Reading truss reactions 2

[JStructsteel]

Got a cut sheet for a girder truss from a truss mfg. Its simple span, but they have a group of reactions. Anyone know why, or how to read the reactions?

Obviously I can figure out the reaction if need be, just want to know what they are trying to report.

Their drawings suck, so it makes it that much harder to read too.

 

[JStructsteel]

rb1957 thanks for the apology. This is all in the prelim stage. I was caught off guard with a truss that had multiple supports, and the mess of a drawing it was not clear. I am leaning on pushing to get this changed to a beam line.

I have confidence in the truss guys, but this does not offer much redundancy if something fails.

Its a big job. Lots of trusses and jack trusses, etc, approx 1500 pieces.

 

[JedClampett]

Let me be Mr. Obvious:
These truss suppliers are very much a commodity. Unless things get real hinky, they'll provide exactly what you ask for. That Alpine program is state of the art and has been for about 20 years . I've dealt with it before, although thankfully, not real often.
If you're having issues, there's no harm in ringing up the actual engineer (it won't be easy to track them down, but it can be done) and asking him/her questions. Most of them are good chaps and don't mind having human phone contact every once in a while. Sometimes there's a language issue, so be patient.

 

[rb1957]

To me it's the presentation of the drawing that's terrible (as I'm sure we'd all agree).

Sure, with a tonne of time we can figure out what they mean, and if this is going to happen 1500 times, it'll be a real pain in the ass.

Maybe these guys don't listen to their customer (that must be a great business to be in).

To ask that the drawings are legible is not great ask. If you're using a program that prints the output, and that messes with your drawing border, "surely" you don't say "meh".
Maybe ask they to send the print-out without the border ? or shrink the output so that it fits the border ?

And they're responsible for the 5 plies, joining them, accounting for the joining in their analysis, etc ?

another day in paradise, or is paradise one day closer ?

 

[Brad805]

Somebody is new to the software or this is an atypical case for some reason. I would ask them to figure out the formatting for the sheets and re-submit. This type of software has a front end for the truss layout/design, and the software generates the truss drawing based on endless settings for different sheet sizes. Someone has messed it up or did not edit the drawing before sending to you.

 

[jayrod12]

Regarding fastening of the plies RB, yes the truss supplier generally specifies all of the fastening of built-up truss members.

As the EOR you are responsible to give the truss guy the proper loads to design for, as well as enough information about the building layout/support conditions that they can use it to determine the truss requirements. You are also responsible as the EOR for the permanent truss bracing (not the temporary erection bracing, that's the contractor and any hold-down connectors required for truss to support structure. The truss guys take care of truss to truss connection.

 

[oldrunner]

It appears that this should have been two drawings (or more). There should be some sort of manual for interpreting the drawing or there is another drawing with standard notes etc.("THIS JOB'S GENERAL NOTES PAGE") All of the special loads should be checked. You probably have the framing drawings showing all of the various members that this truss is supporting. Basically three spans - about 29 feet each side and a 6 foot span in the center. You have lots of heavy point loads - from 7606 lbs to 3074 lbs. Is the drawing supposed to be stamped by a registered engineer? I see that is a "closed" building - but have you checked the amount of windows and doors to determine if the uplift forces might have to be checked? Any snow loads at this location?
Note refer to drawing 160A-Z for standard plate positions. Do you have ANSI/TPI 1? Have you checked the websites indicated "For more information see.......these web sites: WEBSITES (bottom of page note in second from left box!

Hauling truss will probably require permits with two cranes at the site. Maybe three sections with longest section about 29 feet?

Agree with Brad805.

 

[JStructsteel]

This was their prelim layout Oldrunner, nothing set in stone. Final design I will reject this type of shitty drawings. Also will be stamped.

Its a closed building. All roof loads and dl requirements were provided to them

 

[rb1957]

How do you guys feel about the joints ? there are 5 plies of woodwork joint by nail plates on the two (at best) exposed faces ?

Will the final drawings have an accompanying stress report ?

another day in paradise, or is paradise one day closer ?

 

[RWW0002]

Since no one else is, I will take up for the truss supplier a bit... I do not know the project specifics exactly, but it sounds like this is a preliminary truss run provided (likely for free) by a truss supplier on the front end of the project (possibly with very little to go on)..

If that is the case, I would be very happy with the supplied information (even with the formatting issues) to aid me in trying to figure out if the girder truss is a feasible option. Yea, the output has much to be desired, and could likely be tweaked for readability, but beggars can't be choosers. Anyone who is used to reviewing truss packages should be able to glean enough useful information from the output posted to determine 1) whether the truss supplier correctly interpreted your roof layout intent, and 2) if the girder truss is actually a feasible option to consider. In my neck of the woods, it is generally the responsibility of the EOR to provide a reasonable truss layout and design all of the supports and connections for the expected reactions prior to any input whatsoever from the truss supplier.

