Investigation of the Effect of the Force Arm on the Bending Capability of Prestressed Glulam Beam

Prestress enables the Glulam beam could make full use of the compression strength,and then increase the span,but it still could not reduce all drawbacks,such as cross-section weakening and small force arm.To avoid slotting and ensure suitable tension and compression couple,one kind of novel anchor has been proposed,which could meet the bearing capacity requirement.And then the bending test of prestressed Glulam beams with a geometric scale ratio of 1:2 was simulated,to investigate the effect of the force arm on bending capacities,failure modes,and deformation performance.Results show that increasing the force arm could improve the ultimate bending per-formance of the beam significantly,and the anchor arm length has a certain effect on the performance,but it is not obvious.Finally,based on Finite element method analysis,the practice design suggestions have been offered.

Experimental and Numerical Study on Progressive Collapse Analysis of a Glulam Frame Structure:I.Side Column Exposed to Fire

This paper presents experimental and numerical investigations on progressive collapse behavior of a two-story glulam frame when the side column is exposed to ISO834 standard fire.The collapse mechanism initiated by fire is identified.The experimental results show that the progressive collapse of a glulam frame could be described for three stages,namely bending effect stage,catenary effect stage and failure stage,respectively.These stages are discussed in detail to understand the structural behavior before and during collapse.It is demonstrated that the entire frame slopes towards the side of the heated column,and the“overturning”collapse occurs eventually.The catenary effect of beams is the main reason for the progressive collapse of the frame.In addition,a finite element model of a glulam frame is established to simulate the progressive collapse behavior.The effects of axial loads on the columns are summarized.The numerical simulation results agree well with the experimental results,which could verify the effectiveness and practicability of finite element simulation.Furthermore,the progressive collapse resistance of the frame in practical design were proposed.

Experimental Mode and Vibration Comfort Analysis of High-Rise Glulam Building Floor Structure

In order to better meet the objective requirements of the use safety of the high-rise glulam building floor structure and the living comfort of the residents,the transient excitation,environmental excitation and frequency spectrum identification methods were used to carry out experimental modal test in-site on the three rooms numbered A,B and C of the same glulam structural building.The three rooms have different functions,different floor sizes and different floor supporting structures.The research results have shown that the first-order bending frequency of the floor structure of Room A is 27.50 Hz,the transverse second-order bending frequency is 34.75 Hz,the longitudinal second-order bending frequency is 53.25 Hz,and the first-order torsional frequency is 56.25 Hz.The reinforced wooden beam at the bottom of the floor of Room A increases the transverse stiffness of the floor structure,but does not offset the anisotropy caused by the longitudinally installed glulam floors.The fundamental frequency values of the floor structures of the three rooms numbered A,B,and C are 27.5,13 and 18 Hz,respectively.This has a relatively high innovation and reference significance for integrating the theory of structural dynamic characteristics with the dynamic testing technology,improving the design level of high-rise glulam structure buildings,and improving the living comfort of residents.

Stiffness and Shear Stress Distribution of Glulam Beams in Elastic-Plastic Stage:Theory,Experiments and Numerical Modelling

Traditional methods focus on the ultimate bending moment of glulam beams and the fracture failure of materials with defects,which usually depends on empirical parameters.There is no systematic theoretical method to predict the stiffness and shear distribution of glulam beams in elastic-plastic stage,and consequently,the failure of such glulam beams cannot be predicted effectively.To address these issues,an analytical method considering material nonlinearity was proposed for glulam beams,and the calculating equations of deflection and shear stress distribution for different failure modes were established.The proposed method was verified by experiments and numerical models under the corresponding conditions.Results showed that the theoretical calculations were in good agreement with experimental and numerical results,indicating that the equations proposed in this paper were reliable and accurate for such glulam beams with wood material in the elastic-plastic stage ignoring the influence of mechanic properties in radial and tangential directions of wood.Furthermore,the experimental results reported by the previous studies indicated that the method was applicable and could be used as a theoretical reference for predicting the failure of glulam beams.

