The Experimental Failure behaviour of a Prestressed Concrete Electricity Transmission Pole: A Case Study for Kannauj Soil, Uttar Pradesh, India

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The Experimental Failure behaviour of a Prestressed Concrete Electricity
Transmission Pole: A Case Study for Kannauj Soil, Uttar Pradesh, India
Experiment Findings · December 2021
DOI: 10.5281/zenodo.5837583
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Journal of Engineering Analysis and Design
Volume 3 Issue 3
DOI: https://doi.org/10.5281/zenodo.5837583
The Experimental Failure behaviour of a Prestressed Concrete
Electricity Transmission Pole: A Case Study for Kannauj Soil,
Uttar Pradesh, India
Samirsinh Parmar*
Assistant Professor, Department of Civil Engineering, D.D. University,
Nadiad, Gujarat, India.
(Former QIP Research Scholar, Department of Civil Engineering, IIT Kanpur, India.)
*Corresponding Author
E-mail Id:-samirddu@gmail.com
(Orcid Id:-https://orcid.org/0000-0003-0196-2570)
ABSTRACT
Pre-stressed Cement concrete poles are widely used for supporting electricity supply lines
throughout India. Its common observation that the poles fail under heavy wind as well as
earthquakes. The response of the poles depends upon the strength of pole material,
supporting soil, and depth of embedment of the pole. To economize the erection its general
practice to erect the pole as the self-supporting pole. This paper investigates the behaviour of
a prototype self-supporting electric pole for two different kinds of soil compaction material
with respect to monotonic lateral load. Load versus displacement in loading and unloading is
analysed for two different soil conditions. The geotechnical design considerations are
suggested for the embedment of poles in soils.
Keywords:- PSC poles, Full-scale field test, Design wind load, Soil–structure-interaction,
foundation soil analysis.
INTRODUCTION
The major contribution of electricity
distribution and transmission in rural India
is through overhead power lines. Self-
supported single poles are widely used to
support overhead power lines in India due
to ease of installation and low cost. These
self-supporting single poles have smaller
plane dimensions and much fewer
additional components to carry overhead
lines. In India, pre-stressed cement
concrete (PSC) poles have gained wide
popularity to be used for low-voltage (33
kV) electrical power transmission.
These poles are behaving as self-
supporting poles because it is having very
small plan areas and also very less front
area to sustain vertical self-weight and
lateral load respectively. These poles
support the electricity cables overhead at a
height of approximately 7.5 m in a sagging
portion of the wire.
The distance between two poles depends
upon factors like the number of cables,
size of cables (diameter), local average
wind speed, and soil characteristics in
which it is to be erected. In India, the pole
foundation is generally excavated as an
auger hole. The pole is placed inside the
hole and the same soil is backfilled and
compacted to achieve stability of the pole.
The guidelines for pole embedment depth
vary as per different states' power
authorities.
The self-supported electricity poles are
subjected to four types of loads. (i) Self-
weight of the structure plus the weight of
cables as dead load (ii) lateral load due to
tension in cables (iii) Wind load (iv)
Earthquake load.
A large number of poles failure were
observed in the past in monsoon and

Volume 3 Issue 3
storms in India. These failures are due to
faulty pole foundation construction
techniques as well as manufacturing
defects in the pole. The failure of self-
supporting pre-stressed cement concrete
poles can be classified as (i) Structural
failure of poles- no failure in soil (ii) Soil
failure- No pole failure (iii) soil and pole
both fails. If soil and pole both fail then
it’s necessary to investigate that which
element fails first.
Fig.1:-A damaged electricity pole following a storm in Patiala.
(Courtesy: https://www.tribuneindia.com/news/punjab/storms-damage-rs25-cr-power-infra-269983)
Cohen and Perin [1] and Odley [2]
analyzed equipped masts for radio and
television antenna structures at multiple
locations. Gaylord [3] has provided unified
design and manufacturing
recommendations for self-supporting steel
electrical transmission poles.
Ashok and Biggers [4] investigated the
possible use of the analysis of tubular steel
pole structures of arbitrarily defined
geometric configuration using different
numerical methods. Vanderbilt and
Criswell [5] have developed and
implemented a reliable design method for
analyses of single-pole transmission
structures through PDLDAR (Pole Design,
Analysis and Reliability). Dicleli [6]
provided a computer-aided methodology
through ODAPS (Optimum Design and
Analysis of Pole Structures) to inevitably
design the lightest weight pole structure
that meets the boundary criteria set out in
the geometric boundary conditions.
Kalkan and Laefer [7], Khalili and Saboori
[8], and Saboori and Khalili [9] conducted
a static and transient analysis of tapered
self-supporting fiber-reinforced poles
(FRP) using a finite element approach.
Caracoglia and Jones [10] and Caracoglia
and Velazquez [11] performed a series of
full-scale experimental tests on low
structural damped aluminium tapered light
poles to study their reactions during
simulated external actions, particularly
wind loading. Rao et al. [12] have studied
various types of premature failures
observed during full-scale testing of
single-pole steel.
EXPERIMENTAL PROGRAMME
One goal of this research was to evaluate
the performance of multiple PSC electric
poles installed in Kannauj District, Uttar
Pradesh, India, where several poles had
failed in the past few years. To accomplish
this, a test setup was established at the
Indian Institute of Technology Kanpur,
where full-scale poles were transported
from Unnao and erected in a specially
constructed dirt pit to replicate the in-situ
soil condition of the Unnao case-study
location. The poles were then exposed to

Volume 3 Issue 3
constant lateral loading until they failed.
There was a three-month break between
the first and second experiments and a six-
month lag between the second and third
experiments. The soil pit has been properly
prepared each time, compacting each layer
and keeping the desired density. The
general layout of the testing program is
depicted in Figure 2.
Details of the Poles
In the study, a tapered prestressed concrete
(PSC) pole of 8.5 m height was used. It
has a cross- section that measures 27 cm
9.0 cm at the bottom and tapers to 14.5 cm
9.0 cm at the top. Figure 3 depicts the
structural details of the pole as well as the
reinforcement specifications. Table-1
shows the pole's design details.
Fig.2:-Details of the PSC poles used in the study
Table 1:-Details of pre-stressed RCC pole
Grade of concrete M30
Dia. Of Pre-stressed wire 4 mm
No. of tensioned wire 14
Clear cover to wires 16 mm
Weight of pole 223 kg
Soil and Foundation Details
The soil sampling was carried out in the
month of august to simulate the soft soil
situation and increase moisture content at
shallow level depth in the soil. The basic
characteristics of Unnao soil are described
below. The field testing was carried out at
the Indian Institute of Technology Kanpur.
As previously stated, one of the goals of
the study was to investigate the failure
mechanism of PSC electric poles installed
in the Unnao District. To that end, a pit
with dimensions of 3m x 3m x 1.8 m was
carefully prepared using soil brought in
from the Unnao site and meticulously
maintaining the target soil density

