Subject: Re: Supporting loads (was Re: 2X4 joists)

From: [email-masked] (Nick Pine)
Date: 16 Oct 1996 03:08:13 -0400

Paul Valentine <[email-masked]> wrote:
 
>>Why do people want to square the length in bending moment calculations?
 
>The length is squared in the bending moment formula if the load is
>input in load per unit length along the beam. If the total load on the
>beam is used then the length is not squared.

Makes sense to me.

Now, I wonder how much weight a 12' beam like this will hold up?

     www s www s www
 --> www s www s www  <--3 1/2" drywall screws
     www s www s www
     www s www s www
 --> www s www s www  <--
     www s www s www
               ^  ^
               |  | __ 2x4
               |__ 1/16" steel, or perhaps a U-shaped piece of chicken wire,   
                                hardware cloth, stucco mesh, etc...

Harry Parker's _Simplified Design of Structural Timber_, 2nd edition,
gives this procedure on pages 233-235:

1. Assume fs = 20K psi for the steel and fw = 1200 psi for the wood.
2. Find the section modulus of the wood Sw = bh^2/6 = 9.1875 in^3.
3. Find the section modulus of the steel Ss = 0.255 in^3.
4. Find the distributed load that the wood will carry.
   M = WL/8 = 18 in-lb = fwSw, so W = 413 lb. 
5. Find the distributed load that the steel will carry.
   M = WL/8 = 18 in-lb = fsSs, so W = 284 lb. 
6. Add the 2 loads to find the 697 lb max load the flitched beam will carry.
   
Perhaps 2 such collar beams could hold up 2 55 gallon drums full of water,
with a redundant U shaped rope sling around the rafters, and some glazing
to the south, and insulation overhead, and some foil underneath, using a
few stud cavities for the supply airpath, to make a gravity-feed solar
water heater like this:
                                
                      ........                        .
                      drums                     . drum drum .
polyethylene       .g b  b                 .    .collar beam.    .
film sunspace --> . g foil                 .    . solar air .    .
	         .  g     polycarbonate    .    .   heater  .    .
                .   g <-- single glazing   .    .           .    .
            .....................      ..............................

Nick

---

From: [email-masked] (Nick Pine)
Date: 16 Oct 1996 08:53:52 -0400

[email-masked] wrote:

>>The trick is, as =
>>
>>Mr. Pine has figured out, to isolate the sunspace =
>>
>>from the living area. =
>
>Good idea :-)

And put our bare collectors in the sunspace, eg Big Fins, with an ordinary
water heater upstairs that seldom turns on, heated by natural warm water
convection, with no collector glazing nor insulation nor pumps nor controllers
nor antifreeze nor heat exchangers if possible, just a well-managed sunspace
that never freezes.

Or perhaps we can hold up 2 plastic 55 gallon drums full of water under the
peak of a roof, with a redundant U shaped rope sling around the rafters, and
some glazing to the south, and insulation overhead, and some foil underneath, 
using a few stud cavities for the supply airpath, to make a gravity-feed
solar water heater like this:
                                
                      ........                        .               ---
                      drums                     . drum drum .
polyethylene       .g b  b                 .    .collar beam.    .---
film sunspace --> . g foil                 .    . solar air .    .    11'
                 .  g     polycarbonate    .    .   heater  .    . 8'
   pond         .   g <-- single glazing   .    .           .    .
            .....................      ...................................
                                           |          12'        |

During the day, the air from the drum space would slide down the inside of
some south wall stud cavities, between the outside wall and some reflective
insulation, then south through a hole at the bottom, then up through a 6"
air gap between the dark north wall of the sunspace and a single layer of
polycarbonate glazing, and back into the drumspace. There might be a diagonal
layer of oxidized stucco mesh in the air heater, sloped from north to south.

Something like this would be nice for a rustic cabin, as a part of solar
heating our 10'x12' shed. The sunspace frame has curved 1x3 spaced beams
on 4' centers (I just snapped 4 1x3s in bending them to less than an 8'
radius) and the 4x8x8' solar closet might be in the sunspace itself, which
leaves a 4x8' patch of sunspace wall. It would be nice to have a warmwater 
hose in the sunspace, for showers. At some point, the "solar closet" might
become an EPDM-lined strawbale hot tub, as well, with a rigid automatically
movable reflective and insulating cover.

