The latest developments in seismic design philosophy have been geared towards developing of so called "resilient" or "low damage" innovative structural systems that can reduce damage to the structure while offering the same or higher levels of safety to occupants. One such innovative structural system is the Pres-Lam system that is a wood-hybrid system that utilizes post-tensioned (PT) mass timber components in both rigid-frame and wall-based buildings along with various types of energy disspators. To help implement the Pres-Lam system in Canada and the US, information about the system performance made with North American engineered wood products is needed. That information can later be used to develop design guidelines for the designers for wider acceptance of the system by the design community.Several components influence the performance of the Pres-Lam systems: the load-deformation properties of the engineered wood products under compression, load-deformation and energy dissipation properties of the dissipators used, placement of the dissipators in the system, and the level of post-tensioning force. The influence of all these components on the performance of Pres-Lam wall systems under gravity and lateral loads was investigated in this research project. The research project consisted of two main parts: material tests and system tests.
The 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.
The objective of this research was to develop an inter-panel connector capable of sustaining reverse cyclic loads. The prescribed use for the connector was for cross-laminated timber rocking walls. Cross-laminated timber has few current lateral systems. From this need two shear plate inter-panel connectors were designed: A and B. These connectors had high initial stiffness and displacement capacity. The end goal was shake table testing the connectors on a two-story structure. First, finite element modeling was conducted to ensure connectors were sufficient for design. Panels were tested on two scales at Washington State. The first was a single connector level, which had some errors in boundary condition, which limited the output. Second, a rocking wall test, isolating the connectors. This test produced higher quality results, though some errors at high drifts occurred. Stiffness of A and B were 4 and 32 k/in, respectively. Both had equivalent viscous damping for isolated connectors in the range of 20%, however B was dropping to a lower converging value. Due to the buckling behavior of the fuses and connection details, an augmented Fuse A was the sole fuse on the shake table structure. Shake table testing was conducted on a full-scale two-story building at University of California, San Diego. 13 motions were run, ranging in scale from service level earthquakes to scaling higher than a maximum considered earthquake. Four separate records were used to ensure a wide range of frequencies and amplitudes. The connectors experienced less visible residual deformation than in the small tests and the test displacements were lower. The beginnings of lateral torsional buckling began after the last test, scaled above maximum considered earthquake. The period was high for a two-story structure, at approximately one second. The building underwent approximately four percent roof drift and the structure alone had an equivalent viscous damping of approximately 14%. From these two separate scaled tests, the next step was to determine a preliminary design process. This process involves selection of connectors for certain purposes and utilizing modeling and performance based design to ensure the connector is proper for the given lateral system.
Multi-storey platform cross laminated timber (CLT) structures are becoming progressively desirable for engineers and owners. This is because they offer many significant advantages such as speed of fabrication, ease of construction, and excellent strength to weight ratio. With platform construction, stories are fixed together in a way that each floor bears into load bearing walls, therewith creating a platform for the next level. The latest research findings have shown that CLT platform buildings constructed with traditional fasteners can experience a high level of damage especially in those cases where the walls have adopted hold-down brackets and shear connectors with nails, rivets or screws. Thus, the current construction method for platform CLT structures is less than ideal in terms of damage avoidance. The main objective of this study is to develop a low damage platform timber panelised structural system using a new configuration of slip friction devices in lieu of traditional connectors. A numerical model of such a system is developed for a low rise CLT building and then is subjected to reversed cyclic load simulations in order to investigate its seismic performance. The result of these quasi-static simulations demonstrated that the system maintained the strength through numerous cycles of loading and unloading. In addition to this, the system is capable of absorbing significant amount of energy. The findings of this study demonstrate the proposed concept has the potential to be developed as a low damage seismic solution for CLT platform buildings.
