EP1116829A2

EP1116829A2 - Foundation raft

Info

Publication number: EP1116829A2
Application number: EP01300322A
Authority: EP
Inventors: Paul Kiss
Original assignee: Abbey Pynford Holdings Ltd
Current assignee: Abbey Pynford Holdings Ltd
Priority date: 2000-01-17
Filing date: 2001-01-16
Publication date: 2001-07-18
Also published as: GB0001039D0; EP1116829A3

Abstract

A method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprises the steps of erecting formwork (2), which is supported by a number of piles (4) and by a frame (3) to which the formwork is connected; and forming concrete (9) in the formwork to form the raft or beam, wherein at least part of the frame (3) is incorporated within the concrete (9) to provide reinforcement of the concrete.

Description

This invention relates to a structure for use in, and a method for, constructing a concrete foundation raft or low level beam and, in particular, to foundation rafts or beams which are spaced from the ground.
When building on ground, which is liable to subsidence or heave, it is well known to erect the building or other superstructure on a raft or beam, itself supported by piles, with the underside of the raft spaced above the ground by a void or compressible material. The void or compressible material, which prevents any heave from being significantly transmitted to the underside of the raft or beam, has taken a variety of forms. Typically, a collapsible or crushable spacer, made for example of hardboard, cardboard, and/or polystyrene has been used as a temporary support. Once the foundation raft or beam has been constructed, these spacers either degrade or are designed to compress with any uplift of the ground. Generally these techniques are expensive. Collapsible material can collapse prematurely, particularly in wet weather, and compressible spacers require extra space to avoid the transmission of heave to the raft to the crushed material.
In our previous patent application, GB 2329651A, we suggested a method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprising erecting formwork, which is held spaced above the ground by at least one interposed waterproof bag that is inflated with water or other liquid, pouring concrete in the formwork to form the raft or beam and, when the concrete has set, removing the water from the bag(s) to allow the bag(s) to collapse leaving a void between the underside of the raft or beam and the ground.
While this method has a number of advantages such as providing firm support for the formwork throughout the pouring and setting of the concrete and that the method is substantially unaffected by weather, we are now suggesting an alternative to the aforementioned method.
According to the present invention, a method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprises the steps of:
erecting formwork, which is supported by a number of piles and by a frame to which the formwork is connected; and
pouring concrete in the formwork to form the raft or beam, wherein at least part of the frame is incorporated within the concrete to provide reinforcement of the concrete.
Preferably, the frame is constructed of a metal, such as steel, so that the concrete is substantially reinforced.
The frame may be supported on the piles and, preferably, the formwork comprises a deck which is tied to the frame to prevent downward movement at the midpoints of the deck between the piles. The outer edges of the deck may be cut to the exact shape of the property and to accommodate one or more downstand units.
Once the frame has been fixed and the decking secured, the reinforcement is fixed and the one or more downstand units can be positioned at the edge of the decking and may then be secured to the reinforcement and/or the frame. The one or more downstand units provide support for edge shutters which are attached to the formwork. Once the edge shutters are in place, the concrete can then be poured.
This new method has a number of advantages. The frame ensures that any void between the formwork and the ground can be kept completely clear during construction while ensuring that the formwork is securely supported. As there is no direct support between the ground and the formwork, this method can be used when the ground is uneven. The provision of downstand units ensures that the sides of the formwork are supported and provide convenient attachment for the edge shutters. Additionally, the frame provides reinforcement to the concrete and means that additional reinforcement may not be needed. Of course, further reinforcement may be added if required.
According to a second aspect of the present invention, a frame for use in constructing a concrete foundation raft or low level beam for a building or other superstructure comprises at least one pair of elongate tubes, comprising a first and a second tube, which are arranged to be connected, in use, to a deck;
a third elongate tube, substantially parallel to the first and second tubes and which is spaced from the plane in which the other two tubes lie to form, in section, a triangular arrangement; and
connecting means for joining the first and second tubes to the third tube.
According to a third aspect of the present invention, a method of constructing a concrete foundation raft or low level beam for a building or other superstructure comprises the steps of:
erecting formwork, which is supported by a number of piles, by at least one interposed bag that is inflated with air and by one or more downstand units;
pouring concrete in the formwork to form the raft or beam; and
removing the air from the bag(s) when the concrete has set to allow the bag(s) to collapse, leaving a void between the underside of the raft or beam and the ground.
By using air rather than a liquid, the bags can be filled and emptied more quickly and easily.
The bag(s) can be used together with one or, more usually, a pair of formers which are preferably formed from timber. These formers permit the size of the void to be increased without the need for various differently sized bags.
Examples of the present invention will now be described with reference to the accompanying drawings in which:
