Foundation Design using SAFE

CHALLENGE - 12

1. AIM & INTRODUCTION:

• To know the general design procedure of spread footing with SAFE software.
• To know the general design procedure of Pile foundation with SAFE software.

ANSWERS - 1

Given data are:

• Column size 400x400mm
• Compression axial load (1.50DL+1.5 LL) = 2000 KN
• Safe bearing capacity of soil = 150 KN/M2 at 2m depth
• Grade of concrete = M25
• Factored load = 2000 KN
• Unfactored load = 2000/1.5 = 1333.30 KN
• Assume 50 % both DL and LL

ie DL = 1333.30/2 = 666.70 KN

LL = 1333.30/2 = 666.70 KN

Subgrade modulus of soil = SBC x FOS/Allowable settlement

= 150 x 3 / 0.05

= 9000 KN/m³

Rebar yield strength (Fy) = 500 N/mm²

Rebar ultimate strength (Fu) = 575 N/mm²

Elastic modulus of M25 = 5000xSqrt (Fck)

= 5000x5 = 25000 N/mm²

Steps to be involved in SAFE:

• New model initiation:
• Design code: IS 456
• Design preferences
• Units: Metrics
• Assign single footing from template as below.

• Assign materials from Define : M25 & Fe500
• Assign Soil in footing Pad.
• Assign footing , column with M25
• Assign load combination
• Add Column strips

  Run Analysis

  Parameters to be checked in SAFE analysis:

  1. Settlement under service load.

     Settlement is less than 50mm, Hence OK

     1. Safe bearing capacity under service load.

        Soil pressure is less than 150 N/mm^2. Hence OK.

        2. Two way shear check (Punching shear)

        Punching shear is less than 1, Hence OK

        Hence OK

        3. Ultimate bending moment.Flexural reinforcement design for footing slab

        1. ANSWERS - 2

           Given data are:

           • Column size 600x600mm
           • Unfactored load = 1175 KN
           • Grade of concrete = M25
           • Unfactored load = 1175 KN
           • Pile length = 16 m
           • Pile diameter = 500mm
           • Pile load = 200 KN
           • Dead load breakup = 1175/2 = 587.50 KN
           • Live load breakup = 1175/2 = 587.50 KN

           Point spring of pile AE/L

           A = Area

           E = Youngs modulus

           L = Length of pile

           = (3.14x500² / 4 )(25000)/16000

           = (196428) (25000)/16000

           = 306920 N/mm

           = 306.90 KN/mm

           Rebar yield strength (Fy) = 500 N/mm²

           Rebar ultimate strength (Fu) = 575 N/mm²

           Elastic modulus of M25 = 5000xSqrt (Fck)

           = 5000x5 = 25000 N/mm²

           Data required for SAFE analysis and design

           No. of piles required = Unfactored load with self weight

           addition/individual pile capacity

           = 1175x1.10/200

           = 6.50 Nos

           Say 7

           Let’s take 8 Nos (even) for symmetric alignment of piles.

           Take center to center distance between piles = 3 x pile dia

           = 3x 500 = 1500mm

           Edge distance from pile centre = 1 x pile dia

           ie 500 mm

           Assume pile cap depth as 500mm

           Tentative placement of piles

           

           • Assign materials from Define : M25 & Fe500
           • Create Pile , Pilecap and Column datas.
           • Assign load combination

        2. Model of piles,pilecap and column

           

           RUN ANALYSIS after checking design preferences
        3. • Checks to be performed in SAFE analysis:
           • Settlement under service load (Deflected footing)

             

             • Individual pile capacity under service load

             Joint reaction diagram

             • Two way shear check (Punching shear)
             • Flexural reinforcement(Slab design (layer – A)

               Slab design (layer – B)

               Flexural design of Pile footing.