According to current construction practice, concrete structures such as foundation grade beams, concrete walls, columns, suspended and spandrel beams and concrete float structures, are cast in place in a conventional timber or steel formwork system. Precasting off-site is another common concrete structure manufacturing technique.
A conventional foundation grade beam or a concrete wall may be used to support, for example, the exterior wall and upper structure of a building. A grade beam is a cast in place concrete structure reinforced with mild steel rods. A standard type grade beam may have a standard cross-section of 8 in. width and 24 in. depth. The span length between intermediate supports such as footings or piles is variable but is usually anywhere from 12 to 36 ft. Concrete foundation walls, and the like, are usually higher and longer.
A grade beam or concrete wall is typically cast in place in a pre-formed or constructed on site elaborate timber or steel formwork system which is time consuming and labour intensive to construct. A conventional timber formwork system can only be used six or seven times before it deteriorates to the point where it must be discarded. New timber formwork is then erected and used. Steel formwork does not deteriorate with repeated use, but is expensive, heavy and may be labour intensive to install. The concrete grade beam or concrete wall is reinforced throughout its length and height with horizontally placed steel rods and vertical stirrups.
The grade beam or wall sections are cast in a conventional formwork system of timber and/or steel construction which are assembled and erected in place, aligned, plumbed, and adequately braced prior to placement of reinforcing steel and concrete within the interior of the formwork. After the concrete grade beam or wall has been poured in place, the formwork is then dismantled after the concrete has reached an adequate set. The formwork is then positioned and reassembled to continue the previously poured in place concrete beam or wall section, and prepared for the next concrete pour.
The conventional way to construct or assemble a standard timber or steel formwork system, and pour a standard steel reinforced rectangular cross-section grade beam or wall has a number of disadvantages: (1) the assembly and dismantling of the formwork is labour and time intensive; (2) the reuse potential of the conventional timber formwork materials is limited; (3) the formwork does not efficiently adapt to heat or steam cure methods; and (4) the rectangular cross-section of a conventional grade beam has always been the easiest shape to form by conventional methods, but it is structurally inefficient and uses more concrete than is necessary to achieve design strength. (At least 25% more concrete than necessary is required in a standard 8" by 24" cross-section grade beam). This degree of design inefficiency increases in direct proportion with any increase in the depth of the beam. This degree of inefficiency can easily exceed 50% in many practical applications.
In my U.S. Pat. No. 5,219,473, issued Jun. 15, 1993, I disclose and claim an invention which pertains to a novel adjustable formwork system which can be used in the manufacture of a wide range of structurally efficient cross-sectional shaped concrete beams, walls, columns and structures. In one version, a cast-in-place concrete beam form can be constructed comprising at least two spatially oriented upper sleeves with an upper web located on one side of the two sleeves, and extending therebetween, at least two spatially oriented lower sleeves, with a lower web located on one side of the two sleeves, and extending therebetween, and at least two members, each member conducting telescopically the respective upper sleeve with the respective lower sleeve, the telescoping members enabling the two upper sleeves to be raised or lowered relative to the two lower sleeves. FIGS. 30 through 34 of that U.S. patent, in particular, disclose a system for constructing a form of adjustable height comprising a series of upper sleeves 70, which can be raised upon corresponding sliders 98, relative to a corresponding series of lower sleeves 72. The system conforms with standard pieces of lumber, 2.times.4, 2.times.6, 2.times.8, etc., and the like, that are used in commercial concrete construction. The slider 98 is normally formed of aluminum. Keeper plates 82 are secured in place with standard snap-ties 74 extending through the upper sleeve, or the lower sleeve respectively. Among other things, standard walers 96 constructed of standard 2.times.4 inch timber pieces are used, as illustrated in FIG. 32, for instance. Two sizes of snap-tie are required. For example, if a concrete form system is constructed of a pair of spaced apart plywood sheets, reinforced by a pair of walers on opposite sides, and a corresponding pair of strongbacks on opposite sides, the long snap-tie which holds the two sides in place must span not only the distance between the two facing plywood forms, but also must penetrate through the two walers and the two strongbacks. On the other hand, short snap-ties in such a construction need not penetrate the strongbacks but must penetrate only through the space spanned as well as a pair of plywood sheets and a pair of walers.
In one form of concrete formwork system, the membrane, such as a plywood sheet, which is used to construct one side of a form, is reinforced on the side away from the concrete side by a network of horizontal walers, which are usually wood 2.times.4's, and a series of vertical strongbacks, which can also be standard wood 2.times.4's. A matching "mirror" form is placed on the opposite side, the interior is reinforced with a network of reinforcing steel bars and the cavity between the two is then filled with concrete. The two sides can be fastened together with two lengths of form-ties, the short end-ties required for the walers and the long end-ties required for the walers and strongbacks. In an alternative form of construction, however, T-bolts can be used which fit into aluminum I-beams, which are produced by various companies such as Anthes Equipment, Toronto. The T-bolts are constructed to have a square positioning flange, which fits into mating receiving cavities in the I-beam. The T-bolts are usually constructed of steel, while the I-beams, which take the place of walers and strongbacks, are formed of extruded aluminum. The T-bolts are secured in place in the receiving flanges of the aluminum beams by rotating the T-bolts 90.degree. from an open to a locked position. One advantage of the T-bolt system is that it eliminates the need for two lengths of snap-ties.