Fiber Reinforced Structural Member

The present invention relates to a lightweight structural member having sufficient rigidity and strength and, more specifically, to a fiber reinforced structural member.

Fiber reinforced plastics (hereinafter abbreviated to "FRPs") are well-known fiber reinforced materials. Various fibers including glass fibers and carbon fibers have been developed for use in FRPs. These fibers have a strength equivalent to or greater than those of steels. Thus, FRP structural members are capable of replacing reliable steel structural members and various FRPs have been applied to structural members for supporting loads.

On the other hand, since the specific gravity of FRPs, in general, is on the order of one-fifth the specific gravity of steels, the application of FRP structural members to construction structures effectively reduces the total weight of the structures.

FIG. 1 shows a beam member, an exemplary structural member to which the present invention pertains, comprising an elongate beam body 1 formed of a FRP, bearing pads 2 and 3 attached to the opposite ends of the beam body 1, respectively, and a load bearing part 4 provided at the middle of the beam body 1 for supporting an external load. When the beam body 1 supported at the opposite ends thereof is loaded in the middle portion thereof, the bending moment is large in the middle portion and small at the end portions. Since the elastic modulus of such a fiber reinforced plastic structural member is 1/20 to 1/5 that of steels, ordinarily, the beam body 1, namely, the structural member, is provided with an internal reinforcement so as to tend to uniformly distribute the bending stress throughout the section thereof.

FIG. 7 illustrates an exemplary conventional structural member provided with an internal reinforcement. This structural member comprises a beam body 1 having a rectangular cross section, a reinforcing plate 5 formed of the same material as the beam body 1 and provided inside the beam member 1, and a filling material 6 such as, for example, foam polyurethane, filling the inner space of the beam body 1. In this structural member, however, since the reinforcing plate 5 is joined along the narrow side edges thereof to the inner surface of the beam body 1, the strength of the junctions is not large enough to withstand tensile forces and shearing forces which act on the junctions, and hence such a conventional structural member is not satisfactory in reliability.

It is therefore an object of the present invention to provide a fiber reinforced structural member formed of a fiber reinforced material having many advantages as mentioned above and which can eliminate the drawbacks of the conventional fiber reinforced structural member through the application of simple and rational means.

It is another object of the present invention to provide a fiber reinforced structural member comprising a shell element, and a core element or elements having a large joining area joined to the shell element so that the junctions of the shell element and the core element or elements are strong enough to withstand tensile forces and shearing forces which act on the junctions.

In one aspect of the present invention, a fiber reinforced structural member comprises: a shell element formed of a fiber reinforced material and having a closed cross section; and a core element fixedly joined to the inner surface of the shell element, and formed by uniting a plurality of elongate primary core elements each formed of a fiber reinforced material, having a closed cross section or a channel-shaped cross section and internally filled with a filling material.

In another aspect of the present invention, a fiber reinforced structural member comprises: a shell element formed of a fiber reinforced material and having a closed cross section; and a core element fixedly joined to the inner surface of the shell element, and comprising an elongate primary core element formed of a fiber reinforced material, having a closed cross section or a channel-shaped cross section and internally filled with a first filling material, and a second filling material joined to one side surface of the elongate primary core element.

The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a structural member to which the present invention pertains;

FIGS. 2, 3 and 4 are sectional views of fiber reinforced structural members in first, second and third embodiments, respectively, according to the present invention;

FIGS. 5 and 6 are sectional views of fiber reinforced structural members in fourth and fifth embodiments, respectively, according to the present invention; and

FIG. 7 is a sectional view of a conventional fiber reinforced structural member.

