Estimating Mechanical Properties of Wood in Existing Structures—Selected Aspects

The paper presents and discusses selected methods of wood classification and the evaluation of its mechanical properties. Attention was mainly paid to methods that may be particularly useful for examining existing elements and structures. The possibility of estimating the modulus of rupture—MOR and modulus of elasticity—MOE based on the non- destructive (NDT), semi-destructive (SDT), and destructive tests (DT) were considered. Known international, European, and American standards and research approaches were indicated. The selected testing methods and their interpretation were presented. These were, among others, the method of visual assessment, the resistance drilling method, methods of determining the dynamic modulus of elasticity, and procedures for testing small clear specimens. Moreover, some of our own research results from the conducted experimental tests were presented and discussed. In the destructive tests, both large elements and small clear specimens were examined. The results obtained from individual methods were compared and some conclusions were presented. The summary discusses the fundamental difficulties and limitations in applying the presented procedures and interpretations.

Semi-Destructive and Non-Destructive Tests of Timber Structure of Various Moisture Contents

The condition of heritage and historic timber constructions depends on how they are exploited. Numerous environmental factors degrade the physical and mechanical properties of timber and hence, affect the load-bearing capacity of constructions. As a result, frequent evaluations of their technical condition become necessary. Currently, modern technologies allow for extensive diagnostics of timber constructions using non-destructive and semi-destructive methods; yet, in contrast to classical laboratory tests, there is insufficient knowledge of the impact of individual factors on the results of such studies. This article presents an assessment of the influence of the moisture content of timber elements on the results of ultrasonic stress wave, sclerometric, and resistance drilling tests. Additionally, computed tomography scans were performed on selected samples to demonstrate the destruction mechanism occurring during the semi-destructive tests. The research involved three types of wood: pine, spruce, and fir of different moisture contents. The results reveal a strong relation between the moisture of timber and all the tests conducted in terms of both hygroscopic and capillary moisture.

Assessing specific gravity of young Eucalyptus plantation trees using a resistance drilling technique

The resistance drilling technique has been in focus for assessing the specific gravity (SG) of young Eucalyptus trees from plantations for pulpwood production. Namely, the data of 50 34-month-old and 50 62-month-old trees from Eucalyptus grandis×Eucalyptus urophylla clonal plantations was evaluated, while the relative resistance profiles were collected with the amplitude in a scale from 0 to 100% of each tree at the breast height. For laboratory determination of SG and moisture content (MC), 3-cm-thick disks were taken at breast height. The average resistance amplitude of a full drill penetration or a half-diameter penetration showed weak correlations with SG for both 34-month-old and 62-month-old trees. However, when the two age classes were combined, the strength of the relationship was improved significantly, with a correlation coefficient ranging from 0.71 to 0.77 with respect to SG determined from strip samples and from 0.59 to 0.72 with respect to SG determined from wedge samples. The drill penetration depth had a significant effect on the relationship between average amplitude and SG. A clear trend of weakening correlation was observed with increasing drill penetration. As a result, the average resistance amplitude of a half-diameter drilling (from bark-to-pith) is more advantageous for assessing the SG of young Eucalyptus trees than a whole-diameter drilling.