高混凝土重力坝孔口应力非线性数值模拟

为准确描述重力坝孔口应力分布,提出高混凝土重力坝孔口应力的非线性数值计算分析整体方案．首先对坝体进行线性计算获得孔口应力分布规律及峰值以便于配筋,然后基于损伤塑性模型对孔口剖面作非线性应力应变分析,考察钢筋应力及其止裂效果．以某钢筋混凝土重力坝工程为背景,依据规范简化混凝土单轴应力一应变曲线,在Abaqus平台上对中孔的3个剖面进行非线性有限元分析,考察中孔在坝体自重和内水压力作用下的结构特性和损伤分布规律等,并重点探讨损伤区域的演化及钢筋应力等问题．结果表明数值模拟结果与模型试验有较好的一致性,可为同类型工程的数值计算和设计提供一定借鉴．     

Efficient optimum seismic design of reinforced concrete frames with nonlinear structural analysis procedures

Performance-based seismic design offers enhanced control of structural damage for different levels of earthquake hazard. Nevertheless, the number of studies dealing with the optimum performance-based seismic design of reinforced concrete frames is rather limited. This observation can be attributed to the need for nonlinear structural analysis procedures to calculate seismic demands. Nonlinear analysis of reinforced concrete frames is accompanied by high computational costs and requires a priori knowledge of steel reinforcement. To address this issue, previous studies on optimum performance-based seismic design of reinforced concrete frames use independent design variables to represent steel reinforcement in the optimization problem. This approach drives to a great number of design variables, which magnifies exponentially the search space undermining the ability of the optimization algorithms to reach the optimum solutions. This study presents a computationally efficient procedure tailored to the optimum performance-based seismic design of reinforced concrete frames. The novel feature of the proposed approach is that it employs a deformation-based, iterative procedure for the design of steel reinforcement of reinforced concrete frames to meet their performance objectives given the cross-sectional dimensions of the structural members. In this manner, only the cross-sectional dimensions of structural members need to be addressed by the optimization algorithms as independent design variables. The developed solution strategy is applied to the optimum seismic design of reinforced concrete frames using pushover and nonlinear response-history analysis and it is found that it outperforms previous solution approaches.     

Weight optimization for flexural reinforced concrete beams with static nonlinear response

The weight optimization of reinforced concrete (RC) beams with material nonlinear response is formulated as a general nonlinear optimization problem. Incremental finite element procedures are used to integrate the structural response analysis and design sensitivity analysis in a consistent manner. In the finite element discretization, the concrete is modelled by plane stress elements and steel reinforcement is modelled by discrete truss elements. The cross-sectional areas of the steel and the thickness of the concrete are chosen as design variables, and design constraints can include the displacement, stress and sizing constraints. The objective function is the weight of the RC beams. The optimal design is performed by using the sequential linear programming algorithm for the changing process of design variables, and the gradient projection method for the calculations of the search direction. Three example problems are considered. The first two are demonstrated to show the stability and accuracy of the approaches by comparing previous results for truss and plane stress elements, separately. The last one is an example of an RC beam. Comparative cost objective functions are presented to prove the validity of the approach.     

Optimal design of dynamically loaded reinforced concrete frames under displacement and rotation constraints

The paper deals with reinforced concrete beams and frames subjected to short-time, high intensity dynamic pressure. The shape and geometry of the structure and the layout of the longitudinal reinforcement are given and the areas of reinforcement are design variables.The determination of the plastic displacements and deformations caused by pressure is based on the plastic hinge theory and on the assumption that during the dynamic response the structure undergoes stationary displacements. The problem is to minimize the total amount of reinforcement such that the plastic displacements do not exceed the allowable displacements prescribed at certain points of the structure, or alternatively, that the plastic rotations in the plastic hinges do not reach the limits at which brittle failure occurs.A variational formulation of the problem is presented and the solution is based on the optimality criteria approach which requires an iterative procedure. A few examples illustrate the application of the method.     

火灾后预应力双T板的加固设计

针对遭遇火灾损伤的预应力双T板,运用有限元软件Abaqus进行顺序热-力耦合分析,得到预应力双T板的温度场云图、载荷-位移曲线,以及构件破坏时钢绞线和混凝土的应力云图.对混凝土双T板构件受损程度进行判定,确认其具有加固价值.基于该双T板的受弯承载力、挠度和破坏性质分析,提出体外预应力钢绞线结合增大受压区截面的加固方案,并对优化方案进行相应验算,认为加固方案可以满足要求.该方法可为高温作用后预应力双T板的加固提供参考.     

Numerical simulation study of spallation in reinforced concrete plates subjected to blast loading

In the design of protective structures, concrete walls are often used to provide effective protection against blast from incidental events. With a reasonable configuration and proper reinforcement, the protective structure could sustain a specified level of blast without global failure. However, the concrete wall may generate spallation on the back side of the wall, posing threats to the personnel and equipment inside the structure. For this concern, it is important to establish appropriate concrete spallation criteria in the protective design. Earlier analytical studies have been based on simplified one-dimensional wave theory, which does not consider the complex three-dimensional stress conditions in the case of close-in explosion and the structural effects. This paper presents a numerical simulation study on the concrete spallation under various blast loading and structural conditions. A sophisticated concrete material model is employed, taking into account the strain rate effect. The erosion technique is adopted to model the spallation process. Based on the numerical results, the spallation criteria are established for different levels of spallation. Comparison of the analytical results with experimental data shows a favorable agreement. It is also shown that the structural effects can become significant for relatively large charge weight and longer distance scenarios.     

Theorem of optimal reinforcement for reinforced concrete cross sections

A theorem of optimal (minimum) sectional reinforcement for ultimate strength design is presented for design assumptions common to many reinforced concrete building codes. The theorem states that the minimum total reinforcement area required for adequate resistance to axial load and moment can be identified as the minimum admissible solution among five discrete analysis cases. Therefore, only five cases need be considered among the infinite set of potential solutions. A proof of the theorem is made by means of a comprehensive numerical demonstration. The numerical demonstration considers a large range of parameter values, which encompass those most often used in structural engineering practice. The design of a reinforced concrete cross section is presented to illustrate the practical application of the theorem.     

The flexural rigidity of reinforced concrete slabs

To allow reliability analyses and design optimisation, two probabilistic models for the flexural rigidity of effectively uncracked reinforced concrete slabs are developed theoretically from a probabilistic model of concrete compliance. A simulation model uses finite difference equations to model concrete and steel stresses and strains, as concrete creeps and shrinks in a slab section. This model accounts for 17 parameters to yield an unbiased estimate of rigidity with a coefficient of variation of 0.23. A simulation study for a normal class of slabs shows that flexural rigidity is effectively independent of steel reinforcement, so rigidity is well represented by the product of a gross moment of inertia and a time-dependent effective gross modulus of elasticity. This modulus is primarily a function of concrete strength, humidity and duration of loading, and it approaches an effective long-term limiting value at about 5000 days. A simplified (design) model approximates this long-term modulus by a simple function of concrete strength and humidity. This model gives an unbiased estimate with a coefficient of variation of 0.27.     

The computer aided design of structural concrete sections subjected to combined loading

The paper describes a Computer Subroutine that may be employed to design the reinforcing steel of reinforced and prestressed concrete sections subjected to vertical shear, lateral shear, vertical bending, lateral bending, torsion and axial load. The Subroutine, called DEVAST (Design by the Variable Angle Space Truss) is based on a space truss model that is capable of predicting the post-cracking behavior of rectangular structural concrete sections subjected to combined loading. Since the space truss model can be used to predict the full post-cracking response of concrete beams under combined loading (i.e. strain in the longitudinal and web reinforcement, as well as the various deformations of the beam at all load levels), it is possible to predict the load combination that will result in yielding of either the longitudinal or the hoop steel. As a simple and conservative design criterion for use in Sub-program DEVAST, the reliable capacity of the section is taken as the load corresponding to first yielding of the steel. Although conceived as a Sub-program to be used in conjunction with a Main Program that performs the structural analysis, this Subroutine may very simply be modified for use as a self-contained design program. A listing of Sub-program DEVAST written in FORTRAN IV is provided in the paper.     

