Essay: Telecommunications towers

CHAPTER-1
INTRODUCTION
1.0 GENERAL
In present generation, the telecommunication industry is playing a great role in human societies and thus much more attention is now being paid to telecommunication towers than it was in the past. As each and every individual is carrying a mobile with him/her now-a-days the demand for telecommunication services have increased. Telecommunication Towers are the only means for coverage area and network reliability.
Developing countries – like India have realized the importance of communication in the later part of 20th century. According to DoT (2013), today Indian Telecommunication Sector is one of the fastest growing telecom sectors and it has become the second largest network in the world, next to China. The Government of India really has encouraged the telecom sector to penetrate in the new markets across the country by adopting appropriate policies.
Civil Engineering plays a vital role in telecommunication sector, by providing passive and active infrastructure. Passive infrastructure includes towers, cabinets, generators, fuel tanks, etc., whereas Active Infrastructure includes the Telecommunication equipment itself like Antennas, Microwave Dishes, etc. Infrastructure support is provided in the form of site survey, site development, project management and structural assessment.
We as Civil Engineers design and analyse the towers that support the panel antennas and other telecommunication equipment and their foundations. All the equipment like mounts, antennas etc. are mounted on the tower which requires civil engineering expertise.
There are many factors governing the selection of a tower site. The tower height depends on how much coverage area is needed and the reach of the antenna signal and strength. The selection of type of tower depends upon various factors such as availability of land, material, workmanship, purpose, number of carriers etc.
Tower structural calculations include Applied Loads like wind load, dead load, seismic load and Design Strength of structural steel member on superstructure including connections and Foundation.
TYPES OF TOWERS
Towers are classified into different types based upon their structural action, their cross-section, the type of sections used and on the placement of tower.
Based on the structural action:
Monopole Tower
Self-Support Tower
Guy Tower
1.1.1 MONOPOLE TOWER ”’ Cantilever Action
These are hollow tapered steel tubes that fit over each other to form a stable pole of certain height.
Monopoles are either round in shape or consists of flats of 6, 12, 18 etc. Pole Sections are either flange connected or splice connected. The depth of the splice connection or the number of bolts in flange connection, the base width, number of sections, thickness of the pipe walls etc. shall be determined according to the requirements.
There are also different types of monopole towers such as monopines, concealment poles, flag poles etc. Sometimes monopoles are located in between the pine trees and flag poles for stealth purposes.
Monopoles are proved to be best option when there is land availability constraint. Also when the tower height is not so high and antennas, dishes and other equipment is considerably low monopoles are opted.
The main advantage of the Monopole Tower is that the Initial Cost is low, labour required is low, and the steel quantity required is also low comparatively. These can be installed very quickly and can be erected easily.
Equipment can also be easily mounted on top of the tower. Transportation is also feasible, But at the same time the maintenance cost is high for the Monopole Towers since when it fails at its strength or the main functionality for which it is made to stand at a particular location, then the structural modifications required to be installed to bring the tower into respective code conformance is high with respect to cost and workmanship compared to the self-support towers. Also the deflections are high after certain heights compared to the self-support towers.
In case of overstress in any of the pole shafts the tower shall be reinforced with new steel members such as flat plates, solid rods, channels or I-beam members. Cost of reinforcing the tower and bringing it into normal condition depends on the amount of overstress and component that is overstressed. For simple shaft reinforcing by adding plate reinforcement over small portion of the pole shaft might cost less compared to an overstress in the foundation system of the tower. When both the tower shaft and its foundation need reinforcing then the cost is very high and it needs skilled labour to perform the installation of modifications hence the difficulty level involved is high too.
1.1.2 SELF SUPPORT TOWER – Latticed structures with truss elements – Overturning Moment is about its Centroid
As the name suggests the tower supports itself on its legs and is stable from wind and other loads to a certain magnitude.
This is governed by its internal resisting forces in the form of bracing system and the main leg members. Structural action can be said to be similar as that of Frames and Trusses.
Self-Support Towers are again of two types which can be described simply as 3-legged and 4-legged. These can be having truss legs, pipes, solid rounds or schifflerized sections (bent plates) etc. Self- Support type towers are found plenty everywhere.
These are also easy to install, but more steel and labour are required. Though the initial cost is high the maintenance cost is low compared to the monopole towers. Work Platforms, Feed line Ladders etc. can be easily installed and it is easy for a tower climber to climb and do any sort of work on the tower.
The deflections are not so high since there will be number of bracing members on the tower connecting the legs that resist the forces unlike the monopole standing like a single stick.
Self-Support towers are deemed as overstressed from several of the structural members comprising the tower itself. Legs, bracing members, bolt connections and foundation can all be overstressed with either single member failing or entire section being overstressed. Modifications or reinforcements that can bring the overstress level down and into normal conformance include adding higher dimension members, providing additional bracing options, reinforcing the legs or proving stiffeners to connections, etc. Cost of the reinforcements depends on the extent of overstress in the tower or the foundation and it increases with the increase in overstressed members.
1.1.3 GUYED TOWER ”’ Non Moment Resisting, torsion can be resisted by the guy wires ”’ These are the towers that are tethered by wires. The face widths remain same from bottom to top in most of the cases.
1.2 FACTORS EFFECTING THE SELECTION OF TOWERS
There are many factors to be considered before selecting a tower that is to be installed.
Purpose – whether the tower is used for normal telecommunication or stealth or for aviation.
Land availability – if there is less area available for lease then monopoles are more feasible but if the lease area available is more than self-support type tower can be opted for with other requirements met.
Height of the tower – monopole can be opted for upto an overall height of 90m but self-support type towers can typically go beyond 90m and upto a height of 250m. So beyond a tower height requirement of 75m it is more efficient to opt a self-support tower.
Equipment to be installed – if more equipment is to be installed with more than three levels of loading elevations then for a similar height tower self-support type towers are more efficient at resisting loads within their structural capacity compared to monopoles.
Any obstructions like dense urban areas, aviation, etc. – to avoid obstructions and broadcast signals from a higher range and with a larger radius self-support towers are opted but if it is aviation purpose then monopoles shall be more feasible.
Project Cost – including the modification costs if the tower fails and considering a typical life span of 10 years, monopoles are more efficient.
Availability of the labour and steel quantity – monopoles require less steel and less labour to install compared to self-support towers.
Transportation Feasibility – monopoles are generally transported in shaft sections whereas the self-support tower sections can be transported as knocked down units.
Client Requirement – with an overall lower cost and ease of installation with the exception of less equipment and for similar sized towers monopoles are preferred over self-support towers. It is only when tower height, larger reception radius and more equipment is needed self-support towers are preferred.
LOADS ACTING ON THE TOWERS
Wind Loads – loads due to wind force on the structure and on the telecommunication equipment.
Live Loads – typically from man loads such as man load on self-support horizontals, man loads on step pegs and pole shaft from climbers, etc.
Dead Loads – gravity load of structure itself and from the telecommunication equipment.
Earthquake loads – due to seismic forces on the structure.
TYPES OF FOUNDATION USED FOR THE TOWER.
Depending on the type of tower, foundations are of different types such as spread foundations, mat foundations, caisson foundations and rock anchors. For monopole type towers spread foundations are preferred when the soil beneath the tower is sufficiently having a good bearing resistance. In case the soil is loose caisson foundations are considered for monopole towers. A combination of spread footing with rock anchors or caisson with rock anchors is considered when there is rock present at a certain depth.
STAAD(X) TOWER
STAAD (X) Tower was used to evaluate different tower types and tower heights for this project. There are other finite element softwares that are available to use for tower analysis. However, STAAD (X) Tower software has more interactive user interface wherein any changes made in the software user interface is seen in the graphics window. This software was developed for many country codes with India being one of the countries and the main codes used for the tower analyses in this project are IS800, IS802. When self-support or guyed tower is selected in the software’s user interface each beam element is treated as a truss element in the STAAD (X) Tower software for the purpose of analysis. When monopole tower is selected the shaft sections are segregated into small beam elements of varying lengths of 0.5m to 1m with each beam element nodes and member fixities considered as fixed which is typical for monopole type towers. The above mentioned procedure has been adopted for the tower analyses done using this software in this project.
OBJECTIVE OF THE STUDY
Monopole and self-support tower types are considered to achieve the objective of this study. Different heights of 30m, 40m and 50m of Monopole and Self-Support Towers were considered. The main objective of this study was:
To determine the lateral displacements and quantity of steel required for Monopole and Self-Support Towers using STAAD(X) Tower software for three different heights with three different wind speeds.
To compare the lateral displacements and quantity of steel observed for Monopole and Self-Support Towers of considered heights.
The geometrical configurations for all these towers were maintained in such ways that the towers are passing for the respective heights and wind speeds.
SCOPE OF THE STUDY
1) Study was conducted only for two types of towers i.e., Monopoles and Self-Support Towers.
2) Basic wind speeds considered for Analysing were 33m/sec, 47m/sec and 55m/sec only.
