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actually the 1st HUD/FHA approved foundation in the state of texas was placed in 1955. (by my grand fathers company in the DFW area) there was also an engineer here in the houston area (he passed about 5-6 yrs ago i believe and i forget his name) who also designed and placed an fha/hud home in the same rough time period.
concrete CAN NOT "bond" to the rebar, it is chemically not possible. concrete can FORM TO the shape of the rebar but it will never bond to any material without an admix of some sort. this statement is similar to one i hear regularly that is false, "the PT compresses the concrete". as an engineer you would know that concrete is not compressible but is the 2nd weakest tensile material in the world next to raw plastic. concrete would break before being "compressed". PT anchors will not rust even at a remotely close pace as rebar for 3 reasons, the oily coating they have, the material they are made of, and the thickness of the material generally. (now this is obviously not the case in say a #11 rebar or even as large as a #8 rebar.) pt strand will not rust out even half as fast as rebar for 2 reasons, 1 the material it is made from (generally a tempered/hardened steel) 2nd due to the "grease" and plastic it is coated with which where originally used for the sole purpose of lubrication for the tensioning process. with todays standards of capping the "live end" of the cable it is even less likely the pt strand will rust.
just to give some background on me, i worked for my fathers company, houston post tension for about 10 yrs, i also worked for suncoast post tension for a little over a year, and i worked for my grandfathers company as a teen during the summers in the dfw area (post tension systems inc or PSI). i have about 15 yrs in the business with the majority being in the turnkey foundation business along with PT sales/service. i have installed cable, stressed cable, repaired cable, and sold cable. the man who started suncoast (now the largest pt/material supplier in the world) actually worked for my grandfather who was a partner in a company called VSL and was at one point the largest in the world. i have taken numerous courses and seminars on these very subjects. i am in no way an "expert" but i do know a little bit. lol.
all this said, we can definitely agree to disagree.
I am in the beginning stages of building a metal building. The foundation will measure 52' x 90' and will be built in NE Houston were the soil is soft. The endwall span is 90', and 52' is sidewall length. I like the insurance that a PT slab offers, plus the money saving would be very helpful. This building is used, so I don't have the support from the manufacturer to give advice on the slab. I am wondering on how wide to make the footer, and how deep should the footer go. Would this footer be the same width and depth even on non-supporting sides. Also would it be neccessary to make any footers in the middle of the slab. Thanks for your advice.
I am in the beginning stages of building a metal building. The foundation will measure 52' x 90' and will be built in NE Houston were the soil is soft. The endwall span is 90', and 52' is sidewall length. I like the insurance that a PT slab offers, plus the money saving would be very helpful. This building is used, so I don't have the support from the manufacturer to give advice on the slab. I am wondering on how wide to make the footer, and how deep should the footer go. Would this footer be the same width and depth even on non-supporting sides. Also would it be neccessary to make any footers in the middle of the slab. Thanks for your advice.
what the heck.. hire a professional engineer to design your foundation.. you cant just pull numbers up in the air.. we design foundation based on loads you know.. and not just based on experience and gut feel..
what the heck.. hire a professional engineer to design your foundation.. you cant just pull numbers up in the air.. we design foundation based on loads you know.. and not just based on experience and gut feel..
I know that is the logical choice to hire an Eng, but I can't afford it. I am a teacher, not a corporation, so my funds to complete this building are very very limited. I'm doing most everything myself that I possibly can. Can you give the formula to use, and weights for calculations for the metal structure and metal siding and roof. I think it wouldn't take much to figure it out. The roof pitch on this building is 4-12. Thanks to anyone willing to help.
actually i have done foundations for many metal buildings, and not a single one has had an engineered drawing. they all have just a basic "sketch" from the manufacturer. i just got back from the world of concrete where i took a few engineering seminars and slab on ground seminars and while the majority of it was high rise type stuff there was some metal building type material as well. there was not a single metal building (or warehouse) that had beams (or footers if you will) in the foundation at all. they where generally all 5-6" thick flat slabs.
generally the exterior beams are 12 wide by about 26" deep but if the soil is a little sandy or loose i would suggest 18x30. i would also put some rebar (2 #5 bars) in the bottom and leave all the PT on the top. as for interior or not support walls, if they are not there to support anything then minimal under-structure is all you would need.
I know that is the logical choice to hire an Eng, but I can't afford it. I am a teacher, not a corporation, so my funds to complete this building are very very limited. I'm doing most everything myself that I possibly can. Can you give the formula to use, and weights for calculations for the metal structure and metal siding and roof. I think it wouldn't take much to figure it out. The roof pitch on this building is 4-12. Thanks to anyone willing to help.
no way you could design your foundation using "engineer" way.. it's much more complicated than you think..
assuming the loads from the metal building will come from the manufacturer.. you would have to design your beams and slabs based on maximum +/- moment for rebar.. not to mention your foundation against soil bearing capacity.. you have to check one-way shear, punching shear, etc..
if you dont have loads coming from manufacturer then the more you wont be able to design it..
you can design this though if everything is assumed minimum the "gut feel" based on experience way"
5 inch slab you can use #3 @ 12" each way
for 12x26 beam you can use 3 - #4 top and bottom..
