What is the useful life of a tower?

Discussion in 'Design, Development and Standards Discussions' started by kiley, Aug 25, 2011.

  1. kiley

    kiley First Time Poster

    After a tower undergoes a structural analysis, and the owner makes the necessary improvements and investments to the tower as a result of the findings of the structural analysis, what is the result in terms of the useful life of the tower? I know obviously it depends upon the specific improvements done to the tower, but generally speaking, how much longer is the useful life of the tower extended as a result of improvements and investments to it?
  2. Simon Weisman

    Simon Weisman Industry Observer

    I suppose that one may talk of extending the useful life of the tower after upgrades if those upgrades were replacements of worn, damaged, corroded elements that would lead to its early failure. One may also speak about extending the useful life of the structure by making it possible for it to carry new loads that could not be accommodated on the old structure and the old use was no longer needed.

    I suspect, however, that the question has to do with strength alone. If so, then one must keep in mind that the strength design of the structure, although the design wind is stated in terms of a return period, has nothing to do with the useful life of the structure, only with the risk that it may encounter a wind which exceeds the design wind. A fifty year return wind has a 2% probability of being exceeded in any one year. That year can just as easily be the first, or the 20th, or the 50th, or the 150th, although there is a good probability of such exceedence in a 50 year period.

    It is easier to see how not maintaining a tower properly may decrease its usefult life than it is to see how upgrading it may extend it.

    It is not inconceivable (there have been many instances) for the work intended to upgrade a tower to, in fact, cause its early collapse, possibly with dreadful consequences.

    Judging from the many old towers still out there that would most probably not satisfy the latest building code and the numerous tower failures of newer towers which presumably did satisfy more recent building codes, I would say that estimating the useful life of a tower is problematic and need not be directly related to analysis and upgrading, at least not on technical, structural grounds.
  3. Marc LeClair

    Marc LeClair Frequent Poster

    There are hundreds of thousands of towers out there that seem to do well unless there's a collapse by a tornado or high straight line winds that exceed the tower's design...no different than homes being destroyed.

    "Useful life" sounds more like an accounting term used for depreciation versus trying to identify how long the tower will remain standing. With minimum maintenance and no overloading, one could easily say that 75 to 100 years would be a conservative number.

    Due to anchor corrosion, we may see more guyed towers failing over the years because not everyone will spend the money to assess if there is problem with the anchor rods below ground until it's too late.

    It's doubtful that you can get insurance providers to agree upon the useful life of tower. I'm willing to bet that they love writing them because they don't fail often and their loss runs are probably next to nothing.
  4. Bshire

    Bshire Industry Observer

    The useful life of a tower with just Nextel on it could be one month once their iDen is scrap-piled.
  5. JerBo

    JerBo Friend of the Community

    I think that we are all missing the point here.

    First off, from the perspective of a person that did both destructive and non destructive testing, each tower has to be taken on a case by case basis.

    Even with the manufacturing process, the time of day and year when the tower was manufactured, the person who welded each section, the materials used, the corrosion protection, the amount of time the tower laid parrellel and perpendicular, the guying, the corrosion protection used, the amount of guys, the weight of each dead man, the soil and atmosphere around the tower - the list could go on and on.

    I think we see the same results in Nascar with the builders of the race cars used.
    When you get a good one, you run it as much as you can, and when you get a good fabricator - you try to keep them around as long as you can.

    At one time, we didn't throw away a race car just because it was old.
    Marty Robbins had 3 cars his whole carreer.
    All they did was hang a new body on em every year or two.

    Things like a lack of inspection, improper painting and marking, removal of the electroplate when the tower was assembled.
    Spiders climbing up inside of the tower leg before it was assembled and building a nest inside of the leg, causing it to appear good on the outside, yet rusted on the inside.

    I read an article not too long ago about a AM station in Florida that finally took down their tower. WFOY - who's tower stood in a salt water swamp ( 1936 - 2002 ) 56 years! Not a bad track record.

    The real disasters comes not from the lack of proper design or the fault of the building materials, but from some catastropic event such as ice build up on the guys of the tallest of the television transmitter towers in South Dakota and in the mid west where there is no way to predict how much icing can occure during the storm of the century..


    At the same time, I have been at tower sites where one leg was missing because someone backed into the tower.
    A person with a welding truck came out, cut out the broken section, welded in the new section and life went on as if nothing had happened.

    A lattice tower, and most other towers works on the principal of the egg.
    As long as the egg stands on end, it is strong.
    Lay the egg on it's side and it is comparitively weaker - probably 6 times weaker then when stood on end.

    The cell tower industry, with it's hurry up methods and lack of actual safety standards is probably what has given this industry the biggest black eye of all.

    It's not common for a 100 - 300' tower, which has been built propery to fall down.
    Usually it is caused by some idiot that doesn't know or doesn't care what happens to the tower, that causes it to fall down.
    Lack of maintenence, lack of preventative maintenence, over loading, trying to weld something to a tower - after it has been designed and built and erected causes more problems then anything else.

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