Construction method suitable for ultrahigh frame concrete structure with crane beam bracket

Abstract

The invention discloses a construction method suitable for an ultrahigh frame concrete structure with a crane beam bracket. Comprising the following steps of: compiling a scheme and drawing a drawing, measuring a vertical rod positioning line, erecting a full space support frame, paving a beam plate structure template, mounting frame column steel bars, erecting and pouring first-step frame column concrete to the elevation of an upper opening of a bracket, erecting and pouring second-step frame column concrete to the elevation of a beam bottom, mounting the beam plate steel bars, and checking and accepting. Perfecting a template system, checking and accepting the support frame, pouring beam and slab concrete, maintaining, and removing the full support frame. According to the construction method, the full framing can be shared, the beam plate formwork is laid and serves as an operation platform for frame column construction, the frame column formwork is fixed, and therefore synchronous construction of a plurality of crane beams is achieved; cost for erecting an operation platform is greatly saved, and the construction period is remarkably shortened; fixing measures adopted for erecting each column formwork can be shared with the full framing, and the cost of the fixing measures is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the field of construction, and in particular to a construction method for an ultra-high frame concrete structure with a crane beam corbel. Background Art

[0002] In the construction of industrial plants, a common structure is one in which super-high concrete columns are provided with crane beam brackets. The crane beam bracket structure is set at about 2 / 3 of the height of the super-high frame column for use in the later laying of crane rails.

[0003] The traditional construction method of crane beam corbels is: set up the frame column construction route diagram (construction in sequence), then set up the operating platform → carry out the first reinforcement binding, the first formwork installation, the first concrete pouring → carry out the second reinforcement binding, the second formwork installation, the second concrete pouring → remove the operating platform and formwork → complete the construction of all crane beam corbels in sequence → carry out beam and slab support erection, formwork installation, beam and slab reinforcement installation acceptance → concrete pouring and maintenance → remove the beam and slab support frame. This construction method has the following defects: (1) It relies on manual positioning and fixing of formwork, which makes it difficult to control verticality and axis, and the repeated erection and dismantling of the operating platform leads to extended construction period and increased costs; (2) Each frame column requires a separate operating platform, and the operating platform needs to be dismantled when the upper beam and slab structure formwork is erected. The more frame columns there are, the greater the cost of erecting the operating platform and the longer the construction period; (3) Corresponding fixing measures must be taken for each column formwork. The more frame columns there are, the greater the cost of the measures; (4) It is difficult to ensure the axis position and verticality of the frame columns when they are constructed separately, because the axis may shift and the column may tilt during the concrete pouring process, resulting in deviation in verticality.

[0004] To this end, Chinese patent CN108678411A proposes a method for replacing factory joists without dismantling them, improving upon the traditional method. The method includes the following steps: 1) measuring the span of the new columns required for the factory, calculating the required strength, drawing the parts drawings for the new joists and columns, and then fabricating them; 2) fixing temporary columns to the pistons of multiple jacks via flanges. Each jack is fixed to the crane beam bracket on the same side of the factory, and each temporary column is supported on the original joist on the same side. Although this patent proposes a solution for replacing joists without dismantling them, achieving in-situ replacement through temporary columns and jack supports, it relies on the bracket structure to fix the temporary support, limiting its applicability. Although the existing Chinese patent CN108678411A, a method for replacing beams and columns in a factory building without dismantling, has been continuously optimized, the following core problems still exist: (1) Low construction efficiency: The traditional method requires the establishment of an operating platform for each column, and the casting is carried out in batches, resulting in a long construction period; although the patented technology reduces the demolition process, the installation of temporary supports is complicated and the problem of repeated platform occupation is not solved. (2) Quality control is difficult: Manual formwork fixing and casting can easily cause axis deviation, and the patented technology does not clearly mention the verticality calibration mechanism, which may increase the risk of structural deviation; (3) Insufficient economic efficiency: The traditional method has high costs (such as formwork fixing and platform erection and dismantling), while the patented technology requires additional equipment investment (jacks, temporary columns), and the overall cost is still high. Summary of the Invention

[0005] The present invention proposes a construction method for an ultra-high frame concrete structure with a crane beam corbel, which can effectively solve the problems mentioned in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A construction method for an ultra-high frame concrete structure with crane beam brackets comprises the following steps: (1) Plan preparation and blueprint drawing.

[0007] (2) Measure and set up the pole positioning line: establish a three-level measurement control system to control the projection error to ≤±3mm.

[0008] The three-level survey control system includes ground control piles, corbel surface projection and total station verification.

[0009] (3) Erection of full-floor support frame: including arrangement of vertical poles, connection of horizontal poles, and connection of horizontal and vertical scissor braces; among them, the vertical poles in the positive projection area of ​​the corbel are increased, and double vertical poles are set under the cantilevered end of the corbel and the bearing capacity is verified.

[0010] The arrangement of vertical poles shall meet the following requirements: the vertical pole spacing in the orthographic projection area of ​​the corbel shall be increased to ≤0.6m×0.6m, and the distance between the center of the vertical pole and the outer edge of the corbel shall be ≤150mm; within the range of the crane beam support, the longitudinal spacing of the vertical poles shall be ≤0.8m, and the transverse spacing shall be ≤0.9m; an adjustable support shall be provided on the top of the vertical pole to tighten the bottom of the beam; a wooden pad with a thickness of ≥50mm and an area of ​​≥0.15m² shall be laid on the bottom of the vertical pole; around the steel column, the vertical poles shall be arranged in a circumferential manner with a spacing of ≤0.9m, and shall be rigidly connected to the column body through fastener-type clamps; the double vertical poles provided below the cantilevered end of the corbel shall have a bearing capacity calculated from experience of ≥1.5 times the design load; the vertical poles provided around the steel column shall be bidirectional diagonal braces with an angle of 45°±5°.

[0011] The horizontal rod connection includes: setting the horizontal rod elevation line; erecting in the order of vertical first and then horizontal; installing the diagonal rod simultaneously in the corbel area; checking the fastener tightening torque layer by layer; re-tightening the top free end; marking the fasteners that have been accepted as qualified with red marks; adding a short horizontal rod on the inclined surface of the corbel, the length of the short horizontal rod is the corbel width plus 200mm, connected to the vertical rod through double fasteners, and the oblique horizontal rod extends to the adjacent vertical rod to form a rigid multi-directional force-bearing unit; "cross-shaped" hoop rods are used for reinforcement at the crossing of the steel column, ≤300mm from the column surface.

[0012] The horizontal and vertical scissors brace connections include: each scissors brace intersection is fixed with no less than 3 rotating fasteners; the scissors brace diagonal rods are fixed with rotating fasteners, and the distance from the intersection center to the main node is ≤150mm; the top of the vertical scissors brace extends to the top horizontal rod; the horizontal scissors brace is densely set within 500mm above and below the top surface of the corbel; 45° diagonal braces are installed simultaneously in the corbel area; each node is locked with triple fasteners; a torque wrench is used to perform 100% fastener tightening torque testing; and fasteners that have passed the acceptance inspection are marked in red.

[0013] (4) Laying the beam and slab structure formwork; The corbel bevel formwork uses a δ=6mm custom steel formwork and the back rib uses No. 10 channel steel @300mm.

[0014] (5) Install frame column reinforcement; Before installing the formwork in step (4), complete the column reinforcement binding, bend the main reinforcement of the bracket bevel at 45° and anchor it, and weld the studs @200mm on the steel column flange.

[0015] (6) Erect and pour the first step frame column concrete to the top elevation of the corbel.

[0016] (7) Erect and pour the second step frame column concrete to the beam bottom elevation.

[0017] (8) Installation and acceptance of beam and slab reinforcement.

[0018] The three-dimensional coordinate deviation of the embedded bolts of the crane beam is ≤2mm; the coverage rate of the additional reinforcement in the bracket area is 100%; (9) Improvement of formwork system and acceptance of support frame.

[0019] (10) Concrete pouring and curing of beam and slab: Use inclined layered pouring, with the interval time between the upper and lower layers ≤ the initial setting time of the concrete; the beam and slab are poured in two times, the first pouring to the reserved height at the bottom of the beam at the root of the corbel and installing the pre-buried bolts of the crane beam, and the second micro-expansion concrete pouring after an interval of ≥48h; the initial setting time of the concrete ≤6h.

[0020] (11) Removal of the full-floor support frame: After the concrete strength of the beam and slab reaches ≥ 80% of the design value, the support frame will be removed in an orderly manner, with the corbel area being the last to be removed.

[0021] Preferably, the theodolite is replaced by a combination of a total station and a BIM layout robot.

[0022] Advantages compared to existing technologies: This method achieves the following functions: First, the full-floor support can be shared, the beam and slab formwork can be laid, and it can be used as an operating platform for the construction of frame columns and the frame column formwork can be fixed, thereby realizing the simultaneous construction of multiple (or all) crane beams; a lot of costs for setting up the operating platform can be saved, and the construction period can be significantly shortened.

[0023] Secondly, the fixing measures adopted for the erection of each column formwork can be shared with the full-floor bracket, and the cost of fixing measures is significantly reduced.

[0024] Third, the axial position and verticality of the beam and slab formwork and synchronously constructed frame columns are effectively guaranteed with small errors.

[0025] Fourthly, the layered anti-floating system uses ground anchors and steel formwork back ribs to control the deformation of the cantilever structure.

[0026] Fifth, the total station + BIM layout robot achieves millimeter-level positioning of embedded parts.

[0027] Sixth, studs + perforated steel bars enhance the shear resistance of the steel-concrete interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the positioning line of the survey pole in the present invention; Figure 2 This is a schematic diagram of the arrangement of the upright poles of the present invention; Figure 3 This is a schematic diagram of the horizontal rod connection of the present invention; Figure 4 This is a schematic diagram of the connection between the horizontal and vertical scissors braces of the present invention; Figure 5 A schematic diagram of a beam-slab structure template is provided for the present invention; Figure 6 This is a schematic diagram of the column reinforcement installation of the present invention; Figure 7 This is a schematic diagram of the first concrete pouring of the present invention; Figure 8 This is a schematic diagram of the second concrete pouring of the present invention; Figure 9 This is a schematic diagram of the comprehensive synchronous construction of the frame columns of the present invention.

[0029] In the figure: 101. Frame column, 102. Corbel, 201. Vertical bar, 202. Horizontal bar, 301. Scissor brace, 401. Beam-slab structural formwork, 501. Column reinforcement area formwork installation, 601. First concrete pouring area, 602. Second formwork installation, concrete pouring area. DETAILED DESCRIPTION

[0030] Example 1, refer to the attached Figure 1-9 A construction method for a super-high frame concrete structure with a crane beam bracket includes the following steps: 1. Plan preparation and drawing: Determine the full-floor support frame system, erection height, vertical pole 201 spacing, horizontal rod setting, and scissor brace 301 setting to match the requirements of the operating protective frame around the frame column 101.

[0031] Technical parameter requirements for the full-floor support system: ‌1. System confirmation‌: Adopt fastener-type steel pipe full-floor support frame system; ‌2. Erection height‌: Determined according to the floor height, not exceeding 8m (expert verification is required if exceeding); 3. Layout of vertical poles 201: Standard spacing ≤ 1.2m × 1.2m; Spacing in the reinforced area around frame columns 101 ≤ 0.9m × 0.9m; ‌4. Horizontal bars‌: step distance ≤ 1.5m; distance from top horizontal bar 202 to formwork support point ≤ 0.5m; ‌5. Scissor brace 301 setting‌: Set continuously in the vertical and horizontal directions around the periphery and in the middle, with an angle of 45°-60° to the ground; ‌6. Protective frame matching‌: A 1.2m high operating protective frame is simultaneously set up around the frame column 101, and the vertical pole 201 is reliably connected to the support frame.

[0032] 2. Measure the pole positioning line: Standardized construction process for measuring the positioning line of the bracket 102 with the crane beam and setting up the pole 201: 1. Axis control pile setting: According to the plant control network or the end points of the column axis, the crane beam center line (track center line) control piles are measured and set on the ground as reference measurement points.

[0033] 2. Bull leg surface projection measurement: Pop out the cross positioning line on the corbel surface: Use the theodolite to project the center line of the ground control pile to the corbel surface of each column; mark with ink lines, and the projection error must be ≤±3mm.

[0034] 3. Three-dimensional positioning control: Plane positioning: The center lines of the two end faces and the top surface of the crane beam pop out and are aligned with the ink lines on the corbel surface during installation.

