Forum ProfileBack
Advanced

— Forum Scope —




— Match —





— Forum Options —





Minimum search word length is 3 characters - maximum search word length is 84 characters

Lost password?
sp_TopicIcon
Roof Truss Failures
August 9, 2009
5:49 am
Avatar
drp
Member
Members
Forum Posts: 411
Member Since:
July 8, 2006
sp_UserOfflineSmall Offline

[QUOTE]What''s that round thing near the corner at the joining part? [/QUOTE]A sch 40 "crosspipe". This is a heeljoint being researched and tested at Purdue. The bolts simply keep the wood in contact with the "crosspipe". It''s doing the same thing as the gang nail.

This is an older way of accomplishing the same thing;
[IMG]http://windyhilllogworks.com/Shop_files/rafternotch1.jpg[/IMG]

Think about the forces, see the similarity? Not relying on sideplates and dowels in shear. Just another way of resisting the forces.

A nail plate is good for about 80-100 psi depending on wood density. A .120 nail through 1/2" ply in single shear is good for about 50 lbs. One crude way to reverse engineer a truss would be to allow 2 nails per square inch of nail plate. The nails cannot damage the wood so it''ll take more area to accomplish the same goal. There is alot more penetration so I would assume the withdrawal numbers will be better. Add glue and it should shine.

Table R802.5.1(9) is yet another way. The rafter/ceiling joist is really a truss. The table specifies the heeljoint connection. How many times have you seen 2 nails there? Kinda makes me think the truss isn''t that bad by comparison.

August 8, 2009
11:47 am
Avatar
jdrobysh
Member
Members
Forum Posts: 1768
Member Since:
January 25, 2001
sp_UserOfflineSmall Offline

George -

I can agree with you in part. When there are obvious defects in the installation, yes the BO should take action. Not to rehash an entire old thread, if a truss is altered in the field then the BO has a duty to have the modification approved by an engineer, preferably the original Design engineer or a maufacturers'' staff Engineer.

If the trusses were mishandled during installation and the defect(s) are not readily apparent you can hardly blame the BO. There isn''t a Building Department I''m aware of that can afford to put an inspector at every job site for an entire day watching trusses getting set.

I have required contractors to get an Engineers'' sign off when I saw trusses being mishandled. I have also required bracing per mfr specs. Amazing how many contractors don''t bother with the bracing specs.

conarb - Just for the record, I am not aware of any truss failures as described in the OP in any jurisdiction I have worked for.

August 8, 2009
10:43 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline

Kilitact & AlabamaTide:

That was too much personal information.

August 8, 2009
10:00 am
Avatar
alabamatide
Member
Members
Forum Posts: 142
Member Since:
May 10, 2009
sp_UserOfflineSmall Offline

If being performed in the field, care should be taken not to blow the load whilst tightening the nut.

August 8, 2009
9:42 am
Avatar
kilitact
Member
Members
Forum Posts: 990
Member Since:
January 4, 2008
sp_UserOfflineSmall Offline

to tighten your nuts.

August 8, 2009
9:05 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline

What''s that round thing near the corner at the joining part?

August 8, 2009
6:13 am
Avatar
drp
Member
Members
Forum Posts: 411
Member Since:
July 8, 2006
sp_UserOfflineSmall Offline

Wood moves due to a change in moisture content, not heat.

Temperature moves moisture.

This is far from the first time I''ve heard this story conarb, you blame the trusses. I''m not sure, I don''t know whether the trusses were properly designed for the load and what the homemade trusses were designed for. You are referring to anecdotes, that''s fine but how much weight should we give it? There is simply not enough information to draw any real conclusions from.

You''ve referred to Elmhurst for several years. From what I''ve read of that code there it is not a good situation, it appears to be a rogue department. I think it should raise eyebrows, but to analyze and find the truth. They could be on to something, they may be nuts. Where is the engineering and testing behind that solution? Is it even attempting to do what you claim is needed?

The australian plate looks the same, it is light guage and has little teeth. They state there is a manufacturing problem. That is all I know, not much to go on. I''ve asked if others see a rash of failures, what has been the response? It seems to be more related to construction problems than problems with the product as a whole.

