Large wood truss collapse - Lansing, Michigan
Large wood truss collapse - Lansing, Michigan
(OP)
I have seen two major wood roof truss collapses in several years in this area, and I wonder if residential wood trusses should not be built in large sizes. This is the type with 2x4 and 2x6 using formed shear plates with projecting spikes. I suggested using steel trusses as a replacement, and the plant mgr opted for wood, even with no price difference. (???)
The latest collapse was at a state government building. The span was about 150 feet. The failure was in June, not during the winter snow load condition. Any comments?
The latest collapse was at a state government building. The span was about 150 feet. The failure was in June, not during the winter snow load condition. Any comments?






RE: Large wood truss collapse - Lansing, Michigan
DBD
RE: Large wood truss collapse - Lansing, Michigan
RE: Large wood truss collapse - Lansing, Michigan
thread507-127734
www.SlideRuleEra.net
RE: Large wood truss collapse - Lansing, Michigan
The thing most often missed is the lateral bracing of the individual web members - they are long and slender, and truss manufacturers claim that it is the role of the EOR to design them - their design sheets just show where the bracing is needed.
(This came as a surprise, certainly. Why it should be the EOR's responsibility is a mystery to me, since this bracing is entirely within the truss system envelope, and we have no idea when we design a project what will be needed. I think it is just a way for the truss manufacturers to shed some liability and cut their own costs, even if it drives the total project cost up. They can supply members needing bracing every two feet, then palm the design, purchase and installation onto somebody else's budget)
RE: Large wood truss collapse - Lansing, Michigan
RE: Large wood truss collapse - Lansing, Michigan
When we do a truss drawing, we indicate a truss bracing system that is our estimate of the truss designer's requirements. We put a big note next to it stating that the bracing system indicated, is to be assumed by the truss manufacturer.
When the truss calcs are supplied for our review, we correct not only their loading but their bracing assumptions. The bigger companies we deal with now tend to get it right but it is still hit and miss...
RE: Large wood truss collapse - Lansing, Michigan
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
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RE: Large wood truss collapse - Lansing, Michigan
Thanks for your response. Just to clarify your note, are you speaking from the point of view of the Engineer of Record for the project, or the Specialty Engineer that reviews and seals the truss manufacturer's drawings?
RE: Large wood truss collapse - Lansing, Michigan
I confess - I learnt from experience.
RE: Large wood truss collapse - Lansing, Michigan
As your truss span increase the magnitude of the loads which need to be resisted increase significatly. When you are dealing with heavy timber trusses with spans over 100' you need very knowledgeable and experienced designers; because all the design problems which you have to deal with in normal truss design become more critical with the longer spans.
RE: Large wood truss collapse - Lansing, Michigan
RE: Large wood truss collapse - Lansing, Michigan
I claim no special expertise here. My exposure to such trusses is limited to picking through the ruins and making makeshift repairs (including a replacement truss of ~30 foot span) after a couple of hurricanes.
Given how wobbly the individual trusses are without bracing, I'm just amazed that anyone would even try to make them that long. How would you handle them in such a way as to not damage the joints or the members during transportation and erection? If you did accidentally apply enough bending moment to crack a member or partially pull a plate, how would you know? If someone else damaged it and didn't 'fess up, how would you know?
Mike Halloran
Pembroke Pines, FL, USA
RE: Large wood truss collapse - Lansing, Michigan
I think it is evidence of regional complacency in wood construction. Michigan has been a source of lumber in the midwest, and the locals still tend to favor it over steel, even in large projects.
In the aviation accident arena they call it:
CONSPIRACY OF COMPLACENCY.
RE: Large wood truss collapse - Lansing, Michigan
This building is located down the street from my parent’s house, and I happened to be visiting the morning it collapsed. Luckily, it was a Saturday and no workers were in the building. I have several photos of the building just after collapse and during demolition of the collapsed portion of the building, which was done that day. If anyone is interested in the photos let me know (I will need a site to post them on).
The first thing I thought when I saw the collapsed building was the design of the trusses looked very unconventional. The trusses were about 25’ tall. The top 10’ or so each truss was a typical prefab truss and below that was a lattice of vertical members that looked liked they were hand framed and not properly braced. In addition, the bottom chord looked like it was only a couple of 2x4’s. I have no expertise in truss design, but what I saw did not look like a sound design.
Plasgears…are you aware of any report on the cause of collapse?? This happened during the summer and I have yet to hear anything in the local news about the cause.
The contractor who built this building is very big in the area…I hope his other buildings with roof trusses are being review by someone.
RE: Large wood truss collapse - Lansing, Michigan
Signing up for an account and uploading the images, if the files are not too big, is easy. Then you can post the link here.
www.SlideRuleEra.net
RE: Large wood truss collapse - Lansing, Michigan
SRE – That for the hosting site…very easy to use.