Mechanical Characterization of Integrally-Attached Timber Plate Structures: Experimental studies and macro modeling technique

Abstract

Spurred by the recent advancements in Computer-Aided Design (CAD), Integral Mechanical Attachment (IMA) technique has been resurrected. Using IMAs, connections between timber elements are established through their form, instead of using additional connectors. In light of this, a new design framework has been proposed to construct Integrally-Attached Timber Plate (IATP) structures. Despite the recent developments in architectural geometry processing and digital fabrication, there have been very few systematic investigations of the mechanical characteristics of IATPs. As such, the current dissertation is centered around: (i) experimental studies, (ii) introduction of macroscopic model, and (iii) introduction of CAD-to-CAE data exchange framework. Physical experiments are first conducted to understand the behavior of Through-Tenon joints under tensile, edgewise, and flatwise loads and flexural moments. Studying the force flow mechanism for each load case, tab insertion angle (45°, 60°, and 90°) and fiber orientation (parallel and perpendicular to the load direction) are recognized as the key design parameters. A total of 22 specimens, each with minimum five replicates, are designed and tested. The structural performance of the joints is evaluated in both qualitative (i.e. damage propagation) and quantitative (i.e. strength, stiffness, and ductility) terms. Overall, small differences are observed between the yield and maximum strengths, indicating that the timber joints cannot demonstrate post-yield nonlinear behavior. Furthermore, the joints are classified as having low ductility. Moreover, changing the fiber orientation from parallel to perpendicular have a significant influence on the failure mode and damage propagation. Given that detailed (refined) numerical models (i.e. Finite Element (FE) continuum models with shell or brick elements) are typically computationally expensive and require advanced expertise, a novel macroscopic model, which is based on employing only beam and spring elements, is introduced. The kinematic degrees of freedom and force flow mechanism of IATP components are studied, associated equilibrium equations are formulated, and the macro model is proposed. FE continuum models using shell elements, as well as the results from recent experiments performed on full scale prototypes, are used to verify the proposed model. The comparative assessment shows that the response of the macro model is closely in line with the experiments and FE models. Despite its simplicity, the macro model is robust, and relative to the FE models, the computational time is considerably reduced. To harness CAE to integrate architectural and engineering knowledge, a new methodology is introduced to automate the process of receiving the 3D CAD geometry of a custom-defined IATP structure and converting it to the corresponding CAE macro model. The proposed CAD-to-CAE modular data exchange framework generates the components of the macro model, assigns a unique tag to each component while incorporating geometrical information and structural parameters in the modeling process. The framework, which is primary written using Python programming, is applied to a prefabricated timber beam with standard geometry, and a free-form IATP arch. It is concluded that the modular framework considerably reduces the time required for converting thousands of CAD assemblies to CAE macro models and can be used by practitioners.