Estimation on Natural Frequency of Scissors-Type Bridge and Its Validation with Hammering Test Yuki Chikahiro1,*, Ichiro Ario2 1,*Department of Water Env. and Civil Eng., Shinshu University, Wakasato 4-17-1, Nagano, Japan 2Graduate School of Advanced Sci. and Eng., Hiroshima University, Kagamiyama1-4-1, Higashi-Hiroshima, Japan ABSTRACT A scissor mechanism is a widely used intelligent emergency structure in safety engineering due to its advantages in terms of mobility, transformability, and re-usability. The basic scissor unit consists of two linear elements joined at a pivot, creating a hinge-connection at their centres. When fully deployed, the two members are in the shape of an "X," forming a single scissor unit. The scissor units can be connected to each other using hinges to form a larger structure. The authors have proposed a scissors-type of the emergency bridge, called the Mobile Bridge_TM. The feature enables to fold and deploy the whole system easily and quickly with a few workers. Many of our previous research and development were related to the design studies that examine the approximate computation by beam theory and equilibrium equations method. Furthermore, focusing on the dynamic issue, a demonstration experiment using a small experimental bridge of approximately 8.7 m was conducted on a river flowing into the Hiroshima University, to confirm the safety of human walking. However, the basic knowledge on the dynamic problem addressing various structural conditions has not been established yet. Hence, this study conducts a hammering test using the experimental bridge to obtain basic vibration characteristics and explore the change in vibration characteristics under different boundary conditions. The experimental bridge is designed for the pedestrian with a length of 8.67m and a deployable angle of 60 degrees from the vertical direction. Based on the experimental results, the authors proposed an estimation formula for the natural frequency of the scissors-type bridge. The formula was established based on the beam approximation model, which was effective as a simplified design method for past static problems. The applicability of this formula was verified by comparing with the experimentally measured natural frequencies. In the results of the hammering test, the damping constant of the prototype was approximately 0.005–0.025 when excited horizontally and 0.02–0.04 when excited vertically. Besides, it was possible to estimate the natural frequencies with an error of less than 10% compared with the experiment. These values provide useful information for estimating the dynamic behavior of the scissors-type bridge under different boundary conditions. Overall, the results of this study indicate the basic beam theory can be applied to the design of the scissors-type bridge for both static and dynamic problems. This finding has important implications for the safety and reliability of emergency structures that use the scissor mechanism. Keywords: Scissors-type bridge; emergency bridge; natural frequency; hammering test
