Fiber reinforced structural member

Abstract: A fiber reinforced structural member comprises a shell element (13a) formed of a fiber reinforced material such as, for example, a fiber reinforced plastic, and a core element (a₂) having a large joining surface fixedly joined to the inner surface of the shell element (13a), and comprising one or a plurality of primary core elements (a₁) each formed of a fiber reinforced material such as, for example, a fiber reinforced plastic, in the form of a tube or a channel (11a) and internally filled with a filling material (12a) such as, for example, foam polyurethane. Since the shell element (13a) and the core element (a₂) are joined together over the large joining area, an external force applied to the fiber reinforced structural member is distributed over the large joining surface and hence the stress in the joining surface is reduced, so that the durability and reliability of the fiber reinforced structur­ al member is enhanced.

Description: The present invention relates to a fiber reinforced structural member, i.e. a lightweight structural member having a sufficient rigidity and strength. 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 meters and various FRPs have been applied to structural members for supporting load. 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 constructing structures reduces the total weight of the structures effectively. 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 bearing 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 or 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 to uniformize the bending stress in the section thereof. Fig. 6 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 force and shearing force which act on the junctions, and hence such a conventional structural member is not satisfactory in reliability. From the document THE ENGINEER, vol. 231, no. 5979, 27th August 1970, page 7; "Fibre build big blades" a fiber reinforced structural member is known, comprising a shell element formed of a fiber reinforced material and having a closed cross-section; and a core member having two side faces fixedly joined to inner surface sides of said shell element wherein said core member comprises one core element having a closed cross-section internally filled with a filler material and wherein the interior of said shell element except that of said core element is filled with filling or core strips which are attached to the outer surface of said core member. SUMMARY OF THE INVENTION It is 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 eliminated of 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 force and shearing force which act on the junctions. In one aspect of the present invention the fiber reinforced structural member comprises features according to claim 1 and is further embodied by features of claim 2. In another aspect of the present invention the fiber reinforced structural member comprises features of claim 3. With regard to the reference THE ENGINEER the obvious differences of the claimed new fiber reinforced structural members are as follows: I) The core element a₂ is fixedly joined to the entire inner surface of the shell element 13a (see embodiments of Figs. 2 and 3). II) The core element a₂ or b₂ is formed by at least two primary core elements a₁ or b₁, see embodiments shown in Figs. 2 to 4. III) The primary core elements a₁ or b₁ are fixed together and supplemented in view of the external slot by a resin 14, see embodiments shown in Figs. 2 to 4, which further enhances the reinforcement of the structural member and contributes to advantages in distribution of external forces applied thereto. IV) There are additional filling or core strips 15a or 15b with the embodiments shown in Figs. 5 and 6, which are fixed at the opposite side or at the bottom of the core members 11c or 11d. BRIEF DESCRIPTION OF THE DRAWINGS 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: Figure 1 is a perspective view of a structural member to which the present invention pertains; Figures 2, 3 and 4 are sectional views of fiber reinforced structural members in first, second and third embodiments, respectively, according to the present invention; Figure 5 is a sectional view of a fiber reinforced structural member in a fourth embodiment, according to the present invention; and Figure 6 is a sectional view of a conventional fiber reinforced structural member. DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (Fig. 2): 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 a₂ provided inside the shell element 13a in surface contact an fixedly joined over the entire contact surface thereof to the shell element 13a. The core element a₂ comprises two primary core elements a₁ 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 a₁ are united together to form the core element a₂. Gaps formed between the outer surface of the core element a₂ 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 a₂ before inserting the core element a₂ into the shell element 13a. Second Embodiment (Fig. 3): 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 a₂ is constructed by uniting three primary core elements a₁, which are the same in construction as the primary core elements a₁ of the first embodiment. Third Embodiment (Fig. 4): 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 b₂ constructed by uniting, in a back-to-back fashion, two primary core elements b₁ each formed by filling a filling material 12a such as, for example, foam polyurethane, in an elongate channel-shaped core member 11b. The shell element 13b and the core element b₂ are joined fixedly over the entire contact surfaces thereof. Fourth Embodiment (Fig. 5): A fiber reinforced structural member D, in a fourth 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 d₂ comprising a primary core element d₁ 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 15d 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 d₂ is inserted in the shell element 13d, and then the core element d₂ and the shell element 13d are joined fixedly 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.

Claims: A fiber reinforced structural member (1) comprising a shell element (13a, 13b) formed of a fiber reinforced material and having a closed cross section; and at least one core member (11a, 11b) having two side faces fixedly joined to inner surface sides of said shell element (13a, 13b), said at least one core member (11a, 11b) having a closed or a channel-shaped cross section and being internally filled with a filling material (12a, 12b) to form at least one primary core element (a1, b1), said at least one primary core element (a1, b1) being fixedly joined to each other with a large contact surface to form a secondary core element (a2, b2). A structural member according to claim 1, wherein said secondary core lement (a2) is fixedly joined to the entire inner surface of said shell element (13a). A fiber reinforced structural member (1) comprising: a shell element (13d) formed of a fiber reinforced material and having a closed cross section; and a core member (11d) having a channel-shaped cross-section internally filled with a filler (12d) to form a primary core element (d1), the interior of said shell element (13d) except that of said primary core element (d1) being filled with filler or core strips (15b) which are attached to the outer surface of said core element (d1) to form a secondary core element (d2), said secondary core element (d2) being fixedly joined to the inner surface sides of said shell element (13d).

Inventors: AKASHI SHUJI, IWAMURA AKIRA, OKADA YUKIO, AKASHI, SHUJI, IWAMURA, AKIRA, OKADA, YUKIO
Applicants: KAWASAKI HEAVY IND LTD, KAWASAKI JUKOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: B29D31
IPC codes: B29L31, B29C70, B61F5, B29D99