Author Topic: wood beam vrs steel beam  (Read 52397 times)

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Offline Bill in seattle

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wood beam vrs steel beam
« on: February 06, 2009, 03:02 PM »
He is a question that some of you probably will know.
I'd like to pull a center post out of my carport for a clear span so my door does not hit the post when i open it.
I have asked the local lumberyard beam guy for a beam size and he has given me two sizes, 8x18 or 6x21. Seems a little over kill to me.
I have about 14'' of clearance under the roof till the top of a brick side wall so these beams would require the roof to raised or the cars would not fit underneath.
my spec's
The span is 27' and beam would be supported on steel posts on each side into the foundation with a 80''tall brick wall tied to the outside posts.
Flat pitch roof, torchdown with 2x6 tongue and groove fir decking running perpendicular to  4x12's on 13' centers currently there now.
Would a w12x16 steel I beam be sufficient to span and support clear span to remove the center post?
I've looked at some beam estimator programs but they are engineering marvels beyond my figuring.
Any beam comparison charts out there that compare wood size beams to equivalent steel sizes or any simpler way of figuring out?

Bill
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Offline Dovetail65

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Re: wood beam vrs steel beam
« Reply #1 on: February 06, 2009, 03:06 PM »
Bill I had a beam that was 16". When the engineer came he replaced it with a steel I beam barley 8" wide, so you will save a lot of width ie headroom going metal.

There are a bunch of tables on the net.

In our area changing out a beam like that required a licensed engineer or an architect stamped approval. The engineer only charged us 300.00 at the time for his recommendation that the county accepted. The architect wanted 3500.00!
« Last Edit: February 06, 2009, 03:16 PM by nickao »
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Offline Dave Ronyak

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Re: wood beam vrs steel beam
« Reply #2 on: February 06, 2009, 05:13 PM »
Bill,

I would choose the steel I-beam or H-beam.  I did much the same modification to my prior house, except that the span was only about 21 ft.  I replaced a 3pcx2x12 wooden beam and steel center post with a clear span H-section steel beam.  I am not certain of its exact dimensions but they were about 8" x 8".   The steel beam was spec'd by an architect for me; he also gave me a source to order the exact product from, cut to exact length.  Note that beams of with the same overall flange and web dimensions come in different metal thicknesses and thus have different load ratings and weights per unit length.   Per the architect's specifications, I made new reinforced supports for each end of the steel beam and secured a 2' x 8" between the steel beam and the bottom of the floor joists above.   The results included about 2 to 3 inches more head room than before, noticeably less deflection in the floors above, and a convenient pathway along the web of the beam that I used to run a gas line from my house to go the new attached garage.  And replacement of the wooden beam eliminated the seasonal movement that previously caused some of the doors above the wooden beam to not latch perfectly in the winter season (in Ohio).

I am assuming that you know how to shore up your existing structure prior to removal of the old beam.  That is an important step, one in which you later get to go hog wild with your Sawzall or equivalent to remove the old wooden beam.

Dave R.
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Offline Bill in seattle

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Re: wood beam vrs steel beam
« Reply #3 on: February 06, 2009, 09:06 PM »
Dave,
I really would prefer using a steel beam and have located one on c.l.for cheap if I can pick it up and get it on my trailer. ( my back says get help now and make sure the aspirin are close by after.)
Yes, shoring up is no problem already have some post jacks and timber. Won't need much to pull the old beams down, they will probably fall on there own if they were constructed like everything else in this non conforming fixer upper.
Just trying to decipher all the beam load calc's on some of them formulas. Algebra was not my best math.
I was hoping there was some cross chart that maybe listed comparisons. I know there are many variables involved but its just a carport and no ones dancing on the roof. Everyone I talked to can spec wood but haven't found something for steel yet.
Bill
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Offline Dave Ronyak

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Re: wood beam vrs steel beam
« Reply #4 on: February 07, 2009, 12:36 PM »
Do you have any friends or acquaintances who are registered professional engineers?  Any of them could provide you the needed information.  I would think there are a lot of them living in the Seattle area given that Boeing has a major presence there.  You might want that person to accompany you when you go to close your purchase of the used beam to ensure it is suitable for your project.

Here's a PDF publication and set of Steel Beam Tables covering use of steel beams in residential construction from the American Iron and Steel Institute.  They ought to know what they write about!! 

Here's another W-type I-Beam Table which itself contains links to various steel beams and their associated properties.  Within this website and for a chosen beam, you will find further links that you plug in your information as to type of construction (total load, distribution of load, how the beam is supported, etc.) which the site makes very easy for you due to use of miniature picture diagrams for the various possible load types and beam arrangements in the planned construction.  For example, I chose a heavy lbs.ft lenght W8 steel beam, then chose a simple clear span beam supported only at its ends and with an equally distributed load above (which simulates a floor above that will be loaded in use, e.g. furniture, storage, people etc.), then entered the length of the span at 23 ft, and the model returned this Result.  The calculated deflection was only about 0.03 inch!!

If the efunda website blocks your access, try starting HERE.   This site worked for me for a few queries over a short time, then stopped allowing me access and would only display its log in page to me.  Your results may vary   :D.   I am not a member of this doityourself forum or of efunda.  It appears that you can join efunda at a basic level at no cost.  Here's the text of the message on doityourself that led to the useful efunda site and its models and calculators.   Good luck, and let us know how your efforts turn out.


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Steal beam calculator
For those of you who found this by a search engine, I have a spreadsheet I created to do steel beam calculations to figure out what I needed for my 19' span on my deck. I used a stanard liv weight of 40osf for a deck (60psf for house room) and a calculated 7.8psf dead weight instead of the standard 10psf. Then I found a a web site I printed out to find a beam that meets the requirements using the values of S and I Go to: http://www.efunda.com/math/areas/RolledSteelBeamsW.cfm

In my case a W8x10 worked with a Ixx=30.8 and a Zxx=7.81 to meet the calculated I=27.50 and S=6.41 found below.

If you would like a copy, let me know. I wish I could just attach it. Below is a cut and paste from the cells. You might be able to follow it and create your own. Cut and paste in to 4 columns by 24 rows.

Length = L= 19 ft
Width = W= 10 ft

Live Load = 40 psf
Deflection Limitation "= L/360" 0.63 inch
2x10 weight 3.8 lbs/sq-ft
Decking 4 lbs/sq-ft

Load Calculations
# of 2x10 "=(LX12/16) 14
Tributary Area "=W/2*L" 95 sq-ft
Weight of 2x10 "=(#of 2'x10') X Weight X 5)) / L 14.25 lbs/ft
Weight of Decking DeckWeight X W/2 20 lbs/ft
Total Dead Load 34.25 lbs/ft
Live Load 40psf X W/2 200 lbs/ft
Total Load Weight= 234.25

Beam Formula
M=wl^2/8 Weight X Length /8 x 12inches M= 126846.375 in lbs
Allowable bending stress s= 19800 psi

S=M/s S= 6.41 in^3

I=5wl^4/384 ED I= 27.59 in^4 >>>>

Note also that it is important to tie that steel beam to the joists above it, so neither the joists can move laterally or twist, nor can the steel beam move laterally or twist.  This can be accomplished by placing a 2X?? board (plate) between the top flange of the steel beam and the bottom edges of the joists supported by the beam.  When I did this in my former house, I drilled through the top flange of the steel beam and inserted lag screws through the beam flange into the wood plate.  And I toe-nailed the joists to that wooden 2x?? plate.  This method of tying together the steel beam to the wooden structure above should also help to reduce "bounciness" in the floor due to coulomb damping (friction damping between the wood and steel during any movement due to varying the load above).  In my case, the main floor of the house was above the beam.  Proper preparation of the end support columns/walls and the actual bearing on which the ends of the steel beam will be supported are also very important, but not difficult to achieve.


