×
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

Changing the Workline after reinforcing a truss

Changing the Workline after reinforcing a truss

Changing the Workline after reinforcing a truss

(OP)
Good Afternoon,

I recently had to do a large truss analysis / rehab project for a local factory.  There were approx. 20 carrying trusses, all spanning 60' and approx 15 Jack trusses spanning 80'.  After I determined the amount of additional steel that a particular member would need, I'd recalculate the members centriod --> then the members I --> then S --> and down the line to determine the new capacity of the section.  I wired a spread sheet that (depending on the reinforcing type, whether it was a chord member or a diagonal and either compression or tension) would re-calc all those things above using only the dimensions of the additional steel reinforcing plates as input.  

In a nut shell I would try to 'tweak' my reinforcing as to not change the overall centriod of the member too much as that would create an ecentricity (because the axial load would be now multiplied by the distance between the old and new centroids).  Was this too much of an analysis, would you of bothered worrying about that additional moment from the changing centroid.  The code implies that we don't need to worry about eccentricty of connections, but I couldn't find anything stating the same about members in this type of circumstance.  

Also, if anyone does do reinforcing this way, how much eccentricity is acceptable?   

RE: Changing the Workline after reinforcing a truss

Make all added steel symmetric about the centroid, i.e. use two plates, one on each side or four plates with one each on top, bottom, and each side.  This eliminates eccentricity and having to calculate section modus of top and bottom.

RE: Changing the Workline after reinforcing a truss

I think you did the design in a proper manner.  I would worry about introducing eccentricity into the connections.

RE: Changing the Workline after reinforcing a truss

Both civilperson and RARMBJ have good posts...

There is a well-known collapse of a roof to a library in the states which was due to eccentricity at connections in timber trusses.  The "unknown quantity" as I have heard it put which permits OWSJ to have non-alligned panel points does not, in my view, constitute good engineering practice, precisely because it is both unknown and unnecessary.

You did exactly the right thing, and should do it again when faced with similar situations.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

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