Foundation Design using SAFE
1.
Aim:
To Model the isolated footing provided in week 11 challenge on SAFE and to 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 dialogue box will open and name the 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.
Subgrade Modulas = FOS*SBC / Max. Settlement
FOS for soil is =3
S.B.C = 150Kn/m.sq
settelement for isolated footing = 25mm
subgrade modulus = 18000 KNm2
The compression axial load for load combination (1.5DL + 1.5LL) is 2000KN.
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.
- New dialog box will appear
- Select Add new Material
- Now select Section Properties under Define Tab.
- Select Slab Sections.
- Select Add new properties in Slab Properties.
- Define properties for footing and Mat
- Define Footing for Stiff1
- Now define Load Patterrns
- Define Soil Subgrade Modulas / Area spring Property Data
- Assign Point Load as per below
- Define combinations as required
- Check Design Preference as concrete slab/ bream design
- Analyse the model using analyse option then click on check model the modelled structure is verified.
- 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 designed the isolated footing provided in week 11 challenge on SAFE.
2.
Aim:
To design a pile type design of footing with the given data.
- 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
= 25000Nmm2
Area A= (∏4)⋅(500)2
A= (∏4)⋅(500)2= (∏4)⋅(500)2
=196349mm2
Spring length, L = 16000mm
= 25000 x 196349/16000
= 306795 Nmm
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
- Display Units-Metric SI, Select the Region Indian
- Select the Concrete Design Code - IS 456-200
- Click on Ok
- Once you click Ok and Model Quick Template box will be displayed
- Click on grid only
- Enter No of grids in X and Y = 2, Enter spacing in X=3.1m and Enter Spacing in Y = 1.85 m
- Now we have to assign the Material proprties
- Define - Material Properties and Click on Add new materials
- Once you click Add new material add the following parameters
- Material Type-Concrete - Grade - M25 and then Click ok
- 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, Pile cap
- Once slab proerties are defined,Now we have to start the modeling
- Select Quick draw slab options and 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 and Add Spring Constant - 306795 kN/m. Select-Compression
- Spring Constant has been assigned, Now we have to add the loads
- Go to Assign-Joint loads - point force and Assign 587.5 KN dead load and 587.5 KN live load
- Now add load combinations, Define - Load combination
- Now Run the model and Click on Run Analysis
- We found that Displacement is less than allowable settlement.
- Check for Punching Shear
- Click on Display - Punching Shear, As we can see that Punching shear is less than 1.
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 Ctrl+W to see the set display option
- In that tick on Strip width.
- Run the model and Click on slab design
- Select the layer A to see the reinforcement
Result:
After analysis the results were found to be under the standards as per IS codes. Hence, the pile foundation design has been done sucessfully.