A nested damper buckling-restrained brace

Abstract

The present invention relates to the technical field of building components, and specifically relates to a nested damper buckling-restrained brace, which includes an outer brace assembly, an inner brace assembly, and a switching connection assembly; the outer brace assembly and the inner brace assembly form a sliding connection structure through the frictional contact between a first friction cylinder and a second friction cylinder. Through the hierarchical triggering mechanism of friction energy dissipation and rigid force transmission, dynamic seal protection, state visualization detection, and modular design, the present invention realizes the integrated improvement of seismic performance of recoverable energy dissipation in minor earthquakes, precise rigid protection in major earthquakes, and rapid post-earthquake maintenance, effectively solving the core technical problems of easy fatigue in minor earthquakes and easy failure in major earthquakes of traditional buckling braces.

Description

Technical Field

[0001] The present invention relates to the technical field of building components, and specifically to a nested damper buckling-restrained brace. Background Art

[0002] A buckling-restrained brace is a form of steel brace, mainly used to improve the lateral stiffness and energy dissipation capacity of a structure. Especially under seismic action, it can effectively absorb and dissipate seismic energy to protect the main structure from damage. Existing buckling-restrained braces usually consist of the following extrusion structures: 1. Core energy dissipation section: made of low-yield-point steel, responsible for dissipating seismic energy through plastic deformation; 2. Constraint sleeve: wrapped around the core material, usually composed of a steel sleeve or a concrete-filled sleeve to prevent the core material from buckling under compression; 3. Unbonded layer: filled with unbonded materials (such as rubber, mortar) between the core material and the constraint sleeve, enabling the core material to freely expand and contract during the stress deformation process to avoid local stress concentration caused by friction or improper constraint between the core material and the constraint sleeve.

[0003] In the prior art, traditional core-material buckling-restrained braces rely on the plastic deformation of the core material to absorb energy. Although they can cope with large earthquake conditions, they are prone to fatigue damage due to repeated plastic deformation under small earthquake actions with high frequencies, and their service life is significantly limited. Friction-type buckling-restrained braces dissipate energy through interface friction to replace the deformation of the core material. Although they can improve the cyclic use performance under small earthquake conditions, their energy dissipation capacity drops suddenly due to excessive slip or overheating of the friction interface during large earthquakes, and there is a risk of premature failure. Neither of the two types of structures can balance the durability under small earthquakes and the reliability under large earthquakes, restricting the overall improvement of seismic performance. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a nested damper buckling-restrained brace to solve the problem that existing core-material and friction-type buckling-restrained braces, which rely on plastic deformation energy dissipation (prone to fatigue under small earthquakes) and interface friction energy dissipation (prone to failure under large earthquakes) respectively, cannot balance the durability under small earthquakes and the reliability under large earthquakes, resulting in limited seismic performance as described in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A nested damper buckling-restrained brace, which includes: an outer support component, an inner support component, and a switching connection component; the outer support component and the inner support component form a sliding connection structure through the frictional contact between a first friction cylinder and a second friction cylinder for absorbing small earthquake energy; the switching connection component includes a shear pin, a connection component, and an adjustable outer clamping plate. The shear pin passes through a short sleeve and a short inserted tube to form a breakable connection. The adjustable outer clamping plate is triggered to move when the shear pin breaks during a large earthquake, so that the main core rod and the end core rod form a rigid connection to absorb large earthquake energy; a sealing ring and an inner cavity sealing structure are provided between the outer support component and the inner support component.

[0007] Preferably, the outer support component includes a first connection seat. A main core rod is welded to one side of the first connection seat. The main core rod passes through a through groove of a first sealing plate, and a first outer sleeve is welded to one side of the first sealing plate.

[0008] Preferably, a groove is provided on the inner wall of the first outer sleeve, and a sealing ring is installed in the groove. The inner wall of the sealing ring is connected to a first friction cylinder.

[0009] Preferably, the inner support component includes a second connection seat. An end core rod is welded to one side of the second connection seat. A second sealing plate is welded to the outer wall of the end core rod, and a short sleeve is welded to one side of the second sealing plate.

