Hello Chris,
Thank you for the information. I would not use aggregate, just a sand mix
if build it from scratch.
Maybe the whole idea is more trouble than it is worth.
I am using the AL plates right now as you suggested. Maybe I should just
leave the frame construction alone and concentrate getting the sensor back
up and running.
I didn't realize that concrete was so porous. Epoxy is not my glue of
choice for lots of my different projects now.
I have actually had it shatter and have bit shard of it embed in my skin.
Thanks again for the advice.
PauLC
-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@.................
Behalf Of ChrisAtUpw@.......
Sent: Friday, June 06, 2008 4:39 PM
To: psn-l@..............
Subject: Re: Concrete Block framework for horizontal sensor.
In a message dated 06/06/2008, Paulc@........ writes:
I wonder if anyone has had any experience using standard concrete blocks
to form the "L" framework for a horizontal sensor.
Hi Paul,
Ordinary concrete with stone aggregate in it can be quite noisy as the
temperature changes. The expansion coefficients of the cement and the stones
are different. For seismic use, a 50:50 mix of sand and cement is
recommended - definitely no aggregate!
>> For the pivots I would be using crossed rods top and bottom. I
would cement in place the mounts for these and make the top adjustable for
levelling.This amounts to taking my horizontal sensor which constructed on
an AL channel frame, and moving it over to the concrete frame. I have the
space to do this.
You will need to cover the concrete and keep it wet for at least a
fortnight to cure. Then allow it to dry out slowly and coat it with a
sealing paint - concrete can absorb quite a lot of water as the humidity
changes. Damp concrete can be very corrosive to metals.
I am doubtful about trying to cement the mounts in place. They are
usually secured with bolts. Concrete takes compressive forces OK, but it is
not strong in tension and it does not adhere well to metals. Adhesives are
generally used.
The aluminum frame is currently apart and was being readied for welding.
Why weld the Al U channel frame at all? I use 1/8" thick triangular Al
plates and 4 stainless steel bolts to secure the corners. This is simple to
do and works well.
Welding Al can be OK, but you have to know your alloys - not all of
them weld well and quite a bit of skill is required. Welded joints also have
a lot of stress frozen in, which can cause problems if it is not relieved.
Welded metal is usually quite soft. You stress relieve the joints at 180 C
for maybe an hour.
Any comments or suggestions.?
You can also stick Al frame components together with two part acrylic
adhesives. Don't try to use Epoxy. Al sticks better if it is heated first to
drive off the water absorbed on the surface.
Regards,
Chris Chapman
Hello=20
Chris,
Thank you =
for the=20
information. I would not use aggregate, just a sand mix if build =
it from=20
scratch.
Maybe the =
whole idea is=20
more trouble than it is worth.
I am using =
the AL plates=20
right now as you suggested. Maybe I should just leave the frame=20
construction alone and concentrate getting the sensor back up and=20
running.
I didn't =
realize that=20
concrete was so porous. Epoxy is not my glue of choice for lots of =
my=20
different projects now.
I have =
actually had it=20
shatter and have bit shard of it embed in my skin. =
Thanks again =
for the=20
advice.
PauLC
In a message dated 06/06/2008, Paulc@........ writes:
I wonder if anyone has had any =
experience using standard concrete blocks to form the "L" =
framework for=20
a horizontal sensor.
Hi Paul,
Ordinary concrete with stone aggregate in =
it can=20
be quite noisy as the temperature changes. The expansion coefficients =
of the=20
cement and the stones are different. For seismic use, a 50:50 mix of =
sand and=20
cement is recommended - definitely no aggregate!
>> For the =
pivots I=20
would be using crossed rods top and bottom. I would cement in =
place the=20
mounts for these and make the top adjustable for =
levelling.This amounts to taking my horizontal sensor =
which=20
constructed on an AL channel frame, and moving it over to the concrete =
frame. I have the space to do this.
You will=20
need to cover the concrete and keep it wet for at least a fortnight to =
cure.=20
Then allow it to dry out slowly and coat it with a sealing paint =
-=20
concrete can absorb quite a lot of water as the humidity changes. Damp =
concrete can be very corrosive to metals.
I am=20
doubtful about trying to cement the mounts in place. They are usually =
secured=20
with bolts. Concrete takes compressive forces OK, but it is not strong =
in=20
tension and it does not adhere well to metals. Adhesives are generally =
used.
The aluminum frame is =
currently apart=20
and was being readied for welding.
Why weld the Al U channel frame at all? I =
use=20
1/8" thick triangular Al plates and 4 stainless steel bolts to secure =
the=20
corners. This is simple to do and works well.
Welding Al can be OK, but you have to =
know your=20
alloys - not all of them weld well and quite a bit of skill is =
required.=20
Welded joints also have a lot of stress frozen in, which can cause =
problems if=20
it is not relieved. Welded metal is usually quite soft. You =
stress=20
relieve the joints at 180 C for maybe an hour.
Any comments or=20
suggestions.?
You can also stick Al frame components =
together=20
with two part acrylic adhesives. Don't try to use Epoxy. Al sticks =
better if=20
it is heated first to drive off the water absorbed on the =
surface.
Regards,
Chris Chapman