钢筋增强钢夹板-螺栓连接胶合木梁受力性能试验研究

为改善钢夹板-螺栓连接胶合木梁的刚度在到达极限荷载55%~70%区间内存在减小的问题,设计制作了3组共12根钢筋增强钢夹板-螺栓连接胶合木梁,通过改变配筋率进行三分点加载试验,并与相同设计参数的胶合木梁和钢夹板-螺栓连接胶合木梁进行对比试验。观察记录试件的受力过程和破坏现象,实测各组试件的极限承载力、荷载位移曲线和应变曲线,对比分析增强筋对各组试件破坏机理、抗弯刚度和极限承载力的影响规律。试验结果表明:与钢夹板-螺栓连接胶合木梁相比,钢筋增强钢夹板-螺栓连接胶合木梁的抗弯承载力和整体弯曲刚度在增强筋的作用下均有显著提高,钢夹板-螺栓连接试验梁在到达极限荷载55%~70%区间内刚度减少问题得到明显改善。钢筋增强钢夹板-螺栓连接试验梁的破坏形式随着配筋率的增大,逐渐由受拉脆性破坏向受拉延性破坏再到受压延性破坏进行转变。增强梁截面应变沿高度方向的分布基本符合平截面假定。依据试验数据和理论推导,得出了钢筋增强钢夹板-螺栓连接试验梁抗弯计算公式,其理论结果与试验结果吻合较好。研究表明,在钢夹板-螺栓连接胶合木梁受拉区配置增强筋可以有效改善其后期刚度减少的问题,并提升其抗弯性能,可为此类连接木梁的增强提供理论依据和试验支撑。

纤维增强复合材料增强胶合木受弯构件研究综述与展望

针对纤维增强复合材料(FRP)增强胶合木受弯构件研究进行综述,系统梳理了现有增强技术,详细阐述了界面黏结性能、抗弯性能、蠕变性能的影响因素与分析方法。研究表明:FRP增强技术能更有效地利用胶合木受弯构件中木材的强度,提高构件抗弯承载力、控制弯曲变形并改善脆性破坏模式。针对FRP增强胶合木受弯构件在工程应用上的制约因素,提出了在预应力增强技术、长期性能、抗火性能和可靠性方面研究中亟需解决的关键问题。

国产胶合木柱生产碳排放量测算及碳减排研究

碳排放量是评估胶合木生产环境影响的重要指标,现有碳排放数据多引用国外和基于理想模型测算,难以真实反映我国当下生产条件碳排放水平。以赤松(Pinus densiflora)胶合木柱为研究对象,基于现场调研分析胶合木柱生产工艺过程的碳排放源,从辅料、能源两个方面建立碳排放边界模型和物料清单,计算产品碳排放量,并分析生产过程碳排放特征,从生产工艺角度提出减碳方式。结果表明:胶合木柱的碳排放量为330.16 kgCO_(2)e/m^(3);锯材生产阶段、胶合木及木柱制作阶段的碳排放量分别占总量的78.5%和21.5%;窑干、接长、施胶、搬运经优化后,可实现碳减排44.3%,优化效果显著。

结构用竹木材料的高温力学性能研究

为探究竹木材料在高温环境下的力学性能,研究了重组竹和云杉-松木-冷杉(SPF)两类竹木材料在不同温度(80、160、220℃)与不同处理时间(0.5、1、2、3 h)下的抗压、抗拉、抗剪、抗弯强度和重量损失变化。结果表明:重组竹和SPF的力学性能随处理温度和处理时间的增加而逐步降低。在220℃的高温环境下,重组竹和SPF的力学性能降低较为显著。在处理3 h后,其抗压、抗拉、抗剪强度以及抗弯强度剩余率为20%~40%和36%~70%。高温处理后,降温方式对重组竹剩余强度的影响较小,而对SPF的影响较大。研究结果可为竹木建筑的防火处理、火灾后的竹木建筑性能评价提供理论基础。

玻璃纤维加强型胶合木梁柱植筋节点受力性能研究

针对胶合木梁柱纯植筋节点的延性及耗能不足问题,提出采用玻璃纤维增强复合材料(GFRP)的加强型梁柱植筋节点,以使植筋有效发挥作用,改善节点受力性能。运用ABAQUS软件分析了纤维布粘贴方式、层数对植筋节点受力性能的影响,确立合理的粘贴方案后,采用试验与数值模拟相结合的方式,对比分析有、无加强型胶合木梁柱植筋节点在低周往复荷载作用下的破坏形态及滞回性能。结果表明:玻璃纤维增强复合材料对节点的加强效果明显,节点延性和耗能均得到有效改善;但在保证植筋节点承载力达到预期目标的情况下,有必要根据设计承载力要求合理控制GFRP的粘贴层数,以避免浪费。

