Seeking help from the Group...Again. Afghanistan Bridge Project
 

Greetings to All!

I have yet another question to lay before the collective oracle. To
wit, "How much weight can a simply supported steel plate support?"

I was minding my own business when the FOB Mayor showed up. He wanted
to know if a sheet of the steel plate out back would support a HMMWV.
How the heck would I know? We had recently put in a drainage system
around the FOB. We have no more culverts. He wants a leetle bridge.
Super.

I'd rather not give him something that will turn into a taco at the
first usage, so's I thought I'd look up the information. Heh, heh. I
suppose if I really knew what to do with Young's Modulus and Poisson's
Ratio and what-not, I'd be OK. That seems to be all I could find on
the net. Yay.

Could someone tell me the answer, or at least point me in the right
direction?

The ditch is about 2-3 feet wide. I have 4x8 steel plates in 3/8,
1/2, and 1 inch thicknesses. I have SOME 2 in square tube, 1/8 wall
that I could make a support frame of if needed. 1/2 in. plate is the
most plentiful. The HUMMVWs in question list a GVW of 12,500 lbs.
Not. They currently weigh closer to 20k. (Add on armor and turrets,
don't 'cha know.) We'd have to add some type of skirting to keep it
from sliding around. That is no problem. Oh, yeah. I also have a
whole pile of about three inch pipe in 20 ft lengths. 'Bout 3/16 in
wall.

If the whole thing failed under load, the most that would happen is
we'd break out the wrecker and go fish it out. A two foot drop is
uncomfortable, but not all that unsusall for here. Heck, it wouldn't
put as much stress on the vehicle as an IED, and we repair that kind
of thing every now and again.

Thanks in Advance

Ken, in Not-so-Sunny Afghanistan

Seeking help from the Group...Again. Afghanistan Bridge Project
 

wrote:

The ditch is about 2-3 feet wide.

That isn't much.

I have 4x8 steel plates in 3/8, 1/2, and 1 inch thicknesses.

Too small. Much too small! Have a look at how they bridge ditches while
digging them crossing a road. Here, they just lay plain plates (about 1.5m
x 2m, 15mm thick) over them. Trucks go over them without a problem. Be
aware, that there is only one axle at a time that the plate has to carry.

You could calculate that, but it is quite complex. It is a slab with a point
load and this is making things complicated.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Wed, 07 Nov 2007 14:08:32 +0100, Nick Mueller
wrote:

wrote:

The ditch is about 2-3 feet wide.

That isn't much.

I have 4x8 steel plates in 3/8, 1/2, and 1 inch thicknesses.

Too small. Much too small! Have a look at how they bridge ditches while
digging them crossing a road. Here, they just lay plain plates (about 1.5m
x 2m, 15mm thick) over them. Trucks go over them without a problem. Be
aware, that there is only one axle at a time that the plate has to carry.

You could calculate that, but it is quite complex. It is a slab with a point
load and this is making things complicated.


Nick

In PA the most common thing I see across a contruction ditch is 1"
plate, I guess they fiqure that's good for a 80,000 tractor trailer.

The question is,if he tries it, what is the max bow the plate can take
without springing back?

Thank You,
Randy

Remove 333 from email address to reply.

Seeking help from the Group...Again. Afghanistan Bridge Project
 

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Wed, 07 Nov 2007 04:46:14 -0800, wrote:

Greetings to All!

I have yet another question to lay before the collective oracle. To
wit, "How much weight can a simply supported steel plate support?"

I was minding my own business when the FOB Mayor showed up. He wanted
to know if a sheet of the steel plate out back would support a HMMWV.
How the heck would I know? We had recently put in a drainage system
around the FOB. We have no more culverts. He wants a leetle bridge.
Super.

I'd rather not give him something that will turn into a taco at the
first usage, so's I thought I'd look up the information. Heh, heh. I
suppose if I really knew what to do with Young's Modulus and Poisson's
Ratio and what-not, I'd be OK. That seems to be all I could find on
the net. Yay.

Could someone tell me the answer, or at least point me in the right
direction?

The ditch is about 2-3 feet wide. I have 4x8 steel plates in 3/8,
1/2, and 1 inch thicknesses. I have SOME 2 in square tube, 1/8 wall
that I could make a support frame of if needed. 1/2 in. plate is the
most plentiful. The HUMMVWs in question list a GVW of 12,500 lbs.
Not. They currently weigh closer to 20k. (Add on armor and turrets,
don't 'cha know.) We'd have to add some type of skirting to keep it
from sliding around. That is no problem. Oh, yeah. I also have a
whole pile of about three inch pipe in 20 ft lengths. 'Bout 3/16 in
wall.

If the whole thing failed under load, the most that would happen is
we'd break out the wrecker and go fish it out. A two foot drop is
uncomfortable, but not all that unsusall for here. Heck, it wouldn't
put as much stress on the vehicle as an IED, and we repair that kind
of thing every now and again.

