AbstractThis study examines the mechanical performance of large and small cross-laminated timber (CLT) wall panels with different applications. Two CLT structures were subjected to reversed cyclic ...lateral loads. One structure consisted of 90-mm-thick, large CLT wall panels (6×2.7 m), and the other consisted of 90-mm-thick, small CLT wall panels (1×2.7 m). A weight was installed on the roof of two-story structures to simulate the weight of three-story structures, designed by elastic calculations with a base shear coefficient of 1.0. The number of screws for each joint was determined by a linear finite-element method (FEM) analysis. The experimental results showed that the ultimate capacity of these structures is 60–80% higher than the design load, indicating high structural performance. A three-dimensional, nonlinear analysis was conducted via the FEM, which accurately predicted the mechanical performance of the CLT structures. This design procedure, based on linear analysis, resulted in a conservative design, and simulation using the nonlinear FEM provided an effective tool for design optimization.
AbstractPosttensioning low-damage technologies were first developed in the late 1990s as the main outcome of the U.S. Precast Seismic Structural System (PRESSS) program coordinated by the University ...of California, San Diego, and culminated with the pseudo-dynamic test of a large-scale five-story test building. The extension of posttensioned techniques to timber elements led to the development of new structural systems, referred to as Pres-Lam (prestressed laminated timber). Pres-Lam systems consist of timber structural frames or walls made of laminated veneer lumber, glue laminated timber (Glulam), or cross-laminated timber (CLT). Pres-Lam walls consist of a rocking timber element with unbonded posttensioned tendons running through the length and attached to the foundation, which provides a centering force to the wall, while energy dissipation is supplied by either internal or external mild steel dissipaters. Previous tests carried out on posttensioned timber walls focused on small-scale (one-third) specimens with the main objective of evaluating the general response of the system. The main objective of the experimental program herein presented is the testing and estimating of the response of a series two-thirds-scale posttensioned walls, with alternative arrangements and combination of dissipaters and posttensioning, focusing on the construction details adopted in real practice. The paper first presents a brief discussion on the seismic demand evaluation based on the displacement-based design approach. The construction detailing of the steel dissipater connections, posttensioning anchorage, and shear keys are then presented. The main objectives of this experimental program were the investigation of the experimental behavior of large-scale posttensioned timber walls, with particular focus on the system connection detailing and optimization of posttensioning anchorage, fastening of the dissipation devices, and shear keys. The program consisted of several quasi-static cyclic tests considering different steel dissipater configurations, different levels of posttensioning initial stress, and different dissipater options were considered: both internal and external mild steel tension-compression yield devices were used. The experimental results showed the performance of posttensioned timber wall systems, which provide a high level of dissipation while showing negligible residual displacements and negligible damage to the wall element. The final part of the paper presents the experimental evaluation of the area-based hysteretic damping for the tested specimens, and the results highlight the great influence of the connection detailing of the dissipaters.
AbstractMass timber is an attractive and sustainable alternative structural engineering material to concrete and steel. Despite successful midrise to high-rise timber building projects around the ...world, such buildings have not been implemented in regions with high seismicity due in part to a lack of research and development on appropriate ductile seismic load resisting systems for heavy timber construction. This paper describes experiments conducted to develop a resilient lateral force-resisting wall system that combines cross-laminated timber (CLT) panels with vertical posttensioning (PT) to provide postevent recentering. Supplemental mild steel U-shaped flexural plate (UFPs) are intended to yield under cyclic loading while the PT and CLT components remain undamaged until large interstory drifts are experienced by the wall. The experiments were designed to explore various limit states for self-centering CLT (SC-CLT) walls, including their dependence on design variables and their effect on performance, and to investigate strength and stiffness degradation at large interstory drifts. It was found that the SC-CLT walls were able to recenter even after large drift cycles and the crushing of the CLT material was the governing limit state for most specimens. A hierarchy of desirable limit states was identified consisting of UFP yielding, CLT splitting, PT yielding, and CLT crushing.
