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Bridge

Started by Splinter, January 18, 2011, 10:46:29 PM

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Splinter

Well after 18 years finally decided to put in a half mile of woods road to get to the back piece. Diggers are going at it and doing a fine job. Soon they will be at the bridge location. Anyone have a steel beam bridge design for an 18' span that will carry a 40 ton log truck?

Thanks

BaldBob

If there is a railroad salvage yard anywhere near you, try to buy an old flat car ( bed  only). Lots of them have been used for years for logging road bridges.

ScottAR

What he said...  My county has built several of these over the years.  They use two cars side by side for county roads mostly the gravel ones.  if it'll hold fire engines, grain trucks and assorted farm machines, I think it'd hold a log truck too.
Scott
"There is much that I need to do, even more that I want to do, and even less that I can do."
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Meadows Miller

Gday

Down here the engineer we use for the log home computations is also a lecturer at University of Tasmania and and his main area of work in the past was low cost forestry bridge construction for most of the major states in Australia

The main one they used for hi speed logging roads rated for copping up to 80 ton loads at  60mph and spans upto 60' where log stringers set into a concrete deck boxed up on site with reo mesh and then the concrete was poured into that then they would place the logs 10 to 16 top dia depending on the span   ( i think about 6 for a 12' wide bridge into that with random spikes driven in to the top side of the log to tie it into the bridge then they would flip the whole thing over and lift the whole bridge into place they used this method for dual lane bridges upto 22 wide too ;)

Another method used is taking a 12" to 26 " dia log depending on the span and taking a face cut 3 to 8 inches wide of each side to square them up just enough so they sit solid on the concrete poured to take them at each end and butt up to each over along their length then they bolt the whole thing together with through bolts top to bottom through a tie beam 4x8 to 6x10" that holds them all together every 6 to 8 feet along the length they then ad the side skirts about 8 inches high and then cap the top with 4 inches of either gravel or concrete depending on the amount of use it was going to see  ;)they make for a cheap long lasting bush bridge that will take a semi  just remember to use hardwood  ;) ;D ;D 8) 8)

Regards Chris
4TH Generation Timbergetter

sawmillsi

G'day Chris,

I have started work for a company in northern nsw.

they own about 2000 hectares (about 5000 acres).

i have to build a couple of small bridges, no more than 3 meters across.

The load it will carry will be our 100hp 4WD tractor (about 5 tonnes) and in the not to distant future, a forwarding trailer (about 12 tonne).

I was thinking of using some grey gum or tallowood (class 1 durability) and squaring off to make girders about 300 or 350 square, and bolting some 75mm (3") thick decking to it (same timber).

What do you reckon?

Simon

Buck

Railcars are best and quickest. I've seen em on logging roads and in applications using them for offroad articulating dumptrucks. Those guys are pretty heavy too.
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flibob

I don't know how much they cost but I have seen lots of railcars used for bridges.
The ranch is so big and I'm such a little cowboy

Jeff

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SwampDonkey

Quote from: ScottAR on January 19, 2011, 01:24:52 AM
if it'll hold fire engines, grain trucks and assorted farm machines, I think it'd hold a log truck too.

I wouldn't be so sure, most back road bridges here are only 15 tonne bridges. If it's a short bridge, than it's not so bad, but when you have a longer bridge and 40 tonne of hardwood on her. Weeee!!! ;)
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

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bill m

Most single axle fire engines are not as heavy as you might think.
NH tc55da Metavic 4x4 trailer Stihl and Husky saws

SwampDonkey

The fertilizer trucks here only haul 15-16 tonne from the plant. I've seen a straight truck of hard maple logs bust 3" hardwood plank'n on our scales. Not all the way through, but he had to go easy and I grit my teeth as I heard cracking. :D
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

Jasperfield

The railroad flatbeds are the bridge of choice. However, transporting and crane-setup can add cost.

Another option to consider is the vertically laminated bridge. It consists of 2"X10" hardwood boards, laid on edge, and bored through to accept 1.5" black steel pipe about every 3'. You use big washers and pipe caps on the ends of the pipes to clamp the boards together.

In example: You might build a bridge 24' long, by 10' wide, by 10" thick.

You make it wide enough for the vehicles to cross. Your boards don't have to be 24' long. And you can build it on site and drag & lift it into place.

CX3

Thanks for posting that Jeff.  I could probably use that info someday
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captain_crunch

Look at GVW on a flat car if they can haul that kind of weight bridge should not be problem. Wood timbers unless treated don't live long over the dampness of stream
M-14 Belsaw circle mill,HD-11 Log Loader,TD-14 Crawler,TD-9 Crawler and Ford 2910 Loader Tractor

tjdub


You might also want to check into buying a pre-manufactured spanner.

http://www.yardking.com/products/spanners.php

Since you're talking 40 tons, using a truck flatbed is probably out of the question.  A rail car may do it, but it's going to be overkill for a 18' span and those things are costly to transport and install.

WildDog


These are some pics of our railway carriage bridge on the farm, I can't take the credit for building it, the previous owner was pretty handy and put it in so his wife wasn't marooned for weeks at a time.

We have trucked B-Double semis out fully loaded with cattle.
The bridge is 86 foot long (2 carriages) and the approaches are another 100 foot. She made it through the latest major floods and survived when a few of the shire engineered bridges packed it in. We all get something out of the bridge, my wife wouldn't be here without the bridge and my oldest son launchs his boogy board from it in flood and makes it the mile down streamto the house in a couple of minutes...Scares me but he's always been a thrill seeker, if I have my 4 yr old in the car on the way home we usually pull up and look for trhe local turtles, snakes and water dragons.





