Lightweight tower crane jib with high-strength cold-formed steel

Abstract

The present application belongs to the technical field of cranes, and particularly relates to a lightweight tower crane jib rack adopting high-strength cold-bending steel, aiming to solve the problems of stress concentration in the welding joint of chord and web, insufficient buckling resistance of jib rack section, and easy loosening after butt joint of adjacent jib rack sections, the jib rack comprising a tower body, a slewing table, a balance arm and a lifting arm, the lifting arm being composed of multiple jib rack sections spliced end to end, the upper chord and the lower chord of the jib rack section each being composed of a square steel tube and a C-shaped steel fixed on the top and the bottom of the square steel tube, the upper chord and the two lower chords being arranged in an isosceles triangle, the two lower chords and the upper chord being fixedly connected by webs with connecting lugs, the adjacent jib rack sections being connected by three sets of butt joint mechanisms, and the bottom of the adjacent chord being provided with a lower protruding plate with a triangular plate, the jib rack being used for a tower crane, capable of improving the fatigue life and buckling resistance of the joint, and automatically locking the butt joint when the jib rack is bent.

Description

Technical Field

[0001] This invention relates to the field of crane technology, and in particular to a lightweight tower crane boom made of high-strength cold-formed steel. Background Technology

[0002] Tower cranes are widely used on construction sites, and the length and weight of their booms directly affect the transportation and installation costs and lifting performance of the equipment. To reduce boom weight, a common practice is to use high-strength steel and design the boom as a truss structure composed of multiple boom sections. A boom section typically consists of an upper chord, a lower chord, and web members connecting the chords.

[0003] However, in the process of lightweighting existing booms, the connection nodes of the chord and web members are mostly connected by traditional right-angle welding. When subjected to repeated tensile and compressive stresses, stress concentration is easily generated at the weld, which leads to premature fatigue cracks at the nodes.

[0004] Booms are prone to buckling instability under wind loads or suspended loads, especially the middle sections of long booms. Insufficient buckling resistance will limit the improvement of lifting capacity.

[0005] The docking structure between adjacent boom sections may loosen due to vibration or bending during long-term use, affecting the safety and stability of the entire machine.

[0006] Therefore, there is a need for a boom structure that can reduce weight while improving buckling resistance and connection reliability. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing booms, such as stress concentration at the welding joints between the chord and web members, insufficient buckling resistance of the boom sections, and easy loosening after the joints of adjacent boom sections. The invention proposes a lightweight tower crane boom using high-strength cold-formed steel.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A lightweight tower crane boom using high-strength cold-formed steel includes a tower body, a slewing platform, a counterweight boom, and a lifting boom. The lifting boom is formed by splicing multiple boom sections end to end. Each boom section consists of an upper chord and two lower chords arranged in an isosceles triangle. The tops of the two lower chords are fixedly connected to the upper chords through multiple connecting groups II, and the two lower chords are fixedly connected to each other through multiple connecting groups I.

[0010] Two adjacent boom sections are spliced ​​together by three sets of docking mechanisms. The three sets of docking mechanisms are respectively set on the upper chord and the two lower chords, and are used to connect the two adjacent upper chords and the two adjacent lower chords. The docking mechanism includes a movable ring that is slidably sleeved on the outer wall of the lower chord. When the boom section at the far end bends, the movable ring can move along the axial direction of the lower chord and lock the two adjacent lower chords.

[0011] In one possible design, the upper and lower chords have identical structures. The upper chord consists of a square steel tube, two upper C-shaped steel sections, and two lower C-shaped steel sections. The two upper C-shaped steel sections are fixed to the top of the square steel tube, with their adjacent sides fixedly connected. The adjacent ends of the two upper C-shaped steel sections are respectively fixedly connected to the top two sides of the square steel tube. The two lower C-shaped steel sections are fixed to the bottom of the square steel tube, with their adjacent sides fixedly connected. The adjacent ends of the two lower C-shaped steel sections are respectively fixedly connected to the bottom two sides of the square steel tube. An L-shaped cavity is formed between the upper C-shaped steel section and the square steel tube, as well as between the lower C-shaped steel section and the square steel tube. By forming multiple cavities within the upper and lower chords through the upper and lower C-shaped steel sections, the buckling resistance is improved without significantly increasing the weight.

[0012] In one possible design, the docking mechanism further includes a plug strip fixed inside a square steel tube. The end of the plug strip away from the square steel tube slides into the adjacent square steel tube. Four L-shaped inserts are fixed in each of the four L-shaped cavities. One end of each L-shaped insert slides into the adjacent L-shaped cavity. Through the sliding insertion of the plug strip and the L-shaped inserts, the two adjacent upper chords and the two adjacent lower chords are initially axially docked.

[0013] In one possible design, the docking mechanism further includes a lower connecting plate fixed to one side of the moving ring. The lower connecting plate slides on the bottom of the lower chord. Two connecting arms II are fixed to the side of the lower connecting plate away from the moving ring. The ends of the two connecting arms II away from the moving ring are provided with lower protruding plates. The lower protruding plates are fixed to the bottom of adjacent lower chords. Two triangular plates are fixed to the side of the lower protruding plate near the moving ring. The tops of the triangular plates abut against the bottoms of the connecting arms II. The ends of the triangular plates away from the lower protruding plates are provided with arc-shaped heads. A stop bar is fixed to the bottom of the lower connecting plate. The stop bar is provided with arc-shaped grooves on the side near the lower protruding plates. The arc-shaped heads extend into the arc-shaped grooves. When the distal boom section bends, the adjacent lower chords bend the triangular plates through the lower protruding plates. The arc-shaped heads of the triangular plates disengage from the arc-shaped grooves and push the stop bars to move towards the rotary table.

[0014] In one possible design, the docking mechanism further includes an upper connecting plate fixed to the side of the moving ring near the lower connecting plate. The upper connecting plate slides on the top of the lower chord. Two connecting arms I are fixed to the side of the upper connecting plate away from the moving ring. An upper protrusion plate is provided between the two connecting arms I. The upper protrusion plate is fixed to the top of the adjacent lower chord. Each of the two connecting arms I has a slot I at its top. The same horizontal arm is engaged in the slots I. Two bolts II are provided in the horizontal arm. The bottom ends of the two bolts II are threaded to the corresponding connecting arms I. The slot II is provided on the side of the upper protrusion plate away from the upper connecting plate. The slot II engages with the horizontal arm. When the triangular plate pushes the stop bar to move, the stop bar drives the moving ring, the upper connecting plate, and the horizontal arm to move synchronously through the lower connecting plate. The horizontal arm is engaged in the slot II and drives the adjacent lower chord to be axially pulled through the upper protrusion plate, automatically forming an axial lock under bending action.

