Bridge specifications?

[Aspren]

Hi, I've been lurking these forums for a while, and thought I might post what I think the bridges look like.

 

Obviously I'm basing it off of the descriptions in the book, namely these ones:

 

...looked like about thirty-five to forty men per bridge. There was room for five men across—three under the bridge and one on each side—and eight deep

It was a wooden bridge, over thirty feet long, eight feet wide. It sloped down at the front and back, and had no railings. The wood was thick, with the largest boards for support through the center. 

 

 

 

This is the front and top view of the bridge:

 

The bridge is roughly 10.3 meters (34 feet) long and 3.4 meters (11 feet) wide, which is slightly larger than specified in the book.

The bridge is roughly 4.6 m³, which if the density of the wood is 600kg/m³ (but it's probably less) then the bridge has a mass of 2760kg, that's about 70kg per bridgeman, if there's 40 of them. If I remember correctly Brandon did state that Roshar has only 7/10 of the gravity of Earth, which would make 70kg on Roshar have the weight of 48kg on Earth.

 

 

Here's a version with some crude dummy bridgemen:

 

 

 

I'm not too sure that I got the design right. There are quite a few things that confuse me, such as it being stated that the bridge curves down at the ends. If there's anything I've missed (which I undoubtedly have) don't hesitate to tell me.

Edited January 18, 2014 by Aspren

[Moist_von_Lipwig]

Looks good, for some reason I always imagined them having support on the sides to stop them flexing when over the chasm. Though it apparently says otherwise in the book. I assume that it would slope down at the ends to give less of a step for crossing troops and cavalry.

 

Nothing missing immediately comes to mind, good work.

 

-Postmaster Lipwig

Edited January 18, 2014 by Moist_von_Lipwig

[king of nowhere]

clearly it must be lighter than that, or the bridgeman would not be able to carry it. the double advantage of reduced gravity is not only that your bridge will wheight less, but since the troops crossing it will also be lighter you can make a thinner bridge, saving further wheight.

And I really loike your drawings. I think they are fairly accurate.

[Natans]

Nice first post be welcomed =)

 

And I liked you model, the only thing that i imagined diferent was the place to the brigdemen put their heads

 

Take this upvote for your nice work =)

Edited January 18, 2014 by Natans

[Aspren]

Looks good, for some reason I always imagined them having support on the sides to stop them flexing when over the chasm. Though it apparently says otherwise in the book. I assume that it would slope down at the ends to give less of a step for crossing troops and cavalry.

 

Nothing missing immediately comes to mind, good work.

 

Thanks. I agree that the bridge should probably have more struts to strengthen it as a whole. king of nowhere makes a good point, that both the weight of the bridge and those who use it is less than would be on Earth.

 

I did make a version with it sloping down on the ends, but then the problem is that it shields the three centre-front bridgemen, which is clearly indicated that it isn't so.

 

clearly it must be lighter than that, or the bridgeman would not be able to carry it. the double advantage of reduced gravity is not only that your bridge will wheight less, but since the troops crossing it will also be lighter you can make a thinner bridge, saving further wheight.

And I really loike your drawings. I think they are fairly accurate.

 

Very good point. I imagine that the various of types of wood on Roshar would be extremely dense, due to them needing to be able withstand Highstorms.

 

Nice first post be welcomed =)

 

And I liked you model, the only thing that i imagined diferent was the place to the brigdemen put their heads

 

Take this upvote fot your nice work =)

 

Thanks. 

 

Ah, so that's what I forgot. I forgot that it was stated that there were spaces for their heads underneath the bridge.

Edited January 18, 2014 by FeatherWriter
Try to avoid double posting!

[Moist_von_Lipwig]

Yes I believe there was a hollowed out space in the beams, like a semi-circle, where their heads would go. Allowing them to rest the beams on their shoulders. As well as hand-holds, but I'm not sure what they would look like.

 

I see on your drawing you've curved up the bottoms on the ends of the beams, presumably to make it easier to slide onto a plateau. It seems odd that the bridges would slope down on either end, surely this would make them harder to get onto a plateau?

[Aspren]

Yes I believe there was a hollowed out space in the beams, like a semi-circle, where their heads would go. Allowing them to rest the beams on their shoulders. As well as hand-holds, but I'm not sure what they would look like.

