CAST YOUR VOTE! The Great DIY Steel Joist Detailing Competition of 2022 - Win $250 USD 30

[KootK]

Things have been a little slow around here lately for my liking. In an attempt to liven things up, I'm attempting something experimental: an engineering contest with a cash prize of $150 USD. This is your chance to:

A) Earn yourself some KootBucks and;

B) Establish yourself as a GSEL (Goddam Structural Engineering Legend).

THE CHALLENGE

In the spirit of times, develop a scheme for the fabrication of a steel joist that would be fabricated on site rather than by a conventional joist supplier (Vulcraft, Canam, etc).

THE RULES

1) Include sketches or be forever disparaged.

2) Describe the benefits of your proposal as you see them.

3) Submissions will be accepted until midnight on June 5th, Pacific Time.

4) On June 6th, voting will commence.

5) Voting will close at midnight on June 12th, Pacific Time

5) Votes will be cast by way of members visiting the thread and writing a quick note to indicate their favorite scheme.

6) Votes will NOT be cast by way of giving out little purple stars. Give out all the little purple stars that you wish but none will be recorded as a formal vote.

7) Anyone may enter the contest and win the prize. However, you need to have received at least 9 little purple stars on this forum in the past in order to qualify as a judge and cast a vote that will be counted. I'm setting this restriction only as an attempt to prevent this thing from spiraling into some weird, spammy, cheating affair. Basically, if you're to be in charge of awarding the KootBucks, you need a reputation.

8) The prize will be awarded in the form of an Amazon eGift card. The winner will need to send their burner email address to my burner address or whatever. We're smart kids, we'll figure it out.

9) No prize will be awarded if there are not at least five entries to choose from, including my own.

10) If JAE shows up to judge, he can cast my vote along with his own.

May the best engineer win!

 

[KootK]

Ultimately, I suspect that the biggest armor chink for both this and Bone's concept would just be difficulty in running services through the joists.

Much worse than your traditional sawzall hole through a wooden I-joist? I'd think the WWF would be easy to cut and reinforce (for services over 4"), and while the decking might require a reinforcement panel surrounding the opening.. still doesn't feel that onerous.

Much worse in my opinion. I'll go "pessimist" and try and sell my concern to the best of my ability:

1) Wood is pretty shear stiff. Corrugated decking is wildly shear flexible.

2) Wood is pretty shear strong. Corrugated decking is wildly shear weak. We get away with 2' openings in roof deck only because we're dealing with 50' "webs" essentially.

3) Wood is not prone to free edge plate buckling. Corrugated decking very much is.

4) Corrugated decking does an atrocious, torsional looking "dance" when loaded in shear as shown below. Even that relies upon lateral restraint at all edges.

With respect to openings, I think that dold's solution should lean in to the deck being pretty worthless for that. Instead, make a full depth, vierendeel panel out of the opening and use the massive opening potential that would result as a deliberate selling feature. Since WT sections will tend to be over-stocky for K-series joist applications, I suspect that the chords could deal with this successfully.

 

[KootK]

Is your buckling concern during fabrication? Erection? Installed and in service? I had assumed that we could assume a roof deck to brace the top chord out of plane buckling.

Installed and in service. The roof deck will provide lateral restraint to the top chords but not torsional restraint (to the comp chord, not the truss en marcro).

Part of getting that to work, is that the web members generate a moment resistance at the bottom (see the snip below). For a roof truss, I'm not seeing how the bottom chord could possibly develop a resisting moment with the web members to brace the top chord.

The flexural stiffness of the webs converts the twisting tendency in the compression chord into a couple that is resisted by the lateral resistance of the deck at the top and a combination of these things at the bottom:

a) Bridging.
b) Bottom chord lateral bending.
c) Self weight of the chord truss.

Thankfully, because this is a stability thing, the resulting demand is small. This demand is part of what ultimately creates the need for tension chord bracing: Link.

 

[KootK]

FYI: I've decided to extend both the submission period and the voting period by a week. This, because:

1) We've had some fine, 11th hour submissions.

2) It'll take me another day or two to finish badgering folks.

