Optimal design base shear forces for reinforced concrete buildings considering seismic reliability and life-cycle costs

The objective of this study is to propose a novel estimation procedure for optimal design base shear forces for reinforced concrete (RC) buildings while considering the seismic reliability and life-cycle costs (LCCs) incurred by life-cycle earthquake events. By simulating life-cycle earthquake events within a specified period and using nonlinear dynamic analysis, including earthquake occurrences and their peak ground accelerations (PGAs), this study also derives the damage states of an RC building considering the effect of the cumulative damage. Additionally, besides life-cycle earthquake events, a simplified model is developed to modify the structural properties of a structure without seismic repair after earthquakes. Given the uncertainty of the occurrence time and PGAs of earthquake events, the seismic reliability, and expected current values of LCCs are calculated using Monte Carlo simulation. Although the case study addresses only an RC building with five stories in Taipei, optimal design base shear forces for low-rise RC buildings calculated via the same procedure can be derived and utilized when making decisions on the seismic level of a building based on safety and economic considerations. Therefore, the proposed method can help both owners and investors to identify LCCs of RC buildings due to seismic structural damage within a specified service life.     

A hybrid genetic based optimization procedure for aircraft conceptual analysis

The problem to define a methodology for the analysis of aircraft performances, in the phase of conceptual design, is addressed. The proposed approach is based on a numerical optimization procedure where a scalar objective function, the take-off weight, is minimized. Deterministic and stochastic approaches as well as hybridizations between these two search techniques are considered. More precisely, we consider two-stage strategies where the optimum localization is performed by a genetic algorithm, while a gradient-based method is used to terminate the optimization process. Also, another type of hybridization strategy is investigated where a partially converged gradient-based method is incorporated in the genetic algorithm as a new operator. A detailed discussion is made and various different solutions are critically compared. The proposed methodology is consistent and capable of giving fundamental information to the designer for further investigating towards the directions identified by the procedure. A basic example is described, and the use of the methodology to establish the effects of different geometrical and technological parameters is discussed.     

不同位移边界条件下钢筋混凝土深梁拓扑优化

为了探讨位移边界条件对钢筋混凝土深梁拓扑优化的影响,同时为深梁设计提供有效的力学理论依据,以ANSYS有限元分析软件为平台,利用其参数化设计语言的二次开发功能,并借助具有直观高效拓扑寻优能力的渐进演化类算法,分别对4根支座约束条件不同的双侧开洞深梁、4根开洞情形不同的两端固定铰支深梁以及3根支座约束与开洞情形均有一定差别的连续深梁进行拓扑优化,并对不同拓扑解进行对比分析。结果表明：集中力作用下深梁的拓扑解均近似为杆系结构,提高支座约束程度可以使传力路径增加,传力方式更直接;当深梁因工程原因或功能需求而不得不设置洞口时,洞口位置离原传力路径越远则越有利于结构内部的传力;连续深梁与单跨深梁的拓扑解的主要差别体现在中支座处的梁顶拉杆上,这些拉杆能够提高结构的整体刚度。因此,在工程设计中,针对不同位移边界条件下的钢筋混凝土深梁,可以根据它们拓扑解的差异以及造成这些差异的力学机理,采取不同的设计方案,包括支座约束、开洞情形以及配筋方式等的选取。研究结果可为深梁这类复杂受力构件的设计提供力学理论依据。     

Constitutive model for fibre reinforced concrete based on the Barcelona test

Several constitutive models for fibre reinforced concrete (FRC) have been reported in the past years based on the flexural performance obtained in a bending test. The Barcelona test was presented as an alternative to characterise the tensile properties of FRC; however, no constitutive model was derived from it. In this article, a formulation to predict the tensile behaviour of FRC is developed based on the results of the Barcelona test. The constitutive model proposed is validated by simulating the results of an experimental program involving different types of fibres and fibre contents by means of finite element software. Moreover, the simplified formulation proposed is compared with constitutive models from European codes and guidelines.     

基于荷载时程分析法的钢筋混凝土与钢板混凝土墙冲击响应对比分析

为对比核电站核岛厂房钢筋混凝土结构(RC)与钢板混凝土结构(SC)外墙的抗冲击性能,基于荷载时程分析法,用显示非线性动力分析软件ANSYS/LS-DYNA仿真分析1/7.5比例飞机模型撞击RC、SC墙的冲击实验。将RC、SC墙破坏模式、混凝土碎片残余速度及背部钢板变形等计算结果与飞射物-靶体相互作用分析法计算结果及实验结果以及同厚度不同结构类别墙的计算结果进行对比。结果表明,基于荷载时程分析法计算结果有一定保守性,与实验结果吻合较好,且SC墙抗冲击性能优于RC墙,尤其背部钢板能有效约束混凝土撞击方向的运动及限制混凝土碎片飞溅。用于抗飞机撞击的SC结构墙体厚度可适当减薄。     