Last edited by structuralengineer1; 02-08-2010 at 02:48 PM..
no way you could design your foundation using "engineer" way.. it's much more complicated than you think..
assuming the loads from the metal building will come from the manufacturer.. you would have to design your beams and slabs based on maximum +/- moment for rebar.. not to mention your foundation against soil bearing capacity.. you have to check one-way shear, punching shear, etc..
if you dont have loads coming from manufacturer then the more you wont be able to design it..
you can design this though if everything is assumed minimum the "gut feel" based on experience way"
5 inch slab you can use #3 @ 12" each way
for 12x26 beam you can use 3 - #4 top and bottom..
as i said, the manufacturers do not provide loads, they do not even suggest to get a slab design, they will only give a suggestion as to what they think you should build. they generally only give an anchor bolt layout for the foundation as well.
i do not agree with the #4, the #3's mentioned are typical (a little more then the norm in texas, otherwise known as "texas 3's") i do not think with 3 #4's you have enough bar and suggest a minimum of 2 #5 T&B. the last one i did was a horse barn and all that was done was a 16x26 beam around the perimiter (nothing inside as the building was full span) with a 5' deep 24" straight shaft pier under every column and building corner. we then placed a 4" "T" of concrete inside for the owner to drive in and out, a wash room and tack room.
interesting thing i learned at one of the seminars i took last week, up north on high rise/parking garage most engineers suggest an over lap/splice of only 17-24 x the bar diameter while in houston (residential) engineers generally suggest minimum of 30x, and most say 36x bar diameter.
my brother in law built a metal building with an apartment inside and all he had was a 12x30 beam around the outside and a 4" pad for the floor. that was 12 yrs ago and not a crack yet. building a metal building is not like designing a 3-4 story town home, a 2 story brick home, or a 20 story high rise, it is a light, efficient "shell" nothing more.
lap splice depend on many things.. concrete strength is it 3000 psi or 5000 psi or whatever.. it also depends on rebard diameter... you didnt even mention whether they are talking about tension splice or compression splice..
get a hold of ACI book it's all there.. it's the bible of concrete for engineers..
i own an ACI book, i also own PTI books. i have seen them change a lot of the last 15 or so years of being in the concrete business.
apparently you dont understand,
Quote:
interesting thing i learned at one of the seminars i took last week, up north on high rise/parking garage most engineers suggest an over lap/splice of only 17-24 x the bar diameter while in houston (residential) engineers generally suggest minimum of 30x, and most say 36x bar diameter.
the diameter of the bar is a moot point. i did not mention a diameter size because the length of the over lap is based on a multiple of the diameter BUT it is the same multiple regardless of bar diameter. in other words the over lap for a # 4 vs a # 5 are different BUT they are both multiplied by the same number. now the engineers at the seminar suggested 17 times the bar diameter vs the norm here in houston of 30-36 times the bar diameter.
aci 360 and 302 both suggest a compressive strength of 3500 psi, which was just recently changed from a suggested 4000 psi minimum. keep in mind that ACI specs and codes are NOT based on residential construction they are almost 100% based solely on commercial concrete. when speaking of slab on ground it is 95% based on flat floors used for ware house or commercial construction of some sort including super flats.
now on to overlaps. we are not talking actually splicing rebar but over lapping it (you know when your 20, 40, or 60 ft bar is not long enough to make the span needed, you have to over lap the bars to help strengthen the "weak spot" created by none continuous bars.
just curious how exactly is a foundation for a metal building going to suffer punching shear?
bottom line, the only reason i am mentioning this stuff is because you are really trying to go over board on something so simple (hey your an engineer right????). consider this, the question was based on a metal building which he is NOT purchasing from the manufacturer, so where exactly would he get the loads from in the 1st place? how do we know the manufacturer is even in business still? i say instead of giving him a bunch of BS, let him build it his way, if it fails its on him, but 99% he builds his slab, puts the building on it, and never has a problem even without an engineered drawing.
i am not going to argue with you anymore.. this is my last response
i never it will fail in punching shear.. but engineers will check it against it.. how will it fail? you have columns, you have axial, you have pedestal then you have punching shear.. if he didnt put external beams but only 5 inch slab, then you should check for punching shear.. oh i forgot your "gut feel" tells you otherwise.. just like your "gut feel" told you 2 - #5 is greater than 3 - #4..
how great would it be if all buildings and bridges are designed based on "gut feel"
if you will read my very 1st response is for him not to design his slab the "engineer" way coz he cant.. he should hire a professional engineer to do this.. or go with "gut feel" way.. we have a term for that (no racism) we call it hill billy engineer.... get a steel stuck it in the ground there you go pipe support..
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