A beam string structure with high progressive collapse resistance and implementation method thereof

Abstract

The present invention discloses a beam string structure with high resistance to continuous collapse and a method for realizing the same, wherein the beam string structure comprises an upper chord and a lower cable, a plurality of first nodes are arranged on the upper chord, a plurality of second nodes are arranged on the lower cable, a plurality of third nodes are arranged in the space between the upper chord and the lower cable, four oblique struts are arranged on each third node, and the four oblique struts are respectively connected to two adjacent first nodes on the upper chord and two adjacent second nodes on the lower cable. Compared with the traditional beam string structure, the beam string structure of the present invention forms a backup force transmission path through the oblique struts after the cable breaks, which can effectively prevent the structure from collapsing, and at the same time increase the redundancy of the struts; the prestressed clamp at each second node can effectively control the prestress loss of the lower cable during service. The present invention has a simple structure, is easy to implement, and is suitable for application in practical engineering.

Description

Technical Field

[0001] The invention belongs to the field of large-span prestressed space structures and relates to a beam-string structure. Background Art

[0002] The beam string structure is mainly composed of a lower flexible cable and a rigid upper chord beam. The cable is prestressed and anchored at both ends of the upper chord beam. The cable and the upper chord beam are connected by vertical struts. This structure is a self-balancing system that can give full play to the tensile properties of high-strength materials. It has the characteristics of reasonable force performance, light weight and simple structure. With the development of my country's construction industry, the beam string structure is widely used in important public buildings with large spaces such as stadiums and exhibition halls.

[0003] Compared with the frame structure, the beam string structure has a lower redundancy. In the prior art, a single vertical strut is often set between the upper beam and the lower chord. The tension of the lower chord causes the strut to be compressed, and the upper beam is in a state of compression and bending. For the lower chord, unlike rigid components, it can only be tensile, not compressed, and the connection between the strut and the upper beam and the lower chord is hinged. When any section of the lower chord cable fails, the cable will quickly release strain energy, and the entire cable will then completely fail. The failure of the cable will cause all the struts to fail as they rotate. Therefore, when any section of the cable fails, the struts and the lower cable section of the structure will form a mechanism. Finally, the mid-span deflection increases sharply, the upper chord is crushed, and the structure collapses. At the same time, during the service life of the beam string structure, poor anchoring quality at the node will cause the loss of prestress in the lower chord cable and reduce the overall stiffness of the structure, which will also become a potential factor for the failure of the beam string structure.

[0004] In the prior art, researchers have proposed several improved structural forms, such as adding cables for equipment and multi-cable string-truss structures, and the research focus is to improve the redundancy of the lower chord cables. The anti-collapse performance of the string-truss structure with added cables for equipment is related to the horizontal stiffness of the structural support. When a certain section of the cable fails, local string systems are formed on both sides, which leads to the formation of a hinge in the upper chord at the failure point after the structure is deformed. For the string-beam structure system with a solid web beam as the upper chord, when the large-span solid web beam is subjected to force alone, the bending efficiency is low, and collapse is very likely to occur at this time. For the string-beam structure that uses multiple cables to improve the redundancy of the structure, it is also impossible to form a self-balancing force for the entire span after the failure of a single cable, and continuous failure may still occur when the bending capacity of the upper chord beam is insufficient. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a beam string structure and an implementation method which are simple in structure, safe and reliable and can improve the anti-progressive collapse performance of the beam string structure in view of the deficiencies in the above-mentioned prior art.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A tension beam structure with an anti-collapse function comprises an upper chord beam and a lower cable, and is characterized in that: a plurality of first nodes are arranged on the upper chord beam, a plurality of second nodes are arranged on the lower cable, a plurality of third nodes are arranged in the space between the upper chord beam and the lower cable, four oblique struts are arranged on each third node, and the four oblique struts are respectively connected to two adjacent first nodes on the upper chord beam and two adjacent second nodes on the lower cable.

[0008] An edge diagonal brace is arranged between the outermost first node and the outermost second node.

