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.
Ans:-
Aim:- To design the isolated column footing & pile cap by using given loads.
Procedure:-
Given data:-
Square footing for column size - 400mmx400mm
Compression axial loadfor the load combination of (1.5D.L + 1.5L.L) is 2000KN.
The safe soil bearing capacity is 150 kn/m^2 at a depth of 2m below E.G.L
Assume M25 grade concrete.
Data reqired for SAFE analysis & design
Unfactored load = 2000/1.5 = 1333.3 KN
Dead load break up = 1333.3/2 = 666.7 KN
Live load break up = 1333.3/2 = 666.7 KN
For elastic modulus of soil & pile (spring) stiffness
Subgrade modulus of soil = S.B.C x factor to ultimate/ Max.settlement
150*3/0.05 = 9000KN/m^3
rebar yield strength (Fy) = 500 N/mm^2
Elastic modulus of M25 concrete = 5000 sqrt fck = 25000 N/mm^2
SAFE DESIGN :-
Open-File-New model-single footing-give required sizes
Define-materials-M25,Fe415
Define-Slab properties-Footing,stiff
Define-load cases -check for soil surcharge
Define - load combinations- check loads for settlement-d.l-1,l.l-1
Run analysis
Add strips for footing
1) Safe bearing capacity under service loads
Display-reaction forces-settlement-apply
2) Settlement under service load
Display-show deformed shape-settlement-apply
3) two way shear check (Punching shear)
Display-Show punching shear design-value less than 1
Shear force due to acting load/shear force due to concrete =2/2.5
4) Ultimate bending moment:-
display-show strip forces-layerA,laer-B,set display options-tick on display srip layer
5) Display-Slab design-layerA-ok-tick on impose min.reinforcement-due tosome temp.changes,shrinkage effects
From center to edge of footing is not necessary face to edge of footing will give results this is only difference b/w manual and SAFE desin.
Result:- Finally i got to know how to design the footing in SAFE.
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
We must refer IS:2911 (part2) and Sp:34
Answer:
data required for SAFE analysis and design
Unfactored load - 1175KN
dead load breakup - 1175/2 - 587.5 KN
Live load breakup - 1175/2 - 587.5 KN
Point spring of pile - A E/L
=pi d^2/4 * L
196349 X 25000 / 16000
= 306796 KN/M
K for SAFE analysis = 306.8KN/M
Rebar yield strngth - (Fy) - 500 N/mm^2
Rebar ultimate strength (Fu) - 575 N/mm^2
Number of piles required = Unfacored with self wt. addition/including pile capacity
1175*1.1/200 = 6.5
Consider * piles for symmetric placement of piles under pile cap
Take center to center distance between piles = 3*pile dia.(500mm)
SAFE design :-
open-add material properities - slab properties (footing,stiff)
draw raft,take points and insert columns,take offsets and edge dist.
select point-assign-supportdata-point springs-editdata-checks need to be performd in SAFE analysis -run analysis.
1) Individual capacity under service load.
2)Display-punch shear
3) Display-reactions-loadcomb.-service-arrows-F2-apply
4) draw-deformed shape-load comb.-service-apply
5)Display-linear A and B apply.
