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.
Cross-laminated timber (CLT) products are gaining popularity in the North American market and are being used in midrise wood buildings, in particular, in shearwall applications. Shearwalls provide resistance to lateral loads such as wind and earthquake loads, and therefore it is important to gain a better understanding of the behavior of CLT shearwall systems during earthquake events. This paper is focused on the seismic performance of connections between CLT shearwall panels and the foundation. CLT panels are very stiff and energy dissipation is accomplished by the connections. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Furthermore, a test program was conducted to investigate the performance of CLT connections subjected to simulated earthquake loads. Two different brackets in combination with five types of fasteners were tested under monotonic and cyclic loading protocols. In total, 98 connection tests were conducted and the monotonic load-displacement curves and hysteretic loops were obtained. In this paper, an energy-based cumulative damage assessment model was calibrated with the CLT connection test data. Finally, a correlation between the damage index and physical damage is provided.
Wood-frame is the most common construction type for residential buildings in North America. However, there is a limit to the height of the building using a traditional wood-frame structure. Cross-laminated timber (CLT) provides possible solutions to mid-rise and high-rise wood buildings. CLT offers many advantages such as improved dimensional stability, a quicker erection time and good performance in case of fire. In order to introduce the cross-laminated timber products to the North American market, it is important to gain a comprehensive understanding of its structural properties. This paper focuses on the seismic performance of CLT connections. Over the last few years FPInnovations of Canada has conducted a test program to determine the structural properties of CLT panels and its application in shear walls. The test program comprised of more than 100 connection tests which followed the loading procedures of CUREE and ISO test protocols as specified in ASTM Standards ASTM E 2126-09 (2009). These tests were performed parallel and perpendicular to the grain of the outer layer, respectively. The impact of different connections on the seismic performance of CLT walls was investigated in a second phase on full size shearwall. CLT panels are relatively stiff and thus energy dissipation must be accomplished through the ductile behaviour of connections between different shear wall elements and the connections to the story below. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Different approaches for damage indices were compared and discussed. This paper describes how the energy-based cumulative damage assessment model was calibrated to the CLT connection and shear wall test data in order to investigate the damage under monotonic and cyclic loading. Comparison of different wall setup provided a deeper insight into the damage estimation of CLT shear walls and determination of the key parameters in the damage formulation. This represents a first published attempt to apply the damage indices to estimate the seismic behaviour of CLT shear walls.
This research considers the effect of in-plane rotation angles on the structural performance of Cross Laminated Timber (CLT) panels. In the interest of expanding the application of CLT to folded or freeform structures, rectangular CLT panels are likely to be divided into irregular geometries, in which case the loading will be applied at an intermediate orientation between the longitudinal and transverse panel axes. Such a loading condition is not accounted for in the existing analytical methods for dimensioning and designing with CLT. An analytical method is proposed which hybridizes the Shear Analogy method with Hankinson’s equation, allowing a designer to determine the effective stiffness of a CLT panel with any layup and at any in-plane rotation angle. An analytical study, followed by implementation with 3D parametric Finite Element Modelling and an experimental investigation, is used to evaluate this method. Results show that cross-grain/in-plane rotation has considerable effect on strength and stiffness of CLT panels with fewer than 5 laminations.
Interior partition walls for non-residential and high-rise residential construction are an US$8 billion market opportunity in Canada and the United States (Crespell and Poon, 2014). They represent 1.6 billion ft² (150 million m²) of wall area where wood currently has less than 10% market share. To approach this market a new system would be needed to compete against the incumbent system (wood/steel stud plus gypsum). The system would need to have an installed cost before finishing of approximately US$5 per ft² or lower. The system would also need to meet several code requirements for strength, sound transmission and fire resistance (flame spread and burn through). Crespell and Poon further concluded that to be truly transformative, the system would also need to address major trends impacting the building industry including reducing labor, reducing skilled labor, reducing onsite waste, reducing call-backs, and easily recyclable with low environmental impact. A likely market entry point for wood-based interior partition systems may be in taller and larger wood buildings.
