A construction method for a concave core island raft base plate

Abstract

This invention discloses a construction method for a concave core island raft foundation slab, relating to the field of raft foundation slab concrete preparation technology. The construction method includes the following steps: measurement and positioning; reinforcement cage binding; installation of inclined section supports; installation of inclined section steel lining; deformation prevention and reinforcement of the inclined section steel lining; finite element analysis simulation of concrete pouring to determine the construction design parameters of the raft foundation slab concrete through finite element analysis simulation calculations; formwork installation; concrete pouring, adopting inclined layered and full-layered pouring forms, dividing the foundation slab formwork into several pouring areas, and pouring from the center outwards. This method optimizes the process, connecting the formwork and the internal steel lining support frame to form a whole, simulating the deformation of the steel lining caused by the four-in-one construction through finite element analysis, adding design tooling reinforcement structures, and adopting a one-time simultaneous pouring method with radial material distribution from the center outwards to control the pouring quality, thereby ensuring the deformation control of the steel lining.

Description

Technical Field

[0001] This invention relates to the field of raft foundation slab concrete preparation technology, and in particular to a construction method for a concave core island raft foundation slab. Background Technology

[0002] Currently, nuclear power plant reactors widely adopt a new type of concave nuclear island raft base plate structure. Its main structural feature is that it is encased in steel plates on both sides, with self-compacting concrete poured inside to form a composite wall or floor structure. The steel plates act as reinforcement and also serve as formwork during concrete pouring. These structural modules can be prefabricated in a factory, then transported to the site for installation and concrete pouring, which can shorten the overall civil engineering and installation period of the project.

[0003] Based on the existing technical construction layer division and the established construction plan, the construction steps for the concave nuclear island raft base plate during the concrete pouring (FCD) stage of the nuclear power unit reactor pit are as follows:

[0004] Step 1: The lower base plate;

[0005] Step 2: Install the I-beam keel at the bottom of the remaining horizontal steel lining, and level the upper surface of the I-beam keel to determine the leveling layer;

[0006] Step 3: Install the inclined section and vertical steel lining of the ring corridor on the upper surface of the leveling layer;

[0007] Step 4: Construct the base slab of the lower part of the construction corridor.

[0008] During construction, the large-volume raft foundation slab concrete of nuclear power plants is poured in one go, with a large planar area and cross-sectional dimensions. In the early stage of concrete pouring, a large amount of hydration heat is generated during the setting of the concrete. Due to the poor thermal conductivity of concrete, the hydration heat accumulates in large quantities inside the concrete and is not easily dissipated, causing the internal temperature of the concrete to rise sharply. Meanwhile, the heat on the surface of the concrete can be directly dissipated to the outside, with little accumulation and a low temperature rise. This creates a temperature difference between the inside and the outside. This internal and external temperature difference causes thermal stress inside the concrete. When the stress exceeds the tensile strength of the concrete, it will lead to temperature cracks in the concrete.

[0009] In addition, the implementation of steps 2-4 above must be carried out one by one after the FCD stage. This construction process has many disadvantages, such as complex procedures, long construction period, and difficulty in quality control. Summary of the Invention

[0010] The purpose of this invention is to address the problems and shortcomings of existing technologies by providing a construction method for a concave core island raft base plate, which effectively controls construction precision, significantly improves construction efficiency and quality, simplifies construction procedures, shortens installation period, and reduces safety risks.

[0011] To solve the above problems, the present invention adopts the following technical solution:

[0012] A construction method for a concave core island raft base plate, the construction method comprising the following steps:

[0013] S 100 Measurement and positioning;

[0014] Use a total station to measure the central crosshair, the outer radius outline, and the elevation control line of the raft base plate;

[0015] S 200 : Reinforcing cage binding;

[0016] Based on the surveyed central cross lines, outer radius contour lines, and raft base plate elevation control lines, multi-layer structural steel bars are tied to form the internal steel cage module of the concave core island raft base plate.

[0017] S 300 : Installation of inclined section brackets;

[0018] An inclined section bracket embedded part is installed on the internal steel cage module. A single inclined section bracket is prefabricated and hoisted and connected around the inner circle of the internal steel cage module to form an integral whole using inclined braces and horizontal braces.

[0019] S 400 Install inclined section steel lining;

[0020] Measure the positioning reference elevation and the raft base plate inner diameter baseline on the inclined section support, and mark the raft base plate outer diameter baseline and component position line on the outer ring support beam of the raft base plate;

[0021] Identify and mark the 0°, 90°, 180°, and 270° directional baselines and angle control lines;

[0022] Referring to the released reference elevation and baseline, weld the steel profiles onto the inclined section support and spot weld the radius limiting steel plates onto the support beam in advance;

[0023] Based on the number of inclined section steel liners, determine the number of lifting points, and set traction ropes at both ends of the inclined section steel liner assembly. Set auxiliary lifting points at the lower opening of the inclined section steel liner assembly, and clamp the bottom of the inclined section steel liner with steel plate clamps.

[0024] After all components are hoisted into place, adjust the weld gap and weld position of the inclined section steel lining assembly, and simultaneously adjust the verticality of the inclined section, then fix it with spot welding.

[0025] S 500 : Slanted section steel lining for deformation prevention and reinforcement;

[0026] Weld anti-deformation reinforcement structures onto the auxiliary supports of the inclined section steel lining;

[0027] S 600 Finite element analysis of concrete pouring simulation;

[0028] The construction design parameters for the raft foundation slab concrete were determined through finite element analysis and simulation calculations.

[0029] S 700 Template installation;

[0030] Tool-type curved formwork is used on the outer facade of the base slab formwork, and secondary and main keels are installed;

[0031] S 800 Concrete pouring;

[0032] The base slab is divided into several pouring areas using a diagonal layered and full-layered pouring method, and the pouring proceeds from the center outwards.

