Author Topic: WoK: Bridge Crews & Bridges  (Read 27236 times)

Eerongal

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Re: WoK: Bridge Crews & Bridges
« Reply #90 on: September 15, 2010, 07:31:16 PM »
A bit of a jump back in the conversation, but I recall we were discussing bridges being 50 feet long, When Kaladin first sees a bridge on page 101 it is said to be around 30 feet long.

Well, considering inkthinker was talking about the longest gaps they'd be seeing at 25 feet, this doesnt really hinder too much. In fact, it makes it a bit easier in the bridges not being so unwieldy.
But they wouldn't be able to push a 30 foot bridge out accross a gap 25 feet without it toppling, not easily anyway...

Oh, right, i fogot about that issue we were talking about. Yeah, i guess they would have to be weighted somehow.
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SnagglezMaw

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Re: WoK: Bridge Crews & Bridges
« Reply #91 on: September 15, 2010, 08:04:37 PM »
A bit of a jump back in the conversation, but I recall we were discussing bridges being 50 feet long, When Kaladin first sees a bridge on page 101 it is said to be around 30 feet long.

Well, considering inkthinker was talking about the longest gaps they'd be seeing at 25 feet, this doesnt really hinder too much. In fact, it makes it a bit easier in the bridges not being so unwieldy.
But they wouldn't be able to push a 30 foot bridge out accross a gap 25 feet without it toppling, not easily anyway...
Unless it was weighted in the back, but I don't think we know whether it was or not.

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Re: WoK: Bridge Crews & Bridges
« Reply #92 on: September 15, 2010, 08:05:07 PM »
Bear in mind, I was guessing at chasm widths based on estimations of bridge lengths.

He's right, on 101 it describes a bridge as 30 feet long and eight feet wide, wooden, sloping at the front and back and without railings. 5 men across (three beneath, one on each side) and 8 rows deep. The thickest boards run down the center for support.

He also describes the first chasm that they bridge (next page) as being about half as wide as the bridge is long, so maximum widths of 15-20 feet (at bridging points) are probably more accurate.

"About 30 feet" leaves us some room to play, of course.

Unless someone finds a wider chasm being described (and crossed by the bridge crew) I think the math is still valid.

Erunion

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Re: WoK: Bridge Crews & Bridges
« Reply #93 on: September 15, 2010, 08:12:15 PM »
Ermm... They would be able to push a 30 foot bridge over a 25 foot chasm because it is weighted. By the Bridgemen.  :o It would be a simple, even a necessary matter to push down slightly while pushing the bridge over the chasm. This pushing down would keep it sticking out horizontally. Of course, if many bridgemen died the bridge would topple over the edge, but I suspect that that wouldn't be too much of an issue. (The bridges could be replaced with new ones)
To prove my theory, with one hand push a hardcover book to the edge of a table. See how far you can push it without it tipping over, while only using one hand. (Don't grab it.)
You'll be able to get surprisingly far! (Please don't use, WOK, not only is it far too thick for an accurate comparison, the risk of damage to said great tome is too great.)   ;)

SnagglezMaw

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Re: WoK: Bridge Crews & Bridges
« Reply #94 on: September 15, 2010, 08:22:38 PM »
Ermm... They would be able to push a 30 foot bridge over a 25 foot chasm because it is weighted. By the Bridgemen.  :o It would be a simple, even a necessary matter to push down slightly while pushing the bridge over the chasm. This pushing down would keep it sticking out horizontally. Of course, if many bridgemen died the bridge would topple over the edge, but I suspect that that wouldn't be too much of an issue. (The bridges could be replaced with new ones)
To prove my theory, with one hand push a hardcover book to the edge of a table. See how far you can push it without it tipping over, while only using one hand. (Don't grab it.)
You'll be able to get surprisingly far! (Please don't use, WOK, not only is it far too thick for an accurate comparison, the risk of damage to said great tome is too great.)   ;)
That's a good point, it hadn't even crossed my mind.

At the end when Kaladin was running across the bridge, he probably would have tipped it over but having weight in the back might have been the reason the bridge didn't topple into the chasm. Keep in mind, this is the Tower and we were assuming the length of the chasm around the Tower to be roughly 25 feet, as it was noted that the bridge just barely fit. It would have to have weight, I think, otherwise Kaladin would have just brought the bridge, and himself, down.