Dave R.
« Last Edit: February 07, 2009, 12:45 PM by Dave Ronyak »
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Offline Bill in seattle

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Re: wood beam vrs steel beam
« Reply #5 on: February 08, 2009, 12:55 AM »
Thanks Dave,

I have looked at some of those charts before but the one from efunda with the beam specifics will be helpful. Have not seen those before. Efunda does block me out for most of the the info and wants me to renew what I don't have????
Most of the people I know are wood guys and what ever steel related stuff they need I do for them. I do steel fab for  projects now up to 4'' tube small channel or or 2'' solid cantilever stuff but this big beam stuff is new turf and interesting.
I might head to the steel yard on Monday and see if they could help recommend a piece if I can't make heads tomorrow, though they are never very friendly most of the time.

Bill
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Offline Dave Ronyak

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Re: wood beam vrs steel beam
« Reply #6 on: February 09, 2009, 12:16 AM »
Sorry, Bill.  I just retried my link to the doityourself message and from that message to efunda and once again was taken to the table in which I could choose the steel beam cross section I wanted to use for my calculations!  Everything worked for me so I place a checkmark besides 3 different steel beam types, then ran the calculations using the largest of these which has a height of about 12 1/2 inches and weighs a little less than 100 lbs/ft.  I captured all of these using the Print Screen and Paint programs on my PC.  The calculated deflection was about 0.06 inches for a 27 ft span with a line load of 10psi-in.  Increasing this load to 30psi-in caused the deflection to triple to 0.19 inches at mid-span.  Unfortunately, if I try to go back, the efunda site then reverts to blocking me and only displays their sign-in screen.  From that experience, it appears that a completely fresh start at their site may allow a person in to do a few calculations.

Did you note that doubling the beam depth increases the strength by 4 times and decreases the deflection by 8 times.

If I was interested in learning more and getting more help on this type of problem, I would try joining the http://forum.doityourself.com/framing-sub-flooring/258810-steel-beam-calculator-anywhere.html forum and asking the people there for help.  Many of them know how to properly use these resources.

Dave R.
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Offline Tom Bellemare

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Re: wood beam vrs steel beam
« Reply #7 on: February 09, 2009, 12:44 AM »
Bill:

I don't know if you've solved your problem yet, but I've done some work with people here that had interesting solutions to similar problems. It may not apply to your situation...

Rather than use one massive beam, depending on what "The Beam" is actually supporting above, it may be possible to use multiple, parallel, more modern, engineered (out of cheep stuff) structural beams.

They can be easier to work with, or more difficult. It really depends on whether or not you would "EVER" have to penetrate them for utility reasons and how good you are at working with steel.


Tom
« Last Edit: February 09, 2009, 12:48 AM by Tom Bellemare »

Offline Bill in seattle

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Re: wood beam vrs steel beam
« Reply #8 on: February 09, 2009, 01:15 AM »
Thanks Tom,
Being that it is out doors in our high humidity area and the wood beam guys do not offer anything pt'd or wet exposure rated  it is still pushing the span limits of wood products without going large.. I did look at several lvl's, truelams, psl's, ect but the quantity needed far outweighs steel and the cost is tenfold as well.
Parking cars under is not a good time to go with cheap stuff, I'd rather spend a little more now and do it once, but in this case steel is actually less expensive than wood and wood composites
Working with steel is no problem, do it all the time.
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Offline Bill in seattle

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Re: wood beam vrs steel beam
« Reply #9 on: February 09, 2009, 01:49 AM »
Sorry, Bill.  I just retried my link to the doityourself message and from that message to efunda and once again was taken to the table in which I could choose the steel beam cross section I wanted to use for my calculations!  Everything worked for me so I place a checkmark besides 3 different steel beam types, then ran the calculations using the largest of these which has a height of about 12 1/2 inches and weighs a little less than 100 lbs/ft.  I captured all of these using the Print Screen and Paint programs on my PC.  The calculated deflection was about 0.06 inches for a 27 ft span with a line load of 10psi-in.  Increasing this load to 30psi-in caused the deflection to triple to 0.19 inches at mid-span.  Unfortunately, if I try to go back, the efunda site then reverts to blocking me and only displays their sign-in screen.  From that experience, it appears that a completely fresh start at their site may allow a person in to do a few calculations.

