×
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

point supported glass

point supported glass

point supported glass

(OP)
I am analizing a glass canopy that is point supported.  All of the ASTM E1300 tables/ software call for four or two sided support for glass analysis.  Any ideas on how this should be done?  It is 80" x 70" (9/16" laminated glass) with (3) point supports at ea. end of the 80" length and is subject to a 65 psf winload.

RE: point supported glass

Use and analysis of POINT supports for glass ,or anything, are bound to be troublesome since they give EXTREME stresses. Please define and be prepared to distribute the restraints before you can expect any reasonable answers.

RE: point supported glass

I would analyze it as a plate element, supported as noted, using the properties of the laminated glass. Then compare that to a two-sided support analysis using one of the window glass analysis programs.  Compare to E1300 requirements.  

Problem will be the support condition.  You might want to finely mesh the plate and spread the support over more than 1 element.

RE: point supported glass

(OP)
Unfortunately I don't have access to finite element analysis software.

RE: point supported glass

Stan45...that's gonna be a problem for this analysis.  You can try cutting your width into 3 sections with each point support representing the full support noted in E1300. You will analyze one section at 1/3 of the width of the supported size.  This will give you a very conservative answer; however.

Check with your glass supplier. Some of them have analysis software for this purpose.

RE: point supported glass

(OP)
Any advise on which finite element software?

RE: point supported glass

Stan45...we use RISA 3D and mTAB-Stress w/FeMAP Pre/Post Processor for general analysis.  For ASTM E1300 analysis, we use Window Glass Design (WDG).  There are many FEA programs that will do this analysis.  You need one that does plates and is capable of differentiating surface stresses such as Von Mises top and bottom.

RE: point supported glass

I love it Ron...Just love it.

Mike McCann
MMC Engineering

RE: point supported glass

Hey Mike...I'm beginning to suspect you as a co-conspirator!!shadeshappy(assuming you're referring to the designation change!)

RE: point supported glass

(OP)
I have the window glass design software using ASTM E-1300. When I ran the glass as a two sided support for the 80" span with 9/16" tempered laminated glass.  The program said that it would not work.  It just seems like it should for a design pressure of 65 psf.

RE: point supported glass

65 psf is a relatively high load.  You have a large area, almost square, with high deflection. Can you go to 5/8" glass?

RE: point supported glass

(OP)
I don't think its an option.  It will have to be laminated glass.  Are you thinking 3/8" lite laminated to a 1/4" lite?

RE: point supported glass

Think Transparent Aluminum...

Mike McCann
MMC Engineering

RE: point supported glass

If you don't have an FEA software, do you have a copy of Roark's Formulas for Stress and Strain.  I'm not sure if there is point support conditions in there or not, but the other boundary conditions are exceptionally close to an FEA analysis (I ran a few examples just to check).  

If you have Roark's get the stress out of there and use the max allowable stress based on your glass type.  There is a provision near the back of ASTM E-1300 that gives basic allowable stresses for annealed glass, heat strengthened, and fully tempered.  Use those allowables, along with the reduction factors for laminated glass or long-term loads and compare that to your max stress from Roark.

RE: point supported glass

Also, if you're using laminated glass be sure to look at the deflections using the long-term load coefficients in ASTM E-1300.  You can't use the gross I for long duration loads (>3s).  I would also suggest looking at DuPont's interlayer (I think it's Century Glass Plus or something, it's escaping me now, and I haven't looked at in quite a while), it has better creep characteristics than the interlayer assumed in ASTM E-1300, and can reduce long duration deflections and reduce stresses based on a higher % composite behavior (again for longer duration loads).

RE: point supported glass

(OP)
I do have a copy of Rourk's equations.  Which tables shouls I use.  Since it is poin supported I am not sure of the boundry conditions.

RE: point supported glass

(OP)
The wind pressure here in south florida is based on 3 sec gust.  Short term loads

RE: point supported glass

stan45...check your wind load.  You are in a 150 mph zone, but I'm guessing you have a monoslope roof over an open structure.  If that's the case, your 65 psf is high.

RE: point supported glass

(OP)
unfortunately the design pressure requirements are as per engineer of record.

RE: point supported glass

We need to forfeit the need of a proper tool for analysis, assume you have one, and then see if it is feasible within the scope of the contract or whatever. I mean, is it that there is not such thickness of laminated steel being sold that you can meet the structural demands? If there is but too expensive as to think it exceeding the scope of the contract the boss should tell the client. Or you may look at alternatives such dividing the span (I wouldn't love to part it with vertical bands of glass plate, looks to me dangerous).

And this also brings to my mind that for whatever the reason and in spite of having its logic I have never had a feeling by the most commonly seen (at least in print) point supported structural glass system (I think derived from Foster's practiceship, maybe with Arup's?) Maybe ugly is not a politically correct word for technology, but well, I always found it to be ugly.

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