实木拼接地板框架式基材的结构与性能评价

采用速生杨木和桉木,设计一种带侧拼条的实木拼接地板基材,并与三层、多层桉杨复合板地板的基材进行尺寸稳定性的比较。结果表明:带侧拼条的实木拼接结构可有效减小基材的吸湿膨胀率及翘曲度;当采用桉木表板及芯板、杨木底板;侧拼条断面尺寸为12.5 mm×16 mm的组合结构时,地板基材的各项性能优良。     

板式T型构件圆棒榫连接节点稳健优化设计北大核心

为减少家具的质量波动并延长其使用寿命,将稳健设计思想引入板式家具的结构设计中,对以多层板为基材的板式家具T型构件,进行稳健优化设计。试验选取板式家具中最常见的连接件——圆棒榫为优化对象,通过田口法,研究圆棒榫的直径、长度、材料三个因素对18 mm厚多层板T型构件抗弯性能的影响。将抗弯极限承载力设为目标质量特性,信噪比(S/N)作为衡量产品质量稳定性的指标。结果表明:以多层板为基材的T型构件抗弯强度随圆棒榫直径和长度的增加而增强;三种材料中,荷木圆棒榫表现出最好的性能;圆棒榫直径对构件的抗弯性能影响最大。优化后,长为50 mm且直径为10 mm的荷木圆棒榫为最稳健设计方案。三种设计因素中,优化后板式T型构件的抗弯极限承载力增强21.07%,信噪比提高4.42%。试验表明:基于稳健设计原则的田口法可有效增强板式家具T型结构节点的质量稳定性,进而实现板式家具结构质量稳定性的提升,延长家具的使用寿命。     

齿榫类型及参数对指接竹规格材性能的影响

以竹规格材为研究对象,分别探讨指榫类型(垂直型和水平型)、齿榫参数(Ⅰ、Ⅱ、Ⅲ型齿榫)和嵌合度(0、0.1、0.3 mm)等参数对指接竹规格材性能的影响,结果显示垂直型指榫指接竹规格材的力学性能优于水平型指榫;当嵌合度为0.1 mm,采用垂直Ⅱ型齿榫指接竹规格材的性能最优,与未指接竹规格材相比,指接竹规格材较好地保持了竹材的抗弯和抗拉性能,其抗弯性能和抗拉强度分别满足GB/T 26899—2011《结构用集成材》中机械分等层板力学性能M_E16级和最高级M_E18的要求,具备作为结构材的潜力。     

黄荆木重组材家具结点性能分析

对黄荆木重组材家具结点强度进行测试,选用T型、L型结构,对L型结构进行抗弯强度测试,对T型结构进行抗弯、抗拔强度测试,分析试验结果以及试件在试验中、试验后的情况,探讨自攻螺钉接合、双圆榫接合、三合一连接件接合三种连接方式对黄荆木重组材家具结构的适用性。通过对三种连接方式的抗弯、抗拔强度进行综合分析,结果表明:自攻螺钉接合强度双圆榫接合强度三合一连接件接合强度。若是要使用三合一连接件连接时,要配合其他连接方式进行使用。     

截面尺寸、加载方式和指接形式对落叶松大尺寸结构指接材抗弯性能的影响

【目的】研究截面尺寸、加载方式和指接形式等因素对落叶松大尺寸结构指接材抗弯性能的影响,得出不同试验因素下的抗弯强度特征值,为结构指接材的分级技术提供测试数据和可行性建议,为大尺寸结构指接材的抗弯强度测试标准及其特征值的确定方法提供参考,推动落叶松及其他树种作为结构指接材在建筑结构上的应用。【方法】参照LY/T 2228—2013《轻型木结构-结构用指接规格材》标准,选取2种尺寸(截面尺寸为40 mm×90 mm和40 mm×140 mm)的Ⅱc等级落叶松材料加工成结构指接材,采用数理统计方法检验样本数据的正态性和方差齐性,然后用2个独立样本t检验方法判定试验因素对大尺寸结构指接材抗弯强度和抗弯弹性模量是否有显著影响。【结果】截面尺寸、加载方式和指接形式在特定条件下对抗弯强度和抗弯弹性模量有显著影响。截面尺寸对V形指接侧面抗弯强度和侧面抗弯弹性模量均有显著影响,即截面尺寸大的(40 mm×140 mm)侧面抗弯强度和侧面抗弯弹性模量也大;不同加载方式对抗弯强度没有显著影响,但对截面为40 mm×140 mm试样的抗弯弹性模量有显著影响,即侧面加载方式测得的抗弯弹性模量明显高于平面加载方式;不同指接形式对截面为40 mm×140 mm的试样平面抗弯强度有显著影响,即V形指接的平面抗弯强度高于H形指接的平面抗弯强度,而指接形式对截面为40 mm×90 mm的试样侧面抗弯强度和抗弯弹性模量均有显著影响,即H形指接的侧面抗弯强度和抗弯弹性模量高于V形指接的侧面抗弯强度和抗弯弹性模量。在大尺寸结构指接材抗弯性能检测数据的基础上得到了参数法和非参数法计算的强度特征值,参数法计算的特征值低于非参数法。【结论】落叶松结构指接材完全可用作木质工程材料,宽面承载、V形指接以及适宜的截面尺寸有利于保证结构指接材的抗弯性能。截面尺寸较大的结构指接材在侧面加载条件下,其抗弯强度和弹性模量更易受到加载方式和指接形式的影响,因此在保证强度的前提下不建议使用大截面尺寸的结构指接材;侧面抗弯强度也极易受到各试验因素的影响,应尽量避免这种使用方式。强度特征值的计算建议采用非参数法,但是当样本数量不够大时仍会出现参数法计算值低于非参数法计算值的结果,此时建议采用2种方法的低值。     

户外用重组木加速老化耐久性能的评价

采用杨木和落叶松疏解单板制备重组木,参照我国三循环水煮标准和美国六循环试验方法标准加速老化处理,并测定其力学性能和尺寸稳定性。结果表明:两种老化处理后重组木的力学性能和尺寸稳定性均下降,但抗弯性能仍能满足GB/T20241-2006《单板层积材》中结构用材的要求,尺寸稳定性满足GB/T30364-2013《重组竹地板》中室外地板的要求;三循环水煮试验条件较六循环试验条件更严酷,适用于对使用性能要求更高的重组木的性能评价。     

装饰面板及地板结构对实木复合地板导热性能的影响

通过对4种树种的面板和3种不同结构的实木复合地板的导热性能进行温升变化测试分析,测量地板的温度变化,探讨不同的装饰面板及地板结构对不同实木复合地板导热性的影响,旨为改善地热地板导热性能提供技术支持。研究结果表明:装饰面板的种类对实木复合地板的导热性能有明显影响,以黑胡桃作为装饰面板的实木复合导热性能最好,桦木次之,槭木导热性能最差,这主要是由于密度越大的装饰面板,导热性能越好,传热越快,热量损失也越少;地板结构对导热性能也有影响,面板为锯切薄板的三层实木复合地板的导热性能较好,多层实木复合地板的导热性能较差。因此,作为地热地板使用的实木复合地板,其装饰面板应该选择较大密度材种,且为锯切薄板为佳。     

小径材家具榫卯结构的强度研究

以陕西产苹果木小径材为基材,对不同截面形状、断面尺寸的零件"T"型榫卯接合节点进行抗弯和抗拉性能研究。结果表明:在榫卯配合参数一致时,构件节点接合强度随着零件断面尺寸的增大而提高;零件断面尺寸相同时,圆形截面的节点接合强度优于方形截面;同等条件下,小径材榫卯接合节点的抗拉强度明显高于抗弯强度。     

体育馆用木质地板结构的动力特性测试研究

为更好地对体育馆用木质地板的结构性能进行评估与结构优化设计,以南京市两座体育馆的地板为研究对象,采用瞬态激励法,研究分析3种地板结构的自振频率和阻尼比参数。结果表明:3种地板结构均符合建筑舒适度要求;在各组成材料种类和规格相同的前提下,3种地板结构阻尼比由大到小顺序为固定式双层龙骨地板结构、悬浮式单层龙骨地板结构、悬浮式双层龙骨地板结构;与固定式地板结构相比,悬浮式地板结构具有低阻尼比特性,在结构振动过程中能量耗散慢,冲击吸收率较小,对冲击的缓冲能力好,即整体结构的回弹性能好;与单层龙骨构造地板结构相比,双层龙骨构造的地板结构具有低阻尼比特性,结构的冲击吸收率小,回弹性能好。研究结论具有一定的工程应用价值。     

