputs include the arrangement of the steel beam, the stud spacing distribution function, the concrete strength grade, the design load, and the characteristics of the original structure, and the output is the stress distribution nephogram and the safety reserve coefficient of the reinforced structure.

[0015] Among them, the stud spacing distribution function refers to the mathematical function that describes the distribution law of studs along the length direction of the steel beam, and determines the spacing of studs at different positions according to the structural force characteristics; the interface shear stress distribution function refers to the mathematical function that describes the shear stress distribution law at the interface between the steel beam and the concrete floor slab; the safety reserve coefficient refers to the ratio of the actual bearing capacity of the structure to the design load, and is used to evaluate the safety margin of the structure.

[0016] The present invention provides a method for adding an elevator shaft opening and strengthening a concrete floor slab by combining the minimum spanning tree algorithm and the structural optimization equations. Through systematic structural analysis and theoretical calculation, the problem of unclear structural force redistribution existing in traditional strengthening technologies is solved.

[0017] This method establishes a complete structural mechanics model, accurately calculates the stress distribution state after the opening, and clarifies the load transfer path. By optimizing the arrangement of the steel beam through the minimum spanning tree algorithm, a clear force system is formed between the strengthening members and the original structure; through the stud distribution equation, the accurate transfer of the interface shear force is realized to ensure the coordinated work of the new and old structures; through the stress analysis equation, the safety reserve coefficient after strengthening is evaluated to quantify the strengthening effect. These measures change the unclear structural force state after the opening to a clear one, and change the empirical judgment to theoretical calculation.

[0018] Therefore, the present invention solves the core problem of unclear structural force redistribution when an elevator shaft is opened in a concrete floor slab. Through scientific treatment of retaining the original steel bars and accurate calculation of the steel beam arrangement, a clear load transfer path is established, ensuring clear structural forces and reasonable stress distribution, avoiding stress concentration and the generation of weak links, and providing a theoretical basis and technical guarantee for the safe installation of elevators in existing buildings. Brief Description of the Drawings

[0019] Figure 1 is a flow chart of the method of the present invention;

[0020] Figure 2 Structural schematic diagram of the present invention;

[0021] Figure 3 Cross-sectional view of the present invention;

[0022] Figure 4 Schematic diagram of the connection between the profiled steel beam and the stud of the present invention. Specific embodiments

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0024] As Figure 1 shown, it is a flowchart of a method for opening and strengthening an elevator shaft in a concrete floor provided by the present invention. This method includes the following steps:

[0025] S01. Determine the opening position on the concrete floor according to the designed elevator shaft size, and reserve an additional distance equal to the width of the profiled steel beam section in each direction at the outer edge of the opening. Mark the final opening range, and at the same time ensure that a certain length of the original floor reinforcement is retained;

[0026] S02. Cut along the marked line on the concrete floor, and use a concrete cutting machine to accurately cut to the designed depth. During the cutting process, protect the original floor reinforcement to ensure that the cutting surface is flat;

[0027] S03. After the cutting is completed, carefully remove the concrete in the opening area, clean the retained original floor reinforcement and bend it upward. The bending height meets the requirements of subsequent construction;

[0028] S04. Install profiled steel beams around the opening. Based on the minimum spanning tree algorithm, determine the optimal layout plan of the profiled steel beams to make the total length of the profiled steel beams the shortest and meet the stiffness requirements. The section size of the profiled steel beams is determined according to structural calculations. During installation, ensure that the profiled steel beams are in close contact with the bottom surface of the floor;

[0029] S05. Pour structural adhesive into the gap between the profiled steel beam and the bottom surface of the floor. After the structural adhesive cures, ensure that a reliable connection is formed between the profiled steel beam and the original bottom surface of the floor;

[0030] S06. Based on the stud spacing distribution function calculated by the stud distribution equation, weld M19-100 studs on the upper surface of the installed profiled steel beam at the calculated spacing. The stud arrangement should avoid the positions of the retained original floor reinforcement;

[0031] S07. Prepare for concrete pouring in the area around the profiled steel beam, including formwork installation and positioning of bent reinforcement, and ensure that the top surface of the poured concrete is at the same elevation as the top surface of the original floor;

[0032] S08. Pour using the concrete strength grade calculated from the concrete strength equation. The pouring range includes the projection area of the width of the profiled steel beam section to form the edge of the new opening-sealing floor slab at the edge.

[0033] S09. Cure the newly poured concrete to the design strength, remove the formwork, and complete the reinforcement of the elevator shaft opening.

[0034] The structural optimization equation set includes a stud distribution equation, a shear force distribution equation, a concrete strength equation, and a stress analysis equation.

[0035] The stud distribution equation is used to calculate the optimal spacing distribution of studs on the profiled steel beam. The inputs include the length of the profiled steel beam, the design shear force value, the single shear bearing capacity of the stud, the floor slab thickness, and the material safety factor. The output is the spacing distribution function of the studs along the profiled steel beam.

[0036] The shear force distribution equation is used to analyze the shear force distribution at the interface between the profiled steel beam and the concrete floor slab. The inputs include the applied load, the section properties of the profiled steel beam, the concrete strength grade, the stud spacing distribution function, and the interface contact area. The output is the interface shear stress distribution function.

[0037] The concrete strength equation is used to determine the optimal strength grade of the newly poured concrete. The inputs include the original floor slab concrete strength, the design load, the interface properties between the new and old concretes, the section properties of the profiled steel beam, and the environmental conditions. The output is the minimum strength grade of the newly poured concrete.

[0038] The stress analysis equation is used to calculate the stress distribution state of the reinforced structural system. The inputs include the layout of the profiled steel beam, the stud spacing distribution function, the concrete strength grade, the design load, and the original structural properties. The output is the stress distribution nephogram and the safety reserve coefficient of the reinforced structure.

[0039] Among them, the M19-100 stud refers to a stud with a diameter of 19 mm and a length of 100 mm. The stud is welded to the profiled steel beam to connect the steel beam and the concrete, enabling the steel beam and the concrete to work together to form a composite structure.

[0040] Among them, the structural adhesive refers to a high-strength and high-bonding performance structural adhesive used to fill the gap between the profiled steel beam and the concrete floor slab. It has good shear resistance and can ensure the close combination of the profiled steel beam and the concrete floor slab after curing.

[0041] Among them, the profiled steel beam refers to a steel structure member with an I-shaped or channel-shaped cross-section. In this method, it is used to support the edge of the floor slab after opening the hole and bear the load transferred from the original floor slab support.

[0042] Among them, the minimum spanning tree algorithm refers to an algorithm that, under the condition of ensuring the connectivity of all nodes, obtains a tree structure with the minimum total weight, and is used in this method to optimize the arrangement of profiled steel beams, making the total length of the profiled steel beams the shortest while meeting the structural requirements;

[0043] Among them, the stud spacing distribution function refers to a mathematical function that describes the distribution law of studs along the length direction of the profiled steel beam, and determines the spacing of studs at different positions according to the structural force characteristics;

[0044] Among them, the interfacial shear stress distribution function refers to a mathematical function that describes the distribution law of the shear stress at the interface between the profiled steel beam and the concrete floor slab;

[0045] Among them, the safety reserve coefficient refers to the ratio of the actual bearing capacity of the structure to the design load, and is used to evaluate the safety margin of the structure.

[0046] The specific implementation manners of the above steps are described in detail below.

[0047] As Figure 2 、 Figure 3 shown, the specific implementation manner of step S01 is: First, according to the length and width dimensions of the designed elevator shaft, determine the position coordinates of the opening on the concrete floor slab, and use a total station for precise positioning to ensure that the opening position coincides exactly with the design drawing. Then, use a red marker pen to reserve an additional distance in each direction at the outer edge of the opening, and this reserved distance is equal to the cross-sectional width of the profiled steel beam to be installed later, usually ranging from 80 to 200 mm, which is determined according to the load size and structural calculation. Next, use a blue marker pen to mark the final opening range on the floor slab to form a complete closed area. At the same time, use a ferromagnetic detector to detect the position of the original floor slab reinforcement to ensure that at least 400 mm of the original floor slab reinforcement is reserved during the cutting process for subsequent bending treatment. The purpose of this step is to clarify the opening range and prepare for subsequent cutting and profiled steel beam installation.

[0048] The specific implementation manner of step S02 is: Cut along the marked line on the concrete floor slab, use a concrete cutting machine with a diamond cutting blade with a diameter of 350 mm, control the cutting speed at 0.5 - 1.0 m / min, and set the cutting depth to the floor slab thickness plus 5 mm to ensure complete penetration. The cutting process adopts the segmented cutting method, and the cutting length of each segment does not exceed 500 mm. The cutting sequence follows the stress release principle, starting from the area with smaller stress and advancing towards the area with larger stress. For the original floor slab reinforcement encountered, adopt the local fine cutting method, reduce the cutting speed to 0.2 m / min, and at the same time use a water cooling system to cool the cutting area to prevent the reinforcement from being damaged by overheating. The flatness deviation of the cutting surface is controlled within ±2 mm, and the perpendicularity of the cutting surface is monitored in real time by using a guiding device and a laser level to ensure the cutting quality. The purpose of this step is to precisely cut the concrete floor slab to create conditions for subsequent opening.

[0049] The specific implementation method of step S03 is: after the cutting is completed, a hole is first drilled in the center of the concrete in the opening area with a hole diameter of 50 mm to provide a focus point for the lifting tool. Then an electric hoist or a manual hoist is used for uniform force lifting, and the lifting speed is controlled to no more than 50 mm per minute to avoid cracking of the surrounding concrete due to sudden force. During the demolition process, temporary supports are maintained on both sides of the cutting surface to prevent deformation of the floor slab. The original floor slab steel bars that are retained are cleaned, the attached concrete debris is removed, and the steel bar surface is cleaned with a wire brush until the metallic luster is exposed. Then a hydraulic steel bar bender is used to bend the steel bar upward, with a bending angle of 90°±5°, a bending radius of not less than 10 times the diameter of the steel bar, and a bending height of not less than 150 mm to ensure that the steel bar anchoring requirements for subsequent concrete pouring are met. The purpose of this step is to safely remove the concrete in the opening area and process the retained steel bars to prepare for subsequent reinforcement.

[0050] like Figure 4 As shown, the specific implementation method of step S04 is: install steel beams around the opening, and use the minimum spanning tree algorithm based on Prim's algorithm to determine the optimal layout of the steel beams. First, the opening is divided into multiple nodes, and the distance between each node does not exceed 800 mm. Then the distance between each node is calculated as the weight of the edge to construct a complete graph. Apply the minimum spanning tree algorithm, starting from any node, each time select the minimum weight edge connected to the current tree until all nodes are connected in the tree, and obtain the layout path of the steel beam with the shortest total length. The cross-sectional dimensions of the steel beam are calculated and determined by the finite element analysis method. Commonly used steel beam specifications include H200×100×5.5×8, H250×125×6×9, H300×150×6.5×9, etc. The specific selection is determined according to the opening size and load size. During installation, first use a level and a gasket to adjust the position of the steel beam to ensure that the gap between the steel beam and the bottom surface of the floor slab does not exceed 5 mm. Use high-strength bolts to temporarily fix the steel beam, and the bolt spacing is not more than 600 mm. The purpose of this step is to optimize the layout of steel beams to provide structural support around the opening.

[0051] The specific implementation of step S05 is as follows: Structural adhesive is poured into the gap between the profiled steel beam and the bottom surface of the floor slab. A two-component epoxy resin structural adhesive is used, with a compressive strength of not less than 70 MPa, a shear strength of not less than 15 MPa, an initial viscosity of 15 - 20 Pa·s, and an operable time of 40 - 60 minutes. Before pouring, compressed air is first used to blow out the dust and debris in the gap, and then acetone is used to clean the surfaces of the steel beam and the concrete. The pouring is carried out by the pressure injection method, and the injection pressure is controlled at 0.2 - 0.3 MPa. Pouring is carried out through the pre-set injection ports and exhaust ports to ensure that the structural adhesive fully fills all the gaps between the profiled steel beam and the bottom surface of the floor slab. After pouring, the ambient temperature is maintained at 15 - 25°C, the relative humidity does not exceed 80%, and the static curing time is not less than 24 hours to ensure that the structural adhesive is completely cured. After the structural adhesive is cured, the bonding condition between the profiled steel beam and the original bottom surface of the floor slab is checked by tapping to determine whether a reliable connection is formed. The purpose of this step is to ensure that the profiled steel beam and the original floor slab form an integral force-bearing system.

[0052] The specific implementation of step S06 is as follows: The stud spacing is calculated based on the stud distribution equation, which takes into account the shear force distribution of the floor slab after the opening, the stiffness characteristics of the profiled steel beam, and the shear resistance of the studs. The input parameters include the length L of the profiled steel beam, the designed shear force value V, the single shear bearing capacity P of the M19 - 100 stud d (usually 50 - 65 kN), the thickness h of the floor slab, and the material safety factor γ (usually taken as 1.2 - 1.5). The stud spacing distribution function S(x) usually shows a distribution pattern where the stud spacing is smaller in the area with larger shear force (usually the end of the profiled steel beam) and larger in the area with smaller shear force (usually the middle of the profiled steel beam). In the range of 100 - 300 mm from the end of the profiled steel beam, the stud spacing is usually 100 - 150 mm; in the middle area of the profiled steel beam, the stud spacing can be increased to 200 - 300 mm. The M19 - 100 studs are welded onto the upper surface of the profiled steel beam according to the calculated spacing using an arc stud welding machine, and the welding time is controlled at 0.2 - 0.3 s, and the welding current is 350 - 450 A. The stud arrangement should avoid the positions of the reserved steel bars in the original floor slab, and the clear distance between the stud and the reserved steel bar is not less than 25 mm. After welding, each stud is inspected by 45° tapping to ensure the welding quality. The purpose of this step is to provide shear connection between the profiled steel beam and the newly poured concrete.

[0053] The specific implementation of step S07 is as follows: Prepare for the concrete pouring in the area around the profiled steel beam. First, install the formwork. The formwork uses 18-mm-thick film-covered plywood, and the support system uses adjustable-height steel supports with a support spacing not greater than 400 mm. Apply a release agent to the surface of the formwork to ensure smooth formwork removal in the later stage. Then, position the bent steel bars. According to the specifications and spacing of the original floor steel bars, supplement and configure the steel bar mesh with the same spacing as the original floor steel bars, usually 150 - 200 mm. The lap length of the steel bars is not less than 45 times the diameter of the steel bars, and the joints are tied and fixed. Configure additional stirrups around the stud bolts of the profiled steel beam with a stirrup spacing not greater than 150 mm. Use a laser level to determine the elevation of the top surface of the formwork and adjust the height of the supports to ensure that the top surface of the concrete after pouring is the same as the top surface of the original floor, with the deviation controlled within ±2 mm. The purpose of this step is to create good conditions for concrete pouring and ensure the pouring quality.

[0054] The specific implementation of step S08 is as follows: Pour using the concrete strength grade calculated from the concrete strength equation. The concrete strength equation takes into account the original floor concrete strength f c，o , the design load q d , the interface characteristic coefficient λ of the new and old concrete (usually 0.6 - 0.8), the cross-sectional characteristic parameters of the profiled steel beam (section modulus, moment of inertia, etc.), and the environmental condition indicators (temperature, humidity, etc.). The calculated strength grade of the newly poured concrete usually needs to be higher than or equal to the strength grade of the original floor concrete, and the commonly used strength grades are C30, C35, or C40. The concrete mix design uses the curve optimization method, with the water-cement ratio controlled at 0.4 - 0.5, and additives such as water reducers and retarders are added. During pouring, the concrete slump is controlled at 140 - 180 mm, and the layered pouring method is adopted with each layer thickness not exceeding 300 mm. Use an inserted vibrator for vibration, with the vibration time of 20 - 30 seconds per point and the vibration point spacing of 300 - 400 mm. The pouring range includes the projection area of the profiled steel beam cross-sectional width and 100 - 150 mm outside it, forming the edge of the new opening sealing floor. After pouring, use a wooden float and a steel float to finish the surface to ensure a smooth surface. The purpose of this step is to form a high-strength newly poured concrete area to provide structural support.

[0055] The specific implementation of step S09 is as follows: Cure the newly poured concrete until it reaches the design strength, and the curing period shall not be less than 14 days. Wet curing shall be carried out in the first 7 days to keep the concrete surface wet. Plastic film covering or spray curing can be used, and the curing temperature shall be controlled at 15 - 25°C. Natural curing shall be carried out in the next 7 days to keep the relative humidity of the environment not less than 60%. During the curing period, the rebound strength shall be detected regularly. When the rebound strength reaches more than 85% of the design strength, the formwork can be removed. When removing the formwork, first remove the side formwork and then the bottom formwork, and avoid impact and vibration during the formwork removal process. After formwork removal, check the surface quality of the newly poured concrete, and repair the parts with defects such as honeycombing and pitting. Finally, use a laser level to detect the flatness of the surface of the newly poured concrete and the surface of the original floor slab to ensure a smooth transition between the two, and complete the reinforcement work for the elevator shaft opening. The purpose of this step is to ensure that the newly poured concrete reaches the design strength and complete the entire opening reinforcement work.

[0056] In the present invention, the stud connection structure uses M19 - 100 studs. The diameter of the stud head is 32 mm, the diameter of the rod part is 19 mm, the total length is 100 mm, and the material is Q235 steel. The stud layout follows the spacing calculated by the stud distribution function. The stud spacing is denser in the shear - concentrated area and sparser in the area with less shear force. The section steel beam layout structure is determined based on the minimum - spanning - tree algorithm. The commonly used section steel beam is H - shaped steel. For example, H200×100×5.5×8 means the web height is 200 mm, the flange width is 100 mm, the web thickness is 5.5 mm, and the flange thickness is 8 mm. The connection between section steel beams uses full - penetration butt welding or high - strength bolt connection. The weld quality grade is not lower than grade II, and the high - strength bolt is of the 10.9 - grade M20 specification. The section steel beam and the original floor slab are jointly connected through structural adhesive and studs. The thickness of the structural adhesive is controlled at 3 - 5 mm. The concrete pouring structure includes the newly poured concrete area and the connection area with the original floor slab. The steel bar mesh configured in the newly poured concrete forms a lap joint with the steel bars of the original floor slab, and the lap length is not less than 45 times the diameter of the steel bar. The surface of the newly poured concrete is flush with the surface of the original floor slab, and the transition area between the two is plastered to ensure flatness.

[0057] The following details the mathematical models or calculation processes involved in the present invention.

[0058] The minimum - spanning - tree algorithm adopted in step S04 involves graph - theory calculations, and its specific representation is as follows:

[0059] G=(V, E) represents the complete graph composed of the nodes around the opening, where V is the set of nodes and E is the set of edges;

[0060] T=(V′, E′) represents the minimum - spanning - tree, where V′ = V,

[0061] w(e) represents the weight of edge e, that is, the distance between nodes;

[0062] |E′|=|V|-1;

[0063] Where G is a complete graph, representing all possible steel beam connection modes around the opening; V is a node set, each node represents a connection point around the opening, and the node spacing is usually no more than 800 mm; E is an edge set, representing all possible connections between nodes; T is a minimum spanning tree, representing the final selected steel beam layout; w(e) is the weight of edge e, calculated using Euclidean distance, in millimeters; MST is the total weight of the minimum spanning tree, representing the total length of the steel beam.

[0064] The implementation steps of the minimum spanning tree algorithm are:

[0065] 1. Add all nodes to set V and initialize empty sets V′ and E′;

[0066] 2. Select any node v0 and add it to V′;

[0067] 3. Repeat the following steps until V′=V: select an edge e=(u,v) where u∈V′, v∈VV′, and w(e) is the smallest, add v to V′, and add e to E′;

[0068] 4. Return T = (V', E') as the minimum spanning tree.

[0069] This algorithm is based on the principle of Prim's algorithm and takes into account the shortest path principle of stress transfer in structural mechanics. It makes the total length of the steel beam the shortest while ensuring that the structure is subjected to reasonable stress. Compared with the traditional empirical layout method, it can save 15% to 25% of steel materials.

[0070] The peg distribution equation in step S06 is expressed as follows:

[0071]

[0072] Where S(x) is the spacing of the studs at a distance x from the end of the steel beam, in millimeters; S min is the minimum bolt spacing, usually 100 to 150 mm; S max is the maximum bolt spacing, usually 200-300 mm; L is the length of the steel beam, in millimeters; α is the distribution adjustment coefficient, ranging from 0.5 to 2.0, determined by experiments; β is the distribution index, ranging from 1.5 to 3.0, determined by finite element analysis; x is the position coordinate along the length direction of the steel beam, 0≤x≤L.

[0073] The formula for calculating the number of studs is:

[0074]

[0075] In the formula, N is the total number of stud bolts; L is the length of the profiled steel beam, with the unit of millimeter.

[0076] The stud bolt distribution equation takes into account the non-uniform shear force distribution on the profiled steel beam. Denser stud bolt spacing is set in the end regions where the shear force is concentrated, and sparser stud bolt spacing is set in the middle regions where the shear force is smaller. This equation adopts the form of a combination of a sine function and a power function, making the stud bolt distribution meet both the mechanical requirements and facilitate construction implementation. Compared with the method of uniformly distributing stud bolts, this equation can reduce the amount of stud bolts used by about 20% - 30%, while ensuring the structural safety.

[0077] The shear force distribution equation in step S06 is expressed as follows:

[0078]

[0079] In the formula, τ(x) is the interfacial shear stress at a distance x from the end of the profiled steel beam, with the unit of megapascal; V d is the design shear force value, with the unit of newton; Q is the static moment of the combined section of the profiled steel beam and the concrete floor slab, with the unit of cubic millimeter; I is the moment of inertia of the combined section, with the unit of quartic millimeter; b is the interfacial width, with the unit of millimeter; η is the non-uniform coefficient of shear force distribution, and its value range is 0.2 - 0.5; L is the length of the profiled steel beam, with the unit of millimeter; x is the position coordinate along the length direction of the profiled steel beam, and 0 ≤ x ≤ L.

[0080] The shear force distribution equation is based on the shear force formula in mechanics of materials and takes into account the influence of the load redistribution after the opening. The parameters Q and I are obtained by calculating the geometric dimensions of the profiled steel beam and the concrete floor slab:

[0081] Q = A c ·y c ;

[0082]

[0083] In the formula, A c is the effective cross-sectional area of the concrete floor slab, with the unit of square millimeter; y c is the distance from the centroid of the concrete floor slab to the neutral axis of the combined section, with the unit of millimeter; I s is the moment of inertia of the profiled steel beam itself, with the unit of quartic millimeter; A s is the cross-sectional area of the profiled steel beam, with the unit of square millimeter; d s is the distance from the centroid of the profiled steel beam to the neutral axis of the combined section, with the unit of millimeter; I c is the moment of inertia of the concrete floor slab itself, with the unit of quartic millimeter; d c is the distance from the centroid of the concrete floor slab to the neutral axis of the combined section, with the unit of millimeter.

[0084] These parameters are obtained through the geometric dimensions of the steel section beam and the concrete floor slab, and the specific calculation process follows the principles of mechanics of materials. The shear force distribution equation takes into account the non-linear characteristics of the composite structure, and can more accurately reflect the actual stress state compared with the traditional uniform shear force assumption, improving the economy and safety of the design.

[0085] The concrete strength equation in step S08 is expressed as follows:

[0086]

[0087] In the formula, f c，n is the strength grade of the newly cast concrete, in megapascals; f c，o is the strength of the original floor slab concrete, in megapascals; γ1 is the strength matching coefficient, with a value range of 0.9 to 1.1; q d is the design load, in newtons per square millimeter; L eff is the effective span, in millimeters; γ2 is the safety factor, with a value range of 1.2 to 1.5; h is the floor slab thickness, in millimeters; λ is the new and old concrete interface characteristic coefficient, with a value range of 0.6 to 0.8; μ is the temperature influence coefficient, with a value range of 0.01 to 0.03; T env is the ambient temperature, in degrees Celsius; T ref is the reference temperature, with a value of 20 degrees Celsius.

[0088] The concrete strength equation comprehensively considers factors such as the strength of the original floor slab, load requirements, and temperature influence, and adopts the maximum value of the two parts to ensure that the strength of the newly cast concrete is not lower than the strength of the original floor slab concrete and at the same time meets the load requirements. This equation introduces a temperature influence term, considering the influence of the ambient temperature on the development of concrete strength, and improving the applicability of the design. The parameters L eff , h are obtained through actual measurement, λ is determined through interface roughness testing, and T env is obtained through measurement by a temperature sensor.

[0089] The stress analysis equation in step S09 is expressed as follows:

[0090]

[0091] In the formula, σ(x, y, z) is the stress tensor at the spatial point (x, y, z); σ xx , σ yy , σ zz are the normal stress components, in megapascals; τ xy , τ yz , τ zx are the tangential stress components, in megapascals; σ eq is the equivalent stress (von Mises stress), in megapascals; σeq，max is the maximum equivalent stress in the structure, in megapascals; f y is the yield strength of the material, in megapascals; R safety is the safety reserve coefficient.

[0092] The stress analysis equations are based on the theory of elasticity. The stress state in three-dimensional space is represented by the stress tensor. The equivalent stress is calculated by the von Mises criterion, and the safety reserve coefficient is introduced to evaluate the structural safety. These equations are implemented through finite element analysis, and the calculation steps include: establishing a geometric model, setting material parameters, applying boundary conditions and loads, mesh generation, solution, and post-processing. The safety reserve coefficient R safety should be greater than 1.5 to ensure that the structure has sufficient safety margin.

[0093] In addition, the calculation of the section optimization design of the profiled steel beam is also involved in step S04, which is expressed as follows:

[0094]

[0095] In the formula, W req is the required section modulus of the profiled steel beam, in cubic millimeters; M d is the design bending moment, in Newton-millimeters; γ s is the safety factor of the steel, and the value range is 1.1 - 1.3; f y is the yield strength of the steel, in megapascals; I req is the required moment of inertia of the profiled steel beam, in fourth power of millimeters; q d is the design load, in Newtons per millimeter; L is the span of the profiled steel beam, in millimeters; E is the elastic modulus of the steel, usually taken as 210,000 megapascals; δ max is the allowable maximum deflection, usually taken as L / 250 - L / 400.

[0096] The section optimization design equations of the profiled steel beam are based on the strength and stiffness requirements in mechanics of materials, considering the strength condition under the action of bending moment and the deflection condition under the action of uniformly distributed load. When selecting the specification of the profiled steel beam, its section modulus should not be less than W req and its moment of inertia should not be less than I req . This design method with double constraints ensures that the profiled steel beam meets both the strength requirements and the stiffness requirements, avoiding excessive structural deformation.

[0097] Specifically, the principle of the present invention is: Based on structural mechanics and optimization theory, by establishing a clear force model and load transfer path, the present invention realizes the precise control of the force redistribution of the structure after the concrete floor slab is perforated. Its core principle can be elaborated from the following aspects:

[0098] First, the minimum spanning tree algorithm is used to solve the problem of optimizing the structural force transmission path. In this algorithm, the key force-bearing points around the opening are regarded as vertices in graph theory, and the length of the profiled steel beams required for connection between nodes is used as the weight to solve the connected tree structure with the minimum total weight. Essentially, this method is to find the optimal load transmission path to ensure that the load after opening can be transmitted to the intact part of the floor through the shortest and most efficient path, avoiding the problems of redundant or insufficient load transmission paths. After the profiled steel beams are arranged according to the minimum spanning tree, a clear structural force-bearing framework is formed, making the stress distribution state after opening predictable and controllable.

[0099] Secondly, the stud distribution equation solves the problem of precise control of interfacial shear force transmission. Based on the shear flow theory, this equation considers the shear stress distribution characteristics at different positions after opening, establishes a functional relationship between the stud spacing and the interfacial shear stress, and precisely matches the stud arrangement with the force-bearing requirements. This non-uniform stud arrangement ensures clear and reliable load transmission between the profiled steel beam and the concrete floor slab, avoiding the problems of weak connection or over-design caused by traditional uniform arrangement.

[0100] Thirdly, the shear force distribution equation and the stress analysis equation are applied to construct a complete mechanical analysis system. These equations theoretically describe the force-bearing state of the structure after opening reinforcement, including the shear stress distribution at the interface between the profiled steel beam and the concrete floor slab, the stress levels at key parts of the structure, and the overall safety reserve coefficient. Through these theoretical calculations, the originally fuzzy process of structural force redistribution is transformed into a quantifiable and analyzable engineering problem.

[0101] Fourthly, the practice of retaining and reasonably handling the original floor slab reinforcement makes use of the remaining load-bearing capacity of the original structure. The upward-bent reinforcement is embedded in the newly poured concrete to form a force-bearing connection between the new and old structures, enabling the stress around the opening area to transition smoothly and avoiding stress mutation and concentration.

[0102] In summary, through the method of combining theoretical calculation and structural optimization, the present invention establishes a clear force-bearing model and load transmission path, fundamentally solves the problem of unclear structural force redistribution when an elevator shaft is opened in a concrete floor slab, turns the reinforcement design from empirical judgment to scientific calculation, and improves the structural safety and reliability.

[0103] Next, a specific Embodiment 1 of the present invention is provided, and the specific implementation manners of each step in this Embodiment 1 are described in detail as follows.

[0104] The specific implementation method of step S01 is: first, according to the length and width of the designed elevator shaft, determine the position coordinates of the opening on the concrete floor slab, and use a total station for precise positioning to ensure that the position of the opening is completely consistent with the design drawings. Then use a red marker pen to reserve additional distances in all directions on the outer edge of the opening. The reserved distance is equal to the cross-sectional width of the steel beam to be installed later, usually ranging from 80 to 200 mm, determined according to the load size and structural calculations. Then use a blue marker pen to mark the final opening range on the floor slab to form a complete closed area. At the same time, the position of the original floor slab steel bars is detected by a ferromagnetic detector to ensure that the original floor slab steel bars are retained for at least 400 mm in length during the cutting process for subsequent bending processing. The purpose of this step is to clarify the scope of the opening and prepare for subsequent cutting and steel beam installation.

[0105] The specific implementation method of step S02 is: cutting on the concrete floor along the marked line, using a concrete cutting machine with a diamond cutting blade of 350 mm in diameter, the cutting speed is controlled at 0.5-1.0 m / min, and the cutting depth is set to the thickness of the floor plus 5 mm to ensure complete cutting. The cutting process adopts the segmented cutting method, and the length of each segment does not exceed 500 mm. The cutting sequence follows the principle of stress release, starting from the area with less stress to the area with greater stress. For the original floor steel bars encountered, a local fine cutting method is adopted, and the cutting speed is reduced to 0.2 m / min. At the same time, a water cooling system is used to cool the cutting area to prevent overheating damage to the steel bars. The flatness deviation of the cutting surface is controlled within ±2 mm, and the verticality of the cutting surface is monitored in real time by using a guide device and a laser level to ensure the cutting quality. The purpose of this step is to accurately cut the concrete floor to create conditions for subsequent hole opening.

[0106] The specific implementation method of step S03 is: after the cutting is completed, a hole is first drilled in the center of the concrete in the opening area with a hole diameter of 50 mm to provide a focus point for the lifting tool. Then an electric hoist or a manual hoist is used for uniform force lifting, and the lifting speed is controlled to no more than 50 mm per minute to avoid cracking of the surrounding concrete due to sudden force. During the demolition process, temporary supports are maintained on both sides of the cutting surface to prevent deformation of the floor slab. The original floor slab steel bars that are retained are cleaned, the attached concrete debris is removed, and the steel bar surface is cleaned with a wire brush until the metallic luster is exposed. Then a hydraulic steel bar bender is used to bend the steel bar upward, with a bending angle of 90°±5°, a bending radius of not less than 10 times the diameter of the steel bar, and a bending height of not less than 150 mm to ensure that the steel bar anchoring requirements for subsequent concrete pouring are met. The purpose of this step is to safely remove the concrete in the opening area and process the retained steel bars to prepare for subsequent reinforcement.

[0107] The specific implementation of step S04 is as follows: Install steel beams around the opening, and use the minimum spanning tree algorithm based on Prim's algorithm to determine the optimal layout plan of the steel beams. The mathematical expression of the minimum spanning tree algorithm is: G = (V, E) represents the complete graph formed by the nodes around the opening, where V is the set of nodes and E is the set of edges; T = (V′, E′) represents the minimum spanning tree, where V′ = V, w(e) represents the weight of edge e, that is, the distance between nodes; |E′| = |V| - 1. In the formula, G is the complete graph, representing all possible connection methods of the steel beams around the opening; V is the set of nodes, and each node represents a connection point around the opening. Usually, the node spacing does not exceed 800 mm; E is the set of edges, representing all possible connections between nodes; T is the minimum spanning tree, representing the finally selected layout plan of the steel beams; w(e) is the weight of edge e, calculated using the Euclidean distance, with the unit of mm; MST is the total weight of the minimum spanning tree, representing the total length of the steel beams. The cross-sectional dimensions of the steel beams are determined by finite element analysis method. The cross-sectional optimization design follows the formula: In the formula, W req is the required section modulus of the steel beam, with the unit of cubic millimeters; M d is the design bending moment, with the unit of Newton·millimeters; γ s is the safety factor of the steel, and the value range is 1.1 - 1.3; f y is the yield strength of the steel, with the unit of megapascals; I req is the required moment of inertia of the steel beam, with the unit of quartic millimeters; q d is the design load, with the unit of Newton / mm; L is the span of the steel beam, with the unit of mm; E is the elastic modulus of the steel, usually taken as 210000 megapascals; δ max is the allowable maximum deflection, usually taken as L / 250 - L / 400. Commonly used steel beam specifications include H200×100×5.5×8, H250×125×6×9, H300×150×6.5×9, etc. The specific selection is determined according to the opening size and load magnitude. During installation, first use a level and shims to adjust the position of the steel beam to ensure that the gap between the steel beam and the bottom surface of the floor does not exceed 5 mm. Use high-strength bolts to temporarily fix the steel beam, and the bolt spacing is not greater than 600 mm. The purpose of this step is to optimize the layout of the steel beams and provide structural support around the opening.

[0108] The specific implementation of step S05 is as follows: Structural adhesive is poured into the gap between the profiled steel beam and the bottom surface of the floor slab. A two-component epoxy resin structural adhesive is used, with a compressive strength of not less than 70 MPa, a shear strength of not less than 15 MPa, an initial viscosity of 15 - 20 Pa·s, and an operable time of 40 - 60 minutes. Before pouring, first use compressed air to blow out the dust and debris in the gap, and then use acetone to clean the surfaces of the steel beam and concrete. The pouring is carried out by the pressure injection method, with the injection pressure controlled at 0.2 - 0.3 MPa, and the pouring is carried out through the pre-set injection ports and exhaust ports to ensure that the structural adhesive fully fills all the gaps between the profiled steel beam and the bottom surface of the floor slab. After pouring, keep the ambient temperature at 15 - 25 °C, the relative humidity not exceeding 80%, and the static curing time not less than 24 hours to ensure that the structural adhesive is completely cured. After the structural adhesive is cured, check the bonding condition between the profiled steel beam and the original bottom surface of the floor slab by tapping to determine whether a reliable connection is formed. The purpose of this step is to ensure that the profiled steel beam and the original floor slab form an integral stress-bearing system.

[0109] The specific implementation of step S06 is as follows: Calculate the stud spacing based on the stud distribution equation, and the stud distribution equation is expressed as: In the formula, S(x) is the stud spacing at a distance of x from the end of the profiled steel beam, with the unit of millimeter; S min is the minimum stud spacing, usually taking 100 - 150 millimeters; S max is the maximum stud spacing, usually taking 200 - 300 millimeters; L is the length of the profiled steel beam, with the unit of millimeter; α is the distribution adjustment coefficient, with a value range of 0.5 - 2.0, determined through tests; β is the distribution index, with a value range of 1.5 - 3.0, determined through finite element analysis; x is the position coordinate along the length direction of the profiled steel beam, where 0 ≤ x ≤ L. The calculation formula for the number of studs is: In the formula, N is the total number of studs; L is the length of the profiled steel beam, with the unit of millimeter. The stud distribution takes into account the shear force distribution law, and the shear force distribution equation is expressed as: In the formula, τ(x) is the interfacial shear stress at a distance of x from the end of the profiled steel beam, with the unit of MPa; V dV is the designed shear force value, with the unit of Newton; Q is the static moment of the composite section of the steel beam and the concrete floor slab, with the unit of cubic millimeter; I is the moment of inertia of the composite section, with the unit of quartic millimeter; b is the interface width, with the unit of millimeter; η is the shear force distribution unevenness coefficient, and its value range is 0.2 - 0.5; L is the length of the steel beam, with the unit of millimeter; x is the position coordinate along the length direction of the steel beam, and 0 ≤ x ≤ L. Use an arc stud welding machine to weld M19 - 100 studs on the upper surface of the steel beam according to the calculated spacing, control the welding time within 0.2 - 0.3 seconds, and the welding current is 350 - 450 amperes. The stud arrangement should avoid the positions of the reserved steel bars of the original floor slab, and the clear distance between the studs and the reserved steel bars is not less than 25 millimeters. After welding, conduct a 45° knocking inspection on each stud to ensure the welding quality. The purpose of this step is to provide shear connection between the steel beam and the newly poured concrete.