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•Two typical Dou-Gong models of Yingxian Wood Pagoda were tested.•The behaviour and failure modes of Dou-Gong under vertical load were investigated.•The load-transferring path of ...Dou-Gong was researched.•The performance of the prototype Dou-Gong of the pagoda was estimated.
This paper presents an experimental investigation on the structural performance of Dou-Gong brackets of Yingxian Wood Pagoda under vertical load. Two scaled models of typical Dou-Gong brackets of the pagoda were designed, manufactured and tested. Both models behaved similarly to that of a wood component under compression perpendicular to grain. Four failure modes of the components were identified, these included yield of component under compression perpendicular to grain, fracture of component under tension perpendicular to grain, fracture of component due to shear and breaking-off of component under bending. The structural performance of the model Dou-Gong brackets was revealed from test observations, and the initial stiffness and the load-carrying capacity of the prototype Dou-Gong brackets of the pagoda were derived based on the similitude theory. This study provides reference, from a structural point of view, for the preservation of cultural heritage structures such as Yingxian Wood Pagoda.
•Ultimate bearing capacity of bonding steel-plate joints for timber structures.•Creep trends and coefficients of bonding steel-plate joints with different stress levels.•Creep coefficients ...predictions of joints in the duration of service life.•Long-term slip stiffness and the ratio of stiffness reduction for bonding steel-plate joints.
The long-term performance of bonding steel-plate joints in controlled environmental conditions in this work. The bonding steel-plate joint consists of a steel plate with a vulcanized rubber layer and six wood screws. The vulcanized rubber layer is intended to improve the ductility of bonding steel-plate joints. Six pull-pull specimens were tested in order to determine the short-term load bearing capacity of bonding steel-plate joints, and the dimension of the shear plane of each bond line was 80 mm × 80 mm. A total of 12 specimens were employed in long-term tests. Two stress levels, including the 30% and 60% of ultimate bearing capacity, were adopted. All specimens were monitored over 800 days except that one series of specimens with 0.6 stress level which failed during the long-term tests. At the end of 858-day loading, the average slip at the connection for the specimens with 30% and 60% stress level were 0.623 mm and 0.939 mm, respectively. The creep coefficients were calculated according to the measured experimental data. The Burger’s model, two term and six term Kelvin’s model were adopted to fit the curves of creep coefficients, and then predict the creep slip of joints in the duration of service. The long-term slip stiffness and the ratio of stiffness loss are calculated according to experimental curves, and are predicted on the basis of the prediction results of creep coefficients through by six term Kelvin’s model.
AbstractAn experimental program was performed at IVALSA Trees and Timber Institute on single and coupled cross-laminated (CLT) wall panels with different anchoring systems and different types of ...joints between adjacent panels. The mechanical properties of CLT walls were assessed and are critically discussed in the paper. The connector layout and the design of the screwed vertical joints were found to markedly affect the overall behavior of the structural system. The in-plane deformations of CLT panels were almost negligible, whereas concentration of forces and deformations mainly occurred in the connections. Advanced analytical models for nonlinear pushover analysis of CLT wall systems were developed and verified against test results. The models take into account all stiffness and strength components of connectors, as well as the bending and shear deformation of the panels. A parametric study of CLT wall systems with different aspect ratios and wall segmentation was performed, showing that segmentation of CLT walls decreases their stiffness and strength but significantly improves their deformation capacity.
This paper presents a modeling approach to predict the behavior of timber beams strengthened with carbon fiber reinforced polymer (CFRP) composites. A three-dimensional finite element analysis (FEA) ...model is formulated, based on the orthotropic constitutive characteristics of timber species. The model provides the load–displacement relationship, strain development, stress concentration, and failure modes of the CFRP-strengthened timber beams and those responses are compared to the experimental data. The validated models are used for a parametric study to further examine the effect of various CFRP properties on the behavior of five timber species: Douglas Fir, Yellow Birch, Sitka Spruce, Yellow Poplar, and Northern White Cedar that cover most of the engineering properties available in practice. The strengthened beams show improved load-carrying capacity and energy absorption capacity when compared to unstrengthened counterparts. An optimal CFRP-reinforcement ratio is found beyond which no strength increase is achieved. Even though the elastic modulus of the CFRP composites influences the failure mode of the strengthened beams, it may not significantly affect the strength-increase of the beams because the properties of timber species are a dominant factor influencing the failure of the beams, rather than the CFRP properties.
