Ideas for a bridge replacemnt?
- gregh
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Ideas for a bridge replacemnt?
Way back in 1994 when I started building my railway, the 2nd bridge I built was this timber truss. I was really proud of it as it is really all held together by the tension rods just like the real thing.
It’s about 1.2m long, made from tomato stakes. I relocated it slightly in 2003 due to a track realignment, so that it was very close to an overhanging gum tree trunk. Over the years, the tree has grown and leant over so it is pushing on the bridge. I have been cutting into the thick bark for a few years to give clearance, but now I am into the hard wood.
So it is time for drastic action. My first idea was to just invert the truss so the track ran across the top, but some measurements revealed not enough clearance under the bridge at one end. It looks like a new bridge is needed. What a shame – the timber is in perfect condition despite being 26 years young.
I would love to do a masonry or steel arch under the track but it’s a lot of work because the two support ends are different heights.
So I think the simplest design would be a steel girder like this (in styrene) … but I don’t like the absence of ‘safety rails to catch derailed trains! It's a 1m drop to rock for a derailed train!
So something like this through plate girder would be better…
A quick look through this website, let me determine some of the dimensions of the girder.
https://theconstructor.org/structural-e ... dges/2066/
Depth D= L/10
Being 1.2m long would mean a girder depth D of around 120mm.
Flange width D/3 to D/4 (30-40mm). Web width D/125 so only 1mm !!
So it would look something like this: But a lot of work cutting and ‘riveting’ all those angle irons.
I do have a ‘spare’ steel arch bridge that is 6’ long and if I cut it down to 4’ it is only about 5” high at the centre. But it really means completely dismantling the bridge and rebuilding. Is it worth the work??
Maybe just put a piece of timber under the track and forget it??
It’s about 1.2m long, made from tomato stakes. I relocated it slightly in 2003 due to a track realignment, so that it was very close to an overhanging gum tree trunk. Over the years, the tree has grown and leant over so it is pushing on the bridge. I have been cutting into the thick bark for a few years to give clearance, but now I am into the hard wood.
So it is time for drastic action. My first idea was to just invert the truss so the track ran across the top, but some measurements revealed not enough clearance under the bridge at one end. It looks like a new bridge is needed. What a shame – the timber is in perfect condition despite being 26 years young.
I would love to do a masonry or steel arch under the track but it’s a lot of work because the two support ends are different heights.
So I think the simplest design would be a steel girder like this (in styrene) … but I don’t like the absence of ‘safety rails to catch derailed trains! It's a 1m drop to rock for a derailed train!
So something like this through plate girder would be better…
A quick look through this website, let me determine some of the dimensions of the girder.
https://theconstructor.org/structural-e ... dges/2066/
Depth D= L/10
Being 1.2m long would mean a girder depth D of around 120mm.
Flange width D/3 to D/4 (30-40mm). Web width D/125 so only 1mm !!
So it would look something like this: But a lot of work cutting and ‘riveting’ all those angle irons.
I do have a ‘spare’ steel arch bridge that is 6’ long and if I cut it down to 4’ it is only about 5” high at the centre. But it really means completely dismantling the bridge and rebuilding. Is it worth the work??
Maybe just put a piece of timber under the track and forget it??
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
Re: Ideas for a bridge replacemnt?
Hello!
I reckon either option would look good and definitely be worth the effort, but I wonder whether you could modify the existing bridge by simply cutting out the bits where it contacts with the tree? Yes, it would look a little odd (like the tree had somehow grown through the bridge) if you stopped to really look, but how often does anyone do that? Most of the time you'd glance over, your eye would see the bridge and the tree, and your mind would adjust the picture to make it all work... Of course it may not be possible with the design of the bridge - I'm more of an artist than an engineer!
Good luck with it, whatever you decide,
Andrew.
I reckon either option would look good and definitely be worth the effort, but I wonder whether you could modify the existing bridge by simply cutting out the bits where it contacts with the tree? Yes, it would look a little odd (like the tree had somehow grown through the bridge) if you stopped to really look, but how often does anyone do that? Most of the time you'd glance over, your eye would see the bridge and the tree, and your mind would adjust the picture to make it all work... Of course it may not be possible with the design of the bridge - I'm more of an artist than an engineer!
Good luck with it, whatever you decide,
Andrew.
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Re: Ideas for a bridge replacemnt?