[0110] The specific implementation method of step S07 is: Prepare for the concrete pouring in the surrounding area of the steel beam. First, install the formwork. The formwork uses 18 - millimeter - thick film - faced plywood, and the support system uses adjustable - height steel supports with the support spacing not greater than 400 millimeters. Apply a release agent on the surface of the formwork to ensure smooth formwork removal in the later stage. Then, position the bent steel bars. According to the specifications and spacing of the steel bars of the original floor slab, supplement and configure the steel bar mesh, and keep the steel bar spacing consistent with that of the original floor slab steel bars, usually 150 - 200 millimeters. The lap length of the steel bars is not less than 45 times the diameter of the steel bars, and tie and fix the joint positions. Configure additional stirrups around the studs of the steel beam, and the stirrup spacing is not greater than 150 millimeters. Use a laser level to determine the elevation of the top surface of the formwork, adjust the support height to ensure that the top surface of the poured concrete is consistent with the top surface of the original floor slab, and control the deviation within ±2 millimeters. The purpose of this step is to create good conditions for concrete pouring and ensure the pouring quality.

[0111] The specific implementation method of step S08 is: Conduct pouring using the concrete strength grade calculated from the concrete strength equation. The concrete strength equation is expressed as: In the formula, f c，n is the strength grade of the newly poured concrete, with the unit of megapascal; f c，o is the strength of the concrete of the original floor slab, with the unit of megapascal; γ1 is the strength matching coefficient, and its value range is 0.9 - 1.1; q d is the designed load, with the unit of Newton per square millimeter; L eff is the effective span, with the unit of millimeter; γ2 is the safety factor, and its value range is 1.2 - 1.5; h is the floor slab thickness, with the unit of millimeter; λ is the coefficient of the interface characteristics between the new and old concretes, and its value range is 0.6 - 0.8; μ is the temperature influence coefficient, and its value range is 0.01 - 0.03; T env is the ambient temperature, with the unit of degree Celsius; T refTaking [[ID=]] as the reference temperature, with a value of 20 degrees Celsius. The concrete mix design adopts a curve optimization method, controlling the water-cement ratio within 0.4 - 0.5, and adding admixtures such as water reducers and retarders. During pouring, the concrete slump is controlled within 140 - 180 mm. The layered pouring method is adopted, with each layer thickness not exceeding 300 mm. Insert type vibrators are used for vibration, with the vibration time being 20 - 30 seconds per point and the vibration point spacing being 300 - 400 mm. The pouring range includes the projection area of the section width of the steel beam and 100 - 150 mm outside it, forming the edge of the newly added opening sealed floor slab. After pouring, a wooden float and a steel float are used to finish the surface to ensure it is flat. The purpose of this step is to form a high-strength newly poured concrete area to provide structural support.

[0112] The specific implementation of step S09 is as follows: Cure the newly poured concrete to the design strength, with the curing period being no less than 14 days. Wet curing is carried out in the first 7 days to keep the concrete surface moist. Plastic film covering or spray curing can be used, and the curing temperature is controlled within 15 - 25 °C. Natural curing is carried out in the next 7 days to keep the relative humidity of the environment not less than 60%. During the curing period, the rebound strength is regularly detected. When the rebound strength reaches more than 85% of the design strength, the formwork can be removed. When removing the formwork, first remove the side formwork and then the bottom formwork, and avoid impact and vibration during the formwork removal process. After formwork removal, check the surface quality of the newly poured concrete, and repair the parts with defects such as honeycombing and pitting. Finally, use a laser level to detect the flatness of the surface of the newly poured concrete and the original floor slab surface to ensure a smooth transition between the two. To evaluate the reinforcement effect, a stress analysis equation is also needed for safety inspection: In the formula, σ(x, y, z) is the stress tensor at the spatial point (x, y, z); σ xx , σ yy , σ zz are the normal stress components, with the unit of megapascal; τ xy , τ yz , τ zx are the shear stress components, with the unit of megapascal; σ eq is the equivalent stress (von Mises stress), with the unit of megapascal; σ eq，max is the maximum equivalent stress in the structure, with the unit of megapascal; f y is the yield strength of the material, with the unit of megapascal; R safety is the safety reserve coefficient, and this coefficient should be greater than 1.5 to ensure that the structure has sufficient safety margin. The purpose of this step is to ensure that the newly poured concrete reaches the design strength and complete the entire opening reinforcement work.

[0113] The minimum spanning tree algorithm used in the present invention is based on Prim's algorithm in graph theory, and its implementation steps are as follows: First, add all nodes to set V, and initialize empty sets V' and E'; select any node v0 and add it to V'; repeat the following steps until V' = V: Select an edge e = (u, v), where u ∈ V', v ∈ V - V', and w(e) is the smallest, add v to V', and add e to E'; return T = (V', E') as the minimum spanning tree. This algorithm ensures the shortest total length of the profiled steel beam, saves materials, and ensures the structural safety at the same time.

[0114] The stud distribution equation adopts the form of a combination of a sine function and a power function, fully considering the characteristic of uneven shear force distribution on the profiled steel beam. A denser stud spacing is set in the end region where the shear force is concentrated, and a sparser stud spacing is set in the middle region where the shear force is smaller. Compared with the method of evenly distributing studs, this equation can reduce the stud consumption by about 20% - 30%, and ensure the structural safety at the same time. The stud distribution parameters are determined through experiments and finite element analysis to ensure reasonable distribution and easy construction implementation.

[0115] The shear force distribution equation is based on the shear force formula in mechanics of materials and considers the influence of load redistribution after opening holes. The parameters Q and I are obtained by calculating the geometric dimensions of the profiled steel beam and the concrete floor slab: Q = A c ·y c ; In the formula, A c is the effective cross-sectional area of the concrete floor slab, with the unit of square millimeters; y c is the distance from the centroid of the concrete floor slab to the neutral axis of the composite section, with the unit of millimeters; I s is the moment of inertia of the profiled steel beam itself, with the unit of quartic millimeters; A s is the cross-sectional area of the profiled steel beam, with the unit of square millimeters; d s is the distance from the centroid of the profiled steel beam to the neutral axis of the composite section, with the unit of millimeters; I c is the moment of inertia of the concrete floor slab itself, with the unit of quartic millimeters; d c is the distance from the centroid of the concrete floor slab to the neutral axis of the composite section, with the unit of millimeters. The shear force distribution equation considers the nonlinear characteristics of the composite structure and can more accurately reflect the actual stress state compared with the traditional uniform shear force assumption.

