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vikram.jeet
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PostPosted: Tue Apr 12, 2022 3:33 am    Post subject: Reply with quote

Some hypothetical calculations of 9.0 m high mast are as under just to understand calcs.

Assumptions :  Mast dia 0.45m  averaged.

Mast top  lighting ring   dia 1.5m , ht 0.45m say hypothetically

Foundation : Depth of foundation = 2.0m
Size : 2.0m x 2.0 m

Wind forces & their moments at footing base
Wind  pressure = 200 kg/ m2 taking uniform

Mast body H1= 200 * 0.80* 0.45*9.0 = 648 kg
Moment at footing base M1= 648* ( 9.0/2 + 0.30+ 2.0) = 4407 kgm

Top lighting ring H2 = 1.50*0.45  * 200 = 135 kg
M2 = 135* ( 9.0+ 0.3+2.0 -0.45/2 ) *135 = 1495 kgm

Total moment at base = 4407 + 1495 = 5902kgm

Wtof footing +soil over it = 2.0*2.0 * 2.0* 1900 = 15200 kg
Here average unit wt of soil and rcc footing and rcc pedestal taken 1900 kg/m3
Weight of mast + top ring say = 75 kg
Total weight = 15200 + 75 = 15275 kg

Check against Over turning :
Stabilizing moment = 15275* 2.0/2 = 15275 kgm
Overturning moment = 5902 kg m
FOS against OT = 15275/ 5902 = 2.59  cf 2.0 OK

Check against sliding is OK

Base pressures :

P/A +_  M/Z = 15.275 / (2*2) +_ 5.902 / ( 2*2^2 /6)
  = 3.82 +_ 4.43

Since minimum base pr is negative , base will lose contact in some portion and base pressure calculations are as under :
e = M/W = 5.902 / 15.275 = 0.39m

Contact Length = 3*( 2/2 - 0.39) = 1.83m
Contact % = 1.83*100/2.0 = 91.5% .

Max base pressure = 2* 15.275/( 1.83*2.0) = 8.35 T/m2  cf   Gross SBC of soil

This above illustration is purely hypothetical  based on old Wind code , pl follow Wind pressure as per latest code
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vikram.jeet
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PostPosted: Tue Apr 12, 2022 3:37 am    Post subject: Reply with quote

As checked at some  website regarding Andree Nursa formula :

Ms =  { Nc A/2} - {2Nc^2 /(2xAxQg)}
+ { 80A^2Qg^2H^3 / (6561 Nc) }

Ms - STABILISING moment
Nc = weight of foundation + pole
A = Footing side width  
H= Height of concrete block

Qg = Ground boundary resistance

Values of Qg indicated are 0.20mpa / 0.25mpa / 0.30mpa depending upon soil type , but must be checked fm net


Cannot say  on its Derivation . Engineers may verify the equation from net / books   .
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vikram.jeet
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PostPosted: Tue Apr 12, 2022 3:39 am    Post subject: Reply with quote

Some hypothetical calculations regarding concrete block pedestal type foundation of street light pole
A) Based on weight of structure including passive soil resistance plus side friction on block
Pole pedestal design
For street light poles , of height ranging from 6.0 m to 12.0 m , most practicable solution is precast rcc block.

Just to see for comparing with  andree formula :
Ht of pole = 10.0m
Dia of pole = 0.30m
Top arm = 2.o m , dia 0.15 m

Taking pedestal size 1.2x1.2x(1.2mdepth in ground +0.3m above )

Soil data : c=0 ; phi= 30 degree;hence Ka= 0.33 , Kp =3.0  ;  V= 1800 kg/m3
Coefficient of friction u= tan(0.75phi))= 0.414 ; EP rest = 0.50

Wt of block = 1.5x1.2x1.2x2400 = 5184 kg  
Wt of pole and arm ,say = 30 kg ; Arm moment = 10kg x 2/2 =10kgm

Wind load = 200 kg/m2 coastal areas as per old code  (for simplicity of presentation)
Shape factor for pole body = 0.80

Wind moment at base of block= 200x10.0x 0.30 x 0.80x(10.0/2+0.3+1.2 )= 3120kgm
Here Wind load on 0.3m protruding pedestal ignored , as also Wind load taken uniform upto ht , but actual shall be as per latest Wind code

Stabilizing moments :
From self +pole weight = (5184+30)x1.2/2 = 3129 kgm

From passive less active soil resistance = ( 3.0- 0.33) 1800x1.2^3  /6 1.2 = 1661 kg m

Frictional resistance = 0.414 ( 0.50x 1800x1.2^2  /2)1.2 x 2 = 645 kg
Stabilizing  moment  due to friction= 645 x 1.2/3 = 258 kgm

Total Stabilizing  moment  = 3129+1661+258 = 5048 kgm
Total Overturning moment = 3120+ 10 = 3130 kgm

FOS against OT = 5048/3130 = 1.60  in this case


To be continued :
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vikram.jeet
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PostPosted: Tue Apr 12, 2022 3:40 am    Post subject: Reply with quote

Continued from previous  post:

Stabilizing moment as per Andrea norsa formula :

A= 1.2m
Weight Nc = 5184+30 = 5214kg
H=1.2m
Qg = taking average soil = 0.25mpa = 25 tonne/m2 = 25000kg/m2

Stabilizing  moment  Ms :
(i) 5214 x 1.2/2 = 3129kgm

(ii) Minus  2x 5214^2/(21.225000) =  - 906 kgm

(iii) plus 80x 1.2^2   25000^2 1.2^3 / (65615214) = 3637 kgm

Net Stabilizing moment  = 3129 - 906 + 3637 = 5860 kgm as against 5048 kgm calculated from basics in previous post

The above Formula must be verified from books , other sources  And also soil ground resistance value need to be taken as per soil parameters.
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pvv.structure
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PostPosted: Wed Apr 13, 2022 4:12 am    Post subject: Reply with quote

Enclosed attachment for Built Foundation drawings for 12m high light pole with speakers and solar panel.

vikram.jeet wrote:
Continued from previous  post:

Stabilizing moment as per Andrea norsa formula :

A= 1.2m
Weight Nc = 5184+30 = 5214kg
H=1.2m
Qg = taking average soil = 0.25mpa = 25 tonne/m2 = 25000kg/m2

Stabilizing  moment  Ms :
(i) 5214 x 1.2/2 = 3129kgm

(ii) Minus  2x 5214^2/(21.225000) =  - 906 kgm

(iii) plus 80x 1.2^2   25000^2 1.2^3 / (65615214) = 3637 kgm

Net Stabilizing moment  = 3129 - 906 + 3637 = 5860 kgm as against 5048 kgm calculated from basics in previous post

The above Formula must be verified from books , other sources  And also soil ground resistance value need to be taken as per soil parameters.



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12m Giant Voice Poles with Solar Panel and Light.pdf
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vikram.jeet
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PostPosted: Wed Apr 13, 2022 5:27 am    Post subject: Reply with quote

Dear sir ,

Many thanks for uploading the details . Will go thru it .

Best regards & wishes



pvv.structure wrote:
Enclosed attachment for Built Foundation drawings for 12m high light pole with speakers and solar panel.

vikram.jeet wrote:
Continued from previous  post:

Stabilizing moment as per Andrea norsa formula :

A= 1.2m
Weight Nc = 5184+30 = 5214kg
H=1.2m
Qg = taking average soil = 0.25mpa = 25 tonne/m2 = 25000kg/m2

Stabilizing  moment  Ms :
(i) 5214 x 1.2/2 = 3129kgm

(ii) Minus  2x 5214^2/(21.225000) =  - 906 kgm

(iii) plus 80x 1.2^2   25000^2 1.2^3 / (65615214) = 3637 kgm

Net Stabilizing moment  = 3129 - 906 + 3637 = 5860 kgm as against 5048 kgm calculated from basics in previous post

The above Formula must be verified from books , other sources  And also soil ground resistance value need to be taken as per soil parameters.
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vikram.jeet
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PostPosted: Wed Apr 13, 2022 6:00 am    Post subject: Reply with quote

Depth of Transmission towers ,Poles foundation  as per IS 4091

As per Codal requirements minimum depth of foundation shall be H/6 , here H is the height of tower / pole above GL.

For Block (pedestal only) type of foundations for poles , the thickening at top shall be 600mm ( 450mm in ground and 150mm above) and shall be  (B + 2200mm) size , here B is the size of sq / circular block in plan.
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vikram.jeet
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PostPosted: Fri May 13, 2022 9:16 am    Post subject: Reply with quote

QUANTITIES OF CONC MIX INGREDIENTS in volumetric  mix
For very small works of petty nature

Structural engineers are Civil Engineers first , and SE afterwards and shall not limit their knowledge to  designing  but must have knowledge of associated disciplines as also concrete technology .

Working out Quantities of cement , stone dust(Fine aggregate )  & stone aggregate in a conc mix is sometimes asked in a construction where supervision is by owner (non tech) /

Just an illustration :

Concrete Mix  1: 1.5 : 3

Considering conc Quatty = 1.0 m3

The dry volume  is generally taken as 1.54 times

Hence dry volume of ingredients needs = 1.54 m3

Volume of cement needed = (1* 1.54 )/ 5.5 = 0.28 m3

Specific Weight of cement = 1440 kg/m3

Hence et of cement needed = 1440 * 0.28 =  403.2 kg
= 403.2/50 = 8.07 bags

Fine aggregate in form of stone dust
Volume = (1.5 * 1.54)/5.5 =0.42 m3 = 14.8 cubic ft

Coarse aggregate in form of stones 20mm down :
Volume is double the FA I.e
= (3 * 1.54)/5.5 = 0.84 m3 = 29.6  cft
(  1/3rd CA 10mm down + 2/3rd CA   10-20mm)

All above Quantities are for 1.0 m3 conc


Just a generalised view
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vikram.jeet
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PostPosted: Sun Jun 12, 2022 3:25 am    Post subject: Reply with quote

Block foundation  
(  For small medium size sheds , poles , high masts  and structures with light weight but high moments from wind )


Many advantages can be seen using concrete block foundations :

(i) Conventional spread footing not required


(ii) Block excavated to size do not need any shuttering  

(iii) Requirement of reinforcement is much less compared to spread footing

(iv) After placing conc cage and positioning Anchor bolts , concrete can be poured in one go.  Whereas in conventional spread footing first concreting is done for base , then shuttering for pedestal and concreting thereafter, thus taking more time.

(v)Block foundation needs depth from minimum 1.22m to 1.5m and sometimes upto 1.8m. Uplift resistance is thru weight of block . Skin friction is additional. Resistance to moment is from passive soil resistance with some FOS

(vi) It is economical considering multiple benefits
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PostPosted: Sun Jun 12, 2022 4:54 am    Post subject: Reply with quote

Some situations where block foundations can not be proposed:

Primarily it is  adjoining soil enclosing the concrete Block which provides Passive soil resistance against moments from wind , therefore in certain situations  , it may not proposed.


(i) Any side of block - if there exists a nearby drain , it may not be possible to have passive soil resistance on drain side , and it can fail. Drain must be at least  1.5* Df away from block ,  Df being depth of block.


(ii)  Marshy Soils

(iii) Steep sloping terrain
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