3) Linear Static analysis was performed.
4) Study does not include seismic forces. Also connections were not evaluated for the towers.
CHAPTER-2
LITERATURE REVIEW
2.0 GENERAL
Many studies were made regarding the analysis of Telecommunication Towers. Earlier studies were made comparing the self-support towers for different heights but it is observed that nowhere a monopole and self-support tower is compared. In this study the main objective is to compare and analyse monopoles and self-support towers in many aspects like deflections observed on the towers of different heights for three different wind speeds, amount of steel required, optimistic selection of towers according to the available situations etc.
2.1 EARLIER STUDIES
GHODRATI AMIRI5 (2004) investigated the overall seismic response of 4-legged self-supporting telecommunication towers. For this purpose, ten of the existing 4-legged self-supporting telecommunication towers in Iran are studied under the effects of the design spectrum from the Iranian seismic code of practice and the normalized spectra of Manjil, Tabas, and Naghan earthquakes. As part of some of the results, it was observed that the first three flexural modes are sufficient for the dynamic analysis of such towers, even though in the case of taller towers, considering the first five modes would enhance the analysis precision.
BRYAN KEITH LANIER4 (2005) completed research at North Carolina State University who proposes a strengthening solution utilizing high-modulus carbon fiber polymers as a retrofitting mechanism for monopole telecommunication towers. The experimental program, along with development of an analytical model, investigates the behaviour and validates the effectiveness of carbon fiber in increasing the flexural capacity of existing monopole tower structures. The experimental program consists of testing three large scale monopole towers using high-modulus sheets, high-modulus strips and intermediate-modulus strips to determine their respective effectiveness in increasing the flexural strength enhancement. The three tests are designed using approximately the same reinforcement ratios, as well as identically sized monopole towers, to compare the effectiveness of the three strengthening systems regarding the increase in strength and stiffness.
SIDDESHA14 (2010) presented the analysis of microwave antenna tower with Static and Gust Factor Method (GFM). The comparison is made between the tower with angle and square hollow section. The displacement at the top of the tower is considered as the main parameter. The analysis is also done for different configuration by removing one member as present in the regular tower at lower panels.
ABDULMUTTALIB I. SAID1 (2013) had completed the analysis and optimum design of self-supporting steel communication tower. A special technique is used to represent the tower as an equivalent hollow tapered beam with variable cross section. Then this method is employed to find the best layout of the tower among pre-specified configurations. The formulation of the problem is applied to four types of tower layout with K and X brace, with equal and unequal panels. The objective function is the total weight of the tower. The variables are the base and the top dimensions, the number of panels for the tower and member’s cross section areas. The formulations of design constraints are based on the requirements of EIA and ANSI codes for allowable stresses in the members and the allowable displacement at antenna position. The Sequential Unconstrained Minimization Technique (SUMT) is used to perform the process. Direct stiffness method is used for the analysis of the structure, with beam elements. The strain energy is used to derive the stiffness matrix for members of unsymmetrical cross section. A computer program in FORTRAN is developed to represent the tower as an equivalent beam, and generate the tower nodes and members, analysis, design and to find the optimum design. Four types of tower are studied with different load cases. The effects of earthquake and wind loadings are taken in two directions and two positions of antenna are considered in the process to seek the optimum design. The tower type of X-brace with unequal panels has the minimum weight compared with other types of tower and the optimum design is satisfied when the angle of main leg is equal to (87O).
JESUMI8 (2013) has focused on identifying the economical bracing system for a given range of tower heights. Towers of height 40m and 50m have been analyzed with different types of bracing systems under wind loads. The diagonal wind has been found to be the maximum for towers. The optimal bracing system has been identified and reported.
RICHA BHATT12 (2013) analyzed two lattice towers of heights 18m and 40 by modeling them by three different structural idealizations namely, as 3D frame, 3D truss and as a hybrid of the two. Steel lattice tower of height 80 m assume to locate
at rural area with open terrain. The design wind speed and other wind properties as per
different standards were calculated. The comparison of different coefficients and loads were prescribed and comments on the difference are given.
JITHESH RAJASEKHARAN9 (2014) studied the wind effect on the structure by using the gust factor method and the seismic effect on the structure is studied by carrying out the modal analysis and response spectrum analysis. The results obtained from the above analysis are tabulated, compared and conclusions are drawn.
HARSHA JATWA7 (2014) compared Indian code IS: 802(Part l/Sec 1):1995 and ASCE 10-97(2000) code. For this, comparative study has been carried on the two different codes with respect to different types of base width, height and bracings. From the study of these codes we conclude that the Indian IS: 802(Part l/Sec 1):1995 code available for the design of tower requires certain modification as to made design more structural and economical as compare to the ASCE 10-97(2000) code. Through these studies certain recommendation has been made to Indian Code so it make updated with time as the ASCE is updating itself.
KESHAV KR. SHARMA10 (2015) he compared different heights of towers using different bracing patterns for Wind zones I to VI and Earthquake zones II to V of India. Gust factor method is used for wind load analysis, modal analysis and response spectrum analysis are used for earthquake loading. The results of displacement at the top of the towers and stresses in the bottom leg of the towers are compared.
RIYA JOSEPH13 (2015) she dealt with the analysis of monopole mobile towers. Analysis is done using ANSYS finite element software. The model provided by ANSYS is used to simulate the behaviour of monopoles when used as a communication tower. Efficiency of monopole tower is evaluated based on the finite element results.
PATIL VIDYA11 presented a paper investigating the structural response of special structures subjected to the influence of wind loading, as well as the combination of wind loading and ice. For the purpose of research activity, 6 types of steel masts have been analysed, namely 4 masts located on the ground and 2 masts located on buildings.
GUNATHILAKA6 analysed behaviour of existing four legged Greenfield towers under seismic loadings appropriate for Sri Lankan conditions using equivalent static load method given in ANSI/TIA-222-G. This can be considered as an initiative in this research area under local conditions. Results and conclusions based on this analysis are discussed in this paper.
AMIT THAKUR2 (2015) attempted to find out the seismic response of 4-legged angled section telecommunication tower and the dynamic analysis has been performed on this tower which is located on the roof top of setback-step back building by varying positions of tower with the existing host structure built up on ground slope of 300 in the both direction (X and Y). Their dynamic analysis is performed by SAP2000 program.
ANIL SHAKYA3 compared the wind load calculation on lattice tower with different wind load standards in Asia pacific region. Steel lattice tower of height 80 m assume to locate at rural area with open terrain. The design wind speed and other wind properties as per different standards were calculated. The comparison of different coefficients and loads were prescribed and comments on the difference are given.
CHAPTER 3
THEORY/METHODOLOGY
3.0 GENERAL
This chapter was discussed about the tower model specifications, wind parameters considered for the study, modelling of towers, loads and load combinations.
3.1 TOWER MODEL SPECIFICATIONS USED FOR COMPARISON
Tower types : Monopole and Self-Support
Heights : 30m, 40m and 50m
Basic wind speeds : 33m/sec, 47m/sec and 55m/sec
Comparison of lateral displacements at the top of towers is made between the similar sized monopole and self-support towers. The towers are modelled using STAAD(X) Tower software.
3.2 WIND PARAMETERS CONSIDERED FOR THE STUDY
Structure Class [k1] is considered as ”’Important builings and structures”’. The structure under consideration is used for Telecommunication purposes so there should not be any break-down in the services hence the structure class was considered as Important.
Terrain Category [k2] is Category 2. Since the City of Visakhapatnam receives tropical cyclones which pose danger to the performance of obstructions as there are trees that could be blown off damaging other obstructions thus Category 3 conditions might not be maintained effectively. Category 2 is more conservative also.
Structure Classification [k2] is Class B since all the tower models analyzed within the scope of this project are between the heights of 20m to 50m (including 50m).
Topography Factor [k3] is taken as Factor 1 assuming that the structure is on level ground and there will be no wind speed up due to rasied crest level or topographic features nearby.
3.3 MATERIAL PROPERTIES
Monopole ”’ IS1161:1998
Steel grade for shaft – YST-240
Yield stress – 240 MPa
Tensile strength – 410 MPa
Young”’s Modulus – 205000 MPa
Density of the steel – 7850 kg/m3
Self-Support ”’ IS2062:2011
Steel grade for leg members – E410
Yield stress – 410 MPa
Tensile strength – 540 MPa
Steel grade for bracing members – E250
Yield stress – 250 MPa
Tensile strength – 410 MPa
Young”’s Modulus – 205000 MPa
Density of steel – 7850 kg/m3
3.4 MODELLING OF TOWERS
Monopole ”’
A 18 sided polygon structured monopole tower model was considered for STAAD (X) analysis runs. Following are the Monopole Tower Models analysed in the software for three different heights, 30m, 40m and 50m with three different basic wind speeds of 33m/sec, 47m/sec and 55m/sec. The geometry varies for all the wind speeds and for all the three heights i.e., creating 9 different models of Monopoles.
