Model the isolated footing provided in the week 11 challenge on SAFE. Analyse and design it to verify the size, depth and steel provided as per calculations.

AIM

To model an isolated footing provided in the previous challenge and to analyse and design it to verify the size, depth and steel provided according to the calculations.

DATA EXTRACTED

Size of column = 400mm x 400 mm²

Factored load due to the column = 2000kN

Unfactored load = 2000/1.5 = 1333.33kN

Dead load Breakup = 1333.33 / 2 = 666.67kN

Live load Breakup = 1333.33 / 2 = 666.67kN

SBC at the site = 150kN/m²

Concrete grade = M25

Steel grade = Fe415

Max Settlement = 50mm (IS 1904-1986: Table 1)

Subgrade modulus of soil = SBC x FOS /max settlement

150 x 3 / 0.05 = 9000kN/m/m²

Footing thickness = 625mm

Size of footing = 3.2m x 3.2m

PROCEDURE:

Open SAFE

Click on the new model

Use built-in settings

Change the units and codes as per Indian standard, click OK

Choose the Single Footing option from the footing templates and provide the footing details

Go to Define> Material Properties> Add New Property

Add M25 grade concrete and Fe415 grade Steel Rebar

Go to Define> Section Properties> Slab Section> Add New Property

Add Footing Slab and Stiff with the following properties

Go to Define> spring properties> Area spring> Add New Property

Add Soil150 with the following properties

Check the assigned loads

Go to Display> Show Load Assigned> Joints

Go to Define> Load Combination> Add New Combo

Add SLS and ULS as shown below

Go to Design> Concrete Slab/ Beam Design> View/ Revise Preferences

Check design preference

Go to Design> Concrete Slab/ Beam Design> Select design combination

Go to Analyse> Check Model

Run Analysis and Design

Check for Settlement

Go to Display> Show Deformed Shape

Check SLS combo

For isolated footings, maximum displacement OF 50mm is allowed as per IS 1904-1986.

The settlement, in this case, is way less than the said limit. Hence OK.

Check for Soil Pressure

Go to Display> Show Force/ Stress Diagram> Soil Pressure

Check SLS combo

The SBC of soil is 150kN/m/m² > 149. Hence OK.

Punching Shear Check

Go to Display> Show Punching Shear Design

Here it is less than 1. Hence OK.

Longitudinal Reinforcement Requirement

For reinforcement requirements, design strips are needed to be created

Go to Edit> Add/ Edit Design Strips> Add Design Strips Using Grids

Run analysis

Go to Display> Show Slab Design

Maximum Rebar Area for the Strip A

Maximum Rebar Area for the Strip B

A column of size 600x600 carrying an unfactored gravity load (DL+LL) of 1175 kN is to be supported on a pile cap, which ultimately transfers the load to the piles underneath. Piles of 16 metres in length and 500 mm in 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

Note: Participants must refer to IS 2911 (part 2) and SP 34

AIM

To model, analyse and design the pile cap on SAFE to evaluate the Pile group to be used, the Depth of the pile cap, and Longitudinal steel on the top and bottom face in both directions.

GIVEN DATA

Column size: 600 x 600 m²

Unfactored Gravity load (DL+LL): 1175 kN.

Length of the Pile: 16 m.

Diameter of the pile: 500 mm.

Pile Bearing Capacity: 200 kN.

CALCULATIONS

Number of piles

Multiply the total load with the value of 1.1 as this is the multiplier for the soil surcharge pressure

Number of Piles = 1.1 x Total load / Bearing Capacity of single pile

= 1175 x 1.1 / 200 = 6.46

Take the number of piles = 10

Spring Constant

Point spring for the piles = AE/L

Where,

A = Area = π/4 x d² = π/4 x 500² = 196350mm²

E = 5000 √f­_ck = 25000 N/mm²

L = Pile Length = 16000 mm

Spring Constant = AE/L

Spring Constant = 25000 × 196350/ 16000

Spring Constant = 306796.875 N/mm

Dimension of the Pile Cap

Minimum distance between two piles is 2.5 x diameter of pile = 2.5 x 500 = 1250 mm

As the diameter of the pile is given as 500 mm

But for safe designing, we adopt 1300 mm

Now the distance from the edge of the footing to the edge of the pile = 200 mm

Based on the above calculations and the no. of piles, the size of the pile cap = 4.8 x 3.5 m²

PROCEDURE

Open SAFE

Click on the new model

Use built-in settings

Change the units and codes as per Indian standard, click OK

Choose Grid only, click OK

Go to Define> Material Properties> Add New Property

Add M25 grade concrete and Fe500 grade Steel Rebar

Go to Define> Section Properties> Slab Section> Add New Property

Add Pile Cap, Column and Pile500 with the following properties

Go to Define> spring properties> Point spring> Add New Property

Add PSpr1 with the following properties

Draw a Rectangular floor with the property as “Pile cap”

Select “Quick Draw Area around point”

Draw Piles with the property as “Pile500” at each Gridpoint

Select “Quick Draw Area around point”

Draw column with the property as “Column” at the centre

Select all joints of Pile500 and assign point spring

Go to Assign> Joint> Springs

Select the column joint

Go to Assign> Joint Loads> Force

Assign Dead load and Live load

Go to Define> Load Combination> Add New Combo

Add SLS and ULS as shown below

Go to Design> Concrete Slab/ Beam Design> View/ Revise Preferences

Check design preference

Go to Design> Concrete Slab/ Beam Design> Select design combination

Go to Analyse> Check Model

Run Analysis and Design

Check for Settlement

Go to Display> Show Deformed Shape

Check SLS combo

The settlement is 0.764mm is lesser than the permissible value stated by the codes (25mm). Hence OK.

Punching Shear Check

Go to Display> Show Punching Shear Design

Here it is less than 1. Hence OK.

Base Reactions at Piles

Go to Display> Show Force/ Stress Diagrams> Support/ Spring Reactions

The pile capacity is 200kN. Hence OK.

Longitudinal Reinforcement Requirement

For reinforcement requirements, design strips are needed to be created

Go to Draw> Draw design strips

Provide the design strips as shown below

Run analysis

Go to Display> Show Slab Design

Maximum Rebar Area for the Strip A

Maximum Rebar Area for the Strip B

RESULT

The design of the Pile cap foundation and isolated footing using the SAFE software is concluded.