Industrial Building Addition?

[SteelPE]

I am in the process of designing an addition to an existing industrial building. The existing building is 180’ wide x 320’ long. It is split up into 3-60’ bays. The existing building contains multiple 2 cranes in each bay (outside bays have 2–10 ton cranes and interior bay has 2–5 ton cranes). The original building was constructed in the 60’s or 70’s. The new addition is 180’ x 120’ (the 180’ side aligns against the 180’ side of the existing building).

The client would like to extend the cranes into the new building. I am not in charge of designing the crane runway girders, just the structure that supports them.

I did an extensive site visit 3 years ago when the project was first proposed. During that visit, I could not make out any type of lateral force resisting system. The existing building has precast panels up 2/3 of the way above grade and translucent wall panels making up the remainder of the height (see pictures).

As I don’t exactly know how the existing building is standing up, I have the option to install a “flying buttress” brace frame on the outside of the existing building where we are removing the existing exterior façade. The client has agreed to this, but I am a bit nervous that this “flying buttress” brace may will not cause any other issues with the existing building (like making it too stiff along one side).

What do others think of this idea?

 

[dik]

Does the flying buttress take care of half the existing building 'face' area? and can you design the new addition to be totally independent of the existing building? including crane beams?

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

-Dik

 

[SteelPE]

I can design the flying buttress for whatever I like.

The two buildings are currently completely separated from each other.... at least that is what the intent is. We will have a new columns system up against the existing building (maybe 1'-2' away). The crane manufacturer (who is responsible for the design of the girders) will need to make a special joint there that will allow the crane to move from the existing into the new. The plan is to install a flying buttress on the existing.... and a flying buttress on the new... and make some huge footings on the outside of the building to accommodate the load from both buildings.

 

[dik]

I don't see a problem, then... just a matter of execution.

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

-Dik

 

[KootK]

1) Based on the photos, I see three candidates for what is currently stabilizing the building. No doubt you see the same:

a) There appears to be a chevron brace in there somewhere.

b) You've got the knee bracing.

c) Your columns may cantilever up from the a girt member that is tied into those stiff wall panels.

If your observations lead you to favor on of those systems over the others, do share.

2) The buttresses are an awesome engineering solution, particularly given that you've already -- and impressively -- managed to sell them to your client. With respect to your stiffness concern, I feel that the likely danger is that the buttresses wind up being much stiffer than the other sources of lateral resistance. To that end, I'd be inclined to design the buttresses for a load greater than 50% of the conventional, tributary load. If you don't attempt an analysis of some kind, maybe design the buttress for 2/3 of the total lateral or something of that sort.

3) Under the right conditions, I'd be willing to forgo the buttresses, tie the two roof decks together for shear transfer, and drag that load right across to the end wall of the addition. That said, I can also think of fine reasons why the butresses might be better, not least of which is that they simplify the load path a good deal. I'd be more inclined to consider something like this IF your client were pushing back on the buttress concept. Given that's not the case, doing so strikes me as inviting additional pain and uncertainty needlessly.

4) I'm pretty far being any kind of crane expert but I would have expected the crane design to favor tying the two buildings together rigidly. That said, you may already be doing that. I'd be inclined to have the new and existing buildings share a common buttress. Not that that will make a huge difference given that the buttresses will be wickedly stiff and probably share a common footing already. In the other direction, I'd be very tempted to tie the new and existing buildings together laterally.

 

[dik]

Unless you know how the original was designed for lateral loading, I'd be reluctant to tie the two together.

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

-Dik

 

[SteelPE]

KootK

Yes, there are braces that run parallel with the crane girders, but for some reason, these braces do no run all of the way to the ground (I attributed this bracing to bracing the crane columns in the weak direction as there is a bunch of it parallel to the crane girders...... and I can't get the existing column sizes to calculate out). There are also some random knee bracing everywhere. However, from what I could tell, there is no attachment from the WF beam at the top of the concrete panel to the concrete panel (if you look in the picture you won't see any bolts).... unless there is some attachment on the outside of flange of the beam that we can't currently see.

In regards to attaching the two building together. I am not sure if this will trigger a code required upgrade for the existing building. I want to avoid making an attachment to the existing to avoid any questions in regards to upgrading the existing building. The purpose of installing the buttress was to avoid any further questions about the possibility of reducing the capacity of LFRS along the expansion wall.

 

[bones206]

Based on the retaining clip shown in the photos, it looks unlikely that the precast cladding was intended to act as a shear wall. If you can do some more investigation to confirm there are no other hidden connections between the panels and frame, I would think it's safe to assume the lateral system is a knee-braced sway frame, or fixed-base cantilever column frame of some sort. If that's the case, then removing end wall cladding shouldn't make a difference structurally. But definitely do whatever investigation necessary to vet out what the true lateral system is.

The roof looks like a corrugated metal roof, so not really a diaphragm. So if you make that end bent really stiff with the buttress, I wouldn't think it would resist lateral loads beyond its own tributary girt area.

My gut feeling approach on this would be to keep the addition independent, but design it as a sway frame with similar drift as the existing so you don't induce differential drift along the length of the crane runways.

 

[KootK]

The purpose of installing the buttress was to avoid any further questions about the possibility of reducing the capacity of LFRS along the expansion wall.

I would certainly agree that the buttresses accomplish that goal convincingly.

In regards to attaching the two building together. I am not sure if this will trigger a code required upgrade for the existing building. I want to avoid making an attachment to the existing to avoid any questions in regards to upgrading the existing building.

I get that. To play Devil's advocate, however, what will be your approach when the crane guy inevitably asks "so, how much movement do we need to plan for at this joint?". Do you plan to ball park the drift on the existing building assuming that it's just leaning on the knee braces and then plan out a building joint width to preclude the new and existing from bumping into one another?

Ballparking it, what do you foresee for a building separation width here? 2"?

Are we assuming pretty steady state temperature control for this facility? A 320' long building with no concentric bracing probably shrinks and grows about its center a fair bit under thermal cycling, if any exists.

I'm often torn in these situations between two impulses:

1) My client's wallet and my own project management usually favor leaving the existing building alone.

2) I feel as though the right thing to do for a building lacking a decent lateral system is... to give it one. Granted, stabilizing a 320' building is a lot to ask of a 120' addition.