Foundation Design using SAFE
1. Model the isolated footing provided in the week 11 challenge on SAFE. Could you review and design it to verify the size, depth, and steel provided according to calculations?
AIM:- To model the isolated footing by using SAFE and to analyze and design it to verify the size, depth, and calculation of steel provided
INTRODUCTION:- All the steps will be mentioned along with a step-by-step procedure.
PROCEDURE:-
- Open SAFE software
- Create a new model
- Edit the settings
- Edit the structural geometries and properties as per the previous problem, which is given below:-
Size of column = 400 mm * 400 mm
Unfactored gravity load (DL+LL) = 2000 KN
Safe bearing capacity of soil = 150 KN/m^2
Assume M25 grade concrete and Fe 500 HYSD bars
Settlement = 50 mm
Take FOS = 3
Sub- grade modulus = FOS* Safe bearing capacity/settlement = 150*3/0.05 = 9000 KN/m^3
Unfactored gravity load = 2000/1.5 = 1333.33 KN
Dead load = 1333.33/2 = 666.6 KN
Live load = 1333.33/2 = 666.6 KN
Yield strength of steel, fy = 500 N/mm^2
The ultimate strength of steel, fu = 575 N/mm^2
Area of footing = 1333.33/150 = 8.88 m^2
Size of footing = L = B = ">√(8.88) = 3 m
Adopt 4 m * 4 m for square footing
- Define materials
- Add a new material property for M25 concrete
- Add a new material property for Fe 500 HYSD bar
- Define slab property data
- Assign the area spring property
- Assign the load assignment force
- Define load combination
- Check the model
- Run the analysis
Here the displacement for both dead and live load is within the limit
- Check for bearing pressure under the serviceable limit stage
Here the maximum soil bearing pressure is 84 KN/m^2 within the permissible limit, i.e., 150 KN/m^2
- Again, unlock the model
- Create a design strip for design footing
- Again, run the analysis
- Check the flexural reinforcement
Here the maximum reinforcement is 1269.58 mm^2 per meter.
- Check for punching shear
The punching shear is 0.792 N/mm^2 which is less than 1. Hence it is safe.
RESULTS:- Isolated footing has been analyzed by using SAFE software.
2. A column of size 600x600 carrying an unfactored gravity load (DL+LL) of 1175 KN is to be supported on a pile cap, which ultimately transfers the bag to the piles underneath. Piles of 16 meters in length and 500 mm in diameter are to be used. Each bank has a load-carrying capacity of 200 KN. Model, analyze, and design the pile cap on SAFE to evaluate the following:
- Pile group to be used
- Depth of pile cap
- Longitudinal steel on the top and bottom faces in both directions
AIM :- To Model, analyze and design the pile cap on SAFE to evaluate the following:
-Pile group to be used
-Depth of pile cap
-Longitudinal steel on top and bottom face in both direction
Finally to check the following details as per IS 2911 and SP-34.
1) Check for settlement (Unfactored load) [SLS] (Serviceability limit state) (Limited to 50mm).
2) Check for soil pressure (Unfactored load) [SLS] (Serviceability limit state) (should be within safe bearing capacity.
3) Check for two way shear or punching shear (Factored load) [ULS] (Ultimate limit state) which should be less than 1.
4) Checking for reinforcement (Factored) [ULS] (Ultimate limit state). Minimum reinforcement should be 0.12% as per IS-456.
INTRODUCTION:-
Axial load = 1175KN
Length of piles 16m
Diameter of pile = 500mm
Pile capacity = 200KN
No of piles = 1175/200 = 5.875 = Assume 8 piles
Assume grade of concrete is M25
Area of each pile =
E = 5000
Spring constant (k) = EA/L = (25000 x 196349.5)/16000 = 306796.09 N/mm = 306796.09 Kn/m
Take center to center distance between piles= 3 X Pile diameter(500mm) = 1500mm, edge spacing = 500mm
Assume pile cap depth = 1000mm
Length = 4000m and Width = 4000mm
PROCEDURE:-
- Open new model and define coda provisions
Define material property
Assign pile1 to every piles
Assign slab1 to pile cap
Assign stiff1 to column
Click to quick draw area and draw piles of dia 500MM
Now draw the center column of 600MM X 600MM size
Draw the pile cap of size 4000MM X 4000MM
Go to draw tab and then draw points tab
select the central point in column and assign the load
First assign the dead load -1175
Then assign the live load of 1175KN
Define the point spring property
Then assign the point spring property over the each pile
Define the load combinations
Assign the load combination to Ultimate limit state
Draw the design strips
Do a mesh check and set it to 0.1m before running the analysis-
Go to analysis tab and click check model
Run the analysis.
Results:-
1) Check for settlement (Unfactored load) [SLS] (Serviceability limit state) (Limited to 50mm)
Hence all settlements are under satisfactory limit.
2) Check for soil pressure (Unfactored load) [SLS] (Serviceability limit state) (should be within load bearing capacity of pile which is 200KN.
Click to display support reaction-
Support reactions are not exceeded safe bearing capacity of pile which is 200KN
3) Check for two way shear or punching shear (Factored load) [ULS] (Ultimate limit state) which should be less than 1.
All ratio is less than 1.
Hence okay.
4) Checking for reinforcement (Factored) [ULS] (Ultimate limit state). Minimum reinforcement should be 0.12% as per IS-456.
