I wanted to build a 1000 plus gallon aquarium in the new house I was having
built. I wasn't sure how thick to make the front glass. The rest of the tank
would be fiberglass covered steel. The dimensions I arrived at were 8 ft.
across, 6 ft. front to back and 38 in. tall. This would be 1137 gallons. A
friend had a tank that was 38 in. tall but only 18 in. front to back. It was
also 8 ft. long. (284 gallons). The glass in his tank was 3/4 in thick. My
tank would be identical except the front to back dim. would be 72 in.
At first I was concerned that there would more pressure on the front glass.
After much research I became confident there would be no difference
regardless of front to back depth. For simplicity lets call depth the front
to back dim. and height the top to bottom dim. I found charts that told the
pressure at every height of water in inch increments. To figure the total
"push" on the front glass, you just need to find the pressure at the halfway
point(19 inches in this case) and multiply by the total sq. in. of the glass
(3,648). I believe
at 19" the pressure was about .686 or so psi. It figured out to be around
2,500 lbs. of force on the glass. It would be about 9,480 lbs of water. As
I
was filling the tank, a straight edge laid against the front glass showed
the glass bowing outward very noticeably even at 1/4 full. I nervously
filled it full. Now it was very bowed even to the naked eye. The 2,500 lbs
was definitely there on the glass. Now, try to visualize the front glass as
a giant rectangle piston with 2,500 lbs of force on the inside. If you put a
4"x4" in the center of the glass that ran across the room to an opposite
wall and put a bathroom scale (quite a scale!) against the wall or better
yet, an "I" beam, the scale after filling, would read a total of 2500 lbs.
Or 25 men each pushing on the outside at 100 lbs would cancel the pressure
on the glass. Now, here's where the troubling part comes in. Lets say the
back of the tank, instead of being 72" away from the front is moved forward
until it is just 1/8 of an inch away from the front glass. Now there is less
than two gallons of water in the tank. I have trouble seeing the glass (3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500 lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Dixon

"dixon" wrote in message
news:Qg%qd.693019$8_6.466127@attbi_s04...



I wanted to build a 1000 plus gallon aquarium in the new house I was
having
built. I wasn't sure how thick to make the front glass. The rest of the
tank
would be fiberglass covered steel. The dimensions I arrived at were 8 ft.
across, 6 ft. front to back and 38 in. tall. This would be 1137 gallons. A
friend had a tank that was 38 in. tall but only 18 in. front to back. It
was
also 8 ft. long. (284 gallons). The glass in his tank was 3/4 in thick. My
tank would be identical except the front to back dim. would be 72 in.
At first I was concerned that there would more pressure on the front
glass.
After much research I became confident there would be no difference
regardless of front to back depth. For simplicity lets call depth the
front
to back dim. and height the top to bottom dim. I found charts that told
the
pressure at every height of water in inch increments. To figure the total
"push" on the front glass, you just need to find the pressure at the
halfway
point(19 inches in this case) and multiply by the total sq. in. of the
glass
(3,648). I believe
at 19" the pressure was about .686 or so psi. It figured out to be around
2,500 lbs. of force on the glass. It would be about 9,480 lbs of water.
As
I
was filling the tank, a straight edge laid against the front glass showed
the glass bowing outward very noticeably even at 1/4 full. I nervously
filled it full. Now it was very bowed even to the naked eye. The 2,500 lbs
was definitely there on the glass. Now, try to visualize the front glass
as
a giant rectangle piston with 2,500 lbs of force on the inside. If you put
a
4"x4" in the center of the glass that ran across the room to an opposite
wall and put a bathroom scale (quite a scale!) against the wall or better
yet, an "I" beam, the scale after filling, would read a total of 2500 lbs.
Or 25 men each pushing on the outside at 100 lbs would cancel the pressure
on the glass. Now, here's where the troubling part comes in. Lets say the
back of the tank, instead of being 72" away from the front is moved
forward
until it is just 1/8 of an inch away from the front glass. Now there is
less
than two gallons of water in the tank. I have trouble seeing the glass
(3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500 lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Dixon

You are mixing apples and oranges. The force of water at a certain depth
remains the same......Xpsi.

When you take that force and apply it over an area, the cumulative amount of
force reacts against the plane of glass or plexi...

In your thimble example....you only have 1 sq. in of force at 19" so the
force remains .686 psi.....

The plane of glass has to resist two basic forces.......shear and bending
moment.......typically the thickness required to resist the bending is
greater than that required for shear. Bending moment is a relationship of
the total force and the span of the material.

--

"Harry Krause" wrote in message
news:1101825017.A8YvNxGot0vzl0lmZX6wyQ@teranews...
dixon wrote:
I wanted to build a 1000 plus gallon aquarium in the new house I was
having
built. I wasn't sure how thick to make the front glass. The rest of the
tank
would be fiberglass covered steel. The dimensions I arrived at were 8
ft.
across, 6 ft. front to back and 38 in. tall. This would be 1137 gallons.
A
friend had a tank that was 38 in. tall but only 18 in. front to back. It
was
also 8 ft. long. (284 gallons). The glass in his tank was 3/4 in thick.
My
tank would be identical except the front to back dim. would be 72 in.
At first I was concerned that there would more pressure on the front
glass.
After much research I became confident there would be no difference
regardless of front to back depth. For simplicity lets call depth the
front
to back dim. and height the top to bottom dim. I found charts that told
the
pressure at every height of water in inch increments. To figure the
total
"push" on the front glass, you just need to find the pressure at the
halfway
point(19 inches in this case) and multiply by the total sq. in. of the
glass
(3,648). I believe
at 19" the pressure was about .686 or so psi. It figured out to be
around
2,500 lbs. of force on the glass. It would be about 9,480 lbs of water.
As
I
was filling the tank, a straight edge laid against the front glass
showed
the glass bowing outward very noticeably even at 1/4 full. I nervously
filled it full. Now it was very bowed even to the naked eye. The 2,500
lbs
was definitely there on the glass. Now, try to visualize the front glass
as
a giant rectangle piston with 2,500 lbs of force on the inside. If you
put a
4"x4" in the center of the glass that ran across the room to an opposite
wall and put a bathroom scale (quite a scale!) against the wall or
better
yet, an "I" beam, the scale after filling, would read a total of 2500
lbs.
Or 25 men each pushing on the outside at 100 lbs would cancel the
pressure
on the glass. Now, here's where the troubling part comes in. Lets say
the
back of the tank, instead of being 72" away from the front is moved
forward
until it is just 1/8 of an inch away from the front glass. Now there is
less
than two gallons of water in the tank. I have trouble seeing the glass
(3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500
lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Dixon




If you really want some help with this, I suggest that rather than
depend upon wild-assed, theoretical guesses from the readers of this
newsgroup, you consult with some of the real experts who build
commercial display aquariums. That's some floorload by the way...hope
that tank is sitting on a concrete floor.

Thanks for the advice Harry. Actually the tank has been full for 14 yrs.
now. When building the house I poured a thick slab on the ground and built
up a cement block tower to the height I wanted. The weight of the tank and
water place no load whatsoever on any part of the house.

Dixon

Is your tank absolutely level?

dixon wrote:
Now, here's where the troubling part comes in. Lets say the
back of the tank, instead of being 72" away from the front is moved forward
until it is just 1/8 of an inch away from the front glass. Now there is less
than two gallons of water in the tank. I have trouble seeing the glass (3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500 lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Here's my theory:
As you decreased the distance between front and back, and the front
galss bowed out, the volume of the tank would increase and the water
depth would lower, decreasing the water pressure on the glass.

Water depth and density determine the water pressure.

Very clever...

Do you have any photos of the aquarium? Fresh or salt?

My wife wants to set up an aquarium again (she used to have pet oscars
before I showed up), and is looking at a 120-gallon acrylic tank, but
she wants to put it against a wall in the family room, and I am
concerned about the floor load...it would be more than 1000 pounds
pushing down over a relatively small area of floor, a floor that is NOT
ground level in our house.

We had salt for 8 yrs. then went back to fresh. Not as pretty but a lot less
headaches.
Dixon
--
A passing thought:

"As you know, we don't have relationships with Iran. I mean, that's —
ever since the late '70s, we have no contacts with them, and we've
totally sanctioned them. In other words, there's no sanctions — you
can't — we're out of sanctions." —George W. Bush, Annandale, Va, Aug. 9,
2004

"P.Fritz" wrote in message
...

"dixon" wrote in message
news:Qg%qd.693019$8_6.466127@attbi_s04...



I wanted to build a 1000 plus gallon aquarium in the new house I was
having
built. I wasn't sure how thick to make the front glass. The rest of the
tank
would be fiberglass covered steel. The dimensions I arrived at were 8
ft.
across, 6 ft. front to back and 38 in. tall. This would be 1137 gallons.
A
friend had a tank that was 38 in. tall but only 18 in. front to back. It
was
also 8 ft. long. (284 gallons). The glass in his tank was 3/4 in thick.
My
tank would be identical except the front to back dim. would be 72 in.
At first I was concerned that there would more pressure on the front
glass.
After much research I became confident there would be no difference
regardless of front to back depth. For simplicity lets call depth the
front
to back dim. and height the top to bottom dim. I found charts that told
the
pressure at every height of water in inch increments. To figure the
total
"push" on the front glass, you just need to find the pressure at the
halfway
point(19 inches in this case) and multiply by the total sq. in. of the
glass
(3,648). I believe
at 19" the pressure was about .686 or so psi. It figured out to be
around
2,500 lbs. of force on the glass. It would be about 9,480 lbs of water.
As
I
was filling the tank, a straight edge laid against the front glass
showed
the glass bowing outward very noticeably even at 1/4 full. I nervously
filled it full. Now it was very bowed even to the naked eye. The 2,500
lbs
was definitely there on the glass. Now, try to visualize the front glass
as
a giant rectangle piston with 2,500 lbs of force on the inside. If you
put
a
4"x4" in the center of the glass that ran across the room to an opposite
wall and put a bathroom scale (quite a scale!) against the wall or
better
yet, an "I" beam, the scale after filling, would read a total of 2500
lbs.
Or 25 men each pushing on the outside at 100 lbs would cancel the
pressure
on the glass. Now, here's where the troubling part comes in. Lets say
the
back of the tank, instead of being 72" away from the front is moved
forward
until it is just 1/8 of an inch away from the front glass. Now there is
less
than two gallons of water in the tank. I have trouble seeing the glass
(3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500
lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Dixon

You are mixing apples and oranges. The force of water at a certain
depth
remains the same......Xpsi.

I don't see your meaning mixing apples and oranges. I guess I am forced to
accept the pressure at depth principle no matter how illogical it seems at
times.

When you take that force and apply it over an area, the cumulative amount
of
force reacts against the plane of glass or plexi...

In your thimble example....you only have 1 sq. in of force at 19" so the
force remains .686 psi.....

No, actually with the thimble of water would be spread across the same
surface area of glass, not 1 sq. in., but 3,648. So, same "push" on the
glass with a thimble of water as with 9,480 lbs. of water?


The plane of glass has to resist two basic forces.......shear and bending
moment.......typically the thickness required to resist the bending is
greater than that required for shear. Bending moment is a relationship of
the total force and the span of the material.

"Gould 0738" wrote in message
...
Is your tank absolutely level?

It was 14 yrs. ago. Now it's about 1/4 in out. It doesn't matter though
because the surface is hidden by the frame.
Dixon

"John Wentworth" wrote in message
...
dixon wrote:
Now, here's where the troubling part comes in. Lets say the
back of the tank, instead of being 72" away from the front is moved
forward
until it is just 1/8 of an inch away from the front glass. Now there is
less
than two gallons of water in the tank. I have trouble seeing the glass
(3/4
in. thick) bowing from 2,500 lbs of "push" from less than two gallons of
water(16 lbs). I suppose we could even shrink the 1/8 in. to a few
thousandths and put a thimble of water in. Would there still be 2,500
lbs
of outward force from a gram or two of water? Would the heavy duty scale
across the room be forced all the way to the two thousand, five hundred
pound mark?

Here's my theory:
As you decreased the distance between front and back, and the front
galss bowed out, the volume of the tank would increase and the water
depth would lower, decreasing the water pressure on the glass.

Water depth and density determine the water pressure.

Even with bowing you would still fill the tank to the top, it would just
take slightly more water.
Dixon

Here's my theory:
As you decreased the distance between front and back, and the front
galss bowed out, the volume of the tank would increase and the water
depth would lower, decreasing the water pressure on the glass.

The relationship is between depth and pressure. If you built a tank that was a
mile long and a mile wide, but six inches deep, you would need glass thick
enough to support the water pressure associated with a six-inch depth.

One has to remember that, assuming the tank is level, there is equal pressure
on all the vertical structures containing the water, not just the front glass.
As the tank expands in length or width, the amount of
vertical structure to contain the water increases correspondingly, and
continues to support its share of the pressure.