[0010] Preferably, a short inserted tube is sleeved inside the short sleeve. The short inserted tube is connected to an inner inserted tube. A second friction cylinder is fixed to the outer wall of the inner inserted tube. Inner sealing plates are provided at both ends of the inner inserted tube.

[0011] Preferably, the inner cavity is formed by being blocked by the inner sealing plates inside the inner inserted tube, and mortar is poured into the inner cavity.

[0012] Preferably, the switching connection component includes a visual position rod. One end of the visual position rod is connected to a triangular long bracket, and the other end passes through the hole grooves of the short inserted tube and the short sleeve for detecting the working states of the end core rod and the main core rod. Inner clamping plates are provided on the side of the adjustable outer clamping plate of the switching connection component. The first inner clamping plate is connected to the end core rod, and the second inner clamping plate is connected to the main core rod. The adjustable outer clamping plate forms a rigid connection by engaging the first inner clamping plate and the second inner clamping plate.

[0013] Preferably, four groups of the switching connection components are provided and are annularly distributed on the end core rod. The connection component includes a triangular plate member, a long insertion rod, and an insertion plate member. The long insertion rod is inserted into the hole groove of the shear pin, and the insertion plate member is inserted into the slot hole of the triangular long bracket. The triangular long bracket of the switching connection component is connected to the short inserted tube through a spring member. The spring member releases the stored energy after the shear pin breaks and pushes the triangular long bracket to move towards the axis of the end core rod.

[0014] Preferably, sealing rubber strips are coated at the contact positions between the inner sealing plates and the main core rod.

[0015] Preferably, the connecting seat 1 and the connecting seat 2 are fixed at diagonal positions of the building frame.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The friction contact between the outer support assembly and the inner support assembly realizes the energy dissipation of small earthquakes. At the same time, the switching connection assembly is used to automatically trigger the switching of the rigid force transmission path in the event of a large earthquake, forming a graded response mode of "friction energy dissipation in small earthquakes and rigid force transmission in large earthquakes". This design can not only effectively suppress the deformation of the building frame caused by small earthquakes, but also absorb energy through the rigid structure when a large earthquake exceeds the limit, significantly improving the seismic safety of the building structure, and solving the contradiction between the traditional core material support (easy to fatigue in small earthquakes) and the friction support (easy to fail in large earthquakes) that cannot take into account both durability and reliability;

[0018] 2. The displacement change of the sight bar can visually display the working status of the switching connection assembly. After the earthquake, maintenance personnel can quickly determine whether the device has triggered the major earthquake protection mode without disassembling it, reducing the detection cost. At the same time, after the shear pin breaks, only the local parts of the switching connection assembly (such as the shear pin and spring parts) need to be replaced, without the need to replace the entire assembly, which has high maintenance efficiency.

[0019] 3. The switching connection component accurately responds to large earthquake loads through the preset shear strength threshold of the shear pin to avoid false triggering; four groups of ring-shaped switching components ensure uniform load transmission during rigid connection to avoid stress concentration. Mortar is poured into the inner cavity to reduce the friction and viscosity of the main core rod, enhance the overall structural stiffness, and improve the reliability of large earthquake force transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The overall structure of the present invention is shown in FIG. Figure 1 ;

[0021] Figure 2 The overall structure of the present invention is shown in FIG. Figure 2 ;

[0022] Figure 3 It is a schematic cross-sectional structural diagram of the outer support assembly part of the present invention;

[0023] Figure 4 It is a schematic cross-sectional structural diagram of the inner support component part of the present invention;

[0024] Figure 5 It is a cross-sectional structural schematic diagram of the outer support assembly and the inner support assembly of the present invention;

[0025] Figure 6 It is a schematic diagram of the structure inside the outer support assembly and the inner support assembly of the present invention;

[0026] Figure 7 Structural schematic diagram of part A in Figure 4 the present invention;

[0027] Figure 8 Structural schematic diagram of part B in Figure 4 the present invention;

[0028] Figure 9 Structural schematic diagram of the end core rod and the switching connection component part of the present invention;

[0029] Figure 10 Structural schematic diagram of the internal part of the switching connection component of the present invention Figure 1 ;

[0030] Figure 11 Structural schematic diagram of the switching connection component part of the present invention;

[0031] Figure 12 Structural schematic diagram of the internal part of the switching connection component of the present invention Figure 2 ;

[0032] Figure 13 Structural schematic diagram of the adjusting outer splint part of the present invention;

[0033] Figure 14 Structural schematic diagram of the sectional view of the switching connection component part of the present invention;

[0034] Figure 15 Structural schematic diagram of the overall explosion of the present invention.