From the looks of it, if the loading was interpreted and input correctly, I agree that there are likely better options than the girder truss, and the clear-span girder truss originally expected is clearly not feasible.

Also, it looks like the nailing for the plys was provided in the preliminary information (see screenshot below)

 

[dauwerda]

rb, each of the 5 trusses is built individually, i.e. nail plates are installed on each side of each member, then they (each truss) are nailed (and/or bolted) together in the field.

 

[rb1957]

thx, would not have thought that ! I'd've thought that that assembly would make the joints a real "dog's breakfast", with the nail plates getting wedged in where they aren't wanted, but I learn something most days ...

another day in paradise, or is paradise one day closer ?

 

[Brad805]

rb, here is a video of a company building trusses in the plant. TRUSS PLANT

 

[rb1957]

interesting, is there another segment showing joining trusses in multi-ply lay-up like we have here ?

The arm (that sweeps over the truss) is that an NC joiner/nailer ?

I see the guys apparently nailing a single nail? in the joints (or are they "just" aligning the truss to the bed ?

another day in paradise, or is paradise one day closer ?

 

[SteelPE]

I believe they are temporarily nailing the metal plates in place... not putting a single nail in. I also believe the machine that you see moving over the top of the truss is a press that applies a certain amount of pressure to the plates to permanently embeds the plates into the the wood truss.

The metal plates are a guage thickness perforated steel plate with teeth that grab the wood.

https://www.lowes.com/pd/Simpson-St...0XZWB8q2u5J5COrL01AaAvWAEALw_wcB&gclsrc=aw.ds

Someone may be able to explain it better.

The truss manufacturer knows how strong the plate is based upon how many teeth are embedded into the wood. I would hope there is a huge safety factor in these plates.

 

[oldrunner]

If this is a preliminary drawing, then there is enough for determining whether the design is what one expected. I agree with R

http://WWW002.

As I said earlier, blow up the drawing on the screen and read the notes and other items. (Like I finally did as I didn't pull up the drawing on the screen at outset. (I apologize). I have always had to be careful with the various truss manufacturer's submittals. Everything is usually there but hard to find and sometimes you will get submittals of details with some of them crossed out. If you end up using this truss design, it might be very expensive. What was helpful was providing reference data on their website.

 

[JStructsteel]

Talked to the Architect, and he seems to be leaning towards a beam line too, with bottom chord truss bearing along the line. All is good in engineering land now.

 

[jayrod12]

I wouldn't think it would be a bit issue for the truss supplier to build you in a pocket for your steel beam to at least avoid the bulkhead. I get them to do this all the time.

 

[KootK]

would be interested to hear any input from a Manufactured Truss Engineer too.

1) I used to be one of those.

2) I don't feel that the big truss is such a bad idea, especially if the load is coming in from both sides of the truss. It's tough to beat the stiffness of a truss in applications like this.

3) A good strategy in situations like this is to break the truss in two at the middle. Reasons:

a) Easier to handle.

b) Easier to fabricate.

C) Easier to ship.

d) Less potential for weird uplift reactions.

e) Most importantly, it should reduce the interior reactions by eliminating the continuity there which tends to get exacerbated by the depth of the truss at the middle.

 

[KootK]

And, with regard to the crappy look of that drawing:

1) You can bet that any real truss designer who spends all day looking at these damn things doesn't have them looking like that.

2) Preliminary work like this will often be done by a sales guy who:

a) Is a good old boy who could drink you under the table but can barely use windows yet alone Mitek/Alpine.

b) Clearly took the truss loads in from an automated layout plan, probably without much discrimination.

c) Kept pushing enter like Homer simpson until all of the flashing red went away.

So maybe this truss needs to be 5-ply and maybe it doesn't. It's tough to know without the member utilization ratios. A skilled designer might be able to bring the number of plies down by applying some strategic design techniques.

3) Placing panel point at all locations where there are significant loads.

4) Breaking the truss in half as I mentioned.

5) Solving bearing issues with bearing enhancement blocks rather than extra plies.

6) Solving bearing issues by running vertical webs through to the bearing rather than across a chord with perp-2-grain issues.

7) Refining the loads coming in from the layout program where appropriate.

All of this is speculation of course. My crystal ball is more translucent than transparent.

 

[Ron]

It does not always make sense to allow truss designers to dictate your structural system. They will try to make anything work with trusses - because, well, they want to sell you trusses. It does not always mean it is the best tool for the job.

If the only tool you have in your box is a hammer, everything starts to look like a nail.