Fig. 1 is a schematic, vertical cross section through a foundation raft constructed according to the present invention;
Fig. 2 is a section along line A-A of Fig. 1;
Fig. 3 is a plan view of part of the frame of Fig. 1;
Fig. 4 is a cross sectional view showing the use of a downstand unit;
Fig. 5 is a cross-sectional view showing an edge shutter support;
Fig. 6 shows a vertical section through a typical foundation raft;
Fig. 7 is a vertical section showing how the void is formed according to one aspect of the present invention;
Fig. 8 is a partially sectioned elevation of a bag for supporting the formwork;
Fig. 9 shows a plan view of a possible arrangement of the bags beneath the formwork;
Fig. 10 is a perspective view of a bag and a laterally elongate coupling device;
Fig. 11 is a cross-sectional view showing the use of formers; and
Figs 12a and b are partial cross-sectional views showing different sized formers.
As can be seen from Fig. 1, a foundation raft 1 comprises a deck 2 and a frame 3, both of which are supported by a number of piles 4. The piles 4 have been preformed in the ground 5 and the uppermost section of the piles is of a greater diameter to the remainder of the pile. The piles 4 support the foundation raft 1 away from the ground, thus creating a void 7 which can accommodate potential ground heave. A number of spacers 8 are provided between the frame 3 and the deck 2. The frame and deck are connected together through the spacers 8. The spacers are usually formed from concrete and are provided to ensure that, as the concrete 9 is poured, it can flow around the underside of the frame and fully surround the lower part of the frame. Concrete 9 is poured onto the deck 2 and surrounds the frame and any additional reinforcement 10 which may be required.
In Fig. 2, three elongate members of the frame can clearly be seen. First 11 and second 12 members are horizontally spaced and substantially parallel to each other. They lie on the upper surface of a series of spacers 8. A third elongate member 13 is spaced from the first and second members to form, in section, a triangular arrangement. The first 11 and second 12 members are connected to the third member 13 by members 14 to create the framework 3. This framework 3 is then connected to the spacers 8 and the deck 2 by means of ties 15. This tying connection can be clearly seen in Fig. 3.
Figures 4 and 5 show the arrangement at the one edge of the formwork 1 and show the provision of downstand units 20. The downstand unit 20 may be formed from concrete and it is connected to the reinforcement 10 via a steel connecting arm 21. The downstand unit 20 is connected to the reinforcement 10 prior to pouring the concrete 9. The downstand unit 20 is placed on a temporary support 22 during construction and this temporary support may be removed on completion of the construction.
A wall 23 is provided to prevent the ground 5 migrating to the underside of the downstand units. The downstand unit 20 is provided with a step 24 which supports a series of pre-cast beams 25. The beams in turn support the outer skin of brickwork 26 and 27, including air bricks 28. The inner skin of brickwork 29 is supported directly on the raft itself and a damp proof membrane 30 is incorporated within the inner 29 and outer 27 courses of brickwork.
Temporary shuttering 31 is provided and is secured to the downstand unit 20 by support detail 32. Bolts 33 can be removed to allow the removal of the shutter support 32 and then the main shutter 31 which spans adjacent units. The temporary shutters 31 are of sufficient height to form a raised boundary to the foundation raft to ensure that the concrete can be poured to the required depth. Once these edge shutters 31 are in place, the concrete 9 can then be poured.
An air void 34 is provided between the outer skin of brickwork 26 and the downstand unit 20 or concrete 9. This is vented to the atmosphere through air bricks 28.
A second aspect of the invention will now be described with reference to Figure 6 to 10.
Figure 6 shows an alternative foundation raft 50 consisting of a reinforced concrete slab 50 supporting building walls 51 and itself supported by piles 52. The piles are first put down and the slab is integrated with pile caps. A void 53 spaces the bottom of the slab 50 from the ground 54.
Figure 7 indicates in vertical section how the void 53 might be created. Thus, decking 55 forming the bottom wall of formwork is spaced above a layer of blinding 56 on the ground 54 by an array of tubular bags 57, which may be laid out as seen in plan in Figure 9.
As Figures 8 and 9 show, each bag 57 has a closed end 58 and, at its opposite end, is connected to a hose 59 leading to a terminal 60, or a common terminal 60a in Figure 9, containing a non return valve and a tap. The hose may be a canvas hose similar to a fireman's hose. In use, a pump could be connected to the block 60 to inflate the respective bag. The hose 59 could be used to pull the bag from the void after use.
Figure 10 shows a bag 57 with a coupling device 61 having its wider, oval shaped end inserted in the end of the bag opposite the closed end 58. The size of the largest part of the coupling device can pass through a 225mm x 75mm hole. The coupling device has a narrow inlet/outlet tube 62 extending away from the bag. The tube can be connected to the hose.
The substantially tubular bag, connected to the hose, and preferably provided with the non-return valve and tap, forms an independent feature of the invention.
Figure 11 shows the provision of a pair of timber formers 61 comprising a main body 63 and a pair of longitudinally extending raised portions 62. The bag 57 sits between the pair of formers 61 and is shown in the fully inflated configuration. The formers increase that the shown size of the void 53 between the decking 55 and the blinding 56.
Two differently shaped formers 61 are shown in Figures 12a and 12b. The main body 63 of each former has a different depth such that the size of the void can be varied between separate applications or to accomodate inconsistencies in the ground surface.