[0035] In the figure: 01, outer support component; 11, connecting seat one; 12, main core rod; 13, sealing plate one; 14, outer sleeve; 15, sealing ring; 16, friction cylinder one; 02, inner support component; 21, connecting seat two; 22, end core rod; 23, sealing plate two; 24, short sleeve; 25, embedded tube; 251, short embedded tube; 26, friction cylinder two; 27, inner sealing plate one; 28, inner sealing plate two; 29, inner cavity; 03, switching connection component; 31, shear pin; 32, connection component; 321, triangular plate part; 322, long insertion rod; 323, insertion plate part; 33, triangular long frame; 34, adjusting outer splint; 35, inner splint one; 36, inner splint two; 37, spring part; 38, viewing position rod. Detailed implementation manners

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] An embodiment provided by the present invention:

[0038] Reference Figures 1 - 2 , a nested damper buckling-restrained brace, comprising an outer brace assembly 01, an inner brace assembly 02 and a switching connection assembly 03. The structure composed of the outer brace assembly 01, the inner brace assembly 02 and the switching connection assembly 03 is installed at the diagonal position of the building frame; there is a frictional contact between the outer brace assembly 01 and the inner brace assembly 02 for absorbing the energy generated by small earthquakes. The inner brace assembly 02 includes a short inserted tube 251 and a short sleeve 24. The switching connection assembly 03 is installed on the inner brace assembly 02. The switching connection assembly 03 is used to disconnect the connection between the short inserted tube 251 and the short sleeve 24 during large earthquakes, and is used to absorb the energy generated by large earthquakes by connecting the main core rod 12 and the end core rod 22.

[0039] This nested damper buckling-restrained brace adopts a hierarchical nested design. The energy dissipation of small earthquakes is realized through the frictional contact between the outer brace assembly 01 and the inner brace assembly 02. At the same time, the switching connection assembly 03 is used to trigger the switching of the rigid force transmission path during large earthquakes, forming a dual protection mechanism of "frictional energy dissipation in small earthquakes and rigid force transmission in large earthquakes". The outer brace assembly 01 and the inner brace assembly 02 are connected by nested sliding to ensure the stability of frictional contact during small earthquakes; the switching connection assembly 03 accurately responds to large earthquake loads by setting the fracture threshold of the shear pin 31.

[0040] Reference Figure 3 , the outer brace assembly 01 includes a first connection seat 11. A main core rod 12 is welded to the side of the first connection seat 11. The main core rod 12 contacts a first sealing plate 13 through a through groove. A first outer sleeve 14 is welded to the side of the first sealing plate 13. The first outer sleeve 14 contacts a sealing ring 15 through a groove. The inner wall of the sealing ring 15 is connected to a first friction cylinder 16.

[0041] The outer brace assembly 01 is the core force transmission component, and its structural design takes into account both strength and sealing performance: the main core rod 12: as an axial force transmission rod, it is welded to the first connection seat 11 to directly transmit the load of the building frame; the first outer sleeve 14: is fixed to the main core rod 12 through the first sealing plate 13 to form an outer brace skeleton; the first friction cylinder 16: is fixed inside the first outer sleeve 14 to form a sliding friction pair with the second friction cylinder 26 of the inner brace assembly 02; the sealing ring 15: is installed in the groove of the first outer sleeve 14 and cooperates with the inserted tube 25 to form a dynamic seal to prevent external impurities from invading the friction contact surface.

[0042] Reference Figure 4, the inner support assembly 02 includes a second connecting seat 21. A terminal core rod 22 is welded to the side of the second connecting seat 21. A second sealing plate 23 is welded to the outside of the terminal core rod 22. A short sleeve 24 is welded to the side of the second sealing plate 23. A short insert tube 251 is sleeved inside the short sleeve 24. An inner insert tube 25 is connected to the side of the short insert tube 251. A second friction cylinder 26 is sleeved on the inner insert tube 25. An inner sealing plate 28 is connected to the inner wall of one end of the inner insert tube 25. The first inner sealing plate 27 and the second inner sealing plate 28 contact the main core rod 12 through a groove.

[0043] The inner support assembly 02 is nested inside the outer support assembly 01, achieving dual functions through sliding friction and a sealing structure: Terminal core rod 22: Welded to the second connecting seat 21, jointly forming an axial force transmission path with the main core rod 12; Short sleeve 24 and short insert tube 251: The short sleeve 24 is fixed to the second sealing plate 23, and the short insert tube 251 is sleeved inside the short sleeve 24. The two form a breakable connection through a shear pin 31; Inner insert tube 25 and second friction cylinder 26: The inner insert tube 25 slides inside the outer sleeve 14 as the building frame deforms, and the second friction cylinder 26 is in frictional contact with the first friction cylinder 16 to dissipate energy; First inner sealing plate 27, second inner sealing plate 28: Form a closed cavity 29 at both ends of the inner insert tube 25, preventing mortar leakage and reducing the viscous resistance of the main core rod 12.

[0044] Reference Figures 5 - 8 , the outer support assembly 01 and the inner support assembly 02 form a support structure, where the first friction cylinder 16 and the second friction cylinder 26 are in frictional contact. Small earthquake forces are absorbed through the frictional contact between the first friction cylinder 16 and the second friction cylinder 26. The sealing ring 15 is squeezed between the grooves of the inner insert tube 25 and the outer sleeve 14, which is used to ensure the structural sealing between the outer support assembly 01 and the inner support assembly 02, preventing external dust, rainwater, or impurities from entering. During a small earthquake, the structure formed by the outer support assembly 01 and the inner support assembly 02 will be pulled, and then the inner insert tube 25 and the second friction cylinder 26 will move left or right inside the outer sleeve 14, and the force generated by the vibration on the building structure is absorbed through the frictional contact between the first friction cylinder 16 and the second friction cylinder 26.

[0045] The switching connection assembly 03 is a rigid force transmission trigger device during a major earthquake, and its action logic is as follows: Shear pin 31: Passes through the short sleeve 24 and the short insert tube 251, setting a specific shear strength threshold and only breaking when the major earthquake exceeds the limit; Connection assembly 32: Consists of a triangular plate member 321, a long insertion rod 322, and an insertion plate member 323, connecting the shear pin 31 and the triangular long frame 33 to transmit the fracture signal; Adjustable outer clamping plate 34: Connects the terminal core rod 22 through meshing with the first inner clamping plate 35 and the main core rod 12 through the second inner clamping plate 36 to form a rigid force transmission path; Spring member 37 and visual position rod 38: After the shear pin 31 breaks, the spring member 37 releases its stored energy to push the triangular long frame 33 to move, driving the adjustable outer clamping plate 34 to complete a rigid connection; The displacement change of the visual position rod 38 intuitively shows the working state of the structure.

[0046] Reference Figures 9 - 13 Both are the displays of the structure of the switching connection component 03. The switching connection component 03 includes a shear pin 31. An engagement component 32 is arranged on the side of the shear pin 31. The engagement component 32 includes a triangular plate member 321, a long insertion rod 322, and an insertion plate member 323. A triangular long frame 33 and an adjustable outer clamping plate 34 are arranged at the bottom of the engagement component 32. The shear pin 31 is inserted into the short sleeve 24 and the short insertion tube 251 through a hole slot (reference Figure 14 as shown). The triangular plate member 321 connects the long insertion rod 322 and the insertion plate member 323. The long insertion rod 322 is inserted into the shear pin 31 through a slot hole. The insertion plate member 323 is inserted into the triangular long frame 33 through a slot hole. The triangular long frame 33 and the adjustable outer clamping plate 34 are connected (reference Figure 11 as shown). A spring member 37 and a visual position rod 38 are connected to the top of the triangular long frame 33. The spring member 37 is connected between the triangular long frame 33 and the short insertion tube 251. One end of the visual position rod 38 away from the triangular long frame 33 passes through the short insertion tube 251 and the short sleeve 24 through a hole slot. Inner clamping plates 35 and 36 are arranged on the side of the adjustable outer clamping plate 34. The inner clamping plate 35 is connected to the end head core rod 22, and the inner clamping plate 36 is connected to the main core rod 12. There is a gap between the end head core rod 22 and the main core rod 12.