Table 3.4.1: 30m-33m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 30 1.07 457.2 711.2 5
2. 20 1.27 572.4 847.3 7.75
3. 10.25 0 697.97 990.5 10.5
Fig: 3.4.1 Geometry for 30m Monopole for a wind speed of 33m/sec
Table 3.4.2: 30m-47m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 30 1.07 457.2 711.2 6
2. 20 1.27 570.4 845.3 8.75
3. 10.25 0 693.9 986.5 11.5
Fig: 3.4.2 Geometry for 30m Monopole for a wind speed of 47m/sec
Table 3.4.3: 30m-55m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 30 1.07 457.2 711.2 7
2. 20 1.27 568.42 843.3 9.75
3. 10.25 0 689.97 982.5 12.5
Fig: 3.4.3 Geometry for 30m Monopole for a wind speed of 55m/sec
Table 3.4.4: 40m-33m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 40 1.18 457.2 795.87 6
2. 26.67 1.52 652.33 1020.93 8.75
3. 13.33 0 863.34 1240.5 11.5
Fig: 3.4.4 Geometry for 40m Monopole for a wind speed of 33m/sec
Table 3.4.5: 40m-47m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 40 1.18 457.2 795.87 7
2. 26.67 1.52 650.33 1018.93 9.75
3. 13.33 0 859.34 1236.5 12.5
Fig: 3.4.5 Geometry for 40m Monopole for a wind speed of 47m/sec
Table 3.4.6: 40m-55m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 40 1.18 457.2 795.87 8
2. 26.67 1.52 648.33 1016.93 10.75
3. 13.33 0 855.34 1232.5 13.5
Fig: 3.4.6 Geometry for 40m Monopole for a wind speed of 55m/sec
Table 3.4.7: 50m-33m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 50 1.2 457.2 774.7 6
2. 37.5 1.5 630.62 975.32 8.5
3. 25.13 1.8 818.62 1169.13 11
4. 12.83 0 999.81 1371.4 13.5
Fig: 3.4.7 Geometry for 50m Monopole for a wind speed of 33m/sec
Table 3.4.8: 50m-47m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 50 1.2 457.2 774.7 6
2. 37.5 1.5 628.62 973.32 9.5
3. 25.13 1.8 814.62 1165.13 12
4. 12.83 0 993.81 1365.4 14.5
Fig: 3.4.8 Geometry for 50m Monopole for a wind speed of 47m/sec
Table 3.4.9: 50m-55m/sec monopole tower
Section No. Elevation above base height
(m) Lap Splice
(m) Top Dia.
T.D
(mm) Bottom Dia.
B.D
(mm) Thickness
t
(mm)
1. 50 1.2 457.2 774.7 8
2. 37.5 1.5 626.62 971.32 10.5
3. 25.13 1.8 810.62 1161.13 13
4. 12.83 0 987.81 1359.4 15.5
Fig: 3.4.9 Geometry for 50m Monopole for a wind speed of 55m/sec
Self-Support ”’
A 4-legged self-support tower model was considered in the STAAD(X) Tower analysis runs. The taper factor from the straight section to the tapered section from top to bottom of the tower is kept constant at 0.0625m/m with a top face width of 1.5m for all towers. Typical tower geometry and members assumed for the 30m, 40m and 50m self-support tower models for different wind speeds are as follows ”’
Table 3.5.0: 30m-33m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-4 2 X-Brace Leg ISA 90x90x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 4-10 2 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 10-12 1 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.85
Bracing ISA 110x110x12
4 12-18 2 X-Brace Leg ISA 150x150x15 Top ”’ 1.85
Bottom ”’ 2.9
Bracing ISA 130x130x10
5 18-24 1 X-BraceSH1 Leg ISA 180x180x15 Top ”’ 2.9
Bottom ”’ 3.95
Bracing ISA 150x150x10
6 24-30 1 X-BraceSH1 Leg ISA 180x180x15 Top ”’ 3.95
Bottom ”’ 5.0
Bracing ISA 150x150x10
Fig 3.5.0 Geometry of 30m SST for a wind speed of 33m/sec
Table 3.5.1: 30m-47m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-4 2 X-Brace Leg ISA 90x90x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 4-10 2 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 10-12 1 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.85
Bracing ISA 110x110x12
4 12-18 2 X-Brace Leg ISA 150x150x15 Top ”’ 1.85
Bottom ”’ 2.9
Bracing ISA 130x130x10
5 18-24 1 X-BraceSH1 Leg ISA 180x180x15 Top ”’ 2.9
Bottom ”’ 3.95
Bracing ISA 150x150x10
6 24-30 1 Double K1 Brace Down Leg ISA 180x180x15 Top ”’ 3.95
Bottom ”’ 5.0
Bracing ISA 150x150x10 / ISA 90x90x10
Fig 3.5.1 Geometry of 30m SST for a wind speed of 47m/sec
Table 3.5.2: 30m-55m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-4 2 X-Brace Leg ISA 90x90x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 4-10 2 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 10-12 1 X-Brace Leg ISA 130x130x10 Top ”’ 1.5
Bottom ”’ 1.85
Bracing ISA 110x110x12
4 12-18 2 X-Brace Leg ISA 150x150x15 Top ”’ 1.85
Bottom ”’ 2.9
Bracing ISA 130x130x10
5 18-24 2 X-BraceSH1 Leg ISA 180x180x15 Top ”’ 2.9
Bottom ”’ 3.95
Bracing ISA 150x150x10
6 24-30 1 Double K1 Brace Down Leg ISA 180x180x15 Top ”’ 3.95
Bottom ”’ 5.0
Bracing ISA 150x150x10 / ISA 90x90x10
Fig 3.5.2 Geometry of 30m SST for a wind speed of 55m/sec
Table 3.5.3: 40m- 33m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-6 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-16 2 X-Brace Leg ISA 180x180x20 Top ”’ 1.5
Bottom ”’ 2.143
Bracing ISA 130x130x10
4 16-22 2 X-Brace Leg ISA 180x180x20 Top ”’ 2.143
Bottom ”’ 3.107
Bracing ISA 130x130x10
5 22-28 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.107
Bottom ”’ 4.071
Bracing ISA 130x130x10
6 28-34 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 4.071
Bottom ”’ 5.036
Bracing ISA 150x150x12
7 34-40 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 5.036
Bottom ”’ 6.0
Bracing ISA 150x150x12
Fig 3.5.3 Geometry of 40m SST for a wind speed of 33m/sec
Table 3.5.4: 40m- 47m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-6 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-16 2 X-Brace Leg ISA 180x180x20 Top ”’ 1.5
Bottom ”’ 2.143
Bracing ISA 130x130x10
4 16-22 2 X-Brace Leg ISA 180x180x20 Top ”’ 2.143
Bottom ”’ 3.107
Bracing ISA 130x130x10
5 22-28 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.107
Bottom ”’ 4.071
Bracing ISA 130x130x10
6 28-34 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 4.071
Bottom ”’ 5.036
Bracing ISA 150x150x12
7 34-40 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 5.036
Bottom ”’ 6.0
Bracing ISA 150x150x12 / ISA 90x90x10
Fig 3.5.4 Geometry of 40m SST for a wind speed of 47m/sec
Table 3.5.5: 40m- 55m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-6 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x12 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-16 2 X-Brace Leg ISA 180x180x20 Top ”’ 1.5
Bottom ”’ 2.143
Bracing ISA 130x130x10
4 16-22 2 X-Brace Leg ISA 180x180x20 Top ”’ 2.143
Bottom ”’ 3.107
Bracing ISA 130x130x10
5 22-28 1 X-BraceSH1 Leg ISA 200x200x16 Top ”’ 3.107
Bottom ”’ 4.071
Bracing ISA 130x130x10
6 28-34 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 4.071
Bottom ”’ 5.036
Bracing ISA 150x150x12 / ISA 90x90x10
7 34-40 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 5.036
Bottom ”’ 6.0
Bracing ISA 150x150x12 / ISA 90x90x10
Fig 3.5.5 Geometry of 40m SST for a wind speed of 55m/sec
Table 3.5.6: 50m- 33m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face width
(m)
1 0-6 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-14 1 X-Brace Leg ISA 180x180x15 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
4 14-20 2 X-Brace Leg ISA 200x200x16 Top ”’ 1.5
Bottom ”’ 2.25
Bracing ISA 110x110x12
5 20-26 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 2.25
Bottom ”’ 3.0
Bracing ISA 130x130x10
6 26-32 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.0
Bottom ”’ 3.75
Bracing ISA 130x130x10
7 32-38 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.75
Bottom ”’ 4.5
Bracing ISA 150x150x10
8 38-44 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 4.5
Bottom ”’ 5.25
Bracing ISA 150x150x15
9 44-50 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 5.25
Bottom ”’ 6.0
Bracing ISA 150x150x15
Fig 3.5.6 Geometry of 50m SST for a wind speed of 33m/sec
Table 3.5.7: 50m- 47m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face widths
(mm)
1 0-6 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-14 1 X-Brace Leg ISA 180x180x15 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
4 14-20 2 X-Brace Leg ISA 200x200x16 Top ”’ 1.5
