MadModder
The Breakroom => The Water Cooler => Topic started by: vtsteam on July 02, 2018, 08:05:59 PM
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I know Andrew digs digging stuff, so here are some photos of the bridge we're building over the next couple weeks.
Here are the old log and plank footbridge, and the brook on both sides. Very hot and dry weather has shrunk it down quite a bit, which will be good for working.
(http://www.sredmond.com/vtsteam/Bridge/Bridge1.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge2.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge3.jpg)
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Here's the excavator, which was delivered today. Some of the block for abutments has also been staged.
(http://www.sredmond.com/vtsteam/Bridge/Bridge4.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge8.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge5.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge6.jpg)
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Some of the block is tapered, and all of it has channels and keys to assemble it together. Both sides have the decorative facing so the taper can be turned either direction.
(http://www.sredmond.com/vtsteam/Bridge/Bridge7.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge9.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge10.jpg)
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Steve are you planning to do the ground works yourself or are you getting a contractor in ?
Nice digger :thumbup:
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Not me, Andrew. Dave will be the man. I'm just going to be an active spectator! :coffee:
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Pics not showing here. I think you've hit your hosting bandwidth limit Steve.
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That's a first...I'll have to check into it. Thanks Pete.
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The picks were showing 6am this morning but have gone now .
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Yup you're right Pete, looks like I'll have to make some changes to my hosting structure. I'm going to have to temporarily remove these bridge pictures, since I think that was the main cause of the overload. Probably a lot of hits due to search engines because of the thread title.
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All pics (except these bridge pics) in all my threads will be back @ 12 AM. Eastern Daylight time tonight, my host says.
250 mHz bandwidth on the sub-site I use for photos. Didn't realize. I have unlimited bandwidth on on the main site, so maybe I'll move photos over there. Sigh......
A bridge too far.
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Okay as a test, all the photos on the last page of my New Lathe thread have been relocated, and re-linked. They should be visible. prior pages will still not recover for another 8 hours. I figure I'll just add all new photos in future to my unlimited bandwidth site as I post them. That should take the pressure off of the limited bandwidth site.
I hope I won't have to re-link everything here again!
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You should develop dystolexia and write bilge ower trbled vather or sumthing and the bandwidth problem is gone :wave:
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My host wrote a note which said that there were 3 complementary resets per domain.
So I asked what that meant, and they said it meant they could reset the count, which starts at midnight, normally.
Of course they didn't actually reset it.
So then I asked if they would please reset it.
This is like pulling teeth.
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Okay, they said, sure, no problem. :doh:
So they did -- threads back to normal.
Now for this one, I guess I'll re-post to links on the unlimited account. Bridge pics should be back shortly. Sorry for the interruption in your service! But really glad you said something, Pete. :beer:
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This morning before the real heat began, I started to take apart the old footbridge:
(http://www.sredmond.com/vtsteam/Bridge/Bridge11.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge12.jpg)
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Finally, only the two logs were left. They span 33 feet:
(http://www.sredmond.com/vtsteam/Bridge/Bridge13.jpg)
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Dave arrived about noon, something of a disappointment, as I thought we were starting early, and tomorrow is the 4th of July, so no work then either.
Anyway, he pushed quite a few yards of soil around roughing in a road for bringing in the rock fill.
(http://www.sredmond.com/vtsteam/Bridge/Bridge14.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge15.jpg)
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And he set up barrier fence to retain runoff. But by 2 p.m. he was done -- the trucker who would be bringing the gravel fill couldn't be reached. So we'll have to wait until Thursday for much more action on this project. But we do have a start.
(http://www.sredmond.com/vtsteam/Bridge/Bridge16.jpg)
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Crushed rock was delivered for a base for the blocks, for riprap and for building coffer dams.
(http://www.sredmond.com/vtsteam/Bridge/Bridge17.jpg)
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Dave placing stone for coffer dams. These will allow excavation behind without roiling the main stream's flow.
(http://www.sredmond.com/vtsteam/Bridge/Bridge18.jpg)
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He has a very delicate touch with that excavator and could place rock exactly where he wanted it -- sprinkling it in a line like it was sand in his hand hand.
(http://www.sredmond.com/vtsteam/Bridge/Bridge19.jpg)
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We did not like the block that was delivered. Long story on that, and Dave had already placed a few rows of the first abutment. We decided to take it back out and replace it with 4' x 4' x 2' concrete blocks which we would cast ourselves. These will weigh 4800 lbs, vs the pre-cast block weighing 2600 lbs.
Two helpers and I cut and drilled two by lumber, cut sheets of ply for bottoms, leveled locations and drove stakes in order to assemble 6 custom forms yesterday. They were poured this morning.
We will need to unmould them and reassemble them 8 times to complete all the block for the bridge. Once a day. Dave is on vacation until August, and we were hoping to have all the block done by then. But it looks like next week will rain most days. I hope not!
(http://www.sredmond.com/vtsteam/Bridge/Bridge20.jpg)
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A major engineering project Steve!
Are you having the concrete delivered or doing it yourself? That's a lot to mix and place
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Heh heh, Andrew no, I'm not mixing it myself. 4800 lbs times 50 blocks equals 240,000 lbs of concrete. Pretty close to a quarter million. Or in you guys flavor about 110 tonnes. I can wield a shovel pretty good, and I do have a small mixer but truly Andrew you flatter me!
Modesty aside, there's an 18 year old kid working with me -- tall strong kid -- football player material, but he came in uhhhhh, my guess.....hung over--- he normally tends to use a shovel as an arm and chin rest anyway.
I looked up after I'd taken apart and moved single handed 4 of the 6 forms, and he'd disappeared into his car today, obviously texting. I called him back and asked whatsa matter? He said he didn't feel good, had a headache, he wanted to go home. I said okay the concrete truck will be here in forty minutes, call your boss on that cell phone and tell him to send somebody else down here fast. Then I stomped back to the forms we were re-building double-time.
Strange thing, he came back in a minute or so and started doing a small amount of work -- high speed for him. I said "Is he sending somebody?" He said no, he was feeling a little better and might as well stick it out. I said okay, up to you.
I'd started at 6:30 AM -- he got to the site a half hour late at 8:30. I'll be 70 next year. I can do three times the work that kid can do.
Seventy is the new twenty, apparently! :lol:
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I know that the older generation has always bad mouthed the younger generation since time immemorial but it does seem we've managed to raise a particularly work shy lot recently.
I can remember as a teenager being absolutely desperate not to be late for my various holiday jobs, obsessively so, and always being there waiting to be let in!
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Well I wouldn't generalize about a generation, for fear of getting generalized as a geriatric curmudgeon myself, but this kid is in line for some life lessons, I'm sure. Not at my hands -- I just want to get this job done. If he can't work, no problem, send someone else.
Anyway, we just made it in time when the concrete truck arrived. Twelve blocks poured in two days. I may work alone stripping the forms over the weekend. since it will rain Monday, and it will be a lot harder then, even with help, slipping in the mud, etc. fun. Woohoo. Not.
(http://www.sredmond.com/vtsteam/Bridge/Bridge21.jpg)
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What was the issue with the original blocks that you had Steve?
Your picture reminds me of bits of our South Coast when we were preparing to thwart an invasion from across the channel in the early 1940's. Indeed Cuckmere Haven still has the anti tank blocks in place.
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Andrew, they were tapered (pie shaped) -- apparently intended for curved wall landscape use. Front face was 48" wide, rear face was 31" wide. Also they were 18" tall, instead of the plan 24" tall. They weighed 2600 lbs instead of the rectangular block's 4800 lbs.
1.) If laid straight, the front faces abutted, but the embankment faces were spaced apart, the mfr's intention being that 3/4 inch stone would fill the gaps. Fine for static landscape use, but a bridge abutment has moving truck loads over, and tire impact loads, not to mention trees banging into them during a flood. I thought they'd shift too easily.
2.) They were only 42" deep - original design called for 48" deep blocks (4'x4'x2). This difference is particularly critical at the top course, where the steel bridge beams overlap only 1 foot onto the block. Loads could tip the top blocks up a little (or a lot) at each impact in my opinion. Dirt and gravel would enter at the back and further wedge the blocks up
Also affecting tipping resistance: they were less deep, didn't abut each other, thinner (18" vs 24") and weighed about half what he design called for. The centers of gravity of the blocks (and therefore resisting moment) was also further forward toward the wider front face. To me, if you multiply three or four reduction factors by each other, you're left with a very small percentage of the resistance to tipping originally intended.
