# A Review on Design Considerations and Connection Techniques in Modular Composite Construction
## 1 Introduction
While substantial research has been conducted on connection systems in precast structures such as grouted connections [17; 18], bolted connections [19; 20], and hybrid connections [20; 21], there remains a notable gap in analysing these connections specifically within the context of modular construction. Addressing precast structural elements is essential to bridge this gap, as the existing studies provide foundational insights into connection methodologies and their load transfer mechanisms. This serves as a basis for the design of connections and their implementation in modules, which form the structural systems in modular construction. These connections can be collectively categorised as composite connections, as they often involve the interaction of distinct materials such as steel and grout or concrete collaborating to achieve structural continuity. This composite interaction improves modular construction's strength, ductility, and installation efficiency. Recent research has involved experimental and numerical evaluations to study the composite connections under different loading scenarios, emphasising lateral cyclic, monotonic, and pushover load tests to analyse their capacity for bearing loads, ductility, and failure patterns, providing the basis for assessing their applicability in modules. This paper thoroughly reviews these investigations and assesses the structural performance of composite connections, offering insights into their feasibility, practicality, and applicability within modular construction contexts. From this point onward, the discussion on connections will primarily address them within the context of precast structural elements, providing a comprehensive foundation for evaluating their applicability in modular construction systems. A comprehensive analysis of studies from the previous two decades was conducted, focusing on precast structural components and their connection methodologies to comprehend the recent advancements in precast technology and modern construction methodology. Figure 2: Development of publication sources on modular construction. (The colour of each circle represents different journals, while the size of each circle corresponds to the number of published papers, as indicated by the reference scale on the top right). gies. The selection criteria involved organising research publications based on keywords relevant to precast structural components encompassing walls, beams, columns, beam-column joints, frames, and bridges. The resultant papers were then further categorised according to the connection methodologies implemented, including grouted couplers, bolted connections, cast-in-place joints, and hybrid systems. Figure 3 illustrates the distribution of these studies, emphasising the prevalence of various connection techniques across distinct precast structures. Among the diverse connection methodologies, grouted coupler connections have been extensively investigated. These connections are frequently researched due to their effective force transmission, ease of implementation, and compatibility with seismic-resistant designs [21]. Similarly, bolted connections have been thoroughly examined, particularly for their benefits in rapid assembly, structural stability, and potential for reuse. They are particularly suitable for modular construction and are efficiently driven by prefabrication. Conversely, cast-in-place joints predominantly appear in investigations as a benchmark for comparative analysis against precast alternatives. These studies often evaluate variances in stiffness, failure modes, and construction feasibility, reinforcing the benefits of precast solutions regarding quality control and construction efficiency. The significance of hybrid connections has also garnered attention in recent years, integrating mechanical fasteners, grouted sleeves, or partially cast-in-place elements to enhance structural integrity and adaptability [22].