Renovation of Steel Building

[tclat]

Hi,

I am involved with a renovation project. The building is a mall and has a steel frame with precast concrete joists at 2'-0" c/c and masonry filler blocks.

The typical bay size is 20'x 20'. The client would like to demolish the floor of one bay to contruct a new stair. The problem is the steel beams supporting the floor in that bay extend into the adjacent bay which is over another tenant. Under no circumstances can we disrupt the other tenant.

I was considering cutting the existing beams using a flame torch and installing a new trimmer beam to pick up the cut beams. My concern about this option is the kind of workmanship one would expect with this type of operation and the possible impact the heat would have on beams and new connections.

Any thoughts?

 

[msquared48]

I assume the existing beam to be removed is A36 and not a high strength material?

How about installing the "trimmer beam" first, then
removing the existing beam via sawcut and/or torch?

The trimmer beam could be placed in two sections, one to either side of the beam to be removed, and the connection to the existing beam made fixed via full-pen welds. Shore the connection up during the removal process so any relaxation due to heat is not permanent.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[tclat]

Hi Mike,,

I have not been able to confirm the grade of steel yet. Is field cutting a higher strength material (say 44 or 50) in the field for applications like this common?

There are two beams which require cutting has they fall within the bay. The trimmer beam I am proposing will support the cut beam and translate the load back to beams on the primary grid. In that way I believe the beams need to propped, cut and then the new trimmer beam installed.

The new beam will be located right up against the cut beams. To simplify the cutting and connection, I was thinking of adding a plate from top to bottom flange on the new beam with a shear tab to pick up the cut beams by field welding.

What are the guidelines for welding to steel that has been field cut. Any issue with max temp, rate of cooling, deformations etc

Thanks

 

[csd72]

I would worry more about the poor state of the cut edge. Allow plenty of tolerance in your welds on this one as the edge will be far from straight.

Also, are these steels part of a portal frame? If so then you will need to look at laterla load tramsfer.

 

[ToadJones]

if this "trimmer" is like a steel version of a rim joist, is it possible to place the new "trimmer" under the existing beams prior to cutting them?

If it is only two beams and they are not large, they can be cut with a cut-off wheel quite cleanly. You might be surprised.
I have personally cut small W8z18 wideflanges of A36 with a good Sawzall blade many times. Seems crazy, but it works pretty damn well.