Did you note that doubling the beam depth increases the strength by 4 times and decreases the deflection by 8 times.

If I was interested in learning more and getting more help on this type of problem, I would try joining the http://forum.doityourself.com/framing-sub-flooring/258810-steel-beam-calculator-anywhere.html forum and asking the people there for help.  Many of them know how to properly use these resources.

Dave R.

Dave
After a few tries and finding the actual calculator, using the spec's from the beam chart it would keep stopping  me and ask to join. I printed the formulas for the info and  the calc's and gave them to my physics and calculus genius son, and he laughed saying its going to cost me date nite movie money, but he'll take it class tomorrow and let the physics teacher and class have fun with it.

In the meantime I tried different wording on google like  w12x16 i beam load spans and it came up with a site  [url=HTTP://ebterhindustrial.com/?page_id=36  which had a chart which I can't seem to get it to show here but more just specifically what I was looking for. could not get much simpler than this???? I still will double check the info though this is a great starting place in addition to all the other stuff.  Wife would not think it to funny to find her minivan one morning a new subcompact.
The 100lbs per foot you looked at seems it could hold a truck on top of it as well. Don't think I need that heavy duty.

Might be a good site to bookmark if you ever wanted a quick reference. And free so far!


Bill

« Last Edit: February 09, 2009, 02:04 AM by Bill in seattle »
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Offline Dave Ronyak

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Re: wood beam vrs steel beam
« Reply #10 on: February 09, 2009, 01:05 PM »
Bill,

Are you certain of that webaddress?  No matter what routes I tried to go to it, the best I could do was locate your post on FOG!!  Every attempt to go the base website address failed also.

Edit:  found it!!  Here is the link to the table you mentioned.

From that table, it appears that a W12 x 19 steel beam or an EB-300 beam would work if you don't plan on a live load of 50 psf.  I don't recall you fully describing the load(s) to be supported by your beam.  Potential snow load is likely an important piece of information.  Twelve inches of wet snow would add a lot of weight to your flat roof.

Dave R.
« Last Edit: February 09, 2009, 01:17 PM by Dave Ronyak »
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Offline Bill in seattle

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Re: wood beam vrs steel beam
« Reply #11 on: February 09, 2009, 09:43 PM »
Bill,

Are you certain of that webaddress?  No matter what routes I tried to go to it, the best I could do was locate your post on FOG!!  Every attempt to go the base website address failed also.

Edit:  found it!!  Here is the link to the table you mentioned.

From that table, it appears that a W12 x 19 steel beam or an EB-300 beam would work if you don't plan on a live load of 50 psf.  I don't recall you fully describing the load(s) to be supported by your beam.  Potential snow load is likely an important piece of information.  Twelve inches of wet snow would add a lot of weight to your flat roof.

Dave R.


Yes,, that is the site I found. I just could not make it post here with a link however I tried, and the page only posted graphics and smileys. I just figured they did not want ordinary people to see this engineering data.
The roof is just a flat pitch maybe 1/2 ft per 12 pitch with nothing above it and we don't really get much snow at one time, though this year is a exception.
I think the w12x19 is more than adequate as i can put 6'' extra support on the beam ends and be reasonably safe at a minimum 50-75lbs load.
I've bookmarked that page as well, though when I put in other bigger beams it was not as friendly.

Bill

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Offline Bob10

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Re: wood beam vrs steel beam
« Reply #12 on: June 25, 2009, 03:16 AM »
If it were me I would consult a structural engineer and ask if you could bolt steel to the existing beam to increase the unsupported span.  That is what worked for me in a similiar situation.