Foundation Design using SAFE
AIM -
A) To model the Isolated footing on SAFE ,to analyze and design it to verufy the size, depth and steel provided as per calculations.
B) To deisgn Pile Foundation for the given data on SAFE as per IS 2911 (part2) and SP 34.
SOLUTION
A) ISOLATED FOOTING DESIGN ON SAFE :
1. Open SAFE software and start the New model with the following details -
Select IS 456:2000
Choose Default Metric Units
Covers slabs top and bottom - 50mm with bar size 20
2. Loads -
we know, Compression axial load = 2000 kN (given)
hence, Unfactored load = 2000/1.5 = 1333.33 kN
DL=LL = 1333.33/2 = 666.55 kN
Size of Footing = 4m x 4m
Thickness = 900 mm
Subgrade modulus = Factor of Safety (FOS) x Safe Bearing Capacity (SBC) / settlement
= 3 x 150 / 0.025
= 18000 kN/m^3
3. Define > Materials
a) M25
b) Fe500
4. Define > Slab property
a) Footing- grade M25- thickness 900mm
b) Column - grade M25- Thickness 900 (stiff)
5. Define > Soil Subgrade Property Data
6. Quick draw areas around points > draw the footing and column :
7. Select Slab properties > Footing , Select soil > SOIL150 also
8. Check Slab information and Design Preferences and do corrections if needed any :
9. Define > Load Combinations
a)
b)
10. Run Analysis
11. Do the following Checks :
a) Display > Deformed Shape > Load Combination - SLS
All values are between -5.77 to -6.06 , hence OK
b) Display > Reactions > Load Combination - SLS
SBC 150 > values , hence OK
c) Display > show Punching Shear Design
0.367 < 1 , Hence OK
ALL CHECKS VERIFIED .
12. Unlock the model
Edit > Add Design Strips > Add in X and Y directions along A and B layers
13. Display > Show slab design > Check BM values in both A and B layers :
CONCLUSION -
As per design , we can conclude that Isolated footing of 4m x 4m with a depth of 900mm is satisfied.
Reinforcement 20 mm dia bar with 200 mm spacing .
B) PILE FOUNDATION :
GIVEN -
Column size = 600 x 600 mm
Total axial load = DL + LL = 1175 KN
Pile diam = 500 mm
Pile Capacity = 200 KN
L = 16m = 16000mm
SOLUTION -
No. of piles = Total axial load/Pile Capacity
= 1175/200
= 5.8 ~ 6 Piles
Spring constant = EA/L [ E - Young's modulus 5000*5= 25000
A = area of cross section pi/4 *d^2
L = Length 16m ]
Spring constant = 306.64 kN/mm
PROCEDURE -
1. Open SAFE
IS 456:2000 , Add Metric units as default
Grid only
Add dimensions of the grid 3400 x 2150
2. Define Slab Properties as pile, pile_cap and column :
3. Add Point Spring Property Data :
Select centres of all piles and add spring load
Add the required spring constant = 306.64 kN/mm
4. Select the column center and add point load :
5. Run analysis
CHECK 1 - deformed shape values in limits, OK
CHECK 2 - Punching shear value < 1 , OK
6. Unlock model and add design strips along X and Y in layers A and B :
CONCLUSION :
Pile foundation is done with all required checks satisfied .