Need Rational Explanation for Plate Design 2

[eureka]

On an existing structure, one of the levels has a framing which divides it into rectangles (beam center lines) 3'-0&quot; by 12'&nbsp;&nbsp;0&quot;.&nbsp;&nbsp;The framing is covered with a 3/8&quot; deck plate (50 ksi steel) which is welded continuously to the beam flanges.&nbsp;&nbsp;The resulting plate is then divided into rectangles 2'-0&quot; by 11'-0&quot;.&nbsp;&nbsp;On this deck a cart with 4 casters (8&quot; diameter by 4&quot; wide) carries a peice of equipment.&nbsp;&nbsp;Total weight of cart and equipment is 28 kips.&nbsp;&nbsp;Each caster carries 7 kips.<br><br>Analyzing this plate using Roak and also using Finite Elements gives bending stresses far in excess of yield and ultimate for the plate.&nbsp;&nbsp;Inspection of the existing plate does not give any appearance of distress, yielding or deflections.<br><br>I am designing a very similar structure and am unable to justify the 3/8&quot; plate.&nbsp;&nbsp;Can any one give a rational explanation?<br><br>Thanks in advance.

 

[Nigel]

Have you looked at the edge condintions.&nbsp;&nbsp;You may have analysed the plate with simply supported edges which is very conservative.&nbsp;&nbsp;If the plate is welded to beam flanges, you will have some fixity.&nbsp;&nbsp;Try analysis based on fully built in edges and see what that result gives you, then calculate a fixity coefficient based on the combined deflection of the plate and beams which provide the support. <p>Nigel Waterhouse<br><a href=mailto:n_a_waterhouse@hotmail.com>n_a_waterhouse@hotmail.com</a><br><a href= > </a><br>A licensed aircraft mechanic and graduate engineer. Attended university in England and graduated in 1996. Currenty,living in British Columbia,Canada, working as a design engineer responsible for aircraft mods and STC's.

 

[eureka]

Nigel,<br><br>Thanks for the suggestion.&nbsp;&nbsp;I did consider the plate fully fixed on all four sides.&nbsp;&nbsp;However, I did not consider the deflection of the supporting beams.&nbsp;&nbsp;I will try it.<br><br>Thanks again.

 

[JAE]

Are your wheel point loads applied to your model at a single joint and are your high stresses showing up at these load point locations?&nbsp;&nbsp;Finite element models many times reveal very high stresses when a load is introduced at a single joint as opposed to a number of joints under the wheel &quot;footprint&quot;.

 

[eureka]

JAE<br><br>In the finite element analysis the loads were placed at several joints to simulate a line load of 4&quot; (the width of the caster).

 

[Ron]

Agree with Nigel with one addition...consider the torsional response of the beam as well, unless completely restrained from torsion.&nbsp;&nbsp;Have experienced similar results in thin plate, high load applications.&nbsp;&nbsp;You can adjust the model by putting a few strain gages on the plate and correlating actual strain conditions to predicted strains from FEA.<br><br>Thin plates seem to act as though they were a series of interconnected cables, rather than a solid mass.&nbsp;&nbsp;The resulting catenary places more of a tension load on the end constraints than bending, as would be predicted by FEA, particularly if rotation of the top flange occurs in the direction of the load application.

 

[MarkRPflow]

R&Y allows for a wheel load using the wheel &quot;footprint&quot; radius (i.e. Table 26 case 1b).&nbsp;&nbsp;We design our Vertical Reciprocating conveyors (VRC) equipment with INX50 deck plate.&nbsp;&nbsp;Your have high point loads for even for 3/8 plate at the 2' support spacing.&nbsp;&nbsp;We see support spacing @ under 12&quot; for may high capacity decks.&nbsp;&nbsp;We use 4:1 SF to material yield under concentrated loads (12.5K design allow for 50k material).&nbsp;&nbsp;Look at the size of the wheel being used.&nbsp;&nbsp;With the 7k load the type of wheel material should be considered.<br><br>With the stress & deflection controlled the major condition we want to avoid is the &quot;oil canning&quot; of the deck.&nbsp;&nbsp;If the deck weight is not a concern, look to be concervative in deck design.&nbsp;&nbsp;The type of equipment loading the deck (dynamic loads) can become a problem.<br><br>Good Luck.