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

Related Articles


Reinforcement of existing steel joist.

Reinforcement of existing steel joist.

Reinforcement of existing steel joist.

My issue is that I have an open web joist (LH series) that is over stressed about 10%.  I believe I have two options at this point.

A. I can "cover plate" the existing joist.

B. try to spread the RTU weight over additional joists by "x-bridging" between additional joist.  I think this would be the preferred option but I'm a little unsure how much "help" I can get from the additional joists.

If anyone has any insight to this issue I would greatly appreciated it.  

RE: Reinforcement of existing steel joist.

SJI has a book out that outlines various ways to strengthen existing joists.

SJI Technical Digest No. 12


RE: Reinforcement of existing steel joist.

10% is not that much.

Get creative with your new support beams  - you might be able to tie back to existing I-beam or girder joist to pick up to as much as 50% of the load??  Spreading out the load over 4 joists will cut down your overload to like 2.5%!!! - IF done right.

Think outside the box a bit - you might be surprised.

RE: Reinforcement of existing steel joist.

I had worked on projects for pharmaceutical industry where every now and then some thing would go up on the roof. But strengthening of OWSJ was rarely an option since the production could not be stopped, the area could be accessed only on the holidays, and maintaining cleanliness was another factor.
We had to either relocate the equipment if acceptable to other parties, spread out the load, or come up with a dunnage to support the new equipment. Budget was never an issue.
While designing we always kept a provision of additional point load of 2 kips anywhere along the span of the joists, but accessibility for strengthening purposes was always an issue.  

RE: Reinforcement of existing steel joist.

When using a spreader beam to transfer loads to additional joists there are equations to determine how much load gets transfered to each of the joists.  

For instance if you were to hang a load from below the joist, using a beam between two joists, the load would normally be distributed to each joist (based on distance from the load).  If you were to use a larger spreader beam you could spread the load out to additional joists.  It has to do with relative stiffness of the joists vs. the spreader beam.

They reviewed this at a seminar.  I would assume this is in the SJI technical digest that JAE identified.

RE: Reinforcement of existing steel joist.

Use Post-tensioned cables. I've used them before on bar joists, concrete and glu-lams to gain strength.  


RE: Reinforcement of existing steel joist.

I don't know where you are, Miner99er, but here's a dumb question: if you have snow load, have you removed it where the rtu goes?  Depending on your snow load and the size of the unit, you could actually reduce the roof load instead of increase it with rtus or condensers.  I have yet to go on a roof & see any snow drifted on or significantly around medium & small mechanical equipment.

RE: Reinforcement of existing steel joist.

A non-wind snow event is possible.  And snow does accumulate on top of RTU's.  The code does not allow negating snow on top of RTU's that I can see.


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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close