Foundation Design using SAFE

1

Aim - To model the isolated footing from given data in the prior challenge on the SAFE

Procedure

Open a new model in safe

Design code and design preference as IS456 2000

Give top and bottom cover as 50mm

Give bar size of 12mm

The select single footing

Give the footing area and columnn size

Give unfactored dead and live loads

Dead and live loads as 667.7 as we dont know excat values so break the load into half

Give material properties

Add new material as M25

Concrete weight as 25 , E=25000 and compressive strength as 25 and OK

Give next rebar material as FE500

Weight per unit volume is 77 , E = 200000 , Fy = 500 and Fu = 545 then OK

Now define slab properties

Footing and coloumn

For footing give thickness as 450 and type is footing

Now give coloumn as type stiff and thickness as 450

Select and assign both

Give soil subgrade properties

In define tab give soil subgrade as soil 150

And subgrade modulus as 9000

Give compression only and OK

Now assign soil support data

In tghe soil properties select soil 150 and OK

Check the load patterns

And load cases add one more case as settlement

Then check load combinations

Add service and ultimate load for only seeing the deflection purpose

Check all the loads are added or not

Check the design preferences by right clicking on slab

Check the loads and rebar provided

If rebar in any other give FE500

Then run the analysis

Settlement is 140 < 150 it is OK

Deflection

Click on show deformrd shape and add load combo of settlement

It is 8 less than 50 then OK

Click on show punching shear and we got of 0.9 < 1 it is OK

Check the moment and shear in the reaction

For flexural reinforcement remove the service and ultimate loads in the combinations

First add design strips for reinforcement

In edit command add edit design strips add design strips in X and Y direction in auto mode

The re analysis

Click on Show slab design and give min reinforcement

Renforcement detailing

There is min reinforcement on the top so single mat is require

Max bottom reinforcement is 1300

21 x 113 = 2410 (21 no of 12 dia at 150 mm spacing)

2

Aim- To model pile foundation for a given coloumn size according to given loads in SAFE

Procedure

Data required for modelling

We have the unfactored load = 1175Kn

Break by two as dead and live load

Dead and live load is 587.5KN

For piles we have to give point spring AE/l

Area x elestic modulus/length = 196349 x 25000 / 16000 = 306.8

Total no of piles = unfactored load / pile capacity

1175x1.1/200 = 6.5 so we take as 8 piles for symmetric purpose

Centre to centre distance as 3xpile dia = 1500

Edge dist as 1xdia = 500

Modelling in SAFE

Open a new model and give all the data as before and select grids only

Give 3 grids in x and 3 in Ydirection

Spacing of grids in X is 4 and Y is 4m

We have already defined the materials as M25 and Fe 500

Define slab materials

Pile cap , M25, Type as mat , Thickness as 800 and OK

Coloumn as type is stiff and thickness 800 and OK

Piles as type mat and thickness 500

Draw rectangular slab and select grids and pile cap

From starting point drag to end point

Then give points for piles and coloumns

Draw points and give X as 0.45 and Y as 0.45 and click on origin

Then give X as 1.55 and click in forst point

In the same way give all points by giving offset distance in X and Y direction

Then draw piles select quick draw areasType as alsb and property as pile 5000

Shape as circular slab and dia as 0.5 and give piles whereever you wanted on the points we have given

In the same way give the coloumns but select rectanguler slab and give Xand Y as 600

Then place at the centre point

Then assign the springs at the centres of the piles

Select all the centre of the pile points and assign support data and point spring

Then select and modify as in the Z direction and give 613.592 as stiffness

And give compression only and OK

Select the point in the coloumn and give load dats

Give point load as 5500 in Z direction and eccentricity in X-600 and Y- 600

Then cheeck all the loads and design preferences and change the rebar to FE 500

Then Run the analysis

Capacity of piles individually is less than 200 then OK

Settlement under service loads is under 0.7 its OK

Punching shear is less than 1 OK

Service load reactions is almost 200 its good OK

Renforcement detailing

Max top reinforcement is 1200mm2

20 x 113 = 2260 (20 no of 12 dia at 200 mm spacing)

Max bottom reinforcement is 2300

26 x 113 = 3013 (26 no of 12 dia at 150 mm spacing)