I was talked into these blocks (when the excavator couldn't find 4x4x2 blocks locally) because they do have a couple of small tenons at the back that fit into mortise grooves, but no one mentioned that they were tapered wedge shaped overall with intended gravel infill. When I saw them going together, and asked where the straight blocks were (I thought the tapered ones were only for the end blocks, laid tight) I was told abut the gravel infill, and a two day "discussion" ensued. :bugeye: Eventually, reason won. :hammer:
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I should add that the system might have been better if the mfr also offered straight blocks. I was confused by the fact that they didn't, but intended tapered blocks for even straight wall sections.
Then I realized the advantage to the mfr. These blocks sell for premium prices (they have a decorative face, and can curve).
But the cost to cast them is reduced because they weigh less -- and cost is directly related to concrete usage. Thus the maker can charge twice as much and use half the material for each. :smart: Not a mystery after all.
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Sounds logical, as I would expect from you Steve !
How long before you can pick them up with the cast in loops? Big load and a little bit of green concrete.
Talking of loads - are you casting a pad for the beams to sit on to spread the load?
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The cast in loops are rated at 19,600 lbs, Andrew, and they won't be moved for another week and a half, as Dave is on vacation to Nova Scotia -- first cast will have 2 weeks cure by the time he gets back, and first cast, first placed, since we are moving in a line away from the excavator. Fairly likely all will have two weeks before the last ones are moved.
But they are curing very fast anyway in this heat (80-90F). They absorb a tremendous amount of heat during the day. When I unmold them in the cool of the morning after setting overnight, hot steam comes off of the sides. and you can feel the heat like a radiator just standing near. I wet them down twice a day so they don't dry out. Monday a roll of plastic is coming so I can have an easier time of it. But they are definitely moist baking which accelerates cure time..
I have to chip out the small amount of flash in the eye loops - maybe 3/8" thick, and it's tough going with a chisel even though they were cast only a day before. So I think a couple weeks is going to be fine.
The bed base is 4"-6" crushed rock 2' deep, 8' wide, 30' long. This is a rocky shale area anyway, and there is ledge adjacent to the bridge location. I figure the bridge static bearing is < 1000 PSF which would be very conservative for our soil type -- not to mention the rock bedding.
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Here's a SketchUp rendering with the 4x4x2 block and stone bed.
(http://www.sredmond.com/vtsteam/Bridge/Bridge22.jpg)
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Blocks all poured.
4800 lbs ea.
(http://www.sredmond.com/vtsteam/Bridge/36BlocksPoured.jpg)
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Yikes !
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Plus one for 'Yikes'!
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I gotta say when I read the first post I didn't think it'd be such an engineering project!
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That's a serious investment in concrete Steve.
Were there no surplus Bailey Bridges in your neck of the woods ?
https://en.wikipedia.org/wiki/Bailey_bridge
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Yes, guys, it's a lot! Moving and rebuilding the forms every day was extreme. Pouring all that concrete almost two weeks each day by noon was a major deal for me and the two guys who helped. It was all I could do to get a little work done on the new lathe by supper time! :lol:
The reason it is this large a project is the effect of Hurricane Irene on Vermont.
See here:
https://insideclimatenews.org/news/31082016/five-years-after-hurricane-irene-2011-effects-flooding-vermont-damage-resilience-climate-change
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:thumbup:
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Thanks Bob! :beer:
We spent the last week excavating, placing the blocks, and backfilling:
(http://www.sredmond.com/vtsteam/Bridge/Bridge23.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge24.jpg)
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The steel also arrived -- in two sections that will be bolted together. I got two coats of paint on it before moving day:
(http://www.sredmond.com/vtsteam/Bridge/Bridge25.jpg)
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Bridge beams in place. The connecting bolt holes between the two sections were drilled in place with a borrowed portable magnetic drill press, greatly easing that job. What a great machine!
Here I've started decking, as well.
Lots of water for this time of year -- normally the stream would be almost dry. But it has rained most days in the past month and we had a real howler of a thunderstorm last night.
