结构计算简图与工程施工例谈

不论何种建筑工程，在设计和施工中都必须对构件和结构进行各种计算或验算，以确定结构的计算简图，然后根据计算简图计算结构构件中的内力．确定构件截面。工程施工过程中，则应注意施工的计算简圈与设计的计算简图的是否一致。如果有所改变，则应弄清楚这种改变将会导致构件或结构的内力发生什么样的变化，以免造成构件或结构的破坏，甚至酿成工程事故。本文试结合工程实例就结构计算简图的选取原则及施工过程中计算简图与设计简图之间的差异可能导致的后果谈一些看法。     

地质情况不清的条件下天安门广场红飘带景观工程难点解析

红飘带景观工程由于特殊原因,不能进行岩土工程勘察。以红飘带景观工程为例,在地基条件不明确的情况下,通过建立可靠的设计分析方法,保证结构达到所要求的可靠度。上部结构计算分析时,在支座条件设定上,恰当地体现地基刚度的不同,提高上部结构构件内力计算结果的准确度。按照工程结构可靠度理论,控制不同条件下的构件内力,使得结构总体可靠度基本一致。     

某工程主体结构施工质量检测鉴定

工程结构质量检测是指实体结构现状的检测,本工程位于山东省日照市,检测项目包括结构布置调查、建筑外观质量检查、混凝土强度检测、混凝土碳化深度检测、混凝土构件钢筋配置检测、混凝土构件截面尺寸检测、外露钢筋检测、结构构件侧向位移检测,结构计算复核。     

非结构构件抗震设计研究

结合非结构构件的分类和抗震设防目标,介绍了非结构构件抗震设计的两种计算方法：等效侧力法和楼面反应谱法,并着重对非法结构构件中隔墙、女儿墙等的抗震设计加以说明,以期指导实际工程中非结构构件的设计。     

格构式构件整体稳定性分析的等效惯性矩法

通过位移比较的方法得出了格构式构件等效为实腹构件时等效惯性矩的计算公式。在不改变构件长度的情况下,实现了格构式构件到实腹式结构的等效。通过SAP有限元程序进行了大量的实例计算,计算结果表明该方法适合工程计算的应用。     

格构式构件整体稳定性分析的等效惯性矩法

通过位移比较的方法得出了格构式构件等效为实腹构件时等效惯性矩的计算公式。在不改变构件长度的情况下,实现了格构式构件到实腹式结构的等效。通过SAP有限元程序进行了大量的实例计算,计算结果表明该方法适合工程计算的应用。     

单层装配式厂房加固改造综合处理方案实例分析

通过对加固方法进行阐述,介绍加固方法的原理、施工工艺及注意事项。利用结构计算分析软件对厂房排架构件受力性能进行了计算,给出了厂房排架构件承载力计算的数值计算结果。通过加固构件与未加固构件的计算结果对比分析,可以得出,加固构件的加固方法在工业厂房中应用后承载力可以显著提高。通过工程实例的分析,可为类似工程处理提供成功经验。     

基于计算可靠度的在役RC结构构件的安全性评定

对考虑抗力衰减以及后续服役基准期不同的RC结构构件的可靠指标进行计算,通过研究计算得到的可靠指标与其安全等级之间的关系,给出了安全等级评定时的计算可靠指标标准;通过具体工程实例,运用JC法和改进一次二阶矩法,结合MATLAB优化工具箱计算在役RC结构构件的可靠指标。对照给出的安全等级标准,得出构件的鉴定安全等级,实现了RC结构构件安全性评定的定量描述。     

武汉水岸星城超高层结构抗震性能化设计

武汉水岸星城存在超高、楼板不连续、大底盘多塔等超限情况,目前结构性能化设计主要针对结构整体性能指标,少有用于结构构件承载力控制,该工程采用整体结构小、中、大震作用下弹性计算的抗震性能化设计方法,计算构件承载力和控制结构抗震性能,为抗震设防烈度6度地区相似工程抗震性能化设计提供参考。     

楼梯刚度对震区塔式建筑抗震设计的影响分析

按2008年版<建筑抗震设计规范>要求,利用计算机进行结构抗震分析,计算中应考虑楼梯构件的影响.工程实践表明,在计算少楼板大开洞建筑时,楼梯提供的刚度对结构刚度影响比较大,从而导致结构所受地震力有较大差异.设计这类建筑结构时,应严格按规范计算楼梯构件的影响.     

