Extensible and contractible joist

Claim 1

AN EXTENSIBLE AND CONTRACTIBLE JOIST COMPRISING AN OUTER JOIST MEMBER AND AN INNER JOIST MEMBER DISPOSED IN TELESCOPIC RELATIONSHIP TO EACH OTHER, SAID OUTER JOIST MEMBER COMPRISING A TOP FRAME, A BOTTOM FRAME AND SIDE FRAME MEMBERS DEFINING A HOLLOW FRAME CONSTRUCTION, THE INNER JOIST MEMBER HAVING A TOP MEMBER, SIDE MEMBERS AND TERMINATING AT ITS BOTTOM IN A LATERAL PROJECTION SAID INNER JOIST MEMBER BEING OF A HEIGHT LESS THAN THE SPACING BETWEEN THE TOP AND BOTTOM FRAMES OF SAID OUTER JOIST MEMBER, BUT THE TOP FRAME OF THE OUTER JOIST MEMBER AND THE EXTENDED PORTION OF THE TOP MEMBER OF THE INNER JOIST MEMBER DEFINING A GENERALLY CONTINUOUS UNOBSTRUCTED HORIZONTAL LOAD BEARING SURFACE, OVERHANGING PROJECTION MEANS CARRIED BY THE BOTTOM FRAME OF THE OUTER JOIST MEMBER AT AN END THEREOF, SAID OVERHANGING PROJECTION MEANS OVERHANGING SAID LATERAL PROJECTION OF THE INNER JOIST MEMBER PERMITTING SLIDABLE MOVEMENT OF SAID INNER JOIST MEMBER RELATIVE TO SAID OUTER JOIST MEMBER BUT RESTRICTING UPWARD MOVEMENT OF SAID INNER JOIST MEMBER WITHIN SAID OUTER JOIST MEMBER TO SPACE THE TOP MEMBER OF THE INNER JOIST MEMBER A SHORT DISTANCE BELOW THE TOP FRAME OF THE OUTER JOIST MEMBER, AND A PLATE CARRIED BY SAID BOTTOM FRAME OF THE OUTER JOIST MEMBER ADJACENT SAID OVERHANGING PROJECTION MEANS RESTRICTING DOWNWARD MOVEMENT OF SAID INNER JOIST MEMBER WITHIN SAID OUTER JOIST MEMBER TO MAINTAIN THE TOP MEMBER OF THE INNER JOIST MEMBER IN SUBSTANTIALLY PLANE-PARALLEL SPACED RELATIONSHIP TO THE TOP FRAME OF THE OUTER JOIST MEMBER, THEREBY TO CAUSE SAID INNER JOIST MEMBER IN USE TO BE LOADED IN TENSION AT THE JUNCTURE OF SAID INNER JOIST MEMBER WITH THE END OF SAID OUTER JOIST MEMBER AND TO PREVENT THE APPLICATION OF CRUSHING FORCE FROM THE OUTER JOIST MEMBER TO THE TOP FRAME MEMBER OF THE INNER JOIST MEMBER.