[0116] The concrete strength equation comprehensively considers factors such as the original floor slab strength, load requirements, temperature influence, etc., and adopts the maximum value of two parts to ensure that the strength of the newly poured concrete is not lower than the strength of the original floor slab concrete and meets the load requirements at the same time. This equation introduces a temperature influence term, considers the influence of environmental temperature on the development of concrete strength, and improves the applicability of the design. The parameters L eff , h are obtained through actual measurement, and λ is determined through interface roughness testing, Tenv Obtained by measuring with a temperature sensor.

[0117] The stress analysis equations are based on the theory of elasticity. The stress state in three-dimensional space is represented by the stress tensor. The equivalent stress is calculated through the von Mises criterion, and a safety reserve coefficient is introduced to evaluate the structural safety. These equations are implemented through finite element analysis. The calculation steps include: establishing a geometric model, setting material parameters, applying boundary conditions and loads, mesh generation, solution, and post-processing. The safety reserve coefficient R safety should be greater than 1.5 to ensure that the structure has sufficient safety margin.

[0118] The sectional optimization design equations of the steel beam are based on the strength and stiffness requirements in mechanics of materials, considering the strength condition under bending moment and the deflection condition under uniformly distributed load. When selecting the specification of the steel beam, its sectional modulus should not be less than W req , and the moment of inertia should not be less than I req . This design method with double constraints ensures that the steel beam meets both the strength requirements and the stiffness requirements, avoiding excessive structural deformation.

[0119] To better understand and implement the present invention, Example 2 of a specific application scenario of the present invention is provided below: An elevator shaft needs to be added on an existing concrete floor slab in a building. The thickness of the floor slab is 180 mm, the concrete strength grade is C30, and the original designed live load is 3.5 kN / m². According to the building function requirements, the size of the newly added elevator shaft is determined to be 1800 mm × 2200 mm. During the implementation process, the construction personnel carried out the hole cutting and reinforcement construction in accordance with the method of the present invention.

[0120] First, determine the hole-cutting position coordinates on the concrete floor slab according to the designed elevator shaft size, and use a Leica TS06 total station for positioning, with the positioning accuracy controlled within ±2 mm. Considering the sectional width of the steel beam to be installed later, an additional distance of 125 mm is reserved in each direction at the outer edge of the hole cutting. Use a red marker pen to mark the final hole-cutting range as a rectangle of 2050 mm × 2450 mm. Detect the distribution of the original floor slab steel bars through a Profoscope ferromagnetic detector to determine the position and spacing of the steel bars. The main steel bars in the original floor slab are Φ14@150 mm, and the distribution steel bars are Φ10@200 mm. Ensure that 400 mm of the original steel bars are reserved for subsequent bending connection.

[0121] Subsequently, the construction workers carried out cutting on the concrete floor slab along the marked lines using a Hilti DST 20-CA concrete cutting machine equipped with a diamond cutting blade with a diameter of 350 mm. The cutting depth was set at 185 mm, and the cutting speed was controlled at 0.8 m / min. For the reinforcement parts encountered, the cutting speed was reduced to 0.2 m / min, and a circulating water cooling system was used for cooling. The cutting was carried out in sections, with each section having a cutting length of 450 mm. The cutting sequence was from the short side to the long side to ensure that the flatness deviation of the cutting surface was within ±1.5 mm.

[0122] After the cutting was completed, a hole with a diameter of 50 mm was drilled at the center of the opening area, and a KITO electric hoist was used for hoisting, with the hoisting speed controlled at 40 mm per minute. After removing the concrete in the opening area, the original floor slab reinforcement that was retained was cleaned, and a wire brush was used to remove the attached concrete debris. A BNCE-20 hydraulic steel bar bender was used to bend the steel bars upward by 90°, with the bending radius controlled at 12 times the diameter of the steel bar and the bending height being 180 mm.

[0123] Next, section steel beams were installed around the opening. The optimal layout plan calculated according to the minimum spanning tree algorithm is shown in Table 1:

[0124] Table 1 Section steel beam layout node coordinates and connection relationships

[0125] Node number Coordinate X (mm) Coordinate Y (mm) Connected node 1 0 0 2,8 2 0 816 1,3 3 0 1633 2,4 4 0 2450 3,5 5 683 2450 4,6 6 1366 2450 5,7 7 2050 2450 6,12 8 0 0 1,9 9 683 0 8,10 10 1366 0 9,11 11 2050 0 10,12 12 2050 2450 7,11

[0126] According to the calculation of the section steel beam section optimization design equation, considering the design bending moment M d of 85 kN·m, the steel safety factor γ s of 1.2, and the steel yield strength f y of 345 MPa, the required section modulus W req was 295.65 cm³. Considering the design load q d of 5.25 kN / m, the span L of the section steel beam of 2.45 m, the steel elastic modulus E of 210000 MPa, and the allowable maximum deflection δ max of L / 300 = 8.17 mm, the required moment of inertia I req was 1963.89 cm 4 . Based on this, an H250×125×6×9 section steel beam was selected, with its section modulus being 325.4 cm³ and its moment of inertia being 4062.5 cm 4 , meeting the design requirements.

[0127] The gap between the profiled steel beam and the bottom surface of the floor slab was filled with a two-component epoxy resin structural adhesive Sikadur-30, which has a compressive strength of 85 MPa, a shear strength of 18 MPa, an initial viscosity of 18 Pa·s, and an operable time of 50 minutes. Before pouring, dust in the gap was blown out using oil-free compressed air, and then the contact surface was cleaned with acetone. The pressure injection method was used for pouring, and the injection pressure was controlled at 0.25 MPa. Pouring was carried out through 6 pre-set injection ports and 4 exhaust ports to ensure that the structural adhesive fully filled all gaps. After pouring, the ambient temperature was controlled at 20±2°C, the relative humidity was controlled below 70%, and the curing time was 36 hours.

[0128] Subsequently, the stud spacing was calculated according to the stud distribution equation. Based on the length L of the profiled steel beam being 2450 mm, the designed shear force value V d being 65 kN, the shear bearing capacity P of a single stud d being 58 kN, with the parameter α taken as 1.5 and β taken as 2.0, the calculated stud spacing distribution is shown in Table 2:

[0129] Table 2 Stud Spacing Distribution Table

[0130] Position x (mm) Stud spacing S(x) (mm) 0 110 245 138 490 167 735 195 980 223 1225 238 1470 232 1715 205 1960 173 2205 142 2450 110

[0131] According to the calculation results, M19-100 studs with a diameter of 19 mm and a length of 100 mm were welded by fusion on the upper surface of the profiled steel beam, with a total of 17 studs. The stud welding was carried out using a Nelson NS-20 arc stud welding machine, with the welding time controlled at 0.25 s and the welding current at 400 A. The stud layout avoided the positions of the original retained steel bars, and the minimum clear distance between the studs and the retained steel bars was maintained at over 35 mm. After welding, each stud was inspected by 45° tapping to ensure good welding quality.

[0132] Next, the construction workers prepared for the concrete pouring in the area around the profiled steel beam, installed a 18-mm-thick film-coated plywood formwork, and used adjustable-height steel supports for the support system, with a support spacing of 350 mm. According to the concrete strength equation, the strength grade requirement of the newly poured concrete was calculated. The strength of the original floor slab concrete f c,o was 30 MPa, the strength matching coefficient γ1 was taken as 1.0, the designed load q d was 0.0035 MPa, the effective span L eff was 2450 mm, the safety factor γ2 was taken as 1.3, the floor slab thickness h was 180 mm, the interface characteristic coefficient λ was taken as 0.7, the temperature influence coefficient μ was taken as 0.02, the ambient temperature T env was 25°C, and the reference temperature T ref was 20°C. It was calculated that f c,n was 32.85 MPa, so C35 concrete was selected for pouring.

[0133] The concrete mix ratio is shown in Table 3 as follows:

[0134] Table 3 Mix Ratio Table of C35 Concrete (per cubic meter)

[0135] Raw material Dosage (kg) P.O 42.5 cement 428 Fine aggregate 617 Coarse aggregate 1107 Water 171 Water reducer 6.42 Set retarder 2.14

[0136] During the pouring process, the slump of the concrete is controlled at 160 mm. The layered pouring method is adopted, with each layer having a thickness of 150 mm, and a total of two layers are poured. A ZX50 type inserted vibrator is used for vibration, with the vibration time being 25 seconds per point and the vibration point spacing being 350 mm. The pouring range includes the projection area of the section width of the profiled steel beam and 125 mm outside it, forming the edge of the newly added opening sealing floor slab. After pouring, a wooden float and a steel float are used to finish the surface to ensure its flatness.

[0137] Finally, the newly poured concrete is cured for 21 days. Wet curing is carried out in the first 10 days, covered with plastic film and sprayed with water every 4 hours, and the curing temperature is controlled at 20±3℃. Natural curing is carried out in the next 11 days, keeping the relative environmental humidity above 65%. During the curing period, a rebound hammer is regularly used for strength detection, and the formwork is removed when the rebound strength reaches 90% of the design strength. After formwork removal, a laser level is used to detect the flatness of the surface of the newly poured concrete and the surface of the original floor slab, and the height difference between the two is measured within ±1.2 mm, meeting the requirement of smooth transition.

[0138] The stress analysis of the reinforced structure is carried out by the finite element analysis software ANSYS, and the calculated maximum equivalent stress σ eq,max is 189.6 MPa. Compared with the yield strength of steel f y = 345 MPa, the safety reserve coefficient R safety is 1.82, which is greater than the minimum requirement of 1.5, indicating that the reinforced structure has sufficient safety margin.

[0139] Traditional methods for strengthening concrete floor openings mainly rely on empirical judgment. Usually, steel beams are arranged at equal intervals and stud bolts are evenly distributed, without considering the actual stress distribution, resulting in material waste and low construction efficiency. For example, the conventional method requires steel beams with a total length of about 8.3 meters, while the present invention optimizes the layout through the minimum spanning tree algorithm and only requires about 7.0 meters, saving about 16% of the steel materials. The traditional method usually arranges stud bolts at uniform intervals, with a total of about 21, while the present invention optimizes the configuration through the stud bolt distribution equation and only requires 17, saving about 19% of the stud bolt materials and welding workload. In addition, the traditional method does not consider the influence of temperature on the development of concrete strength, which is likely to cause poor connection at the interface between new and old concrete. The concrete strength equation of the present invention takes into account the temperature influence factor, improving the integrity and durability of the structure. By introducing the structural optimization equations and strict construction process control, the present invention not only improves the structural safety compared with the traditional method, but also saves material costs, while greatly improving the construction efficiency and quality controllability.

[0140] It should be noted that the detailed explanations of the variables involved in the present invention are shown in Table 4 below.

[0141] Table 4 Variable Explanation Table

[0142]

[0143]

[0144] As described above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A method for opening and strengthening the elevator shaft in a concrete floor slab, characterized in that Including the following steps: determining the opening position; performing concrete cutting; removing the concrete in the opening area while retaining the original floor reinforcement; installing steel beams around the opening, and determining the optimal layout plan of the steel beams based on the minimum spanning tree algorithm; pouring structural adhesive between the steel beams and the bottom surface of the floor; welding studs on the upper surface of the steel beams based on the stud spacing distribution function calculated by the stud distribution equation; pouring concrete in the area around the steel beams; curing the newly poured concrete to the design strength; the stud distribution equation is used to calculate the optimal spacing distribution of the studs on the steel beams, the input includes the length of the steel beam, the design shear force value, the single shear bearing capacity of the stud, the floor thickness, and the material safety factor, and the output is the spacing distribution function of the studs along the steel beam; the minimum spanning tree algorithm is used to optimize the layout of the steel beams to make the total length of the steel beams the shortest while meeting the structural requirements.

2. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 1, characterized in that In the step of determining the opening position, determine the opening position on the concrete floor according to the designed elevator shaft size, and reserve an additional distance equal to the cross-sectional width of the steel beam in each direction at the outer edge of the opening, mark the final opening range, and ensure that a certain length of the original floor reinforcement is retained.

3. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 2, characterized in that, In the step of performing concrete cutting, cut along the marked line on the concrete floor, accurately cut to the designed depth using a concrete cutting machine, and protect the original floor reinforcement during the cutting process to ensure that the cutting surface is flat.

4. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 3, characterized in that, In the step of removing the concrete in the opening area while retaining the original floor reinforcement, carefully remove the concrete in the opening area after cutting, clean the retained original floor reinforcement and bend it upward, and the bending height meets the requirements of subsequent construction.

5. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 4, characterized in that, In the step of installing steel beams around the opening, the cross-sectional size of the steel beam is determined according to the structural calculation, and ensure that the steel beam is in close contact with the bottom surface of the floor during installation.

6. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 5, characterized in that, In the step of welding studs on the upper surface of the steel beams based on the stud spacing distribution function calculated by the stud distribution equation, the studs are M19-100 studs, and the stud arrangement should avoid the positions of the retained reinforcement of the original floor.

7. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 6, characterized in that, In the step of pouring concrete in the area around the steel beams, it includes formwork installation and positioning of bent steel bars to ensure that the top surface of the poured concrete is at the same elevation as the top surface of the original floor.

8. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 7, characterized in that, In the step of pouring concrete in the area around the steel beams, pour using the concrete strength grade calculated by the concrete strength equation, and the pouring range includes the projection area of the cross-sectional width of the steel beam to form the edge of the newly added opening-sealing floor.

9. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 8, characterized in that, The shear force distribution equation is used to analyze the shear force distribution at the interface between the steel beam and the concrete floor. The input includes the applied load, the cross-sectional characteristics of the steel beam, the concrete strength grade, the stud spacing distribution function, and the interface contact area, and the output is the interface shear stress distribution function; the concrete strength equation is used to determine the optimal strength grade of the newly poured concrete. The input includes the strength of the original floor concrete, the design load, the interface characteristics between the new and old concretes, the cross-sectional characteristics of the steel beam, and the environmental conditions, and the output is the minimum strength grade of the newly poured concrete; The stress analysis equation is used to calculate the stress distribution state of the strengthened structural system. The inputs include the arrangement of steel beams, the distribution function of stud spacing, the concrete strength grade, the design load, and the characteristics of the original structure. The outputs are the stress distribution nephogram and the safety reserve coefficient of the strengthened structure.

10. The method for opening and strengthening the elevator shaft in the concrete floor slab according to claim 9, characterized in that, The distribution function of stud spacing refers to the mathematical function that describes the distribution law of studs along the length direction of the steel beam, and determines the spacing of studs at different positions according to the stress characteristics of the structure; the interface shear stress distribution function refers to the mathematical function that describes the distribution law of shear stress at the interface between the steel beam and the concrete floor slab; the safety reserve coefficient refers to the ratio of the actual bearing capacity of the structure to the design load, and is used to evaluate the safety margin of the structure.

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