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Re: WoK: Bridge Crews & Bridges
« Reply #95 on: September 15, 2010, 08:43:28 PM »
Ermm... They would be able to push a 30 foot bridge over a 25 foot chasm because it is weighted. By the Bridgemen.  :o It would be a simple, even a necessary matter to push down slightly while pushing the bridge over the chasm. This pushing down would keep it sticking out horizontally. Of course, if many bridgemen died the bridge would topple over the edge, but I suspect that that wouldn't be too much of an issue. (The bridges could be replaced with new ones)
To prove my theory, with one hand push a hardcover book to the edge of a table. See how far you can push it without it tipping over, while only using one hand. (Don't grab it.)
You'll be able to get surprisingly far! (Please don't use, WOK, not only is it far too thick for an accurate comparison, the risk of damage to said great tome is too great.)   ;)

Except that every foot or so is going to be literally hundreds of pounds of weight added opposing the bridgemen holding on to it. an 8 foot wide bridge is going to be heavy per foot of it. Plus, as they push it forward, less people are able to help, because there's less room for holding on to.
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rjl

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Re: WoK: Bridge Crews & Bridges
« Reply #96 on: September 15, 2010, 09:14:17 PM »
If it's weighted by anythign other than bridgemen they can't pull it accross after crossing it, of course this doesn't matter for the tower(or any other battle plateau), where they're crossing to fight then crossing back, but for the intermediate plateaus where they need to cross onto the plateau and cross a different gorge off of the plateau ahving the bridge weighted to enable them to cross would mean they couldn't then pull it accross. Unless it's just weighted by the bridge men, remember though, that a wooden bidge that's 30 foot by 8 foot would be pretty heavy, would 20-30 men be enough to weight it? Especially with only 5 feet to weight it in (if they're crossing a 25 foot gorge, just before the bridge reaches the other side it would ahve a mere 5 feet left on the near side, I guess 5 foot by 8 foot is a large-ish area...)
« Last Edit: September 15, 2010, 09:15:57 PM by Rhuan »

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Re: WoK: Bridge Crews & Bridges
« Reply #97 on: September 15, 2010, 09:19:34 PM »
If it's weighted by anythign other than bridgemen they can't pull it accross after crossing it, of course this doesn't matter for the tower(or any other battle plateau), where they're crossing to fight then crossing back, but for the intermediate plateaus where they need to cross onto the plateau and cross a different gorge off of the plateau ahving the bridge weighted to enable them to cross would mean they couldn't then pull it accross. Unless it's just weighted by the bridge men, remember though, that a wooden bidge that's 30 foot by 8 foot would be pretty heavy, would 20-30 men be enough to weight it? Especially with only 5 feet to weight it in (if they're crossing a 25 foot gorge, just before the bridge reaches the other side it would ahve a mere 5 feet left on the near side, I guess 5 foot by 8 foot is a large-ish area...)

Well, an 8 foot long 2x4 weighs about 10 pounds. So that would lead us to presume the part people walk across (to say nothing of the rest of the bridge) would weigh at least 30 pounds on its own per foot. Then we have to figure in all the wood connectors, and and bracing that goes into building a bridge. That's going to get very heavy, very quickly.
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Erunion

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Re: WoK: Bridge Crews & Bridges
« Reply #98 on: September 15, 2010, 09:24:06 PM »
While it's never specifically mentioned, I always imagined the bridgemen moving closer together as the bridge crossed, with everyone having a hand in it until the end. This could easily account for chasms up to about 23 feet wide. Once you start hitting 24-26, things would get very, very difficult, requiring a lot of momentum and a small height advantage to get you over the last foot or so. 27-29 would be basically impossible (only feasible with a full bridge crew, a running start and a major height advantage), and 30 would be impossible. (This is what my experimentation with hardcovers has shown me)
Now, how heavy can the bridges really be? Consider; 25 malnourished, maltreated men, generally the scum of the earth before they were thrown into the bridges, can carry a bridge for hours at a time, at a jog. I don't think this would be possible if the men were carrying more than about 75 pounds each. Under those circumstances, and for that length of time, 75 pounds each would be pushing it, more would be nearly impossible. Less, around 50-60, would be likely. So, the heaviest the bridge could be would be approximately 1875 pounds. A more likely figure would be 1250. As the bridges are likely made from the lightest woods available, this seems an accurate figure. (I am, of course, no woodworker. If someone with more experience in that field could comment on the accuracy of my figures, please do). As the average man, even under those circumstances, would weigh between 150-200 pounds, It would only take 10 men to equal the weight of the bridge. Ten men leaning and pushing the bridge would be able to keep it upright right up to the end. For the very long chasms, you could have more men pile on top of the end of the bridge, keeping it stable. (As such behavior isn't mentioned in the book, I take it to have been unnecessary. Likely they were able to get enough people holding on to the end to anchor it to the plateau.)
As such, it seems likely that the bridges could cross chasms up to 25 feet wide without too much trouble, unless the bridge is overwhelmed by enemy arrows, leaving a bare handful of men to push.

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Re: WoK: Bridge Crews & Bridges
« Reply #99 on: September 15, 2010, 09:45:40 PM »
speaking of "using the lightest wood available", i'd bet dimes-to-dollars that wood in roshar is heavier than just about all wood here. Because the weight of wood depends on the moisture in the environment, and roshar is a very moist climate.

Anywho, like i said before, it would be about 30 pounds per foot of just the walking area of the bridge. This is 900 pounds for the part you walk on alone. This includes none of the supporting structure  nor anything connecting this wood together. 350 pounds of building and structural support is very little on a 30 foot length of wood if you ask me.
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Erunion

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Re: WoK: Bridge Crews & Bridges
« Reply #100 on: September 15, 2010, 10:08:44 PM »
That's assuming they use modern weighted thicknesses and planks. With proper supports, you could make the wood relatively thin, even the crossbeams. 1250-1500 could easily be the weight of the bridge.
Yes, Rosharan wood is likely heavier. But if it is denser, it is also likely stronger, so it doesn't have to be nearly so thick, leaving the weight roughly the same. Of course, even if it were heavier, just add more people to the end. That equals more weight at the end, making the bridge effective over long chasms. 

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Re: WoK: Bridge Crews & Bridges
« Reply #101 on: September 15, 2010, 10:18:47 PM »
That's assuming they use modern weighted thicknesses and planks. With proper supports, you could make the wood relatively thin, even the crossbeams. 1250-1500 could easily be the weight of the bridge.
Yes, Rosharan wood is likely heavier. But if it is denser, it is also likely stronger, so it doesn't have to be nearly so thick, leaving the weight roughly the same. Of course, even if it were heavier, just add more people to the end. That equals more weight at the end, making the bridge effective over long chasms. 

I'm pretty sure using a 2X4 like i was saying (with 4 inches long ways) is all ready incredibly thin for the walking area of a bridge that's 8 feet wide. Regardless of how dense it is, over the length of 8 feet, it'll make it have a lot of give if its thinner.

I know most of the pedestrian bridges in my area use planks a good 4-6" thick on the walking plane on a bridge thats about 4 or 5 foot wide. (at least the ones i played under as a kid did) I'm not saying this is the most efficient bridges ever, but im pretty sure the 2" i gave on the 2x4 would have to probably be a very low minimum thickness to even be possible.

Edit: especially when you consider the fact that mounted cavalry will be charging over it.
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Re: WoK: Bridge Crews & Bridges
« Reply #102 on: September 15, 2010, 10:36:29 PM »
Properly crossbraced, it should be possible. Still, if you are right and it is indeed some 2000 pounds, it would still be manageable up to about 25 feet by a group of 10-15 men. The weight can't be greater than 100 pounds per person for 25 carriers, or it would never get to the battlefield. So my original upper estimate of 1500-1650 still stands as the heaviest feasible weight, with some 1250-1350 more likely.

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Re: WoK: Bridge Crews & Bridges
« Reply #103 on: September 15, 2010, 10:53:53 PM »
Properly crossbraced, it should be possible. Still, if you are right and it is indeed some 2000 pounds, it would still be manageable up to about 25 feet by a group of 10-15 men. The weight can't be greater than 100 pounds per person for 25 carriers, or it would never get to the battlefield. So my original upper estimate of 1500-1650 still stands as the heaviest feasible weight, with some 1250-1350 more likely.