Referring to FIG. 2, a fiber reinforced structural member A comprises a shell element 13a having a closed cross section and formed of a fiber reinforced material such as, for example, a FRP, and a core element a.sub.2 provided inside the shell element 13a in surface contact with and fixedly joined over the entire contact surface thereof to the shell element 13a. The core element a.sub.2 comprises two primary core elements a.sub.1 each formed by filling a filling material 12a such as, for example, foam polyurethane, in a hollow elongate core member 11a having a rectangular cross section and formed of a fiber reinforced material such as, for example, a FRP. The two primary core elements a.sub.1 are united together to form the core element a.sub.2. Gaps formed between the outer surface of the core element a.sub.2 and the inner surface of the shell element 13a are filled with the same resin 14 as that of the FRP forming the shell element 13a. The resin is applied to the outer surface of the core element a.sub.2 before inserting the core element a.sub.2 into the shell element 13a.

In FIG. 3, parts similar to those previously described with reference to FIG. 2 are denoted by the same reference characters.

Basically, the second embodiment is similar to the first embodiment in construction. In the second embodiment, a core element a.sub.2 is constructed by uniting three primary core elements a.sub.1, which are the same in construction as the primary core elements a.sub.1 of the first embodiment.

A fiber reinforced structural member B, in a third embodiment, according to the present invention comprises: a shell element 13b formed of a fiber reinforced material such as, for example, a FRP, and having a closed cross section; and a core element b.sub.2 constructed by uniting, in a back-to-back fashion, two primary core elements b.sub.1 each formed by filling a filling material 12b such as, for example, foam polyurethane, in an elongate channel-shaped core member 11b. The shell element 13b and the core element b.sub.2 are fixedly joined over the entire contact surfaces thereof.

A fiber reinforced structural member C, in a fourth embodiment, according to the present invention comprises: a shell element 13c formed of a fiber reinforced material such as, for example, a FRP, and having a closed cross section; and a core element c.sub.2 comprising a primary core element c.sub.1 formed by filling a filling material 12c such as, for example, foam polyurethane, in a hollow elongate core member 11c formed of a fiber reinforced material such as, for example, a FRP, and having a rectangular cross section, and filling strips 15a formed of a resin such as, for example, foam polyurethane, attached to the opposite sides of the primary core element c.sub.1, respectively. The core element c.sub.2 is inserted into the interior of the shell element 13c, and then the core element c.sub.2 and the shell element 13c are firmly joined over the entire contact surface thereof.

A fiber reinforced structural member D, in a fifth embodiment, according to the present invention comprises: a shell element 13d formed of a fiber reinforced material such as, for example, a FRP, and having a closed cross section; and a core element d.sub.2 comprising a primary core element d.sub.1 formed by filling a filling material 12d such as, for example, foam polyurethane, in a channel-shaped elongate core member 11d formed of a fiber reinforced material, and a core strip 15b formed of a synthetic resin such as, for example, foam polyurethane, and attached to the outer surface of the bottom wall of the channel-shaped elongate core member 11d. The core element d.sub.2 is inserted in the shell element 13d, and then the core element d.sub.2 and the shell element 13d are fixedly joined over the entire contact surface thereof to form the fiber reinforced structural member D.

In accordance with the present invention, there have been described fiber reinforced structural members in preferred embodiments, from which it is apparent that

(a) the core element and the shell element are in contact with each other with a large contact surface extending over the entire inner surface of the shell element and hence an external force applied to the fiber reinforced structural member is distributed over the entire joining surface, so that stress in the joining surface is reduced and the reliability of the fiber reinforced structural member is enhanced;

(b) the primary core element and the core strip or strips of the core element are joined over a large joining surface and an external force acting on the core element is distributed over the entire joining surface, and hence the stress in the joining surface is reduced, so that the reliability of the fiber reinforced structural member is enhanced; and

(c) the primary core element or elements and the shell element are lightweight members formed of a fiber reinforced material such as, for example, a FRP, and hence the weight per unit strength of the fiber reinforced structural member is small, which is advantageous for the structural member.

Although the present invention has been described with reference to preferred embodiment thereof with a certain degree of particularity, it is understood that the foregoing embodiments are merely illustrative of the application of the principles of the present invention and many changes and variations are possible in the invention without departing from the scope and spirit thereof.