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.
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 directionsDesign using 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.
AIM:- 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.
PROCEDURE:
• Open the SAFE software. Click on New model to create new model Now
- New dialogue box will open named model
Initialization.
- Select Units and Codes as per your project.
- we have selected Indian codes and units as Metric SI.
- Now select the uniform grid spacing.
- Select Single Footing. In single footing, Insert the dead loads and live loads.
- Calculations are as per below showing;
Subgrade Modulas = FOS*SBC / Max. Settlement
FOS for soil is =3
S.B.C=150kn/m.sq
settelement for isolated footing = 25mm
hence, subgrade modulus = 18000 KN/m⊃2;
The compression axial load for load combination (1.5DL + 1.5LL) is 2000KN.
Unactored Load = 2000/1.5
= 1333.3 KN
Dead load Breakup = 1333.3/ 2
= 666.5 KN
Live load Breakup = 1333.3/ 2
= 666.5 KN
So,
Footing Thickness is 800mm.
- So single Footing is successfully added.
Select Material properties under define tab.
- New dialogue box will appear named Define Materials.
- Select Add new Material from the window.
- Now select Section Properties under Define Tab.
- Select Slab Sections.
• Select Add new properties in Slab Properties.
- Define properties for footing.
- Define properties for Mat.
- Define Footing for Stiff.
- Assign Point Load.
- Now define Load Patterrns as follows;
- Define Soil Subgrade Modulas / Area spring Property Data.
- Assign Point Load.
- Define combinations are as below;
- Analyse the model using analyse option then click on check model the modelled structure is verified without errors and warnings.
- Check Design Preferences.
- The model is analyzed Successfully.
Safe Bearing Capacity :-
Deformed Shapes :
Two way Shear Check :-
Punching shear seem to be greater than 1 so we have to increase the depth of footing or any other parameter
Bending Moment :-
Shear Force :-
Flexural Reinfoecement Design foe Footing Slab :-
RESULT:
• We have Modeled the isolated footing provided in week 11 challenge on SAFE.
AIM:- 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
Given;
• Column size=600x600mm
• Unfactored load = 1175 kn
• Pile length =16m
• Pile diameter= 500mm
• Load carrying capacity 200kn
Calculations:
Number of piles 1175/2005.8
Therefore no. of pillars = 6
spring constant EX A/L
= 25000 N/ mm⊃2;
Area A =3.14 (500)2 = 196349 mm2
Spring length, L= 16000mm.
= 25000 x 196349/16000
= 306795 N/mm
Edge spacing taken as 200 mm of 300 mm
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.
PROCEDURE:
• Open the SAFE Software.
• Click on New Model
- 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
- 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
- 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.
- Now we have to define Slab properties
- In pile cap we have to define 3 slabs properties
- Footing
- For Column
- For Pile cap
- Once slab proerties are defined
- Now we have to start the modeling
- Select Quick draw slab options
- Draw the slab select Footing as property
- Now we have to mark the position of Pile cap
- For that we have to add the points
- Draw - Draw reference points
- 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
- Now we have to add Springs to the pile because it behaves like a spring
- Click on Define - Spring properties-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
- 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
Now we have to add load combinations
• Define - Load combination
• Define the load combination as follows.
- 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 Safe
Joint Reaction:
• As all the reaction forces are according to the limit, Its safe
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
- Run the model
- Click on slab design
- Select the layer A to see the reinforcement
Similarly layer at 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