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.

ANS:

Data required:

Unfactored load=2000/1.5=1333.3KN

Dead load breakup=1333.3/2=666.7KN

Live load breakup=1333.3/2=666.7KN

Subgrade modulus for soil=safe bearing capacity x factor to ultimate/maximum settlement=150x3/0.05=k=9000KN/m3

Rebar yeild strength(fy)=500N/mm2

Rebar ultimate strngth(fu)=say575N/mm2

Elastic modulus of M25 concret = 25000N/mm2

Size of column = 400 mm * 400 mm

Safe bearing capacity of soil = 150 KN/m2

Assume M25 grade concrete and Fe 500 HYSD bars

Settlement = 50 mm

Take FOS = 3

Sub- grade modulus = FOS* Safe bearing capacity/settlement = 150*3/0.05 = 9000 KN/m^3

• Open SAFE software
• Create a new model
• Edit the settings

• Define materials
• Add new material property for M25 concrete
• Add new material property for Fe 500 HYSD bar

• Define slab property data

• Assign the area spring property

• Assign the load assignment force

• Define load combinations

• Check the model

• Run the analysis

Results:

• Safe bearing capacity under service load

• Settltment under service load

• Two way shear check(punching shear)

• Ultimate pending moment

• flexural reinforcement design for footing slab

Again unlock the model

Create design strip for design footing

Again run the analysis

Check the flexural reinforcement

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

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

ANS:

Data required:

Unfactored load=1175KN

Dead load breakup=1175/2=587.5KN

Live load breakup=1175/2=587.5KN

Point spring of pile=AxE/L=196349x25000/16000=306796KN/m

k for SAFEanalysis=306.8kn/m

Rebar yield strength(Fy)=500N/mm2

Rebar ultimate strength(Fu)=say 575 N/mm2

Elastic modulus of M25 concrete=25000N/mm2

Number of piles required=Unfactored load with self weight addition/individual pile capacity=1175x1.1/200=6.5

consider 8 piles for symmetricplacement of piles under pile cap

Take center to center distance between piles=3 x pile diameter(1500mm)

Edge distance from pile center=1 x pile diameter(500)

Assume pile cap depth=500mm

• Open SAFE software
• Create new model template

• Define material property

• Define slab property type

• Click to quick draw area and draw piles of dia 500MM
• Draw the pile cap of size 4000MM X 4000MM

• Go to draw tab and then draw points tab

• select the central point in column and assign the load
• First assign the dead load -1175
• Then assign the live load of 1175KN

• Define the point spring property

• Then assign the point spring property over the each pile

• Define the load combinations

• Assign the load combination to Ultimate limit state

• Draw the design strips

• Do a mesh check and set it to 0.1m before running the analysis-

• Go to analysis tab and click check model

• Individual pile capacity under service load

• Settlement under srvice load

• Two way shear check(punching shear)

All ratio is less than 1.

Hence okay.

• Flexural reinforcement design for footing slab