The two-way action of Cross Laminated Timber (CLT) is often ignored in the design of CLT due to its complexity. But in some cases, for example, large span timber floor/roof, the benefit of taking the two-way action into account may be considerable since it is often deflection controlled in the design. Furthermore CLT panels are typically limited to widths of less than 3 m. therefore, for practical applications, engaging CLT panels in two-way action as a plate in bending would require connecting two panels in the width/minor direction to take out-of-plane loading.
To address this technically difficult situation, an innovative connection was developed to join the CLT panels in the minor direction to form a large continuous two-way plate. The two-way action of CLT was also quantified. Static bending test was conducted on CLT panels in the major and minor directions to measure the Modulus of Elasticity (MOE). This provided a benchmark for the following connection test, and data for the future development of computer modeling. The average apparent MOE was 9.09 GPa in the major direction and 2.37 GPa in the minor direction. Several connection techniques were considered and tested, including self-tapping wood screws, glued in steel rods, and steel connectors. One connecting system was found to be effective. For the panel configuration considered, the system was consisted of steel plates, self-tapping wood screws, and 45° screw washers. Two steel plates were placed on the tension side with sixteen screws, and one steel plates was placed on the compression side with four screws. When the screws were driven into the wood, the screws were tightly locked with the washers and steel plates, and at the same time, the wood members were pulled together by the screws. This eliminated any original gap within the connection. The connector was installed to join two CLT members in the minor direction. They were tested under bending with the same setup as above. The connected panels had an average apparent MOE of 2.37 GPa, and an average shear-free MOE of 2.44 GPa, both of which were higher than the counterpart in the full panels. The moment capacity of the connected panels was also high. The minimum moment capacity was 3.2 times the design value. Two large CLT panels were tested under concentrated loading with four corners simply supported. The deflection of nine locations within the panels was measured. This data will be used to validate the computer modeling for CLT two-way action.
‘Mass timber’ engineered wood products in general, and cross-laminated timber in particular, are gaining popularity in residential, non-residential, as well as mid- and high-rise structural applications. These applications include lateral force-resisting systems, such as shear walls. The prospect of building larger and taller timber buildings creates structural design challenges; one of them being that lateral forces from wind and earthquakes are larger and create higher demands on the ‘hold-downs’ in shear wall buildings. These demands are multiple: strength to resist loads, lateral stiffness to minimize deflections and damage, as well as deformation compatibility to accommodate the desired system rocking behaviour during an earthquake. In this paper, contemporary and novel hold-down solutions for mass timber shear walls are presented and discussed, including recent research on internal-perforated steel plates fastened with self-drilling dowels, hyperelastic rubber pads with steel rods, and high-strength hold-downs with self-tapping screws.
Effects of Arrangement of Steel Plates on Strength of Dowel-Type Cross Laminated Timber Joints with Two Slotted-In Steel Plates Subjected to Lateral Force
Cross-laminated timber (CLT) has received particular attention as a structural material, and its material and joint strengths have been researched. This study derived a strength formula for dowel-type CLT joints with slottedin two steel plates, based on Johansen’s yield theory. When the steel plate is inserted in CLT that has five laminae, the dowel-type joints with slotted-in two steel plates have thirty-nine yield modes. This study derived the formulas for each yield mode and compared them with experimentally obtained results. The yield mode assumed by the yield theory was congruent with the failure mode of the CLT specimens after the experiments. The strength of dowel-type joints calculated based on the yield theory was close to the yield strength obtained in the experiments.
This thesis discusses a novel timber-steel core wall system for use in multi-storey buildings in high seismic regions. This hybrid system combines Cross Laminated Timber (CLT) panels with steel plates and connections to provide the required strength and ductility to core walled buildings. The system is first derived from first principles and validated in SAP2000. In order to assess the feasibility of the system it is implemented in the design of a 7-storey building based off an already built concrete benchmark building. The design is carried out following the equivalent static force procedure (ESFP) outlined by the National Building Code of Canada for Vancouver, BC. To evaluate the design bi-directional nonlinear time history analysis (NLTHA) is carried out on the building using a set of 10 ground motions based on a conditional mean spectrum. To improve the applicability of the hybrid system an energy based design methodology is proposed to design the timber-core walled building. The methodology is proposed as it does not rely on empirical formulas and force modification factors to determine the final design of the structure. NLTHA is carried out on the proposed methodology using 10 ground motions to evaluate the suitability of the method and the results are discussed and compared to the ESFP results.
