The construction industry has experienced a growing trend in the use of insulated concrete forms (ICFs), wherein forms for pouring concrete are constructed from multiple modular form units. Each unit includes inner and outer sidewalls, at least one of which is formed of foamed polystyrene, foamed polyurethane, or other cellular plastics or insulating materials. The sidewalls of the form units are stacked or otherwise interconnected at the construction site to form opposing insulated inner and outer form walls between which concrete is poured. The insulated form walls are then left with the poured concrete at the site to define a portion of the poured concrete wall(s) of the structure being constructed, resulting in concrete walls with insulated surfaces. Examples of insulated concrete forms and form units of this nature can be found, for example, in U.S. Pat. Nos. 4,706,429 and 4,866,891 to Young; U.S. Pat. Nos. 4,765,109 and 4,889,310 to Boeshart; U.S. Pat. Nos. 5,390,459 and 5,809,727 to Mensen; and U.S. Pat. No. 6,314,697 to Moore.
As these patents illustrate, it is common to have each sidewall of a form unit bear tongue-and-groove structures (or other interfitting structures) at its edges so that the inner sidewall of each form unit can be interfit at its edges to inner sidewalls of other form units, thereby allowing the inner sidewalls to be combined to form an inner wall of a concrete form. The outer sidewalls can likewise include interfitting structure allowing them to be combined into an outer form wall. Additionally, the inner and/or outer sidewalls often include “webs,” structures which are generally formed of plastic and which extend within and engage the foamed insulating material of the sidewalls. Connecting members which are often referred to as “ties” or spacers then extend between the inner and outer sidewalls and engage their webs to hold the sidewalls in opposing parallel relationship. When the concrete is poured between the sidewalls to solidify, the ties are left embedded within the concrete and maintain the insulated sidewalls as cladding on the opposing sides of the concrete wall.
While form units and forms of the foregoing nature are beneficial in that they conveniently use the forms for casting the concrete walls as insulating cladding for the walls, and they eliminate any need to disassemble or remove the forms after the walls are poured, they suffer from the disadvantage that their form units—being formed of a pair of sidewalls (generally foamed of bulky foamed plastic) joined by spacers—occupy substantial volume, and are therefore expensive to ship. Some of the aforementioned patents address this disadvantage by providing detachable/reattachable spacers which rigidly but disconnectably affix the sidewalls together. Such form units allow users to provide sidewalls and spacers separately, whereby the sidewalls of each form unit are stacked and shipped separate from the spacers (and thus without including a wasted intermediate space between the sidewalls), and each form unit can then be assembled at the construction site by fastening the spacers between the sidewalls. However, these forms trade shipping costs for labor costs, since hundreds or even thousands of spacers must be installed between the sidewalls to construct the form units and forms.
To overcome the foregoing difficulties, some ICF manufacturers have developed concrete form units wherein the spacers are pivotally affixed to their opposing sidewalls, with the various spacers thereby effectively form parallelogram linkages with the sidewalls. As a result, the sidewalls can be brought together (their intermediate space may be eliminated) by moving the sidewalls in opposing longitudinal directions. Examples of such arrangements are found in U.S. Pat. No. 3,985,329 to Liedgens, and U.S. Pat. Nos. 6,230,462 and 6,401,419 to Beliveau. Form units of this nature are useful because the concrete form units may be collapsed (their sidewalls may be brought into closely spaced relationship with the intermediate space eliminated), and the form units may be stacked in close relationship for shipping. The form units may then be readily unloaded at the construction site, unfolded to their expanded states, and assembled to construct larger concrete forms. However, these are disadvantageous in that the parallelogram linkage arrangement gives rise to “racking”: the sidewalls, when collapsed, are offset and do not rest end-to-end, and therefore generate unused volume which is effectively wasted during shipping. This is undesirable since the form units are already quite bulky, and expensive to ship. Additionally, while users need not install the spacers between the sidewalls because the spacers are already pivotally affixed therebetween, the expanded form units are subject to buckling because the spacers do not rigidly situate the sidewalls in spaced relation. Such buckling can lead to difficulties, particularly when using the concrete form units to construct a larger concrete form.