Browse Forums General Discussion 1 Jun 02, 2020 11:59 pm Hi all. We're considering a 7/8 ft aquarium + sump that'll weigh well over 1000kg on a frame that spans 210/240cm x 60cm (weight distribution is obviously only at contact points). We have a waffle slab with laminate wood over the top of it. How do we get a structural engineer to confirm if the slab can hold that weight? Or alternatively, what the maximum weight rating is for waffle slabs? To me it's confusing. Some people (not engineers) say no, you shouldn't...but then I ask, how does a car/SUV weighing 2000kg+ park on the same waffle slab in the garage where it has only 4 small contact points? Happily take advice/input. Thanks. Re: Waffle Slab - Large Aquarium 2Jun 03, 2020 7:35 am Hey Brannor I suggest you get bearing pad or thickening/footings added to your waffle under the tank to prevent Slab punching shear through the void former's Cheers Chris Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Waffle Slab - Large Aquarium 3Jun 03, 2020 7:53 am StructuralBIMGuy Hey Brannor I suggest you get bearing pad or thickening/footings added to your waffle under the tank to prevent Slab punching shear through the void former's Cheers Chris Thanks Chris. So the aim of the bearing pad would be to distribute the weight across the entire area the aquarium would cover? Is this something the aquarium guys would know about, or do you need to get this specially made? Re: Waffle Slab - Large Aquarium 4Jun 03, 2020 7:57 am It would be cheaper to remove the polystyrene void former and have it incorporated into the concrete slab The void formers are 1m2 x .3m deep = 1m3 (aprox $250) concrete Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Waffle Slab - Large Aquarium 5Jun 03, 2020 8:00 am StructuralBIMGuy It would be cheaper to remove the polystyrene void former and have it incorporated into the concrete slab That doesn't sound cheap at all (cutting a big hole in an existing house's floor) - though I guess shear is far costlier. So the reality is that waffle slabs can't hold much weight? How is it possible for cars to park in your home garage then? Re: Waffle Slab - Large Aquarium 6Jun 03, 2020 8:05 am If you have the legs positioned over a rib it might be OK, you will need to x-ray the slab It is recommended that you don't jack up a car on a waffle slab the polystyrene beneath is the problem Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Waffle Slab - Large Aquarium 7Jun 03, 2020 8:12 am StructuralBIMGuy It is recommended that you don't jack up a car on a waffle slab Yes, that'd be because of the very localised focus area of the jack - though I've read the story of the guy that was crushed beneath the jack and it was because of the jack, not the concrete failure. I'm not exactly going to test that out. The frame of the aquarium (using a 7ft example) would be a 5cm base frame, spanning 2100mm x 600mm. That'd mean it would span at least two ribs, possibly 3. And possibly along a perpendicular rib. But yes, an x-ray might show exactly how many ribs. Re: Waffle Slab - Large Aquarium 12Jun 04, 2020 11:30 am Yes. Thanks Chris. A question regarding bearing pads. If we put in a rigid pad that spanned multiple ribs and potentially one or more points where horizontal/vertical ribs cross, do you think that might distribute the load 'enough'? I still believe our first port of call is to get the x-ray done to know what's where. Re: Waffle Slab - Large Aquarium 14Jun 04, 2020 7:28 pm You know, I'm not an engineer and I'm happy to be corrected, but each point will have 250kg max. A 2400x600x600 tank holds 864L so it may only be 220kg per leg. I honestly can't see that punching a hole in the floor. You could sit that tank on concrete paving slabs and I don't think it would crack them. Sometimes I think we over think things. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Waffle Slab - Large Aquarium 15Jun 04, 2020 7:43 pm The tank will likely be 210x60x60. But it will have a 150x40x40 sump and then there is the weight of the glass of both tanks as well as the frame, excluding any sand/rock. That said, the frame will be 5cm all the way around. The weight will be closer to 1500kg...so I kinda need to be sure. Re: Waffle Slab - Large Aquarium 16Jun 04, 2020 8:11 pm If you run another rail across the bottom on the long sides then you are going to span across ribs on the waffle pods and increase the load area enormously. How thick is the slab over the top of the pods? Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Waffle Slab - Large Aquarium 18Jun 04, 2020 8:18 pm I just can't see how a 50x50 leg is going to punch a hole in 85mm of reinforced concrete. If you have ever got on the end of a jackhammer you will appreciate just how hard it is to drive a 25mm chisel through concrete. I just don't see it happening. Even the laminate flooring will spread the load. I'd love to see a verified account of a jack punching through a 85mm concrete floor. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Waffle Slab - Large Aquarium 19Jun 04, 2020 8:41 pm Alexp79 the pad footings doesn't need to be reinforced, besides its pointless anchoring into a 85mm slab? Brannor The specs say a lot of things ie 85mm +/-10mm BTW, it's always wise to check Some slabs can be out/under as much as 20mm here posted today Concrete Slab Level Tolerance OT, 20mm is too much deviation Once you have located and verified the ribs, Frame /truss over the supporting ribs I suggest you make a feature of the frame Cheers Chris Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Waffle Slab - Large Aquarium 20Jun 04, 2020 9:31 pm Chris. Do you honestly think that a 50x50 steel leg will punch a hole in a concrete slab? I'm not trolling, I just can't see it happening. I'd expect 50x50 rhs to bend or buckle before it punched through the floor. Surely as an engineer you can crunch the numbers and give us the force required to push through the floor. 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