Comment on this cement job

[etat]

Remember when I said I like to give my opinion.

Anyways, this is still bugging me so I did a bit of research.  In relation to floor truss systems I came across this bit of information.  There can be designed into the trusses such a thing as bottom cord bearing trusses, mid cord bearing trusses, and top cord bearing trusses.  In the case of a mid cord bearing, or top cord bearing, it would be ok to cut the bottom cord, if the top cord is properly supported. .  Also I found that on exceptionally long floor truss conditions a 'squash block', would have to be installed center ways. That could be very well the purpose of the center beam cut into the trusses, not to weaken but to prevent them from squashing.  Let's hope, and it is possible acording to my research, and full knowing that it might not be worth the whole 2 and 1/2 cents, that this design and application, is acceptable.  Although I found lots of information I did not find a picture of a top cord bearing truss.  I did find a picture of a bottom cord bearing truss, and a mid cord bearing truss.  The mid cord, with the bottom cut back would be the best  example of what I am describing.  

You'll notice that the top cord is sitting on a couple of 2/'s which the beam could very well replace.  

http://www.timbertruss.com/floortruss.htm

[ADfields]

The trusses are correctly installed and completely to the code hear.   If you place the beam under the bottom plate of that type truss it will just crush down till it fails or the top plate rests on the beam. That bracing will not hold a compression load at all, it has to be in tension, pulling not pushing.   If it were intended to have the beam under the bottom it would have a vertical support in the place that the beam sits under, this support transfers the load to the top and the bottom is just there because it's there.   Now I live in Alaska, home of 20% of the worlds earth quakes and 6 of the 10 biggest ever recorded so I would want the bottom ends tied off.   Like it is they could roll on their side and fail in the right quake movement.  Also they would pop the screws threw sheet rock if it is hung from them like they are I bet.
Andy

[etat]

AD, I agree with EVERYTHING you said!!!!!

[Bruce_A]

The concrete is held together with a glue called cement.  A good finisher can redo anything that may be wrong with that wall for less than fifteen hundred dollars american. The trusses appear to be what is usually called a web joist.  They are supported by the top cord.  I don't believe they were cut to put them in place, but are built this way instead.  Most commercial buildings built in the lower states use a similar type truss and have for many years.  Try to get a look at a safeway store during construction or remodling and you will see what I am talking about. If this was done according to the uniform building code as it should have been, it will outlast solid wood construction. And is stronger to boot.

[SwampDonkey]

Well the floor hasn't collaspes yet and its not springy. Good sign.

I'm going to research it a bit from here

Canadian Wood Counsel

You folks in the US will find the info here pertanent and there are links to US sites. Well off to the woods 'til later.    

Thanks for all your knowledge and input, Trusses aren't my thang.

[slowzuki]

Well, that depends now!  Slap a couple of layers of 5/8" fire rock and the steel will be good for better than 2 hours.

My day job is as a fire protection engineer which mean a lot of things but the funnest is fire investigations!  

Swampy is right, unprotected steel in the thicknesses small building are built with won't last near as long as heavy timber or even some light wood framing.

Now in big buildings you can get some huge steel that can absorb so much heat it will outlast the fuel sources in the area.

When I was working on an investigation of a large plywood mill fire, there where a bunch of differerent types of construction to look at.  

The masonory kiln area was still standing but you could pull it apart with your hands.  Some of the small leantos etc were ok (well, standing) because they had aluminum roofing that melted off and vented.  The main building had glulam trusses that stayed up a long time and didn't have any delamination.  The 2" t&g roof deck (spruce I think) was completely reduced to coals.  The steel framed building stayed upright as the huge doors were open to vent the heat through it.

Nothing quite like fire spread in a veneer mill, would have been scary for the fellows working there.

By the way, steel beams will fail before wooden beams in a house fire.

[ADfields]

I've been told that pound for pound wood is stronger then steel in compression and the other way round in tension.   I know from blacksmithing 800 degrees in mild steel is the start of red hot, around 400 degrees it's getting real bendy, it's burning at around 1300.   I wonder what the flash point of dry spruce is.   We had a old log shack down the road burn, the floor and roof went but the log walls are just a bit black.   That was with out any fire fighting on it at all, just containment.

[beenthere]

AD  Interesting point about strength of wood vs. steel, but that comparison to steel might ( I think) be the other way around, i.e. wood is stronger than steel (pound for pound) in tension (and that even needs to be qualified to be straight-grained wood free of any defect, and measured in tension parallel to the grain).  Across the grain, many species, such as red oak are pretty weak in tension. Those woods are the ones that are easy to split with a splitting maul when making firewood.

Measuring the tensile strength of wood is difficult, and special grips and specimen shapes are made to test wood.  I remember seeing huge machines set up to test full size lumber specimens, and the grips were huge and often crushed the wood (compression) under the grips before the specimen would break in tension. And then, it would break where there was a knot or was squirrely grain around the knot.

[ADfields]

I think I have it right, a dry 2"x4"x8' spruce will come in about the same poundage as a 1-1/4"x1/4"x8' hot roll steel.  Off the top of my head without looking it all up.   The 2x4 would hold me at center span and I don't think the steel would.   Maybe a steel stud is a better choice but I don't think that would hold up much better then the hot roll.   You are right on about selecting wood.  
Andy

[Egon]

Perhaps a few uneducated  comments on the beams/trusses.  Simple Beams are designed to meet shear, bending moment and buckling requirements. Shear is usually greatest at the support, Bending moment at midpoint and buckling at midpoint. Usually bending moment is the dominant requirement of the beam design. This would indicate the placement of the trusses as shown for the layout of the truss will be correct.

On fires:  Large solid wooden structural components fare well in fires. This happens due to a layer of charcoal forming on the exterior portion of the beam which cuts off the oxygen supply to the fire. Metal structural components lose strenght when heated and may be insulated for fire protection.  

Egon

[etat]

So....in the case of my 22 foot beams wrapped with wood, all but the top and bottom flange, seems like I'm getting the best of both worlds.  Ten inch beam, 2/10's bolted to each side, and additional wood fastened to that, Maybe I'm gonna be ok.



By the way, we put them beams up there by 'hand power' and quite a bit of 'southern ingenuity'! .  Had us lotsa fun that day!  Worst part was when I put em up I decided they was 1 foot too high.  It was a LOT harder lowering em than it was puttin em up there to begin with.

[SwampDonkey]

 

One of them fella's that's got to do everything twice eh CK?

[ADfields]

, no doubt you got enough beam.  Now do you have enough wall or post to hold that big thing up.   Make for a bad day if that knocked you in the head as it fell.

SwampDonkey, I wish I got most stuff right in just 2 tries!
Andy

[etat]

AD, I'm a hoping it orghta  stay there, lots and lots of doubled up wood under them beams.  Not ever been earthquakes around here but occasionally we get some straight line wind, and every once in a while a tornado sets down around here somewhere.  I wanna be as ready as I can be. One end the wood and floor is sitting and bolted to  the main foundation of the house, which is probably dug dang near deep enough to hold up in yall's high frost conditions, and got some BIG rebar buried in the concrete.  Seems sometimes them big construction types working haul bunches of that stuff to the dump, and I've got a good friend who's in charge of burying it! It don't always get buried, he saved rebar for me off and on for 6 or 8 months, before I started the house.  Had to heat that junk with a torch to bend some of it!  The other side's I dug holes about 3 foot diameter and as deep as the backhoe on my tractor would dig em, throwed some steel in there, filled em full of concrete, and then cemented doubled up concrete block pillows, and filled them full of concrete.   In fact they's a bunch of them homemade pillow blocks under the house.

There probably ain't enough space on this forum to list all the stuff I've done, and redone, and redone!  The things that I know that I'll never get perfect, I'll just learn to look at it as character!

[SwampDonkey]

 

CK:

I spend a good part of my time lookin for the tool I just sat down.  

And I never read directions, so them home assembly jobs I do over 2 or 3 times so I don't forget next time.