Joists vs Wide Flange at Column

[Stenbrook]

So I am just curious as to what people typically specify and what the reasoning is behind the methods used, but I have worked for two companies and the first one would always provide Wide Flange beams at the column lines for steel roof and floors and then infill with joists between them. My new company however does not think there is any need to provide a beam at the column and that it is cheaper just to use a joist. So my questions are as follows:

1. Do you typically provide joists or wide flanges at your column lines?
2. Is it really cheaper to go with joists or is this inaccurate?
3. Are there any other reasons to go with one way over the other?

Thanks in advance for your input!

 

[jayrod12]

1. Interior lines we provide strut joists, exterior lines always beams
2. Generally it appeared it's cheaper, for us up here north of the 49 it also passes liability on to the joist supplier.
3. The second half of my previous answer is a good alternative reason.

 

[BSVBD]

1. Interior lines we provide joists. Exterior lines vary.

- I'm not sure what jayrod's strut joist is unless you are referring to the OSHA required extended bottom chord at column locations.​

2. It is typically deemed cost efficient to stay with a repetitive member that is already in a repetitive fabrication order than to interrupt the trend.
3. Lateral-resisting systems may require or prefer beams that may provide moment connections.

 

[KootK]

1) Generally joist for me.

2) Considerably cheaper on a steel weight basis. Also, having the odd non-standard length joist doesn't seem to add any real cost with modern fabrication processes.

3a) Reasons to go with joists:

- Cheaper.
- Jayrod's interesting point regarding liability.
- I kinda like the uniformity in floor stiffness, particularly with a poured concrete floor deck.
- I like the idea of being able to maintain a uniform camber across column lines.
- Often mech stuff is run through the joists. Interrupt that with a beam and that sort of goes away or, at minimum, gets more complex.


3b) Reasons to go with beams:

- probably better for erection stability. Joists, however, seem to be good enough.
- probably better for column bracing. Joist, however, seem to be good enough.
- probably better for tying the building together as a whole (seismic etc). Joists, however, seem to be good enough.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Stenbrook]

I have come across one item that is worth noting and that is that joists that are on the columns must have the bridging installed prior to releasing from the hoist cable. This would mean that the installation order would be: the joist has to be installed on the column (to brace laterally), (the hoist cable must remain in place), the rest of the joists are installed and then the bridging is installed. Then you could release the hoist cable from the original joist on the column. This leads me to believe that they would have to have 2 cranes on site to install the joists correctly. Wouldn't the cost of an additional unneeded crane offset the cost savings on a joist in lieu of wide flanges?

 

[Brad805]

In addition to the other comments I would add that in long span situations I prefer joists so the pre-camber matches. If your specs are not clear or someone chooses not to read we have had cases where the WF's were not cambered equally and it made attaching the deck a problem where the WF's were too close to adjacent joist(s).

 

[KootK]

Interesting point Stenbrook. While I'm not sure how that typically gets handled, I feel that it must get handled somehow. Otherwise, the two crane issue would be a big deal on a lot of projects. I'm sure one of our steel guys will set us straight on this soon.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[sbisteel]

Joists only need to be bridged before releasing cables if they are over 60ft in length. If they're under 60 ft in length, bolting the seats down and the bottom chord stabilizer plates satisfy OSHA requirements.

I will also agree that mixing WF and joists on floors & roofs often leads to camber problems, especially with long spans and/or short spacings.

 

[jayrod12]

strut joist is just a bottom chord extension in most cases, but there are also times where i use them as part of my lateral system either as collectors or drags.