![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
At the end of this article there is a reference to a well-known book by Jobst Brandt and a statement that "it contains several serious factual engineering and math errors". I am aware that there is some controversy about aspects of Brandt's book but I feel it is not appropriate to make an assertion like this without either expanding on it to give one or more examples (however briefly)or provide a link to a text that explains those errors. Chrisrustsheffield ( talk) 20:20, 16 December 2010 (UTC) As there has been no response to my comment above I've removed the statement referred to and replaced it with a more balanced one indicating that there is some controversy about Brandt's work. Chrisrustsheffield ( talk) 23:08, 9 March 2011 (UTC)
You all obviously don't understand the concept of prestressed structures. If you would actually read what I wrote I never claimed the spokes at the bottom aren't under tension. The bottom spokes support the load as rigid columns because they are prestressed. That's what the term means. It's the same as how you can have prestressed concrete spans work under tension. Concrete is the opposite case of a wire spoke. It works under compression, but not tension. By itself, it can't be used as a horizontal beam, like small bridges, because there is tension at the bottom of beams. To use concrete under tension, it is cast around tensioned steel bars, and then the tension is released when the concrete cures, transferring the tension of the steel beam into the concrete. Thus prestresses the concrete, putting it under compression. Then, the beam can handle tensile stresses, as the total normal stress is just the compressive stress - the normal stress. If that's positive, the beam is still under net compression, and everything is fine and dandy. It's the same with bicycle wheels. As long as the tension is greater than the compression, it's under net tension, and the spoke can support the rim. When the compression exceeds tension, the spoke detensions, and does not support the rim and is subject to more fatigue. This is how prestressed structures work, if you want to argue with me about it I'd appreciate it if you got an understanding of basic continuum mechanics and basic engineering.
On an unloaded wheel, the spokes are all under tension. Upon loading, the tension on the bottom spokes is reduced by the action of the rim deflecting inward. This load is balanced by the downward force that the hub exerts. The tension in the top spokes is unchanged, because the reduced downward pull of the bottom spokes is made up for by the increased downward pull of the hub. The top spoke's tension is completely unchanged. — Preceding unsigned comment added by 205.175.113.16 ( talk) 02:02, 3 March 2012 (UTC)
< The last cross is normally "interlaced" by wrapping the spoke around the one from the other side of the flange. >
Why is this done? What is lost by not doing it?
86.181.114.89 ( talk) 02:02, 11 August 2011 (UTC)
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
At the end of this article there is a reference to a well-known book by Jobst Brandt and a statement that "it contains several serious factual engineering and math errors". I am aware that there is some controversy about aspects of Brandt's book but I feel it is not appropriate to make an assertion like this without either expanding on it to give one or more examples (however briefly)or provide a link to a text that explains those errors. Chrisrustsheffield ( talk) 20:20, 16 December 2010 (UTC) As there has been no response to my comment above I've removed the statement referred to and replaced it with a more balanced one indicating that there is some controversy about Brandt's work. Chrisrustsheffield ( talk) 23:08, 9 March 2011 (UTC)
You all obviously don't understand the concept of prestressed structures. If you would actually read what I wrote I never claimed the spokes at the bottom aren't under tension. The bottom spokes support the load as rigid columns because they are prestressed. That's what the term means. It's the same as how you can have prestressed concrete spans work under tension. Concrete is the opposite case of a wire spoke. It works under compression, but not tension. By itself, it can't be used as a horizontal beam, like small bridges, because there is tension at the bottom of beams. To use concrete under tension, it is cast around tensioned steel bars, and then the tension is released when the concrete cures, transferring the tension of the steel beam into the concrete. Thus prestresses the concrete, putting it under compression. Then, the beam can handle tensile stresses, as the total normal stress is just the compressive stress - the normal stress. If that's positive, the beam is still under net compression, and everything is fine and dandy. It's the same with bicycle wheels. As long as the tension is greater than the compression, it's under net tension, and the spoke can support the rim. When the compression exceeds tension, the spoke detensions, and does not support the rim and is subject to more fatigue. This is how prestressed structures work, if you want to argue with me about it I'd appreciate it if you got an understanding of basic continuum mechanics and basic engineering.
On an unloaded wheel, the spokes are all under tension. Upon loading, the tension on the bottom spokes is reduced by the action of the rim deflecting inward. This load is balanced by the downward force that the hub exerts. The tension in the top spokes is unchanged, because the reduced downward pull of the bottom spokes is made up for by the increased downward pull of the hub. The top spoke's tension is completely unchanged. — Preceding unsigned comment added by 205.175.113.16 ( talk) 02:02, 3 March 2012 (UTC)
< The last cross is normally "interlaced" by wrapping the spoke around the one from the other side of the flange. >
Why is this done? What is lost by not doing it?
86.181.114.89 ( talk) 02:02, 11 August 2011 (UTC)