I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in the
hole, not all the way but it competely broke the concrete lid on this
concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid of
about 6 inches thick and about 4 feet in diameter.
I have only worked with concrete just a bit by pouring it into some holes
for a few t-posts and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it, put
in some welded wire and some rebar and pour away? Yes, I will keep a center
hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

On Wed, 16 Sep 2009 22:02:48 -0500, justme wrote:

I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in
the hole, not all the way but it competely broke the concrete lid on
this concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid
of about 6 inches thick and about 4 feet in diameter. I have only worked
with concrete just a bit by pouring it into some holes for a few t-posts
and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it,
put in some welded wire and some rebar and pour away? Yes, I will keep
a center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

Good thing you have a backhoe to put it in place with!

I suspect you need to suspend the rebar where you want it in the final
pour, although I understand that you can lift up reinforcing net by
reaching down through the glop and pulling up on it.

Surely someone's done this on a web page before. I know there used to be
a Popular Mechanics article on this -- my dad built my grandmother's
septic tank from the afore-mentioned article. Of course, to use _that_
one you'll need a Popular Mechanics collection that goes back to 1940 or
so...

--
www.wescottdesign.com

"justme" wrote in message
...
I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in the
hole, not all the way but it competely broke the concrete lid on this
concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid
of about 6 inches thick and about 4 feet in diameter.
I have only worked with concrete just a bit by pouring it into some holes
for a few t-posts and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it,
put in some welded wire and some rebar and pour away? Yes, I will keep a
center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

This won't help construct a lid, but don't feel so dumb. The pro that
installed my septic tank, had just finished when he backed over the tank
with his big diesel hoe and broke the tank. He had to get the broken one
out and go get another tank. I don't think that was a high profit day for
him.

stu

Thanks, Tim.

Final pour? I don't understand. As I foresee it, I will be mixin and
pouring all until it is done. I planned to put the wire and rebar on
supports where they would be at half of the final thickness.

j/b


"Tim Wescott" wrote in message
...
On Wed, 16 Sep 2009 22:02:48 -0500, justme wrote:

I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in
the hole, not all the way but it competely broke the concrete lid on
this concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid
of about 6 inches thick and about 4 feet in diameter. I have only worked
with concrete just a bit by pouring it into some holes for a few t-posts
and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it,
put in some welded wire and some rebar and pour away? Yes, I will keep
a center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

Good thing you have a backhoe to put it in place with!

I suspect you need to suspend the rebar where you want it in the final
pour, although I understand that you can lift up reinforcing net by
reaching down through the glop and pulling up on it.

Surely someone's done this on a web page before. I know there used to be
a Popular Mechanics article on this -- my dad built my grandmother's
septic tank from the afore-mentioned article. Of course, to use _that_
one you'll need a Popular Mechanics collection that goes back to 1940 or
so...

--
www.wescottdesign.com

"justme" wrote in message
...
Thanks, Tim.

Final pour? I don't understand. As I foresee it, I will be mixin and
pouring all until it is done. I planned to put the wire and rebar on
supports where they would be at half of the final thickness.

j/b

If they're right at half the final thickness, they'll contribute *nothing*
to preventing initial cracks. However, they will contribute considerably to
the final bending strength.

You can look this up for specifics but the general idea is to use the
reinforcement close to the side that's in tension, with just enough concrete
covering the mesh and rebar on the tension side to minimize corrosion. That
means that you want it concentrated near the low side.

If you're into structural design, the point is that concrete has great
compression strength but almost no tensile strength. And the center of any
section -- half the final thickness of your lid, in this case -- is known as
the "neutral axis" in a member that is under a bending load. Structural
material on or near the neutral axis contributes nothing to initial bending
resistance. But once you get some small cracks on the down side, the steel
reinforcement is loaded, and it prevents further cracking. In effect, as it
appears to tension loads on the downside resulting from compression loads on
the topside, the steel is now the "bottom" of the section.

Still, the best strength is obtained by putting your reinforcement near the
bottom of a concrete slab of any kind that's going to have loads imposed
only from the top side. That's the way that most well-made sidewalks and
other concrete structures are reinforced.