[0047] Four groups of switching connection components 03 are provided, and the four groups of switching connection components 03 are annularly distributed on the end head core rod 22. The inner sealing plate 27 and the inner sealing plate 28 form an inner cavity 29 by blocking in the insertion tube 25. Mortar is injected into the inner cavity 29 to prevent the main core rod 12 from sticking during use. And sealing rubber strips are coated at the positions where the inner sealing plate 27 and the inner sealing plate 28 contact the main core rod 12 through slots to prevent the leakage of mortar.

[0048] The welding mentioned in this application is a connection method between structural members, not limited to only being connected by welding. Other connection methods such as bolt connection can also be used. And the shear pin 31 used in this application is of the prior art, and its specific shape and principle will not be elaborated too much in the text.

[0049] Instruction manual attachment Figure 15 This is the explosion structure schematic diagram of the overall buckling restraint brace, showing the structures of various components in the overall device, where the structure of the switching connection component 03 is located inside the structure of the inner support component 02.

[0050] Working principle:

[0051] The second connection seat 21 and the first connection seat 11 are pre-cast in the diagonal positions of the building frame, or the second connection seat 21 and the first connection seat 11 are pre-connected to the building frame using bolts, mainly to enable the second connection seat 21 and the first connection seat 11 to form a stable connection with the building frame;

[0052] Subsequently, the structures of the inner support assembly 02 and the outer support assembly 01 except for the first connecting seat 11 and the second connecting seat 21 are assembled. After assembly, the end core rod 22 is welded to the second connecting seat 21, and one end of the main core rod 12 away from the end core rod 22 is welded to the first connecting seat 11. At this time, the installation of the overall buckling brace in the building frame is completed.

[0053] When a minor earthquake occurs, the vibration force of the building frame is transmitted to the outer support assembly 01 and the inner support assembly 02. The two absorb energy through the sliding friction contact between the first friction cylinder 16 and the second friction cylinder 26, and suppress the deformation of the building frame. This friction energy dissipation mechanism can act repeatedly to ensure stable performance after multiple minor earthquakes.

[0054] When the deformation of the building frame exceeds the limit due to a major earthquake:

[0055] Limit trigger: The embedded tube 25 moves to contact the inner wall of the outer sleeve 14 or the first friction cylinder 16 (see Figure 8 ), restricting the further relative displacement between the outer support assembly 01 and the inner support assembly 02.

[0056] Shearing pin 31 fails: Continuous deformation forces the shearing pin 31 between the short embedded tube 251 and the short sleeve 24 to be sheared and broken (see Figure 14 ), releasing the connection between the two and causing the sliding friction structure to fail.

[0057] Rigid connection switching:

[0058] After the shearing pin 31 breaks, the spring member 37 releases its stored energy and pushes the triangular long frame 33 towards the axis of the end core rod 22. The triangular long frame 33 drives the adjustable outer splint 34 to displace synchronously, making it engage between the first inner splint 35 connecting the end core rod 22 and the second inner splint 36 connecting the main core rod 12, forming a rigid force transmission path between the end core rod 22 and the main core rod 12 (see Figure 9 ); The energy of the major earthquake is absorbed by the rigid structure composed of the end core rod 22, the adjustable outer splint 34, the first inner splint 35, the second inner splint 36, and the main core rod 12, greatly reducing the deformation of the building frame.