Volume 3 Issue 3
throughout the pit through compaction.
Following the compaction of each layer,
sand cone tests were conducted at various
locations throughout the pit to ensure that
the field density is close to the desired
laboratory-measured density. The size of
the pit is determined by the pole
foundation's zone of influence.
Table 2:-Geotechnical Characteristic of field soil
Physical properties Values
Soil Type Clayey Silt
OMC 14.72%
Void ratio 0.52
Specific Gravity 2.65
Max. dry unit weight 17.26 KN/m3
Cohesion 17 KN/m2
Angle of internal
friction 17º
The parameters such as rain, wind and
average seasonal temperature the soil
properties on upper crust of earth changes
considerably hence periodical
characterization of the foundation soil
were carried out extensively along with
consideration of mixing of soil with brick
ballast. The upper and lower values hence
fixed by characterization experiments,
which is demonstrated in Table-3
Table 3:-Details of relevant parameters.
Soil Parameter Range Mean Std. Deviation
Friction Angle ϕ ° 0-39 12.7 7.45
Cohesion (kPa) 0-71.6 23.3 18.76
Unit Weight (kN/m3
) 14.0 -2079 18.23 1.94
Shear Modulus (Mpa) 18.47 - 52.6 35.3 8.25
Poles-1 was supported by square footings
measuring 45 cm x 45 cm x 150 cm and 53
cm x 53 cm x 150 cm, respectively. Pol-2
was supported in the underground by a
compacted crushed brick of the same size
as Pole-1 around the embedded region.
Poles 1 was supported by square footings
measuring 45 cm x 45 cm x 150 cm and 53
cm x 53 cm x 150 cm, respectively.
Pole 2 was supported in the underground
by a compacted crushed brick of the same
size as Pole 1 around the embedded region.
Table-2 shows the basic soil properties
obtained in the laboratory. The soil is
classified as silty clay according to
IS:1498–1970.
Erection of the Pole
The poles were installed in the augured
hole, and the base was grouted with a 1:2:4
concrete mixture (cement: sand: coarse
aggregates = 1:2:4). The concrete had been
tamped continuously to prevent the
formation of air pockets and thus ensure
proper concrete setting. The erection of the
pole is depicted in Figure 4c. To achieve
sufficient compressive strength for the
experiments, the pole foundation had been
cured for 28 days.
A tapered pre-stressed concrete (PSC) pole
of 8.5 m height as shown in Figure 4 is
used in the study. It has a cross section of
0.27 m x 0.09 m at the bottom which
tapers to 0.145 m x 0.09 m at the top. The

Volume 3 Issue 3
pole had been set in the augured hole and
the base has been backfilled by the same
soil by manual compaction. The
information about the density of
compacted fill and surrounding soil, sand
cone test performed.
Fig.3:-Field experimental setup schematic diagram.
(a) Erection of Electric pole (b) Sand cone test to measure
field density
(c) Pit for Electric pole
Fig.4:-Tests performed on field.
Reaction Frame
The lateral load has been applied to the
PSC pole through a reaction frame fixed at
the base (Figure 3). The reaction frame is
made out of two ISMC250 channels held
together with 8 batten plates (0.24 m x 0.2
m x 0.08 m) each on both sides. The
reaction frame is 8.0 m high with a cross-
section of 0.25 m x 0.25 m. The near-fixity
at the base of the reaction frame was
assured by providing an additional factor
of safety in its footing design. An isolated
square footing with a base area of 4.84 m2
is provided for the reaction frame. Four
anchor bolts of a diameter of 24 mm are
used to connect the base plate of the
reaction pole to the footing.

Volume 3 Issue 3
(a) load application mechanism (b) Load cell
(c) string potentiometer (d) data acquisition system
Fig.6:-Field set-up for experimental measurements.
Loading and Instrumentation
A monotonically increasing lateral load
had been applied at the top of the pole
through a lead screw and nut system,
which translates the turning motion into
linear motion. The load cell is placed in
direct compression to prevent errors due to
the imperfect rigidity of the reaction
frame. The lateral load is applied at the
point where lateral forces act on the pole
through three-conductor cables. It is
located 63 cm from the top of the pole.
The plates and bolts were designed for the
placement load cell with a factor of safety
of 4. A load cell is used to measure the
lateral load applied to the pole by
recording the gradual load increment with
time. A donut load cell of 500 kN capacity
was used in the experiment. Figure-6 (a,c)
& (d) show the load application
mechanism, string potentiometer, and data
acquisition system used in the study for
recording and processing the data.
The function of a string potentiometer is to
measure either linear or angular
displacement. The displacement readings
are measured using three-string
potentiometers located at a height of 0.5
m, 3.5 m, and 6.95 m from the ground
surface system.
EXPERIMENTAL RESULTS
The load-deformation behavior of the
poles recorded in the experimental studies
is shown in Figure 7.
In each experiment, the pole was applied
to the top of the lateral monotone load
until the displacement keeps increasing
without further increasing the load or
stopping as per the limitation of the
displacement sensors. After the loading
was completed, the poles were allowed to
unload and the displacements
corresponding to the unloading were also
recorded.
Figure 7 shows the force deformation
behavior of Pole 1, where the load channel
record is plotted with the displacement
sensor records at the top and middle
channels. (at a height of 6.95 m and 3.5 m,
respectively, from the ground) The load
capacity is observed to be 1.74 kN, where
the displacement at the top is observed.