Actually, now that you mention it, you're right, it couldn't possibly be more than 100 pounds per person for it to realistically carry it. However, a bridge that size with that weight restriction, i couldnt see it being reinforced enough to support cavalry. I'm honestly really starting to doubt the physics behind it as being possible.

bear with me here, this is just off the cuff, but wikipedia concerning horses in war, back in ancient times a "Light" war horse was anywhere from 800-1000 pounds. However, for it to use an armored rider (im pretty sure it mentioned his cavalry was armored, right), at least a medium horse is required, which weighs in about 1000-1200 pounds. Add in an armored rider, and we're looking at 1300-1700 or so pounds for a SINGLE cavalry man (200-300 or so for the man, and 100-200 for the armor).

Obviously, for a cavalry charge, we're going to have more than one cavalry man on the bridge, and they wont be moving single file. Realisticly, i would bet they're either moving double or triple file, considering the bridge width of 8 feet (beyond that, its going to get very crowded very fast)

So likely scenario, cavalry will be charging in double file. that's anywhere from 2600-3400 pounds on the bridge at any given moment.

To put that in perspective, a 2001 Nissan Altima weighs about 2945 pounds (so sayeth a quick google search)

So per rank of cavalry man, we're looking at the weight of a good-sized sedan or more depending on what file they use.

This is going to utterly crush your average pedestrian walking bridge (which earlier i estimated at about 4-6" in thickness for the walking part).

I cant honestly see a 30 foot long bridge weighing a mere 2000 pounds able to hold so much weight, however, as established, it cannot possibly weigh more than this for carrying purposes.

I just can't see these numbers working themselves out.

Honestly, i think this is just going to have to be one of those issues where we just agree that suspension of disbelief takes over, and we just assume "it works", because the author said so (i'm sure brandon didnt do terribly much research into the mechanics of it, and just wrote it as is because its a believable situation at face-value)
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SnagglezMaw

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Re: WoK: Bridge Crews & Bridges
« Reply #104 on: September 15, 2010, 11:03:05 PM »
Properly crossbraced, it should be possible. Still, if you are right and it is indeed some 2000 pounds, it would still be manageable up to about 25 feet by a group of 10-15 men. The weight can't be greater than 100 pounds per person for 25 carriers, or it would never get to the battlefield. So my original upper estimate of 1500-1650 still stands as the heaviest feasible weight, with some 1250-1350 more likely.

Actually, now that you mention it, you're right, it couldn't possibly be more than 100 pounds per person for it to realistically carry it. However, a bridge that size with that weight restriction, i couldnt see it being reinforced enough to support cavalry. I'm honestly really starting to doubt the physics behind it as being possible.

bear with me here, this is just off the cuff, but wikipedia concerning horses in war, back in ancient times a "Light" war horse was anywhere from 800-1000 pounds. However, for it to use an armored rider (im pretty sure it mentioned his cavalry was armored, right), at least a medium horse is required, which weighs in about 1000-1200 pounds. Add in an armored rider, and we're looking at 1300-1700 or so pounds for a SINGLE cavalry man (200-300 or so for the man, and 100-200 for the armor).

Obviously, for a cavalry charge, we're going to have more than one cavalry man on the bridge, and they wont be moving single file. Realisticly, i would bet they're either moving double or triple file, considering the bridge width of 8 feet (beyond that, its going to get very crowded very fast)

So likely scenario, cavalry will be charging in double file. that's anywhere from 2600-3400 pounds on the bridge at any given moment.

To put that in perspective, a 2001 Nissan Altima weighs about 2945 pounds (so sayeth a quick google search)

So per rank of cavalry man, we're looking at the weight of a good-sized sedan or more depending on what file they use.

This is going to utterly crush your average pedestrian walking bridge (which earlier i estimated at about 4-6" in thickness for the walking part).

I cant honestly see a 30 foot long bridge weighing a mere 2000 pounds able to hold so much weight, however, as established, it cannot possibly weigh more than this for carrying purposes.

I just can't see these numbers working themselves out.

Honestly, i think this is just going to have to be one of those issues where we just agree that suspension of disbelief takes over, and we just assume "it works", because the author said so (i'm sure brandon didnt do terribly much research into the mechanics of it, and just wrote it as is because its a believable situation at face-value)

Remember this isn't our world either. This is a world that takes place in a sort of medieval time. The "average joe" is probably very strong from laboring anyways (and presumably a murderer or convict even more so).