结构可靠度算法的比较

讨论了现有结构可靠度的计算方法,介绍了JC法、二次二阶矩的ESORM法、一次渐近积分法、序列响应面法、Monte Carlo法以及直接重要抽样的Monte Carlo法,通过算例,对这些方法的精度以及适用范围作了分析,为可靠度的计算提供了一个有价值的参考。     

结构可靠度分析中Monte Carlo法的研究

结构可靠度作为一种预测结构破坏的量化形式,现已得到广泛运用.根据实际工程的需要,采用合适的可靠度计算方法非常重要.论文通过对结构可靠度的MonteCarlo法的具体方法,如直接抽样法、重要抽样法、方向抽样法和基于神经网络的MonteCarlo法进行了分析,得出了各种计算方法的特点.     

沥青路面结构的可靠度分析

介绍了沥青路面结构可靠度分析的基本概念和分析方法,探讨了进行沥青路面结构可靠度计算时所选计算指标的计算公式及概率分布类型,通过建立数学模型阐述了具体的计算方法.     

JC法在柔性路面结构可靠度计算中的应用

本文对目前研究的柔性路面结构可靠度的计算方法进行了讨论.在近十年的研究工作中,对于柔性路面结构可靠度的计算,我们采用过直接蒙特卡罗法、蒙特卡罗模拟统计分析法等,经过新近一些比较分析,发现采用JC法比较合适.该法不仅符合我国《工程结构可靠度设计统一标准(GB 50153-92)》推荐的方法,而且计算速度快,适应性好,精度又能满足工程设计的要求,故而推荐在今后柔性路面结构可靠度计算中采用.     

神经网络技术在预应力混凝土桥梁可靠度分析中的应用

预应力混凝土桥梁结构的极限状态函数往往是通过有限元分析得到的一种隐式的数值关系,而不是通常的显式表达式,采用响应面法进行该类结构可靠度分析较其他方法更为简便.相比于基于多项式的响应面法,神经网络拟合可以以任意精度逼近极限状态函数,从而提高响应面法在预应力混凝土桥梁可靠度分析中的精度.研究表明,神经网络技术可以直接用于预应力混凝土桥梁结构可靠度分析且具有较高的工程应用价值.     

基于悬索结构的体系可靠度方法研究

在悬索结构构件可靠度的基础上,以可靠度指标为失效模式识别的约界依据,通过对体系可靠度主要失效模式识别的3种计算方法的比较分析,生成较为精简的失效树,计算分析悬索结构的体系可靠度.分析表明:修正的β约界法在保证计算结果正确性的前提下,可以较大程度地精简失效树;悬索结构包含两个失效阶段的体系可靠度比包含一个失效阶段的体系可...     

工程结构可靠度理论综述

文章论述了工程结构可靠度理论的基本概念,总结了结构可靠度国内外研究现状;针对一次二阶矩法、响应面法及蒙特卡罗法三种常用的可靠度计算方法,分析研究了各个计算方法的特点。     

可靠度响应面有限元及其工程应用

可靠度响应面有限元是可靠度计算与响应面有限元的直接耦合,是采用有限元数值模拟来解决功能函数不能用解析式表示的结构可靠度问题的一类方法,对于大型复杂结构的可靠度分析有重要的意义.本文简述了响应面方法的研究发展,给出了可靠度响应面有限元的几类算法和可靠度计算的两种途径,并介绍了响应面有限元方法在实际工程中的应用情况.     

