this post is a word of caution, to friends in the great land of China, about an engineering marvel they recently completed( the Aizhai bridge in Chadong), that is very similar to one we had here in the states...that had a rough ending--
"galloping girdie"
also known as the "Tachoma narrows bridge", that collapsed in 1940, in Puget sound, Washington...there is a video of the issue, viewable on youtube, called( Tachoma narrows bridge collapse "gallopin' gertie" ) that was posted by GonzoNugent dec 9, 2006--
if the video is watched carefully, the issue is apparent, the weight of the road in this suspension bridge was the force being counted on, to hold the road flat( parallel), to the earth, and with no wind, this was the case...but unfortunately, the road was flat, like a wing...and this caused upward lifting forces, in high, or medium, winds( as canyons produce them regularly), this wind condition reduced the weight load, on the forward, or "windward", side of the bridge's road-surface( facing the wind), causing a "rhythmic-twist" to occur, in the roads structure...
the concept--
the road was made of steel and concrete, thus it acted like an automobiles torsion bar, and when twisted, it tried to go back to it's original shape...in the Tachoma narrows bridge's case, the road twisted farther back, than flat( it's original position), from the force of the initial twist being released, and thus pressure was gained, moving in the opposite direction, on the next twisting/wind lifting cycle( at this point, a "regular harmonic cycle" was established, and the wind gained increased lifting power, on each additional harmonic cycle thereafter)...this small gain, each cycle, of rhythmic-twisting, magnified the lift from the wind, and once started, the cycle could not be arrested--
note--
also of note, most auto mechanics know, that if you twist, or bend, a piece of metal, it breaks, as the strength of the material is lost( after enough bends occur)...this suggests to me, that as the bridge was swaying, in a greater, and greater, arch( from the winds lift factors being enhanced, by twisting harmonic forces), that the metal in the bridge was also weakening( enhancing wind lift/twist forces), causing a larger, and larger, sway, until absolute failure, of the structure, was reached--
the point--
what to do??...scrapping the bridge is not viable, or needed, in my opinion...i suggest, the answer to this issue is an "inverse cable system"( below the road of the bridge)--
overcoming wind factors--
when considering wind factors, the bridge can be seen as a wing, on on older "bi-plane"( a "sopwith camel" perhaps??), this model displays the value of having an inverse, or identical cable system, beneath a bridge, wing, or other similar structure, that must maintain it's position( the bridge's road surface), without counting on the weight of the structure alone( gravity)...to resist harmonics, twisting, and structural failures--
in fact, i believe this concept worked so well, that the "red baron" liked to have three( wings), to make possible severe acrobatic stresses, with very light materials...allowing him to very nearly shoot down the entire world at the time--
summary--
i believe that, by utilizing a cable system, identical to the one on the top of the bridge, underneath, the problem could be solved, without changing the bridges design radically, the two large cables underneath, with lines going upwards( to the bottom of the bridge's road), would lock them in position, eliminating the possibility of sway from wind, and a possible dangerous "harmonic twisting cycle", to develop...in addition, the cables underneath would act like the "flaps", that airplanes use to foil lift, when it is not desired( also similar to a screen in a person's doorway, that reduces wind flow through the portal), lastly, the weight of the cables underneath, would add to the total pull of gravity towards the earth, and further eliminate the possibility of road lifting, and twist, from wind forces--
speaking of weight, the neat thing about suspension bridges, is that they allow very long expanses to be connected, the longer a bridge is, the lighter it must be constructed, as the longer the distance between the load-bearing towers, or pylons, the more fragile the open area, and the less weight it can support...for this reason, in my opinion, cables are the best choice for building materials( in large bridge construction), as they are very light, compared to huge girders, and are more effective in the long term( also, i feel cables maintain their strength, through cycles of expansion, or stress, much better, for some reason)...i hope this concept will eliminate bridge-twist, and failure, is of use to China...and the rest of the bridge crossing world--
--to me, the Aizhai bridge is both an engineering marvel of this world, and very beautiful...may it stand for all time--
--best wishes, john kruschke--
an "after thought"--
--for situations involving bridges over heavy seas, and large divides, i feel that load-bearing "pylons" with bases shaped like ice-braking vessels, would be needed, and possibly the use of "wave canceling harmonics"( "wave boards", see "aquatic wave building" post), to cancel waves around the bridges supporting members, thereby clearing a lane( calming), the heavy waters, to reduce stress loads even further, on the load-bearing "pylons"--
example--
i have heard that there is no bridge across the "English channel", due to the heavy seas there-in, i agree...we may have to due without the "chop"...i suggest, to obtain this condition, small waves might be created, at the "pylons" bases( bridge supports), that travel outward from them, to cancel any "wave-action", headed in the direction of the "pylons", that support the bridge...i feel these small waves could be created via "wave-boards", that would "paddle", or "push", a small wave outward from the bridge's supports, at regular intervals, thus cancelling/nullifying any incoming waves, thereby clearing a lane in the sea, of "chop"...( i believe this concept can be modeled in the bathtub at home)--
--as for the best two points for a bridge, one either side of the channel, and the cost of "fish-n-chips" there( of a certain quality)...more study will be needed( attention able assistants)--
--bon voyage--
"galloping girdie"
also known as the "Tachoma narrows bridge", that collapsed in 1940, in Puget sound, Washington...there is a video of the issue, viewable on youtube, called( Tachoma narrows bridge collapse "gallopin' gertie" ) that was posted by GonzoNugent dec 9, 2006--
if the video is watched carefully, the issue is apparent, the weight of the road in this suspension bridge was the force being counted on, to hold the road flat( parallel), to the earth, and with no wind, this was the case...but unfortunately, the road was flat, like a wing...and this caused upward lifting forces, in high, or medium, winds( as canyons produce them regularly), this wind condition reduced the weight load, on the forward, or "windward", side of the bridge's road-surface( facing the wind), causing a "rhythmic-twist" to occur, in the roads structure...
