EP0085681B1

EP0085681B1 - A concrete foot-structure for posts or a concrete-post plinth having a fracture mechanism cast therein; and a method for manufacturing such a foot structure or plinth

Info

Publication number: EP0085681B1
Application number: EP82901032A
Authority: EP
Inventors: Stig Thim
Original assignee: A-BETONG AB/SABEMA MATERIAL AB; Sabema Material AB; Abetong AB
Current assignee: A-BETONG AB/SABEMA MATERIAL AB; Sabema Material AB; Abetong AB
Priority date: 1981-03-20
Filing date: 1982-03-19
Publication date: 1985-08-07
Also published as: SE8101798L; WO1982003241A1; DK513082A; DE3265158D1; NO823857L; EP0085681A1

Abstract

A concrete foot structure for posts or a concrete post plinth (4) is intended to form a stiffening element or foundation element for a post (1) made, for example, of wood or concrete. The foot structure or plinth is provided with a fracture mechanism arranged to facilitate shearing of the foot structure or plinth when subjected to horizontally acting forces, for example when in collision with a motor vehicle. The fracture mechanism comprises a thin plastics plate (6) cast in situ with the foot structure or plinth. The plate can be used as a distance and holder means for reinforcing rods (5) when casting the foot structure or plinth.

Description

The present invention relates to a concrete foot structure for posts or a concrete-post plinth having a fracture mechanism cast therein. The foot structure or plinth is intended to reinforce a wooden post or column erected in the ground, and to eliminate the disadvantages created by the rotting of the post at ground level. A foot structure or plinth according to the invention, however, can also be used as a foundation element for concrete posts, or posts made of some other material, it not being necessary for the post to have previously been in contact with the ground.
When such a foot structure is used in connection with, for example, wooden posts or poles erected by the sides of roads used by vehicle traffic, the damage to a vehicle colliding with such a post or with the foot structure is liable to be very extensive, due to the inability of the post or foot structure to yield with any degree of softness under impact, as a result, inter alia, of the relatively large mass of said post or foot structure, and therewith a relatively high inertia. Consequently, in the event of such a collision there is a grave risk of serious injury to the occupants of the vehicle.
The PCT publication WO 80/02167 and the Swiss Patent Specification Number 572 131 described the manufacture of a metal foot structure for posts provided with shear-facilitating weakened areas. None of these publications, however, teaches a concrete foot structure or plinth having a fracture mechanism cast centrally therein.
Another kind of fracture mechanism in foot structures is illustrated and described in U.S. Patent Specification Number 3 837 752. This publication, however, does not teach the concept of a fracture mechanism incorporated within a concrete floor structure for posts.
A prime object of the present invention is to provide a concrete foot structure for posts or a concrete plinth with which the risk of injurytothe occupants of a vehicle colliding therewith is far less than would previously have been the case.
A further object of the invention is to provide a foot structure or plinth of the aforementioned kind which can be readily manufactured and mounted to an existing post or pole in the ground and/or which can serve as a separate or integral foundation element.
A foot structure or plinth according to the invention is mainly characterized in that the fracture mechanism comprises a plate which is cast in the central region of the foot structure or the plinth and which is arranged to facilitate shearing of the foot structure or plinth when they are subjected to horizontally acting impact forces.
A foreign body of the aforementioned kind made, for example of a plastics material or metal, which will not adhere to the concrete when cast therein will weaken the foot structure or plinth to the extent desired, so that said foot structure or plinth will shear when subjected to impact forces.
The fracture plate is preferably placed in the region of the largest cross-sectional area of the foot structure or plinth, approximately on a level with the surface of the ground or at a location somewhat above the ground surface. When the post is subjected to impact forces, the concrete will crack around the plate, particularly in the region of the reinforcing rods when such rods are included in the foot structure or plinth. As a result of the weakening of the post caused by the fracture plate, the concrete will break up causing the foot structure to shear. When the foot structure or plinth incorporate reinforcing rods, the rods will bend under impact in regions above and beneath the fracture plate, and probably cause the concrete to crack in these regions.
A wooden post or pole is normally weakened by rotting of that part of the post located within the ground, and hence is readily broken off at said part when subjected to impact.
Despite the fact that a foot structure according to the invention greatly stiffens the post or pole with which it is used, the shear strength is considerably reduced because of the inventive design of said foot structure, thereby enabling the extent of damage to a vehicle colliding with a wooden or concrete post to be greatly reduced.
In practice, the configuration of the fracture mechanism is suitably adapted to the cross-sectional shape of the foot structure, and said mechanism is suitably provided with holes or openings through which reinforcing rods can extend in the longitudinal direction of the foot structure.
In addition to facilitating manufacture of the foot structure, this adaptation of the configuration of the fracture mechanism to the cross-sectional shape of the foot structure enables the fracture mechanism to be correctly positioned and reliably held within the foot structure. According to a further embodiment of the invention, the openings provided in the fractured plate are arranged to accommodate sleeve-like holder means for reinforcing rods, permitting said rods to move relative to the plate. This facilitates the aforementioned desired formation of cracks in the foot structure when the post is subjected to impact forces.
The formation of cracks is further facilitated when, in accordance with a preferred embodiment of the invention, the plate is slotted or grooved in the region of said openings, such as to promote the formation of cracks when the post or foot structure is subjected to impact forces.
As before mentioned, the configuration of the fracture plate is suitably adapted to the cross-sectional shape of the foot structure. Thus, the fracture plate may have a substantially triangular shape with a corresponding opening in the region of the side thereof located adjacent that part of the foot structure intended to lie against the periphery of the wooden post.
Alternatively, the fracture plate may have substantially the shape of the letter Y, whereat the foot structure itself can also be given an aesthetic Y-profile.
In practice, the foot structure may include three fracture mechanisms, namely one in its central part and one in the region of each end of the structure.
The foot structure may have a length of about 1.5m and can be driven into the ground adjacent a wooden post or pole, using suitable tools, whereafter the foot structure can be connected to the post by means of, for example, iron strip, iron hoops or like securing elements, using tools suitable herefor. Alternatively, the foot structure may be placed in a hole and optionally arranged to support the post.
The invention also relates to a method of manufacturing a concrete foot structure, said method being mainly characterized by the steps of arranging reinforcing rods in a horizontal mould and passing said rods through respective openings in at least one plate-like fracture mechanism having a shape adapted to the cross-sectional shape of the mould, such that the fracture mechanism supports the reinforcing rods in the mould; and casting concrete into the mould and allowing said concrete to set, whereafter the finished foot structure obtains a weakened part in the region of the plate-like fracture element which will yield when subjected to shear forces.
Manufacture is facilitated by using one or more plate-like fracture elements as jigs, which ensure that the reinforcing rods are correctly positioned in the mould. Simple means are used at the same time to ensure that the plate-like fracture mechanism or mechanisms used is or are also correctly positioned.
A number of exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings.

Figure 1 is a perspective view of a wooden post having a rotten base and supported by a foot structure according to the invention.
Figure 2 is a perspective view illustrating a cut- away central portion of the foot structure illustrated in Figure 1, provided with a weakening or fracture mechanism arranged on reinforcing rods.
Figure 3 is a sectional view taken on the line 111-111 in Figure 2.
Figure 4 is a cross-sectional view of a foot structure which has been subjected to impact forces, the Figure being intended to illustrate what occurs in the event of such impact forces.
Figure 5 is a perspective view illustrating a foot structure provided with a modified fracture mechanism.
Figure 6 is a sectional view taken on the line VI-VI in Figure 5.

A wooden post 1 having a rotten base portion 1a is shown positioned in the ground 2 and joined to a foot structure 4 by means of clamps 3, comprising, for example, iron hoops mounted by means of a suitable tool (not shown). The foot structure 4 will be described initially with reference to Figures 1-4.
The illustrated foot structure has a substantially Y-shaped configuration with a longitudinally extending receiving portion 4a arranged to abut the periphery of the wooden post 1.
The thickest part of the foot structure 4 lies approximately centrally of said structure, or slightly above said centre, the foot structure tapers slightly towards the ends thereof. The lower end of the foot structure is somewhat pointed, enabling the foot structure to be driven into the ground using a suitable percussion tool, and then connected to the wooden post 1.
The shape of the foot structure in the region of its maximum cross section is illustrated in Figure 2.
Extending through the foot structure 4 are three reinforcing rods 5, which between them support a Y-shaped fracture mechanism 6. To this end, the fracture element 6 is provided with slots or recesses 6a and with slotted sleeves 6b, in which the reinforcing rods 5 are inserted. The cross-sectional view in Figure 3 also contributes to illustrating the design of sleeves 6b.
The fracture element 6 is suitably made of a polyethylene plastics material and may have a thickness of about 3mm. In accordance with the aforegoing, the fracture element weakens the foot structure so that said structure will shear when the wooden post 1 is subjected to powerful impact forces, for example when a vehicle is in collision with the post.
Figure 4 is intended to illustrate what happens inside the foot structure when the post or said foot structure are subjected to impact forces. The reinforcing rods 5 are able to move freely through the plastic sleeves 6b to a certain extent, which sleeves also exhibit crack-promoting means in the form of slots 6a. Thus, when the foot structure is subjected to impact forces of the kind beforementioned, the reinforcing rods are able to deform to a certain extent, causing a greater amount of concrete to break up. As a result, the amount of concrete which is broken up is so great that the whole of the post can be compressed on one side thereof. On the opposite side of the post, the reinforcing rods are bent outwardly instead. This breaking up of the concrete causes the kinetic energy of the vehicle to be progressively absorbed, while slowing the vehicle down.
Figures 5 and 6 illustrate a modified foot structure 4, provided with a triangular fracture mechanism 6 provided with holes and recesses for accommodating four reinforcing rods 5. In this embodiment, two plastics, fracture elements 6 are welded together to form a single unit. The fracture mechanism of this embodiment is also provided with slots 6a accommodating sleeves 6b which surround the reinforcing rods 5.
Preferably, the foot structure 4 according to the invention includes four fracture mechanisms 6 of the kind illustrated in Figure 2 and Figure 5 respectively. In addition to a fracture mechanism arranged in the region of maximum cross section of the foot structure, a fracture mechanism can be arranged in the region of each end of said structure.
