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Thanks everyone for your invaluable insights. I am starting to lean toward shrinkage restraint cracks aggravated by bad and wet weather conditions. Still a bit doubtful about it since there different slab types with different slab restraints, thicknesses and spans. Yet all those slabs exhibited...

Enable, Yes I have asked the contractor to take three core samples and test for compressive strength. To my amaze the contractor is unwilling, saying the problem will be fixed once they waterproof the top which they will. But I will not sign final certificate without the cores, as you mentioned...

Jumstructures, You are right, it is wrong to post it that way, sorry I did not check the preview and I was previously checking the photos on my phone. I have updated the post. Rscassar, The cracks appeared when the formwork was stripped at 28 days. Since then in 6 month the slab was fully...

Hi all, I have designed a suspended slab over a basement (so one level). After formwork was removed the slab showed hairline cracks in numerous places particularly around small plumbing openings. The cracks do not follow a pattern that I know, they show near supports, in mid-spans, on the face...

Thanks for your responds! What I meant by formwork settlement is what we have when we pour a fresh slab on formwork that is in turn supported on a susbended slab that again is supported on formwork supported on a suspended slab. Ultimatly this would create some kind of cumulative defelction as...

Hi, I am designing my first building over two-storey height including sizing slabs for longterm deflection. I read in the design codes that the support settlements and formwork settlements should be accounted for when considering refined defelection calculations. This points is very unfamiliar...

Dear JC456, I can only relate to this through what ACI and AS3600 impose on designing vertical ties to withstand forces from offseted bars in columns( 1 in 6 inclination in bars)

Dear Rapt, I am only discussing torsion reinforcement and how AS3600 and ACI specify different spacing for it. I have a basic understanding of the punching shear model. The issue for me is, how come AS3600 specify spacing of ties to be max of D or 300 while ACI limits it to d/2. same goes for...

Dear hokie66 and rapt, thank you for your great responses. I thing that's exactly what it is. The bottom bars are to take the horizontal force developed in the offset bars ( I was thinking the offset always happen to be in the slab which is why I didn't see this explanation) And rapt, although I...

Dear Motorcity, i believe shear from lateral loads would be uniform in anyone column, as the moment diagram is linear thus shear is constant. Therefore, adding ties at the ends of the columns only doesn’t make sense from shear point of view.

Rapt, can you please elaborate. I have read both commentaries still can't seem to get an answer

There seem to be a clear confident between the way AS3600 distribute the punching shear reinforcement and what ACI318 thing reinforcement should be spaced. first AS3600 chapter 9 c.9.2.6 states that maximum spacing of punching shear reo ( ties) should not exceed 300 or Depth of slab. ACI...

I have recently noticed that a lot of structural engineering companies based in Australia give this attached typical details for column ties between floors. You notice two main thing in that detail: 1) 3 sets of ties at 80 below every slab 2) half the ties spacing at lap length. I could not...

Thank you all for responding, it has been a pleasure hearing great opinions from you guys!

If we pin the columns, then wouldn't this reduce the force transferred to the walls? in that case how can we make sure that shear walls as the sole lateral resisting system is effective?

Dear all, since the columns would be considered to be fixed under gravity dead and live loads. How about analysis for lateral loads wind and earthquakes, if my lateral resisting system is limited ductility shear walls and my columns are not supposed to contribute to my lateral loads. The...

Dear all, Thank you for your great replies. I have come to the conclusion that columns must definitely be designed as fixed ended not pinned, though I have seen people pinning columns even at connecting to beams! I also understand that engineers choose not to include moments on their transfer...

Dear Hokie66 Thank you for your answer. But how could the designer justify not designing for moments from columns above in transfer slab specially as you mentioned it will affect punching shear outcomes and even if one would want to check bearing stress under columns it would also be perhaps...

Dear All, This is my first thread and I have heaps of questions, so please bear with me :D Question 1: I have recently read this clause in the Australian Standard AS3600 cl 10.3.1: " Le = effective length determined in accordance with Clause 10.5.3; or alternatively may be taken as— (i) for a...