Foundation Design using SAFE
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
Aim
- To model the isolated footing provided in week 11 challenge on SAFE.
- To Analyze and design it to verify the size, depth and steel provided as per calculations.
- To model the pile cap on SAFE software.
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)
- Open the SAFE 2020 Software.
- Click on New Model
Step 2)
- Once you click on New model
- A following Dialog box will open.
- Display Units-Metric SI
- Select the Region Indian
- Select the Concrete Design Code - IS 456-200
- Click on Okay
Step 3)
- Once you click Okay
- Model Quick Template box will open
- Click on Single Footing - As we are designing Isolated Footing.
Step 4)
- Enter the dimension as per calculation we have done in Week 11 challenge.
- As we have got Footing Size = 3.8mx 3.8m
- Enter the Direction Along X and Y direction as = 1.9 m
- Footing Slab Thicknes = 800 mm
- For Modulus Subgrade
- we know the formula,
- Modulus of Subgrade = (FOS X SBC)/ (Allowable Settlement)
- Assume FOS = 3 as per IS 13290
- SBC = 150 given
- Allowable Settlement (For Isolated footing)=0.025 m (AS per Is 1904)
= (3 X 150 )/0.025
= 9000 (Kn)/(m^3)
- Now we have to add the Load
- For Dead load and Live load
- = (Total Unfactored load)/2
- = (1333.3/2)
- = 666.65 Kn
- Load Size = In that we have to enter Column Size = 400 mm
- Once you enter all the details Click in Okay
Step 5)
- Once you click ok
- You will see the geometry is created in model spaces as follows
Step 6)
- Now we have to add material properties
- Click on define - Materials Properties
- Click on add new materials
- Once you click Add new material add the following parameters
- Material Type - Concrete
- Grade - M25
- Click on ok
- Similarly add the rebar properties
- Click on ok
- Properties has been define
Step7)
- Now we have to define slab properties
- As we already define slab properties in grid section
- Click on Modify properties
- Select the slab Materials M-25
- Assign the thickness - 800mm
- Similarly Modify the stiff slab
Step 8)
- Now we have to assign soil properties
- Define soil properties
- Right click on slab you will see the soil properties has been assigned
Step 9)
Now we have to check if loads are defined or not
Step 10)
- Now we have to define the Load Combinations
- For that Define - Load Combinations - Either you can Add New combo or you can Add default Combo
Step 11)
- Now we can run the model
- Click on Run Analysis
- Save the File
- Now you will see the Displacements
- Click On Defotmed Shape - Select Combination as - SLS and see the displacement
- As displacement is -12 mm which is less than 25 mm...Safe
Check for Bearing Pressure
- For that Click On Display - Soil Pressure - Select Combination as - ULS
- As we can see that Bearing pressure is more than SBC
- i.e 169.22kn/m2 > 150 kN/m2.............Unsafe
- We have to Increase the area to see if we can reduce the bearing pressure below the SBC
- Now provide the area as 4m x 4m
- Here we can see that after increasing the area Bearing pressure is reduced
- i.o-143.30 150 kn/m2..
Check of Punching Shear
- Click on Display - Punching Shear
- As we can see that Punching shear is less than 1
- i.e 0.39 <1......... Safe
Step 12)
- Now we have to add the Design srips
- Click on Edit - Add/Edit Design Strips
- Add the Strips in both X and Y direction
- Strips has assigned
- Command Cntrl + W to see the set display option
- In that tick on Strip widtht to see the Strip width
Step 13)
- Now again Run the model
- Click on Slab Design
- Select Layer A
- Similarly Select layer B
Results
- Isolated Footing is Designed for Square column of size 400mm x 400 mm
- We have to provide Footing Size as 4m x 4m
- Bearing soil pressure is checked and found to be safe
- Punching shear ratio is check and found to be safe
Q.2)
Aim - To Model, analyse and design the pile cap on SAFE
Procedure -
Step 1)
Given data
- Column Size
- Unfactored load
- Pile Length
- Pile diameter
- Load carrying capacity
- Calculations:
- Number of pilers
- Spring Constant EXA/L
- Where E is 25000N/mm2
- Area A /4 x 500² = 196349 mm²
- Pile length, L 16000mm
- Spring Constant EXA/L = 25000 x 196349/16000 = 3069795 N/mm
- Edge spacing is taken as 200mm or 300mm
As per IS 2911 (part 2) the spacing between the piles is taken as 2.5 times the diameter of pile ii) The edge spacing we have assume it as 300 mm.
Step 2)
- Open the SAFE 2020 Software.
- Click on New Model
Step 3)
- Once you click on New model
- A following Dialog box will open.
- Display Units-Metric SI
- Select the Region Indian
- Select the Concrete Design Code - IS 456-200
- Click on Okay
Step 4)
- Once you click Okay
- Model Quick Template box will open
- Click on grid only
- Enter No of grids in X and Y = 2
- Enter spacing in X=3.1m
- Enter Spacing in Y = 1.85 m
Step 5)
- Now we have to assign the Material proprties
- Define - Material Properties
- Click on Add new materials
- Once you click Add new material add the following parameters
- Material Type-Concrete
- Grade - M25
- Click on okay.
- Similarly add the Rebar Properties
- Click on OK
Step 6)
- Now we have to define Slab properties
- In pile cap we have to define 3 slabs properties
- Footing
- For Column
- For Pile cap
Step 7)
- Once slab proerties are defined
- Now we have to start the modeling
- Select Quick draw slab options
- Draw the slab select Footing as property
Step 8)
- Now we have to mark the position of Pile cap
- For that we have to add the points
- Draw - Draw reference points
Stop 9)
- Now we have to add column slab
- Click on Quick draw area / points
- Select the property
- and draw the columns
- Similarly draw the pile caps
Step 10)
- Now we have to add Springs to the pile because it behaves like a spring
- Click on Assign - Support Data - point springs
- Spring Constant from above calculation is taken as
- Add Spring Constant - 306795 kn/m
- Select-Compression Only
- Click on ok
- Spring Constant has been assigned
Step 11)
- Now we have to add the loads
- Go to Assign-Joint loads - point force
- Assign 587.5 Kn dead load and 587.5 Kn live load
Step 12)
- Now we have to add load combinations
- Define - Load combination
- Define the load combination as follows
Step 13)
- Now Run the model
- Click on Run Analysis
- We found that Displacement is less than allowable settlement
i.e 0.8< 25mm
Check for Punching Shear
Click on Display - Punching Shear
As we can see that Punching shear is less than 1
Le 0.49 <1...........Safe
Joint Reaction
- As all the reaction forces are according to the limit, Its safe
Step 14)
- Now we have to add the Design srips
- Click on Edit - Add/Edit Design Strips
- Add the strips in both X and Y direction
- Strips has assigned
- Command Cntrl + W to see the set display option
- In that tick on Strip widtht to see the Strip width
Step 15)
- Run the model
- Click on slab design
- Select the layer A to see the reinforcement
-
Similarly in Layer B
Results
- Pile Cap is Designed for Square column of size 600mm x 600 mm
- We have to provide pile cap Size as 3.1m x 1.85m
- Bearing soil pressure is checked and found to be safe
- Punching shear ratio is check and found to be safe