The fracture mechanisms 6 can also facilitate the manufacture of a foot structure. When manufacturing a foot structure, reinforcing rods 5 of adjusted lengths are passed through the sleeves 6b of a respective fracture mechanism 6, whereafter the fracture mechanism, which may optionally include three fracture plates, is placed in a horizontal mould. This ensures that both the reinforcing rods 5 and the fracture mechanisms 6 are correctly positioned in the mould. Concrete is then poured into the mould and allowed to harden, whereafter the foot structure is ready for use. In this way, the foot structure will have a weakened portion in the region of the central fracture mechanism 6, which causes the foot structure to shear off when subjected to forces of the kind beforementioned.
Although not shown, the foot structure may be used as a foundation element or plinth, for example, for a concrete or wooden post. The foot structure can then be accommodated, either completely or partially, in, for example, a hole dug in the ground to anchor the post. The foot structure may comprise a part separate from the post arranged to support the major part of the post in some suitable fashion, or may also be an integral part of the post itself. In all cases the foot structure has a weakened portion which facilitates shearing of the post when said post is subjected to impact forces.

Claims

1. A concrete foot structure for posts or a concrete post plinth having a fracture mechanism cast therein, characterized in that the fracture mechanism (6) comprises a plate (6) cast in the central portion of the foot structure (4) or post plinth and arranged to facilitate shearing of the foot structure or plinth when subjected to horizontal impact forces.

2. A foot structure or plinth according to Claim 1 characterized in that the plane of the plate (6) coincides approximately with the horizontal plane.

3. A foot structure or plinth according to Claim 1 or Claim 2, characterized in that the fracture mechanism (6) has a configuration adapted to the cross-sectional shape of the foot structure or plinth and exhibits a recess (6a) for accommodating a reinforcing rod (5) extending in the longitudinal direction of the foot structure or plinth.

4. A foot structure or plinth according to Claim 3, characterized in that the fracture mechanism comprises sleeve-shaped holder means (6b) for reinforcing rods (5), said holder means permitting the reinforcing rods to move relative to said fracture mechanism.

5. A foot structure or plinth according to Claim 4, characterized in that the fracture mechanism is provided with slots or recesses (6c) in the region of the reinforcing-rod-accommodating openings, said slots or recesses serving as crack-forming means promoting the formation of cracks in the foot structure or plinth when subjected to horizontal impact forces.

6. A foot structure or plinth according to any one of Claims 1-5, characterized in that the fracture mechanism (6) is of substantially triangular configuration (Figure 5).

7. A foot structure or plinth according to any one of Claims 1-5, characterized in that the fracture mechanism (6) is of substantially Y-shape configuration (Figure 2).

8. A foot structure or plinth according to any one of Claims 1-7, characterized in that in addition to a central fracture mechanism (6) in the region of its maximum cross-section, said foot structure or plinth is also provided with a similar fracture mechanism at each end thereof, each fracture mechanism being arranged to serve as holder means for reinforcing rods (5) associated with said foot structure or said plinth, during the casting thereof.

9. A method of manufacturing a concrete foot structure for posts or a concrete post plinth, characterized by arranging in a horizontal mould reinforcing rods (5) inserted in recesses in at least one plate-like element (6) whose configuration is adapted to the cross-sectional shape of the mould, such that the plate-like element supports the reinforcing rods in said mould; and by pouring concrete into said mould and allowing said concrete to harden, whereupon the cast foot structure or plinth (4) obtains a weakened portion in the region of the plate-like element (6) for facilitating shearing of the post when subjected to shear forces.