Thanks in Advance

Ken, in Not-so-Sunny Afghanistan


"Trench plates" are what they use to cover work in progress when they
cut holes in streets. Most of those Ive seen are 1"-1.5" thick and
can span up to about 6 feet.

Id think that for 3', a 1" plate simply laid over the ditch would be
ok.

Now you got to figure out how to keep somone from putting an IED under
it in the ditch.

Gunner

Political Correctness is a doctrine fostered by a delusional,
illogical liberal minority, and rabidly promoted by an
unscrupulous mainstream media, which holds forth the
proposition that it is entirely possible to pick up a turd by the clean end.

Seeking help from the Group...Again. Afghanistan Bridge Project
 

Randy wrote:

In PA the most common thing I see across a contruction ditch is 1"
plate, I guess they fiqure that's good for a 80,000 tractor trailer.

The key is load per axle. And not the overall weight. I guess you to do have
a limit in the range of 8 tons / axle.


The question is,if he tries it, what is the max bow the plate can take
without springing back?

Again, it's difficult to calculate (by hand). The common method nowadays
would be finite elements method. Feed your CAD with the data and pray it
has a FEM-module.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Nov 7, 2:29 pm, Nick Mueller wrote:
Randy wrote:
In PA the most common thing I see across a contruction ditch is 1"
plate, I guess they fiqure that's good for a 80,000 tractor trailer.

The key is load per axle. And not the overall weight. I guess you to do have
a limit in the range of 8 tons / axle.

The question is,if he tries it, what is the max bow the plate can take
without springing back?

Again, it's difficult to calculate (by hand). The common method nowadays
would be finite elements method. Feed your CAD with the data and pray it
has a FEM-module.

Nick
--
The lowcost-DRO:
http://www.yadro.de




It is NOT a difficult calculation; but without stiffening ribs welded
on, a plate as a bridge won't carry much.

There is a BIG difference between a plate used as a beam (supported at
the ends only), and a plate supported around its perimeter (4 sides in
case of a square or rectangle), as is typically used to cover a
temporary access hole in a roadway.

Wolfgang

Seeking help from the Group...Again. Afghanistan Bridge Project
 

If I was in the military and was tasked with this, I would make a
sandwich like construction, with 1/2" plate on top, 2x4 ribs
underneath, and then a 1/4 plate welded to the bottom. Drill some
holes in the 1/4" plate to weld it to the inner beams.

This has two advantages, one is rigidity, and another is that it is
not easy to place an IED under the bridge between ribs that could
easily me missed during a quick visual check.

i

Seeking help from the Group...Again. Afghanistan Bridge Project
 

"Trench plates" are what they use to cover work in progress when they
cut holes in streets. Most of those Ive seen are 1"-1.5" thick and
can span up to about 6 feet.

Id think that for 3', a 1" plate simply laid over the ditch would be
ok.

Now you got to figure out how to keep somone from putting an IED under
it in the ditch.

Gunner


IED is not a problem. The drainage system is on the FOB proper, and
the crossing point is about 80 meters out from a guard tower. If some
dude manages to breach the outer HESCOs and emplace an IED, I'd be
hunting the guard more than the bomber. All the trench plates I've
seen at construction sites in Italy, cover a hole rather than a
trench. Supported on 4 sides rather than two. Does that make a huge
difference in this application? They also generally hold up a 2000 lb
FIAT pretty well, but a 20,000 lb HMMWV is almost twice as heavy. g
Think it'd work anyway? Or are the stiffening ribs in order?

Just to satisfy my curiosity, how DOES one go about calculating the
stress?

Thanks Again,

Ken

Seeking help from the Group...Again. Afghanistan Bridge Project
 

wrote:

It is NOT a difficult calculation;

Is it? This can't be reduced to a beam. You do have a slab supported on two
opposing sides and a *point* load (looking from above). And not a linear
load.

but without stiffening ribs welded
on, a plate as a bridge won't carry much.

No, but for short gaps it is a common temporary solution.


There is a BIG difference between a plate used as a beam (supported at
the ends only), and a plate supported around its perimeter (4 sides in
case of a square or rectangle), as is typically used to cover a
temporary access hole in a roadway.

The task was to cover a trench, not a hole. Point missed. :-)


Nick
--
The lowcost-DRO:
http://www.yadro.de

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Nov 8, 3:34 am, Nick Mueller wrote:
wrote:
It is NOT a difficult calculation;

Is it? This can't be reduced to a beam. You do have a slab supported on two
opposing sides and a *point* load (looking from above). And not a linear
load.

but without stiffening ribs welded
on, a plate as a bridge won't carry much.

No, but for short gaps it is a common temporary solution.

