Estimating Quantities Of Concrete

Exactly just how grateful would you be, kissy-face?!

You need to know calculus. find the area of all the non-geometrical shapes then multiply by depth. It's that easy.

Are they really suggesting that you create a house with unreinforced concrete walls? Are they homicidal? Better check this out.

lol cheeky, great full l from the bottom of my kind heart.

I'm a bit puzzled, where do I find the depth on these drawings?. I only see the length, width and height of the house. When i spoke to the lecturer, he said make assumptions where necessary. What do you mean find the area of the non-geometrical shapes lol, i feel like i'm lost in translation here. I'm a 1st year student, so please take it easy on me, my small brain can only take so much arghhhhh.

I need to first identify the concrete elements of the house from the drawings and indicate them on the drawing. What will they be? I can see walls duh, obviously there are footings, slabs and umm concrete beams?

by the way vermin.thankyou for the reply, I am very appreciative

HI Tiffany,

I also have a son in College in the U.S. studying Civil Engineering, so we have a little common ground.

I forgot in my earlier email, to make sure and use a safety factor regarding bearing capacity on the soil, for me it would be x2, i am not sure what a professor expects from you, just willing to help if possible.

Rick

Tiffany,

This is actually a much simpler process than you might think. It is an estimate. Keep in mind that most estimators for residential have no higher math or college education. Keep it simple. Estimate the large components in simple geometries. I am a Civil Engineer in the US, so we do these things in Standard units, and in California we tend not to build houses completely of concrete (usually just floors and footings). However, I work municipal public works projects, and we do those in mostly concrete and masonry. I think the biggest thing is to note all assumptions on your estimate. Have a column in a spreadsheet that itemize the components, e.g. Walls, floor slabs, footings, columns, walkways. Then a line for cost per unit, e.g. $ per cubic meter. Finally, a collumn for cost. at bottom sum the cost into a subtotal. Typically add a contingency line below the subtotal for something like 10% (this is highly subjective).

Then total. you could also do other columns to aid your estimating for square footage and depths for walls, or linear footage, depth and width for footings. Concrete weight typical 150 pcf (convert to kg per cubic meter).

Hey rick, this post is very helpful,

thanks

That's cool rick. Only thing me and my dad have in common is football (soccer) lol.

HI Tiffany Ann,

Before you can come up with a concrete quantity on this problem, you need to know the bearing capacity of the soil.

If you have no bearing capacity, assume about the worst, 500# per square foot. Take a good running guess at what the weight on the soil will be with concrete included. You also need reinforcement, for a typical foundation on a house, you can assume #5 bar longitudinal on 8" centers with #4 stirrups on 6" centers and be plenty safe in a box beam configuration. The configuration of the box beam will depend on the capacity of the soils you are on. To be on the safe side, specify compressed strength of the concrete, my suggestion is 4000#. One of your pictures shows a pretty good indication of foundation requirements Ie bearing walls. Since im american, i do not speak metric well. Also my designation is a construction superintendent for the last 25 years or so, i am not an engineer, but I enjoy this forum.

Rick

Hey Rick, thanks for the reply. Wow where do i start, thats a lot to take in, not sure i understand what youre talking about exactly lol. I think i have to just assume alot of things, what you see on the drawings is all i have to go by. Hold on i will post what exactly is asked of me , maybe that will make things more clear.

Again thanks for the reply Rick.

The attached diagrams show the plans for a housing project - 13 houses (5 detached and 8 terraced) each with 2 storeys plus rooms in roof space at Green Willow Little Orchard Tanglewood and Blue Tiles Portsmouth Road Esher Surrey in the Esher Ward coming under the Elmbridge Borough Council

You are required to give a breakdown of materials required for the volume of concrete required in any of the houses of your choice shown in the drawings, making any suitable assumptions wherever required. Please follow the following procedure.

• Study the drawings provided carefully and identify the slabs, beams, columns etc that will be constructed out of concrete.

• Determine the volume of concrete for all these elements (Note assume the concrete will be of same type though in reality they could be different).

• Determine a suitable mix design assuming the following conditions.

Characteristic cube strength 40 N / mm² at 28 days (structural)

Type of work simply reinforced with vibration

Degree of exposure moderate

Nominal cover to reinforcement 25 mm

Cement ordinary Portland

Coarse aggregate crushed gravel (max size 20 mm )

Fine aggregate natural sand (50% passes a 600 mm sieve)

Specific gravity

coarse aggregates 2.45

fine aggregates 2.65

cement 3.18

Moisture content of aggregate 3% (by weight) out of which 1% is absorbed by it

As this is a first year course, the Prof. probably will not expect you to determine the slab thickness, but assume its thickness, as it will be learned later on in your 3rd year rein. conc. course. I feel that he is trying to get you to think creatively and to start you on problem solving. Hint: You can estimate the wall thicknesses by creating a scale for the drawing. As you know the actual dimensions and can measure the "on-plan" dimensions, you can determine the plan's scale. Then use this scale to determine the rest of the dimensions that you need. We had a similar prob in my course.

Hi there, what you say is very useful and makes sense, i will do that. Another thing , which other dimensions should i be looking for apart from the wall thickness?

From the method described you can get all of the thicknesses. Average room clear height is 8 feet here, but may be different in UK. He also might be testing you on whether you can determine commonly used design dimensions (i.e. measure the floor thickness of your dorm or engineering building on campus).

Good luck....

That last item on the list of URL's I couldnt open, but based on the first four drawings, there is not enough info for a contractor to estimate the concrete. Those are architectural drawings, not engineering plans. But in general, to make assumptions, typically on a frame type structure like that looks to be, the basement slab (floor plan area of the house x the slab thickness of usually 6") and the foundation walls (basement height of usually 8 ft x the thickness os 8") x the perimeter of the house) are concrete. Wall footings are 1 ft thick x the perimeter of the building x 2 ft minimum wide. Interior columns can be supported on the slab if it is reinforced and the loads are light, otherwise they need to be on reinforced footings, minimum 3 ft square x 1ft thick. Beams and columns and above-grade building walls are expected to be wood or steel as these items are not typically made of reinforced concrete for single-family residential structures. Number of columns depends on the engineering design. If this is all the info you have, you could assume the basement slab of 6 " thick (~150 mm) times the plan area of the basement floor. Wall footing 30 cm thick times the perimeter X 65 cm. Basement wall 2 to 2.5 meters times the perimeter, times ~20 cm min. If the interior column loads are light they could be supported on a reinforced and haunched floor slab, otherwise they will require individual footings sized to the load and soil bearing capacity. Typically 1 meter square times 30 to 40 cm depth each. Keep in mind the above are mnimums for thicknesses and widths. For heavy loads or weaker soils, these will need to be increased. Concrete requirements : 28-day strength 4000 psi (~28mPa), air content 3-5%, w/c 0.43-0.50. Mix design will depend on the local supplier as concrete is sold by volume but batched by weight, thus specific gravity of the ingredients must be known. HTH, good luck

Hey there JDK, thanks for youre reply, it's very helpful. You sure do know youre stuff and i think youve made things much more clearer. I have a question though, when you say "Basement" do mean the ground floor or an actual basement room (a room below the ground floor)? lol. I'm not familiar with a lot of the terminology

Hi, thanks.

Basement (cellar) here means the below grade portion of the building. This looks like the type of building that would have a full basement with the floor slab at the bottom of the basement excavation which is typically about 2 to 2-1/2 meters deep to give you enough headroom when in the basement room. If the building is built on a slab-on-grade with no basement, then you would still have the perimeter foundation wall extending to the wall footing below frost level which where i live is about 80-100 cm. If you do not have a frost depth to worry about, the wall footing can be shallower, maybe half a meter or so, depending on the depth to good soils. The foundation must be built on "competent" soils which are firm, well drained, free of organic matter, fill, etc. For your exercise, you could assume a depth and so state, but give the assumption of good soils, with a bearing capacity of at least 1000 psf (about 5 kg/sq. meter). If the soils are poorly drained, you would have to provide some type of subsurface drainage which is more important for a basement. If the soils are weak, you have to either remove and replace them with engineered fill, go deeper to a stronger bearing layer, or if it is very deep, use a different foundation type (piles, caissons) to reach the firmer bearing layer. Typically this would be stated on the engineering plans, in the foundation plan sheet. If you do not go with the basement, but rather with a slab on grade, the quantities assumed as from my earlier post would not change much except the foundation wall concrete quantity would be less as you would only be 1/2 to 1 meter high versus 2 to 2-1/2 meters for the full basement. If I had the money to build a house like that, I'd go with the full basement, tho. Information on proportioning concrete mixtures can be found from publications of the Portland Cement Association (PCA), American Concrete Institute (ACI) or whatever versions of these organizations you have on your side of the pond. You could search on the net or your engineering library.

HTH

My credentials : NY State registered PE, 33 years in construction inspection and engineering.

Dear:

This is a very general comment:

Besides technical details, it is important that all assumptions used to complete the take off have to be clearly stated in the report. This allow to know the scope considered and the introduction of further corrections/improvements.

Another is the estimate break down (by type, house, total), to allow using the results in different ways: concrete usage by type, manpower, construction progress, etc.

And the most important: Continue using this forum...

Cheers

Hi torcuato, yes i will makesure I state all the guess work and assumptions when doing the write up. I will also continue to use this great forum as it's been very helpful.

hey there again Jd, looking at the the plans I'm pretty sure there isn't a basement room.

Ground floor > first floor> and attic

You've been a great help , but it seems a lot to take in, i got to read over you're posts bit by bit to try and fully understand.

Kissy-face,

On taking a second look at your drawings, I can see your challenge! I would not want to have this problem to solve with the information given.

My suggestion is you study both the outside drawings and floor plans until you can convert them in your head to the various components that make up one of the homes. Sketch out the walls and beams and other components in a 3D perspective drawing, just to get an idea of how each component fits together. Next, with dimensions known, split the house up into it's concrete components. From there, knowing the height, length, and "width" calculate how many cubic feet are contained in each piece. I think you can use algebra and geometry to make 99% of your guesstimates. Then, finally, sum them all up as cubic feet. This should be a close approximation to the concrete you need.

As I've said, I think the real challenge here is looking at the plans and translating the various walls, beams, etc. into 3-dimensions. I hope you have a good mind's eye, and a lot of paper.

hey Vermin lol. Yes i think i need to study these drawings a little harder and maybe re-draw using a scale. I'm tired now , i'll start over in the morning..

goodnight everybody

Wait! Wait! I need your address!

Lol i doubt you'll get passed the big security guard outside the dorm entrance.

Vermin are wise, vermin have ways... That's why everyone is pissed-off at us.

Tiffany,

I apologize for the fact that all of the previous commenters have unnecessarily complicated your task. The simple solution is to first determine the dimensions of a cube that would fully enclose the project with minimal excess. Once you have the dimensions of that cube, it's simple to calculate its volume (l x w x d). Once you have the volume for the cube, you merely subtract the sum of the volumes for the elements and the voids that will NOT be made of concrete and--Voila!--you have the volume of the concrete elements. Glad to help.

Hey texlex. no need to apologize. This post has further confused me lol. Everyone seems to have a different asnwer to how best approach the concrete volume task. I'm not sure i understand what you are saying exactly, forgive me. I'm beginning to feel a little dumb now.

thanks for your reply texlex.

No, no, my comment was a lame joke that was based on a recording I heard of a guy attempting to explain how a guided missile finds its target. That went something like this:

The guided missile is programmed to seek a certain location. It does this by comparing where it is to where it's supposed to be. If where it is is not where it's supposed to be, it simply subtracts where it is from where it's supposed to be to derive where it next needs to go...

merely meaningless and only mildly humourous drivel...

I should apologize for confusing you. I, in fact, have been mixing a a good number of small batches of concrete (I bought a small electric mixer that does about 50 kilos at a time) and am making a waterfall, grotto, slide, lounging pool, next to my swimming pool. It's a lot more work and a lot more concrete than I initially predicted. I feel your pain. No, really, I feel it...in my back...in my shoulders...in my arms...

Good luck!

:-)

OMG

texlex you meanie

Good guess, but, actually, "Meanie" is my wife. No, really. It's true. You could ask her. She's Meanie.

Hey guys i just uploaded a picture of the east elevation of the house, as you can see there is a proposed garage on there. I also uploaded the plans of this garage. Wouldnt the garage height be the same as the height of the ground floor room of the house?

http://i134.photobucket.com/albums/q82/wrca/pro.jpg

http://i134.photobucket.com/albums/q82/wrca/pro2-1.jpg

Tiffany.

when you have rested your brain from all the ideas being sent to you, work on the theory that the only concrete elements you will need to use in this house build are the foundations, and if it is on chalk or limestone strata then 1mtr depth will suffice, if it is on clay then base your figures on 2 to 2.5 mtr depths. The wall construction will be aerated block and brick, and no need to use concrete lintels over doors and windows anymore galvanised steel is easier and better environmentally.

Garage floor slab only needs to be 6 inches 150mm thick on good base strata.