A CONNECTING STRUCTURE FOR MECHANICALLY CONNECTING STEEL PIPE PROFILES TO EACH OTHER TO FORM A TRUSS STRUCTURE AND A TRUSS STRUCTURE

The object of the invention is a connecting structure for mechanically connecting steel pipe profiles (1, 2, 3) to each other to form a truss structure, comprising at least one elongated frame beam (1) with a rectangular cross-section, to which several cross struts (2, 3) with a rectangular cross-section forming a truss structure and extending diagonally and/or perpendicularly with respect to the frame beam are connected. According to the invention, receiving openings (4, 5) are formed on one side (6) of the frame beam (1) for receiving one end (2a, 3a) of each cross strut (2, 3) into the frame beam. Fastening holes (12) and/or outlines thereof are formed in the region of the end (2a, 3a) of the cross strut (2, 3) extending into the frame beam (1), and corresponding fastening holes (12′) and/or outlines thereof are formed on the sides (7, 8) of the frame beam (1) perpendicular to the side (6) having the receiving openings (4, 5). Guide holes (9, 9′) are formed on the sides (7, 8) of the frame beam perpendicular to the side (6) having the receiving openings (4, 5) and equipped with at least one guide pin (10, 10′) extending in the transverse direction of the frame beam. A guide groove (11, 11′) extending in the longitudinal direction of the cross strut (2, 3) is formed at the end (2a, 3a) of the cross strut, which, in cooperation with said at least one guide pin (10, 10′), positions the fastening holes (12) of the cross strut (2, 3) and the corresponding fastening holes (12′) of the frame beam (1) in exact alignment, enabling fastening means (13) to be inserted precisely through the fastening holes (12, 12′), thereby rigidly connecting the pipe profiles (1, 2, 3) to each other. A further object of the invention is a truss structure (16) utilizing the connecting structure.

The object of the invention is a connecting structure and a truss structure utilizing such a connecting structure. The connecting structure is a connecting structure for mechanically connecting steel pipe profiles to each other to form a truss structure, comprising at least one elongated frame beam with a rectangular cross-section, to which a plurality of cross struts with a rectangular cross-section forming a truss structure and extending diagonally and/or perpendicularly to the frame beam are connected.

There are various uses for truss structures made of pipe profiles, such as in roof trusses, footbridges, masts, escalators, etc. Joints between the pipe profiles are often made by welding, but mechanical joints, such as those implemented with hard metal screws, are also used. These joints are as such functional with typical structural steels, but with high-strength structural steels having a yield strength of preferably approximately 700 MPa or more, the problem in welded joints is a decrease in strength in the heat-affected zone, and on the other hand, in mechanical joints, hard metal screws do not sufficiently penetrate high-strength steel. The invention may already prove useful with steels having a yield strength of approximately 500 MPa or more and a hardness in the order of 160 to 215 HV or more.

Previously known solutions have been presented in publications U.S. Pat. No. 3,826,057A and JP2009197437A, for example. In these solutions, pipe profiles are mechanically connected to each other to form a truss structure.

The aim of the present invention is to provide a connecting structure in which pipe profiles can be mechanically connected to each other to form a truss structure also when using high strength structural steel.

To achieve this aim, the connecting structure of the invention is characterized in that receiving openings are formed on one side of the frame beam for receiving one end of each cross strut into the frame beam;that fastening holes and/or outlines thereof are formed in the region of the end of the cross strut extending into the frame beam, and corresponding fastening holes and/or outlines thereof are formed on the sides of the frame beam perpendicular to the side containing the receiving openings;that guide holes are formed on the sides of the frame beam perpendicular to the side containing the receiving openings, said guide holes being equipped with at least one guide pin extending in the transverse direction of the frame beam; andthat a guide groove is formed at the end of the cross strut, preferably a guide groove extending in the longitudinal direction of the cross strut, wherein said guide groove, in cooperation with said at least one guide pin, positions the fastening holes of the cross strut and the corresponding fastening holes of the frame beam in exact alignment, enabling fastening means to be inserted precisely through the fastening holes, thereby connecting the pipe profiles rigidly to each other.

Preferably, said guide groove formed at the end of the cross strut is a guide groove extending in the longitudinal direction of the cross strut. Alternatively, said guide groove formed at the end of the cross strut extends at an acute angle with respect to the longitudinal direction of the cross strut, wherein the angle is essentially less than 90 degrees, preferably at most 45 degrees.

