Fire Damaged Steel Trusses 5

[Mark_J]

Hi,

I was hoping to get some recommendations on how to fix one steel roof truss that has buckled top chord in 3 bays and fire likely diminished the adjacent truss and brace truss at same location. Trusses spanning about 75'. It seems that the owner may be OK with putting a beam under the buckled truss but I'd like to offer a solution that may be around the same cost and no beam with columns. It's a beer warehouse, I wouldn't want columns in a warehouse.

Good ways to shore. All the roof in that area is coming off and getting replaced as well.

 

[jerseyshore]

Years ago we were doing some tenant work for a client in NYC, ground floor of a 40+ story building. Some simple mezzanines and a floor opening or two. The landlord apparently hated this tenant so they hired Thornton Tomasetti to review our work. Every single simple beam to beam shear connection they wanted a full analysis on, not just the number of bolts. They wanted the existing steel beams tested because we assumed 36 ksi for a later 1950s building and they said, but what if old steel was used (I think it was 33 or 30 ksi in the 40s). You get the idea. We didn't have to change any designs, but I just spent a month issuing about 12 calc packages for 20 beams.

Now not every reviewer is like this, especially outside of a lawsuit situation, but I always keep it in mind when I approach projects like in the OP. Whatever assumption(s) I make as an engineer, I want to be able to prove it on paper if TT or anyone else knocks on my door for proof.

If you take a rivet and test it, are you confident putting your license on the line that the steel members will give you the same results if someone requests it a month or year or 5 years later? If so, that's fine. You may do more fire damaged steel work than I do and have a better grasp at the situation in hand. All I know is that the steel is right up there and should be just as easy to test as a rivet.

 

[dik]

I have an SMath program that does that to determine the % UDL and you input the beam properties (dimensions and material), and span, as well as the weld and fasterner and it checks beam, bolt (snug tight/slip critical), clip angles, weld, etc. I'd also send them a letter, thanking them for review and confirmation of the design. There is no way they are avoiding liability for the design.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Aesur]

Since it seems you are adamant about reusing what's there, here are few items to consider:
1. Are you modeling the joists? How else do you know what strength of steel you need to achieve from testing, based on pictures, I suspect there are no "as-builts" or any kind of documentation even providing the steel strengths.
2. How do you propose straightening the steel joists, I can't picture how this would be an easy task.
3. Who hired you, the owner or the insurance company? Who are you representing here and you working in their best interests?
4. Who pays for the steel inspections/testing? Most likely your client will, and most likely they will not be reimbursed by the insurance if your client is the owner.
5. It looks to me like more than "cardboard boxes" burned here, look at the steel deformations, look at the charred wood. Was there anything in the boxes? If the fire is hot enough to buckle steel, I suspect it was potentially hot enough to change the properties, else why would it have buckled?

Based on what I have read thus far, this seems like a lot of guess work going into the project, I personally would not be ok with that as an engineer nor owner.

 

[EdStainless]

You know for a fact that the rivets are a different grade of steel from the formed members.
I wouldn't consider them representative.
Can you splice in a new full length top cord?
That might be the easiest way to get a high confidence fix.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

With rivets, the steel may not be weldable... another good reason for taking coupons.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

Are we not mentioning the need to analyze these for the current code loads (or the past ones?), and then model the original structure?

I think there's also a very speculative leap being made here - the fire was "hot enough" to warp the steel, yet it wasn't hot enough to change the grain structure? Paper fires can be very hot, and there's what looks like a lot of char to the bottom of that wood decking as well. That all suggests a significant fire.

If you want to work on this, I'd suggest writing up an RFP and having the owner bid it out to a few engineering firms. People who actually do design work, mind. These look like old proprietary steel joists to me. You could probably shore them up, sure, bring in a heat-straightening guy, sure, do the fire watch after the work is done, sure. But what's the original structure good for? What's the load on them? I suspect you'll see a lot of scatter in those bids. Some folks will want to repair, others will want to be more rigorous.

 

[Mark_J]

I can understand why some are hesitant to discuss steel exposed to
Thank you for the AISC link, makes very clear sense.
The steel that will be the vehicle to straightening bent steel will also be the reinforcing steel left in place, connected to existing for max force.
If anyone has any experience with straightening steel in the field with success that would be valuable to this thread, and me.

 

[structSU10]

The owner should get their own independent public adjuster involved. They dig into the insurance and help get more money when necessary. I would think the owner would much prefer getting enough money to remove and replace than repair if at all possible.

 

[WesternJeb]

I am with the others. With such a high liability, the amount of fee it would require for me to thoroughly investigate every member size, section loss, etc., it would be as much as just paying for the new steel members and replacement. If the owner isn't careful, they will sink more money into the engineering than just doing the difficult path forward.