Research of Elastic and Elastic-Plastic Deformation on Bending Problems of Variable Stiffness Beams

A novel variable stiffness model was proposed for analyzing elastic-plastic bending problems with arbitrary variable stiffness in detail.First,it was assumed that the material of a rectangular beam is an ideal isotropic elastic-plastic material,whose elastic modulus,yield strength,and section height are functions of the axial coordinates of the beam respectively.Considering the effect of shear on the deformation of the beam,the elastic and elastic-plastic bending problems of the axially variable stiffness beam were studied.Then,the analytical solutions of the elastic and elastic-plastic deformation of the beam were derived when the cross-section height and the elastic modulus of the material were varied by special function along the length of the beam respectively.The elastic and elastic-plastic analysis of the variable stiffness beam was carried out using Differential Quadrature Method(DQM)when the bending stiffness varied arbitrarily.The influence of the axial variation of the bending stiffness on the elastic and elastic-plastic deformation of the beam was analyzed by numerical simulation,DQM,and finite element method(FEM).Simulation results verified the practicability of the proposed mechanical model,and the comparison between the results of the solutions of DQM and FEM showed that DQM is accurate and effective in elastic and elastic-plastic analysis of variable stiffness beams.

Arterial stiffness expressed as brachial–ankle pulse wave velocity and gait assessment independent of lower extremity strength:a cross-sectional study in the older men population

BACKGROUND Older men are more vulnerable to fatal falls than women,and gait disturbances contribute to the risk of falls.Studies have assessed the association between arterial stiffness and gait dysfunction,but the results have been inconclusive.This study aimed to conduct a cross-sectional analysis to evaluate the association between brachial–ankle pulse wave velocity(baPWV)and gait assessment in older men.METHODS Data from the 2014–2015 Korea Institute of Sport Science Fitness Standards project were used for the analysis.The inclusion criteria were men aged>65 years with gait assessment[the 30-s chair stand test(30s-CST),the timed up and go(TUG)test,the figure-of-8 walk(F8W)test,the 2-min step test(2MST),and the 6-min walk test(6MWT)]and baPWV measurement data.Generalized linear regression analysis was conducted with multiple confounding factor adjustments,including lower extremity isometric strength.RESULTS A total of 291 participants were included in the analysis.The mean age was 71.38±4.40 years.The mean values were as follows:(1)30s-CST,17.48±5.00;(2)TUG test,6.01±1.10 s;(3)F8W test,25.65±4.71 s;(4)2MST,102.40±18.83 per 2 min;and(5)6MWT,500.02±85.65 m.After multivariable adjustment,baPWV was associated with the 6MWT(β=−0.037,95%CI:−0.072–−0.002),TUG test(β=0,95%CI:0.000–0.001),and F8W test(β=0.002,95%CI:0.000–0.004).baPWV was not associated with the 30s-CST and 2MST.CONCLUSIONS The current study showed a statistically significant association between gait assessments and arterial stiffness,independent of lower extremity strength.However,this association was modest.Future prospective studies are needed to elucidate the complex relationship between arterial stiffness and gait dysfunction.

An elastic-plastic analysis of short-leg shear wall structures during earthquakes

Short-leg shear wall structures are a new form of building structure that combine the merits of both frame and shear wall structures. Its architectural features, structure bearing and engineering cost are reasonable. To analyze the elastic-plastic response of a short-leg shear wall structure during an earthquake, this study modified the multiple-vertical-rod element model of the shear wall, considered the shear lag effect and proposed a multiple-vertical-rod element coupling beam model with a new local stiffness domain. Based on the principle of minimum potential energy and the variational principle, the stiffness matrixes of a short-leg shear wall and a coupling beam are derived in this study. Furthermore, the bending shear correlation for the analysis of different parameters to describe the structure, such as the beam height to span ratio, short-leg shear wall height to thickness ratio, and steel ratio are introduced. The results show that the height to span ratio directly affects the structural integrity; and the short-leg shear wall height to thickness ratio should be limited to a range of approximately 6.0 to 7.0. The design of short-leg shear walls should be in accordance with the ＂strong wall and weak beam＂ principle.

Prediction Model for Fatigue Stiffness Decay of Concrete Beam Based on Neural Network

With the method of neural network, the processes of fatigue stiffness decreasing and deflection increasing of reinforced concrete beams under cyclic loading were simulated. The simulating system was built with the given experimental data. The prediction model of neural network structure and the corresponding parameters were obtained. The precision and results were satisfied and could be used to investigate the fatigue properties of reinforced concrete beams in complex environment and under repeating loads.

Research on Performance of a Rectangular Floatation Cushion with High Stiffness for a Pneumato-static Slideway

In this paper, a high stiffness rectangular floatation cushion with a variable-section pressure equalizing groove of an elastic membrane for a pneumato-static slideway is presented and designed in order to increase stiffness of the floatation cushion. Gas film pressure distribution and carrying capacity of the floatation cushion are studied through theoretical analysis and by using the overlapping stitching technique. The carrying capacity and stiffness were obtained by using the coupling procedure of the gas lubrication governing equation and elastic deformation of the membrane governing equation. The results of theoretical calculations can obtain a conclusion that the effect of the gas pressure makes the annular elastic membrane elastically deform that brings about changes of throttling area and pressure groove depth of the floatation cushion. It makes carrying capacity and stiffness of the new style floata- tion cushion markedly improve over the conventional flotation cushion. The new floatation cushion has a wider ap- plication and popularization of space. Key words： floatation cushion; variable-section pressure equalizing groove;stiffness

Development of a Passive Ankle Foot Prosthesis with Manually Adjustable Ankle Stiffness

Major advancements have been made in the field of prosthetics, but devices remain largely out of reach for the amputee population domiciled in the developing nations, which makes up 80% of the entire amputee population of the world. The amputees are left to contend with low function prosthetics that do not mimic the behavior of the natural lost limb, with the long-term use of such devices leading to physical injury to the user. This work was aimed at developing a low-cost ankle-foot prosthesis that affords the user the opportunity to manually alter the stiffness of the ankle, as well storing energy in a forefoot section to aid push-off in late stance. In this paper, the design and results of structural analysis performed on critical parts of the prosthesis are presented, as well as the future direction of the work.

A family history of diabetes is not associated with arterial stiffness in non-diabetic Japanese population

Prevalent diabetes is at high risk for cardiovascular diseases and has a high familial inheritance. However, little is known whether a non-diabetic subject with a family history of diabetes is at high risk for vascular damage or not. The purpose of this study was to evaluate the association between a family history of diabetes and arterial stiffness in adult non-diabetic Japanese population. We analyzed eligible 787 non-diabetic subjects (502 men and 285 women) aged 35-69 years who enrolled in the baseline survey of a cohort study in Tokushima Prefecture, Japan and who underwent a brachial-ankle pulse wave velocity (ba-PWV) measurement. Information on individual life-style characteristics including medical history and treatment for diseases and a first-degree family history of diabetes was obtained through a structured self-administered questionnaire. Analysis of covariance and logistic regression analyses were used to evaluate the association between a family history of diabetes and ba-PWV. We found no differences in age-and-systolic blood pressure-adjusted and multivariate-adjusted means of ba-PWVs between subjects of both sexes with and without a family history of diabetes. Logistic regression analyses including both sexes also revealed that subjects with a family history of diabetes showed no differences in age-and-systolic blood pressure-adjusted and multivariate-adjusted odds ratios for high ba-PWV compared to those without that trait. Our results suggest that a family history of diabetes itself is not associated with arterial stiffness in adult non-diabetic Japanese population.

Development of component stiffness equations for thread-fixed one-side bolt connections to an enclosed rectangular hollow section column under tension

The derivation and validation of analytical equations for predicting the tensile initial stiffness of threadfixed one-side bolts(TOBs),connected to enclosed rectangular hollow section(RHS)columns,is presented in this paper.Two unknown stiffness components are considered:the TOBs connection and the enclosed RHS face.First,the trapezoidal thread of TOB,as an equivalent cantilevered beam subjected to uniformly distributed loads,is analyzed to determine the associated deformations.Based on the findings,the thread-shank serial-parallel stiffness model of TOB connection is proposed.For analysis of the tensile stiffness of the enclosed RHS face due to two bolt forces,the four sidewalls are treated as rotation constraints,thus reducing the problem to a two-dimensional plate analysis.According to the load superposition method,the deflection of the face plate is resolved into three components under various boundary and load conditions.Referring to the plate deflection theory of Timoshenko,the analytical solutions for the three deflections are derived in terms of the variables of bolt spacing,RHS thickness,height to width ratio,etc.Finally,the validity of the above stiffness equations is verified by a series of finite element(FE)models of T-stub substructures.The proposed component stiffness equations are an effective supplement to the component-based method.

Plate reinforced square hollow section X-joints subjected to in-plane moment

The static test of 13 square hollow section(SHS) X-joints with different β and different types of plate reinforcement under in-plane moment in brace was carried out. Experimental test schemes, failure modes of specimens, moment-vertical displacement curves, moment-deformation of the chord, and strain strength distribution curves were presented. The effect of β and plate reinforcement types on in-plane flexural property of SHS X-joints was studied. Results show that punching shear of chord face disappears, brace material fracture appears and concave and convex deformation of chord decrease when either collar plates or doubler plates were welded on chord face. Moment-vertical displacement curves of all specimens have obvious elastic, elastic-plastic and plastic stages. As β increases, the in-plane flexural ultimate capacity and initial stiffness of joints of the same plate reinforcement type increase, but ductility of joints decreases. With the same β, the in-plane flexural initial stiffness and ultimate capacity of doubler plate reinforced joints, collar plate reinforced joints, and unreinforced joints decrease progressively. Thickness of reinforcement plate has no obvious effect on in-plane flexural initial stiffness and ultimate capacity of joints. As thickness of reinforcement plate increases, the ductility of reinforced X-joints decreases. The concave and convex deformation of every specimen has good symmetry;as β increases, the yield and ultimate deformation of chord decrease.

考虑衬砌截面协调变形约束的既有隧道受盾构下穿施工影响的Fourier能量变分解

目前关于新建盾构开挖诱发既有地铁隧道变形的理论研究,大多将既有隧道简化为不含接头的Euler-Bernoulli梁,而忽视了衬砌截面的剪切变形与管片接头的局部刚度削弱。此外,既有地基模型理论较少考虑衬砌管片与接触土体的协调变形约束。首先,采用Loganathan-Polous公式计算盾构开挖诱发的土体自由位移场,并将既有隧道视为考虑剪切变形的Timoshenko梁,基于沿轴线变化的抗弯与剪切刚度函数来描述管片接头的局部削弱作用;然后,结合能量变分原理与连续弹性体Mindlin解,建立考虑衬砌截面协同变形约束的隧道位移控制方程,将盾构开挖诱发的附加荷载施加于既有隧道,并使用Fourier级数方法求解既有隧道纵向变形;最后,将Fourier能量变分解与3组工程实测数据进行对比验证,取得了较好的一致性。此外,考虑隧道抗弯刚度、剪切刚度、接头刚度削弱作用、土体参数与隧道空间位置等因素的共同影响,使用抗弯系数、剪切系数及接头系数进行敏感性分析。结果表明,考虑截面变形协调约束的理论解更为符合实际,不考虑变形协调约束所得隧道位移结果偏大;衬砌接头局部刚度的削弱作用将造成隧道弯矩沿轴线在接头处发生明显锯齿状突变;抗弯系数与剪切系数的增长均导致隧道结构所受弯矩降低;剪切系数由低到高的增长将导致隧道变形模式发生“弯曲控制-弯剪混合-剪切控制”三阶段变化;隧道变形模式进入“剪切控制”阶段的过程中,抗弯刚度的变化对隧道内力影响逐渐降低;接头系数的增长将造成隧道所受弯矩降低,但隧道抗弯刚度较大时其影响逐渐减弱。

