In-plane rotational performance of a slotted-in plate overlap joint for reciprocal frame timber gridshells: Experimental, theoretical, and numerical study

Timber reciprocal frame (RF) gridshells are favored for their unique aesthetics in large-span buildings. Nevertheless, the lack of characterized connection systems hinders their structural applications. This paper proposes a novel semi-rigid overlap joint using an angled slotted-in steel plate and investigates its critical in-plane rotational performance. The behavior of joints with 90° and 60° overlap angles was studied through monotonic and cyclic experiments, demonstrating ductile failure combinations of steel plate torsion and timber embedment failures. The experimental results showed the 60° joint configuration was superior, with 48% higher initial stiffness, 56% greater moment capacity, and 33% higher cumulative energy dissipation than those of the 90° joint. The assembly gap was found to be the primary cause of the observed pinching effect and significantly influenced stiffness during load reversals. Besides, a theoretical model was developed for the proposed joint, whose predicted initial stiffness showed good agreement (less than 8% error) with the test results. Then, a detailed finite element model was also validated to replicate the performance metrics, hysteretic envelopes, and directional asymmetry. Finally, a numerical case study of a 56-meter span RF gridshell, conducted via a progressive multi-scale modeling strategy, demonstrated that in-plane bending was the dominant load effect and that a structure utilizing the proposed joints satisfied all strength, stability, and serviceability code requirements. This study provides a complete set of validated design tools for a safe and efficient connection in timber RF gridshells. • A novel semi-rigid overlap joint is proposed for timber RF gridshell. • 60° joints show 56% higher capacity and 48% higher stiffness than 90° joints. • Case study verifies structural safety of a 56 m span RF gridshell. • Analysis identifies in-plane bending as the dominant structural action.