JP4490853B2 - Brace structure using shape memory alloy - Google Patents

Description

  The present invention relates to a brace structure in which initial tension is introduced by a shape restoring force of a shape memory alloy piece when reinforcing a column beam frame, and a method for reinforcing the brace.

  In the conventional brace structure, the compressive strength is lower than the tensile strength due to buckling, and when the brace is designed to resist horizontal force both in compression and tension, the cross-section of the brace is determined by the compressive strength. To do. For this reason, the brace has a disadvantage that it leaves a surplus in the tensile strength on the tension side and cannot exhibit all the performance. In order to improve this, as disclosed in Japanese Patent Application Laid-Open No. H10-228707, there is known a technique in which an initial tension that leaves a predetermined surplus force before the yield stress is applied to the brace. This is designed so that not only the tensile force of the extension side brace but also the contraction side brace can bear a load by reducing the tension when the frame receives a horizontal force. Moreover, as a method for introducing initial tension, a method using a turnbuckle mechanism as disclosed in Patent Document 2, and if the brace is a pipe material, a pipe material and a joint are used as a screw mechanism as disclosed in Patent Document 3. There is a way.

  As described above, in the conventional method for introducing an initial tension into a brace, both the disclosed technique of Patent Document 2 and the disclosed technique of Patent Document 3 attach a screw-type expansion / contraction mechanism to an intermediate portion of the brace.

On the other hand, when reinforcing a brace attached to an existing column beam frame, a reinforcing member 62 made of a steel plate or the like over the entire length of the brace 61 as shown in FIG. 7 and FIG. Is known to be attached by in-situ welding and reinforced by increasing the cross-sectional area of the member.
JP 59-173470 A Japanese Patent Laid-Open No. 8-200345 Japanese Patent Laid-Open No. 10-317508

  The methods described in Patent Document 2 and Patent Document 3 require that an expansion / contraction mechanism be attached to the brace before attaching the brace to the frame, and can be used as a method for introducing tension to the brace already attached to the frame. Absent. Furthermore, the method described in Patent Document 3 has a drawback that it cannot be applied unless the brace is made of a pipe material.

  On the other hand, the conventional method of reinforcing existing braces is that the construction period is long because it is welded over the entire length of the member, it is difficult to ensure construction quality on site, and the amount of steel necessary for reinforcement is large Has drawbacks.

  Accordingly, the present invention solves such problems of the prior art, and is a method that enables the introduction of initial tension even to existing braces, and that requires less field welding compared to conventional reinforcement methods. It aims at providing the structure which reinforces a brace.

A first invention is a brace structure disposed in a column beam frame, and has at least two pairs of tabs attached at predetermined intervals in the axial direction of the braces, and the tabs are arranged on a central axis of the braces. A tension is applied to a part of the brace in the axial direction by a contraction force at the time of shape recovery of the shape memory alloy piece attached at a point-symmetrical position and fixed with a bolt between the tabs. This is a brace structure.

  In the present invention, the initial tension is applied to the brace to obtain a reinforcing effect. However, as shown in FIG. In the region 77, on the contrary, a compressive force is generated by the restoring force of the shape memory alloy piece. However, even in this part, there is a cross-sectional reinforcing effect due to the shape memory alloy piece being attached, and since the compression region 77 is partial to the entire brace length, resistance to buckling compared to before reinforcement Power can be secured. From the above, since the reinforcing effect can be obtained also in the compression region 77, the reinforcing effect can be obtained with respect to the entire brace.

A second invention has at least two pairs of tabs attached to an existing brace disposed in a column beam frame at a predetermined interval in the axial direction of the brace, and the tabs are the center of the brace. Attached at a point-symmetrical position with respect to the shaft, the shape memory alloy piece is fixed to the tab with a bolt and attached, and then the shape memory alloy piece is heated to apply tension to a part of the brace in the axial direction. This is a brace reinforcing method.

  The first aspect of the present invention can introduce tension without limiting the member cross-sectional shape of the brace when introducing initial tension to the brace, and can also be applied to an existing brace in a column beam frame. There is an effect that there is.

  In the second invention, in the case of reinforcing an existing brace, since it is only necessary to perform partial construction as compared with the conventional method, there is an effect of improving the construction quality, shortening the work period, and reducing the amount of steel required for reinforcement.

  Hereinafter, as a best mode for carrying out the present invention, a brace reinforcing method for introducing an initial tension by a shape restoring force of a shape memory alloy piece will be described in detail with reference to the drawings.

    1 and 2 show an embodiment for a steel pipe brace. Incidentally, FIG. 1 is a front view of the reinforcing structure of the brace 1, and FIG. 2 is a cross-sectional view of the brace 1 taken along the line BB. A tab 4 having a hole to be fixed with a bolt is provided at a side surface portion of a brace 1 as a steel pipe to which initial tension is introduced, and is attached by welding at a predetermined interval in the axial direction. It is preferable that the two tabs 4 to be attached are paired and at least two pairs are attached in consideration of avoiding the occurrence of an eccentric moment and the effect of preventing buckling in the compression region. And the shape memory alloy piece 3 is fixed and attached with the volt | bolt 5 between the tab 4 which became a pair. In order to avoid the occurrence of the eccentric moment, it is preferable to attach the two shape memory alloy pieces 3 to the pair of tabs 4, but when the tab has a sufficient strength against the eccentric moment, There is no problem even if one shape memory alloy piece 3 is attached to a pair of tabs 4.

