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.

Aim:

• To Analyze and design the isolated footing from week 11 challenge on SAFE
• To 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 provide easiness to engineer towards the safe design of structures with powerful tools like draw, analyze, design and detailing etc.
• Laying out models is quick and efficient way with the user-friendly drawing tools, or user can import model from AutoCAD or loading conditions from other software’s like CSI ETABS & CSI SAP2000.

Procedure:

Step:1

• Open the SAFE Application.
• Select New model.
• Followed by the input settings, Units was selected as metric & code IS 456-2000.

Single Footing was selected.

Subgrade modulus = F.O.S x S.B.C / max settlement

                              = (3x150) / 0.05 = 9000 KN/m³

The compression axial load for the load combination (1.5DL + 1.5LL) is 2000 KN.

Unfactored load = 2000 / 1.5 = 1333.3 KN

Dead load breakup= 1333.3 / 2 = 666.5 KN

Live load breakup= 1333.3 / 2 = 666.5 KN

Therefore, Footing thickness 800 mm.

 

Step:2

• Define materials
• Add new materials property, M25 concrete.

• Add rebar Fe500

• Material property data:

Click define > material properties

Rebar yielding strength(Fy) = 500 N/mm²

Rebar ultimate strength (Fu) = 545 N/mm²

M25 grade of concrete

Modulus of elasticity

E = 25x5000 = 25000 N/mm²

Step:3

• Define Slab properties.
• Define properties for footing.
• 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

• Two way shear check.

Two-way shear is 0.719, Hence OK.

Step:12

• Ultimate Bending moment & shear force check.

Bending Moment.

Shear Force.

Step:13

• 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.
• Two-way shear is 0.79.
• Ultimate Bending moment & shear force check done successfully.
• Flexural Reinforcement design for Footing slab done successfully.

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

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 = 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.

• Define column.

• Define pile_500 dia details.

Step:5

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

 

Step:6

• Add piles at the point
• Modify the edge distance to 0.2m

Step:7

• Create a column of 600 x 600 mm
• Draw the column in center using quick draw tool.

Step:8

• Spring were added.
• Define spring property data, as shown below. 

• Select pile > assign > support data > point springs.

• Springs constant is taken from above calculation.
• Dead load & live load of 587.5 KN are added next.

Step:9

• Load case combination was define next.

• After defining the load combination run the analysis.

• Max displacement was found as shown, So its Safe.

• Also, all the punching shear values are less the 1, So its Safe.

• Joint reaction diagram, as all the reaction forces are according to the limit, So its Safe.
• Reinforcement details are added next as shown in both X & Y-direction.

 

• Run the analysis again.

Step:10

• Reinforcement Slab Design.

• Pile cap foundation design. (or)

• Ultimate Bending moment & shear force check.

Bending Moment.

Shear Force.

RESULT:

• Complete design of pile cap foundation using SAFE software is done successfully.
• Max displacement was found as shown.
• All the punching shear values are less the 1.
• Ultimate Bending moment & shear force check done successfully.
• Flexural Reinforcement design for slab done successfully.