Precast concrete footing beam structure

Abstract

To secure yield strength with respect to an in-plane tensile force generated by a torsional moment which acts in a beam cross section, in a footing beam in which precast beam members are oppositely installed.SOLUTION: In a footing beam 1 which has stirrup reinforcements 16, 26 partly protruding from a side surface, in which a pair of precast beam members 10, 20 having a substantially symmetrical shape regarding a center line in a beam width direction are placed on a bottom plate by protrusion portions of the stirrup reinforcements 16, 26 opposing to each other so as to secure a joint space S in the beam width direction, and concrete 11 is placed at a job site in the joint surface S, the footing beam 1 has a lower part connection auxiliary reinforcement 25 extending to the vicinity of a concrete member C of the other precast beam member 10 mounted on a lower side of the one stirrup reinforcement 26, out of the pair of precast beam members 10, 20.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a precast concrete foundation beam structure, and particularly to a precast concrete foundation beam structure constructed using half-precast concrete members arranged opposite to each other in the beam width direction.

Background Art

[0002] When precast concrete is used for the foundation beam structure of a building, in large buildings such as condominiums and buildings, the beam depth and beam span of the foundation beam become large, so the precast concrete foundation beam becomes considerably heavier than the precast concrete column. For this reason, a large crane corresponding to the weight of the foundation beam is required on site, which causes factors such as an increase in construction costs.

[0003] In order to address these problems, the applicant has proposed a foundation beam structure in which two precast concrete beam members arranged in the beam width direction are integrated with in-situ concrete to reduce the weight of the precast concrete beam members (Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The invention described in Patent Document 1 is a structure in which a precast beam member with a part of the shear reinforcement protruding from the side surface is installed on the foundation with the side surface where the shear reinforcement protrudes facing each other, and in-situ concrete is placed between the oppositely installed precast beam members to integrate them.

[0006] In this foundation beam structure, since the site-cast concrete is placed with the shear reinforcement bars arranged opposite to each other at a predetermined distance apart, a rebar-free range is formed near the center in the beam width direction, that is, between the opposing shear reinforcement bars. Even if there is such a rebar-free range within the foundation beam cross-section with respect to the shear force in the beam length direction, it has no adverse effect on the member performance of the foundation beam. However, as schematically shown in Fig. 6(a), in the case of a planar foundation design where the foundation beam 50 is arranged to connect between the pile head foundations 52 and further the secondary beam 51 is joined to the foundation beam 50 at the center of the span in the material axis direction of the foundation beam 50, an in-plane torsional moment may occur in the foundation beam 50 at the position supporting the secondary beam 51 (Fig. 6(b)).

[0007] By the way, in the reinforcement arrangement example (Fig. 7(a)) with the precast beam member of the foundation beam 50 disclosed in Patent Document 1, the shear resistance, flexural resistance, and bond resistance in the material axis direction of the foundation beam 50 are maintained. However, in the case of the structural examples shown in each of Fig. 6, since the longitudinal main rebars 57 are pre-embedded and arranged at the upper and lower side positions of the shear reinforcement bars (stirrup bars) protruding from the precast beam members 55A and 55B, the ranges surrounded by the shear reinforcement bars 56 of the opposing precast beam members 55A and 55B cannot be overlapped and made continuous with each other. For this reason, sufficient resistance to torsion (torsional resistance) generated within the completed foundation beam 50 (Fig. 7(b)) cannot be obtained, and it cannot sufficiently resist the tensile stress T generated at the upper and lower ends of the beam deflection caused by the in-plane torsional moment acting on the beam.

[0008] Also, even if it is planned to add a predetermined reinforcing bar to the precast beam member disclosed in Patent Document 1, in the foundation beam 50 planned to be installed in the groove 60 as shown in Fig. 7(a), no space can be secured to move in the beam width direction from the installation stage of the precast beam member, and the precast beam member is carried in and installed by moving it only in the vertical direction by a crane or the like. Therefore, it is not possible to add a reinforcing bar and arrange it under the foundation beam after installing the precast beam member, and there is a possibility of damage occurring in the rebar-free section where the shear reinforcement bars are not continuous.

[0009] Therefore, an object of the present invention is to provide a foundation beam structure constructed using a precast beam member, in which a foundation beam structure is constructed using a precast beam member in which lower connection reinforcing bars are arranged in advance at the lower end of the beam.

