Foundation Design using SAFE

QUESTION:-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.

ANSWER:

AIM:-

1. To model the isolated footing provided in week 11 challenge on SAFE.
2. To Analyze and design it to verify the size, depth and steel provided as per calculations.
3. To model the pile cap on SAFE software .

INTROUDACTION -

• 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

i) Open the SAFE 2020 Software .

ii) Click on New Model .

Step:- 2

1. Once you click on New model
2. A following Dialog box will open .
3. Display Units- Metric SI
4. Select the Region Indian
5. Select the Concrete Design Code - IS 456-200
6. Click on Okay

Step -3

1. Once you click Okay
2. Model Quick Template box will open

1. Click on Single Footing - As we are designing Isolated Footing .

Step :-4

1. Enter the dimension as per calculation we have done in Week 11 challenge .
2. As we have got Footing Size = 4m x 4m
3. Enter the Direction Along X and Y direction as = 2m
4. Footing Slab Thicknes = 800 mm
5. For Modulus Subgrade =

we know the formula ,

Modulus of Subgrade = `(FOS X SBC )/ ( Allowab l e Set tl ement )`

i) Assume FOS = 3 as per IS 13290 `

ii) SBC = 150 given

iii) Allowable Settlement ( For Isolated footing ) = 0.025 m ( AS per Is 1904 )

= `(3 X 150 )/0.025`

= 9000 `(Kn )/(m^3)`

vi) Now we have to add the Load

a) For Dead load and Live load - = (Total Unfactored load ) / 2

= `(1333.3 / 2)`

= 666.65 Kn

vii) Load Size = In that we have to enter Column Size = 400 mm

viii) Once you enter all the details Click in Okay .

Step:- 5

1. Once you click okay
2. You will see the geometry is created in Model space as follows

Step :-6

1. Now we have to add Material Properties
2. Click on Define - Material Properties
3. Click on Add new materials

1. Once you click Add new material add the following parameters
2. Material Type - Concrete
3. Grade - M25
4. Click on okay .

1. Simialarly add the Rebar Properties .
2. Click on Okay

i) Properties has been Define

Step:- 7

1. Now we have to define Slab properties
2. As we already define slab properties in Grid Section

1. Click on Modify properties - Add
2. Select the Slab Material - M25
3. Assign the thickness = 800 mm

iv)Similarly Modify the Stiff slab

Step:- 8

1. Now we have to assign Soil Properties
2. Define - Soil Properties
3. 
4. 

5. Right Click on slab you will see the Soil Properties has been assigned .

Step:-9

i) Now we have to check if loads are defined are not .

Step:10

1. Define Load pattern.

Step :-11

1. Now we have to define the Load Combinations
2. For that Define - Load Combinations - Either you can Add New combo or you can Add default Combo

1. 
2. 

Step:12

1. Check design preference (min cover 50mm)

Step 13

1. Now we can Run the model
2. Click on Run Analysis
3. Save the File
4. Now you will see the Displacements
5. Click On Defotmed Shape - Select Combination as - comb1 and see the displacement

1. The displacement is for -11.114mm consider aproximately-12mm
2. As displacement is -12 mm which is less than 25 mm ............Safe

2) Check for Bearing Pressure

1. For that Click On Display - Soil Pressure - Select Combination as - comb2
2. 143.30 < 150 Kn/m2..............................Safe

3) Check of Punching Shear

1. Click on Display - Punching Shear
2. As we can see that Punching shear is less than 1
3. 0.697 <1.....................................Safe

Step 14

1. Now we have to add the Design srips
2. Click on Edit - Add / Edit Design Strips
3. Add the Strips in both X and Y direction

1. Strips has assigned
2. Command Cntrl + W to see the set display option
3. In that tick on Strip widtht to see the Strip width

Step:15

• Ultimate Bending moment & shear force check.
• 
• 

Step:16

• Flexural Reinforcement design for Footing slab.