结构动力反应计算中几种数值方法的精度、速度和稳定性分析

直接积分法和振型叠加法系计算结构动力反应的两大类数值方法。本文对其中几种常用方法,如:Duhamel积分法、中心差分法,Z变换法、双线性Z变换法和Wilson-θ法等的计算速度、精度和稳定性进行了比较分析。结果表明,Duhamel积分法、Fox-Goodwin法、Z变换法和双线性Z变换法是比较理想的。在较宽的周期范围和阻尼比很小的情况下,具有较高的精度和稳定性,适用于具有不同自振周期和阻尼比的结构。其中,尤以Z变换的计算速度为最快,是值得推广的好方法。对短周期、小阻尼的结构,其它方法会产生较大的误差或不稳定。     

基于MATLAB的平面框架结构位移可靠度分析研究

基于结构可靠度分析数值模拟方法———蒙特卡罗法和响应面法的基本原理,利用MATLAB软件对一榀2跨3层框架在水平荷载作用下进行位移可靠度分析,分别采用了直接抽样蒙特卡罗法、响应面法、响应面—蒙特卡罗法、响应面—重要抽样蒙特卡罗法编制相应的计算程序,得到了结构水平位移最不利点的失效概率和可靠指标。计算结果表明,利用MATLAB可以编制结构可靠度分析程序,计算速度较快,数据合理,并为复杂结构的可靠性分析提供参考。     

Review: The Direct Strength Method of cold-formed steel member design

The objective of this paper is to provide a review of the development and current progress in the Direct Strength Method for cold-formed steel member design. A brief comparison of the Direct Strength Method with the Effective Width Method is provided. The advantage of methods that integrate computational stability analysis into the design process, such as the Direct Strength Method, is highlighted. The development of the Direct Strength Method for beams and columns, including the reliability of the method is provided. Current and ongoing research to extend the Direct Strength Method is reviewed and complete references provided. The Direct Strength Method was formally adopted in North American cold-formed steel design specifications in 2004 as an alternative to the traditional Effective Width Method. The appendices of this paper provide the Direct Strength Method equations for the design of columns and beams as developed by the author and adopted in the North American Specification.     

Effective Width Method for determining distortional buckling strength of cold-formed steel flexural C and Z sections

This paper proposes a design method, based on the Effective Width Method, for determining the nominal distortional buckling strength of typical cold-formed steel C and Z sections subjected to bending. The method can be integrated into the classic effective width design provisions specified in AISI S100, and it allows the conventional design approach to cover more comprehensive limit states. The proposed method is calibrated by the flexural distortional buckling strength predicted by the Direct Strength Method. Comparison with experimental results indicates that the proposed method yields reasonable predictions for the flexural distortional buckling strength of industrial standard C and Z sections. The method offers the same level of accuracy and reliability as the Direct Strength Method.     

冷弯型钢受压构件的LRFD抗力系数

目前,冷弯型钢抗压构件的LRFD抗力系数取值为0.85,该文旨在研究该系数能否增大。数据库中包含675组同中心荷载柱的试验数据,包含平口卷边C截面、平口卷边Z截面、帽形截面和角形截面以及开孔构件。采用美国钢铁协会标准和直接强度法计算每个试样的强度。直接强度法的计算结果更加精确,其在计算部分有效截面柱的强度时尤为精确。采用一阶二次矩法计算的LRFD抗力系数,与美国钢铁协会标准和直接强度法的规定相符。对于柱的两种破坏情况,达到畸变屈曲极限状态而破坏和由于整体失稳或局部-整体失稳相互作用而破坏,前者的计算结果更为精确。单角钢柱的试验强度与计算强度的比值有很大变化,随着整体长细比的增加,计算结果逐渐变得极为保守。     

Remarks to the Direct Strength Method

The effects of local plate buckling on the load carrying capacity of thin walled members are usually accounted for by the established method of effective widths. As a consequence, the current design concepts of such members are often complicated. Part of these complications arise from the need to determine effective properties of members. Therefore Schafer and Peköz developed the Direct Strength Method as an alternative to current practice. A strength curve for the entire member is used similarly to the strength curve for the effective width of an element.The Direct Strength Method is here compared to the approaches of effective width, reduced stress and effective thickness. A more profound understanding of the method's conception can be gained on this basis. As a result, the Direct Strength Method assumes the plastic reserve of the section shape to influence the cross-section capacity of locally buckled members. This assumption is checked by our own tests on thin-walled I-sections. A proposal to extend the Direct Strength Method to the interaction between axial force and bending is presented in a second step. Here, the limitations of the method will become clear. Particularly, the Direct Strength Method may lead to an overestimation of the ultimate load, if a shift of the effective centroid causes an additional bending moment. For the time being, the Direct Strength Method can therefore not be a general design concept and further investigations are necessary.     

