123456789_123456789_1123456789Case Study and Research
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Cable-stayed bridge during construction 


Cable-stayed Bridge
Model Examples



Model description



Input



BIM model



Analysis model



Landscape model



ICDAS Basis of Design



Workflow of Software



Additional features



Rendering, Animation &
Vitural Reality
  


Case Study and 
Research

 

Natural mode shapes of full bridge supported at deck ends


Mode 1, f = 0.244 Hz

is the 1st symmetric lateral mode of the bridge (1st SL), where both of the pylons and the deck are vibrated to the

same side. DY modal displacements (on one side) shows the pylons vibrations are the dominant. This mode can also

called the 1st bending mode of the pylons about the bridge axes. 






 

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Mode 2, f = 0.275 Hz

is the 2nd bending mode of the pylons about the bridge axes, where the pylons vibrate to the opposite side.
DY modal displacements show that the bridge deck do not vibrate in this mode.






Mode 3, f = 0.283 Hz

is the 3rd bending mode of the 1st pylon while the 2nd pylon is vibrated with very small amplitude.





Mode 4, f = 0.283 Hz

has the same frequency as mode 3, where the pylons vibration are switched.




 

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Mode 5, f = 0.394 Hz

is the 1st symmetric vertical bending mode of the deck (1st SV). In this mode the pylons are vibrated about the
axes perpendicular to the deck.





Mode 6, f = 0.439 Hz

is the 2nd symmetric lateral mode of the bridge (2nd SL), where the pylons and the deck are vibrated to the
opposite side compared to the 1st SL mode (mode no. 1)





Mode 7, f = 0.559 Hz

is the 1st asymmetric vertical bending mode of deck (1st AV). Note that the pylon legs are vibrated with mode
shapes of higher frequency than the previous modes.


 

  

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Mode 8, f = 0.824 Hz

is the 2nd symmetric vertical bending mode of the deck (2nd SV)




Mode 9, f = 0.855 Hz

is the 1st asymmetric lateral mode of the bridge (1st AL). Note that the longest cables on the one side span vibrate
also out of the cable plan in this mode.






Mode 10, f = 0.897 Hz

is the 2nd asymmetric vertical bending mode of the deck (2nd AV). Note that the deck vibrates on the cross beams
at the pylons is due to big scale of animation. There are no vertical fixing between the deck and the cross beams
because the cables
here are assumed to carry the deck totally. DZ modal displacement (non dimension) is 0.009 at
the centre side span. Lusas annotation (Units: m) is in question (of only 9mm). Further analysis is needed to check
the physical displacement in this mode, for potential fixing the deck to the cross beams in the vertical direction,
possibly in the upwards direction only.


 

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   Mode 15, f = 1.192 Hz
is the 1st vertical mode of the longest cables in the side span. The two cables from a side span are vibrated
in opposite direction, created torsion in the main span as the 1st symmetric torsional of the deck (1st ST).
The 1st ST mode can be seen if the cables are hidden.






 

Mode 21, f = 1.227 Hz

is the 2nd vertical mode of the longest cables in the main span. The two cables from one side of the pylons' legs are vibrated up by turns with the other two on the other side of the pylons down, created the 2nd symmetric torsional of
the deck (2nd ST)






Show below is the 2nd ST mode of the deck where the cables are hidden (mode 21)


Updated 31-01-2015

 

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The  frequency ratio fST/fSV are found at mode 21 and 5, they are


fT21/fV5 = 1.227/0.394 = 3.114


which is better that the ratio 2.939  found for the cantilever bridge. The increasing fST in the full bridge is due to

the increasing initial tensions of the cables as compared in the table below


Table: Factors on initial tensions T of cables


150+302+150

 

 

Further, 


 -  There are also two different support conditions for the two bridges. The cantilever bridge has free

    supports at the deck ends for investigation of the bridge's vibration during construction, see

    support conditions


- Because of the sloping deck (highest point at the centre main span), the full bridge has the second 

  cantilever as the mirror of the first. I.e. the full bridge behaviour can not be expecting as the two

  symmetric cantilever bridges connected at the centre main span.

 

 

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123456789_123456789_1123456789ICDAS  •  Hans Erik Nielsens Vej 3  •  DK-3650 Ølstykke  •   E-mail: th@icdas.dk   •  Tel.: +45 29 90 92 96  •  CVR no.: 34436169