foundation design
DESCRIPTION
concrete foundation designTRANSCRIPT
REVISION INDEX:-
DESIGN OF ISOLATED FOOTINGFoundation Committee members
Sl.No Rev.No Prepared Checked Approved Remarks K. Chandra SekharanBy Date By Date By Date P. Balachandran
1 0 PGL PBC KCS S. VidhyadaranD. JacobP. Gajalakshmi
DESIGN OF ISOLATED FOOTING WITH BIAXIAL ECCENTRICITY:-
1.0 HOW TO USE THIS WORK SHEET
Step 1 Read this page carefully and completely.
Step 2 In case of any doubts / discrepancies, contact : Foundation committee members
Step 3 Identify carefully the coordinate directions for the foundations with respect to
the cardinal (geographical) directions
Step 4 Enter all basic input datas required for the foundation design into tab "USER
INTERFACE"
Step The user can take the advice of the lead engineer for the allowable bearing pressure
ratio and allowable percentage of contact length.
Step 5 Copy the applicable support reactions from STAAD output into tab "STAAD
OUTPUT(UNFACT) & STAAD OUTPUT(FACT)"
The worksheet will convert the support reactions to actions as per
(FOUNDATION 3D) COORDINATE SYSTEM (see 2.2 below)
Step 6 Enter the bearing capacity factor and the load case number into tab "SUMMARY-SBC"
These factors are the only manual inputs in the tab "SUMMARY-SBC". Table function
is used to perform repetitive calculation for various inputs at one shot. This function is
available under tools menu. The results of reference calculations are kept at the row
above the table function starts, which is linked from the sheet "SBC- SAMPLE
CALCULATION". Everything is linked through the "Column input cell" in table function.
Whatever the formulae used to calculate the X & Y direction forces , is performed for all
other rows (with in the Table array) by reading the corresponding input forces(ouside
the Table array). Attention : Before editing or customizing this Table function, kindly,
get the proper knowledge base from the experts.
Step 7 The tab "SBC-SAMPLE CALCULATIONS" is a locked worksheet where all the sample
calculations for the SBC calculation,stability and sliding check are carried out step by
step.All the inputs required for the calculations are taken from the tab"USER
INTERFACE" and from "SUMMARY-SBC".
Step 8 Enter the Dead Load factor and the load case number into tab "SUMMARY-DSN
VALUES" These are the only manual inputs in the tab "SUMMARY-DSN
VALUES". Table function is used to perform repetitive calculation for various inputs at
one shot. Kindly go through the Step 6 mentioned above to know about the Table
function.
Step 9 The tab "DSN VALUES-SAMPLE CALCULATIONS" is a locked worksheet where all
the sample calculations for the design moment,one way shear and punching shear are
carried out step by step.All the inputs required for the calculations are taken from the
tab"USER INTERFACE" and from "SUMMARY-DSN VALUES".
Step 10 Based on the design standard ,the sheet is selected for the footing design
Step 11 Tab "DSN BS8110" will give the footing design done as per british standard.
The user has to cross check the maximum value taken for the design calculation
with the maximum value in the tab"SUMMARY-DSN VALUES"
Step 12 The above mentioned check has to be done in the tab "DSN IS456" also.
Step 13 While doing the documentation, the user has to submit the following sheets
a)USER INTERFACE(optional)
b)SUMMARY-SBC
c)SBC-SAMPLE CALCULATIONS
d)SUMMARY-DSN VALUES
e)DSN VALUES-SAMPLE CALCULATIONS
f)DSN-BS8110/DSN-IS456(Based on the selected design standard)
