吊顶主次龙骨节点受剪和受弯性能试验研究

近年发生的地震中吊顶的震害显著,主次龙骨节点失效是吊顶破坏的主要原因之一。为评估吊顶主次龙骨节点的受剪和受弯性能,对其开展单调加载和低周往复加载试验,考察了节点的破坏模式、承载力、变形能力、滞回性能和耗能能力,建立了节点的易损性曲线。研究结果表明：主次龙骨节点主轴受剪和次轴受剪的破坏模式分别为节点剪切破坏和节点面外弯曲并脱出,主次龙骨节点受弯的破坏模式是节点脆性脱出破坏。对比节点主轴受剪,节点次轴受剪时强度更低,但节点变形能力更强。对比节点主轴受弯,节点次轴受弯时强度更高,但节点转动能力稍低。主次龙骨节点受剪和受弯时的荷载-位移滞回曲线捏拢效应显著,耗能能力不强。易损性分析表明,主次龙骨节点次轴受剪和主轴受弯时更容易破坏。     

A highly efficient user-defined finite element for load distribution analysis of large-scale bolted composite structures

This paper presents the development of a highly efficient user-defined finite element for modelling the bolt-load distribution in large-scale composite structures. The method is a combined analytical/numerical approach and is capable of representing the full non-linear load-displacement behaviour of bolted composite joints both up to, and including, joint failure. In the elastic range, the method is generic and is a numerical extension of a closed-form method capable of modelling the load distribution in single-column joints. A semi-empirical approach is used to model failure initiation and energy absorption in the joint and this has been successfully applied in models of single-bolt, single-lap joints. In terms of large-scale applications, the method is validated against an experimental study of complex load distributions in multi-row, multi-column joints. The method is robust, accurate and highly efficient, thus demonstrating its potential as a time/cost saving design tool for the aerospace industry and indeed other industries utilising bolted composite structures.     

Analysis of dowelled timber to timber moment-resisting joints

Dowelled joints, widely used in timber structures, are designed to transfer shear forces and bending moments between timber members. The anisotropic non-linear behaviour of the timber beneath the fasteners controls the stiffness of these joints. At the ultimate load-carrying capacity, the failure modes result from the shear stresses induced by the load distribution among the fasteners. The paper presents the experimental results obtained for beam to column joint with or without reinforcement using glued plywood plates. Based on these results, a two-dimensional finite element model was developed in two stages to describe the three-dimensional behaviour of the joint. At the single fastener scale, the model considers the non-linearity induced by the timber embedding and the fastener bending. At the structural scale, the modelling approach considers the timber as an elastic orthotropic material whereas each fastener is modelled by two non-linear springs. The elastic-plastic behaviour of each spring element is defined by the local scale model defined in two perpendicular directions. The load distribution among the fasteners is compared to the analytical results according to design rules. Considering the global load displacement curves, the results show that the modelling approach provides a good estimation of the structural response.     

Fatigue life estimation of coach peel riveted joints using multi-axial fatigue criteria

This study investigates fatigue behaviour of riveted joints in a coach peel configuration under various load ranges and load ratios. Three well-known multi-axial fatigue criteria of Smith–Watson–Topper, Glinka and Fatemi–Socie are used to predict the fatigue life of the joint based on the stress and strain components obtained from a finite element analysis. A three-dimensional finite element model was developed with considering elastic–plastic behaviour of aluminium alloy 2024-T3 for the joint plates as well as frictional contact between all the contacting parts. Fatigue life estimation results agreed well with existing experimental data for the same joint. This verifies the finite element results and shows how well the multi-axial fatigue equations can predict fatigue life of the riveted joints. The finite element modelling approach may be then used with confidence for fatigue life estimations of different configurations of riveted joints.     

Thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint

Adhesive bonding technique is used successfully for joining the carbon fibre reinforced plastics to metals or composite structures. A good design of adhesive joint with either simple or more complex geometry requires its stress and deformation states to be known for different boundary conditions. In case the adhesive joint is subjected to thermal loads, the thermal and mechanical mismatches of the adhesive and adherends cause thermal stresses. The plate-end conditions may also result in the adhesive joint to undergo large displacements and rotations whereas the adhesive and adherends deform elastically (small strain). In this study, the thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint with single support plus an angled reinforcement made of unidirectional CFRPs were carried out using the non-linear finite element method. In the stress analysis, the effects of the large displacements were considered using the small displacement–large displacement theory. The stress states in the plates and the adhesive layer of the tee joint configurations bonded to a rigid base and a composite plate were investigated. An initial uniform temperature distribution was attributed to the adhesive joint for a stress free state, and then variable thermal boundary conditions, i.e. air flows with different velocity and temperature were specified along the outer surfaces of the tee joints. The thermal analysis showed that a non-uniform temperature distribution occurred in the tee joints, and high heat fluxes took place along the free surfaces of the adhesive fillets at the adhesive free ends. Later, the geometrical non-linear thermal-stress analysis of the tee joint was carried out for the final temperature distribution and two edge conditions applied to the edges of the vertical and horizontal plates (HP). High stress concentrations occurred around the rounded adherend corners inside the adhesive fillets at the adhesive free ends, and along the adhesive–composite adherend interfaces due to their thermal–mechanical mismatches. The most critical joint regions were adhesive fillets subjected to high thermal gradients, the middle region of HP, the region of the vertical plate corresponding to the free end of the vertical adhesive layer–left support interface. In addition, the support length had a small effect of reducing the peak stresses at the critical adherend and adhesive locations.     

Implication of unequal rivet load distribution in the failures and damage tolerant design of metal and composite civil aircraft riveted lap joints

Riveted lap joints are being used widely in civil aircraft structures. Conventional design procedures assume that the joint can be designed as if all rivets carry load equally. As found in literature associated with fatigue and fracture, forensic studies on structural failures, this assumption is not entirely valid. In this paper, the regulatory codes for civil aircraft as applicable to riveted joints in the form of FAR 25 regulations are briefly reviewed. The regulatory code discusses safety factors in an implied way, but has little specific recommendations for riveted joints. However, studies on the failures of specific aircraft illustrated in this paper add to the argument that both static strength and life are affected by the initial design procedures for the riveted joints. In this paper, finite element models for metal–metal, composite–metal, composite–composite lap joints are studied. A three row lap joint used in commercial aircraft and which was part of failure studies is also examined. Unequal rivet loads and in cases, nearly 50% more than conventional design has been seen in linear finite element analysis. Elasto-plastic analysis using rivet flexibility shows re-distribution of loads. Based on these observations, the effect of rivet loads on life estimation including the use of concepts such as by-pass stresses is discussed. These results have implications for static strength at ultimate load, damage tolerance and fail safety and are discussed in this paper. Next, in a composite–composite lap joint, the influence of ply-angle on the rivet loads is studied. Also, a composite–metal lap joint is studied for the rivet load distribution and life estimation. It is found that the load shared by the rivet rows in a composite–metal lap joint are not symmetric and therefore are more susceptible to cracking and subsequent failure as the unequal distribution can cause some of the rivet loads to be high. In conclusion, the issue of fail safe and damage tolerant design of civil aircraft structures with riveted joints are addressed, especially the implication of unequal load distribution on the failures of such joints and it is suggested that these unequal rivet load distributions be catered for at the early design stage itself via finite element analysis and the possibility of an over-arching safety factor could be considered that incorporates both ultimate load and damage tolerance conditions.     

An analytical model for the prediction of load distribution in highly torqued multi-bolt composite joints

This paper presents the development of an enhanced analytical approach for modelling the load distribution in multi-bolt composite joints. The model is a closed-form extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The enhancement accounts for static friction effects between the laminates, a primary mechanism of load transfer in highly torqued bolted joints. The method is validated against detailed three-dimensional finite element models and where possible, experimental results. The effect of varying bolt-torque and bolt-hole clearance on the load distribution in a three-bolt, single-lap joint is investigated and the method proves to be robust, accurate and highly efficient. Finally, the method is employed in a parameter study, where increasing bolt torque levels can be used for achieving a more even load distribution in multi-bolt joints.     

Towards approximate models of Coulomb frictional moments in: (I) revolute pin joints and (II) spherical-socket ball joints

In general, the rigid-contact assumption has been used to estimate the frictional moment between two bodies in contact. In a multi-body connection, two types of passive interconnection are considered in this paper, namely pin joint and spherical-ball joint. The joints are assumed to be passive at the localized configuration space of the multi-body systems and are assumed to be actuated remotely. The traditional approach for modelling such frictional contact does not consider the elastic deformation of joints. Two approximate models are presented for both revolute pin joints and spherical-socket ball joints. The proposed models offer a more accurate estimation of the Coulomb frictional moment. The new models offer a compact solution which can be easily extended to other geometrical multi-body contact configurations with various degrees of clearance. The proposed models can be used in the dynamic modelling and control of multi-body systems in frictional contact.     

Thermoelastic Stress Analysis of a GRP Tee Joint

A detailed study of the stresses that are developed in a glass reinforced plastic (GRP) tee joint under service loads is described. The joints are fabricated by laminating a boundary angle over a radiused fillet on either side of the ‘tee’. Full-field stress characterisation data is provided by a thermoelastic analysis of the tee joint. Calibration procedures that allow the thermoelastic data to be compared with the results of a finite element analysis are detailed. The results of the thermoelastic analysis are compared with values obtained from the finite element analysis. The applicability of thermoelastic analysis as a validation tool for finite element models of composite materials is assessed.     

半刚性节点网壳结构研究进展及关键问题

装配式节点通常采用单根或多根螺栓与构件连接,往往具有一定的半刚性特性。但目前,由于对装配式节点认识不足,在装配式网壳结构分析和设计时,通常假定其节点连接为铰接;然而,通过研究发现实际装配式节点具有较好的半刚性性能;为适应实际工程所研发的新型装配式半刚性节点具有刚度更大、更加高效等优点,可应用于更大跨度的单层网壳结构中。半刚性节点网壳结构具有广阔的应用前景,针对半刚性节点及其网壳性能的研究逐渐成为建筑结构领域的热点研究课题之一。该文综述了国内外半刚性节点及半刚性节点单层网壳结构的现有研究成果以及尚需深入研究的主要问题。文献分析表明,目前针对半刚性节点及半刚性节点网壳结构静力性能的研究已取得一定的成果。然而,关于空间半刚性节点在复杂荷载作用下节点抗弯性能、空间半刚性节点耗能性能、适用于更大跨度的新型空间节点研发、半刚性节点网壳结构动力稳定性等方面有必要进行更多更深入的试验和理论研究,以推动半刚性节点单层网壳结构的实际工程应用。     

A global bolted joint model for finite element analysis of load distributions in multi-bolt composite joints

This paper presents the development and validation of a global bolted joint model (GBJM), a highly efficient modelling strategy for bolted composite joints. Shell elements are used to model the composite laminates and the bolt is represented by a combination of beam elements coupled to rigid contact surfaces. The GBJM can capture effects such as bolt–hole clearance, bolt-torque, friction between laminates, secondary and tertiary bending in the laminates as well as the load distribution in multi-bolt joints. The GBJM is validated using both three-dimensional finite element models and experiments on both single- and multi-bolt joints. The GBJM was found to be robust, accurate and highly efficient, with time savings of up to 97% realised over full three-dimensional finite element models.     

Use of FRP for RC Frames in Seismic Zones: Part I. Evaluation of FRP Beam-Column Joint Rehabilitation Techniques

Multi-storey reinforced concrete frames that were built prior to the 1970's generally do not meet current seismic design code requirements. The lateral load carrying capacity of these structures is often insufficient due to non-ductile reinforcement detailing, which includes either insufficient or no beam-column joint transverse reinforcement. It was observed during recent earthquakes that deficient beam-column joints can jeopardise the integrity of entire structures. Thus, several beam-column joint rehabilitation techniques have emerged to upgrade such substandard joints. It is essential to evaluate the standings of joints rehabilitated with such techniques based on current design code requirements. This paper critically examines beam-column joint rehabilitation techniques using FRP that emerged in the last decade. For this purpose, a full-scale code-conforming beam-column joint was made and tested under reversed cyclic load to serve as a benchmark for this comparison. Enhancements imparted to substandard beam-column joints by FRP rehabilitation techniques in terms of strength, ductility and energy dissipation gains are assessed. It is shown that FRP joints repair schemes generally enhanced the performance of substandard joints, but they often came short of satisfying current standard level performance, and that different rehabilitation strategies can be adopted depending on the type of joint deficiency and the purpose of the rehabilitation scheme.     

超高层建筑伸臂桁架-核心筒剪力墙节点受力性能数值与理论研究

基于对两种适用于超高层建筑的伸臂桁架-核心筒剪力墙节点的试验研究,对该类节点的抗震性能和受力机理进行精细有限元和理论分析,并给出设计方法和建议。首先利用通用有限元软件MSC.MARC(2010)对节点进行非线性数值模拟,将有限元分析结果与试验结果进行对比分析,取得满意的结果。随后根据有限元计算结果对伸臂桁架、墙体端部暗柱、外包(内嵌)钢板和混凝土剪力墙的受力机理进行深入分析,同时给出节点承载力简化计算方法。最后在整体节点模型的基础上,建立节点板的局部模型,着重对节点板的受力机理进行分析,并考察该类节点板简化设计公式的适用性。分析结果表明:混凝土墙受到上下部钢板的剪切作用从而形成斜压杆受力机制;在剪切荷载存在且节点板长度较小时,节点板危险截面正应力分布并不符合平截面假定。该文研究可为超高层建筑中伸臂桁架-核心筒节点的设计与施工提供参考。     

沉管隧道接头力学模型及刚度解析表达式

接头刚度是表征沉管隧道接头性能的最重要参数. 目前沉管隧道接头刚度的取值既无现成的解析表达式或图表可循, 也无接头力学性能试验数据支持. 该文根据接头构造设计特点提出力学假定, 将接头GINA止水带抽象为弹簧, 接头板则假定为不产生挠曲变形的刚性板, 在此基础上建立了接头的力学模型. 根据受力平衡方程和变形协调方程, 推导出接头刚度的解析表达式. 通过与所设定的接头三维精细化基准模型在相同设计参数下的结果对比, 验证了接头力学模型及刚度解析解的合理性. 最后应用该力学模型进行了接头参数敏感性分析, 预测了各种因素对接头刚度的影响规律.     

Tensile strength and failure simulation of simplified spot weld models

A simple model for spot weld joints is desirable in body-in-white automotive structures which contains thousands of them. Hence, comparative performance and failure prediction study of six simplified spot weld models in terms of their geometric and constitutive properties are presented in this paper. The stiffness characteristics of these models under tensile loading condition were compared with the experimental results. It was found that the current spot weld modelling practice in the automotive industry predict the strength with 45.33% of error. To simulate the joint failure a material damage criterion correlating ultimate tensile strength of material was implemented in the developed models. The comparative study with respect to the accuracy was also related with the computational cost incurred by the different models. Hence, suitable modelling conditions to design a finite element model for spot welded joints are established which is very simple to develop, relatively cheap in terms of computational costs but yet predicts reasonably accurate results.     

交变载荷对CFRP复合材料-铝合金粘接接头剩余强度的影响

为了给碳纤维增强聚合物（CFRP）复合材料粘接结构的安全设计及应用提供参考,针对CFRP复合材料-铝合金对接接头,研究了拉-拉交变载荷作用下的疲劳寿命特性及剩余强度变化规律。设计专用夹具,完成接头的制作及固化,并测试其拉伸、剪切准静态失效强度,在此基础上进行不同载荷水平下的疲劳寿命测试。选取特定载荷水平,测试不同循环次数后的接头剩余强度,并对失效形式进行观察分析。结果表明:CFRP复合材料-铝合金对接接头强度-寿命（S-N）曲线在单对数坐标上符合线性函数规律;随着交变载荷循环周期的增加,接头剩余强度呈先慢后快的下降趋势,而且在较大的载荷水平下,下降幅度更为明显;经历交变载荷循环前、后接头失效形式发生改变,由局部CFRP复合材料表层撕裂转变为局部界面破坏。结合试验测试所获得的初始失效准则,并引入疲劳退化因子,建立内聚力模型对交变载荷作用下的粘接接头强度衰减进行数值模拟,结果表明所建立模型能够有效预测交变载荷作用下的接头剩余强度。      

Residual stresses due to gas arc welding of aluminum alloy joints by numerical simulations

This study deals with the numerical simulation of the gas arc welding process of Aluminum tee joints using finite element analysis and evaluation of the effect of welding parameters on residual stress build up. The 3D simulations are performed using ABAQUS code for thermo-mechanical analyses with moving heat source, material deposition, solid-liquid phase transition, temperature dependent material properties, metal elasticity and plasticity, and transient heat transfer. Quasi Newton method is used for the analysis routine and thermo-mechanical coupling is assumed; i.e. the thermal analysis is completed before performing a separate mechanical analysis based on the thermal history. The residual stress build up and temperature history state in a three-dimensional analysis of the tee joint is then compared to experimental results. Hole drilling method is used for measuring the residual stress, while temperature history is measured by thermocouples. After carrying out numerical simulations, the effects of voltage/current, welding speed, material thickness and size of electrode on residual stress build-up and resulting distortions are evaluated.     

Mechanical characterization of steel/CFRP double strap joints at elevated temperatures

This paper examines the mechanical performance of steel/CFRP adhesively-bonded double strap joints at elevated temperatures around the glass transition temperature (T_g, 42 °C) of the adhesive. A series of joints with different bond lengths were tested to failure at temperatures between 20 °C and 60 °C. It was found that the joint failure mode changed from adherend failure to debonding failure as the temperature approached T_g. In addition, the ultimate load and joint stiffness decreased significantly at temperatures near to and greater than T_g, while the effective bond length increased with temperature. Based on the ultimate load prediction model developed by Hart-Smith for double lap joints and kinetic modelling of the mechanical degradation of the adhesive, a mechanism-based model is proposed to describe the change of effective bond length, stiffness and strength degradation for steel/CFRP double strap joints at elevated temperatures. The modelling results were validated by the corresponding experimental measurements.     

Strength prediction of adhesive joints after cyclic moisture conditioning using a cohesive zone model

This paper presents a methodology to predict the strength of adhesive joints under variable moisture conditions. The moisture uptake in adhesive joints was determined using a history dependent moisture prediction methodology where diffusion coefficients were based on experimental cyclic moisture uptake of bulk adhesive samples. The predicted moisture concentrations and moisture diffusion history were used in a structural analysis with a cohesive zone model to predict damage and failure of the joints. A moisture concentration and moisture history dependent bilinear cohesive zone law was used. The methodology was used to determine the damage and failure in aluminium alloy – epoxy adhesive single lap joints, conditioned at 50 °C and good predictions of failure load were observed. The damage in the adhesive joints decreased the load carrying capacity before reaching the failure load and a nonlinear relationship between the load and displacement was observed. Changes in crack initiation and crack propagation were also observed between different types of joints. The presented methodology is generic and may be applied to different types of adhesive joint and adhesive.     

CFRP复合材料螺栓连接失效载荷不确定性的评估方法

螺栓连接是先进复合材料结构的薄弱环节。因此,螺栓连接力学性能显著的不确定性不仅阻碍了先进复合材料的高效应用,且给整体结构的安全性和可靠性带来威胁。为定量评估碳纤维增强树脂(CFRP)复合材料螺栓连接失效载荷的不确定性,将数值的渐进损伤模型和区间分析方法结合,提出了一种高效、准确的分析方法。采用该方法预测了典型T800碳纤维/X850环氧树脂复合材料螺栓连接失效载荷的不确定性,并与试验结果进行对比。预测结果与试验结果的误差不超过2%,证明本文所提出方法的有效性。采用本文所提方法预测的T800碳纤维/X850环氧树脂复合材料螺栓连接失效载荷的区间为[19.25 kN, 22.75 kN],与设计期望值的偏差为[?9.8%, 6.6%]。