A prestressed composite string truss used in foundation pit engineering

Abstract

The present invention discloses a prestressed composite tensioned truss used in foundation pit engineering, including a purlin; a tension rod; a cable; a web member; an anchor seat; and a multi-hinge node; the purlin, the tension rod, the cable, the web member, the anchor seat and the multi-hinge node are combined to form a parabolic truss; the purlin is used to withstand the pressure generated by the truss, and the web member is provided with a plurality of web members, and the plurality of web members are vertically fixed to the purlin, and the length of the web member decreases from the middle of the purlin to both sides; the tension rod is provided with a plurality of web members, and the tension rods are respectively connected to the ends of the web members; the connection position between the tension rod and the web member is provided with the multi-hinge node, and the tension rod is rotatably connected to the web member through the multi-hinge node; the anchor seats connected to the ends of the tension rods on both sides are provided on both sides of the purlin, and the cables and the tension rods are used in combination to withstand the tension of the truss; a transverse tensioning device is provided between the cables.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, in particular to the technical field of foundation pit engineering, and in particular to a prestressed composite string truss used in foundation pit engineering. Background Art

[0002] In underground structure projects, special foundation pit retaining construction is required to meet construction excavation conditions and control deformation of the surrounding environment. Some foundation pit retaining projects use a plate support system, that is, retaining walls such as cast-in-place piles, steel piles, and underground continuous walls are set around the foundation pit. An in-pit support system is required at the top and middle of the retaining wall in the foundation pit to serve as the reaction fulcrum of the retaining wall to balance the soil pressure outside the retaining wall. The support system generally uses steel support or reinforced concrete support.

[0003] Steel supports are widely used in foundation pit projects due to their advantages, including fast installation, ease of construction, recyclability, balanced loading and control of pit deformation, and low cost. Commonly used steel supports in foundation pit projects include section steel and steel pipe supports. Purlins are installed along the retaining piles of the foundation pit, and the steel supports serve as the fulcrums for these purlins, sharing the earth pressure surrounding the foundation pit. Purlins are generally designed as continuous beams, with spans limited by cross-section and earth pressure values. Spans generally should not exceed 10 meters, so the spacing between steel supports is usually within 10 meters. However, common practical problems include the following: a large number of steel supports with small spacing, which impacts excavation within the foundation pit; a large number of supports with dispersed arrangement, requiring numerous columns. This large number of columns not only increases the cost of the foundation pit project but also compromises construction convenience. Passing through the basement slab can also have adverse effects. Purlins are flexural members, subject to some bending deformation at mid-span, which increases local deformation in the foundation pit and compromises the protection of the surrounding environment. Summary of the Invention

[0004] The purpose of the present invention is to provide a prestressed composite chord truss used in foundation pit engineering to solve the problems raised in the above background technology.

[0005] Based on the above ideas, the present invention provides the following technical solutions: A prestressed composite tensioned truss used in foundation pit engineering includes a purlin; a tension rod; a cable; a web member; an anchor seat; and a multi-hinge node; the purlin, the tension rod, the cable, the web member, the anchor seat and the multi-hinge node are combined to form a parabolic truss; the purlin is used to withstand the pressure generated by the truss, and a plurality of web members are provided, and the plurality of web members are vertically fixed to the purlin, and the length of the web member decreases from the middle of the purlin to both sides; a plurality of tension rods are provided, and the tension rods are respectively connected to the ends of the web members; the connection position between the tension rod and the web member is provided with the multi-hinge node, and the tension rod is rotatably connected to the web member through the multi-hinge node; the two sides of the purlin are provided with the anchor seats connected to the ends of the tension rods on both sides, and the combination of the cables and the tension rods plays a role in bearing the tension of the truss; a transverse tensioning device is provided between the cables.

[0006] Preferably, the inner side of the anchor seat is provided with a corbel for bearing the component of the tension of the anchor seat by the pull rod and the cable along the direction of the purlin; and a steel plate embedded part is provided at the intersection of the purlin and the web to improve the local compressive bearing capacity of the purlin.

[0007] Preferably, the pull rod is made by cutting from metal plates, and an enlarged head and a pin hole are provided at both ends of the pull rod. The pull rod is connected to the anchor seat and the multi-hinge node respectively by pins to form a rotatable hinge node; the pull rod serves as the tension chord of the truss, and during use, it only bears tension, and does not bear pressure, bending, or shear force, and can fully utilize the tensile properties of the steel.

[0008] Preferably, the cable comprises a cable body, a cable anchor head and a threaded anchor rod, the threaded anchor rod is provided with a spherical nut, the cable anchor head is provided at both ends of the cable body, the cable anchor head is connected to the threaded anchor rod through the spherical nut, the cable is tensioned and used in combination with the cable rod as the tension chord of the truss, the threaded anchor rods at both ends pass through the pressure-bearing plate of the anchor seat and are anchored to the anchor seat, the cable body bypasses the multi-hinge node and passes through the trumpet-shaped opening of the multi-hinge node, wherein the cable body is composed of seven Φ. high-strength steel strands, which are covered with PE sheaths and can slide between the inner walls of the trumpet-shaped openings of the multi-nodes; the cable is a flexible cable with high strength and its length can be customized as needed, the threaded anchor rod adopts an extended screw and is used in combination with the spherical nut, and a torque wrench is used to tighten the spherical nut during installation to tension the cable and straighten it, and a certain amount of pre-stress can be applied to fully utilize the tensile strength of the cable. Because the cable will produce a certain amount of elongation deformation when prestressing is applied, considering the influence of this deformation, the threaded anchor rod adopts an extended screw rod, and the additional length is not less than the elongation deformation of the cable when pre-tensioning.

[0009] Preferably, the web member comprises a profile section, a jack and a web member fork ear; the profile section comprises a profile, a first end plate and a second end plate, the profile is subjected to axial pressure in a working state, and can be made of steel pipe, hot-rolled steel and other materials, the two ends of the profile are fixedly connected to the first end plate and the second end plate respectively, the outer edges of the first end plate and the second end plate are provided with bolt holes for connecting with the jack and the web member fork ear; the jack is connected to the first end plate, the end of the jack is perpendicular to the surrounding purlin, the jack is pressed against the surrounding purlin, and the end of the jack The surface is provided with a ball joint gasket for allowing the jack axis to be stressed even when the angle of the surrounding purlin is slightly deflected; the web fork ear includes a double ear plate, a bottom plate and a web pin; the web fork ear is connected to the second end plate, and the double ear plates are provided with a pin hole for connecting with the web pin and the multi-hinge node. A hinge structure is formed between the web fork ear and the multi-hinge node, thereby ensuring that the web is an axially compressed component. When the profile is subjected to axial pressure, the cross section is subjected to uniform stress and the deformation is axial compression. No bending deformation will occur, and no compression-bending instability will occur, so it can be utilized to the greatest extent.

[0010] Preferably, the side of the anchor seat away from the truss is also connected to a tie rod and a main support, and the anchor seat includes a web, a thickened ear plate, a bottom plate, a top plate, an end plate, a corbel support plate, a first rib plate, a second rib plate, a third rib plate, a pressure plate, a fourth rib plate, a connecting anchor rod and a reinforcing anchor rod; the web is fixedly connected to the thickened ear plate, and a pin hole for connecting the tie rod is provided in the middle of the thickened ear plate, and the thickness of the thickened ear plate is greater than that of the web; the bottom plate, the top plate and the end plate are all vertically welded to the outer edges of the web and the thickened ear plate, and a group of bolt connection holes for connecting the main support are provided on the top plate; a group of anchor holes for passing the connecting anchor rod buried in the purlin and the exposed ends of the reinforcing anchor rod are provided on the bottom plate; a group of connection holes for passing the tie rod are provided on the end plate.

[0011] Preferably, the connecting anchor rod is pre-embedded in the interior of the purlin, and the end of the connecting anchor rod is provided with a first nut and a gasket; the reinforcing anchor rod is pre-embedded in the interior of the purlin, the diameter of the reinforcing anchor rod is larger than the connecting anchor rod, the outer sleeve of the reinforcing anchor rod is provided with a sleeve, one end of the reinforcing anchor rod embedded in the purlin is provided with the anchor plate, and the end of the reinforcing anchor rod exposed from the purlin is provided with a second nut; the reinforcing anchor rod is a directly reinforced connection component between the anchor seat and the purlin, which can provide greater tensile resistance and can transmit the tensile force of the pull rod and cable to the purlin through the anchor seat; the corbel support plate is vertically arranged on the side of the thickened ear plate; there are multiple first rib plates, which are rectangular steel blocks, and the three sides of the first rib plate are respectively vertically connected to the web plate, the bottom plate and the top plate, so as to improve the overall strength and deformation resistance of the anchor seat; There are multiple second ribs, which are rectangular plates. The second ribs are respectively fixed vertically to the web and the thickened ear plates to strengthen the local stiffness and deformation resistance of the anchor seat, and improve the strength of the base plate when it is subjected to the tension of the anchor rod; the three sides of the third rib are respectively fixed vertically to the web, the end plate and an adjacent first rib, to strengthen the local stiffness and deformation resistance of the anchor seat, and improve the strength of the end plate when it is subjected to the tension of the tension rod; one side of the pressure plate is vertically fixed to the web, and a hole is opened in the middle of the pressure plate. The anchor end of the cable can pass through the hole of the pressure plate and be locked and fixed with a nut; the fourth rib is three rectangular plates. The fourth rib is located in the middle and on both sides of the two cables. The fourth rib is respectively fixed vertically to the web and the pressure plate to strengthen the strength of the pressure plate when it is subjected to the tension of the anchor cable.

[0012] The anchor seat is the core component connecting the purlin, tension rod, cable, main support and tie rod. It bears the tension of the connecting anchor rods and reinforcing anchor rods of the tension rod, cable, tie rod and purlin anchor rod, as well as the pressure of the main support, purlin and corbel. Its strength requirements are relatively high, so more additional reinforcement plates are set up. It has a compact structure, high strength, strong deformation resistance, simple and convenient installation and disassembly, and high component reuse rate.

[0013] Preferably, the multi-hinge node includes a fork ear, a channel bottom plate, a channel middle plate, a channel cover plate and a pull rod pin; the fork ear is two steel plates, the fork ear is fixedly connected to the channel bottom plate, the fork ear is provided with a pin hole in sequence, the pin hole in the middle is connected to the web fork ear through the web pin; a pull rod pin is provided in the pin holes on both sides to connect with the pull rod; the channel bottom plate, the channel middle plate and the channel cover plate are all the same in length, width and thickness, the channel bottom plate, the channel middle plate and the channel cover plate are assembled by multiple bolts, two semicircular grooves are provided on the upper surface of the channel bottom plate, and two semicircular grooves are provided on the lower surface of the channel middle plate. When the channel bottom plate and the channel After the middle plates are overlapped, two circular channels are formed at the joint of the channel bottom plate and the channel middle plate, and the two ends of the circular channels are trumpet-shaped openings; at the same time, two semicircular grooves are also provided on the upper surface of the channel middle plate, and two semicircular grooves are also provided on the lower surface of the channel cover plate. When the channel middle plate and the channel cover plate are overlapped, two circular channels are also formed at the joint of the channel middle plate and the channel cover plate, and the two ends of the circular channels are trumpet-shaped openings. Therefore, when the channel bottom plate, the channel middle plate and the channel cover plate are overlapped and assembled, four channels with trumpet-shaped openings are formed in the middle. The smallest diameter of the four circular channels is located in the middle, and the diameter is slightly larger than the outer diameter of the cable, and the circular channel can be passed through by the cable.

