Abstract
Several parameters affect the bridge’s natural frequencies while parameters related to the geometric characteristics of bridge components are more important. Maximum span length (SL) (length of the main or longest span), deck width, number of girders and spans, and girder’s height can be regarded as the main influencing parameters. In this paper, the first bending natural frequency (FBNF) of bridge superstructures of typical structural systems is assessed analytically using a simple conceptual model considering the main analytical parameters. The results show that the FBNF of bridges is strongly related to the SL of the longest span. It means that the other parameters are considered indirectly and may not be essentially considered as influencing parameters.
Highlights
Assessing the bridge superstructures’ natural frequencies via a simplified approach is a subject matter of interest for decades. is is carried out in order to quantify the main dynamic characteristics of bridges as key issues in recognition of their dynamic behavior as well as the key parameters influencing the bridges’ service life
According to the AASHTO Standard Specifications [1], the maximum midspan vertical deflection is restricted to a given relative value of span length (SL) to avoid excessive vibrations which is related to the first bending natural frequency (FBNF) (e.g., 1/800 of SL for ordinary bridges and 1/1000 for urban bridges)
It is clear that the dispersion of the results reduces while the maximum SL (MSL) increases
Summary
Assessing the bridge superstructures’ natural frequencies via a simplified approach is a subject matter of interest for decades. is is carried out in order to quantify the main dynamic characteristics of bridges as key issues in recognition of their dynamic behavior as well as the key parameters influencing the bridges’ service life. When the response of the superstructure is only considered, in between the natural frequencies of bridges in different vibration modes, the first bending mode (FBM) is more important. According to the AASHTO Standard Specifications [1], the maximum midspan vertical deflection is restricted to a given relative value of span length (SL) to avoid excessive vibrations which is related to the FBNF (e.g., 1/800 of SL for ordinary bridges and 1/1000 for urban bridges). Some other codes such as the Canadian or Australian codes ([2]; AS5100, 2004) do not explicitly limit liveload deflections, and a different approach is used. According to the obtained results, the obtained formulae have been compared with those reported by previous researchers
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