[0015] In one possible design, the connecting group I consists of web member III and web member IV, which are arranged in a V-shape. Both ends of web member III and web member IV are fixed with connecting lugs II, and both connecting lugs II are welded to one side of the corresponding lower chord to increase the stability between the two lower chords.

[0016] In one possible design, a plate is fixed to the side of the connecting lug II near the lower chord, and a strip groove is formed between the upper and lower adjacent C-shaped steels. The plate extends fixedly into the strip groove to increase the stability between two adjacent lower chords, and the plate is inserted into the strip groove to increase the overall strength of the lower chord.

[0017] In one possible design, the connecting group II consists of web member I and web member II arranged in a V-shape. Both web member I and web member II have connecting lugs I fixed at their top and bottom. The two connecting lugs I are fixedly connected to the upper chord and the corresponding lower chord, respectively. The connecting lugs I allow the stress to gradually diffuse from the center of contact between web member I and web member II and the upper and lower chords to the surrounding area, avoiding stress concentration in the weld. A connector existing in the insert plate structure is fixed on the side of the connecting lug I near the upper chord, and the connector extends into the strip groove located on top.

[0018] In one possible design, two bolts I pass through both the upper and lower chords. The bottom ends of the two bolts I pass through corresponding upper C-shaped steel, L-shaped inserts, square steel tubes, plug strips, and lower C-shaped steel in sequence, which is used to increase the connection stability between two adjacent upper chords and two adjacent lower chords.

[0019] In one possible design, multiple triangular guide plates are provided on both sides of the upper chord and on the opposite sides of the two lower chords. The triangular guide plates are isosceles triangles with their two isosceles sides arranged vertically. Multiple fixing strips are welded and fixed in the strip groove, and the multiple fixing strips are fixedly connected to one side of the corresponding triangular guide plate. The triangular guide plates cut and disperse the airflow, reducing the continuous vortex vibration formed in the boom section.

[0020] Beneficial effects: In this invention, by using a composite section composed of square steel tubes and C-shaped steel as the upper and lower chords, multiple L-shaped cavities are formed inside the members, increasing the moment of inertia of the section and improving the buckling resistance of the members. Under the premise of ensuring the same load-bearing capacity, the amount of steel used can be reduced and a higher load-bearing capacity can be obtained under the same weight, realizing the lightweighting of the structure. The composite section design allows the advantages of high-strength cold-formed steel to be fully utilized, overcoming the disadvantage of single-section cold-formed steel being prone to local buckling.

[0021] In this invention, the web members in connection group I and connection group II are fixedly connected to the upper chord and lower chord by connecting ears. The setting of connecting ears allows the stress to gradually diffuse from the end of the web member to the surface of the chord member, avoiding the severe stress concentration generated at the root of the weld in traditional right-angle welding joints. The stress diffusion design reduces the peak stress in the weld area and improves the fatigue resistance of the joint under cyclic load, thereby extending the service life of the entire boom. It is suitable for tower cranes that bear frequent lifting and unloading operations.

[0022] In this invention, adjacent boom sections are spliced ​​together by three sets of docking mechanisms. The docking mechanisms not only provide high-precision guiding and positioning through plug strips and L-shaped inserts, but also achieve mechanical locking through bolts and crossarms. At the same time, the displacement generated when the boom bends and deforms is utilized. Through the linkage of triangular plates, stop strips, moving rings, crossarms and upper convex plates, the bending deformation is converted into axial locking force, forming a self-locking mechanism. This can effectively resist the loosening tendency of the connecting bolts under alternating loads and vibration environments, and improve the long-term stability and safety of the connection.

[0023] In this invention, multiple isosceles triangular guide plates are set on both sides of the upper chord and on the side of the two lower chords that are far apart from each other. These plates can cut and disperse the airflow flowing over the surface of the boom, destroy the continuous boundary layer and periodic vortex shedding formed along the surface of the chord, thereby suppressing the formation of the Karman vortex street, avoiding large-scale vortex-induced resonance of the boom under specific wind speeds, reducing the risk of wind-induced fatigue damage to the structure, and improving the stability and safety of the boom under wind load.

[0024] In this invention, the insert plate fixed on the connecting lug II extends into the strip groove formed by the upper C-shaped steel and the lower C-shaped steel. This not only increases the connection area and anti-rotation capability between the connecting lug and the lower chord, and improves the lateral support effect of the connecting group I on the two lower chords, but also, as a stiffening rib embedded in the strip groove, the insert plate itself increases the local stiffness and strength of the chord at the connection point, preventing the local weakening effect caused by openings or welding, and making the structure more uniformly stressed.

[0025] In this invention, a composite section chord design is used to form a multi-cavity structure by combining square steel tubes with upper and lower C-shaped steel, which improves the buckling resistance of the components without significantly increasing the weight, thus achieving a lightweight boom. By setting connecting lugs between the web members and the chord members, the stress transmission path is optimized, eliminating the stress concentration problem of traditional welded joints and improving the fatigue resistance of the structure. By using plug strips and L-shaped inserts to ensure installation accuracy, and by using the energy generated by the bending deformation of the boom to drive the linkage of components such as triangular plates, moving rings, and cross arms, automatic axial locking at the connection is achieved, improving the reliability and durability of the connection. By arranging triangular guide plates on the surface of the chord members, the conditions for vortex-induced resonance caused by wind flow are destroyed, enhancing the boom's resistance to wind vibration. Attached Figure Description

[0026] Figure 1 A three-dimensional structural schematic diagram of a lightweight tower crane boom using high-strength cold-formed steel provided by the present invention;

[0027] Figure 2 A three-dimensional structural schematic diagram of the boom of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0028] Figure 3 A three-dimensional structural schematic diagram of a boom section of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0029] Figure 4 A three-dimensional structural schematic diagram of the upper chord of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0030] Figure 5 A three-dimensional exploded structural diagram of the upper chord of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0031] Figure 6 A three-dimensional exploded structural diagram of the lower chord and connecting group I of a lightweight tower crane boom using high-strength cold-formed steel, provided for the present invention.