 

I see on your drawing you've curved up the bottoms on the ends of the beams, presumably to make it easier to slide onto a plateau. It seems odd that the bridges would slope down on either end, surely this would make them harder to get onto a plateau?

 

I don't think it was stated that there were semi-circular hollowed out spaces, though. I will make more enclosed spaces for their heads though. maybe just by putting support beams through the main lateral beams, sectioning off each of the bridgemen's spaces.

 

Hand-holds are the other thing I forgot. I'm also not sure how I'd make the handholds look though. Wooden rods attached to the main lateral beams maybe?

 

Exactly my thoughts, It is possible that it was just a typo, unlikely as that is, maybe it was meant to be said that they curved upwards.

 

I by mistake clicked the downvote button instead of the upvote button. Could somebody please upvote that comment to negate the downvote?

Edited January 18, 2014 by Aspren

[FeatherWriter]

Whoa that looks super cool! I really like it! It's funny, my first few readthroughs I pictured the bridge as completely flat, but then when I caught that "sloped in the front and the back" I immediately read it as way more curved. I think I like your version best of all! I can definitely see how that could be turned on its side and used like a shield in side-carry.

 

Also, you did math, so as an English person, that is intolerably impressive to me! Good to have you around!

 

Quick note, since I'm a mod now and I've got to earn my keep: Try to avoid double posting! You can quote multiple people in one post with the "multiquote" button, and there's an edit button if you need to change or add anything! It helps keep the forums uncluttered. I've gone ahead and changed yours for you, it's just something to keep in mind in the future!

[Aspren]

Whoa that looks super cool! I really like it! It's funny, my first few readthroughs I pictured the bridge as completely flat, but then when I caught that "sloped in the front and the back" I immediately read it as way more curved. I think I like your version best of all! I can definitely see how that could be turned on its side and used like a shield in side-carry.

 

Also, you did math, so as an English person, that is intolerably impressive to me! Good to have you around!

 

Thanks.  

 

For some reason, on my first readthrough, I thought the bridges were typical frame bridges, triangulation and all. 

 

 

 

Quick note, since I'm a mod now and I've got to earn my keep: Try to avoid double posting! You can quote multiple people in one post with the "multiquote" button, and there's an edit button if you need to change or add anything! It helps keep the forums uncluttered. I've gone ahead and changed yours for you, it's just something to keep in mind in the future!

 

Okay, will do so, thanks.

[Chrono]

This model is great! I honestly imagined the bridge as more curved, but now that I think about it, your design makes a lot more sense. Although, my question is, how does a bridge crew actually push a bridge across a chasm? The only way I could think was that most of the men on the sides would push while the guys in the middle and back would push down on the back of the bridge so that it doesn't topple over. Any ideas?

[Inkthinker]

MWAHAHAA... I just did this tonight, I wish I'd thought to look here sooner (I hope I'm not hijacking by inserting my own idea, but it seemed sensible to keep any ideas for bridge specs in one thread).

-EDIT- In light of some feedback from both fans and Peter/Isaac, I made a couple revisions. The posts are removed, the height increased by half, and the horizontal posts extended to make room for two men. I think that pushes this a bit closer to "correct".

Edited January 19, 2014 by Inkthinker

[Inkthinker]

I really like the OP design, but it suffers from the concerns that made me want to modify the specs a little... most importantly, how would your bridgemen place themselves to push the bridge? The horizontal beams give you something to push against, but only for about one person, and if they're too low to the ground then that would be very difficult to push. I've got the horizontal bars about 1.5 feet up, and the vertical bars so that you can have at least two on each side, but in doing so I've really pushed the line on "no railing".

Anyone got a third idea?

[FeatherWriter]

Whoaaaaa. Hello there new bridge headcanon. Ben never ceases to amaze with his designs. That is absolutely fantastic!

[Inkthinker]

Not canonized in any way, bear in mind! I haven't run this past Brandon or Isaac or Peter (well, actually I sent this out to them at the same time I put it up here, but who knows when I'll hear back). I'm working off the reservation, here.