Does light framing burn faster than heavy timber? Sure. We are apparently comfortable with light framing. It is economical and has passed what we consider to be the appropriate testing. I don''t have a problem if you wish to go through the process of changing those standards. I don''t believe the gang nail is the problem there. Cover the nail plate and I''ll lay odds the truss will collapse in a fire in pretty much the same amount of time.

I worked for a few years in the furniture industry. During that time we were testing our joinery. I built a test bench, glued, nailed and stapled thousands of samples and sheared them. I also built a 150 degree hot box and tested samples. There is not an adhesive commonly available at the building supply that I''m going to stand up and call structural for field application. We had hydraulic presses to control clamping pressure on stock machined lumber and couldn''t get what I would be comfortable calling a reliable structural joint. Freshly, accurately, machined lumber glued with a structural adhesive under controlled conditions can produce a reliable joint. Add heat, the titebonds and the like turn to a smeared mess that fail with very little wood tearout. If a joint is made with fasteners designed to take the full load and the adhesive is gravy, I''m comfortable with that.

As an aside glues are natural products, adhesives, synthetic. I can disassemble a glued fiddle with nothing more than a hot knife.

In these types of joints I would rather see many smaller fasteners spreading the load across a relatively large area of the relatively weak wood than say a few grade 8 bolts that will surely not fail but will greatly overstress the wood in the area of contact. The gang plate is using this thinking, distributing the load. I''m open to other methods.

The NDS gives allowable loads of various fasteners with plywood side plates. That''s fine, don''t destroy the wood in making that connection. I''ve used trusses that have some serious stresses in the joints. I''m not sure whether I could adequately connect them this way, maybe an engineer will chime in.

I think you know my leanings, I ordered a large gluelam and heavy timber for a roof this week however I do realize there are many ways to the top of the hill, if it works I''m fine with that.
My suggestion is to show us something from credible research and testing that shows a great reason for alarm. I would be much more inclined to give weight to something from the FPL or a university than a contractor, inspector, or the media. Or do it the American way, build a better mousetrap. If a plywood glued and nailed truss is shown to be superior in independent testing I think you''ll be able to gain market share.

Not sure if you''ve seen the research on this type of connection, I quickly mocked one up in timber but the research was done down to dimensional sizes.
[Image Can Not Be Found]

I trust that was a Freudian typo... Untied States 😀

August 8, 2009
12:13 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline

I''m not sure if it is a cover-up but "industry down-playing", maybe.

August 7, 2009
9:04 pm
Avatar
constructionarbitrator
Member
Members
Forum Posts: 3713
Member Since:
January 12, 2003
sp_UserOfflineSmall Offline

[QUOTE] "DRP said:" Evidence?...or biased anecdote? I''m not sure. Do we ban cars because they crash so easy?[/QUOTE]I started out this thread by asking three questions:
[QUOTE]1) Has this been covered up in the Untied States?[/QUOTE]This is the first I''ve mentioned my experiences with trusses and my return to hand framing roofs, I laid the problems to a bad truss fabricator so I bit my lip and corrected my problems out of my own pocket. Then I see AHJs passing labeling requirements, [URL=http://dickseibert.com/truss_labels.pdf]like New Jersey[/URL], San Francisco, and a proposed national standard becasue of collapsing trusses in fires, in effect allowing trussed homes to burn to the ground with possible insurance ramifications. When I happened upon the Australian experience I had to wonder about the possibility of a cover up in the Untied States.

[QUOTE] 2) What steps, if any, has the truss industry taken to eliminate the problem, the pictured gang-nail plate looks the same as what''s being used today.[/QUOTE]I proposed that maybe it hasn''t been a cover up, maybe the problems have been corrected by the industry, if so why aren''t we informed about it?

[QUOTE] 3) If the good CBO in Elmurst could see this problem and address it in a code amendment, shouldn''t all CBOs address this very real problem, isn''t it malfeasance if they don''t?[/QUOTE]The fact that at least one city in the nation has addressed the problem should put all on notice that something stinks in Denmark.