[0032] Figure 7A three-dimensional exploded structural diagram of the connection group I of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0033] Figure 8 A three-dimensional exploded structural diagram of the lower chord and L-shaped insert of a lightweight tower crane boom using high-strength cold-formed steel, provided for the present invention.

[0034] Figure 9 A three-dimensional structural schematic diagram of the docking mechanism and lower chord of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0035] Figure 10 A three-dimensional structural schematic diagram of the docking mechanism of a lightweight tower crane boom using high-strength cold-formed steel provided by the present invention.

[0036] Figure 11 A three-dimensional exploded structural diagram of the arc groove and triangular plate of a lightweight tower crane boom using high-strength cold-formed steel provided by the present invention.

[0037] Figure 12 This is a three-dimensional exploded structural diagram of the connecting arm I and the upper convex plate of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0038] Figure 13 This is a three-dimensional exploded structural diagram of the lower chord and triangular guide plate of a lightweight tower crane boom using high-strength cold-formed steel, provided by the present invention.

[0039] In the diagram: 1. Tower body; 2. Turntable; 3. Counterweight boom; 4. Lifting boom; 5. Boom section; 6. Upper chord; 7. Lower chord; 8. Square steel tube; 9. Upper C-shaped steel; 10. L-shaped cavity; 11. Lower C-shaped steel; 12. Strip groove; 13. Web member I; 14. Web member II; 15. Connecting lug I; 16. Web member III; 17. Web member IV; 18. Connecting lug II; 19. Insert plate; 20. Plug strip; 21. L-shaped insert strip; 22. Bolt Ⅰ; 23. Moving ring; 24. Upper connecting plate; 25. Connecting arm Ⅰ; 26. Slot Ⅰ; 27. Cross arm; 28. Bolt Ⅱ; 29. ​​Upper convex plate; 30. Slot Ⅱ; 31. Lower connecting plate; 32. Connecting arm Ⅱ; 33. Stop bar; 34. Arc groove; 35. Lower convex plate; 36. Triangular plate; 37. Arc head; 38. Triangular guide plate; 39. Fixing strip; 40. Docking mechanism; 41. Connecting group Ⅰ; 42. Connecting group Ⅱ. Detailed Implementation

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0041] In one embodiment: Refer to Figures 1-3 A lightweight tower crane boom using high-strength cold-formed steel is disclosed, relating to the field of crane technology. It mainly includes a tower body 1, a slewing platform 2, a counterweight boom 3, and a lifting boom 4. The lifting boom 4 is composed of multiple boom sections 5 spliced ​​end-to-end. Each boom section 5 consists of an upper chord 6 and two lower chords 7, arranged in an isosceles triangle. This triangular arrangement provides good geometric stability, ensuring that when the lifting boom 4 is subjected to vertical loads, the upper chord 6 bears the compressive force, and the two lower chords 7 bear the tensile force, resulting in a clear force distribution. The tops of the two lower chords 7 are fixedly connected to the upper chord 6 via multiple connecting groups II 42, and the two lower chords 7 are fixedly connected to each other via multiple connecting groups I 41. Adjacent boom sections 5 are spliced ​​together via three sets of docking mechanisms 40, which are respectively installed on the upper chord 6 and the two lower chords 7 to connect adjacent upper chords 6 and adjacent lower chords 7.

[0042] Reference Figure 3 The boom section 5 is the basic unit that constitutes the boom 4. Multiple boom sections 5 are connected end to end through the docking mechanism 40 to form the boom 4 of the required length. This modular design allows the boom length to be flexibly adjusted according to actual construction needs, and also facilitates transportation and storage. The upper chord 6 and the lower chord 7 have the same structure. The cross-sectional structure of the upper chord 6 and the lower chord 7 will be described in detail below.

[0043] Reference Figure 3 and Figure 4 The upper chord 6 is composed of a square steel tube 8, two upper C-shaped steels 9, and two lower C-shaped steels 11. The two upper C-shaped steels 9 are fixed to the top of the square steel tube 8, and the two upper C-shaped steels 9 are fixedly connected on their adjacent sides. The two upper C-shaped steels 9 are also fixedly connected to the two sides of the square steel tube 8 respectively. The two lower C-shaped steels 11 are fixed to the bottom of the square steel tube 8, and the two lower C-shaped steels 11 are fixedly connected on their adjacent sides. The two lower C-shaped steels 11 are also fixedly connected to the two sides of the square steel tube 8 respectively. Thus, an L-shaped cavity 10 is formed between the upper C-shaped steels 9 and the square steel tube 8, as well as between the lower C-shaped steels 11 and the square steel tube 8. Through the arrangement of the upper C-shaped steels 9 and the lower C-shaped steels 11, multiple cavities are formed in the upper chord 6 and the lower chord 7.

[0044] Specifically, the square steel tube 8 itself is a closed cavity. The square steel tube 8 and the upper C-shaped steel 9 form two left-right symmetrical L-shaped cavities 10, and the square steel tube 8 and the lower C-shaped steel 11 also form two left-right symmetrical L-shaped cavities 10. This multi-cavity design improves the buckling resistance of the members without increasing the weight significantly. When the upper chord 6 is under compression, the square steel tube 8 inside acts as the main load-bearing component, while the surrounding C-shaped steel and L-shaped cavities 10 act like ribs, increasing the moment of inertia of the section and thus improving the stability of the members. This prevents local or overall instability before reaching the yield strength. This closed-semi-closed composite section composed of cold-formed steel has higher load-bearing efficiency and fatigue resistance than a single section steel of the same weight.

[0045] Reference Figure 3 , Figure 6 and Figure 7 The connecting group I41 consists of web members III16 and IV17, which are arranged in a V-shape. Both ends of web members III16 and IV17 are fixed with connecting lugs II18. Both connecting lugs II18 are welded to one side of the corresponding lower chord 7. Here, the corresponding lower chord 7 refers to the lower chord 7 connected to the end of the web member. Web members III16 and IV17 are connected between two parallel lower chords 7, forming a transverse truss structure to increase the stability between the two lower chords 7. The V-shape arrangement allows the web members to effectively transmit and disperse the tensile or compressive forces borne by the lower chord 7, avoiding deformation of the lower chord 7 due to insufficient transverse stiffness. The design of connecting lugs II18 changes the connection method between the web members and the lower chord 7 from direct butt welding to welding through connecting lugs II18. This method increases the contact area of ​​the weld and allows the weld to avoid the stress concentration area on the edge of the main chord, thereby improving the reliability of the connection node.