The posts are certainly a cheat... having now gone and re-read that chapter, there's references to handholds and men grouping at the sides and back, but I'm sure he didn't have these posts in mind. Problem is that if you've ever tried to push something at a point around your knees or lower, it's REALLY hard to direct force forward rather than down. And at the back, if you're pushing on that sloped surface, you almost certainly can't get traction or apply a forward push effectively. I added little runners about four inches high so that you're not impacting the crossbeams along the bottom against the surface of the plateau.

It probably could work at 30' or somewhere between, but since I'm not on the clock I decided to try it the way I wanted it. If I wanted to shorten it up a bit, I'd make the ramps half their length... that would bring it to 35' or so, but they'd be quite steep.

The narrative isn't clear how far back they start pushing, but I reckon if all eight ranks start off then you can get some momentum and inertia will help carry it forward as the first four ranks clear off to the sides or get taken out by arrows. Ideally those men peeling away as they cross would run to the back and keep helping the push, but in practice they probably just run out of the firing lane or die. So long as you have at least 20 men pushing, it ought to keep going, I think.

[Vauric]

Perhaps it's not that there's no railing, but that the distance between the top of the bridge and the bottom is larger than we're thinking. More like 4 feet, giving the bridgemen something to push against along the sides, but also not counting as a railing when crossing the top.

[Inkthinker]

As noted above, I revised the design to remove the posts, extend the bars and increased the height to place those bars at a a better pushing position. I reckon 4 feet is a bit too steep, that would be a near 45-angle coming on and off, but 2-3 feet seems right to me... pushing at about the height of a car bumper, which is something I think we can all relate to easily.

Thoughts?

Edited January 19, 2014 by Inkthinker

[DocHoliday]

You've done a great job revising the OP in the exact same way I did InkThinker. Upvote.

 

Upon review however, I'm noticing a major problem with the Side Carry. I doubt more than 9 men have proper leverage to be any real aid in momentum in this position.

 

 If we assume the bars are long enough to allow two men to push to 1 bar, these side rails/ pushing bars are a minimum of 4-5 long, a major issue if Bridge 4 uses the bridge as a shield. 

Also of we increase the size of the rear rails/push bars then we encounter a similar issue of people unable to utilize the bridge as a shield.

[Inkthinker]

I think you could fit as many as 20-30 if they shuffle more than run, but yeah... not as many people are carrying that weight, even on a diagonal. I'll mess around a bit and see if I can work it out. Some of them are going to end up lifting by pushing and some will lift by pushing. We need a minimum of 25 to lift the bridge, according to the text.

Hah. It's even more important that it be a little longer than 30'. Thank goodness for that "about", it's the weasel word we can squeeze until it's squeaks.

I don't think the push bars need to be more than three feet out each side in order to let two men push on them, and I imagine the Side Carry as more of a diagonal angle than straight up/down. And in the end it was a really awkward technique that never worked well, and got several other, less-coordinated crews killed.

Edited January 19, 2014 by Inkthinker

[DocHoliday]

It's mentioned that it is indeed at an angle, though I imagine something like a 65° - 70° angle to be about right, something else might be appropriate.

 My main issue is that gap  for the side pushing bars. Even a 3' gap, and we have to agree that Bridge 4 isn't dragging the handles(so 3'6") that is a significant area for Parshendi arrows.

[Inkthinker]

The side-carry!



I can fit five men per rank for the full 40 (not that Bridge 4 had a full 40) but they need to stagger in 3/2 rows and double up in the space. The shortest man is lifting most of the weight, doing a sort of low-roadie-run, but he gets to lift more with his back so maybe it's okay,. And they trade the short position every time they flip the bridge to the other side. The Parshendi could skip arrows under the edge, but that's a heck of a trick shot (and the narrative does mention arrows skipping around their feet).

You can see how this messed up the other bridge crews that hadn't practiced the side-carry. But I think this works.

Edited January 19, 2014 by Inkthinker

[Cromptj]

So if the bridge is just over 10m long, the chasms are probably around 5m across max because it gets difficult to stop the bridge from falling into the chasm otherwise. I do think that the bridge needs to be a bit thicker as it has to support a cavalry charge of about 8 horses at a time (2x4). The weight of a medium warhorse is around 450-540kg so including a guy with armour, the max weight for a horse is probably around 450kg on Roshar. That would make the weight that the bridge is supporting about 3600kg and the horses would be at a gallop.

