Moving a bridge

[Catch95]

I replaced the bridge on my 100 acre farm a year or so ago.

The new bridge was placed on a concrete section of roadway that was built about 20 years ago. I then built the roadway up to the new bridge. The original plan was to position the bridge on a new location higher above the water, but on the day excavator was booked along with a bunch of friends to help, the excavator didn't arrive and I had to use the location of the bridge that was being replaced.

A few weeks back we had a one in a 100 year flood with 30 inches of rain in just 3 days. Even though the bridge was submerged by the torrent, it survived unscathed. Unfortunately part of the concrete base was undermined and collapsed.

After much deliberation the "simplest" option seemed to be to shift the bridge to a new location only 20 metres or so away where the banks of the creek were much higher. The was an old timber and earth bridge there that had partially collapsed so that had to be removed first.

I put in some new footings for the bridge and some rock baskets at the base of the bank most susceptible to washout. Only one sentence but a few weekends work including hiring an excavator.

The big question now was to work out how heavy the bridge was. A bit of research came up with the weights of various sorts of timber and the calculations were done. 40 foot long and I estimated the bridge at 6 tons.

The property is 40 minutes from the nearest town with a crane for rent, along some very windy dirt roads. The crane operator insisted on visiting the property first to see that it was feasible and then gave me the quote. So much for a holiday this year....

On the day it happened remarkably quickly. The slowest process was levelling the crane on the sloping ground. They had brought a sling to fit under under the bridge and after a bit of jiggling to get it balanced, it slowly lifted from its footings. It's weight was only 5 ton so I was on the right side for safety.

We had trimmed some trees to make the swing into its new location more straightforward and within 10 minutes it was sitting perfectly.

Many tons of road base later the roadway was level with the bridge.

We've since had another heavy rain event with moderate flooding and the water missed the bridge by a few feet so I'm much happier with the new location.

Major job but very satisfying.

 

[EddieWalker]

Nicely done. Thanks for sharing the pics, I enjoyed seeing them.

Eddie

 

[Ed of all trades]

Big job done well. thanks for the pics.

 

[BeezFun]

Great project. Seems like 100 year floods come about every 10 years around here.

 

[MotorSeven]

Great project. Seems like 100 year floods come about every 10 years around here.

56, 77, 93 and waiting. Someone needs to change it to the 20 year-ISH flood around these parts.

Nice job moving that intact. Are those telephone poles under it used as the main beams and what do you safely rate it at for capacity?

 

[Ken45101]

Good job, I hope it works well for you.

Do you have the bridge well anchored? As mentioned, those 100 year floods seem to come every couple of years lately, I guess we are getting the next millenium's worth over soon.

A fellow down the road put in nice concrete piers and stone approaches and a flatbed trailer for the bridge deck. First good storm washed out the approaches and moved the deck a couple of feet. A few months later, the next storm washed the deck out totally. We can now see the end of it buried and peaking out of the creekbed a couple of hundred feet downstream.

 

[Catch95]

Many thanks for the comments. The bridge is anchored to the footings with two bolts and straps on each beam end. The poles were cut from a neighbouring property where some loggers were removing selected trees. Memory serves me right they are Tallowood. Lots of discussion about dismantling the bridge and moving without a crane but to be honest my back wasn't up to doing all those bolts on the decking again!

I'll put some pictures below of this "rain event" as they now call them. We are quite high up so the creeks and rivers rise very quickly and go down the same. The first shots show the rising water on the the road into our area. Note the road sign. The shots cover a 24 hr period.

The others show some of my fencing that got ripped straight out of the ground and the re-arrangement of my creek. Been doing lots of erosion works since to sort this out.

Final shots are a neighbours bridge- built by engineers at great expense. Because the bolts didn't break when the bridge got hit by a large tree being washed downstream, the head walls broke. Start again time.

Finally a pic showing the sun does come out eventually and why we do it!

































Mark

 

[MotorSeven]

I have to wonder why the approaches to many bridges are not built 4-6' above normal flood stage? A few years ago the county replaced the older wooden decked bridge with a brand spanking concrete one. They put the bridge just about at known max flood stage with no extra height at all even though raising the approach would have cost very little. I have seen water washing over this bridge on several occasions.

Here is the County bridge during a moderate flood:

Jan2013Flood_zpsf93fe375.mp4 Video by motorseven | Photobucket

Trying a link:
Jan2013Flood_zpsf93fe375.mp4 Video by motorseven | Photobucket

 

[Ken45101]

I have to wonder why the approaches to many bridges are not built 4-6' above normal flood stage? A few years ago the county replaced the older wooden decked bridge with a brand spanking concrete one. They put the bridge just about at known max flood stage with no extra height at all even though raising the approach would have cost very little. I have seen water washing over this bridge on several occasions.

Properly designed, a bridge should be able to handle flooding. Our driveway bridge floods periodically and the only real concern was the approaches washing away, not the bridge.

I'm not a civil engineer, but when you raise a bridge above the roadway, it cuts visibility as well as increasing the load on the bridge: think of a speeding truck that comes up the approach, lifts slightly as it crests the approach, and then comes down with extra weight when it lands on the bridge proper.

Many older bridges over small streams around here used to be the way you propose but that seems to have disappeared as they now design for more level roads and better sight lines. Covered bridges especially used to be the way you mention but, of course, they were subject to being floated away, unlike modern concrete and steel structures.

 

[MotorSeven]

Ken that does make sense on the larger bridges and your right our concrete one can handle any debris. I do think that for smaller home built driveway type bridges raising it so that debris can't grab it is a good idea. I have seen 30" diameter trees w/rootball rolling down stream here in my creek which is why I raised my walk bridge as high as I did: