结构用胶合木性能若干影响因素

以落叶松、杉木为研究对象,研究了影响胶合木强度性能的齿顶宽、指接方向、指接单元等级、指接头、层积施胶量和压力等若干重要因素.试验选取744块落叶松锯材、2516块杉木锯材,采用2种结构用胶、5种齿长、2种指接单元等级、6种层积涂胶量、5种层积压力等作为指标变量,测试了指接材抗弯、抗拉强度和层积材的胶合性能.结果表明：指接材的强度不总是随齿长的增大而提高,其胶合后的强度主要受同截面内齿顶宽累积量所决定;垂直指接材的平向抗弯、顺纹抗拉强度不低于水平指接材,指接方向应由产品的承载方向确定;指接工艺不会降低大尺寸指接材的强度设计指标;层积施胶量和压力应与使用设备的实际产出相协调.     

指接足尺层板胶合木梁抗弯试验研究

目前层板胶合木梁的研究主要按照国家规范进行标准尺寸的抗弯强度试验,不能为工程中常用的大尺寸、小跨高比的胶合木梁的力学性能提供依据。针对这一问题,设计制作了3组不同梁高指接足尺层板胶合木梁,对其进行抗弯性能试验研究,着重对其抗弯性能、破坏形态及机理进行探讨,并分析截面高度对其力学性能的影响。结果表明:足尺层板胶合木梁有纯弯段梁底纤维拉断、弯剪段梁底指接纤维拉断及脱胶三种弯曲破坏形式。排除胶接质量的影响,梁高为300mm和400mm时为梁底纤维拉断破坏,梁高为500mm时为弯剪段梁底指接纤维拉断破坏,且均为脆性破坏。胶合质量是影响木梁抗弯强度的主要因素,木节、指接位置及梁高对其抗弯性能及破坏形式均有一定影响;在保证胶结质量的前提下,层板胶合木梁具有较稳定的抗弯承载力及弹性模量,且其抗弯承载力随着梁高的增大而逐渐减小。研究结果具有较强的工程应用价值,可为层板胶合木梁的工程设计及应用提供参考。     

基于灰度与彩色图像处理的木破率测量法

提出了基于灰度、彩色图像处理的正交胶合木木破率数字快速测量方法，并且通过对以落叶松和碳化竹为基材、酚醛树脂和异氰酸酯为胶黏剂的试样进行干湿剪切条件下的破坏试验，验证了该方法的可行性.结果表明：基于灰度与彩色图像处理法计算出的木破率均与试验值符合较好，满足了工程应用的要求；木材破坏层次和木破率图像颜色的变化对测量精度的影响较大，胶黏剂固有色的变化对阈值分割的木破率灰度图像测量法的精度影响较大，环境影响则是像素统计的木破率彩色图像测量法的主要影响因素.     

不同组胚层板胶合木力学性能研究

利用花旗松、欧洲云杉、赤松3种树种的规格材制作胶合木。通过对胶合木加工过程中相关力学性能检验,发现3种树种的组胚层板(层板、指接层板)抗弯强度有不同程度折损。控制合理的生产工艺可达到胶合木相应设计强度等级。通过测试材料组胚单元基本力学性能及成品设计值,可为胶合木产品提供检测依据。     

胶合木曲梁横纹应力及开裂研究

研究了胶合木曲梁纯弯曲区横纹应力与各向同性材料曲梁纯弯曲区径向应力.结果表明：胶合木曲梁纯弯曲区横纹应力与各向同性材料曲梁纯弯曲区径向应力分布规律大致相同,都是中性轴附近大,随距中性轴距离的增大而减小;胶合木曲梁纯弯曲区横纹应力以胶缝为分界线,呈锯齿状分布,层板髓心位置对应力峰值影响较大,髓心位于层板大面的胶合木其横纹应力最大,应力峰值是简化计算式的1.5倍.根据胶合木的应力特点和脆性开裂特点,建立了胶合木开裂损伤本构模型,并编制了相应的有限元软件ABAQUS用户材料子程序UMAT,成功预测了曲梁的横纹开裂及其极限承载力,与曲梁承载力试验相比,其刚度和极限承载力吻合良好.     

胶合竹木梁抗弯性能试验研究

以重组竹、胶合竹和云杉为层板材料,设计制作10组共计30根由六层层板胶合成的胶合竹木梁试件,并对其进行受弯性能试验,试验参数包括工程竹种类、层数、布置位置等;分析了各组试件的破坏模式、等效弹性模量、屈服荷载、承载力、变形能力及应变分布,通过不同胶合竹木梁组合方式的对比,提出最优组合方案;并根据组合梁的应变分布和简化本构关系,采用分层叠加法计算了各种层板组合方式胶合竹木梁的受弯承载力,同时对层板间胶层抗剪强度需求进行了分析。结果表明,在云杉胶合木梁的受拉一侧胶合工程竹板后,胶合竹木梁破坏时的变形能力较相同尺寸的纯云杉胶合木梁有明显提升,提升幅度为64.8%~123.9%;而在云杉胶合木梁的拉压区都胶合工程竹板后,承载能力和变形能力较相同尺寸的纯云杉胶合木梁都有显著提升,承载力提升幅度为63.9%~97.0%,破坏时的变形能力提升幅度为124.8%~167.5%;上部一层和下部两层木板替换成工程竹板后,承载力较纯云杉胶合木梁提高了82.3%,基本接近纯工程竹梁的力学性能,是较优的层板组合方案。     

基于SAP2000的预应力胶合木张弦桁架结构分析

根据东北落叶松胶合木顺纹抗拉和抗压强度实验结果,提出预应力胶合木拉杆及24 m跨预应力胶合木张弦桁架设计方案,通过SAP2000建立模型,研究了张弦桁架(拱架)的桁架厚度、张弦垂度、荷载分布方式对结构内力分布以及破坏模态的影响,得出了一些有益的结论。     

正交胶合木墙板火灾炭化试验研究

采用耐火试验炉,开展了正交胶合木墙板试件在标准火灾条件下的炭化试验,研究正交胶合木墙板内部不同深度处的温度变化曲线、炭化深度和炭化速率等变化规律,分析不同胶粘剂对层板脱落和炭化速率的影响,对比层板脱落或不脱落情况下炭化深度的计算方法。结果表明,对于采用普通PUR 胶的试件,第一层层板50～60 min 时发生脱落,脱落后试件的炭化速率明显变大;采用耐热型PUR 胶的试件,未出现明显的层板脱落现象,炭化速率恒定,与欧洲标准中的普通木结构的名义炭化速率0.65 mm/min 相当。     

胶合木植筋黏结锚固性能试验研究

对25个胶合木植筋（带肋钢筋）试件进行对拉试验,研究植筋长细比(λ=la/d)及胶层厚度对胶合木植筋的连接承载力及界面黏结性能的影响,并对试件的破坏形态和破坏机理进行分析。为获得胶层界面黏结应力的分布,设计钢筋内贴片试件进行试验。结果表明,试件的破坏形态主要有钢筋拔出、木材环向剪切、木材劈裂、钢筋屈服;植筋连接的拉拔承载力随锚固长度及胶层厚度的增加而增大,当植筋长细比λ达到12.5时,试件发生钢筋屈服破坏,属延性破坏模式;锚固长度与胶层厚度对植筋 木材的黏结性能影响显著,不同锚固长度和胶层厚度的试件,其胶层界面黏结应力分布符合Volkersen(1938)理论,总体上沿锚固长度方向呈两端附近大而中部小趋势;在胶层厚度2~6mm范围内,随着胶层厚度的增加,钢筋-胶层界面与木材-胶层界面平均黏结应力呈不同的变化规律,前者随胶层厚度的增加而增大,而后者随胶层厚度的增加而减小,且胶层厚度的适当增加有利于加载端部的黏结应力峰值的降低。     

层板胶合木结构受压性能试验研究

为了避免过度依赖国外木材和木结构技术,高效利用我国的木材资源,选取SPF（云杉—松—冷杉）、杨木、东北落叶松和桉木,分两个批次8组,加工成48个立方体试块,对其弹性模量、顺纹抗压强度和破坏形态进行试验研究.结果表明,与1级SPF相比,杨木的弹性模量比较接近,东北落叶松和桉木的的弹性模量分别提高了23.97％和14.29％,杨木和东北落叶松的顺纹抗压强度分别提高了38.18％和12.48％,桉木的强度降低了7.59％,立方体试块破坏形态主要为剪切破坏和劈裂破坏,总体上国产木材的抗压性能优于进口SPF,研究结果可为层板胶合木结构的选材提供依据.     

Structural performance of the finger-jointed strength of some wood species with different joint configurations

This study was conducted to evaluate the effects of adhesive type, wood species, and finger joint configurations on structural performance of the finger joint. The wood species studied were oriental beech (Fagus orientalis lipsky.), oak (Quercus robur), Scots pine (Pinus sylvestris lipsky.), poplar (Populus tremula lipsk.) and Uludağ fir (Abies bormülleriana Matff.) and adhesives were poly(vinyl acetate) (PVAc), Desmodur-VTKA (D-VTKA). However, there is little information available concerning the bending strength and modulus of elasticity for finger joints in these field. In this study, it was aimed to determine the bending strength and modulus of elasticity for finger joints. For this purpose, samples were tested according to the TS EN 310 standard. It was observed that the highest bending strength and modulus of elasticity were obtained in beech control (solid wood) samples. As for the finger joints, after the control samples, the highest bending strength value (57.4 N/mm²) was obtained from Oriental beech wood samples having a 21 mm finger length and bonded with PVAc adhesive, the highest modulus of elasticity (8885.3 N/mm²) was obtained from beech wood samples having a 21 mm finger length and bonded with PVAc adhesive. As a result of the effects of finger joints on bending strength and modulus elasticity test, if the length of finger joints increases up to 21 mm, the properties of bending strength increase.     

Visko‐elastisches Verhalten von Holz‐Klebstoff‐Verbindungen unter zyklischer Zug‐Druck‐Belastung

Visco‐elastic behavior of bonded wood under cyclic tensile and compression loading In the present contribution, a test method is used to simulate the static, cyclic loading of adhesive joints due to swelling and shrinking of the wood and to demonstrate the plastic deformation in the low load range. For tensile shear specimens prepared from beech wood and bonded with three different adhesives (MUF, PRF, PUR), the elastic behavior under cyclic tensile and compression loading was investigated and the loss and storage of energy was determined. All tested adhesives showed viscose parts even at a very low load level of 3 MPa. At a load level of 7 MPa, the PRF joints revealed a more elastic behavior than the other. The increased loss energy determined for the PUR bonding indicates a softening of the adhesive joint.     

一种测试胶体与钢质基体间粘结剪切性能的新方法

中国现行国家标准试验方法中的单层金属片搭接接头拉伸剪切试件,由于粘结区剪应力分布极不均匀,并在粘结面上产生很高的拉应力,试验结果不能真实反映胶体与金属基体之间的粘结强度,只能作为胶体质量的检验指标,不能作为强度条件使用.该文采用的组合圆盘粘结试件用于胶层粘结剪切性能测试时,胶层及结合面剪应力分布很均匀,均匀系数可达0....     

自修复混凝土修复性的试验研究

采用普通混凝土为基材,分别制作了内注环氧树脂、氯丁万能胶、聚氯乙烯胶粘剂为修复剂的简支梁,进行弯曲试验,测试这三种胶粘剂的修复效果,并比较分析其修复能力和造成修复差异的原因,得出氯丁万能胶修复效果最好的结论。     

化学加固琉璃与自然气候下抗老化观测

环氧树脂粘接剂，在抗压，抗拉、抗剪等性能方面都超过传统粘接材料。为了得到环氧树脂在自然气候下老化的科学数据，将五台县佛光寺和介休县后土庙设为观测点。分别经过10年和5年的观测。观测构件均没有发现环氧树脂龟裂、松脆等老化现象，粘接处也没出现碱化和分离现象。这说明环氧树脂粘接剂，在抗压，抗拉、抗剪等性能方面都超过传统粘接材料。     

Untersuchungen zum Einfluss von Temperatur und Holzfeuchte auf das Versagensverhalten von ausgewählten Klebstoffen bei Zugscherbeanspruchung

