# Forensic Analysis on Damage of a Cable-Stayed Bridge without Backstays Using BIM Information
## 1 Introduction  
A cable-stayed bridge without backstays is a modern novel bridge form that gives a sense of lightness and strength. This bridge type could realize a harmonious unification of function and aesthetics and has received wide engineering practice in recent years, especially in urban landscape environments [1]. Cable-stayed bridges without backstays began to appear when the Alamillo Bridge was built in 1992 to welcome the Sevilla Expo in Spain. The bridge was designed as a novel structure with a tilt pylon and single cable. When the bridge was completed, it became the landmark of Sevilla and a model for the world's bridges [2]. Though the structure of the bridge is not so efficient, the innovative appearance is undoubtedly an unusual example of cable-stayed bridges in the late 20 th century [3]. Later, in 1998, the Marinsky Bridge, built in the Czech Republic, was designed as a cable-stayed bridge without backstays and with a fan side. The bridge was selected as one of the top ten outstanding buildings of the International Engineering Association [4]. Since then, cable-stayed bridges without backstays have become more and more popular worldwide. A broad application of cable-stayed bridges without backstays was undertaken in China, such as the Changsha Hongshan Bridge, the Hefei Tongling Road Bridge, the Harbin Sun Island Bridge, and the Changchun Yitong River Bridge [5,6], and these bridges became unique landmarks. In a cable-stayed bridge without backstays, the pylon can be regarded as a cantilever beam bearing forces of cables and self-weight, and the overturning moment of the pylon is entirely balanced by the forces of cables. Therefore, static analysis of this bridge form mainly focuses on the selection and consonance of girder weight, girder stiffness, pylon weight, pylon stiffness, and pylon-girder angle using the force equilibrium method [7]. Scholars and engineers have carried out theoretical analyses, numerical calculations, and experimentalstudies on the design method and dynamic characteristics of cable-stayed bridges without backstays [5; 8; 9; 10; 11]. However, the mechanical behavior and force transmission path of cable-stayed bridges without backstays are quite different from those of conventional cable-stayed bridges. Complicated construction processes and environmental factors also lead to changes in the stress state of the bridge over time [12; 13]. After years of operation, the bridge may present an unreasonable internal force state, resulting in potential hazards [14]. There are many factors affecting the occurrence and development of engineering structure diseases. Researchers have used forensic engineering to investigate the diseases and performance of structures by combining engineering principles with field investigations [15; 16; 17]. The application cases include the collapse and damage of buildings and bridges in the US [18; 19; 20], Italy [21; 22; 23], and Turkey [24; 25]. These studies have identified the causes of structural disease or collapse and provided experience for future structural design, construction, operation, and maintenance. The force state of cable-stayed bridges is closely dependent on the construction process. Incorporating the building information model (BIM), the whole-process finite-element (FE) software such as Ansys can clearly and accurately simulate the force state change process of bridges from constructed stage to current service condition. In fact, several studies have illustrated the advances of incorporating BIM and FE for bridge analysis. [PERSON] et al. proposed a Web- and database-supported visualization method that enables real-time information sharing of BIM to analyze bridge performance and display construction states [26]. [PERSON] et al. combined BIM and FE to analyze and manage process conflicts and structural safety during construction [27]. [PERSON] et al. presented a method using BIM software (Revit) to link and analyze inspection, evaluation, and management data of bridges [28]. [PERSON] et al.