[0014] The four trumpet-shaped openings allow four cables to pass through multiple hinged nodes. Installation involves first routing two cables through the semicircular grooves on the upper surface of the channel baseplate, then installing the channel midplate. The baseplate and midplate then restrain the two cables. Furthermore, two more cables are routed through the semicircular grooves on the upper surface of the midplate, and then installing the channel cover. The midplate and cover then restrain the remaining two cables. All four cables can slide within the channel and smoothly bend to a certain angle, following the longitudinal curve of the trumpet mouth without creating sharp corners.

[0015] In order to cooperate with the transverse tensioning cable device to implement the transverse tensioning of the upper and lower layers of cables, the opening angles of the channel bell mouths of the upper and lower layers are also different. The opening angle of the upper channel bell mouth is smaller, the mouth diameter is also smaller, and the overall structure is more compact; because the cables are all bent inward, the groove depths on the lower surfaces of the channel middle plate and the channel cover plate are the same, such as Figure X As shown, each bell mouth is a non-circular opening, the lower half is circular, and the upper half is an arc-shaped shape with a smaller curvature.

[0016] Preferably, the transverse tensioning device includes a jack cylinder, a jack piston rod, a pull plate and a head plate; the pull plate is threadedly connected to the mouth of the jack cylinder, the pull plate has a center hole and is provided with an internal thread, and the mouth of the jack cylinder is provided with an external thread for connecting the pull plate; the head plate is threadedly connected to the head of the jack piston rod, the center hole of the head plate is provided with an internal thread, and the head of the jack piston rod is provided with an external thread; the pull plate and the head plate are provided with arc-shaped grooves at positions corresponding to the cable, so that the cable bends smoothly when it passes along the groove, and the inner radius of the turn is consistent with the curve of the groove to avoid damage to the cable.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The span of the foundation pit is greatly increased, so that the main supports can be arranged in a centralized manner with large spacing, making excavation construction convenient and quick;

[0019] 2. Reduce the amount of columns and minimize the impact on the structural basement floor;

[0020] 3. It can actively balance the deformation of the foundation pit, reduce the amount of deformation, and achieve micro-deformation of the entire span;

[0021] 4. The combined application of pull rods and cables fully utilizes the advantages of high-strength steel strands, making the force-bearing system have a higher safety redundancy and greater anti-collapse safety;

[0022] 5. It can be fully reused, has strong versatility, and is energy-saving and environmentally friendly;

[0023] 6. The support system has a simple structure, is easy to install and dismantle, and has a fast construction speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the main structure of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0025] Figure 2 This is a schematic plan view of a tension rod of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0026] Figure 3 This is a structural diagram of a single-piece tie rod and a multi-hinge node in Example 1 of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0027] Figure 4 This is a structural diagram of double-piece tie rods and multi-hinge nodes in Example 1 of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0028] Figure 5 This is a schematic diagram of the main structure of a cable of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0029] Figure 6 This is a schematic diagram of the main structure of a web member of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0030] Figure 7 This is a schematic diagram of the end portion of a web member of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0031] Figure 8 This is a schematic diagram of the main structure of an anchor seat of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0032] Figure 9 This is a structural schematic diagram of a web of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0033] Figure 10 This is a schematic diagram of the connection between the anchor seat and the tension rod of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0034] Figure 11 This is a schematic diagram of the connection between the bearing plate and the web of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0035] Figure 12 This is a schematic diagram of the connection between the web and the thickened ear plate of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0036] Figure 13 This is a schematic structural diagram of a connecting anchor rod of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0037] Figure 14 This is a schematic structural diagram of a reinforcement anchor rod of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0038] Figure 15 This is a schematic structural diagram of a multi-hinge node of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0039] Figure 16 This is a schematic diagram of the connection structure of multiple hinge nodes and cables of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0040] Figure 17 This is a schematic diagram of the connection structure between the web members and the multi-hinge nodes of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0041] Figure 18 This is a schematic diagram of the connection between the channel bottom plate 62, the channel middle plate 63 and the channel cover plate 64 of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0042] Figure 19 This is a schematic diagram of a channel formed by a channel bottom plate 62, a channel middle plate 63 and a channel cover plate 64 of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0043] Figure 20 This is a schematic diagram of the main structure of a transverse tensioning device of a prestressed composite string truss used in foundation pit engineering according to the present invention;

[0044] Figure 21 This is a schematic diagram of a transverse tensioning device of a prestressed composite string truss used in foundation pit engineering according to the present invention before tensioning;

[0045] Figure 22 This is a schematic diagram of a transverse tensioning device of a prestressed composite string truss used in foundation pit engineering after tensioning according to the present invention;

[0046] Figure 23 This is a schematic structural diagram of a tension rod in Example 2 of a prestressed composite chord truss used in foundation pit engineering according to the present invention;

[0047] Figure 24 The deformation trend of the nodes in Example 3 of a prestressed composite chord truss used in foundation pit engineering of the present invention;

[0048] Figure 25 This is an overall deformation diagram of the truss in Example 3 of a prestressed composite chord truss used in foundation pit engineering of the present invention;

[0049] Figure 26 The present invention is a prestressed composite string truss used in foundation pit engineering Figure 25 Comparison chart;

[0050] Figure 27 This is a schematic diagram of the connection between the tie rods and the anchor seats in Example 3 of a prestressed composite string truss used in foundation pit engineering of the present invention. DETAILED DESCRIPTION

[0051] Example 1

[0052] like Figure 1-22A prestressed composite string truss used in foundation pit engineering includes a purlin 1; a tension rod 2; a cable 3; a web member 4; an anchor seat 5; and a multi-hinge node 6. The purlin 1, the tension rod 2, the cable 3, the web member 4, the anchor seat 5, and the multi-hinge node 6 are combined to form a parabolic truss. The purlin 1 is used to withstand the pressure generated by the truss. The web members 4 are provided with a plurality of them. The plurality of web members 4 are vertically fixed to the purlin 1. The length of the web members 4 is from the middle of the purlin 1 to the two sides. The sides decrease in sequence; there are multiple tie rods 2, and the tie rods 2 are respectively connected to the ends of the web members 4; the connection position of the tie rods 2 and the web members 4 is provided with the multi-hinge node 6, and the tie rods 2 are rotatably connected to the web members 4 through the multi-hinge node 6; the two sides of the purlin 1 are provided with the anchor seats 5 connected to the ends of the tie rods 2 on both sides, and the combination of the cables 3 and the tie rods 2 plays a role in bearing the tension of the truss; a transverse tensioning device 7 is provided between the cables 3.

[0053] Specifically, the inner side of the anchor seat 5 is provided with a corbel 11 for bearing the component of the tension of the pull rod 2 and the cable 3 on the anchor seat 5 along the direction of the purlin 1; a steel plate embedded part 12 is provided at the intersection of the purlin 1 and the web 4 to improve the local compressive bearing capacity of the purlin 1.

[0054] Specifically, the pull rod 2 is made by cutting metal plates, and an enlarged head and a pin hole are provided at both ends of the pull rod 2. The pull rod 2 is connected to the anchor seat 5 and the multi-hinge node 6 respectively by pins to form a rotatable hinge node; the pull rod 2 serves as the tension chord of the truss, and only bears tension during use, and does not bear pressure, bending moment, or shear force, and can fully utilize the tensile properties of the steel.

[0055] The pull rod 2 is made by cutting steel plates with a thickness of 80 mm. If multiple layers of steel plates are used, the total thickness is 80 mm.

[0056] Specifically, the cable 3 includes a cable body 31, a cable anchor head 32 and a threaded anchor rod 33. The threaded anchor rod 33 is provided with a spherical nut 34. The cable anchor head 32 is provided at both ends of the cable body 31. The cable anchor head 32 is connected to the threaded anchor rod 33 through the spherical nut 34. After the cable 3 is tensioned, it is combined with the pull rod 2 to serve as the tension chord of the truss. The threaded anchor rods 33 at both ends pass through the pressure plate 510 of the anchor seat 5 and are anchored to the anchor seat. The cable body 31 bypasses the multi-hinge node 6 and is connected from the multi-hinge node The cable body 31, consisting of seven 15.24 Φ high-strength steel strands encased in a PE sheath, slides against the inner wall of the trumpet-shaped opening at point 6. The cable 3 is a flexible, high-strength cable whose length can be customized. The threaded anchor 33 utilizes an extended screw, combined with a ball nut 34. During installation, the ball nut 34 is tightened with a torque wrench to tension and straighten the cable 3. A certain amount of prestress can also be applied to maximize the cable's tensile strength. Because the cable 3 experiences a certain amount of elongation when prestressed, the threaded anchor 33 utilizes an extended screw, with the additional length being no less than the elongation of the prestressed cable 3.

[0057] Specifically, the web 4 includes a profile section 41, a jack 42 and a web fork ear 43; the profile section 41 includes a profile 411, a first end plate 412 and a second end plate 413. The profile 411 is subjected to axial pressure in a working state and can be made of steel pipes, hot-rolled steel and other materials. The two ends of the profile 411 are fixedly connected to the first end plate 412 and the second end plate 413 respectively. The outer edges of the first end plate 412 and the second end plate 413 are provided with bolt holes for connecting with the jack 42 and the web fork ear 43; the jack 42 is connected to the first end plate 412, and the end of the jack 42 is perpendicular to the surrounding purlin 1, and the jack 42 presses the surrounding Purlin, the end face of the jack 42 is provided with a ball joint gasket for allowing the jack 42 to be subjected to axial force when a slight deflection occurs in the angle of the surrounding purlin 1; the web fork ear 43 includes a double ear plate 431, a bottom plate 432 and a web pin 433; the web fork ear 43 is connected to the second end plate 413, and the double ear plate 431 is provided with a pin hole for connecting with the multi-hinge node 6 through the web pin 433, and a hinge structure is formed between the web fork ear 43 and the multi-hinge node 6, thereby ensuring that the web 4 is an axially compressed member. When the profile is subjected to axial pressure, the cross section is subjected to uniform force, the deformation is axial compression, no bending deformation will occur, and no compression and bending instability will occur, so it can be utilized to the greatest extent.

[0058] The profile 411 is made of Φ351X16 steel pipe; the first end plate 412 and the second end plate 413 are made of 30mm thick steel plate; the ear plate 431 is made of 50mm thick steel plate; the bottom plate 432 is made of 40mm thick steel plate; and the web pin 433 is a Φ100 round steel pin.

[0059] Specifically, the side of the anchor seat 5 away from the truss is also connected to the tension rod 8 and the main support 9, and the anchor seat 5 includes a web 501, a thickened ear plate 502, a bottom plate 503, a top plate 504, an end plate 505, a corbel support plate 506, a first rib plate 507, a second rib plate 508, a third rib plate 509, a pressure plate 510, a fourth rib plate 511, a connecting anchor rod 512 and a reinforcing anchor rod 513; the web 501 is fixedly connected to the thickened ear plate 502, and a pin shaft hole for connecting the pull rod 2 is provided in the middle of the thickened ear plate 502. The thickness of the thick ear plate 502 is greater than that of the web 501; the bottom plate 503, the top plate 504 and the end plate 505 are all vertically welded to the outer edges of the web 501 and the thickened ear plate 502, and the top plate 504 is provided with a group of bolt connection holes for connecting the main support 9; the bottom plate 503 is provided with a group of anchor holes for passing the connecting anchor rods 512 buried inside the purlin 1 and the exposed ends of the reinforcing anchor rods 513; the end plate 505 is provided with a group of connection holes for passing the tension rods 8.

[0060] Specifically, the connecting anchor rod 512 is embedded in the interior of the purlin 1, and the end of the connecting anchor rod 512 is provided with a first nut 5121 and a gasket 5122; the reinforcing anchor rod 513 is embedded in the interior of the purlin 1, and the diameter of the reinforcing anchor rod 513 is larger than that of the connecting anchor rod 512. The outer sleeve of the reinforcing anchor rod 513 is provided with a sleeve 5133, and the end of the reinforcing anchor rod 513 embedded in the purlin 1 is provided with the anchor plate 5131, and the end of the reinforcing anchor rod 513 exposed to the purlin 1 is provided with a first The first rib plate 507 is provided with a plurality of ribs, each of which is a rectangular steel block. The three sides of the first rib plate 507 are respectively connected vertically with the web 501, the bottom plate 503 and the top plate 504, thereby improving the overall strength of the anchor seat 5. The second ribs 508 are provided with a plurality of them, and the second ribs 508 are rectangular plates. The second ribs 508 are respectively fixed vertically to the web 501 and the thickened ear plates 502 to strengthen the local stiffness and anti-deformation ability of the anchor seat and improve the strength of the bottom plate 503 when it is subjected to the tension of the anchor rod; the three sides of the third rib 509 are respectively fixed vertically to the web 501, the end plate 505 and an adjacent first rib 507 to strengthen the local stiffness and anti-deformation ability of the anchor seat and improve the end plate 50 5 strength when bearing the tension of the tension rod; one side of the pressure plate 510 is vertically fixed to the web 501, and the middle of the pressure plate 510 is opened. The anchor end of the cable 3 can pass through the opening of the pressure plate 510 and be locked and fixed with a nut; the fourth rib plate 511 is three rectangular plates, and the fourth rib plate 511 is located in the middle position and on both sides of the two cables 3. The fourth rib plate 511 is respectively fixed vertically to the web 501 and the pressure plate 510, thereby strengthening the strength of the pressure plate 510 when bearing the tension of the anchor cable.

[0061] The anchor seat 5 is the core component connecting the purlin 1, the tension rod 2, the cable 3, the main support 9, and the tie bar 8. It bears the tension of the connecting anchor rod 512 and the reinforcing anchor rod 513 of the tension rod 2, the cable 3, the tie bar 8, and the purlin anchor rod, as well as the pressure of the main support 9, the purlin 1, and the corbel 11. Its strength has high requirements, so more additional reinforcement plates are set. It has a compact structure, high strength, strong deformation resistance, simple and convenient installation and disassembly, and a high component reuse rate.

[0062] The web 501 is made of 40mm thick steel plate with a width of 620mm; the thickened ear plate 502 is made of 80mm steel plate and is triangular; the bottom plate 503, the top plate 504, and the end plate 505 are made of 40mm thick steel plate, all with a width of 400mm; the corbel support plate 506 is made of 20mm thick steel plate, with a width of 400mm; the first rib plate 507, the second rib plate 508, and the third rib plate 509 are all 25mm thick steel plates, and the pressure plate 510 is made of 40mm thick steel plate; the fourth rib plate 511 is a 20mm thick steel plate; the connecting anchor rod 512 is made of Φ25mm high-strength threaded steel bar; the reinforcing anchor rod 513 is made of Φ40mm high-strength threaded steel bar.

[0063] Specifically, the multi-hinge node 6 includes a fork ear 61, a channel bottom plate 62, a channel middle plate 63, a channel cover plate 64 and a pull rod pin 65; the fork ear 61 is two steel plates, and the fork ear 61 is fixedly connected to the channel bottom plate 62, and the fork ear 61 is provided with 3 pin holes in sequence, and the pin hole in the middle is connected to the web fork ear 43 through the web pin 433; a pull rod shaft pin 65 is provided in the pin holes on both sides to connect with the pull rod; the channel bottom plate 62, the channel middle plate 63 and the channel cover plate 64 are all the same in length, width and thickness, and the channel bottom plate 62, the channel middle plate 63 and the channel cover plate 64 are assembled by multiple bolts, and two semicircular grooves are provided on the upper surface of the channel bottom plate 62, and two semicircular grooves are provided on the lower surface of the channel middle plate 63. When the channel bottom plate 62 and the channel middle plate 63 are superimposed, two circular channels are formed at the joint of the channel bottom plate 62 and the channel middle plate 63, and the two ends of the circular channels are trumpet-shaped openings; at the same time, two semicircular grooves are also provided on the upper surface of the channel middle plate 63, and two semicircular grooves are also provided on the lower surface of the channel cover plate 64. When the channel middle plate 63 and the channel cover plate 64 are superimposed, two circular channels are also formed at the joint of the channel middle plate 63 and the channel cover plate 64, and the two ends of the circular channels are trumpet-shaped openings. Therefore, when the channel bottom plate 62, the channel middle plate 63 and the channel cover plate 64 are all superimposed and assembled, four channels with trumpet-shaped openings are formed in the middle thereof. The smallest diameter of the four circular channels is located in the middle, and the diameter is slightly larger than the outer diameter of the cable 3. The circular channel can be passed through by the cable 3.

