Title of Invention: WEB MEMBER OF COMPOSITE TRUSS

GIRDER AND NODE CONNECTING STRUCTURE OF

COMPOSITE TRUSS GIRDER USING THE SAME

Technical Field

[1] The present invention relates to a web member of a composite truss girder that uses a steel tube for structural purposes as the web member and a node connecting structure of a composite truss girder using the same, which allows an outer diameter of the steel tube used as the web member to be kept as a single value over the entire span of a target bridge. Background Art

[2] Cross-Reference to Related Application

[3] This application claims priority to Korean Patent Application No. 10-2009-0034087 filed in Republic of Korea on April 20, 2009, the entire contents of which are incorporated herein by reference.

[4] A web member of a composite truss girder plays a structural role of converting a vertical force in a gravity direction, generated by a weight of the girder itself, an overburden load and a travelling load such as a vehicle load, into an axial force in a node region and transferring it to a bridge bearing.

[5] The magnitude of an axial force generated at the web member by a travelling load is constant over the entire span of a bridge, but the magnitude of an axial force generated at the web member by a weight of the girder itself and an overburden load of kerbs and pavement is increased as the distance between the web member and the bridge bearing is shorter.

[6] In these reasons, dimensions (e.g., outer diameter and thickness) of the steel tube serving as the web member of a composite truss girder are generally set into three to five different types over the entire span of the bridge when a bridge is designed and constructed.

[7] Chords (upper and lower chords) used in a composite truss girder are coupled with the web member through a node. In a composite truss girder in which the chords are entirely made of concrete and only the web member is made of steel, a node structure with rigid connection in which a web member is directly buried in the chord is usually used.

[8] In the node structure in which the web member and chords are treated with rigid connection, a bending moment generated at the chord is partially transferred to the web member. Here, the magnitude of the bending moment transferred to the web member is increased as a diameter of the steel tube used as the web member is greater.

[9] At this time, the steel tube should be designed to resist the axial force and the bending moment at the same time. Here, as the diameter of the steel tube is greater, the stress caused by the bending moment is increased, so it is required to use a steel tube with a greater diameter. Disclosure of Invention Technical Problem

[10] A ready-made steel tube mass-produced using a rolled coil in a factory is usually used for a web member of a composite truss girder. However, on occasions, a manufactured steel tube made by directly rolling a steel plate for structural purposes may be used.

[11] The manufactured steel tube is advantageous in that a designer may select strength, thickness and diameter of a steel plate as desires, but the manufactured steel tube is much more expensive than the ready-made steel tube, and also the manufactured steel tube does not ensure uniform quality.

[12] The ready-made steel tube is cheaper than the manufactured steel tube, but its dimensions (strength, diameter and thickness) are already set, so a designer has a limitation in selecting the dimension of a steel tube. Also, in order to optimize an amount of steels used for the web member and the connecting structure, the entire span of a subject bridge should be divided into three to five regions, and steel tubes with different dimensions should be used for each region.

[13] If the dimension of a steel tube used for the web member is changed over the entire span of a subject bridge, a connecting structure at a truss node region where the web member encounters the chord should be changed accordingly. Thus, as the number of kinds of steel tubes is increased, the costs required for making and assembling the web member and the connecting structure are increased.

[14] In addition, a diameter of a steel tube located at the center of the span is significantly different from a diameter of a steel tube located near the bridge bearing in case they are designed suitably for a section force applied to each steel tube, which deteriorates an appearance. If the difference in diameter of the steel tubes is decreased to improve the appearance, an amount of used steel tubes is greater than an amount actually demanded in consideration of stress, which deteriorates economics.

[15] Meanwhile, in a conventional composite truss girder, it was designed to resist a section force (namely, the axial force and the moment) applied to the web member only by the steel tubes, so there was a structural limit in that the diameter of the steel tube is increased as the section force applied to the steel tube is greater.

[16] If the diameter of the steel tube used for the web member is increased, a size of the node where the web member encounters the chord should be increased accordingly. However, if the size of the node is increased, a volume of concrete used as the chord is also increased, and a size of the connecting structure made of steel for connecting the web members with each other at the node region is also increased, so a amount of consumed steel is increased, which deteriorate the economics.