Means for Solving the Problems

[0010] In order to achieve the above object, the precast concrete foundation beam structure of the present invention has stirrup bars partially protruding from the side surface of a concrete member, and a pair of precast beam members having a substantially symmetrical shape with respect to the center line in the beam width direction are placed on a chassis with the protruding portions of the stirrup bars facing each other so as to secure a joining space in the beam width direction, and a foundation beam in which concrete is cast in place in the joining space is arranged to connect between pile head foundations. In the precast concrete foundation beam structure, the foundation beam is characterized in that a lower connection reinforcing bar extending to the vicinity of the concrete member of the other precast beam member is attached to the lower side of one of the stirrup bars among the pair of precast beam members.

[0011] Preferably, the lower connection reinforcing bar has a substantially L shape composed of a horizontal bar whose end is fixed to the lower end beam main bar held by the stirrup bar via a hook and a vertical bar bent upward while securing a predetermined fixing length in the vicinity of the concrete member of the other precast beam member.

[0012] Preferably, an upper connection reinforcing bar is attached to the upper side of the opposing stirrup bars of the foundation beam.

[0013] Preferably, the upper connection reinforcing bar has an inverted U shape straddling between the opposing stirrup bars and is fixedly supported by the upper end beam main bar.

[0014] Preferably, the upper connection reinforcing bar and the lower connection reinforcing bar are arranged at the same reinforcement spacing as the stirrup bars.

[0015] The base beam is preferably constructed by placing the pair of precast beam members on a chassis with the protruding portions of the stirrup bars facing each other so as to secure a joining space in the beam width direction by inverting one precast beam member with respect to the other precast beam member, with the two precast beam members having the same shape, and then casting concrete on site in the joining space.

Advantages of the Invention

[0016] According to the present invention, when integrating precast beam members, it is possible to eliminate the rebar-free section, thereby ensuring sufficient shear strength against the in-plane torsional moment acting on the base beam.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0018] The foundation beam structure of the present invention will be described below with reference to the accompanying drawings. The same reference numerals are given to the same components.

[0019] [Schematic Configuration of Foundation Beam 1] FIG. 1 shows the cross-sectional shape of the foundation beam 1 according to the present invention. The foundation beam 1 of the present embodiment is applied to a structure similar to the planar foundation plan shown in FIG. 6(a). Here, regarding the planar shape of the foundation beam 1 of the present invention at the time of completion, it shall follow the foundation beam 50 in FIG. 6(a). That is, the foundation beam 1 is arranged to connect between the pile head foundations 52 and has a structure that supports the secondary beams 51 and the like, for example, at the central part in the material axis direction of the foundation beam 1. The foundation beam 1 is provided at a predetermined position on a leveling concrete base (not shown), and the same-shaped half-precast concrete beam members 10 and 20 (hereinafter referred to as precast beam members 10 and 20) are installed such that the stirrup bars 16 and 26 protruding from the concrete side surfaces face each other with a slight gap at a predetermined interval. Further, the lower connection reinforcement bars 25 and the upper connection reinforcement bars 17 are arranged in the non-reinforced section where the stirrup bars 16 and 26 between the juxtaposed precast beam members 10 and 20 are not continuous. The foundation beam concrete 11 is cast in place in the space (joint space S) of the gap in the beam width direction of the precast beam members 10 and 20, and the state where the beam cross-sectional shape is completed is shown. Note that the beam cross-sectional shape of the foundation beam 1 of the present embodiment has a beam depth H = 2000 mm and a beam width W = 1000 mm. Also, the member length L of the precast beam members 10 and 20 is the same as that of the beam described in Patent Document 1 as the prior art, and as an example, the member length L = 5250 mm.

[0020] [Configuration of Precast Beam Member 10] The configuration of the precast beam member 10, which is the main component of the foundation beam 1, will be described with reference to Figs. 1, 2(a) to (c), and Figs. 3(c) and (d). The precast beam member 10, which forms part of the cross-section of the foundation beam 1, is an elongated precast concrete member in the height (vertical) direction with stirrup bars 16 arranged at predetermined intervals in the material axis direction, as shown in Figs. 1 and 3(c). As shown in Fig. 2(a), the stirrup bars 16 are vertically long rectangular shapes, and are arranged so that a predetermined length of the side half range protrudes into the joint space S, and hold a predetermined number of beam main reinforcements 14 at the upper and lower side positions. The dimensions of the precast beam member are set such that the width of the joint space S is 500 mm and the width of each precast beam member 10 is 250 mm out of the beam width of 1000 mm of the completed cross-section of the foundation beam 1 (Fig. 1).

[0021] [Configuration of Precast Beam Member 20] The precast beam member 20 has the same member length as the precast beam member 10. The stirrup bars 26 are arranged in a vertically long square shape and protrude a predetermined width into the joint space S, as shown in Fig. 2(b). The width of the precast beam member 20 is set to 250 mm. The points where the beam main reinforcements 24 are arranged at the upper and lower ends of the beam are the same as those of the precast beam member 10.

