Rigid Frames


Short shells may be used with concrete rigid frames as the principle structural element. The rigid frame without a horizontal tie at the low point of the shell is suitable only for short spans because of the massive proportions required for the knees. It is not necessary to have the spans of all the rigid frames equal, and the bending moments in the frames may be reduced if shorter side spans are used.

The ribs are shown in this sketch and are placed below the shell. To save the cost in the forming, it may be better to place the ribs above the shell so they may be moved with very little decentering.

Skylights may be used in a short shell and they may be continuous transversely if they are placed in every other span so the shell on each side of the skylight cantilevers out from the adjacent span. Rigid frames are usually built with tie rods connecting the base of the columns, especially if soil conditions will not permit lateral loads on the soil material.