Bottom ”’ 2.25
Bracing ISA 110x110x12
5 20-26 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 2.25
Bottom ”’ 3.0
Bracing ISA 130x130x10
6 26-32 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.0
Bottom ”’ 3.75
Bracing ISA 130x130x10
7 32-38 1 X-BraceSH1 Leg ISA 200x200x25 Top ”’ 3.75
Bottom ”’ 4.5
Bracing ISA 150x150x10
8 38-44 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 4.5
Bottom ”’ 5.25
Bracing ISA 150x150x15 / ISA90x90x10
9 44-50 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 5.25
Bottom ”’ 6.0
Bracing ISA 150x150x15 / ISA90x90x10
Fig 3.5.7 Geometry of 50m SST for a wind speed of 47m/sec
Table 3.5.8: 50m- 55m/sec self-support tower
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description Face widths
(mm)
1 0-6 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x10 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
3 12-14 1 X-Brace Leg ISA 180x180x15 Top ”’ 1.5
Bottom ”’ 1.5
Bracing ISA 90x90x10
4 14-20 2 X-Brace Leg ISA 200x200x16 Top ”’ 1.5
Bottom ”’ 2.25
Bracing ISA 110x110x12
5 20-26 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 2.25
Bottom ”’ 3.0
Bracing ISA 130x130x10 / ISA 90x90x10
6 26-32 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 3.0
Bottom ”’ 3.75
Bracing ISA 130x130x10 / ISA 90x90x10
7 32-38 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 3.75
Bottom ”’ 4.5
Bracing ISA 150x150x10 / ISA 90x90x10
8 38-44 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 4.5
Bottom ”’ 5.25
Bracing ISA 150x150x15 / ISA90x90x10
9 44-50 1 Double K1BraceDown Leg ISA 200x200x25 Top ”’ 5.25
Bottom ”’ 6.0
Bracing ISA 150x150x15 / ISA90x90x10
Fig 3.5.8 Geometry of 50m SST for a wind speed of 55m/sec
3.5 LOAD COMBINATIONS CONSIDERED
1.0 DL +1.5 Wind 0 (Design)
1.0 DL + 1.5 Wind 45 (Design)
1.0 DL + 1.5 Wind 90 (Design)
1.0 DL + 1.0 Wind 0 (Service)
1.0 DL + 1.0 Wind 45 (Service)
1.0 DL + 1.0 Wind 90 (Service)
3.6 TYPICAL EQUIPMENT CONSIDERED ON THE TOWER FOR ANALYSIS
3.6.1 Monopole Tower:
For 30m – (3) Sectors each consisting of T-Arm Mount with 3 Andrew SBNH-1D6565B panel antenna at 27m elevation. (1) Andrew HP4-44 Dish each at 25m and 23m elevations.
For 40m – (3) Sectors each consisting of T-Arm Mount with 3 Andrew SBNH-1D6565B panel antenna at 37m elevation. (1) Andrew HP4-44 Dish each at 35m and 33m elevations.
For 50m – (3) Sectors each consisting of T-Arm Mount with 3 Andrew SBNH-1D6565B panel antenna at 47m elevation. (1) Andrew HP4-44 Dish each at 45m and 43m elevations.
Note ”’ The equipment coax is considered to be run internal to the monopole tower in the STAAD(X) Tower analysis.
3.6.2 Self-Support Tower:
For 30m – (3) Sectors each consisting of T-Frame Mount with 3 Andrew SBNH-1D6565B panel antenna at 27m elevation. (1) Andrew HP4-44 Dish each at 25m and 23m elevations.
For 40m ”’ (3) Sectors each consisting of T-Frame Mount with 3 Andrew SBNH-1D6565B panel antenna at 37m elevation. (1) Andrew HP4-44 Dish each at 35m and 33m elevations.
For 50m ”’ (3) Sectors each consisting of T-Frame Mount with 3 Andrew SBNH-1D6565B panel antenna at 47m elevation. (1) Andrew HP4-44 Dish each at 45m and 43m elevations.
Note ”’ The equipment coax is considered to be run on the face of the self-support tower in the STAAD(X) Tower analysis.
CHAPTER-4
RESULTS AND DISCUSSIONS
4.0 GENERAL
Lateral Displacement is the displacement occurred when the tower is subjected to certain wind force. Generally it increases with the increase in height from ground level, hence manximum displacement of a structure will occur at its top. In this chapter the lateral displacements and quantity of steel are tabulated for Monopoles and Self-Support Towers of three different heights subjected to three different basic wind speeds along with graphs plotted.
4.1 MONOPOLE
4.1.1 30m Height Monopole
A Monopole tower of 30m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speeds has been considered and graphs were plotted for the respectvie lateral displacements.
4.1.1.1 Subjected to 33 m/sec basic wind speed:
Table 4.1.1 : Lateral Displacement vs Height for 33 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service condition)
5 5.7 1.0 DL + 1.0 WL
10 23.0 1.0 DL + 1.0 WL
15 52.1 1.0 DL + 1.0 WL
20 93.1 1.0 DL + 1.0 WL
25 144.7 1.0 DL + 1.0 WL
30 201.3 1.0 DL + 1.0 WL
Fig 4.1.1 : Lateral Displacement vs Height for 33 m/sec basic wind speed
From fig 4.1.1, it was observed the maximum lateral displacement of 201.3 mm occurs at top of the monopole (i.e., at 30m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.1.1.2 Subjected to 47 m/sec basic wind speed:
Table 4.1.2 : Lateral Displacement vs Height for 47 m/sec basic wind speed
Height, m Lateral Displacement,
mm Load Case (Service condition)
5 11.0 1.0 DL + 1.0 WL
10 45.0 1.0 DL + 1.0 WL
15 101.4 1.0 DL + 1.0 WL
20 180.8 1.0 DL + 1.0 WL
25 279.7 1.0 DL + 1.0 WL
30 387.0 1.0 DL + 1.0 WL
Fig 4.1.2 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.1.2, it was observed the maximum lateral displacement of 387.0 mm occurs at top of the monopole (i.e., at 30m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.1.1.3 Subjected to 55 m/sec basic wind speed:
Table 4.1.3 : Lateral Displacement vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service condition)
5 14.4 1.0 DL + 1.0 WL
10 58.7 1.0 DL + 1.0 WL
15 132.1 1.0 DL + 1.0 WL
20 234.6 1.0 DL + 1.0 WL
25 361.4 1.0 DL + 1.0 WL
30 498.4 1.0 DL + 1.0 WL
Fig 4.1.3 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.1.3, it was observed the maximum lateral displacement of 498.4 mm occurs at top of the monopole (i.e., at 30m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.1.2 40m Height Monopole
A Monopole tower of 40m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speeds has been considered and graphs were plotted for the respectvie lateral displacements.
4.1.2.1 Subjected to 33 m/sec basic wind speed:
Table 4.1.4 : Lateral Displacement vs Height for 33 m/sec basic wind speed
Height, m Deflections, mm Load Case (Service condition)
5 4.5 1.0 DL + 1.0 WL
10 18.3 1.0 DL + 1.0 WL
15 42.2 1.0 DL + 1.0 WL
20 75.6 1.0 DL + 1.0 WL
25 120.6 1.0 DL + 1.0 WL
30 176.1 1.0 DL + 1.0 WL
35 241.1 1.0 DL + 1.0 WL
40 310.5 1.0 DL + 1.0 WL
Fig: 4.1.4 : Lateral Displacement vs Height for 33 m/sec basic wind speed
From fig 4.1.4, it was observed the maximum lateral displacement of 310.5 mm occurs at top of the monopole (i.e., at 40m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.1.2.2 Subjected to 47 m/sec basic wind speed:
Table 4.1.5 : Lateral Displacement vs Height for 47 m/sec basic wind speed
Height, m Deflections, mm Load Case (Service condition)
5 8.8 1.0 DL + 1.0 WL
10 35.9 1.0 DL + 1.0 WL
15 82.9 1.0 DL + 1.0 WL
20 147.9 1.0 DL + 1.0 WL
25 235.3 1.0 DL + 1.0 WL
30 343.5 1.0 DL + 1.0 WL
35 467.6 1.0 DL + 1.0 WL
40 599.8 1.0 DL + 1.0 WL
Fig: 4.1.5 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.1.5, it was observed the maximum lateral displacement of 599.8 mm occurs at top of the monopole (i.e., at 40m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.1.2.3 Subjected to 55 m/sec basic wind speed:
Table 4.1.6 : Lateral Displacement vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service condition)
5 11.5 1.0 DL + 1.0 WL
10 46.9 1.0 DL + 1.0 WL
15 108.3 1.0 DL + 1.0 WL
20 193.2 1.0 DL + 1.0 WL
25 306.5 1.0 DL + 1.0 WL
30 445.4 1.0 DL + 1.0 WL
35 605.3 1.0 DL + 1.0 WL
40 775.0 1.0 DL + 1.0 WL
Fig: 4.1.6 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.1.6, it was observed the maximum lateral displacement of 775.0 mm occurs at top of the monopole (i.e., at 40m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.1.3 50m Height Monopole
A Monopole tower of 50m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speeds has been considered and graphs were plotted for the respectvie lateral displacements.
