## 9 Building Occupancy and Use
### Structural Systems for Modular Buildings  
#### Building Level  
Structural systems for modular high-rise buildings are pivotal in ensuring stability, safety, and efficiency. Various approaches are employed to address the unique challenges posed by the vertical expansion of modular structures. Here we present the key considerations and structural systems commonly used in high-rise modular buildings. [PERSON] et al. [85] provided a complete overview of the sub-categories of structural systems that appeared during their project analysis (Table 1). [PERSON] et al. [48] identified six structural systems for tall buildings in their study (Figure 7). Figure 7: Structural systems for tall buildings. Adapted from [PERSON] et al. [48]. Within the domain of stacked Prefabricated Volumetric Modular Systems (PFVMS) buildings, a vertical augmentation of modular units facilitates the establishment of multi-story structures. This modular system optimizes vertical space utilization without encroaching upon ground space [102]. Particularly prevalent in low-to-mid-rise residential apartments, this solution combines modules in a linear or planar fashion, allowing for the pursuit of space efficiency [93]. This approach is applied similarly regardless of the chosen material. The modules in this stack are interconnected using rigid intermodular connections [103] (Figure 8a). Nevertheless, relying solely on intermodular connections may not effectively contribute to load resistance, necessitating the incorporation of stability technologies to withstand lateral forces in high-rise Modular Steel Buildings (MSBs). These stability systems may include steel braces, steel-plate shear walls, multi-column walls, base isolation systems, concrete cores, and moment frames. The development of these stabilization technologies can follow traditional or modern modular methodologies, utilizing precast, steel, composite, or steel-concrete hybrid materials [104]. Another option is a superstructure of beams and columns as the main structure into which prefabricated modules are inserted, avoiding direct overloading on the underlying elements (Figure 8b). This approach is common practice in modular constructions, where the support infrastructure is established using vertical (columns) and horizontal (beams) elements. Prefabricated modules, manufactured off-site, are then positioned, and secured within this framework. This configuration offers advantages as it allows for a more efficient assembly of modules, simplifies the construction process, and provides flexibility in the design of interior spaces. The beams-and-columns superstructure provides the necessary stability and the ability to support vertical loads, ensuring that modules can be integrated safely and effectively. This methodology is commonly employed in modular construction projects, where coordination between the superstructure and prefabricated modules is essential to ensure the structural and functional integrity of the building. However, this solution also presents challenges, including additional costs due to structural redundancy and complexities in the connections between the megastructure and the modules. The third structural solution involves anchoring the modular units directly to the central core of the building, contributing to structural cohesion (Figure 8c). This approach