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Re: [coldwarcomms] Re: Capstones & Ankle Braces was: tower foundations

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  • David
    ... 4th of 5 Tower Base Plate shots. So the new square donut pours sit atop an existing plate, somewhere below grade? And the 45
    Message 1 of 13 , Jan 12, 2013
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      On 1/12/13 11:24 PM, widebandit wrote:

      > How about Chapin SC:
      > <http://tinyurl.com/ChpnSC88678>

      >

      > 212'6" H-Tower with two side-platforms added later at the 75' level.
      > This required wing angles up to the side platforms, ankle braces,
      > capstones. Check out the tower baseplate photos - the 4" drainage tubes
      > for the base-plate wells are a nice touch. The leg bolts that look like
      > rivet heads are called structural rib-bolts; they have a ribbed shank
      > that makes an interference fit in the hole, resulting in a much stronger
      > joint. SRBs are secured with Anco self-locking nuts...


      <http://bit.ly/W1o2pX> 4th of 5 "Tower Base Plate" shots.

      So the new square donut pours sit atop an existing plate, somewhere below
      grade? And the 45 degree braces go through dirt between the old base column
      and the new donut...

      BTW, how far down would the vertical studs do, and what was attached along
      the way, inside the original column pour?
    • David
      I m now thinking Long-Lines radio relay and L4/L5 were secretly schemes created by the US cement lobby & the structural steel cartel...
      Message 2 of 13 , Jan 12, 2013
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        I'm now thinking Long-Lines radio relay and L4/L5 were secretly schemes
        created by the US cement lobby & the structural steel cartel...
      • Dexter McIntyre W4DEX
        ... Hartsville was added to my list of sites to maintain in 1991. All equipment was still in place but just about all service had been rerouted. I don t know
        Message 3 of 13 , Jan 13, 2013
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          rjfrank1@... wrote:
          >
          >
          >
          > Another example of a tower foundation capping slab further
          > illustrating Widebandit's comments can be found at Hartsville, SC.
          > was there an earlier tower in-service at the site prior to the
          > existing tower?
          >
          Hartsville was added to my list of sites to maintain in 1991. All
          equipment was still in place but just about all service had been
          rerouted. I don't know the history of this site but I suspect it was
          once considered a maintenance center due to all the file cabinets and
          office furniture that was in the front of the building. Seems like the
          front part may have been added because there was a masonry wall
          separating the office area from the radio room. I suspect the original
          tower was built in the early 50's and was replaced with the existing one
          about mid 60's. Everyone I knew that would know the station's history
          is now gone.

          Hartsville was was my first encounter with fire ants. Many thing I have
          forgot but that experience is in permanent memory.

          Dex
        • widebandit
          ... The term tower base plate refers to the steel weldment in the form of a reinforced leg stub attached to an approximately 10 square by 2 thick steel
          Message 4 of 13 , Jan 14, 2013
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            > > How about Chapin SC:
            > > 212'6" H-Tower with two side-platforms added later at the 75' level.
            > > This required wing angles up to the side platforms, ankle braces,
            > > capstones. Check out the tower baseplate photos - the 4" drainage tubes
            > > for the base-plate wells are a nice touch. The leg bolts that look like
            > > rivet heads are called structural rib-bolts; they have a ribbed shank
            > > that makes an interference fit in the hole, resulting in a much stronger
            > > joint. SRBs are secured with Anco self-locking nuts...
            >
            >
            > 4th of 5 "Tower Base Plate" shots.
            >
            The term 'tower base plate' refers to the steel weldment in the form of a reinforced leg stub attached to an approximately 10" square by 2" thick steel plate that is secured to the anchor bolts forming the base of each tower leg. All vertical dimensions associated with the tower are referenced to the top of the base-plates - top of TBP.

