Foundation Design using SAFE
QUESTION.01
AIM: - To Analyse 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, analyse 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 and CSI SAP2000.
PROCEDURE: -
- Open the SAFE software, click on the option NEW MODEL that is available at the start page of the SAFE software.
- The SAFE software has almost similar interface as of the ETABS software interface. So, it becomes little bit easy to work on the SAFE software as we are aware of some functions by using ETABS software.
- Now after opening the New Model there will be a new dialogue box named as the New Model Quick Templates in that template there is an option called single footing in Add Structural Objects options click on that.
- After this there will be another dialogue box named as the Structural Geometry and Properties for Single Footing in that dialogue box fill all the data as required.
- After this filling the data in the New Model Quick Template just as shown in the below given image:
- After this we have to define the material property just go to the define option then there will be a drop-down list and, in that list, there will be an option called Material Property just click on that option.
M25:
Fe500:
- Go to the Define option then Section Property click on that option after that Slab Section click on that option.
- After that click on Slab Properties then Add New Property click on that option.
- Here for designing the footing we need to define only 2 different properties of slab; one is the footing slab and the other one is the stiff slab for the column area over the footing. But the depth of both types of slabs remains the same as calculated from the pressure formula.
- Select the Property type as Footing for the footing slab and Stiff for the stiff slab.
FOOTING SLAB:
Load combination:
- For define the load combinations we need to define two types of loads here. One load is Service Load and the other load is Ultimate Load.
- In the service load combinations, we consider the total unfactored column load and in case of the ultimate load combinations we consider factored load which means a factor of 1.5 is to be multiplied by the dead and the live load.
- For applying the load combinations first, we go to the Define tab then Load Combinations.
- Then Load Combinations Then Add New Combo just click on that option.
Serviceability Limits State (SLS) Load Combinations:
Ultimate Limit State (ULS) Load Combinations:
- Now go to the Display option click on that after that click on Show Loads assigned then click on joint.
DEAD LOAD:
LIVE LOAD:
- That means the loads have been already assigned for the footing.
- Now the loads are assigned now we will assign the Soil Spring property.
Formula for spring constant:
Factor of Safety X Soil Bearing Capacity/Allowable settlement.
- For the defining and assigning the soil spring property.
- First, we need to select the footing and then go to the option Assign then Shell clicks on that option.
- Then click on Area Spring option.
- After this there will be a dialogue box appeared name as Shell Assignment-Area Spring in that dialogue box select option Spring 1 and click OK.
AREA SPRING:
- After assigning the all properties now model is ready for the analysis.
- For run the analysis just press the Run icon or press F5.
- Now the analysis is completed.
CHECK FOR SETTLEMENT:
- For checking the total footing slab settlement measurement.
- Go Display option then Show Deformed shape click on that option.
- After this select load combo as SLS.
- Then the SAFE software will show the total displacement in mm due to the load combinations.
- The maximum displacement allowed according to the IS code is 25mm.
- So here as we can see the displacement in our case is way lesser than 25mm.
SOIL PRESSURE:
- Now go to the Display option Then Force/Stress Diagram.
- Click on that option then select Soil Pressure.
- According to the IS code the soil pressure must be less than the 150 KN/sq.m. Hence OK.
PUNCHING SHEAR:
- For checking the punching shear go to the display option.
- Then there will be a drop-down list in that list select Punching Shear Design click on that option.
- According to the codebook the punching shear should be less than 1 Hence OK.
LONGITUDINAL REINFORCEMENT REQUIREMENT:
- Now we need to add the design strips in model.
- We can add the design strip automatically go to the Edit option
- Then there will be an option Add/Edit Support Lines click on that option.
- Then there will be another option called Add Support Lines just click on that option and the strips in both the directions have been added.
QUESTION.02
AIM: - To model analyse and design the pile Cap on the SAFE software.
