|
Posted by Curbie on February 25, 2009, 4:05 pm
Please log in for more thread options
On Wed, 25 Feb 2009 20:42:09 GMT, "vaughn"
>
>> Good points vaughn.
>>
>> Initial tension on the guys and weight of the rigging.
>>
>> How do they "tune" the pre or static (no horizontal loading) stress of
>> guys?
>
>The professionals use dtrain guages to do the measuring & turnbuckles and/or
>sliding preforms to do the adjusting.
>
>>
>> Do you know if 100% the above-anchor rigging-weight is transferred to
>> the base through the mast, or only a part of the weight because of guy
>> tension?
>
>Is this a trick question? ;-)
>
>Yes, on reflection I think all of the rigging weight gets transfered to the
>base. Any wizards out there agree or disagree?
>
>Vaughn
>
Sorry about the dumb question, but there seems to a lot of
counter-intuitive math results in involved in this subject.
Thanks for the help.
Curbie
|
|
Posted by daestrom on February 25, 2009, 5:06 pm
Please log in for more thread options
>
>> Good points vaughn.
>>
>> Initial tension on the guys and weight of the rigging.
>>
>> How do they "tune" the pre or static (no horizontal loading) stress of
>> guys?
>
> The professionals use dtrain guages to do the measuring & turnbuckles
> and/or sliding preforms to do the adjusting.
>
>>
>> Do you know if 100% the above-anchor rigging-weight is transferred to
>> the base through the mast, or only a part of the weight because of guy
>> tension?
>
> Is this a trick question? ;-)
>
> Yes, on reflection I think all of the rigging weight gets transfered to
> the base. Any wizards out there agree or disagree?
>
Yes, all the weight of the rigging (except for the tie down blocks
themselves) is supported by the tower. Just think about the guy-to-tie-down
connection. It isn't 'stiff' and can't 'push' up on the guy wire at all.
So the vertical component of all that rigging has to be supported by the
tower base alone.
As you rightly pointed out, the guy is typically under a preload tension
even with no wind, so the net force vector the block is exerting on the guy
is in a straight line into the ground along the line of the guy.
Now, "How much preload?" That's a tricky question and I'm not sure what I'm
about to say is the whole story, so caveat OP. The idea of a preload is to
tension the cables such that the tower won't have any 'slack' and move back
and forth. If it did, then the motion and sudden 'jerk' when a cable comes
tight will be a much larger shock load and could snap the cable(s).
But you can't just 'snug them all done' on a calm day and call it good.
When the wind starts to blow and one cable (or a pair) are under more
tension, they will stretch a bit. If the downwind guy was just 'snug'
before the wind started to blow, now with the stretch in the upwind cable,
the downwind cable will become slack. A sudden change or any vibration
could cause the tower to bounce sideways and shock load this now-slack guy.
So I think you'll find that professional guys are tensioned up to something
a little more than what they'll see in wind loading. That means when the
wind blows the 'upwind' cable has almost double the preload tension in it,
and the 'downwind' cable is not quite slack. Sort of like pre-tensioning
the rebar in pre-stressed concrete.
But I could be wrong on this, so be sure to double check this.
daestrom
P.S. So obviously if the wind load is expected to be 100 lbf on a 45 degree
guy, the 'calm day' preload on all four guys would be a bit more than 141
lbf (say, 150 lbf). And on that windy a day the upwind cable has
150+141=291 lbf tension (and so does its anchor block!!!).
P.P.S And four guys, each preloaded to 150 lbf would mean an additional base
load of 150lbf*sin(45)*4=424lbf on a calm day. Under the design wind it
would be (291 lbf + 150 lbf + 150 lbf + 9lbf)*sin(45)=424 lbf
|
|
Posted by Jim Wilkins on February 23, 2009, 9:52 pm
Please log in for more thread options > For guyed towers there are two points of ground contact (support), 1)
> the tower base and 2) the guy wire anchors.
>
> Is the loading on the base only vertically downward from weight of the
> mast and turbine, or does horizontal forces from wind velocity place
> upward forces from the guy anchors that translate into increased
> downward forces on the base?
>
> Thanks.
>
> Curbie
The physics of this is called 'Statics".
http://darkwing.uoregon.edu/~struct/courseware/461/461_lectures/461_lecture=
8/461_lecture8.html
High school algebra and geometry are enough to understand the basics,
the trouble is that most explanations assume you will go further and
need calculus so they use it early on.
|
|
Posted by ralleyrat on March 2, 2009, 6:51 pm
Please log in for more thread options > For guyed towers there are two points of ground contact (support), 1)
> the tower base and 2) the guy wire anchors.
>
> Is the loading on the base only vertically downward from weight of the
> mast and turbine, or does horizontal forces from wind velocity place
> upward forces from the guy anchors that translate into increased
> downward forces on the base?
>
> Thanks.
>
> Curbie
The guy wires add a compression, (or 'down') load to the mast.
Their tension takes side loads to the ground.
Stress on the anchor points is a resultant vector.
Draw the triangles and figure it out.
|
|
Posted by Curbie on March 3, 2009, 3:24 am
Please log in for more thread options On Mon, 2 Mar 2009 15:51:10 -0800 (PST), ralleyrat
>Draw the triangles and figure it out.
It is exactly what I did after reading the first couple replies to the
start of this thread, that and begin study on very basic Trigonometry.
I never took trig in high school (over 30 years ago), but was exactly
what I needed to have any understanding of this stuff.
Thanks,
Curbie
|
| Similar Threads | Posted | | Re: Calculating wind turbine tower loads | February 25, 2009, 12:54 pm |
| Re: Calculating wind turbine tower loads | February 25, 2009, 3:45 pm |
| Re: Calculating wind turbine tower loads | February 25, 2009, 3:52 pm |
| Re: Calculating wind turbine tower loads | March 2, 2009, 5:37 pm |
| Re: Calculating wind turbine tower loads | March 3, 2009, 4:43 am |
| Re: Calculating wind turbine tower loads | March 3, 2009, 10:30 am |
| Wind-Turbine Tower Forces | October 1, 2009, 5:09 pm |
| are you happy with your wind turbine? | January 18, 2007, 7:25 am |
| Looking at a gryphon wind turbine | October 18, 2007, 9:55 am |
| New (to me) type of wind turbine | May 12, 2007, 11:11 pm |
|
|
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap