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Old 06-11-2012, 02:10 PM   #1
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Steel Replacement Girder


Hello all, after reading the threads here and elsewhere I have been able to obtain really helpful information. My question is more of a request for someone to check my calculations. If you are an engineer, or have experience calculating beam sizes please let me know what you think. I understand the well- intentioned "hire a structural engineer comments", but please do not add these to the thread, I have already spoken with an engineer, and my plan is based on his advice.

The beam being replaced is made up of 3 old 2x10 (real 2x10's, oak, from 100 years ago), making up a basement girder which holds up three floors. It is 21 ft long from wall to wall of the foundation, and appears to have been reinforced with relatively new vertical 4x6 post and a telescoping post, but is sagging and has been destabilized by termites.

My question, will a 4 inch wide W12x16, supported at 7 ft intervals provide an adequate replacement? According to my calculations this is stronger than the present beam, but I would like someone else to check my calculations since statics was not my best class.

Thank you.
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D.

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Old 06-11-2012, 02:13 PM   #2
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Originally Posted by DsMoneypit View Post

According to my calculations this is stronger than the present beam, but I would like someone else to check my calculations
Post your calcs, then, so we can check them.

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Old 06-11-2012, 07:10 PM   #3
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Originally Posted by DsMoneypit View Post
I have already spoken with an engineer, and my plan is based on his advice.
what did your engineer say?????????
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Old 06-11-2012, 07:13 PM   #4
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Steel Replacement Girder


Quote:
Originally Posted by DsMoneypit
Hello all, after reading the threads here and elsewhere I have been able to obtain really helpful information. My question is more of a request for someone to check my calculations. If you are an engineer, or have experience calculating beam sizes please let me know what you think. I understand the well- intentioned "hire a structural engineer comments", but please do not add these to the thread, I have already spoken with an engineer, and my plan is based on his advice.

The beam being replaced is made up of 3 old 2x10 (real 2x10's, oak, from 100 years ago), making up a basement girder which holds up three floors. It is 21 ft long from wall to wall of the foundation, and appears to have been reinforced with relatively new vertical 4x6 post and a telescoping post, but is sagging and has been destabilized by termites.

My question, will a 4 inch wide W12x16, supported at 7 ft intervals provide an adequate replacement? According to my calculations this is stronger than the present beam, but I would like someone else to check my calculations since statics was not my best class.

Thank you.
Regards,
D.
You spoke to an engineer. What's the problem? How come he's not answering your question?
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Old 06-11-2012, 08:59 PM   #5
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Steel Replacement Girder


maybe the engineer was not paid and only gave partial free advice
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Old 06-11-2012, 09:32 PM   #6
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Steel Replacement Girder


Quote:
Originally Posted by Joe Carola

You spoke to an engineer. What's the problem? How come he's not answering your question?
Quote:
Originally Posted by hand drive
maybe the engineer was not paid and only gave partial free advice
Joe and Hand: unhelpful. If you can't contribute useful information please don't reply.


Tony, my back of the envelope calc went something like this

Present wood beam
I= bh^3/12=500
s=bh^2/6=100

W12x16 steel I beam I=103, s=17.1 from:
http://www.toolbase.org/PDF/DesignGu...SpanTables.pdf

Steel approx 30x stronger than wood in bending and tensile strength (36k psi vs 1-8k psi)

Hence my ibeam choice, I>= 500/30 and s >=100/30. However, the above link places the max span at 4.1 ft for Mc in the charts (largest moment), so I'm thinking my material property approximation is incorrect enough to make my beam choice too weak, or at least perhaps at my 7ft support length, since it has 3 floors above it.
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Old 06-11-2012, 11:02 PM   #7
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Steel Replacement Girder


You probably won't think my post is useful either, but why in the would you talk to an engineer and THEN go to a DIY site? You have already done the calculations, checked with a professional, right? Are you looking for a pat on the back or what?
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Old 06-11-2012, 11:24 PM   #8
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Quote:
Originally Posted by DsMoneypit View Post
Joe and Hand: unhelpful. If you can't contribute useful information please don't reply.


