Typical building wood of Norway spruce and European larch was chosen as experiment subject. Our researchers focused not only to joints but also to screws and wood itself.
There are many interesting conclusions:
- Freezing did not cause any significant change in the density and moisture content of the wood.
- Although there were variations in the withdrawal parameter in the two anatomical directions (radial and tangential) in both the species, these variations were not statistically significant from each other.
- Between the two species tested, the screw withdrawal parameter of larch wood was significantly higher (~70%) as compared to spruce wood, irrespective of the type of screw and thermal loading. This is due to the higher wood density of larch as compared to spruce.
- Universal (B) type screws (full-shank single thread) exhibited the highest withdrawal parameters at each thermal loading followed by construction (C) screws (partial intertwined thread) and construction (A) screws (partial double thread). The variation in the withdrawal parameters among the three types of screws can be attributed to their diameter as well as pitch of the threads.
- Thermal loading did not cause any detrimental effect on the screw withdrawal parameter. Rather, it caused an improvement in the screw withdrawal resistance.
- The study presents the results of one thermal cycle; however, in real use, wood and wooden joints get exposed to such extreme temperatures periodically and for longer duration. With increased number of cycles and increased exposure duration, the results can be better generalized. In addition, long-term exposure to natural climatic temperature variation is also necessary to better corelate the laboratory data with the natural exposure results.
The whole article was published at Construction and Building Materials (more here).