January 26-28, 2009, San Francisco, California, USA
Fire-resistive wood construction is achieved either by having the structural elements be part of fire-rated assemblies or by using elements of sufficient size that the elements themselves have the required fire-resistance ratings. For exposed structural wood elements, the ratings in the United States are calculated using either the T.T. Lie method or the National Design Specifications (NDS) Method. There is no widely accepted methodology in the United States to determine the fire-resistance rating of an individual structural wood element with the protective membrane directly applied to the exposed surfaces of the element. In these tests, we directly applied one or two layers of 16-mm thick fire-rated gypsum board or 13-mm thick southern pine plywood for the protective membrane to the wood element. The wood elements were Douglas-fir laminated veneer lumber (LVL) specimens and Douglas-fir gluedlaminated specimens that had previously been tested without any protective membrane. The methodology for the tension testing in the horizontal furnace was the same used in the earlier tests. The fire exposure was ASTM E 119. For the seven single-layer gypsum board specimens, the improvements ranged from 25 to 40 min. with an average value of 33 min. For the three double-layer specimens, the improvement in times ranged from 64 to 79 min. with an average value of 72 min. We concluded that times of 30 min. for a single layer of 16-mm Type X gypsum board and at least 60 min. for a double layer of 16-mm Type X gypsum board can be added to the fire rating of an unprotected structural wood element to obtain the rating of the protected element.
In October 2007 a series of seismic tests were carried out on a 7-storey building made of cross laminated (XLam) wooden panels in natural scale on a shaking table E-Defence in Japan within the SOFIE project. The paper presents calculation procedure, prediction of dynamic behaviour of the tested structure excited by the earthquake record "Kobe JMA 1995" and comparison between predicted, that means calculated and measured response. Due to blind prediction approach some construction details were not known before dynamic time history response calculation. Therefore some assumptions, engineering judgment and rough static analyses were needed to define all construction parts which were in modelling approach assumed as important and could have had influence on dynamic response of the analyzed structure. The most important assumptions related to the definition of the stiffness and load bearing capacity of mechanical connections, types of anchors and their positions in each floor level, were determined on the basis of static analysis where the structure was loaded with equivalent horizontal seismic forces and then were used in dynamic analysis. A mathematical model was developed in program SAP2000 where modal and time history analyses were carried out. Comparison of calculated and measured results is described and evaluated on the basis of the model assumptions and its simplification.
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.
This paper illustrates a research project about the calculation and design of Cross Laminated Timber (CLT) elements stressed by concentrated loads. Its focus lies on the shear design of CLT-elements next to punctual supports including reinforcements with self-tapping screws with continuous threads in areas of high shear stresses. Different influencing parameters on the distribution of shear forces next to a punctual support were evaluated by using comparative FEM-analyses. In the course of laboratory tests material-mechanical principles were determined to consider the interaction of rolling shear stresses and compression perpendicular to the grain. In addition to FEM simulations several experimental tests were carried out to describe the load bearing behaviour and the strengthening effect of CLT-elements reinforced by self-tapping screws. The investigations aim at developing a design concept including the effects mentioned above.
The Equivalent Viscous Damping (EVD) parameter is used to simplify the dynamic problem, passing from a non-linear solution of the system to a simple linear-elastic one. In the case of Direct Displacement-Based seismic Design (DDBD) methods, the EVD value allows direct design of structures, without an iterative computational process. This paper proposes a rational analytical formula to evaluate the EVD value of timber structures with dowel-type metal fastener connections. The EVD model is developed at the ultimate limit state, as a solution of the equilibrium problem related to an inelastic configuration. For a specific joint configuration, the EVD predicted via an analytical model was compared to experimental results. The proposed EVD model was validated using non-linear dynamic analysis on a portal frame, built with dowel-type fasteners arranged in two concentric crowns.
The applicability of the Direct Displacement-Based Design (DBD) procedure is strictly related to a priori evaluation of the design displacement and the matching Equivalent Viscous Damping (EVD) of the structure. In this paper we propose analytical models of these design parameters, at the ultimate limit state, for wooden structures built with engineered joints. Experimental results show that the plastic resources and dissipative capabilities of timber structures under earthquake conditions are ensured by the connections between the members. Therefore, the formulation of the design DBD parameters is based on the mechanical model of the single connector and assumes the inelastic deformation of the structure to be concentrated at the joints. The expected non-linear response of the connections can be either ductile or brittle. However, through an appropriate choice of the geometry and strength characteristics of the materials, in the design process we can control the expected ductile behavior of joints.
European experience shows that besides single family housing, Cross-Laminated Timber (CLT) can be competitive in mid-rise and high-rise buildings. Although this system has not been used to the same extent so far in North America, it can be viable wood structural solution for the shift towards sustainable densification of urban and suburban centres. FPInnovations has undertaken a multidisciplinary project on determining the structural properties of a typical CLT construction, including quantifying the seismic resistance and force modification factors of CLT buildings. In this paper, some of the results from a series of quasi-static tests on CLT wall panels are presented as well as preliminary estimates for the force modification factors (R-factors) for seismic design of CLT structures. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panels without openings with three different aspect ratios, panels with openings, as well as multi-panel walls with step joints and fasteners between them. Connections for securing the walls to the foundation included off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; a combination of steel brackets and hold-downs; and custom made brackets with timber rivets. Results from two storey configurations that include two walls and a CLT slab in between are presented and discussed. Finally preliminary estimates and recommendations for the force modification factors (R-factors) for seismic design of CLT structures according to National Building Code of Canada (NBCC) are also made.