Strength of concrete slabs?

[Andregeman]

I have a garage roof cast in 1973 with the professional methods of the time (drawing for the slab provided by the house manufacturer). The slab is 15 cm thick at the thinnest point and well reinforced. The span is 5x6 meters and it rests on walls all around. According to the drawing, it is cast with "K300, class 1, waterproof concrete."

Is it possible to get an idea of how much load it can handle without more information? I'm asking because I'm considering insulating it on the outside and want a thin layer of gravel/stone chippings on top and decking partially. And the stone weighs 1400 kg/m3. Even with a 2 cm layer, it becomes 28 kg/m2. Not much, admittedly, but added to that is the usual snow load, foot traffic, etc. In other words, does 28 kg/m2 make a significant difference for safety, or do I have some margin on my side?

 

[justusandersson]

With information about the current snow zone, you can use the historical concrete regulations to calculate what the roof must withstand at a minimum. If you have a complete reinforcement drawing, you can work backwards. If you're lucky, there might be information on the drawing about the calculation basis. K300 means that the concrete's compressive strength is 300 kp/cm² (29.4 MPa), which was the highest class at that time. However, it doesn't indicate what the roof can withstand beyond suggesting high ambitions. Do you have any information about potential shelter requirements? 28 kg/m² is peanuts in this context.

 

[Andregeman]

With information about the current snow zone, you can use the old concrete regulations to calculate what the roof must at least withstand. If you have a complete reinforcement drawing, you can calculate backwards. If you're lucky, there is information on the drawing about the calculation basis. K300 means that the concrete's compressive strength is 300 kp/cm2 (29.4 MPa), which was the highest class at the time. However, it doesn't say what the roof can withstand more than indicating high ambitions. Do you have any information about possible shelter requirements? 28 kg/m2 is peanuts in this context

Thank you! Here is the documentation available. The snow zone is Stockholm.

 

[justusandersson]

I don't think one needs to delve so deeply into this. It is clear from the drawing that the roof is built as a terrace, which means it is designed for a live load of at least 200 kg/m2 in addition to snow load, according to SBN 67, the applicable building code at the time.

A correction: K400 was the highest strength class of the concrete, I remembered incorrectly.

 

[Andregeman]

I don't think one needs to delve too much into this. It is evident from the drawing that the roof is built as a deck, which means it is designed for an imposed load of at least 200 kg/m2 in addition to snow load, according to SBN 67, the building code in effect at the time.

A correction: K400 was the highest strength class for the concrete, I remembered incorrectly.

Thank you very much!