Foundation Design using SAFE
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.
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:-
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/m2
The compression axial load for load combination (1.5DL + 1.5LL) is 2000KN.
Unactored Load = 2000/1.5
= 1333.33 KN
Dead load Breakup =1333.33/2
= 666.66 KN
Live load Breakup =1333.33/2
= 666.66 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.
Define the materials of concrete M25 Grade and longitudinal reinforcement as 500 Grade.
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.
Now define Load Patterrns as follows;
Define Soil Subgrade Modulas / Area spring Property Data.
Assign Point Load.
Define combinations are as below;
Check Design Preferences.
Analyse the model using analyse option then click on check model the modelled structure is verified without errors and warnings.
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 = 1175/200 = 5.8
Therefore no. of pillars = 6
spring constant = E X A/L
= 25000N/Square mm
Area A= (∏/4)(500)2
=196349 Square mm
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 <1...........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 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