(Please visit the site to view this file)I have a model where I modeled the steel roof deck (with plates) using the equivalent thickness of deck based on the ratio of equivalent shear stiffness to the shear modulus of steel (tequiv = G' / G). The equivalent thickness was approximately 0.0464 inches. I had the modulus of elasticity set for 29,500 ksi (standard steel deck modulus). When I did this I was getting huge vertical deflections of the deck from the seismic load combinations even with no vertical load on the deck.
I then changed the deck thickness to 1/2", but changed the modulus of elasticity to 2737.6 ksi (29500 * 0.0464 / 0.5) to get approximately the same stiffness (EA). This time there was hardly any vertical deflection in the deck.
Does STAAD.Pro not like really thin deck? What is going on here?
Picture 1 shows the results with the thin deck: max vertical deflection in the steel deck is approximately 5000" for a load case with zero vertical load.
Picture 2 shows the results with the thicker deck: the deflection for the same node of 1191 is 0.013".
The horizontal deflection/drift is about the same for both thicknesses of steel deck. Why the high deflections for the thin plates?