Application of Metal Plate Connector on the Wood Roof Truss Assembly

• Main Authors: Yuan-Chang Liu, 劉原彰
• Other Authors: Min-Chyuan Yeh
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/64201661594801000158

碩士 === 國立屏東科技大學 === 木材科學與設計系 === 94 === The purpose of this study was to design and develop metal plate connection（MPC）products and a related assembly equipment and to evaluate the manufacturing technique and structural performance of roof wood truss systems. The 2x4 and 2x6 structural sawn lumber of Japanese cedar(Cryptomeria japonica) and Spruce-Pine-Fir（SPF）were used for truss assembly and the grading method based on CNS 14630 standard. The Howe and Fink wood roof truss systems assembled with developed metal plate were subjected to the four-point bending tests for the investigation of the flexural properties. The wood roof truss systems subjected to the roof design loads were first analyzed by using the truss analysis software for force distribution and the results were them compared to the experimental works. The joint inspections of the wood roof truss systems were performed following the requirements of ANSI/TPI and the tensile tests were also performed for strength of the MPC in the truss member connections. A portable hydraulic MPC assembly machines featuring with conveniences of operation and mobility were developed and to suitable for wood roof truss systems fabricated with structural dimension lumbers. Three MPC specifications（D6-12, D12-12 and D16-18）of tooth length 9 mm, thickness 0.9 mm, and tooth density 1 teeth/cm2 were designed and developed from SS 400 structural quality steel sheet. Four MPC joints investigated were A：MPC axis and wood grain parallel to loading direction for Japanese cedar and SPF（J-A and S-A）；E：MPC axis parallel to loading direction and wood grain perpendicular to loading direction for Japanese cedar and SPF（J-E and S-E）. Result of MPC joints showed higher tensile capacity of J-A and S-A modes than that of J-E and S-E modes about 18-26％. The average loading capacity of Japanese cedar joint was 27 kgf/tooth and SPF for 26 kgf/tooth. The failure mode for all joints was teeth withdrawal out of the lumber surface. The maximum loading capaciting of the same MPC joint pattern weren’t difference between two species. Result of the tensile tests of MPC joints showed satisfied loading capacity. Maximum bending capacity of the 2x6 wood roof truss system is 81-107％ higher than that of 2x4 wood roof truss system. The maximum bending capacity are no difference in both wood roof truss system types and species used. The maximum bending capacities of eight kinds of wood roof truss systems are 6.5-13.5 times of design loads. The 2x6 wood roof truss systems with Japanese cedar and SPF showed 75％ and 50％, respectively higher in average bending stiffness than those of 2x4 wood roof truss systems. The stiffness of Howe wood roof truss is 20-39％ higher them that Fink truss. The flexural deflection of the roof wood truss system measured at the design load level are 5-21％ of design limitation. The maximum equivalent distributed loads measured at failure are 4.6-8 times of design load and the design load of eight kinds of woof roof truss system is 10-20％ of the maximum equivalent distributed load measured at failure. It indicated that the developed wood roof truss is practical in structural application. The most critical failures for 2x4 and 2x6 roof wood truss are located at heel joint and account for 69％ and 75％, respectively. The major failure mode of 2x4 roof wood truss is teeth withdrawal and for 2x6 truss is a combination of teeth withdrawal and plate failure, two failure modes account for 82％. Based on the strain gauge measurements, the stresses for each member of roof wood truss at design load are lower than the allowable stresses for Japanese cedar and SPF. The resulted compressive stresses of members are 2-32％ of allowable stresses, while the resulted tensile stresses of members are 2-16％ of the allowable stresses.