Foundation Design using SAFE
Q1 Given a square isolated footing with a column size : 400x400
Compression axial load for the load combination of (1.5DL + 1.5LL ) = 2000KN
The safe bearing capacity is 150kN/m^2 at a depth of 2m below E.G.L
Grade of concrete M25
Taking unfactored load assumption as 2000/2 =1333.3kN
DEAD load = 1333.3/2 = 666.7kN
LIVE load = 1333.3/2 = 666.7 kN
Subgrade modulus for soil= safe bearing capacity x factor of safety / maximum settlement = 150 x 3/ 0.025 = 18000 kN/m^3
Rebar yield strength Fy = 500 N/mm^2
Rebar ultimate strength Fu = 575 N/mm^2
Elastic modulus = 25000N/mm^2
After designing the given footing with the predefined option of single footing
Assigning all the loads and properties . Now checking the analysis
> The safe bearing capacity under service load
We got 143 kN/m^2 and maximum limit was 150 , Therefore passed the check.
>Settlement under service load
Maximum limit specified as per code is 25mm and we got 7.4 , therefore acceptable.
>Two way shear check ( also known as punching shear )
Punching shear above 1 will be considered as failure we got 0.4 , Therefore passed the check.
Design strips are to be assigned for calculation reinforcement details
>Ultimate bending moment
>Flexural reinforcememnt design for footing slab
Depth assigned for the footing as per code and analysis is 550mm
Below is the SAFE file and autocad file attached .
DEVELOPMENT LENGTH OF COLUMN = 300 mm to 50 d as per IS code 456:2000
Q2 Given a PILE footing with a column size : 600x600
Unfactored load combination of (DL + LL ) = 1175KN
Each pile has a capacity of 200kN
Grade of concrete M25
Length of piles = 16m
Dia of piles = 500mm
Taking unfactored load assumption as 1175 KN
DEAD load = 1175/2 = 587.5kN
LIVE load = 11752 =587.5kN
Point spring of each pile= area of pile x young's modulus / length of pile = 196349 x 25000/ 16000 = 306796 kN/m
Rebar yield strength Fy = 500 N/mm^2
Rebar ultimate strength Fu = 575 N/mm^2
Elastic modulus = 25000N/mm^2
Number of piles required = unfactored load with self weight addition / individual pile capacity = 1175 x 1.1 /200 =6.5 ~ 7 , but for symmetry we take = 8 piles
Taking centre to centre distance between piles = 3 x pile dia = 1500mm
Edge distance from pile center = 1 x pile diameter = 500mm
Assumed pile cap depth = 500mm
Shown above is the placement of piles and column ready for analysis
> Settlement under service load
Maximum displacement here is upto 3 , allowable is upto 25mm so , passed check
>Individual pile capacity under service load
Maximun we need is 200 ,each carrying maximun upto 140 , therefore acceptable.
>Two way shear check also known as PUNCHING SHEAR
Punching shear above is considered as failure but everything under 1 so check passed.
> Flexural reinforcement design for footing slab
36 bars of dia 16mm is provided @100 c/c spacing.
DEVELOPMENT LENGTH OF COLUMN = 300 mm to 50 d as per IS code 456:2000
Below is the SAFE file and autocad file attached .