3) I'd like to see discussion "settle" some before we close up shop. I feel that we may have a few interesting things left to discuss still.

4) I need time for a bottle depot run so that I can make good on the $$$.

I'll talk to management about editing the OP accordingly to capture both the extensions and the updated, $250 purse.

 

[bones206]

@canwesteng - I had the same exact idea with the rods and pipe before taking a hard left into the crazy WWF idea. One thought I had to workaround the protruding hardware problem is to put it inside the tube, and have access holes on the opposing tube walls. In the end I thought it was too cumbersome and probably not very stiff, but probably not impossible.

 

[canwesteng]

I'm thinking you could swap out the HSS with channels instead, and drop a cap on the channel to support the roof deck once everything is bolted together. Or maybe just leave it as is, and you stick a 2x4 on the top, cut around the bolt protrusions.

 

[Enable]

On more of the true DIY side how about a combination of wood chord members combined with pre-fabricated scaffolding braces? The braces already come paired and bent so could nicely be insert between chords. I think the smallest brace I can obtain readily works for a 2'x3'-6" tower so the brace would have an opening something like 20"x36". Note: not sure of extension of those plate pieces so edge distance may be a problem. Dont know.

....my hand drawing needs work

 

[KootK]

I'm still not convinced that WT is the way to go but, for this post, I'm suspending my disbelief and jumping on the bandwagon.

I contend that I can do a better kipfoot than kipfoot. Henceforth, this shall be known as the KootFoot WT Solution.

The idea is to use end slotted channels for the truss webs and weld them to only one side of the tee stems.

BENEFITS

1) Only two kinds of cross sections needed.

2) Concentric.

3) Dirt simple.

4) Uniform shear capacity like KCS.

5) Easy to paint.

6) Clean look for exposed applications.

7) Nested stack width of 3.5" which is not terrible.

8) Can be built with out flipping like this:

a) Set the WT chords in the jig.

b) Slide the slotted channel webs into place diagonally. This works because the channels are 1/2" narrower than the WT.

c) Weld the channel webs to the tee stems on one side of the tee stems only.

The sketch below is a "to scale" version of this using the smallest cross sections available without getting into ST's.

 

[KootK]

In defense of this approach - if you're building and selling these trusses at even moderate commercial scale, the cost to buy ironworker dies for coping and cutting to length of the angles in one operation would be trivial, and thus coping of the angle would add very close to zero additional fabrication time.

That is all new and quite surprising to me. Are you able to elaborate any further:

1) Can you put a number on "moderate commercial scale"? 100 pc? 10,000 pc?

2) Can you post a pic of, or otherwise describe, what an ironworker die for a simultaneous cope and end cut would look like?

Over the years, I've been quite deliberate in minimizing coping. If there are situations where I can relax that, I'd love to know about it.

 

[Enable]

- Steel Costs

Pretty much any steel shop should have an ironworker. The larger variable is tonnage/size that it can accommodate. Here's a video of how easy copes can be done with it.

I bought mine used and it was my brother who handled it so I don't quite recall the specifics of what we paid but I think ours cost $20,000 - $30,000 CND or so (65 ton unit). You can get a new 65 ton Edwards for about $37,000 or their 60 ton unit for $25,000.

I mean, really it's one of the first investments you make when doing steel. Coping of beam flanges is much tougher. Still on torch for us. But you can buy robotic units to do it for you. The king right now for that is PythonX but i'll set you back about $1million CND.

 

[KootK]

On more of the true DIY side how about a combination of wood chord members combined with pre-fabricated scaffolding braces?

Clever, thanks for your contribution.

Given that the scaffolding pieces will possess significant compression capacity, I suspect that you could do away with the OSB verticals at all locations except, perhaps, at the ends of the web runs.

Note: not sure of extension of those plate pieces so edge distance may be a problem. Dont know.

We can make that work. So long as the scaffolding pieces meet at a common bolt, the primary truss shear will spend no time at all within the chord members. As such, the bolts will also not deliver any shear perpendicular to the chord members. The one place where this will not be true is at the end of your web runs. There, you might introduce a hanger of sorts to "collect" the truss shear and deliver it to the far sides of the chords.

This approach is a big part of the "secret sauce" behind RedBuilt trusses which would never survive edge distance checks at the pins otherwise.

 

[Enable]

My program had convocation today and I actually saw some sexy joists / trusses (i've never been to this campus previously). In the spirit of this thread thought I'd share some of the photos! We were in the aviation hanger so also got to see the inside of a wing and yup, little mini-truss like fabrications. Pretty neat

 

[KootK]

The polls are now open and shall remain so until midnight on June 24th! The cash prize is up to $250 USD thanks to the generous $50 contributions of Enable and SwinnyGG.

Note that it shall not be considered ungentlemanly for contestants to vote for their own entries if they legitimately prefer them. To that end, I cast my vote as follows:

FIRST CHOICE: The angle/channel thing that I started with at the top.

SECOND CHOICE: My channel web modification to kipfoot's WT scheme listed near the bottom.

THIRD CHOICE: CANPRO's general concept of a highly eccentric setup that would be the joist equivalent of a channel beam. That makes sense to me for efficiency but it's tough to vote for it without specifics and some evaluation of the implications of the eccentricities. My gut feel is that the implications would be quite minor were the concept explored rigorously.

We're not doing ranked choice voting or anything fancy like that. I only listed my 2nd and 3rd choices for fun.

 

[ALK2415]

@ Kootk
Double angles & channel web { joist design} by (Kootk)

 

[jayrod12]

My vote would be for Milkshakelake's CFS option. Sure, maybe the strength is lacking in comparison to the other options on the table, but there's no welding and easily manipulatable materials. I think that is really in the spirit of the whole DIY joist thing. Those would be so simple a homeowner could build them.

 

[CANPRO]

wow, my half-assed no-sketch concept cracked kootk's top 3. I wish I had time to explore this in more detail.

My top 3:

Milkshakes' CFS option. Agree with jayrod's take on this - this option does seem the check the major boxes of this competition
Celt83's round bar web + channel chords
dold's concept of using deck as the web...using the deck as a beam web is too clever not to make the short list, in my opinion

kootk - you probably don't want to drag this on for too long, but for the sake of comparing apples to apples, it'd be interesting to set a span and basic design criteria to see how some of these concepts compare to each other

 

[jayrod12]

dold's deck as web was my other one I was toying with. I feel if those were all intended to be bottom chord bearing, then it would be no different from I-joists in theory.

 

[Brad805]

My vote is for SECOND CHOICE. I think kipfoot's suggestion on span is about the minimum where any of this would be feasible. Below those spans I believe a WF is more cost effective and practical without all the fancy equipment one uses to produce these.

 

[Celt83]

I'm down for Kipfoot's

I like milkshakelake's and dold's but I imagine those options may not be feasible for some of longer joists spans.

I'm making a thing:

http://www.thestructuraltoolbox.com

(It's no Kootware and it will probably break but it's alive!)

 

[phamENG]

I'm going to vote for Celt83's channel/rebar idea. I read through some of the reports on failures of the Robb joists, but I was getting that most of the problems were with quality control and inadquate design. Things like using unqualified welds, not removing slag, etc. Pretty sure that would be a problem for any and all of these ideas. With proper design and detailing with AWS D1.4 for welding rebar I think it could work. And keeping splices away from the welded areas using mechanical couplers would keep the welding consistent. I think this is a great option for shorter to medium duty joists that don't need to span too far and aren't going to be holding up an auditorium floor.

Second choice is kipfoot's design. Robust and simple. Good for medium to heavy duty use. Longer spans, larger loads. KootK's mod is good, but credit still goes to kipfoot.

Third is dold for shear boldness and gumption. I like the idea a lot - like jayrod said it's sort of the I-Joist of the steel world.

(Since a bunch of people are listing multiple votes, I'm assuming this is going to be a ranked choice/instant runoff type process?)

 

[bhiggins]

Hey everyone, sorry late for the party! Here's a cool concept I came up with today:

Tested this out in RISA, 0.25 deflection for 24 ft span. Not bad,