钢夹板—螺栓连接胶合木抗剪性能试验研究

为了研究钢夹板—螺栓连接胶合木的抗剪性能,以东北落叶松胶合木—钢夹板螺栓连接件为研究对象,共设计12组(36个)钢夹板—螺栓连接胶合木进行剪切静载试验,结合理论分析和试验结果表明:材料规格和螺栓数目相同时,螺栓错列布置的抗剪能力明显高于并列布置;随着螺栓列数的增加,屈服荷载与极限荷载明显提高,且螺栓列数与剪切荷载呈非线性关系;在多螺栓连接件中,随着螺栓间距的增大,连接件的初始刚度与屈服后刚度呈减小趋势,极限荷载与屈服荷载呈增大趋势。     

木-钢组合箱梁抗弯性能试验及有限元对比分析

【目的】为促进木结构在大型工程中的应用范围,本研究提出了一种以落叶松胶合木板作为上下翼板、焊接冷弯薄壁槽钢作为腹板并通过螺栓连接的木-钢组合箱梁。【方法】采用分级加载的方式分别对3根木-钢组合箱梁和1根木箱梁进行弯曲加载试验,观测组合箱梁和木箱梁在荷载作用下翼缘和腹板的应变变化、挠度的发展、破坏过程及形态变化,研究其抗弯极限承载力和抗弯刚度等力学性能,并基于ABAQUS建立了有限元模型对组合箱梁及胶合木箱梁进行数值模拟分析。【结果】组合箱梁的翼板与腹板组合性能较好,最终均为下翼缘木板受拉断裂的破坏模式,同时伴随着钢材局部屈曲和上翼缘木材的局部劈裂等破坏;木箱梁为腹板顺纹剪切破坏。相比胶合木箱梁,组合箱梁的抗弯极限承载能力平均提升了30.33%,但初始刚度平均降低了34.42%;根据翼板横向应变分布计算了木箱梁和木-钢组合箱梁上翼缘的剪力滞系数以及有效分布宽度。有限元模型与试验结果吻合良好,能有效预测木-钢组合箱梁及胶合木箱梁的弯曲性能。【结论】木-钢组合箱梁充分发挥了木材和钢材的力学性能,相比于纯木箱梁,抗弯承载力提升显著,说明木-钢组合箱梁是一种科学合理的组合形式,研究成果可为木-钢...     

胶合木拱桥静力性能全桥模型试验与数值分析研究

落叶松胶合木是我国自产加工的工程材,开展了一座落叶松胶合木人行拱桥的静力模型试验与有限元数值分析。模型比例1/3,模拟跨径38.07 m的实际木结构拱桥。模型拱肋、横撑、拱上框架及桥面板等主要构件均采用落叶松胶合木及钢板螺栓连接,连接件与支座采用Q235钢。对制作模型桥木材,进行了顺纹拉、压试验和抗弯弹性模量与泊松比试验。考虑结构配重、人群荷载及拱肋控制截面最不利受力,分9个工况加载,测试拱肋的应变与位移。采用有限元软件,针对木拱桥模型,建立有限元模型进行数值分析。试验与分析结果表明,落叶松胶合木拱桥的强度与刚度满足我国木结构设计规范要求,证明了落叶松胶合木可以用于实际工程。     

空心胶合木-钢插板螺栓节点承载力试验研究

为研究空心胶合木-钢插板螺栓连接节点承载力及延性性能,探讨了不同胶合木宽度和螺栓直径对破坏模式的影响,分析了不同宽径比、承压宽度对节点承载力、延性等的影响。结果表明:增加宽径比及承压宽度,可有效提高节点延性。宽径比12.5~16.4的节点延性较佳;宽径比10.0~10.9是单、双塑性铰破坏模式的临界点,可作为工程设计参考值。     

胶合木-混凝土组合楼板受弯性能有限元分析北大核心

为研究胶合木-混凝土组合楼板受弯性能,采用ABAQUS有限元软件建立9个组合楼板模型,其中楼板部分采用实体单元,钢筋采用桁架单元。有限元分析采用三分点加载方式,研究组合楼板模型纯弯段混凝土强度、连接方式、混凝土层厚度以及胶合木厚度等因素对组合楼板抗弯强度的影响,并探究组合楼板纯弯段的破坏形态。结果表明:采用胶结加抗剪连接件连接的组合楼板其受弯极限承载力比采用胶结连接的组合楼板提高了11.35%,比采用抗剪连接件的组合楼板提高了32.64%。混凝土强度、胶合木层厚度及混凝土层厚度的增加均能提高组合楼板的极限承载力。胶合木-混凝土组合楼板表现出良好的抗弯性能,且能减少混凝土用量,发挥木材的优势,值得在实际工程中推广应用。     

