sybie99
Structural
- Sep 18, 2009
- 150
Hi,
This has been discussed before, but I have a few new questions.
I have a waffle (coffer) slab, continuous in one direction and single span in other. The single span is 10.25m and the continuous spans are 8.5.
It is for office floors, so quite light loading. I am using a 450 thick waffle slab, with 550mm deep beams in the 10.25m span.
Deflections are borderline if considering long term deflections and using span over 250 as limit. Total long term deflection is 40mm.
I am concerned that construction loading of floors above will impose a load higher than designed load on this slab, at an early age, further increasing deflection.
So, I want to pre-camber. Short term deflection under self weight only are only about 5mm. I am considering specifying a 15mm pre camber. That should limit long term to 30mm which I am comfortable with.
But how to go about it. I intend on instructing the Contractor to pre-camber his shuttering only on the long span 550mm beam so that at midspan staging is 15mm high.
In order to control pre-camber, is it best for contractor to use a dip stick to ensure he is casting to required thickness? How does one most effectively control the construction of pre-camber?
I have 30mm cover on top of rebar. So another way would be to tie concrete spacer blocks on top of rebar over area to be pre-cambered and ensure slab is cast flush with these spacers. Any suggestions?
This has been discussed before, but I have a few new questions.
I have a waffle (coffer) slab, continuous in one direction and single span in other. The single span is 10.25m and the continuous spans are 8.5.
It is for office floors, so quite light loading. I am using a 450 thick waffle slab, with 550mm deep beams in the 10.25m span.
Deflections are borderline if considering long term deflections and using span over 250 as limit. Total long term deflection is 40mm.
I am concerned that construction loading of floors above will impose a load higher than designed load on this slab, at an early age, further increasing deflection.
So, I want to pre-camber. Short term deflection under self weight only are only about 5mm. I am considering specifying a 15mm pre camber. That should limit long term to 30mm which I am comfortable with.
But how to go about it. I intend on instructing the Contractor to pre-camber his shuttering only on the long span 550mm beam so that at midspan staging is 15mm high.
In order to control pre-camber, is it best for contractor to use a dip stick to ensure he is casting to required thickness? How does one most effectively control the construction of pre-camber?
I have 30mm cover on top of rebar. So another way would be to tie concrete spacer blocks on top of rebar over area to be pre-cambered and ensure slab is cast flush with these spacers. Any suggestions?
