共查询到20条相似文献，搜索用时 656 毫秒
1.
This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due to snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50%-70% of load level at limit point. 相似文献
2.
It is of importance to study and predict the possible buckling of submarine pipeline under thermal stress in pipeline design.Since soil resistance is not strong enough to restrain the large deformation of pipeline,high-order buckling modes occur very easily.Analytical solutions to high-order buckling modes were obtained in this paper.The relationships between buckling temperature and the amplitude or the wavelength of buckling modes were established.Analytical solutions were obtained to predict the occurrence and consequence of in-service buckling of a heated pipeline in an oil field.The effects of temperature difference and properties of subsoil on buckling modes were investigated.The results show that buckling will occur once temperature difference exceeds safe temperature;high-order pipeline buckling occurs very easily;the larger the friction coefficients are,the safer the submarine pipeline will be. 相似文献
3.
A numerical investigation of thin-walled complex section steel columns with intermediate stiffeners was performed using finite
element analysis. An accurate and reliable finite element model was developed and verified against test results. Verification
indicates that the model could predict the ultimate strengths and failure modes of the tested columns with reasonable accuracy.
Therefore, the developed model was used for the parametric study. In addition, the effect of geometric imperfection on column
ultimate strength and the effect of boundary conditions on the elastic distortional buckling of complex section columns were
investigated. An equation for the elastic distortional buckling load of fixed-ended columns having different column lengths
was proposed. The elastic distortional buckling load obtained from the proposed equation was used in the direct strength method
to calculate the column ultimate strength. Generally, it is shown that the proposed design equation conservatively predicted
the ultimate strengths of complex section columns with different column lengths. 相似文献
4.
The buckle and collapse of offshore pipeline subjected to combined actions of tension, bending, and external pressure during
deepwater installation has drawn a great deal of attention. Extended from the model initially proposed by Kyriakides and his
co-workers, a 2D theoretical model which can successfully account for the case of simultaneous tension, bending, and external
pressure is further developed. To confirm the accuracy of this theoretical method, numerical simulations are conducted using
a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness
of this theoretical method. The model is then used to study the effects of several important factors such as load path, material
properties, and diameter-to-thickness ratio, etc., on buckling behaviors of the pipes. Based upon parametric studies, a few
significant conclusions are drawn, which aims to provide the design guidelines for deepwater pipeline with solid theoretical
basis. 相似文献
5.
The buckling response of pipe-in-pipe(PIP)systems subjected to bending is investigated in this paper. A set of parameterized models are established to explore the bending characteristics of the PIP systems through eigenvalue buckling analysis and nonlinear post-buckling analysis. The results show that the length of PIP systems and the height of centralizers are the most significant factors that influence the buckling moment, ultimate bending moment and buckling mode; the other geometric characteristics, such as initial geometric imperfection and friction between centralizers and outer pipes, evidently influence the post-buckling path and ductility of PIPs; the equivalent bending stiffness is dependent on the length and centralizers. Moreover, the range of equivalent bending stiffness is also discussed. 相似文献
6.
SUNG Wen-pei SHIH Ming-hsiang LIN Cheng-I GO Cheer Germ 《浙江大学学报(A卷英文版)》2005,6(8):878-885
INTRODUCTION The conventional design of rails uses steel clipboards and bolts to link rails, and avoids bucklingcaused by thermal expansion effect by mountingexpansion joints to solve axial restraint generated byseasonal or day-and-night temperature changes. Butthe discontinuity at the rail joints brings discomfortand noise to passengers when the train has suddenlystops or starts, during which train speed cannot beeffectively increased, rails are more easily damaged,and the cost of mainte… 相似文献
7.
Buckling design of large steel silos with various slendernesses 总被引：1，自引：0，他引：1
Large steel silos are typical kinds of thin-walled structure which are widely used for storing huge quantities of granular solids in industry and agriculture. In the present analyses, the buckling design of large steel silos subject to Eurocode-specified solid pressure is demonstrated. The finite element model is established using the commercial general purpose computer package ANSYS. Six types of buckling analyses are carried out for the geometrically perfect and imperfect models with and without consideration of material plasticity. The load cases of concentric discharge, discharge patch load, large eccentricity discharge, and large eccentricity filling are considered. The buckling behavior of six example steel silos with capacities of 30 000–60 000 m3 is investigated. The silos’ slenderness ranges from 4.77 to 0.35, comprising very slender, slender, intermediate slender, squat, and retaining silos. The index called the ratio of capacity to steel consumption (RCS) is initially defined in the paper, which provides an effective measure for the economical design of steel silos. It is validated that the RCS index increases rapidly with the decrease of silo slenderness, and the storage efficiency of steel silo improved greatly as the slenderness changes from slender silo to retaining silo. The effects of patch load reveal that the buckling modes in the case of discharge patch load are very different from those of silos under concentric solid pressure, and the effect is unfavorable for buckling resistance of all levels of slenderness of the example silos, but contributes a small decrease to the RCS index (less than 10%). The buckling deformations from both the linear and nonlinear buckling analyses in large eccentric discharge are strongly asymmetrical arising from the circumferential and meridional non-uniform distribution of the solid pressures. The buckling is mainly governed by the non-uniform distribution of the solid pressure other than other influential factors such as the weld imperfection, geometrical and material nonlinearity, compared with the load case of concentric discharge. The RCS index of example silos under large eccentric discharge is reduced substantially, and is approximately half that of silos under concentric discharge. The linear and nonlinear buckling deformations in large eccentric filling are also asymmetrical, deviating from the center to the side where the most friction locates to the highest wall contact. The RCS index of example silos under large eccentric filling is also reduced substantially, and is approximately 70% that of silos under concentric discharge. This reveals that the large eccentricity both in discharging and filling could result in a strong decrease of storage efficiency of steel silos. 相似文献
8.
9.
志愿服务在美国有着悠久的历史和传统,近现代以来发展迅速。其历史大致分为萌生阶段、发展阶段和规范阶段。当前,美国大学的志愿服务运行机制较为健全,主要包括招募机制、培训机制、评价机制和保障机制,这些机制的不断完善,有效地保障了美国大学志愿服务的有序运行。 相似文献
10.
Muhammad Abid Saleem Lynne Eagle Naveed Akhtar Allah Wasaya 《Journal of Marketing for HIGHER EDUCATION》2020,30(1):45-65
ABSTRACT This empirical investigation was aimed at conceptualizing, developing and validating a scale for the measurement of the quality of higher degrees by research (HDR-QUAL). For that purpose, this study specifically measured perceptions of higher degrees by research (HDR) students about the constituents of HDR quality in Pakistani tertiary education institutions. Following the 7-step process of scale development, three studies were conducted in order to develop an initial pool of scale items, establishing proposed scale validity and reliability, and assessing nomological behavior of the proposed scale. The principal component analysis with Varimax rotation method resulted in a 3-factor solution, subsequently proposing a 15-item scale. The model fit indices of measurement and the higher-order model indicated a satisfactory fit to data. Finally, the resultant three factors, i.e. financial assistance, supervisory expertise, and infrastructural support, converged into a unidimensional HDR-QUAL scale that was found positively associated with student satisfaction, thus, confirming nomological validity as well. Important policy measures and directions for future research are proposed at the end. 相似文献
11.
设计了一种热泵驱动的溴化锂溶液深度除湿机组,该机组适用于无回风可利用、低湿度需求的场合.机组的性能测试结果显示,当室外温度为28～31℃,含湿量为11～14g/kg时,机组的送风温度为1.6～2.6℃,含湿量为2.6～3.0g/kg,系统COP为1.8.测试时发现了一个造成冷热溶液混合损失的管路链接问题,并对其进行修改.然后,对修改后的新机组进行了性能测试,结果显示,在室外温度为25～32℃,含湿量为18～21g/kg时,机组的送风温度为3.2～4.0℃,含湿量为3.4～3.6g/kg,系统COP为2.8.最后,对机组建立数学模型,并将模拟结果与实测数据进行比较,结果表明管路改动使机组性能提升约20%. 相似文献
12.
2012年《刑事诉讼法》赋予技术侦查证据以证据能力,但由于技术侦查证据规范的不完善导致技术侦查措施面临从幕后走到台前的滥用风险,并引发了三大层面的价值矛盾,即保守秘密与人权保障的矛盾、证据价值发挥与司法资源合理配置的矛盾、真实发现与程序正义之间的矛盾。矛盾冲突的化解有赖于制度的力量,技术侦查证据规范本土化的构建思路为：对证据审查模式进行梯度设计、明确技术侦查证据使用的决定主体、构建非法技术侦查证据排除规则。 相似文献
13.
泉州木偶戏具造型风格及审美意蕴 总被引：1，自引：0，他引：1
陈晓萍 《泉州师范学院学报》2009,27(3):22-25
木偶的身份本体是雕塑,但它的身份主体却是一种戏具,所以它与一般雕塑所追求的终极美学价值是不一样的。通过对作为戏具的泉州木偶展开分析,认为其在雕刻时十分注重假定性、戏剧性和装饰性等舞台规律,从而塑造出数百个个性鲜明的舞台形象,折射出独特的审美价值。 相似文献
14.
The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40% 相似文献
15.
张烈洲 《石家庄铁路工程职业技术学院学报》2014,(2):70-73
随着社会发展以及科学技术的进步,控制爆破技术在城市规划尤其是棚户区改造项目中应用越来越广泛。由于控制爆破技术的不完善性以及爆破本身的危险性和不确定性,在进行爆破时实施安全防护尤为重要。结合贵州贵安新区摆门棚户区改造项目,介绍爆破施工方案、爆破施工技术设计、控制爆破的防护、爆破施工安全技术措施等。为今后同类工程施工提供借鉴。 相似文献
16.
为研究6061-T4铝合金方管压弯构件平面内稳定力学性能,建立ANSYS有限元模型,分析初始缺陷幅值和单元划分精度对数值计算稳定承载力的影响,并通过现有试验数据对ANSYS有限元模型加以验证。在此基础上,进一步分析构件长细比和荷载偏心率对构件稳定承载力的影响。将《铝合金结构设计规范》GB50429-2007压弯构件面内稳定计算公式得到的相关曲线与数值计算的相关曲线进行比较,发现规范公式偏保守较多。基于大量参数分析,建议对于强硬化铝合金,GB50429相关公式中修正系数η1改取0.8,将文中建议结果和数值计算结果进行比较,较原公式吻合更好。 相似文献
17.
A shelter system based on cable-strut structures,consisting of compressive struts and high-tensile elements,is described in this paper.The deployment of the shelter is achieved by tightening inclined cables.Lower cables are used to terminate the deployment.The state of self-stress of the cable-strut structures in the fully deployed configuration is given,and the minimum strut length and the maximum load design of the shelter are discussed.The mechanical behavior of the system was studied under symmetrical and asymmetrical load cases.The results show that the shelter in the deployed configuration satisfies the ultimate limit and the serviceability limit state conditions.Finally,the stability of the cable-strut system is investigated,considering the effect of imperfections on the buckling of the shelter.We conclude that the influence of imperfections based on the consistent imperfection mode method is not significant. 相似文献
18.
杨铭 《阿坝师范高等专科学校学报》2006,23(4):63-65
十六国时期以羌族为主导建立的后秦政权,其初期由于采取了一系列有助于社会稳定、恢复生产的措施,所以在姚兴执政的前十多年间,即公元四、五世纪交替之际,成为十六国后期入主中原的诸少数民族政权中的较为强盛者。但姚兴执政后期,沉溺佛教,有碍于政;加之朝臣频乱,内部不稳,故刘裕一朝北伐,后秦终致败亡。 相似文献
19.
In recent years, the extraction of fossil resources, especially oil and gas in deep and ultra-deep water areas has been playing a more important role and been paid more attention to. For this reason, the working depth of submarine pipelines, which are used for the transportation of oil and gas, has been increasing sharply. As the main failure pattern of deep-water pipelines, buckling and its propagation problem have drawn more attention of many research institutions and engineering units around the world. Based on the existing research, the summary of experiments and their outcomes of deep-water pipeline buckling failure is made in this paper. Research status and developing prospects of the experiments of buckling propagation and buckle arrestor are discussed in detail. 相似文献
20.
李良庚 《深圳职业技术学院学报》2010,9(1):50-53
水力过渡过程是大型输水管道工程运行维护管理中常见的现象,一旦引发水锤,会导致不必要的经济损失甚或人身危害．本文结合实例进行了水力过渡过程的数值模拟及水锤防护策略的制定,以期防患于未然,为工程设计、维护人员提供水锤问题的分析和处理思路． 相似文献