Again, thankyou for responding and challenging the logic behind this.
The outrigger pads exert approx. 20 t/m2 onto the rc slab (50t over 1.5m x 1.5m mat area). The sub-base is well prepared (well-graded, well-compacted) and is at least 1m thk of mot type 1 (installed before I was involved in...
Thanks for that OldDawgNewTricks - that does make sense. I'll read the reference material recommended.
Would the logic thus also extend to the situation of a crane set up on an existing RC road? Could the RC road also be expected behave in such manner in which the flexural stresses occurring...
Thanks everyone.
I've got a meeting with the site team later to discuss. I think the preference is now:
1)have an large RC slab area (as agreed with client)
2)consider 4 individual pads cast incorporated into the slab area (challenging to possibly get the outriggers on centrally due to...
Unfortunately it appears the client is expecting an RC slab (not a gravelled area) and that is what must be provided. I've got plate bearing tests undertaken on the underlying stoned area and they are showing a well-compacted, firm ground.
Having spoken with a few more colleagues, they akin...
Good points!
It's new construction - the intention is we would leave site providing an RC slab-on-grade such that a maintenance crane could use it in say 1 year or (possibly even 5-10 years time!). However, I'm now toying with the idea of just leaving a gravelled area, and no RC slab at all, so...
I guess what makes me think there is some mileage in my colleagues approach, is that if this were an existing concrete area (well constructed, but unknown reinforcement quantities), I suspect that the only checks that would be undertaken would be to take a 1:1 load spread through the concrete...
Because of the overall size of the slab, I had thought about the requirement for control joints (contraction, saw-cut type) for shrinkage - to prevent undesirable cracking-patterns. But not sure if this is a wise decision now (cutting top reinforcement).
Thanks for the replies.
It's provision for a maintenance lift (probably once every 20 years), very much a temporary case. Yes - I think we could dictate the position of the outriggers.
I've got the Lift Plan which provided the max and min point loads under each outrigger (the max. = 50t...
I need to design a slab-on-grade that can withstand 4 outrigger loads from a 130t mobile crane. I've designed a fair few crane pads on compacted gravel, but never a permanent concrete area.
So far I've got spreader mats under each outriggers to spread the (huge!) point loads. I've checked the...
The backfill is taken to be earth, groundwater and surface surcharge.
As the groundwater level was unknown at start of design, I took GWL at ground level which also made the analysis using published tables easier for triangular and UDL pressures.
Tank is open (no roof).
As the base slab is...
Excellent points raised.
I agree with the caution for careful control and detailing wrt to crack widths (flexural and thermal), indeed its what's governing the design.
I'll post put a free body diagram tomorrow, look forward to more discussion.
It's a substantial nib (more than 1.5m) needed for a variety of reasons (flotation, base prop to shoring and for access during construction).
I've drawn a free body diagram, but I've become a little unstuck due to the base and walls both acting two-way spanning.
I think I may need to simplify...
Let's take the case for the tank full. For equilibrium, would the downward component of the internal contents cause a relieving effect to the base slabs bending moments?
Similarly, for the backfill case - would the weight of the soil acting on the nib cause a reduction in the base slab bending...
Buried RC Tank - 9m x 9m (square) x 6m deep, plus 1.5m nib. Simplified the geometry for discussion purposes.
I've considered two loads cases; 1) tank full and no backfill, and 2) tank empty with backfill in place.
The walls are designed as two-way spanning 'panels' (using boundary conditions...
