A COMPARATIVE STUDY ON ANALYSIS OF … · to identify the efficient member cross section suitable for the telecommunication tower by carrying out a comparative analysis of telecommunication

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 2017, pp. 1002-1011, Article ID: IJCIET_08_04_114 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed

A COMPARATIVE STUDY ON ANALYSIS OF TELECOMMUNICATION TOWER WITH DIFFERENT MEMBER CROSS SECTION

J. Vinotha Jenifer Department of Civil Engineering, KCG College of Technology, Chennai, India

P.K. Umesha TTRS, CSIR-SERC, Chennai, India

Priya A. Jacob Department of Civil Engineering, North Malabar Institute of Technology,

Kerala, India

ABSTRACT Over past three decades there is an increasing demand for wireless

communication which leads to dramatic increase of communication tower construction. Stability of such structure is a major concern. Therefore among the various cross section of members used for the construction of telecommunication towers, efficient cross section of the member has to be identified for maintaining the stability of the structure under various conditions. The main objective of this paper is to identify the efficient member cross section suitable for the telecommunication tower by carrying out a comparative analysis of telecommunication towers with different member cross section for different heights. The towers are modelled and modal analysis has been carried out for various member cross sections of telecommunication towers for four different heights using FEA package ANSYS Workbench. As a result, frequencies are compared for different member cross section for the corresponding mode shapes. The results of this comparative analysis demonstrate the efficiency of a particular member cross section of tower which can be adopted for communication purposes. Key words: Ansys, Circular Hollow Section, Square Hollow Section, Modal Analysis. Cite this Article: J. Vinotha Jenifer, P.K. Umesha and Priya A. Jacob, A Comparative Study on Analysis of Telecommunication Tower with Different Member Cross Section. International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 1002-1011. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=4

A Comparative Study on Analysis of Telecommunication Tower with Different Member Cross Section


1. INTRODUCTION The structures which are tall with relatively small cross sections, has a large ratio between the height and the maximum width are generally known as towers. They can be standalone structures or be supported by adjacent buildings or be mounted on any other structure. Towers are classified into various categories based on their purposes such as Power transmission towers, Telecommunication towers, Wind turbine towers etc. Among these entire towers telecommunication tower is considered as one of the key driving forces for the socio economic development of a nation. Telecommunication towers serves for the purpose of supporting one or more antennas for communication purposes.

It has two types of infrastructure: Electronic segment of the infrastructure includes Base tower station, switches, antennas,

transceivers etc. which is called as the active part of the structure

Non-Electronic segment of the infrastructure includes tower, shelter, electrical equipment etc. which is called as passive part of the structure.

Telecommunication towers are of different types based on, Structural action

Cross Section of tower

Material sections

Placement of tower

Number of segments The current study is carried out based on the different types of member cross sections of

tower such as Angular section, Circular Hollow section, Square Hollow section and its different combinations. The main aim of this study is to figure out the efficient cross section of member which can be incorporated in telecommunication towers.

2. LITERATURE REVIEW Several researches have been carried out on analysis of telecommunication towers as listed below:

Glanville and Kwok (1995) [2] have presented the results of a field measurement program which was conducted on a steel frame tower. A microwave communication steel fame tower was erected and their effect upon the dynamic response was analyzed. The natural frequencies and mode shapes of the tower were obtained using a Finite Element program STRAND6. The natural frequency values obtained through full scale measurement are compared to the values of STRAND6. Damping was determined by large amplitude free vibration decay and low amplitude autocorrelation analysis. An increase in tower response was found with increasing wind speed fluctuation and lateral turbulence.

Murtagh et. al (2004) [4] demonstrates simple approximate methods for determining natural frequencies and mode shapes of towers supporting utilities. Free vibration analysis was carried out in ANSYS with no external source of excitation or damping. The values obtained from the FE model and the reduced order model is compared. Further analysis using the approximate cantilever system can be used to predict the response of an arbitrary lattice tower.

Prasad Rao et. al (2004) [3] derived a relationship between the ratio of the test to theoretical deflection and a non-dimensional parameter to serve as an index for monitoring the structural displacement during testing. The towers are analyzed using SAP/NASTRAN

J. Vinotha Jenifer, P.K. Umesha and Priya A. Jacob


programs. The natural frequencies obtained from the analysis program were higher than the experimental ones. The proposed equation to predict natural frequency was derived based on the test and analytical deflections as well as geometrical parameters.

Siddesha (2010) [5] presented the analysis of microwave antenna tower with static and Gust factor method. They have compared the tower with angle and square hollow section. The modelling and analysis is done by Finite Element Package ANSYS. Modal analysis of tower has been carried out by subspace iteration method in ANSYS. The natural frequencies and mode shapes are obtained. From the analysis, the author concludes that the square hollow sections can be used more effectively in the leg member compared to the angle sections. The square hollow sections as bracing did not show much reduction in displacement compared to the square hollow sections as leg member.