[0022] In the precast beam member 20, lower connection reinforcement bars 25 are further arranged on the lower side of the stirrup bars 26. As shown in Fig. 2(b), the lower connection reinforcement bars 25 are reinforcing bars having a substantially L shape arranged in a direction parallel to the stirrup bars 26. The bar diameter of the lower connection reinforcement bars 25 is set to be equal to or less than the bar diameter of the stirrup bars 26. The horizontal bar 25h of the substantially L-shaped lower connection reinforcement bar 25 is in contact with the lower side beam main reinforcement bars 24, and a part thereof is embedded and fixed in the concrete member C, and the 135° hook 25f formed at the end of the horizontal bar 25h is locked to the beam main reinforcement bars 24 embedded at the corner end in the precast beam member 20. The horizontal bar 25h extends to the vicinity of the inner surface of the concrete member C (Fig. 2(a)) of the other precast beam member 10 installed opposite, and becomes a vertical bar 25v bent upward by a predetermined length therefrom. The upward bending length of the vertical bar 25v is set to be 8 times or more the diameter of the lower connection reinforcement bar 25. As shown in Fig. 2(c), the reinforcement pitch of the lower connection reinforcement bars 25 in this embodiment is the same as that of the stirrup bars 26 arranged in the material axis direction, and is arranged between the arrangement intervals of the stirrup bars 26. Each of the lower connection reinforcement bars 25 is used as a fixing bar, and since a sufficient fixing length is ensured, it can be arranged without being bundled with the beam main reinforcement bars 14 at the lower end of the precast beam member 10.

[0023] [Construction of the foundation beam 1 - Installation and integration of precast beam members] The construction procedure of the foundation beam 1 (Fig. 1) using two precast beam members 10 and 20 will be described with reference to each figure in Fig. 3. First, the ground surface on which the foundation beam 1 is to be constructed is excavated in a groove shape slightly wider than the beam width to a depth at which the foundation beam 1 is buried over almost the entire height. The precast beam member 20 is erected and placed on the bottom plate of the leveling concrete (not shown) cast in advance with a predetermined thickness at the bottom of the formed excavation space 6, and is positionally held by a support or the like (not shown) (Fig. 3(a)). Next, using a crane or the like, the precast beam member 10 is vertically lowered into the narrow groove-shaped excavation space 6 and placed statically on the leveling concrete, and is positionally held by a support or the like (not shown) so as to secure a joint space S corresponding to the designed width of the foundation beam 1 (Fig. 3(b)). The upper connection reinforcement 17 is attached so as to be supported on the upper sides of the stirrup bars 16 and 26 in the formed joint space S where the precast beam members 10 and 20 are installed (Fig. 3(c)). As shown in Fig. 3(c), this upper connection reinforcement 17 is a processed reinforcing bar forming a U shape, and is placed from above so as to straddle the stirrup bars 16 and 26 and the upper side beam main reinforcements 14 and 24 in an inverted U shape so that the vertical bars are fixed in the range surrounded by the stirrup bars 16 and 26, and are installed at a predetermined pitch in the material axis direction. In this embodiment, the upper connection reinforcement 17 is arranged at the same pitch as the lower connection reinforcement 25. It should be noted that the upper connection reinforcement 17 is preferably bundled and held to the beam main reinforcements 14 and 24 at the upper end (Fig. 3(d)). Thereafter, the reinforcement and formwork for other parts are installed, and finally, the foundation beam concrete 11 (Fig. 1) is cast in place in the joint space S formed between the precast beam members 10 and 20, and the precast beam members 10 and 20 and the foundation beam concrete 11 are integrally joined to construct the foundation beam 1 (Fig. 1: completed cross section).

[0024] In the present invention, a lower connection reinforcing bar 25 is provided at the lower side portion of the stirrup bar 26 of the precast beam member 20. A modified example of this lower connection reinforcing bar 25 will be described with reference to each figure in FIG. 4. Each figure in FIG. 4 shows several modified examples in which the shape and attachment means of the lower connection reinforcing bar 25 attached to the precast beam member 20 are changed. FIG. 4(a) shows a shape example in which the length of the vertical bar is shortened by forming a hook 25g at the upper end of the vertical bar of the lower connection reinforcing bar 25. As the hook shape, in addition to the illustrated 135° hook, a semi-circular (180°) hook, a right-angled (90°) hook, etc. can be used to sufficiently shorten the fixing length, and the lower connection reinforcing bar 25 can be made into a compact shape to avoid interference with the stirrup bar 16 of the precast beam member 10 installed opposite.

