# Numerical Analysis of Reinforcing Effect for Scissors-Type Bridge with Strut Members
## 1 Introduction  
Climate change caused by global warming has a wide range of effects, including an increase in the frequency of heavy rains and the growing typhoons' power. In Japan, the annual number of short-time heavy rainfall over 50 mm per hour has been increasing [1], and there are concerns about the damage to bridges [2, 3]. After a disaster, rapid transportable and constructable bridges are essential for saving human lives and supporting restoration activities. Most of those structures are modular type bridges so as to reduce the number of workers and construction time on site. For example, the Bailey bridge designed by [PERSON] consists of a modular bridge and deck parts. The usability of this bridge is found in its extensibility by adding a variety of modular parts both vertically and horizontally to increase the load capacity, and it is possible to use in a wide range of post-disasters [4, 5]. In some cases, the bridges have continued to be used as permanent bridges without being removed [6]. The Bailey bridge has evolved through a series of improvements as the Mabey and Arrow bridges (e.g., [7, 8]). On the other hand, this type of bridges usually requires heavy machinery to bring and construct the bridge parts on site. There is, however, another type of rapid bridge system using a deployable structure that is more suitable for use in severe situations with timelimitations. Typical deployable bridges are two-fold or three-fold girder bridges such as the Portable bridge by ERE Logistics [9; 10] and the Armored Vehicle-Launched Bridge [11; 12]. The parts of the prefabricated bridge are equipped on a trailer and tank, and it is installed by working using an oil pressure system. Besides these, [PERSON] et al. proposed a deployable tied-arch bridge. Unlike the above deployable bridges, the entire bridge is folded into a roll to enable simple deployment [13]. Because of the prefabricated bridge parts, these bridges can be installed on-site more quickly than modular bridges despite the limitation of the utilization area. This paper focuses on the advantages of a deployable structure and proposes a foldable emergency bridge, called the Mobile Bridge (herein called MB), with a scissor mechanism [14; 15; 16]. The basic scissor unit consists of two linear elements joined at a pivot, providing a hinge-connection at their centres [17]. In the fully deployed state, two members are in the shape of the character 'X' creating a single scissor unit, and it is connected to a next unit by hinges. These features allow one or two dimensional folding [18; 19; 20; 21]. It is also possible to fold and/or deploy the whole system easily and quickly with a few workers. Up to now, we have demonstrated the design performance using a prototype of a full-scaled MB (herein called MB version 1.0 with two scissors units [22]) and MB version 1.1 with three scissors units [23]). These articles indicated the basically analytical method of the scissor structure based on an equilibrium equation and proved its experimental validation. The latest MB version 4.0 can be referenced in [24]. On the other hand, the structural safety of the MB must be ensured for practical use. The scissors-type bridge is typically weak at its pivot due to the effect on high bending moments (e.g., [16; 25]). Studies on the functionality of recent scissors structures (e.g., [26; 27]) have been presented; however, most of the structures are not bridges but relatively lightweight structures for roofing materials. Heavy temporary structures, such as bridges, need not only to support moving objects, but also a combination of reinforcing elements. Hence, some research was conducted to improve the performance of the scissors-type bridges, focusing on the type of the cross sections and decks [28; 29]. However, since the basic structural form remains the same, it is difficult to expect significant changes. On another front, modular bridges are applying additional reinforcement parts and cable before/after installation aimed at improving the load capacity and stability [30].