experimental study of a single-layer free-form envelope node under axial loadings

For a single-layer structure system, a specific node system with axial and moment capacities is required. in particular, sufficient axial strength is necessary, because membrane stress is typically the dominant distributed stress throughout the structure. in this study, to assess the safety of the proposed free (flexible, resilient, efficient, and economical) node in sustaining tensile and compressive forces, the failure and ultimate strengths are obtained under monotonic and cyclic loads. the implemented tests are mainly classified into two. a welding connection type test is performed to evaluate the capacity of the node subjected to monotonic loading. to investigate the stiffness of the entire system, a bolted connection was tested under monotonic loading. results showed that the free node could safely sustain tensile forces. the yield load of specimens t-mo-n1 and n2 (432 and 434 kn) satisfy the required capacity 250 kn. however, when the node was subjected to compressive force (considering specimens c-mo-n and c-mo-b6), bending moment occurred, such that the total strength significantly decreased. a hollow sphere reinforced by an additional steel plate was found to provide satisfactory strength and results. the yield load is 768 kn that satisfy required capacity (435 kn). consequently, the improved free node had excellent capacity for axial forces. © the author(s), under exclusive licence to the iran university of science and technology 2023.