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  1. #251
    Super Member mjncad's Avatar
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    Default Re: New Home Begins

    Quote Originally Posted by sdkubota View Post
    Then you have never worked with a real one.
    Without this becoming a royal pissing contest; let me just say that for 16 of the 24 years I was in the engineering business was working for a heavy industrial engineering company. The structural engineers I had the pleasure of working with designed structures for power plants, refinieries, modular oil processing failities for the north slope of Alaska, mining facilities, military facilities, chip plants, an occasional highrise office building and the like. I'd say they were REAL engineers who knew how to make sure structures didn't fall down.

    That company was Stearns-Roger, and through numerous buyouts, mergers, etc became known as Stearns-Catalytic, United Engineers & Constructors, and Raytheon Engineers & Constructors when I left the company after I was fed up with dodging the layoff bullet for 14 out of 16 years there. After Raytheon sold off RE & C, I understand the remnants hooked up with M-K (Morrison-Knudsen) and are now known as The Washington Group, assuming management hasn't run the company into the ground.
    Paraphrasing Douglas Adams - So long and thanks for all the bacon.

  2. #252
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    Default Re: New Home Begins

    I should have used different wording but the principles I have posted regarding concrete and reinforcing steel are elementary engineering topics. Any engineer would agree 100% with what I have posted. Sometimes I get frustrated for actually trying to explain and describe engineering science in an effort to educate people over "this is how we do it here" attitude. I run into this routinely with concrete contractors telling me they have done it that way for 30 years and truth is they have been doing it wrong for 30 years. There is a tremendous amount of knowledge that can be learned from contractors and I am a good listener and always consider their point of view. However that said, I am an engineer and base my opinions on proven science developed over decades by research institutions. Every project I develop and oversee I am responsible for. If the concrete doesn't perform as intended I am the individual they come to court over seeking a large settlement. Because of this I am only allowed to deal in facts and science as established by the industry. Many building codes were developed "because that is how it has always been done". Doesn't make them right but they need to be followed until someone challenges them or when the codes are updated. The statement I made regarding "they aren't real engineers" is probably from my personal frustrations as anybody and everybody loses the term "engineer" without the proper credentials and professional registrations. Something that takes 8 years to obtain then listen to janitors being called xxx engineers is disheartening. Sorry for the rant and I will keep my "educating" to myself.

    Merry Christmas!

  3. #253
    Super Star Member EddieWalker's Avatar
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    Default Re: New Home Begins

    Quote Originally Posted by sdkubota View Post
    I should have used different wording but the principles I have posted regarding concrete and reinforcing steel are elementary engineering topics. Any engineer would agree 100% with what I have posted. Sometimes I get frustrated for actually trying to explain and describe engineering science in an effort to educate people over "this is how we do it here" attitude. I run into this routinely with concrete contractors telling me they have done it that way for 30 years and truth is they have been doing it wrong for 30 years. There is a tremendous amount of knowledge that can be learned from contractors and I am a good listener and always consider their point of view. However that said, I am an engineer and base my opinions on proven science developed over decades by research institutions. Every project I develop and oversee I am responsible for. If the concrete doesn't perform as intended I am the individual they come to court over seeking a large settlement. Because of this I am only allowed to deal in facts and science as established by the industry. Many building codes were developed "because that is how it has always been done". Doesn't make them right but they need to be followed until someone challenges them or when the codes are updated. The statement I made regarding "they aren't real engineers" is probably from my personal frustrations as anybody and everybody loses the term "engineer" without the proper credentials and professional registrations. Something that takes 8 years to obtain then listen to janitors being called xxx engineers is disheartening. Sorry for the rant and I will keep my "educating" to myself.

    Merry Christmas!
    Thank you for taking the time to share your knowledge with us. I might be one of those guys who has been doing it wrong. I do a fair number of pads using 2x4s as forms, that gives me a 3 1/2 inch thick pad. I've worked in CA and TX. I've been a helper and I've tied rebar on dozens of houses in CA that where inspected to meet code and the rebar was all set on plastic chairs to keept he rebar in the middle fo the concrete. This was always stressed to me as the only way to do this by everyone I've ever been involved with.

