Foundation Design using SAFE
ANSWER 1.
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 :
- SELECT THE NEW MODEL
- FOLLOWING THE INPUT SETTING , UNIT ARE SELECTED AS metric & code IS 456-2000.
- FIG.
SINGLE FOOTING WAS SELECTED:
SUBGRADE MODULUS = (FOS X SAFE BEARING CAPACITY OF SOIL ) / MAX. SETTLEMENT
= ( 3X 150 ) / 0.05 = 9000KN/M^3.
- 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.
FIG.
STEP 2 :
- DEFINE MATERIALS
- ADD NEW MATERIALS PROPERTIES , M30 CONCRETE .
- ADD REBARS Fe 500.
- Material property data:
-
Click define > material properties
Rebar yielding strength(Fy) = 500 N/mm²
Rebar ultimate strength (Fu) = 545 N/mm²
M30 grade of concrete
Modulus of elasticity
E = ( 30)^ (1/2)x5000 = 27386.12 N/mm.
- STEP 3:
- DEFINE SLAB PROPERTIES.
- DEFINE PROPERTIES FOR FOOTING.
- DEFINE PROPERTIES FOR MAT.
- Define properties for Stiff.
STEP 4 :
RUN ANALYSIS AND DESIGN :
STEP 5 :
SAFE BEARING CAPACITY UNDER SERVICE LOAD 86.15 KN/ M^2 < 150 KN/M^2.
HENCE OK .
STEP6 :
PUNCHING SHEAR DESIGN :
PUNCHING SHEAR DESIGN IS = 0.641, HENCE OK .
STEP 7 .
ULTIMATE BENDING MOMENT AND SHEAR FORCE CHECK .
- BENDING MOMENT :
SHEAR FORCE :
- 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 86.15 KN/m2< 150KN/M^2, Hence OK.
- Two-way shear is 0.641, Hence OK.
- Ultimate Bending moment & shear force check done successfully.
- Flexural Reinforcement design for Footing slab done successfully.
ANSWER :
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 DATA :
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 X1.1 / 200 = 5.6 = 6.46
BUT WE ARE CONSIDER TOTAL 8 PILE FOR SYMETTRICAL .
Spring constant = ExA / L
Where, E = 25000 N/mm²
A = `(pi/4)`(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.
- we are selected the blank window.
STEP 2:
- Draw > DRAW JOINT OBJECT.
- QUICK DRAW AREA AROUND THE POINT ( PLAN)
STEP 3.
- Add piles at the SPECIFY POINT SPACING 2.5 time pile dia .
- Modify the edge distance to 1 pile dia .
- Draw the slab by using quick draw tool > draw points.
STEP 4:
- 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 REBARS:
STEP 5:
- Create a column of 600 x 600 mm
- Draw the column in center using quick draw tool.
STEP 6:
- 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 = 1175 /2 =587.5 KN.
- LIVE LOAD = 1175/ 2 = 587.5 KN.
- Dead load & live load of 587.5 KN are added next.
STEP 7:
- Load case combination was define next.
STEP 8:
- RUN ANALYSIS:
STEP 9:
- ULTIMATEMATE BENDING MOMENT AND SHERFORCE CHECK:
- BENDING MOMENT:
- SHEAR FORCE:
STEP 10:
- Reinforcement Slab Design.:
- REINFORCEMET CALCULATION :
- NO OF BARS= 1161.78 /(PI/4) X16^2 =5.77 ~6 PER METER
- SPACING =1000/6 =166.66MM BUT WE CAN TAKE 150 MM
- SO WE CAN TAKE T-16MM dia @ 150 MM AT BOTTOM
- WE CAN TAKE AT SUPPORT AND TOP T-16MM dia @ 250 MM.
ASSUME SIZE OF BAR 16MM.
STEP 11:
PUNCHING SHEAR DESIGN:
SHOW CRACK WIDTH :
- SLAB BOTTOM FACE:
- SLAB TOP FACE :
RESULT:
- Complete design of pile cap foundation using SAFE software is done successfully.
- Max displacement was found as shown, So its Safe.
- All the punching shear values are less the 1, So its Safe.
- Ultimate Bending moment & shear force check done successfully.
- Flexural Reinforcement design for slab done successfully.