2.0 DESIGN PROCEDURE USED IN THIS WORKSHEET
2.1
2.2 The following Foundation-3D co-ordinate system is be adopted for loads and basic input datas..
All basic input datas except factored and unfactored loads shall be entered in the worksheet USER
INTERFACE in magenta color
Conversion of Staad Co-ordinates to Foundation-3D coordinates
Multiply By WorksheetStaad
ReactionMultiply
ByStaad Action
Fx -1 (-)Fx - (-)Fx
Fy -1 (-)Fy -1 Fy
Fz -1 (-)Fz -1 Fz
Mx -1 (-)Mx -1 Mx
Mz -1 (-)Mz -1 Mz
2.4 SBC & Stability Calculations:-
2.4.1 Max Bearing Pressure is calculated using the Teng chart (see tab : "Teng Chart")
& Partial Contact conditions
2.4.2 Calculated max bearing pressure for each loadcase is checked against Gross Bearing
2.4.3 Stability ratio is calculated as the ratio of the resisting moment (Pv x L/2 or B/2) to the
overturning moment in each direction (i.e., the moment at the bottom of foundation,Mxx or
2.4.4
each direction and it is checked with the allowable sliding ratio
2.4.5 The calculated stability ratio and sliding ratio more than 100 is taken as 100.
2.4.6 The contact length along X and Y direction is calculated using Teng's Chart
3.0 DESIGN CALCULATIONS (STRESSES & REBAR)
3.1 The design calculations can be done with either IS 456-2000and BS 8110-2000
(ACI 318 to be implemented)
3.2 The design forces acting at bottom of foundation is calculated for each load case.
3.3 Since the dia of bar to be placed in each direction is not known intially, the effective depth of
footing is calculated as follows,
Overall depth - clear cover - Bar dia in X-Dirn - Bar dia in Z-Dirn/2
3.4 Both moment and beam shear is calculated based on the assumption that the max bearing
Note:-Using Teng chart, max bearing pressure can be calculated for both Full contact
Capacity of soil(see Additional Note 1 below)
Mzz) and it is checked with the allowable stability ratio specified by the user (see Additional Note 2)
Sliding ratio is calculated as the ratio of the resisting force ie., m x Pv.to the lateral force in
Note:- The resisting lateral force is calculated based on the Friction coeffcient between
the soil and concrete.Passive resistance of soil is not considered here. (see Additional Note 3)
Note:-Max bar dia is taken for effective depth calculation in both direction
pressure(Pmax) calculated for factored loads is acting uniformly under the bottom of
Actual Adopted
moment and shear calculations,the following worksheet can be used(Foundation-3D validation.xls)
3.5 The base slab is designed for the max design moment at the face of the pedestal / column in both directions
3.6 The depth of footing is checked for one way shear acting at 'd' distance and '2d' distance from the face
of pedestal in both direction
3.7 The one way shear at 'd' distance and '2d' distance is checked with Enhanced Shear Strength and
Actual Shear Strength respectively.
3.8 The depth of footing is also checked for two way shear at the face, 0.75d from the face of
pedestal and 1.5d from the face of pedestal.
3.9 The punching shear force calculation is as per cl.3.7.6 of BS8110 i.e., considering the effect
of moment in each direction independently.
shear calculation as per BS is followed in both IS and BS designs.
case a: Effective shear force for internal column
foundation as shown in fig 2. (see Additional Note 4)
Note:- If the user want to do accurate calculations,i.e., considering the variation of pressure in the
(see also Additional Note 5)
Note:- If the user do not want to use the Enhanced shear strength in one way shear check, then he has
to enter the word " Not Used" in the User Interface Sheet.
Note:-Since the additional shear developed due to the moment is taken care in the BS code , Punching
Pmax Pmin
Fig.1
Pmax
Fig.2
case b: Effective shear force for corner column
Veff = 1.25Vt
case c: Effective shear force for edge column
Where
Vt - design shear transferred to the column
x - the length of the side of the perimeter
considered parallel to the axis of bending
Mt - is the design moment transmitted from the
column to the footing at the connection
Note:-
a) From the above three cases ,'case a' is used in this worksheet
b) The effective shear force is calculated in each direction independently .
4.0 Top Reinforcement is provided as per the following criteria:-
Case a: Depth of footing less than or equal to 600mm
Tension Max(Percentage of reinforcement required for factored
downward Pressure,Minimum Percentage of reinforcement)
Compression No Top Reinforcement required
Case b: Depth of footing more than 600mm
Tension Max(Percentage of reinforcement required for factored
downward Pressure,Minimum Percentage of reinforcement)
Veff = Vt(1+1.5Mt/Vtx)
Veff = Vt(1.25+1.5Mt/Vtx)
Compression 0.5 times the Minimum Percentage of reinforcement
Additional Notes:-
1 Use net bearing capacity if the footing is just below a basement raft : ie additional bearing
capacity due to overburden will not be available.
2 Refer project DBR for the allowable FOS for stability. Code specified values may be used
where DBR does not specify these.
3 Passive resistance from soil shall be considered only with the specific permission of the
Lead Engineer and if and where permitted by the Project DBR
4 A uniform pressure is used for strength design for the following reasons :
a In many cases we do not know the final loads of equipment etc at the time
the foundation design is completed. A conservative approach is essential.
b Soil conditions vary over site / sites. The pressure distribution under the
footing would vary depending on the type of soil, rigidity of footing etc
Many of these factors are not taken into account in normal design office
environment.
5 "More accurate" approach shall only be used for checking adequacy in case of shorfall by
the "uniform" pressure approach of this worksheet
ISOLATED FOOTING - SAMPLE CALCULATION
Footing Mark F1 NODE: 1, 3, 8 & 10
Design StandardIS456-2000 2
BS8110-1997
INPUT DATA:- RESULTS:-
Project Dirn. E-W N-S VERT Actual Allowable Utilization Ratio Remarks
Fdn 3D direction X Z Y BEARING PRESSURE #REF! #REF! #REF! #REF!
Pedestal Size(mm) 300 300 1000CONTACT LENGTH
X-Direction #REF! 60% - #REF!
Footing Size(mm) 1300 1300 300 Z-Direction #REF! 60% - #REF!
Eccentricity,e(mm) 0 0 -STABILITY
X-Direction #REF! 1.50 - #REF!
Z-Direction #REF! 1.50 - #REF!
Bottom of Foundation below FFL = (-)1.30 mSLIDING
X-Direction #REF! 1.50 - #REF!
Net Safe Bearing Capactity = 150 Z-Direction #REF! 1.50 - #REF!
Depth of Foundation below FGL dfgl = 1.00 m Required Provided
% %
= 0.00 m Governing L/C #REF!
Grade slab thickness = 0.00 mm X-Direction #REF! #REF! #REF! #REF! #REF! #REF!
Live load on grade slab LL = 0.00 Governing L/C #REF!
Unit Weight of soil = 18.00 Z-Direction #REF! #REF! #REF! #REF! #REF! #REF!
Increament of Bearing Pressure for X-Direction #REF! #REF! #REF! #REF! #REF! #REF!
non-permanent loads = 33.33 % Z-Direction #REF! #REF! #REF! #REF! #REF! #REF!
Angle of internal friction f = 35 degree
m = 0.47 Governing L/C #REF!
Allowable FOS against Overturning = 1.50 X-Direction #REF! #REF! #REF! #REF!
Allowable FOS against sliding = 1.50 Governing L/C #REF!
Maximum Teng value k = #REF! Z-Direction #REF! #REF! #REF! #REF!
ex/L = #REF! Governing L/C #REF!
ez/B = #REF! X-Direction #REF! #REF! #REF! #REF!
ex = #REF! Governing L/C #REF!
ez = #REF! Z-Direction #REF! #REF! #REF! #REF!
At face #REF! #REF! #REF! #REF!
Load acting at(Top of Pedestal/Bottom of Footing): TOP OF PEDESTAL 2 At 0.75d #REF! #REF! #REF! #REF!
BOTTOM OF FOOTING At 1.5d #REF! #REF! #REF! #REF!
Characteristic strength of concrete fck = 25
kN/m2
Depth of foundation from the level of point of application of forces (for pedestals only)
mm2 mm2
dforc
BOTTOM REINFORCEMEN
TTgs
kN/m2
gs kN/m3
TOP REINFORCEMEN
T
Actual(N/mm2) Allowable(N/mm2)
Coeffcient of friction, m=2/3TANfONE WAY SHEAR
AT 'D' FROM FACE OF
PEDESTAL
ONE WAY SHEAR AT '2D' FROM
FACE OF PEDESTAL
PUNCHING SHEAR FORCE
kN/m2
Characteristic strength of steel fy = 500
Clear Bottom cover = 50 mm
Clear Top cover = 50 mm
Enhanced shear strength for one way : USED 2
shear (Used / Not Used):- NOT USED
PROVIDE BOTTOM REINFORCEMENT(B):-
X-Direction T12 @ 200mm c/c spacing
Z-Direction T12 @ 200mm c/c spacing
PROVIDE TOP REINFORCEMENT(T):- Z (N-S)
X-Direction T12 @ 200mm c/c spacing
Z-Direction T12 @ 200mm c/c spacing
X (E-W)
kN/m2
Cb
Ct
Bz &Tz
Bz&Tz
Bx & Tx
DESIGN CALCULATIONS(As per EC-2-2004):-
DESIGN CALCULATIONS:-
1.0 Design Data:-
Thickness of footing D = 300 mm
Clear Bottom cover = 50 mm
Clear Top cover = 50 mm
Characteristic strength of con = 25
Characteristic strength of stee = 500
2.0 Design of Bottom Reinforcement:-
X-DIRECTION - Main Z-DIRECTION - Secondary
Assumed bar diameter = 12 mm = 12 mm
Effective depth provided = #VALUE! mm = ### mm
Maximum design Moment Mu = #REF! kNm = #REF! kNm
= #REF! #REF! = #REF! #REF!
#REF! #REF!
z = 0.5*d[1+sqrt(1-3.53 K)] ≤ 0.95 d = #VALUE! mm = ### mm
Tension Reinforcement Ast = #REF! = #REF!
% of reinforcement = #REF! % = #REF! %
Minimum % of steel = 0.135 % = 0.135 %
Minimum Tension Reinforceme = 404 = 404
= #REF! = #REF!
Ast per metre provided 12 tor @ 200 c/c spacing 12 tor @ 200 c/c spacing
= 565 = 565
= #VALUE! % = ### %
#REF! #REF!
Cb
Ct
fck N/mm2
fy N/mm2
f1 f2
dprov
K = Mu / bd2 fck
mm2 mm2
Ast,min mm2 mm2
Ast ,required ( max ( Ast , Ast,min) mm2 mm2
mm2 mm2
3.0 Design for Top Reinforcement:-
Downward pressure due to
Soil weight = 18.00
Foundation wt = 7.50
Grade slab = 0.00
Live load LL = 0.00
Dead load factor = 1.4
Live load factor = 1.6
Max Factored downward pressure
1.4(gs(dfgl-D)+gcD+gcTgs = 35.70
X-Direction Z-Direction
Max Projection proj = #REF! m = #REF! m
Ultimate Moment = #REF! = #REF!
= #REF! kNm/m = #REF! kNm/m
Effective depth provided 300-50-12-12/2
= 232 mm = 232 mm
= #REF! = #REF!
= #REF! = #REF!
z = 0.5*d[1+sqrt(1-3.53 K)] ≤ 0.95 d = #REF! mm = #REF! mm
Top Tension Reinforcem = #REF! = #REF!
% of reinforcement = #REF! % = #REF! %
Minimum % of steel = 0.135 % = 0.135 %
Minimum Top Tension Reinforcement reqd = 404 = 404
Area of steel required = #REF! = #REF!
