Structural Steel Bolted Connection Repair (occupied building) 3

[Enable]

I have an interesting one to look at. Existing three story building corner where steel lintels that pickup the brick façade, CMU backup wall, and OWSJ + floor loads from the interior (and roof) have corroded about 50% of the way through at the connection. As far as I am aware shoring is in-place and the intent now is to figure a way to repair the connection. As an FYI I'm not the EOR on this project. I am the sub-trade who is gently trying to push people in the right direction.

No existing DWGs available. Age unknown but not terribly old. Perhaps 70s construction.

Detail is a bit funky. It appears like the corroded beams are supported via block on one side, and on the other, they are picked up by a bolted T-section. The T-section is cantilevered off a nearby HSS column on the inside.

There are multiple of these connections to be repaired.

The original flange was cut-out at the connection during construction, which we suspect was done because the T-section interfered with it. As well, the holes are vertically slotted (read: torched on-site). I do not think this was the original intent because A) slotted holes were definitely site adds and B) the edge distance at some of these bolts is way below min code. Looks like it was hacked in-place to fit and not picked up during review.

The EOR has proposed a simple plate detail, which is rather wanting. Can't perform the specified welds (no field access) and they have us welding into corroded base metal. Doesn't deal with edge distance issues. Doesn't deal with the fact that the flange is missing at the most critical shear area.

I'm going to propose my own detail but wanted to run it by this crowd to see if I have missed anything. This is a rather unique situation that I have not previously come across.

Here is my intent:

A) I want to restore (in some way) the cut out flange for shear concerns

B) I want to add plate/steel area vertically to make sure bolts have min edge distances

C) I do not want to rely on the corroded metal and therefore want to design a repair that extends back further along the beam

To accomplish this I am proposing to weld a doubler plate that extends beyond the corroded area and is designed as an eccentric weld group. I want to stiffen the "cantilevered" part of the doubler with plates top and bottom to form a "C-channel" shape extending to good material. This should restore the shear capacity of the section. Stiffeners are thrown in to help load transfer back to the web (prime welds on the doubler are to flanges). The edges of the plates forming the top and bottom flange of my new "c-channel" shape to be on an angle to by-pass fillet welds to doubler plate. Same goes for doubler plate edges at radius of beam-web connection.

I'll compute the weakest link in the T-flange connection (I suspect it's the weld to the plate welded to the HSS) and design for that load. No loads provided by EOR and on restoration projects I almost never get them.

Here is a little schematic of what I am thinking. Have I missed anything obvious?

 

[dik]

I would think something like B-B, welding to the existing beam if there is enough of it. I would not normally rely on bolts as A-A shows. What is the source of the corrosion? Leak? or condensation? Is there an issue with the building envelope? Clean the welding flux of really well and zinc-rich primer...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Enable]

The envelope consists of brick mortar onto CMU backup wall. No waterproofing or air cavity (perhaps a 1" cavity at most but mortar droppings have bridged pretty much everywhere). As far as I know the scope includes new waterproofing over the backup wall / beams but that is not within my scope as I am just the metal sub not the GC.

A-A is through the existing bolt group. So the bolts shown in A-A are just the bolts that connect the beam to the existing T-section (not part of the new repair). Also, no matter what repair we do the connection will be via those bolts. Of course that is only true unless we go to the inside and rework from the HSS. But that would be heavily frowned upon as it involves destroying corner office space. If we can perform the repair mostly from the outside that is ideal.

 

[dik]

OK

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[phamENG]

Nice. I like the simple plate with no weld access and nothing to weld to. (I'd say more, but I remember making a few gaffs like that myself and I probably still have a few left in me...)

Just so I understand - you have a square HSS column coming up in the corner of the building with your cantilevered brackets to catch that end of the beam, and the other end of the beam is bolted to the block?

Is the plan to have the full length web "doubler" and the replacement flange shop welded, field weld that weldment into place, add then field weld the flange doublers and web stiffeners into place?

I think your detail makes sense. Perhaps a little overdone, but given the level of unknowns you're dealing with that's probably a good thing. On my first attempt I'd try to keep the eccentrically loaded weld group (I assume the intent is to make the new material strong enough to carry all the load and splice it into the existing in that region) limited to a space where I have a full, usable section of the existing beam. If that doesn't work or you don't have enough room to engage enough of it, I'd make doubly sure of the shear flow at the replacement flange to existing web region. My concern there is the state of the material. I imagine there could be some irregular section loss along the top and the weld may not be as reliable as you might wish for. But you've actually put your hands on it so if you think it's reasonable to expect a decent weld then I'll believe you.

