Cracking walls after RSJ installed

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I have never had this problem myself (cracking above a newly placed steel. But it is always a concern. The task of adequately propping the upper house load is not as simple as is being intimated here. If a 1mm crack had to be factored in to the calculation of the size of steel required and the propping. Then you would need 100 props and steel so thick that the masonary supporting it would have to be trebled in thickness.

Also, there is no 'light' that comes on when winding the props up to let you know, for sure, when the props have taken the weight. This is very much a 'feel' job. The rigidity of masonary allows a very very small margin. On a 5m RSJ there is every chance that, however many props you use, there will be a hairline crack above as you release props and the weight is taken up by the steel.

Also(2), If the joists of the room above have joists that are built in then there is every chance that they will be out of level with each other by anything up to 10mm. This descrepancy in ceiling joists (the tops of the joists are likely to be more level with each other than the underneath of joists) is an unknown until the propping is in place. I know the correct method is to take the section of ceiling down but this is often not followed.

If i were doing a job like this i would warn the client that there may well be hairline cracks above and they will be fixed at the end of job as more settlement may occur. I would assure them not alarm them. This is the real world. And although i haven't had any comebacks on RSJs or cracking from any of my jobs i am realistic enough to know that it isn't easy to get it spot b*****k right. And that there is every likelihood that it will happen sometime.

To the OP .... were the props left in place after steel was fitted for a few days ? I've noticed that in their haste to get on with the rest of the job that some builders take the props away the next day. Always too soon if there has been bricking up between steel and masonary above

"TONY, are you awake at the back?"

As a matter of fact, I did sit at the back in lectures, next to Jane H, and was very much awake. Jane, bless her, quietly gave me a fascinating and alternative view of suspension structures, elastic theory and bolt-hole clearances.

By the way, if that's your image, you're far better looking than I imagined.
(Also, read, learn and digest the previous post by EB1caneyeB) :LOL:
They bend but they are not made of rubber. Its a tiny amount which is not enough to cause cracking. That is what you don't seem to be able to under stand
They bend but they are not made of rubber. Its a tiny amount which is not enough to cause cracking. That is what you don't seem to be able to under stand

OK then. On a 5m span such as the OP has, would you care to state what amount of deflection (in mm) would be acceptable under dead load only, for there to be no cracking of the brickwork above?

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