水草情迷

after calculating, I find this is very difficult wor.......
suppose I have a 2 feet tank directly put on floor, the area occupy is 0.24 sq. m (60cm x 40cm), so the weight can only be 60kg (250kg x 0.24), that is 60L.......so, the height of water can only be 25cm (60/6/4)............the results is that even only one tank directly put on floor, the water level can only be 25cm height......it's quite impossible wor............is there anything wrong with my calculation?

The relationship:

1 kg of mass weighs 9.8N
1 Pa = 1 Newton/m^2 = 0.102 kg/m*s^2
1 kPa = 1000 Pa

From elementary Physics, force = mass x acceleration due to gravity (g, g=9.8m/s^2).
So Force (Newton) = mass (kg) x g (m/s^2).

So minimum of 2.5 kPa means 2500 Newton per sq meter area under the earth gravity.
But 1 kg weighs 9.8 newton, so 2.5kPa -> 2500/9.8 = 255kg
of mass over an area of 1 m^2.

The above is pure theoretical calculation, the actual practice might have other considerations. Building expert should be consulted for big project. But still, normal
tank should be pretty safe as the load is not concentrated.

ps: Fox's link pointed to the mistake in my earlier posts, ie, the 9.8 factor due to g was missing !

the final conculsion seemed to be 250 kg per m^2 for average weighting.......

Ken T,
I'm sorry there's problem. You may find from this url
http://www.macdizzy.com/formulas.htm
that 1.02 kg/sq-cm = 100 kPa
ie. 1kPa =102 kg/sq-m, not 1000 kg/sq-m
And go back to your question, as we are not filling every inch of our house with weights, the load of the tank is actually spread across the floor slap. If the overall loading has not exceed the floor's capacity and your tank have not exceed the concentrated loading limit, that's OK.

Fox: Thanks for pointed out. I recheck my comments and found that i miss out sth.

Actually the accelaration due to gravitational force, g = 9.8m/s^2. So a mass of 1 kg will weigh 9.8 Newton, since
weight (or force, in Newton) = mass x g = 1 kg x 9.8 m/s^2.
And pressure is defined as force per unit area, and in SI uint,
1 Pa (N/m^2)=0.102 kg/m*s^2.
So, 1kPa=102kg/m*s^2. Since 1 m^2 = 100cm x100cm=10000 cm^2,
so 1 kPa=0.0102kg/cm*s^2.
So, for a load of 2.5kPa, the mass distributed on a 1 m^2 area is 255kg.

So, Fox, your link agrees with my calculation ( just the unit is not correct, ie Pascal is in N/m^2 (or N/cm^2), or kg/m*s^2, (or kg/cm*s^2), not kg/cm^2)

Maybe sb with building code expertise would like to elaborate on how the code is supposed to be interpreted. Any structural engineers out there?

Alan2002,

I really enjoy this discussion, so harmonic.

Fox: I should thank you for pointing out my silly mistake. It has been a long time since I studied physics and mechanics and i think i must have returned a large part of my knowledge to my instructors!

As u said, the 255kg/m^2 seems to be the average weight distributed across the whole floor, or else several persons standing on a 1 m^2 area (would easily fit in!) would easily exceed that limit. Hmm..., I am still puzzling out of curiosity how the 2.5 kPa should be interpreted, or am i missing sth here...

Yes, I agreed that the average limit is easy reached. But it's the minimum governed by law, the actual may be higher. Moreover, the concentrated limit is 3kN over any square of 300mm (I don't know what's kN), so I think that won't be a problem for the example you listed.

1 kN =1000 Newton, and Newton is the SI unit for weight.
1 kg of mass weighs 9.8N on earth.
I don't believe it is so "chemical" as well, but just curious to know.

every building have designed to have a safety load. sometimes, designed load is the times of the actual live load. it is satety enough for the structural stability. don't want to mansion detail, however, the impose of addition live load of about 100kg is safety.

in HK, less news have lessen that building collapse due to overloading.

如果一味只係計埋論值...
咁如果一間屋住左幾個大肥人, 個個成百公斤...個地面咪會下陷囉..
肥人企在地上的kPa 仲大好多倍...

我個缸放窗台, 又係唔係一樣計法, 我怕魚魚做空中飛人!

窗台 loading 同地台一樣
等於 1平方米 2.5噸 (not 250kg!!!)

if there is any Chartered Architect over here? i would like to know what is the actual live loading safety factor nowadays?