(http://www.sredmond.com/vtsteam/Bridge/Bridge26.jpg)
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The bridge decking is pressure treated 2 by 6s laid on edge and nailed together with 20d hot dipped galvanized nails on 18" centers. Nails penetrate 2-1/2 boards. All hand nailed as nail guns don't do spikes that large. I'm the hammer man, and Sam, my helper, who burned his hand Monday on a pot of macaroni, just supplied me with boards. I drove about 500 nails today with a 26 ounce hammer, and we got about half way across the span. I was ready for a break by 4:00, for sure.
(http://www.sredmond.com/vtsteam/Bridge/Bridge27.jpg)
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:lol:
Looks like you nailed it!
That's a serious slab of lumber....
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Coming along well.
Will you then cover the wood with Tar or something?
Mark
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A very ambitious project you've taken in there.... :bow:
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A very impressive quantity of straight-looking lumber to hand nail. Do you just depend on the bulk to keep it central to the steel or is it/ will it be secured in any way?
I doubt there is that much straight wood in the UK, certainly not in any of the woodyards I've visited anyway.
Pete
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Thanks gents ! :beer: :beer: :beer: :beer: -- just on lunch break from nailing today.
Quick answers to questions -- the bridge will be secured central to the beams with toe clips driven from below. I didn't want to drill through the flanges.
The ends will be secured for-n-aft by additional concrete blocks -- abutments -- in the true sense of the word. behind them will be gravel fill at road level.
The lumber is pressure treated (preservative) made from fast farm grown southern yellow pine species. Not like the old-growth southern yellow pine, which was heavy and very rot resistant on its own, but rare now.
The fast grown stuff depends on the preservative for outdoor use. It can be very wonky if allowed to dry out unsupported. It is always received sopping wet -- like green wood. So yes it's straight, as long as you don't leave it out in the sun for long! There are plenty of knots in it, and a fair amount of waney edges, which I turn downwards for the deck, as much as possible.
It's not a high class of lumber, here. But it is good for outdoor stuff.
I had thought about covering with asphalt roofing compound, but I haven't sen others do that on wooden deck bridges. Not sure if that would protect the wood, or trap moisture into it. Undecided, at this point. Likely I would delay that anyway, until the pressure treated wood is more dried out.
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a bit slippery in the wet I'd assume Steve :scratch:
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Hi Steve,
That is some impressive work :thumbup:
I can see some more concrete "blocks" in the backround of one of the photos
Is there a plan for them?
John
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a bit slippery in the wet I'd assume Steve :scratch:
Nope. Many town road wooden decked bridges here.
To lighten your dour anticipations, Andrew, don't forget embedded road grit. Or the fact that bridges are always level. And driveway speeds necessarily low, at least here.
ps. Concrete and blacktop are slippery in snow. This is Vermont.
Eight months of winter, and four months of damn poor sledding!
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John, thanks! :beer:
The 6 blocks left will be placed at either end of the bridge as abutments (mentioned above). Then gravel fill goes behind them.
They are 21" tall, which will be the height of the bridge deck plus the runner strips, yet to be added
Steel beams are 12" tall, wooden deck is 5-1/2" tall, and runner strips are 3-1/2" tall (and 40" wide), total 21" tall.
Beams are wide flange W12X26 meaning 12" tall, 26 lbs/ft weight. Fortuitously, they had mfr stickers on them when they arrived, and those showed ASTM A992 steel instead of the A-36 steel I thought they would be. That means they are stronger than I thought.
A-36 is 36,000 psi yield. A992 is 50,000 psi yield.
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Steve, we have a wooden decked bridge crossing a small stream by our back door. It's ten foot wide and spans maybe twenty feet. Formed on a pair of heavy RSJ's that I had curved slightly (12 inch rise in the middle) for added strength and aesthetics. It's rated for four tons.
The deck is made from oak railway 'crossing sleepers' as ordinary sleepers (ties, USA speak?) weren't long enough. At certain times of the year you cannot walk over it without holding the hand rail, as even that slight arch has you skidding a over t .
It's probably a reflection on our different climates. External woodwork can suffer very badly from mosses and microscopic slimes.
Here is a picture of it being decked out for my youngest daughters wedding, interrupted by the Emu incident !