GIVEN DATA:
Column size: 600X600 sq.m
Unfactored Gravity load (DL+LL): 1175 KN
Length of the Pile that is to be used: 16 m
Diameter of one pile: 500 mm
Pile Bearing Capacity: 200 KN
CALCULATIONS: -
(A) Number of piles:
Formula for calculating number of piles
Total load/Bearing capacity of single pile
Now we have total load of 1175 KN
and Bearing capacity of single pile is 200 KN
Now we have to multiply the total load with the value of 1.1 as this is the multiplier for the soil surcharge pressure.
Therefore, Number of Piles = (1175×1.1)/200
Number of Piles = 6.46 = 8 numbers
The number of piles is 8.
(B) Spring Constant:
Formula for calculating spring constant
Point spring for the piles = AE/L
where A = Area = π4×d2
E = 25000 N/sq.mm.
L = Pile Length = 16000 mm.
Spring Constant = EA/L.
Spring Constant = (25000×196349)/16000
Spring Constant = 306796.15 N/mm
(C) Length of the Pile:
According to the IS code the minimum distance between two piles is 2.5 x diameter of pile.
The minimum distance between two pile 2.5 X 500 = 1250 mm
As the diameter of pile is given as 500 mm
But for the safe designing we adopted 1300 mm
Now the distance from the edge of the footing to the edge of the pile = 1 x diameter of pile = 1 X 500 = 500 mm
Based on the calculations and the number of piles, the size of the footing is 4.1 x 4.1 sq.m
PROCEDURE: -
- Open the SAFE software then open a new model and that option is available on the Start Page of the software.
- After opening the New Model, instead of using the quick templates that are provided in the SAFE software use the option Custom grid spacing.
- After that select the Set View Option and in that dialogue, box edit the grid spacing in the X and Y direction.
- After defining the grid spacing according to the calculation we have done before, now we will be defining the material and the section properties.
- Now go to the define option then Material Property click on that.
M25:
Fe500:
- Go to the Define option then there will be a drop-down list in that list select Section Property then slab section.
- After that there will be a dialogue box comes there select Add New Property click on that option.
PILE CAP:
COLUMN STIFF:
CIRCULAR PILES:
- Now go to the quick draw slap and choose Pile cap then draw the pile cap.
- Here we draw 8 piles from the calculation we have done.
- Before drawing the piles, we have to draw the points which act as the centre for circular piles.
- Now go to quick draw area around point.
- Then draw the circular pile using the point reference.
- Now go to Assign option click on it.
- Then click on joint then springs.
- Now click on modify/show definition option in bottom.
- Now click on Add New Property click on that option.
- After this another dialogue box appears as Point Spring Property Data there fill all necessary data.
- Now Apply point spring properties.
- Now go to the Assign menu then select joint loads then force.
- After that there another dialogue box will appears there fill all details.
DEAD LOAD:
LIVE LOAD:
- Now we define two types of loads here. One load is Service Load and the other load is Ultimate Load.
- In the service load combinations, we consider the total unfactored column load and in case of the ultimate load combinations we consider factored load.
- Now go to Define tab then select their load combinations.
- Now click on Add New Combo.
Serviceability Limits State (SLS) Load Combinations:
Ultimate Limit State (ULS) Load Combinations:
- Now we have to assign the design strips.
- Go to the Edit option after that Add/Edit Design Strips click on that then Add design strips using grids click on that.
DESIGN STRIPS ALONG X-A:
- For running the analysis press the run icon or press F5.
CHECK FOR SETTLEMENT:
- First thing we need to check the total footing slab settlement measurement.
- Go to the Display option then Show Deformed shape click on that option.
- After this select load combo SLS.
- After that the SAFE software will show the total displacement in mm due to the load combinations.
- According to the IS code displacement allowed maximum 25mm.
PUNCHING SHEAR:
- Go to the Display option then Show Punching Shear Design click on that option.
- According to the codebook the punching shear should be less than 1.
LONGITUDINAL REINFORCEMENT REQUIREMENT:
- Now we add the design strips in our model.
- Go to edit option then click on Add/Edit support line then Add support lines then strips are added to both directions.
LAYER A:
LAYER B:
RESULT: - Completed the design of Pile cap foundation and isolated footing using the SAFE software.