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"Joints (timber)"
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Calibration and Validation of a Linear-Elastic Numerical Model for Timber Step Joints Based on the Results of Experimental Investigations
The paper is dedicated to the numerical analysis of a single-step joint, enabling the prediction of stiffness and failure modes of both single- and double-step joints. An experimental analysis of the geometrically simplest version, the single-step joint, serves as a reference for the calibration of the subsequent finite element model. The inhomogeneous and anisotropic properties of solid timber make detailed modelling computationally intensive and strongly dependent on the respective specimen. Therefore, the authors present a strategy for simplified but still appropriate modelling for the prediction of local failure at certain load levels. The used mathematical approach is based on the linear elasticity theory and orthotropic material properties. The finite element calculations are performed in the environment of the software Abaqus FEA. The calibrated numerical model shows a good conformity until first failures occur. It allows for a satisfactory quantification of the stiffness of the connection and estimation of the force when local failure begins and is, therefore, recommended for future, non-destructive research of timber connections of various shapes.
Journal Article
“HINGE HOUSE”: Space embracing plural people, activities, and objects by devising a timber frame joint
We designed a house that embraces plural people, activities, and objects and where people act autonomously in a suburb of Tokyo. A new hinge joint and innovative timber framework were devised to implement the liberated ample space, and environmental strategies were adopted. By devising new hinge joints and innovative timber framework, we designed a house that embraces plural people, activities, and objects and where people act autonomously in a suburb of Tokyo.
Journal Article
Experimental investigation of bonding behavior of anchoraged timber-to-timber joint
The comprehensive experimental study examining the general load–displacement behavior, stress distributions and shear stress–shear-displacement behaviors in the connection area when wood structural elements are combined with adhesive or adhesive with mechanical anchorages have been found in very limited number of studies in the literature. Therefore, an experimental study was planned. In this study, the general load–displacement behavior of the timber connection regions which are connected by adhesive and mechanical anchorages together with adhesive, with varying lengths of 180, 240 and 350 mm are investigated experimentally. Besides, the effect of changing the number and location of mechanical anchorages used in the connection area on the general load–displacement behavior and shear stress–shear-displacement behavior was also investigated. Using the load–displacement graphs obtained as a result of the experimental study, a generalized material model is proposed for the shear stress–shear-displacement interfacial adhesion surface for wood–wood junction points. This material model, which is proposed for wood–wood connection points with mechanical anchors, is a model that can be useful and can be used in the analysis of structural systems containing such connections using finite element software. It is thought that the overall capacity and load–displacement behavior of structural systems containing such connection points can be calculated more realistically using the proposed interfacial material model.
Journal Article
Shear Rate Effects on the Post-peak Shear Behaviour and Acoustic Emission Characteristics of Artificially Split Granite Joints
Rock joints may be sheared at different rates under quasi-static or dynamic loading. Understanding the mechanical response of rock joints at different shear rates is of great importance for the mitigation of dynamic geo-hazards such as earthquakes, fault slip rockbursts and landslides. In this study, direct shear tests at various shear rates (0.001–0.1 mm/s) under different normal stresses (3–40 MPa) are conducted on split granite joints, and the influences of shear rates on the shear strength, post-peak shear behaviour and acoustic emission (AE) characteristics are analysed and discussed. The research findings suggest that both peak and residual shear strengths tend to decrease with increasing shear rate. Stick–slip occurs on all the joints, during which stress drop values increase with increasing shear displacement and normal stress. The stress drop magnitudes during stick–slip decrease with shear rate, while the time intervals between stress drops during stick–slip increase with shear rate. Further, the energy rate tends to increase while the AE events decrease with increasing shear rate, which is caused by the time-dependent deformation behaviour. The AE b value decreases linearly with the shear rate on a logarithmic scale, and the influence is more significant under high normal stress conditions. The variations in the b value can reflect the evolution process (first loading at lower and then higher shear rates) of dynamic geo-hazards and can be used as an effective indicator to predict the dynamic shear failure of granite joints in a temporal sequence. The results of this study will encourage better understanding of the rate-dependent shear behaviour of rough granite joints, particularly under high normal stress, and will provide some references for the monitoring and prediction of dynamic geo-hazards with respect to the AE (or micro-seismic) technique.
Journal Article
Review: Hydrogeology of weathered crystalline/hard-rock aquifers—guidelines for the operational survey and management of their groundwater resources
Hard rocks or crystalline rocks (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, and are particularly exposed at the surface in the large shields of Africa, India, North and South America, Australia and Europe. They were, and are still in some cases, exposed to deep weathering processes. The storativity and hydraulic conductivity of hard rocks, and thus their groundwater resources, are controlled by these weathering processes, which created weathering profiles. Hard-rock aquifers then develop mainly within the first 100 m below ground surface, within these weathering profiles. Where partially or noneroded, these weathering profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) the permeable stratiform fractured layer (SFL). The development of the SFL’s fracture network is the consequence of the stress induced by the swelling of some minerals, notably biotite. To a much lesser extent, further weathering, and thus hydraulic conductivity, also develops deeper below the SFL, at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). The demonstration and recognition of this conceptual model have enabled understanding of the functioning of such aquifers. Moreover, this conceptual model has facilitated a comprehensive corpus of applied methodologies in hydrogeology and geology, which are described in this review paper such as water-well siting, mapping hydrogeological potentialities from local to country scale, quantitative management, hydrodynamical modeling, protection of hard-rock groundwater resources (even in thermal and mineral aquifers), computing the drainage discharge of tunnels, quarrying, etc.
Journal Article
Effect of Cyclic Loading on the Shear Behaviours of Both Unfilled and Infilled Rough Rock Joints Under Constant Normal Stiffness Conditions
The present study experimentally investigated variations in the mechanical behaviours of natural rough rock joints during shearing under cyclic loading and constant normal stiffness conditions, using a servo-controlled shear testing apparatus. The influences of initial normal stress (σn0), normal stiffness (kn) and shear velocity (v) on the shear behaviours are estimated and analysed. The results show that the shear stress (τ), normal stress (σn) and normal displacement (δv) for both unfilled and infilled rock joints decrease with the increase in the number of cycles (N), especially in the N range of 1–2. This is because some asperities on the joint surface are sheared during the first shear process, and the subsequent shear tests for N > 2 were subjected to the frictional process. The σn0 and kn both contribute significantly to the variations in the shear behaviour of rock joints. For unfilled rock joints, increasing σn0 from 2 to 4 MPa increases the shear stress and normal stress by 128.5% and 106.5%, respectively, when shear displacement (δh) = 2 mm and N = 1. Increasing kn from 3 to 5 GPa/m enhances the shear stress and normal stress by 19.4% and 10.4%, respectively, when δh = 2 mm and N = 1. For infilled rock joints, the shear stress and normal stress increase with increasing σn0 when N < 5, and decrease first and then increase with increasing kn. The shear stress, normal stress and normal displacement for infilled rock joints increase with increasing v, especially in the v range of 1–2 mm/min. Finally, six empirical models are proposed to evaluate the shear stress, normal stress and normal displacement of the unfilled and infilled rock joints under cyclic loading and CNS conditions. These models take into account parameters such as σn0, kn, v, δh and N, and the experimental results agree well with the fitting results with the correlation coefficient R2 > 0.78. Using the proposed models, the fillings decrease the τ and σn by approximately 24.96–65.52% and 9.38–57.95%, respectively, while increasing the normal displacement (δv) by 0.5 mm on average during the entire shear process.
Journal Article
Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters
Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.
Journal Article
Analytical Prediction of the Shear Behaviour of Rock Joints with Quantified Waviness and Unevenness Through Wavelet Analysis
We present an analytical model for the shear behaviour of a rock joint with waviness and unevenness. The waviness and unevenness of a natural joint profile are quantitatively separated through wavelet analysis. The critical waviness and critical unevenness of a joint profile are subsequently determined. The degradation process of each-order asperity is predicted by considering the role of plastic tangential work in shear, by which the sheared-off asperity area and the dilation angle are quantified. Both the dilation angles of critical waviness and critical unevenness decay, as plastic tangential work accumulates. The analytical predictions are compared with the experimental data from direct shear tests on both regular- and irregular-shaped joints. Good agreement between analytical predictions and laboratory-measured curves demonstrates the capability of the developed model. Therefore, the model is capable of assessing the stability of rock-engineering structures with ubiquitous joints.
Journal Article