ISOLATED FOOTING DESIGN ES EN 1992-1-1:2015
1Foundation Design (Isolated Footing)
An internal column transferring the loads given in table 1 is considered for isolated footing
design. The material to be used for are C25/30 and S400. If the column size is 600mm by 600
mm. and the soil has presumptive bearing capacity of 280 Kpa(Allowable), determine the size and
reinforcement necessary for the isolated footing to safely transfer the load.
ETABS OUTPUT
Fx Fy Fz Mx My Mz
Story Joint33Label Load
Base Case/Combo
Comb1-Ultimate
Base 33 Comb2-Service -7.3925 -2.4641 3587.939 3.9611 -11.7307 -3.0603
Table 1: Joint Reaction from ETABS to an internal column
1.1 Material data
For C25/30 : 𝑓𝑐𝑘= 25 𝑀𝑝𝑎
For S400: 𝑓𝑦𝑘= 400 𝑀𝑝𝑎
Concrete design strength
-5.1324 -1.8362 2564.1252 2.9776 -8.1731 -2.1384
fcd = αccfck [ES EN 1992 −1 −1: 2015, Eqn. 3.15 ]
γc
Where: the recommended value of αcc is 0.85.
fcd = 0.85 ∗25 1.5 = 14.17 𝑀𝑝𝑎
Steel design strength
fyd = 𝑓𝑦𝑘 [ES EN 1992 −1 −1: 2015, Figure 3.8 ]
𝛾𝑠
fyd =400 1.115 = 347.83 Mpa
1.2 Footing proportioning
Factor of safety (F.S)
F . Ultimate load 358 . 11 . .3 96 .1 399
S 7 . 939
2564 125 .273 .8 173
Service load
978
all 280 Kpa
ult .1 * 280 Kpa 391.81 Kpa
399
Eccentricity at service load
Isolated footing Page |1 Af
, ISOLATED FOOTING DESIGN ES EN 1992-1-1:2015
e M y .8 173
x .3 x 3
P 256 . 188 10
4 125
e M x .2 978 .1 x 3
y
P 2564 . 161 10
125
Now, the stress at the four corners of the footing can be determined from:
P 1( 6e x 6 e y )
A B B
Figure 1 Stress distribution on isolated footing with eccentric loading.
Any plan dimension of footing, B and L, must satisfy two things:
a)The maximum stress must be less than or equal to the allowable bearing
capacity.
b)The minimum stress must be greater than zero.
Condition a)
Since the eccentricity is relatively equal in both axis’s, a square footing is ideal.
P 6 6e y
max
1( e x ) all
A B B
2564.1252 6 * .3 x 3 6 * . 16 x 3 )
1
1 1B 10
B2 188B 10 all
(
2564.125 26 . x 3 )
1 all
2 B2 094
B 10
(
Isolated footing Page |2 Af
1Foundation Design (Isolated Footing)
An internal column transferring the loads given in table 1 is considered for isolated footing
design. The material to be used for are C25/30 and S400. If the column size is 600mm by 600
mm. and the soil has presumptive bearing capacity of 280 Kpa(Allowable), determine the size and
reinforcement necessary for the isolated footing to safely transfer the load.
ETABS OUTPUT
Fx Fy Fz Mx My Mz
Story Joint33Label Load
Base Case/Combo
Comb1-Ultimate
Base 33 Comb2-Service -7.3925 -2.4641 3587.939 3.9611 -11.7307 -3.0603
Table 1: Joint Reaction from ETABS to an internal column
1.1 Material data
For C25/30 : 𝑓𝑐𝑘= 25 𝑀𝑝𝑎
For S400: 𝑓𝑦𝑘= 400 𝑀𝑝𝑎
Concrete design strength
-5.1324 -1.8362 2564.1252 2.9776 -8.1731 -2.1384
fcd = αccfck [ES EN 1992 −1 −1: 2015, Eqn. 3.15 ]
γc
Where: the recommended value of αcc is 0.85.
fcd = 0.85 ∗25 1.5 = 14.17 𝑀𝑝𝑎
Steel design strength
fyd = 𝑓𝑦𝑘 [ES EN 1992 −1 −1: 2015, Figure 3.8 ]
𝛾𝑠
fyd =400 1.115 = 347.83 Mpa
1.2 Footing proportioning
Factor of safety (F.S)
F . Ultimate load 358 . 11 . .3 96 .1 399
S 7 . 939
2564 125 .273 .8 173
Service load
978
all 280 Kpa
ult .1 * 280 Kpa 391.81 Kpa
399
Eccentricity at service load
Isolated footing Page |1 Af
, ISOLATED FOOTING DESIGN ES EN 1992-1-1:2015
e M y .8 173
x .3 x 3
P 256 . 188 10
4 125
e M x .2 978 .1 x 3
y
P 2564 . 161 10
125
Now, the stress at the four corners of the footing can be determined from:
P 1( 6e x 6 e y )
A B B
Figure 1 Stress distribution on isolated footing with eccentric loading.
Any plan dimension of footing, B and L, must satisfy two things:
a)The maximum stress must be less than or equal to the allowable bearing
capacity.
b)The minimum stress must be greater than zero.
Condition a)
Since the eccentricity is relatively equal in both axis’s, a square footing is ideal.
P 6 6e y
max
1( e x ) all
A B B
2564.1252 6 * .3 x 3 6 * . 16 x 3 )
1
1 1B 10
B2 188B 10 all
(
2564.125 26 . x 3 )
1 all
2 B2 094
B 10
(
Isolated footing Page |2 Af
