Top of Steel vs Deck Bearing 1

[JAV72]

My firm has used "Top of Steel" elevations noted along side the beam designation for years. Once the project goes out I try to ask the detailers and the contractor about our drawings and what we could do better. I have heard from detailers that "Deck Bearing" elevations would be helpful, particularly on more complicated roofs. I'm wondering if it's worth switching? My boss who has worked for large firms (100+ employees) says that that they used Deck Bearing when he was just getting into the field. Perhaps a switch to "Top of Beam"? Would Deck Bearing be confusing for the contractor? Just looking for other opinions. Thanks

 

[XR250]

I think TOS is easier. The guy setting the steel only wants to know top of beam - he "generally" could care less about the top of the bar joist or deck elevations.

 

[EngineeringEric]

I lean towards towards specifying in terms of work order, first trade sets the frame work for the others. so since steel erection governs everything above it, I'd use TOS. If concrete/masonry wall, I'd give TO CMU/Conc.... Wood goes truss bearing or TO Top plate (height of wall)

 

[a2mfk]

Always used TOS. Plus, who is confused by this very standard designation, since TOS= Deck Brg. most of the time anyway?

Also you may have a situation with a sloped beam, or a sloped deck bearing on a bent plate, where you may need to call out multiple TOS.

 

[JAE]

We use the term "Bottom of Metal Deck" (BMD)

The problem with Top of Steel (TOS) is that if you use a joist system with 2 1/2" seats, and you label TOS on the plans, you run the risk of confusion over whether the top of steel is the north-south bearing steel or the east-west top of joist steel. Remember that in joists, some beams are 2 1/2" lower than their orthogonal beam cousins.

The use of BMD creates a consistent definition of the plane of the roof deck and steel fabricators can easily detail the steel to be correct in creating the elevations you need.

 

[EngineeringEric]

JAE, in the case of labeling TOS for orthogonal steel... isn't that the reason we label TOS, so it becomes clear that the member is upset from the girder-beams? or is this something you use for the case of placing a single note on a plan indicating BMD elevation? We typical say ""TOS=100.0' uon"" and would call on the plan those special cases, which i think is pretty clear...?

Sorry for hijacking, but I think it is on the same page as original question.

 

[ACE58]

I agree that TOS creates confusion; is it "top of steel beam" or "top of steel joist"? I'm considering a change to "Bottom of Roof Deck" (BORD), because we have had projects that have had metal, vented wood & plywood roof decks (of different thicknesses)over steel beams, steel joists or light gage trusses all on the same project. Even that won't stop the RFI's, I'm afraid. If you note the "top of joist" (TOJ) for sloped joists on steel beams, the contractors want you to establish the beam bearing elevation for the masons. The preferred joist seat depth can vary widely among joist fabricators & no one wants to pay for extra material so they want to use their company's seat depth. That leaves beam bearing elevation to vary until the joist contract is awarded & shop drawings are submitted. Shop drawing review takes much more time than in the past because no one wants to take the responsibility to establish elevations - leave it to the EOR.

 

[a2mfk]

JAE- Don't disagree with your points, I could see how in many instances that may be less confusing. As long as you are clearly conveying the info, it is good to me... We would put TOS right under our WF beam callouts for instance, or along a column grid line.

Also use JST BRG = joist bearing elevation, as necessary, for when joists are bearing on or connected to a CMU or concrete wall. With odd geometries and slopes, sometimes also supply the joist seat depth or say "sloped joist seat".

Haven't been doing much steel design lately, but elevations were one of the more annoying aspects of doing structural drawings. I'd rather design the steel and connections and have somebody else coordinate all that dimensional stuff- which in fact, many a good structural CAD tech can work most of that out with the architect.

 

[JAE]

I think if you use TOS on the beam label itself then that can work - assuming the beam is level.

If the beam slopes, then you have to use TOS at each end of the beam - again you can probably do it on each beam individually to avoid confusion.

Usually we have a 1/4"/ft. sloped roof and we like to delineate the elevations on the main grid lines. This is where the confusion comes in if you use TOS.

If the TOS is labeled on the grid line - and refers to beams on the grid line, then that would work - but there are also perpendicular beams that would be 2 1/2" higher and
we always feared that confusion would result from that - especially in unique areas with a lot of jogs in the roof layout, re-entrant corners, etc.

 

[JLNJ]

It depends on the nature of your construction type. We did a large high school with huge hip roofs. With long sloping beams in the hips and valleys supporting joists which support deck, the top of steel of the beam (even just the workpoints at the ends) is hard to track and not really important. The important plane was the bottom of deck. The detailer did an excellent job with a complex roof.

On other projects, top of steel is the most appropriate. Either way we need to give the detailer all the info.

 

[KootK]

Having used both methods:

1) I like that TOS makes shop drawings easy to check. I've always understood TOS to essentially mean "top of non-joist steel".
2) I feel that u/s of deck reduces my liability somewhat. If I've failed to consider something in a complex situation, the steel detailer should still at least know where the steel has to get to at the end of the day.
3) The main reason that I use underside of deck now is that it seems to yield a better coordination review from the architects that I work with. They seem to think in terms of top of deck. Underside of deck's a pretty short leap from there.

 

[JAV72]

Thanks guys. I appreciate the input. I think I will move to a Deck Bearing (DB) or Bottom of Metal Deck (BMD) {I like that JAE} format for most all our projects. There will most likely be instances where Top of Beam may be appropriate.
KootK: {Item 3} Interestingly, what sparked my question was getting an email from an architect reading me the Riot Act for showing Deck Bearing. In his opinion I was providing "meaningless information" which he "cannot use" and would only serve to "confuse the detailer and contractor".
So for his projects I'll have to stick with TOS/TOB.
Thanks again.

 

[msquared48]

TOS is relative, depending which member you are pointing to for the elevation delineation.

If you want to keep it in a general note UNO on the plan set, just state the top of steel for both the W sections and the steel joists. BOD is OK too, and more generalized still, and even applicable to the swimsuit issue.

Mike McCann
MMC Engineering

 

[paddingtongreen]

A TOS elevation should be given for the floor or roof and apply to any member that is not given a plus or minus in brackets, e.g. W14x22(-2½); that says, "the top of this beam is 2½" below the top of steel for the floor". They were doing this when I started work in the early fifties and still doing it when I retired in 2002, I didn't ever see it done another way. I pretty well only worked for large companies.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin