Foundation Design using SAFE

Question 1

AIM

To model the isolated footing provided in week 11 challenge on SAFE.

INTRODUCTION

SAFE offers a single user interface to perform modeling, analysis, design and reporting. A new model explorer is available for quick access to objects, properties and forms. It is ideal for modeling foundations, basemats, and footings. Easily model soil supports and zero tension soil models with uplift analysis. The area assignment of soil supports is based on the subgrade modulus, and they automatically adjust whenever the mesh changes. Basemat foundation models can include pedestals, walls, columns, beams, and piles in addition to the foundation area.

CALCULATIONS

Data from week 11 challenge

Square footing for a column size of 400x400 Compression 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 m below E.G.L Assume M25 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

PROCEDURE

• Open SAFE Software

STEP 1: Model Initialization

• Click 'New Model' and select 'Use Built-in Settings With:'
  • Assign all options as given below
  • Click 'OK'

• Click 'Single Footing'

• Assign all options as given below
• Click 'OK'

• Click 'OK'

STEP 2: Material Properties

• Click 'Material Properties' under the 'Define' tab

M25

• Click 'Add New Material'

• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

Grade 500

• Click 'Add New Material'
• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

STEP 3: Add Slab Properties

• Click 'Slab Section' in the 'Section Properties' under the 'Define' tab

Footing

• Select 'Footing1' and click 'Modify/Show Property'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

Column

• Select 'Stiff1' and click 'Modify/Show Property'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

STEP 4: Add Soil Subgrade Modules/Area Spring Property Data

• Click 'Area Springs' in the 'Spring Properties' under the 'Define' tab

• Assign all options as given below
  • Click 'OK'

STEP 5: Add Load Patterns

• Click 'Load Patterns' under the 'Define' tab

• Assign all options as given below
  • Click 'OK'

STEP 6: Add Load Combinations

• Click 'Load Combinations' under the 'Define' tab

• Click 'Add Default Design Combos'

STEP 7: Run Analysis

• Click 'Run Analysis' from top menu

STEP 8: Soil Pressure

• Click 'Display Soil Pressure' in the top menu

• Assign all options as given below
  • Click 'OK'

• 154 kN/m² > 150 kN/m²
• Therefore, increase the area (4.2mX4.2m)

STEP 9: Punching Shear

• Click 'Show Punching Shear Design' in the top menu

STEP 10: Deformed Shape

• Click 'Show Deformed Shape' in the top menu

STEP 11: Design Strips

• Click 'Add Design Strips' under the 'Edit' tab
• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

• Run the model again
• Click 'Display Strip Forces' in the top menu

• Assign all options as given below
  • Click 'OK'

• Click 'Slab Design' in the top menu

• Assign all options as given below
  • Click 'OK'

RESULTS

The isolated footing provided in week 11 challenge is modeled and analysed on SAFE. The graphs needed to obtain result for the checks are given in the procedure. The final result is shown in the table below.

Checks	Results
Safe bearing capacity under Service load	Safe
Settlement under Service load	Safe
Two way shear check (Punching shear)	Safe
Ultimate bending moment	Safe
Flexural reinforcement design for Footing slab	Safe

Question 2

AIM

To model, analyse and design the pile cap on SAFE.

INTRODUCTION

SAFE offers a single user interface to perform modeling, analysis, design and reporting. A new model explorer is available for quick access to objects, properties and forms. It is ideal for modeling foundations, basemats, and footings. Easily model soil supports and zero tension soil models with uplift analysis. The area assignment of soil supports is based on the subgrade modulus, and they automatically adjust whenever the mesh changes. Basemat foundation models can include pedestals, walls, columns, beams, and piles in addition to the foundation area.

CALCULATIONS

Data required for SAFE analysis & Design

Column Size = 600X600 Unfactored load = 1175 kN Pile Length = 16 m Pile diameter = 500 mm Load carrying capacity = 200 kN Calculations: Dead load breakup = 1175/2 = 587.5 kN Live load breakup = 1175/2 = 587.5 kN Spring Constant, k = (ExA)/L Where, E is 25000 N/mm2 Area, A = (pi/4)5002 = 196349 mm Pile length, L = 16000 mm 25000 X 196349 306795 N/mm Spring Constant = (25000X196349)/16000 = 306795 N/mm Edge spacing is taken as 200mm or 300mm i) As per IS 2911 (part 2) the spacing between the piles is taken as 2.5 times the diameter of pile ii) The edge spacing we have assume it as 300 mm.

PROCEDURE

• Open SAFE Software

STEP 1: Model Initialization

• Click 'New Model' and select 'Use Built-in Settings With:'
  • Assign all options as given below
  • Click 'OK'

• Click 'Grid Only'
• Assign all options as given below
• Click 'OK'

• Click 'OK'

STEP 2: Material Properties

• Click 'Material Properties' under the 'Define' tab

M25

• Click 'Add New Material'

• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

Grade 500

• Click 'Add New Material'
• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

STEP 3: Add Slab Properties

• Click 'Slab Section' in the 'Section Properties' under the 'Define' tab

Footing

• Select 'Footing1' and click 'Modify/Show Property'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

Column

• Select 'Stiff1' and click 'Modify/Show Property'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

Pile Cap

• Click 'Add New Property'
• Assign all options as given below
  • Click 'OK'

• Click 'OK'

STEP 4: Draw Slab Properties

• Click 'Quick Draw Floor' in the side menu

• Assign 'Footing' as the property

• Click inside all the grids

STEP 5: Add Points

• Click 'Draw Reference Points' under the 'Draw' tab

• Assign appropriate values for X and Y, draw the points

STEP 6: Add Column Slabs

• Click 'Quick Draw Area Around Point'

• Assign all options as given below
  • Click 'OK'

• Draw column in the center point
• Assign all options as given below
  • Click 'OK'

• Draw the pile caps in the reference points

STEP 7: Add and Assign Point Spring Property Data

• Click 'Point Springs' in the 'Spring Properties' under the 'Define' tab

• Assign all options as given below
  • Click 'OK'

• Select the center points of all pile caps
• Click 'Springs' in the 'Joint' under the 'Assign' tab

• Select 'PSpr1' and click 'OK'

STEP 8: Assign Loads

• Select the center of the column
• Click 'Force' in the 'Joint Loads' under the 'Assign' tab

• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

STEP 9: Add Load Combination

• Click 'Load Combinations' under the 'Define' tab

• Click 'Add New Combo'

• Assign all options as given below
  • Click 'OK'

• Click 'Add New Combo'

• Assign all options as given below
  • Click 'OK'

• Click 'OK'

STEP 10: Run Analysis

• Click 'Run Analysis' from top menu

STEP 11: Punching Shear

• Click 'Show Punching Shear Design' in the top menu

STEP 12: Joint Reaction

STEP 13: Design Strips

• Click 'Add Design Strips' under the 'Edit' tab
• Assign all options as given below
  • Click 'OK'

• Assign all options as given below
  • Click 'OK'

• Run the model again
• Click 'Display Strip Forces' in the top menu

• Assign all options as given below
  • Click 'OK'

• Click 'Slab Design' in the top menu

• Assign all options as given below
  • Click 'OK'

Layer A

Layer B

RESULTS

The pile cap is modeled and analysed on SAFE. The graphs needed to obtain result for the checks are given in the procedure. The final result is shown in the table below.

Checks	Results
Individual pile capacity under Service load	Safe
Settlement under Service load	Safe
Two way shear check (Punching shear)	Safe
Flexural reinforcement design for Footing slab	Safe