The car analogy isn''t on point, it would not require banning all trusses, just require them to be fit and safe for the purposes intended like all code requirements. If we can require a building to built to withstand earthquake and snow loads we can certainly require trusses to withstand withdrawal and collapse in the event of fire.

August 7, 2009
8:56 pm
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #10

DRP: Temperature can effect wood and can effect moisture content in wood.

There can also be multiple compounding issues all the way down to ground and such that you may not visually notice because no major cracking occuring in drywall or noticable warping.

August 7, 2009
6:47 pm
Avatar
drp
Member
Members
Forum Posts: 411
Member Since:
July 8, 2006
sp_UserOfflineSmall Offline
sp_Print Print Post Post #11

[QUOTE]Like Elmhurst did, amend the code to require plywood gussets applied over the plates? Shouldn''t every jurisdiction be doing that with the evidence at hand?
[/QUOTE]Evidence?...or biased anecdote? I''m not sure. Do we ban cars because they crash so easy?
I''m still waiting to see what Elmhurst is attempting to do and what due diligence is behind it, it sure seems like an arbitrary, common sense, "do it because I said so" law. Again, no connection is specified and it is hiding the plate from inspection that some seem to feel is neccessary. Is there independent testing to show that whatever they are attempting to do works? If there is a problem I''m not sure I agree that this is the path to correcting it.

The Australian example seems to be a run of bad plates. Does a manufacturing defect condemn an industry? We are learning creatures, absorb the lesson and move forward not backward. If twisting is the problem, that is slope of grain related, perhaps tighten the grade requirement there, visually slope of grain can be tough to detect though, alot slips through.Wood moves due to a change in moisture content, not heat. If the moisture content needs to be lower for that hot environment to decrease movement then that might be worth exploring. The FPL does test these things, have you written them about your feelings and seen if the evidence corroborates your anecdotes? It may well.

I''m not opposed to plywood or osb gusseted trusses. How are you going to handle QC? Is it a shop produced product with third party oversight or a field built product? If the problem and solution are legit it looks like a wide open market niche. Conarb Strongply Truss Co.

August 7, 2009
1:24 pm
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #12

lol. That would not be good news for the AHJ.

August 7, 2009
1:20 pm
Avatar
george roberts
Member
Members
Forum Posts: 1722
Member Since:
December 29, 2001
sp_UserOfflineSmall Offline
sp_Print Print Post Post #13

no truss system is installed correctly.

Then the AHJ is at fault.

August 7, 2009
11:47 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #14

I would say amendment but not just plywood plate over the metal plate but also include an "engineered" solution that addressed the plate issues. It should however consider any other conditions of the truss design and not cause a problem in overall operation of the truss.

August 7, 2009
11:44 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #15

Should they and do they are two different things.

August 7, 2009
11:36 am
Avatar
constructionarbitrator
Member
Members
Forum Posts: 3713
Member Since:
January 12, 2003
sp_UserOfflineSmall Offline
sp_Print Print Post Post #16

[QUOTE] [b]"Rick said:"[/b] CA: Your only solution is code amendments or law amendments (local ordinance) banning the use certain types of metal plates that are prone to failure[/QUOTE]Like Elmhurst did, amend the code to require plywood gussets applied over the plates? Shouldn''t every jurisdiction be doing that with the evidence at hand?

August 7, 2009
10:18 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #17

CA: Your only solution is code amendments or law amendments (local ordinance) banning the use certain types of metal plates that are prone to failure. This is all you can do. Your responsibility is to review the plans in accordance with all applicable code and laws (local, state and federal) in your jurisdiction in which the project is being reviewed by you.

That responsibility is outlined in the code. Because you are not suppose to be designing/engineering the building or its components while on duty as the B.O. If you want to design, you do that on your off-hours.

Then responsibilities in that article would generally apply.

