## 10 Progressive Collapse Resistance of Composite Structures: State-of-the-Art  
Progressive collapse in composite structures, especially steel-concrete composite buildings under seismic loads, is a complex phenomenon that has received considerable attention in structural engineering. This form of collapse occurs when localized damage triggers a chain reaction of failures, potentially leading to disproportionate and catastrophic structural collapse. The interaction between steel and concrete elements in composite buildings plays a crucial role in their seismic performance. During earthquakes, these structures experience intense lateral forces and dynamic loading, which can cause steel members to yield and the concrete to crack or be crushed. The composite action between steel and concrete has the potential to improve overall structural ductility and energy dissipation capacity, thereby potentially reducing the risk of progressive collapse. However, the behavior of connections between composite elements, load redistribution mechanisms, and the potential for sudden failure of key structural components are critical factors that must be carefully considered in the design and assessment of these buildings to ensure their resilience against progressive collapse under seismic conditions. [PERSON] et al. (2019) [159] focused on steel-concrete composite frames in the event of column loss. Two geometrically distinct three-dimensional composite full-scale substructures were selected from reference buildings and tested to simulate the column collapse scenario. They outlined the preparatory studies, the main features of the specimens, and the results of the initial test. The test provided insight into the need for an improved design of joints and emphasized key aspects of the response of the floor system. Additionally, static tests on six two-story three-span composite frames with CFST columns were conducted by [PERSON] et al. (2022) [160] under a penultimate column removal scenario. The effects of weld-bolted connection and RC slab on progressive collapse resistance were analyzed. The results showed that the torsion in steel beams at the directly affected region was reduced for frames with composite beams. Differences in failure modes were observed between the penultimate and middle-column removal scenarios. It was also found that frames with weld-bolted connection had lower resistance but multiple protection measures against progressive collapse. [PERSON] et al. (2022) [161] initially presented a fiber-based model that incorporates nonlinear beam-column elements and zero-length elements to account for the composite relationship between the slab and beam, as well as the material's damage evolution for composite members. Then, the suggested modeling method was applied to an anti-collapse analysis of composite frames with various connections. Additionally, design suggestions obtained through parameter analysis were provided to prevent the development of a chain reaction. Furthermore, a multi-scale model was used by [PERSON] et al. (2017) [162]to study the collapse performance of CFT column-to-steel beam connections. Nonlinear static and dynamic analysis methods were used to reveal resistance mechanisms, failure modes, and stress distribution of joints. The results showed that these joints could prevent progressive collapse by forming resistance mechanisms and providing alternate load paths. The adjacent framework also enhanced the anti-collapse ability of the joints. [PERSON] and [PERSON] (2017) [163] examined the use of steel cables for retrofitting steel-concrete composite buildings to prevent progressive collapse. They also investigated the impact of the building's characteristics on the overall cost of retrofitting to identify the best cost-effective approach for each scenario. To achieve this, an optimization algorithm known as Evolution Strategies was used to determine the solution that offers the desired performance at the lowest cost.