Foundation Design using SAFE

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.
• 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 :

Data Required for SAFE analysis and design :

Unfactored load = 2000/1.5 = 1333.3 KN.

Dead load break up = (Total Unfactored load)/2

=1333.3/2= 666.7 KN.

Live load break up = (Total Unfactored load)/2

=1333.3/2=666.7 KN.

Subgrade module for soil= (Safe bearing capacity x Factor to ultimate)/maximum settlement.

=150x3/0.05=k=9000 kn/m3.

Rebar Yeild strength ( Fy)=500 N/MM2.

Rebar ultimate strength (Fu)= 575 N/MM2 (SAY).

Elastic modules of M25 concrete = 25000 N/mm2.

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

Once you enter all the details Click in Okay

Step 1)

• Open the SAFE 2016 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 footing Okay.
• Model Quick Template box will open.
• Click on Single Footing - As we are designing Isolated Footing.

Step 4)

• Once you click ok
• You will see the geometry is created in model spaces as follows

Step 5)

• Now we have to add the materials 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

Step6)

• 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 7)

• Now we have to assign soil properties
• Define soil properties

• Right click on slab you will see the soil properties has been assigned

Step 8)

• Now we have to check if loads are defined or not

Step 9)

• 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 10)

• 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 11)

• 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 12)

• Now again Run the model
• Click on Slab Design
• Select Layer A

• Similarly Select layer B

RESULTS :

Model the isolated footing to Analyze and design it to verify the size, depth and steel provided and to model the pile cap is successfully completed by using the SAFE software2016.

Q2). 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

AIM :

To Model,analyses and design the pile cap on SAFE.

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)

Data Required for SAFE analysis and design :

Unfactored load = 1175 KN.

Dead load break up = (Unfactored load/2)

=1175/2= 587.5 KN.

Live load break up = (Unfactored load/2)

=1175/2=587.5 KN.

point spring of pile = A X E / L

=(196349 X 25000 ) / 16000=306796 KN/m.

K for SAFE analysis =306.8 kn/mm

Rebar Yeild strength ( Fy)=500 N/MM2.

Rebar ultimate strength (Fu)= 575 N/MM2 (SAY).

Elastic modules of M25 concrete = 25000 N/mm2.

Data Required for SAFE analysis and design :

No of piles required = unfactored load with self weight addition / individual pile capacity.

=(1175 x 1.1) / 200 =6.5

consider 8 piles for symentrical placement of piles under pile cap.

Take centre to centre distance between piles = 3 xpile diameter (1500mm)

Edge distance from pile centre = 1 x pile diameter (500mm)

Assumue pile cap depth =500mm.

Open new project with IS456:200 recommendation

Step 2)

• Open the SAFE 2016 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=4m
• Enter Spacing in Y = 4m

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 - 613595 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

RESULTS :

To Model,analyses and design the pile cap is sussessfully completed. The Pile Cap is Designed for Square column of size 600mm x 600 mm the Bearing soil pressure is checked and found to be safe and Punching shear ratio is check and found to be safe by using the SAFE Software2016.