Analysis of force transmission mechanism in cantilever-supported beam joint assemblies

To enhance the energy consumption capacity and assembly efficiency of precast concrete structures, a novel design of cantilever-supported beam-end precast joints is proposed. In this study, we elucidate the force transmission mechanism of such joints and identify potential failure issues at the structural interface connection formed by embedded reinforced concrete and structural steel.

Cantilever-supported beam-end assembly node specimens were fabricated according to the requirements of the current national standard drawings and specifications, such as the Concrete Structure Design Code and Steel Structure Design Code. Various analysis methods, including low-cycle cyclic testing, simulation modeling, and theoretical analysis, were employed. Node damage patterns were observed throughout the process, and high-density strain data from the entire beam section (reinforcing bars and structural steel) were collected for comparative analysis. The low-cycle fatigue testing employed interlayer displacement angle control for loading using an MTS servo actuator. Simulation methods were based on rapid building information modeling of precast special-shaped components and CAE finite element analysis. Theoretical analysis primarily focused on node failure patterns, reinforcement stress, and structural steel stress.

Novel design of cantilever-supported beam-end precast joints avoids the structurally complex and installation-restricted core zone at beam-column junctions. This approach enhances construction efficiency, minimizes impact on the core zone, and effectively uses steel to achieve plastic energy dissipation. In this study, we analyzed and summarized the stress distribution patterns in cantilever-supported beam-end precast joints, along with how changes in the strength ratio between beam segments and structural steel sections affect joint load-bearing capacity. We also reveal the interaction mechanism between embedded structural steel and concrete interfaces.

Cantilever-supported beam-end precast joints transfer forces through concrete compression by the steel section. Bending moments and shear forces are transmitted from the reinforced concrete main beam section to the steel section. Bolted connections then distribute these forces to the steel flange (bending moment) and web (shear force) of the cantilever-supported beam section. Subsequently, the forces are transferred to the reinforced concrete via the compression of the embedded zone within the steel section, ultimately reaching the core joint region. Node failure primarily occurs when the embedded depth is too shallow or the reinforced concrete section's flexural strength is insufficient, causing excessive concrete compression by the steel section. This compression exceeds the cube compressive strength, leading to premature failure. Increasing the embedded depth or enhancing the reinforced concrete section's strength can effectively prevent premature node failure. The load-bearing capacity of a node primarily relies on the reinforced concrete beam segment's sectional strength. When the beam segment's sectional strength is lower than that of the structural steel, the beam segment's longitudinal reinforcement will reach its yield strength before the structural steel, thereby reducing the load-bearing capacity. When the beam segment's sectional strength exceeds that of the structural steel, the structural steel reaches its flexural yield strength first but has not yet reached its shear yield strength, thereby increasing the load-bearing capacity. When both strengths are equal, the beam segment's longitudinal reinforcement and the structural steel's weakened section simultaneously reach their flexural yield strength.