Volume 3 Issue 3
Fig.7:-Experimental force-deformation behavior of (a) Pole 1, (b) Pole 2
The central locations corresponding to the
final load are approximately 40 cm and 13
cm respectively. Note that the load
capacity is defined as the maximum
displacement load of 35 cm (i.e., a drift
ratio of 5 per cent). Figure 9 shows the
results of the Pole 2 experiments, where a
load capacity of 2.68 kN is observed. This
increase in capacity is due to an increase in
foot size (53 cm×53 cm instead of 45
cm×45 cm in pole-1).
It is noted that increasing the size of the
base by only 20 % increases the capacity
of the pole by approximately 54 %. Figure
9 shows the behaviour of Pole 2, where the
pole foundation soil is made of compact
crushed bricks and stones. It is interesting
to note that the behaviour of Pole 2 is very
identical to that of Pole 1 with a slightly
greater capacity (1.79 kN), which confirms
that for a competent soil with reasonable
strength, a brick-stone foundation can
replace a concrete foundation without
much alteration in the final load capacity
or load-deformation behaviour. This is
necessarily significant in a country like
India, where compact crushed brick-stone
aggregates are often used to provide cost-
effective support for simple structures such
as the Poles.
It can be noted that, in most cases,
unloading stiffness is slightly lower than
loading stiffness. Note that small
undulations in the load-deformation curves
are the result of discreet movements of
machine screws and slipping. Table-4
summarizes the different response
parameters obtained in this experiment.
In relation to the load capacity, the
displacement due to rigid body rotation of
the flexural component, the displacement
of the yield, and the force at the first
output point are included in the summary

Volume 3 Issue 3
table, as these are equally important design
parameters for assessing the performance
of the constructed facilities. The yield
displacement is estimated graphically by
obtaining a point of intersection between
the initial and the post-yield tangents of
the load-displacement curves.
Table 4:-Response parameters derived from the experiment.
Sr.
No.
Parameters Pole-1 Pole-2
1 Load Capacity (kN) 1.76 1.81
2 Max. displacement at top (m) 0.395 0.410
4
Max. displacement at middle
(m)
0.118 0.129
6
Disp. Due to rigid body rotation
(cm)
2.58 2
7 Disp. Due to flexure (cm) 37.58 36.48
8 Yield Disp. (m) 7.44 6.19
9 Load at first yield (kN) 1.31 1.28
10 Foundation Material Compacted Soil
Compacted soil + Broken brick
ballast
Figure 10 shows the method of analysis
used to obtain the displacement of yield
and the yield strength of the poles. This is
one of the best practices for predicting the
first yield point or transition point in
between elastic and post-elastic behaviour
of any material from a nonlinear force-
deformation curve [15]
.
Fig.8:-Load Vs Settlement - Pole-1

Volume 3 Issue 3
Fig.9:-Load Vs Settlement - Pole-2
Fig.10:- Estimation of yield displacement and yield force from experimental force-
deformation behavior.