[Inkthinker]

I'm painfully stuck with the Imperial measuring system, but the basic premises are the same... if the bridge extends beyond it's mid-point, it will start to tip. If the opposite side is further than half the length of the bridge, it had better be lower because that bridge is about to slide down.

But if we go with 40' (cheating), then that's a 20' gap, which is not small... about the width of a two-lane street common to most suburbs. Much farther than anyone can jump. I'm thinking Dalinar's tower-bridges can cross gaps up to twice that distance, because the design I have for that would let almost the whole bridge extend over the chasm rather than half, but his bridges are slow. He can take a more direct route, but he's not as fast.

 

Does it say the horses charge in double-wide formation? The width is about 8 feet, so that's possible, but man that's a tight fit. I figured troops for double-wide with a shield wall and set spears (see the charge of the orcs up the ramp at Helm's Deep in Jackson's LotR for a similar formation, sans battering ram), but that cavalry would charge single-file across multiple bridges. If I were sending in the troops, I'd send over a shield-heavy spear group to clear the immediate area around the bridge, then blast in the cavalry to wreck their lines deep, and follow through with more troops. But I know when Kaladin wrecks the plan with the side-carry, he's expecting a cavalry charge first. I just don't recall it specifically saying they charge two abreast.

Structurally, all the weight is born by the outer walls, distributed along a grid of crossbeams. I'm not enough of an engineer to know if that would hold a couple tons of galloping horse and armored rider, but I think that might be the point where we start shuffling our feet and waving our hands. There's beams and a box and It's only got to be believable enough.

When calculating weight, don't forget that Rosharan gravity is .7 of Earth, and the oxygen count is higher. I'm also not sure their common cavalry horses are on weight with a warhorse, Ryshadium horses being another beast altogether... I have a feeling that if we nailed it down, the cavalry horse of the Alethi would probably be a hardy little charger rather than a lumbering warhorse. Outside of Shinovar grass is a sneaky little devil, which means that grazing has got to be expensive and tricky, and I feel like lighter, smaller horses would be the norm.

Edited January 19, 2014 by Inkthinker

[Cromptj]

The horses that we know have only been around for 1500 years or so. Even in Alexander the Great's time, his heavy cavalry only had horses the size of ponies. The Shin probably have not implemented a breeding program for their horses so we should expect the horses to be even smaller than that. This is fiction, however, so guessing the heaviest warhorse outside of a Ryshadium is about the size of a medium sized warhorse seems about right. the weight I calculated was at .7 gravity with a man in light plate armour.

EDIT: for reference, 1kg is 2.2lbs. So the total weight of the horses and riders is about 8000lbs. The cavalry charge almost has to be 2 across per bridge because otherwise the cavalry would get isolated before the infantry would arrive. At this point the bridges probably don't really work because the horses would break them. The bridge could probably take the weight if they were walking but the boards may well break if they are at a gallop.

Edited January 19, 2014 by Cromptj

[Inkthinker]

I feel like you could get away with single-file charge so long as you were following up in close formation and zippering off as you cross. That first horseman really has to power through the infantry on the other side, but if he leans left and the man behind leans right and the next fellow left and etc, they could clear space pretty fast. Of course, if the Parshendi set spears it's gonna be a mess (such is ever the fear for cavalry), but if they have good front barding and a horse trained to bite and kick and slash in concert with his rider, I can see them pounding through at a full gallop with longspears set, shafting a few Parshendi on the run, then dropping the lance and laying in with the sword, mace, axe and hoof, creating pools of constantly moving havoc in the enemy lines.

But I think if you ride stirrup-to-stirrup you could do the same double-wide, and at 8 feet across I guess there's just enough room to get away with it.

 

We're gonna have to presume for now (in lack of someone with engineering experience) that the bridge can take it.

Edited January 19, 2014 by Inkthinker

[Aspren]

I really like the OP design, but it suffers from the concerns that made me want to modify the specs a little... most importantly, how would your bridgemen place themselves to push the bridge? The horizontal beams give you something to push against, but only for about one person, and if they're too low to the ground then that would be very difficult to push. I've got the horizontal bars about 1.5 feet up, and the vertical bars so that you can have at least two on each side, but in doing so I've really pushed the line on "no railing".

