Hydraulic and earth engineering – Foundation – Columnar structure
Reexamination Certificate
1999-12-27
2002-02-05
Schoeppel, Roger (Department: 3672)
Hydraulic and earth engineering
Foundation
Columnar structure
C405S252000, C405S257000, C249S013000, C249S112000, C249S168000
Reexamination Certificate
active
06343894
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus and method for producing building foundations from poured concrete, particularly an essentially reusable concrete foundation form apparatus and method of use.
Poured concrete foundations for buildings have been used for many years and usually require disposable formwork such as lengths of lumber and plywood sheets, which are temporarily installed on the ground or site surfaces. Installing conventional foundation forms is a time-consuming, labour-intensive task and is often conducted in poor conditions of loose topsoil and/or rocks etc. These conditions are often aggravated by rain or ground water which further destabilizes the soil and commonly requires pumping prior to pouring the concrete. Preferably, such foundations are installed on relatively level ground or site surfaces, and the above difficulties are compounded when the site is not level, i.e. it slopes in one or more directions. Installation costs increase because a sloping site usually requires additional excavation to level the site prior to installing foundation forms.
When a single storey building is to be built on a level site, sometimes relatively simple foundations can be installed. Simple foundations usually require a footing with or without a relatively low wall extending thereabove to receive longitudinal horizontal timbers upon which the building can be erected. On the other hand, a foundation for a building with a basement usually requires a footing with a relatively high basement wall extending upwardly therefrom, the basement wall having a width typically between one half and one quarter of the width of the footing, depending on building code requirements. A footing combined with a high wall is commonly made in two stages, the first stage being the preparation of the footing form and footing by itself. After the first pour of concrete has set to produce the footing, wall forms are erected above the footing to receive the second pour of concrete to form the wall itself. This two-stage type of foundation is relatively time consuming because it requires relatively close control of the locations of two sets of the form members to ensure compliance with building code requirements.
Both types of foundation formwork described above use lengths of lumber and plywood sheets which, after stripping from the set concrete, are contaminated with concrete and thus are usually unsuitable for use elsewhere in the building, except perhaps in low-grade or temporary construction work. Consequently, when constructing conventional concrete foundation forms, there is usually a high labour input both in installing the forms and stripping the forms after pouring the concrete, and there is also high wastage of form material when the poured foundation has been stripped.
U.S. Pat. No. 5,224,321 discloses an earlier invention of the present applicant in which a foundation form assembly is secured to a temporarily supported prefabricated floor assembly. The foundation form assembly extends downwardly from the floor assembly towards a building site surface which supports jacks which in turn temporarily support the floor assembly. The form assembly comprises inner and outer rigid sheet panels which serve as upper forms and are connected to the floor assembly. Lower portions of the rigid sheet panels are connected to upper edges of a flexible fabric sheet lower form element which rests on the site surface and extends as a generally U-shaped elongated container between the inner and outer sheet forms. The flexible fabric sheet form conforms to undulations of the site surface when it receives a flowable concrete mixture, and thus accommodates variations in height between the form and the site surface, thus reducing work required to prepare the site surface. Form ties extend between the inner and outer rigid forms to restrict movement thereof and to resist forces from the concrete before it sets. The poured concrete has an upper surface in contact with the floor assembly to provide permanent support therefor. When the concrete sets, the jacks are removed and the outer rigid sheet forms can be removed or can remain in place. This patent discloses a flexible sheet form element which provides a footing to accommodate site undulations and slope, and while it has many advantages over prior art foundation structures, the time for installing and levelling the prefabricated floor assembly and attaching the rigid sheet forms thereto increases the cost of both materials and labour when compared with the present invention.
German Patent Publication 2062998, in which the applicant is Beton-U. Monierbau AG, discloses several embodiments of poured concrete foundations in which a flexible fabric sheet form is located adjacent or beneath a temporarily supported component, and thus resembles to some extent the device of the above patent. In one embodiment, upper edges of the fabric sheet form are connected to the component to provide an elongated container below the component to receive flowable concrete, which when set supports the component. The sheet form assumes a shape determined to some extent by optional stiffeners positioned within the form, but not connected thereto, or other constraints located externally of the sheet form. This invention is particularly applicable for providing foundations for structure to be supported above a body of water.
Both of the references discussed above use a flexible fabric sheet form element which permits the footing to conform to the site surface, but require restraining structure to maintain the sheet form element in place and to attempt to control shape of the flexible sheet form element to reduce the volume of concrete required. In both references, when unrestrained lowermost portions of the flexible sheet form hold fluid concrete, a contact portion of the fabric sheet form is forced into contact with the ground and, when the concrete is solidified carries weight of the building. Hoop stresses are generated in the fabric sheet form and the sheet develops curved bulging marginal portions which extend upwardly and outwardly from the contact portion to upper portions of the fabric sheet which are supported. Thus voids are formed between the marginal portions and the site surface and therefore the contact portion always has a width which is less than maximum or overall width of the footing due to the outwardly bulging marginal portions. Because building load is transferred to the ground only through the contact portion, and not through the bulging marginal portions, concrete in the marginal portions is not used efficiently to transfer load to the ground and thus represents a waste of concrete. Hoop stresses in the fabric increase and width of the contact portion decreases as the concrete mixture is made more fluid, and thus wastage of concrete can become excessive. In addition, the fabric of the sheet form element does not permit concrete to pass therethrough, and thus relatively small voids can be formed between the contact portion of the sheet and the ground immediately beneath the contact portion, thus reducing shear strength between the foundation itself and the ground. If the sheet has a low friction surface, shear strength is reduced still further, which can cause problems during seismic activity.
SUMMARY OF THE INVENTION
The invention reduces the difficulties and disadvantages of the prior art by providing a building foundation form apparatus which can be quickly installed on a building site for considerably less cost than conventional foundation forms. In addition, volume of concrete used can be much less than that used with conventional rigid forms and the flexible fabric sheet forms disclosed in said prior art references. Installation costs are reduced because the invention provides a plurality of pre-fabricated form supports which can be assembled quickly and easily, accurately aligned, and readied for concrete pouring in a fraction of the time required for conventional foundation forms.
The invention uses a flexible sheet form element whic
Kolisch Hartwell Dickinson & McCormack & Heuser
Schoeppel Roger
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