The water supply might be a 16x24' pond to the south, as well as the 8x12'
sunspace and 10x12' roof and 12x16 adjacent greenhouse area, about 800 ft^2
of rain catchment area, which should provide 64 gallons of water a day, where
I live, for an average water consumption of 8 gallons per hour over an 8 hour
day. Enough water for 16 showers with 4 minutes of water usage at 2 gpm.

Heating the water from 65 F to 105 F takes about (105-65)64x8 = 20K Btu/day,
which could come from the 4x8' air heater, and raising it from 32 F to 65 F
takes about (65-32)64x8 = 16K Btu/day. Could this be done with a 4" x 10'
tempering pipe hanging inside the cabin, near the ceiling? It would hold 
about 56 pounds of water, with a surface area of about 10.5 ft^2, and the
main thermal resistance might be a (US) R2/3 still air film on the outside,
which would make RC = 0.67/10.5x56 = 3.5 hours. Hmmm. We need something
closer to a half hour to keep up with the average water usage.

Add some sort of fins and a small fan and a 6" concentric pipe to double the
first pipe area and reduce the R-value to about 0.2, by moving air past the
pipe at 8 mph? With a half-hour time constant, 7 gallons of water in a 70 F
room would warm up to 70-(70-32)exp(-1/0.5) = 65 F in an hour. Or should we
put the pipe outside, near the peak of the warmer sunspace, with some
insulation above it? 

Or hang a dark drum in the sunspace, and let it lose heat all night? A 55
gallon drum has about 25 ft^2 of area, so RC = 2/3/25x55x8 = 12 hours. Suppose
we surround it with insulation on the back, and R1 glazing on the front. Most
of the heat loss will be through the glazing, and on an average day, with some
sun, if the drum starts out at 32 F, and the sunspace is 80 F for 6 hours,
the water temp at the end of the day would be 80-(80-32)exp(-6/12) = 51 F.
Adding 12ft^2x0.9x0.9x1000 Btu/ft^2/dayx1.3reflective gain = 13K Btu of direct
sun to this might raise the water temp another 13K/450 lb = 28 F to 79 F.
Looks like the right ball park.

Jade Mountain's $59 4 gpm 12V 7A #WP100 Amazon submersible pump might run
for 2 minutes every hour, with a float switch or 2 in one of the drums.

Nick

---

From: Greg Marion <[email-masked]>
Date: Wed, 16 Oct 1996 08:50:51 -0400

This is a great thread! 

BTW - Their is a span calculator at http://www.btw.com/himprove.htm

Now - what about beam supports. How much weigth can a double
2x8x12 support using double 2x4 criples on both sides? Any
pointers? 

Thanks!

-- 
==================================================================

Greg Marion                                                   SDRC
SDRC North American Customer Services
[email-masked]

---

From: [email-masked] (Nick Pine)
Date: 16 Oct 1996 10:47:43 -0400

>This is a great thread! 

It does seem like fun.

>Now - what about beam supports. How much weigth can a double 2x8x12
>support using double 2x4 criples on both sides? 

I dunno. What's a cripple? I've decided to hold up my 2 55 gallon drums full
of water with 2 composite beams, each made with a 12' 2x6 with 2 12' 2x4s
and a metal U-shaped sandwich on either side of the 2x6 at the bottom, made
>from  2 10' pieces of drywall corner bead. How much will that hold up?

Nick

---

From: Henry Bloom <[email-masked]>
Date: Wed, 16 Oct 1996 21:06:23 -0400

The first one (www.nrel.gov) is especially well done. (A US
government department of energy site.) 

http://www.nrel.gov/  
http://www.eskimo.com/~trace/   
http://www.realgoods.com/   
http://www.bergey.com/index.html 
http://keynes.fb12.tu-berlin.de/luftraum/konst/engwindkraft.html
http://www.me3.org/issues/wind/gipebk1.html 
http://www.gridwise.com/ 
http://www.webpage.com/wpt/  
http://solstice.crest.org/

---

From: [email-masked] (Hank Roberts)
Date: Wed, 16 Oct 1996 18:56:37 GMT

[email-masked] (Nick Pine) writes:

 ...
>peak of a roof, with a redundant U shaped rope sling around the rafters, and
 ...
>polycarbonate glazing, and back into the drumspace. There might be a diagonal

    How do you handle 
    -- condensation, when the water in the system is cool, so you
       don't get mold growing in the system?
    -- fire blocks, so you don't get a fire going up the stud space 
       (which usually, by code in many places, have fire blocks across them)
       (and, remember, polycarbonate burns pretty fast and hot)

The ideas are attractive, but I don't see any built in ways to handle
either air quality/mold/condensation or fire safety considerations in them.