斜螺钉连接胶合木梁柱节点抗侧性能研究

设计了一种适用于装配式胶合木建筑的新型梁柱斜螺钉连接节点。采用全螺纹自攻螺钉将金属钢板和梁、柱分别连接,通过高强度螺栓完成梁和柱的基础连接。试验表明:3组斜螺钉连接胶合木梁柱节点低周反复试验得到的弯矩-转角滞回曲线,在拉向和压向加载循环中基本对称,呈"反S形",转角较大时,表现出一定的"捏缩"现象,随着循环次数的增加,骨架曲线的斜率逐渐减小,出现了刚度退化,表明节点在反复荷载作用下因累积吸收的能量而产生损伤;全螺纹自攻螺钉可以有效地将胶合木梁柱节点处的荷载传递到胶合柱的内部,具有较强的抗侧承载性能;节点在变形角1/100循环前,耗能能力处于较低水平,随着转角的增大,耗能能力明显增强,直至最后循环,节点仍保持较强的耗能能力。     

典型直榫梁柱节点在现代木结构中的应用研究

基于Abaqus有限元分析,对不同榫长的实木榫卯连接梁柱节点和榫长为75 mm的不同层数的正交胶合木(CLT)榫卯连接梁柱节点进行数值模拟,分析其受力状态并提取荷载-位移曲线,与使用金属连接件连接的梁柱节点承载力进行对比,探究将榫卯连接应用在现代木结构中的理论依据。研究表明:竖向荷载作用下,榫长75 mm的榫卯连接梁柱节点承载能力处于M8和M10螺栓连接梁柱节点的理论承载力之间;当榫长增大时,节点的最大承载力逐渐提高,榫长150 mm的榫卯节点承载力已经略微超过M12螺栓连接时的理论承载强度,说明榫卯连接梁柱节点在承载能力上可以满足现代木结构建筑的使用要求。由于榫卯节点的承载力主要受到顺纹抗压强度的影响,因此相比于实木连接榫卯节点,CLT榫卯节点的承载力无显著提高。     

日本柳杉木构件内嵌钢填板销连接横纹承载性能

【目的】研究日本柳杉木构件内嵌钢填板销连接在横纹荷载作用下的破坏机制和承载性能,为木结构梁、柱构件金属件连接时梁端销连接设计提供依据。【方法】在梁端部开槽钻孔后将单个钢销连接到内嵌钢填板,分别对日本柳杉锯材梁和胶合木梁进行横纹荷载作用下的弯曲剪切加载试验,按照日本通行数据分析方法确定销连接短期承载力标准值,并与5个不同国家标准规定的屈服荷载计算值进行比较。【结果】加载初期,荷载-位移曲线呈线性关系,构件处于线弹性阶段,随着位移增加曲线呈非线性,构件进入弹塑性阶段,当位移增加到一定数值,梁端出现初始脆性开裂,荷载瞬间急速减小,随后荷载又随位移增加再次上升,加载至极限状态时,梁构件产生劈裂破坏丧失承载力;最终的破坏形态为梁构件沿销孔水平剪切面开裂、销连接屈服模式Ⅲ型;通过足尺试验得到断面尺寸120 mm×240 mm锯材梁和胶合木梁的钢填板单个销连接短期承载力标准值取决于屈服荷载,分别为8.6和13.7 k N,初始开裂对应的荷载平均值分别为15.0和21.1 k N,屈服荷载平均值分别为14.50和15.00 k N,最大荷载平均值分别为27.0和30.8 k N。【结论】胶合木梁钢填板销连接的最大荷载和屈服荷载平均值均大于锯材梁,且变异系数明显小于锯材梁,含水率低而变异小,从而导致试验获得胶合木梁销连接的短期承载力标准值明显高于锯材梁,当销连接作为中小断面梁柱构件的主要连接方式时,宜选用强度等级确定、质量合格的胶合木作为木构件,比锯材具有更高的连接承载力。梁端销连接节点承载力与单个销连接承载力和销数量具有良好的相关性,可作为梁柱节点梁端销连接设计依据。销连接部位发生销屈服后木材开裂,初始开裂取决于木材抗剪强度、横纹抗拉强度和销所在的梁高部位以及销孔到梁端的距离,发生初始开裂后钢销仍能起到支撑作用,连接节点延性较好;锯材梁和胶合木梁短期承载力标准值与标准中规定的屈服荷载公式计算值吻合度较好。各国标准中关于脆性破坏计算公式均能较好预测销连接木材的脆性破坏,与试验值比较,日本标准对于劈裂破坏的计算值最为接近,欧洲和加拿大标准的计算结果更趋于保守,我国现行标准在销连接设计中尚未考虑木材的脆性破坏,今后应进一步研究完善销连接计算公式和参数,更好地保证木构件连接安全可靠度。     