[0046] Reference Figure 4 and Figure 7A plate 19 is fixed to the side of the connecting ear II 18 near the lower chord 7. A strip groove 12 is formed between the upper C-shaped steel 9 and the lower C-shaped steel 11 that are adjacent to each other. Specifically, in the upper chord 6, two upper C-shaped steel 9 and two lower C-shaped steel 11 are symmetrically arranged on the upper and lower sides of the square steel tube 8. A gap is left between the upper C-shaped steel 9 and the lower C-shaped steel 11, which is the strip groove 12. The plate 19 is fixedly extended into the strip groove 12. The plate 19 has two functions: first, the plate 19 and the strip groove 11 form a groove. The fit of the groove 12 increases the connection strength between the connecting lug II 18 and the lower chord 7, which can further increase the stability between two adjacent lower chords 7 and prevent the connecting lug II 18 from rotating or disengaging when subjected to large loads. Secondly, the insertion plate 19 is inserted into the groove 12, which is equivalent to adding a transverse stiffening rib to the cross section of the chord, which can increase the overall bending and torsional strength of the lower chord 7. This local reinforcement measure is particularly important for chords composed of cold-formed thin-walled steel sections.

[0047] Reference Figure 3 and Figure 5 Connection group II42 consists of web members I13 and II14, which are arranged in a V-shape. Both web members I13 and II14 have connecting lugs I15 fixed at their top and bottom. The connecting lug I15 at the top of web member I13 is fixedly connected to the upper chord 6, and the connecting lug I15 at the bottom of web member I13 is fixedly connected to one lower chord 7. Similarly, the connecting lug I15 at the top of web member II14 is fixedly connected to the upper chord 6, and the connecting lug I15 at the bottom of web member II14 is fixedly connected to another lower chord 7. Connection group II42 forms a triangular web member system in the main view direction of boom section 5, and is a key component connecting the upper chord 6 and the two lower chords 7. The V-shaped web members I13 and II14, together with the upper chord 6 and lower chords 7, form a series of continuous triangular structures, which is the basis for the stability of the truss structure. The connecting lugs I15... The setting of 5 allows stress to gradually diffuse from the center of contact between web members I13 and II14 and the upper chord 6 and lower chord 7 to the surrounding area. In traditional direct welding of web members and chord members, the root of the weld is prone to forming a stress concentration zone under triaxial stress, which is very easy to generate fatigue cracks under alternating loads. However, by using connecting lug I15, stress is transferred from the web member to connecting lug I15, and then diffused from connecting lug I15 to a larger area of ​​the chord member through its welding surface with the chord member. This avoids the stress concentration in the weld that is easy to form in traditional right-angle welding joints, and greatly improves the fatigue life of the joint. In addition, a connector with the same structure as the insert plate 19 is fixed on the side of connecting lug I15 near the upper chord 6. This connector is also fixedly extended into the strip groove 12 on the upper chord 6 to increase the joint strength of connecting group II42 and ensure that the load transfer between the upper chord 6 and the lower chord 7 is uniform and reliable.

[0048] Reference Figure 3 and Figure 8 The docking mechanism 40 is the core component for achieving rapid, precise, and reliable connection of multiple boom sections 5. The docking mechanism 40 includes a plug strip 20 fixed inside a square steel tube 8. The plug strip 20 is a long strip of metal whose outer contour matches the inner contour of the square steel tube 8. At the end of one boom section 5, one end of the plug strip 20 is firmly welded or otherwise fixed inside the square steel tube 8. When two boom sections 5 are docked, the end of the plug strip 20 away from the square steel tube 8 slides and extends into the square steel tube 8 of the adjacent boom section 5. Simultaneously, four L-shaped inserts 21 are fixed in each of the four L-shaped cavities 10. The shape of the L-shaped inserts 21 is consistent with the shape of the L-shaped cavities 10. Similarly, in one boom section 5... At the end of boom section 5, one end of the L-shaped insert 21 is fixed inside the L-shaped cavity 10. During docking, one end of each of the four L-shaped inserts 21 slides into the L-shaped cavity 10 of the adjacent boom section 5. Through the arrangement of the insert 20 and the L-shaped insert 21, the two adjacent upper chords 6 and the two lower chords 7 can be initially docked. This multi-cavity, multi-instrument guiding docking method ensures the coaxiality and positional accuracy of the two adjacent boom sections 5, providing a foundation for subsequent fastening connections. The insert 20 and the L-shaped insert 21 not only play a guiding role, but also act as shear keys in the final connection structure, bearing the shear force from the end of the boom section 5 and reducing the shear load borne by the connecting bolts.

[0049] Reference Figures 9-11The docking mechanism 40 also includes a movable ring 23 slidably sleeved on the outer wall of the lower chord 7. The movable ring 23 is an annular part with an inner diameter slightly larger than the outer contour of the lower chord 7, allowing the movable ring 23 to slide freely axially on the outer wall of the lower chord 7. A lower connecting plate 31 is fixed to one side of the movable ring 23, and the lower connecting plate 31 slides on the bottom of the lower chord 7. The lower connecting plate 31 is a downward extension of the movable ring 23, and its top contacts the bottom surface of the lower chord 7 and can slide relative to it. Two connecting arms II 32 are fixed to the side of the lower connecting plate 31 away from the movable ring 23. These two connecting arms II 32 are parallel to each other and extend from the lower connecting plate 31 away from the movable ring 23. One end of ring 23 is provided with a lower convex plate 35, which is fixed to the bottom of the adjacent lower chord 7. The lower convex plate 35 is fixed to the lower chord 7 of another boom section 5 to be connected with. Two triangular plates 36 are fixed on the side of the lower convex plate 35 near the moving ring 23. The positions of the two triangular plates 36 correspond one-to-one with the positions of the two connecting arms II 32. The top of the triangular plate 36 abuts against the bottom of the connecting arm II 32. The end of the triangular plate 36 away from the lower convex plate 35 is provided with an arc-shaped head 37. A stop bar 33 is fixed to the bottom of the lower connecting plate 31. The stop bar 33 is a plate-shaped structure perpendicular to the lower connecting plate 31. The side of the stop bar 33 near the lower convex plate 35 is provided with an arc-shaped groove 34, and the arc-shaped head 37 extends into the arc-shaped groove 34. When the boom undergoes initial bending, the deformation of the triangular plate 36 will force the arc-shaped head 37 to generate a separation tangential force in the arc-shaped groove 34. Even if the degree of bending is small and the arc head 37 fails to completely disengage, the thrust it applies will be transmitted to the stop bar 33 through the inclined surface of the arc groove 34, thereby initiating the movement of the moving ring 23. As the bending intensifies, this thrust increases non-linearly, ensuring reliable execution of the locking action. This curved wedge clamping design overcomes the shortcomings of traditional rigid triggering mechanisms that require excessively high deformation accuracy.

