The focus of this research is the connection between steel frame and the infill wall. Over 100 conventional bracket-type connections with various combinations of bracket and fasteners with cross-laminated timber were tested, investigated and assessed for damage under seismic loading protocols for a hybrid application. An energy-based formulation according to Krätzig was applied to calculate the development of the damage index, and the resulting index was validated with visual observation. Six of the connections were modeled in OpenSees. For the modeling, a CUREE-10 parameter model was chosen to reproduce the test curves. The load-displacement results from both test and model were analyzed; the first method according to ASTM standards, where the envelope curve of the hysteretic results are considered and plotted in an equivalent energy elastic-plastic curve (EEEP). The second analyzing method used, was Krätzig’s damage accumulation model. Throughout all six combinations and both loading directions (parallel- and perpendicular-to-the-grain) a major difference was found in the analyzing methods. The EEEP curve roughly approximates the performance but with the damage accumulation method showed that analysis of the subsequent cycles is required to better reflect the empirical performance of the connections. To avoid the extensive destruction of a bracket type connection after completion of seismic loadings, a new approach was chosen. It was found that a tube connection can obtain comparably similar strength results as a conventional bracket connection. The computed mechanical properties of bracket-type and tube-type connections were compared and evaluated. The new tube connection showed great potential for future timber-steel hybrid structures and their connecting challenge. A total of 27 connection assemblies were tested under quasi-static monotonic and reversed cyclic loads. The tube connections showed two major differences when compared to traditional bracket connections: i) the completely linear elastic behaviour at the beginning, and ii) the continued load increase after yielding. Both phenomena are founded in the geometry of that connector effectively making the novel connector a very promising alternative.
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.
This paper presents selected results of connector testing and wall testing which were part of a Forest Products Lab-funded project undertaken at Colorado State University in an effort to determine seismic performance factors for cross laminated timber (CLT) shear walls in the United States. Archetype development, which is required as part of the process, is also discussed. Connector tests were performed on generic angle brackets which were tested under shear and uplift and performed as expected with consistent nail withdrawal observed. Quasi-static cyclic tests were conducted on CLT shear walls to systematically investigate the effects of various parameters. Boundary constraints and gravity loading were both found to have a beneficial effect on the wall performance, i.e. higher strength and deformation capacity. Specific gravity also had a significant effect on wall behaviour while CLT thickness was less influential. Higher aspect ratio panels (4:1) demonstrated lower stiffness and substantially larger deformation capacity compared to moderate aspect ratio panels (2:1). However, based on the test results there is likely a lower bound of 2:1 for aspect ratio where it ceases to have any beneficial effect on wall behaviour. This is likely due to the transition from the dominant rocking behaviour to sliding behaviour.
This paper summarises the experimental and numerical investigation conducted on the main connection of a novel steel-timber hybrid system called FFTT. The component behaviour of the hybrid system was investigated using quasi-static monotonic and reversed cyclic tests. Different steel profiles (wide flange I-sections and hollow rectangular sections) and embedment approaches for the steel profiles (partial and full embedment) were tested. The results demonstrated that when using an appropriate connection layout, the desired strong-column weak-beam failure mechanism was initiated and excessive wood crushing was avoided. A numerical model was developed that reasonably reflected the real component behaviour and can subsequently be used for numerical sensitivity studies and parameter optimization. The research presented herein serves as a precursor for providing design guidance for the FFTT system as an option for tall wood-hybrid buildings in seismic regions.
This thesis fills the existing knowledge gap between detailed design and global behaviour of hybrid systems through an experimental study on an innovative timber-steel hybrid system called “FFTT”. The FFTT system relies on wall panels of mass timber such as CLT for gravity and lateral load resistance and embedded steel sections for ductility under the earthquake loads. An important step towards the practical application of the FFTT system is obtaining the proof that the connections facilitate the desired ductile failure mode. The experimental investigation was carried out at the facility of FPInnovations, Vancouver. The testing program consisted of quasi-static monotonic and reverse cyclic tests on the timber-steel hybrid system with different configurations. The two beam profiles, wide flange I-sections and hollow rectangular sections were tested. The interaction between the steel beams and CLT panels and the effect of the embedment depth, cross-section reduction and embedment length were closely examined. The study demonstrated that when using an appropriate steel section, the desired ‘Strong Column–Weak Beam’ failure mechanism was initiated and excessive wood crushing was avoided. While wide-flange I-sections were stiffer and stronger, the hollow sections displayed better post-yield behaviour with higher energy dissipation capacity through several cycles of deformation under cyclic loads. The out-of-plane buckling at the point of yielding was the major setback of the embedment of wide-flange I-sections. This research served as a precursor for providing design guidance for the FFTT system as one option for tall wood buildings in high seismic regions.
IASS WORKING GROUPS 12 + 18 International Colloquium 2015
April 10-13, 2015, Tokyo, Japan
This paper summarizes an experimental investigation on several innovative reinforcing techniques for the “Single Large Diameter Dowel Connection”, SLDDC in timber truss structures. Besides lateral reinforcing or prestressing, also steel plates glued on two sides of the glulam specimens were used as reinforcing measure. To study the efficiency of these techniques, 15 full-scale quasi-static tensile tests on glulam members with a SLDDC on either ends of each member were performed. It was found that the reinforcement significantly enhanced the bearing capacity of the SLDDCs. All of the reinforcing techniques showed a satisfactory efficiency, preventing splitting of wood. Moreover, most of the specimens remains showed a remarkable post failure strength.
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.
In recent years, hybrid systems have grown in popularity as potential solution for mid-rise construction. There is also an increased interest in using timber for such systems. The lack of established design guidance, however, has tabled the practical implementation of timber-based hybrid structures. The aim of this thesis is to address the existing knowledge gap regarding the detailed connection design of hybrid systems through combined experimental and numerical investigations on a novel timber-steel system called “FFTT”. The FFTT system relies on wall panels of mass timber such as Cross-Laminated-Timber (CLT) for gravity and lateral load resistance and embedded steel beam sections to provide ductility under seismic loading. A vital step towards practical implementation of the FFTT system is to obtain the proof that the connections facilitate the desired ‘strong column – weak beam’ failure mechanism.
The numerical work applied the software ANSYS; a parametric study based on the results of previous tests was conducted to obtain a suitable connection configuration for improved structural performance. The experimental work, carried out at FPInnovations, consisted of quasi-static monotonic and reversed cyclic tests on two different connection configurations: fully and partially embedded ASTM wide flange sections in combination with 7 ply CLT panels. The combination of partial embedment length and full embedment depth, even when using the smallest wide flange section, did not facilitate the desired behavior. The connection performance was significantly improved when reducing the embedment depth (to avoid creating stress peaks on a weak cross layer) and increasing the embedment length (larger center to center distance between bearing plates). The used small size steel beam, however, is not practical for a real structure; therefore, further studies with larger beams and a modified geometry are recommended before the FFTT system can be applied in practice.
The work presented in this report is a continuation of the FPInnovations' research project on determining the performance of the CLT as a structural system under lateral loads. A two storey full-scale model of a CLT house was tested under quasi-static monotonic and cyclic lateral loading in two directions, one direction at a time. In total five tests were performed; one push-over and two cyclic tests were conducted in the longer symmetrical direction (E-W), and two cyclic tests were performed in the shorter asymmetrical direction (N-S). In addition, before and after each test, natural frequencies of the house in both directions were measured. The main objective of the tests was to investigate 3-D system behaviour of the CLT structure subjected to lateral loads. The CLT structure subjected to lateral loads performed according to the design objectives.