Topic: CMU Buildings

[Greg B]

This is a good spot to ask this question since it's full of civil people.  Pun intended


Why would a civil drawing call out non-standard lengths on a building that is clearly CMU with standard block lengths?

[LE]

This is a good spot to ask this question since it's full of civil people.  Pun intended


Why would a civil drawing call out non-standard lengths on a building that is clearly CMU with standard block lengths?

They do not know how to use a module... 

[Dinosaur]

Is it an existing building?  If so, they are just measuring how it was built - inconsistant mortar thickness and all.  The tech just gets the coordinates from the surveyor and connects the dots so there is some estimating on everybody's part concerning the thickness of the rod to get to the real corner.  If you check, you will likely find the corners are not exactly square either.  If it is for staking new construction, they may be using the foundation footprint or a column line and measuring off of that from a detail, remember they are converting the inches into decimals of feet which will give some rounding problems.

[Keith™]

If I understand your question correctly, perhaps the reason is that the building is the dimension called out?

Ok, now that I have stated what many would call obvious, let me say a few things that most people don't understand.

While a typical CMU is a nominal 8x8x16, there are many other sizes available.
The home owner could care less if his 27'x33' building is divisable by 16" evenly
Over a single course of blocks the mortar joint can vary from 1/4" to 3/4" while the ideal size is 3/8" (a standard CMU is 7-5/8"x7 5/8"x15 5/8") This means that for every 1.333' I can gain anywhere from -1/8" to 3/8". So, that being said, if a building is 32' wide, the blocks will likely be spaced about 3/8" apart and have 24 blocks. The same building could conceivably be stretched out to +/- 32'-9" with the addition of more mortar in the joints. This is not a good solution,  but it works, particularly when they are filling all the cells with concrete anyway.

Anyway ... that is the lesson on block laying today ...
btw ... you DO NOT want to be a block layer ... it is a hard hard job ... and the pay is not the best. Been there done that .. don't want to do it again.

[Greg B]

I do understand how when a building is actually built it can vary from what the drawing says.  I do know that typically in commercial construction (at least we do this) that we try to keep with the nominal block sizes.  We don't vary if we can help it.

It is rather annoying that civil gives off decimals more accurate then whole numbers.  This doesn't seem right.  Especially for civil.

My opinion mind you.