简支钢箱梁截面设计主要影响因素分析

该文采用迈达斯civil软件建立了相同截面面积下不同梁高、底板宽、顶板厚、底板厚和腹板厚的简支钢箱梁计算模型,对比分析强度和刚度值,确定简支钢箱梁截面设计的主要影响因素。

双块式无砟轨道端梁区高温拱曲影响因素及控制技术

针对高速铁路双块式无砟轨道线路路基段两头端梁区附近道床板上拱问题,采用有限元方法,研究不同温度组合、路基段长度及端梁桩土约束刚度对道床板上拱的影响规律。结果表明:道床板的温度变形是引起上拱的主因,但支承层的变形扰动及其与道床板的温度变形组合效应不可忽视;随着路基段长度的增加,上拱幅值增加趋势明显;端梁的桩土约束对上拱的影响较为复杂,在中间某一特定约束刚度时上拱达到峰值,而当约束刚度无论变大或变小,上拱都呈现变小的趋势;断开支承层对控制高温上拱变形效果不显著,断开道床板则效果显著,但需协调考虑对应区段的钢轨受力。

基于等效刚度法优化的风力机叶片刚度计算

风力机叶片刚度由于非线性且截面变化程度大的特点,针对叶片建模初期刚度的评估问题通常采用刚度展项分布图体现叶片刚度,存在评估叶片刚度的参考参数不够直接、宏观的问题。基于变刚度梁挠度计算的等效刚度法,将叶片等效成变截面悬臂梁,根据叶片特征合理选取边界条件,以叶片建模的截面数据特点为基础,优化原始等效刚度法的计算方式,使该方法更加贴合叶片模型,从而适用于叶片,达到方法优化的目的。利用ANSYS有限元软件进行叶片的预应力模拟实验,得出叶片的挠度模拟数值,以该模拟计算的挠度值为参考,验证优化后方法的有效性。结果表明:优化后的等效刚度法得到的刚度值,在低均布载荷值22.5 Pa下理论计算的挠度值与试验挠度值的误差达到9.68%,减小原始方法计算的误差贴近叶片模型,可用于叶片刚度估算,为叶片的刚度计算提供新方法。

全铁尾矿混凝土梁受弯性能试验研究

为了充分利用铁尾矿,对铁尾矿混凝土结构的力学性能进行探究,以铁尾矿粉为掺合料,铁尾矿碎石和铁尾矿砂分别作为粗、细骨料,制备成全铁尾矿混凝土(FITC)梁,并与以粉煤灰作掺合料,普通碎石及河砂作粗、细骨料的常规混凝土(CC)梁进行弯曲试验对比。首先,测试铁尾矿的各项参数,验证其作为混凝土原材料的可行性;其次,基于现行规范公式计算梁各阶段的承载力和挠度;最后,将FITC梁和CC梁的实测数值和计算数值对比分析。结果表明:FITC的强度比CC略低,弹性模量显著降低;FITC梁的开裂弯矩和极限弯矩与CC梁相当,梁的抗裂能力与承载力并未因FITC的强度和弹性模量比CC低而明显降低;在裂缝出现之前,FITC梁的混凝土应变与平截面假定基本一致;在荷载作用下,FITC梁受拉区混凝土应变比CC梁的大;FITC梁的延性、裂缝开裂间距均与CC梁接近,FITC梁弯剪区斜裂缝比CC梁更接近梁的顶部;在同等弯矩下,FITC梁的挠度大于CC梁的挠度,FITC梁的受拉纵筋应变也大于CC梁;中国现行设计规范对FITC梁的承载力计算是安全的,但挠度计算公式需要修正。

超大截面大跨度劲性梁的混凝土浇筑施工技术

劲性混凝土结构具有抗震性能好、节约用钢量、防火防腐性能好、提高混凝土利用率等优势,被广泛应用于超高层、大跨度建筑物和桥梁结构等。基于佛莞城际莲花工区盖板工程,介绍了一种超大截面大跨度劲性梁混凝土的浇筑施工技术,解决了大截面大跨度劲性梁混凝土浇筑难度大、质量要求高的难题。