Ast per metre provided 12 tor @ 200 c/c spacing 12 tor @ 200 c/c spacing
= 565 = 565
= 0.244 % = 0.244 %
#REF! #REF!
gs(dfgl-D) kN/m2
gcD kN/m2
gcTgs kN/m2
kN/m2
kN/m2
Mu
dprov
Mu/Fckbd2
Ast = ( Mu / 0.87 fy z ) mm2 mm2
ptmin
mm2 mm2
mm2 mm2
mm2 mm2
4.0 One way shear:-
X-Direction Z-Direction
4.1 Check for One Way Shear at d from face of pedestal:-
Max Shear Force at 'd' distance from face of Vu = #REF! kN/m = #REF! kN/m
Shear Stress per meter width v = #REF! = #REF!
= #REF! N/mm² = #REF! N/mm²
Design Concrete Shear Stress/m = ≥
= 0.12
k = #VALUE! ### k = ### #VALUE!
= #VALUE! % = ### %
= 0.00 No Axial Load Envisaged
= #VALUE! ≥ ### N/mm² = ### ≥ #VALUE!
= #VALUE! N/mm² = ### N/mm²
= #VALUE! N/mm² = ### N/mm²
Allowable Concrete Shear Strength = ### N/mm² = ### N/mm²
### ###
5.0 Check for Punching Shear:-
5.1 Design Shear Stress at the face of the Pedestal
Maximum Punching shear force = #REF! kN
Perimeter of the loaded area u =
= #VALUE! mm
=
Shear Stress = #REF! N/mm²
< #VALUE! N/mm²
< ###
vRd,c
CRd,c
≤ 2.0 ≤ 2.0
ρ1 ρ1
σcp
vRd,c
Enhanced Concrete shear strength,2dvc/av
(Where av = d)
Vat face
Column Perimeter + 4 x π x d
VEd Vat face/ (u x d)
VEd
VEd vRd,c
DESIGN CALCULATIONS(As per IS456-2000):-
DESIGN CALCULATIONS:-
1.0 Design Data:
Thickness of footing D = 900 mm
Clear Bottom cover = 75 mm
Clear Top cover = 75 mm
Characteristic strength of concrete = 30
Characteristic strength of steel = 500
2.0 Design of Bottom Reinforcement:-
X-DIRECTION
Assumed bar diameter = 16 mm
Effective depth provided = 809 mm
Mx 7
Maximum design moment Mu = 7.42 kNm
= 0.011
% of reinforcement req = 0.00 %
xu/d for balanced section = 0.46
% of reinforcement for balanced section = 1.13%
> 0.00 %
No Comp Reinf Req
Minimum % of steel = 0.12 %
= 0.12 %
Ast / m = 0.12 x 1000 x 900/100
Area of steel required = 1080
Ast per metre provided 16 tor @ 125 c/c spacing
= 1608
= 0.20%
3.0 Design for Top Reinforcement:-
Downward pressure due to
Soil weight = 18.00
" Foundation wt = 22.50
Grade slab = 0.00
Live load LL = 0.00
Dead load factor = 1.5
Live load factor = 1.5
Max Factored downward pressure
= 60.75
X-direction
Max Projection proj = #REF! m
Cb
Ct
fck N/mm2
fy N/mm2
f1
dprov
k=Mu / bd2
% of Ast ,required ( max ( pt , pt,min)
Ast
mm2
mm2
gs(dfgl-D) kN/m2
gcD kN/m2
gcTgs kN/m2
kN/m2
1.5(gs(dfgl-D)+gcD+gcTgs)+1.5LL kN/m2
pt≡1−√1− 4k
0 .87FckFy
50Fck
xu ,maxd=7001100+0 .87 fy
pt ,lim=41 .3(FckFy )( xud )
Ultimate Moment = #REF!
= #REF! kNm/m
Effective depth provided 900-75-12-12/2
= 807 mm
= #REF!
= #REF!
% of reinforcement req = #REF!
Minimum % of steel = #REF!
= #REF!
Ast / m = #REF!
Area of steel required = #REF!
Ast per metre provided 12 tor @ 200 c/c spacing
= 565
= 0.070%
#REF!
4.0 One Way Shear:-
X-direction4.1 Check for One Way Shear at d from face of pedestal
Maximum design shear at d from face of pedestal Vu = #REF! kN/m
Shear Stress t = #REF!