[0064] The four trumpet-shaped openings serve as passages for four cables 3 to pass through the multi-hinge node 6. Installation is accomplished by first routing two cables 3 through the semicircular grooves on the upper surface of the channel base plate 62, then installing the channel midplate 63. The base plate 62 and midplate 63 then restrain the two cables 3. Furthermore, two more cables 3 are routed through the semicircular grooves on the upper surface of the channel midplate 63, and then installing the channel cover plate 64. The midplate 63 and cover plate 64 then restrain the remaining two cables 3. All four cables 3 can slide within the channel and smoothly bend to a certain angle following the longitudinal curve of the trumpet mouth without creating sharp corners.

[0065] In order to cooperate with the transverse tensioning cable device 7 to implement the transverse tensioning of the upper and lower layers of cables 3, the opening angles of the channel bell mouths of the upper and lower layers are also different. The opening angle of the upper channel bell mouth is smaller, the mouth diameter is also smaller, and the overall structure is more compact. Since the cables are all bent inward, the depth of the grooves on the lower surfaces of the channel middle plate 63 and the channel cover plate 64 are the same. Figure X As shown, each bell mouth is a non-circular opening, the lower half is circular, and the upper half is an arc-shaped shape with a smaller curvature.

[0066] The fork ear 61 is made of 80mm thick steel plate, the diameter of the pin hole connected to the pull rod 2 is Φ160mm, and the diameter of the pin hole connected to the web rod 4 is 100mm; the thickness of the channel bottom plate 62 is 110mm, the thickness of the channel middle plate 63 is 120mm, and the channel cover plate is 6470mm. A trumpet-shaped channel groove is opened at the joint; the pull rod pin 65 is a pin with a diameter of Φ100mm.

[0067] Specifically, the transverse tensioning device 1 includes a jack cylinder 71, a jack piston rod 72, a pull plate 73 and a head plate 74; the pull plate 73 is threadedly connected to the mouth of the jack cylinder 71, the center of the pull plate 73 is opened and provided with an internal thread, and the mouth of the jack cylinder 71 is provided with an external thread for connecting the pull plate 73; the head plate 74 is threadedly connected to the head of the jack piston rod 72, the center of the head plate 74 is provided with an internal thread, and the head of the jack piston rod 72 is provided with an external thread; the pull plate 73 and the head plate 74 are provided with arc-shaped grooves at the positions corresponding to the cable 3, so that the cable 3 bends smoothly when it passes along the groove, and the inner radius of the turn is consistent with the curve of the groove to avoid damage to the cable 3;

[0068] The jack cylinder 71 and the jack piston rod 72 are two main components of the same jack. The nominal top pressure of the jack is 100kN, and the mouths are both provided with external threads; the pull plate 73 is made of 32mm steel plate, and the center hole is provided with internal threads, which match the external threads of the mouth of the jack cylinder 71; the head plate 74 is made of 32mm steel plate, and the center hole is provided with internal threads, which match the external threads of the head of the jack piston rod 72.

[0069] Example 2

[0070] The pull rod 2 is made by welding a steel tube 21 and a lug plate 22. A V-shaped notch is opened at the end of the steel tube 21. The connecting portion of the lug plate 22 and the steel tube 21 is cut into a wedge shape to match the V-shaped notch at the end of the steel tube 21. The wedge-shaped section of the lug plate 22 is inserted into the steel tube 21 and then welded to the entire length of the joint. A sealing plate 23 is welded to the remaining opening at the end of the steel tube 21.

[0071] The pull rod 2a is made by welding a steel pipe 21 and an ear plate 22, wherein the end connected to the multi-hinge node 6 is made in the same manner as the pull rod 2; at the end connected to the anchor seat 5, two ear plates are provided at the end of the steel pipe 21, and two V-shaped notches are required to be opened. The connecting part of the ear plate 24 and the steel pipe 21 is cut into a single-sided wedge, which matches the V-shaped notch at the end of the steel pipe 21. After the wedge-shaped section of the ear plate 24 is inserted into the steel pipe 21, the joint is welded along the entire length; sealing plates 25 and 26 are welded at the remaining opening at the end of the steel pipe 21; the steel pipe 21 adopts Φ273X20 steel pipe, and a mold-shaped groove is opened at the end; the ear plate 22 is processed from 80mm thick steel plate, and the pin shaft hole diameter is Φ160mm. The welding section with the steel pipe adopts a wedge-shaped cross-section, and is welded with a wedge-shaped butt weld to avoid sudden stress changes in the joint section; the sealing plate 23 adopts 20m steel plate, which is welded to the steel pipe 21 to seal the steel pipe.

