Foundation Design using SAFE

1.

Aim:

• To simulate the isolated footing offered in the SAFE challenge for week 11
• Verify the size, depth, and steel offered based on calculations by analyzing and designing the structure. should use SAFE software to simulate the pile cap.

Introduction

The finest tool for planning concrete slabs and foundations is CSI SAFE (Slab Analysis by the Finite Element Method).
With strong capabilities like sketching, analysis, design, and details, Secure makes it simple for engineers to create buildings that are safe.
With the help of user-friendly drawing tools or by importing model layouts from AutoCAD or loading conditions from other programs like CSI ETABS and CSI SAP2000, setting up models is done quickly and effectively.

Procedure:

Step-1:

• Open the SAFE 2020 Software.
• Click on New Model

step-2:

• Once you click on the New Model
• The 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 the 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 Thickness = 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 have been define

Step-7

• 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

Step9:

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 Deformed 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 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 strips
• Click on Edit - Add/Edit Design Strips
• Add the Strips in both X and Y direction

• Strips has assigned
• Command Ctrl + 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:

• Square column with dimensions of 400 mm x 400 mm is designed for isolated footing.
• We must offer a footing size is 4m x 4m
• The soil pressure has been examined and confirmed to be safe.
• A check of the punching shear ratio reveals that it is secure.

Q.2)

Aim - To Model, analyze 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 to assume it as 300 mm.

Step-2

• Open the SAFE 2020 Software.
• Click on New Model

Step 3)

• Once you click on the New Model
• The 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 a column slab
• Click on Quickdraw 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 the 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 strips
• Click on Edit - Add/Edit Design Strips
• Add the strips in both X and Y direction

• Strips as assigned
• Command Ctrl + W to see the set display option
• In that tick on Strip width 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:

• We must give a pile cap dimension of 3.1 m x 1.85 m for a square column that is 600 mm x 600 mm in size.
• A safety check of the bearing soil pressure has been performed.
• A check of the punching shear ratio reveals that it is secure.