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The model was used to generate natural frequencies and mode shapes in the
three-orthogonal directions. Ambient vibration tests on the bridge deck
under natural excitation such as traffic, human walking, and wind loads were
conducted using operational modal analysis. Sensitive seismic accelerome-
ters are used to collect signals obtained from the experimental tests. To
obtain experimental dynamic characteristics, two output-only system iden-
tification methods were employed, which were enhanced frequency
domain decomposition method in the frequency domain and stochastic sub-
space identification method in time domain. The authors found good agree-
ment between dynamic characteristics in all measurement test setups
performed on the bridge deck. It was demonstrated that the ambient vibra-
tion measurements using enhanced frequency domain decomposition and
stochastic subspace identification methods were enough to identify the most
significant modes of steel highway bridges. It was also shown that there were
some differences between analytic and experimental natural frequencies,
with experimental natural frequencies generally bigger than the analytic fre-
quencies. A 3D finite element model of the bridge was constructed using the
static, and dynamic analyses of 3Dmodels of structures. The program is used
to determine the analytic dynamic characteristics based on its physical and
mechanical properties. The selected highway bridge was modeled as a space
frame structure with 3D prismatic beam elements, which have two end
nodes with each end node having 6 degrees of freedom (three translations
along the global axes and three rotations about its axes). The key modeling
assumptions were as follows:
(1) In the finite element model of the bridge, the fictitious elements were
used to determine the torsional and moment effects that are composed of
asymmetrical load cases. These elements were massless defined on the
axis through the gravity center of uniform and linear loads.
(2) In the finite element model of the bridge deck, diagonal fictitious ele-
ments were used to reflect the rigid diaphragm effect of the concrete.
(3) Fictitious elements were modeled as two ends hinged and one end axial
sliding.
(4) Rigid link elements were modeled as two higher bending rigidity ends
to ensure the torsional moments in the carrier system elements. To
determine the length of the rigid element, it was assumed that fictitious
elements were located near the gravity center of the loads. For the
deck-type arch bridge, the boundary conditions of the side columns
connected between the arch and the main girder were fixed in order
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