七种多层地板的结构和物理力学性能分析

对市售常见七种多层复合木、竹地板进行了结构观察和物理力学性能测试。分析结果表明，七种地板试件均可满足地板的使用要求。对某些品种提出了进一步提高其性能质量的改进建议。     

杨木—秸秆层合梁失效分析与优化设计

分析了杨木一秸秆层合梁在弯曲变形中的失效情况,并根据实际需要,在层合梁结构总厚度一定的情况下,以梁的弯曲变形和弯曲应力为约束,以减少复合结构的总质量为目标,利用ANSYS有限元工程分析软件对梁的横截面结构尺寸进行优化设计.     

Development of test methods for wooden furniture joints

Abstract

Joints are generally the weakest part of furniture and they are primary cause of failure. To ensure durability and performance of furniture, it is important for a designer to understand the stresses acting on the joints for preparing suitable design and specification of a furniture. Since each type of joint is unique in construction, it is important to know their strength, when subjected to various stresses namely shear, bending, and tensile, by testing the joints. Since there is no established test method for joints, this study was carried out to categorize joints based on their shape, identify the stresses acting over them and develop test methods for testing furniture joints in three modes namely shear, bending, and tension, which are required for designing joints of any furniture and also provide means of comparing strength of different types of joints. Different types of furniture joints were taken for the study and were classified based on their shapes such as L-shaped, T-shaped, straight, and corner joints. Six types of jigs (one type for bending, two types for shear, and three types for tension) were designed and developed for testing the joints, in such a way that any type of joint can be tested in three modes, i.e., bending, shear, and tension using a universal testing machine. The criteria for section of jigs for performing tests on joints, based on their shape and stresses acting on a particular joint, were reported. Tests were carried out using all the six type of jigs to check the suitability of jigs and test methods developed in the study.     

Bending strength adjustments for moisture content for structural lumber

Summary Effects of moisture content on bending strength and section capacity have been studied assuming that strength properties are linearly related to moisture content below the fiber saturation point. The models developed using the linear strength vs. moisture content relationships are compared with quadratic models developed earlier. The linear representation of strength variation with moisture content leads to predicted member bending capacity relationships which show that increases in member bending strength with moisture content will compensate for section property decreases at all bending strength property levels. Comparisons of bending strength and bending capacity models show that the two modelling approaches lead to similar predicted member performance. Simplified procedures are provided for adjusting member bending strength for moisture content which are suitable for materials properties codes or standards.     

Critical section effect during derivation of settings for grading machines based on dynamic modulus of elasticity

Testing of the critical section between the load points in four-point bending testing is required according to [DIN EN 384:2010–08, Structural Timber – Determination of Characteristic Values of Mechanical Properties and Density (Brussels European Committee for Standardization)]. However, strength grading machines based on measurements of the dynamic modulus of elasticity (MOEdyn) benefit as the strength of the weakest section is not always measured when deriving settings. According to the current procedure for derivation of settings, violation of the critical section requirement is accepted. The extent of such violation and its impact on grading settings of strength classes are quantified in two ways using about 3500 recently tested specimens of Norway spruce: empirically and modelled. The results show that for strength grading machines based on MOEdyn, the settings would be higher if the weakest section was always placed between the inner load points. The current procedure, however, leads to lower settings and hence better yields in practice. The settings for machines based on MOEdyn are up to more than 20% higher if the lowest bending strength of the entire board is applied. To treat different grading principles equally, a correction factor for settings of MOEdyn-based grading machines should be introduced – especially for lower strength classes. A simplified factor between 1.00 and 1.20 for standardization is recommended.     

西南桤木木塑复合材料的研究

采用乙烯基类系列单体——丙烯腈(AN)、甲基丙烯酸甲酯(MMA)、丙烯酸(AA)三元共聚单体注入西南桤木木材中，制成新型的高分子复合材料(AMA—WPC)。单体的注入用满细胞法，聚合用热引发法，并采用添加氯化锌对木材细胞壁进行活化等工艺对木塑复合材进行了研究和分析。实验样品按照国标GBl927—1943有关规定进行测试，并结合傅立叶红外光谱和扫描电镜探讨了各因素对AMA—WPC材料接枝率及性能的影响。结果表明：改性后西南桤木木塑复合材料具有优异的物理、力学性能。与素材相比较，AMA—WPC的密度提高了59．8％，顺纹抗压强度提高了76．7％，抗弯强度提高了90．4％，抗弯弹性模量提高22．2％，端面硬度提高102．3％，径面硬度提高153．6％，弦面硬度提高152．2％，吸水率降低56．7％，湿膨胀率降低19．0％。     

Load-carrying capacity of steel-to-timber joints with a pretensioned bolt

Previous experimental studies reported that bolt pretensioning greatly increases the initial stiffness and load-carrying capacity of bolted joints. It is also a matter of great importance to structural designers to understand the effect of pretension on the load-carrying capacities of bolted joints, and this study presents an extended yield model that considers the fastener’s pretension force. In the extended yield model, the load-carrying capacity was defined as the load at a slip of 15 mm. The ultimate fastener bending angle at the yielded cross section equivalent to this joint slip, which was affected by the fastener’s axial force, was iteratively evaluated in numerical analyses. The introduction of bolt pretensioning largely increased the joint slip resistance at initial loading, but it decreased the ultimate fastener bending angle. This decrease of fastener bending angle resulted in a relatively low stiffness hardening (or secondary stiffness), which is caused by secondary axial forces associated with embedment of steel plates into the wood member. Prediction was verified by the tests of 36 steel-to-timber joints under three different pretension forces and two loading directions relative to the grain. Some of the observed load-carrying capacities of the joints, particularly in loading perpendicular to the grain, however, were not as high as those expected by the numerical analyses considering the given pretension forces.     

橡胶木粉／聚乙烯复合材料弯曲破坏载荷与吸水性能研究

为优化橡胶木粉/回收聚乙烯复合材料生产工艺配方,以马来酸酐接枝聚丙烯（ MAPP）和铝酸酯作为偶联剂,调节配方组成制备了3组木塑复合材料试件,对试件的弯曲破坏载荷、吸水性能进行测定,并观察其断面的相容性,结果表明,以MAPP作为偶联剂的试样性能优于使用铝酸酯的试样,同时无机填料添加剂量的适当下调也有利于材料性能的提升,并通过断面分析印证了材料内部界面相互作用越强则复合材料性能也越好。     

Fresh-stem bending of silver fir and Norway spruce

The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from different stem heights were subjected to four-point bending tests. From the bending test records, we calculated stress-strain curves, which accounted for detailed log taper, shear deformation and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest stability protection.     

Glass fibre reinforced holes in laminated timber beams

Summary An experimental investigation of glass fibre reinforcement of glued laminated timber beams is presented. A polyester resin is used both as matrix and adhesive between the reinforcement and the wood. The main part of the work considers beams with large holes tested in three point bending. Circular and rectangular holes, centred at quarter length of the beams make the strength of wood perpendicular to the grain become critical. Great improvements of strength are obtained with the glass fibres. A comparison between various kinds and combinations of glass fibre reinforcement is made. Further, the reinforcement applied as repair of earlier cracked beams is investigated with positive results. One series of beams without holes is reinforced and tested in four-point bending.This reseach project was initiated to improve the ability of glued laminated timber to compete with steel and concrete, in large free span constructions. The project was funded by the Nordic Industrial Fund (NI), Svenskt Limträ AB and the Swedish National Board for Industrial and Technical Development (NUTEK)     

Evaluation of wood-based panel durability using bending properties after accelerated aging treatments

The durability of wood-based panels was evaluated by comparing the bending properties of panels subjected to five accelerated aging treatments with the bending properties of panels that had experienced 5 years of outdoor exposure in Shizuoka City, Japan. In each accelerated aging treatment, methylene diphenyl diisocyanate-bonded panels showed higher bending retention than phenol formaldehyde (PF)-bonded panels. The bending retentions after six repeated cycles of the JIS-B, APA D-1, and ASTM treatments showed a correspondence of nearly one-to-one in the data for the three different treatments. The Shizuoka City 5-year outdoor exposure test data showed that the bending retentions of all panels decreased with time. In particular, the bending retentions of PF resin-bonded particleboard and oriented strandboard made from aspen were less than 30% and 10% of the original values, respectively, after the 5-year exposure period. The deterioration of the bending properties after the 5-year outdoor exposure in Shizuoka City was the same as that for six repetitions of the ASTM treatment.