• 

RESULT:

• The Isolated footing was designed and analyzed using SAFE software successfully.
• Safe bearing capacity under service load is 143.5KN/m2, Hence OK.
• Two-way shear is 0.679, Hence OK.
• Ultimate Bending moment & shear force check done successfully.
• Flexural Reinforcement design for Footing slab done successfully.

QUESTION:-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

Note: Participants must refer to IS 2911 (part 2) and SP 34 for 2nd challenge

ANSWER

AIM:

• To Model Analysis 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.

Procedure:

Given.

• Column size = 600 x 600 mm
• Unfactored load = 1175 KN
• Pile length = 16m
• Pile diameter = 500 mm
• Load carrying capacity = 200 KN.

Calculations.

• Number of pilers = 1175 / 200 = 5.6 = 6
• Spring constant = ExA / L

Where, E = 25000 N/mm²

A = (π4)">(π/4)(500)² = 196375 mm²

L = 16000 mm

Spring constant =25000 x 196375 / 16000=306835 N/mm or 306835 KN/m

Edge spacing is taken as 200 or 300 mm.

i) 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

1. Open the SAFE 2020 Software .

1. Click on New Model

Step :-3

1. Once you click on New model.
2. A following Dialog box will open .
3. Display Units- Metric SI
4. Select the Region Indian
5. Select the Concrete Design Code - IS 456-200
6. Click on Okay

Step :-4

1. Once you click Okay
2. Model Quick Template box will open .
3. Click on grid only.
4. Enter No of grids in X and Y = 2
5. Enter spacing in X = 3.1 m
6. Enter Spacing in Y = 1.85 m

Step:- 5

1. Check design preference (min cover 50mm)
2. 50mm each was provided as cover at top and bottom and bar size was defined as 16mm.

STEP-6

1. Now we have to assign the
2. Material proprties Define - Material Properties
3. Click on Add new materials

1. Once you click Add new material add the following parameters
2. Material Type - Concrete
3. Grade - M25

1. Click on okay .

1. Simialarly add the Rebar Properties
2. 
3. Click on Okay

   

4. Properties has been Define

5. 

Step :-7

1. Now we have to define Slab properties
2. In pile cap we have to define 3 slabs properties
3. Footing
4. For Column
5. For Pile cap

I: Footing

II. COLUMN

3: PILE CAP

Step :-8

1. Once slab proerties are defined
2. Now we have to start the modeling
3. Select Quick draw slab options
4. Draw the slab select Footing as property

Step :-9

1. Now we have to mark the position of Pile cap .
2. For that we have to add the points .
3. Draw - Draw reference points .

Step:10

• Add piles at the point
• Modify the edge distance to 0.3m
• 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 11

1. Now we have to add Springs to the pile because it behaves like a spring
2. Click on Assign – Support Data – point springs
3. Spring Constant from above calculation is taken as
4. Add Spring Constant - 306795 Kn/m
5. Select - Compression Only

1. Click on Okay
2. Spring Constant has been assigned .

Step 12

1. Now we have to add the loads
2. Go to Assign - Joint loads - point force
3. Assign 587.5 Kn dead load and 587.5 Kn live load

Step :-13

1. Now we have to add load combinations
2. Define - Load combination
3. Define the load combination as follows.

STEP-14

1. Now Run the model
2. Click on Run Analysis

1. We found that Displacement is less than allowable settlement

i.e 0.8 < 25mm is the safe ok.

2) Check for Punching Shear -

1. Click on Display - Punching Shear
2. As we can see that Punching shear is less than 1
3. i.e 0.49 <1.....................................Safe

1. 
2. 3) Joint Reaction :
3. As all the reaction forces are according to the limit, Its safe

Step 15

1. Now we have to add the Design srips
2. Click on Edit - Add / Edit Design Strips
3. Add the Strips in both X and Y direction
4. 

1. Strips has assigned
2. Command Cntrl + W to see the set display option
3. In that tick on Strip widtht to see the Strip width

1. Run the model
2. Click on slab design
3. Select the layer A to see the reinforcement

iv.Similarly in Layer B

RESULT -

• 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
•