[17] In this reason, the web member used in a composite truss girder is generally designed to have a diameter of 500 mm or less. In some cases, an external unbonded tendon causing an upward force is used together so as to decrease the diameter of the web member. However, if the span length exceeds 110 meters, the demanded length of steel tubes based on structural calculation is greatly increased, which can be hardly applied to a composite truss girder. Solution to Problem

[18] The present invention is directed to developing a web member structure in which manufactured steel tubes with only one dimension are used for web members of a composite truss girder over the entire span of a subject bridge and also an amount of steel consumed for the web members may be optimized to a demanded value based on structural calculation, thereby saving costs for making the web members and the connecting structure and also reducing processes and costs used for purchasing steel tubes.

[19] The present invention is also directed to developing a web member structure in which a diameter of steel tubes used for the web member is limited within 500 mm though a span length of the composite truss girder exceeds 110 meters, and which may resist an axial force and a moment applied to the web member, thereby allowing to expand an available span length of the composite truss girder even to 200 meters.

[20] In one aspect of the present invention, there is provided a web member of a composite truss girder, in which an additional structural steel is disposed in a steel tube and then the additional structural steel and the steel tube are structurally integrated at an end of the web member such that the steel tube and the structural steel disposed in the steel tube may share the section force applied to the web member with magnitudes intended by a designer.

[21] In other words, a designer may control the magnitude of a section force resisted by the steel tube over the entire span of a subject composite truss girder, so steel tubes of the same dimension may be used for the entire bridge. In addition, the other section force exceeding a resisting ability of the steel tube may be resisted by the structural steel disposed in the steel tube.

[22] The change of a section force according to the location of the web member may be coped with by adjusting dimensions of the structural steel disposed in the steel tube. [23] Meanwhile, the section force applied to each web member is divided to the steel tube and the inner steel member with given magnitudes through the end connecting plate installed at an end of the web member. However, when a compression force is applied to the web member, the steel disposed in the steel tube shows a structural behavior vulnerable to buckling. To reinforce it, the steel tube is filled with concrete such that the steel tube and the inner steel member behavior integrally.

[24] In case a tensional force is applied to the web member, the steel tube and the inner steel member do not cause buckling, but the steel tube is filled with concrete so as to improve a resistance of the steel tube against a bending moment transferred to the web member by burying the steel tube in the chord.

Advantageous Effects of Invention

[25] If the web member and the node connecting structure according to the present invention are applied to a composite truss girder, it is possible to use manufactured steel tubes of only one dimension as web members over the entire span of a subject bridge. Thus, the following effects are expected: firstly saving a cost for purchasing the steel tubes, secondly greatly reducing costs required for making the node connecting structure by simplifying the node connecting structure, and thirdly improving an appearance of a bridge by exposing steel tubes with a regular size.

[26] In addition, since the change of a section force according to the location of the web member may be coped with by adjusting dimensions of the structural steel disposed in the steel tube, it is easy to control stresses applied to each web member over the entire bridge in a substantially equivalent level, so an amount of consumed steel may be greatly reduced rather than the cases of conventional composite truss girders using only steel tubes as web members. Brief Description of Drawings

[27] Other objects and aspects of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawing in which:

[28] Fig. 1 is sectional view showing a web member of a composite truss girder according to the present invention;

[29] Fig. 2 is a perspective view showing a node of a composite truss girder according to the present invention;

[30] Fig. 3 is a diagram illustrating the flow of force at a node connecting structure according to the present invention;

[31] Fig. 4 is a diagram showing an additional moment generated due to the discord of axial lines of the web members at the node;

[32] Figs. 5a to 5c illustrate the sequence of making the web member according to the present invention; and

[33] Figs. 6a to 6c show examples of constructing a composite truss girder using the web members according to the present invention.

[34] <Brief Description of Reference Numeral in Drawings>

[35] 10: web member 11: external steel tube

[36] 12: inner steel member 13: end connecting plate

[37] 14: side connecting plate 15: hole

[38] 16: lower chord 20: upper chord

Best Mode for Carrying out the Invention

[39] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[40] Fig. 1 is a sectional view showing a web member according to the present invention.

The web member 10 according to the present invention includes an external steel tube 11, an inner steel member 12 and an end connecting plate 13.

[41] As shown in Fig. 1, the web member 10 according to the present invention is configured to distribute an axial force transferred through the end connecting plate 13 respectively to the external steel tube 11 and the inner steel member 12. By using this configuration, the external steel tube 11 may cope with the change of a section force applied to the web member 10 at each location while keeping the dimensions of the external steel tube 11 constantly by changing only size and thickness of the inner steel member 12 buried in the steel tube.