SPF胶合木植筋抗拔性能研究

采用“拉-拉”荷载模式研究SPF(云杉-松木-冷杉)胶合木植筋抗拔性能,探讨了边距、胶层厚度以及长径比等对胶合木植筋连接抗拔强度和破坏模式的影响.结果表明:边距对植筋连接抗拔强度有显著影响,胶层厚度对植筋抗拔强度有极显著影响,长径比是影响植筋连接抗拔强度的重要因子;植筋连接抗拔强度随长径比的增大而增大,当长径比达到一定值时植筋抗拔强度取决于植筋杆的屈服强度;胶合木开裂、植筋杆拔出和植筋杆屈服是试验中的3种主要破坏模式.     

云杉胶合木钢板斜螺钉连接的剪切性能研究

为准确评价斜螺钉连接钢 木节点的剪切性能,探明其受力机理,以云杉胶合木、钢板和自攻螺钉作为研究材料,测试不同荷载方向与受力情况下斜螺钉连接节点的承载性能,将试验数据与国外规范中的计算模型进行对比,提高了侧边钢板 胶合木(钢 木)斜螺钉连接节点承载性能的预测能力。结果表明:自攻螺钉与剪切面之间的角度变化对其在钢 木节点承受剪 压复合应力的承载力影响不明显,当偏转为剪 拉复合应力时,节点承载力明显增大,并在30°~45°获得最大值;剪 压复合应力时,现行EC5公式计算剪 压节点的极限承载力非常不安全;EC5的刚度预测结果在剪 压复合应力区和垂直剪切面钉入时,与试验值吻合度很高,但对剪 拉区节点的滑移模量没有预测性;将Tomasi模型应用于斜螺钉连接钢 木节点滑移模量理论计算时,在45°~90°时与试验值吻合度极高。单颗自攻螺钉的抗拔刚度计算节点滑移模量的方法极为有效,具有较高的借鉴意义。     

空心胶合木柱轴心受压性能研究

【目的】节能环保理念越来越受关注,木材作为绿色环保的可再生建筑材料可应用在工程中,目前国内木建筑中应用的木柱主要局限于原木圆柱,为了提高木材利用率,同时降低成本,改善受力性能,满足工程需要,提出一种新型的空心胶合木柱,并进行试验研究分析。【方法】使用相同尺寸拱形锯材作为骨架,利用环氧树脂胶粘剂进行胶合,制作3根空心胶合木柱试件进行轴心加载受压试验,研究空心胶合木柱的轴压力学性能,在试验过程中通过仪器记录应变、应力和位移等数据,主要分析木柱的竖向与横向应变、竖向与侧向位移、稳定承载力等特性,并利用ABAQUS有限元软件进行建模对比分析,探讨木柱最终破坏特征。【结果】空心胶合木柱破坏形态主要是整体压屈破坏,达到极限荷载80%左右时,承载能力快速下降,侧向位移随荷载增加而迅速增大,加载过程中存在多个增长台阶;与同截面积原木圆柱比较,理论承载力提高了4.3%,计算得承载能力稳定系数为0.9,材料缺陷对轴心承载力有影响;通过有限元建模分析,材料在弹性阶段理论值与试验值吻合程度较好。【结论】空心胶合木柱应用在实际工程中是可行的,能够满足工程使用需求,充分利用小型锯材,提高了木材利用率,降低了成本,相较于原木圆柱受力性能更好。     