Jithesh Rajasekharan and Vijaya (2014) [1], have studied about the telecommunication towers of varying heights with different bracing form seismic along with the wind effect. The wind effect is studied using the gust factor method whereas the seismic effect is studies by carrying out modal analysis and response spectrum analysis. The lattice tower of three different heights with different types of bracings is modelled in STADD PRO 2007 software program. During the FE analysis of tower, initially the joint displacements at the top of the tower and the member stress at the base leg members were compared for different wind zones. And then the modal analysis has been carried out determining the natural frequencies and their mode shapes. In the modal analysis, there were gradual decreases in frequency as the height of tower increases.

3. MODELLING OF TOWERS The telecommunication tower is analyzed for 4 different heights such as 20m, 29m, 60m and 70m. The towers are analyzed for 9 different combinations of member cross sections to understand the better behavior of the member sections under various heights. The different combinations of member cross sections incorporated in the telecommunication towers are shown in table 1. The modelling and analysis has been carried out in ANSYS WORKBENCH. The material properties of the towers are as follows:

Density (ñ) = 7.85e-006 kg mm^-3 Young's Modulus (E) = 2.e+005 MPa Poisson's ratio = 0.3 Yield Strength = 250 MPa

Table 1 Combinations of member cross section on tower

Leg Bracing/Belt Angle Angle Circular Hollow Circular Hollow Square Hollow Square Hollow Angle Circular Hollow Square Hollow Circular Hollow Angle Square Hollow Circular Hollow Square Hollow Circular Hollow Angle Square Hollow Angle



The dimensions of member cross sections (CHS & SHS) are determined from the dimensions of angular cross section by equating the Area and Moment of Inertia of the member sections as per the Table 2. The towers are supposed to have equal mass and volume for all the 9 combinations of tower for the same height since the area and Moment of Inertia are equal for one particular height. For e.g. a tower of 20m have nine different combinations of member cross section as per Table 1. All the 9 towers have the same mass and Volume for the same height. That is how the analysis is carried out. The behavior is observed for the equal weight of 9 towers of different member cross section subjected to free vibration.

Figure 1 Member Cross Sections (Angle, CHS, SHS)

Table 2 Area and Moment of Inertia of CHS & SHS

CHS SHS

Area

Moment of Inertia

The dimensions of individual members of equivalent weight of the three member sections

are as follows:

Table 3 Dimensions of individual members of 20m Tower for different member cross section

Angle Section CHS SHS L(mm) B(mm) t(mm) D(mm) t(mm) L(mm) B(mm) 75 75 5 69.68 6.97 60.48 54.16 75 75 6 69.93 8.35 60.725 53.14 130 130 12 121.62 16.73 105.64 90.47 65 65 6 60.81 8.36 52.82 45.24 130 130 10 121.12 12.12 105.162 92.52 100 100 8 93.25 11.16 80.97 70.85 45 45 5 67.33 4.15 36.77 30.45

Table 4 Dimensions of members of 29m tower for different member cross section

Angle Section CHS SHS L(mm) B(mm) t(mm) D(mm) t(mm) L(mm) B(mm) 75 75 5 69.68 6.97 60.48 54.16 75 75 6 69.93 8.35 60.72 53.14 130 130 12 121.62 16.73 105.64 90.47



65 65 6 60.81 8.36 52.82 45.24 130 130 10 121.12 12.12 105.16 92.52 100 100 8 93.25 11.16 80.97 70.85 45 45 5 67.33 4.15 36.77 30.45 75 75 8 70.43 11.15 61.23 51.11 150 150 16 140.87 22.30 122.42 102.2


Angle Section CHS SHS L(mm) B(mm) t(mm) D(mm) t(mm) L(mm) B(mm) 75 75 5 69.68 6.97 60.48 54.16 75 75 6 69.93 8.35 60.72 53.14 130 130 12 121.62 16.73 105.64 90.47 65 65 6 60.81 8.36 52.82 45.24 130 130 10 121.12 12.12 105.16 92.52 100 100 8 93.25 11.16 80.97 70.85 45 45 5 67.33 4.15 36.77 30.45 75 75 8 70.43 11.15 61.23 51.11 150 150 16 140.87 22.30 122.42 102.2 90 90 8 84.13 11.16 73.04 62.92 90 90 6 83.61 8.37 72.58 65 80 80 6 74.25 8.4 64.66 57.06

200 200 20 187.5 27.85 163 137.61 200 200 16 186.5 22.31 161.94 141.7 150 150 20 141.88 27.86 123.39 98.1 50 50 6 47.14 8.36 40.97 33.38


Angle Section CHS SHS L(mm) B(mm) t(mm) D(mm) t(mm) L(mm) B(mm)