长螺杆加强型胶合木梁柱节点力学性能

胶合木梁柱螺栓钢填板节点由于抗弯刚度较低,在结构设计中通常被视为铰接。提出了一种长螺杆加强型胶合木梁柱节点,为无支撑或剪力墙的中高层木结构体系中提供较好的刚性连接。设计并加工了3组不同长螺杆直径的节点试件,通过单调加载和往复加载试验探究了节点的抗弯刚度、抗弯承载力、破坏模式及耗能性能。通过ABAQUS有限元软件建立了节点力学模型,模拟结果与试验结果较为吻合,并基于该模型开展了参数分析。结果表明:该节点具有较高的抗弯刚度与抗弯承载力,经过合理构造后节点损伤主要集中在长螺杆,而长螺杆在破坏后易于更换,可提高节点韧性与使用寿命。参数分析结果表明,转动刚度与长螺杆直径及力臂呈正相关。基于试验与模拟的结果,提出了该类节点抗弯刚度及抗弯承载力的计算方法,为其在实际工程中的设计与应用提供参考。

定向重组展平竹集成材生产工艺

以竹展平板为基本单元制造定向重组竹集成材的工艺方法。将竹展平板涂布间苯二酚树脂胶黏剂,涂胶量为200-300 g/m 2,按照竹青面对竹青面、竹黄面对竹黄面的方式进行组坯,热压加工制成展平竹层积材,再采用指接的方式进行接长,获得性能优异的定向重组展平竹集成材,产品的尺寸规格一般为长1000-3500 mm,宽50-300 mm,厚60-150 mm。指接时相邻层板的指接接口需错开组坯,在常温下冷压4-5 h,冷压压力为1.0-1.5 MPa,后固化养生。

不同销钉加固胶合木螺栓洞口处节点拉伸性能

木结构螺栓节点在螺栓洞口周围易因应力集中而导致螺孔周围木材开裂,降低节点承载力。采用销类连接件垂直于木材纹理加固有望改善上述破坏现象。为探究不同种类销钉垂直于木材纹理的加固时对胶合木螺栓洞口处节点的增强效果,以及为木钉在增强胶合木螺栓洞口处节点的工程应用上提供试验基础和理论依据,以销钉的材料种类及直径为变量,参考美国标准(ASTM D1761-20)对4组共26个开孔胶合木试件在顺纹方向进行了1 mm/min的匀速单调加载拉伸试验。记录分析了试验前后各个试件洞口处节点的破坏形态、荷载-位移曲线、极限承载力、刚度和能量耗散。结果表明:(1)木钉和钢钉垂直于试件纹理的钉入对试件洞口处节点的破坏模式影响不大,但对试件节点的承载性能有一定提升;(2)木钉对试件洞口处节点的增强效果明显优于钢钉,木钉增强组SS2、SS3和钢钉增强组SS4试件与未加固组SS1试件相比,极限承载力分别提高了19.75%,19.18%和10.83%,能量耗散分别提高了87.48%,82.59%和28.33%;(3)木钉直径的较小变化对节点的增强效果影响不大。采用木钉垂直于木材纹理加固可显著提升螺栓洞口的承载力,有利于提升木结构螺栓节点的承载力。

考虑螺栓布置的胶合木螺栓-钢插板连接抗拉性能

多螺栓—钢插板连接是应用较为广泛的胶合木结构节点连接方式。依据螺栓数目、排列方式、螺栓直径、木材厚度4个影响因素将试件分为了12组(每组6个)进行受拉试验,得到了各试件的破坏模式以及初始刚度、屈服荷载、峰值荷载和延性系数等参数,试验结果表明在木材厚度和螺栓直径相同的条件下,破坏现象随着螺栓数量增加,破坏模式的变化规律比较相近,木材的左右侧面产生不同程度的劈裂裂缝,裂缝从顶部延伸至最后一行螺栓以下。对比力学性能,随着螺栓数量的增加,试件的初始刚度、屈服荷载和峰值荷载均增加,而延性会发生减小。最后以螺栓直径与数量为自变量对多螺栓—钢插板连接节点初始刚度和峰值荷载的公式进行了拟合,结果与试验数据有良好的一致性。