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Seen that in UK!. Beautiful pier or bridge covered with ugly metal net, after one person plunges into pond.
Pekka
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Mosses and slimes would mean little or no vehicular traffic -- Yours seems to be a footbridge, I see flower vases on yours. and a 1 in 10 incline (1 foot at center, 20; long) is not a minor slope. No dirt road lead-ins to add grit.
As I said there are many wooden surfaced town road bridges here in regular use. And our wooden covered bridges are famous. We have a large network of dirt roads here. I think problems may arise when people pave up to older wooden bridges. It may also be that the wood chosen has something to do with it. Softwoods absorb grit and fray differently than hardwoods.
Anyway, tired of this kind of discussion with you, Andrew, like Rob, which is why I do wonder why I post projects at all sometimes.
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Seen that in UK!. Beautiful pier or bridge covered with ugly metal net, after one person plunges into pond.
Pekka
What piers or bridges would those be Pekka? as NONE of the six piers near me, nor have any of the wooden staithes, wooden queys have mesh on them :scratch: NONE of which are slippy when wet!
Rob
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Nice job Steve , real engineering at home . I like the use of simple , but still costly materials , to do a major job . I would never have thought of using timber of that section but having thought it through it makes good sense , hope it last's for many years ! Nathan.
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Seen that in UK!. Beautiful pier or bridge covered with ugly metal net, after one person plunges into pond.
Pekka
What piers or bridges would those be Pekka? as NONE of the six piers near me, nor have any of the wooden staithes, wooden queys have mesh on them :scratch: NONE of which are slippy when wet!
Rob
I know there's a slippery pier somewhere in this area. On the Tyne I think - I'm just trying to remember where. I think I was fairly tired when I visited it so all i've got is a foggy memory of trying very hard to not lean too far and slip while also dodging the goose crap.
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Thanks guys :beer: :beer: :beer: I should have added earlier that it has rained practically every day here for a month during construction. the wood is totally non-skid under foot when wet -- which has been practically every day -- I've spent weeks working on it. That's actual user experience.
And, the former footbridge which served us for eight years was not slippery at all when wet. And our porch and front steps are unpainted wood, and they've supported our family traffic for 18 years, without a single slip when wet. Unscraped ice and snow are another matter, but no, not from rain.
Yucky slick toppings, like the aforementioned mold, slime, goose crap, banana peels, etc. are not the exclusive property of wood, but can coat any little used surface. The expression, a rolling stone gathers no moss applies here. This bridge will see probably eight or more 5 mph vehicular crossings a day. It will have substantial railings.
The wood is also preservative treated -- moss and slime don't favor it.. The lead-ins are bank run gravel, which tires will certainly track across the bridge runners. The bridge will be sanded in winter when there is ice, as will the entire driveway. Geese pass our property by for better grazing down the road. We compost banana peels.
Should I post more progress pictures before I plummet off the thing? :)
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Yes, please continue Steve! I find all these real live matters highly interesting and educating.
/Peter
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Keep them coming Steve ! If you do fall in please post a selfie!!
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More pics please Steve, i love this stuff.
Lyn.
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Peter Nathan Lyn thanks, and here you are then:
Curbs and runners added -- ready for end blocks and backfill.
(http://www.sredmond.com/vtsteam/Bridge/Bridge28.jpg)
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The south end will need a LOT of fill -- estimated at 8 truck loads.
(http://www.sredmond.com/vtsteam/Bridge/Bridge29.jpg)
Nathan, if I fall I promise a selfie for sure, or an assisted one! :lol:
Actually, a more realistic concern is for Dave the excavator operator who plans to put his machine in the middle of the bridge and backfill from there. He says he will have the trucks empty on the north side, and rotate it over to the south side. I think his excavator is close to 35,000 lb, or so. I'm not real keen on this operation, but he's confident about it. The bridge deck itself weighs in the neighborhood of 6,000 lbs. so 40,000 lb load.
Technically a midspan point load of 80,000 lbs should come in under 66% of yield for four A992 W12x26 beams, but that's back of the envelope, and this operation does have me feeling concerned. He will be taking it slow, and I'll be watching for bridge deflection. It shouldn't be anything more than a quarter inch with that load, so if I see practically anything, I'm waving him back.