[0033] Furthermore, in S 200 The step of binding the steel cage includes:

[0034] S 210 Reinforcement construction;

[0035] A total of 6 layers of main reinforcement with a diameter of 40mm and HRB500E steel bars are used, and 2 layers of double-layer bidirectional structural reinforcement with a diameter of 25mm are designed in the middle of the bottom slab.

[0036] Two layers of double-layered, bidirectional structural steel bars with a diameter of 25mm are designed in the middle of the base plate. The steel bars are connected using straight threaded sleeves, and the percentage of joints is no more than 50%.

[0037] After the bottom 1st, 2nd, 3rd and 4th layers of steel reinforcement are installed, install the steel reinforcement bracket, steel lining bracket and support beam bracket;

[0038] Perform the tying of the 5th and 6th layers of reinforcing bars;

[0039] S 220 An additional layer of anti-crack steel mesh is added to the side of the raft foundation slab to control shrinkage cracks on the concrete surface.

[0040] Furthermore, in step S 300 The specific steps for installing the inclined section bracket include:

[0041] Step S 310 : Inclined section support design;

[0042] A base plate steel lining support structure is set at every 7.5 degrees circumferentially. The base plate steel lining support structure includes I-shaped steel columns, tie angle steel, circumferential columns, connecting rods and support beams. The tie angle steel is set at the top of the I-shaped steel columns, and the connecting rod is set at the top of the circumferential columns.

[0043] Step S 320 : Install the embedded parts of the inclined section support;

[0044] Step S 330 Prefabricate single-piece inclined section brackets and spot weld the bottom of the inclined section brackets to the embedded parts of the inclined section brackets.

[0045] Step S 340 Each inclined section bracket is connected into a whole by diagonal bracing and horizontal bracing, and then spot-welded to the bottom steel bars for reinforcement.

[0046] Furthermore, in S 400 The specific steps for adjusting the perpendicularity of the inclined section include:

[0047] Use a plumb bob and steel ruler to check the verticality deviation of the inclined section plate and determine the amount of deviation that needs to be adjusted.

[0048] A lead screw is welded between the back rib of the inclined section angle steel and the reinforcing bar;

[0049] The verticality of the inclined section is finely adjusted by rotation. After the verticality is adjusted, the inclined section is connected and fixed to the upright.

[0050] A 4.5m template ruler was used to detect the curvature, and a 1m template ruler was used to detect the local concavity and convexity.

[0051] Furthermore, in step S 400 and step S 500 The welding of the inclined section bracket is carried out using semi-automatic gas shielded welding or manual electric arc welding, and the welding of the inclined section steel lining is carried out using manual electric arc welding.

[0052] Furthermore, in step S 500 The specific steps for reinforcing the inclined section steel lining against deformation include:

[0053] Step S 510 A ring-shaped channel steel is installed at the top of the inclined section auxiliary support and welded to the support column;

[0054] Step S 520 Use steel bars with a diameter of φ25 or larger or L76*6 angle steel to connect the back rib angle steel of the inclined section to the inclined section support.

[0055] Furthermore, in step S 600 The specific steps of the finite element analysis for simulating concrete pouring include:

[0056] Step S 610 The raft foundation slab concrete uses B40 grade, W8 impermeability, F100 frost resistance, slump of 160±30mm, and a volumetric weight of not less than 2350kg / m³. 3 ;

[0057] Step S 620 Finite element analysis was used to simulate and calculate the concrete, and crack-resistant steel mesh was added to the surface of the raft foundation to control the temperature before placement in the formwork.

[0058] Step S 630 The tooling platform and angle steel are established using beam elements, and the inclined section is established using plate elements. Finite element analysis is performed on the structural strength of the steel tooling.

[0059] Furthermore, in step S 700 The specific process for installing the template is as follows:

[0060] Step S 710 Positioning and layout: Based on the drawings, lay out the positioning radius lines, angle axes, and reference control lines;

[0061] Step S 720 Four layers of high-strength tie rods are installed on average, and the high-strength tie rods are tied to the horizontal beams of the steel-lined steel bracket.

[0062] Step S 730 One end of the reinforcing bar connecting rod is tied to the horizontal beam of the channel steel of the steel frame and welded to the web of the channel steel.

[0063] Step S 740 The wire mesh is double-layered 8000 mesh. The secondary keel is made of 50*100mm timber with a horizontal spacing of 200mm. The main keel is made of 48mm steel pipe. The tie rod is made of 16mm high-strength tie rod + 12mm steel bar and tied to the bottom reinforcement or steel frame of the foundation.

[0064] Furthermore, in step S 800 The specific steps for concrete pouring include:

[0065] Step S 810 The elevation section is divided into a first elevation section and a second elevation section. The first elevation section is poured in oblique layers, while the second elevation section is poured in horizontal layers.

[0066] Step S 820 The base plate is divided into 6 pouring areas, and the corresponding pouring equipment and pouring time are set to pour from the center outwards.

[0067] Step S 830The tamping is performed using an immersion vibrator, with the insertion points arranged in rows and columns.

[0068] Step S 840 Monitoring points are set at intervals on the steel lining vertical plates, and a total station is used to track and monitor the displacement and elevation of the steel lining.

[0069] Step S 850 Before the concrete initially sets, the surface concrete is re-vibrated, and after the re-vibration is completed, the concrete surface is finished.

[0070] Step S 860 The raft foundation concrete is cured using a heat-insulating and moisture-retaining curing method.

[0071] Furthermore, in step S 810 In the process, the first elevation section is divided into 17 layers, the second elevation section is divided into 6 layers, and the pouring time is divided into 5 stages, each stage lasting 8 hours.

