Foundation Design using SAFE
Q.1. Model the isolated footing provided in week 11 challenge on SAFE. Analyze and design it to verify the size, depth and steel provided as per calculations.
Ans=
AIM:- Model the isolated footing provided in week 11 challenge on SAFE. Analyze and design it to verify the size, depth and steel provided as per calculations.
INTRODUCTION:-
CSI SAFE (Slab Analysis by the Finite Element Method) is the best tool for designing concrete slabs and foundations.
SAFE provide easiness to engineer towards the safe design of structures with powerful tools like draw, analyze, design and detailing etc.
Laying out models is quick and efficient way with the user-friendly drawing tools, or user can import model layouts from AutoCAD or loading conditions
from other software’s like CSI ETABS and CSI SAP2000.
PROCEDURE:-
Step-1:-
Column size 400x400mm
Axial load = 2000/1.5 = 1333.33
Take DL = 1188.96KN , LL= 144.37KN
Soil bearing capacity = 150KN/m2
Area = 3.6x3.6m = 12.96m2
Grade of concrete is M25
Lets assume thickness of footing is 450mm
Soil subgrade modulus = (Soil bearing capacity x FOS) / Settlement
= (150x3)/0.05
= 9000 KN/m3
The compression axial load for the axial load combination of (1.5DL + 1.5LL) is 2000 KN.
Unfactored load = (2000/1.5) = 1333.33 KN
Dead load breakup = (1333.33/2) = 666.7 KN
Live load breakup = (1333.33/2) = 666.7 KN
Rebar yield strength (fy) = 500 N/mm^2
Rebar ultimate strength (fu) = 575 N/mm^2
Elastic modulus of M25 concrete = 5000 X fck^0.5 = 25000 N/mm^2
Step-2:-
Open the SAFE Application and select New Model followed by Input Settings, Units was selected as Metric SI and Code IS 456-2000 and steel design code as BS-5950.
Then select sigle footing system and fill the all required details
Then quick draw slab around point
Again do the step to create column area
Add design strip
Define area spring property and assign it to the central point
Assign the load combination to Ultimate limit state
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 safe bearing capacity which is 150 KN/m^2
Click to display support reaction-
Hence, all support reactions are 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.
So we will provide 20mm dia bars @ 215mm spacing (Max Limit is 300mm)
Q.2. A column of size 600x600 carrying an unfactored gravity load (DL+LL) of 1175 KN is to be supported on pile cap, which ultimately transfers load to the piles underneath. Piles of 16 metres length and 500 mm diameter are to be used. Each pile has a load carrying capacity of 200 KN. Model, analyse 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 directions
Ans=
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 = `pi/4(d^2)` = `pi/4(500^2)` = 196349.5mm2
E = 5000`sqrtfck` = 25000
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.