Computer graphics in sizing and analysis of aircraft structures

A computerized system for preliminary sizing and analysis of aircraft wing and fuselage structures is described. The system is based upon repeated application of analytical program modules, which are interactively interfaced and sequence-controlled during the iterative design process with the aid of design-oriented graphics software modules. The entire process is initiated and controlled via low cost interactive graphics terminals driven by a remote computer in a time-sharing mode.     

An interactive design algorithm for prestressed concrete girders

The primary purpose of this paper is to discuss an interactive design and analysis algorithm for prestressed concrete girders. Prestressed concrete highway bridge girder design is used for the prototype computer program to simplify the incorporation of design code requirements and loading conditions. The computer code can be extended to include other prestressed concrete girder applications. The second purpose arises from the search for the optimum prestressed concrete girder design. Linear programming is discussed as a possible method to arrive at the optimum girder cross-section and prestressing strand design. However, manufacturing standardization and techniques make selection of the optimum crosssection, prestressing force, and strand centroid eccentricity by mathematical methods rather academic. Therefore, design optimization, to be practical, must be based on standard cross-sections and prestressing strand position templates. The algorithm, guided by the engineer, selects, from tabulated standard crosssections and associated combinations of prestressing forces and eccentricities, the cross-section, prestressing force, and eccentricity to satisfy the problem constraints. The kern boundaries are calculated in the analysis portion of the algorithm. The engineer, using the kern boundaries, determines the path of the strands by specifying the strand hold-down points and associated strand centroid eccentricity. The algorithm also provides for shear reinforcement, dead load deflections at transfer and after placement of the slab, and auxiliary nonprestressed tension reinforcement at transfer.     

基于空间组合式单元模型的表面求交算法

在空间埋置组合式单元模型中，钢筋单元可埋置于混凝土单元任何位置，混凝土单 元网格剖分不受钢筋位置的限制，方便实用，但需确定钢筋单元两端在混凝土单元表面的位置坐 标。因此，求解钢筋线与混凝土单元表面的交点坐标是应用该单元模型的前提，现有的求解方法 只适用于混凝土单元表面是平面的情况。为此，提出了牛顿迭代法和分块解析法两种处理方法， 能求解钢筋线与混凝土单元表面为任何形状时的交点坐标，增强了该模型的适用性。通过算例验 证了这两种方法的正确性。从适用性而言，分块解析法要优于牛顿迭代法。     

Mesh, gravity and load effects on finite element simulations of blast loaded reinforced concrete structures

The behavior and design of reinforced concrete blast resistant structures are supported by intensive numerical simulations, and the effects of various parameters on the results is of great interest. Finite element simulations were performed in the nonlinear dynamic domain with modified concrete and steel constitutive models. Ten different cases were implemented, each with different reinforcement details. In addition, each case included both a coarse mesh and a fine mesh to determine the effects of mesh resolution on the numerical simulations. Gravity and loading conditions were altered to investigate their influences on the results. Deformations and stress distributions in both the concrete and steel were examined to determine the composite structural behavior and the extent of predicted damage for the various cases. The observations from these analyses highlighted relationships between the simulation parameters and the corresponding outcome. Conclusions and recommendations are presented that could assist in the development of efficient numerical simulations in this general area.     