C型木质薄壁结构材的轴压性能

【目的】利用杨木单板制备C型木质薄壁结构材,研究其轴压性能及屈曲变形模式,为新型木质结构材在建筑工程领域的应用提供理论基础。【方法】借鉴冷弯薄壁型钢的截面形式,探讨组坯结构、玻璃纤维布(GFC)、卷边和厚度等因子对C型木质薄壁结构材短柱轴压性能的影响。【结果】顺纹单板组坯结构、表层横纹芯层顺纹单板组坯结构和顺纹横纹交错单板组坯结构的平均极限载荷分别为12.5、14.6和12.97 kN。GFC-杨木单板复合C型木质薄壁结构材试件截面的有效性整体较大,在46.46%~50.21%之间;表层GFC芯层顺纹单板组坯结构与表层横纹芯层顺纹单板组坯结构试件相比,用GFC代替横纹弯曲单板,平均截面面积减少26.90%,质量减少5.17%,而极限载荷提高8.63%。外转角表面贴GFC芯层顺纹单板组坯结构与表层GFC芯层顺纹单板组坯结构相比,极限载荷降低34.17%,且局部屈曲半波发生在翼缘和腹板的中间位置。表层GFC芯层顺纹单板组坯结构、表层GFC芯层顺纹单板组坯卷边宽度25 mm结构和表层GFC芯层顺纹单板组坯卷边宽度50 mm结构,对应实际极限承载力分别为15.86、16.76和18.98 kN。表层GFC芯层顺纹单板组坯卷边宽度50 mm结构与表层GFC芯层加厚顺纹单板组坯卷边宽度50 mm结构相比,芯层杨木单板组坯厚度增加从而截面面积增大52.96%,平均每米质量增加33.33%,极限载荷提高90.31%。【结论】 C型木质薄壁结构材相同层数组坯时,表层横纹芯层顺纹单板组坯结构较顺纹单板组坯结构和顺纹横纹交错单板组坯结构合理,轴向承载性能好;用GFC代替横纹弯曲单板,可增强C型木质薄壁结构材轴向承载性能,表现出塑性破坏模式;仅对C型木质薄壁结构材外转角处表层局部粘贴GFC,不能提高无卷边的C型木质薄壁结构材的轴向承载性能。卷边对C型木质薄壁结构材轴向承载性能有强化作用,在0~50 mm卷边宽度范围内,试件轴向承载性能随卷边尺寸增大而增大。C型木质薄壁结构材芯层顺纹单板总厚度增加,C型材试件轴向承载能力也随着提高。     

An experimental approach to determine pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain

ABSTRACT

A glued-in rods' connection is generally constituted by a group of steel bars bonded by an adhesive into timber elements. In the past, most of the research focused on single-rod connections, in order to exploit the maximum resistance of the connection without accounting for interaction among bars or splitting failure in the timber member due to close edge distances or spacing between bars. Such interaction problems arise when dealing with multiple rods, thus requiring specific investigation to fully understand the behavior of the connection as a whole and to determine its capacity. In both cases, existing test procedures determine bond strength in specific geometrical configuration. The paper aims to determine the pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain differentiating the adhesive failure from the other failure modes. After an initial review of typical applications and existing design procedures, test results on single rod with confined or unconfined test setup on single rod at different embedment depths are presented and discussed, indicating that the confinement has a negligible influence on the pull-out capacity. Subsequently, interaction between bars is investigated by a specific unconfined configuration. The accounted parameters are the embedment depth of the bars, the dimensions of the timber section, and the spacing between bars. Results are discussed and compared with three-dimensional numerical simulations. Both experimental and numerical results suggest that the critical value at which the transition from pull-out to timber-related failure is observed depends on the mechanical properties of the timber and on the properties of the adhesive, such that a single value of spacing should not be provided in design standard if the full capacity of the adhesive is to be exploited.     