[0050] Specifically, after the two boom sections 5 are spliced ​​together, when the boom 4 bears a load, especially when the far boom section 5 bends, the corresponding lower chord 7 will bend accordingly. This bending deformation will cause the lower convex plate 35 and the triangular plate 36 fixed to the lower chord 7 to have a downward displacement or angle change. Since the arc-shaped head 37 of the triangular plate 36 is initially located in the arc-shaped groove 34 of the stop bar 33, when the lower convex plate 35 and the triangular plate 36 bend with the lower chord 7, the triangular plate... One end of the triangular plate 36 will abut against the stop bar 33, and the arc-shaped head 37 of the triangular plate 36 will push the stop bar 33. Since the stop bar 33 is fixed on the lower connecting plate 31, and the lower connecting plate 31 is fixed on the moving ring 23, the pushing force will cause the stop bar 33 to drive the lower connecting plate 31 and the moving ring 23 to move towards the rotary table 2. In other words, the bending deformation of the distal boom section 5 is transformed into a force that pulls the moving ring 23 to move axially through the interaction between the triangular plate 36 and the stop bar 33.

[0051] Reference Figure 9 , Figure 10 and Figure 12 The docking mechanism 40 also includes an upper connecting plate 24 fixed to the side of the moving ring 23 near the lower connecting plate 31, and the upper connecting plate 24 slides on the top of the lower chord 7. Similar to the lower connecting plate 31, the upper connecting plate 24 is an upward extension of the moving ring 23, and its bottom contacts the top surface of the lower chord 7 and can slide relative to it. Two connecting arms I 25 are fixed on the side of the upper connecting plate 24 away from the moving ring 23. The two connecting arms I 25 are parallel to each other and extend from the lower connecting plate 31 away from the moving ring 23. An upper protrusion 29 is provided between the two connecting arms I 25, and the upper protrusion 29 is fixed on the top of the adjacent lower chord 7. The position of the upper protrusion 29 is between the two connecting arms I 25. The top of each of the two connecting arms I 25 is provided with a slot I 26. The same horizontal arm 27 is engaged in the two slots I 26. The horizontal arm 27 is a long strip-shaped part that spans across the two The connecting arm 25 is embedded in the slot 126. The cross arm 27 is provided with two bolts 228. The bottom ends of the two bolts 228 are threaded to the corresponding connecting arm 125 to fix the cross arm 27 to the connecting arm 125. The upper convex plate 29 is provided with a slot 30 on the side away from the upper connecting plate 24. The slot 30 is engaged with the cross arm 27. During initial installation, the cross arm 27 is simultaneously engaged in the slot 126 of the connecting arm 125 and the slot 30 of the upper convex plate 29 and fixed by bolts 228. This forms a solid connection, connecting the moving ring 23, the connecting arm 125, the cross arm 27 and the upper convex plate 29 into a whole. The upper convex plate 29 is fixed on the lower chord 7 of another boom section 5. Therefore, this connection actually connects the boom section 5 where the moving ring 23 is located to the lower chord 7 of the adjacent boom section 5.

[0052] Now, combining the actions of the two parts mentioned above, when the distal boom section 5 bends and pushes the stop bar 33 to move through the triangular plate 36, the stop bar 33 drives the moving ring 23 to move synchronously to the upper connecting plate 24 and the cross arm 27 through the lower connecting plate 31. Since the cross arm 27 is engaged in the slot II 30, the movement of the moving ring 23 will apply a pulling force to the upper convex plate 29 through the cross arm 27. This pulling force can drive the corresponding lower chord 7 to be pulled axially through the upper convex plate 29. In other words, when the distal boom section 5 bends and attempts to separate the connection of the two lower chords 7, the bending deformation generates a force that pulls the two lower chords 7 together through the path of triangular plate 36, stop bar 33, moving ring 23, cross arm 27, and upper convex plate 29. Therefore, under its own weight or bending action, the docking mechanism can automatically form an axial lock. This self-locking mechanism effectively utilizes the deformation of the structure to resist further deformation, improves the fatigue resistance and reliability of the connection, and prevents the bolts from loosening under long-term vibration.

[0053] Reference Figure 4 and Figure 8 To further increase the connection strength between the two adjacent upper chords 6 and the two lower chords 7, two bolts I22 are inserted into each of the upper chords 6 and the lower chords 7. After the insertion of the plug bar 20 and the L-shaped insert bar 21, the two bolts I22 pass through the pre-machined holes. The bottom ends of the two bolts I22 pass through the corresponding upper C-shaped steel 9, L-shaped insert bar 21, square steel tube 8, plug bar 20, and lower C-shaped steel 11 in sequence. Specifically, one bolt I22 enters from the top of an upper C-shaped steel 9 on the upper chord 6, and passes through the upper C-shaped steel 9, the L-shaped insert bar 21 below it, the top wall of the square steel tube 8, the plug bar 20, and the lower C-shaped steel 11 in sequence. The bottom wall of steel pipe 8, the lower L-shaped insert 21, and finally the lower C-shaped steel 11 are passed through and locked with nuts. Another bolt I 22 passes through in the same way. Through these two bolts I 22, the upper C-shaped steel 9, L-shaped insert 21, square steel pipe 8, plug bar 20, and lower C-shaped steel 11 are all fastened together to form a high-strength mechanical connection. Bolt I 22 provides preload, which generates friction between the components and can effectively transmit axial force and bending moment. At the same time, bolt I 22, plug bar 20, and L-shaped insert 21 together form a shear-resistant connection system, ensuring the reliability and integrity of the connection between boom sections 5.

