A prerequisite for a sensible estimate of moisture induced stresses in timber members is an accurate prediction of the members’ moisture states during their service life. This work presents realizations of envelop curves over the possible moisture states in a timber member for some carefully chosen harmonic humidity variations. The calculations, on which the realizations were made, are based on a fully coupled transport model including a model for the influential sorption hysteresis of wood.
COBISS.SI-ID: 5458273
We present correlations between visually determined characteristics of structural sawn timber produced from Slovenian spruce (Picea abies (L.) Karst.) and its mechanical properties. Dried sawn timber was visually graded into sorting classes according to SIST DIN 4074-1. Results of visual grading were compared with grade determining properties (bending strength, modulus of elasticity and density). The main strength reducing charasteristics were the rate of growth (r =- 0.52), knot ratio (r =- 0.50), twist (r =- 0.23) and distance from the pith (r = 0.12). The most decisive factors to judge lower grade were however knots, followed by twist, the presence of pith and rate of growth. 10% of the specimens were graded to class S13, 58% to class S10, 15% to class S7, 17% of the specimens were rejected. The determined characteristicvalues of sorting classes S13, S10 and S7 were higher than the requirements of SIST EN 338 for the strength classes C30, C24 and C18 respectively. The results of this study represent a basis on which visual grades can be assigned to a strength classes.
COBISS.SI-ID: 1874313
Moisture transport of a hygroscopic and open porous material such as wood is a complex system of coupled processes. For seasoned wood in natural climate three processes active in the moisture transport are readily identified, diffusion of vapor in pores, sorption and diffusion of bound water in wood (cell wall) tissue. A mathematical model used to predict moisture transport in wood for a given condition must at least consider the dominating active processes to be accurate and all active processes to abide physics. Since the processes constituting the moisture transport are fully coupled, experimental studies have found it difficult to investigate each process isolated from the others. In this study a theoretical investigation on the influence of the material parameters on the model response to a given change in surrounding humidity.
COBISS.SI-ID: 5154401
This paper presents the preliminary results of strength grading of spruce structural timber based on non-destructive testing using the dynamic method - the single mode transverse damped vibration method. The main objective of this study was to evaluate the used method through the examination of correlations between the MOEdyn determined by transverse damped vibration of simply supported edgewise oriented boards, global edgewise MOEstat, and MOR. In the study the European standards dealing with the strength grading was also considered. The correlations between the investigated properties were identified to be within the range reported by other researchers. Numbers of correctly graded, upgraded and downgraded specimens were established according to the EN 14081-2 with the size matrix. 38% of specimens were assigned correctly, 60% of specimens were downgraded and only 3% of specimens were upgraded. We can evaluate the used dynamic method as an entirely reliable method but for final statistically significant conclusions a larger pattern should be considered.
COBISS.SI-ID: 1907849
The characteristic properties of Slovenian spruce and fir timber were assessed on 1074 elements with different cross sections. Simple nondestructive methods for the determination of indicative properties of timber and evaluation of their applicability are presented. On the basis of the research, described in the article, we found out that the strength, density and modulus of elasticity, compared to the countries of the “Central and Eastern Europe” growth area, are high enough to grade our softwood species according to European standards into comparable or even higher strength classes.
COBISS.SI-ID: 254377216