Sagging prefab wood Girder Truss on custom home under construction 3

[AELLC]

I am the EOR for said house. When the concrete roof tile was stacked on, a girder sagged badly, probably big mistake by truss co.

They sent me a repair method for my approval, but to me it looks bogus. This just happened late today, and I will study it more closely tomorrow.

My question- who is responsible for what here?

 

[AELLC]

ps

I meant, if I suggest what I think is a better repair, that shifts liability to me. So what to do?

 

[Ron]

AELLC....just reject it as insufficient and have them re-submit a different proposal. Keep rejecting until you're happy with it. You don't have to design the fix...they do as a delegated engineering function.

 

[AELLC]

Ron,

Thanks, that sounds like a smart plan.

 

[Triangled]

Agreed

 

[AELLC]

I looked at the truss calcs. The reactions show only about 1/4 of what I calculated. I thought truss software was very automatic, I wonder what happened?

 

[JAE]

I thought truss software was very automatic, I wonder what happened?

It isn't the software - it is the user of the software.

So many of these pre-fab'd wood trusses are punched out by local "techs" who then send the print-outs to some PE in a far away land who seals them.

I once investigated a hog barn in northern Iowa (in the middle of winter) where the roof had collapsed under unbalanced snow on a gable roof.
Windward load was about 5 psf. Leeward roof snow was about 3 ft. deep. The truss shop drawings were developed with a 20 psf live load.
Ground snow in this area was about 45 psf so I think someone didn't know what they were doing.

 

[AELLC]

They had the loads exactly right. I thought truss software functioned like RISA FLOOR to automatically figure the load from each truss connected to the girder in question.

But it is true, you would think the tech and the PE would have noticed something was not copasetic, more like septic.

 

[AELLC]

I even gave them a few hints on my drawings, like bottom chord of this girder shall be(3)- 2x8 minimum, post at right is a 6x8 DF-L#1, post at left is (4)- 2x6 DF-L#2, ftg at right is 3-6" sq, ftg at left is 3'-0" sq.

 

[XR250]

I am surprised the software did not take care of it.
Sounds hard to fix
Big column in the middle of the family room is an option :>

 

[ztengguy]

Keep us posted, and how soon they try to blame you, for not catching it at shop drawing approval.

 

[AELLC]

The fix so far is threading a 5-ply girder thru the stub trusses about 11" into the span of the common trusses, and they have this idiot detail to cut the stub trusses web diagonal and put in truss hangers - here is the detail

 

[AELLC]

zteng,

There was no shop drawing submittal.

 

[AELLC]

There also must be something wrong with the way their truss software calculates deflections for their new girder truss.

When I try a glulam beam that is same depth, 2'-4", and almost same width, 6.75" compared to 7.5", the deflection is only slightly less than theirs.

Their new girder is 33' long, 5-ply with 2x8 top and bottom chords. I would think their girder truss would deflect much more because I believe the area moment of inertia would be calculated as including only the top and bottom chords.

Is this the correct logic?

 

[ztengguy]

Is the right side of the truss open as they show? Can a flitch beam be made out of the truss?

 

[AELLC]

No, I will hand draw a version of what the stub truss is now, give me a few minutes.

They have not suggested a flitch plate.

What they are suggesting is the absolutely cheapest repair, however bogus. They should consider themselves lucky no one was killed, and spend a little more money.

 

[AELLC]

Here it is.

My new scanner is malfunctioning, I think it is leaning to the right.

 

[AELLC]

Should I inform a supervisor at the Bldg Dept who approved all this?

Their plans checker reviewed the truss calculations w/o any red flags. I never saw them because that is the Bldg Dept's policy. The girder in question was in conflict with a note on my dwgs saying it should have had a minimum of (3)-2x8 bott. chord.

Their building inspector never red-flagged the installation of the girder. It is 33' long, with 44' span trusses attached to one side and a lesser girder truss attached to it on the other side. It was only 2-ply, 2x6 chords, and I had massive posts supproting it, and very large footings, relatively, for a one-story house.

