×
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

Rectangular uniform surface loading on semi-infinite area

Rectangular uniform surface loading on semi-infinite area

Rectangular uniform surface loading on semi-infinite area

(OP)
I am doing an elastic stress analysis for a rectangular uniform surface loading on semi-infinite area. The formulus are on P54 of "Elastic Solution for Soil and Rock Mechanics" by H. G. Poulos and E. H. Davis (1973). The normal stresses of Eqns 3.18a~c are not dependent on Poisson's Ratio (They are only the function of pressure p and geometry). However, the normal stresses of Eqns 3.19b~c become dependent on Poisson's Ratio. Why? Which should we use? Thank you very much.

RE: Rectangular uniform surface loading on semi-infinite area

tipsabc,

I'd like to help, but it's practically impossible to get a copy of that book nowadays. (I knew I should have photocopied it when a previous employer had a copy in their library...)

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com

RE: Rectangular uniform surface loading on semi-infinite area

You might have to go back to Holl's original 1940 work to find out if he assumed a specific poisson's ratio - if so, then his formulations would be solely for that particular ratio; though he does give the shear stresses as well to go along with the normal stresses.  Not 100% positive, but perhaps this covers the effect of the poisson's ratio - when you find that the "normal stresses" no longer lie in the x-y-z directions.

Giroud (1970) obviously derived an expression that would permit a deviation in the poisson ratio - the tables of page 55 would be developed accordingly. He gives no shear stresses.  So his computed stresses would be the normal ones in the x-y-z directions but the maximum stresses might/would? be in an skewed axis to the normal directions.

This is one of the weak points of the Polous and Davis book - it is shy on some of the underlying principals.  But, all in all, it is a great book to have in your library and I wouldn't be without it.

RE: Rectangular uniform surface loading on semi-infinite area

I am going to take a guess that the first set of equations are for an undrained conditon. In that case pore water controls lateral pressure and poisons ratio is 1.0. The second , again, I am guessing, is for drained material, where the material itself contols the lateral pressure and is signifcantly less than 1. Again I am not familar with the book, but not letting that slow me down, so value my free advise at the price you paid!

RE: Rectangular uniform surface loading on semi-infinite area

Don't think that the undrained condition for poisson's ratio is 1.  Are you sure of that?  I've never seen the max taken more than 0.5 which means an incompressible soil (elastic).  Conduto:  "The magnitude of v [sic., poisson's ratio] in elastic materials varies from 0 to 0.5.  Those with v = 0.5 are said to be incompressible because the compression in the direction of the load is exactly matched by the expansion in the two perpendicular direction, resulting in no net volume change."

RE: Rectangular uniform surface loading on semi-infinite area

Big H:
I thought I was, but went back and checked and you are right - the maximum value for v is .5
Sorry!

RE: Rectangular uniform surface loading on semi-infinite area

(OP)
Thank you for your comments. Does anyone know any other reference papers or books to give the tools or the formulus to do the stress analysis calculation with poisson's ratio effect instead of Eqn 3.19a~c in the book by Poulos & Davis? I checked the paper by Giroud (1970). But I cannot find any further information. Thanks again.

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