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.

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.

Effects of Freeze-Thaw Cycles on Physical and Mechanical Properties of Glulam Exposed to Outdoor Environment

This paper presents an experimental investigation to identify suitable indices to assess durability of glulam when subjected to freeze-thaw cycles in an exposed enviroenment.In this study,two types of glulam specimens were tested for their performance when subjected to different levels of aging due to freezing and thawing.Effect of aging treatment on various parameters including thickness swelling rate,static bending strength,elastic modulus,shear strength,and peeling rate of adhesive layer were studied.Obtained results showed that freeze-thaw aging treatment did not affect the water-resistance of the specimens as measured by thickness swelling rate and had little effect on the dimensional stability of the material.However,the applied aging treatment weakened the bending resistance of the glulam specimens with more pronounced effects on on low-density wood.On the other hand,bond strength of high-density wood was relatively more affected due to the appliedfreeze-thaw cycles.For highdensity wood,it is suggested that the shear strength of the adhesive layer be taken as an important index to determine the durability of freeze-thaw cycles aging.For low-density wood,on the other hand,the static bending strength can be used as an index to determine the durability of glulam under freeze-thaw cycles aging.

Long-Term Bending Behaviour of Prestressed Glulam Bamboo-Wood Beam Based on Creep Effect

Creep is an important characteristic of bamboo and wood materials under long-term loading.This paper aims to study the long-term bending beha-viour of prestressed glulam bamboo-wood beam(GBWB).For this,14 pre-stressed GBWBs were selected and subjected to a long-term loading test for 60 days.Then,a comparative analysis was performed for the effects of pre-tension values,the number of pre-stressed wires,and long-term load on the stress variation of the steel wire and the long-term deflection of the beam midspan.The test results showed that with the number of prestressed wires increasing,the total stress of the steel wire in the beam midspan and the ratio of the long-term deflec-tion to the total deflection decreases decreased,but when the number of steel wires exceeded 4,the total stress and long-term deflection was less infuenced;with the pre-tension value increasing,the ratio of the total stress of the steel wire in the beam midspan and the ratio of the long-temm deflection to the total deflec-tion also decreased,but when the prestress force was greater than 3.975 kN,the:total stress and long-term deflection were less affected;with the other parameters unchanged,when the value of the long-term load increased,the total stress of the steel wire decreased,and the long-temm deflection of the beam midspan increased,which shall be more significant with the long-term load greater than 30%of the standard ultimate bearing capacity.After the test,the experimental data were fitted,and the creep coefficient was given.Finally,the long-term stiffness calcula-tion fommula of the pre-stressed GBWB based on creep effect was proposed.The research findings have certain theoretical significance and engineering value.

Flexural Property of String Beam of Pre-Stressed Glulam Based on Influence of Regulation and Control

Applying pre-stress in glulam beam can reduce its deformation and make full use of the compressive strength of wood.However,when the glulam with low strength and the pre-stressed steel with high strength form combined members,materials of high strength can’t be fully utilized.Therefore,this study puts forward the idea of regulating and controlling string beam of pre-stressed glulam.By regulating and controlling the pre-stress,a part of the load borne by the wood is allocated to the pre-stressed tendon,which is equivalent to completing a redistribution of internal force,thus realizing the repeated utilization of the wood strength and the full utilization of the strength of the high-strength pre-stressed tendon.The bending experiments of 10 beams under 5 working conditions are carried out.The failure mode,bearing capacity and deformation of the beams are analyzed.The results show that 90%of beams are deformed under compression.The ultimate load of the regulated and controlled beam is obviously larger than that of the unregulated beam,and the ultimate load of the beam increases with the increase of the degree of regulation and control.Compared with that of the unregulated beams,the ultimate load of beams regulated by 7.5%-30%increases by 25.42%-65.08%,and the regulated and controlled effect is obvious.With the increase of the regulation and control amplitude of pre-stress,the stiffness of string beam of pre-stressed glulam increases.In addition,with the increase of the regulation and control amplitude,the compression height of the beam increases before the failure,and it reaches the state of full-section compression at the time of failure,giving full play to the compressive property of the glulam.At the end of the experiment,the constitutive relation which can reflect the anisotropy of the wood is established combined with the experimental data.The finite element analysis of the beam under 7 working conditions is carried out by using ABAQUS finite element program,and the influence of the regulation and control amplitude on the stress distribution and ultimate bearing capacity of the beam is discussed.

Fire resistance performance of glulam beam

A glulam beam with the size of 4700 mm×300 mm×480 mm(L×W×H) was tested in the furnace to investigate the fire resistance performance of glulam beam according to the temperature curve of ISO834. Three surfaces, the bottom and the two flanks, of the glulam beam were exposed to fire in the test. Simply supported bearings were used to support the beam on which the load of 0.76 kN/m was uniformly set. The experimental results show that: 1) Sectional dimension of glulam beam was greatly diminished due to the serious decomposition and carbonization of the timber. 2) The largest vertical deformation is relatively small and it has not exceeded 3.95 mm until the end of experiment. The maximum temperature on the top surface of the glulam beam attains 180 ℃ at 3437 s, which indicates that the beam have failed according to the European standard of fire resistance tests. 3) The right end of the beam with 16 connecting holes(the connecting holes were used for the connection between bolt and column) and the slit in the beam both burnt intensely and carbonized seriously because the fire could reach the holes and slit of beam facilitating the burning.

Experimental Investigation of the Creep Behaviour of Glulam Compression-Bending Members

Creep test results of glulam members under compression and bending were studied in this paper.The creep tests were conducted to investigate the influence of the stress level and relative eccentricity on the creep deformation of glulam members.The test results showed that the creep deformation trends of glulam members under long-term compression and bending loading were similar;the creep deformation increased with increases in both the stress level and relative eccentricity.However,the relative creep deformation decreased with the increase in both the stress level and relative eccentricity under long-term loading,and a five-parameter creep model was proposed to analyse the creep mechanism of glulam members under compression and bending.The good fitness of the test results indicated that the five-parameter model was able to accurately simulate the creep deformation of glulam compression-bending members.Moreover,a numerical model was developed using the creep equation,which was related to the parameter a and b.The simulation results were in good agreement with the test results,and the parameters a and b were correlated to the relative eccentricity and stress level,respectively.Based on the corrected parameters a and b,the relative creep deformation of glulam compression-bending members was predicted over 50 years.

Long-Term Loading Test of Reinforced Glulam Beam

Due to creep characteristics of wood,long-term loading can cause a significant stress loss of steel bars in rein-forced glulam beams and high long-term deflection of the beam midspan.In this study,15 glulam beams were subjected to a 90-day long-term loading test,and the effects of long-term loading value,reinforcement ratio and prestress level on the stress of steel bars,midspan long-term deflection,and other parameters were compared and analyzed.The main conclusions drawn from this study were that the long-term deflection of the reinforced glulam beams accounted for 22.5%,20.6%,and 18.2%of the total deflection respectively when the loading value was 20%,30%,and 40%of the estimated ultimate load under the long-term loading.The higher the loading level was,the smaller the proportion of the long-term deflection in the total deflection was.Compared with ordinary glulam beams,the long-term deflection of the reinforced glulam beam was even smaller.Under the condition of the constant loading level,the total stress value of the steel bars decreased by 17.5%,13.6%,and 9.1%,and the proportion of the long-term deflection of the beam midspan in the total deflection was 26.9%,24.2%,and 20.6%respectively when the reinforcement ratio was 2.05%,2.68%,and 3.39%.With the increase of the reinfor-cement ratio,the stress loss of the steel bars decreased,and the proportion of the long-term deflection decreased as well.When other conditions remained constant and the prestress level of the steel bars was 0 MPa,30 MPa,and 60 MPa,the total stress value of the steel bars decreased by 9.1%,9.4%,and 10.2%,respectively,and the propor-tion of the long-term deflection in the total deflection was 20.6%,26.1%,and 64.9%,respectively.With the increase of the prestress value,the stress loss of the steel bars increased,and the proportion of the long-term deflection increased as well.

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。

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。

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。