# Influence Line-Based Design of Scissors-Type Bridge
## 1 Introduction  
Natural disasters occur frequently. However, their impact is worsening and is becoming a challenging issue affecting global development.  
Global warming has been noted as a factor in the increasing frequency of natural disasters, owing to development-related activities, such as industrial manufacturing, transportation, energy supply, and deforestation. Kumamoto (2020) and Hiroshima (2018) in Japan witnessed flooding and overflow of rivers, which led to the destruction of bridges (refer to [PERSON] et al. (2021) [1, 2]) and severed the mode of transportation between the two regions, as shown in Figure 1. The impact and probable reasons for demolition were investigated by [PERSON] (2006) [3].  
Previously, there were many kinds of temporary bridges in Japan that used different construction methods, such as the pre-gider bridge, kiln-dried truss, HS truss, Hi-BRIDGE construction, Hi-RoRo construction, double-Warren truss (hereinafter DWT) [4], and dry support bridge methods; these techniques for Accelerated Bridge Construction require between one and ten weeks for bridge assembly WFIEL (2012) [5], Unibridge (2015) [6] (seeFigure 2a). The Army Forces Bridge required approximately 8 h and 80 soldiers for assembly (see Figure 2b). Bridge assemblies require extensive labor as well as high-capacity cranes.  
Historically, the first emergency bridge, the Bailey Bridge, was proposed in 1943 by [PERSON] and was a modularized truss bridge. Studies have been conducted to evaluate the usability of lightweight materials such as fiber-reinforced plastic (FRP) ([PERSON] (2006) [7]). Generally, the scissors-type structure (hereinafter SCI) uses FRP for domes and roofs ([PERSON] (1965) [8], [PERSON] (1976) [9], [PERSON] (1985) [10]), as shown in Figure 3b,c [11]. [PERSON] (1975) [12] proposed a space structure for bridge construction. The deployable structures have demonstrated more complexity, such as the matrix formulation of macro-elements ([PERSON] & [PERSON] (1994) [13]), smart deployable skeletal structures for safety engineering ([PERSON] & [PERSON] et al. (2013) [14]), and a rapidly deployable bridge system ([PERSON] (2013) [15]).  
In this paper, we propose the influence line method for a smart bridge engineering that employs the SCI to expand and fold itself within an hour with the requirement of only a few people (see Figure 3). This makes it possible to evacuate people from the bridge within a short time. Many types of mobile bridges (hereinafter MB), structures with expanding and folding equipment, have been patented previously by [PERSON] (2006) [3]. A prototype deployable bridge based on origami principles was also developed by [PERSON] & [PERSON] et al. (2013) [16]. Studies were conducted on the theory and design of a full-scale SCI ([PERSON] & [PERSON] et al. (2016) [17]) and bridge design for scissors-type bridges based on Origami engineering ([PERSON] & [PERSON] et al. (2017) [18]). This study investigated the influence line (hereinafter I.L.) of axial forces, bending moments, and shear forces on the scissors structure to establish a practical design theory. The I.L. of the SCI was compared with the standard DWT model and advanced couple scissors-type bridge (hereinafter CSCI) models [19]. The concept involves moving live loads along the structure using a truck model.  
Figure 1: Collapsed bridges due to flooding in Kumamoto, Japan (July 2020).  
Figure 2: Types of temporary bridges and a military bridge in Japan. (**a**) A temporary bridge built by a company. (**b**) A temporary bridge built by the military.