4. INTRODUCTION
A Transmission Tower or Power Tower is a
tall structure, usually a steel lattice tower, used to support
an overhead power line.
Typical height ranges from 15 to 55 m (49 to
180 ft), though the tallest are the 370 m (1,214 ft) towers
of a 2,700 m (8,858 ft)
In addition to steel, other materials may be used,
including concrete and wood.
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5. Design and analysis of a steel transmission line towers
of a power system located in wind zones II & IV situated
in Delhi and Panjim.
Delhi & Panjim have same seismic zone but there is a lot
of difference in the basic wind speed as Panjim is a
coastal area .
This study is performed to check whether the same
structure can be safe for both the places without any
change in structural configuration
Analysis & Design is carried as per recommendation
even in IS: 800-2007 ( LSM ).
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6. Scope of Work
I. This study is performed as per the requirement and recommendation of
the management for the validation of the results according to the IS
codes to check whether the same structure can be safe for both the
places without any change in structural configuration and for the
different loading conditions for both the places.
II. From the study of literature review, it is reported that the predominant
external loads which act on these towers are wind and earthquake
loads.
III. For the economical purpose and uniformity in power system, it is an
important study to save the cost of designing and maintenance as it is
easy and beneficial to have uniform towers.
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7. The load calculations are performed manually but the analysis
and design results are obtained through STAAD.ProV8i.
The study on the “Effect of medium wind intensity on 21
meter-132KV transmission towers” with medium wind
intensity has been observed.
The Recommendations of IS 875-1987 are followed ,the basic
wind speeds, influence of height above ground and terrain,
Design wind speed, design wind pressure, design wind force
are explained in detail .
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8. METHODOLOGY
The software tool used in the design and analysis of the tower
is STAAD.ProV8i
Manual calculations is important for the recommendations of
IS codes but the validation of these results and study of
effects of these loads on the structure is also an important
part to do.
Analysis of the performed task is the key to success for the
safe and durable serviceability of the structure under various
load combinations.
Now based on the validation of results through
STAAD.ProV8i, the important conclusions are made.
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9. Problem formulation
Research study on problem solution
Project planning
Manual calculation of load
Design of steel transmission tower using
STAAD.ProV8i
Application of loads using STAAD.ProV8i
Analysis of results and conclusion
FLOWCHART
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10. Configuration of the Tower:-
I. The two towers lies in wind zones II and IV
(Both seismic zone IV).
I. The locations are Delhi and Panjim.
II. The factor of safety of the tower is 1.2
III. The height of the tower is 30m.
IV. The base width of the tower is 3.75 m.
V. The top width of the tower is 1.75m.
VI. The flange width in the tower is 1.50m.
VII. Number of cables supported by tower are 7.
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11. FOR DELHI
1. The basic wind speed in Delhi is 47 m/sec.
2. The probability factor k1 is taken as 1.07
3. The Terrain, height and structure size factor k2 is
varying at different levels of the tower and is taken
from IS code as follows:
4. k at 16m height = 0.948
5. k2 at 20m height = 0.98
6. k2 at 24m height = 1.00
7. k2 at 28m height = 1.02
8. k2 at 30m height = 1.03
9. The Topography factor k3 is assumed to be 1 for plain
terrain of Delhi.
FOR PANJIM
1. 1. The basic wind speed in Panjim is
39m/sec.
2. 2. The probability factor k1 is taken as 1.05
3. 3. The Terrain, height and structure size
factor k2 is varying at different levels of the
tower and is taken from IS code as follows
4. k2 at 16m height = 1.03
5. k2 at 20m height = 1.05
6. k2 at 24m height = 1.07
7. k2 at 28m height = 1.09
8. k2 at 30m height = 1.10
9. 4. The Topography factor k3 is assumed to
be 1 for plain terrain of Panjim.
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12. Calculation of wind load
The design wind speed is calculated as:
1. Vz= Vb×k1×k2×k3
2. Vz at 16m = 47×1.07×0.88 ×1 = 47.67
m/sec
3. Vz at 20m = 47× 1.07 × 0.98 ×1=
49.28m/sec
4. Vz at 24m = 47 × 1.07 × 1.×1 =
50.29m/sec
5. Vz at 28m = 47×1.07 × 1.02 ×1=
51.29m/sec
6. Vz at 30m = 47×1.07 × 1.03 ×1=
51.79m/sec
Calculation of wind load
The design wind speed is calculated as
1. Vz = Vb×k1×k2×k3
2. Vz at 16m = 39× 1.05 × 1.03 ×1=42.12
m/sec
3. Vz at 20m= 39 × 1.05 × 1.05 ×1= 42.99
m/sec
4. Vz at 24m = 39 × 1.05 × 1.07×1 = 43.82
m/sec
5. Vz at 28m = 39 × 1.07 × 1.09 ×1= 44.63
m/sec
6. Vz at 30m = 39 × 1.07 × 1.10 ×1= 45.05
m/sec
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13. Calculation of Design Wind Pressure
1. Pz= 0.6 Vz²
2. Pz at 16 m = 0.6×(47.67)2=1363.46 N/m2
3. Pz at 20 m= 0.6 × (49.28)2 = 1457.11
N/m2
4. Pz at 24 m = 0.6 × (50.29)2 = 1517.45
N/m2
5. Pz at 28 m= 0.6 × (51.29)2 = 1578.39
N/m2
6. Pz at 30 m= 0.6 × (51.79)2 = 1609.32
N/m2
Calculation of Design Wind Pressure
1. Pz= 0.6 Vz²
2. Pz at 16 m = 0.6 × (42.12)2 = 1064.46
N/m2
3. Pz at 20 m = 0.6 × (42.99)2 = 1108.88 N/m2
4. Pz at 24 m = 0.6 × (43.82)2 = 1152.11 N/m2
5. Pz at 28 m = 0.6 × (44.63)2 = 1195.1 N/m2
6. Pz at 30 m = 0.6 × (45.05)2 = 1217.16 N/m2
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14. Results
*LOCATION BEAMS AXIAL FORCE FX (KN) SHEAR FORCE FY(KN) BENDING MOMENT MZ (KNm)
1. 728 86.65 7.37 -2.94
2. 493 303 9.88 2.015
3. DELHI 566 286.5 156 -17.65
4. 602 17231 471.5 -115
5. 622 12009 -84.6 741
6. 278 83.6 7.85 3.15
7. PANJIM 493 340.5 3.06 -0.775
8. 566 2714.5 87.3 -78.65
9. 602 13548 380.5 1141.5
10. 622 9586 -118.15 320.5
* First five readings are for Delhi and next five are for Panjim 10/26/2016
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17. Conclusion
There is large difference in the bending moment forces on the members on the two
specified locations with the slight change of the wind pressure force but is in safe limits
and it is maximum on member no. 602 and 622.
There is huge change in the axial force in the cross arm members of the transmission
tower in these two locations for which maximum axial force is shown on member no.
566.
The parallel beam of the cross arm have very less difference in axial force in the same
members i.e. member no. 278 which shows that there is more effect of wind pressure
in axial force on the front members.
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18. There is large change in the bending moment of the front
members of the cross arm at the two different locations.
Transmission tower with same bracing can be used at these
two different wind zones with same seismic zone by using
different steel members at different phases of the
transmission tower according the effect of the load on the
specific location members.
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