The deck box stiffness is increased by its depth and the longitudinal plates. It will increase both bending
and torsional stiffness of the deck box girder.
To separate the bending and torsional natural frequencies of the bridge, only the torsional stiffness is wished
to be increased. It can be obtained by increasing e.g. thicknesses of the cross plates. More details are found in
Case Study.
Shown below is the deck cross section, which is increased to 4m depth in Revit and Lusas, by changing the input of the bottom lines of deck.
Figure: Deck depth increased from 3 to 4m, Revit family file.
Figure: Deck depth increased from 3 to 4m. Add additional longitudinal plates, Lusas models
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Shell elements
Shown below are the shell elements and thicknesses assigned to the longitudinal and the cross plates of the deck
(here only two longitudinal plates were created on each side of the cross section except at the pylon). With shell
elements one can get detailed results on each plates of the deck.
Figure: Additional plates at the pylon
To obtain also detailed results for the pylons it is tested to model in shell elements too (not default in CSB 2014.06R). However, with respect to nonlinear analysis convergence it is recommended that the pylon is modelled using 3D Thick nonlinear beam BTS3 element.