[42] Also, seeing a sectional shape, the end connecting plate 13 is partially inserted into the external steel tube 11, so there is no need of forming slots at both ends of the external steel tube 11 for the attachment of the end connecting plate 13. In this reason, a manufacture cost of the external steel tube 11 may be reduced.

[43] Fig. 2 is a perspective view showing a detailed structure of a node that connects the web members 10 according to the present invention with each other. Seeing the detailed structure of the node according to the present invention, a side connecting plate 14 with a predetermined thickness is welded to both sides of the upper or lower end connecting plate 13 of web members 10 adjacent to each other, and a plurality of holes 15 with a predetermined size are formed in front and rear portions of the side connecting plate 14.

[44] Fig. 3 is a diagram showing the process of transferring a force at the node, generated when the detailed structure of the node according to the present invention is applied. Seeing both web members 10 coupled by the side connecting plate 14, a compression force C is applied to one web member and a tensional force T is applied to the other web member in the structural aspect. Hereinafter, in the following explanation, it is assumed that a compression force C is applied to the right web member for the convenience.

[45] An axial force Cl applied to the external steel tube 11 and an axial force C2 applied to the inner steel member 12 of the web member, which receives a compression force, are combined together into one force (C=C 1+C2). The force C applied to the end connecting plate 13 is transferred again to the side connecting plate 14 through the welding surface.

[46] The force C transferred to the side connecting plate 14 is divided into a horizontal force Ch and a vertical force Cv, respectively. The horizontal force Ch is transferred to the concrete chords 16, 20 through a bearing pressure of the concrete located at the front of the end connecting plate 13.

[47] Meanwhile, the vertical force Cv is combined with a part of a shear force transferred through the concrete chords 16, 20 (Tv=Cv+V) and then transferred again to the end connecting plate 13 installed at the left web member 10 through the side connecting plate 14. In this process, a tensional force is generated at the left end connecting plate 13 in an inclined direction of the web member, and a horizontal force Th is generated at the side connecting plate 14.

[48] The horizontal force Th is transferred to the concrete chords 16, 20 through a bearing force (R=Th+Ch) of the concrete located at the front of the end connecting plate 13, and the tensional force T transferred to the left end connecting plate 13 is divided into a force applied to the external steel tube 11 of the left web member and a force applied to the inner steel member 12, respectively.

[49] As understood from the above explanation, in the detailed structure of the node according to the present invention, the side connecting plate made of steel resists the vertical force causing a harmful behavior toward the concrete chords, and the bearing force of the concrete located at the front of the end connecting plate resists the horizontal force of the node. In this way, the safety of the concrete chords located at the node region is greatly improved rather than existing node structures.

[50] Meanwhile, it is most advantageous in aspect of the structural behavior that axial lines of the web members located at both sides of the node encounter the axial line of the chord at one point. However, in actual structures, three axial lines are frequently not encountered at one point due to diameter and angle of the external steel tube used for the web member or a sectional shape of the chord.

[51] As shown in Fig. 4, if the axial lines of the above three members do not encounter at one point, an eccentricity e is generated. As a result, an additional bending moment M is generated at the node region due to the vertical force applied to both web members.

[52] A plurality of holes 15 with a predetermined size are formed at the front and rear portions of the side connecting plate 14 such that the side connecting plate 14 and the concrete chords 16, 20 surrounding the side connecting plate 14 may integrally make a rotational strain with respect to the bending moment M. At this time, the size and number of prepared holes are determined to make a resistance against a coupling force R caused by the bending moment M.

[53] Figs. 5a to 5c illustrate the sequence of making the web member according to the present invention.

[54] First, the external steel tube 11, the inner steel member 12 and the end connecting plate 13 are prepared with suitable shapes. After that, the external steel tube 11 and the end connecting plate 13 are welded with each other as indicated by the reference numeral 18, and then the inner steel member 12 and the end connecting plate 13, inserted into the external steel tube 11, are welded with each other as indicated by the reference numeral 19.

[55] Figs. 6a to 6c illustrate examples of constructing a composite truss girder using the web members according to the present invention.

[56] First, a web member 10 prepared in a factory are carried to a bridge construction spot, and then the side connecting plate 14 is welded to the end connecting plate 13 of the web member, thereby forming a truss web framework.

[57] And then, a lower concrete chord 16 is constructed, and then the lower chord 16 is integrated with the truss web framework.

[58] After that, each web member 10 is filled with concrete, and then an upper concrete chord 20 is constructed to completely make a composite truss girder.

[59] The web member of a composite truss girder, the node connecting structure and the method for constructing a composite truss girder according to the present invention have been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.