Roof raise thoughts

[2kool4skool]

First, I am not a structural or automotive engineer. I am a retired pole climbing, dirty old linemen.
I have no experience doing roof raises.
I am NOT anti-roof raise.

I have been poking around the internet, looking at the way buses are built.

Skoolies are not built like other buses.

Big old over the road tour buses have a truss frame that doesn't rely on roof/walls for stability. A Skoolie needs it's box intact to be strong.

Build the crap out of your roof raise, return the box to it's original integrity.

These observations are probably worth what you paid for them.

We all know what a Skoolie looks like with the roof (and walls) cut off.
This is what a big bus looks like in the same condition.

I find this very interesting, you may not. :wink1:

 

[musigenesis]

First, I am not a structural or automotive engineer. I am a retired pole climbing, dirty old linemen.
I have no experience doing roof raises.
I am NOT anti-roof raise.

I have been poking around the internet, looking at the way buses are built.

Skoolies are not built like other buses.

Big old over the road tour buses have a truss frame that doesn't rely on roof/walls for stability. A Skoolie needs it's box intact to be strong.

Build the crap out of your roof raise, return the box to it's original integrity.

These observations are probably worth what you paid for them.

We all know what a Skoolie looks like with the roof (and walls) cut off.
This is what a big bus looks like in the same condition.

I find this very interesting, you may not. :wink1:

A central part of a school bus body's integrity is the ribs forming the walls and roof, bent from single pieces of homogenous hat channel material. A roof raise cuts these ribs in two places, and even the best-quality welding and bolting of the rib extenders will still concentrate stresses at those cuts (even if the welds and extenders are stronger than the channel material this will happen) making them prone to fail.

I am also not anti-roof raise, I just don't think people should be expecting their raised buses to be as structurally strong as they were before the modification. Just don't ride in the back of the damn things.

 

[Sleddgracer]

First, I am not a structural or automotive engineer. I am a retired pole climbing, dirty old linemen.
I have no experience doing roof raises.
I am NOT anti-roof raise.

I have been poking around the internet, looking at the way buses are built.

Skoolies are not built like other buses.

Big old over the road tour buses have a truss frame that doesn't rely on roof/walls for stability. A Skoolie needs it's box intact to be strong.

Build the crap out of your roof raise, return the box to it's original integrity.

These observations are probably worth what you paid for them.

We all know what a Skoolie looks like with the roof (and walls) cut off.
This is what a big bus looks like in the same condition.

I find this very interesting, you may not. :wink1:

lets just say, 'there is less work in doing a roof raise in a tour bus'

 

[david.dgeorge07]

Seems like the tour bus has far fewer structural members supporting the roof. The roof looks strong, but man, so few pillars.

School busses are designed by law to resist a roof cave in in the event of a roll over. I wonder how a coach fares in that scenario.

 

[david.dgeorge07]

Some survivors, but some fatalities as well.

 

[Brad_SwiftFur]

School busses are designed by law to resist a roof cave in in the event of a roll over. I wonder how a coach fares in that scenario.

View attachment 34353

Some survivors, but some fatalities as well.

That answers that.

 

[david.dgeorge07]

Found another angle. Looks like this may not have been a coach style bus. I see a driveshaft so it must be a puller.

That roof though. Just a disaster.

38 onboard, only 1 dead. Hard to believe it wasn’t worse.

 

[Mark_In_MA]

I think there are other important differences about the weight distribution of a skoolie and a tour bus as well.

If you look at a school bus head-on, it's a fairly short rectangle - it's taller then it is wide, but not by much. (I think general consensus is 8 feet by 10 feet or so.)
A tour bus is a LOT taller. (8 x 11 or 8 x 12).

That extra height means a couple different things. First, if a tour bus rolls over, it's more likely to roll onto it's side, and stay there. It's a tall rectangle sideways - there's not that much of a chance that it's going to continue to roll onto the roof. I also wouldn't be surprised if tour buses have a lower center of gravity in the first place- larger engines, closer to the ground, and just more weight in axles, engines, luggage bays, etc. So if you look at the framing on the tour bus, the heavy stuff is down low - it goes to the bottom of the windows, which is enough to support the bus on its side. The roof and windows are designed to keep it from rolling over, not exactly to fully support it upside down. While you're giving up a bit of roof integrity, you're also helping to keep the center of gravity lower - which lets you have a nice, tall roof height in the first place. (At least, that's what I believe the design logic is.)

There's also the fact that a school bus, at 55mph, is going to have vastly different physics then a coach bus doing 75. Not to be morbid, but at some point, it doesn't matter what you do, the results aren't going to be pretty. That said -


There are roughly 128 people killed every year in school-bus related crashes in the US. 9% of those (11 people) were passengers riding the bus - the vast majority were either pedestrians, or occupants of other vehicles in the crash(es).

https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812476.pdf



If you go here, in 2016, there were 10 people killed in motor coach accidents. (14 in transit buses, 3 in vans, and 27 in "other" buses. Also 10 in school buses.)

https://www.fmcsa.dot.gov/safety/data-and-statistics/large-truck-and-bus-crash-facts-2017
(Scroll down to Trends Table 25.)

So overall, at least as buses, these things are pretty darn safe. I'm not qualified to say that 10 lives/year is enough to re-design the way we build over the road buses.

 

[david.dgeorge07]

I think there are other important differences about the weight distribution of a skoolie and a tour bus as well.

If you look at a school bus head-on, it's a fairly short rectangle - it's taller then it is wide, but not by much. (I think general consensus is 8 feet by 10 feet or so.)
A tour bus is a LOT taller. (8 x 11 or 8 x 12).

That extra height means a couple different things. First, if a tour bus rolls over, it's more likely to roll onto it's side, and stay there. It's a tall rectangle sideways - there's not that much of a chance that it's going to continue to roll onto the roof. I also wouldn't be surprised if tour buses have a lower center of gravity in the first place- larger engines, closer to the ground, and just more weight in axles, engines, luggage bays, etc. So if you look at the framing on the tour bus, the heavy stuff is down low - it goes to the bottom of the windows, which is enough to support the bus on its side. The roof and windows are designed to keep it from rolling over, not exactly to fully support it upside down. While you're giving up a bit of roof integrity, you're also helping to keep the center of gravity lower - which lets you have a nice, tall roof height in the first place.




Also, interesting statistic - there are roughly 128 people killed every year in school-bus related crashes in the US. 9% of those (11 people) were passengers riding the bus - the vast majority were either pedestrians, or occupants of other vehicles in the crash(es).

https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812476.pdf



If you go here, in 2016, there were 10 people killed in motor coach accidents. (14 in transit buses, 3 in vans, and 27 in "other" buses. Also 10 in school buses.)

https://www.fmcsa.dot.gov/safety/data-and-statistics/large-truck-and-bus-crash-facts-2017
(Scroll down to Trends Table 25.)

So overall, at least as buses, these things are pretty darn safe.

Good analysis.

 

[musigenesis]

Found another angle. Looks like this may not have been a coach style bus. I see a driveshaft so it must be a puller.

That roof though. Just a disaster.

38 onboard, only 1 dead. Hard to believe it wasn’t worse.

View attachment 34355

I just watched the helicopter video that this still was taken from. Looks like this was a shuttle bus, so not surprising that it was crushed like this. A good reason not to base your conversion on something made out of fiberglass.

Here's the video: https://www.facebook.com/WYFF4/videos/10155445552094114/ At about 6:55 the camera pans back to a second bus (undamaged) from the same church that appears to be the same type of bus.

 

[capnron-SKO]

Roof raise

One consideration, depending where you drive will be cross winds. A roof raise may require extra caution in a heavy cross wind.

 

[o1marc]

A central part of a school bus body's integrity is the ribs forming the walls and roof, bent from single pieces of homogenous hat channel material. A roof raise cuts these ribs in two places, and even the best-quality welding and bolting of the rib extenders will still concentrate stresses at those cuts (even if the welds and extenders are stronger than the channel material this will happen) making them prone to fail.

I am also not anti-roof raise, I just don't think people should be expecting their raised buses to be as structurally strong as they were before the modification. Just don't ride in the back of the damn things.

I think this statement is not based on fact at all. You are only cutting the rib in one place, not 2. if the extenders are long enough, the cuts of the rib will sustain zero stresses. You make it sound as though the ribs were designed to function at their maximum, when they are probably manufactured to sustain at least 50% more than normal use. Will the weld areas be weaker past the weld, yes, but certainly not enough to make it "prone to failure". There's no reason a proper roof raise can't be as strong as before, or at least way stronger than it needs to be. Prone is a strong word to use for an issue I've never seen an example of.I can think of other reasons I wouldn't do a lift, none of them involve the strength of the raise.

 

[Sleddgracer]

I think there are other important differences about the weight distribution of a skoolie and a tour bus as well.

If you look at a school bus head-on, it's a fairly short rectangle - it's taller then it is wide, but not by much. (I think general consensus is 8 feet by 10 feet or so.)
A tour bus is a LOT taller. (8 x 11 or 8 x 12).

That extra height means a couple different things. First, if a tour bus rolls over, it's more likely to roll onto it's side, and stay there. It's a tall rectangle sideways - there's not that much of a chance that it's going to continue to roll onto the roof. I also wouldn't be surprised if tour buses have a lower center of gravity in the first place- larger engines, closer to the ground, and just more weight in axles, engines, luggage bays, etc. So if you look at the framing on the tour bus, the heavy stuff is down low - it goes to the bottom of the windows, which is enough to support the bus on its side. The roof and windows are designed to keep it from rolling over, not exactly to fully support it upside down. While you're giving up a bit of roof integrity, you're also helping to keep the center of gravity lower - which lets you have a nice, tall roof height in the first place. (At least, that's what I believe the design logic is.)

There's also the fact that a school bus, at 55mph, is going to have vastly different physics then a coach bus doing 75. Not to be morbid, but at some point, it doesn't matter what you do, the results aren't going to be pretty. That said -


There are roughly 128 people killed every year in school-bus related crashes in the US. 9% of those (11 people) were passengers riding the bus - the vast majority were either pedestrians, or occupants of other vehicles in the crash(es).

https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/812476.pdf



If you go here, in 2016, there were 10 people killed in motor coach accidents. (14 in transit buses, 3 in vans, and 27 in "other" buses. Also 10 in school buses.)

https://www.fmcsa.dot.gov/safety/data-and-statistics/large-truck-and-bus-crash-facts-2017
(Scroll down to Trends Table 25.)

So overall, at least as buses, these things are pretty darn safe. I'm not qualified to say that 10 lives/year is enough to re-design the way we build over the road buses.

either way, buses in general are MUCH safer than factory built motorhomes

 

[Sleddgracer]

I think this statement is not based on fact at all. You are only cutting the rib in one place, not 2. if the extenders are long enough, the cuts of the rib will sustain zero stresses. You make it sound as though the ribs were designed to function at their maximum, when they are probably manufactured to sustain at least 50% more than normal use. Will the weld areas be weaker past the weld, yes, but certainly not enough to make it "prone to failure". There's no reason a proper roof raise can't be as strong as before, or at least way stronger than it needs to be. Prone is a strong word to use for an issue I've never seen an example of.I can think of other reasons I wouldn't do a lift, none of them involve the strength of the raise.

l agree - most raises even buttress the welded joins in the hat channel

 

[musigenesis]

You are only cutting the rib in one place, not 2.

The rib is a single piece of hat channel material that forms both walls and the ceiling. To do a raise, you make one cut on each wall side - that is 2 cuts.

Prone is a strong word to use for an issue I've never seen an example of.