= #REF! N/mm²
= 17.519
Design Concrete Shear Strength = 0.33 N/mm²
= 0.67 N/mm²
(As per cl.40.5 of IS456)
Allowable Concrete Shear Strength = #REF! N/mm²
#REF!
4.2 Check for One Way Shear at 2d from face of Pedestal
Maximum design shear at 2d from face of pedestal Vu' = #REF! kN/m
Shear Stress = #REF!= #REF! N/mm²
Design concrete shear strength = 0.33 N/mm²
#REF!
5.0 Check for Punching Shear:-(Punching shear calculations as per BS8110-1997)5.1 Maximum Allowable Shear Stress
V max = = 4.38
5.00
whichever is less. Therefore = 4.38
5.2 Design Shear Stress at the face of the Pedestal
(As Per Cl 3.7.6.4 of BS 8110 : Part 1: 1997)
Maximum Punching shear force = #REF! kN
Perimeter of the loaded area, U = 1200 mm
Mu
dprov
k=Mu/bd2
ptmin
% of Ast ,required ( max ( pt , pt,min)
Ast
mm2
mm2
Enhanced Concrete shear strength,2dtc/av(Where av = d)
t'
tc'
(As Per Cl 3.7.7.2 of BS 8110 : Part 1:1997, max shear strength is max of 0.8(fcu)1/2 and 5N/mm2)
0.8 x (fcu)1/2 N/mm2
N/mm2
n max N/mm2
Vatface
pt≡1−√1− 4k
0 .87FckFy
50Fck
τc=(−1+√1+5 β )×0 .85×√0 .8 fck
6 β
β=0.8 fck6 .89 pt
Nominal Design Shear Stress, == #REF!= #REF!
Check : = #REF! <
#REF!
5.3 Design of Shear Stress at the Distance of 0.75 d from the face of Pedestal
(As Per Cl 3.7.7.4 of BS 8110 : Part 1: 1997)
Maximum Punching Shear force = #REF! kN
Perimeter of the loaded area, U = 6054 mm
Distance from the loaded area av = 607 mm
Allowable Shear Stress at 0.75d, = (1.5 d / av )
= 0.33 x 1.5 x 809 / 607
= 0.67
Nominal Design Shear Stress, == #REF!= #REF!
Check : = #REF!
#REF!
5.4 Design of Shear Stress at the Distance of 1.5 d from the face of Pedestal
(As Per Cl 3.7.7.4 of BS 8110 : Part 1: 1997)
Maximum Punching Shear force = #REF! kN
Perimeter of the loaded area, U = (2*(300+3*809)+2*(300+3*809))
10908 mm
Nominal Design Shear Stress, == #REF!= #REF!
Check : <vc = #REF!
#REF!
n Vat face/ (u x d)
n N/mm2
n < n max
V0.75d
n c ' n c .
N/mm2
n V0.75d /(U x d)
n N/mm2
n < n c' < n max
V1.5d
n V1.5d /(U x d)
n N/mm2
n
Z-DIRECTION
= 16 mm
= 809 mm
Mz = (Wl^2)/2
7 kNm
= 7 kNm
= 0.0113
= 0.00 %
= 1.13 %> 0.00 %
No Comp Reinf Req
= 0.12 %
= 0.12 %
= 0.12 x 1000 x 900/100
= 1080
16 tor @ 100 c/c spacing= 2011
SAFE = 0.25% SAFE
Z-direction
= #REF! m
f2
mm2
mm2
= #REF!
= #REF! kNm/m
= 807 mm
= #REF!
= #REF!
= #REF!
= #REF!
= #REF!
= #REF!
= #REF!
12 tor @ 200 c/c spacing= 565= 0.070%
#REF!
Z-direction
= #REF! kN/m= #REF!= #REF! N/mm²
= 14.016
= 0.37 N/mm²
= 0.74 N/mm²
= #REF! N/mm²
#REF!
