**1. Introduction**

Various important infrastructure facilities are currently under construction, both domestically and internationally. The 9/11 terrorist attacks in the United States aroused social awareness of the safety of important infrastructure facilities such as cable-stayed bridges. Furthermore, the preparedness of infrastructure facilities against disasters has emerged as a major issue, and the need for an engineering review of the safety of infrastructure facilities has been recognized; at present, many countries are making continuous budget investments in maintenance and related fields to prepare for such disasters. In particular, disaster-induced accidents on long-span bridges (e.g., cable-stayed bridges) can result in enormous losses of life and significant damage to the economy, because these infrastructure facilities are of a highly public nature. Disasters can be classified into natural disasters (e.g., earthquakes, typhoons, and floods) and social disasters caused by accidents (e.g., fire, collisions, explosions) and terrorist activities. Among the latter category, blast accidents in cable-stayed bridges can occur as a result of explosions caused by vehicle collisions and terrorist attacks; these can lead to significant deterioration in their structural performance, which may cause the bridge to collapse.

Over the last seven decades, more than six hundred terrorist attacks on bridges and other infrastructure facilities have been recorded [1]. In addition, the Seohae Bridge in South Korea was exposed to a blast risk from a large vehicle accident in 2006. In 2007, the Al-Sarafiya Bridge in Bagdad, Iraq, collapsed due to an attack by a suicide bomber. Furthermore, vehicle blast accidents have occurred on the Riyadh Bridge, Saudi Arabia (2012) and the Sanmenxia Bridge, China (2013). Despite these bridge accidents, no criteria or method has been established to evaluate entire bridge structures prior to construction. Several studies have conducted full-scale experiments to evaluate the performances of piers and decks (structural components of general road bridges) in the event of blasts [2–7]. Based on previous experiments, Williamson et al. [8] suggested three blast design categories, and Williams and Williamson [9] developed a numerical model to describe the spalling of concrete piers using the simulation software package LS-DYNA. Furthermore, several studies have conducted blast analyses for general road bridges using 2D and 3D models [10–13]. However, previous studies had limited capacity to directly or indirectly evaluate the overall performance of cable-stayed bridges subjected to blasts; thus, many researchers have recently begun to numerically simulate blasts in such bridges. Deng and Jin [14] examined stress distributions in a bridge using a 3D cable-stayed bridge model in the simulation software ANSYS AUTODYN; they used a blast pressure derived from 1D analysis, without distinct blast scenario settings. Tang and Hao [15,16] verified the response of a cable-stayed bridge to displacement and stress by numerically analyzing the case of a truck blast occurring 0.5 m from the pier and 1.0 m above the deck. Son and Lee [17] conducted fluid-structure interaction analyses for two types of pylons (hollow steel box and concrete-filled composite pylons) by applying a compressive force to the pylon top. Bojanowski and Balcerzak [18] introduced the procedure and results of a numerical analysis method for evaluating the performance of a complete cable-stayed bridge system under a blast load, and they specified and applied the blast load cases of cars and trucks. Hashemi et al. [19,20] conducted blast analysis for steel cable-stayed bridges, by setting bridge blast scenarios with three load levels (small, medium, and large) and examining the damage and responses of components. Pan et al. [21] defined several scenarios of human-installed explosives and blast accidents caused by trucks, and they analyzed blast load responses for a slab-on-girder, box-girder, and long-span cable-stayed bridges. Farahmand-Tabar et al. [22] evaluated the risks of a progressive collapse and performance degradation in suspension bridges by using a 2D suspension bridge model.

To evaluate the performance of cable-stayed bridges under different blast loads, the aforementioned studies analyzed the overall behaviors and damage characteristics of bridges by modeling either the deck and pylon only or the entire structure [14–22]. Furthermore, when setting the blast loads, they often chose randomized blast loads, rather than setting them according to specific scenarios [14–17,22]. Most of the existing studies have focused on the behaviors of entire bridges, and very few cases have analyzed the damage types or levels of major components (e.g., the cables) according to different scenarios. Therefore, this study conducts blast analysis by defining a detailed finite element model for the major components of the target bridges and setting appropriate blast scenarios, as shown in the procedure in Figure 1. Furthermore, the effects of the blast load are examined by analyzing the component responses and damage types.

**Figure 1.** Blast analysis process.

## **2. Target Structure and Numerical Modeling**
