Figure 16 is derived from the following empirical formulae:
| (A) |
Wall restrained at both ends but not at the top |
| |
t > L/40 and t > H/90 |
or |
t > H/15 with no restriction on the value of L |
or |
t < L/40 and t > L/59 and t > (H+2L)133; |
| |
|
| (B) |
Wall restrained at both ends and at the top |
| |
t > L/40 and t > H/90 |
or |
t >H/30 with no restriction on the value of L |
or |
t < L/40 and t > L/110 and t > (3H+L)/200; |
| |
|
| (C) |
Wall restrained at the top but not at the ends |
| |
t > H/30; |
where: |
t is the thickness assumed (mm); |
| |
H is the height (mm); |
| |
L is the length (mm) |
| |
|
4.7.3 Floors
Beam and Aircrete block floors offer a whole range of design benefits at both ground and upper floors.
• Over poor, wet or contaminated ground, avoiding problems from ground heave or settlement of the floors, in addition no blinding is required
• Speedy, dry construction minimising weather related delays
• Accommodating voids for services
• Saving the cost of filling and blinding under in-situ floors
• Providing a lower floor weight with a U-value to meet the Building Regulations
• Sometimes avoiding the need for intermediate sleeper walls
• Providing a structurally and acoustically superior first floor in dwellings
• Providing reduced dead loading enabling longer spans
• Providing support for loadbearing partitions subject to supporting the partition by two floor beams designed to carry the loading.
The ground beneath the floor should be free from top soil and vegetable matter. It does not need to be sealed or covered with oversite concrete.
A void of at least 75mm should be provided between the underside of the floor and the ground surface. Where the soil is heavy clay, the depth should be increased to at least 150mm to accommodate possible heave. The void should be ventilated by perimeter ventilators providing 600mm of open area per metre run of external wall.
The void should have adequate drainage so that there is no standing water and no build up of water against the perimeter walls.
Aircrete blocks are produced which are suitable for domestic floor loading. The design requirement is that blocks installed between the beams, should be capable of withstanding a point load of 3.5kN applied through a 100mm square plate. This is usually sufficient to withstand the type of temporary loads expected during the construction of the floor.
In the final finished floor, higher point loads can be sustained (for example in domestic garage floors) when screeds or other appropriate finishes are applied.
In such cases, it may be that the design of the beams is the governing factor. In all cases the supplier of the reinforced or prestressed concrete inverted Tee beams should advise on the design of the beams.
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