Work described in this report investigated the fabrication, installation, acoustic and combustion properties of prototype interior partition wall designs.
Two types of non-structural prototype interior wall panels designated Type A and Type C were installed between two offices in the FPInnovations Vancouver laboratory. Wood sill plates for mounting the prototype panels were fastened to the concrete floor, sides and top of the opening between the two offices to produce a frame for mounting the test panels. Panels were fastened to the frame using dry wall screws. This same method of installation is envisioned in practice. The installation method makes it easy and fast to both install and remove the wall panels.
Acoustic tests showed the difference in ASTC rating measured between a double wall composed of Type A and Type C prototype panels compared with a double wood stud wall with gypsum board faces was approximately 6 ASTC points. A 6 point difference would be clearly noticeable. Although the results of this study are largely qualitative, they suggest that the prototype interior partition panels would have an acoustic advantage compared to stud wall designs.
In a related study summarized in this report, the combustion properties of three prototype interior panel constructions, including Types A and C evaluated in this report, indicated that any of the three types of partition constructions could be used in combustible construction in accordance with Division B of the National Building Code of Canada.
A second related study, also summarized in this report, estimated an installed cost of US$4.07 per ft² including overhead and profit for unfinished panel partitions comparable to panel construction Type C (gypsum/OSB/wood fibre insulation) as evaluated in this study. Thus, there would appear to be potential installed and finished cost advantages for the wood-based panel partitions compared to steel or wood stud walls with gypsum faces.
Other potential advantages of the prototype interior partition panels compared with the most common, currently-used systems (wood/steel stud plus gypsum) include ease and speed of installation, ease and speed of removal, design flexibility, prefabrication including pre-finishing, and easy installation of services.
Based on the positive results of these exploratory studies, further development of wood-based interior partition systems including design, fabrication, installation and in-service performance would appear justified. Knowledge of the products and testing methods developed in these studies would be expected to speed further development.
The paper presents some experimental data and phenomenon on bracket anchor connections for Cross-Laminated-Timber. The goal of this research is to provide a better understanding of the seismic performance of bracket connections subjected to seismic actions and how to choose and design bracket connections for Cross-Laminated-Timber structures. Test configuration and experimental setups are illustrated in details; cyclic displacement schedules of the connections in two directions are presented considering that CLT wall has horizontal sliding in the plane and uplift at the end in quasi-state tests. Different failure modes and force transmission mechanisms of different connections under the loading protocol were analysed. And important quantities for seismic design such as strength, and stiffness, equivalent yield load, peak load and ductility of the connections are evaluated and compared among different kinds of connections; an excellent connector is revealed in ductility and load capacity by test data analysis. In addition, some suggestions to choose and design bracket anchor connections are given.
In this paper, some of the results are presented from a series of quasi-static tests on CLT wall panels conducted at FPInnovation-Forintek in Vancouver, BC. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panel walls with three different aspect ratios, multi-panel walls with step joints and different types of screws to connect them, as well as two-storey wall assemblies. Connections for securing the walls to the foundation included: off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; combination of steel brackets and hold-downs; diagonally placed long screws; and custom made brackets with timber rivets. Results showed that CLT walls can have adequate seismic performance when nails or screws are used with the steel brackets. Use of hold-downs with nails on each end of the wall improves its seismic performance. Use of diagonally placed long screws to connect the CLT walls to the floor below is not recommended in high seismic zones due to less ductile wall behaviour. Use of step joints in longer walls can be an effective solution not only to reduce the wall stiffness and thus reduce the seismic input load, but also to improve the wall deformation capabilities. Timber rivets in smaller groups with custom made brackets were found to be effective connectors for CLT wall panels. Further research in this field is needed to further clarify the use of timber rivets in CLT.
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.