Wettability of Sitka spruce timber stored in a Scottish sawmill yard

Kiln-dried and air-dried Sitka spruce battens were exposed to outdoor weathering within stickered, close packed and wrapped packs and at the upper surface of these packs. A four-week exposure period was used in James Jones and Sons Ltd. sawmill yard near Aboyne, NE Scotland. The wettability of batten samples removed from the packs of timber was determined by a drop contact angle method using a video tape technique. Timber exposed to air drying before weathering in the experimental packs generally had a greater wettability than kiln-dried timber at the end of the exposure period. However, kiln-dried timber stored in stickered packs developed a greater wettability than similarly stored air-dried timber, suggesting that the kiln drying process increased the susceptibility of timber to developing increased wettability. Close-packed timber protected from sunlight and rain water, by covering the upper surface of the pack with microporous plastic sheeting, maintained a lower wettability than unprotected close-packed or stickered timber. Fungal spoilage was unlikely to develop on timber stored in pack types which developed high timber wettability, the storage conditions leading to an increase in wettability were adverse to fungal development. Kiln-dried timber stored in stickered packs in the sawmill yard may become particularly vulnerable to fungal attack if subsequently exposed to damp conditions in service. Received 15 October 1998     

石场复绿工程施工技术

简述石场复绿整治方式,详细介绍现浇法板槽施工复绿技术.     

加强木材货场管理提高林场效益

通过制定并实行严明的固定货场木材进出仓制度;实行分规格整堆,木材排列商品化、超市化;推陈出新,防止木材降等变质;把好木材进出仓检量关,确保进出仓数据准确;做好优质服务,创建文明窗口;做好木材进销库台帐和报表,及时准确提供数据;做好安全生产防火及防盗工作七个方面的工作,就不会发生木材亏仓和安全事故,并能取得更显著的经济效益.     

中国木材市场研究

通过对商品材、农民自用材、人造板用材及进口材等的测算,确定出全国2000～2002年木材总供给,其中2002年为2.01亿m3。同时,从工业与建筑用材、农民自用材及出口几个方面测算全国2000～2002年的木材消耗,其中,2002年木材总消耗为2.14亿m3。2002木材供需矛盾有所缓和。     

Structural health assessment of in situ timber: An interface between service life planning and timber engineering

Abstract

The in situ assessment of timber structures has gained considerable attention in recent years due to some unexpected failures of public buildings. The assessment of timber, however, has been used in the evaluation of historic structures for a number of years, and the methods employed have evolved from visual observation (which is still one of the most effective ways of evaluating in situ timber) to more sophisticated methods that use various physical phenomena such as stress-wave or X-ray energy attenuation. In the health assessment of timber, effects of biotic elements such as insects and fungi are of interest, which, of course, is always connected with the presence of water in wood. The structural assessment encompasses questions related to the structural integrity of in situ members and the performance of components and the system. The structural health assessment not only focuses on biotic elements but also attempts to quantify engineering properties of the material such as strength degradation, modulus of elasticity, loss of cross-section, extent of checks, and other quantitative parameters needed for subsequent evaluation of the structural system, frequently expressed as load-bearing capacity. Service life planning of a structure is a complex issue that is related not only to the materials but also the environment and the use of the structure. Assessment of the health and properties of existing timber elements yields a piece of information that is necessary but not sufficient for the service life estimate. In the evaluation of structural timber, a mere use of various assessment techniques is not sufficient and usually an involvement of disciplines such as wood anatomy, wood physics, and statistics is needed. A reliable estimate of the parameters of in situ timber requires careful planning of measurements (experiments) since the material is highly variable and any statement about the properties of an element or even the entire system must reflect the random character of the wood properties. This paper will summarize the state-of-the art methods used in the assessment of in situ timber and analyze the strengths and the weaknesses of selected methods. An attempt will be made to outline future directions in the development of in situ assessment methods.     

硬杂小径木材干燥技术初探

我国森林资源中小径材的蓄积量占有相当大的比重,其中以硬杂树种数量最多。小径材具有带髓心、弯曲度大、节疤多等自然生长特征及干燥易裂开等问题,给干燥技术和后续加工增添了很大难度。通过对柞木、桦木等树种小径材的实验室及工业试验,认为:硬杂小径材在干燥过程中不宜采用高温介质处理,以采用较缓和的水分蒸发强度和中、低温介质为宜,应保持锯材厚度方向较平稳的温度梯度。     

Feasibility of automatic detection of knots in maritime pine timber by acousto-ultrasonic scanning

In order to assess the lengthwise variation of mechanical properties of maritime pine (Pinus pinaster Ait.) a study on the possibility of automatically detecting knots by ultrasonic readings across the grain was carried out. A through-transmission acousto-ultrasonic (AU) setup was implemented allowing acquisition of AU profiles along the central mid-third of each specimen. An algorithm was proposed and successfully implemented for enhancing variations on the AU profiles due to knot presence. Discriminant analysis was applied to the AU profiles. The results show the possibility of automatically differentiating clear wood zones from zones with a knot area ratio value above 20% or 30%, with a success rate of 75% to 83% depending on the dimension of the specimens tested.This research project was supported by the Foundation for Science and Technology (FCT) under contract Nos. PBIC/C/AGR/2296/95 and POCTI/33967/AGR/2000     

Elastic layer model for application to crack propagation problems in timber engineering

A fracture mechanics model for analysis of crack initiation and propagation in wood is defined and applied. The model has the advantage of being simple, yet it enables reasonably general and accurate analysis commonly associated with more complex models. The present applied calculations are made by means of the finite element method and relate to progressive cleavage fracture along grain. The calculations concern a tapered double cantilever beam specimen and an end-notched beam. Comparisons are made of experimental test results. The fracture properties of the wood are modelled by means of a very thin linear elastic layer located along the crack propagation path. The properties of the layer are such that the strength and fracture energy of the wood are represented correctly. This makes a single linear elastic calculation sufficient for strength prediction. Both crack development and pre-existing cracks can be analyzed. Both material strength and fracture energy and stiffness are taken into account, their relative influence on structural strength being different for different elements. The fracture layer is in the finite element context represented by joint elements. Propagation of a crack can be analyzed either by a series of elastic calculations corresponding to different crack lengths or by use of a finite element code for non-linear analysis. The computational results include sensitivity analysis with respect to the influence of the various material parameters on structural strength.     

人工针叶用材林生态系统涵养水源功能的研究

从树冠截留降雨、枯落物持水及土壤蓄水三个方面对辽东山区人工针叶用材林生态系统的涵养水源功能进行了定量研究。结果表明:各人工针叶用材林生态系统树冠的截流率为18.3%~28.5%;枯落物贮量为10.1~19.4 t.hm-2,枯落物最大持水量取决于枯落物贮量及其最大持水率,最大持水率为自身干重的1.5~2.5倍;0~40 cm土层的土壤蓄水量为840~1520 t.hm-2。综合分析表明:6种人工针叶用材林的涵养水源功能主要决定于土壤蓄水量,树冠截留雨水和枯落物持水起辅助和调节作用,其中,长白落叶松林的涵养水源功能最强,其次是华山松林、日本落叶松林、红松林、油松林,而云杉林的涵养水源功能相对最弱。