cracks in concrete wall: what is the reson for it? 2

[lolobau]

Hi

we spoka about cracks in plaster already. The answers were very clear for the introduced crack patern

now what is the reason when you have the same patern of crack in a reinforced concrete wall?
see attachment

this can#t be shrinkage because it is reinforced Y12 every 200mm each face horizontal and vertical

 

[CELinOttawa]

Oh, and I call a spade a spade - Correctly slandering Calcium Chloride with the vernacular "salt" is the most derogatory (while being polite) I can think of. It catches builders and makes them think. I hope it helps keep it out of my projects!

 

[lolobau]

Hi guys

thank you fro the valuable tips.

The comment reagrding the columns: The columns just next to the cracked wall are only supporting a roof. Nothing much so even they sizes is far overdesign as it is

@ Hokie: this is quite interesting what you observe here "the vertical cracks are restraint shrinkage cracking. The slab was cast first, then the upstands, and the restraint of the slab caused tension in the newly cast " but somehow I can´t understnad exactly why the slab woudl trigger this vertical cracks? I woudl understand the vertical column next to the wall much more but the slab is restreining the wall?

 

[KootK]

Check this out lolobau: Link
And this: Link

When the plastic, second pour concrete tries to shrink, the hardened, first pour restrains that shrinkage. I got burned on this in the past when having a new curb installed over an existing composite deck system. I provided standard T&S reinforcing and it cracked like nobody's business. 0.2% temperature and shrinkage reinforcing is really only appropriate for "free shrinkage". For restrained conditions, I've been told that 0.4% is better.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[CELinOttawa]

There is a calculation for further reducing shrinkage cracking, but I'm told it was tuned before super-p was popular. I've seen that spit out 0.55 and 0.6 percent steel; Huge!

 

[hokie66]

lolobau,

KootK has explained it. The picture in his first link of cracking in a wall just above a footing shows what happens. I like to put some extra reinforcement there to control those cracks better. The cracks will probably still form, at roughly 3 metre centres, but will be smaller as the reinforcement increases. These cracks may not be structurally significant, depending on the exposure, but may still be undesirable aesthetically.

 

[KootK]

When I first started out, I noticed that many standard concrete details for vertical elements contained 2-15M T&B in addition to distributed reinforcing. These would be elements like up stands, frost walls, and walls that connected slabs above and below. When I'd ask about this, people would tell me that the reason was to provide a nominal moment capacity to the element under consideration. Often times I would find that peculiar as many elements wouldn't seem to need the extra capacity. In a story high wall, for instance, surely the two bars top and bottom would have an almost negligible impact on moment capacity.

I'm starting to wonder if the intent all along was to give a nod to shrinkage restraint.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.