Tony, my back of the envelope calc went something like this

Present wood beam
I= bh^3/12=500
s=bh^2/6=100

W12x16 steel I beam I=103, s=17.1 from:
http://www.toolbase.org/PDF/DesignGu...SpanTables.pdf

Steel approx 30x stronger than wood in bending and tensile strength (36k psi vs 1-8k psi)

Hence my ibeam choice, I>= 500/30 and s >=100/30. However, the above link places the max span at 4.1 ft for Mc in the charts (largest moment), so I'm thinking my material property approximation is incorrect enough to make my beam choice too weak, or at least perhaps at my 7ft support length, since it has 3 floors above it.
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You are miss using the tables. Lc is the maximum length of an unsupported beam (i.e. cantilever). Using the worst case scenario table, a W12x16 beam supportted every 7 feet can support joist spanning a total of 48 feet. These tables assume that the beam is not supporting any roof load, which is not necessarily valid for a 100 year old house.

Following the tradition of this group, you have shown sufficient lack of knowledge that I would recommend you hire a professional. In this case the savings in the cost of the beam will more than pay for the cost of an SE.
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Old 06-11-2012, 11:43 PM   #9
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Quote:
Originally Posted by Missouri Bound
You probably won't think my post is useful either, but why in the would you talk to an engineer and THEN go to a DIY site? You have already done the calculations, checked with a professional, right? Are you looking for a pat on the back or what?
Perhaps you are assuming by "speaking" that my combination of ibeam and column support distances have been verified, which is not the case. We spoke about my plan generally but the approximation aspect was my idea. I'm not sure i understand the animosity toward a guy who simply wants a second opinion on a very important structural decision. As my first post states, I only requested someone else examine my analysis. I'm not looking to create friction here, if someone has the knowledge and time, please let me know what you think. Thank you.
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Old 06-12-2012, 07:25 AM   #10
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DsMoneypit,
I doubt anyone here is deliberately trying to be unhelpful. Your figures seem OK as far as they go. However, there is far more to this than simply computing 'I' and 's' and checking in charts/tables.
To give one example; steel beams can carry a considerable load, but they are slender can fail by buckling long before they reach maximum load capacity. Could you prove that the load your beam will carry will not exceed
its buckling capacity, or altrnatively could you show that the top flange will be sufficently restrained so as to achieve its maximum capacity?
There are other considerations, such as bearings, and post supports and foundations.
As it is a structural alteration, presumably your local authority will want to see calcs. They will not accept that just because the loads are the same, and steel is 'stronger' than timber, that it will be OK.
Your idea may well work, but it is a case of proving it. I know this is a DIY site, but some aspects are beyond DIY competence, and in these cases the best advice is to get a proper appraisal and supporting figures.
Gopd luck.
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Old 06-12-2012, 08:31 AM   #11
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Quote:
Originally Posted by tony.g
DsMoneypit,
I doubt anyone here is deliberately trying to be unhelpful. Your figures seem OK as far as they go. However, there is far more to this than simply computing 'I' and 's' and checking in charts/tables.
To give one example; steel beams can carry a considerable load, but they are slender can fail by buckling long before they reach maximum load capacity. Could you prove that the load your beam will carry will not exceed
its buckling capacity, or altrnatively could you show that the top flange will be sufficently restrained so as to achieve its maximum capacity?
There are other considerations, such as bearings, and post supports and foundations.
As it is a structural alteration, presumably your local authority will want to see calcs. They will not accept that just because the loads are the same, and steel is 'stronger' than timber, that it will be OK.
Your idea may well work, but it is a case of proving it. I know this is a DIY site, but some aspects are beyond DIY competence, and in these cases the best advice is to get a proper appraisal and supporting figures.
Gopd luck.
Thanks Tony. I have thought about the post supports and footers, but I understand your point regarding the difficulty. I will look into the restraining suggestion.
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Old 06-12-2012, 11:47 AM   #12
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Steel Replacement Girder


I agree with others here. I AM a trained professional, working side-by-side with structural engineers daily, and myself have taken several structural engineering courses as part of my degree requirements, and I wouldn't even try to DIY the design. Maybe installation, but not the design of the steel.

Based on the information contained in this post, a Structural Engineer should really be hired to run all the calculations. There are intricacies of replacing structural steel in a building that you may not even be aware.

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