Hi PD's & thanks Jim for this

RIVITING stuff
"The plate must be secured to prevent uplift, which would otherwise occur at the plate corners"
w = a7 py t2 / k B2 [ 1 + a8(1-k) + a9(1-k)2]
dmax = a10 k wimp B4 [1+a11(1-k) + a12(1-k)2] / E t3I did this calculation :computer today in OZ & think I understand the need to secure the plate in each corner as my ABBUCUS result suggests that the 3ft x 3ft square plate X 6.25 mm thick is actually 87.9 Kg of negative weight.... :twisted: yes the reason you must secure the

: corners is to ensure it dosn't float away

......maybe I used
(1+k) instead of (1-k)
