[Still no definition of (working).]
Are the white parts in the image a Polyline? Or separate Lines? It would be far easier to Offset the Polyline [see @john.uhden's link], or to Join the Lines into a Polyline and then Offset it, than to go through all the complications you have. Adjusting the ends of the Offset result, and drawing from them to the original Polyline, should not be difficult.
An example of part of it that seems peculiar to me:
(setq xw (getdist "\nDepth of exposed slab edge <4\">: "))
(if (= xw nil)(setq xw 4.0))
; SO 'xw' WILL ALWAYS BE EITHER THE USER INPUT OR 4.0, WHICH MEANS:
(if
(or (= xw nil) (= xw "")); NEITHER OF THESE WILL EVER BE THE CASE [the 2nd one can't be anyway]
(eval nil); then ; SO IT WILL NEVER DO THIS [what would the purpose be, anyway?]
(setq w xw); else ; BUT WILL ALWAYS DO THIS
); if
So just do that last line (setq w xw) without the (if) function enclosing it.
Kent Cooper, AIA