高层胶合木建筑楼盖结构模态试验及振动舒适性评价

【目的】为了更好地满足高层胶合木建筑楼盖结构的住户居住舒适性等客观要求,提出对其合理评价及减振措施与方法。【方法】本文利用瞬态激励法、环境激励法和频谱识别法分别对同一栋6层胶合木结构建筑的A,B,C三个不同尺寸房屋进行试验模态现场测试研究,对C房间楼盖频谱识别法测试的振动特性进行有限元分析,评价了该胶合木结构建筑楼盖的动力特性和整体振动舒适性。【结果】研究结果表明,A房间楼盖结构的一阶弯曲频率为27.50 Hz,横向二阶弯曲频率为34.75 Hz,纵向二阶弯曲频率为53.25 Hz,一阶扭转频率为56.25 Hz。该房间楼盖底部的加强筋木横梁增大了楼盖结构的横向刚度,但并未抵消纵向排列的胶合木楼盖所导致的各向异性,其楼盖整体的纵向刚度大于横向刚度;A、B、C三个房间楼盖结构的基频值分别为27.5、13和18 Hz,均符合自振频率与跨度的关系式要求,频谱识别法与有限元计算模态分析得到的C房间一阶固有频率非常相符。【结论】胶合木建筑楼盖结构的木横梁起加强其整体刚性作用,并提高了其居住舒适度。由于木质楼板的各向异性,在其宽度方向上设置加强筋木梁尤其重要。该胶合木建筑楼盖整体上满足建筑固有频率规定的舒适度水平要求,瞬态激励和环境激励方式下的试验模态法、频谱识别法,能够有效应用于木建筑楼盖舒适度的测试,具有现实可靠性。

大小跨高比落叶松胶合木梁抗弯性能对比研究

为对比大小跨高比落叶松胶合木梁的抗弯性能,对2组6根落叶松胶合木梁进行了四点弯曲试验研究,其中两组试件跨高比分别为20和12。结果表明:大、小跨高比胶合木梁的破坏形式分别为顺纹受拉脆性破坏和顺纹受剪脆性破坏;与大跨高比胶合木梁相比,小跨高比胶合木梁受弯极限承载力相对较高;大跨高比胶合木梁受弯过程中,中性轴位置基本不变;小跨高比胶合木梁受弯过程中,中性轴略有下移。小跨高比胶合木梁抗弯刚度约为大跨高比胶合木梁的3.4倍;大跨高比胶合木梁延性系数约为小跨高比胶合木梁的3.9倍。最后,基于极限应变分析方法,提出了胶合木梁发生受拉和受剪破坏界限跨高比的计算公式,并求得落叶松胶合木梁的界限跨高比为12.62。

高层胶合木结构建筑气密性测试研究

我国作为人口大国,人均能源资源占有量低,每年的能源消耗数额巨大,其中建筑能耗所占比重极大。为进一步控制具有低碳环保的天然优势的木结构建筑运行能耗,以一栋6层胶合木梁柱框架-轻型木结构剪力墙建筑为研究对象,通过围护结构传热系数与建筑气密性能的现场测试,对其建筑能耗展开研究。结果表明:该大楼建筑能耗使用情况符合中小型办公楼能耗现况,且建筑得热主要因太阳辐射,建筑失热主要因围护结构热传导所致。建筑气密性能对该大楼的能耗影响最大,其次为地理位置,而建筑结构类型与窗墙比对建筑能耗影响较小。