Reliability-based strength limit state for steel railway bridges

Railway bridges require special attention to provide safe and economical service. To assess the reliability of a structure, all critical parameters need to be specified. Load and resistance are random in nature; hence, the probabilistic approach is the best method for accurate evaluation of the performance of a bridge. In this study, identification of critical parameters was conducted on a typical through-plate girder, riveted, open deck railway bridge. This type of structure is a weakest link system. In such a system, the failure of one component can lead to failure of the entire structural system. This research involved identification of the basic load and resistance parameters and the development of analytical procedures for modelling the structural behaviour. The finite element method (FEM) was used to investigate the structural performance characteristics of the evaluated bridge. A three-dimensional structural model was developed to determine stress distribution in the members and connections. Based on the results of FEM analysis, the reliability indices were calculated for critical components.     

Redundancy-based service life assessment of corroded reinforced concrete elements considering parameter uncertainties

In order to assess the structural reliability and redundancy with respect to deterioration, appropriate models have to be selected which adequately describe the deterioration process. The parameters associated with these models have to be estimated based on statistical inference. In general, the uncertainties that arise from the estimation of parameters are not accounted for in reliability assessment and the obtained structural reliability indices are assumed to be constant values. When parameter uncertainties are considered, the structural reliability index can, however, be considered as a random variable which inevitably influences the full-probabilistic decision-making process. Furthermore, the structural reliability indices which are used in a reliability-based redundancy factor can be considered as random variables. Hence, this redundancy factor itself is a random variable as well. In this paper, a full-probabilistic framework is developed which allows for the service life assessment of reinforced concrete elements subjected to corrosion based on a probability-based redundancy factor and taking into account parameter uncertainties. It is proven that these parameter uncertainties have a significant influence on the lifetime estimates of concrete elements subjected to corrosion. Finally, a simplified method is proposed which allows to incorporate parameter uncertainties in the redundancy assessment.     

混凝土结构耐久性的概率极限状态设计法

混凝土结构耐久性设计中的一个重要方法就是概率极限状态设计法,这种方法根据描述耐久性劣化过程的数学模型,首先建立耐久性极限状态方程,再将环境作用与抗力作用的某个特征值与相应的分项系数代入极限状态方程,经验算就可在一定可靠度水准上得到耐久性设计参数的设计值.该法与我国混凝土设计规范的结构设计方法一致,其中的关键问题是选取描述耐久性劣化过程的数学模型与合适的设计参数.根据理论与经验相结合的碳化深度模型.选择混凝土保护层厚度与混凝土立方体抗压强度作为耐久性设计参数,建立了基于碳化寿命准则的耐久性概率极限状态设计方法,给出了碳化寿命耐久性接受准则、分项系数与设计表达式.该法适用于一般大气环境下不允许出现钢筋锈蚀的混凝土结构,根据设计表达式可直接确定满足使用寿命要求的保护层厚度与混凝上强度.     

An examination of methods for approximating implicit limit state functions from the viewpoint of statistical learning theory

The reliability analysis of complex structures is hindered by the implicit nature of the limit-state function. For their approximation use has been made of the Response Surface Method (RSM) and, more recently, of Neural Networks. From the statistical viewpoint this corresponds to a regression approach. In the structural reliability literature little attention has been paid, however, to the possibility of treating the problem as a classification task. This enlarges the list of methods that are eventually useful to the purpose at hand and justifies an overall examination of their distinguishing features. This task is performed in this paper from the point of view of the Theory of Statistical Learning, which provides a unified framework for all regression, classification and probability density estimation. The classification methods are grouped into three categories and it is shown that only one group is useful for structural reliability, according to some specific criteria. In this category are the Multi-Layer Perceptrons and the Support Vector Machines, which are the recommended methods because (a) they can estimate the function on the basis of a few samples, (b) they use flexible and adaptive models and (c) they can overcome the curse of dimensionality. The paper also includes an in-depth analysis of the RSM from the point of view of statistical learning. It is shown that the empirically found instability of this method is explained with statistical learning concepts.     

An incremental load formulation for limit states in the reliability analysis of nonlinear systems

The present paper outlines a method for system reliability analysis of framed structures considering nonlinear structural behaviour. Limit states are formulated using an incremental load formulation in differential form considering both random strengths and stiffnesses. The first order partial derivatives thus obtained can directly be used in the First Order Reliability Methods.

A simple example study is presented to illustrate the formulation and the importance of the refinements included compared to earlier formulation. The application of the approach to more general non-linear structures is outlined.     

Two-step seismic limit state design procedure based on non-linear LRFD and dynamic response analyses

Recently, the limit state design (LSD) or performance-based design have got popularity in the field of building design in Japan as well as in other countries. In the two design methods the structural reliability theory plays an essential role in setting design criteria as well as demonstrating the target reliability level to society. However, the conventional load and resistance factor design (LRFD) has been basically formulated supposing that safety checking is done on the basis of linear assumption of member forces and displacement. Therefore, when applying the LRFD for seismic design, for more accurate treatment of the non-linearity, a new procedure has to be explored especially for the ultimate limit state. Although several procedures for the structural reliability evaluation, treating non-linear displacement responses, have been proposed, they require complex procedures that may not be used in the practical design process. Accordingly, for applying it to a seismic LSD format based on the probabilistic concept, it is essential to manage two important requirements at the same time, accuracy and simplicity of procedure. In the present study, a new design format using the following two-step procedure is proposed to maintain both accuracy and simplicity; (1) a non-linear LRFD formulation, and (2) a formulation based on non-linear dynamic response analysis. Also, two design examples are presented.     

基于极限平衡法和有限元法的边坡协同式可靠度分析

极限平衡法和有限元法是两种常用的边坡稳定分析方法。基于极限平衡法的边坡可靠度分析计算效率较高,但需要假定失效模式,从而导致计算结果不准;与之相反,基于有限元法的边坡可靠度分析更为严格,但计算效率较低。为此,提出了一种新的基于随机模拟的边坡可靠度分析方法——边坡协同式可靠度分析方法。该方法包括初步可靠度分析和精细可靠度分析两步,可以同时利用极限平衡法和有限元法的优势,实现既高效又准确的边坡可靠度分析。通过一个考虑空间变异性的两层土坡算例验证了该方法的有效性,结果表明:协同式可靠度分析方法与基于有限元法的蒙特卡洛模拟或子集模拟相比,不仅具有一致的可靠度分析结果,而且显著提高了小概率水平下的计算效率,促进了基于有限元法的边坡可靠度分析在实际工程中的应用。该方法可以将基于极限平衡法的边坡可靠度分析成果合理纳入到基于有限元法的边坡可靠度分析中,从而获得大量的失效样本,以制定合理的边坡防治措施。该方法非常适用于高维可靠度问题,如考虑空间变异性的边坡可靠度问题。     

关于结构设计可靠性的探讨

按照规设计准则进行结构设计，只保证了结构构件极限状态的可靠度对目标可靠度的最小偏离，实际上无法得知构件的状态究竟是安全的还是不安全的；并且对于复杂的结构，规范难以保证分项系数的合理性。此时应该如何判断结构件设计的合理性：为此从结构设计中设计参数的确定方法出发，通过对设计过程进行几何描述，指出按照传统的设计方法得到的设计参数并不一定能保证结构构件的可靠性。问题解决的方法是对结构构件进行可靠度分析。通过对文末一个算例的分析，说明了以可靠度理论为基础的设计参数确定准则。     

“生命之环”结构设计关键技术

"生命之环"采用空间钢桁架+钢筋混凝土基座的混合结构体系,上部结构正立面投影为竖立在地面的变截面环,环内外轮廓为非同心圆,内圆直径150m,底部相切于人工湖面,外圆直径约170m,横截面为顶点朝外的正三角形。整体建筑高度约为160m,是目前世界上已建成最高的同类型构筑物。结构形体确定、抗风设计、多参数化空间钢桁架设计、施工模拟计算、钢桁架与混凝土基座连接支座构造以及大直径圆钢管相贯焊节点设计等均为结构设计的重点和难点。为了检验设计的可靠性,同时加强此类复杂工程的施工监控,在施工和使用过程进行了结构健康监测。     

一般大气环境下既有混凝土结构的耐久性评定与剩余寿命预测

结构耐久性设计是针对拟建结构而言的,相对于拟建结构,既有结构已转化为现实的空间实体,环境条件也更为明确,这种根本性的转变使得既有结构的可靠性分析和评定具有其自身的特点,原设计采用的分析模型和参数可能不再适用于既有结构的可靠度分析。以混凝土保护层开裂作为耐久性寿命的终结标准,将混凝土立方体抗压强度与混凝土保护层厚度作为耐久性评定参数,结合混凝土结构服役期间的碳化深度与钢筋锈蚀深度的实测数据,研究了一般大气环境中既有混凝土结构的耐久性评定问题,提出了耐久性评定的接受准则,建立了基于可靠度的耐久性评定的实用方法,包括极限状态函数、剩余寿命评定表达式以及耐久性评定的分级原则,并通过算例说明了评定过程。该法为一般大气环境下既有混凝土结构的耐久性评定提供了参考。