Rigid reticulated bar joist system

Claim 1

A rigid composite lightweight bar joist structure supported horizontally by spaced supports to support floor and ceiling structures and the like and loads thereon and comprising in combination, a set of substantially parallel bar joists arranged in even transversely spaced relationship, another set of substantially parallel joists similar to said first-mentioned set arranged in even transversely spaced relationship to each other, said joists of both sets each having coNtinuous upper and lower stress members and said sets being substantially vertical and respectively positioned transversely in crossover juxtapositioned overlapping relationship to each other to provide an assembly of upper and lower joists, the lower stress members of the upper set of joists being rigidly connected to the upper stress members of the lower set at all crossover overlapping portions of said sets of joists by weldments to provide a rigid reticulated bar joist system which is gridlike in plan view and capable of supporting concentrated loads of substantial magnitude with minimum deflection in comparison with the dead weight of the bar joist structure, the spacing of the joists in the lower set being substantially no greater than twice the spacing of the joists in the upper set, at least the lower stress members of the upper set of joists having horizontal flanges extending longitudinally along opposite sides thereof and outwardly therefrom in opposite directions, and then rigid panels of impervious material extending horizontally between and resting by gravity upon the flanges of adjacent pairs of lower stress members of said upper set of joists for sole support thereby to form separate plenum chambers above and below said sheets of material.