W5 Shelters Towers

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EEE EEE TTT PPP / / / BBB SSS N N N L L L SILVER

CERTIFICATION COURSETELECOM SUPPORT INFRASTRUCTURE

PRE-FAB SHELTERS AND TOWERSVersion 2 June 2014


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Telecom Support I nf rastructur e (TSI ) Pre-FAB Shelters and Towers

EETP/ BSNL Silver Certification Course /Ver.02/June’2014 Page 1 of 26

For Restricted Circulation

PRE-FAB SHELTERS AND TOWERS

INDEX

5.1 Introduction .................................................................. 2

5.2 Objective ....................................................................... 3

5.3 Various Components Of Ground Based Bts ..................... 3

5.4 Site Selection For Bts ..................................................... 3

5.5 Telecom Shelters ............................................................ 4

5.6 Technical Specifications For Pre Fabricated Shelters ........ 6

5.7

Dimensions Of Shelter .................................................... 7

5.8 Communication Towers ............................................... 10

5.9 Evolution Of Towers .................................................... 12

5.10 Infrastructure For Mobile Communication Tower ......... 14

5.11 Overview Of Tower Material & Tower Specifications ..... 18

5.12 Erection Of Tower ....................................................... 21

5.13 Summary .................................................................... 24

5.14 Self Assessment Questions ............................................ 24 5.15 References & Suggested Further Readings ..................... 24


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5 PRE-FAB SHELTERS AND TOWERS

STRUCTURE

5.1 INTRODUCTION

5.2 OBJECTIVE

5.3 VARIOUS COMPONENTS OF GROUND BASED BTS

5.4 SITE SELECTION FOR BTS

5.5 TELECOM SHELTERS

5.6 TECHNICAL SPECIFICATIONS FOR PRE FABRICATEDSHELTERS

5.7 DIMENSIONS OF SHELTER

5.8 COMMUNICATION TOWERS

5.9 GUYED TOWER

5.10 EVOLUTION OF TOWERS

5.11 INFRASTRUCTURE FOR MOBILE COMMUNICATIONTOWER

5.12 OVERVIEW OF TOWER MATERIAL & TOWERSPECIFICATIONS

5.13 ERECTION OF TOWER

5.14 SUMMARY

5.15 SELF ASSESSMENT QUESTIONS

5.16 REFERENCES & SUGGESTED FURTHER READINGS

5.1 INTRODUCTIONTelecom Shelters are to provide protection to the high value telecom equipment .

Any closed structure which can house the communication equipments is called Telecomshelter. Tower is used to achieve the elevation or height for better communication ofradio waves or Microwaves. Steel towers are widely used for communication.

Communication towers were being used in the field of radio communication sincethirties. In the field of telephony, use of towers was extensively started, in the then P&Tdepartment in the era of Microwave Communication superseding the co-axial technology

for long distance communication somewhere in 1975.


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5.2 OBJECTIVEAfter reading this, the participant will be able to:

Learn about the purpose and requirements of Shelter. Learn about important aspects of shelter planning & construction. List the Classification of Communication Towers Enumerate the Infrastructure requirements of Mobile Communication Towers Explain the Layout of Towers Learn about the Tower Material Specifications

5.3 VARIOUS COMPONENTS OF GROUND BASED BTSVarious components of ground based BTS are

(i) Tower Foundation and Tower.(ii) Pre-Fab Shelter.(iii) Canopy Type Engine/Alternator.

5.3.1 Layout Planning:-

Since the area of the land available & provided for BTS is very small (HardlyAbout 20m x 15m), meticulous planning of each component is must.

a) Engine/Alternator:-

It should preferably be provided in front or near the main gate of BTS site so thatunloading of E/A can be done easily with the help of crane or chain pulley.

This location will also be very helpful for maintenance operations of E/A.

b) Tower Foundation & Tower:-

(i)It can be located in the rear side of the plot. Because once tower is erected, itwill not create any problem subsequently, if it is provided in the rear side.

(ii) Rather if it is provided in the front side, it will hinder the other components fortheir functioning.

c) Pre-Fab Shelter:-

It may be planned near the gate for convenient installation & maintenanceoperations.

5.4 SITE SELECTION FOR BTS Site should be suitable as per RF survey. Size of the plot should be about 20m x 15m. Sufficient place for locating

the earth & storage of tower material should also be available. Position of adjacent foundation, U/G tank, W/S & Sewer Line etc. should

not foul with tower foundation. Overhead high tension wire should not cross the site. There should be proper approach to the site for transportation of

equipment & tower material. Land should be generally leveled.

Land should not be low lying.


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Land having rocky strata should be avoided. Power supply should be available nearby.

5.5 TELECOM SHELTERSAny closed structure which can house the communication equipments is called

Telecom shelter. It is also popularly known as BTS/WLL/GSM shelter.

Figure 1. Types of Shelters

Figure 2. Prefab shelter

Figure 3. Security room


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5.5.1 General Requirements of a Telecom Shelter:-

(i) Closed Chamber.(ii) Heat Resistant.(iii) Weather Resistant.(iv) Sound / Noise Insulation.(v) Sealed from external environment.(vi) Easy to install.

5.5.2 Locations for Telecom Shelter:-

(i) Roof Top Sites.(ii) Ground Fields proximity to the communication tower.

5.5.3 Material for Shelter

Sandwich Construction

Insulated panels with high insulation properties are used for such type of shelters.

Advantages of Sandwich Panels:-

(i) Light Weight.(ii) Structurally Stable.(iii) Easy to Maintain.(iv) Easy to Replace.(v) Available in desired thicknesses.(vi) Flexibility of surface laminate.

Typical Telecom Shelter Details:-

4 walls. Roof. Floor. Door. (with perfect sealing).


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Figure 4. Parts of Telecom Shelter

5.5.4 Brief Specifications of a Typical Shelter Work Executed

The contractor shall be responsible for:-

(i) Supply of complete shelter including base frame as per specifications inknockdown conditions.

(ii) Construction of Suitable foundation for distribution of shelter load.(iii) Erection and fixing of shelter on the foundation constructed (on ground or roof

top as the case may be).(iv) Delivery, off-loading and lifting to final location.(v) Site survey(s), design and its approval, drawings, specifications etc, as

required.(vi) The shelter shall be made of “sandwich insulated panels” 80 mm thick with

PU foam as filler material between galvanized pre-coated steel sheets. Thesheet on inner-side of shelter shall have thickness of 0.8 mm (min.) and outersheet shall have thickness of 0.6 mm.

(vii) The colour shall be off white on both sides. The density of foam shall beminimum of 40 +/- 2 Kg/cum with K value of 0.023 W/m-deg. K. The foamshould be fire retarding and self-extinguishing as per relevant IS codes.

5.6 TECHNICAL SPECIFICATIONS FOR PRE FABRICATEDSHELTERS

(i) Roof structure & cover :-Pre painted galvanized sheets (PPGI) of 0.4 mmthick trapezoidal sheets laid over a framework of trusses, columns and purling (made outof rectangular hollow sections of size suitable as per design requirements fixed usingsuitable HSD screws. A pre painted galvanized ridge cover to be fixed on top junction ofthe roof using suitable fasteners / HSD screws. PPGI end flashings or drain water guttersconsidered as per drawing. Insulated roof sheets can be supplied as per requirement.

(ii) Wall:- Providing & fixing of wall using 50 / 75 mm thick interlockingaerated concrete wall panels made out of two 5mm thick cement fiber boards (Asbestosfree) conforming to IS 14276 - 1995 and with fill by aerated concrete and expandable


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polystyrene granules/ Polyurethane foam (PUF). The boards shall be fixed on floor andtop using 25/52c 1mm thick GI Channels.

(iii ) Wall finish:- Further 12mm thick plaster (gypsum) board layer on all internalexposed surfaces of walls fixed directly on the wall panels complete with joint finishusing jointing compound & fiber tape to give smooth joint less finish. Alternative wall

papers shall be considered.

(iv) False Ceiling :-Providing & fixing of false ceiling using 595x595x12mmmineral fiber board / gypsum board. The false ceiling panels should be placed on asuspended grid frame made of pre painted GI steel consisting interlocking main runner,intermediate tee sections and wall L angles to form 600 x 600mm grid suspended fromceiling using GI wire of required thickness from roofing structure.

(v) Doors :-Frame shall be made of pressed steel using powder coated CR coil1.25mm thick, shutter will be made out of 32 mm thick wooden / ERP flush door withnecessary hardware and approved shade oil paint / laminated finish.

(vi) Windows :- Frame made from Pressed steel using powder coated CR 1.25mmThick C Channels of size 30x52 or 77mm ( as per wall thickness) and MS / aluminum /UPVC window frame with glazed panel using 6mm thick float glass & necessaryhardware

(vii) Painting: -Outside walls are painted with 2 coats of acrylic paint and insidewalls are applied with 2 coats of oil bound distemper or any other paint as per choice.

5.6.1 Aluminum Prefabricated Shelter:-

Aluminum prefab shelters are uniquely pre-engineered using special AluminumAlloy profiled roofing sheet for roof & side wall anchored on column and roof beam also

made of preformed Aluminum alloy plain sheet. Aesthetically pleasing appearance, highresale value after prolonged use and semi permanent living space have wide usage &application.Light weight yet structurally sturdy, maintenance free long service life, easytransportation to high altitude camps and also preferred for application under extreme ofcold as the properties of Aluminum enhances to sub zero temperature.

5.7 DIMENSIONS OF SHELTERThe shelters generally shall have the following internal dimensions (all in mm):

(i) 4000 L x 3500 W x 3000 H and(ii) 5000 L x 3500 W x 3000 H

5.7.1 Steel Work in Base Frame of Shelters etc. All structural steel shall conform to IS – 2062 & IS-226 All structural MS pipes shall conform to IS – 1239 pt. 2 All steel work shall be hot dip galvanized after full fabrication as per IS-

4759 and the minimum coating thickness to be greater than or equal to 127micron.

All welding shall be as per IS-816 All hardware used shall be galvanized as per relevant IS Code

/specifications.


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5.7.2 Floor and Roof:-

(i)The floor shall consist of standard PUF Sandwich Panels over which 19 mmMarine Plywood covered with antistatic PVC flooring shall be laid .

(ii)A base frame consisting of Galvanized steel channels /square tubes and ISMBor suitable alternatives as per manufacturers approved design to carry and transfer load ofshelter and superimposed floor loads to foundations pedestals /columns /beams /joists etc.shall be provided.

(iii)Anti static flooring shall be done by using anti-static vinyl robust rolls of 2mm thickness. Floor operation and adhesive used shall be as per manufacturer’srecommendations.

(iv) Design loads for :-

Floor: 1000 Kg/Sq.m. (Superimposed Load)

Roof: 200 Kg/Sq.m. (Superimposed Load)

(a) Roof

(i)Roof shall be made of the panels same as used for walls. A secondary slopingroof of pre-coated sheet shall be provided to protect the primary roof from direct sunlightand water.

(ii)A down slope of 1:50 to be maintained from front to back. The secondary roofshall not have any projections and shall be hidden by rectangular profiles on roof top todecrease the aerodynamic affect and improve on aesthetics.

(b) Door of Shelter

Shelter shall have one door for main entrance. The door dimensions shall beapprox. 1000 W x 2000 H (mm). Main door opening outwards and shall be provided withexternal, internal handles/knob respectively. Door sealed by a peripheral (double) sealingframe with silicon rubber gaskets. Locking mechanism with cylinders or number lock.The locking should be of approved make like Godrej or equivalent make. The door is to

be hinged with heavy duty hinges (stainless steel/brass). Gaskets shall be provided on allsides of the door to ensure perfect sealing. The door shall be equipped with a hydrauliccloser. A canopy is to be fixed above external light/door.

5.7.3 Joints of Panels:-The joining of panels shall be done with the use of eccentric cam locks (preferably

cam-lock pin should be metallic). All panel joints shall be sealed silicon sealant. Siliconsealant shall be used for waterproofing in the panel joints or wherever necessary.Flashing shall be provided on the inner and outer side corner joints between vertical wallsand roof/floor.

5.7.4 Shelter Openings:-

The shelter shall have provision for opening for air conditioner, piping cabling onwall, etc. Cable entry ports in the wall panel for AC power supply cabling, DG cable andearthing. Suitable wall opening in side wall for entrance of wave guides and feedercables. All openings shall be custom built and cutting shall be typically done on site.


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5.7.5 Temperature Range:-

(i)Internal temperature +25 + 2degree C

(ii)Maximum outside temp. +50 degree C (avg. + 45 degree C)

(iii)Minimum outside temp. +5 degree C

5.7.6 Environmental Conditions:-

(i)Humidity 100 %

(ii)The shelter shall have heat transmission coefficient K less than or equal to 0.3

5.7.7 Earthing and Electrical Conductivity:-

All metal parts shall be interconnected for good electrical conductivity. Inside theshelter a long Copper bar of size 400 x 35 x 6 mm with M 8 bolt size rounded holes in itshall be provided near the door for earthing of equipment.

5.7.8 Structural Stability:-

(i) Design of shelter shall be in accordance to the relevant Indian StandardCodes.

(ii) Resistant to various volumes of rain, dust and sand with different speeds.(iii) Resistant to corrosion against water, industrial air and saline air.(iv) Resistant to vegetation, termites and micro organisms.

5.7.9 Outdoor Installation:-

(i ) Survival wind speed : 160 Km/h

(ii) To cope with these conditions, provision is to be made for threaded bolts,connecting the shelters to the base frame & foundations respectively.

5.7.10 Installation:-

(i)The shelter is to be installed on the base frame supported on RCC foundation oron suitable supporting structures.

(ii)The construction of shelters shall be such that it can be transported in adismantled form to the site and assembled there.

5.7.11 Foundation System for Shelter:-

(i)Foundation made of RCC isolated footing & columns should be properlydesigned as per superimposed load (Dead Load + Live Load) of shelter & soil conditionsof site.

(ii)The base frame shall be fabricated and mounted on the constructed columnsand properly leveled to support the shelter.


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EETP/ BSNL Silver Certification Course /Ver.02/June’2014 Page 10 of26


5.7.12 Steps for Entrance:-

(i)Brick steps (3 nos) or MS bolted/welded Steel stairs with treads of 25 cm andriser of 15 cm in front of door, supported on suitable foundation, should be provided forentry.

5.7.13 Base Frame of Shelter:-

(i)All the panels will rest on a galvanized steel floor which will further rest on base frame consisting of ISMB 150x75mm grid.

(ii)All the sections used for base frame shall be hot dip galvanized to provide azinc coating of minimum 127 microns.

(iii)The galvanized base shall be placed on four to six RCC columns of size notless than 400 x 400 of mix 1:1.5:3 and bolted on to the concrete structure to providestability.

(iv)The length of I-beams used in base frame may vary for roof top sites, however, based on column grid pattern.

5.7.14 Guarantee /Life Periods of Shelters:-

The manufacturer shall submit a guarantee bond of 20 years life period of shelter.

5.8 COMMUNICATION TOWERS

5.8.1 Classification of Towers:-

Classification of Towers Based on Structural Behavior:-

Based on structural behavior, steel towers are of two types:-

Free standing or self supporting or Lattice towers (e.g. Eiffel Tower). Guyed Towers.

5.8.2 Self Supporting Tower:-

Following are the characteristics of self supporting towers:-

Self supporting towers transfer the load to ground by cantilever action. Moments due to wind in case of self supporting towers are very high. These towers are supported on ground or on tall buildings by four /three

legs. Weight of tower, in these towers is high, due to which these are costly. These towers occupy less space. These towers are used for heavy antenna loads. These towers are used in microwave & mobile communications.


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Figure 5. Self supporting Tower and Guyed tower

5.9 GUYED TOWERFollowing are the characteristics of guyed towers:-

These towers are supported by the tensile stress of guy wires whichtransmits the wind loads to the ground.

Moments due to wind are quite less at the base of the mast. Supported on ground as well by the guy wires. Weight of tower, in these towers is less, due to which these towers are

cheaper as compared to self supporting towers. These towers require large space to anchor guy wires. These towers are used for light antenna loads. These towers are used in Radio/mobile communication & wireless

communication.

5.9.1 Classification of towers based upon shape:-

Based upon shape, steel towers are of three types:-

Four legged towers. Triangular Towers. Guyed Masts.

5.9.2 Delta structures.

A) Four Legged Towers:-

Four legged towers have four legs. They may be of following type:-

(a) Angular Towers:- M.S. angles are used as structural members connected bygusset plates, nuts & bolts.


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(b) Tubular Towers:- In tubular towers, M.S. pipes are used as structuralmembers.

(c) Hybrid Towers:- M.S. angles and pipes, both are used as structural members.

B) Triangular Towers:-Triangular towers have three legs. They may be of following type:-

(a) Angular Towers:- M.S. angles are used as structural members connected bygusset plates, nuts & bolts.

(b) Tubular Towers:- In tubular towers, M.S. pipes are used as structuralmembers.


C) Guyed Mast:-Structural mast is supported by guy wires of high tensile strength.:-

(a) Angular Towers:- M.S. angles are used as mast.

(b) Tubular Towers with rods:- M.S. pipes and MS rods are used for mast.


D) Delta structures:-

Delta shape structures are vertical in height and not tapered. Generally made ofM.S. pipes & used in RTT (roof top towers).

5.10 EVOLUTION OF TOWERS

5.10.1 Guyed towers/Mast:-

Guyed towers/masts were being used by the, the then P&T department in India forradio and wireless communication since pre-independence era.

5.10.2 Microwave Towers:-

(i) With the induction of Microwave Technology for long distance communicationobsoleting the co-axial technology. Use of Microwave tower was started somewhere in1975.

(ii) Four legged towers, self supporting angular towers were used for the same.

(iii)Height of these towers was ranging from 30m to 100m.100m high towers were predominantly used in those days.

(iv)Depending upon the number of parabolic (solid or grid) antenna, these towerswere categorized as:-


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Light Weight Tower. Heavy Weight Tower. Special heavy Weight Tower.

5.10.3 Triangular Tubular Hybrid Towers (T.T.H. Towers):-(i) In the year 1992-93, Govt. of India started a massive programme for rural

communication through UHF/VHF systems in Deptt of Telecom.

(ii) For rural communication programme, large number of light weight towerswere required, hence TTH (Triangular Tubular Hybrid) towers were introduced.

(iii) These towers were in triangular in plan and design was standardized for 40m,60m, 80m & 100m.

(iv) In TTH towers both MS pipes and MS angles were used. Main leg memberswere made of pipes and bracings, were made of MS angles. Joints of main leg was

welded with connecting plates and also to accommodate the bracing members.(iv) TTH towers are light in weight and cheaper as compared to 4 legged angular

towers. However perfection is required in welding of joints.

5.10.4 15m Mast:-

For rural communication, 15m high masts were introduced somewhere in 1992. Itwas triangular mast (base width of triangle was 70cm). It was made by MS pipes and MSrods. This mast was made of 5 panels of 3m height each.

5.10.5 Mobile Technology Towers:-

(i) For GSM mobile Technology, era of 40 meter high towers was started.

(ii) Tower of mobile technology was to be provided in the populated areas,therefore, space for tower was restricted and base width of tower was reducedsubstantially.

(iii) Accordingly era of narrow base 40 metre towers was started. Base width ofthese towers was restricted to 2.0m only. Following type of 40m high Narrow BaseTowers were developed by Telecom Factories:

40m Narrow Base Tower ( Wt. – 16T) 40m Narrow Base Light Weight Tower (Wt.- 10T) 40m Narrow Base Feather Light Weight Tower (Wt.- 8T)

5.10.6 Roof Top Towers (RTT):-

(i) RTT is used in congested city areas to use the height of building as additionalelevation.RTT is supported on tall buildings by its legs.The following types of RTT aregenerally used.

4/3 legged, Angular Self Supporting Tower. TTH Tower. Delta Structure. Guyed Mast.


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5.11 INFRASTRUCTURE FOR MOBILE COMMUNICATIONTOWER

They are basically of two types.

Self supporting type And the Guy- wire supported type.

These can be either ground based or roof top towers. Now a days, depending uponthe requirement, mostly ground based towers are being executed for 40 m & 60 m height.They are designed for different heights & varying wind speeds. Generic Requirement(G.R.’s) for light weight and medium weight ground based towers & roof top towers areavailable and contain all the details for execution of a particular tower includingfoundation and erection both.

5.11.1 B.T.S Plinth / Bed + B.T.S Shelter:-

For outdoor sites, where towers are not, near to telephone exchange building, BTSequipment has to be located in an open site. Thus, to support the BTS, a structural R.C.C.slab is required to be constructed supported by R.C.C beams & columns as per standarddrawing/design worked out on the basis of size, dimensions and weight of BTSequipment. Further to protect the costly and sophisticated BTS equipment from externalagents like Sun, Rains, etc, its desirable to make a shelter preferably of F.R.P.(FiberReinforced Plastic) sheets of minimum 3mm thickness or even G.I sheet roofingsupported by M.S angles frame-work embedded in the concrete bed blocks well below theGround level up to 45 cm depth. The sides should be covered with thick M.S. wire meshfor at least up to 5ft above the plinth bed for dissipation of heat & effective air circulation.

5.11.2 E/A (Engine Alternator) Bed for Generator/Engine Alternator (E/A):-

Due to heavy vibration of the Engine, a suitable foundation for dynamic loading isdesigned for the engine bed to support the Engine Alternator. For this, P.C.C. platformwith light steel reinforcement is constructed over the bed of Earth/Moorum, fillingretained by suitable Random Rubble or Brick masonry of 30 cm to 45 cm height abovethe ground or formation level. Angle nosing should be provided on the edges of the E/A

bed to protect the edges. Earlier, there was a practice of making a trench of sand bed,made all around the engine bed for containing and absorbing dynamic vibrations.However, now-a-days, Engines are coming with rubberized pads beneath them, and sothere is no need to provide the sand bed any more.

5.11.3 Compound wall or Fencing for site protection:-

As per standard practice and guide lines issued in this regard, the compound wallsare constructed.

5.11.4 Name – Board:-

Depicting the name of the site location & date of commissioning of B.T.S etc.along with other relevant details, is required to be fixed on to the tower at a suitableheight so that it is conveniently visible.


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5.11.5 Earthing:-

This is required to pass on electric charge due to Electric- Lightening received bythe lightening conductor fixed on the top of the tower into the earth with minimum

possible resistance of 0.5 ohms and thus save the Tower/ BTS/Antenna/ Human life etc.from any electric hazard.

5.11.6 . Lightening Conductor:-

To absorb all the electric charges from lightening and pass it to the earth for safetyof the tower and other associated equipments from any damages; due to electrical hazard.The lightening conductor is fixed at top of tower. The copper-lightening conductor is1500 mm long and 25mm dia hollow tube of minimum wall thickness of 1.6 mm. Thelightning spike shall be fixed to the tower with Teflon Sleeve to avoid direct contact withtower. The spike is connected to plate earth by 70 sqmm. insulated multistrand copperwire. The copper wire shall be fixed to the tower with necessary lugs.

5.11.7 . Aviation Lamp:-

This is the mandatory requirement as per Civil Aviation bye laws in order to keepthe top of the tower visible in Night/Darkness to protect it from any untoward happeningdue to aviation services by maintaining safe distances of the air services from the towerlocation. 230V AC LED aviation obstruction lamp (Saraj, Binoy, Aviads, Litten orequivalent) with Light Dependent Resistance Sensor (day night automatic timer) withnecessary MCB switches shall be provided at top of the tower.

5.11.8 Vertical Gantry & Horizontal Gantry:-

For carrying 3 pairs of the R.F. cables, each pair (one for inward and the other for

outward communication), being for one of the three antennas in a secured & supportedway from Antenna at top of the tower to B.T.S (Base Transmission System). Thisstructure is made of M.S. angles properly galvanized and painted to prevent them fromrusting, in a ladder type fashion.

5.11.9 Vertical Ladder:-

Vertical ladder is provided with protection rings for climbing the tower safely.

5.11.10Resting Platform & Operative Platforms of mild steel:

For attending to the antenna fixing/adjustment at desired altitude (38.5 m for 40 mTower), operation platform made of mild steel is provided & a resting platform is fixed at

mid height of tower (Ground based) for the workers and technicians to take rest. A ladderfrom roof top up to top of platform at tower is provided with safety rings. Width of laddershall be minimum 300 mm and safety ring of 750 mm shall be provided. Entry fromladder up to top of platform shall be such that no extra efforts will require to reach at the

platform. Width of platform should be minimum 600mm.

5.11.11. Wave Guide:-

Waveguide is provided in towers to carry the feeder cables from Antenna, fixed attop of tower up to Transmission room. It is a tray of galvanized M.S. angles and Flats of600 mm width. This should not bend sharp at right angles at turning points to avoiddamage to running feeder cables.


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5.11.12. Providing & Fixing of Antenna mount on which antennas are fixed /supported:-

Three antenna mounts are provided spaced at 1200 apart for covering signal fromall the directions.

5.11.13. Security Huts for Remote Tower Locations:-Provided particularly in rural areas.

Figure 6. Lay out of Tower site


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Figure 7. Mobile Call-Route Network


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5.12 OVERVIEW OF TOWER MATERIAL & TOWERSPECIFICATIONS

Steel tower works shall be carried out as per the following specifications:-

5.12.1 MATERIALS:-

(i) The tower materials consisting of legs/bracings shall be of M.S. angles of grade‘A’ as per IS: 2062 -1999 & IS: 808-1989 and satisfy the relevant tests as per IS codes.

(ii)The material for gusset/splice plates shall be of M.S. angles of grade ‘A’ as per

IS: 2062 & IS 3502-1994.

(iii) The materials for nuts, bolts shall be of grade 4.6 and as per 6639-1972, IS1364(Part I toV) – 2002, IS 1367(Part VIII) – 1992, plain washers as per IS 6610-1972 andspring washers of Type-B as per IS 3063-1994, IS 1148-1982, IS 2015-1977.

(iv) A test certificate bearing IS certification marks for materials are acceptable.If test certificates are not available, the materials shall be tested in the approved lab orwhere authorized by the Engineer-in-Charge.

(v) Two or more pieces shall not be welded or joined to make up for the requiredlength of member. If required, properly designed joint should be provided.

5.12.2 FABRICATION:-

(i) The fabrication of towers shall be done in accordance with IS 800-1984.

(ii) The fabrication of various components of the tower shall be done inaccordance with the approved drawings. Suitable markings for manufacturer’s identity

shall be done. Item marking for each section shall be done for easy assembling andtraceability at site. All dimensions shall be checked on the template floor with referenceto drawings before manufacturing and if, any deviation is required after check, and thesame shall be done only with the approval of the Engineer-in-charge.

(iii) The contractor shall maintain a master steel tape of an approved make besidesother measuring instruments.

5.12.3 STRAIGHTENING:-

All materials shall be straightened and or flattened by pressure unless required fora shape of curvilinear form before fabrication and shall be free from twists. Straighteningshould not damage the material. The parts when assembled; adjacent surfaces should bein close contact. Hammering shall not be permitted for straightening. Sharp kinks or

bends shall be rejected.

5.12.4 CUTTING:-

Cutting may be affected by shearing, flame cutting or sawing. The surface so cutshall be clean, smooth, square and free from any distortion.

5.12.5 BENDING AND WELDING:-

Mild steel angle sections up to 75x75 mm (up to 6mm thick) may be bent cold and(up to and including) bend angle of 10 degree. Angles above 75x75 mm (thickness up to6mm) and up to and including 100x100mm (thickness up to 8mm) may also be bent cold,


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up to the bend angle of 5 degree. All other angle sections not covered above shall be hot bent. Butt-welding, if used, in members shall be carried out either by submerged arc orshielded arc welding. Welding shall be free from cracks, discontinuity in welding, under-size, over-size or under cutting. It should be cleaned off slag and other deposit. Weldsshall be adequately tested using radiography or other well-known methods of non-

destructive testing.5.12.6 HOLES:-

(i)Holes for bolts shall be drilled using jigs provided with hardened steel bushesand shall not be punched or formed by flame cuttings process. All drill burns shall becompletely removed. Drilling of holes shall be done before galvanizing.

(ii)Holes on both sides of the bend line in a bent member shall be drilled after bending. The relative position of these holes shall be checked using proper templates.

(iii) Holes shall be circular and of a diameter 1.5 mm more than the dia of the bolt.

(iv) Holes shall be drilled at right angles to the surface of the plates or angles,unless otherwise specified.

(v)The accuracy of location of hole shall be such that for any group whenassembled they shall admit the bolt at right angles to the plane of the connection.

(vi)Spacing of bolts and edge distances shall be in accordance with IS 800-1984.

(vii) Butting ends of main leg members shall be cut with saw. Flame cutting orshearing shall not be permitted.

5.12.7 MARKING:-

Identification marks allotted to each member shall be distinctly stamped with

marking dyes of 16mm size before galvanizing.5.12.8 TOLERANCES:-

Fabrication tolerance shall not exceed those specified in IS 7215-1974 asapplicable to group “B” structure.

5.12.9 GALVANIZING:-

(i) Hot dip galvanizing protects steel from corrosion by providing a thick, toughmetallic zinc coating, which completely covers the steel surface and seals it from thecorrosive action of environment. The galvanized coating provides outstanding abrasionresistance. Where there is damage or minor discontinuity in the coating of zinc,

protection of the steel is maintained by the cathodic action of the surrounding galvanizedcoating. Metallic zinc is strongly resistant to the corrosive action of normal environmentsand hot dip galvanized coatings therefore provide long-term protection for steel.

(ii) Zinc for galvanizing should conform to IS 13229-1991.

(iii) All members and fasteners of tower structures are to be hot dip galvanized.Galvanizing of members of the tower shall conform to IS 4759 and 2629. Bolts and otherfasteners shall be galvanized in accordance with IS 1367 (part 13). The total mass ofgalvanizing coating shall not be less than 610gm/sqm (i.e.85 micron) thickness.


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5.12.10 PAINTING:-

Painting of galvanized steel towers is required to give additional protection and togive ‘Day warning’ as per additional protection and civil aviation specifications.

5.12.11 COASTAL AREA:-

All steel galvanized sections like L angles, flats, tubular sections, bolts and nutsetc. shall be given a coat of ETCH primer. Zinc Chromate primer shall be applied overETCH primer. Synthetic enamel paint of two or more coat thickness shall be applied overthe above.

5.12.12 NON COASTAL AREA:-

In the non-coastal area zinc chromate may be applied instead of zinc phosphate.Painting shall be done in accordance with IS 1477 Part I & II.Priming coat of zincchromate/phosphate shall conform to IS 104.

5.12.13 CLEANING:-

Dust, grease and rust on galvanized tower members namely angles, tees, plates,railing, ladders, racks etc. shall be removed by wire brushing and cleaned with a piece ofcloth.

5.12.14 APPLICATION OF ETCH PRIMER:-

After cleaning the tower members, first coat of an etch primer has to be applied tothe tower structure members. The etch primer consists of polyvinyl butyral phosphoricacid catalyst and zinc chromate base and are supplied separately. They should bemixed before use in the specified ratio of four parts base to one part catalyst or asspecified by the manufacturer. The primer is to be applied uniformly to get a very thinand almost invisible coat and every part of the tower structure should be treated with this

primer. Subsequent painting of the zinc chromate primer should be commenced withintwo hours of application of the primer. The etch primer once mixed should be used upimmediately.

5.12.15 APPLICATION OF PAINT:-

After 48 hours of application of primer, the first coat of the paint should beapplied carefully, well brushed into the surface, corners, crevices etc. Should be uniformand even. The second coat of paint should be applied after 48 hours of the application ofthe first coat. Care should be taken to see that the painting is not carried out at the hottesttime of the day and air pockets should be avoided.

5.12.16 SPECIAL REMARKS:-The painting shall be done carefully so that all corners and crevices of the mast

receive the paint and no base surface is left exposed anywhere. Special care is to be takenin applying paint at the places where galvanized coating has got removed. No drierssuch as Litharge or Turpentine are to be used. The practice of mixing kerosene oil with

paint is strictly forbidden.

5.12.17 PAINTS:-

Paints shall be synthetic enamel of the best quality and anticorrosive and shouldwithstand exposures to outside conditions. They should be of standard quality equivalentto synthetic enamel paint of Shalimar or Berger paints or Asian paints.


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5.12.18 ORANGE AND WHITE BANDS (DAY MARKINGS):-

To conform to Civil Aviation regulations, the towers shall be painted in alternate bands of international orange and international white, terminating with orange at top andthe bottom, Height of each band should be not exceeding 6 metres and should not beless than 0.5 meters. The correct shade for the international orange corresponds to ISIshade 592 as given in the Indian Standard Institution Publication (Colours for readymixed paint).

5.12.19 RECTIFICATION/REPAIRS TO DAMAGED PARTS:-

Damaged components of the steel work should be rectified as per directions of theEngineer-in-charge. Minor damages to the galvanizing shall be made good by cleaningthe damaged portion, free of all rust and applying a zinc rich paste to the same thicknessas the original coat of galvanizing. Members of components, which are dented, bent ortwisted in transit or by handling during erection shall not be used on work but shall bereplaced as directed by the Engineer-in-Charge.

5.13 ERECTION OF TOWERIt shall be ensured that structural components with correct markings as indicated

in drawings are used in correct position. At the base connection, the foundation bolts shall be located correctly using templates and grouted ensuring; that all templates are in onehorizontal plane. After erection of the first panel, its verticality shall be checked andcorrected if necessary.

Further erection work shall proceed panel by panel, bolts and nuts shall be finally be tightened up to the specified torque using torque wrenches. Verticality of the towershall be checked after complete erection of each panel. Each panel shall be completed inall respects and shall have the approval of the Engineer-in-charge before proceeding tothe next panel.If a panel is to be left incomplete, it shall be ensured if necessary; byerection of temporary bracings, that all the members erected form a stale configuration;sufficient to withstand dead and wind loads.

The joint shall be made by drawing the light members into position with barreldrifts. Drifts may be used on the heavier members only to secure them in correct

position. No member shall be force fitted. Any error in steel work, which prevents theassembly and fitting up to the parts by the proper use of drifts, shall be investigatedimmediately. If any defect or deficiency in the member comes to notice, the same shall berectified As per directions of the Engineer-in-Charge.

Packing plates shall be provided at the joints as shown in approved drawings inorder to make up the change in the thickness of the parts, jointed. No other packing platesshall be used. Hot dip galvanized bolts and nuts and washers of class 5.6 shall be

provided in all connections involving leg members, main diagonals as well as horizontalthrough inter- section of the main diagonals in k brace, panels and plain bracings

Hot dip galvanized contact surfaces of joints providing with hot dip galvanized bolts nuts and washers shall be free of oil, paint and lacquer or other coatings and shall bescored by wire brushing or light blasting after galvanization and prior to assembly.

Bolts used for connections shall not be not less than 12mm in diameter. and thelength shall be such that not more than half of the pitch of the thread lies inside the grip


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length. The threaded portion of the bolt shall protrude by not less than 3mm beyond thelock nut after it has been fully tightened.

Bolts and nuts shall be tightened by using the part turn method. The nut shall be brought to the snug tight position after which it will be given a further half to one turndepending upon the length of the bolt. In joints with several fasteners, all the nuts, boltsshall be brought to the snug tight position, before tightening further systematically. Thenut rotation from snug tight condition is given in the table below:-

5.13.1 NUT ROTATION FROM SNUG TIGHT CONDITION:-

Bolt length(As measuredfrom underside of head toextreme end of point)

Boltsfacesnormal to

bolt axis.

One face normalto bolt axis & other facesloped not more than1:20 (bevel washernot used)

Bolt faces slope notmore than 1:20 fromnormal to bolt axis(bevel washers notused).

Upto including 4 dia. 1/3turn 1/2 turn 2/3 turn

Over 4 dia. But notexceeding 8 dia.

1/2 turn 2/3 turn 5/6 turn

Over 8 dia. But notexceeding 12 dia.

2/3 turn 5/6 turn 1 turn.

(xi) Alternatively nuts may be tightened using a calibrated wrench so that the proof load of the bolt specified in IS 1367 is achieved. “Snug tight is defined as thetightness attained by a few impacts of an impact wrench or the full effort of a manusing an ordinary spud wrench. Following this initial operation, bolts shall be placed inremaining holes in the connection and brought to snug tight position”.

5.13.2 VERTICALITY TOLERANCES:-

The verticality for towers of different heights shall be within the provisions ofTable 1 (III) (b) of IS 12843:1989 viz., + H/1000 or +/- 20mm (whichever is less) fortowers up to and including 30 mtrs height and H/1500 or +/- 25mm (whichever is less)for towers over 30mtrs height respectively. (H Refers to the height of tower).


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Figure 8. Excavation of tower foundation


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5.14 SUMMARYTelecom shelter is popularly known as BTS/WLL/GSM shelter. Prefab shelter is

an important component of Ground Based BTS system. Prefab shelter should be plannednear the gate of compound for convenience in installation & maintenance. Prefab shelter

should be heat and weather resistant as well as should have sound/noise insulation. Now adays sandwich panel construction is used for construction of Prefab shelters.Communication Towers can be Ground based or Roof top towers and are classified on the

basis of structural behavior, shape and sections used in the tower. Proper planning oftower layout site and installation of Civil/Electrical Infrastructure of Towers is necessary.Fabrication of towers is done in accordance with IS 800-1984. Proper erection of Towerwith snug tight jointing of connections and verticality needs to be ensured.

5.15 SELF ASSESSMENT QUESTIONS1 General requirement of Telecom Shelter are____________________2 For convenience of installation & maintenance operations, Pre-Fab shelter should

be located___________3 Jointing of panels in Prefab Shelter shall be done with the use of machine lock

((T/F)4 For outdoor installations of Telecom Shelter, the design survival wind speed taken

is___5 Foundation of Telecom shelter, made of R.C.C. isolated footing & columns, shall

be properly designed for__________________6 All structural steel work in Base Frame of Shelters shall conform to________ .7 Towers are designed to withstand _______,_______ &________ loads8 The material of lightening conductor of Tower is ________9 In hybrid towers only M.S. angles are used as structural members (T /F)10 Based on shape, the towers can be classified as_________11 The erection work of tower proceeds_____ (bottom to top / Panel by panel)

5.16 REFERENCES & SUGGESTED FURTHER READINGSwww.tec.gov.in

www.tnd.bsnl.co.in

intranet.bsnl.co.in/digital library

www.wikipedia.org

BIS codes mentioned in the text above

BSNL Handbook On Tower Infrastructure


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Answers to Self Assessment Questions.

1. Should be heat resistant and Sound/Noise insulated.2. Near to the Gate of Compound.

3. False4. 160 Km/Hr5. Dead Load plus Live Load6. 127 Micron7. Dead Load, Self Weight And Wind Load8. Copper9. False10. Four Legged, Three Leged And Delta Structure11. Panel By Panel

Date post:	06-Jul-2018
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