Volume 3 Issue 3
Fig.11:-Displacement profile of the pole
Discussion: All 2 poles produced a
substantial number of fine cracks along
with the height due to a large flexural
deformation (Fig. 10a, b, and c). However,
no evidence of plastic hinge formation has
been observed and the structure has not
failed or collapsed. Subsequently,
significant cracks were observed on the
surface of the soil, although there was no
significant upheaval of the soil (Fig. 10c).
In addition, for Pole-2, a clear gap between
the structure and the soil has been
observed on the ground surface (Fig. 10b).
Fig.12:- (a) Deflection of pole after experiment, (b) cracks observed on the pole, and (c)
cracks observed on the ground
Ground Level

Volume 3 Issue 3
This is an evidence that the basis of this
case is relatively weaker than the previous
case, which may be due to the use of a
compact brick-stone aggregate instead of a
concrete base. Pole-2 also exhibits a larger
deformation at mid-height (14.77 cm)
compared to the other two poles (12.62 cm
and 11.58 cm) at their respective load
capacity. In addition, the yield capacity
and load at the first yield point are also the
lowest in Pole-2 (as shown in Table- 4),
indicating the early yield of the adjacent
soil in this case.
CONCLUSION
In this work, a field investigation is carried
out to understand the mechanism of failure
of shallow embedded pre-stressed concrete
poles in the rural area of the Unnao district
of Uttar Pradesh, India, where several
failures of such poles have been reported
during recent windstorms. Full-scale field
tests were carried out to understand the
failure mechanism of the Pre-Stressed
Concrete poles embedded in the silky-clay
soil bed subject to monotonic lateral loads.
The 8.5-meter chamfered poles had the
very same structural dimensions and
properties, but they were supported by two
different basic conditions: pole 1 with a
base of 45 cm×45 cm made of concrete
and brick-stone aggregates, respectively,
while pole-2 with a base of 53 cm×53 cm
of concrete.
Load capacity for 2 poles is 1.74 kN and
1.79 kN where the load capacity is defined
as the load corresponding to the top 5
percent drift ratio. It is noted that the
capacity is 0.94 and 0.97 times the design
wind load of the region as per IS-875[18],
indicating that two poles may undergo a
drift of up to 5% if they are subject to a
design wind speed. Pole-2 showed a higher
capacity, which is due to the increased size
of its base. It is observed that increasing
the footprint from pole 1 to pole 2 by only
19% increases the capacity by
approximately 53.4 %
The selection of the foundation material
does not have much influence on the
capacity or load-deformation behaviour.
The base of the compact crushed brick-
stone mixture in Pole-2 had similar
capacities to that of Pole-1, which was
made of a concrete base of the same size.
This finding is particularly relevant for
rural India, where brick-stone aggregates
are often used as a cost-effective support
option. The experiments demonstrated a
flexicurity type of structural deformation
of the poles with fine visible cracks.
However, no evidence of plastic hinge
formation was observed and the structure
did not collapse or fail completely.
ACKNOWLEDGEMENT
The author is thankful to Structure
Engineering / Civil Engineering
Department, IIT Kanpur, under which
during summer internship the above work
was carried out. The Project client was
electricity board, Uttar Pradesh Govt.
hence fully funded by them. Special thanks
to Mr. Abrar Ahmad & Mohit Dwivedi for
the execution of field experimental set-up
and data acquisition.
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Volume 3 Issue 3
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Volume 3 Issue 3
26. IS: IS 1678: 1998- Prestressed
concrete poles for overhead power
traction and telecommunication lines –
specification.
Cite this article as: Samirsinh Parmar.
(2022). The Experimental Failure
behaviour of a Prestressed Concrete
Electricity Transmission Pole: A Case
Study for Kannauj Soil, Uttar Pradesh,
India. Journal of Engineering Analysis
and Design, 3(3), 1–13.
https://doi.org/10.5281/zenodo.5837583
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The Experimental Failure behaviour of a Prestressed Concrete Electricity Transmission Pole: A Case Study for Kannauj Soil, Uttar Pradesh, India