I need to pour concrete pads (footings) in an existing basement upon which will sit a steel post. The posts will hold up a steel i-beam that will be used to take some bounce out of the floor above. There will be two posts holding up a 4″ i-beam spanning 23′. This beam will sit at the midway point of the perpendicular 2 x 8 floor joists which span 18′.
The concrete pads will be 18″ x 18″ x 12″ deep.
My question is how long after the pour until I can put load on the posts and thus the pads?
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Replies
28 days
Is there anything I can do to speed up the process without risking failure of these pads? I need to pour a new floor once the posts and beam is in place and would like to do that before winter sets in here in the midwest.
what you do is pour the pad dry, take some sample of the concrete. concrete normal meet strength in 28 days. But some do make strength earlier. some as early as 7 days. take sample, have a lab break them and when you make 2/3 of strength, it will be safe.
You can pour a higher strength concrete than specified, i.e. if 3000 psi is per the design, pour 5000 psi concrete this and have a testing lab take a few test cylinders, have them break one at 3 days and if at 75% of 3000 psi (original design strength), then you are good to go. (be sure and check with the structural engr. who designed the footing) have done that guite a few times with good results, just cost a little more but the time saved is worth it.
If I were doing this, I would wait about three days. The situation you describe does not sound extreme in any way.
I would wait 3 or 4 days also and use a bearing plate under the post to distribute the load a bit, maybe 4x4 or so
............Rik........
you could prolly start building on it the next day or two. You wouldnt want to throw a heavy load on right quick, but Ive poured footings in the am, peeled the forms in the pm and started laying block the next day.
4" x 23' is quite a span, I'd want at least one more post in the center if possible. Not many of us can wait 28 days. We're building within a few days. Never use wood blocking under support posts especially if they will be covered in concrete. This isn't a major carrying beam so I wouldn't worry too much. Sure must be a springy floor with 2x8 @ 18'!
Beat it to fit / Paint it to match
A four inch I beam? How are you measuring that? Hopefully you are referring to the width or flange. When I have referred to a single measurement of a beam it was depth. That would include the web and both flanges. Of course flange thickness and web thickness can vary. The concrete pad has rebar right? The 28 days refers to how long standard concrete takes to reach full strength. High early strength concrete reaches 5000 psi in 28 days but sets up in about 1/2 the time of 4000 psi concrete. Prep the pad hole right including no back fill, no compacting. Who specified the floor joists? Sounds light to me. Could be important if anyone plans on using the basement and needs the headroom. A 2X10 or 2X12 should have a deeper hole and longer lally columns. Don't forget a vapor barrier under the floor slab and poly-iso insulation makes all the difference under the floor and along the exterior of the foundation wall. Waterproof the exterior of the foundation wall first, then the insulation board and depending on the terrain a socked drain. Have you ever done any of this stuff? Try using Google for a Quickrete web site. FYI bagged Quickrete generally tests out stronger than some formula of sand/cement/aggregate you mix up on site in a mixer. Tyr
Is this truly a 4" "wide flange" beam? (to the other poster- yes indeed, they do make a 4" deep wide flange, 13#/ft being the only weight listed in Machinery's Handbook, as well as 4" "S" sections (regular I beams) at 9.5 and 7.7#/ft). I'm no structural engineer, but I agree that even though it's just a stiffener for the undersized joists above, even the 4" wide flange sounds pretty wimpy over a 23' span. It'll make a difference, but another mid-span pier under this beam would make the floor rock-solid.
Doubt your concrete is going anywhere- you're probably good to go in a lot less than 28 days for a non-critical application like this.
Since this is an existing basement and you are only trying to take some bounce out to reduce your vibrations, all you need to do is wait three days and place a steel plate under the column. You could even make it one day if you used warm water, mixed it dry and tamped it hard, then covered it with plastic or a foam scrap.
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From a testing lab point of view.
DO NOT USE QUIKCRETE. that stuff is iseless, its for fence post. Either buy the concrete from ready mix, or mix it yourself, sand, gravel, cement.
Thanks to everyone for their input.
Hammer- The floor is very springy right now. Built in 1922, it was an attached office over a below grade garage. We plan on converting it to kitchen over a home office.
Tyr- I was measuring the flange. I am just a homeowner/renovator, so my terminology and point of reference may not always be up to snuff. I will put rebar in the pad for sure. As for concrete, these will be poured as part of a larger project so the concrete will come from a mix plant.
Moltenmetal - I too thought a mid span post might be necessary. I would prefer to avoid that as it would interfere with the layout of the proposed office in this space. My thought was to start without the mid span post. If there was still to much bounce after the beam is in, I could always add another post at that mid span, before the concrete floor is in. I have an alternative floor plan that accommodates a mid span post by creating a four sided book case around it..
Brownbagg - It will be from a ready mix plant. They owe me on trade out for marketing work I performed for their company.
Thanks again everyone for your insights.
Why not pour the floor with integraed pads and do it all in one step?
Let's talk about terminology for just a minute.
I-beams are normally specified in something like W10x33. The 'W' means it is an I-beam. The 10 means the beam is approximately 10" tall, actually a little less, and that it weighs 33 pounds per foot. The width of the top and bottom flange is not specified as it is less important than the height of the web; that is what gives the beam it's rigidity, and the thickness of the steel which translates to weight per linear foot.
Span - if you have a 28' long I beam and it has a post in the center, then the span is not 28'. The beam is broken into 2 spans, each being 14' minus the width of the bearing surfaces. So, if the 28' beam has 4" of bearing at each end and in the center, then there are 2 spans of 13'6".
Not trying to be picky here, just trying to get us all on the same page. Matt
Just to clarify (or be pickier still), the "W" specifically means "wide flange I beam". An "S" is also an I-beam, but one with a slender top and bottom flange. Depending on the weight per foot, some W sections can look like some S sections. You need a table and a tape measure (or a scale and a tape measure) to be sure.
I admit to being a little confused by these "I" beam references. Although I realize "I" beam terminology has been ingrained in the public mind, as builders we should be more specific. "I" beams are not longer manufactured and have not been for decades. They have been replaced, due to improvements in mill technology, with W and S sections. W sections, viewed in cross-section, have a flange of constant thickness, while S sections (used as columns) taper (become thicker) toward the web. In a visual inspection, this difference is normally obvious.
You said: "DO NOT USE QUIKCRETE. that stuff is iseless, its for fence post"
I have always felt hand mix stuff was not nearly as strong, so I'm not disagreeing with you, just trying to learn something here. Why is it not as good? Is it because it rarely gets mixed fully, not enough cement content, what?Thanks,Matt
the last ten or twenty bags that I have use, after just added enough water to get wet, the mix is like sand and gravel, no cement. come back couple days later and it still sand and gravel. I have add to rip all of these out and replace. Its really bad. Its not a 4000, 3000 or even 1500 mix. there no cement in it.
there no cement in it. That's the special Alabama Gulf Coast mix. The manufacturer figgers that, since the family tree has no branches there, no one will notice the problem.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
I guess now youre going say, since we have so many hurricanes its easlier to sweep up the concrete instead of jack hammers.
It sounds like there may be no real need to LOAD the posts right away. Certainly you can set the posts in place the next day, if they aren't carrying any significant load.
If you need to load them soon, some sort of spreader plate is probably a good idea. If the footing is deep enough it doesn't need any real strength -- it's just there to make a bigger "footprint" for the post, and a pile of crushed rock would work just about as well.
Something is not right here. The beam load over the footing travels downward through the footing at a 45 degree angle. Looking in cross-section, assuming a 4x4 plate on top, you have 7" each side of the plate. Projecting a 45 angle down from the edge of the plate...whoa...you run out of footing before the projection line hits the ground. Either the footing is too deep (everything above the projection line is just filler), or the footing is too small in plan view.
Checking: Load on beam is 18'/2 x 50 psf (floor dead (15psf)and live load (35psf)estimated) = 450 # lin ft. If bm is 23' half TOTAL goes to each footing or Footing load = 23/2 x 450 =5175 #. Unless you know soil bearing capacity, assume conservative 1100 PSF. Footing area = 5175/1100= 4.7 sf or 2'2" x 2'-2". Using projection line, we have 11" each side of plate... use 11" or to keep it simple, form footing w 2x12 (11-1/4" deep) x 2'-4" sq. The extra 2" is added to account for the cover over the rebar, so the physical size is 2'-4" while the "structural size is 2'-2".
That 18 x 18 x 12 sounded like a guess?
I love having a resident engineer!
FWIW, I have a clear span w12x50 that is in the middle of a 22' wide floor. So I take 22/2 x 50 psf. Beam spans about 23'. It is supported on either end, no middle posts. One end on foundation, other end on steel column with footing. Engineer spec'd the footing at 3'9" square (was 3'6", then changed his mind). He's pretty conservative though, so I'm sure the footing size could be smaller. But no how would I toss that on an 18" square unless you were building on glacially compacted soil. And I'd also just go ahead and throw in that middle column. 4" x 23' -- will it even hold up it's own weight without deflection (over time)? Did you have an engineer size this beam -- did he give you deflection calculations?
MERC
No I did not have an engineer calculate the deflection.
Given that the structure has stood solid for nearly 82 years my intention was only to reduce bounce and to compensate for the added dead weight once the kitchen conversion is complete. I had assumed this was a pretty simple project that would not require outside expertise. Looks like maybe I was wrong.
I had hoped to keep the beam to a minimal height to maintain maximum ceiling height in the basement which will become an office. If I understand you correctly, you are suggesting that a 4" wide flange beam may not be structural significant enough over the long haul.
Sounds like I need to have an engineer look at this and possibly bump up the beam size. Were this to be necessary, I suppose I could box in the beam and use it as a design element, therefore maintaining the higher ceiling height. I am going to spend the rest of my life working in this office and I want it to feel as un-basement like as possible, hence the concern with ceiling heights.
Thanks for your thoughts. I will find myself an engineer before proceeding any further.
An alternative, if it works with your floor plan, is to decrease the space between the posts and cantilever the ends of the beam a bit. That way you can increase strength/reduce bounce and stay with 2 posts. I'm not an engineer so wouldn't begin to suggest appropriate spacing, but worth looking into.
If you don't like the height problem, look at building a flush or inset beam. My w12x50 is inset and carries 2x10 joists and so only protrudes down about 3.5" (with 3/4" top plate attached to it). It's gonna be a lot more work and the weight of the beam will start being an issue too (my w12x50 is at least 1200 lbs, packed out with wood in the web).
I really doubt that 4" beam is going to do much to stiffen the floor. I could be totally wrong, but spanning 23' I would think it would have a hard time maintaining reasonable deflection for it's own weight let alone a flooring system. I'd like to see an engineer help you at least with deflection calculations so that you don't totally waste money. If the 4" can't even hold itself up, why go through all the work?
I've rarely found the correct thing to be easy or cheap.
Some other approaches you could look at
1. sister on 2x12 SYP (same height reduction as 4" beam). Maybe one on each side. This would be difficult if mechanicals need to be preserved.
2. Sister on full length steel plates to the side or even both sides of the 2x8, through bolted. Problem again with mechanicals.
3. Use double/triple/quadruple 2x12 LVL and set them as an inset beam. Same height reduction and you can lift one in at a time and then bolt them together in place.
Also keep in mind that (if I recall correctly), beam deflection goes up with the fourth power of span, so anything you can do to reduce span helps tremendously. As another poster suggested, if you can pull in the end supports and reduce the span to say 18' or so, I think the LVLs would be the way to go.
MERC.
I tend to think that increasing the size of the beam based on an engineers recommendations is my best option. It would be much easier than sistering all the joists given the existing mechanicals in this old house.
Boxing in the beam and creating a similar false boxed beam that runs perpendicular might solve some design issues. I want an open floor plan yet I also want to loosely define a sense of seperate spaces (i.e. entry, workspace, library) within the open space. Increasing the beam size, raising the ceiling above the beam and tastefully boxing in the beams with some choice wood might solve structural and design problems together.
Thanks again for the input.
You can have the batch plant send a load of high early strength concrete for the column pads, if you are concerned aboiut putting too much load on green concrete.
The proposed third column in the middle of the span doesn't have to be exactly in the middle. Especially since this new beam is just for stiffening purposes. The closer to the middle the better, but you could put it off center to fall into an already planned wall.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
"I love having a resident engineer"
That would be nice, but David is not an engineer
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Hmmm... must be confused then. I remeber a guy posting a week or so ago who taught many engineering courses at a college and was interested in helping us out. Thought his name was David, but must be wrong.
MERC.
Same guy, but in that thread, he claimed that he was not an engineeer, leaving us all confused. He never did finish what he started in that thread.
Not that his advice here isn't sound, but he still leaves much confusion when he claims to have taught and practiced engineering while offering to help us learn engineering and then says that he is not an engineer.
Like the John Kerry of the engineers society, LOL
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Hmmm...interesting again. I didn't follow that thread all the way so I didn't realize something fishy was going on.
Like when I did my house in MA I hired a guy to draw some plans, led me to believe he was an architect, but he wasn't. Found out when some structural work came into play and he was, well, useless.
If you are familiar with Seinfeld, I call him Art Van de Lay.
Maybe we should call David "Art Van de Lay" too. Life sure is humorous.
MERC
Piffin-
Yes, David is NOT a PE. As I recall, we all have the option to include, or exclude, bio info in this forum. Imagine the BS in this forum if we all posted our resume's. I chose not to as I think most everyone else has. I guess that means buyer beware... of all of us!
I also do owe everyone the completion of that engineering primer stuff... just with the consultation fees being charged thought it a good idea to earn some income. As soon as project is finished, will get back.
Love ya all!
"That 18 x 18 x 12 sounded like a guess?"
Actually, it was the recommendation of a home builder/friend. But if I understand your calculations correctly, you are suggesting a 26" x 26" by 12 inch deep pad? I see no reason not to increase the size based on your post.
Thanks.