Steel joists at columns

[jdbpe]

I have a single story building with 44LH9 roof joists that span 69 feet to W18x40 girders. The girders span between 10 inch columns at 26 foot spacing between column lines. The building is resisting lateral loads by perimeter masonry shear walls. The joists are simple span. At the column lines, does the bottom chord of the joist need to straddle a stabilizer plate (not welded though). The stabilizer plate will be welded to the flange of the column.

 

[structural01]

Yes, the bottom chord of the truss needs to be sanchwiched between the plate. This is to prevent twisting of the truss out of plane. I believe the truss manufacturer might even require it done. You can check Vulcraft catalog.

 

[JedClampett]

One thing to consider is construction sequencing. If you use joists at the column lines, they will have to be supported by a crane until bolted bridging is installed. This is per OSHA. The alternative is to install the joists, one by one, until you get to the column line, install that joist and attach its bridging. But then you're loading the column while it's unbraced in the joist direction.
I would bite the bullet and install a wide flange beam at the column in place of that one joist.

 

[JAE]

I believe that ALL joists of that length must be supported by the crane until bridging is in place...not just the joists on the column lines.

In answer to the first question - you do not have to extend the bottom chord to a stabilizer plate for LH joists when they occur at columns. You only need to supply a bolted connection. Stabilizer plates are required for joist girders, not joists.

Having said that, many engineers do provide an extension to the bottom chord and tie into columns for a some feel good, traditional reasons:
1. To provide some minimal lateral structural integrity of the overall building frame.
2. To provide for lateral restraint of the top of the column to restrict lateral buckling, or roll-over of the beam when the beam runs continuous over the top of the column.

 

[Lutfi]

JAE,

You bring good points. However, if the engineer is going to use the joist or girder as part of moment frame to resist lateral loads, I think this should be indicated on the plans in addition to the axial for anticipated. This will afford the joist designer the opportunity to design the joist or girder properly.


Regards,
Lutfi

 

[JAE]

Lufti - you are absolutely correct. I was just going off of jdbpe's statement above that perimeter masonry shearwalls were the lateral framing system. For a moment connection, then the bottom chord gets welded to the column and the engineer should indicate required end moments.

But for non-moment frames, there is no need to extend the bottom chords. Its just that a lot of engineers do to create a feel-good extra lateral stability.

 

[Lutfi]

JAE,

I agree and I have my standard detail that calls for the stabilizer plate at columns for joist and joist girders.

I was lucky and won a book that was written by Dr. James Fisher and others tilted "Designing with Vulcraft steel joists, joist girders and steel deck"

I think it is an excellent addition to any SE library.


Regards,
Lutfi

 

[JedClampett]

At the risk of being corrected by everyone who reads this thread, I'll try again. Yes I know that every joist needs to be supported until its bolted bridging is installed. I also know that OSHA requires that columns need to be braced as soon as possible. So if the contractor is expecting the joist attached to or near the column to brace the column, he'll need to put it in first and keep it rigged until adjacent joists are flown in to put in the bolted bridging.
If you use wide flange sections at column lines, you save the issue of worrying about keeping them supported until they're bridged.
I don't know how contractors are implementing these requirements. And if you put in wide flange shapes, I'm not sure the contractor will know the reason and put them in first.

 

[JAE]

JedClampett - no correction, but a question. I don't see the difference between a joist bolted to the column, on the column line, and a wide flange bolted to the column. Can you expand a bit on your point?

Both are simple "pinned" supports and provide no substantial lateral bracing to the frame - that should be dealt with by other means such as cable tie-downs.

SJI/OSHA requires the joists on the column lines to be bolted connections (vs. welded) so the attachment can be made quickly and for the purpose of dis-allowing the joist bays to spread apart and allow intermediate joists to fall.

 

[JedClampett]

The difference between a joist bolted to a column and a wide flange is with regards to the OSHA requirement that the hoisting lines not be removed until the joist is attached to the bolted bridging. So if you put the joist in first (to brace the column), you'll have to leave it supported by the crane until the joists are built adjacent to it and the bridging advances to it. The problems with this are that now you now need two cranes and that the rigging for the joist on the column line is in the way.
Since there is no OSHA requirement that wide flange members be supported until bridging is installed, you can fly them in to brace the column and then continue with the joist installation.
Are there any contractors out there that have dealt with this?

 

[haynewp]

Is the requirement that bridging be installed prior to hoist release required for all joist types now or is that just for certain spans?

 

[JAE]

Just for longer spans - look through the SJI specs or Vulcraft's specs and you'll see that at certain lengths and joist types there are requirements for X bridging (either one or two rows) to be installed prior ot hoisting rigs being released.

 

[haynewp]

That is what I thought. So you could just use a joist that does not require bridging at the column line instead of a WF beam.

 

[JAE]

Well, the adjacent joists would still need the bridging, but in dealing with JedClampett's points - that would meet the intent I guess. But it would also be a potential source of confusion with erection - I always worry about getting too many joist types on one job and having them placed in the wrong location.

 

[UcfSE]

The problem with the bolted X-bridging is why I pick joists that do not require that bridging. You pay a little more for the joists but make it back again in saved time and labor. I've never had a single problem with this approach. I've also required a stabilizer plate at the bolted tie-joist as is company policy and had no complaints with that either. Sometimes adding more material can save money and hassle.

 

[haynewp]

I agree, the economical joist guide does not figure in bridging into the cost, so some times it may be best to go up a size or two and avoid the bridging.

The joists I usually pick are based on at least 240plf uniform load on a 50ft or less span. By the economical joist guide, the best pick is a joist that does not require bridging before release anyway.

 

[WMO]

My interpretation of osha is that all joist at columns require a stabilizer plate at the bottom chord.
Here is a link to osha & joist

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12748

regards,
Mark

 

[WMO]

Of course with the caveat that they are not restrained in 2 directions. Osha does not appear to distinguish between joist types.

Mark

 

[JAE]

Good link.

I think I stand corrected as this document appears to indicate that stabilizer plates are required. I'll have to look into this a bit more but I know there are lots of jobs out there that don't have them. I'll check with a local SJI joist supplier.

 

[haynewp]

Is it the EOR's responsibility to check for OSHA compliance with all items like that or is it the manufacturer's or contractor's responsibility to ensure they are installed? I understand usually when there is a jobsite accident, that everyone gets sued anyway.