Grading of Low-Quality Wood for Use in Structural Elements

Abstract

Timber is a sustainable resource, environmentally friendly and aesthetically pleasing. Using locally grown timber as building material leads to economic, social and environmental benefits. Being an organic material, timber is not homogeneous; hence, it is crucial to predict the base material quality. International codes require the use of wood previously graded according to the current regulations in order to verify its reliability when used as structural material. An exhaustive analysis of the state of art of different methodologies and code requirements for structural timber grading is presented herein. Structural timber grading methods and their applicability to low-strength timber is analysed and discussed with reference to Maritime Pine locally grown in Sardinia (Italy). Several physical and morphological parameters such as density, the presence of knots, clusters of knots, grain deviation, warping, annual ring width and moisture content had to be measured. Moreover, mechanical parameters (tensile strength and modulus of elasticity in tension) were measured and analysed in order to identify the strength class of Sardinian Maritime Pine. The operational issues related to the application of the different methodologies and code requirements for structural grading of low-quality wood are also discussed and analysed.

Pressure prediction model in cross laminated timber manufacturing for low-quality lumber

“…The model was divided into three parts for clarity: twist, bow, and cup. Bow and cup were based upon classic mechanics of materials equations, while twist used Lekhnitskii 17 approach considering the orthotropic nature of the wood. Despite being treated individually, the forces computed for each out-of-plane defect will be summed up for a final estimation of a pressure.…”

“…For the twist component of the model, the derived relationship from Lekhnitskii 17 was chosen, which is a particular case of the principle of Saint Venant for rectangular sections in orthotropic materials (see Figure 5 and equation ( 1)). All geometric parameters such as twist angle (θ) and twist length (L1, L2) can be taken from the laser measurement and the surface graph.…”

Feasibility of a Local Production Chain for Structural Timber in Sardinia, Italy

“…The benefits brought by the cross-layer configuration to the mechanical characteristics of the CLT also allow the use of wood species with poor mechanical properties. This has a positive impact in terms of sustainability, as it favors the use of local wood species that have mechanical characteristics lesser than those of Central Europe species traditionally used in the production of laminated timber [11,12]. CLT is very suitable for prefabrication, as it allows most elements to be produced in the factory and essentially only the connections to be left to construction site operations.…”

Prediction of Maritime Pine Boards Modulus of Elasticity by Means of Sonic Testing on Green Timber

“…It is generally characterized by medium-low quality due to the presence of defects (knots, clusters of knots, resin pockets, grain deviation, etc.). Previous research about its yield for structural use showed that about 50% of the boards had to be rejected due to their defects [40][41][42], so that the possibility of defining the structural quality of the boards already in the wet state is a fundamental step to ensure the sustainability of the entire production process. In fact, the ability to provide a pre-grading on wet boards could significantly increase the profitability by saving the cost of drying and subsequent processing for non-structural grade boards sold at the same price whether wet or dry.…”