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Wooden truss splice connection

Wooden truss splice connection

Wooden truss splice connection

(OP)
Here is my situation

While doing repairs on a condo complex, I found an exterior deck that was dropping, with a large separation of the vertical siding where it met building.

Opened wall and found double trusses which are cantilevered out of the side wall of building, at the end of the trusses is a joist hanger on which a double 2x10 beam is connected, which in turn has all the deck floor joists attached.

The truss is sheathed and sided, and topped with a cap to form a half wall.

Truss has suffered major water damage and rot, top chord is cracked and seperated, cross member and bottom chord crumbing. Apparently this type damage has been found before on other decks in complex.

I was told by the management that the previous repair has been to splice in a new section of truss, and was given a sheet explaining the procedure.

I am curious for an expert opinion of the method recommended for the splice.

End of new trusses are butted to the solid end of old trusses, then a steel plate is sandwiched between the trusses and secured with two ½” carrage bolts on each side of splice.



I am wondering if a stronger splice could be made. Possibly instead of just butting the whole truss, make a long lap joint using glue and nails, then using a steel plate and bolts where the butt ends meet.





Any help would be greatly appreciated.


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RE: Wooden truss splice connection

Did this fix come from the truss manufacturer, or another structural engineer, or????????/

If it came from the truss manufacturer, I would go with it...

That being said, how did they solve the rot/water intrusion problem so that it will not happen again?

Mike McCann
MMC Engineering

RE: Wooden truss splice connection

(OP)
Not sure where the fix came from, sheet was dated July 2002 with no name or seal.

Just seemed to me that it's putting all the stress on two holes 4 and 8 inches from the end of the cuts.

I was hoping for a better way to splice the truss, something stronger.

However, I know that the perviously repaired decks haven't failed.

I called a local truss company to order replacements, but they offered no engineering help for repairs, only new design.

As to the water problem :

Problem was due to the vertical siding on the walls being cut even with the top of the wall and just having a 3/4 inch board as a wall cap. Water ran under the cap and behind the siding. Complex was built in the late 70's, early 80's, so has had a lot of time to suffer damage.

Problem was fixed by having aluminum flashing bent to cover top of wall and hang over siding an inch and a half, then capped with a 3/4" PVC board held with stainless steel screws. This was done gradually over the last ten years, roughly 400 decks.

While this was an effective fix to stop water infiltration, as I noticed even the broken truss was dry, it doesn't do much for already compromised structure within the wall.

Also, not all decks are truss supported, most are supported by a steel I-beam with joist hanger welded on. Since those walls just sit on the I-beam it isn't a support issue when they rot. Trusses are only used where deck half wall extends out from the side wall of the building.




RE: Wooden truss splice connection

(OP)
Truss company now refuses to make me new trusses since I plan to splice them.

Not only do they leave you in a hole, they throw dirt on you.

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RE: Wooden truss splice connection

You need to go back to them and restate you case, asking for their recommendations, rather than stating your solution from the outset.

Obviously, they feel the liability is not worth the risk, and, it seems to me from your post, that they may look upon you as a "loose cannon" of sorts (no offense intended). You really need to defuse their concerns, real or imagined.

Mike McCann
MMC Engineering

RE: Wooden truss splice connection

Generally, for relatively small members I found that it is better to get a field press and make splices with the usual truss plates. If you work with a truss manufacturer on the repair design to be sure they know is is designed and installed competently, they should work with you, and let you buy plates for field installation. Some brands of plates are easier to get, but be sure they are rated for structural trusses (not the ones from the hardware store.)

It takes a lot of nails to get full 2x4 strength. Finding and properly using a structural-rated glue is problematic, as are screws. Bolts are usually better, so run the numbers before you decide. I would shy away from carriage bolts and use hex bolts and washers (or use steel plates on the outside of the wood, to avoid crushing the wood.)

RE: Wooden truss splice connection

Looks like this is a fairly old thread, and I just stumbled on to the forum.

I've been in the truss business a long time. When someone comes to me with a situation like this, I tell them they need to get an engineer to design the splice connection. Our software does not have the capacity to do that.

I'm happy to work with an engineer to come up with a design & splice detail, and offer any help I can. But no way would I design one myself.

Are you aware there's no statute of limitations on engineering? If you design a splice with some sketches as were presented above with no calcs to back them up, you'd be liable for that design as long as the building existed.

The splice needs to be designed, not just done based on some sketches you post on the internet.

RE: Wooden truss splice connection

(OP)


Quote:

If you design a splice with some sketches as were presented above with no calcs to back them up,

The splice needs to be designed, not just done based on some sketches you post on the internet

I wasn't designing the trusses, I had the existing trusses to take measurements from.

All I wanted from the truss company was to fabricate duplicate sections, that I could then splice into the existing trusses.

Also I am at a loss to see why this is so complicated, from an engineering aspect.

If you have an existing truss, and replace part of it, solidly splicing the members, how would the loads be carried differently?

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RE: Wooden truss splice connection

I wasn't saying you're designing the truss - Just the splice.

The splice connections would have to be designed based on the tension or compression at the splice location, as well as designed for bending moments.

So it isn't simple at all.

RE: Wooden truss splice connection

RonTheRedneck:

As for the liability issue, it is not as long as the building exists where I am. It's only for 6 or 7 years here.

As long as the building exists seems totally unreasonable to me, especially considering problems encountered as the building ages of which you have no control.

Mike McCann
MMC Engineering

RE: Wooden truss splice connection

The engineering doesn't change as a structure ages. If the engineering is flawed, you're screwed.

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