The material of the pipe profiles is preferably high-strength structural steel with a yield strength of approximately 700 MPa or more, and a hardness typically in the order of 230 to 300 HV or more, wherein the fastening holes and/or guide holes are made smaller than the diameter of the fastening means/guide pins used by means of laser machining, and the edges of the holes have been softened by means of laser machining or heat treatment so as to allow the fastening means/guide pins to penetrate through the undersized holes. Preferably, the edges of the holes are softened such that the hardness of the edge is approximately ⅓ to ½ of the hardness of the fastening means/guide pins. The fastening means are preferably hard metal screws penetrating the pipe profile when driven in. The surface hardness of hard metal screws is usually approximately 450 HV or more. The surface hardness of self-tapping screws is at least 450 HV 0.3 according to SFS-EN ISO 2702:2011, and the surface hardness of self-drilling screws is at least 530 HV 0.3 according to SFS-EN ISO 10666:2000. Thus, the edges of the holes are softened to a value of approximately 225 HV or less. The target value can be considered to be 0.38 of the value of the surface hardness of the screw. Sufficient softening is confirmed with the help of tests depending on the type of fastening means (e.g. the thread size and the hardness profile beyond the surface) and the material thickness of the high-strength structural steel plate in relation to the diameter of the fastening means. With a thicker plate, the probability of the thread breaking increases, hence in a thicker plate, the edge of the hole should be relatively softer. The fastening means may also be, for example, slightly conical fastening pins inserted into the fastening holes by shooting or pressing.

FIG.1shows a truss structure utilizing the connecting structure according to the invention before assembly. The truss structure consists of frame beams1having cross struts2,3connected therebetween. The frame beams1, as well as the cross struts2,3, have a rectangular cross-section. Receiving openings4,5are formed on one side6of the frame beam1for inserting one end2a,3aof each cross strut2,3into the corresponding frame beam1to form a connecting structure. The receiving openings4,5may be formed as a continuous opening for receiving the ends of the adjacent diagonal2and perpendicular3cross struts through the same opening, as in the example shown in the figures. Guide holes9,9′ equipped with guide pins10,10′ extending in the transverse direction of the frame beam are formed on the sides7,8of the frame beam perpendicular to the side6containing the receiving openings. The guide holes9,9′ are preferably undersized and their edges are softened such that a self-tapping screw constituting the guide pin10,10′ can be driven into place. The part of the guide pin10,10′ extending into the frame beam is preferably smooth. The guide pin can also be formed so as to be continuous across the entire interior of the frame beam. A guide groove11,11′ extending in the longitudinal direction of the cross strut is formed at the end of the cross strut2,3and arranged to cooperate with corresponding guide pins10,10′. Several, preferably undersized fastening holes12are formed in the region of the end2a,3aof the cross strut2,3extending into the frame beam, and corresponding, preferably undersized fastening holes12′ are formed on the sides7,8of the frame beam perpendicular to the side6containing the receiving openings. The fastening holes12,12′ and the guide holes9,9′ are preferably formed by means of laser machining, which provides precise positioning of the holes. Laser machining can also be used to heat-treat the edges of the holes to allow the fastening means to penetrate through the undersized holes for fastening the parts to each other rigidly. Heat treatment can be performed when the fastening holes are made, or afterwards. In the case of screw fasteners13, heat treatment of the edges of the holes is preferably extended so as to cover the thickness of the thread. The fastening holes12,12′ of the cross struts2,3and the frame beam1can be guided into alignment with the help of the guide groove11,11′ of the cross strut and the guide pins10,10′ of the frame beam. It is also possible to just form outlines for the fastening holes by marking the positions of the fastening holes and softening the cross strut and/or the frame beam at the fastening hole positions so that the fastening means, such as self-drilling hard metal screws, can be inserted through the steel at the outlined position without a pilot hole. The end2aof the cross strut2inserted diagonally to the frame beam is preferably shaped so that it is positioned at a short distance from the inner bottom14of the frame beam. The end3aof the cross strut3perpendicular to the frame beam is, on the other hand, preferably shaped so that it is positioned at a short distance from the top surface2′ of the diagonal cross strut2.

Assembling the truss structure preferably takes place on a horizontal surface by placing the end2a,3aof each cross strut2,3inside the frame beam1through the corresponding receiving opening4,5.FIG.2shows the parts of the connecting structure before the assembly phase in more detail as a perspective view.FIG.3shows the parts of the connecting structure before the assembly phase as a side view. InFIG.3, the guide pins10on the front side7are positioned in the guide holes9, and the guide pins10′ on the back side8respectively in the corresponding guide holes9′. InFIG.4, the cross struts2,3have been installed in place as guided by the guide grooves11,11′ and the guide pins10,10′, after which the fastening screws13are inserted through the undersized fastening holes12,12′, thereby firmly attaching the cross struts and the frame beam to each other.FIG.5shows the connecting structure in the assembled state as a side view.FIG.6shows the cross-section of the connecting structure as seen in the direction of the arrows A-A.FIG.7shows the connecting structure as a side view, wherein the parts inside the frame beam are shown with dashed lines to illustrate the position of the cross struts in the assembled state. The lower end of the diagonal cross strut2is preferably spaced at a short distance from the inner bottom14of the frame beam. The lower end of the perpendicular cross strut3is preferably spaced from the top surface2′ of the diagonal cross strut by a small gap. In the embodiment ofFIG.7, more fastening screws13are used than in the embodiments ofFIG.1-6.