AbstractA 2-story full-scale model of a cross-laminated timber (CLT) house was tested under quasi-static monotonic and cyclic loading. The primary objectives were to investigate 3D system performance ...of a CLT structure subjected to lateral loads in terms of lateral strength and deformability capacity, global behavior of the structure, frequency response of the structure before and after each test, and performance of anchoring connectors (hold-downs, brackets) and connections between CLT panels. The house was 6.0×4.8 m in plan with a height of 4.8 m. A total of five (one push-over and four cyclic) quasi-static tests were performed, one direction at a time. Parameters, such as the direction of loading, number of hold-downs, and number of screws in perpendicular wall-to-wall connections, were varied in the tests. The CLT structure performed according to the design objectives, with the ultimate resistance being almost identical in both directions. Failure mechanisms, i.e., shear failure of nails in the brackets in the first story as a result of sliding and rocking of the CLT wall panels, were similar in all tests. Even after the maximum force was reached, no global instabilities of the house were detected. Torsion effects did not compromise the integrity, stability, or the lateral resistance of the building. The outcomes of the full-scale CLT house tests will be used for further analytical and numerical analyses to help the implementation of CLT as a structural system in the North American building codes and material standards.
AbstractThe research presented in this paper examines the shear resistance performance of self-tapping screws (STS) in three-ply cross-laminated timber (CLT) panels. Specifically, the feasibility of ...using innovative STS assemblies with double inclination of fasteners was investigated for the shear connection of CLT panels. The specimens (1.5×1.5 m) were subjected to quasi-static and reversed-cyclic loading. The tests were set up to approximate pure shear loading, with three-panel CLT assemblies connected with STS. The resulting load-displacement and hysteretic curves were used to determine an equivalent energy elastic-plastic curve to estimate assembly capacity, yield load, yield displacement, ductility ratio, stiffness, and damping. Excellent structural performance in terms of capacity and stiffness was obtained while still providing the required ductility for the system to be used in seismic applications. The average static and cyclic yield loads were 6.0 kN/screw and 5.9 kN/screw, respectively. Average static and cyclic and ductility ratios were 7.7 and 4.1, respectively, allowing the connection to be classified as highly ductile under quasi-static loading and moderately ductile under reversed cyclic loading. The data obtained allow engineers to specify an innovative connection assembly with double inclination of fasteners for lateral load–resisting systems of CLT structures.
In this paper, the authors present research into autonomously responsive architectural systems that adapt to environmental changes using hygroscopic material properties. Instead of using superimposed ...layers of singular purpose mechanisms–for sensing, actuation, control and power–in the form of high-tech electronic equipment as is emblematic for current approaches to climate responsiveness in architecture, the presented research follows an integrative, no-tech strategy that can be considered to follow biological rather than mechanical principles. In nature plants employ different systems to respond to environmental changes. One particularly promising way is hygroscopic actuation, as it allows for metabolically independent movement and thus provides an interesting model for autonomous, passive and materially embedded responsiveness. The paper presents a comprehensive overview of the parameters, variables and syntactic elements that enable the development of such meteorosensitive architectural systems based on the biomimetic transfer of the hygroscopic actuation of plant cones. It provides a summary of five years of research by the authors on architectural systems which utilize the hygroscopic qualities of wooden veneer as a naturally produced constituent within weather responsive composite systems, which is presented through an extensive analysis of research samples, prototypes at various scales, and two comprehensive case studies of full scale constructions.
•Access and instrumentalisation of computational capacities within organic systems.•Formal complexity through singular parametric differentiation in material behaviour.•Environment cognisant architectural systems with climate dependent formal behaviour.•Embedded biomimetic intelligence through material programming.
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