You're up a gum tree here.... sorry. That tree is at a heck of an angle by the look of it. Does it sway much in the wind ? That could affect the alignment. Is there no way you could keep the existing bridge? It is clearly a goodun and one that you are fond of. Can the approach to the bridge be realigned some way so that bridge is further from the tree trunk?
Re: Ideas for a bridge replacemnt?
I wonder if the tree would tolerate having a bigger bite taken out of it? Trees seem to happily survive all sorts of abuse and this would be on the inside of the lean and hence under compression rather than tension.
Any arboreologists out there?
Rik
Any arboreologists out there?
Rik
- gregh
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Re: Ideas for a bridge replacemnt?
Lots of brilliant lateral thinking there. Thanks.
I will consider and let you know.
I will consider and let you know.
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
Re: Ideas for a bridge replacemnt?
I like invicta280's idea about moving your track slightly to the left of the tree. It really would be a shame to cut into your beautifully built bridge Greg. And just putting a plank under the track is just the same as your first photo, when you say it is a 1m drop....
ROD
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
- gregh
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Re: Ideas for a bridge replacemnt?
I'll try and explain why it is impossible to realign the track.
The bridge supports sit on the edge of a high rock shelf. Below that rock shelf there are other tracks at Sandstone, so I cannot even build longer piers.
These pics might help illustrate.
On the right end the bridge sits on the rock but the support wall is right on the edge - no moving it out!! The left end is on a high pier, but you can see it is impossible to move outwards.
I don't mean to be negative and thanks everyone for the ideas. All the offered ideas involve lots of work. I'm still procrastinating!
The bridge supports sit on the edge of a high rock shelf. Below that rock shelf there are other tracks at Sandstone, so I cannot even build longer piers.
These pics might help illustrate.
On the right end the bridge sits on the rock but the support wall is right on the edge - no moving it out!! The left end is on a high pier, but you can see it is impossible to move outwards.
I don't mean to be negative and thanks everyone for the ideas. All the offered ideas involve lots of work. I'm still procrastinating!
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
Re: Ideas for a bridge replacemnt?
It probably not what you want to hear but it seems to me that it's the tree that has got to go. The angle that it's leaning at seems to indicate that its only a matter of time before it falls of it's own accord.
Phil
Re: Ideas for a bridge replacemnt?
Your'e not being negative Greg. It's a problem you have asked for ideas from members and I can now see what a quandary you have. It is looking like you may need to put a new bridge in like you have suggested yourself with an underslung one. You have the skills to make another in the same mould has the old one and maybe you can put the old one to good use somewhere else on your line..
Has for that tree.....
Has for that tree.....
ROD
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
- Peter Butler
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- Location: West Wales
Re: Ideas for a bridge replacemnt?
Have you considered moving house Greg?
The best things in life are free.... so why am I doing this?
- gregh
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Re: Ideas for a bridge replacemnt?
Having procrastinated long enough, I decided that since I had to remove the track and bridge in any case, I would do that and look for inspiration.
And…………
I took the easy way out and just cut further into the tree.
It was much easier to cut with the bridge out of the way! So I have got another few cm of clearance which puts off a new bridge for a few more years.
While I had the bridge out I gave it a few coats of paint.
And here it is all re-instated. Looks just the same as before!
And…………
I took the easy way out and just cut further into the tree.
It was much easier to cut with the bridge out of the way! So I have got another few cm of clearance which puts off a new bridge for a few more years.
While I had the bridge out I gave it a few coats of paint.
And here it is all re-instated. Looks just the same as before!
Greg from downunder.
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
The Sandstone & Termite's website: https://members.optusnet.com.au/satr/satr.htm
Re: Ideas for a bridge replacemnt?
Looks fabulous Greg. Will be ok now for another 20 years or more...
ROD
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
Life is so easy when I run my trains.
https://gardenrails.org/forum/viewtopic ... 41&t=11364
https://www.youtube.com/@fairywoodlightrailway
- Peter Butler
- Driver
- Posts: 5304
- Joined: Sun Sep 09, 2012 10:33 pm
- Location: West Wales
Re: Ideas for a bridge replacemnt?
Greg, you might have solved the problem as far as the railway and bridge are concerned, but tree surgeons are now in tears. I do hope it forgives you!
The best things in life are free.... so why am I doing this?
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