--
Ed Huntress



"Tim Wescott" wrote in message
...
On Wed, 16 Sep 2009 22:02:48 -0500, justme wrote:

I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in
the hole, not all the way but it competely broke the concrete lid on
this concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid
of about 6 inches thick and about 4 feet in diameter. I have only worked
with concrete just a bit by pouring it into some holes for a few t-posts
and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it,
put in some welded wire and some rebar and pour away? Yes, I will keep
a center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

Good thing you have a backhoe to put it in place with!

I suspect you need to suspend the rebar where you want it in the final
pour, although I understand that you can lift up reinforcing net by
reaching down through the glop and pulling up on it.

Surely someone's done this on a web page before. I know there used to be
a Popular Mechanics article on this -- my dad built my grandmother's
septic tank from the afore-mentioned article. Of course, to use _that_
one you'll need a Popular Mechanics collection that goes back to 1940 or
so...

--
www.wescottdesign.com

Thanks, E.

I will then put the rebar/welded wire near the bottom of the lid. That is,
the side facing the tank.

j/b



"Ed Huntress" wrote in message
...

"justme" wrote in message
...
Thanks, Tim.

Final pour? I don't understand. As I foresee it, I will be mixin and
pouring all until it is done. I planned to put the wire and rebar on
supports where they would be at half of the final thickness.

j/b

If they're right at half the final thickness, they'll contribute *nothing*
to preventing initial cracks. However, they will contribute considerably
to the final bending strength.

You can look this up for specifics but the general idea is to use the
reinforcement close to the side that's in tension, with just enough
concrete covering the mesh and rebar on the tension side to minimize
corrosion. That means that you want it concentrated near the low side.

If you're into structural design, the point is that concrete has great
compression strength but almost no tensile strength. And the center of any
section -- half the final thickness of your lid, in this case -- is known
as the "neutral axis" in a member that is under a bending load. Structural
material on or near the neutral axis contributes nothing to initial
bending resistance. But once you get some small cracks on the down side,
the steel reinforcement is loaded, and it prevents further cracking. In
effect, as it appears to tension loads on the downside resulting from
compression loads on the topside, the steel is now the "bottom" of the
section.

Still, the best strength is obtained by putting your reinforcement near
the bottom of a concrete slab of any kind that's going to have loads
imposed only from the top side. That's the way that most well-made
sidewalks and other concrete structures are reinforced.

--
Ed Huntress



"Tim Wescott" wrote in message
...
On Wed, 16 Sep 2009 22:02:48 -0500, justme wrote:

I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in
the hole, not all the way but it competely broke the concrete lid on
this concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own
lid
of about 6 inches thick and about 4 feet in diameter. I have only
worked
with concrete just a bit by pouring it into some holes for a few
t-posts
and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around
it,
put in some welded wire and some rebar and pour away? Yes, I will keep
a center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

Good thing you have a backhoe to put it in place with!

I suspect you need to suspend the rebar where you want it in the final
pour, although I understand that you can lift up reinforcing net by
reaching down through the glop and pulling up on it.

Surely someone's done this on a web page before. I know there used to
be
a Popular Mechanics article on this -- my dad built my grandmother's
septic tank from the afore-mentioned article. Of course, to use _that_
one you'll need a Popular Mechanics collection that goes back to 1940 or
so...

--
www.wescottdesign.com

Sounds like something that I would do just after a new lid.

The very large broken pieces of the lid are still in the 3/4 full tank. I
may construct a grappling hook to get them.

"**** Happens"

j/b


"Stu Fields" wrote in message
...

"justme" wrote in message
...
I drove my (new to me), big, diesel backhoe over the last tank in my
two-tank septic system. Still, not too smart but I thought that I had
cleared it by a foot or two. NOPE! So, one of the rear tires fell in
the hole, not all the way but it competely broke the concrete lid on this
concrete tank.

Now, not only being dumb but being cheap, too, I want to make my own lid
of about 6 inches thick and about 4 feet in diameter.
I have only worked with concrete just a bit by pouring it into some holes
for a few t-posts and a few vertical landscape timbers.

I do have a small (unused by me) concrete mixer.

Do I simply lay out some plywood on solid ground, build forms around it,
put in some welded wire and some rebar and pour away? Yes, I will keep a
center hole open and install some hooks to lift it on the tank.

Does this sound like a plan?

