UBC Theses and Dissertations
Tensile strength and performance of the INDUO®-heavy-timber connector in combination with structural composite lumber and Douglas fir Steiniger, Markus
The INDUO-connection is a new steel-to-wood joint for highly loaded heavy-timber structures. Embedded in the end-grain of laminated timber beams, the special INDUOconnector is designed to transfer axial and transverse loads. Due to the weaker strength properties of solid wood perpendicular to the grain direction, the connection's capacity under transverse loading is comparatively small. Parallel to the grain, however, the connection is capable to transfer loads of up to 180kN and is thus predominantly suited for tension applications. Since the introduction to the European market in the Mid-90s, the INDUO-connection system has been mainly deployed in Post-and-Beam structures using softwood timber and Glulam as beam material. This thesis investigates the tensile strength and performance of the INDUO-connector in combination with different beam materials. Static tension tests were performed in two separate test series with a total of 99 specimens of different member cross-sections (100x100mm and 120x120mm), connector types (A and B) and beam materials (Microllam®LVL, Parallam®PSL, TimberStrand®LSL, thick Douglas-Fir plywood and Douglas-Fir lumber). In test series 1 all possible combinations of beam material, connector type and member cross-section were tested with a sample size of up to three, providing trends on strength properties and failure performance. For test series 2 it was decided to focus on fewer combinations with a larger sample size to create statistically more significant results on ultimate tensile strength and connection stiffness for the most advantageous setups. By modeling and calculating the INDUO-connection according to different international timber codes (German DIN1052-2000, European EC5, Canadian CSA 086.1 and US ASCE 16-95) as a bolted or tight-fitting dowel connection, characteristic tensile strength data was computed and compared with the characteristic values derived from the results of series 2. In terms of tensile strength and performance, TimberStrand®LSL presented the best test results, outperforming Microllam®LVL, Parallam®PSL and Douglas-Fir lumber, which showed significantly lower tensile strengths accompanied by brittle failure modes. Thick Douglas-Fir plywood was only examined in test series 1, presenting high tensile strength for larger beam-cross-sections, whereas smaller cross-sections failed brittely. The comparison of different design approaches for the INDUO-connection showed that based on the same connection model (dowel-type fasteners with inside steel plate) the Canadian timber code provided by far the most conservative design values, whereas all other codes presented significantly higher numbers relative to the Canadian code . The comparison of characteristic tensile strength properties generated from the test results and values derived from the different design strengths indicate all four timber codes have more or less similar results.
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