The structural use of wood in North America is dominated by light wood-frame construction used in low-rise and – more recently – mid-rise residential buildings. Mass timber engineered wood products such as laminatedveneer-lumber and cross-laminated timber (CLT) panels enable to use the material in tall and large wood and woodbased hybrid buildings. The prospect of constructing taller buildings creates challenges, one of them being the increasein lateral forces created by winds and earthquakes, thus requiring stronger hold-down devices. This paper summarises the experimental investigation on the performance a high-capacity hold-down for resisting seismic loads in tall timberbased structural systems. The connection consists of the Holz-Stahl-Komposit-System (HSK)™ glued into CLT with the modification that ductile steel yielding was allowed to occur inside the CLT panel. The strength, stiffness, ductility and failure mechanisms of this connection were evaluated under quasi-static monotonic and reversed cyclic loading. The results demonstrate that the modified hold-down-assembly provides a possible solution for use in tall timber-based structures in high seismic zones
The research presented in this paper examines the performance of a shear connection using self-tapping screws (STS) in 3-ply Cross-Laminated Timber (CLT) panels. CLT panels were connected with STS assemblies at an inclined angle in two directions. The capacity of the STS assemblies was tested for the purpose of designing a CLT roof diaphragm of a large storage facility where a high-performance and low-manufacturing-cost solution was required. A total of eleven full-scale specimens were subjected to quasi-static and reversed-cyclic shear loading. Resulting forcedisplacement and hysteretic curves were used to determine an equivalent energy elastic-plastic curve based on ASTM E2126-11 procedures to estimate assembly yield strength, yield displacement, and ductility ratio. The performance in terms of strength and stiffness was excellent, and the STS provided the required ductility for the system to be used in seismic applications. Static yield strength averaged 80kN/m with an average ductility ratio of 7.7 while cyclic yield strength averaged 68kN/m with an average ductility ratio of 4.1. The data obtained allows engineers to specify low-cost lateral load resisting connection systems for large scale CLT structures.
This paper presents the results of an on-going program of the mechanical behaviour of bolted glulam beamto-column connections. The program included testing and modelling of connections of various bolt size, edge distance and lamina alignment patterns. This paper presents part of the obtained results, including monotonic and reversed cyclic loading test results of 10 full-scale beam-to-column connections and the corresponding modelling results. The test results indicated that the perpendicular-to-grain properties of glulam and the localized contact between the bolts and surrounding glulam had significant influence on the stiffness and the maximum moment of the connections. A finite element method based model, which can be easily incorporated in commercial available software packages, was developed and verified based on the test results. Good agreement was achieved. Parametric study results indicated that the tolerance of the bolt holes can significantly affect the mechanical behaviour of the bolted beam-to-column connections.
This paper presents a study on the moment resistance of post-and-beam joints with concealed metallic connectors aimed at replacing in a more modern design the wood-wood joints of traditional Korean Hanok timber houses. Several variations of the design of the connectors are investigated to optimize the moment resistance of the joints. Experimental tests are conducted under monotonic and reversed cyclic loading. The performance of the joint is evaluated in terms of peak moment resistance, as well as ductility and energy dissipation. Results show that optimization in the design can improve the moment resistance of the joint while preventing the brittle wood fracture and favoring a more ductile plasticizing of the connector, for the benefit of safety.
This paper presents the results of a study whose objective was to investigate the behaviour of a hybrid wood shearwall system defined herein as a combination of traditional light-frame wood shear walls with post-tensioned rocking cross laminated timber (CLT). The post-tensioned CLT panels in the hybrid system offer both vertical and lateral load resistance and self-centering capacities. The traditional light wood frame shearwalls (LiFS) provide additional lateral load resistance along with energy dissipation through the slip of nail connections. Thus a combination of these two types of structures will provide an excellent structural solution for mid-rise to tall wood buildings, where there is a need for resisting large lateral and vertical loads as well as structural stability. A conventional test on the hybrid system subjected to a reverse-cyclic loading protocol and a real-time hybrid simulation using the new algorithm were conducted. In real-time hybrid simulation, a three-story building was modelled as a numerical substructure. In the first story of the three-story building the experimental CLT-LiFS substructure was tested and integrated in real time with the numerical substructure as described herein. The experimental observation of the behaviours and damage of the hybrid shear wall are presented and discussed in this paper.
Seismically resilient, lateral systems for tall timber buildings can be created by combining cross laminated timber (CLT) panels with post-tensioned (PT) self-centering technology. The concept features a system of stacked CLT walls where particular stories are equipped to rock against the above and below floor diaphragms through PT connections and are supplemented with mild steel U-shaped flexural plate energy dissipation devices (UFPs). Experiments were conducted to better understand rocking CLT wall behavior and seismic performance. The testing program consisted of five single wall tests with varying PT areas, initial tensioning force, CLT panel composition, and rocking surface and one coupled wall test with UFPs as the coupling devices. The walls were tested with a quasi-static reverse-cyclic load protocol. The experimental results showed a ductile response and good energy dissipation qualities. To evaluate the feasibility and performance of the rocking CLT wall system, prototype designs were developed for 8 to 14 story buildings in Seattle using a performance-based seismic design procedure. Performance was assessed using numerical simulations performed in OpenSees for ground motions representing a range of seismic hazards. The results were used to validate the performance-based seismic design procedure for tall timber buildings with rocking CLT walls.