[0035] Elevation control: Measure the design elevation point along the column body according to the ±0 elevation line and adjust the flatness of the corbel surface.

[0036] 4. Composite verification: After installation, you need to check: Span deviation ≤ ±5mm (center line spacing measured with a steel ruler); The elevation deviation of the beam surface is ≤±3mm (checked with a level).

[0037] The total station is used to check the position of the embedded bolts of the steel column, and the deviation is ≤2mm.

[0038] Pop-up poles are set to locate the grid lines (spacing error ≤ 10mm).

[0039] That is, a three-level measurement system consisting of ground control piles, corbel surface projection and total station verification is used to control the projection error to ≤±3mm.

[0040] 3. Set up the full-hall support frame: 1. Pole arrangement: In the orthographic projection area of ​​the corbel 102, the spacing between the vertical poles 201 is ≤0.6m×0.6m, and the distance between the center of the vertical pole 201 and the outer edge of the corbel 102 is ≤150mm.

[0041] Within the crane beam support range, vertical spacing of vertical poles 201 is ≤ 0.8m, and horizontal spacing is ≤ 0.9m. Adjustable U-shaped supports are installed at the top of vertical poles 201 to tighten the bottom of the beam. A 50mm thick wooden backing plate with an area of ​​≥ 0.15m² is laid at the bottom of vertical poles 201.

[0042] Around the steel column, the vertical poles 201 are arranged at a spacing of ≤0.9m in a circular direction and are rigidly connected to the column body with a fastener-type clamp.

[0043] Add double vertical poles below the cantilevered end of corbel 102 (bearing capacity verification ≥ 1.5 times the design value) The vertical poles 201 around the steel column are provided with two-way diagonal braces (angle 45°±5°).

[0044] 2. Horizontal rod connection: (1) Mark out the horizontal bar elevation line.

[0045] (2) Build vertically first and then horizontally.

[0046] (3) Install the diagonal tie rods simultaneously in the corbel area.

[0047] (4) Check the tightening torque layer by layer.

[0048] (5) Tighten the top free end again.

[0049] (6) Mark the inspected fasteners with red paint (i.e. mark the fasteners that have passed the acceptance inspection with red paint).

[0050] Among them: the longitudinal horizontal bars 202 are connected by butt fasteners, the joints are staggered ≥500mm, and the distance from the main node is ≤1 / 3 of the span; the transverse horizontal bars 202 are fixed by right-angle fasteners, and the ends extend out of the vertical bars 201 by not less than 100mm and not more than 150mm.

[0051] (7) Add a short horizontal rod on the inclined surface of the corbel 102. The length of the short horizontal rod is equal to the width of the corbel 102 + 200 mm. The short horizontal rod is connected to the vertical rod 201 with a double fastener. The oblique horizontal rod extends to the adjacent vertical rod 201, forming a rigid triangular force transmission unit with the adjacent vertical rod 201. The steel column crossing point is reinforced with a "cross" shaped hoop rod (≤300 mm from the column surface).

[0052] 3. Horizontal and vertical scissors brace connection: (1) Each intersection of the scissors support 301 is fixed with no less than 3 rotating fasteners.

[0053] (2) The diagonal rods of the scissors support 301 are fixed with rotating fasteners, and the distance from the center of the intersection to the main node is ≤150mm.

[0054] (3) The top of the vertical scissors support 301 extends to the top horizontal rod 202.

[0055] (4) The horizontal scissors support 301 is densely arranged within a range of 500 mm above and below the top surface of the corbel 102.

[0056] (5) Install 45° diagonal braces simultaneously in the corbel area.

[0057] (6) Triple fastener locking at each node.

[0058] (7) 100% inspection of torque wrenches.

[0059] (8) Mark the inspected fasteners with red paint (i.e. mark the fasteners that have passed the acceptance inspection with red paint).

[0060] 4. Laying beam and slab structure formwork 401: The inclined surface of the corbel 102 adopts a customized steel mold with δ=6mm, and the back rib uses No. 10 channel steel @300mm.

[0061] Anti-floating ground anchors (Φ20 steel bars @ 800mm, pull-out force ≥ 15kN) are installed and implanted at an angle of 45°-60°.