[0059] By observing the position of the visual position rod 38 extending from the end face of the short sleeve 24: If the end face of the visual position rod 38 is flush with the surface of the short sleeve 24, it indicates that the switching connection assembly 03 has not been triggered and the structure is in the minor earthquake working mode; If the end face of the visual position rod 38 protrudes or retracts, it indicates that the switching connection assembly 03 has acted, and the buckling restrained brace needs to be inspected or replaced.

[0060] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A nested damper buckling restrained brace, characterized in that: include: An outer support component (01), an inner support component (02) and a switching connection component (03); The outer support assembly (01) and the inner support assembly (02) form a sliding connection structure through the friction contact between the friction cylinder 1 (16) and the friction cylinder 2 (26), which is used to absorb small earthquake energy; The switching connection assembly (03) comprises a shear pin (31), a connection assembly (32) and an adjustable outer clamping plate (34), wherein the shear pin (31) penetrates the short sleeve (24) and the short embedded tube (251) to form a breakable connection, and the adjustable outer clamping plate (34) is triggered to move by the shear pin (31) breaking during a major earthquake, so that the main core rod (12) and the end core rod (22) form a rigid connection to absorb the energy of the major earthquake; A sealing ring (15) and an inner cavity (29) sealing structure are provided between the outer support component (01) and the inner support component (02); The outer support assembly (01) comprises a connecting seat 1 (11), a main core rod (12) is welded to the side of the connecting seat 1 (11), the main core rod (12) passes through a through slot of a sealing plate 1 (13), and an outer sleeve (14) is welded to the side of the sealing plate 1 (13); The inner wall of the outer sleeve (14) is provided with a groove, and a sealing ring (15) is installed in the groove, and the inner wall of the sealing ring (15) is connected to a friction cylinder (16); The inner support assembly (02) comprises a second connection seat (21), a terminal core rod (22) is welded to the side of the second connection seat (21), a second sealing plate (23) is welded to the outer wall of the terminal core rod (22), and a short sleeve (24) is welded to the side of the second sealing plate (23); The short sleeve (24) is sleeved with a short embedded tube (251), the short embedded tube (251) is connected to the embedded tube (25), the outer wall of the embedded tube (25) is fixed with a second friction cylinder (26), and both ends of the embedded tube (25) are provided with an inner sealing plate 1 (27) and an inner sealing plate 2 (28); The inner cavity (29) is formed by inner sealing plate 1 (27) and inner sealing plate 2 (28) blocking the inner tube (25), and mortar is poured into the inner cavity (29); The switching connection assembly (03) includes a sight rod (38), one end of which is connected to the triangular long frame (33), and the other end of which passes through the hole grooves of the short embedded tube (251) and the short sleeve (24) for detecting the working status of the end core rod (22) and the main core rod (12). The side of the adjustment outer clamping plate (34) of the switching connection assembly (03) is provided with an inner clamping plate 1 (35) and an inner clamping plate 2 (36). The inner clamping plate 1 (35) is connected to the end core rod (22), and the inner clamping plate 2 (36) is connected to the main core rod (12). The adjustment outer clamping plate (34) forms a rigid connection by engaging the inner clamping plate 1 (35) and the inner clamping plate 2 (36). The switching connection assembly (03) is provided in four groups and is distributed in an annular manner on the end core rod (22). The connection assembly (32) comprises a triangular plate member (321), a long insertion rod (322) and an insertion plate member (323). The long insertion rod (322) is inserted into the hole groove of the shear pin (31), and the insertion plate member (323) is inserted into the slot of the triangular long frame (33). The triangular long frame (33) of the switching connection assembly (03) is connected to the short embedded tube (251) via a spring member (37). The spring member (37) releases the stored force after the shear pin (31) breaks, thereby pushing the triangular long frame (33) to move toward the axis of the end core rod (22).

2. A nested damper buckling restrained brace according to claim 1, characterized in that: The contact positions between the inner sealing plate 1 (27) and the inner sealing plate 2 (28) and the main core rod (12) are coated with sealing strips.

3. A nested damper buckling restrained brace according to claim 1, characterized in that: The connecting seat 1 (11) and the connecting seat 2 (21) are fixed at the diagonal position of the building frame.

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