Prediction of compression strength of wood usually used in ancient timber buildings by using resistograph and screw withdrawal tests
Ultimate compression strength parallel to grain (UCS) of wood is one of important performance to evaluate the structural security of old wood buildings. Poplar wood (Populus tomentosa Carrière), Chinese larch wood (Larix gmelinii (Rupr.) Kuzen.) and Chinese fir wood (Cunninghamia lanceolata (Lamb.) Hook) were selected as the models in this paper. The aim of study is to predict UCS of wood by using resistograph and screw withdrawal methods. Compared with the screw withdrawal method (SW), resistograph method (RM) is generally more reliable, but because of the expenses involved, SW should also be considered as a much cheaper alternative. The results showed that the correlation coefficient between the RM and the UCS ranged from 0.5 to 0.7. The correlation coefficient between the double-start thread screw withdrawal force (SWDST) and the UCS distributed from 0.1 to 0.65, while the values of coefficients for the singlestart thread screw withdrawal (SWSST) differed from 0.4 to 0.65. In screw withdrawal method, greater pitch of screw resulted in higher correlation coefficient.