Statika s.r.o.

Pipeline bridge HN II at Kralupy nad Vltavou (span 189m):

ing. Emanuel Novák, ing. Jan Moták, 2001

kmitání mostu - 1. vlastní tvar 0,5Hz Checking of technical state of the bridge and recalculation (new) of the maximal load usefulness. A calculation has been made due to linear theory of 1st order, non-linear calculation due to theory of 2nd order, dynamical calculation of it´s mode shapes and frequencies and dynamical effect of the wind. Lowest natural frequency and shapes of the bridge are in the area of the step frequency, because of that it is not possible to use the foot bridge as a foot bridge for pedestrians (the food bridge dosn´t have sufficient entering stairways and even isn´t build for useful load of 4 to 5 kN/m2), because even one person, who´s step frequency is same as the structure´s frequency f0 can make the foot bridge to oscillate, and that is restricted (forbidden) due to the effect on man. That is the reason why some regulations recommend or even direct to avoid these frequencies. Changes of frequncy can be made by the change of the whole structural concept (rigidity, weight, width of span or by shock absorbers).

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