First, he made a number of leathern tubes the ends of which he contrived to fix among the joists and flooring of a fine upper-room in which Zeno entertained his friends, and then subjected it to a miniature earthquake by sending steam through the tubes.
In large levels only the cap pieces for the roof are made of steel joists, but in smaller ones complete arches made of pieces of rails fish-jointed at the crown are used.
For shaft linings steel rings of H or channel section supported by intermediate struts are also used, and cross-bearers or buntons of steel joists and rail guides are now generally substituted for wood.
If the loads to be carried are largely stationary, and if the span is small, the floor joists can be readily proportioned by means of tables given in the handbooks issued by many steel companies.
The distance between joists should be limited to 5 or 6 ft.; horizontal bracing by means of diagonal rods is sometimes used, but should be avoided.