Metal Building Tie Rod Modification 3

[SteelPE]

I have a client who owns a metal building which is currently being renovated. I was asked to work on a different portion of the project and made a visit to the site to assess conditions pertinent to the work that I was performing. While I was onsite, I had noticed that the client had demolished the existing slab on grade. I gave a stern warning to the owner regarding tie rods which fell on deaf ears.

This week a received a call from the owner saying that while they were installing a trench drain in the middle of the building, they had the building tie rods and proceeded to rip them out (this is why we shouldn’t install tie rods people). Luckily, they only damaged the rods in the middle of the building so there is something at each end. I told the client that they needed to be repaired/replaced in like kind with new rods. The requesting an alternative solution which doesn’t interfere with their proposed trench drain (to save a nickel they are going to spend $100).

In the attached sketch you will find a proposed revised layout for the tie rods together with some back of the envelope calculations to figure the force in the tie rod (which comes out extremely close considering I am using a somewhat large DL). I don’t particularly care for making modifications to the rods, but don’t see any other way to accommodate the owners’ requirements. Has anyone made modifications to tie rods like this before?

Code = IBC 2015

 

[canwesteng]

What's the ballpark force in the tie? I would be inclined to do something like what Pham skecthed, except instead of a structural steel type of thing, just anchor the rod to the trench and reinforce the trench.

 

[SteelPE]

What's the ballpark force in the tie?

35,000-40,000 lbs allowable

 

[KootK]

One minor thing to watch with phamENG's steel thingy, and canwesteng's derivative, is that the thingy needs to be nice and stiff in the middle. Otherwise, it will tend to bow upwards a bit (self limiting).

 

[phamENG]

it will tend to bow upwards a bit

I wonder if you could solve some of the negative effects of that in service by threading the end and using a nut with a plate washer on each end to pretension it a bit?

 

[SteelPE]

All of the ideas presented I find interesting. Unfortunately, I don't think that any of them have made me change my mind in regards to what I would like to do. All of them have their positives and negatives. At this point, I don't like the concrete option as the slab may need to be removed again and we run the risk of being in the same situation again (or worse because they don't realize what they have done and don't repair the slab properly).

Are there any other issues with what I was originally proposing?

 

[canwesteng]

The only things in your original sketch I would check how you are bending the rod at the ends and at the middle and how the new shear in the rod is being resisted. I think if it's a kink it will cause the rod to go partially plastic, reducing capacity. Plus the rod will now have shear at the ends and the hold down point, needs to be checked in combination with tensile and flexural stresses.

There's also slightly more vertical load on the footings but that is probably so small you can wave it away.

 

[TLHS]

I can sketch this if it'd help, but my lazy trench drain detail (if the trench is deep enough to make it practical) is to just run an angle or other shape across the trench with an embed on each end. Depending on the code you're working with and level of comfort, your embed can either mechanically splice to the rod, or you can have rebar welded to the embed with enough length to develop into a breakout cone and put a plate of something at the end of the rod.

Basically canwesteng's sketch, but connect the rods with a piece of steel that runs through the trench.

Keep everything nice and straight, and the depth of the trench doesn't really matter.

 

[bones206]

You're probably not looking for more ideas lobbed in from left field at this point, but what about letting the tie rod pass through the trench drain? The drain covers would hide it from view and it could be suitably protected by a sleeve or painted-on coating.

 

[dik]

Can you not just locally thicken the slab to include the tie rods and leave them cut in the middle... surely in 40' you can develop a smoothe BAR in tension... if not, weld an end plate (to function like a headed stud).

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

-Dik

 

[le99]

Do you know if the tie was provided for seismic concern or else?

 

[KootK]

I wonder if you could solve some of the negative effects of that in service by threading the end and using a nut with a plate washer on each end to pretension it a bit?

You could. Basically, you would bake much of the uplift tendency into the cake from the outset that way. The effect would be small, however, and other strategies might be more cost effective:

1) Just design the zigzag bracket thing with enough stiffness to mitigate the effect and/or:

2) Tie the zigzag bracket thing to the mass of the trench somehow.

 

[KootK]

Are there any other issues with what I was originally proposing?

I think that it's a solid idea. I feel that many of the valid issues that have been raised get ameliorated by the recognition that we're only talking about a 6 degree angular change here. I wouldn't mind see a detail showing how your plan to connect the rods to the footing mass and whether or not you plan to pre-tension the rods. That said, I'm also happy to leave that in your capable hands if you've gotten what you need from this thread already.

 

[SteelPE]

Sorry I haven't updated this thread in a bit.

I decided to pull a page from my old professor who once said "when faced with a problem it's sometimes best to walk away and let the contractor sort things out". With that in mind, I let the contractor stew on the situation for a bit and never really offered the bent rod detail to them. I was hoping that they would come to their senses and they eventually did after a bit of silence. They ultimately decided to run the rod through the trench drain. We are going to sleeve the rod in PVC to prevent the rod from corroding. At each end we are going to weld new 1/2" thick plates to allow for transfer of load from the existing tie rod to the new tie rod.

I like this idea better than what we were proposing above.