Shoring of Open-Web steel joist

[GreenJug]

Hi all.

I'm currently designing a shoring system for a demolition job on an existing structure. It's a 2-storey steel structure with open web steel joists as secondary beams and I beams as primary beams. They are removing columns along the middle portion of the building and the primary beam spanning across the columns to install a new extension to the front facade of the structure. As I currently understand it, nothing above the second floor decking will be removed (still to be confirmed). Regardless, my question is that if the column on on the first floor is removed, and we are shoring at the location shown in my sketch (check out the attached sketch)... Will there not be an eccentric load from the column above that is remaining in place? As I see it, the load from that column would have to transfer through the diagonal tubing (compression) of the OWSJ in order to reach our shoring post. The engineer of record had requested that the shoring be done at the location I showed on my sketch but I have some serious doubts about this.

Thoughts? opinions?

Thanks.

 

[SWComposites]

I’m not a civil str guy, but I highly doubt that truss was designed for or is capable of supporting the upper floor thru that lower point as shown.

 

[GreenJug]

@SWComposites

My thoughts exactly. Something is not right here. Perhaps they will not be removing the Primary I beam. But again, I don't understand why the engineer of record would specify on the demolition plans that the OWSJ should be shored and not the primary I beam. Very odd to me.

 

[bones206]

Although your concern about the column above is valid, the primary beam is being demolished so it can’t really be shored in place.

 

[human909]

I'd be worried about the lack of lateral restrain on the head of the column. Also the added load from the column is an unknown base on the provided information. Shoring at the top of the joist should fix the former issue. The latter depends on the upper column loads.

 

[structSU10]

So the beam frames through columns as shown? I may weld two channels to the column on the second floor and bear that on new shoring to permit demolition. I would likely ask the 1st floor column be removed, then to shore the joists. you may need to modify the joist still but in this cased you make sure the upper level column load is picked up and not delivered through the joist shoring.

 

[JAE]

If you are changing the load path from above (that upper column load) from a straight path downward to the lower column,

and INSTEAD,

flowing the load from the upper column through a wimpy floor joists adjacent to that column, and through the joist's small diagonals at that, then you need your head examined.
The joist was never designed for that kind of loading, essentially making it a cantilever taking a load possibly many times the original designed shear force in the joist.

The upper columns should be separately shored above the second floor, possibly requiring holes through the floor to allow temporary support columns to support the upper columns.

Now...having said all that...if the shoring of the joists is only to allow removal of the BEAM (and teh columns supported otherwise) then it may be possible to shore the joists as suggested by the others.

I would tend to agree with human909 on shoring at an upper panel point as this at least eliminates the concern of joist instability (overturning) when supporting off the bottom flange so that temporary diagonal bridging won't be needed.

But pay attention to the shears in the joists.
And the columns would still need to be shored separately.

 

[bones206]

I like to provide a direct load path through joists using blocking as shown in this photo. But that’s with a concentric stacked load path from above, and doesn’t fully address the eccentric column load in the OP’s situation.