= #REF! kN/m
= #REF!= #REF! N/mm²
= 0.37 N/mm²
#REF!
(OR)
mm2
mm2
4.38
(2*(300+3*809)+2*(300+3*809))
N/mm2
N/mm2
N/mm2
DESIGN OF FOUNDATION:1.0 Footing Data
Unit Weight of Concrete 25.00 kN/m3Grade of Concrete 30.00Net SBC 250Increament factor for BC 1.00Concrete cover 75.00 mm
0.95 mPedestal height above Ground level 0.50 mTenion load 7.00 kNUnit Weight of soil 18.00Angle of internal friction f 30 degreeCoeffcient of friction m 0.50FOS against Overturning 2.00FOS against sliding 1.5
X-Dirn Z-Dirn Y-DirnPedestal Size(mm) 350 450 50Footing Size(mm) 1000 1000 900Eccentricity,e(mm) 0 0 0
Load acting at(Top of Pedestal/Bottom of Footing):
Shear, Fx(kN)
D.L+W.L 0.1 2.746 0.2 0 3.248
Gross SBC = = = 267
2.0 Vertical load acting at bottom of foundation
Axial Load Py = 0.10 kNWeight of Pedestal Wp Lp x Bp x (Hp) x 25 = 0.20 kNArea of foundation ( Provided ) A L * B = 1.00Load due to soil Ws = 0.76 kNWeight of footing Wf A*D*25 = 22.50 kN
Total Vertical Load Pv Py+Wp+Ws+Wf+Wgs+Wll = 23.56 kN
3.0 Moment acting at bottom of foundation(about x-axis)
Moment Mx = 0 kNmMoment due to lateral force = 0.19 kNmMoment due to eccentricity (ez) (Py+Wp)*ez = 0.00 kNm
Moment acting at bottom of foundation Mxx = 0.19 kNm
Eccentricity along Z-Direction from cg of Footing, ez' Mxx/Pv = 0.008 m <B/6
4.0 Moment acting at bottom of foundation(about z-axis)
Moment Mz = 3.248 kNmMoment due to lateral force Fx = 2.6087 kNmMoment due to eccentricity (ex) (Py+Wp)*ex = 0.00 kNm
Moment acting at bottom of foundation Mzz = 5.86 kNm
Eccentricity along X-Direction from cg of Footing, ex' Mzz/Pv = 0.249 m >L/6
5.0 Bearing Pressure Calculation:-
Eccentricity along X-Direction from cg of Footing, ex' Mzz/Pv = 0.249 mEccentricity along Z-Direction from cg of Footing, ez' Mxx/Pv = 0.008 m
N/mm2
SBCnet kN/m2
fbc
Depth of foundation below ground level ,dfgl
gs kN/m3
Load case/Node
number
Axial Load, Py(kN)
Shear, Fz(kN)
Moment, Mx(kNm)
Moment, Mz(kNm)
fbc x SBCnet + gs x dfgl kN/m2
m2
gs*(dfgl - D)*(A - (Lp x Bp))
Mlfx Fz * dforc Mecc
Mx+Mlfx+Mecc
Mlfz Fx * dforc Mecc
Mz+Mlfz+Mecc
Teng Value k = 2.724
Maximum Bearing Pressure fmax kPv/A = 24.70Minimum Bearing Pressure fmin Pv/A(1-6ex'/L-6ez'/B) = 22.42
Bearing capacity Ratio BCR fmax/Gross SBC = 0.09Safe
6.0 Check for Stability:-X-Direction Z-Direction
Overturning Moment = 0.19 kNm = 5.86 kNmRestoring Moment = 11.78 kNm Pv x B/2 = 11.7776 kNmStability Ratio = 61.99 = 2.01
>2 Safe >2 Safe
7.0 Check for Sliding:-
X-Direction Z-Direction
Sliding Force = 2.746 kN = 0.2 kNResisting Force = 11.78 kN = 11.7776 kNSliding Ratio = 4.29 = 58.8878
>1.5 Safe >1.5 Safe
8.0 DESIGN FORCE CALCULATIONS:-8.1 X-Direction:-
Pressure variation :-
