The Influence of Moisture Content on Strength of Window Corner Joint

The tendency to improve the energy efficiency of windows has led to an increase in the number of panes used. The greater weight of the window sash leads to a loss of its geometry during normal usage. This deformation of geometry is caused by its own weight, and thus reduces the efficiency of preventing heat loss. All the positive effects that are obtained by using multiple panes of glass are thus lost. As window manufacturers often try to cut production costs by shortening the time of kiln drying, this paper researches the effect of using elements with different moisture content. Articles on similar topics were reviewed and it was found that there were no available data on the researched topic. Only about 20 different articles on similar topics were found, but the starting conditions or input was greatly different. Also, there are no official standards that cover the strength of window corner joints. This paper analyzes the influence of the change in moisture of the elements on the strength of the joint. Three groups of window corner joint samples were examined. The first group of samples was the control group that was supposed to determine the strength of the joint when the window beams were made with the recommended moisture according to a corresponding standard (12 +/- 2%). In the second and third groups, the moisture of the beams was taken as a variable factor, namely the moisture content of 18 +/- 2%. The results of this study show that the strength values of the currently used corner joints (double mortise and tenon) are different at different moisture contents. As expected, the samples with the recommended moisture content had higher strength values than the samples with the higher moisture content. There are many challenges in proper kiln drying and the final moisture content has a crucial impact on window strength. As windows have a specific purpose in buildings, they should have sufficient strength to be properly used over a long period. These obtained results should demonstrate the importance of the moisture content of wooden beams used in window production.