FD-FQ-01. How do I select
the type of Isolated Footing?
Answer: Usually the footing shall
be designed as isolated footings but when two columns
are very near each other and both the footings are
fouling each other, footing can be made combined
for 2 or multiple columns.
A
separate Combined Footing Design program for designing
footing with 2 columns is available.
There
are four options in Isolated Footing Design:
a.
Concentric Load: When Grids Only option is used
in building idealization footing shall be designed
with this type (Only for Concentric Vertical Loads).
b.
Uniaxial Moment: This type of footing can be designed
only in case of industrial shade structures where
the moments are predominant in one direction only.
c.
Biaxial Moment : When the building is analyzed for
Horizontal Loads such as EarthQuake / Wind Loads
all the footings shall be designed for this type.
A pyramidal shape of footing sloping in all four
directions is used in this type.
d.
Constant Depth : This type shall be used when footings
are to be designed with constant depth without any
slope. In case of designing footings of this type
only for Concentric Loads the moment values for
Mx and My shall be entered as Zero.
FD-FQ-02. How do I design
Raft Foundation ?
Answer : Raft Foundation Slab
without beams provided below the entire are of
the building cannot be designed with the software.
However
the design is possible if the beams are provided
connecting the columns in the raft slab. The raft
slab shall be treated as a separate floor grid with
beams and slabs supported by the columns above.
The
analysis and design of this grid shall be carried
out as a normal floor slab except here the loading
is applicable from bottom (due to water table).
The reinforcement detailing shall be reversed (top
and bottom bars in beams and slabs). The upward
load on the raft slab usually will be due to the
water pressure for a depth of slab below ground
level.
If
the multiple columns are in one line and the combined
footing is to be provided, then this slab shall
be treated as a continuous beam, and the analysis
of this beam shall be performed. The beam design
program shall be used for calculating the area of
reinforcement. However the reinforcement detailing
shall be reversed (top and bottom bars in beams
and slabs).
FD-FQ-03.
How do I design Combined Footing?
Answer : Usually the footing
shall be designed as isolated footings but when
two columns are very near each other and both
the footings are fouling each other, footing can
be made combined for 2 or multiple columns.
A
separate Combined Footing Design program for designing
footing with 2 columns is available.
FD-FQ-04. What is the difference
between Gross Bearing Capacity & Net Bearing
Capacity?
Answer : Properties of different
types of soils are as follows :
Permissible Net Bearing Capacity of Soil (T/mt2)
|
a. |
Hard
Rock |
above
100 |
|
b. |
Soft
Rock |
40
- 90 |
|
c. |
Moorum |
20
- 45 |
|
d. |
Hard
& Stiff Clays |
30
- 20 |
|
e. |
Sand
with Clay |
20
- 30 |
|
f. |
Moist
Clay |
10
- 20 |
|
g. |
Black
Cotton Soil |
5
- 10 |
Density
of Soil (T/mt3)
|
a. |
Earth
Dry to Wet |
1.6
- 2.4 |
|
b. |
Sand
Dry to Wet |
1.4
- 2.0 |
|
c. |
SoftSlit
Dry to Wet |
1.6
- 1.8 |
Safe
Bearing Capacity increases with increase in Depth
the footing from original ground level. The Gross
Bearing Capacity of soil is equal to Net Bearing
Capacity + (Depth of Footing X Density of Soil).
If
you want to ignore the increase in bearing capacity
of soil with footing depth, the value of density
of soil shall be entered as Zero.
FD-FQ-05.
What should be the value for Soil Inc.
during Footing Design?
Answer : If the Frame Analysis is performed
for Earthquake and Wind Loads, IS Code 1893 allows
to increase the Soil Bearing Pressure by 25%.
That means,for the Load Combination for which,
Earthquake and Wind Loads are considered the Soil
Inc. value can be changed to 1.25. For the first
Load combination, i.e. DL+LL, this value should
be 1.0 only.
However
the design is possible if the beams are provided
connecting the columns in the raft slab. The raft
slab shall be treated as a separate floor grid with
beams and slabs supported by the columns above.
|