A computational model for failure analysis of fibre reinforced concrete with discrete treatment of fibres

Failure patterns and mechanical behaviour of high-performance fibre reinforced cementitious composites depend on the distribution of fibres within a specimen. In this contribution, we propose a novel computational approach to describe failure processes in fibre reinforced concrete. A discrete treatment of fibres enables us to study the influence of various fibre distributions on the mechanical properties of the material. To ensure numerical efficiency, fibres are not explicitly discretized but they are modelled by applying discrete forces to a background mesh. The background mesh represents the matrix while the discrete forces represent the interaction between fibres and matrix. These forces are assumed to be equal to fibre pull-out forces. With this approach experimental data or micro mechanical models, including detailed information about the fibre-matrix interface, can be directly incorporated into the model.     

A plasticity based model and an adaptive algorithm for finite element analysis of reinforced concrete panels

This paper deals with an adaptive finite element procedure for the analysis of plain and reinforced concrete panels in a state of plane stress. Therefore, we will present a plasticity based model for plain concrete which captures the two failure modes of concrete within one formulation. In spite of a simple formulation the model is capable to describe the different mechanisms for tensile failure as well as for compression fracture. To restrict the time discretization error and the spatial discretization error to certain tolerances, the constitutive model is embedded in an adaptive algorithm which controls the size of the incremental load steps and leads to a hierarchical mesh refinement if necessary. The application of the model will be shown by various numerical examples. Copyright © 2002 John Wiley & Sons, Ltd.     

Energy absorption evaluation of reinforced concrete beams under various loading rates based on particle swarm optimization technique

This study proposes an energy absorption model for predicting the effect of loading rates, concrete compressive strength, shear span-to-depth ratio, and longitudinal and transverse reinforcement ratio of reinforced concrete (RC) beams using the particle swarm optimization (PSO) technique. This technique avoids the exhaustive traditional trial-and-error procedure for obtaining the coefficient of the proposed model. Fifty-six RC slender and deep beams are collected from the literature and used to build the proposed model. Three performance measures, namely, mean absolute error, mean absolute percentage error and root mean square error, are investigated in the proposed model to increase its accuracy. The design procedure and accuracy of the proposed model are illustrated and analysed via simulation tests in a MATLAB/Simulink environment. The results indicate the minimal effect of swarm size on the convergence of the PSO algorithm, as well as the ability of PSO to search for an optimum set of coefficients from within the solution space.     

A framework for data-driven structural analysis in general elasticity based on nonlinear optimization: The dynamic case

In this article, we present an extension of the formulation recently developed by the authors to the structural dynamics setting. Inspired by a structure-preserving family of variational integrators, our new formulation relies on a discrete balance equation that establishes the dynamic equilibrium. From this point of departure, we first derive an “exact” discrete-continuous nonlinear optimization problem that works directly with data sets. We then develop this formulation further into an “approximate” nonlinear optimization problem that relies on a general constitutive model. This underlying model can be identified from a data set in an offline phase. To showcase the advantages of our framework, we specialize our methodology to the case of a geometrically exact beam formulation that makes use of all elements of our approach. We investigate three numerical examples of increasing difficulty that demonstrate the excellent computational behavior of the proposed framework and motivate future research in this direction.     

基于GA－RS的规则钢筋混凝土桥梁圆形单柱桥墩延性抗震优化设计

提出抗震结构集成优化设计的新方法,将多目标遗传优化算法与反应谱分析很好地结合起来,建立规则钢筋混凝土圆形单柱桥墩多目标抗震优化设计的通用框架,以圆形单柱桥墩的截面半径、纵向钢筋配筋率和横向箍筋配筋率为设计变量,以结构的初始材料造价、抗震强度需求能力比、抗震延性需求能力比为优化目标函数。通过把延性抗震设计问题转化为多目标优化问题,从而使设计者可以很好地平衡抗震设计的各种关键因素,并以可控的方式处理多个优化目标而获得Pareto意义上的最优设计参数。     

基于神经网络遗传算法的GFRP拉挤双目标优化

为研究玻璃钢(GFRP)拉挤工艺参数对复合材料性能的影响,优化最佳拉挤工艺参数,建立了拉挤工艺过程数学模型,结合基于有限元/有限差分的间接解耦法进行求解,模拟得到了拉挤过程中GFRP内部的非稳态温度场和固化度变化情况.分别采用布拉格光栅光纤温度传感器和索氏萃取法检测拉挤GFRP内部的温度与固化度,实测温度和固化度均与模拟温度和固化度吻合,验证了数值模拟程序的正确性.以数值模拟结果为样本,建立反向传播神经网络,得到拉挤工艺参数(固化温度、拉挤速度)与GFRP固化度之间的非线性相关关系,再结合遗传算法解决拉挤过程中固化炉温度和拉挤速度双目标优化问题.优化得到的拉挤工艺参数可在保证复合材料固化度达标的情况下,提高拉挤速度降低固化炉温度,优化效果显著.神经网络遗传算法优化方法能有效解决此类具有复杂非线性关系的多目标优化问题.     

