Author Topic: Speed/weight limits of historical bridges  (Read 4207 times)

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Offline jamespetts

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Speed/weight limits of historical bridges
« on: April 17, 2013, 11:01:55 PM »
The issue of weight limits applies, I appreciate, only to Experimental, but the issue of speed limits is common to Experimental and Standard, so I thought it best to post here about it: where, may I ask, do the speed limits for historical bridges come from in the pakset? I ask because I am put in mind of the Wharncliffe Viaduct (otherwise known as the Hanwell viaduct), completed in 1837, and carrying the heaviest trains (some of the aggregates trains that run on the slow lines in that area must weigh more than a megatonne in all) and also passenger trains on the express lines at the full 125mph. Likewise, the Maidenhead Bridge, built in 1838, carries the same heavy and fast traffic. This seems inconsistent with having lower speed limits (and, in Experimental, weight limits) on these earlier bridges.
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Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #1 on: April 17, 2013, 11:14:07 PM »
Really the speed limit across bridges is in real life most often dependent on track condition rather than the bridge structure. However this can't be simulated easily in simutrans. Hence the lower limits for older bridges - if these didn't apply then they would be an easy way to get faster speed track earlier than should be possible. In itself this isn't a huge issue as rolling stock probably couldn't take advantage of it - however it would make balancing much more complicated (if you can buy a 200km/h bridge in 1840 how much should that cost relative to track with a speed limit of 50km/h?).

Offline jamespetts

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Re: Speed/weight limits of historical bridges
« Reply #2 on: April 18, 2013, 12:23:41 AM »
Hmm - this is a difficult issue indeed. It forces people to upgrade bridges whereas that would not in reality be necessary. The code in this area may need re-thinking: ideally, it would be highly beneficial to separate the underlying bridge and the way on top of it, and likewise with tunnels.
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Offline Bear789

Re: Speed/weight limits of historical bridges
« Reply #3 on: April 18, 2013, 07:18:28 AM »
I always thought that Simutrans needs a locomotion-style approach to ways: for those who haven't played that game, there is only a base way tool, then you can drag it on different levels and use it for both tunnels and bridges, with all the freedom allowed by the way tool (diagonals, slopes, curves, etc).
In Simutrans we already can raise or lower the final tile of a road or track with the terraforming tools, adding a terrain slope under it. Ideally we could merge the ground ways, the elevated ways and the tunnels in the same tool, specifying in the dat file the appropriate graphics.
Instead of a terrain slope it should add a bridge start when raised, then everything you drag from that point stays at that height with. The same with the underground tracks, with possibly the added bonus of being able to start a tunnel on a straight cut rather than a slope.
« Last Edit: April 18, 2013, 07:54:24 AM by Bear789 »

Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #4 on: April 18, 2013, 07:31:18 AM »
Tunnels in simutrans are fully flexible - it's just bridges and elevated ways that aren't. Locomotion does have two types of bridges itself (effectively equivalent of bridges and elevated ways in simutrans). The problem with a fully flexible way of building bridges is that it would require lots of graphics (especially with double heights).

Offline Bear789

Re: Speed/weight limits of historical bridges
« Reply #5 on: April 18, 2013, 07:54:05 AM »
I don't remember Simutrans-style bridges in Locomotion. I know that tunnels are fully funcional (except for the slope requirement), I just thought that if a locomotion-style approach to ways will ever be added, it may as well hadle both elevated and underground.
For graphics, I was thinking at Pak 128 and 128 Britain, both have matching elevated ways and bridges for all the railway tracks kind. For pak 128 I think thatall the  roads too have matching elevated versions.

Offline The Hood

Re: Speed/weight limits of historical bridges
« Reply #6 on: April 18, 2013, 02:07:55 PM »
Pretty much as kierongreen says. I would support separating bridge/tunnel structures and the tracks which occupy them, but appreciate this would probably be a difficult coding task.

Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #7 on: April 18, 2013, 10:08:35 PM »
Locomotion has two types of bridges - a brick viaduct which can be fully flexible, and all other types which can only be level and straight - the same as Simutrans bridges. The brick viaduct with it's fully flexible layout is the tricky one to create something similar in Simutrans. Elevated ways don't have the graphics necessary for fully flexible layout - as this would need graphics for every combination of base slope and way slope. This is totally impractical, here's graphics requirements for different types of bridges:

Straight bridges: 12 (including pillars)
Elevated ways: 19
Fully flexible bridges: 462 - I think... This is split into 225 flat way images on various slopes, 12 way slope images and 225 pillar images

Note, this is for single height slopes, for double height slopes numbers are:
Straight bridges: 22
Elevated ways: 23
Fully flexible bridges: 12844 - 6800 flat way images on various slopes, 44 way slope images and 6800 pillar images.

I'm not sure how to go about implementing fully flexible bridges, it's actually something that been lurking in my mind for a while now. Restrictions of various kinds would cut down the number of images required, or would need some way of defining images for each corner.

Offline ӔO

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Re: Speed/weight limits of historical bridges
« Reply #8 on: April 19, 2013, 12:23:12 AM »
There are only a few types of bridges that can be curved.
They are mainly arch viaducts and girder derived that can take dynamic loads that curves can induce.
There are exceptions in the real world, but in simutrans I don't think it is necessary to have truss, arch or suspension bridges with curves.


If there was a block/tile/pillar that allowed ways to be built underneath, while allowing various ways or structures on top, then one would only need to build those instead of having needing slopes to build tunnels or bridges.
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Offline Fabio

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Re: Speed/weight limits of historical bridges
« Reply #9 on: April 19, 2013, 12:03:30 PM »
Ways should be built on top of bridges, so no new images should be needed.

Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #10 on: April 19, 2013, 04:09:54 PM »
The new images needed would be for the bridges themselves rather than the ways.

Offline jamespetts

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Re: Speed/weight limits of historical bridges
« Reply #11 on: April 19, 2013, 09:14:47 PM »
We should only need new bridge deck images, without ways, which should not be too difficult.
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Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #12 on: April 19, 2013, 11:00:39 PM »
If existing bridge restrictions are kept yes.

Offline jamespetts

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Re: Speed/weight limits of historical bridges
« Reply #13 on: April 19, 2013, 11:17:41 PM »
Removing the existing restrictions seems to be a larger task than separating the bridge from the way.
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Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #14 on: April 19, 2013, 11:56:08 PM »
A complete rework of bridges once double heights are implemented is on my todo list. It's one reason why I've not fully extended bridges to take advantage of double heights in my patch.

Offline jamespetts

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Re: Speed/weight limits of historical bridges
« Reply #15 on: April 20, 2013, 12:12:32 AM »
Interesting! What have you in mind?
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Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #16 on: April 20, 2013, 12:16:08 AM »
Bridges that link up with neighbours, can vary in height and can be made out of different images. With track independent of structure below. So realistic multi track brick viaducts, motorway flyovers and suspension bridges would be possible. Will see how far I'll get, still got ferries to look at after all!

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Re: Speed/weight limits of historical bridges
« Reply #17 on: April 20, 2013, 12:24:04 AM »
Very nice ideas! For what it's worth, I think that the bridges project would be more important than the car ferries project.
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Offline Carl

Re: Speed/weight limits of historical bridges
« Reply #18 on: April 20, 2013, 06:45:34 AM »
Sounds incredible, Kieron!

Offline Vonjo

Re: Speed/weight limits of historical bridges
« Reply #19 on: April 20, 2013, 07:05:02 AM »
For the time being, if you want bridge and track separation, you can build road bridges and lay tram track on it. So, you can upgrade the track without upgrading the bridge. The same trick can be used for tunnels too. ;)

Bridges that link up with neighbours, can vary in height and can be made out of different images. With track independent of structure below. So realistic multi track brick viaducts, motorway flyovers and suspension bridges would be possible. Will see how far I'll get, still got ferries to look at after all!
Wow 8)

Offline Bear789

Re: Speed/weight limits of historical bridges
« Reply #20 on: April 20, 2013, 07:46:34 AM »
Locomotion has two types of bridges - a brick viaduct which can be fully flexible, and all other types which can only be level and straight - the same as Simutrans bridges. The brick viaduct with it's fully flexible layout is the tricky one to create something similar in Simutrans. Elevated ways don't have the graphics necessary for fully flexible layout - as this would need graphics for every combination of base slope and way slope. This is totally impractical, here's graphics requirements for different types of bridges:

Straight bridges: 12 (including pillars)
Elevated ways: 19
Fully flexible bridges: 462 - I think... This is split into 225 flat way images on various slopes, 12 way slope images and 225 pillar images

Note, this is for single height slopes, for double height slopes numbers are:
Straight bridges: 22
Elevated ways: 23
Fully flexible bridges: 12844 - 6800 flat way images on various slopes, 44 way slope images and 6800 pillar images.

I'm not sure how to go about implementing fully flexible bridges, it's actually something that been lurking in my mind for a while now. Restrictions of various kinds would cut down the number of images required, or would need some way of defining images for each corner.

I don't understand this completely. We have elevated ways that are basically freeform 1 height bridges, what would be the differences with the number or graphics (except 1 additional tile for pillars)? I'm not arguing, just asking to understand the issue.

Anyway, I see that you have really interesting plans for bridges.

Offline kierongreen

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Re: Speed/weight limits of historical bridges
« Reply #21 on: April 20, 2013, 01:30:17 PM »
Elevated ways aren't freeform bridges,  they have to follow landscape, and as such can only be built on a limited number of tiles. Whereas genuine freeform bridges are much more complex. For example here's my current thoughts:
Pillars: Lowest level has to match slope of ground beneath it, followed by any number (or no) sections to get to bridge deck level
Under structure: (e.g. arches)
Bridge deck: Deck, back wall and front wall.
Way: Back layer and front layer.
Over structure: (e.g. suspension cables).

Currently bridges only have one tile repetition - there needs to be a more flexible way of defining this also as spans for some arches should be greater than a tile, and definitely in case of suspension bridges.

One issue with replacing tracks on bridges is what happens when bridges normally wouldn't have ballast on them? Some concrete beam designs fix track directly to bridge, and some bridges don't even have a solid deck! Example http://www.hera.org.nz/Category?Action=View&Category_id=468


Bridges joining to neighbours goes hand in hand with tracks having ballast between  neighbouring tracks as well...

Random sketches and mocked up screenshot attached.
« Last Edit: April 20, 2013, 01:50:21 PM by kierongreen »