10
   

LVL or steel I BEAM?

 
 
farmerman
 
  1  
Reply Sun 1 Apr, 2012 08:14 pm
@raprap,
Im lost on considering shear forces on the floor. How do I envision that?

I think Ive overdesigned (What with the columns at each end of the building length and 2 in the middle where the central beam will lie)

Where does shear come in?

JTT
 
  1  
Reply Sun 1 Apr, 2012 08:38 pm
@farmerman,
Quote:
Its actuay the ability of the beam (or LVL) to damp any sponginess in each of the three sub segments of the floor >


The beam could be humongous in depth, a veritable bridge girder and sponginess in the floor could still come from undersized floor joists.

Are you sizing this I beam/LVL to handle only floor loads, 30 or 40 pounds per square foot live loads and 10 PSF dead loads? Does the same beam have to carry roof loads - snow load ???/ dead load 10PSF?

Is the loading equal in all of your described sections?



0 Replies
 
Fido
 
  1  
Reply Mon 2 Apr, 2012 06:26 am
@parados,
parados wrote:

Quote:
I did have an engineer buddy do a load analysis on the building shape but I didnt ask him about the floor. I only came up with having this decision in the last two days.

You might want him to do an analysis if you are planning on lifting anything heavy with the chain hoist you will attach to the beam. The floor might not like it if you start flexing that beam during heavy lifts.
Yes; he should go heavy in any case, over build and build in moment resistence at the same time if possible... I saw a nice home in Atlanta once... The garage was sort of built into a hill, but on top of an eight bay garage with beam and bar joist construction was built a beautiful patio... Every two cars had to park end to end, and the bays were narrow, but with a deeper, longer bar joist, and six bays instead of eight, the same area would be made available for out door living and auto protection...
0 Replies
 
raprap
 
  1  
Reply Mon 2 Apr, 2012 07:02 am
@farmerman,
Consider the ends of the beam--the loading is supported by the shear perpindicular to the length of the beam. The load is the same as used for the beam in bending, it is just concentrated at the support. The shear is the loading divided by the beam cross section--for instance a 2 by 4 has a cross section of 8, a 3 by 4 has a cross section of 16.

Now take the load at the support and divide by the cross section--that's the shear of the beam--compare this shear to the allowable shear of the beam material (usually established by the vendor). If the shear is greater than listed for the material with a safety factor (multiplyer, usually more than three) its good, if not use a beam with a bigger shear strength.

BTW a good structural engineer or an experienced contractor effectively does this for trusses, rafters, and joists--although a good fule of thumb (within reason--eg normal live floor loads 50#/ft^2 ) for pine joists supported at the ends (nominal 2 inch width on 16 inch centers) is 1 inch of depth for every 2 feet of span plus 2 inches. That is 2x4 joists on 16" centers is good for 4 foot spans, 2X6 good for 8 foot, 2X8 good for 12 foot, 2X10 good for 16 foot.

Caveat--cantilever joists and beams with cantilevers over 2 foot should be individually engineered.

Rap
parados
 
  1  
Reply Mon 2 Apr, 2012 07:10 am
@raprap,
Speaking of trusses. I just saw for the first time a multifamily home being built with steel roof trusses instead of wooden ones. A high pitch probably at least 12/12 but everything looked like light weight steel. I'm curious what the life time is for them if anyone knows anything about them.

Similar to this product from Australia
http://stratco.com.au/products/steel_framing/types/x1/images/gallery/E%20Stratco%20X1%20steel%20truss%20system.jpg
farmerman
 
  1  
Reply Mon 2 Apr, 2012 07:16 am
@raprap,
My frame of reference for shear forces are always out of synch with my engineer friends. However, on my plans I do hve one interiror wall that rund the width of the building (This separates the RV garage from the main building. I would assume that a shear force (in this case) would be a live or cyclic load applied on the length of the building (as in a storm)?