    3-5 has shown the reinforcement structure of the brace 1 which consists of H-section steel. 3 is a side view of the reinforcing structure, FIG. 4 is a front view thereof, and FIG. 5 is a cross-sectional view taken along the line C-C. Tabs 4 are erected along the upper and lower surfaces of the flange of the brace 1, and the shape memory alloy pieces 3 are attached to the tabs 4 in two rows so as to be substantially parallel to each other.

  The shape memory alloy constituting the shape memory alloy piece 3 has a characteristic that it returns to its original shape when heated to a necessary temperature after being processed below a certain critical temperature. Accordingly, the alloy is subjected to a predetermined amount of rolling at a temperature lower than the critical temperature in advance, and is heated after being attached at a predetermined position, whereby initial tension is introduced into the brace by its restoring force.

  The shape memory alloy used as the shape memory alloy piece 3 has a tensile strength of 680 to 1000 MPa, a transformation temperature of 300 to 350 ° C. at which the shape is completely recovered, a shape recovery stress of 180 MPa, and a shape recovery strain of 2.5 to 4.0. Preferred are iron-based shape memory alloys such as 16% Mn-5% Si-12% Cr-5% Ni-Fe and 20% Mn-5% Si-8% Cr-5% Ni-Fe having a performance of about%. .

  The following examples further illustrate the present invention. This embodiment is based on the steel structure design standard defined in the steel structure design standard (Architectural Institute of Japan). A brace structure composed of a column beam frame having a height of 5 m and a column interval of 10 m and one brace 1 as shown in FIG. 6 is taken as an example. The brace 1 uses SN400B class H-300 × 300 × 10 × 15 defined in JISG3136 and JISG3192, and all the horizontal force 8 applied to the column beam frame is borne by the axial force of the brace. Further, the yield strength in this embodiment is a load when the stress level generated in the member reaches the short-term allowable stress level.

  The total length of the H-shaped steel brace is 11.18 m. If this is the buckling length, the yield strength of the brace against the tensile force is 2782 kN, and the yield strength against the compression force is 757 kN. Therefore, the horizontal force 8 that can be supported by the column beam frame is determined by the proof stress on the compression side and becomes 677 kN.

  Next, an example will be described in which the brace is reinforced by the present invention when the horizontal force 8 supported by the column beam frame increases by about 15% to 779 kN. The axial force that the H-shaped steel brace needs to bear is 871 kN, which exceeds the compressive strength by 114 kN. This lack of proof stress on the compression side is reinforced by introducing an initial tension.

  When the initial tension is introduced by the shape memory alloy piece, in addition to the actually required initial tension, the reaction force from the compression region must be borne by the shape memory alloy piece. Since the extension length in the range where the tensile force is generated by introducing the initial tension is equal to the contraction length in the compression region, the initial tension actually introduced by the shape memory alloy piece 3 is the initial tension required. Is multiplied by the value obtained by dividing the total length of the brace by the length of the compression region.

If the length of the compression range is 1.0 m, the total length of the brace is 11.18 m and the necessary initial tension is 114 kN, so the magnitude of the tension introduced by the shape memory alloy is 1275 kN. When the shape restoring force of an iron-based shape memory alloy is 180 MPa and eight shape memory alloy pieces having a thickness of 9 mm and a width of 100 mm are attached, the total cross-sectional area thereof is 72 cm ² and the introduced tension is required to be 1296 kN Exceeding tension.

  Next, the compression range is examined. Since the compression range is 1.0 m, if the buckling length is 1.0 m, the compression side yield strength is 2759 kN. The maximum compressive force generated in the compression region is 2053 kN, which is the sum of the difference between the axial force 1296 kN introduced by the shape memory alloy piece and the initial tension 114 kN introduced into the tension portion and the load borne by the brace. Since this is smaller than the yield strength of the compression range, it can be said that the compression range has sufficient yield strength.

  As described above, in this embodiment, as shown in FIGS. 3, 4, and 5, four pairs of tabs 4 paired with the brace 1 are attached with an interval of 1 m. Next, two shape memory alloy pieces 3 each having a thickness of 9 mm and a width of 100 mm are attached to each of the pair of tabs 4, and a total of eight pieces are attached and fixed with bolts 5. The shape memory alloy piece 3 is heated to 350 ° C. with a burner. A predetermined initial tension is introduced to the brace by the shape restoring force of the shape memory alloy piece 3 to complete the construction.

It is a side view which shows the reinforcement method of the brace by a prior art. It is AA sectional drawing of FIG. It is a side view which shows the introduction range of the initial stage tension to a brace. It is a side view of the shape memory alloy attachment part to a steel pipe brace. It is BB sectional drawing of FIG. It is a side view of the shape memory alloy attachment part to an H-shaped steel brace. FIG. 8 is a plan view of FIG. 7. It is CC sectional drawing of FIG. 6, FIG. It is a side view which shows the brace structure used as the object of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brace 2 Reinforcement material 3 Shape memory alloy piece 4 Tab 5 Bolt 6 Initial tension introduction part 7 Compression area 8 Horizontal force

Claims (2)

In the brace structure disposed in the column beam frame, the brace structure has at least two pairs of tabs attached at predetermined intervals in the axial direction of the braces, and the tabs are point-symmetrical with respect to the central axis of the braces. A brace structure characterized in that tension is applied to a part of the brace in the axial direction by a contraction force at the time of shape recovery of the shape memory alloy piece attached to the tab and fixed with a bolt between the tabs. At least two pairs of tabs attached to the existing braces arranged in the column beam frame at predetermined intervals in the axial direction of the braces, the tabs being point-symmetric with respect to the central axis of the braces After the shape memory alloy piece is fixed to the tab with a bolt and attached, the shape memory alloy piece is heated to apply tension to a part in the axial direction of the brace. How to reinforce braces.

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