the concept--
the road was made of steel and concrete, thus it acted like an automobiles torsion bar, and when twisted, it tried to go back to it's original shape...in the Tachoma narrows bridge's case, the road twisted farther back, than flat( it's original position), from the force of the initial twist being released, and thus pressure was gained, moving in the opposite direction, on the next twisting/wind lifting cycle( at this point, a "regular harmonic cycle" was established, and the wind gained increased lifting power, on each additional harmonic cycle thereafter)...this small gain, each cycle, of rhythmic-twisting, magnified the lift from the wind, and once started, the cycle could not be arrested--
note--
also of note, most auto mechanics know, that if you twist, or bend, a piece of metal, it breaks, as the strength of the material is lost( after enough bends occur)...this suggests to me, that as the bridge was swaying, in a greater, and greater, arch( from the winds lift factors being enhanced, by twisting harmonic forces), that the metal in the bridge was also weakening( enhancing wind lift/twist forces), causing a larger, and larger, sway, until absolute failure, of the structure, was reached--
the point--
what to do??...scrapping the bridge is not viable, or needed, in my opinion...i suggest, the answer to this issue is an "inverse cable system"( below the road of the bridge)--
overcoming wind factors--
when considering wind factors, the bridge can be seen as a wing, on on older "bi-plane"( a "sopwith camel" perhaps??), this model displays the value of having an inverse, or identical cable system, beneath a bridge, wing, or other similar structure, that must maintain it's position( the bridge's road surface), without counting on the weight of the structure alone( gravity)...to resist harmonics, twisting, and structural failures--
in fact, i believe this concept worked so well, that the "red baron" liked to have three( wings), to make possible severe acrobatic stresses, with very light materials...allowing him to very nearly shoot down the entire world at the time--
summary--
i believe that, by utilizing a cable system, identical to the one on the top of the bridge, underneath, the problem could be solved, without changing the bridges design radically, the two large cables underneath, with lines going upwards( to the bottom of the bridge's road), would lock them in position, eliminating the possibility of sway from wind, and a possible dangerous "harmonic twisting cycle", to develop...in addition, the cables underneath would act like the "flaps", that airplanes use to foil lift, when it is not desired( also similar to a screen in a person's doorway, that reduces wind flow through the portal), lastly, the weight of the cables underneath, would add to the total pull of gravity towards the earth, and further eliminate the possibility of road lifting, and twist, from wind forces--
speaking of weight, the neat thing about suspension bridges, is that they allow very long expanses to be connected, the longer a bridge is, the lighter it must be constructed, as the longer the distance between the load-bearing towers, or pylons, the more fragile the open area, and the less weight it can support...for this reason, in my opinion, cables are the best choice for building materials( in large bridge construction), as they are very light, compared to huge girders, and are more effective in the long term( also, i feel cables maintain their strength, through cycles of expansion, or stress, much better, for some reason)...i hope this concept will eliminate bridge-twist, and failure, is of use to China...and the rest of the bridge crossing world--
--to me, the Aizhai bridge is both an engineering marvel of this world, and very beautiful...may it stand for all time--
--best wishes, john kruschke--
an "after thought"--
--for situations involving bridges over heavy seas, and large divides, i feel that load-bearing "pylons" with bases shaped like ice-braking vessels, would be needed, and possibly the use of "wave canceling harmonics"( "wave boards", see "aquatic wave building" post), to cancel waves around the bridges supporting members, thereby clearing a lane( calming), the heavy waters, to reduce stress loads even further, on the load-bearing "pylons"--
example--
i have heard that there is no bridge across the "English channel", due to the heavy seas there-in, i agree...we may have to due without the "chop"...i suggest, to obtain this condition, small waves might be created, at the "pylons" bases( bridge supports), that travel outward from them, to cancel any "wave-action", headed in the direction of the "pylons", that support the bridge...i feel these small waves could be created via "wave-boards", that would "paddle", or "push", a small wave outward from the bridge's supports, at regular intervals, thus cancelling/nullifying any incoming waves, thereby clearing a lane in the sea, of "chop"...( i believe this concept can be modeled in the bathtub at home)--
--as for the best two points for a bridge, one either side of the channel, and the cost of "fish-n-chips" there( of a certain quality)...more study will be needed( attention able assistants)--
--bon voyage--
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