Replacing a previously remove building column

[jfrey414]

I am looking for some guidance on replacing a building column that has been removed during previous building modifications. Currently in place is a transfer truss that spans to the adjacent columns. My concern is that if we just tilt up a column and weld it into place it won't take any dead load from the structure. The reason we need to replace the column is to add a bridge crane runway of significant capacity.

My preliminary thoughts would be to attempt to pre-load the column using hydraulic jacks but determining how to quantify this pre-loading is eluding me. Also considering potential settlements and general construct-ability issues I felt the need to reach out. I figured this situation may have been encountered before.

Thanks for any guidance.

 

[oldestguy]

Can you apply a lift to the truss, lifted to where a new column will sit by using a calibrated hydraulic jack? Then lift a little more, place the new column and lower the truss to meet it. Elastic compression distance of the column can be figured in, but likely not much.

Edit: the initial lift would be to the load that eventually will be carried by the column, as indicated by the jack dial. Jack sits on (or under) a makeshift column.

 

[canwesteng]

Tilt the column up, weld into place and modify the truss so it is simply supported.

 

[dhengr]

Jfrey414:
Your instinct is correct. You want to load the transfer truss at a panel point, and must still check it for the new loading, unless you are going to remove the truss. The two hydraulic jacks are right too, all you are missing is a couple hydraulic pressure gauges and the size of the jack cylinders. You jack the structure up with 10k force (some calc’ed. force/amount, F=PA) on each jack; place the new column snuggly under the structure, and you should transfer 20k to the new column when you release the jacks. Watch the structural movement while you are doing the jacking/lifting, you should have some feel for the amount of lifting you can tolerate without breaking anything.

 

[jfrey414]

All:

Thank you for the quick replies. I will discuss these comments with the rest of the team.

 

[BridgeSmith]

I agree with OG. You could do alot of complicated modeling of the system and still miss the actual reactions by a mile. Much simpler to use a jack and test it.

If you use a hydraulic jack (I recommend a low profile one for stability) that has a separate pump with a pressure gauge, the force can be measured quite easily.

 

[hokie66]

You have been given good advice, but I wonder why you need to take the building load on the new column. Is the new column just for the crane runway? If so, it would just need to be laterally braced like any other separate crane column. Maybe I don't understand your situation.

 

[dhengr]

Hokie:
Maybe the two adjacent columns carrying the transfer truss are close enough, or beyond their max. cap’y., with their added DL and the new crane loads too. Thus, he wants to transfer some of the DL back to the original column location. Otherwise, I agree with you that the new column might be designed primarily/just for the new crane loadings.

 

[jfrey414]

Hokie:

We are having that same internal debate. However dhengr is also on the right track. We are having to weld channels to the flanges in order to take the new crane loading. So it was our thought to return the building back to "original conditions" to reduce the load on the columns.

 

[hokie66]

OK, as long as you are internally arguing about the right things. You know the building, we don't.

Still a bit confused. Are you using the transfer truss as your crane runway beam as well as a building beam? How does that work?