[0072] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically reflected in the following aspects:

[0073] 1. This invention combines the structural characteristics of a circular raft foundation slab with four adjacent construction steps: installation of the inclined section steel lining → pouring of the inclined section concrete → installation of the steel support frame for the foundation slab steel lining → pouring of the foundation slab steel lining cushion layer. After the foundation slab reinforcement is tied, the installation of the inclined section steel lining and the installation of the steel support frame for the foundation slab steel lining continue. Finally, the inclined section concrete and the foundation slab steel lining cushion layer concrete are poured together with the foundation slab concrete in one go. Because the four consecutive steps are combined into one construction, it is summarized as a "four-in-one" construction method. This construction method avoids the large-area construction joint treatment work before the subsequent two concrete constructions after the first foundation slab concrete construction. At the same time, the use of the steel frame in the large volume concrete increases the internal structural rigidity, which plays an important role in offsetting temperature stress, reducing construction quality risks, and improving construction progress.

[0074] 2. A pioneering "center-blooming" pouring method was employed. The concave raft foundation was divided into six equally sized sector areas based on the central angle. Pouring equipment was arranged around the circumference of the foundation, with each sector's concrete laid out diagonally in layers from the center outwards. This achieved stress balance during the pouring of the surrounding formwork and steel lining, effectively controlling the deformation of the formwork and the inclined steel lining. In the construction of the concave raft foundation concrete, the "center-blooming" method, where concrete is laid out diagonally from the center outwards, was adopted, with pouring lasting 40 hours. The central area has a slab thickness of 1.14m, while the inclined circumferential area has a slab thickness of 3.75m. This center-blooming pouring method naturally adjusts the time interval between the central and inclined circumferential areas to approximately 24 hours, creating a time difference between the two areas. This allows the central area to be poured earlier and heat up earlier, while the central area begins its cooling phase during the heating phase of the circumferential area. This allows the concrete temperature stress to self-regulate and balance within the structure, reducing the impact of temperature stress and controlling cracking. This construction method is called the "deformation time history differential" technology. By utilizing the natural time difference in the construction organization, the temperature field distribution of the concrete pouring body is adjusted, effectively controlling the formation of cracks. Attached Figure Description

[0075] Figure 1 This is a schematic flowchart of the construction method for the concave core island raft base plate in an embodiment of the present invention;

[0076] Figure 2 Step S in the embodiment of the present invention 200 A flowchart;

[0077] Figure 3 Step S in the embodiment of the present invention 300 A flowchart;

[0078] Figure 4 Step S in the embodiment of the present invention 600 A flowchart;

[0079] Figure 5 Step S in the embodiment of the present invention 700 A flowchart;

[0080] Figure 6 This is a schematic diagram of the front view of the concave core island raft base plate in an embodiment of the present invention;

[0081] Figure 7 This is a schematic diagram of the raft foundation plate construction process in an embodiment of the present invention;

[0082] Figure 8 This is a schematic cross-sectional view of the bottom plate reinforcement arrangement in an embodiment of the present invention;

[0083] Figure 9 This is a schematic diagram of the central flowering pouring method in an embodiment of the present invention;

[0084] Figure 10 This is a schematic diagram of the installation structure of the inclined section bracket and steel lining in an embodiment of the present invention;

[0085] Figure 11 This is a diagram showing the arrangement of the support brackets for the supporting beams in an embodiment of the present invention;

[0086] Figure 12 This is a schematic diagram of the deformation time history adjustment region of the finite element model of the concave core island raft base plate (including bedrock) in an embodiment of the present invention;

[0087] Figure 13 This is a cross-sectional temperature analysis diagram of the nuclear island raft base in an embodiment of the present invention;

[0088] Figure 14 This is a temperature time history curve calculated by finite element method in an embodiment of the present invention;

[0089] Figure 15 This is a measured concrete adiabatic temperature rise curve in an embodiment of the present invention;

[0090] Figure 16 This is a finite element analysis diagram of concrete in an embodiment of the present invention;

[0091] Figure 17 This is a graph showing the measured ambient temperature in an embodiment of the present invention;

[0092] Figure 18 This is a schematic diagram of the finite element analysis of the steel tooling in an embodiment of the present invention;

[0093] Figure 19 This is a schematic diagram of the template tie rod structure arrangement in an embodiment of the present invention;

[0094] Figure 20 This is a layered diagram of the concrete pouring process for the base slab in an embodiment of the present invention.

[0095] Explanation of reference numerals in the attached figures:

[0096] 1-Raft foundation slab; 11-Lower raft foundation; 12-Outer ring raft foundation; 2-Sloping section support; 3-Sloping section steel lining; 4-Formwork; 5-Reinforcing cage. Detailed Implementation

[0097] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0098] Please refer to Figure 6 As shown, the concave core island raft base 1 of the UJA plant consists of a lower raft base 11 and an outer raft base 12, wherein:

[0099] Lower raft foundation 11: A circular reinforced concrete structure with a radius of 25.800m, a central area R = 19.535m, a central thickness of 2.114m within the radius, an elevation of -10.850m to -8.736m, an area of ​​1188㎡, and a concrete volume of 2511m³. 3 .

[0100] Outer ring raft foundation 12: The corridor radius is R = 19.535m - 25.8m, the foundation thickness is 3.35m, the elevation is -10.850m to -7.5m, the area is 640㎡, and the concrete volume is 2729m3 (the total concrete volume of the central area and the ring corridor is 5240m3). 3 A steel lining is designed and installed at the inclined section with a radius of R = 19.535m in the central area of ​​the raft foundation and within the central area.

[0101] In the existing technology, the construction of the central area of ​​the foundation slab of the UJA plant, the corridor foundation, the leveling layer of the raft foundation center and the I-beam (support beam) need to be completed in four stages, using a flat pouring method. This construction process has many disadvantages, such as complex procedures, long construction period and difficulty in quality control.

