Q:Do you know of any good refer-ences for designing for uplift for

steel joists?

A:We’d recommend the SJI TechnicalDigest No. 6 for Uplift (for more in-

formation, visit www.steeljoist.org)and Designing with Steel Joists, JoistGirders and Steel Deck by Fisher, Westand Van de Pas and published by Vul-craft.

Q:How many consultants out thererequire in their specs that joist

manufacturers to submit detailed cutsheets and calculations for each joist onthe job?

A:Most typical steel joist jobs do notrequire a calculation submittal.

Q:Are there any good references fordetermining old joist designa-

tions? For example, I once saw a draw-ing call out a “Longspan underslungjoist type 3214” and did not knowwhere to find properties.

A:SJI has produced the 60-year SteelJoist Manual that lists all the stan-

dard designations from the past 60years.

Q:Is there a physical meaning forthe “section number” called on

several joist tables; for example, thechords area?

A:There may be a correlation be-tween the “section number” and

the chord size for a specific manufac-turer, but there is not an industry-wideuniversal size related to the chordnumber.

Q:A basic question...What is themeaning of the “9” in a 26K9 bar

joist? I believe that the “26” is the depthin inches and it is a K series joist, butwhat is the “9”?

A:A: The “9” is commonly referredto as the chord size that relates to

an approximate size for the chord. Theactual size of chord may vary betweenmanufacturers. It is most commonlyused to match to the standard SJI loadtables to select a load value.

Q:When using a joist on a low-risemetal building where the roof

and the frame to which a joist is to beattached is sloped (and thus the joist isnot plumb), does the vertical load (suchas live load) on the joist need to be re-solved into a load applied through thestrong axis of the joist and a load ap-plied in the plane of the roof-taken upwith bridging? Is there a maximum

Meet the Experts

On January 8, 2002, Richard A. Phaneuf, P.E., Chief Engineer atValley Joist, Marlon Broekemeier, P.E., Engineering Manager withVulcraft, Tim Holtermann from Canam, and Don Murphy from the

Steel Joist Institute joined Modern Steel Construction readers online to answer questions about steel joists.

at MSC’s Online Chats

May 2002 • Modern Steel Construction

Modern Steel Construction • May 2002

slope to which steel joist should be de-signed in this manner?

A:For joists on a side-slope, the hor-izontal component of load can be

taken by the metal deck diaphragmand not the top chord and bridging ifthe deck has sufficient strength and isdesigned accordingly. However, for ametal building with a standing seamroof, the deck diaphragm would not bean option.

A:I take this as meaning that thejoist is not perpendicular to the

ground. We usually place cross-boltedbridging rows at least at the center ofthe span to keep the joist from sweep-ing during steel erection. Then the roofsystem would later be called upon totake the in-plane resultant load compo-nent. So with a standing seam roof, thejoist top chord and bridging wouldneed to resist the out of plane forces.

Q: Considering side sloped joists—what about the dead load of the

joist wanting to twist the joist itself?

A:The joist self-weight componentwould need to be resisted by the

bridging. However, the slope wouldneed to be severe, or the joists veryheavy, before a detailed analysis isneeded. With joists placed on a side-slope, bridging anchorage is more crit-ical than bridging size. The bridgingcan take the load in tension as long asthere is a path to resolve the forces.

Q:Should we only insist on calcula-tion sheets for special joists or

should we require them for all? I tendto think that we should only requirethem on larger projects at the mini-mum.

A:To answer the joist calculation-sheet question, it depends on

what you are doing with them. Themajority of the consultants do not re-quest calculations for any joists. If youhave a concern that the manufacturer isnot designing the joists properly, youshould request calculations for review.Otherwise, it is probably more impor-tant to review the joist approval draw-ings thoroughly to make sure that allthe load information, etc. is on thesedrawings to be incorporated into thejoist design.

Q:Why does Vulcraft not publishthe Designing with Steel Joists and

Joist Girders book any more?

A:Vulcraft is in the process of revis-ing and printing a new version of

Designing with Steel Joists and Joist Gird-ers. If should be available mid-April2002.

Q:On large warehouse roofs thereis frequently an uplift require-

ment in the center of the building of 5psf. Even at this small load, additionalbridging is required. Why is this?Would it be possible to design the joistfor the uplift without requiring addedbridging, and would that be less ex-pensive than installing bridging?

A:For typical K-series, joists, theend web member may have a

slenderness ratio of close to 200 with aK = 1.0 for the typical gravity load de-sign. If the bottom chord bridging isnot present, K should be taken as 2.0,which would require a very signifi-cantly stiffer web. If K = 2.0 for the endweb, it may no longer be possible touse a round bar for the end web, whichis the industry standard. This in turnwould change the configuration ofother joist components, such as theseat, which would add considerably tocost.

A:The bottom chord goes into com-pression and is not attached at the

ends to the structure; therefore, the hor-izontal bridging row near the first bot-tom chord panel point is required forthe uplift forces. This row of bridging ischeaper than designing the joist to dothe job.

Q: So an option would be to “x-brace” between rows of bridging

to transfer the load back to the sup-porting rafter, where the bracing wouldbe located near the edges of the roofand any intermediate locations if nec-essary? I’ve heard tieing bridgingacross the building ridge is becomingunpopular if an unbalanced load con-dition is used on opposite slopes.

A:Yes, the “x” to resolve forces is agood idea.

Q:What’s the status of the conflictbetween OSHA and SJI?

A:There are no longer any remain-ing legal challenges between SJI

and OSHA.

Q:So SJI now will satisfy all OSHArequirements?

A:SJI will meet the OSHA rules asthey will currently be applied.

Research is still ongoing relative to col-umn-joist stability and the proceduresto be used when this part of the ruletakes effect in July 2003.

Q:If I have two joist 26K10 comingfrom two different suppliers, can

I expect to have different chord sizes?

A:Yes—and different geometricpanels, too. Each manufacturer

will design the joist to take the speci-fied loads.

Read transcripts of other online chats atwww.aisc.org/chat.html.