Week 4

Question 1

What is the typical nature of ground floors in commercial and industrial buildings?

Answer 1

They usually non-structural.

Question 2

What is the primary characteristic of residential ground floor systems?

Answer 2

Residential ground floor systems are mostly structural.

Question 3

What is the key responsibility of residential ground floor systems?

Answer 3

Must distribute loads to foundation materials safely.

Question 4

What is the main cause of ground movement?

Answer 4

Moisture changes in reactive soils cause ground movement.

Question 5

What type of soils are reactive soils?

Answer 5

Reactive soils are clay-based.

Question 6

What happens to reactive soils during wetting and drying?

Answer 6

Reactive soils undergo significant volume changes during wetting and drying.

Question 7

How does the ground floor act in slab-on-ground/footing construction?

Answer 7

The ground floor acts as an impermeable membrane.

Question 8

What does the impermeability of the ground floor lead to?

Answer 8

Impermeability leads to moisture imbalance.

Question 9

What result does moisture imbalance between the center and edges of the ground floor cause?

Answer 9

Causes differential volume changes between the center and edges of the ground floor.

Question 10

What are the 5 primary steps of ground floor system design?

Answer 10

1. Site classification
2. Assessment of site typography
3. Selecting ground floor system and wall types
4. Assembly of the details
5. Preparation of documentation (calculations, specifications & drawings)

Question 11

What can professionals notice in a preliminary ground investigation?

Answer 11

They can notice the presence of clay-based soil.

Question 12

How can clay-based soil be identified?

Answer 12

Clay-based soil can be identified through simple observations.

Simple observations facilitate decision-making during site selection.

Question 13

What ground floor procedures can be more suitable for sloping sites?

Answer 13

• Cut and fill requirements
• Earth retaining structures
• Drainage compliance

Question 14

What are the characteristics of a ‘Footing Slab’?

Answer 14

• Concrete floor with separately poured strip footing
• Minimizes floor construction time (excavations left open)
• Does not require extensive formwork
• Only requires two concrete pours

Question 15

What are the characteristics of a ‘Stiffened Raft’?

Answer 15

• Reinforced concrete slab on ground
• Stiffening beams as support to the structure
• Generally require only one concrete pour
• Economical
• Beam sizes and quantity of reinforcement required differs based on site conditions

Question 16

What are the characteristics of a ‘Slab on Ground’?

Answer 16

• Theslab itself acts as a raft footing, without stiffened beams in the center.
• Integral edge beam, requiring complex edge formwork, suitable for unstable foundations.
• Used in domestic construction on stable to moderately reactive soils

Question 17

What are the characteristics of a ‘Waffle Raft’?

Answer 17

• Stiffened raft with spaced ribs constructed on the ground
• Slab panels suspended between each of the ribs
• Cardboard/polystyrene void formers are often used to produce close grid of reinforced concrete ribs
• Suited for levelled sites
• Can be designed to support piers/piles

Question 18

What are the 6 construction requirements for slabs?

Answer 18

1. Concrete surface must be leveled (troweled/screeded)
2. Positioning of drains, pipes, and other utilities then covering them with course sand/gravel (which is then levelled)
3. Plastic film is placed to prevent moisture
4. Perimeter insulation is laid and reinforcement is placed
5. Concrete is poured
   (then tamped and levelled)
   **Beams & girders are usually supported by separate footings
6. Fabric mesh reinforcement should be used in concrete floors
   (top 1/3 of the slab)

Question 19

What are the general requirements for construction of concrete rafts & slabs? (AS 2870)

Answer 19

• Grade of concrete: N20
• Slump: 100mm
• Aggregate size: 20mm maximum
• Slab mesh placed in the top 1/3 of the slab
• Raft or slab mesh shall be lapped
• Minimum concrete cover for the reinforcement shall be 40mm to unprotected ground, 40mm to external exposure, 30mm to a membrane in contact with the ground, and 20mm to an internal surface;
• Trench mesh in beams overlapped by the width of the mesh at T and L intersections.
• Reinforcing bars shall have a lap length at splices
  (min.500mm for 12mm bar) (min.700mm for 16mm bar)

Question 20

What does DPM stand for?

Answer 20

Damp Proof Membrane

Question 21

What is DPM?

Answer 21

• 0.2mm thick polythene
• Sealed at all joints with waterproof tape

Question 22

How is DPM installed?

Answer 22

• Membrane is placed beneath the slab (slab and beams, including internal beams)
• Membrane may be terminated at the internal face of external beams;
• Pipes or plumbing fittings shall be taped or sealed with a close-fitting sleeve or made continuous with DPM by taping or by lapping.

Question 23

List the characteristics of edge rebates
(for slab on ground, stiffened raft or waffle raft with masonry cavity)

Answer 23

• Minimum rebate depth 20mm. The edge rebate may be stepped along its length.
• Minimum depth of concrete below the edge rebate 150mm.
• Edge rebates are not required for construction with single-leaf masonry.