[0009] The four diagonal struts connected to the third node include two upper diagonal struts and two lower diagonal struts; the lower ends of the upper diagonal struts are rigidly connected to the upper ends of the lower diagonal struts; the upper ends of the upper diagonal struts and the upper ends of the side diagonal struts are hinged to the upper chord beam, and the lower ends of the lower diagonal struts and the lower ends of the side diagonal struts are hinged to the lower cable.

[0010] A connecting plate is provided at the lower end of the upper chord beam, and the first node is formed on the connecting plate.

[0011] The second node is formed by a prestressed clamp fixed on the lower cable.

[0012] The prestressed fixture comprises a sleeve into which the lower cable can be placed and clamped, a node plate is arranged on the sleeve, and anchor plugs are arranged at both ends of the sleeve to clamp the lower cable at the ends; the lower diagonal brace is connected to the node plate.

[0013] The sleeve is formed by connecting two half sleeves via fasteners.

[0014] A tooth-like protrusion is arranged inside the sleeve.

[0015] The upper chord beam is a steel beam or a truss beam.

[0016] A method for realizing a beam string structure, characterized in that: by adjusting the height between a third node and an upper beam, the bending efficiency of the remaining structure of the beam string structure after the cable fails is changed; the greater the height between the third node and the upper beam, the higher the bending efficiency of the remaining structure.

[0017] The beam string structure of the present invention overcomes the problem of insufficient redundancy of the beam string by setting up multiple cross-type diagonal struts. If an unexpected situation such as cable breakage occurs, the prestressed clamps at the nodes prevent the retraction of the remaining cables and transfer the internal force of the cables to the lower diagonal struts, which then transfer the internal force to the upper diagonal struts and finally to the upper beam, thereby forming a new effective force transmission path and improving the continuous collapse resistance of the beam string structure. The setting of multiple struts also increases the redundancy of the struts. At the same time, the prestressed clamps at each second node can effectively control the loss of prestress of the lower cables during service.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) The novel beam-string structure proposed in the present invention changes the force transmission path in the traditional beam-string structure. When the cable at any position breaks, the preload force generated by the prestressed clamp and the anchor plug can effectively limit the retraction of the remaining cable. The spare force transmission path of the remaining structure is clear. The retraction force of the remaining cable at the second node is transmitted by the prestressed clamp to the lower diagonal strut or the side strut hinged to the node plate. The lower diagonal strut is then transmitted to the connected upper diagonal strut, and finally to the upper chord. The remaining cable and the lower diagonal strut at the failed cable form a new force transmission path to continue to provide tension. Due to the existence of the upper diagonal strut, the plastic hinge of the upper chord at the broken cable is avoided to increase the vertical deflection.

[0020] 2) The cross arrangement of the oblique braces increases the redundancy of the braces. At the same time, the prestressed clamps at each node can effectively control the prestress loss of the lower cable during service.

[0021] 3) The structure is simple in form, the connection nodes are easy to handle, the construction is convenient, and the design and implementation methods are similar to those of traditional beam string structures. It is easy to implement and suitable for application in practical engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the force transmission path of the beam string structure after the cable fails;

[0023] Figure 2 Beam string structure configuration - structural schematic diagram;

[0024] Figure 3 Schematic diagram of the second structure of the beam string structure;

[0025] Figure 4 Schematic diagram of the three structures of the beam string structure configuration;

[0026] Figure 5 Schematic diagram of the prestressed fixture structure, where a is the overall schematic diagram and b is the split schematic diagram;

[0027] Figure 6 Schematic diagram of the connecting plate structure;

[0028] Figure 7 The node displacement time history of the new beam string after the failure of the intermediate cable;

[0029] Figure 8 The node displacement time history of the new beam string after the side cable fails;

[0030] Fig. 9 Time history of node displacements of a conventional beam string after cable failure;

[0031] Fig.10 The new beam string configuration is in a deformed state after the middle cable fails;

[0032] Fig.11 The second deformation state of the new beam string configuration after the failure of the intermediate cable;

[0033] Fig.12 The three deformation states of the new beam string configuration after the failure of the intermediate cable;

[0034] Fig.13 The new beam string configuration is in a deformed state after the side cables fail;

[0035] Fig.14 The second deformation state of the new beam string configuration after cable failure.

[0036] Fig.15 The three deformation states of the new beam string configuration after the side cable fails;

[0037] The figure includes: an upper chord beam 1; diagonal struts 2, upper diagonal struts 21, lower diagonal struts 22, and side diagonal struts 23; a lower cable 3; a connecting plate 4; a prestressed clamp 5, a prestressed clamp sleeve 51, a node plate 52, an anchor plug 53, and a high-strength bolt 54; a fixed hinge support 6; and a sliding hinge support 7. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below in conjunction with the accompanying drawings:

[0039] like Figure 1-Figure 4 As shown, the present invention has an anti-collapse beam structure, including an upper chord beam 1 and a lower cable 3, wherein the upper chord beam is a beam structure such as a steel beam or a truss beam. A plurality of first nodes are arranged on the upper chord beam, a plurality of second nodes are arranged on the lower cable, a plurality of third nodes are arranged in the space between the upper chord beam and the lower cable, four oblique struts are arranged on each third node, the four oblique struts are respectively connected to two adjacent first nodes on the upper chord beam and two adjacent second nodes on the lower cable, and a side oblique strut is arranged between the outermost first node and the outermost second node.

[0040] The four diagonal struts connected to the third node include two upper diagonal struts 21 and two lower diagonal struts 22; the lower end of the upper diagonal strut 21 is rigidly connected to the upper end of the lower diagonal strut 22; the upper end of the upper diagonal strut 21 and the upper end of the side diagonal strut 23 are hinged to the upper chord beam 1, and the lower end of the lower diagonal strut 22 and the lower end of the side diagonal strut 23 are hinged to the lower cable 3.

[0041] The first node is formed by a connecting plate 4 fixed to the lower end of the upper chord beam 1. The connecting plate is an arc-shaped connecting plate made of steel. A hole is opened on the arc-shaped connecting plate, and the two sides of the main board are welded to the opening. The upper part of the arc-shaped connecting plate is welded to the lower side of the upper chord beam, and the lower part is hinged to the upper ends of the upper diagonal brace and the side diagonal brace through a pin shaft.

[0042] The second node is formed by a prestressed clamp 5 fixed on the lower cable 3. The prestressed clamp 5 includes a sleeve 51 that can be placed in and clamp the lower cable 3, a node plate 52 is arranged on the sleeve 51, and anchor plugs 53 are arranged at both ends of the sleeve to clamp the lower cable at the end; the lower diagonal brace 22 is connected to the node plate 52. The lower ends of the lower diagonal brace 22 and the side diagonal brace 23 are hinged to the node plate 52 through a pin.

[0043] The casing 51 is formed by two half casings connected by high-strength bolts 54. Tooth-like protrusions are arranged inside the casing 51. The lower cable 3 passes through the casing 51. After the tensioning of the lower cable 3 is completed, the cable PE sheath of the prestressed clamp 5 section is peeled off, so that the cable is in direct contact with the clamp, and the two half casings are tightened by high-strength bolts 54 on both sides of the casing 51 to ensure that the lower cable 3 and the casing 51 do not slide relative to each other. Then, the anchor plugs 53 are inserted at both ends to clamp the lower cable 3.

[0044] When the beam string of the present invention is implemented, the strut configuration is optimized to achieve better progressive collapse resistance. Figure 1 This is the force transmission path of the new beam string structure after the cable fails. When the middle cable breaks, the two lower diagonal braces at node a balance the remaining cable internal force F1. The corresponding mechanical equilibrium equation is:

[0045] F2×cos(β)+F3×cos(γ)=F1 (1)

[0046] Where, F2 and F3 are the internal forces of the lower diagonal braces on the left and right sides of node a; α is the angle between the lower diagonal braces on the left and right sides of node a; β is the angle between the lower diagonal brace on the left side of node a and the cable; γ is the angle between the lower diagonal brace on the right side of node a and the cable.

