Stiffeners layout design of thin-walled structures with constraints on multi-fastener joint loads

The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures. Multi-fastener joint loads and manufacturing constraints are considered simultaneously. On one hand, the joint loads are calculated and constrained within a limited value to avoid the failure of fasteners. On the other hand, the manufacturing constraints of the material distribution in the machining directions of stiffeners are implemented by an improved piecewise interpolation based on a beveled cut-surface. It is proven that the objective function is strictly continuous and differentiable with respect to the piecewise interpolation. The effects of the extended method with two different constraints are highlighted by typical numerical examples. Compared with the standard topology optimization, the final designs have clearly shown the layout of stiffeners and the joint loads have been perfectly constrained to a satisfying level.

Topology optimization of joint load control with geometrical nonlinearity

This paper presents an extended topology optimization approach considering joint load constraints with geo-metrical nonlinearity in design of assembled structures.The geometrical nonlinearity is firstly included to reflect the structural response and the joint load distribution under large deformation.To avoid a failure of fastener joints,topology optimization is then carried out to minimize the structural end compliance in the equilibrium state while controlling joint loads intensities over fasteners.During nonlinear analysis and optimization,a novel implementation of adjoint vector sensitivity analysis along with super element condensation is introduced to address numerical instability issues.The degrees of freedom of weak regions are condensed so that their influences are excluded from the iterative Newton-Raphson(NR)solution.Numerical examples are presented to validate the efficiency and robustness of the proposed method.The effects of joint load constraints and geometrical nonlinearity are highlighted by comparing numerical optimization results.

Responses of jointed rock masses subjected to impact loading

Impact-induced damage to jointed rock masses has important consequences in various mining and civil engineering applications. This paper reports a numerical investigation to address the responses of jointed rock masses subjected to impact loading. It also focuses on the static and dynamic properties of an intact rock derived from a series of laboratory tests on meta-sandstone samples from a quarry in Nova Scotia, Canada. A distinct element code(PFC2D) was used to generate a bonded particle model(BPM) to simulate both the static and dynamic properties of the intact rock. The calibrated BPM was then used to construct large-scale jointed rock mass samples by incorporating discrete joint networks of multiple joint intensities into the intact rock matrix represented by the BPM. Finally, the impact-induced damage inflicted by a rigid projectile particle on the jointed rock mass samples was determined through the use of the numerical model. The simulation results show that joints play an important role in the impactinduced rock mass damage where higher joint intensity results in more damage to the rock mass. This is mainly attributed to variations of stress wave propagation in jointed rock masses as compared to intact rock devoid of joints.

Evaluation on Fracture Toughness at Dynamic Loading for Welded Joint Based on the Local Approach

The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.

Effect of Weld Parameters on Effective Notch Stress at Weld Root and Toe of Load Carrying Cruciform Joints

Cruciform joints in ships are prone to fatigue damage and the determination of type of weld plays a significant role in thefatigue design of the joint. In this paper, the effect of weld geometry on fatigue failure of load carrying cruciform joints inships is investigated using Effective Notch Stress (ENS) approach. A fictitious notch of 1 mm radius is introduced at theweld root and toe and fatigue stress is evaluated. The effect of weld leg length (l) and weld penetration depth (p) on ENS atweld root and toe are determined. The critical weld leg length (lcr) at which fatigue failure transitions from weld root toweld toe is investigated. An approximation formula for determination of the critical weld leg length considering weldpenetration depth (p) is proposed.

Shape design of the reinforcement for bending load-carrying capacity of under-matched butt joint under four-point bending load

To improve the bending load-carrying capacity （ BLCC） of under-matched butt joint under four-point bending load in the elastic stage, the shape design of the reinforcement is studied based on the theoretics of mechanics of materials. The concept, criterion, realization condition and design proposal of equal bending load-carrying capacity （EBLCC） are put forward. The theoretical analysis results have been verified by the finite element method. The simulation results are coincident basically with the ones of theoretical analysis. The research results show that the shape design of the reinforcement of EBLCC can improve BLCC of under-matched butt joint and the unilateral-side type reinforcement can replace double-side symmetry

Uncertainty and joint probability of sea ice loads

Ice load is one of the most important factors for design of marine stuctures in cold sea area.The designcriteria of ice loads for marine structures consist of two parts: level ice thickness and crushing strength. Due to thestrong randomness of the affecting factors on ice thickness and crushing strength, such as ice temperature,air temperature, water temperature,salinity,wind field, numerical simulation method method can not produce satisfactory results. Thispaper proposes a method of uncertainty analysis and joint probabilistic prediction of level ice thickness and crushingstrength instead of traditional ice load criteria for marine structures.

Behaviour of a Moment Resisting Composite Steel and Concrete Joint Under Alternate Loading

The authors show the results of a study conducted on a joint connecting a concrete column to a composite steel concrete floor,subjected to tension on the beams as a result of the decomposition of sagging bending moment.The beam to column connection is achieved by means of headed studs welded to the beam and embedded in the concrete cast.Five different configurations have been tested at failure and the results are compared to formulae proposed in literature.Different degrees of ductility,reliability and strength have been obtained varying geometry and reinforcement ratio on the joints tested.

Finite Element Analysis (FEA) for the Beam-Column Joint Subjected to Cyclic Loading Was Performed Using ANSYS

This paper analyses the seismic performance of exterior beam-column joints strengthened with unconventional reinforcement detailing. The beam-column joint specimens were tested with reverse cyclic loading applied at the beam end. The samples were divided into two groups based on the joint reinforcement detailing. The first group (Group A) of three non-ductility specimens had joint detailing in accordance with the construction code of practice in India IS456-2000, and the second group (Group B) of three ductility specimens had joint reinforcement detailed as per IS13920-1993, with similar axial load cases as the first group. The experimental studies are proven with the analytical studies carried out by finite element models using ANSYS. The results show that the hysteresis simulation is satisfactory for both un-strengthened and ferrocement strengthened specimens. Furthermore, when ferrocement strengthening is employed, the strengthened beam-column joints exhibit better structural performance than the un-strengthened specimens of about 31.56% and 38.98 for DD-T1 and DD-T2 respectively. The analytical shear strength predictions were in line with the test results reported in the literature, thus adding confidence to the validity of the proposed models.

Seismic Behavor of RC Beam-Column Joint with Additional Bars under Cyclic Loading

The behavior of Beam-Column Joints in moment resisting frame structures are susceptible to damage caused by seismic effects due to poor performance of the joint.A good number of researches were carried out to understand the complex mechanism of RC joints which are considered in seismic design code practices presently adopted.The traditional construction detailing of transverse reinforcement have shown serious joint failure. This paper introduces a new design philosophy involving the use of additional diagonal bars within the joint particularly suitable for low to medium seismic effects in earthquake zones throughout the world.In lieu to this study,ten(10) full-scale interior beam-column specimens were constructed with various additional reinforcement details and configurations as will be discussed in the later.The experiment provided adequate results to proof the idea of additional bars as suitable approach in reinforced concrete structures where earthquake is eminent.While compared with overall cracking observation during the test,the specimen with additional bars (diagonal and straight) had shown few cracks on the column than the ones without.Furthermore,concrete confinement is certainly an important design method as recommended by certain international codes.

基于孔洞扩张模型的偏心受力焊接球节点延性断裂数值模拟

在单层网壳结构中,焊接球节点偏心受力,常规有限元分析无法准确确定其与延性断裂对应的极限承载力。该文采用孔洞扩张模型(VGM)对偏心受力焊接球节点的延性断裂进行研究,明确了偏心受压和偏心受拉焊接球节点的失效模式,准确确定了偏心受拉焊接球节点延性断裂的位置和极限承载力。针对孔洞扩张模型要求极小有限元网格、计算效率较低的问题,采用基于VGM的连续损伤模型(CDM),编制用户子程序,在有限元分析中删除满足断裂判据的单元,对偏心受拉焊接球节点延性断裂全过程进行了数值模拟,通过与孔洞扩张模型的对比,验证了基于VGM的连续损伤模型对焊接球节点延性断裂分析的适用性。基于VGM的连续损伤模型允许采用较大网格进行断裂后裂纹扩展的数值模拟,极大地降低了计算成本。

Reinforcement Method of the Tubular Joints under Combined Loads Based on ANSYS Software

The jacket offshore platform structures working in the environment are subjected to various external conditions,such as wave loads,wind loads and corrosion of sea water.Therefore,the research on reinforcement of tubular joints has great practical value for the safety of offshore platforms.In this article,the finite element(FE)models of T-type tubular joint(T-joint)and K-type tubular joint(K-joint)are established by ANSYS software.Triangular rib reinforcement and collar plate reinforcement are used to reinforce the tubular joints.The reinforcement effects are assessed through the ultimate bearing capacity,and the influences of parameters of the rib and the collar plate on the ultimate capacity are analyzed.Besides,the effects of the two reinforcement methods are compared under the combined loads,and the results show that the reinforcement of the ribbed plate is more effective in resisting the deformation caused by bending moment,while the reinforcement of the collar plate is more effective to avoid the plastic damage caused by the axial pressure.

往复荷载作用后钢管混凝土柱-组合梁节点耐火性能数值分析

为研究钢管混凝土柱-组合梁节点在往复荷载作用后的耐火性能,利用有限元软件ABAQUS建立了该节点的有限元分析模型,并与已有试验结果进行对比验证。在此基础上,分析了往复荷载作用后塑性损伤和残余变形对组合梁节点火灾下的应力和变形的影响,以及不同损伤程度、荷载作用水平和防火保护层厚度对节点耐火极限和破坏模态的影响。结果表明:地震预损伤对节点的耐火极限有不利影响,且随损伤程度的增加,耐火极限下降明显;重度损伤下节点的耐火极限与无损伤节点相比降低了23.5%;重度损伤的节点在火灾作用下形成塑性铰,且产生较大的耗能损伤,轻度和中度损伤下未形成明显塑性铰,耐火极限分别仅下降1.0%和3.6%;对于以梁损伤作为预损伤模式的节点,梁荷载比和防火保护层厚度是影响有地震预损伤节点耐火极限的主要因素;随柱荷载比的增大,耐火极限呈降低趋势,但整体影响不大。

装配式钢结构全栓接刚节点的抗震性能分析

地震时强烈振动可能导致栓接节点的螺栓松动、滑移甚至断裂,影响节点的整体承载能力和稳定性,增加结构倒塌的风险。为减轻对主体结构的破坏,对装配式钢结构全栓接刚节点的抗震性能进行分析。计算出高强螺栓的用量并构建结构的几何模型,输入Abaqus有限元软件,考虑节点参数构建有限元模型,确定加载制度,以及地震载荷影响下该结构节点的抗震性能。模拟结果表明:相比于普通钢结构节点,用高强螺栓连接的装配式钢结构栓接节点,翼缘塑性铰外移,地震时稳定性更高;不同阶段该节点上的螺栓均发挥较强作用,不会出现严重应力集中,节点不易开裂;峰值载荷后该节点骨架曲线平滑稳定地下降,不会失去稳定性,具有较强抗震性能。

Seawater Corrosion Fatigue of Welded Joints Under Random Variable Amplitude Loading

Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine environment, random variable amplitude fatigue tests have been carried out on welded plate joints in sea water. The tests have been conducted under the conditions of loading frequency of 0.2 Hz/, stress ratio of -1, seawater temperature of about 20°C and cathodic protection with the potential about -850 mV, SCE. The test results have been compared with the seawater corrosion fatigue life under constant amplitude loading. Miner's linear cumulative damage summation rule has been used to predict the corrosion fatigue life under variable amplitude loading. The predicted life is in good agreement with the test data.

不同加速方式执行侧移动作对膝关节负荷的影响——基于一维统计参数映射分析

目的探讨以自由落地为加速方式执行侧移动作时对膝关节负荷的影响,为降低和预防前交叉韧带损伤提供生物力学依据。方法右90°方向的助跑侧移(RLS)和落地侧移(LLS),应用一维统计参数映射分析不同加速方式执行侧移动作对触地期膝关节负荷的影响。结果除身体重心垂直运动外,其余一维连续参数的显著性差异时段均出现在触地期的前21.38%;LLS的身体重心在触地时刻处于压力中心(COP)前方,未出现重心起伏增大现象;LLS的屈膝力矩、关节垂直受力、三维GRF及垂直负荷加载率均显著高于RLS;LLS表现出显著更高的膝外展和内旋力矩。结论落地侧移动作的膝关节损伤信号出现时段更早,膝关节承受更高的垂直负荷;在均受到胫骨近端前向剪切力情况下,落地侧移更高的膝关节外展与内旋力矩致使ACL张力负荷更大,这些因素均预示ACL损伤风险提高。

建筑钢结构梁柱节点的疲劳裂纹检测

钢结构在长期使用过程中,受到循环载荷的作用,梁柱节点处易出现疲劳裂纹。若不及时检测和处理,裂纹会扩展,最终导致断裂,严重影响建筑物的安全性和稳定性。为此,进行极端冲击载荷下建筑钢结构梁柱节点疲劳裂纹检测。统一用H300 mm×150 mm×6.5 mm×9 mm规格的H型钢梁、10.9级M20高强螺栓等制备3种梁柱节点试件LZ1、LZ2、LZ3。其中,LZ1、LZ2试件用相同的T型钢连接件,LZ2、LZ3试件均用材料和形状相同的H型柱,分别向3种试件施加相同的冲击载荷,用双探头穿透检测方法检测每种试件的疲劳裂纹。结果表明:LZ2、LZ3试件在极端冲击载荷下的疲劳裂纹长度、深度明显大于LZ1试件,且裂纹扩展速率相对较高;而用钢管-混凝土组合柱制成的LZ1梁柱节点试件在极端冲击载荷下的疲劳裂纹扩展速率仅为0.02×10^(-4)m/次,其裂纹长度、深度均较小。双探头穿透检测方法可选出最适用于建筑钢结构的梁柱节点材料。

空气手势教学法在肩关节运动解剖教学中的应用

目的基于学习投入分层分析空气手势教学法对康复治疗学专业学生肩关节运动解剖教学认知负荷的影响。方法将空军军医大学第二附属医院康复医学科实习的44名实习生随机分为手势教学组(n=22)和常规教学组(n=22)。常规教学组采用传统讲座形式对肩关节运动解剖进行教学,手势教学组由同一教师采用空气手势法进行教学。根据其学习投入水平进行分层,对比不同群体内两组实习生的认知负荷、成绩,以及教学效果情况。结果高投入群体中,手势教学组的相关认知负荷(Germane Cognitive Load,GCL)显著高于常规教学组(P<0.05);低投入群体中,手势教学组内在认知负荷(intrinsic cognitive load,ICL)得分显著低于常规教学组(P<0.05),GL得分显著高于常规教学组(P<0.05)。高投入群体两组学生的理论成绩与实践成绩均无统计学差异(P>0.05);低投入学习群体中手势教学组理论考试得分均显著高于常规教学组(P<0.05)。高投入群体手势教学组实习生仅教学热情方面评分显著高于常规教学组(P<0.05);而在低投入群体中,手势教学组学生的学习价值、知识宽度方面的评分显著高于常规教学组(P<0.05)。结论空气手势法的应用在不同学习投入群体中存在差异,具有降低学生内在认知负荷、提高相关认知负荷,并从多维度改善教学满意度的优势。

Analysis profile of the fully grouted rock bolt in jointed rock using analytical and numerical methods

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3 and T4with load transfer capacity,respectively 180 and 195 kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with2 NO flexi bolt 4 m better than other patterns within the faulted zone.

The joint long-term distribution of design environmental factors for offshore structures Multivariate probabilities and simulating method

With the development of ocean engineering, it is one of the most important factors which determine the structural safety, cost and suitable forms of engineerings to select the ocean environmental design criteria. Owing to the complexity , variation and randomness of ocean environmental conditions, the commonly used methods for determining design criteria cannot consider the joint occurring probabilities of several environmental factors ,therefore, lead to overestimate design criteria of them and result in an unnecessary overspend invest in engineering. On the basis of the measured and hindcasting data and the multi-demension joint probability theory, this paper presented the study of the joint loads of wind , wave and current on the offshore structures and its responsible joint probability level with the application of random simulation techniques, and presented the joint design criteria of environmental loads for the realistic design of engineerings.