STRESS-STRAIN FINITE ELEMENT ANALYSIS AND FATIGUE LIFE PREDICTION FOR BOLTED CONNECTIONS

A cyclic plasticity model is used into finite element (FE) method to obtainthe details of elastic-plastic stress-strain in the bolts under cyclic axial loading. Two criteriain multiaxial fatigue are employed to predict fatigue lives of bolts. The predicted fatigue livesare in favorable agreement with the experimental results for machined bolts.

Mechanical Behavior of Light Trusses Made of Poplar Laminated Veneer Lumber and Connected with Bolts and Tooth Plates

Poplar Laminated Veneer Lumber(Poplar LVL)is a new type of engineering materials with high strength,good reliability and small variability.Poplar LVL is manufactured from the fast-growing poplar,which is widely used in packaging,furniture and others,however,is rarely adopted in construction.In order to explore the feasibility of poplar LVL trusses in construction of roof,four 4.5-m-span Fink-and-Howe trusses were designed and assembled,which were made of poplar LVL with bolted-and tooth-plated connections.Vertical static loading on the upper chord joints of a truss was imposed by self-balancing test device.The mechanical properties of trusses were examined.The ultimate load,deformation character and failure mode of each truss were measured,observed and analyzed.Furthermore,four types of analytical models with different joint connection assumptions were used to estimate the ultimate load and deflection.The results showed that the poplar LVL trusses were basically in elastic stage before the design load was reached,showing good working performance under the action of design load.The bearing capacity of the trusses of bolted connections was greater than that of the tooth-plated connections.As for the same joint connection type,the bearing capacity of Fink trusses exceeded that of Howe trusses.The poplar LVL light trusses of both types of connections showed good structural performance,which could be reasonably used for building roof systems.

A global-local finite element analysis of hybrid composite-to-metal bolted connections used in aerospace engineering

Efficient bolted joint design is an essential part of designing the minimum weight aerospace structures, since structural failures usually occur at connections and interface. A comprehensive numerical study of three-dimensional(3D) stress variations is prohibitively expensive for a large-scale structure where hundreds of bolts can be present. In this work, the hybrid composite-to-metal bolted connections used in the upper stage of European Ariane 5ME rocket are analyzed using the global-local finite element(FE) approach which involves an approximate analysis of the whole structure followed by a detailed analysis of a significantly smaller region of interest. We calculate the Tsai-Wu failure index and the margin of safety using the stresses obtained from ABAQUS. We find that the composite part of a hybrid bolted connection is prone to failure compared to the metal part. We determine the bolt preload based on the clamp-up load calculated using a maximum preload to make the composite part safe. We conclude that the unsuitable bolt preload may cause the failure of the composite part due to the high stress concentration in the vicinity of the bolt. The global-local analysis provides an efficient computational tool for enhancing 3D stress analysis in the highly loaded region.

Mechanical Experimental Study on Tensile Bolted Connections of Cross-laminated Timber

In order to explore a kind of high-strength,earthquake-resistant,eco-nomical and suitable connection,4 groups of cross-laminated timber wall-to-floor and wall-to-wall bolted connections were tested under monotonic and cyclic load-ing.The defommation characteristics and failure modes of the cross-laminated tim-ber wall-to-floor and wall-to-wall bolted connections were exploited.Load-slip curves,bearing capacity,yielding point,stiffness and ductility of each group of specimens were analyzed.The test results indicate that the loading process of cross-laminated timber bolted connections under tension can be categorized as five stages,namely the elastic stage,the slip stage,the embedding stage,the yield-ing stage and the ultimate stage.The ultimate tensile capacity of cross-laminated timber bolted wall-to-floor connections is 2.67 times that of the wall-to-wall bolted connections.Compared with cross-laminated timber self-tapping screwed connections,the ultimate tensile capacity of the cross-laminated timber wall-to-floor bolted connections is 2.70 times that of the self-tapping screwed connec-tions,and the ultimate tensile capacity of the cross-laminated timber wall-to-wall bolted connections is 3.83 times that of the self-tapping screwed connections.The crosslaminated timber bolted connections have larger yielding displacement and wider plastic range,and they are more energy dissipative and more ductile.Furthermore,the cost of the cross-laminated timber wall-to-floor bolted connec-tions is 46%that of the self-tapping screwed connections,while the cost of cross-laminated wall-to-wall bolted connections is 53%that of the self-screwed connections.

The Simple Model for Bolted Connections in Fire

Recent structural collapses caused by fire have focused attention on research concerning fire safety in building design. Steel connections are an important component of any structural steel building as they provide links between the principal structural members. Considering the importance of this matter this paper describes a spring-stiffness model developed to predict the behavior of bolted angle connections bare-steel joints at elevated temperature. The joint components are considered as springs with predefined mechanical properties i.e. stiffness and strength. The elevated temperature joint’s response can be predicted by assem-bling the stiffness of the components which are assumed to degrade with increasing temperature based on the recommendations presented in the design parameters code. Comparison of the results from the model with existing experimental data showed good agreement. The proposed model can be easily modified to describe the elevated temperature behavior of other types of joint as well as joints under large rotations.

木-混凝土螺栓连接力学性能试验及承载力计算模型

连接节点的设计是保证木-混凝土混合结构中两种材料协同工作的基础.为研究常用工程木-混凝土螺栓连接节点的力学性能及破坏模式,分别选用正交胶合木(Crosslaminated timber,CLT)-混凝土螺栓连接和云杉-松木-冷杉(Spruce Pine Fir,SPF)规格材-混凝土螺栓连接作为试验对象,设计了27组单调加载试验和低周往复加载试验,归纳并对比了两类木-混凝土螺栓连接的典型破坏模式.结果表明:木-混凝土螺栓连接节点承载力大小与螺栓屈服模式相关,CLT-混凝土螺栓连接相较于SPF-混凝土螺栓连接更易发生双铰破坏,且CLT-混凝土螺栓连接具有更好的延性.基于对两类连接力学性能差异的影响机理分析,考虑钢垫板对承载力的影响,并引入CLT等效截面,提出了木-混凝土螺栓连接的承载力力学模型.计算结果与试验结果对比的平均误差为12.18%,表明计算值与试验值吻合良好,可为木-混凝土螺栓连接的设计与应用提供参考.

带拼接板螺栓连接耗能梁段的可恢复功能钢框筒结构抗震性能研究

为了提升传统钢框筒结构的延性和耗能能力,提出采用拼接板螺栓连接的可恢复功能剪切耗能型钢框筒结构(FTS-SRSL),该结构结合了可更换剪切型耗能梁段和钢框筒结构具有良好的抗震性能。该文对一个2/3缩尺的单层单跨FTS-SRSL子结构试件进行了往复加载试验,试验结果表明,FTS-SRSL子结构试件具有良好的抗震性能,结构损伤集中于耗能梁段,且耗能梁段可实现更换。在试验的基础上,以耗能梁段长度比、耗能梁段腹板加劲肋间距、螺栓直径、翼缘拼接板和腹板拼接板厚度为参数,利用ABAQUS建立了15个足尺的单层单跨FTS-SRSL有限元模型,探究各模型的抗震性能,包括承载力、刚度、耗能以及塑性变形能力。有限元分析结果表明:改变拼接板螺栓连接的剪切型耗能梁段长度比会显著影响结构的承载力、刚度及耗能,建议FTS-SRSL中的拼接板螺栓连接剪切型耗能梁段长度比取0.73~1.09;改变耗能梁段腹板加劲肋间距对结构的承载力、刚度和耗能影响较小,基于该文的分析结果,建议FTS-SRSL中的拼接板螺栓连接剪切型耗能梁段腹板加劲肋间距取e/4~e/3(e为耗能梁段长度),且间距应满足我国抗规的规定;改变翼缘拼接板和腹板拼接板厚度对结构的承载力、刚度及耗能基本无影响;改变螺栓直径对结构承载力、刚度及耗能影响较小。

螺栓连接装配式墙板结构连接节点本构模型及体系建模方法

螺栓连接装配式墙板结构体系具有建造快速、施工便捷、连接可靠、可拆卸和可修复等优势,适合低多层乡村住宅建筑,近年来工程应用逐渐增多。该体系预制墙板之间采用离散的干式螺栓连接,受力时接缝处产生滑移变形,与传统的现浇剪力墙结构或湿法连接的剪力墙结构存在本质区别,为了分析结构体系的整体性,建立适合该结构体系的“非等同现浇”的抗震设计方法具有重要意义。本文结合已进行的螺栓连接节点轴向拉伸试验和剪切试验,提出螺栓连接节点拉伸和剪切的本构模型。在此基础上,将单个螺栓连接节点简化为3个平动自由度(x、y、z)的非线性弹簧,模拟连接节点的力学行为,建立简化计算模型。借助螺栓连接预制墙板的拟静力试验结果验证了螺栓连接节点简化模型的有效性,显示可用于分析结构体系的抗震性能。基于节点简化模型,依托Midas Gen软件,提出了螺栓连接装配式墙板结构体系的建模方法。以实际工程为例,建立了该结构的设计模型,并进行在小震、中震作用下的弹性分析及大震作用下的弹塑性时程分析。结果表明:在各地震工况下,螺栓连接装配式墙板结构体系侧向位移较小,层间位移角分别小于弹性位移角限值的1/1200和弹塑性层间位移角限值的1/120,符合规范要求,螺栓连接节点承载力满足抗震需求,墙板角部混凝土没有被压溃,说明螺栓连接装配式墙板结构体系抗震性能优越。研究成果可为螺栓连接装配式墙板结构体系的工程建设提供设计依据,为该新型结构体系的推广奠定理论基础。

螺栓钢板连接预制混凝土轴压性能及承载力计算公式

预制混凝土墙板结合夹心保温技术可大幅提升墙体的保温隔热性,提高建造速度和节能效率。本文设计了螺栓钢板拼接预制混凝土夹心墙板试件,开展试件的轴向压力荷载试验,研究其轴压性能,提出了考虑螺栓钢板拼接影响下的墙板轴心受压极限承载力计算公式。试验结果表明:夹心墙板破坏模式主要为螺栓钢板节点上方以及墙趾两端混凝土的压溃,混凝土面板与夹心保温层在墙体底部轻微分层,墙体侧面出现较大竖向裂缝。将试件的试验轴向荷载承载力与本文提出的公式及现有的公式进行了对比,结果表明:国内现有公式计算值与试验值的差值百分比为5%,国外现有计算公式与试验值的差值百分比为45.7%~77.2%,然而本文提出的公式与试验值差值百分比仅为0.4%。国外现有的公式非常保守,本文提出的公式能够准确预测此种螺栓连接墙板的轴向承载力。在试验研究基础上,考虑了长细比、墙体厚度、连接件布置、混凝土边肋等参数,进一步建立有限元模型验证本文提出的公式。分析结果表明:数值模型的计算结果与本文提出的计算公式误差在–8.05%~2.65%之内,国内现有公式和国外现有公式与计算值误差分别在–2.25%~8.58%和41.61%~78.41%范围内,本文公式预测结果较为准确。最后,分析了各个参数对螺栓钢板拼接预制混凝土夹心墙板轴向承载能力的影响,发现墙板的配筋率对极限承载力无明显影响;合理布置GFRP连接件、设置竖向混凝土肋、减小墙板长细比和增加混凝土板厚度可以提高墙体承载性能。

基于BP神经网络的复合材料螺栓连接强度预测

针对复合材料螺栓连接强度预测问题,设计拉伸试验并记录极限载荷。将试验变量数值化抽象为神经网络输入神经元参数,基于BP神经网络理论,建立强度预测模型。使用三组预留的试验结果验证模型的准确性,三个测试组预测误差分别为6.13%、1.63%、3.34%。调整训练组的组成并重新训练模型,结果表明,本文模型针对训练组未出现参数值有着较好的预测能力。最后建立有限元分析模型进行对比分析,结果表明,针对复合材料螺栓连接强度预测问题,相比有限元方法,神经网络方法精度相当,且具有明显的速度优势。

服役条件下螺栓弹性应力建模及性能保持研究

为了揭示螺栓连接在长期服役过程中的应力松弛机理,对服役条件下螺栓连接的蠕变机理与性能保持行为进行了系统性分析,结合简化解析方法和有限元分析,对螺栓和法兰在不同服役时间内的应力松弛进行了深入探讨。采用了一种简化的解析方法,以解决螺栓法兰连接中的蠕变应力松弛问题,特别关注法兰和螺栓材料的蠕变松弛。通过与三维数值有限元方法比较,验证了该方法的有效性,分析了不同服役时间对螺栓预紧力衰退的影响。仿真结果显示,仿真模型1 000 h时整体蠕变松弛为45.2%,3 000 h时整体蠕变松弛为50.8%,6 000 h时整体蠕变松弛为63.3%。解析结果显示,解析模型1 000 h时整体蠕变松弛为53.4%,3 000 h时整体蠕变松弛为60.5%,6 000 h时整体蠕变松弛为73.4%。结果表明,服役时间越长,预紧力先快速下降,随后逐渐趋于稳定。总之,通过详细的理论分析和数值模拟,揭示了螺栓连接在长期服役中的应力松弛机理,提供了可靠的预测方法和设计优化方案。

预制装配无粘结预应力栓钉连接组合梁受弯分析

通过局部坐标完善Coupling法准确模拟无粘结预应力筋与钢筋混凝土梁间的相对滑移,进而基于ABAQUS有限元软件研究弯曲荷载作用下预制装配无粘结预应力栓钉连接组合梁的受力性能,得出如下主要结论:栓钉的连接强度较高,梁体在弯曲荷载作用下仅无栓钉连接的跨中区域混凝土被压溃,梁和板的交界面发生了破坏;梁体的极限承载与变形能力均与栓钉的抗剪连接强度相关,但极限承载力和栓钉的连接强度并非为简单的线性相关;影响梁体极限承载力的最主要因素是混凝土板的强度,而混凝土梁的强度对极限承载力的影响并不显著,主要原因是梁体破坏模式为梁与板的交界面发生破坏时梁体本身几乎不出现损伤。

Research of Surface Coating Influence on Loose Life of Bolt

The rust⁃proof ability relate to the reliability of bolt connection,and the painting is the most simple and effective rust⁃proof method in industry.Because of lacking general standard,there are different coating thicknesses painted on the surface of workpieces,which influences the loose life of connecting bolt.For the longer loose life,Three kinds of applied coatings(primer coating,primer+top⁃coat coating,primer+intermediate⁃coat+top⁃coat coating)in industry are tested in the experiment,and the best coating is found.All the conclusions gotten by analyzing the testing phenomenon of every coating shown in experiment,have profound meaning for practical industry application.

风力发电机轮毂-主轴连接螺栓强度影响因素分析

基于VDI2230的基本理论,从螺栓刚度、螺栓组参数、夹紧件结构3个方面对轮毂-主轴连接螺栓的极限和疲劳性能进行研究。采用有限元的计算方法,基于大型计算软件模拟了不同规格、不同节圆、不同边距等不同方案下轮毂主轴连接螺栓的力学性能。结果表明:对于无缩径螺栓,增大螺栓规格可以改善极限强度但不能改善螺栓疲劳强度。在缩径相同的条件下,增大螺栓规格可以改善抗疲劳性能。增加螺栓数量及增大节圆直径均可以提升轮毂-主轴连接螺栓的极限强度。夹紧件结构对螺栓疲劳损伤值影响明显,增大轮毂-主轴连接螺栓的边距可以大幅度改善螺栓的抗疲劳性能。

Research Review of Principles and Methods for Ultrasonic Measurement of Axial Stress in Bolts

Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the e ective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer(EMAT) and the permanent mounted transducer system(PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed.

A two-scale method to include essential behaviour of bolted connections instructures including elevated temperatures

A two-scale method is proposed to simulate the essential behavior of bolted connections in structures includingelevated temperatures.It is presented,verified,and validated for the structural behavior of two plates,connectedby a bolt,under a variety of loads and elevated temperatures.The method consists of a global-scale model thatsimulates the structure(here the two plates)by volume finite elements,and in which the bolt is modelled bya spring.The spring properties are provided by a small-scale model,in which the bolt is modelled by volumeelements,and for which the boundary conditions are retrieved from the global-scale model.To ensure the small-scale model to be as computationally efficient as possible,simplifications are discussed regarding the materialmodel and the modelling of the threads.For the latter,this leads to the experimentally validated application ofa non-threaded shank with its stress area.It is shown that a non-linear elastic spring is needed for the bolt inthe global-scale model,so the post-peak behavior of the structure can be described efficiently.All types of boltedconnection failure as given by design standards are simulated by the two-scale method,which is successfullyvalidated(except for net section failure)by experiments,and verified by a detailed system model,which modelsthe structure in full detail.The sensitivity to the size of the part of the plate used in the small-scale modelis also studied.Finally,multi-directional load cases,also for elevated temperatures,are studied with the two-scale method and verified with the detailed system model.As a result,a computationally efficient finite elementmodelling approach is provided for all possible combined load actions(except for nut thread failure and netsection failure)and temperatures.The two-scale method is shown to be insightful,for it contains a functionalseparation of scales,revealing their relationships,and consequently,local small-scale non-convergence can behandled.Not presented in this paper,but the two-scale method can be used in e.g.computationally expensive two-way coupled fire-structure simulations,where it is beneficial for distributed computing and densely packed boltconfigurations with stiffplates,for which a single small-scale model may be representative for several connections.

马鞍山长江公铁大桥Z3号桥塔施工关键技术

巢马城际铁路马鞍山长江公铁大桥主航道桥为(112+392+2×1120+392+112)m三塔钢桁梁斜拉桥,Z3号桥塔为超高多肢钢-混组合塔,高308 m。上塔柱钢结构高87.5 m,分13个吊装节段,最重505 t;中、下塔柱混凝土结构高217.5 m,分38个节段液压爬模施工;钢-混结合段高3 m,内部采用PBL键+剪力钉+高强度钢锚杆+高强度混凝土结构形式。在中塔柱设置钢管临时横撑控制塔柱线形及应力;下横梁采用落地支架法分层施工,与对应塔柱同步浇筑;钢-混结合段混凝土采用C60细石补偿收缩混凝土+高强度灌浆料,保证了混凝土施工质量;采用工厂“2+1”立体匹配制造、“提升站+运输栈桥”钢塔节段转运等技术,并研制15000 t•m超大型塔吊,实现了钢塔柱大节段的制造、整体滩地运输和吊装;钢塔节段间采用栓焊组合连接形式,通过设置工艺隔板、双面坡口等措施控制了钢塔焊接变形;利用定位桁架临时锁定钢塔合龙段实现了钢塔的精确合龙,定位桁架受力及变形均满足要求。

钢管混凝土柱-钢梁外加强环螺栓连接节点抗震性能有限元分析

为深入研究钢管混凝土柱-钢梁外加强环螺栓连接节点的抗震性能,建立了螺栓连接节点的精细化三维实体有限元模型。在对已有试验成果进行验证分析的基础上,研究加劲肋、螺栓连接数量对节点塑性耗能分配机制的影响。结果表明:当钢材本构后期考虑韧性损伤后,有限元计算结果与已有拟静力试验结果更吻合;CFST-1节点(梁高300 mm,有螺栓垫板)耗能能力最优,但仅达到相应焊接节点的一半;与CFST-1节点相比,CFST-3节点(梁高300 mm,无螺栓垫板)及CFST-2节点(梁高250 mm,有螺栓垫板)的总耗能更低;各螺栓节点的塑性耗能分配机制主要依靠梁耗能,而相应的加强环焊接节点主要依靠梁与加强环耗能;当螺栓节点采用环板加劲肋、4排螺栓以及腹板加劲肋构造优化后,刚度、承载力、延性与相应焊接节点一致,总塑性耗能达到刚接节点的79.1%,基本达到刚接节点的抗震水平。

模块化钢结构梁柱子结构抗连续倒塌性能研究

模块化钢结构作为一种高度预制的装配式建筑,具有工业化程度高、绿色节能环保等优点。但是,由于模块化钢结构体系超静定次数较低,其在极端荷载工况下的抗连续倒塌性能应予以特别关注。模块化钢结构梁柱子结构作为主要的传力路径,具有多梁多柱等有别于传统框架梁柱子结构的特点,需对其抗连续倒塌性能开展研究工作。该文针对采用螺栓-角件连接节点的模块化钢结构梁柱子结构进行Pushdown试验及数值模拟,分析了在双柱失效、单柱失效工况下试件的破坏模式和抗连续倒塌机理。结果表明,梁柱子结构在两种工况下的受力机理不同:在双柱失效工况下,梁柱子结构抗力主要由梁机制提供,加载后期抗力提供方式体现出一定的悬链线机制,并随水平连接板厚度的增加而增强;在单柱失效工况下,子结构抗力主要由模块间水平连接抗剪能力提供,由梁机制及悬链线机制提供的抗力较小。

装配式双槽钢拼合PEC柱受压性能试验研究

为发挥钢-混组合结构优良性能及装配式结构施工节能、质量可控的优势,满足建筑模块化、工业化发展需求,提出螺栓连接装配式双槽钢拼合部分包裹混凝土(PEC)组合柱,开展1个纯钢拼合柱、5个组合拼合柱轴心受压及偏心压弯性能试验,结合数值模拟对组合柱破坏形态、应变发展规律、变形性能和承载能力进行分析研究,揭示了螺栓间距、混凝土外伸宽度、相对偏心距大小等因素对双槽钢拼合柱受压力学性能的影响规律.研究结果表明:轴心受压双槽钢拼合柱破坏模式均为整体失稳破坏,偏心受压双槽钢拼合柱均为压弯破坏,使用钢板及螺栓能可靠连接构件,加载过程双肢未发生分离;加密螺栓间距能有效增强组合柱峰后延性,在一定间距范围内构件具较高刚度,由1000mm加至500 mm极限承载力提高4.43%;开孔钢板连接件能约束且保证混凝土与型钢协同工作,破坏阶段前混凝土与型钢未出现明显黏结分离;混凝土外伸宽度增加能提高构件稳定性能.提出考虑单肢影响的轴压承载力计算方法与基于Eurocode 4规范双槽钢拼合柱轴力-弯矩(N-M)相关曲线,理论结果与试验吻合较好,可为装配式拼合柱设计应用提供理论支撑.