Optimum RC column reinforcement considering multiple load combinations

A general method is proposed to determine optimal reinforcement distributions for rectangular reinforced concrete column sections subjected to multiple combinations of axial load and moment. The design problem is formulated as a general constrained nonlinear optimization problem and is solved both mathematically and graphically. Ultimate strength and strength reduction factors are evaluated using ACI code provisions. The method provides a simple approach to determine optimal reinforcement under multiple loading combinations. The use of optimal reinforcement rather than conventional (symmetric) distributions of reinforcement can lower construction costs and environmental impacts.     

A study of finite element and mathematical programming models for inelastic analysis of concrete framed structures

This paper presents an investigation of three analytical models for inelastic analysis of reinforced concrete framed structures. The first model employs a plane stress reinforced concrete element formulation with reinforcement oriented in any direction. The second model is based on a simplified layered frame element. The third model is a mathematical programming model in which the inelastic analysis is formulated as a linear complementarity problem. Formulation and significant computational steps of the three models are explained briefly. The performance of the three models in predicting the bending moment distribution at ultimate load stages is discussed through application to a number of frames and the results are compared with the experimental investigation conducted on 14 frames. This study concludes that the mathematical programming model is a computationally efficient model for inelastic analysis and offers scope for practical application for limit-state design of concrete frames.     

Nonlinear analysis of reinforced concrete

This paper discusses the development of two different computer programs for nonlinear analysis of reinforced concrete structures.The first program handles plane stress problems. Flow theory of plasticity is used in the modelling of concrete and reinforcement. General four-noded quadrilateral elements with selective sampling of strain are used in the discretization.The second program is developed for analysis of plates and shells. Endochronic theory is used in the constitutive law for concrete whereas an overlay model is utilized for the reinforcement. Geometric nonlinearities are accounted for through updating of coordinates for the triangular shell elements.Several examples of applications of the two programs are given. The plane stress program is used for analysis of a beam and two different corbels, while the shell program has been applied to a square plate and a shell with geometric nonlinearities.     

Probabilistic analysis of reinforced concrete columns

The subject of this work is the probabilistic finite element analysis of reinforced concrete columns. Concrete properties are represented as homogeneous Gaussian random fields. The yield stress and position of steel reinforcement, dimensions of the column cross-section and axial load are considered as random variables. The Monte Carlo method is employed to obtain expected values and standard deviations of the rupture load. The partial safety factors method is used for columns design and structural safety is evaluated by means of the reliability index, which is obtained through simulations. The effects of main parameters on the reliability index are investigated. It is shown that the correlation length of random fields for concrete properties may have a significant effect on reliability. Therefore, simplified procedures, which do not consider spatial variations of concrete properties are inappropriate for safety analysis.     

混凝土内应力测量的应变砖传感器设计与应用

针对混凝土内应力传感器匹配误差问题,设计制作埋入式应变砖传感器,将混凝土作为传感器一部分整体进行标定,从而减少实际测量中匹配误差的影响。传感器设计中考虑温度和干扰补偿,并对应变计进行良好防护以确保20MPa压力下传感器绝缘性能良好。进行50kN静态加载试验,得到加载力同传感器输出的函数关系和非线性误差。经过激波管动态加载试验,得出应变砖固有频率大于30kHz,可用于动态加载的混凝土内应力测量。     

擦窗机悬挂轨道三维结构有限元分析

为探究某擦窗机悬挂结构的合理性,在AIP中创建其悬挂轨道的三维参数化特征模型,并根据轨道的结构、材料和特定工况受力等边界条件,建立悬挂系统的有限元模型,模拟计算2种有代表性的偏栽荷工况受力情况,得到悬挂轨道的三维应力分布、结构变形和安全因数．根据工程设计要求和初步分析结果,在保持边界条件和载荷条件不变的情况下,快速更新轨道结构参数,并通过比较分析确定塔楼悬挂轨道的最佳断面参数．该轨道及其固定间距、滑车滚轮和导向轮等构件均满足设计安全要求．