[0054] In another embodiment: Refer to Figure 3 and Figure 13Multiple triangular guide plates 38 are provided on both sides of the upper chord 6 of the boom section 5 and on the side of the two lower chords 7 that are far apart from each other. The triangular guide plates 38 are isosceles triangles, and the two isosceles sides of the triangular guide plates 38 are arranged vertically, that is, one vertex of the triangular guide plate 38 faces upward and the other vertex faces downward, and its base is set vertically. Multiple triangular guide plates 38 are arranged at equal or unequal intervals along the length of the chord. Multiple fixing strips 39 are welded and fixed in the strip groove 12. Multiple fixing strips 39 are fixedly connected to one side of the corresponding triangular guide plate 38. The fixing strips 39 are embedded in the strip groove 12, providing a solid installation base for the triangular guide plates 38. Multiple triangular guide plates 38 are arranged in the length of the chord, avoiding the welding positions of connecting ears I 15 and connecting ears II 18, and are firmly embedded in the strip groove 12 by fixing strips 39. This arrangement ensures that the guide plate will not interfere with any connecting structure in space. At the same time, the fixing strip 39 at its bottom also serves to locally strengthen the strip groove 12, making up for the weakening of the heat-affected zone caused by welding the guide plate. With the setting of the triangular guide plate 38, when the airflow passes through the boom section 5, the airflow will be cut and dispersed when it encounters the isosceles hypotenuse of the triangular guide plate 38. This structure destroys the continuous boundary layer formed along the chord surface and prevents the regular shedding of periodic vortices, thereby reducing the possibility of continuous vortex vibration in the boom section 5. Vortex-induced vibration is one of the main causes of fatigue failure of tall and long-span structures. As a passive control device, the triangular guide plate 38 can effectively suppress wind-induced vibration at a very low cost and extend the fatigue life of the boom 4.

[0055] A method for using a lightweight tower crane boom made of high-strength cold-formed steel includes the following steps:

[0056] S1. The boom 4 is composed of multiple boom sections 5 spliced ​​end to end. The upper chord 6 and two lower chords 7 of each boom section 5 are arranged in an isosceles triangle. This triangular spatial truss structure has geometric invariance. When the boom 4 bears the lifting load, the bending moment generated by the lifting load acts on the boom as a whole. Under this bending moment, the upper chord 6 located at the vertex of the triangle bears axial pressure, and the lower chords 7 located at the two ends of the base of the triangle bear axial tension. Since the triangular structure does not allow geometric deformation, all external loads are converted into axial forces of each member. The pressure of the upper chord 6 is transmitted to the lower chord 7 through the connecting group II 42, while the tension of the lower chord 7 is balanced between the two lower chords 7 through the connecting group I 41. This force mechanism makes full use of the strength of the material and avoids the members bearing additional bending stress.

[0057] S2, the upper chord 6, and the lower chord 7 adopt the same composite section structure. This section consists of a square steel tube 8 at the center and upper C-shaped steel 9 and lower C-shaped steel 11 welded to the upper and lower sides of the square steel tube 8. The square steel tube 8 serves as the main load-bearing component, providing the foundation with compressive and bending stiffness. After the upper C-shaped steel 9 and lower C-shaped steel 11 are fixedly connected to the square steel tube 8, multiple L-shaped cavities 10 are formed inside the member. These cavities are equivalent to multiple longitudinally distributed reinforcing ribs in the cross-section. According to the principles of mechanics of materials, the buckling resistance of a member is positively correlated with its moment of inertia. By adding C-shaped steel around the square steel tube 8, the moment of inertia of the cross-section is significantly improved. The increase in material weight is relatively small. Specifically, when the upper chord 6 is compressed, the square steel tube 8 inside it bears the compressive stress first. If only the square steel tube 8 is used, the tube wall may buckle locally when the wall thickness is thin. However, the presence of the L-shaped cavity 10 divides the tube wall of the square steel tube 8 into multiple smaller plate units. The aspect ratio of each unit is reduced, and its local buckling critical stress increases accordingly. Therefore, this composite section provides higher resistance to local buckling and overall buckling under the same amount of steel, realizing the lightweight of the boom. Conversely, under the same load requirements, thinner steel can be used to further reduce the structural self-weight.

[0058] In S3, the web members in connection groups I 41 and II 42 are not directly welded to the surface of the chord members. Instead, they are fixed to the chord members via connecting lugs. These lugs are typically trapezoidal or triangular in shape, with the smaller end connecting to the web member and the larger bottom welded to the chord member. When the web member is subjected to axial tension or compression, the stress is first transferred from the end face of the web member to the small area of ​​the connecting lug. As the stress propagates within the connecting lug, the stress lines gradually disperse due to the increasing cross-sectional width of the lug. By the time the stress reaches the weld interface between the connecting lug and the chord member, the stress has diffused from a concentrated point or line load into a distributed stress over a larger area. The surface load in the region is much lower than the peak stress at the weld root in a conventional right-angle welded joint. Meanwhile, the insert plate 19 fixed on the connecting lug II 18 extends into the strip groove 12 formed between the upper C-shaped steel 9 and the lower C-shaped steel 11. The cooperation between the insert plate 19 and the strip groove 12 increases the contact area between the connecting lug and the chord and directly transmits some of the shear force to the internal cavity of the chord, further dispersing the stress concentration in the joint region. This stress diffusion mechanism avoids the triaxial stress concentration state caused by the sharp notch at the weld root in conventional welded structures and reduces the probability of fatigue crack initiation under alternating loads.

[0059] S4. Two adjacent boom sections 5 are connected by three sets of docking mechanisms 40. Each set of docking mechanisms 40 corresponds to an upper chord 6 or a lower chord 7. The working process of the docking mechanism 40 is divided into three stages.

[0060] S4.1 The first stage is the guiding and positioning stage: At the end of a boom section 5, a plug strip 20 is fixed inside the square steel tube 8, and L-shaped insert strips 21 are fixed inside the four L-shaped cavities 10 respectively. During splicing, the plug strip 20 slides into the square steel tube 8 of the adjacent boom section 5, and at the same time, the four L-shaped insert strips 21 slide into the four L-shaped cavities 10 of the adjacent boom section 5. This multi-point and multi-section matching method ensures the precise alignment of the two adjacent boom sections 5 in the radial and axial directions, and allows the end faces of the two boom sections 5 to fit tightly together.

[0061] S4.2 The second stage is the mechanical locking stage: After the plug bar 20 and L-shaped plug bar 21 are guided and inserted, the bolt I22, which passes through the upper C-shaped steel 9, L-shaped plug bar 21, square steel tube 8, plug bar 20 and lower C-shaped steel 11, provides a strong axial preload, making the components of each layer fit tightly together. The huge friction force generated by the contact surface is used to resist the axial tensile and compressive loads between adjacent boom sections 5. At the same time, at the lower chord 7, the moving ring 23 is sleeved on the outer wall of the lower chord 7, and the two connecting arms on the moving ring 23 are locked together. II32 and the lower convex plate 35 on the adjacent lower chord 7 are positioned by the triangular plate 36 and the arc-shaped head 37 and arc-shaped groove 34 of the stop bar 33. The cross arm 27 between the two connecting arms I25 on the moving ring 23 is simultaneously inserted into the slot I26 of the connecting arm I25 and the slot II30 of the convex plate 29 on the adjacent lower chord 7. The cross arm 27 is locked to the connecting arm I25 by bolt II28. This mechanical locking structure provides initial connection stiffness and preload, ensuring that the boom section 5 will not undergo relative displacement under normal working conditions.