How many skoolies have ever rolled? Real-world testing is the only way these issues could ever really be resolved. Without that, we're all just guessing.

 

[Mark_In_MA]

I think this statement is not based on fact at all. You are only cutting the rib in one place, not 2. if the extenders are long enough, the cuts of the rib will sustain zero stresses. You make it sound as though the ribs were designed to function at their maximum, when they are probably manufactured to sustain at least 50% more than normal use. Will the weld areas be weaker past the weld, yes, but certainly not enough to make it "prone to failure". There's no reason a proper roof raise can't be as strong as before, or at least way stronger than it needs to be. Prone is a strong word to use for an issue I've never seen an example of.I can think of other reasons I wouldn't do a lift, none of them involve the strength of the raise.

Part of the problem actually could be that the roof raise is STRONGER. When you engineer something, you engineer the whole thing as a system - certain components are engineered to fail in certain ways (and at certain times.) Think about adding leaves to the springs of an old dump truck - it will carry the weight for a while, but that extra stress is still going to go somewhere - until eventually you hit a pothole, and instead of the suspension giving way, the frame cracks and gives way instead.

If the bus rolled, the factory ribs might all bend, and the bus gets squashed, but stays intact. Example : It's crushed a bit, it's bent (a LOT), but it's intact.

If the ribs were too strong, it's possible that the roof /could/ snap right off the rest of the bus. Maybe the roof wouldn't snap right off, but it if was strong enough, it could bow out or tear the side wall instead.

Designing points of failure can be complicated.
(I still think I'd trust a roof raise over a sticks n staples though.)

 

[Sleddgracer]

Part of the problem actually could be that the roof raise is STRONGER. When you engineer something, you engineer the whole thing as a system - certain components are engineered to fail in certain ways (and at certain times.) Think about adding leaves to the springs of an old dump truck - it will carry the weight for a while, but that extra stress is still going to go somewhere - until eventually you hit a pothole, and instead of the suspension giving way, the frame cracks and gives way instead.

If the bus rolled, the factory ribs might all bend, and the bus gets squashed, but stays intact. Example : It's crushed a bit, it's bent (a LOT), but it's intact.

If the ribs were too strong, it's possible that the roof /could/ snap right off the rest of the bus. Maybe the roof wouldn't snap right off, but it if was strong enough, it could bow out or tear the side wall instead.

Designing points of failure can be complicated.
(I still think I'd trust a roof raise over a sticks n staples though.)

we're talking granite and bunny fluff - bus to motorhome

 

[o1marc]

The rib is a single piece of hat channel material that forms both walls and the ceiling. To do a raise, you make one cut on each wall side - that is 2 cuts.



How many skoolies have ever rolled? Real-world testing is the only way these issues could ever really be resolved. Without that, we're all just guessing.

I stand corrected on the number of cuts.
My point exactly on the real world testing lacking any results at all, so saying a roof raise is prone to failure is pure speculation on your part.

 

[EastCoastCB]

A central part of a school bus body's integrity is the ribs forming the walls and roof, bent from single pieces of homogenous hat channel material. A roof raise cuts these ribs in two places, and even the best-quality welding and bolting of the rib extenders will still concentrate stresses at those cuts (even if the welds and extenders are stronger than the channel material this will happen) making them prone to fail.

I am also not anti-roof raise, I just don't think people should be expecting their raised buses to be as structurally strong as they were before the modification. Just don't ride in the back of the damn things.

Bluebird commercial buses and Wanderlodges have half the ribs of the vastly overbuilt school bus.
The timidness of this forum is palpable.

 

[EastCoastCB]

The rib is a single piece of hat channel material that forms both walls and the ceiling. To do a raise, you make one cut on each wall side - that is 2 cuts.



How many skoolies have ever rolled? Real-world testing is the only way these issues could ever really be resolved. Without that, we're all just guessing.

The ribs are actually 3 pieces on most of the buses I've owned.