[0102] Please see Figure 1-20 As shown in the figure, an embodiment of the present invention provides a construction method for a concave core island raft base plate, the construction method comprising the following steps:

[0103] S 100 Measurement and positioning;

[0104] The central crosshair, the outer radius contour line, and the elevation control line of the raft base plate 1 were measured using a total station.

[0105] Specifically, in this step, a total station is used to mark out two circles with the center of the raft foundation slab 1 as the center and radii of R = 19.535m and R = 25.800m respectively. Simultaneously, the cross lines of the raft foundation and the elevation control lines of the foundation slab are drawn.

[0106] S 200 : Reinforcing cage 5 binding;

[0107] Based on the surveyed central cross line, radius outer contour line and raft base plate elevation control line, multi-layer structural steel bars are tied to form the internal steel cage module of the concave core island raft base plate, and crack-resistant steel mesh is added to the outer contour surface of the concave core island raft base plate 1.

[0108] Please see Figure 8As shown, in this specific step, multiple layers of structural steel bars are tied inside the raft foundation slab 1. The structural steel bars are connected by straight threaded sleeves, and crack-resistant steel mesh is added to the side surface of the raft foundation slab 1. The diameter of the crack-resistant steel mesh is φ8mm@200mm, which is used to control shrinkage cracks on the concrete surface.

[0109] S 300 : Installation of inclined section bracket 2;

[0110] Install inclined section bracket embedded parts on the internal steel cage module, prefabricate single inclined section brackets, and use diagonal braces and horizontal braces to hoist and connect the single inclined section brackets around the inner circle of the internal steel cage module to form a whole;

[0111] S 400 : Install inclined section steel lining 3;

[0112] Measure the positioning reference elevation and the raft base plate inner diameter baseline on the inclined section support 2, and mark the raft base plate outer diameter baseline and component position line on the outer ring support beam of the concave core island raft base plate.

[0113] The specific steps for installing the inclined section steel lining 3 are as follows:

[0114] Identify and mark the 0°, 90°, 180°, and 270° directional baselines and angle control lines;

[0115] Based on the released reference elevation and baseline, weld the steel profiles onto the inclined section support 2 in advance, and spot weld the radius limiting steel plates onto the support beams;

[0116] Based on the number of inclined section steel liners, determine the number of lifting points, and set traction ropes at both ends of the inclined section steel liner assembly. Set auxiliary lifting points at the bottom of the inclined section steel liner assembly and clamp the bottom of the inclined section steel liner 3 with steel plate clamps.

[0117] After all components are hoisted into place, adjust the weld gap and weld position of the inclined section steel lining assembly, and simultaneously adjust the verticality of the inclined section, then spot weld to fix it.

[0118] S 500 : Slanted section steel lining 3 anti-deformation reinforcement;

[0119] Weld a deformation-resistant reinforcement structure onto the auxiliary support of the inclined section steel lining 3;

[0120] S 600 Finite element analysis of concrete pouring simulation;

[0121] The construction design parameters for the raft foundation slab concrete were determined through finite element analysis and simulation calculations.

[0122] S 700 Template 4 installation;

[0123] Tool-type curved formwork is used on the outer facade of the base plate formwork 4. The panel is made of 18mm plywood with 16mm cones, and secondary and main keels are installed.

[0124] S 800 Concrete pouring;

[0125] The base slab is divided into several pouring areas using a diagonal layered and full-layered pouring method, and the pouring proceeds from the center outwards.

[0126] Please see Figure 10 As shown, in this specific step, taking into account the structural characteristics of the circular raft foundation slab, a pioneering "center-blooming" pouring method was adopted. That is, the concave raft foundation is divided into 6 fan-shaped areas of equal area according to the central angle. The pouring equipment is arranged around the circumference of the foundation, and the material is laid out in layers from the center outward in each area. This achieves the stress balance during the pouring process of the surrounding formwork and steel lining, and effectively controls the deformation of the formwork and the inclined section steel lining.

[0127] Please see Figure 1 As shown, in a specific embodiment of the present invention, the construction method of the concave core island raft base plate is as follows:

[0128] Measurement and positioning → Binding of bottom layer reinforcement → Installation of steel lining and I-beam support → Binding of surface layer reinforcement → Installation of inclined section steel lining → Formwork erection → Steel lining reinforcement → Concrete pouring → Curing.

[0129] Therefore, by optimizing the construction process, installing the I-beams and inclined section steel lining, structural layer and leveling layer together in advance, adding anti-crack steel mesh to the surface, using Midas finite element analysis software for analysis, and determining concrete performance and pouring method through simulation tests, the raft foundation adopts the "four-in-one" overall construction method for the bottom slab. That is, the construction of the lower bottom slab of the corridor, the horizontal steel lining, the lower I-beam keel and its leveling layer, the inclined section and the vertical steel lining of the corridor will not occupy the main construction period. The main critical path construction period can be effectively optimized, effectively reducing the main construction period and quality risks. Without additional resource input, the construction of the bottom slab and the ring corridor foundation can be completed in one construction organization. After the overall curing is completed, the construction conditions for the bottom slab steel lining and the corridor steel lining are immediately available, while controlling the quality risks between the processes.

[0130] This construction method avoids the need for extensive construction joint treatment before the subsequent two concrete pours after the first foundation slab concrete pour. At the same time, the use of steel frame in large-volume concrete increases the internal structural rigidity, which plays an important role in offsetting temperature stress, reducing construction quality risks, and improving construction progress.

[0131] Furthermore, in S200 The steps involved in tying the reinforcing cage include:

[0132] S 210 Reinforcement construction;

[0133] The main reinforcement consists of 6 layers of 40mm diameter HRB500E steel bars, with 4 layers at the bottom and 2 layers on the top surface.