    Wire was never allowed on a house.

    Fiber was never a substitute for rebar.

    On the flat, rebar is to hold the concrete together when it cracks. so the crack doesn't get bigger and move up and down. It is not to make concrete stronger. 3,000 psi is plenty for any residential floor, so the goal is not to increase the psi, but to minimalize cracking so the floor remains flat and level over the decades.

    Where am I wrong?

    You suggested useing fiber instead of wire or rebar. I don't believe that fiber is a substiute for either, and I don't believe that it increases the psi of concrete. A dry mix is important, but it wont increase psi. A wet mix will lower psi, so you want it dry so that the mix cures to it's maximum strength. Not to increase anything.

    As a remodeler, I repair houses and modify them on a regular basis. In every case that I cut out concrete with wire, I find the wire either under the concrete, or at the very bottom of it. I have never found wire in the middle of the concrete!!!!! Has anybody?

    If what you are saying is true about requireing 3 inches of concrete above the rebar, then would it be true with wire as well? In my experenice, the big cracks in concrete always happen when their isn't any rebar or the wire is at the bottom of the pad.

    Are we comparing apples to apples? Are you talking about adding strength or decreasing cracking for a residential floor?

    My comments and advice is to help to achieve the best, longest lasting floor possible. If I'm wrong, then I will admit it, apologize, and bow out.

    Eddie

  4. #254
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    Default Re: New Home Begins

    You are correct in that concrete would keeps cracks from getting larger as well as keeping proper alignment after a slab cracks. However it is my opinion that is an extremely expensive method of crack control and wouldn't prevent random cracking. All concrete is going to crack. The best solution is to get it to crack in straight lines which can be easily maintained. Sawing 1/3 depth within 24 hours of placement can achieve this. The width of the slab sections sawed are a function of depth which I believe for a 4" concrete depth is 8 ft maximum. The sawed joints need to create individual panels shorter then 8 ft and each panel should be close to being square when possible. Even when doing that won't guarantee 100% success but will come close. You can look at any concrete slab and see the cracking randomness and what distance between cracking is prevalent. Water has everything to do with strength as mix design is based on a dry cement weight to water weight ration. The aggregate is nothing more then filler and makes up the matrix of the concrete mix although the strength of the aggregate plays a role in the maximum compressive strength available with any given mix. A 3" to 4" slump is generally considered maximum allowable although you can find many concrete crews that would never consider working with this stiff of a mix. Adding plasticizers can greatly reduce the slump, improve workability, without jeopardizing the strength. They are added at the plant but a fair warning is when the effects of the plasticizer wears off it really wears off. In my profession steel is used to add strength to concrete making a structural element. I would also agree with your statement mesh always gets trampled down and does little good.

  5. #255
    Super Star Member EddieWalker's Avatar
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    Default Re: New Home Begins

    Quote Originally Posted by sdkubota View Post
    4" of concrete is not thick enough for rebar to do any good. As far as wire or rebar, both provide additional strength only after a crack has formed. Personally, I would add poly-fiber mesh in the concrete mix. Everyone is entitled to their own beliefs but I would much rather have 4" concrete, un-reinforced, with sawed joints every 8' both directions then adding wire or rebar. All concrete will crack and if you give it a straight line to crack in, little future damage will occur. If you do not provide a weakened path (sawing) you will get random cracking and the possibility for future problems. Attack away (not you Eddie)!
    I'm back to this statement that you made in post #234.

    It is my believe that rebar is needed to hold the concrete together tight when it cracks. Placement needs to be in the middle to achieve this. I question your placement of rebar or wire at the bottom of the pad to hold the pad together when it cracks. The only way that I know to keep the crack tight and level is for rebar to be in the middle.

    I do not believe that fiber can do this. My thought is that fiber will add something to the pour, but it's not strong enough to withstand the movement of concrete once it cracks. Fiber will not stop cracking.

    Cutting expansion joints is only done on exterior concrete because when it heats up, it expands, and when it cools, it contracts. This is a major cause of cracking on a pad poured over compacted soil. A pad inside a house doesn't have these temperature swings and doesn't crack like concrete does that's outside. This is also why you always pour your porches and outdoor features seperate from your house pad.

    Cutting the concrete weekens it where it is cut and causes it to crack at that location. How do you keep it from moving once it's cracked in a straight line without rebar in it? I have never cut interior concrete and don't believe it's a good idea. I believe that a random crack is going to be better able to remain tight and level with rebar in it then a straight cut with rebar and definately a straight cut without rebar.

    Did you build your house? How did you do yours?

    Eddie

  6. #256
    Super Member mjncad's Avatar
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    Default Re: New Home Begins

    For light weight slabs (e.g. 4" - 6" thick), placing rebar in the middle has always been the preferred design of all the structural engineers I've worked with. Once concrete gets thicker for footings and other structural elements, than I've I've seen rebar placed towards the bottom of the slab, or multiple layers of rebar have been specified depending on thickness and application. Regardless of concrete thickness and application, the preferred minimum cover of concrete over rebar has always been 3" where possible.

    SDKubota: Please keep educating us readers; but please don't take the college professor attitude that what you say is gospel and shouldn't be questioned. I'm sure it's frustrating when people disagree with you, as I know I get frustrated when people disagree with my CAD expertise; but I would rather see people have a discussion about the pros and cons of a subject and not just blindly follow an expert's advice.

    I also agree with your frustration with the term "sanitation engineer" for a garbage collector, etc. My pet peeve is "CAD Operator" when the person doing the key slapping has achieved the knowledge and skill to be a designer in one or more disciplines in addition to being an expert in the use of the design software itself.
    Paraphrasing Douglas Adams - So long and thanks for all the bacon.

  7. #257
    Platinum Member ENG18LT's Avatar
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    Default Re: New Home Begins

    Wow. Now that we have that out of the way.....


    Kappler,

    Happy holidays! How did you make out with the floor pour?


    Lee

    Long road home

    Mahindra 5530 w/ FEL, Bushhog 286 cutter, 8' disc, 2 bottom plow, pallet forks, 22' American trailer, geotextile carrier, PHD w/ 12" auger, tooth bar, landscape rake, trailer hitch, broadcast spreader, toolbar, cultipacker, grain drill, and more to come!

  8. #258
    Elite Member J F's Avatar
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    Default Re: New Home Begins

    Meanwhile, back at the ranch....
    ____
    Jay

  9. #259
    Platinum Member tkappeler's Avatar
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    Default Re: New Home Begins

    Quote Originally Posted by ENG18LT View Post
    Wow. Now that we have that out of the way.....


    Kappler,

    Happy holidays! How did you make out with the floor pour?
    Whew. I thought I was going to have to put my referee jersey on.

    Well, the weather and holidays and other things have played havoc. I had to rent a 2" pump 3 times to get rid of rainwater, including trying to get one set up while I was on a well needed break in the Florida keys.

    Then the inspection was delayed due to township closings and vacations. We are finally back on track. Inspections are complete, permanent columns are in and temperatures look promising for a pour on Monday. Subfloor framing will commence on Tuesday.

    Once the subfloor and concrete are in, I can finally backfill and cut down on some of the water that makes it inside.

    It was truly painful seeing the delays and added costs.

    BTW: Happy new year everyone.
    Tom

    "Opportunity is missed by most people because it is dressed in overalls and looks like work" - Thomas A. Edison

  10. #260
    Super Member mjncad's Avatar
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    Default Re: New Home Begins

    Quote Originally Posted by tkappeler View Post
    Whew. I thought I was going to have to put my referee jersey on.

    BTW: Happy new year everyone.


    Happy New Year to you as well, and you are making remarkable progress as far as I'm concerned.
    Paraphrasing Douglas Adams - So long and thanks for all the bacon.

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