            So far as I know, the cap-slab is simply poured into a form on top of the ground. Close examination of the Chapin cap-slab photos reveals where stress caused by the foundation pier and settlement of the replaced overburden has created spall fractures inside the wells.
            >
            > So the new square donut pours sit atop an existing plate, somewhere below
            > grade? And the 45 degree braces go through dirt between the old base column
            >
            Most L-L tower foundations are of the pier-and-pad variety - a tapered reinforced pier about 3' square at the top protruding from a much larger 'pad' anywhere from ten to twelve-feet square, about four feet thick, and resting somewhere between six and twelve feet below finish grade. Sometimes, in soft soil conditions, the pads are also anchored to pilings. There are also cases where soil conditions near the surface required most of the concrete to be above finish grade. At Madison Florida, you get to see naked tower foundations in all their glory: http://tinyurl.com/MdsnFl-ATC88449

            When excavating the foundation holes, the contractor was required to stop at precisely the required depth. He was not allowed to use any replacement fill - which is subject to settling - to 'adjust' the depth of excavation. If he excavated too deep - he was required to make the pad that much thicker and eat the cost of additional labor and material. Obviously, a savy contractor will take this into account when bidding a foundation job - and dig very carefully.

            When a tower required additional leg support, a new excavation was made for addtiional blocks of reinforced concrete - usually outboard of the existing pads. The 45-degree brace angles terminate into an anchor plate encased in the center of the new concrete blocks - the same rules applied to depth of excavation for the new blocks as applied to the original foundation pads.

            Needless to say, since the contractor was now removing overburden from a foundation supporting an existing tower, he had to be very careful not to place the structure at risk of overturning. The usual procedure was to prepare the forms, the rebar, and the steel beforehand, attach the bracing gussets to the tower leg, dig the hole, place the forms the rebar and the structural steel; then pour the concrete; all within a single 24-hour period. Then he had to get everything covered and properly compacted again as soon as the new mud had cured to its minimum yield strength. This procedure was done one-leg at a time - one block at a time.
            >
            > and the new donut...
            >
            > BTW, how far down would the vertical studs do, and what was attached along
            > the way, inside the original column pour?
            >
            Tower anchor bolts were usually an L-shaped assembly separate from the foundation rebar and long enough to reach down into the center of mass of the pad block. The foundation forms and rebar were usually placed first then the anchor bolts - which were usually held in precise relative alignment by a template - were set and precisely located with respect to the other tower legs:
            http://www.normantower.com/tower_erection.php
            Once the pour began the concrete crew had to be very careful not to disturb the anchor bolt settings. I know of one L-L tower where two of the baseplates show evidence of heavy sledge-hammer blows - presumably to 'adjust' an improperly placed anchor bolt set.

            When the piers were sufficiently cured for construction, the tower base-plates were secured to the anchor bolts with nuts both above and below the plate, but not directly against the concrete. There was an adjustment gap allowing final leveling of the base-plates to insure the tower started up plumb. Once the plates were leveled and the nuts were tightened, a layer of grout was forced into the gap to make a firm bond with the pier surface. Tower erection could now commence.

            Are you ready for your contractor's license? - wa -
          • David
            ... I assume that if the tower is on bedrock itself, all the rules change. You put anchors into it, and little cement is needed... True?
            Message 5 of 13 , Jan 14, 2013
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              On 1/14/13 3:05 AM, widebandit wrote:

              > Most L-L tower foundations are of the pier-and-pad variety - a tapered
              > reinforced pier about 3' square at the top protruding from a much larger
              > 'pad' anywhere from ten to twelve-feet square, about four feet thick,
              > and resting somewhere between six and twelve feet below finish grade.
              > Sometimes, in soft soil conditions, the pads are also anchored to
              > pilings. There are also cases where soil conditions near the surface
              > required most of the concrete to be above finish grade. At Madison
              > Florida, you get to see naked tower foundations in all their
              > glory:http://tinyurl.com/MdsnFl-ATC88449



              I assume that if the tower is on bedrock itself, all the rules change.
              You put anchors into it, and little cement is needed...

              True?
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