This is the old girl in flood during winter, the latest flood a couple of weeks back was a touch higher









I took this pic today when everything had settled down.
If you start feeling "Blue" ...breath    JD 5510 86hp 4WD loader Lucas 827, Pair of Husky's 372xp, 261 & Stihl 029

HCF

We have decked and re-decked rail car bridges in Oregon for years now. Yarders, shovels and loaded log trucks have run over them time and time again. As long as you keep the deck in good shape they will last for ever. Here's a link to Rick Franklin Corporation in Lebanon Or. These guys have been supplying rail car bridges all over the country for years. Hope this helps.

http://rfc-nw.com/bridges/

Best regards,

HCF

shinnlinger



if you do go wood, consider building a covered bridge or at least putting a tent/tarp over it in the winter.
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

Splinter

Thanks for the input.  Think i am headed for 4 wide flange beams with 6" hemlock decking. Will probably hold a 60 ton truck, but i'd rather put the extra grand into it and breath easy when the first fully loaded truck goes across.
nothing like the image of an overturned 40 ton truck to focus the mind...


tjdub

Quote from: Splinter on January 25, 2011, 07:44:25 PM
Thanks for the input.  Think i am headed for 4 wide flange beams with 6" hemlock decking. Will probably hold a 60 ton truck, but i'd rather put the extra grand into it and breath easy when the first fully loaded truck goes across.
nothing like the image of an overturned 40 ton truck to focus the mind...

That's going to take some seriously massive W-beams!  Someone made me a little I-beam calculator for a footbridge here:

http://spreadsheets.google.com/ccc?key=0Akm9W1cMc_ZHdG1zQ2szSHhBdzZOSHFlbnVocTdkMnc&hl=en

Obviously, it's not an engineering tool, but it can give you a good idea of steel costs.  I plugged in your 18' span at 80,000lbs with 4 beams and guessed 1500lb for decking weight.  It suggests using nothing smaller than W10x112 or W12x96 beams.  BIG STEEL :)

It's also probably well worth paying an engineer for a consult to check you figures before you order ($6000+ ?) worth of beams.  In my state you would need that for the permit as well as an environmental impact study by a hydrologist.  You can get around that if it's a freestanding temporary bridge without moorings (like a rail car, timber bridge or manufactured spanner).  It just needs to be anchored with a cable for flooding.

SwampDonkey

There goes 5 loads of hardwood pulp into the steel for the bridge.  :o
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

tyb525

LT10G10, Stihl 038 Magnum, many woodworking tools. Currently a farm service applicator, trying to find time to saw!

Splinter

TJ, The bridge will only hold half the truck at a time, which changes things considerably.
Prior to your spreadsheet i came up with 4 10w30 beams.
beams used are 50ksi yield
assume 2.6 of the 4 beams are "available" for loading (from army bridge manual)
also i think your moment calc may be incorrect.
for a point load in the center the moment is 40kips*18ft*12inchft/4 or 2160 kips inch.

I come up with in^3 required of 33.2 which is very close to 10wx30 in^3 of 32.4


These calcs are only the yield calcs and there are about 3-4 more ways for the beams to fail. Most apply if the ends are not fixed and the beams are not adequately braced against lateral and torsional movement, which is not a trivial detail.

Beams priced out at $1600 delivered without holes. hemlock decking is almost free got a landing full of the stuff. prefab bridge priced out at $4500+delivery.

D

tjdub

Quote from: Splinter on January 26, 2011, 04:14:13 PM
TJ, The bridge will only hold half the truck at a time, which changes things considerably.
Prior to your spreadsheet i came up with 4 10w30 beams.
beams used are 50ksi yield

It looks like that calculator assumed A36 steel (36ksi), but it seems that has largely been phased out and replaced with A992 (50ksi) for W-beams?  

Quote
assume 2.6 of the 4 beams are "available" for loading (from army bridge manual)
also i think your moment calc may be incorrect.
for a point load in the center the moment is 40kips*18ft*12inchft/4 or 2160 kips inch.

The calculator just assumed all beams would distribute evenly (I think).  In this case it assumed 4 beams would increase your 50ksi to 200ksi, but then due to the safety factor of 2, it brings the maximum stress back down to 100ksi.  The rule of thumb for bridges is that they're not supposed to fail until loaded with twice the weight they're designed to support.  I'm guessing this is what the Army manual is referring to, but instead of requiring that you double the number of beams, you can get by with a little less than doubling?

The moment calc is for the bending moment.  

Maximum Stress = M / S

M is (Force x Distance) = (40kips x 18ft) = 720,000 lb*ft = 8640 kips*in

Maximum Stress is 100ksi (50ksi beams * 4 beams = 200ksi, but divide by 2 for safety)

S = M / Maximum Stress = 8640 kips*in / 100ksi = 86.4 in³

That would mean minimum beam of W12x72 (which has S x-x of 97.4in³ according to my chart)

So, I guess it comes down to where you factor in the 4 beams in the calculation and if you're using a safety factor of 2.  I think it's better to err on the side of caution since your calculation considers the beams in the M calculation instead of the Maximum Stress calculation.  

Even without the safety factor of 2, according to this way of calculating, you would bend anything smaller than a W10x39 with 20 tons at 18ft.

I'm not an engineer though, so I might just be full of crap :) :)

Edit: On further review, I'm full of crap :)  When calculating M, I think you use half the span distance not the full span distance, so this would put S at only half of that: 43.2 in³   That would still call for W10x39 to get close to a safety factor of 2 though, your W10x30s will probably work though.

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