Foundation Design using SAFE

Q1.

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.

• Square footing, Column size 400x400
• Compression axial load for the load combination (1.5DL+1.5LL) is 2000 KN
• The safe soil bearing capacity is 150KN/m2 depth of 2m below G.L
• M25 Concrete grade

Aim:

• To Analyze and design the isolated footing from week 11 challenge on SAFE and verify the size, depth and steel provided as per calculations.

Introduction:

• CSI SAFE (Slab Analysis by the Finite Element Method) is the best tool for designing concrete slabs and foundations.
  
  
• SAFE used to engineer towards the safe design of structures with powerful tools like draw, analyze, design and detailing etc.

Solution:

STEP: 1

Open the SAFE Application and select New Model

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 = Soil bearing capacity x factor to ultimate / maximum settlement
• k = 150x3 /0.05., k= 9000KN/m3
• Rebar yeild strength (Fy) = 500 N/mm2
• Rebar ultimate strength (Fu) = 575 N/mm2
• Elastic modulus of M25 Concrete = 25000 N/mm2

STEP: 2

Open Define materials

Add rebar Fe500

Material Property data:

Click define followed by Material properties

M25 grade of concrete

Modulus of elasticity,

E=25×5000">E=√25×5000

= 25000N/mm2">mm2.

STEP: 3

Define slab properties

Define properties for mat

Define properties for stiff

STEP: 4

Define Load pattern

Step:5

• Define Soil subgrade modules/ Area spring property data.

STEP: 6

• Assign point load

Step:7

• Assign load combinations.

Step:8

• Check design preference (min cover 50mm)

Step:9

• Run Analysis & Design.

Step:10

• Safe bearing capacity under service load is 152 KN/m2.

Step:11

• Ultimate bending moment and shear force check.

Shear force check

Step:12

• Flexural Reinforcement design for Footing slab.

RESULT:

• The Isolated footing was designed and analyzed using SAFE software successfully.
• Safe bearing capacity under service load is 152 KN/m2, Hence OK.
• Two-way shear is 0.79, Hence OK.
• Ultimate Bending moment & shear force check done successfully.
• Flexural Reinforcement design for Footing slab done successfully.

Q2.

AIM:

• To Model Analysis 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.

Procedure:

Given:-

Column size = 600 x 600 mm

Unfactored load = 1175 KN

Pile length = 16m

Pile diameter = 500 mm

Load carrying capacity = 200 KN.

Calculations.

Number of pilers = 1175 / 200 = 5.6 = 6

Spring constant = ExA / L

Where, E = 25000 N/mm²

A = (π/4)²(500)² = 196375 mm²

L = 16000 mm

Spring constant =25000 x 196375 / 16000=306835 N/mm or 306835 KN/m

Edge spacing is taken as 200 or 300 mm.

Step:1

• Open the SAFE Application.
• Select New model.
• Followed by input settings, units was selected as metric and code Is 456-2000.

Step:2

• Co-ordinates was defined next.
• Grid spacing in X-direction and Y-direction was taken as 3.20m and 2.0m respectively, as shown below.

• Check design preference (min cover 50mm)
• 50mm each was provided as cover at top and bottom and bar size was defined as 14mm.

Step:3

• Material property data:

Click define > material properties >M25 grade of concrete.

Modulus of elasticity

E = 25x5000 = 25000 N/mm²

Fe 500 rebar was added next as shown below.

• Add Rebar Fe500

Step:4

• Define Slab properties.
• Define pile cap.

Step:5

• Draw the slab by using quick draw tool > draw points.