A new formula for estimation of vertical natural frequency for a scissors-type bridge through hammering tests and numerical simulation

Abstract A scissors-type bridge that applies a deployable scissors mechanism to its structural form has been researched and developed to support emergency restoration activities after disasters. The vibration characteristics of this bridge have been evaluated by eigenvalue analysis and walking experiments in past studies. However, the basic knowledge, including the design method for this bridge, was still limited. Hence, this study conducts a hammering test to obtain basic vibration characteristics and explore the change in vibration characteristics under different boundary conditions through eigenvalue analysis. Although the total weight is increased by installing the decks, it can be seen that installing the decks on the top or bottom of the scissors-type bridge significantly improves rigidity in the horizontal direction. Still, the influence in the vertical direction is less than that in the horizontal direction. Furthermore, based on the experimental and numerical results, an estimation formula for the natural frequency approximating a scissors-type bridge as a simple beam structure was proposed. It was possible to estimate the natural frequencies in the vertical primary mode with errors of less than 3 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> compared with the experimental results and errors of less than 10 $$\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>%</mml:mo> </mml:math> compared with the numerical results. This finding has important implications for the developing a simple and reliable design of emergency structures that use the scissor mechanism.