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Hi Steve,
That method will "settle" the structure for sure
It looks great to me
Dave sounds to be a "Mad Digger" rather than a Mad Modder :lol: :lol:
John
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Steve , that looks like a 15/18 tonne machine , if so , your math looks as good as usual ! I've seen 21 tonne (PC210) and 35 tonne machines work on much more flimsy structures than your bridge . PC 350/450 were not uncommon in my previous employment working in very delicate situations, operator skills can make a problematic situation run of the mill. As always I'm enjoying your posts, I'd never realised the extent that you ( and others) would have to go to cope for future rainfall events. Keep the photo's and report going, I'm loving it !! Nathan.
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John and Nathan, re settlement -- of interest is that Dave first built coffer dams to enclose the stream, using the big crushed rock you see as rip-rap stone, then he excavated 2' below stream grade behind the dams and filled that excavated bed with smaller crushed stone. That's what the blocks were placed on. BTW the material removed was very bony anyway, so I think the foundation is really good. I'm sure there will be minor adjustment over time, but we have expansion joints naturally with the block construction, vs a solid poured abutment.
Dave said he would be back-filling tomorrow starting at 8:00 sharp. He said he has decided to only put the excavator tracks a few feet onto the bridge from the north abutment, because he has enough reach, and then put a massive pile behind the south abutments -- built up much higher than them initially, because he can't tamp it down as well from as far away. Once it's big enough he'll cross. The dump truck will be dropping off to the south of him initially.
The first step will be placing the 3 north end blocks against the bridge beams, then filling behind them, then venturing to his loading position.
Fingers crossed, depending on how it goes, I might actually be able to drive my pickup truck across tomorrow evening. :dremel:
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Sounds like good progress Steve :thumbup:
I know that you said Dave formed a track for the lorries initially, is there much to do to make the roadway, or is it close to your previous access road?
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Andrew, I had roughed in a second lower drive last year with the old Ford 850. That was also what we built the concrete blocks on. But Dave is upgrading it and fairing it into the bridge. Here he is spreading crushed stone gravel on the north side. We've already placed the last abutment blocks against the bridge beams here.:
(ps. the larger stack of blocks in the background were commercial blocks, which we had rejected last month, in favor of casting our own. Long story, but they weren't suitable for abutments, both Dave and I agreed.)
(http://www.sredmond.com/vtsteam/Bridge/Bridge30.jpg)
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The dump truck had a 14 yard capacity. It dropped off in front of Dave on the excavator after he had ventured a few feet onto the bridge.
(http://www.sredmond.com/vtsteam/Bridge/Bridge31.jpg)
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Dave would pick up a bucket load and swivel around across the bridge. He has a longer than stock dipper arm, and his excavator is heavier than stock for this size, as there is also a counterweight added to offset the longer arm. He also has a thumb and other additions. He says the weight is about 35,000 lbs.
(http://www.sredmond.com/vtsteam/Bridge/Bridge32.jpg)
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You can see the thumb here, as he is backfilling behind the lower blocks on the south side.
(http://www.sredmond.com/vtsteam/Bridge/Bridge33.jpg)
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Finally it was time to edge out onto the bridge. This went very slowly and carefully. I set a piece of 1/2" rebar into the stream as a vertical guide to check bridge deflection. A piece of orange tape marked the bridge resting position -- against a piece of wood that extended out. We dubbed the Bridge-O-Meter.
(http://www.sredmond.com/vtsteam/Bridge/Bridge34.jpg)
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Amazingly (and gratifyingly) the Bridge-O-Meter barely registered his full excavators weight. We had maybe 1/16" deflection with the excavator sitting at mid span. It was hard to see at all. I had earlier calculated that a 40,000 point load, at center span, would deflect .25" on 4 beams of this section of A-992 steel.
The excavator however isn't a point load -- tracks spread it out, and the 9" of solid wood does the same, as well as adding some stiffness, probably. So deflection was minimal. We were really glad to see this, and it meant we had confidence to bring the dump truck over.
Heres the Bridge-O-Meter with Dave mid span. The deflection is not even visible.
(http://www.sredmond.com/vtsteam/Bridge/Bridge36.jpg)
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With the lower blocks sufficiently supported with back fill, it was time to place the north side's upper abutment blocks.