IASS WORKING GROUPS 12 + 18 International Colloquium 2015
Research Status
Complete
Notes
April 10-13, 2015, Tokyo, Japan
Summary
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.
Investigations showed that large timber members exposed to fire have excellent fire-resistance. But very little research has been done on the performance of connections in timber structures exposed to fire. The dowel-type connections with slotted-in steel plates have widely been used in timber structures, sometime as moment resisting...
The concept of combining folded thin steel plates and glued laminated timber in the beam element to gain increased structural and fire performances was developed at the Institute of Structural Design and Timber Engineering (ITI) in Vienna University of Technology. The authors conducted non-loaded combustion tests and numerical simulations of the three different types of such cross-sections, and results from combustion tests and numerical simulations are discussed.
Cross-laminated timber (CLT) constitutes a promising solution for numerous structural applications, including for large and tall residential and commercial buildings. The prospect of building larger timber structures creates some structural challenges, amongst them being that lateral forces created by high winds and strong earthquakes are higher and create higher demands of “holddowns”. The Canadian Standard for Engineering Design in Wood CSA-O86 does not (yet) provide any specific procedures to estimate the resistance of mass-timber Lateral Load Resisting Systems (LLRS) nor how to facilitate the targeted kinematic mode, especially for multi-panel walls where the LLRS behaviour is a function of connection behaviour.
The project investigated the viability of internal-perforated-steel-plates (ISP) with self-drilling dowels as high-performance connections for CLT LLRS. The project objective was to contribute towards the development of reliable design guidance for ISP connections. To achieve this objective, first at the material level, the properties of the used steel-plates and dowels were verified. Then, at the component level, the performance of shear connections and hold-downs were investigated by performing quasi-static monotonic and reversed cyclic tests.
The most significant finding of the component level tests was the proof that it is possible to control the strength, stiffness, and ductility only through the IPSP and avoid bending of the SDD or crushing of the wood. Furthermore, the length of the steel perforations had a large impact on the performance with the steel-plates with the long slots (Type-D and Type-E) exhibiting lower strength and stiffness. For the hold-down tests, the same perforation geometry as for the shear-connection tests was chosen. As already determined in the shear-connection tests, the hold-down specimens with the short perforation slots resulted in the strongest and stiffest connection.
The results from this project will be used to design and test CLT shear walls with ISP connections.
The objective of this research is to develop a model to predict the distribution of loads within connections with multiple self-tapping screw fasteners and steel side plates, and use this model to predict the strength and stiffness of multiple-inclined self-tapping screw connections. These results would facilitate the design of large scale connections with long rows of self-tapping screw fasteners, such as may be used for mass timber shear wall connections or splice joints for long-span timber beams.
The load distribution in multi-dowel timber connections under bending moments was investigated by means of an integrative evaluation of a hierarchically organized test program, which encompassed component tests as well as single-dowel and multi-dowel connection tests. It was demonstrated that the anisotropic material behaviour of Laminated Veneer Lumber, and consequently of wood in general, leads to a non-uniform load distribution among the dowels, even for multi-dowel connections with a circular arrangement of dowels. Model predictions from this study highlight inefficiencies of the simplified calculation approach, based on the polar moment of inertia, i.e., based on isotropic theory. Loads of dowels loaded parallel to the grain were found to be underestimated by up to 50%. Through the hierarchically organized experimental campaign with full-field deformation measurement techniques, load distribution effects could be related to the orthotropic material behaviour of wood expressed in terms of load-to-grain angle dependent slip curves of single-dowel connections.
