Application of loads to wood truss

[AELLC]

See attached girder truss.

The psf loads in the lower right corner (TC LL=20 psf, TC DL=14 psf, etc,) are all proper and tidy - however, look at Special Loads in the upper left hand corner - where I have red arrows - and then look at the drawing, at the bottom chord on the right, where I have colored it red.

The majority of the dead and live load does exist on the roof deck, near the top chord, but the common trusses at 24" oc that impose the their loads to this girder apply it to the BOTTOM chord because that is where the truss hangers are.

Now doesn't that signify that these calculations are garbage, i.e., the web forces are in reality completely different, and the top and bottom chord forces are slightly off?

The design of the truss plates for web to chord is completely incorrect as a result?

Or am I completely not seeing that these calculations are indeed correct, because the truss plates H1315 and H1014 are relatively large?

These truss calculations, for some reason, do not identify each member and what axial force exists in it.

 

[AELLC]

The entire gist of this thread seems to be applying to other truss softwares also. I am checking 3 other jobs in depth, and finding the same problem.

Also, occasionally, there is a girder here and there with totally wrong loads input to it. I can see which ones because I estimate the girder reactions in my automated calcs anyway, and I am writing down reactions on the hardcopy of the truss mfr's layout.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[dhengr]

AELLC:
Maybe we’ll have to start doing a cursory check/review of the shop drawings, particularly when we relegate half of the structural engineering to someone else who doesn’t share our responsibility. Most truss manuf’ers. are selling a commodity, so you better know what you want and need. This is particularly true of any roof trusses which are at all out of the ordinary, and particularly true of some of the crazy roof framing schemes we see these days. If it’s a 28' long std. roof truss 2' o/c, they seem to know what they are doing, beyond that you better have a look-see. They don’t give a rip where the loads come from or where the large reactions go, that better be your job. Have they even provided blocking in their girder truss so you can attach hangers for the trusses which frame in? My experience has been about like Charliealphabravo’s, I know a couple truss manuf’ers. I can trust to do something special for me, and on the engineering aspects it’s pretty much dealing directly with someone from Alpine or Mitek.

 

[AELLC]

"Have they even provided blocking in their girder truss so you can attach hangers for the trusses which frame in?"

Not really needed - the bottom chord is always at least 2x6, to match hanger nominal size, and if the number of plies is greater than one, then full listed hanger value applies. LUS26, MUS26, HUS26, MUS28, LGUS26-3 etc.

The problem is getting them to provide the above exactly as noted on plan

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[AELLC]

All the above seems (now) to be an error with this old Alpine software.

I am looking at 3 other projects that use Mitek software, and the truss reactions all seem to be applied to the girder's bottom chord, correctly.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.