Moving these 4800 lb units by driving the tracks, rather than by rotating did cause momentary deflections of up to 1/8" on the meter, but again, surprisingly little compared to our expectations.
The greatest deflection I saw all day was one 1/4" bounce, when Dave was sitting mid span, and tamping down the gravel hard enough to lift the front tracks 6" with a fully extended arm, and then dropping back down.
(http://www.sredmond.com/vtsteam/Bridge/Bridge37.jpg)
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Bill the trucker decided he trusted the bridge, and again we had a first slow crossing with my eyes glued to the Bridge-O-Meter. He said his truck weighed about 77,000 lbs with a full load of gravel, as he had here.
About 2/3 of his truck weight is on the back axles, and here they are mid-span.
(http://www.sredmond.com/vtsteam/Bridge/Bridge38.jpg)
(http://www.sredmond.com/vtsteam/Bridge/Bridge42.jpg)
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Again, the Bridge-O-Meter showed only a deflection of tiny 1/8". And because the tires did a smoother job of crossing than the steel tracks of the excavator, there was no bounce at all.
Dumping made no difference in deflection either..
(http://www.sredmond.com/vtsteam/Bridge/Bridge39.jpg)
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Dave and I were super happy with the bridge's performance at this point. :ddb: :ddb:
A calculated point load at center of 88,000 lbs would theoretically give a 1/2" deflection for those beams alone, and represent 66% of yield strength. We didn't even come close to that deflection with a real life 77,000 lb load, and proved that for any use I'm likely to need, the bridge will handle it.
The only conventional vehicle likely to exceed what we've already tried would be a fully loaded concrete mixer with three back axles. I think they're around 80,000 lbs Of course that would be a more spread out three axle load as well, and not a point load. So fairly likely to be another small fraction of max permissible deflection.
I have no plans to ever pour concrete again however! Two weeks of that was enough! :doh:
(http://www.sredmond.com/vtsteam/Bridge/Bridge40.jpg)
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The end of a long, but exciting day:
(http://www.sredmond.com/vtsteam/Bridge/Bridge41.jpg)
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Wow, that is one hefty bridge! Well done :clap: :clap: :clap:
One question though; Will you also build retaining walls to protect the backfill for the abutments? I can imagine a good spring flow wanting to eat into the backfill if it gets the chance. Perhaps a good use for the discarded blocks?
/Peter
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Peter, thanks kindly! :beer:
There will be more rip-rap added, but the main part of the backfill will be planted to control erosion.
Maximum "Base Flood Elevation" (meaning predicted height for a "100 year flood") is 4" below the second layer of block in the above photo. Not very high if you imagine it -- and the amount of water you see flowing now is unusually high for August -- it's raining again today -- almost a solid month of it. So a long berm (with logs buried lengthwise in it) on the right (upstream) far side (not very visible in the second photo above) should easily shunt over-the-bank water above stream of the bridge back into the channel before the rip-rap even starts.
The near bank on the right, upstream of the bridge is solid, near vertical ledge. It can't erode.
The state Agency of Natural Resources and the local Floodplain Administrator approved the plans, and they did require a hydrologic survey and report, which was performed beforehand. This has been a long term planned project with all the I's dotted and T's crossed. We've had 3 visits from the state during construction, and the final approval will happen when we're done -- possibly as early as next Monday.
ps. oh, re. the older block -- Dave will use that for some other landscaping project -- they will be removed when he's finished here. They're fine for landscape retaining walls, and can do nice attractive curved embankments. He doesn't feel it will be hard to use for someone else. They're just not right for bridge abutments with steel beams crossing them.
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Thanks for the answer Steve, I guessed you had it under control. It was just me thinking of spring flooding here in Sweden, which can be very violent at times and require quite a lot of preparation for structures like bridges.
Can't wait for the rest, its ever so interesting.
BR
/Peter
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Hi Peter, no problem, we've had as much water last month and this one so far to equal spring ice-out flooding. No problems so far at all.
re. progress, we're in road topping and cleanup mode, so there's nothing much interesting to see, yet. Yesterday Bill the trucker brought in 11 loads across the bridge.-- 154 cubic yards, and this morning, two loads of crushed rock topping. Just before supper I got an okay from Dave to begin building the railing, meaning excavator and trucking work are finished. I drove across the bridge myself yesterday, and my wife did this afternoon with groceries....a new convenience!