75 75 5 69.68 6.97 60.48 54.16 75 75 6 69.93 8.35 60.72 53.14 130 130 12 121.62 16.73 105.64 90.47 65 65 6 60.81 8.36 52.82 45.24 130 130 10 121.12 12.12 105.16 92.52 100 100 8 93.25 11.16 80.97 70.85 45 45 5 67.33 4.15 36.77 30.45 75 75 8 70.43 11.15 61.23 51.11 150 150 16 140.87 22.30 122.42 102.2 90 90 8 84.13 11.16 73.04 62.92 90 90 6 83.61 8.37 72.58 65 80 80 6 74.25 8.4 64.66 57.06 200 200 20 187.5 27.85 163 137.61 200 200 16 186.5 22.31 161.94 141.7 150 150 20 141.88 27.86 123.39 98.1 50 50 6 47.14 8.36 40.97 33.38 110 110 8 59.45 22.36 88.87 78.76



The following figure 2 shows the elevation of tower of 4 different heights of angle section:

Figure 2 Elevation of towers (70m, 60m, 29m, 20m)

4. MODEL ANALYSIS OF TOWERS Model analysis has been carried out for all the towers of 4 different heights with 9 different combinations of 3 member cross sections. Natural frequencies and their corresponding mode shapes were determined using the FE software ANSYS WORKBENCH for the total of 36 towers.

Figure 3 Model of 20m Tower (Angle Section) Figure 4 Model of 29m Tower (Angle Section)

Figure 5 Model of 60m Tower (Angle Section) Figure 6 Model of 70m Tower (Angle Section)



Figure 7 (a) Angle Section Figure 7 (b) CHS

Figure 7 (c) SHS Figure.7 (d) Leg: CHS, Bracing/Belt: SHS

5. RESULTS AND DISCUSSIONS The modal analysis has been carried out and their natural frequencies are tabulated below:

Table 7 Natural frequency of 20m tower

Graph 1 Natural frequency Vs configuration (20m tower)






Graph 3 Natural frequency Vs configuration (60m tower) Table 10 Natural frequency of 70m tower




Figure 8 Six Mode Shapes of 29m tower (CHS)

6. CONCLUSION From the comparison of the tabulated frequencies of different heights of tower and different combinations of member cross sections, the following conclusions are obtained:

As the height of the tower increases, the natural frequency decreases.

Among the combinations of member cross section of towers at different heights, the following table 11 shows the highest frequency of member cross section of tower for their corresponding heights.

Table 11 Maximum Frequency of towers for different heights

Height Frequency 20 Leg: CHS, Bracing/Belt: Angle 29 SHS 60 Leg: SHS, Bracing/Belt: CHS 70 Leg: SHS, Bracing/Belt: Angle

Even though all the 9 towers at one particular height have equal volume and mass, there is change in frequency mainly due to the difference in centroid of the section and polar moment of inertia. Also, more the mass is away from the CG, the frequency decreases. That is why hollow sections have better frequency compared to the other sections.

From the overall discussion, the analytical results are in total agreement with the theoretical results.



ACKNOWLEDGEMENT The paper is published with the permission of the director of CSIR Structural Engineering Research Centre, Chennai.

REFERENCES [1] Jithesh Rajasekharan, S. Vijaya (2014), “Analysis of Telecommunication tower subjected

to seismic and wind loading”, Internation Journal of Advancement in Engineering Technology, Management & Applied Science, Volume 1, Issue 2 July 2014.

[2] M.J. Glanville, K.C.S. Kwok (1995), “Dynamic characteristics and wind induced response of a stee frame tower”, Journal of Wind Engineering and Industrial Aerodynamics 54/55 (1995) 133-149.

[3] N.Prasad Rao, S.J. Mohan, N.Lakshmanan (2004), “A semi empirical approach for estimating displacements and fundamental frequency of transmission line towers”, International journal of structural stability and Dynamics Vol 4, No.2 (2004) 181-195. [PK]

[4] P.J.Murtagh, B.Basu, B.M. Broderick (2004), “Simple models for natural frequencies and mode shapes of towers supporting utilities”, Computers and structures 82 (2004) 1745-1750.

[5] Siddesha. H (2010), “Wind analysis of Microwave antenna towers”, International journal of applied engineering research Vol 1, No 3, 2010.

[6] Arpit Chawda, Vijay Baradiya (2015), “Influence of structrure characteristics on earthquake response under different position of rooftop telecommunication towers”, International journal of engineering sciences & research technology.

[7] Bibitha K Eldhose, Harinarayanan S, S.Usha (2014), “Linear analysis of guyed mast subjected to wind, ice and seismic loading”, International journal of engineering research and applications.

[8] J.D.Holmes, B.L.Schafer and R.W.Banks (1992), “Wind induced vibration of a large broadcasting tower”, Journal of Wind Engineering and Industrial Aerodynamics, 41-44 (1992) 2101-2109.

[9] Marcel Isandro, Jose Guillherme S. da Silva (2007), “Structual analysis of guyed steel telecommunication towers for radio antennas”, Journal of the Brazilian society of Mechanics science and engineering Vol XXIX No.2/185.

[10] Marcelo Greco, Ivone passos Ferreira (2010), “Geometric nonlinear dynamic analysis of a telecommunication tower”, 9

th Brazilian conference on dynamics.

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A COMPARATIVE STUDY ON ANALYSIS OF … · to identify the efficient member cross section suitable for the telecommunication tower by carrying out a comparative analysis of telecommunication