Maximum Pressure Pv/A(1+6ex'/L) = 24.70Minimum Pressure Pv/A(1-6ex'/L) = 22.42Design Moment:-Distance from left edge to face of pedestal = 0.325 mDistance from right edge to face of pedestal = 0.275 mMoment at west face of pedestal 24.7*0.325*1000*0.325 = 1.30 kNm/mMoment at east face of pedestal 24.7*0.275*1000*0.275 = 0.93 kNm/mDesign Moment Mxu = 1.30 kNm/m
One way Shear:-Effective Depth = 817.00
= 0.8170 mDistance from left edge to d distance from west face of pedestal = 0.000 mDistance from right edge to d distance from east face of pedestal = 0.000 mShear at d distance from west face of pedestal 24.7*0 = 0.00 kN/mShear at d distance from east face of pedestal 24.7*0 = 0.00 kN/mDesign Shear at d from face of pedesVxu Max Vx = 0.00 kN/m
Shear Stress at critical section = 0.00As per Clause 3.4.5.8 of BS 8110 Part= (0.79*0.2^(1/3)*max of((400/817,1)^0.25/1.25*(30/25)^(1/3))Alllowable Shear Strength of concrete 0.459
9 Z-Direction:-Pressure Variation:-Maximum Pressure Pv/A(1+6ez'/B) = 58.70Minimum Pressure Pv/A(1-6ez'/B) = -11.59
Design Moment:-Distance from top edge to face of pedestal = 0.325 mDistance from bottom edge to face of pedestal = 0.325 mMoment at north face of pedestal 58.7*0.325*0.325/2 = 3.10 kNm/mMoment at south face of pedestal 58.7*0.325*0.325/2 = 3.10 kNm/mDesign Moment Mzu = 3.10 kNm/m
kN/m2
kN/m2
Mo
Mr=Pv x L/2Mr/Mo
Hs
Hr = mPvHs/Hr
kN/m2
kN/m2
dx
N/mm2
N/mm2
kN/m2
kN/m2
10 Punching Shear Force:-At face of the pedestalCritical section of at a distance 2d from face of footingCritical perimeter = 2A + 2B
A = 1167.000B = 1267.000
= 4868.00 mm
Area with the perimeter = ###= 8.38E+06 mm^2
Punching shear force = 36.514 kNd = 817 mm
Shear Stress = 0.01
= 0.8 Roof of Fck
= 4.38
11 Design of Bottom Reinforcement:-Thickness of footing D = 900 mmClear Bottom cover = 75 mm
Clear Top cover = 75 mm
Characteristic strength of concrete = 30
Characteristic strength of steel = 500
Effective Thickness of Footing = 817.00 mm
Mx = Base Pressure * Width of Footing * Cantilever projectionMx = 1.104 kN.m
K = M / Fck*b*d^2= 0.000
K' = 0.156K < K'
(No need Compression Reinforcement)Z = d*(0.5+SQT (0.25-k/0.9)Z = 817 mm
0.95*d = 776.15 mmAs = 3.27 mm^2
Minimum Percentage of Steel = 0.13 %= 1062.1 mm^2
Provide Reinforcement = 14 mmNo of Rod Required = 10.5810477057Provide number of Reinforcement = 5.6Provide Area of Steel = 1134.09333333 mm^2
Provide 14.00 mm Dia @ 150.00 mm both ways12 Check Uplift:
Tension in Pedestal = 7.00 kNTotal Vertical load in Footing= 22.80 kN
Factor of safety = 3.256696429 > 1 Safe
VEd
vRd,c N/mm2
(As Per Cl 3.7.7.2 of BS 8110 : Part 1:1997, max shear strength is max of 0.8(fcu)1/2 and 5N/mm2) N/mm2
Cb
Ct
fck N/mm2
fy N/mm2