FIG.8shows the connection of steel pipe profiles1-3into a truss structure in an installation jig using the connecting structure according to the invention as a schematic principle view. The installation jig shown as an example includes lateral supports14placed on a horizontal installation surface and extending in the longitudinal direction (y-direction) of the installation surface, wherein frame beams1extending in the transverse direction (x-direction) are placed at a longitudinal distance from one another between said lateral supports. Cross struts2,3are placed between the frame beams and arranged at the receiving openings4,5of the frame beam. The frame beams1are then moved evenly in the y-direction towards the cross struts2,3and each other using displacement means15while keeping the longitudinal axes of the frame beams in alignment with the x-direction. The lateral supports14prevent the frame beams1from moving in the x-direction. When the ends of the cross struts2,3move through the openings4,5and the guide grooves11,11′ therein meet the guide pins10,10′, the cross struts2start to twist slightly, and in their final position, reach an angle in which the fastening holes12,12′ are aligned. The connecting structure can also be put together without an installation jig by inserting the end2a,3aof the cross strut2,3through the receiving opening4,5so that the guide groove11,11′ meets the guide pins10,10′. When the guide pins are positioned against the bottom of the guide groove, the fastening holes can be aligned manually and the fastening means13inserted into the fastening holes12,12′. When the first fastening means is installed in place, the rest of the fastening holes remain aligned without further adjustment.

Structurally, the guide groove11,11′ is preferably such that it extends through the opposite sides of the cross strut2,3. The guide groove11,11′ has an open end in the longitudinal direction of the cross strut2,3. The guide groove11,11′is dimensioned such that said at least one guide pin10,10′ fits to move into the guide groove11,11′ via the open end of the guide groove11,11′ in the longitudinal direction of the cross strut2,3, particularly when moving the cross strut2,3in its longitudinal direction or at least essentially in its longitudinal direction towards said at least one guide pin10,10′.

In the embodiments presented, a plurality of fastening holes12and/or outlines thereof are formed on each opposite side of the respective cross strut2,3in the region of the end2a,3aof the cross strut2,3extending into the frame beam1for improving the rigidity of the connection between the cross struts2,3and the frame beam1. Corresponding fastening holes12′ and/or outlines thereof are formed on the sides7,8of the frame beam1perpendicular to the side6containing the receiving openings4,5. In the embodiment presented, said plurality of fastening holes12and/or outlines thereof comprises at least two, preferably more than two fastening holes12and/or outlines thereof, the number being nine in the case of the diagonal beam2and six in the case of the perpendicular beam3in the preferred solution presented. When there are several fastening holes12and/or outlines thereof, their positions may be distributed evenly, and they may be dimensioned to be relatively small so that they fit well in the beams to be connected without issues with space. Fastening through several fastening holes contributes to the rigidity of the joint and can be implemented without excessively weakening the structure. Therefore, it is generally preferable that said plurality of fastening holes12and/or outlines thereof comprises at least six fastening holes12and/or outlines thereof.

In the embodiments presented, said plurality of fastening holes12and/or outlines thereof comprises two adjacent lines extending in the longitudinal direction of the cross strut2,3, wherein each line comprises two or more fastening holes12and/or outlines thereof in succession in the longitudinal direction of the cross strut2,3. With the holes being relatively small in size and large in number, the line formation allows a large number to be positioned in a small area.

As stated above, to increase the rigidity of the joint, it is preferred that a plurality of fastening holes12and/or outlines thereof are formed on each opposite side of the respective cross strut2,3in the region of the end2a,3aof the cross strut2,3extending into the frame beam1. This is advantageous, but not compulsory. In some cases, it may be possible to achieve sufficient rigidity with only one fastening hole12and/or outline thereof formed on each opposite side of the respective cross strut2,3in the region of the end2a,3aof the cross strut2,3extending into the frame beam1. Even one fastening hole12on each side, together with the guide holes9,9′ and the fastening means13and respective guide pins10,10′ installed thereto, may be enough to form a rigid joint that cannot twist.

FIG.5-7show details of the assembled truss structure16. As shown in the figures, the truss structure16comprises an elongated frame beam1with a rectangular cross-section and cross struts2,3with a rectangular cross-section (of which two are shown) connected to the frame beam1with any previously described connecting structure such that the cross strut2extends diagonally with respect to the frame beam1and the cross strut3extends perpendicularly with respect to the frame beam1. One end2a,3aof each cross strut2,3extends into the frame beam1through a receiving opening4,5formed on one side6of the frame beam1. The truss structure16comprises fastening means13extending through the fastening holes12of the cross struts2,3and the fastening holes12′ of the frame beam1. The truss structure16further comprises guide pins10,10′ extending through the guide holes9,9′ into the guide grooves11,11′.

Generally, each said frame beam1and cross strut2,3is preferably an elongated beam with a rectangular cross-section, which is a steel pipe profile.

It is obvious to a person skilled in the art that the idea and operating principle of the invention may be implemented in various ways. The invention and its implementation are therefore not limited to the examples described hereinbefore but may vary within the scope of the claims.