How strong is wood? Need to drive a car over it....

[JesusNinja]

Odd question, but is there a guide as to the strengths of different timbers? My new garage is having an inspection pit (with ventilation, gas sensor, tanked and with a sump etc before we get into a conversation about the pros and cons of inspection pits )

Typically, a pit would be covered with boards to prevent people falling in when it's not in use. More often than not though, the pit is in a location eg a single garage) where a car would not be able to get a wheel down the middle of the boards, and so the boards only really need to support the weight of a person.

My garage is going to be quite large, and it will be quite feasible to drive a car with the wheels of one side right down the middle of the boards covering the pit. Now, of course I don't want to end up parking a car in the pit, so what sort of thickness timbers should I be aiming for, and what type of wood? The pit is 3.5m long, so there will be few of them, and I don't want them to be so heavy they can't easily be moved, nor do I want them to be so many that it takes forever to move them.

The pit is 910mm wide, internally, with a 100mm recess around the top for the timbers to pick up on at each side - so the timbers will be 1.11m long. The recess will be 150mm deep, so this is the maximum I can go to, but ideally I'd go thinner and fix a timber along the recess for the boards to sit on.

Any suggestions?

 

[big-all]

you may or may not have enough strength with say 2 thicknesses of scaffold board screwed together and battened 3 planks together giving you around 3" thick by 27" long covering in about 5 very very heavy panels

you will need structural calculations

why not offset it and only drive accross it rather than on it

 

[JesusNinja]

It makes sense for it to be central, as typically that's where I'll be working on a car, and it's good to have the space all around both sides.

If I were to offset it to one side, then I'd still have the problem if I wanted to put a car bang in the middle, which will be essential for spraying etc.

Oh, and the pit is already dug, rebar in, and concrete being poured in the bottom tomorrow

I'm thinking that maybe 300mm panels made from 50mm box or angle with 13mm ply on top would do quite well. Even if the ply gives, the steel surround will not.

 

[big-all]

try a minimum18mm ply angle iron every 6-8" and drive over it on the driveway

you could try bricks in lines to see what happens

 

[JesusNinja]

So long as I don't end up with something like this!

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[foxhole]

When I bought my house the garage had 10" x 2" timber covering the pit , very heavy to move so I used cable trunking trays reinforced with a 3X2 timber at each edge, welded three together so only had a few panels to move for access.Its galvanized so no rust and perforated so keeps pit ventilated [they get very humid if sealed].Got mine free from local tip.
http://www.cableindia.net/cabletrays.htm

 

[Jasonb]

I'd say you want something around 6"x3" laid flat as thats a bit wider than most pits I've seen.

Alternative would be to get some frames welded up from 100x50 steel hollow section with chequer plate on the top.

J