[0047] The internal force F2 of the lower diagonal brace section is transmitted to the upper diagonal brace through node b, and the vertical equilibrium equation of node b is:

[0048] F2×cos(ε / 2)=F4×cos(θ / 2) (2)

[0049] Where F4 is the internal force of the upper diagonal brace on the upper side of node b, θ is the angle of the upper diagonal brace on the upper side of node b, and ε is the angle of the lower diagonal brace on the lower side of node b.

[0050] This cross-type bracing arrangement can avoid the need for staggered arrangement when using a single diagonal brace, which would result in eccentric stress on the structure. On the other hand, when the cable fails, due to the certain height between node b and the upper chord beam, it will produce a function similar to that of a vierendelete truss, thus improving the bending resistance of the remaining structure.

[0051] According to the adjustment of the support rod angles α and θ, the support rod has three optimized configurations:

[0052] From the above analysis, we know that the greater the height between node b and the upper chord beam, that is, the lower the spatial position of node b, the higher the bending efficiency of the remaining structure. By moving node b downward, the angle α at node a and the angle ε at node b are increased, while the angles β and γ at node a and the angle θ at node b are reduced. According to the equilibrium conditions of equations (1) and (2), under the same residual cable retraction force, the internal force of the brace section is smaller, the brace efficiency is higher, and the force transmission path is more optimized.

[0053] To this end, the relative position parameter δ of the cross brace connection node is defined, and its calculation formula is:

[0054]

[0055] Where l i '、l i They are the height of the upper diagonal brace and the height of the upper and lower chord spaces at the corresponding positions respectively.

[0056] According to the above analysis, the higher the height of the upper diagonal brace, the more obvious the effect of the venter truss of the remaining structure after the cable fails, which is more conducive to the anti-progressive collapse performance of the beam string structure. Due to the symmetrical arrangement of the diagonal braces, the internal forces F2 of the lower diagonal brace section at node b offset each other in the horizontal direction, and the upper diagonal brace only needs to provide vertical balancing force. Therefore, by adjusting the angle θ and the relative position parameter δ of the cross brace connection node, configurations 1, 2, and 3 are obtained.

[0057] The installation method of the beam string structure of the present invention comprises the following steps:

[0058] 1) Based on the basic design information such as the structural span and load conditions, the new type of beam string structure can be determined according to the existing design method, including the rise, upper chord size, number and size of diagonal braces, area of ​​the lower cable and initial pretension. Then the strength and size of the connecting plate, the radius of the half sleeve section of the prestressed clamp, the size of the anchor plug and the number of high-strength bolts can be determined.

[0059] 2) The upper and lower diagonal braces are rigidly connected, and the upper and lower diagonal braces at the same position form a group of cross braces, which can be pre-welded in the factory according to the designed angle. Then, each group of cross braces is installed between the upper chord and the lower cable on site, wherein the side diagonal braces and the upper diagonal braces are hinged to the upper chord beam through the pin shaft, and the lower ends of the side diagonal braces and the lower diagonal braces are hinged to the prestressed clamp through the pin shaft.

[0060] 3) The lower cable is passed through all prestressed clamp sleeves in advance, and then the end of the lower cable is tensioned. After the internal force of the cable reaches the designed initial prestressing force, the two ends of the cable are anchored and fixed to the two ends of the upper chord beam.

[0061] 4) Peel off the PE sheath of the cable in the prestressed clamp section, allow the cable to directly contact the clamp, then tighten the high-strength bolts on both sides of the clamp sleeve to apply preload, and insert anchor plugs at both ends.

[0062] 5) The beam string structure is hoisted as a whole, with both ends connected to the supports on the lower support structure, and lateral support is applied to the structure to ensure its out-of-plane stability.

[0063] In order to verify the anti-collapse beam string structure provided by the present invention, the nonlinear dynamic calculation method in the load path transformation method was used for simulation analysis based on ANSYS / LS-DYNA software. The nonlinear dynamic calculation takes into account the dynamic effect and nonlinearity, and can simulate the entire collapse process, which is closest to the actual collapse of the structure. The dynamic response of the remaining structure was investigated by removing a single cable and compared with the traditional beam string structure. The span of the traditional beam string structure of the selected embodiment is 63m, the upper chord rise is 3.15m, the lower chord sag is 3.5m, the upper chord beam uses 740mm×560mm×18mm square steel pipe, the lower cable uses φ5×163, the strut uses φ245mm×24mm round steel pipe, the number of struts is 8, and they are arranged equidistantly along the span direction. With reference to this beam string structure, a new beam string structure benchmark model is established, and the cross section of the oblique strut is optimized according to the above optimization method.