Anyone got a third idea?

 

The posts are a great idea. I don't think they can be considered rails, so I think you can get away with it.

 

The posts are certainly a cheat... having now gone and re-read that chapter, there's references to handholds and men grouping at the sides and back, but I'm sure he didn't have these posts in mind. Problem is that if you've ever tried to push something at a point around your knees or lower, it's REALLY hard to direct force forward rather than down. And at the back, if you're pushing on that sloped surface, you almost certainly can't get traction or apply a forward push effectively. I added little runners about four inches high so that you're not impacting the crossbeams along the bottom against the surface of the plateau.

The narrative isn't clear how far back they start pushing, but I reckon if all eight ranks start off then you can get some momentum and inertia will help carry it forward as the first four ranks clear off to the sides or get taken out by arrows. Ideally those men peeling away as they cross would run to the back and keep helping the push, but in practice they probably just run out of the firing lane or die. So long as you have at least 20 men pushing, it ought to keep going, I think.

 

I don't think it'd be too hard to push the bridge even if the placement of the pushing points (I don't know what else to call them) are low, as it's implied that the Shattered Plains terrain is fairly smooth and hard. Even heavy wooden constructs like the bridges would most likely slide across it fairly easily.

 

I'm painfully stuck with the Imperial measuring system, but the basic premises are the same... if the bridge extends beyond it's mid-point, it will start to tip. If the opposite side is further than half the length of the bridge, it had better be lower because that bridge is about to slide down.

But if we go with 40' (cheating), then that's a 20' gap, which is not small... about the width of a two-lane street common to most suburbs. Much farther than anyone can jump. I'm thinking Dalinar's tower-bridges can cross gaps up to twice that distance, because the design I have for that would let almost the whole bridge extend over the chasm rather than half, but his bridges are slow. He can take a more direct route, but he's not as fast.

 

Does it say the horses charge in double-wide formation? The width is about 8 feet, so that's possible, but man that's a tight fit. I figured troops for double-wide with a shield wall and set spears (see the charge of the orcs up the ramp at Helm's Deep in Jackson's LotR for a similar formation, sans battering ram), but that cavalry would charge single-file across multiple bridges. If I were sending in the troops, I'd send over a shield-heavy spear group to clear the immediate area around the bridge, then blast in the cavalry to wreck their lines deep, and follow through with more troops. But I know when Kaladin wrecks the plan with the side-carry, he's expecting a cavalry charge first. I just don't recall it specifically saying they charge two abreast.

When calculating weight, don't forget that Rosharan gravity is .7 of Earth, and the oxygen count is higher. I'm also not sure their common cavalry horses are on weight with a warhorse, Ryshadium horses being another beast altogether... I have a feeling that if we nailed it down, the cavalry horse of the Alethi would probably be a hardy little charger rather than a lumbering warhorse. Outside of Shinovar grass is a sneaky little devil, which means that grazing has got to be expensive and tricky, and I feel like lighter, smaller horses would be the norm.

 

 

It's stated that spearmen cross the bridge in rows of four:

 

Soldiers crossed the bridge four across, spears held high, shields forward.

 

It's a good point you make concerning the horses. I hadn't considered that.

 

There's just two problems I can see with your design. It's stated that the bridgemen in the front row are fully exposed, head to toe, but with your bridge the ramp shields their heads and upper bodies. Which is the same problem I had with one of my initial ridge design.

I had to design my bridge with a steps at the ends instead of ramps, which is problematic, because it limits how high the bridge can be.

 

Kaladin stood at the very front with...   ...Five men in front. The deathline.

Shafts struck the ground at Kaladin's feet, shattering, and a good half dozen hit the wood around Kaladin's head and hands.

 

 

It's hard telling what exactly your bridge is constructed out of, It's stated that the bridge is mainly constructed out of thick boards and broad beams, but your bridge seems to be mainly framework constructed out of fairly thin beams (which I admit probably has better structural integrity for less mass).

 

Overall, great design!