What kind of wood should I specify for deck repairs 1

[jimaitken]

I have a wooden bridge that my client is going to be repairing. The superstructure is glu-lam beams (6' o.c.) with a wood deck that consists of 2x4's laid on the narrow edge over the entire length of the bridge. The deck is deteriorting and the client wants to replace decking in kind to retain the aesthetics of the existing structure.

Is there a specific type of wood or treatment for new wood would work well in this application? The deck leaks like a sieve and the the wood will need to be able to withstand being continually soaked every time it rains.

Any suggestions would be appreciated.

Jim

 

[hokie66]

Where are you located and what is available? In Australia, we would use a Class 1 durable hardwood such as forest red gum or ironbark, but I am probably not speaking your language. If you are using a treated softwood, need to specify treatment suitable for the application.

What are the the glulam beams made of? Are they in good condition? That might give you a clue as to what to use for the decking.

 

[jimaitken]

Hokie66
I am in Atlanta, Georgia, USA.
We use a lot of southern pine, but we believe that the original wood (at least the beams)was hardwood brought in from the western US. We have no existing plans or information about the bridge other than what we have been able to observe through measurements and non-destructive testing.

The bridge is about 30 years old from what the owner can tell us. The glu-lams are in generally good condition. There appears to be some minor defects, the water leaking through the deck is probably not doing the beams any good but they seem to be holding up well.

We are also trying to determine how cost effective the deck repair is at this point in the life cycle of the bridge. Is a deck repair only delaying full bridge replacement by a few years or could we get another 15 to 20 years out of the structure? In your experience what would the design life be for a bridge of this type? Thanks.

 

[hokie66]

If the beams are in good condition, no reason to replace the whole bridge. There are plenty of timber bridges in Australia that have been in service for 80 years or longer. I suppose the question should be what is the intended future life of the bridge. Knowing that, you can plan any repairs or protection of the beams and select the decking material from what is practically available. As to the hardwood which would have been used in the original deck, I don't think there are any native North American timbers which have the durability of the heartwood of some of the Australian hardwoods.

 

[hokie66]

jimaitken,

One more thought. With decks like you describe, it is desirable to provide some clamping force by installing rods through the members. Helps with load sharing and decreases water penetration.

 

[jimaitken]

Thanks Hokie66.

I appreciate your help. I am making the recommendation to replace the deck due to its condition and to monitor the structure with a regular inspection program. I like the idea of clamping the bridge deck members and will make this recommendation as well.

Jim

 

[RARWOOD]

Contact the US Forestry Service or the Forest Products Lab in Madision Wisconsin. Both of these organizations have done quiet a bit of work on modern timber bridges. You could also contact AITC. In adition there should be ASHTO requirements that need to be met.