Foundation Design using SAFE

QUESTIONS :

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 meters 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

ANSWERS 1: 

AIM:  Design of the isolated footing provided in week 11 challenge using SAFE V22.

INTRODUCTION:

CSI SAFE (Slab Analysis by the Finite Element method) is the best tool for designing concrete slabs and foundations.

SAFE provides easiness to engineer towards the safe design of structures with powerful tools like draw, analyze, design and detailing, etc.

Laying out models is the quick and efficient way with the user-friendly drawing tools or users can import models from AutoCAD or loading conditions from the other software like CSI ETABS and CSI SAP2022.

PROCEDURE:

• Open the SAFE Application

• Select New Model

• Select the Units and Design codes.

• Single Footing was selected next

Subgrade Modulus =  F.O.S×S.B.C/(SETTELEMENT)

Where, FOS for soil = 3

S.B.C = 150 KN/m^2

Settlement for Isolated footing = 25 mm

Hence ; Subgrade modulus = 18000 KN/m/m^2

The compression axial load for the load combination (1.5DL + 1.5LL) is 2000KN. 

Unfactored load = 20001.520001.5 = 1333.6 KN

Live Load = 1333.621333.62 = 666.5 KN

Dead load = 1333.621333.62 = 666.5 KN 

Footing thickness 600mm

Column Load Size  = 400 x 400 mm

Give data for the footings as shown in figure below.

Define Materials

• Go to the Define Tab and select Material property.
• Add M25 Concrete

• Add new property as Rebar HYSD Grade 500

Define Section Property 

• Next, Define Section Property
• Go to slab property.
• Add Mat > Thick shell < Mat type < 600 mm thickness

• Add next STIFF property.
• Change the type as Stiff.

Now right click on Slab/floor and change the Section Property as Mat.

Now Right Click on Column and change the Section Property as STIFF.

Check the Forces Applied by Right click on Column joints.

• Apply Live load of 2KN/m on the Footing/Slab
• Select the slab and assign the uniform load of 2 KN.

Check the Load Patterns

• Go to Define Tab then Spring properties.
• Click on Area Spring and change the name of (Aspr) as Soil.

Define Load Combination

• Go to Define Tab and select Load combination
• Add New Combo as SLS

• Add new combo as ULS.

• Click on the Icon (Concrete slab/Beam Design) and check the preferences like cover, bar dia. etc.

• Again, click on the Icon (Concrete slab/Beam Design) and go the Design Load Combination.
• Add the Combination.

Add Design Strips

Go to the edit tab and select Add/Edit Design Strips.

Or Add Manually Design Strips from the Draw Design Strips Tool.

Check the Model and Analyse.

Check the Displacements :

Max Displacement = 0 @(-2,-2,3)

Check the Soil Pressure :

Max Soil Pressure = -132.387 @(-2,2,3) in SLS condition.

Checking Punching Shear

Here Punching shear is 0.696 < 1, hence ok.

Check Strip Slab Design.

RESULT:

 Hence, The Isolated Footing was designed and analyzed using SAFE successfully. The results of each drawing drawn in SAFE are attached.

ANSWERS 2: 

AIM: 

• To model analyze 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

INTRODUCTION :

• Pile foundations are deep foundations.
• They are formed by long, slender, columnar elements typically made from steel or reinforced concrete, or sometimes timber.
• A foundation is described as 'piled' when its depth is more than three times its breadth.

PROCEDURE:

Given Data:

Column Size:- 600X600 

Unfactored load:- 1175KN

Pile length:- 16m

Pile Diameter:- 500mm

Load carrying Capacity:- 200KN

Calculations:

Number of piles:- (1175×1.1)/200 =6.4

But we take 8 piles for the symmetric load distribution.

Point Spring Constant:- (A×E)/L

where E is:- 5000*Fck^0.5

Area (A) is:- π/4*d^2 =196250 mm^2

Pile Length, L is:- 16000mm

Spring Constant:- 306640 KN/m (Using point spring constant formula)

Edge spacing is taken as 300mm.

Open the SAFE Application

• Select New Model
• Followed by input settings.
• Units were selected as Metric and code IS:456-2000.

• Add the grid in X and Y ordinates.

Define Material Property

• Go to Define Tab and select Material Property.
• Add New Property.
• M25 grade of concrete
• Add new property as rebar Fe500

Define Section Properties 

• Go to the Define Tab and Select Section Property
• Add New Section Property as Pile (As Mat material), Pile_Cap (As Mat material) and Column (as STIFF material)

Draw the Floor/Slabs 

• Go to the Slab/Floor tool and select property as slab as Pile_Cap.
• Drag diagonally and draw slab/floor.

Draw points 

• Go to the Draw tab and select Draw Joints Objects.
• Now the Draw the Joints where i want.
• Now Draw the Pile
• Go to the Quick draw area around point Tool.
• Select Shape as Circular and Property as Pile.
• Draw piles on all the joints except centre joints.
• Now Draw Column in centre.
• Again, select quick draw area around point and shape as rectangle and Property name as Column.

Define Point Spring 

• Go to Define Property and select Spring Property.
• Click on Point Spring Property and change the Data

Assign the Point Spring.

• Select the all-Piles joints and go to assign and select Joint Assignment.
• Select point Spring to assign it.

Assign Point load:

• Select middle Joints of Column and apply Load by assigning Tab > Joints Load
• Next, Add Dead and live load of 587.5KN

Define Load Combination

Add Design Strips:

•  Go to edit Tab and select Add Design Strips Along X-A and Y-B.

Add Design Load Combination.

Check the model & run the Analysis 

Results :

• Max displacement =0@ (0,0,3)
• Min displacement =-0.414 @ (1.75,1.75,3)

• Punching shear is less than 1 . Hence OK

• Max RXN (unfactored dead +live load)= 183.12 KN

PILE DESIGN

• Reinforcement detailing 

Max in X-A = 952.77 mm^2

Max in Y-B = 1162.33 mm^2

Hence, Completed the design of the pile cap foundation using SAFE Software.