Slabs & Footings Flashcards
What are the 3 main foundation systems
Strip Footing
Waffle Slab
Raft Slab
What is a strip footing?
Rectangular cross section poured in a continuous horizontal reinforced strip for placement underneath a wall
What is a stiffened raft slab?
Concrete slab on ground with external and internal stiffening beams
What is a waffle pod slab?
Stiffened slab constructed on ground
Foundation movement for slabs & footings are measured as how much chance of happening over what period?
Less than 5% chance of being exceeded over 50 years.
Site Classifications
A, S, M, H1, H2, E, P
Site Classification, what does A stand for?
Sand and rock sites - Little or no movement
Site Classification, what does S stand for?
Slight movement - Clay sites
Site Classification, what does M stand for?
Moderately reactive clay site
Site Classification, what does H1 stand for?
Highly reactive clay site with high ground movement from moisture change
Site Classification, what does H2 stand for?
Highly reactive clay site with very high ground movement from moisture changes
Site Classification, what does E stand for?
Extremely reactive site with extreme ground movement from moisture changes.
Site Classification, what does P stand for?
Problem - Soft or unstable foundations, reactive site subject to abnormal moisture conditions
Maximum length of slab before control joint required?
AS 2870 - 30m
NCC - 18m
What are vapour barrier requirements?
-.2mm thick
-Medium impact resistant vapour barrier
-Damp-proofing membrane - High impact resistant
-200mm overlap
-Taped penetrations
Minimum bearing pressure required for an edge beam & Strip footing kPa
Edge Beam 100kPa
Strip Footing 50kPa
What are the MPA, aggregate size and nominal slump requirements for a slab
NCC 4.2.10 (a) (i) Strength @ 28 days not less than 20MPA
(ii) 20mm max aggregate
(iii) Nominal 100mm slump
Trench Mesh and Slab Mesh overlap requirements?
Trench Mesh - 500mm (full width across section)
Slab Mesh - 2 outermost transverse wires must overlap the same other sheet
Minimum edge rebate depth?
20mm
What is required at the internal corners of a slab?
Re-entrant or internal corner reinforcing 2000mm long on a 45degree angle
If an edge beam requires deeper excavation this becomes?
Deepened edge rebate
How many strips of reinforcement need to be placed in a strip footing?
2 - Top and Bottom
Df meaning?
Depth of footing
What is the maximum spacing of an internal beam from an external corner?
4 meters
Where 1 side of a re-entrant corner is less than 600mm, what is the minimum length of the continuity beam?
2 X D minimum.
What is the maximum offset for a LBW?
1000mm
Concrete Cover to Unprotected Ground
40mm
Concrete cover to a membrane in contact with the ground?
30mm
Concrete cover to an internal surface?
20mm
Concrete cover to external exposure?
40mm
Bar chair spacings centeres?
800mm
Minimum splice for reinforcing bars
Up to 12mm
12mm - 16mm
Up to 12mm - 500mm minimum
12mm - 16mm - 700mm minimum
For design purposes, the life of a structure is said to be how long?
50 years
On a stiffened raft slab how thick must a slab be where slab thickening supports a load bearing wall?
150mm
On a stiffened raft slab how wide must the slab thickening be where it supports a LBW?
500mm
In a stiffened raft slab up to 18m long what size mesh is used?
SL72
In a stiffened raft slab between 18m and 25m long what size mesh is used?
SL82
In a stiffened raft slab greater than 25m long what size mesh is used?
SL92
In a waffle raft slab what is the allowable thickness of a garage slab?
85mm
List the requirements for fireplace footings on a Class A and S site
Single storey pad thickness?
Double storey pad thickness?
Pad footings to be reinforced with what size mesh and extending how far past the edges of masonry?
Single storey - 150mm
Double storey - 200mm
Mesh size SL72
Extended 300mm past masonry edge
Where can service penetrations sit in edge and stiffening beams?
Middle 3rd
What is the minimum depth of concrete below the edge rebate?
150mm
Where the edge rebate is greater than 400mm, what is the minimum stem width?
200mm
What are the 3 re-entrant reinforcement options?
2 Strips of 3-L8TM
1 Strip of 3-L11TM
or
3 x N12 Bar
At external corners what is the MAXIMUM distance from external beam to 1st internal beam?
4m centre
If a beam cannot be placed in a straight line what is the maximum deviation ratio allowed?
1 in 3
Slab beam layout
What are the angle of repose degrees for sand and clay?
Sand 30 Degrees
Clay 45 Degrees