[0072] Example 3

[0073] Installation method:

[0074] Due to unpredictable factors in actual engineering, such as the earth pressure outside the purlin 1 significantly exceeding the design value and the tensile stress in the tie rod 2 having reached the allowable strength of the material, the jack 42 of the web member 4 should not be used for top loading. Since the cables 3 are made of high-strength steel strands with a higher tensile strength than the steel used for the tie rods, there is still sufficient loading capacity, so the cables 3 can be loaded separately. In this case, the transverse tensioning device 7 is installed according to the following steps to further tension the cables 3, thereby improving the overall load-bearing capacity and deformation control capabilities of the prestressed composite string truss.

[0075] At the middle point of each cable section, between the four cables, place a pull plate 73 and a head plate 74. Insert the jack between the two outer cables 3. First, extend the jack piston rod 72 for a certain length and screw it into the inner threaded hole in the center of the head plate 74. Then retract the jack piston rod 72 and screw the jack cylinder 71 into the inner threaded hole in the center of the pull plate 73. After the jack is installed, Figure X Then the jacks are loaded and simultaneously support the cable 3 in opposite directions. Since the straight section of the cable 3 is transformed into a curved curve during the support, the total length increases and the tension of the cable 3 increases.

[0076] The diagram of this case shows that transverse tensioning devices 7 are set up with four middle sections of cables. In actual engineering applications, any one or more sections can be used for tensioning. Since the cables 3 and the multi-hinge nodes 6 are slidably connected, tensioning at any section can increase the tensile stress of the entire cable 3, thereby increasing the total tension of the lower chord of the prestressed composite tensioned truss. By increasing the supporting force by the web members 4, the deformation value of the purlin 1 toward the inside of the foundation pit can be further reduced.

[0077] The brace 8 is positioned between two symmetrically arranged anchor blocks 5 and secured via connection holes in the end plates 505 of the anchor blocks 5. It balances the tension exerted by the tie rods 2 and cables 3 on the anchor blocks 5 along the axis of the brace 8. Working in conjunction with the corbels 11, it further enhances the shear resistance between the anchor blocks 5 and the purlin 1, meeting the engineering requirements. (The tie rods and nuts are identical to those used for the main support brace, with a diameter of 40mm.)

[0078] Based on the above technical features: when the jacks of multiple web members 4 are supported synchronously in a certain proportion, due to the tight connection between the anchor seat and the purlin, the pull rod and the steel strand are deflected toward the inside of the foundation pit, and at the same time, the purlin 4 has a tendency to deflect toward the outside of the foundation pit. The deformation of each node is larger in the middle node and smaller in the edge node. The deformation trend is as follows: Figure 24 As shown, the dotted line in the figure is a schematic diagram of the position of the component after deformation.

[0079] When the soil in the foundation pit is excavated downward, the soil pressure inside the foundation pit is released, and the soil pressure outside the foundation pit is transmitted to the purlin 1 through the retaining piles, pushing the purlin 1 toward the inside of the pit; when the jack is set to an appropriate extension, the deformation of the purlin 1 toward the outside of the pit can be achieved, which is balanced with the displacement of the purlin 1 toward the inside of the pit caused by the soil pressure, thereby achieving no displacement or slight displacement of the purlin 1; at the same time, each multi-hinge node 6 deflects toward the inside of the pit, and its displacement is the same as the extension of the jack.

[0080] According to the principle of the curve prestressed load balance algorithm, when the intersection points of the broken lines formed by the pull rods 2, the cables 3, and the multi-hinge nodes 6 are all located on the same parabola, the soil pressure outside each segmented purlin 1 and the axial pressure of the web members at the corresponding position are balanced one by one, and the entire purlin reaches the most ideal mechanical equilibrium state, that is, the force of the purlin 1 is transformed into a continuous beam with each web member as the support, and its span is greatly reduced, so the maximum values ​​of the bending moment and shear force are also greatly reduced, and the overall deformation is a wave shape close to 0. The overall deformation is as follows: Figure 25 As shown, the dotted line in the figure is a schematic diagram of the position of the component after deformation;

[0081] In contrast, if a conventional foundation pit uses a non-prestressed truss as a support beam, its deformation is too large to meet the needs of controlling the foundation pit deformation. Figure 26 shown.

[0082] When the pull rod 2 reaches the design strength, the cable 3 has not yet reached the allowable strength and there is still a large strength redundancy. If the project encounters extremely unfavorable conditions and there is a safety risk in the foundation pit, the transverse tensioning device 7 can be used to further tension the cable 3. The secondary tensioning construction in this case is simple and convenient, and the stress control is accurate. By making full use of the allowable strength of the cable 3, most engineering problems caused by foundation pit deformation can be solved.

Claims

1. A prestressed composite string truss used in foundation pit engineering, characterized in that: include: purlin; tie rod; cable; belly bar; anchorage; Multi-hinge nodes; The purlin, the tension rod, the cable, the web member, the anchor seat and the multi-hinge node are combined to form a parabolic truss; the purlin is used to withstand the pressure generated by the truss, and the web member is provided with a plurality of web members, and the plurality of web members are vertically fixed to the purlin, and the length of the web member decreases from the middle of the purlin to both sides; the tension rod is provided with a plurality of tie rods, and the tie rods are respectively connected to the ends of the web members; the connection position of the tie rod and the web member is provided with the multi-hinge node, and the tie rod is rotatably connected to the web member through the multi-hinge node; the two sides of the purlin are provided with the anchor seats connected to the ends of the tie rods on both sides, and the combination of the cable and the tie rod plays a role in bearing the tension of the truss; a transverse tensioning device is provided between the cables; The anchor seat is further connected to a brace and a main support on a side away from the truss, and the anchor seat includes a web, a thickened ear plate, a bottom plate, a top plate, an end plate, a corbel support plate, a first rib plate, a second rib plate, a third rib plate, a bearing plate, a fourth rib plate, a connecting anchor rod and a reinforcing anchor rod; The web is fixedly connected to the thickened ear plate, a hole for connecting a pull rod pin is provided in the middle of the thickened ear plate, and the thickness of the thickened ear plate is greater than that of the web; The bottom plate, the top plate and the end plate are all vertically welded to the outer edges of the web and the thickened ear plate. The top plate is provided with a group of bolt connection holes for connecting the main support; the bottom plate is provided with a group of anchor holes for passing the connecting anchor rods buried inside the purlin and the exposed ends of the reinforcing anchor rods; the end plates are provided with a group of connection holes for passing the tension rods.

2. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The inner side of the anchor seat is provided with a corbel for bearing the component force of the tension of the pull rod and the cable on the anchor seat along the purlin direction; the steel plate embedded part is provided at the intersection of the purlin and the web.

3. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The pull rod is made by cutting a metal plate, and both ends of the pull rod are provided with an enlarged head and a pin shaft hole.

4. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The cable comprises a cable body, a cable anchor head and a threaded anchor rod. The threaded anchor rod is provided with a spherical nut. The cable anchor heads are provided at both ends of the cable body. The cable anchor heads are connected to the threaded anchor rod through the spherical nuts.

5. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The web member comprises a profile section, a jack, and a web member fork ear; the profile section comprises a profile, a first end plate, and a second end plate, the two ends of the profile are fixedly connected to the first end plate and the second end plate respectively, and the outer edges of the first end plate and the second end plate are provided with bolt holes for connecting with the jack and the web member fork ear; The jack is connected to the first end plate, the end of the jack is perpendicular to the purlin, the jack presses against the purlin, and the end surface of the jack is provided with a ball joint washer for allowing the jack axis to bear force when the purlin angle is slightly deflected; The web rod fork ear includes two ear plates, a bottom plate and a web rod pin; the web rod fork ear is connected to the second end plate, and the two ear plates are provided with pin holes for connecting to the multi-hinge node through the web rod pin, forming a hinge structure between the web rod fork ear and the multi-hinge node.

6. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The connecting anchor rod is pre-buried inside the surrounding purlin, and the end of the connecting anchor rod is provided with a first nut and a washer; The reinforcing anchor rod is pre-buried inside the purlin, the diameter of the reinforcing anchor rod is larger than that of the connecting anchor rod, a sleeve is sleeved on the outside of the reinforcing anchor rod, one end of the reinforcing anchor rod embedded in the purlin is provided with the anchor plate, and one end of the reinforcing anchor rod exposed from the purlin is provided with a second nut; The corbel support plate is vertically arranged on the side of the thickened ear plate; There are multiple first ribs, each of which is a rectangular steel block, and three sides of the first rib are vertically connected to the web, the bottom plate, and the top plate respectively; There are multiple second ribs, each of which is a rectangular plate, and each of which is vertically fixed to the web and the thickened ear plate. The three sides of the rib plate are respectively fixed vertically to the web plate, the end plate and an adjacent first rib plate; One side of the pressure-bearing plate is vertically fixed to the web, and a hole is opened in the middle of the pressure-bearing plate. The anchor end of the cable can pass through the hole of the pressure-bearing plate and be locked and fixed with a nut; The fourth stiffeners are three rectangular plates, and are located in the middle and on both sides of the two cables. The fourth stiffeners are respectively fixed vertically to the web and the pressure plate.

7. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The multi-hinge node includes a fork ear, a channel bottom plate, a channel middle plate, a channel cover plate and a pull rod pin; the fork ear is two steel plates, the fork ear is fixedly connected to the channel bottom plate, the fork ear is sequentially provided with a pin hole, the pin hole in the middle is connected to the web rod fork ear through the web rod pin; pull rod pins are provided in the pin holes on both sides to connect with the pull rod; The length, width and thickness of the channel bottom plate, the channel middle plate and the channel cover plate are the same. The channel bottom plate, the channel middle plate and the channel cover plate are assembled by multiple bolts. Two semicircular grooves are provided on the upper surface of the channel bottom plate, and two semicircular grooves are provided on the lower surface of the channel middle plate. When the channel bottom plate and the channel middle plate are superimposed, two circular channels are formed at the joint of the channel bottom plate and the channel middle plate, and the two ends of the circular channels are trumpet-shaped openings; at the same time, two semicircular grooves are provided on the upper surface of the channel middle plate A semicircular groove is provided, and two semicircular grooves are also provided on the lower surface of the channel cover plate. When the channel middle plate and the channel cover plate are overlapped, two circular channels are also formed at the joint of the channel middle plate and the channel cover plate. Both ends of the circular channels are trumpet-shaped openings. Therefore, when the channel bottom plate, the channel middle plate and the channel cover plate are overlapped and assembled, four channels with trumpet-shaped openings are formed in the middle. The smallest diameter of the four circular channels is located in the middle, and the diameter is slightly larger than the outer diameter of the cable. The circular channel can be passed through by the cable.

8. The prestressed composite truss string used in foundation pit engineering according to claim 1, characterized in that: The transverse tensioning device includes a jack cylinder, a jack piston rod, a pull plate and a head plate; the pull plate is threadedly connected to the mouth of the jack cylinder, the pull plate has a center hole and is provided with an internal thread, and the mouth of the jack cylinder is provided with an external thread for connecting the pull plate; the head plate is threadedly connected to the head of the jack piston rod, the center hole of the head plate is provided with an internal thread, and the head of the jack piston rod is provided with an external thread; the pull plate and the head plate are provided with arc grooves at the positions corresponding to the cables.

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