The roof live load here is only 20 psf construction, it can be reduced to the 12 psf minimum per trib area, the roof pitch is 4:12, and the girder was unusually shallow because it was a hip roof condition located only 8' away from the parallel ext wall. The dead load is substantial - about 22.5 to 24 psf with concrete roof tile.

 

[MileyDiley]

This piqued my interest because I remembered a project we had with a similarly long girder truss. However, I had nowhere near the supported span that you have (hell, we very rarely let the single span truss go over 40' and you have 44').

Anyway, the truss I had was also 33' long, but it supported 28' long trusses for ~10' and then one end of a continuous 40' span for the rest. The intermediate bearing on the 40' supported trusses was 28' from the girder truss, so I have significantly less load than you.

That girder was designed as 4-ply with 2x8 DF-SS bottom chords and 2x4 top chords.

 

[structuralsteelhead]

Odd you were not able to review the truss package prior to submittal for permit. I am required to write a letter of review and compliance of truss packages and calculation when submitting to some review agencies. Even so, I still put the earnest on the truss manufacturer to make things right, without doing the design for them, when issues arise during/after construction.

Not to pass the buck, but my shop drawing review stamp does say, "reviewed for general design conformance." What does your shop drawing review stamp say? Let's face it, for a residential all wood framed project that we've been awarded (which means we've already undercut our peer's "how much are we willing to lose on this one, bid") we as structural and/or civil/structural engineers, would blow 10% of our design and detailing budget on a fine tooth review of a truss calculation submittal even if you had the chance. I wouldn't dream of getting too involved with the design of the trusses unless that is your specialty, and further, you're familiar with the truss design software the truss engineer/designer is using. I check lengths, pitch, drag forces, top and bottom chord loads, and girder loads, but I am still not the designer or producer of the product. You're shop drawing review stamp is not a statement that the engineer who has stamped the truss package that he and/or a technician has set up has made no mistakes. You're relying on this engineering subcontractor's specialty, hold him to it, be critical of it, but do not design it unless this is within your area of expertise (yes it's within your engineering discipline, not the same thing).

Building department plan checker/reviewer's depth of review directly proportional to work load and/or third party out sourcing. Regardless, his/her responsibility can stop at making sure you've got a professional stamp on the required submittal documents. His/her shop drawing stamp might only say, "Has a stamp on everything". In other words, it's not his/her design specialty or responsibility either. Yes as the EOR, you are forever linked to the structural performance of the structure you are in responsible charge of. When dealing with third party, subcontracted,"by owner" professional engineering and product manuf. supplier companies, as you would review his original shop drawing for design conformance, I suggest you do the same for their repair detail, and hold them, per their contract with the homeowner not you, for the "performance" of their supplied product and this repair along with it.

That said, at length, my apologies!!!!!!............provided you take a peak at this 5 panel truss print out and check loading, span, member size/species, etc., there is no user error in the retrofitted truss design input data which another professional engineered regularly engaged in the design of trusses has stamped, the hanger "and don't forget lateral ties" are properly sized, the retrofitted truss bearing panel point connection is addressed, (they may sister a parallel web member below to resolve chord/web bending moments) and all looks reasonable, wouldn't this repair detail "appear" to be in general design conformance? If installed and the performance is not within acceptable tolerances, unfortunately, they may have to make another one.

(Meanwhile, while you may be a good engineer, you'll have to ask yourself how good of a businessman you are when it comes to receiving compensation for your time effort fixing the truss designer's error. Sorry I turn this topic into a money issue, but we must defend our right to compensation for our time and effort, especially when it is required due to errors, omissions, and changes of others. I hate seeing our profession get beat up, especially when it comes to owner builder residential projects. While I studied both Architect and Engineering in college and love home design, I rarely get involved with residential projects anymore, unless designed, managed, and permitted by a registered Architect. I don't even come close to getting most home projects I bid, because I am truly realistic about the time and effort involved. Franly, I don't know how some of my peers survive. There seem to be less and less home design and construction overseen by registered Architects these days and owner builder clients rely on the structural engineers to help manage and permit their projects bleeding us dry in the process while they laugh all the way to the bank) Second apologies for the rant,....up almost all night completing my last custom home design for awhile,...while I love what I do most days,...I do need to make some money. Strictly commercial for awhile again until the right residential project comes along.