[0134] Two layers of double-layered, bidirectional structural reinforcement are designed in the middle of the base slab;

[0135] After the bottom 1st, 2nd, 3rd and 4th layers of steel reinforcement are installed, install the steel reinforcement bracket, steel lining bracket and support beam bracket;

[0136] Perform the tying of the 5th and 6th layers of reinforcing bars;

[0137] S 220 An additional layer of anti-crack steel mesh is added to the side of the raft foundation slab to control shrinkage cracks on the concrete surface.

[0138] Please see Figure 8 , 9 As shown, in this specific step, the rebar cage binding process includes the construction of structural rebar and the construction of anti-cracking rebar mesh for shrinkage cracks on the concrete surface. The bottom slab contains a total of 8 layers of rebar, all of which are double-layered, bidirectional rebar. The main rebar uses 6 layers of 40mm diameter HRB500E rebar, with 4 layers at the bottom and 2 layers on the upper surface. Two layers of double-layered, bidirectional 25mm diameter structural rebar are designed in the middle of the bottom slab. Rebar connections are made using straight threaded sleeves, with a joint percentage not exceeding 50%. After the installation of the first, second, third, and fourth layers of rebar, the rebar supports, steel lining supports, and bottom slab I-beam (support beam) supports are installed, followed by the binding of the fifth and sixth layers of rebar.

[0139] After the structural reinforcement is completed, an anti-crack steel mesh with a diameter of φ8mm@200mm is added to the side of the raft foundation slab to control shrinkage cracks on the concrete surface.

[0140] Furthermore, in step S 300 The specific steps for installing the inclined section bracket 2 include:

[0141] Step S 310 Design of oblique section support 2;

[0142] A base plate steel lining support structure is set at every 7.5 degrees circumferentially. The base plate steel lining support structure includes I-shaped steel columns, tie angle steel, circumferential columns, connecting rods and support beams. The tie angle steel is set at the top of the I-shaped steel columns, and the connecting rod is set at the top of the circumferential columns.

[0143] Specifically, in this step, the inclined section support 2 is a base plate steel lining support structure with an inner diameter of 40 meters. It adopts a portal structure with a spacing of 1000mm and is equipped with scissor bracing. One frame is set every 7.5 degrees in the circumference, for a total of 48 frames. The I-shaped steel column is 3700mm high, and tie angle steel with material L50*5 is set at the top of the column.

[0144] In addition, scissor bracing is installed between the circumferential columns, and connecting rods are installed at the top of the columns. The bottom elevation of the bracket installation is -10.850m.

[0145] The support beam is made of I10 I-beams (material Q355B), channel steel (material Q235B), and φ20 steel bars (material HRB400).

[0146] Step S 320 : Install the embedded parts of the inclined section support;

[0147] Please see Figure 9 As shown, in this specific step, the installation position of the embedded part is measured and positioned in advance on the raft foundation slab membrane. A tower crane is used, and a lifting sling of 3t or more or a steel wire rope of φ10mm or more is selected to install the bracket embedded part at an elevation of -10.850m. The installation is carried out simultaneously when the waterproof membrane protective layer is poured. After the waterproofing and concrete curing at an elevation of -10.850m are completed, the inclined section bracket 2 is installed before the bottom reinforcement is tied.

[0148] Step S 330 : Prefabricate a single-piece inclined section bracket 2, and spot weld the bottom of the inclined section bracket 2 to the embedded part of the inclined section bracket;

[0149] Specifically, in this step, the inclined section bracket 2 is prefabricated into individual pieces and hoisted into place on site one by one. Starting from one end, the pieces are hoisted sequentially around the circle. After the individual inclined section bracket 2 is hoisted to the position, the bottom is temporarily spot-welded to the inclined section embedded part, and then the hook is released. The column is then adjusted to be vertical using a plumb line or laser vertical instrument before the bottom is fully welded to the embedded part.

[0150] Step S 340 Each inclined section bracket 2 is connected into a whole by diagonal bracing and horizontal bracing, and then spot-welded to the bottom steel bars for reinforcement.

[0151] In this specific step, the inclined section bracket 2 is installed and fixed by welding. After the bottom steel bars are installed, the inclined section bracket 2 is spot welded to the steel bars to strengthen it and improve the overall stability.

[0152] Furthermore, in S 400 The specific steps for adjusting the perpendicularity of the inclined section include:

[0153] Use a plumb bob and steel ruler to check the verticality deviation of the inclined section plate and determine the amount of deviation that needs to be adjusted.

[0154] A lead screw is welded between the back rib of the inclined section angle steel and the reinforcing bar;

[0155] The verticality of the inclined section is finely adjusted by rotation. After the verticality is adjusted, the inclined section is connected to the upright and fixed.

[0156] A 4.5m template ruler was used to detect the curvature, and a 1m template ruler was used to detect the local concavity and convexity.

[0157] Furthermore, in step S 400 and step S 500 The welding of the inclined section support 2 is carried out by semi-automatic gas shielded welding or manual electric arc welding, and the welding of the inclined section steel lining 3 is carried out by manual electric arc welding.

[0158] Furthermore, in step S 500 The specific steps for the deformation-resistant reinforcement of the inclined section steel lining 3 include:

[0159] Step S 510 A ring-shaped channel steel is installed at the top of the inclined section auxiliary support and welded to the support column;

[0160] Step S 520 Use steel bars with a diameter of φ25 or larger or L76*6 angle steel to connect the inclined back rib angle steel to the support.

[0161] like Figure 9 As shown, in this specific step, the upper layer is connected every other back rib, and the connection can be appropriately increased. The lower layer is connected to each back rib. If the gap between the steel bars on site allows, the connecting angle steel should be T-jointed with the back rib angle steel as much as possible to facilitate the welder's operation.

[0162] In addition, the welding parameters should refer to the corresponding welding process specifications. Angle steel or steel bars with a diameter of φ25 or larger should be lapped above or below the channel steel. Adjustments can be made according to the steel bars on site. Angle steel reinforcement is divided into lapping with the channel steel and T-jointing with the inclined section back rib. The total length of the weld for both welding methods should not be less than 50mm. Steel bars with a diameter of φ25 or larger should be fully welded on the contact surface, and the weld leg height should not be less than 4mm.

[0163] Furthermore, in step S 600 The specific steps of the finite element analysis for simulating concrete pouring include:

[0164] Step S 610 The raft foundation slab concrete uses B40 grade, W8 impermeability, F100 frost resistance, slump of 160±30mm, and a volumetric weight of not less than 2350kg / m³. 3 ;

[0165] Step S 620Finite element analysis was used to simulate and calculate the concrete, and crack-resistant steel mesh was added to the surface of the raft foundation to control the temperature before placement in the formwork.

[0166] Step S 630 The tooling platform and angle steel are established using beam elements, and the inclined section is established using plate elements. Finite element analysis is performed on the structural strength of the steel tooling.

[0167] Please see Figure 12 As shown, in this specific step, the raft foundation slab concrete uses B40, with W8 impermeability, F100 frost resistance, 160±30mm slump, and a volumetric weight of not less than 2350kg / m3.

[0168] Simulation tests were conducted to determine whether the design parameters related to the raft foundation slab concrete and concrete construction met the design requirements. The tests included the following technical indicators:

[0169] Serial Number Test content Design Indicators 1 Concrete flow ratio 1:8 2 Concrete pouring temperature ≤28° 3 Concrete slump 160±30mm 4 Initial setting time of concrete 4h 5 Final setting time of concrete 8h

[0170] The calculation software used is MIDAS. Based on the finite element analysis simulation results, in order to reduce or avoid cracks in the raft foundation structure, the main measures are to reduce the internal and external temperature difference, add anti-crack steel mesh to the surface of the raft foundation, improve the crack resistance of the concrete itself, and control the temperature of the concrete entering the formwork.

[0171] Furthermore, in step S 700 The specific process for installing the template is as follows:

[0172] Step S 710 Positioning and layout: Based on the drawings, lay out the positioning radius lines, angle axes, and control lines;

[0173] Step S 720 Four layers of high-strength tie rods are installed on average, and the high-strength tie rods are tied to the horizontal beams of the steel-lined steel bracket with a horizontal spacing of 600mm.

[0174] Step S 730 One end of the reinforcing bar connecting rod is tied to the horizontal beam of the channel steel of the steel frame and welded to the web of the channel steel.

[0175] Step S 740 The wire mesh is double-layered 8000 mesh. The secondary keel is made of 50*100mm timber with a horizontal spacing of 200mm. The main keel is made of 48mm steel pipe. The tie rods are made of 16mm high-strength tie rods + 12mm steel bars and tied to the bottom reinforcement or steel frame of the foundation with a horizontal spacing of 600mm.

[0176] Please see Figure 9As shown, in this specific step, the template is equipped with an average of 4 layers of high-strength tie rods. The tie rods are tied to the horizontal beams of the steel-lined steel bracket with a horizontal spacing of 600mm. The position of the tie rods can be adjusted appropriately when they are arranged on site to avoid the reinforcing bars, but the total number of tie rods should remain unchanged.

[0177] The inner threaded rod uses a 16mm diameter steel bar as the connecting rod between the inner threaded rod and the tie point. One end of the steel bar connecting rod is tied to the horizontal crossbeam of the channel steel of the steel frame and welded to the web of the channel steel. The weld height is 5mm and the weld length varies from 30 to 140mm depending on the stress of different parts.

[0178] A wire mesh formwork is erected on the side closest to the UJE factory building. The wire mesh is double-layered 8000 mesh. The secondary joists are 50*100mm timber with a horizontal spacing of 200mm. The main joists are 48mm steel pipes. The tie rods are 16mm high-strength tie rods + 12mm steel bars, which are tied to the bottom reinforcement bars or steel frame of the foundation with a horizontal spacing of 600mm.

[0179] Furthermore, in step S 800 The specific steps for concrete pouring include:

[0180] Step S 810 The elevation section is divided into a first elevation section and a second elevation section. The first elevation section is poured in oblique layers, while the second elevation section is poured in horizontal layers.

[0181] Step S 820 The base plate is divided into 6 pouring areas, and the corresponding pouring equipment and pouring time are set to pour from the center outwards.

[0182] Step S 830 The vibratory rods are used for compaction, with the insertion points arranged in rows and columns and the spacing between the insertion points being 38-42cm.

[0183] Step S 840 Monitoring points are set at intervals on the steel lining vertical plates, and a total station is used to track and monitor the displacement and elevation of the steel lining.

[0184] Step S 850 Before the concrete initially sets, the surface concrete is re-vibrated, and after the re-vibration is completed, the concrete surface is finished.

[0185] Step S 860 The raft foundation concrete is cured using a heat-insulating and moisture-retaining curing method.

[0186] Therefore, the raft foundation slab of a nuclear power plant is poured as a whole in one go, with a large vibration working surface. If the concrete sets too quickly after being poured into the formwork and is not vibrated in time, the two layers of concrete may not bond effectively, resulting in cold joints and affecting structural safety. The concrete in this embodiment has better vibratory performance, which can adapt to the situation of a large vibration working surface and a long interval between concrete pouring into the formwork and vibration, ensuring the vibration effect of the concrete, so that the upper and lower layers of concrete can bond effectively and ensure the quality of pouring.

[0187] Please see Figure 11 As shown, in this specific step, the raft foundation slab concrete is poured in a slanted layered and fully layered manner. The first four layers are poured with a thickness of 500mm, and the other layers are poured with a thickness of 250mm.

[0188] in:

[0189] The section from -10.85 to -8.736m elevation was constructed using inclined layered pouring, consisting of 17 layers in total.