Thanks

j/b

This won't help construct a lid, but don't feel so dumb. The pro that
installed my septic tank, had just finished when he backed over the tank
with his big diesel hoe and broke the tank. He had to get the broken one
out and go get another tank. I don't think that was a high profit day for
him.

stu

On Sun, 20 Sep 2009 14:29:11 -0500, justme wrote:
....
"Ed Huntress" ... wrote ...
If you're into structural design, the point is that concrete has great
compression strength but almost no tensile strength. And the center of
any section -- half the final thickness of your lid, in this case -- is
known as the "neutral axis" in a member that is under a bending load.
Structural material on or near the neutral axis contributes nothing to
initial bending resistance. But once you get some small cracks on the
down side, the steel reinforcement is loaded, and it prevents further
cracking. In effect, as it appears to tension loads on the downside
resulting from compression loads on the topside, the steel is now the
"bottom" of the section.

Still, the best strength is obtained by putting your reinforcement near
the bottom of a concrete slab of any kind that's going to have loads
imposed only from the top side. That's the way that most well-made
sidewalks and other concrete structures are reinforced.

I will then put the rebar/welded wire near the bottom of the lid. That
is, the side facing the tank.

Concentrating the rebar in the bottom inch or so makes sense, but
it probably is worthwhile to put at least a little reinforcement
in the top inch also. If you pick up the lid on forks, or if you
happen to drop it while moving it, the loading will be reversed.

--
jiw

Get some fiber made for cement strength - add it to the mix and
it will be stronger. Also - a stronger type of cement is possible.

Some use fiber in place of rebar - some use both.

Martin

James Waldby wrote:
On Sun, 20 Sep 2009 14:29:11 -0500, justme wrote:
...
"Ed Huntress" ... wrote ...
If you're into structural design, the point is that concrete has great
compression strength but almost no tensile strength. And the center of
any section -- half the final thickness of your lid, in this case -- is
known as the "neutral axis" in a member that is under a bending load.
Structural material on or near the neutral axis contributes nothing to
initial bending resistance. But once you get some small cracks on the
down side, the steel reinforcement is loaded, and it prevents further
cracking. In effect, as it appears to tension loads on the downside
resulting from compression loads on the topside, the steel is now the
"bottom" of the section.

Still, the best strength is obtained by putting your reinforcement near
the bottom of a concrete slab of any kind that's going to have loads
imposed only from the top side. That's the way that most well-made
sidewalks and other concrete structures are reinforced.

I will then put the rebar/welded wire near the bottom of the lid. That
is, the side facing the tank.

Concentrating the rebar in the bottom inch or so makes sense, but
it probably is worthwhile to put at least a little reinforcement
in the top inch also. If you pick up the lid on forks, or if you
happen to drop it while moving it, the loading will be reversed.

On Sun, 20 Sep 2009 14:29:11 -0500, justme wrote:

Thanks, E.

I will then put the rebar/welded wire near the bottom of the lid. That
is, the side facing the tank.

If you insist on pouring one rather than just buying one, I'd make the
form convex, such that the lid forms a sort of "dome" shape, to transfer
the stress to the rim rather than straight down.

Cheers!
Rich

On Sun, 20 Sep 2009 21:17:35 -0500, Martin H. Eastburn wrote:

Get some fiber made for cement strength - add it to the mix and it will be
stronger. Also - a stronger type of cement is possible.

Some use fiber in place of rebar - some use both.

Or just make the whole thing out of fiberglass, in a dome shape. ;-)

Cheers!
Rich

On Sat, 19 Sep 2009 15:52:04 -0400 in rec.crafts.metalworking, "Ed
Huntress" wrote,
Still, the best strength is obtained by putting your reinforcement near the
bottom of a concrete slab of any kind that's going to have loads imposed
only from the top side. That's the way that most well-made sidewalks and
other concrete structures are reinforced.

Which means it will crack when he lifts it from the center, right?

"David Harmon" wrote in message
m...
On Sat, 19 Sep 2009 15:52:04 -0400 in rec.crafts.metalworking, "Ed
Huntress" wrote,
Still, the best strength is obtained by putting your reinforcement near
the
bottom of a concrete slab of any kind that's going to have loads imposed
only from the top side. That's the way that most well-made sidewalks and
other concrete structures are reinforced.

Which means it will crack when he lifts it from the center, right?

If you're going to lift it from the center, you might want to add some
welded mesh up high in the center.