An drei verschiedenen Klebstoffen wurde der Einfluss von Temperatur und relativer Luftfeuchte auf die Scherfestigkeit im Zugscherversuch geprüft. Es wurden zwei handelsübliche Klebstoffe (PVAc, Harnstoffharz) und ein labortechnisch hergestellter 1KPUR bei erhöhter Temperatur und relativer Luftfeuchte geprüft. Ergänzend wurde mittels Video Image Correlation die Verzerrung im Bereich der Klebfuge ermittelt und daraus ein Schubmodul der Klebfuge berechnet. Studies on the influence of temperature and timber moisture on the failure behaviour of selected adhesives under tensile shear load. The influence of temperature and relative humidity on shear strength was tested in a tensile shear test with three different adhesives. Two standard adhesives (PVAc, urea resin) and a 1KPUR (one‐component polyurethane adhesive) produced in the laboratory were tested at a high temperature along with relative humidity. In addition distortion around the glue joint was measured by means of video image correlation and a shear modulus of the glue joint calculated from this.     

碳纤维布(CFRP)与钢结构粘结性能的试验研究

采用弯拉试验方法对碳纤维布与钢构件粘结性能进行了试验。研究了碳纤维布粘贴厚度、宽度与长度对粘结强度的影响。试验结果表明：随着粘贴厚度的增加,极限承载力逐渐增加,但不是简单的线性关系;随着粘贴宽度与钢试件的宽度比值增加,极限承载力逐渐降低;纤维布与钢结构的有效粘结长度大约在120—150mm之间。     

Performance of steel bridge deck pavement structure with ultra high performance concrete based on resin bonding

This research investigated a pavement system on steel bridge decks that use epoxy resin (EP) bonded ultra-high performance concrete (UHPC). Through FEM analysis and static and dynamic bending fatigue tests of the composite structure, the influences of the interface of the pavement layer, reinforcement, and different paving materials on the structural performance were compared and analyzed. The results show that the resin bonded UHPC pavement structure can reduce the weld strain in the steel plate by about 32% and the relative deflection between ribs by about 52% under standard axial load conditions compared to traditional pavements. The EP bonding layer can nearly double the drawing strength of the pavement interface from 1.3 MPa, and improve the bending resistance of the UHPC structure on steel bridge decks by about 50%; the bending resistance of reinforced UHPC structures is twice that of unreinforced UHPC structure, and the dynamic deflection of the UHPC pavement structure increases exponentially with increasing fatigue load. The fatigue life is about 1.2 × 10⁷ cycles under a fixed force of 9 kN and a dynamic deflection of 0.35 mm, which meets the requirements for fatigue performance of pavements on steel bridge decks under traffic conditions of large flow and heavy load.     

钢-混凝土组合梁的有限元参数分析

钢–混凝土组合梁比传统的组合梁更有优势。基于推出试验,建立三维非线性有限元模型,用于分析钢–混凝土组合梁的力学性能。通过数值分析结果和试验结果的对比,证实了该模型的有效性。特定参数影响分析包括:黏合剂的弹性模量,黏结层的厚度,混凝土强度,黏结强度及黏结面积。数值结果显示:当黏结层的厚度为3～15mm时,大多数分析的参数对钢-混凝土组合梁的影响非常显著。     

Optimisation of the shear stress transfer in structural bonded assemblies using a curved bonded joint geometry

Structural adhesive bonding is coming into increasing use in civil engineering either for strengthening operations involving the adhesive bonding of external reinforcements or to replace traditional assembly techniques in new structures. However adhesive bonding induces stress concentrations at the edges of the joint, which have been studied by a large number of researchers in order to reduce these phenomena and increase the capacity and service life of the assembly. These studies are all, therefore, concerned with optimizing shear stress transfer in adhesively bonded joints. This paper investigates the role of the hydrostatic pressure on the ultimate capacities of common civil engineering adhesives. This led us to investigate a new joint geometry, the “curved” bonded joint that naturally creates compressive stresses on the edge of the joint. Initially, classical modelling is conducted to determine how the geometry affects the stresses in the joint. Then, fracture mechanics is used to investigate crack propagation. After this theoretical modelling, several experimental investigations are presented. These are quasi-static tests which compare classical shear lap joints to curved joints. The experimental results are then exploited using the modelling described before. Additional testing is currently in progress, but the curved bonded joint seems to hold good prospects and a patent has been filed.