Macroscopic Model for Spatial Timber Plate Structures with Integral Mechanical Attachments

The use of integral mechanical attachments (IMAs) in spatial free-form timber plate structures has been revitalized by the production of engineered boards and recent developments in digital fabrication and computer-aided design. Despite the widespread interest in utilizing such structural systems, there have been very few efforts to develop modeling strategies that can be used by practitioners. Detailed finite-element (FE) models are typically computationally expensive and require advanced expertise. Accordingly, this paper introduces a simplified yet robust macroscopic modeling technique for spatial free-form timber plate structures with IMAs. This approach employs only beam and spring elements to simulate the structural behavior. The macromodel was introduced and the associated mechanical properties were computed. FE models constructed using shell elements and the results from recent experiments performed on a full-scale prototype were used to verify the proposed macromodel. The results showed that the response of the macromodel was closely in line with that of the experiments and FE models. Despite its simplicity, the macromodel is robust and can simulate the behavior of integrally attached timber plates. It was also demonstrated that the computational time for the macromodel is significantly less than the FE simulation.

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

Aryan Rezaei Rad

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.

EPFL2020

Experimental and numerical study on structural behavior of a single timber textile module

Markus Hudert, Laurent Humbert, Meisam Sistaninia, Yves Weinand

The present work investigates an innovative class of timber structure with potential applications in roofing, facade and bridge construction, called Timberfabric. The development of Timberfabric structures originates from the approach of harnessing the structural, modular and qualities of textiles in timber construction (Weinand and Hudert, 2010) [9]. Timberfabric structures are comprised of repetitive arrangements of one or more structural unit cells called Textile Modules. When properly designed, one obtains a modular and lightweight structure with interesting and unusual geometrical and structural qualities.This paper focuses on the single timber Textile Module. Based on the finite element (FE) method, a reliable procedure is proposed for modeling the overall assembly process of the Textile Module. For comparison, Textile Module prototypes are constructed at two different scales (large and intermediate scales) with different assembly conditions. The proposed geometrically nonlinear FE model allows evaluation of the stresses that are induced during the construction process and which may affect the structural integrity of the module. In particular, the risk of failure during assembly is identified using the anisotropic Tsai-Hill criterion. The structural behavior of the timber Textile Module is then investigated through bending tests using the constructed prototypes. During the loading procedure, the vertical deflections are measured at different locations on the prototype surface by means of external displacement transducers. Using the FE model, the corresponding deformed shapes are simulated by applying the bending loads on the prestressed Textile Module. Experimental displacements and FE predictions are thus compared and found to be in good agreement.

Elsevier2013

Numerical Simulation of the Semi-Rigid Behaviour of Integrally Attached Timber Folded Surface Structures

Anh Chi Nguyen, Aryan Rezaei Rad, Andrea Stitic, Yves Weinand

Timber folded surface structures assembled using semi-rigid multiple tab and slot joints (MTSJ) have been shown to form feasible structural systems with high load bearing potential. However, for their further development and use on large building scales, a pertinent model for prediction of their structural behaviour has yet to be developed. This paper focuses on simplified numerical methods for accurately modelling the semi-rigid structural behaviour of bidirectional timber folded surface structures with multiple tab and slot connections. Within this scope, the structure behaviour is considered to be in the elastic stage. Three practical methods of analysis for such structural systems are presented. The first two approaches use the Finite Element Method (FEM), where the theory of plates and shells are applied. In the first method, the MTSJs are modeled using strip element models, while, in the second strategy, spring models are used. The third modeling strategy elaborates on the new macroscopic mechanical models, referred to as macro models. Sets of one-dimensional (1D) elements are used to represent the mechanical behaviour of the entire system. Both linear and geometric nonlinear analysis are performed for all three modeling strategies. The numerical results are then validated against the large scale experiments. Comparison of the strip and spring element model results have shown that the strips represent more accurately the experimentally obtained values. Concerning the macro modelling approach, very good agreement with both detailed FE modelling approaches, as well as experimental results, were obtained. The results indicate that both linear and nonlinear analysis can be used for modelling the displacements within the elastic range. However, it is essential to include geometric nonlinearities in the analysis for accurate modelling of occurring strains as well as for displacements when considering higher load levels. Finally, it is demonstrated that including semi-rigidity in the numerical models is of high importance for analysing the behaviour of timber folded surface structures with MTSJ.