Claims

A method of constructing a concrete foundation raft or low level beam for a building or other superstructure, the method comprising the steps of:

erecting formwork (2), which is supported by a number of piles (4) and by a frame (3) to which the formwork is connected; and

forming concrete (9) in the formwork to form the raft or beam, wherein at least part of the frame (3) is incorporated within the concrete (9) to provide reinforcement of the concrete.
A method according to claim 1, wherein the frame (3) is supported by one or more piles (4) in the ground.
A method according to either claim 1 or claim 2, wherein the formwork (2) comprises a deck.
A method according to claim 3, wherein the formwork (2) is tied to the frame (3) to prevent downward movement at the mid points of the deck between the piles (4).
A method according to either claim 3 or claim 4, wherein the outer edges of the deck (2) are cut to the precise shape of the property in order to accommodate one or more downstand units (20).
A method according to claim 5, wherein the downstand unit (20) provides support for edge shutters (31) attached to the formwork (2).
A method of constructing a concrete foundation raft or low level beam for a building or other superstructure, the method comprising steps of:

erecting formwork (2), which is supported by a number of piles (4), by at least one interposed bag (57) that is inflated with air and by one or more downstand units (20);

pouring concrete (9) in the formwork to form the raft or beam; and

removing the air from the bag(s) (57) when the concrete (9) has set to allow the bag(s) to collapse, leaving a void (53) between the underside of the raft or beam and the ground.
A method according to claim 7, further comprising the step of providing one or more formers (61) which cooperate with at least one of the bags (57) to increase the size of the void (53).
A method according to any one of claims 5 to 8, wherein each downstand unit (20) comprises an L-shaped concrete body and has means (21) for connecting the downstand units to the reinforcement (10).
A frame (3) for use in constructing a concrete foundation raft or low level beam for a building or other superstructure, the frame comprising:

at least one pair of elongate tubes, comprising a first (11) and a second (12) tube, which are arranged to be connected, in use, to a deck (2);

a third elongate tube (13), substantially parallel to the first (11) and second (12) tube and which is spaced from the plane in which the other two tubes lie to form, in section, a triangular arrangement; and

connecting means (14) for joining the first and second tube to the third tube.