Decks, Patios, Porches and Docks - Bridge

I have a 40 X 100 ft pond next to my home and wish to build a walking bridge across it. I have 6 12ft 6X6 treated beams and would like to join them together to make the two span rails. The span doesn't have to be the full 40 ft as the water is down about 6 ft below grade, so I can set the span below ground level and have steps down to the bridge.

How do I best join the beams together Half joint, butt, scarf joint etc?

Grateful for any advice.

Thanks.
Madi's Marsh

Madi's Marsh,

When planning the width of the bridge and basing it on the width of the pond, because of the amount of work to build it you should be sure that the level won't come up so as to flood it out.
To go that wide with a 6x6 would need to have a support structure under the timber, much like how a rafter is made.
A 6x6 is no where near heavy enough to carry the weight by itself.

I went through the exact same thing as you.

I live behind a marsh where waterfowl nest that is ringed by a dike.
For the first four years that we lived here, we couldn't access the dike from our property due to a 50' waterfilled ditch. We had to travel a half mile to an access point and then go a half mile back to get to the back of our place.
It took me a few years to come up with a solution, mostly because of how hard it is to get engineering information.
Any that is out there is either too complicated for a novice or too vague to be usefull.
Liability is the reason.
I even was prepared to purchase two "silent floor" housing beams but the mfr wouldn't sell them to me when it was discovered what I was doing with them.
A neighbour, spanned the ditch with two, 50' telephone poles. They were 18" at the butt and about 6" a the tip. One cracked when a snowmobile went over it.
I settled on some 22" deep metal truss rafters, welded end to end to make a double run, 46' long.
The engineering consisted of building one, securing it and myself and a weighty friend, jumping in the middle of it and noting the deflection.
After this amateur engineering I successfully built the bridge structure out of steel with a 4' 2x6 pt deck and metal posts supporting a 2 x 4 handrail.
It's a source of much pride!

So, a rather lenghty story I know, but told to highlight the fact that your bridge will take some carefull planning.

Mind you..................... if you can put supports in the middle, it's a whole different story.

Thanks Greg.

The 6x6s were plan B. Plan A was a failure which I just finished tearing out. Ran steps down both sides of the slope and then dug posts as deeply as I could and then pounded them in a far as I could. Used 2X10s to build a 12 ft span between the posts over the channel (the pond was an hourglass). Almost all my 60 acres is pure beach sand except for the pond which was dug in a pocket of clay. End result, the Wisconsin frost heaved the posts and my bridge twisted 6 ways from Sunday. After spending a weekend down in the mucky clay tearing out the entire project and swearing at myself for building it so well, I took my backhoe and dug out the hourglass, so now I have an approximate 25 foot span.

After the heaving experience and the comments my wife made about both my ability and sanity, don't want to further besmudge me credibility by trying posts again.

The pond sits right next to our house and I'm bulding a 20 ft waterfall down the slope on the one end, so the bridge was to be a viewing point for that.

Guess I need to ponder a bit and come up with Plan C.

Thanks for preventing another opportunity for my wife to capitalize on.
B.

Madi's Marsh,

Ya, I know what you mean.

I wrestled with my bridge planning for over three years before I came up with what I have.
A bridge with a centre support is a piece of cake if you can lick the heaving problem. You would have to dig past the frost line to do this.
I gave up on the centre support idea because of the heaving problem but also for the fact a freespan is much more pleasing to the eye and simpler to install.

Before getting my steel rafters for free, I was seriously considering copying the design of those engineered floor trusses.
All it takes is two 2x4's with a groove cut lengthwise to sandwich a section of plywood.
My backyard engineering sense tells me that for this method a 24" web on two spans with a bit of bracing would be good for a footbridge .

There are quite a few ways to go with this though.
I'm sure as little as possible but how much are you prepared to spend on this?

Getting the metal rafters for free, I spent about $400.00CDN on a pressure treated 2x6 deck and railing and about another $400.00 on steel, bolts and welding supplies.
Next spring I think I'll spruce it up a bit and add a side rail and side stop to the deck.