[0190] The elevation range of -8.736 to -7.50m was constructed using a horizontal, fully layered pouring method, consisting of a total of 6 layers.

[0191] The base slab was divided into 6 pouring zones, using a total of 6 pouring machines, as shown in the table below:

[0192]

[0193] Based on the pouring time, the entire pouring process is divided into 5 stages, each lasting 8 hours.

[0194] Phase 1 consists of floors 1-6; Phase 2 consists of floors 7-9; Phase 3 consists of floors 10-12; Phase 4 consists of floors 13-17; and Phase 5 consists of floors 18-23.

[0195] Furthermore, in step S 810 In the process, the first elevation section is divided into 17 layers, the second elevation section is divided into 6 layers, and the pouring time is divided into 5 stages, each stage lasting 8 hours.

[0196] Specifically, in this step, the first to fourth stages are the pouring stages from -10.85 to 8.736m elevation. The concrete is poured in oblique layers. The volume of concrete in the first stage is relatively small. For the small area in the center of the No. 5 concrete pump that cannot be covered, the No. 6 concrete pump can assist in the placement. For the small area in the center of the No. 1 concrete placing machine that cannot be covered, the No. 2 concrete placing machine can assist in the placement.

[0197] When placing concrete, try to ensure that all placing machines operate synchronously. When there are differences in pumping speed, the placing machine with a faster pouring speed should increase its coverage area to ensure that the placing machines move in a consistent manner, so as to avoid inconsistent pouring speeds and the occurrence of under-vibration or excessive exposure time of freshly poured concrete.

[0198] When the fourth stage of pouring reaches the inclined section of the steel lining, since the inner side of the concrete is lower than the outer side, the pouring can be changed to be done on one side of the lower foundation slab of the corridor. As the pouring height increases, the concrete on one side of the lower foundation slab of the corridor will overflow into the inner side along the lower part of the steel lining. The overflowing concrete can be used to fill the inner part, avoiding the large amount of overflowing concrete when pouring the outer side after directly filling the inner concrete. The overflowing concrete is collected manually into buckets, and then transferred and poured into the outer ring foundation.

[0199] Therefore, please refer to Figure 12-17 As shown, in the construction of the concave raft foundation concrete, a "center-blooming" method was adopted, where concrete was laid diagonally from the center outwards towards the circumference, with pouring lasting 40 hours. The central slab thickness was 1.14m, while the thickness of the inclined circumferential slab was 3.75m. This center-blooming pouring method naturally adjusted the time interval between the central and inclined circumferential slabs to approximately 24 hours, creating a time difference between the two areas. This allowed the central area to be poured earlier and heat up earlier, while the central area began its cooling phase during the heating phase of the circumferential slab. This allowed the concrete temperature stress to self-regulate and balance within the structure, thereby reducing the impact of temperature stress and controlling cracking. This construction method, through the natural time difference in the construction organization, adjusted the temperature field distribution of the concrete pour, effectively controlling crack formation.

[0200] Unlike the traditional method of pouring concrete for nuclear island raft foundations in all oblique layers along one direction, this construction method innovates the pouring method for the lower raft foundation of the reactor building. It divides the lower raft foundation of the reactor building into 6 pouring areas of the same size and uses a pouring form that combines oblique layering and full layering, applying the "center-blooming" method.

[0201] Please see Figure 13-20 As shown, due to the heat conduction of the concrete hydration heat on the foundation of the nuclear island raft foundation, the temperature also changes accordingly. In order to reduce calculation errors, when establishing the finite element model of the nuclear island raft foundation, the foundation within a certain depth range below the raft foundation is also included in the finite element model. That is, the finite element model adopts the simultaneous modeling of the raft foundation and the bedrock. The thickness of the bedrock is taken as 5m, and the width is 3m wider than that of the nuclear island raft foundation.

[0202] During the modeling process, the impact of concrete pouring time on the transient temperature field simulation analysis was considered. Based on the "center-blooming" pouring stages, a finite element model of the nuclear island raft foundation was established according to five pouring stages. A finite element model of the nuclear island raft foundation (including bedrock, representing on-site conditions) was also included for each pouring stage. Please refer to [link to relevant documentation]. Figure 12 As shown.

[0203] While the invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A construction method for a concave core island raft base plate, characterized in that, Includes the following steps: S 100 Measurement and positioning; Use a total station to measure the central crosshair, the outer radius outline, and the elevation control line of the raft base plate; S 200 : Reinforcing cage binding; Based on the surveyed central cross lines, outer radius contour lines, and raft base plate elevation control lines, multi-layer structural steel bars are tied to form the internal steel cage module of the concave core island raft base plate. S 300 : Installation of inclined section brackets; An inclined section bracket embedded part is installed on the internal steel cage module. A single inclined section bracket is prefabricated and hoisted and connected around the inner circle of the internal steel cage module to form an integral whole using inclined braces and horizontal braces. S 400 Install inclined section steel lining; Measure the positioning reference elevation and the raft base plate inner diameter baseline on the inclined section support, and mark the raft base plate outer diameter baseline and component position line on the outer ring support beam of the raft base plate; The specific steps for installing the inclined section steel lining are as follows: Identify and mark the 0°, 90°, 180°, and 270° directional baselines and angle control lines; Referring to the released reference elevation and baseline, weld the steel profiles onto the inclined section support and spot weld the radius limiting steel plates onto the support beam in advance; Based on the number of inclined section steel liners, determine the number of lifting points, and set traction ropes at both ends of the inclined section steel liner assembly. Set auxiliary lifting points at the lower opening of the inclined section steel liner assembly, and clamp the bottom of the inclined section steel liner with steel plate clamps. After all components are hoisted into place, adjust the weld gap and weld position of the inclined section steel lining assembly, and simultaneously adjust the verticality of the inclined section, then fix it with spot welding. S 500 : Slanted section steel lining for deformation prevention and reinforcement; Weld anti-deformation reinforcement structures onto the auxiliary supports of the inclined section steel lining; S 600 Finite element analysis of concrete pouring simulation; The construction design parameters for the raft foundation slab concrete were determined through finite element analysis and simulation calculations. S 700 Template installation; Tool-type curved formwork is used on the outer facade of the base slab formwork, and secondary and main keels are installed; S 800 Concrete pouring; The base slab is divided into several pouring areas using a diagonal layered and full-layered pouring method, and the pouring proceeds from the center outwards.

2. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In S 200 The step of binding the steel cage includes: S 210 Reinforcement construction; A total of 6 layers of main reinforcement with a diameter of 40mm and HRB500E steel bars are used, and 2 layers of double-layer bidirectional structural reinforcement with a diameter of 25mm are designed in the middle of the bottom slab. After the bottom 1st, 2nd, 3rd and 4th layers of steel reinforcement are installed, install the steel reinforcement bracket, steel lining bracket and support beam bracket; Perform the reinforcement binding of the 5th and 6th layers; S 220 An additional layer of anti-crack steel mesh is added to the side of the raft foundation slab to control shrinkage cracks on the concrete surface.

3. The construction method of the concave core island raft base plate according to claim 2, characterized in that, In step S 300 The specific steps for installing the inclined section bracket include: Step S 310 : Inclined section support design; A base plate steel lining support structure is set at every 7.5 degrees circumferentially. The base plate steel lining support structure includes I-shaped steel columns, tie angle steel, circumferential columns, connecting rods and support beams. The tie angle steel is set at the top of the I-shaped steel columns, and the connecting rod is set at the top of the circumferential columns. Step S 320 : Install the embedded parts of the inclined section support; Step S 330 Prefabricate single-piece inclined section brackets and spot weld the bottom of the inclined section brackets to the embedded parts of the inclined section brackets. Step S 340 Each inclined section bracket is connected into a whole by diagonal bracing and horizontal bracing, and then spot-welded to the bottom steel bars for reinforcement.

4. The construction method of the concave core island raft base plate according to claim 3, characterized in that, In S 400 The specific steps for adjusting the perpendicularity of the inclined section include: Use a plumb bob and steel ruler to check the verticality deviation of the inclined section plate and determine the amount of deviation that needs to be adjusted. A lead screw is welded between the back rib of the inclined section angle steel and the reinforcing bar; The verticality of the inclined section is finely adjusted by rotation. After the verticality is adjusted, the inclined section is connected and fixed to the upright. A 4.5m template ruler was used to detect the curvature, and a 1m template ruler was used to detect the local concavity and convexity.

5. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In step S 400 and step S 500 The welding of the inclined section bracket is carried out using semi-automatic gas shielded welding or manual electric arc welding, and the welding of the inclined section steel lining is carried out using manual electric arc welding.

6. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In step S 500 The specific steps for reinforcing the inclined section steel lining against deformation include: Step S 510 A ring-shaped channel steel is installed at the top of the inclined section auxiliary support and welded to the support column; Step S 520 Use steel bars with a diameter of φ25 or larger or L76*6 angle steel to connect the back rib angle steel of the inclined section to the inclined section support.

7. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In step S 600 The specific steps of the finite element analysis for simulating concrete pouring include: Step S 610 The raft foundation slab concrete uses B40 grade, W8 impermeability, F100 frost resistance, slump of 160±30mm, and a volumetric weight of not less than 2350kg / m³. 3 ; Step S 620 Finite element analysis was used to simulate and calculate the concrete, and crack-resistant steel mesh was added to the surface of the raft foundation to control the temperature before placement in the formwork. Step S 630 The tooling platform and angle steel are established using beam elements, and the inclined section is established using plate elements. Finite element analysis is performed on the structural strength of the steel tooling.

8. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In step S 700 The specific process for installing the template is as follows: Step S 710 Positioning and layout: Based on the drawings, lay out the positioning radius lines, angle axes, and reference control lines; Step S 720 Four layers of high-strength tie rods are installed on average, and the high-strength tie rods are tied to the horizontal beams of the steel-lined steel bracket. Step S 730 One end of the reinforcing bar connecting rod is tied to the horizontal beam of the channel steel of the steel frame and welded to the web of the channel steel. Step S 740 The wire mesh is double-layered 8000 mesh. The secondary keel is made of 50*100mm timber with a horizontal spacing of 200mm. The main keel is made of 48mm steel pipe. The tie rod is made of 16mm high-strength tie rod + 12mm steel bar and tied to the bottom reinforcement or steel frame of the foundation.

9. The construction method of the concave core island raft base plate according to claim 1, characterized in that, In step S 800 The specific steps for concrete pouring include: Step S 810 The elevation section is divided into a first elevation section and a second elevation section. The first elevation section is poured in oblique layers, while the second elevation section is poured in horizontal layers. Step S 820 The base plate is divided into 6 pouring areas, and the corresponding pouring equipment and pouring time are set to pour from the center outwards. Step S 830 The tamping is performed using an immersion vibrator, with the insertion points arranged in rows and columns. Step S 840 Monitoring points are set at intervals on the steel lining vertical plates, and a total station is used to track and monitor the displacement and elevation of the steel lining. Step S 850 Before the concrete initially sets, the surface concrete is re-vibrated, and after the re-vibration is completed, the concrete surface is finished. Step S 860 The raft foundation concrete is cured using a heat-insulating and moisture-retaining curing method.

10. The construction method of the concave core island raft base plate according to claim 9, characterized in that, In step S 810 In the process, the first elevation section is divided into 17 layers, the second elevation section is divided into 6 layers, and the pouring time is divided into 5 stages, each stage lasting 8 hours.

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