Tower is a Capital expenditure with operational life of several decades. Hence buying a tower needs careful determination of requirements or specifications. Important specification include
1. Survival wind Speed.
2. Physical size, Type, Number and levels of Antennas.
3. Twist & Sway requirements.
While offering a product, almost all bidders, uniformly say Complied against all the required specifications including above i.e. wind speed, antenna loading etc.
While compliance for some of the specifications is easily confirmable, the requirement of wind speed and antenna loading cannot be checked without looking into detailed design calculations. Hence experienced and shrewd buyers always insist on design calculations, before finalization of purchase contract.
Unfortunately these two parameters are main parameters, which determine suitability of tower and are responsible for cost of tower also.
Factors like size of antennas, type of antenna, level of antenna have considerable effect on the required strength (read cost) of tower.
Placing antenna at mid height of tower will reduce the loading on tower by 50%. On the other hand, if the wind speed is double, the forces acting on tower are 4 times.
Buying a communication tower is not the same as buying a bunch of steel angle, pipes, plates etc. Tower is matched set of its various components.
Each component of this set has a vital role to play in the strength of WHOLE tower, for example, if one small segment of the leg is slightly weaker than required, that the entire towers strength will be determined by this small component, because tower will fail from this point only when full loading occurs. Moreover, putting extra strength at any non-required point is wastage of materials, because strength of the tower is determined by weakest link in the structure only. Hence it becomes imperative that all members should be capable of resisting the applied loads to the same extent uniformly.
To ensure that all these things have been considered properly, availability of design competency with the tower supplier is the most desirable eligibility criterion. Design competency in supplier is a must for copying also. For example, if bolt grade changes, the joints have to be redesigned. If any member is replaced due to non availability of any section then also detailing of all adjoining members has to be changed.
Approx. 95% of price paid by buyer for tower, consists of materials cost. In todays competitive world, all bidders work on small margins. Hence material cost is the all encompassing component of total cost. Anybody can reduce the cost by reducing the materials. That reduction is normally not without compromising on the performance or strength. The buyer has no way to recognize this compromise without looking into detailed calculations and verify that the product is as per design calculations.