JPH0124196Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Field of Industrial Application] The present invention relates to piles suitable for foundation piles of structures, particularly reinforced piles made by reinforcing PC or RC piles. [Prior Art] Conventionally, there is an invention disclosed in Japanese Unexamined Patent Application Publication No. 178026/1989, which relates to reinforcing the head of a foundation pile of this type of structure. This is a reinforcement consisting of multiple vertical main reinforcements and spiral ties that connect these main reinforcements to each other.The lower part of this reinforcement is inserted into the center hole of the head of the foundation pile. This invention aims to strengthen the heads of foundation piles by doing this. However, the above invention has a structure in which the lower part of the reinforcing bar is simply inserted into the center hole of the head of the foundation pile, so the foundation pile and the reinforcing bar only function independently, and both No synergistic effects can be expected from an integrated structure. In other words, when a horizontal load is applied to a foundation pile due to an earthquake, etc., the load first acts on the foundation pile,
Next, when a shearing force or bending moment that exceeds the allowable range of the pile occurs, it acts on the reinforcing bars inserted inside the pile. Therefore, there is a problem in that when such a situation occurs, the foundation piles may have already been damaged. In order to solve these conventional problems, the applicant previously proposed a device as shown in Japanese Utility Model Application Publication No. 59-5642. This is a hollow concrete pile that is made by fixing reinforcing reinforcing bars to the axial reinforcement of the hollow concrete pile or spiral reinforcement wrapped around the axial reinforcement using means such as welding so that the reinforcing reinforcing bars protrude into the hollow part of the pile. This is a pile in which the hollow portion is filled with concrete and the reinforcing reinforcing bars are buried, and the two are integrated through the reinforcing bars. [Problems to be solved by the invention] As a result, the problems of the invention disclosed in JP-A No. 57-178026 can be solved, but in the pre-process of forming concrete piles by centrifugal molding, This requires a processing step in which the reinforcing reinforcing bars are fixed by welding or the like to the shaft bars or spiral bars wrapped around the shaft bars (reinforcing bar cages), which poses problems in terms of workability and cost. [Means for solving the problem] The present invention is based on the invention disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-178026 and the invention disclosed in Japanese Utility Model Application Publication No. 59-5642, in which reinforcing bars are embedded. The purpose is to provide piles that have the same or greater strength without
The gist is that multiple steel bars are arranged vertically in a circular shape when viewed from above, and that the steel bars are wound spirally around the outer periphery of a cylindrical body formed by these steel bars, and connected to each steel bar at contact points. A pile formed by centrifugal molding with a tightened spiral thread as a core, the inner diameter of the hollow part formed at the center of the pile being 20% or less of the outer diameter of the pile. It is characterized by a reinforced pile. [Example] Generally, foundation piles and structures are connected via footings, but according to recent earthquake engineering research, large horizontal movements, including resonance of buildings during large earthquakes, As a result, an unexpectedly large horizontal load acts on the foundation piles mentioned above, especially the foundation piles near the ground surface, and this causes a large shear force and bending moment that exceeds the allowable range, which may cause the pile to fail in extreme cases. It has been found that breakage may occur. As a countermeasure, use large-diameter PC piles,
Naturally, it is conceivable to increase the number of them, but there are limits to this due to geology, construction methods, costs, etc. On the other hand, research conducted by the applicant, to whom the inventor belongs, has revealed that the conventionally used PC piles have a fundamental weakness against the horizontal load (load in the direction perpendicular to the pile). In other words, from the test results when a high-strength PC pile with an outer diameter of 30 cm and a length of 2.7 meters with specifications as shown in Table 1 is supported at both ends and a concentrated load is applied to the center, when the amount of spiral reinforcement is small, In addition to the fact that it was found that shear failure was likely to occur, the neutral axis position in the cross section of the pile when a load was applied as described above was curvature ψ of 5.10 when the axial force A was 35 tons, as shown in Figure 3. , 15 and 20 (each x 10 ^-4 ) are near the upper edge of the hollow part 4a, so as shown in Fig. 5, the bending strength (moment) M
maintains a high value even when the curvature is around 20×10 ^-4 ,
When the axial force A is 70 tons, as shown in Figure 5, crushing occurs on the compression side (above the horizontal center line on the figure in Figure 4) near the curvature of 12 x 10 ^-4 (point A). As a result of the subsequent neutral axis position moving to the tension side (Fig. 4),
It was found that the bending strength suddenly decreased as shown by the dashed line in FIG. 5, and finally the bending crushing occurred.

[Effect]

The reinforced pile 10 configured in this way is
The inner diameter r of the hollow part 10a is the outer diameter R of the pile 10.
Since the size is 20% or less, the strength against the resulting shear force and bending moment is significantly improved even when a horizontal load as described above is applied. In other words, according to an experiment similar to the one described above, ^the neutral axis is As shown in Figure 2, it is concentrated at a little more than 1/3 from the upper edge of the cross section, and as a result, the cross-sectional area especially on the compression side increases and the initial crushing on the compression side is prevented. Prevented. Therefore, the bending strength (moment) is the fifth
As shown by the solid line in the figure, approximately 80% of the maximum value can be maintained even at a curvature of 20×10 ^-4 . [Effects of the invention] As mentioned above, the reinforced pile according to the invention consists of a plurality of vertical steel bars arranged in a circular shape in plan view and a cylindrical body formed by these steel bars. A pile formed by centrifugal molding with a spiral wire wound around the outer periphery and connected to each steel rod at contact points as a core, and the inner diameter of the hollow part formed at the center of the pile is defined as Since it is formed so that it is 20% or less of the outer diameter of the pile, it completely prevents collapse on the compression side caused by bending, and maintains high bending strength by keeping the neutral axis almost constant. can. Therefore, it is possible to form foundation piles without increasing the diameter or number of piles and to suppress an increase in cost, which has the great effect of preventing buildings from being destroyed by large-scale earthquakes.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the original reinforced pile after it has been placed, Figure 2 is a cross-sectional view showing the neutral axis of the original pile to which a bending moment has been applied, and Figures 3 and 4 are the same PC.
FIG. 5 is a cross-sectional view showing the neutral axis when a bending moment is applied to the pile, and FIG. 5 is a view showing changes in bending strength (moment) with respect to curvature. 1...Steel bar, 2...Spiral reinforcement, 3...Concrete, 10...Pile, 10a...Hollow part, R...
...outer diameter of the pile, r...inner diameter of the hollow part.

Claims (1)

[Scope of utility model registration request] Multiple steel rods are arranged vertically in a circular shape when viewed from above, and spiral reinforcement is wound spirally around the outer periphery of a cylindrical body formed by these multiple steel rods and connected to each steel rod at contact points. A pile formed by centrifugal molding with a core of
% or less.