 

[Enable]

We all have a few gaffs left in us!

Just so I understand - you have a square HSS column coming up in the corner of the building with your cantilevered brackets to catch that end of the beam, and the other end of the beam is bolted to the block?

Correct on the HSS side. The block side hasn't been exposed so I do not know for sure but based on what we can see looks to be bearing on the backup wall.

Is the plan to have the full length web "doubler" and the replacement flange shop welded, field weld that weldment into place, add then field weld the flange doublers and web stiffeners into place?

Correct.

On my first attempt I'd try to keep the eccentrically loaded weld group (I assume the intent is to make the new material strong enough to carry all the load and splice it into the existing in that region) limited to a space where I have a full, usable section of the existing beam.

This is my intent. I don't know how far back I'll need to go as yet but basically I want to somehow get the shear into the web where there is good material. I will more or less tell the EOR that we need to remove brick as far as is needed to accomplish this; so I don't really have any limitations on how far back we can go.

My concern there is the state of the material. I imagine there could be some irregular section loss along the top and the weld may not be as reliable as you might wish for. But you've actually put your hands on it so if you think it's reasonable to expect a decent weld then I'll believe you.

That's a good call if I need to rely on the existing. But the point of designing it as an eccentric connection is that I won't have to rely on the existing W-section at the bolted connection anymore (I will weld as close to the connection as I can but only rely on the welds beyond deteriorated area for design purposes). Whatever is added there from existing should just be gravy.

Just really needed a double check on this one to make sure I haven't done anything stupid or introduced odd load paths that I didn't consider. I'd usually bounce ideas off my brother but he's about to have a kid and so I have been left to my own devices on this one (scary thought haha).

 

[phamENG]

Makes sense to me. You maybe introduce a little torsion with the plane offset of your two webs, but this is an eccentric lintel - torsion is what it does.

Congrats to the uncle-to-be.

 

[Enable]

I really had no part in the decision of becoming an uncle but I appreciate it! Any day now!

Update:

Turns out there have been some developments with many other parties in the mix. Long story short for a bunch of reasons the GC had another engineer design the repair detail, which we were asked to price on a deadline. However, while solving some of the EOR's detail issues it introduced a host of other issues and we could not price it (and funny enough it also retains the lovely property of being unwedable in the field). So unfortunately we will not be involved.

Shame because I really thought this was a neat little project to be involved on. Though it's not a total waste of time as I'm writing a book on structural repairs to buildings and at the very least this will make it into the structural steel chapter where I talk about field concerns.

 

[phamENG]

Writing a book, you say? Interesting. Keep us posted on publication dates and availability.

Sorry you won't be involved, but sometimes what looks like an opportunity is really a bullet in disguise.

 

[Ron]

@Enable....good luck with the book. Not an easy task! I'm now editing the 11th edition of my book. Even editing takes a ton of time.

I like the welded repair vs. the bolted repair (agree with dik). Welding in the field is much easier than dealing with bolts in the field.

 

[Enable]

It’s probably more of a struggle than anything I have ever done professionally…not so much for the content as for the degree of difficulty in trying to write clearly and concisely.

I am now convinced that there are only ever shades of more / less clear especially when discussing technical concepts. It is crazy how many things one has working in the back of their head when they decipher the meaning of even the most simplest of sentence constructions. Add to that there are probably many more things that the reader might not know than know, and you have an unworldly conundrum: how much do you explain, how many caveats do you provide, what gets relegated to a footnote, and on top of that, as these things are accumulating are we making this thing too damn long for anyone to ever want to read except out of curtesy?!


CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[Ron]

@Enable...LOL! You got it. Pain in the A$$ but rewarding as well. Best wishes!

 

[Ron]

Connect on the alternate site (which can't be mentioned as it gets immediatly deleted) and we can share misery with publishing!

 

[Enable]

Ron, I think you are forgetting...I am new here, what is the other site lol? I have visited the site in SRA's signature previously, is that the one you are referring to?

If not might just be easier to email me via my information email on my website. It's a small office meaning the mail goes directly to me, ha!

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

https://www.enable-inc.com/

 

[SlideRuleEra]

Enable - On my site, go to the link at the top of the home page, the line just below "SlideRuleEra".

http://www.SlideRuleEra.net

 

[Ron]

Thank you SRE...helpful as always!!