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Q 24. What are the pitfalls of specifying required performance of a tower ?

Ans: The requirement specifications given by the buyer can be read in different ways. The result could be that, although the supplier claims that product offered by him meets the requirements specified by buyer yet it could be 30% less than some other supplier, who has read the requirements in a different manner. Variation occurs due to different interpretations , which are possible in absence of clear definition of requirements. Described below are certain terms, which can be interpreted in different ways. Wind speed : Wind speed varies with time and height. Different countries have different averaging intervals. For example, Canada has one hour. Denmark has 10 minutes, Soviet Union has Approx 2 minutes. India has 3 seconds. UK has 3sec to 15 seconds depending on vertical dimension of the obstruction. USA has fastest mile speed, which translates into 30 seconds for 120 miles per hour( or 60 seconds for 60 miles per hour). Similarly the height for basic wind speed also varies with country. Uk has sea level. India has 10 meters above existing ground level. When the buyer specifies wind speed for design purpose, then he does not mention which type of speed is being specified. 3 sec wind speed is about 30% more than average hourly wind speed. It is suggested that design wind speed be specified. Or alternatively Design wind pressure in tons/sqmeter or pounds/sqft may be specified. Antenna loads Buyer specifies the size, weight and level of installation of antennas. Direction of antenna installation is either not known or not specified. Amount of shielding provided by various antennas has to be decided by designer. This decision could make a lot of difference in loading on the tower. And hence on cost of tower also. It is suggested that antenna loading may be specified in square meters of wind area. Factor of safety If buyer has not asked for any factor of safety, supplier may decide to offer a tower with factor of safety as 1.0 to make his offer most attractive. It is suggested that a factor of safety be specified.