4.1.3.1 Subjected to 33 m/sec basic wind speed:
Table 4.1.7 : Lateral Displacement vs Height for 33 m/sec basic wind speed
Height, m Deflections, mm Load Case (Service condition)
5 4.4 1.0 DL + 1.0 WL
10 17.8 1.0 DL + 1.0 WL
15 41.0 1.0 DL + 1.0 WL
20 73.0 1.0 DL + 1.0 WL
25 116.8 1.0 DL + 1.0 WL
30 171.1 1.0 DL + 1.0 WL
35 237.6 1.0 DL + 1.0 WL
40 315.8 1.0 DL + 1.0 WL
45 403.2 1.0 DL + 1.0 WL
50 496.1 1.0 DL + 1.0 WL
Fig: 4.1.7 : Lateral Displacement vs Height for 33 m/sec basic wind speed
From fig 4.1.7, it was observed the maximum lateral displacement of 496.1 mm occurs at top of the monopole (i.e., at 50m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.1.3.2 Subjected to 47 m/sec basic wind speed:
Table 4.1.8 : Lateral Displacement vs Height for 47 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service condtion)
5 8.7 1.0 DL + 1.0 WL
10 35.6 1.0 DL + 1.0 WL
15 81.5 1.0 DL + 1.0 WL
20 145.2 1.0 DL + 1.0 WL
25 231.8 1.0 DL + 1.0 WL
30 338.8 1.0 DL + 1.0 WL
35 469.2 1.0 DL + 1.0 WL
40 621.6 1.0 DL + 1.0 WL
45 791.9 1.0 DL + 1.0 WL
50 970.2 1.0 DL + 1.0 WL
Fig: 4.1.8 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.1.8, it was observed the maximum lateral displacement of 970.2 mm occurs at top of the monopole (i.e., at 50m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.1.3.3 Subjected to 55 m/sec basic wind speed:
Table 4.1.9 : Lateral Displacement vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service condition)
5 11.5 1.0 DL + 1.0 WL
10 46.9 1.0 DL + 1.0 WL
15 108.2 1.0 DL + 1.0 WL
20 192.3 1.0 DL + 1.0 WL
25 306.8 1.0 DL + 1.0 WL
30 447.2 1.0 DL + 1.0 WL
35 617.5 1.0 DL + 1.0 WL
40 816.1 1.0 DL + 1.0 WL
45 1037.1 1.0 DL + 1.0 WL
50 1267.0 1.0 DL + 1.0 WL
Fig: 4.1.9 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.1.9, it was observed the maximum lateral displacement of 1267.0 mm occurs at top of the monopole (i.e., at 50m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.2 SELF-SUPPORT TOWER
4.2.1 30m Height Self-Support Tower
A Self-Support tower of 30m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speeds has been considered and graphs were plotted for the respectvie lateral displacements.
4.2.1.1 Subjected to 33 m/sec basic wind speed:
Table 4.2.1 : Lateral Displacements vs Height for 33 m/sec basic wind speed
Height, m Lateral Displacements, mm Load Case (Service condition)
5 1.3 1.0 DL + 1.0WL
10 4.0 1.0 DL + 1.0WL
15 7.6 1.0 DL + 1.0WL
20 13.0 1.0 DL + 1.0WL
25 19.8 1.0 DL + 1.0WL
30 27.2 1.0 DL + 1.0WL
Fig: 4.2.1 : Lateral Displacements vs Height for 33 m/sec basic wind speed
From fig 4.2.1, it was observed the maximum lateral displacement of 27.2 mm occurs at top of the self-support tower (i.e., at 30m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.2.1.2 Subjected to 47 m/sec basic wind speed:
Table 4.2.2 : Lateral Displacements vs Height for 47 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 2.4 1.0 DL + 1.0WL
10 8.7 1.0 DL + 1.0WL
15 16.2 1.0 DL + 1.0WL
20 27.6 1.0 DL + 1.0WL
25 42.0 1.0 DL + 1.0WL
30 57.5 1.0 DL + 1.0WL
Fig: 4.2.2 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.2.2, it was observed the maximum lateral displacement of 57.5 mm occurs at top of the self-support tower (i.e., at 30m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.2.1.3 Subjected to 55 m/sec basic wind speed:
Table 4.2.3 : Lateral Displacements vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 4.7 1.0 DL + 1.0WL
10 16.0 1.0 DL + 1.0WL
15 32.5 1.0 DL + 1.0WL
20 55.0 1.0 DL + 1.0WL
25 79.9 1.0 DL + 1.0WL
30 106.8 1.0 DL + 1.0WL
Fig: 4.2.3 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.2.3, it was observed the maximum lateral displacement of 106.8 mm occurs at top of the self-support tower (i.e., at 30m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 900mm (reference taken from TIA-222-G).
4.2.2 40m Height Self-Support Tower
A Self-Support tower of 40m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speeds has been considered and graphs were plotted for the respectvie lateral displacements.
4.2.2.1 Subjected to 33 m/sec basic wind speed
Table 4.2.4 : Lateral Displacement vs Height for 33 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 1.7 1.0 DL + 1.0WL
10 4.3 1.0 DL + 1.0WL
15 8.1 1.0 DL + 1.0WL
20 13.8 1.0 DL + 1.0WL
25 20.8 1.0 DL + 1.0WL
30 29.1 1.0 DL + 1.0WL
35 38.5 1.0 DL + 1.0WL
40 48.4 1.0 DL + 1.0WL
Fig: 4.2.4 : Lateral Displacement vs Height for 33 m/sec basic wind speed
From fig 4.2.4, it was observed the maximum lateral displacement of 48.4 mm occurs at top of the self-support tower (i.e., at 40m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.2.2.2 Subjected to 47 m/sec basic wind speed:
Table 4.2.5 : Lateral Displacement vs Height for 47 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 2.5 1.0 DL + 1.0WL
10 9.3 1.0 DL + 1.0WL
15 17.1 1.0 DL + 1.0WL
20 29.3 1.0 DL + 1.0WL
25 44.0 1.0 DL + 1.0WL
30 61.4 1.0 DL + 1.0WL
35 81.3 1.0 DL + 1.0WL
40 102.1 1.0 DL + 1.0WL
Fig: 4.2.5 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.2.5, it was observed the maximum lateral displacement of 102.1 mm occurs at top of the self-support tower (i.e., at 40m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.2.2.3 Subjected to 55 m/sec basic wind speed:
Table 4.2.6 : Lateral Displacement vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 3.5 1.0 DL + 1.0WL
10 11.0 1.0 DL + 1.0WL
15 24.5 1.0 DL + 1.0WL
20 43.3 1.0 DL + 1.0WL
25 66.3 1.0 DL + 1.0WL
30 92.7 1.0 DL + 1.0WL
35 122.4 1.0 DL + 1.0WL
40 153.4 1.0 DL + 1.0WL
Fig: 4.2.6 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.2.6, it was observed the maximum lateral displacement of 153.4 mm occurs at top of the self-support tower (i.e., at 40m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1200mm (reference taken from TIA-222-G).
4.2.3 50m Height Self-Support Tower
A Self-Support tower of 50m height subjected to 33m/sec, 47m/sec and 55m/sec basic wind speed has been considered and graphs were plotted for the respectvie lateral displacements.