中等减振梯形轨枕轨道结构关键设计参数

为研究中等减振梯形轨枕轨道的动力学特性,采用直接刚度法建立了车辆-梯形轨枕轨道-隧道垂向耦合动力学模型,分析了减振垫垂向静刚度和梯形轨枕厚度对钢轨、轨枕和隧道动力响应的影响。结果表明:当减振垫静刚度在15~30 kN/mm时,减振效果均达到了中等减振要求,梯形轨枕减振垫的垂向静刚度可以根据环境敏感点的具体振动超标量进行选取;与普通整体道床相比,当梯形轨枕的板中减振垫垂向静刚度为25 kN/mm时,梯形轨枕在40 Hz以上的频率范围具有较好的减振效果;增加梯形轨枕厚度可以降低钢轨和轨枕的垂向位移,并通过增加参振质量的方式提高减振性能;当梯形轨枕厚度从0.15 m增至0.35 m时,钢轨垂向位移、轨枕垂向位移和隧道垂向加速度减小幅度达7.73%、和6.82%和18.18%;中等减振梯形轨枕轨道与普通整体道床衔接时,需要在梯形轨枕铺设段设置3块5.8 m过渡梯形轨枕,过渡梯形轨枕的减振垫静刚度应优先按照三级刚度过渡方案进行选取。

含裂纹少片变截面钢板弹簧的刚度特性分析

利用SolidWorks和ANSYS软件建立了含裂纹的少片变截面钢板弹簧三维仿真模型,通过分析不同位置、角度、深度的裂纹影响下钢板弹簧的刚度特性,探究了裂纹位置、角度、深度对弹簧刚度的影响规律。结果表明:横向裂纹对钢板弹簧刚度影响显著,裂纹位置越接近板簧根部平直段1/3长度处、裂纹角度越接近90°、裂纹越深,影响程度越大,钢板弹簧刚度越小;纵向裂纹对钢板弹簧刚度的影响轻微,刚度变化很小;一定深度范围内,含裂纹钢板弹簧的刚度较无裂纹钢板弹簧的刚度略大。

横梁截面形状对扭力梁扭转刚度影响分析

横梁是构成扭力梁总成最重要的零件,它直接影响扭力梁总成的扭转刚度。文章通过对扭力梁横梁形状和设计参数的研究,找出满足扭力梁扭转刚度的最佳的横梁结构,为设计类似扭力梁提供参考。通过CATIA软件建立3D扭力梁模型,并采用CATIA软件分析模块工具,分析不同横梁顶部半径R、横梁中间空间面积S、横梁中间高度差Z等对扭力梁刚度影响情况,总结出横梁形状优化的方法。经不同横梁形状参数计算结果表明,该方法对扭力梁横梁优化设计很有效,对设计管状扭力梁有很好的指导作用。

装配式变电站钢框架梁截面选型与优化研究

钢框架结构已取代钢筋混凝土框架结构成为装配式变电站配电装置楼的主要结构型式。不同于钢筋混凝土结构,钢结构设计标准未对钢框架梁高跨比做出明确规定,其截面选型依赖于设计人员经验和多次试算,选型不当易造成用钢量浪费。文章通过对钢框架结构简化模型静力分析和理论推演,得到最优梁柱线刚度比和梁临界高跨比,并结合变电站实际案例分析,从而推导出适合变电站的钢框架梁推荐高跨比,为变电站钢框架梁截面选型和优化提供依据。

楔形劲性复合桩水平承载特性的影响因素研究

为了分析楔形劲性复合桩的水平承载特性,以及不同桩身尺寸参数对其水平承载力的影响,采用数值模拟的方式建立三维有限元分析模型,对比分析楔角、平均截面含芯率和芯长比对楔形劲性复合桩水平承载特性的影响。结果表明,在线弹性阶段,同体积下1°楔角楔形劲性复合桩的水平承载力明显高于普通劲性复合桩,增大楔角能够有效减少桩身位移;增大楔角对水平承载能力的提升最大,平均截面含芯率次之,芯长比的影响最小。