Tomorrow I hope to have the railings done, Dave will bring his tractor and York rake to crown and smooth the drive. Sam will show up to spread hay and grass seed on the areas beside the bridge and drive. By tomorrow evening we may be finished with this project! :thumbup:
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(http://www.sredmond.com/vtsteam/Bridge/Bridge43.jpg)
A belated last photo of the bridge with the railings up in the low October sunlight.
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Steve,
Looks a "Proper Job"!
:thumbup: :thumbup: :thumbup:
Phil.
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Looks nicely settled in Steve, I bet you're pleased with that :thumbup:
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A superb achievement. Sorted for the next hundred years. Well Done
Will [needs to repair a footbridge over a drainage ditch at the rugby club]
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Looks really good.
Surprising how much work goes into ground and how little is finally visible from all that earth moving and sabilizing. Now when I see a "little bridge" I will give it a nod.
Pekka
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I'm just wondering why there are three lower levels in the bridge surface.
Does this serve any useful purpose.
A great project and I followed it with interest.
John
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Reallyb nice job and well done. Also interesting to see the speed limit sign before the bridge. Is that sign mandatory from a regulations point of view or just a precation by you?
BR
/Peter
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Nice job Steve, I love the speed warning sign! Does the central section allow some "spring" to the deck when the running sections are loaded or does it aid drainage (or both!) . Nathan.
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Thanks guys, sorry I haven't been able to participate here much lately, still preparing for winter...
There are two wear strips which I guess technically divides the bridge deck itself into three sections. The wear strips do what they say in their name, but also, being 3" deep, spread out the loads further across the main deck planking, which runs cross-wise. And of course they in turn spread the loads across the four steel deck beams and add additional stiffness. As mentioned the deck is made up of 2x6's on edge. The wear strips add 3".
Drainage has not been a problem -- the corners and ends drain. There hasn't been any standing water despite all the rain we've had -- seems to rain every other day.
The wear strips are at the level of the tops of the concrete abutments, so tires neither drop onto the bridge, nor bump up onto it at vehicle entry and exit. I figured, it's best not to have every 20,000 lb axle load acting like a hammer twice per crossing. Driving across it feels very smooth. There is no bump.
The strips are quite wide so compact cars and wide axle trucks alike will stay on the treads, rather than fall off the side onto the bridge deck. Not that it would hurt anything to do that, but it might make for a disconcerting moment for a small car. I've crossed the strips on purpose while maneuvering my tractor into position for auguring holes for posts at the ends, but I hardly noticed it.
There are no regulations about road signage on private property, but I do want people to slow to 5 mph when crossing. Especially my in-laws! I'm sure it can handle much higher speeds, but why subject it to that? Besides in winter, I don't want anybody slipping into the rails, etc. 5 mph is an intelligent speed then.
I've also posted it at 30 tons, since I had a few delivery trucks balk at crossing un-posted and their drivers walk packages up to the house. Thought I'd save them some time and trouble! They were used to no bridge here.
Nathan, there just isn't any perceptible spring when big loads cross. 35 tons of loaded dump truck was only 1/8" over 16' And rainwater just drains naturally off the ends. We did a good job of leveling the deck apparently, and last I checked nothing had changed with use.
Almost a quarter million pounds of concrete, plus a few truck loads of 6" crushed rip-rap stone is keeping it pretty stable.
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brill
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I always thought that it could help in handling frost as being colder it would roll off to the lower area. The Incans had agriculture set up like that crops raised to protect against frost!
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Thanks Bob. :beer:
Tom, could be. Coincidentally we had our first frost this morning. I didn't notice it on the bridge though, when I walked my daughter to the road for school bus pickup.
The bridge does get sun during the day in winter. When snow gets here, the wear strips will definitely dry first after shoveling. I'm planning to set up a sand barrel nearby.
Another advantage of having a bridge and driveway is bringing in sand. After every icing I used to hand carry it in and spread it along all 600 feet to the house. Even then, we routinely wore ice grippers in the walk to the cars, and back, carrying groceries and heating fuel.