Application of direct strength method to axially loaded perforated cold-formed steel studs: Distortional and local buckling

A study to develop methods of analyzing perforated, axially loaded, cold-formed steel studs using the provisions of the Direct Strength Method [American Iron and Steel Institute (AISI). North American Specification for the Design of Cold-Formed Steel Structural Members 2001 Edition with Supplement 2004 (AISI/COFS/NASPEC 2004) and Commentary (AISI/COFS/NASPEC 2004), Washington, DC; 2004] was undertaken using the Finite Strip Method as the method for determining the elastic buckling stresses. Several different models were developed to represent the effect of the web perforations. The capacities predicted using the Direct Strength Method for the limit states of distortional and local buckling were compared to capacities calculated using the equations contained in the AISI Specification [American Iron and Steel Institute (AISI). North American Specification for the Design of Cold-Formed Steel Structural Members 2001 Edition with Supplement 2004 (AISI/COFS/NASPEC 2004) and Commentary (AISI/COFS/NASPEC 2004), Washington, DC; 2004]. The limit state of longwave buckling is considered in a companion paper [Sputo T, Tovar J. Application of direct strength method to axially loaded perforated cold-formed steel studs: Part 1. Longwave buckling. Thin Walled Struct, submitted for publication]. The validity of the results is discussed and recommendations are made for the use of the Direct Strength Method for these members.     

Thin-walled steel columns with partially closed cross-section: Tests and computer simulations

Cold formed sections can be optimized for different purposes and they are fairly inexpensive to produce in small series. They have an inherent weakness in their small torsional stiffness, which is unfavourable for columns. One solution presented here is to make a closed section by adding a thin cover plate connected discretely with self-tapping screws. It is here called a partially closed cross-section because it is not continuously and rigidly connected. The aim of this paper is to evaluate the efficiency of this solution by comparing the behaviour of partially closed and open cross-section. Four columns were tested within the project, two of them with centric axial load and two with eccentricities. Numerical analysis was performed using ABAQUS for establishing the influence of the cover plate on the critical load and the resistance. A good agreement between non-linear FEM and experiments were found. After this verification of the FE model a parametric study was carried out. Results of experiments and numerical analysis were compared with the predicted resistance by Eurocode 3, Part 1–3, and the Direct Strength Method. Both design methods give good predictions of the resistance.     

可靠度及其反问题理论在桥梁中的应用

本文介绍了概率随机可靠度计算理论中改进的一次二阶矩法及可靠度反问题计算理论。为便于理解 ,以一算例简单介绍了多个设计参数可靠度反问题的计算思路。最后以一斜拉桥为例 ,应用改进的验算点法对斜拉桥主梁作了静力可靠性及相应的反问题计算 ,并对结果进行分析。     

大跨桥梁风致抖振疲劳可靠度近似分析及寿命估算

论述了大跨桥梁风致抖振疲劳分析及寿命估算方法。按寿命服从Ｗｅｉｂｕｌｌ分布假定,确定桥梁结 构抖振疲劳可靠度。根据桥梁结构疲劳目标可靠度,给出了简单的寿命计算公式。以虎门悬索桥为工程算例表 明,本文所述方法较之其它桥梁抖振疲劳分析方法更加简单明了,便于实用。     

外加预应力加固RC梁挠度计算的可靠度分析

以外加预应力加固RC梁挠度计算的工程实例,应用改进一次二阶矩法建立基于挠度计算的极限状态方程,通过四次迭代计算,得到外加预应力加固RC梁挠度计算的可靠度指标,并与一次二阶矩法得到的结果进行对比,结论表明,应用改进一次二阶矩法计算得到的可靠度指标具有更好的精度。