基于BP网络和遗传算法的枪架结构优化

为提高机枪的射击精度,需要对机枪枪架的结构参数进行优化设计。基于CAE软件的结构优化有其自身的局限性,所以提出了一种新的优化方法,即联合应用BP网络和遗传算法。本文以此为基础,根据机枪有限元模型,对枪架结构参数进行了优化设计,结果表明：BP网络和遗传算法相结合的方式可适用于多设计变量的枪架参数优化设计,为其它复杂结构的参数优化提供了新的思路。     

钢筋混凝土空间网格结构曲率模态曲面拟合损伤识别研究

本文介绍了钢筋混凝土空间网格结构的体系组成及构造特点;提出了曲率模态曲面拟合损伤识别理论,定义了曲率模态曲面拟合损伤指标CMSFDIi和平均曲率模态曲面拟合损伤指标CMSFDIiA,通过曲率模态与曲面拟合值的差异进行损伤定位,方法仅需利用从损伤结构获得的实测数据即可进行结构损伤识别,无需利用完好结构的基本信息和理论模型;最后通过钢筋混凝土正交正放空腹网架结构实例,验证了方法的有效性。计算结果表明,本文方法不仅可以识别单位置损伤还可以识别多位置损伤,对钢筋混凝土空间网格结构的损伤识别和健康监测是可行的。     

Displacement back analysis for underground engineering based on immunized continuous ant colony optimization

The objective function of displacement back analysis for rock parameters in underground engineering is a very complicated nonlinear multiple hump function. The global optimization method can solve this problem very well. However, many numerical simulations must be performed during the optimization process, which is very time consuming. Therefore, it is important to improve the computational efficiency of optimization back analysis. To improve optimization back analysis, a new global optimization, immunized continuous ant colony optimization, is proposed. This is an improved continuous ant colony optimization using the basic principles of an artificial immune system and evolutionary algorithm. Based on this new global optimization, a new displacement optimization back analysis for rock parameters is proposed. The computational performance of the new back analysis is verified through a numerical example and a real engineering example. The results show that this new method can be used to obtain suitable parameters of rock mass with higher accuracy and less effort than previous methods. Moreover, the new back analysis is very robust.     

基于激光超声二次谐波技术检测纤维增强树脂复合材料加固混凝土结构剥离损伤

纤维增强树脂(FRP)复合材料加固混凝土结构的早期剥离损伤往往趋向于闭合状态,传统线性超声技术对这种剥离损伤不敏感.本文提出了基于连续激光激发窄带超声波技术结合非线性超声二次谐波法检测FRP复合材料加固混凝土剥离损伤的方法,该方法通过强度调制激光技术在加固结构的表面激励窄带超声表面波,在超声波的扰动下,依据弹簧模型的接...     

A refined diffuse cohesive approach for the failure analysis in quasibrittle materials—part II: Application to plain and reinforced concrete structures

This work presents the numerical application of the diffuse cohesive interface model introduced in the Part I paper to the failure analysis of plain and reinforced concrete structures, subjected to complex loading conditions, inducing mixed‐mode fracture initiation and propagation. With the aim of capturing the interaction between concrete and steel reinforcements, the adopted fracture model is incorporated in a novel, more general numerical framework for the nonlinear analysis of reinforced concrete structures. Such a framework includes a newly proposed embedded truss model for the reinforcing bars, allowing them to be crossed by the neighboring propagating cracks. Comparisons with available experimental results are provided, assessing the reliability and the numerical accuracy of the proposed concrete model, with reference to plain specimens subjected to single‐crack propagation as well as to reinforced elements subjected to multiple cracking.     

A thermodynamic model based on exergy flow for analysis and optimization of pulse tube refrigerators

A thermodynamic model based on exergy flow through pulse tube refrigerators (PTRs) is developed. An exergetic efficiency parameter representing the losses in the pulse tube itself is proposed. The effects of control parameters representing a general phase shifter and their effect on the system performance are discussed. Analytical solutions representing important parameters in the design of PTRs such as the load curve, cooling power and efficiency in terms of basic system input parameters are developed. It is shown that the analytical model is powerful and convenient for optimization of PTRs and in quantifying its operational bound and important losses. Results indicating a compromise between cooling power and efficiency in PTRs under certain conditions are presented and discussed.