---

From: [email-masked] (Nick Pine)
Date: 17 Oct 1996 10:33:31 -0400

Hank Roberts <[email-masked]> wrote:
>>polycarbonate glazing, and back into the drumspace.
>
>    How do you handle 

Where would the condensation occur, exactly? The whole building would leak
enough air to eliminate moisture buildup, and the sunspace would have a vapor
barrier on the floor, and the drums would almost always be warmer than the
ambient air. They might have a shallow liner underneath, in case one of them
leaked, or a little condensation formed. Condensation might be a larger
problem in the preheater, if any, ie the tempering tank/heat exchanger that
raises the water temp from 32 F to 70 F or so, but that might live in the
sunspace.

>       (which usually, by code in many places, have fire blocks across them)

Perhaps stud spaces are used in this way now as HVAC ducts.

I'm not impressed with some parts of the code, altho I like the part in the
front that says you can do whatever you want, notwithstanding the following
text, if the building inspector approves. Sprinklers? Dampers with fusible
links, as in envelope houses? Halon? Some old fashioned carcinogenic-if-used-
but-perhaps-less-harmful-than-immolation carbon tetrachloride glass bulbs
near the top of the stud cavities? A good and reliable fire detection and
extinguishing system? Seems like there are lots of solutions, including just
insulating the stud cavities in the normal way, and making the air heater on
the outside of the wall a little thicker.

>       (and, remember, polycarbonate burns pretty fast and hot)

I think it's been through some big city flame spread tests OK.

>During the day, the air from the drum space would slide down the inside
>of the south wall, south through a hole at the bottom, and up through a
>4" air gap between the dark north wall of the sunspace and a single layer
>of polycarbonate glazing, and back into the drumspace.
 
This solar closet may end up in the ceiling. I ended up making all the collar
beams super-strong yesterday, and realized 6 drums will fit in the ceiling,
(few earthquakes here.) This could be enough for a combined space and water 
heating system, with no separate solar closet in the sunspace. Like the attic
warmstores of Norman Saunders, except it would have an air heater built into
the back wall of the sunspace, to make a higher temp, and the warm sunspace
air, ie the "waste heat" from that air heater glazing, would heat the cabin
on an average December day, with some sun. 

Nick

---

From: [email-masked] (Nick Pine)
Date: 18 Oct 1996 09:49:23 -0400

........ R20                    .     R20       ---
                       6 drums                  . drum drum .
polyethylene       .g b  b                 .    .collar beam.    .---
film sunspace --> . g R20                  .    . solar air .    .    11'
                 .  g     polycarbonate    .    .   heater  .    . 8'
   pond         .   g <-- single glazing   .    .           .    . R
            .....................      ...................................
                                           |          12'        |

During the day, the air from the drum space would slide down the outside of
the south wall, south through a hole at the bottom of an air heater, and up
through a 6" air gap between the dark north wall of the sunspace and a single
layer of polycarbonate glazing, and back into the drumspace. At night, the
air heater would get cold, and the heat would stay trapped in the attic.
Steve Baer and Norman Saunders, PE, have been building systems like this 
for the last 30 years.
 
Suppose there are 6 plastic 55 gallon drums in the attic. 

A few numerical questions: 
 
1. What would the average stagnation drumwater temperature be in December?  

With a frozen pond to the south, about 1300 Btu/ft^2/day would fall on the
sunspace glazing, of which about 1050x8'x12' = 100K Btu would enter the air
heater, on an average December day in Philadelphia, with a 24 hour average
outdoor temperature of 36 F. So if the drumwater has temp T, and the sunspace
air is 70 F, and the solar energy that flows into the drumwater equals the
water heat loss, on an average day, we have  

100K Btu =   6 hr(T-70)8x12/R1   from the air heater during the day
           +24 hr(T-36)10x12/R20 from the roof, 24 hours a day
         = 576T - 40320 + 144T - 5184 = 720T - 45504, or
T = (100K+45.5K)/720 = 202 F.

OK, altho radiation losses would make this temperature closer to 130 F,
without a selective surface, and this doesn't consider house heating or
hot water consumption, yet. 

2. If the average drumwater temp were 110 F, what is the minimum average
R-value needed for the cabin walls, so the drums can keep the cabin at 68 F 
for 8 hours per day for 5 days without sun? 

The drums store about 6(110-80)55x8 = 80K Btu, and the cabin walls have an
area of about 350 ft^2, so ignoring the heat loss through the roof, we have
80K = 5x8x(68-36)350/R = 450K/R, so R = 450K/80K = 5.6. Suppose we use an
R10 average. R20 for the walls themselves, and window losses that make the
total no less than R10. Then the cabin needs 8hr(68-36)350ft^2/R10 = 9K Btu
to stay warm on an average 8 hour day.

3. Would the sunspace really be 70 F, during the day?

The heat loss from the air heater would be about (110-70)8x12/R1 = 3840
Btu/hour, and the 12'x8'x8' curved sunspace has about 400 ft^2 of R1 glazing,
and the avg daytime high temp in Phila in December is 43 F, for an approximate
sunspace temp Tss = 43 + 3840xR1/400 = 52.6 F. We could put less energy into
the water to make the average sunspace temp 70 F, so we can heat the cabin
with sunspace air, by impeding the air heater airflow so the air temp goes up 
and we lose 12K vs 4K Btu/hr. Then Tss = 43 + 12K/400 = 73 F. Better. But
the sunspace loss would increase to 6hrx12K = 72K Btu/day. We could double
glaze the sunspace to cut this in half... Or just remove 9K Btu/day of 110 F
air from the air heater, ie 40 cfm, and leave the sunspace cooler. It seems
to me a human or plant might be fairly warm in a 53 F room full of still air,
if exposed to direct sun.

Or we could use a larger sunspace. We might add on another curved poly film
12'x 8' sunspace to the east, with a poly film covered strawbale wall to the
north. This would collect an additional 100K Btu of sun per day, and increase
the sunspace glazing area to about 700 ft^2. How much leftover energy will
there be if we keep the whole sunspace at 70 F on an average day? 

200K - 6(70-43)700ft^2/R1 = 87K Btu/day.

4. How many 4 minute 2 gpm showers can we take on an average day, while
heating 32 F water to 110 F? 

Each shower takes 4x2x8(110-32) = 5K Btu, so with N showers/day, we have

87K Btu =  24 hr(110-36)10x12/R20  from the roof, 24 hours a day
         + 9K Btu                  for space heating
	 + 5K N Btu                for water heating
         = 10.6K + 9K + 5K N, so N = (87K - 19.6K)/5K = 13.

Did I do this arithmetic correctly?

This would work better with 55 F well water. 

Off to do more hammering, on this cool and blustery day.

Nick

It's a snap to save energy in this country. As soon as more people become
involved in the basic math of heat transfer and get a gut-level, as well as
intellectual, grasp on how a house works, solution after solution will appear.

                                          Tom Smith, 1980

---

From: [email-masked] (jong son pyo)
Date: 19 Oct 1996 17:49:33 GMT

Henry Bloom ([email-masked]) wrote:
: The first one (www.nrel.gov) is especially well done. (A US
: government department of energy site.) 

: http://www.nrel.gov/  
: http://www.eskimo.com/~trace/   
: http://www.realgoods.com/   
: http://www.bergey.com/index.html 
: http://keynes.fb12.tu-berlin.de/luftraum/konst/engwindkraft.html
: http://www.me3.org/issues/wind/gipebk1.html 
: http://www.gridwise.com/ 
: http://www.webpage.com/wpt/  
: http://solstice.crest.org/

---

From: [email-masked] (Tooie)
Date: 16 Oct 1996 23:01:19 GMT

Nick Pine ([email-masked]) wrote:
: Greg Marion  <[email-masked]> wrote:
: 
: >This is a great thread! 
: 
: It does seem like fun.
: 
: >Now - what about beam supports. How much weigth can a double 2x8x12
: >support using double 2x4 criples on both sides? 
: 
: I dunno. What's a cripple? I've decided to hold up my 2 55 gallon drums full
: of water with 2 composite beams, each made with a 12' 2x6 with 2 12' 2x4s
: and a metal U-shaped sandwich on either side of the 2x6 at the bottom, made
: from 2 10' pieces of drywall corner bead. How much will that hold up?
: 

Just load it til it breaks, rebuild it and put a little less on it ;-)

tooie