August 7, 2009
10:10 am
Avatar
rickastoria
Member
Members
Forum Posts: 1174
Member Since:
January 5, 2007
sp_UserOfflineSmall Offline
sp_Print Print Post Post #18

Boo1:

I agree. In the case of Oregon where exemption applies also in the engineering act - "Truss Designer" would mean both licensed and unlicensed person designing truss. "Truss Engineer" means a person who is a registered engineer who works for a truss manufacturing facility or is an independent engineer who was responsible for the design. In practice for purpose of distinguishing the two - Truss Designer would be a person not registered in the state in which the project is to be built (for example - lets say Oregon). If registered in Oregon, the title "Truss Engineer" would be referred to that person.

When we talk about truss manufacturer, we talk about the company responsible for the construction of the truss in a preconstructed/pre-engineered fashion.

As a building designer (not registered architect or engineer) - I have the Building Designer responsibility and if I design it - I have the Truss designer responsibility as well except for maybe the assemblage but have responsibility to review assemblage.

This article presents a nice break-down. It can be articulated to Oregon with a few minor adjustments and in Oregon - there is no "registered building designer" except for an Architect or Engineer as both can be consider building designers.

I could adjust it for Oregon and other state but for the purpose of the document - Building Designer (or Building''s Designer) shall refer to both unlicensed and licensed RDP.

It is generally legal to use "truss designer" title for designing trusses for use in exempt buildings and not require a license. It however, has to be associated with such projects.

In case of one or more unlicensed persons designing for the exempt project, the tasks could be broken down and title usage is adjusted appropriately. Say I design the trusses and another person design the house. You get the idea. I agree predominately with the responsibilities listed.

Boo!, thanks for sharing that.

August 7, 2009
9:30 am
Avatar
constructionarbitrator
Member
Members
Forum Posts: 3713
Member Since:
January 12, 2003
sp_UserOfflineSmall Offline
sp_Print Print Post Post #19

[QUOTE] [b]"John said"[/b] What level of responsibility should the BO bear? [/QUOTE]I don''t know, the system is wrong, lightweight trusses worked with plywood gussets, truss plates gained approval, but wood twists in time, when the wood twists the plates come out. The problem is in the approval process, so the BO is approving somethings he knows are going to fail over time.

Much is made of the poor quality of labor today and that''s very truss however, not enough is made of the poor quality of materials being foisted on the industry in the interests of first affordability, and now green building and energy efficiency.

August 7, 2009
9:02 am
Avatar
jdrobysh
Member
Members
Forum Posts: 1768
Member Since:
January 25, 2001
sp_UserOfflineSmall Offline
sp_Print Print Post Post #20

conarb -

What level of responsibility should the BO bear? He didn''t design it, didn''t fabricate it, ship it or install it. Simply verified it was what it was supposed to be - a ministerial act. No ''special duty'' has been created. The BO did his job. Someone else dropped the ball, they''re to blame.

Had the BO signed off on it without proper documentation/inspection there may be a case for malfeasance, but lacking that you''re barking up the wrong tree. How many BOs are being sued over asbestos? None that I''m aware of.

U B -

I sincerely appreciate your disillusionment.

What really needs fixing is the quality of workmanship and level of integrity of many (NOT ALL) on the construction side. The manufacturers will honor their warranties for the things they can control - materials and assembly defects.

Once the trusses leave the factory the mfr has virtually no control over the handling and installation of the product. Most of the problems I have seen are defects in handling and installation.

The responsible party becomes the contractor and/or DP. Sometimes the lumber yard delivers them badly, but the contractor or DP should flag them and send them back if improperly delivered and the lumber yard won''t make that mistake too often as it gets expensive.

If, as a code official, you have reason to believe there are defects - be they manufacturing, delivery or installation related - you have every right and the responsibility to de-certify the offending components.

Remember, the mfr WANTS their product to work properly. The DP wants his design to work.

If I were to install plumbing materials with duct tape and crazy glue and the system leaks, is that the pipe manufacturers fault? Hell no! It''s mine.

If someone mishandles an engineered wood product we can''t hold the mfrs feet to the fire. Now if that truss has a punky piece of crap web member that slipped thru quality control, different story, different ending. That IS the mfrs responsibility no matter what else may be wrong.