[0062] S4.3 The third stage is the self-locking stage: This stage utilizes the displacement energy generated by the bending deformation of the boom. When the boom section 5 at the far end of the boom 4 bends downward due to the load or wind load, the tension on the two lower chords 7 of the boom section 5 increases, and there is a tendency for axial separation at the connection. At the same time, the bending deformation causes the lower convex plate 35 and triangular plate 36 fixed at the end of the lower chord 7 to have a downward displacement relative to the stop bar 33 on the moving ring 23. The arc-shaped head 37 of the triangular plate 36 slides in the arc-shaped groove 34 of the stop bar 33 and applies a thrust to the stop bar 33. Since the stop bar 33 is fixedly connected to the moving ring 23 through the lower connecting plate 31, and the moving ring 23 is connected to the upper convex plate 7 of the lower chord 7 of the adjacent boom section 5 through the upper connecting plate 24, connecting arm I 25, and cross arm 27, the lower convex plate 35 and triangular plate 36 are fixedly connected to the moving ring 23 through the upper connecting plate 24, connecting arm I 25, and cross arm 27. The plate 29 is fixedly connected, so the thrust is converted into a force that pulls the moving ring 23 toward the boom root. This movement is transmitted through the cross arm 27 and the upper convex plate 29, and is finally converted into a force that pulls the lower chord 7 of the bent boom section 5 axially toward the boom root. Therefore, the greater the bending deformation of the boom, the greater the self-locking tension generated by this mechanical linkage. This tension directly counteracts the tendency that causes the connection to separate, which is equivalent to an adaptive enhancement of the structural stiffness. This passive self-locking mechanism effectively suppresses the relative slippage of the connection under dynamic load and automatically compensates for the possible loosening of the bolt preload. It improves the connection stability from the mechanical structure level. This self-locking mechanism automatically compensates for the bolt loosening that may be caused by vibration or deformation, so that the connection always remains tight under dynamic load.

[0063] S5. Multiple isosceles triangular guide plates are arranged on both sides of the upper chord 6 and on the opposite sides of the two lower chords 7. These guide plates are welded to the strip groove 12 by fixing strips 39, with their two isosceles sides arranged vertically. When the airflow flows over the chord surface in a direction perpendicular to the boom axis, without guide plates, the airflow will form periodic vortex shedding on the back of the cylindrical or prismatic chord, i.e., the Karman vortex street phenomenon. When the vortex shedding frequency is close to a certain natural frequency of the boom, it will cause severe lateral vibration. The function of the isosceles triangular guide plates 38 is to force the airflow around the chord surface to the first edge (i.e., the triangle) through their protruding edges. Separation occurs at the side of the deflector, thus disrupting the development of the boundary layer and preventing the formation of regular Karman vortex streets. At the same time, the deflector itself forms a raised turbulence element on the chord surface, disrupting the continuous boundary layer formed along the chord surface. As the airflow passes through each deflector, it is cut into small turbulent streams. These turbulent streams interfere with each other, making the shedding of vortices random and irregular, and unable to form periodic pulsating pressure with concentrated energy. This avoids the coupling between the vortex shedding frequency and the boom's natural frequency, eliminating the conditions for vortex-induced resonance. As a result, the boom is only affected by the average wind pressure and not by periodic alternating wind vibration excitation, ensuring the fatigue life of the structure.

[0064] Considering the outdoor dusty working environment of tower cranes, dustproof sealing rings (e.g., rubber or polyurethane skeleton oil seals) are installed between the two ends of the moving ring 23 and the lower chord 7, and dust scrapers (e.g., scrapers made of wear-resistant polyoxymethylene) are provided on both sides of the sliding contact surface between the lower connecting plate 31 and the bottom of the lower chord 7. These sealing and dust scraping structures are used to prevent external sand and mud from entering the sliding mating surface, ensuring the reliability and sensitivity of the docking mechanism 40 throughout the entire life cycle of the boom.

[0065] Although this device is designed with a dustproof structure, given the extreme nature of the working environment, it is recommended to clean and lubricate the sliding parts such as the moving ring 23 after each large project or after every 500 hours of work to ensure its long-lasting automatic locking function.

[0066] The accompanying drawings in this application are for illustrative purposes only. The dimensions and shapes of the components shown are not actual limitations but are merely schematic representations. In actual implementation, the components can be reasonably configured and adjusted according to specific needs and actual conditions.