I amost did this building in post and beam but the design kit sent me by the P&B company made it economically infeasible (Over 250K for a fuckin garage). These P&B guys seem to think that everyone ois trying to build a barn like a Holiday Inn..

Thanks for al the ideas and alerts. Its been a real trip.
Today we are pouring concrete and rebar into all the block foundation ports (Amish dont like the pre hung concrete slabs cause its too much machine work that they lose control over)

So, my today job will be to place and secure all the ties for the sill plates in the concrete as its poured. The other guys are now cutting the rebar and getting it paced around the foundation wall.
I spent yesterday with a backhoe, pushing dirt around to create work space for the concrete truck. We had a hell of a rain last night so it may be dicey re the concrete truck getting stuck in my field .

ossobuco
 
  1  
Reply Mon 2 Apr, 2012 08:00 am
@farmerman,
Now there's a drama I'd not like, a stuck concrete truck. Good luck!

All this has been reassuring re our sizing of beams et al, back in the day (but I knew that).
0 Replies
 
Fido
 
  1  
Reply Mon 2 Apr, 2012 08:08 am
@raprap,
wouldn't that shear, and the moment as well be considered as half the beams length???
0 Replies
 
farmerman
 
  1  
Reply Mon 2 Apr, 2012 08:09 am
@parados,
STEEL trusses may obviate our needs for lightning arrestors. We get struck at least once a year and even with lightning arrestors we lose well pumps every few years.

However, I didnt like the look of those spider web interiro trusses. That wopuld totally wipe out any use of the upstairs except as a board storage bin. We will be using scissor trusses and will still have a room size of about 30 by 56 (we will have a knee wall 4 ft off each length and then we will have a cutout for two shed dormers on each side. The shed dormers define two steel loly columns that root right onto the brick columns down stairs These two coumns carry the roof axis .

Anyway, I dont .ike hip roofs for anything except in ARts and Crafts or HAcienda styles. It doesnt go with colonial style, Ive seen it force fit into colonial or Federalist and it ooks terrible to me.
0 Replies
 
Fido
 
  1  
Reply Mon 2 Apr, 2012 08:11 am
@parados,
That looks like an ironworker death trap... If some one pointed that job at me I would point myself toward home...
farmerman
 
  1  
Reply Mon 2 Apr, 2012 08:13 am
@Fido,
I know rap is a civil engineer, are you in construction?
raprap
 
  1  
Reply Mon 2 Apr, 2012 12:32 pm
@farmerman,
Not Civil I consider myself a Rogue Engineer. License is in Chemical Engineering--but a stamp is a stamp is a stamp by any other name.
0 Replies
 
raprap
 
  1  
Reply Mon 2 Apr, 2012 12:36 pm
@parados,
I'd opine that steel frames have a lifespan that is longer than wood frame---the only hazards would be if dissimilar metals were used and it was put in a corrosive environment (salt spray). But even then cathodic protection is easily maintained.
farmerman
 
  1  
Reply Wed 4 Apr, 2012 02:03 pm
@raprap,
weve picked the STeel beam . Only thing is that it has to verap on the columns.
0 Replies
 
Fido
 
  1  
Reply Thu 5 Apr, 2012 08:36 am
@farmerman,
farmerman wrote:

I know rap is a civil engineer, are you in construction?
Retired Ironworker... Still have some manuals and one engineering book.
farmerman
 
  1  
Reply Thu 3 May, 2012 12:00 pm
@Fido,
well, we went with an LVL flooring held up by a deep foundation and a central Steel I beam. The upstairs floor measures 36 X 64 ' Inside, and its as solid as a sidewalk, No "trampolining" that I feel with some of these huge modern "Mcmansions" I was in one in York county near a cement quarry project of mine and the owner let me walk around to take pictures (The house overlooked the quarry hole tahts why the lot was cheap). I was on the second floor and it felt spongy to me . The house was about 6000 square feet so it wasnt tiny. and the majority of the rooms were more open rather thanlike rabbit warrens like my house.
0 Replies
 
 

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