4.2.3.1 Subjected to 33 m/sec basic wind speed:
Table 4.2.7 : Lateral Displacement vs Height for 33 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 2.7 1.0 DL + 1.0WL
10 6.1 1.0 DL + 1.0WL
15 16.1 1.0 DL + 1.0WL
20 22.5 1.0 DL + 1.0WL
25 34.2 1.0 DL + 1.0WL
30 47.6 1.0 DL + 1.0WL
35 63.1 1.0 DL + 1.0WL
40 78.2 1.0 DL + 1.0WL
45 95.2 1.0 DL + 1.0WL
50 112.9 1.0 DL + 1.0WL
Fig: 4.2.7 : Lateral Displacement vs Height for 33 m/sec basic wind speed
From fig 4.2.7, it was observed the maximum lateral displacement of 112.9 mm occurs at top of the self-support tower (i.e., at 50m height) at a basic wind speed of 33m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.2.3.2 Subjected to 47 m/sec basic wind speed:
Table 4.2.8 : Lateral Displacement vs Height for 47 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 4.0 1.0 DL + 1.0WL
10 12.6 1.0 DL + 1.0WL
15 28.2 1.0 DL + 1.0WL
20 47.5 1.0 DL + 1.0WL
25 72.2 1.0 DL + 1.0WL
30 100.4 1.0 DL + 1.0WL
35 133.0 1.0 DL + 1.0WL
40 164.8 1.0 DL + 1.0WL
45 200.6 1.0 DL + 1.0WL
50 237.7 1.0 DL + 1.0WL
Fig: 4.2.8 : Lateral Displacement vs Height for 47 m/sec basic wind speed
From fig 4.2.8, it was observed the maximum lateral displacement of 237.7 mm occurs at top of the self-support tower (i.e., at 50m height) at a basic wind speed of 47m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.2.3.3 Subjected to 55 m/sec basic wind speed:
Table 4.2.9 : Lateral Displacement vs Height for 55 m/sec basic wind speed
Height, m Lateral Displacement, mm Load Case (Service Condition)
5 5.5 1.0 DL + 1.0WL
10 17.9 1.0 DL + 1.0WL
15 39.1 1.0 DL + 1.0WL
20 67.1 1.0 DL + 1.0WL
25 101.9 1.0 DL + 1.0WL
30 142.6 1.0 DL + 1.0WL
35 187.9 1.0 DL + 1.0WL
40 231.8 1.0 DL + 1.0WL
45 281.1 1.0 DL + 1.0WL
50 332.4 1.0 DL + 1.0WL
Fig: 4.2.9 : Lateral Displacement vs Height for 55 m/sec basic wind speed
From fig 4.2.9, it was observed the maximum lateral displacement of 332.4 mm occurs at top of the self-support tower (i.e., at 50m height) at a basic wind speed of 55m/sec. The obtained lateral displacement from the analysis is within permissible limit i.e., 3% of tower height which gives 1500mm (reference taken from TIA-222-G).
4.3 COMPARISON OF LATERAL DISPLACEMENTS AND QUANTITY OF STEEL BETWEEN MONOPOLE AND SELF-SUPPORT TOWER
4.3.1 30m Height Monopole and Self-Support
4.3.1.1 Lateral Displacements of 30m monopole tower and 30m self-support tower for 33m/sec basic wind speed:
Table 4.3.1.1 : Lateral Displacements for Monopole and Self-Support Towers for 33m/sec basic windspeed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 5.7 1.3
10 23.0 4.0
15 52.1 7.6
20 93.1 13.0
25 144.7 19.8
30 201.3 27.2
Fig 4.3.1.1
From Fig 4.3.1.1, it was observed that for a 30m tower height with 33m/sec basic wind speed, lateral displacement for Monopole Tower is 7.4 times higher than Self-Support Tower.
4.3.1.2 Quantity of Steel required for 30m monopole tower and 30m self-support tower for 33m/sec wind speed:
Table 4.3.1.2: Quantity of Steel for Monopole and Self-Support Tower of 30m Height for 33m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 4.63 10.12
Fig 4.3.1.2
From Fig 4.3.1.2, it was observed that for a 30m tower height with 33m/sec basic wind speed, quantity of steel required for Self-Support Tower is 2.19 times higher than Monopole Tower.
4.3.1.3 Lateral Displacements of 30m monopole tower and 30m self-support tower for 47m/sec wind speed:
Table 4.3.1.3 : Lateral Displacements for Monopole and Self-Support Towers for 47m/sec wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 11.0 2.4
10 45.0 8.7
15 101.4 16.2
20 180.8 27.6
25 279.7 42.0
30 387.0 57.5
Fig 4.3.1.3
From Fig 4.3.1.3, it was observed that for a 30m tower height with 47m/sec basic wind speed, lateral displacement for Monopole Tower is 6.73 times higher than Self-Support Tower.
4.3.1.4 Quantity of Steel required for 30m monopole tower and 30m self-support tower for 47m/sec wind:
Table 4.3.1.4: Quantity of Steel for Monopole and Self-Support Tower of 30m Height for 47m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 5.16 10.81
Fig 4.3.1.4
From Fig 4.3.1.4, it was observed that for a 30m tower height with 47m/sec basic wind speed, quantity of steel required for Self-Support Tower is 2.01 times higher than Monopole Tower.
4.3.1.5 Lateral Displacements of 30m monopole tower and 30m self-support tower for 55m/sec basic wind speed:
Table 4.3.1.5 : Lateral Displacements for Monopole and Self-Support Towers for 55m/s basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 14.4 4.7
10 58.7 16.0
15 132.1 32.5
20 234.6 55.0
25 361.4 79.9
30 498.4 106.8
Fig 4.3.1.5
From Fig 4.3.1.5, it was observed that for a 30m tower height with 55m/sec basic wind speed, lateral displacement for Monopole Tower is 4.67 times higher than Self-Support Tower.
4.3.1.6 Quantity of Steel required for 30m monopole tower and 30m self-support tower for 55m/sec basic wind speed:
Table 4.3.1.6: Quantity of Steel for Monopole and Self-Support Tower of 30m Height for 55m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 5.71 11.47
Fig 4.3.1.6
From Fig 4.3.1.6, it was observed that for a 30m tower height with 55m/sec basic wind speed, quantity of steel required for Self-Support Tower is 2.01 times higher than Monopole Tower.
4.3.2 40m Height Monopole and Self-Support Tower
4.3.2.1 Lateral Displacements of 40m monopole tower and 40m self-support tower for 33m/sec basic wind speed:
Table 4.3.2.1: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 4.5 1.7
10 18.3 4.3
15 42.2 8.1
20 75.6 13.8
25 120.6 20.8
30 176.1 29.1
35 241.1 38.5
40 310.5 48.4
Fig 4.3.2.1
From Fig 4.3.2.1, it was observed that for a 40m tower height with 33m/sec basic wind speed, lateral displacement for Monopole Tower is 6.42 times higher than Self-Support Tower.
4.3.2.2 Quantity of Steel required for 40m monopole tower and 40m self-support tower for 33m/sec basic wind speed:
Table 4.3.2.2: Quantity of Steel for Monopole and Self-Support Tower of 40m Height for 33m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 8.14 18.53
Fig 4.3.2.2
From Fig 4.3.2.2, it was observed that for a 40m tower height with 33m/sec basic wind speed, quantity of steel required for Self-Support Tower is 2.27 times higher than Monopole Tower.
4.3.2.3 Lateral Displacements of 40m monopole tower and 40m self-support tower for 47m/sec basic wind speed:
Table 4.3.2.3: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec windspeed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 8.8 2.5
10 35.9 9.3
15 82.9 17.1
20 147.9 29.3
25 235.3 44.0
30 343.5 61.4
35 467.6 81.3
40 599.8 102.1
Fig 4.3.2.3
From Fig 4.3.2.3, it was observed that for a 40m tower height with 47m/sec basic wind speed, lateral displacement for Monopole Tower is 5.88 times higher than Self-Support Tower.
4.3.2.4 Quantity of Steel required for 40m monopole tower and 40m self-support tower for 47m/sec basic wind speed:
Table 4.3.2.4: Quantity of Steel for Monopole and Self-Support Tower of 40m Height for 47m/sec wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 8.97 19.30
Fig 4.3.2.4
From Fig 4.3.2.4 it was observed that for a 40m tower height with 47m/sec windspeed, quantity of steel required for Self-Support Tower is 2.15 times higher than Monopole Tower.
4.3.2.5 Lateral Displacements of 40m monopole tower and 40m self-support tower for 55m/sec basic wind speed:
Table 4.3.2.5: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 11.5 3.5
10 46.9 11.0
15 108.3 24.5
20 193.2 43.3
25 306.5 66.3
30 445.4 92.7
35 605.3 122.4
40 775.0 153.4
Fig 4.3.2.5
From Fig 4.3.2.5 it was observed that for a 40m tower height with 47m/sec basic wind speed, lateral displacement for Monopole Tower is 5.05 times higher than Self-Support Tower.
4.3.2.6 Quantity of Steel required for 40m monopole tower and 40m self-support tower for 55m/sec basic wind speed:
Table 4.3.2.6: Quantity of Steel for Monopole and Self-Support Tower of 40m Height for 55m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 9.81 19.99
Fig 4.3.2.6
From Fig 4.3.2.6, it was observed that for a 40m tower height with 47m/sec basic wind speed, quantity of steel required for Self-Support Tower is 2.04 times higher than Monopole Tower.
4.3.3 50m Height Monopole and Self-Support Tower
4.3.3.1 Lateral Displacements of 50m monopole tower and 50m self-support tower for 33m/sec basic wind speed:
Table 4.3.3.1: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 4.4 2.7
10 17.8 6.1
15 41.0 16.1
20 73.0 22.5
25 116.8 34.2
30 171.1 47.6
35 237.6 63.1
40 315.8 78.2
45 403.2 95.2
50 496.1 112.9
Fig 4.3.3.1
From Fig 4.3.3.1 it was observed that for a 50m tower height with 33m/sec basic wind speed, lateral displacement for Monopole Tower is 4.39 times higher than Self-Support Tower.
