28 identical to the beams 16 to assemble the beams beam 10 is inserted down through the opening in beam 12 at which point the elongated member 28 is passed beneath beam 12 through the opening 18 in beam 10 beam 10 is then pulled upwardly until the member 28 snugly seats beam 12 and then the keypost 26 is passed through the top part of the pass through opening 18 in beam 10 to lock all the parts together the resulting joint illustrated in fig1 is quite strong without the use of any fasteners it is easy to provide adequately controlled tolerances so that the keypost 26 is a reasonably tight frictional fit this construction is substantially similar to that described in the prior issued patents and the patent applications referenced in the background which illustrate the replication of joints to produce multiple cells and complex structures the instant joint differs however in several respects first each beam is substantially elliptical in cross section as can be seen best in fig2 and 4 this is because the ellipse is a very strong shape and eliminates sharp edges which stress problems each of the structural members which defines half of a structural member pair or beam has a flat edge 30 with radiused edges 32 again to eliminate the added stress susceptability which sharp edges create in the prior art patents and patent applications the six structural members which form the joint forming into three structural member pairs each of which constitutes a beam have been shown as solid in this disclosure the elongated structural members are not solid but rather hollow and reinforced with a web structure the webs of the web structure are two in the preferred embodiment for each elongated.