钢夹板-螺栓连接胶合木梁疲劳试验研究

钢夹板-螺栓连接胶合木梁在实际工程运用中受到循环往复动荷载的作用,极易产生损伤累积而造成构件失效。为了研究钢夹板-螺栓连接胶合木梁的疲劳特性,通过不同应力水平下的等幅疲劳试验及静力对比试验,分析了钢夹板-螺栓连接胶合木梁的疲劳破坏形态与机理,研究了其刚度退化规律,探讨了疲劳极限荷载。试验结果表明,钢夹板-螺栓连接胶合木梁的疲劳破坏主要发生在加载点附近。随着疲劳循环次数的增多,钢夹板-螺栓连接胶合木梁的跨中挠度以及沿截面高度的拉、压应变均显著增大,压应变增幅大于拉应变,且应变分布情况基本符合平截面假定。试验梁的弯曲刚度随着疲劳循环次数的增加而呈现出线性退化,基于刚度退化的疲劳寿命预测与试验实测寿命基本吻合。钢夹板-螺栓连接胶合木梁的疲劳寿命随着应力水平的增大而降低,在应力比为0.2,应力水平不超过0.5倍静力极限荷载时,疲劳寿命均大于200万次,表明钢夹板-螺栓连接胶合木梁具有较好的疲劳特性。此外,还对疲劳载荷的振幅和疲劳寿命进行了线性回归分析,得到的疲劳极限载荷为0.5435 F_(u)。最后,利用ANSYS nCode软件对试验梁进行疲劳有限元分析,分析表明,该软件能较好地模拟钢夹板-螺栓连接胶合木梁在不同应力比下的疲劳响应。

无黏结预应力胶合木T梁受弯性能

胶合木梁刚度小、承载力低且易发生脆性受拉破坏,为了改善其短期受弯性能,提出了一种胶合木T梁和无黏结预应力相结合的新型构件。通过对4根落叶松胶合木T梁的四点弯曲试验,包括1组未增强试件和1组无黏结预应力筋增强试件,对比分析了两组试件的破坏形态和破坏机理,探讨了无黏结预应力对其受弯性能的影响。结果表明:施加0.25fptk(fptk为钢绞线抗拉强度标准值)预应力后,胶合木T梁未产生受拉破坏,而为腹板剪切破坏;相比未增强试件,无黏结预应力筋增强试件的受弯极限承载力提高了38.2%,抗弯刚度提高了22.5%,延性提高了45.8%;施加预应力还能有效减小木材缺陷对胶合木梁受弯性能的影响。

结构胶与螺栓混合连接的型钢-胶合木组合梁受力性能研究

为了研究螺栓连接及结构胶+螺栓复合连接方式下型钢-胶合木组合梁的受力性能,通过建立有限元三维实体模型进行参数化分析,改变螺栓间距、设置加劲肋及翼缘连接方式等参数,研究其对组合梁刚度、承载力和变形能力的影响规律和破坏机制。结果表明:钢-胶合木组合梁的破坏特征主要包括端部界面脱胶翘起、螺栓剪切及翼缘木材螺孔塑性变形和钢板局部屈曲;在组合梁上下翼缘外表面受拉压应力集中现象较为明显,施加荷载过程中,螺栓孔洞处会改变临近钢材和木材应力应变传递和分布路径,且容易首先发生屈服破坏;结构胶+螺栓复合连接可以有效增强组合梁的整体刚度,屈服荷载增幅为30.65%,可充分发挥翼缘承载能力。

Experimental Research on Structural Behaviors of Glulam I-Beam with a Special-Shaped Section

In order to enhance the bearing capacity of structural components,save materials,and reduce cost,a glued laminated timber(glulam)I-beam that is theoretically suitable for engineering application was proposed.In this study,18 glulam specimens were fabricated using larch dimension lumber and resorcinol-formaldehyde resin.Four-point bending tests were carried out to compare the ultimate bearing capacity,strain,and deflection of various specimens.The results showed that:(1)The typical failure mode at bending is the web shear failure parallel to grain.Before the failure,cracks and sounds appear at the beam web,which represent the sudden brittle failure.(2)The cross-sectional strain of glulam beam changed linearly with the beam height,indicating that the plane section assumption was basically established.(3)Stiffener could improve the initial flexural stiffness of glulam beam,which experiences an increase of 28.21%.Larger the shear span ratio,smaller the initial flexural stiffness.The initial flexural stiffness improves by 10-23.5%with the increase in the thickness of the lower flange.(4)The effects of stiffener and shear-span ratio on shear strength are relatively significant.After the stiffeners are set at the support and the loading point in pairs,the shear strength of the glulam beam increases by 15.05%averagely.With the increase in the shear-span ratio,the shearing strength of the glulam I-beam gradually reduces.The equation of the shearing strength with the shear span ratio is obtained,which is shown by high fitting precision.(5)The shear strength correlation,as proposed by Soltis and Rammer,is suitable not only for rectangular beams,but also for glulam I-beams.