4.3.3.2 Quantity of Steel required for 50m monopole tower and 50m self-support tower for 33m/sec basic wind speed:
Table 4.3.3.2: Quantity of Steel for Monopole and Self-Support Tower of 50m Height for 33m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 12.74 24.62
Fig 4.3.3.2
From Fig 4.3.3.2, it was observed that for a 50m tower height with 33m/sec basic wind speed, quantity of steel required for Self-Support Tower is 1.93 times higher than Monopole Tower.
4.3.3.3 Lateral Displacements of 50m monopole tower and 50m self-support tower for 47m/sec basic wind speed:
Table 4.3.3.3: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 8.7 4.0
10 35.6 12.6
15 81.5 28.2
20 145.2 47.5
25 231.8 72.2
30 338.8 100.4
35 469.2 133.0
40 621.6 164.8
45 791.9 200.6
50 970.2 237.7
Fig 4.3.3.3
From Fig 4.3.3.3, it was observed that for a 50m tower height with 47m/sec basic wind speed, lateral displacement for Monopole Tower is 4.08 times higher than Self-Support Tower.
4.3.3.4 Quantity of Steel required for 50m monopole tower and 50m self-support tower for 47m/sec basic wind speed:
Table 4.3.3.4: Quantity of Steel for Monopole and Self-Support Tower of 50m Height for 47m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 13.84 26.10
Fig 4.3.3.4
From Fig 4.3.3.4, it was observed that for a 50m tower height with 47m/sec basic wind speed, quantity of steel required for Self-Support Tower is 1.89 times higher than Monopole Tower.
4.3.3.5 Lateral Displacements of 50m monopole tower and 50m self-support tower for 55m/sec basic wind speed:
Table 4.3.3.5: Lateral Displacements for Monopole and Self-Support Towers for 55m/sec basic wind speed
Height, m Lateral Displacement, mm
Monopole Self-Support
5 11.5 5.5
10 46.9 17.9
15 108.2 39.1
20 192.3 67.1
25 306.8 101.9
30 447.2 142.6
35 617.5 187.9
40 816.1 231.8
45 1037.1 281.1
50 1267.0 332.4
Fig 4.3.3.5
From Fig 4.3.3.5, it was observed that for a 50m tower height with 47m/sec basic wind speed, lateral displacement for Monopole Tower is 3.82 times higher than Self-Support Tower.
4.3.3.6 Quantity of Steel required for 50m monopole tower and 50m self-support tower for 55m/sec basic wind speed:
Table 4.3.3.6: Quantity of Steel for Monopole and Self-Support Tower of 50m Height for 55m/sec basic wind speed:
Tower Type Monopole Self-Support
Quantity of Steel (tons) 14.96 27.83
Fig 4.3.3.6
From Fig 4.3.3.6, it was observed that for a 50m tower height with 55m/sec basic wind speed, quantity of steel required for Self-Support Tower is 1.86 times higher than Monopole Tower.
CHAPTER-5
CONCLUSIONS
The study was done on comparison between monopole and self-support type towers with different heights of 30m, 40m and 50m for different basic wind speeds of 33m/sec, 47m/sec and 55m/sec. From the study, following conclusions were drawn,
1. For a 30m Height Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was a decrease in the lateral displacement by 7.4times, 6.7times, and 4.7times respectively when compared to similar height Monopole Tower.
2. For a 40m Height Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was a decrease in the lateral displacement by 6.4times, 5.9times, and 5.1times respectively when compared to similar height Monopole Tower.
3. For a 50m Height Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was a decrease in the lateral displacement by 4.4times, 4.1times, and 3.8times respectively when compared to similar height Monopole Tower.
4. For a 30m Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was an increase in the quantity of steel by 2.9times, 2.0times, and 2.0times respectively when compared to similar height Monopole Tower.
5. For a 40m Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was an increase in the quantity of steel by 2.3times, 2.2times, and 2.0times respectively when compared to similar height of Monopole Tower.
6. For a 50m Self-Support Tower at basic wind speeds of 33m/sec, 47m/sec and 55m/sec there was an increase in the quantity of steel by 1.9times, 1.9times, and 1.9times respectively when compared to similar height of Monopole Tower.
From the study it can be concluded that Self-Support towers have lower lateral displacements compared to the similar height Monopole towers for same amount of loading due to the fact that they have higher stiffness. However, the steel quantity required for Self-Support towers is more than the Monopole towers and it is approximately more by 2times over Monopole steel quantity for a given tower height, wind speed and loading.
But due to their rigidity, Self-Support towers have more load carrying capacity than Monopoles. For towers of height below or equal to 30m and 40m, Monopoles might be preferred but with the increase in height like 50m and above Self-Support Towers are more suggestible so that when there are any unexpected higher wind speeds during cyclones (like Hud-Hud) the structural rigidity will be intact and the damage and the repair for the structure wouldn”’t be so high unlike Monopole.
It should also be noted that strengthening a monopole is difficult compared to self-support tower. Unlike self-supporting towers, where reinforcement is as simple as replacing a smaller, over-stressed member with a larger, stronger one, a monopole has only one member, thus replacement means installing a new pole. Finally, monopoles have lower lateral stiffness as compared to self-supporting towers. Although the monopole may be structurally stable, its lack of stiffness may exceed the twist and sway tolerances of some antenna or dish equipment.
Based on the above mentioned, it is more economical to opt for a Self-Support tower since they can support more equipment, can go for greater heights, higher stiffness and are easy to modify in case of failure.
REFERENCES
Abdul Muttalib I. Said ”’Analysis and Optimum Design of Self Supporting Steel Communication Tower”’
Amit Thakur, Deepankar Kr. Ashish ”’Review on the Effect of Seismic Waves on the Rooftop Telecommunication Towers”’
Anil Shakyab ”’Wind Load Assessment For Steel Lattice Tower With Different Codes”’
Bryan keith Lanier ”’Study in the Improvement in Strength and Stiffness Capacity of Steel Multi-Sided Monopole Towers Utilizing Carbon Fiber Reinforced Polymers as a Retrofitting Mechanism”’
G. Ghodrati Amiri ”’Seismic behaviour of 4-legged self-supporting telecommunication towers”’
Gunathilaka A.M.L.N ”’Analysis and Design of Telecommunication Tower for Earthquake Loading in Sri Lanka for sustainability”’
Harsha Jatwa ”’Comparative Study of Indian and ASCE Codes Provision for Design of Transmission Tower”’
Jesumi. A, Rajendran M.G ”’Optimal Bracing System for Steel Towers”’
Jithesh Rajasekharan ”’Analysis of Telecommunication Tower subjected to Seismic & Wind Loading”’
Keshav Kr. Sharma and Deepak Kumar Singh ”’Comparative Analysis of Steel Telecommunication Tower subjected to Seismic & Wind Loading”’
Patil Vidya and Lande Abhijeet C ”’Structural Response of Lattice Steel Masts for Seismic Loading”’
Richa Bhatt, A.D. Pandey, Vipul Prakash ”’Influence of modeling in the response of steel lattice mobile tower under wind loading”’
Riya Joseph ”’Analysis of Monopole Communication Tower”’
Siddesha. H ”’Wind Analysis of Microwave Antenna Towers”’
IS: 1161: 1998, ”’Indian Standard Code of practice for Steel Tubes for Structural Purposes-Specification”’, Bureau of Indian standards, New Delhi.
IS: 2062: 2011, ”’Indian Standard Code of practice for Hot Rolled Medium and High Tensile Structural Steel ”’ Specification”’, Bureau of Indian standards, New Delhi.
IS: 806: 1968, ”’Indian Standard Code of practice for use of steel tubes in general building construction”’, Bureau of Indian standards, New Delhi.
IS: 802 (Part 1_Sec 2): 1992, ”’Indian Standard Use of Structural Steel in Overhead Transmission Line Towers ”’ Code of Practice”’, Bureau of Indian standards, New Delhi.
APPENDIX-I
DEFLECTION PROFILE FOR SELF-SUPPORT TOWER AND MONOPOLE
SELF-SUPPORT TOWER MONOPOLE
DESIGN CALCULATIONS
1.Design Calculations for Monopole using IS: 806-1968
An example hand calculation was done for a monopole section of 50m for a wind speed 55m/sec
Length of Member, L = 12830mm
Effective Length Factor, K = 0.6 (From Table-7 in IS 806-1978)
Diameter of the section at the bottom = 1359.4mm
Moment of Inertia, I = ”/64 [outer dia.4 ”’ inner dia.4]
Thickness = 15.5mm
Inner dia. = outer dia. ”’ (2xthickenss)
= 1359.4 ”’ (2×15.5mm) = 1328.4 mm
Moment of Inertia, I = 1.477577 x 1010 mm4
Area, A = ”/4 [outer dia.2 ”’ inner dia.2]
= 65440.78869mm4
Least Radius of Gyration, r = ”'(I”’A)
= 475 mm
Slenderness ratio, KL/r = 15.6
For the above slenderness ratio and steel grade used, the respective axial stress from Table-2 was considered and according to clause 5.2 of IS: 806
Permissible Axial Compressive Stress = 1421.12 kg/cm2
For the Steel Grade used the respective permissible bending and axial stresses from Table 3 & 4 of IS: 806 were considered
Permissible Bending Stress = 1655 kg/cm2
Permissible Shear Stress = 1100 kg/cm2
From STAAD (X) Input it was observed that:
Applied Axial Force = 140.98KN
Applied Axial Stress = Axial Force / Area
= 140.9819 KN / 66042.29 mm2
= 2.1347×10-3 KN/mm2
= 21.768 kg/cm2
Applied Bending Stress = MY/I
Where Y = diameter of the section/2
= (3990.7822 KN-m x 679.7mm)
3012929871.69mm4
= 918.09 kg/cm2
Applied Shear Stress = Shear load/Area
= 140.162 KN / 6602.29mm2
= 21.64 kg / cm
2.Design Calculations for Self-Support using IS: 802 (Part1/Sec2: 1992)
Two members from a 30m self-support tower with 55m/sec were considered for design check and following calculations were made:
Leg Member ISA 180x180x15
According to IS 802: 1992 Clause 5.2.2
b/t = 180/15 = 12
(b/t)””lim = 210/ sq.rt Fy = 10.4 where Fy = 410 MPa
Where b = distance from edge of fillet to the extreme fibre in mm
t = thickness of flange, mm
Fy = minimum guaranteed yield stress of the material, MPa
Since b/t > (b/t)””lim according to clause 5.2.2.2 Fcr was substituted instead of Fy
Fcr = [1.677 ”’ 0.677 (b/t)/ (b/t)””lim] x Fy when (b/t)””lim <= b/t =< 378/”'(F_y )
Fcr = 367.29 N/mm2
According to Clause 5.2.2
Ce = ” ”'(2E”’F_y )
= 103.67
Where E = Young”’s Modulus = 2 x 105 MPa
KL/r = 1500/35.4
= 42.37
Where, KL/r = largest effective slenderness ratio of any unbraced segment of the member,
L = unbraced length of the compression member
r = appropriate radius of gyration
Since KL/r < Ce
Fa = [1-1/2( KL/r)2] x Fy
= [1-1/2(42.37/103.67)2] x 367.29
= 336.6 MPa
Hence Allowable Axial Stress = 336.6 MPa
Applied Axial Stress = P/A = (1341.519 KN x 1000) / 5210 mm2
= 257.489 MPa
Axial Capacity Ratio = 0.765
Diagonal Member 150x150x10
According to IS 802: 1992 Clause 5.2.2
b/t = 150/10 = 15
(b/t)””lim = 210/ ”'(F_y ) = 13.28 Fy = 250 MPa
Since b/t > (b/t)””lim according to clause 5.2.2.2 Fcr was substituted instead of Fy
Fcr = [1.677 ”’ 0.677 (b/t)/ (b/t)””lim] x Fy when (b/t)””lim =< b/t =< 378/ ”'(F_y )
Fcr = 228.08 N/mm2
According to Clause 5.2.2
Ce = ” ”'(2E”’F_y )
= 131.56
KL/r = 3910/29.8
= 131.2
Since KL/r < Ce
Fa = [1-1/2(KL/r)2] x Fy
= [1-1/2(131.2/131.56)2] x 228.08
= 114.66 MPa
Hence Allowable Axial Stress = 114.66 MPa
Applied Axial Stress = P/A = (98.49 KN x 1000) / 2920 mm2
= 33.73 MPa
Axial Capacity Ratio = 0.294
3.Quantity of Steel Calculations
50m Monopole with a wind speed of 55m/sec was considered for the following calculation purpose:
Section 1:
Shaft Top Outer Diameter; Td1 = 457.2 mm
Shaft Top Inner Diameter; Td1 = 441.2 mm
Shaft Bottom Outer Diameter; Bd1 = 774.7 mm
Shaft Bottom Outer Diameter; Bd2 = 758.7 mm
Shaft thickness = 8 mm
Shaft Length = 12500 mm
Top Shaft area A1 = ”/4 [Td12 ”’ Td22]
= 0.0112896 m2
Bottom Shaft area A2 = ” /4 [Bd12 ”’ Bd22]
= 0.019269272 m2
Shaft Volume = H/3 [A1 + A2 + (”'(A_1 A_2 ))]
= 0.18878 m3
Weight = 0.18878 x 7850 kg/m3
= 1481.9 Kg
Section 2:
Shaft Top Outer Diameter; Td1 = 626.6 mm
Shaft Top Inner Diameter; Td1 = 605.6 mm
Shaft Bottom Outer Diameter; Bd1 = 971.3 mm
Shaft Bottom Outer Diameter; Bd2 = 950.3 mm
Shaft thickness = 10.5 mm
Shaft Length = 13570 mm
Top Shaft area A1 = ”/4 [Td12 ”’ Td22]
= 0.020324 m2
Bottom Shaft area A2 = ”/4 [Bd12 ”’ Bd22]
= 0.031694 m2
Shaft Volume = H/3 [A1 + A2 + (”'(A_1 A_2 )))]
= 0.350098 m3
Weight = 0.350098 x 7850 kg/m3
= 2748.3 Kg
Section3:
Shaft Top Outer Diameter; Td1 = 810.6 mm
Shaft Top Inner Diameter; Td1 = 784.6 mm
Shaft Bottom Outer Diameter; Bd1 = 1161.1 mm
Shaft Bottom Outer Diameter; Bd2 = 1135.1 mm
Shaft thickness = 13 mm
Shaft Length = 13800 mm
Top Shaft area A1 = ”/4 [Td12 ”’ Td22]
= 0.032575 m2
Bottom Shaft area A2 = ”/4 [Bd12 ”’ Bd22]
= 0.04689 m2
Shaft Volume = H/3 [A1 + A2 + (”'(A_1 A_2 ))]
= 0.545324 m3
Weight = 0.545324 x 7850 kg/m3
= 4280.8 Kg
Section4:
Shaft Top Outer Diameter; Td1 = 987.8 mm
Shaft Top Inner Diameter; Td1 = 956.8 mm
Shaft Bottom Outer Diameter; Bd1 = 1359.4 mm
Shaft Bottom Outer Diameter; Bd2 = 1328.4 mm
Shaft thickness = 15.5 mm
Shaft Length = 14630 mm
Top Shaft area A1 = ”/4 [Td12 ”’ Td22]
= 0.047346 m2
Bottom Shaft area A2 = ”/4 [Bd12 ”’ Bd22]
= 0.065441 m2
Shaft Volume = H/3 [A1 + A2 + (”'(A_1 A_2 ))]
= 0.821476 m3
Weight = 0.545324 x 7850 kg/m3
= 6448.6 Kg
Total Weight = 14959.6 Kg
50m Monopole with a wind speed of 55m/sec was considered for the following calculation purpose:
Weight for single face was calculated and was multiplied for the other 4 faces.
Section No. Tower Elevation (from top) (m) No. of bays Bracing Pattern Member Description
1 0-6 2 X-Brace Leg ISA 150x150x10
Bracing ISA 90x90x10
2 6-12 2 X-Brace Leg ISA 150x150x10
Bracing ISA 90x90x10
3 12-14 1 X-Brace Leg ISA 180x180x15
Bracing ISA 90x90x10
4 14-20 2 X-Brace Leg ISA 200x200x16
Bracing ISA 110x110x12
5 20-26 1 Double K1BraceDown Leg ISA 200x200x25
Bracing ISA 130x130x10 / ISA 90x90x10
6 26-32 1 Double K1BraceDown Leg ISA 200x200x25
Bracing ISA 130x130x10 / ISA 90x90x10
7 32-38 1 Double K1BraceDown Leg ISA 200x200x25
Bracing ISA 150x150x10 / ISA 90x90x10
8 38-44 1 Double K1BraceDown Leg ISA 200x200x25
Bracing ISA 150x150x15 / ISA90x90x10
9 44-50 1 Double K1BraceDown Leg ISA 200x200x25
Bracing ISA 150x150x15 / ISA90x90x10
ISA 150x150x10
Area of Angle = (140×10) + (150×10)
= 0.0029m2
Volume = Area x Length
= (0.0029×6)
= 0.0174m2
Weight = 0.0174 x 7850 kg/m3
= 136.59 kg
ISA 180x180x15
Area of Angle = (165×15) + (180×15)
= 0.00518m2
Volume = Area x Length
= (0.00518×6)
= 0.01035m2
Weight = 0.01035 x 7850 kg/m3
= 81.2475 kg
Similarly weights for the other members were calculated and added in order to calculate the total weight of the self-support tower.
Total Weight for one face = 6793.429 kg
Total Weight for 4 faces = 27829.4796 kg