NUMERICAL MODAL ANALYSIS OF THE FRP COMPOSITE BEAM

The paper presents models of the beam made of a fibre-reinforced polymer (FRP)
composite, which will act as a girder in simply supported footbridges.
The behaviour of the composite beam can be described by various models
with good results. The aim is to investigate which parameters, describing
the model, significantly affect the results in the modal analysis. This research
is focused on creating the most accurate numerical beam model. The material
is assumed to have the averaged material constants of individual components.
In the first approach the beam is treated as a prismatic beam with a continuous
distribution of mass, for which the natural frequency is calculated using
the closed-form solutions. Euler-Bernoulli beam theory is applied and followed
by Timoshenko theory, which takes into account the influence of shear
deformation and rotational inertia effects. Using FEM analysis software ADINA
in following steps are included: overhangs, stiffening by ribs, load caused
by concrete fillings in supports area and the cross-sectional warping phenomenon.
The results for all the numerical models are presented as eigen-frequencies
and corresponding mode shapes. Then they are compared with results obtained
for the shell FEM model. The author’s aim is to find a simple model of the beam,
which could successfully replace the complicated shell or solid FEM model,
which are not applicable for practical design.

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[1] Poneta, P., Kulpa, M., Siwowski T., Material and performance research on the FRP
composite bridge girder, Academic Journals and Conferences of Lwow Polytechnic
National University, 38, pp. 235-242.
[2] Piechnik S.: Strength of materials in Civil Engineering, Warsaw-Cracow 1978
(in Polish).
[3] Lewandowski R. Dynamics of civil engineering structures. Poznan University
of Technology Publishing House, Poznan 2006 (in Polish)