[0062] The anti-floating anchors are located on both sides of the inclined projection line of the corbel 102, with the first row of anchors set ≤300mm away from the root of the corbel 102, and the subsequent rows are staggered at 800mm intervals; The ground anchor is implanted into the lower layer of concrete that has been poured to a depth of ≥800mm, with the exposed end 50mm higher than the formwork surface, and is welded to the back rib of the formwork through a Φ12 anti-floating tie rod (weld length ≥80mm).

[0063] 5. Install frame column reinforcement: Complete the reinforcement binding of frame column 101 before installing the formwork in step 4; The main reinforcement of the inclined surface of the corbel 102 is bent at 45° and anchored (the horizontal section is ≥ 0.4LaE, and the total length is ≥ LaE); Welded studs @200mm on steel column flange (shear connector).

[0064] 6. Erect and pour the first step frame column concrete to the top elevation of the corbel: 1. Set up the first step frame column template and install it to the upper elevation of the corbel 102. That is, the column reinforcement area installation template 501 is installed to the upper elevation of the corbel 102.

[0065] 2. Pour the first step frame column concrete to the upper elevation of the corbel 102.

[0066] 7. Erect and pour the second step frame column concrete to the beam bottom elevation; 1. Set up the second-step frame column formwork and install it to the top elevation of the beam and slab.

[0067] 2. Pour the second step frame column concrete to the bottom of the beam.

[0068] 3. The frame column formwork is removed and consolidated with the full-floor support system.

[0069] 8. Installation of beam and slab reinforcement and acceptance: The three-dimensional coordinate deviation of the embedded bolts of the crane beam is ≤2mm (verified by total station); the coverage rate of additional reinforcement in the corbel area is 100% (detected by scanner).

[0070] IX. Formwork system improvement and support frame acceptance: The verticality of the upright pole 201 in the corbel area is ≤H / 500 and ≤30mm; the height of the free end of the U support is ≤300mm.

[0071] 10. Pouring and curing of beam and slab concrete: 1. First pouring: 50mm from the root of corbel 102 to the bottom of the beam; that is, a 50mm micro-expansion concrete reinforcement strip is reserved at the root of corbel 102 to compensate for shrinkage stress. The expansion rate is limited to ≥ 0.025% (GB 50119). The first concrete pouring area 601 is shown in the attached Figure 7 .

[0072] 2. Install the embedded bolts of the crane beam.

[0073] 3. The interval time after the first pouring is ≥48h, and then the second pouring is carried out.

[0074] Second pouring: Micro-expansion concrete is formed as a whole; Second formwork installation, concrete pouring area 602 see attached Figure 8 During the pouring process, the slope is poured in layers (thickness ≤ 500mm); the vibrator should avoid embedded parts by ≥ 100mm.

[0075] 11. Removal of the full-hall support frame: After the beam and slab concrete strength reaches ≥80% of the design value (test blocks under the same conditions), the full-height support frames will be removed in an orderly manner, with the corbel area removed last (symmetrical unloading sequence). When removing the support frames, the corbel area will be unloaded in stages using hydraulic jacks (controlling the settlement difference to ≤3mm).

[0076] This construction method complies with the safety requirements for special-shaped structure support systems in the "Technical Specifications for Safety of High-Altitude Operations in Construction" (JGJ80-2016), ensuring that the installation accuracy of the crane beam is ≤3mm.

[0077] Example 2: Based on Example 1, the theodolite is replaced by a combination of a total station and a BIM layout robot to achieve millimeter-level positioning of embedded parts.

Claims

1. A construction method for super-high frame concrete structure with crane beam brackets, characterized in that: The following steps are involved: (1) Plan preparation and blueprint drawing; (2) Measure and set up the pole positioning line: establish a three-level measurement control system to control the point error to ≤±3mm; (3) Erection of the full-floor support frame: including the arrangement of vertical poles, connection of horizontal poles, and connection of horizontal and vertical scissor braces; the vertical poles in the positive projection area of ​​the corbel are increased, and double vertical poles are set under the cantilevered end of the corbel and the bearing capacity is verified; (4) Laying the beam and slab structure formwork; (5) Install frame column reinforcement; (6) Erect and pour the first step frame column concrete to the top elevation of the corbel; (7) Erection and pouring of the second step frame column concrete to the beam bottom elevation; (8) Installation and acceptance of beam and slab reinforcement; (9) Improvement of formwork system and acceptance of support frame; (10) Concrete pouring and curing of beam and slab: Use inclined layered pouring, with the interval time between the upper and lower layers ≤ the initial setting time of the concrete; the beam and slab are poured in two times, the first pouring to the reserved height of the beam bottom at the root of the corbel and installing the crane beam embedded bolts, and the second micro-expansion concrete pouring after a rest of ≥48h; (11) Removal of the full-floor support frame: After the concrete strength of the beam and slab reaches ≥ 80% of the design value, the support frame will be removed in an orderly manner, with the corbel area being the last to be removed.

2. The construction method according to claim 1, characterized in that: The arrangement of the vertical poles in the step (3) satisfies the following requirements: the vertical pole spacing in the corbel projection area is increased to ≤0.6m×0.6m, and the distance between the center of the vertical pole and the outer edge of the corbel is ≤150mm; within the range of the crane beam support, the vertical pole longitudinal spacing is ≤0.8m, and the horizontal spacing is ≤0.9m; an adjustable support is provided on the top of the vertical pole to tighten the bottom of the beam; a wooden pad with a thickness of ≥50mm and an area of ​​≥0.15m² is laid on the bottom of the vertical pole; the vertical poles are arranged in a circumferential direction around the steel column at a spacing of ≤0.9m and are rigidly connected to the column body through a fastener-type clamp; the double vertical poles arranged below the cantilevered end of the corbel have a bearing capacity calculated from experience of ≥1.5 times the design load; the vertical poles around the steel column are provided with bidirectional diagonal braces with an angle of 45°±5°.

3. The construction method according to claim 1, characterized in that: The horizontal rod connection in step (3) includes: setting the horizontal rod elevation line; erecting the horizontal rod in the order of vertical first and then horizontal; synchronously installing the diagonal rod in the corbel area; checking the fastener tightening torque layer by layer; re-tightening the top free end; marking the fasteners that have been accepted as qualified with red marks; adding a short horizontal rod on the inclined surface of the corbel, the length of the short horizontal rod being the corbel width plus 200mm, connecting it to the vertical rod through double fasteners, and extending the diagonal horizontal rod to the adjacent vertical rod to form a rigid multi-directional force-bearing unit; using "well-shaped" hoop rods for reinforcement at the steel column crossing point, with a distance of ≤300mm from the column surface.

4. The construction method according to claim 1, characterized in that: The horizontal and vertical scissors brace connections in step (3) include: each scissors brace intersection is fixed with no less than 3 rotating fasteners; the scissors brace diagonal rods are fixed with rotating fasteners, and the distance from the intersection center to the main node is ≤150mm; the top of the vertical scissors brace extends to the top horizontal rod; the horizontal scissors brace is densely arranged within 500mm above and below the top surface of the corbel; 45° diagonal braces are installed simultaneously in the corbel area; each node is locked with triple fasteners; 100% fastener tightening torque is tested using a torque wrench; and qualified fasteners are marked.

5. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 1, characterized in that: Step (4) In laying the beam-slab structure formwork, the corbel slope formwork adopts a δ=6mm customized steel formwork and the back rib adopts No. 10 channel steel @300mm.

6. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 1, characterized in that: Step (5) Install the frame column reinforcement: Complete the column reinforcement binding before installing the formwork in step (4), bend the main reinforcement of the bracket bevel at 45° and anchor it, and weld the studs @200mm on the steel column flange.

7. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 1, characterized in that: In step (10), the three-dimensional coordinate deviation of the embedded bolts of the crane beam is ≤2mm; the coverage rate of the additional reinforcement in the corbel area is 100%.

8. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 1, characterized in that: Initial setting time of concrete ≤6h.

9. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 1, characterized in that: The three-level survey control system includes ground control piles, corbel surface projection and total station verification.

10. The construction method for a super-high frame concrete structure with crane beam brackets according to claim 6, characterized in that: The 45° bend anchorage of the main reinforcement of the corbel slope requires the horizontal section to be ≥0.4LaE and the total length to be ≥LaE.

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