×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Need Rational Explanation for Plate Design
2

Need Rational Explanation for Plate Design

Need Rational Explanation for Plate Design

(OP)
On an existing structure, one of the levels has a framing which divides it into rectangles (beam center lines) 3'-0" by 12'  0".  The framing is covered with a 3/8" deck plate (50 ksi steel) which is welded continuously to the beam flanges.  The resulting plate is then divided into rectangles 2'-0" by 11'-0".  On this deck a cart with 4 casters (8" diameter by 4" wide) carries a peice of equipment.  Total weight of cart and equipment is 28 kips.  Each caster carries 7 kips.

Analyzing this plate using Roak and also using Finite Elements gives bending stresses far in excess of yield and ultimate for the plate.  Inspection of the existing plate does not give any appearance of distress, yielding or deflections.

I am designing a very similar structure and am unable to justify the 3/8" plate.  Can any one give a rational explanation?

Thanks in advance.

RE: Need Rational Explanation for Plate Design

Have you looked at the edge condintions.  You may have analysed the plate with simply supported edges which is very conservative.  If the plate is welded to beam flanges, you will have some fixity.  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.

Nigel Waterhouse
n_a_waterhouse@hotmail.com

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.

RE: Need Rational Explanation for Plate Design

(OP)
Nigel,

Thanks for the suggestion.  I did consider the plate fully fixed on all four sides.  However, I did not consider the deflection of the supporting beams.  I will try it.

Thanks again.

RE: Need Rational Explanation for Plate Design

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?  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 "footprint".

RE: Need Rational Explanation for Plate Design

(OP)
JAE

In the finite element analysis the loads were placed at several joints to simulate a line load of 4" (the width of the caster).

RE: Need Rational Explanation for Plate Design

Agree with Nigel with one addition...consider the torsional response of the beam as well, unless completely restrained from torsion.  Have experienced similar results in thin plate, high load applications.  You can adjust the model by putting a few strain gages on the plate and correlating actual strain conditions to predicted strains from FEA.

Thin plates seem to act as though they were a series of interconnected cables, rather than a solid mass.  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.

RE: Need Rational Explanation for Plate Design

R&Y allows for a wheel load using the wheel "footprint" radius (i.e. Table 26 case 1b).  We design our Vertical Reciprocating conveyors (VRC) equipment with INX50 deck plate.  Your have high point loads for even for 3/8 plate at the 2' support spacing.  We see support spacing @ under 12" for may high capacity decks.  We use 4:1 SF to material yield under concentrated loads (12.5K design allow for 50k material).  Look at the size of the wheel being used.  With the 7k load the type of wheel material should be considered.

With the stress & deflection controlled the major condition we want to avoid is the "oil canning" of the deck.  If the deck weight is not a concern, look to be concervative in deck design.  The type of equipment loading the deck (dynamic loads) can become a problem.

Good Luck.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources