• Question11. Should high Strength steel be used for Tower manufacture?

    To achieve desired strength of tower, use of HSS (High Strength Steel) instead of normal mild structural steel will result in lighter tower (Not necessarily cheaper tower because of cost differential of normal mild structural steel and HSS). Reduction in weight may be very important in certain applications e.g. airplanes, motor cars etc. In such applications, irrespective of the initial cost, low weight results in low operational cost. In case of towers, operational costs do not depend on weight of tower. Hence no special advantage is obtained by using HSS. HSS is normally used by manufacturer to achieve cost savings.

  • Question12. Will a tower made from high strength steel be stronger than the one made from normal mild structural steel?

    The strength of tower is determined by “Total Resistance” offered by the tower to the applied loads. Total resistance offered by the tower is ‘Strength of material per unit area’ X (multiplied by) ‘Area of material available for resistance’ If ‘Strength of material per unit area ‘ is less then designer provides more ’ area of material’ to get the same total resistance. If ‘Strength of material per unit area’ is more then designer will provide less ‘area of material’ to get the same total resistance and not increase the cost unnecessarily. Designer will normally build some reserve structural capacity in the tower. Other things being equal, a factor of safety of 1.5 me Answer a reserve capacity of 50% is provided in the design. Total structural capacity (required + reserve) is determined by the decisions of the designer and not by the strength of steel. As a matter of fact, tower can be constructed with any structural material. We do have towers made of reinforced cement concrete, Aluminum, wood, combination of RCC and steel etc. Whichever be the material of construction, adequate strength of tower can be achieved, provided the designer has done his work properly.

  • Question13. Is the tower made from high strength steel economical than one made from normal mild structural steel?

    Not necessarily.
    It depends on
    a) weight of steel saved in tower by using High strength steel and
    b) price differential between high strength steel and normal mild structural steel.

  • Question14. Does the tower made from High strength steel have ALL the members made from High strength steel?

    Normally not
    Some members are designed on the basis of permissible slenderness ratio. These members are not made from HSS. Only few members of tower are made from HSS generally.

  • Question15. Can steel of very high strength be used for manufacture of towers?

    As strength of steel increases, the brittleness of steel goes up. As communication towers are designed to be stressed within the elastic range, percent elongation of material is an important property to be kept in mind while choosing the grade of steel. Brittle materials are not suitable for applications where metal fatigue is generated by applied loads. Normal mild structural steel has a yield strength of 230 to 275 MPa. While high strength steels with yield strength up to 480 to 500 Mpa are commonly used in some applications, High strength steel for tower applications is normaly limited to steels with yield strength upto 350 Mpa. What is important is that - the strength of steel should as per the strength taken by designer in his calculations.

  • Question16. Will hot dip galvanizing affect the strength of steel?

    If the steel used is normal mild structural steel, which has not been heat treated to achieve any increased strength then galvanizing does not affect the properties in any way. If steel used is work hardened, then hot dip galvanizing (dipping in temp up to 415deg C will certainly have some annealing affect on steel, which may reduce the strength of steel.

  • Question17. Does country of origin of steel has any role to play in quality of tower/steel?

    In a situation, where it is not possible to measure the various parameters which affect the quality of material, country of origin of material may be considered to be a reasonable assurance of quality. Today, when all parameters, which have effect on quality, can be quantitatively measured, there is no significance or relevance of the origin of materials. Quantitative testing to ascertain value of desired properties should be used to establish quality of steel. For quality of tower to be as desired, the strength of steel should be as assumed by designer in his design calculations.

  • Question18. Which properties of steel should be measured to evaluate the suitability of steel for tower manufacture?

    End use of steel determines the properties required from raw material used. If the end use of steel is to cut another piece of steel on a lathe machine then it is important the steel must maintain its strength even when it is red hot. If steel is to be used for making an acid tank, it becomes necessary that the material should not be attacked by that acid. Resistance for other acids may not be of any consequence. If steel is to be used as stampings, then the magnetic characteristics of the steel are important. All properties are not important for any one end use. For example the magnetic properties of steel may not be of any importance, if it is being used as a structure. When end use of steel is tower manufacture, then the following properties should be evaluated.
    a) Yield strength - elastic strength of steel
    b) Percent Elongation - ability to bend and return to original shape
    c) Chemical composition - for establishing grade of steel.

  • Question19. How do you say that given two grades of steel are equivalent?

    The end use of the material should be ascertained. For example, if the end use is tower manufacture for both samples then following properties should be found out for two samples.
    a) Yield strength
    b) Percent Elongation
    c) Chemical composition If values of these properties are within the ranges specified then two steels are equivalent.

  • Question20. What is meant by terms BS, GB, IS, ISO, ASTM ….. etc?

    These terms stand for standards of various countries. For example BS stands for British Standard, GB for Chinese standard, IS stands for Indian Standard, ISO stand for International Standards Organization, ASTM is an American Society of Testing materials. Etc