[0025] FIG. 4(b) shows a modified example in which a mechanical joint is provided in a part of the connection reinforcing bar. Since the protruding length of the reinforcing bar is large in the connection reinforcing bar shown in FIGS. 1 and 3(a) described above, it may be bulky during transportation. Therefore, as shown in FIG. 4(b), a mechanical joint such as a screw coupler 30 is embedded in a part of the connection reinforcing bar located in the concrete member during the manufacture of the precast beam member 20, and after the precast beam member 20 is carried into the site, a part of the horizontal bar 25h of the lower connection reinforcing bar 25 protruding from the concrete member C is joined to the screw coupler 30, so that a reinforcing bar equivalent to the lower connection reinforcing bar 25 shown in FIG. 1 etc. can be provided. Also, in order to shorten the fixing length, as shown in FIGS. 4(c-1) and (c-2), it is also preferable to provide a mechanical fixing portion in which a circular plate 27 is attached to the end of the horizontal bar 25h, or the end of the horizontal bar 25h is hot-press formed to integrally form a disc-shaped portion 28.

[0026] Fig. 5(a) shows an embodiment in which the precast beam member 20 with the lower connection reinforcement 25 attached is arranged opposite to the precast beam member 10 described above. In this embodiment, two precast beam members 20 are used. One of the precast beam members 20 is turned upside down and installed opposite to the other precast beam member 20 already installed on the chassis, with their stirrup bars 26 facing each other. In this embodiment, the lower connection reinforcement 25 of the precast beam member 20 placed upside down is arranged at a position corresponding to the upper connection reinforcement 17 as shown in Fig. 3(c). As a result, the reinforcement arrangement state equivalent to that in Fig. 3(d) can be achieved. In this embodiment, by manufacturing and installing a single type of precast beam member, the same effect as when the upper connection reinforcement 17 is not used can be obtained.

[0027] In addition, it is also preferable to enhance the adhesion between the in-situ cast foundation beam concrete 11 and the inner surfaces of the precast beam members 10 and 20 by arranging uneven portions on the concrete surfaces of the opposing inner surfaces between the opposing precast beam members 10 and 20, grooves of various cross-sectional shapes along the material axis direction, or a plurality of cotters.

[0028] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in each claim. That is, embodiments obtained by appropriately combining technical means modified within the scope shown in the claims are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0029] 1 Foundation beam 10, 20 Half-precast concrete beam members (precast beam members) 11 Foundation beam concrete (in-situ cast concrete) 14, 24 Main beam reinforcement 16, 26 Stirrup bars 17 Upper connection reinforcement 25 Lower connection reinforcement S Joint space

Claims

1. In a precast concrete foundation beam structure in which a pair of precast beam members having stirrup bars partially protruding from the side surfaces of concrete members and having a substantially symmetric shape with respect to the center line in the beam width direction are placed on a chassis with the protruding portions of the stirrup bars facing each other so as to secure a joining space in the beam width direction, and concrete is cast in place in the joining space, and the foundation beam is arranged to connect between pile head foundations, the precast concrete foundation beam structure is characterized in that a lower connecting reinforcing bar extending to the vicinity of the concrete member of the other precast beam member is attached to the lower side of one of the stirrup bars among the pair of precast beam members.

2. The precast concrete foundation beam structure according to Claim 1, wherein the lower connecting reinforcing bar comprises a horizontal bar fixed to a lower end beam main bar whose end is held by the stirrup bar via a hook, and a vertical bar bent upward while securing a predetermined fixing length in the vicinity of the concrete member of the other precast beam member, and forms a substantially L shape.

3. The precast concrete foundation beam structure according to Claim 1, wherein an upper connecting reinforcing bar is attached to the upper side of the opposing stirrup bars.

4. The precast concrete foundation beam structure according to Claim 1, wherein the upper connecting reinforcing bar forms an inverted U shape straddling between the opposing stirrup bars and is fixedly supported by an upper end beam main bar.

5. The precast concrete foundation beam structure according to any one of Claims 1 to 3, wherein the upper connecting reinforcing bar and the lower connecting reinforcing bar are arranged at the same bar arrangement interval as the stirrup bar.

6. The precast concrete foundation beam structure according to Claim 1, wherein the pair of precast beam members have the same shape, and the other precast beam member is turned upside down with respect to one precast beam member to secure a joining space in the beam width direction, and the protruding portions of the stirrup bars are opposed to each other and placed on a chassis, and concrete is cast in place in the joining space.

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