Foundation Design using SAFE

question 1

AIM - Model the isolated footing, Analyze and design it to verify the size, depth and steel provided as per calculations.

• Square rooting for a column size of 400x400
• compress on axial load for the load combination of 1.5 DL+ 1.5 LL is 2000 KN

• The safe Soil bearing capacity is 150 KN/m2 at a depth of 2 metres below E.G.L

  Assume 25 concrete grade

Data required for SAFE analysis & Design

• Unfactored load = 2000/1.5= 1333.3 KN
• Dead load breakup = 1333.3/2=666.7 kN Live load breakup = 1333.3/2=666.7 kN
• Subgrade modulus for soil = Safe bearing capacity x factor to Ultimate / maximum settlement 150 x 3/0.05= k = 9000 kN/m3
• Rebar yield strength (Fy) = 500 N/mm2
• Rebar ultimate strength (Fu) = Say 575 N/mm2
• Elastic modulus of M25 concrete = 25000 N/mm2

DESIGN PROCEDURE USING ETABS

• First we need to selected isolated footing assign material like M25 and FE500 for conc and steel respectively
• Then we have to assign those properties and add load combinations of service limit state and ultimate limit state
• We should assign design strips for r/f details

RUN THE ANALYSIS

CHECK AFTER THE ANALYSIS

• Safe bearing capacity under service load

The safe bearing capacity is 150kn/m3 here we are getting less than that hence safe

• Settlement under service load

The max allowable deflection is 50mm we are getting deflection upto 16mm hence safe

• punching shear check

section passed in 2 way shear check.

• Shear force and bending moment

• Flexural Reinforcement of design

QUESTION 2

AIM - 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

Data required for SAFE analysis & Design

• Number of piles required - Unfactored load with self weight addition/ individual pile capacity= 1175 x 1.1/200=6.5

• Consider 8 piles for symmetric placement of piles under pile cap
• Take center to center distance between piles = 3 x pile diameter (1500 mm) Edge distance from pile center = 1 x pile diameter (500 mm)
• Assumed pile cap depth = 500 mm

Tentative pile arrangement

where center is columns sorrounded by piles 8 nos

• DESIGN CALCULATIONS

Unfactored load = 1175 kN

Dood load breakup = 1175/2 = 587.5 kN

Live load breakup = 1175/2 = 587.5 kN

Point spring of Pile = A x E/L = 196349 x 25000/16000 = 306796 kN/m

k for SAFE analysis = 306.8 kN/mm

Rebar yield strength (Fy) = 500 N/mm2

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

Elastic modulus of M25 concrete = 25000 N/mm2

DESIGN PROCEDURE USING ETABS

• First we need use grid for the plan and assign material like M25 and FE500 for conc and steel respectively
• Then we have to assign pilecaps, piles and columns in the data, also add the point where we can add those pile caps, using add point in draw command.
  
• using add pile cap we can add those pilecaps and then later after selecting the points we can assign spring to those points from assign menu
• we should add design strips and load combos for SLS
• Select all piles individually and change steel to FE500 and check design preferences

RUN THE ANALYSIS

CHECK AFTER THE ANALYSIS

• individual pile capacity under service load
  

We can the pile sharing the point reaction is less then 200kn hence safe

• Punching shear check

passed in punching shear

• Settlement under service load

The max deflection is less than 1mm hence safe

• Flexural Reinforcement of design