[0064] The traditional beam string structure and three new beam string structures were taken as the research objects, and the progressive collapse analysis of the structure after the failure of the middle cable and the side cable was carried out. The vertical displacement time history of the mid-span node of the upper chord beam was extracted, such as Figure 7-9 As shown in the figure. The analysis shows that after the failure of the intermediate cable, the maximum displacement of the mid-span node of the traditional beam string upper chord reaches 30m, indicating that the traditional beam string has completely collapsed. For the new beam string structure, the maximum vertical displacement of the mid-span node of the three configurations is 0.312m, 0.305m, and 0.286m respectively; the final displacement after stabilization is 0.235m, 0.223m, and 0.208m respectively; the final deformation state is shown in the figure. Figure 10-12 .

[0065] After the side cables failed, the maximum displacement of the traditional beam string structure reached 35m, indicating that the structure had completely collapsed. For the new beam string structure, the maximum displacements of the three configurations were 0.295m, 0.266m, and 0.308m, respectively, and the final displacements after stabilization were 0.218m, 0.165m, and 0.265m, respectively; the final deformation state is as follows Figure 13-15 In summary, the progressive collapse resistance of the novel beam string structure proposed in the present invention is significantly improved compared with the traditional beam string structure.

[0066] The above embodiments are only preferred implementation modes of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and equivalent substitutions without departing from the principles of the present invention. These technical solutions after improvements and equivalent substitutions to the claims of the present invention all fall within the protection scope of the present invention.

Claims

1. A beam string structure with high progressive collapse resistance, comprising an upper string beam and a lower cable, characterized in that: A plurality of first nodes are arranged on the upper chord beam, a plurality of second nodes are arranged on the lower cable, a plurality of third nodes are arranged in the space between the upper chord beam and the lower cable, four oblique struts are arranged on each third node, and the four oblique struts are respectively connected to two adjacent first nodes on the upper chord beam and two adjacent second nodes on the lower cable; The four diagonal struts connected to the third node include two upper diagonal struts and two lower diagonal struts; the lower ends of the upper diagonal struts are rigidly connected to the upper ends of the lower diagonal struts; the upper ends of the upper diagonal struts and the upper ends of the side diagonal struts are hinged to the upper chord beam, and the lower ends of the lower diagonal struts and the lower ends of the side diagonal struts are hinged to the lower cable.

2. The beam string structure according to claim 1, characterized in that: An edge diagonal brace is arranged between the outermost first node and the outermost second node.

3. The beam string structure according to claim 1, characterized in that: A connecting plate is provided at the lower end of the upper chord beam, and the first node is formed on the connecting plate.

4. The beam string structure according to claim 1, characterized in that: The second node is formed by a prestressed clamp fixed on the lower cable.

5. The beam string structure according to claim 4, characterized in that: The prestressed fixture comprises a sleeve into which the lower cable can be placed and clamped, a node plate is arranged on the sleeve, and anchor plugs are arranged at both ends of the sleeve to clamp the lower cable at the ends; the lower diagonal brace is connected to the node plate.

6. The beam string structure according to claim 5, characterized in that: The sleeve is formed by connecting two half sleeves via fasteners.

7. The beam string structure according to claim 6, characterized in that: A tooth-like protrusion is arranged inside the sleeve.

8. The beam string structure according to claim 1, characterized in that: The upper chord beam is a steel beam or a truss beam.

9. The method for realizing the beam string structure according to any one of claims 1 to 8, characterized in that: By adjusting the height between the third node and the upper chord beam, the bending efficiency of the remaining structure after the cable fails is changed; when the height between the third node and the upper chord beam is larger, the bending efficiency of the remaining structure is higher.

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