Experimental Research Of Timber Components Subjected To Decay

Decay is the main factor that influences the destruction of wood and the durability of timber structures.However,the research on decay is less and alaways concentrated on the corrosion resistance of wood species.Besides,there is still a lack of durability assessment methods for timber structures.From the perspective of the durability evaluation of timber components and the prediction of residual durability,the decay depth is a more suitable indicator for durability assessment.Therefore,it is of great significance to realize the quantitative detection of the decay depth of the timber components and the evolution law of the decay depth.In order to find a reasonable wood material and decay depth discriminating method,this thesis is based on the wood Drill-Resistograph to carry out detection on the timber components removed from the actual building.Through the detailed analysis of the detection resistance curve and the related literature research,the waveform discrimination method,regional resistance mean value discrimination method and the decay boundary discrimination method based on resistance ratio are proposed.The resistance curves of sapwood and heartwood are obviously different,so the curces can be divided according to their waveform characteristics.Besides the material discrimination can be performed by calculating the regional resistance mean value of each partition.Under common circumstances,the average resistance of the heartwood area is higher than the average resistance of the sapwood area.If not,different degrees of heart decay will be considered.The decay boundary discrimination method based on resistance ratio is mainly applicable to discriminate the surface decay depth of timber components.The resistance ratio refers to the ratio of the mean value of the resistance in the decay zone to the mean value of the resistance of the healthy section.This method can be used to discriminate the decay boundary more accurately and then the specific surface decay depth can be obtained.The results show that the average depth of crack extend decay in the heartwood area is 22 mm,and the average depth of the surface decay in the sapwood area is 13.5mm.In this thesis,a 112-day constant temperature and humidity indoor accelerated decay experiment is carried out to provide a basis for the evolution analysis of decay in the natural environment.The test procedure includes coupon preparation,incubator modification,selection and cultivation of bacteria species,medium preparation,inoculation infection and coupon decay,etc.Then the phenomenon of the coupons subjected to different decay time,the nominal weight loss rate,the decay depth detected by Drill-Resistograph and the nominal Mechanical properties test are carried out.Considering that the change of mechanical properties is sensitive to decay,this thesis also proposes the concept of the equivalent decay depth and deduces it by the nominal mechanical performance degradation rate.The results show that the average decay depth of the decayed 84-day coupon is 1.8mm and its relative decay depth is 9%.Because the size of the compression coupon is small,it is easier to form uniform decay,therefore the equivalent relative decay depth(8%)which derived from the nominal compressive strength degradation rate is close to the actual test results.Based on this,the variation of the decay depth of accelerated decay coupons with time is discussed.The decay evolution in the natural environment can be divided into two stages: before the start of decay and after the decay,and this thesis studies these two stages.Through literature research and data analysis,the modified transformation is carried out on the basis of existing research.The decay start time is analyzed under different temperature and humidity environments.At the same time,according to the analysis of the influencing factors of wood decay,the reduction coefficient for the transformation of the ideal environment into the natural environment is proposed and the depth evolution model of decay in the natural environment is established,which provides a basis for the prediction of the remaining years of durability.