[0067] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A lightweight tower crane boom using high-strength cold-formed steel, comprising a tower body (1), a slewing platform (2), a counterweight boom (3), and a lifting boom (4), characterized in that, The boom (4) is formed by splicing multiple boom sections (5) end to end. Each boom section (5) consists of an upper chord (6) and two lower chords (7). The upper chord (6) and the two lower chords (7) are arranged in an isosceles triangle. The tops of the two lower chords (7) are fixedly connected to the upper chord (6) through multiple connecting groups II (42). The two lower chords (7) are fixedly connected to each other through multiple connecting groups I (41). The upper chord (6) and lower chord (7) have the same structure. The upper chord (6) is composed of a square steel tube (8), two upper C-shaped steels (9), and two lower C-shaped steels (11). The two upper C-shaped steels (9) are fixed to the top of the square steel tube (8). The two upper C-shaped steels (9) are fixedly connected to each other on their adjacent sides. The two upper C-shaped steels (9) are fixedly connected to the top two sides of the square steel tube (8) respectively at their adjacent ends. The two lower C-shaped steels (11) are fixed to the bottom of the square steel tube (8). The two lower C-shaped steels (11) are fixedly connected at their close sides, and the ends of the two lower C-shaped steels (11) are fixedly connected to the bottom sides of the square steel tube (8). The upper C-shaped steel (9) and the square steel tube (8) and the lower C-shaped steel (11) and the square steel tube (8) form L-shaped cavities (10). Multiple cavities are formed in the upper chord (6) and the lower chord (7) by the upper C-shaped steel (9) and the lower C-shaped steel (11), thereby improving the buckling resistance without increasing the weight significantly. Two adjacent boom sections (5) are spliced ​​together by three sets of docking mechanisms (40). The three sets of docking mechanisms (40) are respectively set on the upper chord (6) and the two lower chords (7) to connect the two adjacent upper chords (6) and the two adjacent lower chords (7). The docking mechanism (40) includes a movable ring (23) that is slidably sleeved on the outer wall of the lower chord (7). When the boom section (5) at the far end bends, the movable ring (23) can move along the axial direction of the lower chord (7) and lock the two adjacent lower chords (7). The docking mechanism (40) also includes a plug bar (20) fixed inside the square steel tube (8). The end of the plug bar (20) away from the square steel tube (8) slides into the adjacent square steel tube (8). Four L-shaped inserts (21) are fixed in each of the four L-shaped cavities (10). One end of the four L-shaped inserts (21) slides into the adjacent L-shaped cavity (10). Through the sliding insertion of the plug bar (20) and the L-shaped inserts (21), the two adjacent upper chords (6) and the two adjacent lower chords (7) are initially docked axially. The docking mechanism (40) further includes a lower connecting plate (31) fixed to one side of the moving ring (23). The lower connecting plate (31) slides on the bottom of the lower chord (7). Two connecting arms II (32) are fixed on the side of the lower connecting plate (31) away from the moving ring (23). A lower convex plate (35) is provided at the end of the two connecting arms II (32) away from the moving ring (23). The lower convex plate (35) is fixed to the bottom of the adjacent lower chord (7). Two triangular plates (36) are fixed on the side of the lower convex plate (35) near the moving ring (23). The top of the triangular plate (36) is connected to the connecting arm II (32). 2) Bottom contact, the triangular plate (36) is provided with an arc head (37) at the end away from the lower convex plate (35), the bottom of the lower connecting plate (31) is fixed with a stop bar (33), the stop bar (33) is provided with an arc groove (34) on the side near the lower convex plate (35), and the arc head (37) extends into the arc groove (34); when the far end of the boom section (5) bends, the adjacent lower chord (7) drives the triangular plate (36) to bend through the lower convex plate (35), and the arc head (37) of the triangular plate (36) comes out from the arc groove (34) and pushes the stop bar (33) to move towards the turntable (2).

2. The lightweight tower crane boom using high-strength cold-formed steel according to claim 1, characterized in that, The docking mechanism (40) further includes an upper connecting plate (24) fixed to the side of the moving ring (23) near the lower connecting plate (31). The upper connecting plate (24) slides on the top of the lower chord (7). Two connecting arms I (25) are fixed on the side of the upper connecting plate (24) away from the moving ring (23). An upper protrusion plate (29) is provided between the two connecting arms I (25). The upper protrusion plate (29) is fixed to the top of the adjacent lower chord (7). The top of each of the two connecting arms I (25) is provided with a slot I (26). The same cross arm (27) is engaged in the two slots I (26). Two bolts II are provided in the cross arm (27). (28) The bottom ends of the two bolts II (28) are threaded to the corresponding connecting arms I (25). The upper convex plate (29) is provided with a slot II (30) on the side away from the upper connecting plate (24). The slot II (30) is engaged with the cross arm (27). When the triangular plate (36) pushes the stop bar (33) to move, the stop bar (33) drives the moving ring (23), the upper connecting plate (24) and the cross arm (27) to move synchronously through the lower connecting plate (31). The cross arm (27) is engaged in the slot II (30) and drives the adjacent lower chord (7) to be pulled axially through the upper convex plate (29). Under the bending action, it automatically forms an axial lock.

3. A lightweight tower crane boom using high-strength cold-formed steel according to claim 2, characterized in that, The connecting group I (41) consists of a web member III (16) and a web member IV (17). The web members III (16) and IV (17) are arranged in a figure-eight shape. Both ends of the web members III (16) and IV (17) are fixed with connecting lugs II (18). The two connecting lugs II (18) are welded to one side of the corresponding lower chord (7) to increase the stability between the two lower chords (7).

4. A lightweight tower crane boom using high-strength cold-formed steel according to claim 3, characterized in that, The connecting ear II (18) is fixed with a plate (19) on the side near the lower chord (7). A strip groove (12) is formed between the upper C-shaped steel (9) and the lower C-shaped steel (11) that are adjacent to each other. The plate (19) is fixedly extended into the strip groove (12) to increase the stability between the two adjacent lower chords (7). The plate (19) is inserted into the strip groove (12) to increase the overall strength of the lower chord (7).

5. A lightweight tower crane boom using high-strength cold-formed steel according to claim 4, characterized in that, The connecting group II (42) consists of web member I (13) and web member II (14), which are arranged in a figure-eight shape. The top and bottom of web member I (13) and web member II (14) are fixed with connecting lugs I (15). The two connecting lugs I (15) are fixedly connected to the upper chord (6) and the corresponding lower chord (7) respectively. Through the connecting lugs I (15), the stress gradually diffuses from the center of the contact between web member I (13) and web member II (14) and the upper chord (6) and the lower chord (7) to the surrounding area, avoiding stress concentration in the weld. The connecting lugs I (15) near the upper chord (6) are fixed with the existing connector of the insert plate (19) structure, and the connector extends into the strip groove (12) located on the top.

6. A lightweight tower crane boom using high-strength cold-formed steel according to claim 5, characterized in that, Two bolts I (22) are inserted into both the upper chord (6) and the lower chord (7). The bottom ends of the two bolts I (22) are inserted into the corresponding upper C-shaped steel (9), L-shaped insert (21), square steel tube (8), plug strip (20) and lower C-shaped steel (11) in sequence, which are used to increase the connection stability between the two adjacent upper chords (6) and the two adjacent lower chords (7).

7. A lightweight tower crane boom using high-strength cold-formed steel according to claim 6, characterized in that, Multiple triangular guide plates (38) are provided on both sides of the upper chord (6) and on the side of the two lower chords (7) that are far apart from each other. The triangular guide plates (38) are isosceles triangles, and the two isosceles sides of the triangular guide plates (38) are arranged vertically. Multiple fixing strips (39) are welded and fixed in the strip groove (12). The multiple fixing strips (39) are fixedly connected to one side of the corresponding triangular guide plate (38). The triangular guide plates (38) cut and disperse the airflow, reducing the continuous vortex vibration of the boom section (5).

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