There is a BIG difference between a plate used as a beam (supported at
the ends only), and a plate supported around its perimeter (4 sides in
case of a square or rectangle), as is typically used to cover a
temporary access hole in a roadway.

The task was to cover a trench, not a hole. Point missed. :-)

Nick
--
The lowcost-DRO:
http://www.yadro.de


2 wheels spaced what? 5 - 6 feet apart on an 8 ft wide plate....
assuming point loading for beam calculation would a reasonable first
assumption.

(I wonder what people did before F.E. analysis?)

My comments regarding the plate on a hole was in response to someone's
statement that they had seen this done; I merely cautioned on the
difference between the 2 applications.

Here is what I would try: Place one 1" thick plate with its 4 ft
dimension straddling the ditch, ie. an 8 ft wide "bridge".

Place 2 more 1" thick plates the long way over the first 1" plate with
a 2" gap along their length. (the 8 ft dimension over the ditch).

Weld everything together lengthwise with, say, 3/8" fillets (4 fillets
4 feet long). Burn holes through the top plates, say 1 ft from their
ends and drive in 8 ft long pipe stakes to anchor things against
sliding. Weld plate to stakes.

No guarantees or error & omissions insurance on this off-the-cuff
opinion, but I think it worth trying considering the low risks
associated.

Let us know what you try and how it works out.

Wolfgang

Seeking help from the Group...Again. Afghanistan Bridge Project
 

wrote:

2 wheels spaced what? 5 - 6 feet apart on an 8 ft wide plate....
assuming point loading for beam calculation would a reasonable first
assumption.

You will end in a too big possible load. Because the part between the two
wheels will only partially contribute to the stiffness. Now the guess is
how much. *I* wouldn't guess that.
The other approach to calculate only a strip as wide as a tire is will end
in a too stiff plate. Maybe double the tire width? Or threefold?


(I wonder what people did before F.E. analysis?)

It can be calculated and it has been done. The results were printed in
books. Slabs are a common problem for floors in buildings and that is
exactly what those books have been printed for.


Nick
--
The lowcost-DRO:
http://www.yadro.de

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Nov 7, 12:46 pm, wrote:
Greetings to All!

I have yet another question to lay before the collective oracle. To
wit, "How much weight can a simply supported steel plate support?"

I was minding my own business when the FOB Mayor showed up. He wanted
to know if a sheet of the steel plate out back would support a HMMWV.
How the heck would I know? We had recently put in a drainage system
around the FOB. We have no more culverts. He wants a leetle bridge.
Super.



The ditch is about 2-3 feet wide.

I would essentially make some more culvert out of your 3/8 sheet. Cut
a sheet lengthwise into three pieces 16 inches wide and then weld them
into a triangle shape. Put it in the ditch so a flat part is down and
an apex is up to have the maximum strength. If that is not a big
enough culvert, you will have to use more than one sheet.

Dan


Thanks in Advance

Ken, in Not-so-Sunny Afghanistan

Seeking help from the Group...Again. Afghanistan Bridge Project
 

In article ,
Ignoramus26797 wrote:

If I was in the military and was tasked with this, I would make a
sandwich like construction, with 1/2" plate on top, 2x4 ribs
underneath, and then a 1/4 plate welded to the bottom. Drill some
holes in the 1/4" plate to weld it to the inner beams.

This has two advantages, one is rigidity, and another is that it is
not easy to place an IED under the bridge between ribs that could
easily me missed during a quick visual check.

i

This is my thinking, too, and I'm not an engineer. Make one big steel
torsion box. The wooden ones I've made were stronger than sin itself.

-Frank

--
Here's some of my work:
http://www.franksknives.com/

Seeking help from the Group...Again. Afghanistan Bridge Project
 

On Fri, 09 Nov 2007 08:34:17 -0800, "
wrote:

On Nov 7, 12:46 pm, wrote:
Greetings to All!

I have yet another question to lay before the collective oracle. To
wit, "How much weight can a simply supported steel plate support?"

I was minding my own business when the FOB Mayor showed up. He wanted
to know if a sheet of the steel plate out back would support a HMMWV.
How the heck would I know? We had recently put in a drainage system
around the FOB. We have no more culverts. He wants a leetle bridge.
Super.



The ditch is about 2-3 feet wide.

I would essentially make some more culvert out of your 3/8 sheet. Cut
a sheet lengthwise into three pieces 16 inches wide and then weld them
into a triangle shape. Put it in the ditch so a flat part is down and
an apex is up to have the maximum strength. If that is not a big
enough culvert, you will have to use more than one sheet.

Dan


Thanks in Advance

Ken, in Not-so-Sunny Afghanistan

I like that idea!

Gunner

Political Correctness is a doctrine fostered by a delusional,
illogical liberal minority, and rabidly promoted by an
unscrupulous mainstream media, which holds forth the
proposition that it is entirely possible to pick up a turd by the clean end.