# Temporary bridge question



## CliffyJ (Apr 29, 2009)

Hi friends, sorry for being so absent over the last 6 months. 

A question or two about a temporary bridge method. 

As backstory, I've been (s-l-o-w-l-y) pouring concrete roadbed, leaving gaps for future trestles. The current temp bridge is the gray plastic board, in the upper left. I place the board in the form, blocking off the form beneath the board (about 3" inward). This leaves a step for the board to rest in, which will become a pocket once I slap some concrete against the sides of the board's ends (haven't done that yet). 











The same section, with board removed, and another section being formed up.











Anyway, the plastic board isn't going to work well as the actual temporary bridge: too much sag, requiring too many supports. The problem becomes larger for the big bridge I'd like to form up for (later in the summer), which is on a long curve. So that rules out a simple span of pressure-treated board.

With all that said, here's the idea that I would be grateful for opinion on. I'm considering 3 layers of 3/8" tile backer board, bonded together with some sort of mastic, supported every... I don't know, 30"? That way, I could cut for a long curved bridge, and not worry about it warping all over the place. 

Anyone tried something like that? And / or does it sound like something that would hold up for, say, a couple years? Or maybe there's a better idea out there?

Thanks,

===> Cliff


----------



## RickV (May 25, 2012)

If it's only temporary, you could do what I have done for my temporary bridges and use a fence paling cut to size. As for the curved bridge - you may need to build it in sections with a support or two in the middle. Or find a wide piece of timber from your local hardware shop and cut it to the curve you need.


----------



## CliffyJ (Apr 29, 2009)

Thanks Rick. Maybe laminate (glue-screw) a couple of sheets of PT plywood? Probably a lot easier to cut than backer board.


----------



## RickV (May 25, 2012)

How temporary are you talking about? Will the plywood survive the weather long enough until you put in a more permanent solution?


----------



## wigginsn (Jan 9, 2008)

I used an old piece of rectangular section downpipe, has worked well for several years now. 

Span is about 4'. 

Cheers 
Neil


----------



## Greg Elmassian (Jan 3, 2008)

You'll find backer board needs supports fairly frequently, it will sag unsupported. 

Greg


----------



## CliffyJ (Apr 29, 2009)

Thanks for the further tips guys. 

If the backer board sags as well (although a 3-ply laminate might do better?), and assuming 2 years max lifespan, perhaps a double-ply of marine-grade plywood is in order (maybe painted). It's mainly that longer curved bridge (not shown) that I'm wanting to plan for at this point. 

Thanks again, 

====>Cliff


----------



## John J (Dec 29, 2007)

To Correct for Sag on your board......Get a piece of angle Iron. 3/4 x 3/4 or what ever. Bolt it to the bottom of the Plastic board. It will stiffen the plastic. Or.....Get some sheet rock screws and screw a 2x4 on edge to the bottom of the plastic board. This will also stiffen the board. 

Done it many time on my RR 

JJ


----------



## D-n-H - Kirkville Branch (Jan 14, 2008)

You could always just use a metal stud from Home Depot or another box store, the stud will span 4' easily, the remaining 4' section can be ripped in half then attached for sides =


----------



## CliffyJ (Apr 29, 2009)

Excellent ideas guys, nice and simple.


----------



## jake3404 (Dec 3, 2010)

Glad to see your still progressing along Cliffy. Was wondering the other day how you were doing.


----------



## CliffyJ (Apr 29, 2009)

Hey Jake, I just noticed your reply to this thread. Sorry for the delay, and thanks for the welcome-back. 
I hope you're making good progress; if there's a particular thread that shows where you're at, please post me a link.


----------



## jake3404 (Dec 3, 2010)

Sure, this is what I've been working on.

Trestle on DBH


----------