空心胶合木梁柱式结构抗侧力性能研究

为研究空心胶合木梁柱式结构体系抗侧力性能,对纯框架及框架-人字撑两种单跨结构试件进行了单调及低周反复加载试验,考察了结构破坏模式、耗能能力、刚度等抗震性能。结果表明:纯框架与框架-人字撑结构均具有一定抗侧力性能,但纯框架结构承载能力较弱,不建议单独用于工程实践;框架-人字撑结构具较大抗侧刚度及承载力,分别为纯框架的6.3倍及2.68倍,但其延性仅为纯框架的67%。两种结构失效前强度退化小于30%,具足够剩余承载力。     

Feasibility of improved slotted bolted connection for timber moment frames

This note examines the feasibility of an improved slotted bolted connection for timber moment frames. In the improved connection, steel tubes are inserted into drill holes in glulam and fixed to the glulam with resin injection. Aluminum splice plates with curved slots, or curved elongated holes, are fastened mechanically by using high-strength bolts that go through the steel tubes. Since the compression due to bolt tension is fully supported by the steel tubes, the reduction of bolt tension due to shrinkage of the glulam can be avoided. The use of slotted aluminum splice plates allows stable energy dissipation due to smooth sliding between the aluminum splice plates and the end surfaces of the steel tubes within the specified range of rotation angle. Through quasistatic cyclic loading tests of two connection specimens, it was demonstrated that stable and nearly rigid-plastic hysteresis loops were obtained whose equivalent viscous damping ratio was more than 30% in the range of rotation angle close to or greater than 1/50 radian. Although further improvement is necessary, the experimental results demonstrate the feasibility and potential of the present connection.     

Comparisons of bearing properties for various oriented glulam using digital image correlation

The goal of this study was to analyze the bearing properties of the differently oriented glulam using digital image correlation (DIC). Six differently oriented specimens associated with three anatomical directions including longitudinal (L), radial (R), and tangential (T), and 12-mm drift pins were used to analyze the bearing properties, including yield load and bearing strength. The highest bearing strength of 22.57 MPa from RL was found, whereas the lowest bearing strength of 6.47 MPa from LR was found. Different strain distributions were observed from the differently oriented bearing specimens using DIC. Different failure ratios of the differently oriented specimens were highly related to the strain distributions. Although the bearing properties were found to be different between the differently oriented specimens, for the connection design aspect, the bearing properties of glulam could be grouped as RL and TL specimens, RT and TR specimens, and LR and LT specimens.     

Study on the estimation of the strength properties of structural glued laminated timber I: determination of optimum MOE as input variable

There have been many attempts to predict the performance of glulam beams. Several approaches have been taken, from early empirical techniques to more sophisticated stochastic methods. In recent years, more emphasis has been placed on the modeling of material properties. Generally, the modulus of elasticity (MOE) has been used as a criterion of laminar strength for the prediction of glulam performance in the traditional models. Most of the current models are based on MOE that was measured using the long span test; that is, they account only for variability between pieces of lumber. Therefore, these models do not account for the variation of material properties within a given piece of lumber. Five methods were considered to choose the appropriate one that could effectively predict the performance of glulam in this study. Prediction of glulam performance was done by the transformed section method. MOEs measured with the five methods were applied to a strength prediction program to compare the actual test results and the predicted results. MOEs used as input variables are as follows: long span MOE of the static bending test, localized MOE of the static bending test, long span MOE of the stress wave test, localized MOE of the stress wave test, and MOE of the machine stress rating (MSR) test. Results of the localized test showed excellent signification compared to those of the long span test. The MSR method, when used as input variable, obtained the most approximate result, so it is considered adequate for predicting the strength of glulam.An outline of this paper was presented at the 48th annual meeting of the Japan Wood Research Society, Shizuoka, April 1998     

Investigation of the structural performance of glulam beam connections using self-tapping screws

The characteristic strength properties of structural glulam connections assembled with self-tapping screws were examined following the ASTM testing procedure in the study. Four screw types with various numbers were designated at each connection of the beam–girder structure with different nailing schedules. The results indicated that the maximum load capacity and dissipated energy of a connection fastened with 10-mm self-tapping screws were higher than those with 8-mm screws. And, the screws with both double-threaded sections and fully threaded shanks were higher than those of single-threaded screws. An improvement on the initial stiffness of a connection was found when the number of self-tapping screws increased. The connections assembled with the toe-nailing approach from the beam’s bottom surface provided higher maximum loading capacity, medium initial stiffness, and a larger ductility factor, resulting in higher dissipated energy with less fragile failure. The derived allowable loading values for a beam–girder connection fastened with self-tapping screws using the face-nailing approach were close to the code values for bolted and pinned connections. And, a toe-nailing approach provided higher allowable loads for connections than using a face-nail approach.