Just wondering, I've seen a few guyed towers where, at the bottom section, the 3 main tower legs are made so they angle inward almost to a point where the tower is bolted to the concrete base, usually with one very large bolt thread set in the concrete base.
What are the advantages and disadvantages of this method, as compared to setting a normal triangular base section down in the concrete ?
Guyed tower bases
Re: Guyed tower bases
Maybe the towers you've seen started life as AM broadcast antennas where the mast (i.e. antenna) sits on a large ceramic insulator at the base.
Iain
Iain
73
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih
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VK2GOM
Re: Guyed tower bases
Hi Leigh, there is probably some elaborate maths behind it, but for a tower guyed all round, I wouldn't think it matters whether the base had 3 legs or came to a central point like that. Properly guyed, it is a stable structure with equal stress and strain.
I too have seen plenty of (large) towers that the base is a central point like that.
73 - Rob VK2GOM / G0MOH
I too have seen plenty of (large) towers that the base is a central point like that.
73 - Rob VK2GOM / G0MOH
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VK2KRR
Re: Guyed tower bases
Hi Rob,
It must somehow make the bottom section stonger some what, but Im not sure. Trying to figure it out in my head but not having much luck so far.
It must somehow make the bottom section stonger some what, but Im not sure. Trying to figure it out in my head but not having much luck so far.
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VK2KRR
Re: Guyed tower bases
OK ive done a few searches on the subject.
"Guyed tower bases buried in the footing suffer from a system limiting feature that is caused by guy stretch. The elongation of the cable allows the tower to lean over enough to create large base bending stresses. Freeing up the tower base connection to rotate, eliminates this problem. Making this change increases the guy loads, but does not cause them to exceed acceptable safety margins. "
"commercial users understand the problem, and agree that the base of the tower should not only be free to rotate about the vertical axis to reduce torsional load development, but also be free to lean over just as far as the guys will allow. The small tapered bases sit on bearing plates on a pier pin. It is obvious from the drawings that these connections will allow enough rotation, about the horizontal axes, to prevent development of significant bending loads. "
"Guyed tower bases buried in the footing suffer from a system limiting feature that is caused by guy stretch. The elongation of the cable allows the tower to lean over enough to create large base bending stresses. Freeing up the tower base connection to rotate, eliminates this problem. Making this change increases the guy loads, but does not cause them to exceed acceptable safety margins. "
"commercial users understand the problem, and agree that the base of the tower should not only be free to rotate about the vertical axis to reduce torsional load development, but also be free to lean over just as far as the guys will allow. The small tapered bases sit on bearing plates on a pier pin. It is obvious from the drawings that these connections will allow enough rotation, about the horizontal axes, to prevent development of significant bending loads. "
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VK2KRR
Re: Guyed tower bases
Also one other point was that, with the pier pin type base, that it allows water buildup in the tower legs to drain through weep holes.
Where as (tube) tower bases encased in concrete will are more problematic for moisture causing corrosion.
Where as (tube) tower bases encased in concrete will are more problematic for moisture causing corrosion.