Seismic analysis of reinforced concrete frame-wall systems considering ductility effects in accordance to Eurocode

This paper presents the results of experimental and numerical analysis of the seismic resistance of a reinforced concrete coupling system considering the plastic capacity in accordance with the standard requirements STN ENV 1998 (2005), ENV 1998 (2003), Önorm B4015 (2002) and FEMA 368 (2001). The plastic capacity of the structure can be established by parameter q in the case of the spectral analysis to determine the seismic response. The experience from dynamic analysis of a hospital structure in accordance with standard requirements is presented in this paper. Dynamic parameters of the building structure are checked by experiment and the calculation model is modified on the basis of the experiment. The nonlinear analysis of the coupling system was realized in the program CRACK under system ANSYS for Kupfer’s failure condition and ?ervenka’s model of the concrete strength reduction.     

Models of reinforced concrete structures for reliability analysis

The semi-probabilistic design approach to reinforced concrete structures may be substantially improved through probabilistic analysis of the systems or their members. Models are proposed for this purpose, covering all possible failures, the deformability characteristics of the failure zones, and the variability of the general factors.Members in compression (columns and walls) and the cracking resistance of beams are considered. It is shown that, in important specific cases, the analysis may be reduced in practice to use of constants.     

Progressive collapse performance analysis of precast reinforced concrete structures

In this paper, the progressive collapse performance analysis of precast reinforced concrete (RC) structures is performed. A numerical simulation framework for precast RC structures is developed on the basis of the OpenSEES software, where the fiber frame element is used for beam and column type members and Joint2D element is used for the beam‐to‐column connections. The conjugated material models are then introduced, and a min–max failure criterion is imposed on the original models to reflect the steel fracture and concrete crushing when the structure is undergoing progressive collapse. In addition, to overcome the computational difficulties arisen from progressive collapse behavior, two enhanced nonlinear solutions , that is, the consistent quasi‐Newton algorithm and the explicit KR‐α algorithm, are employed, respectively, for static and dynamic analysis. A 10‐storey prototype precast RC structures is designed to verify the developed numerical framework, and the progressive collapse resisting mechanism of the structures is investigated through both static pushdown analysis and dynamic column‐removal analysis. Finally, influences of some typical parameters in precast RC structures on their progressive collapse performance are studied.     

Reliability evaluation in nonlinear analysis of reinforced concrete structures

Modern building codes provide a basis for development of advanced nonlinear models for analysis and design of reinforced concrete (RC) structures. Application of nonlinear models permits direct evaluation of reliability of the whole structure at the stage of a structural analysis. In this paper a probabilistic method for reliability evaluation of plane frame structures with respect to ultimate limit states is proposed. The method is based on a combination of the nonlinear finite element structural model and the first-order reliability method (FORM). Implementation of the FORM for nonlinear analysis of RC structures is considered. Uncertainties associated with the structural model are taken into account and their influence on structural reliability is examined via sensitivity analysis.     

钢筋混凝土结构裂缝的分析与控制

探讨了钢筋混凝土结构裂缝的种类及其成因,通过分析裂缝的种类和产生的原因,合理选择结构形式,并从设计、材料、施工等方面提出解决措施,从而有效地控制和减少混凝土结构裂缝的产生。     

钢筋混凝土框架结构的损伤状态相关余震易损性分析

一次主震过后通常伴有多次余震发生,由于主、余震间隔时间较短,主震损伤结构通常要遭受进一步的余震作用.为了评估震损结构的余震安全,提出了一种损伤状态相关的余震易损性分析方法.该方法采用有限次整体调幅的主余震序列作为输入,利用Park-Ang指数描述结构在主余震序列作用下的主震损伤和累积损伤,基于logistic回归方法生...     

Seismic fragility analysis of reinforced concrete structures considering reinforcement corrosion

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素，会引起结构的自振周期延长、地震需求变化及抗震能力衰减，使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象，分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数，对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平，建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

Life-cycle cost analysis of reinforced concrete structures in marine environments

Chloride-induced corrosion of carbon steel reinforcement is the main cause of deterioration of reinforced concrete (RC) structures in marine environments. One of the ways to protect RC structures from corrosion is to use corrosion-resistant stainless steel reinforcing bars. However, stainless steel is between six and nine times more expensive than carbon steel. Thus, its use can only be justified on a life-cycle cost basis. In the paper a time-variant probabilistic model was presented to predict expected costs of repair and replacement which was then used to calculate life-cycle costs for RC structures in marine environments under different exposure conditions. Results of the life-cycle cost analysis can be applied to select optimal strategies improving durability of RC structures in marine environments, including the use of stainless steel reinforcement.     

锈蚀钢筋混凝土结构地震易损性分析

钢筋锈蚀是影响钢筋混凝土结构耐久性的一个重要因素,会引起结构的自振周期延长、地震需求变化及抗震能力衰减,使得锈蚀钢筋混凝土结构的地震易损性分析不同于未锈蚀钢筋混凝土结构。以一栋按我国规范设计的RC框架结构为研究对象,分别建立了未锈蚀和锈蚀结构的非线性有限元模型并进行了模型验证。分别采用云图法和条带法计算得到了钢筋混凝土结构在未锈蚀和锈蚀两种工况下的地震易损性曲线和函数参数,对锈蚀钢筋混凝土结构地震易损性分析的特殊性及其对地震易损性分析结果的影响进行了分析。分析结果表明：不考虑钢筋锈蚀引起的结构自振周期延长会错误估计锈蚀钢筋混凝土结构的地震易损性水平。采用云图法分析锈蚀钢筋混凝土结构的地震易损性会出现锈蚀结构的极限状态失效概率低于未锈蚀结构的情况。而条带法比云图法可以更好地反映钢筋锈蚀对钢筋混凝土结构地震易损性的影响。忽略钢筋锈蚀引起的结构抗震能力衰减会低估锈蚀钢筋混凝土结构地震易损性水平,建议在锈蚀钢筋混凝土结构地震易损性分析中采用基于Pushover的极限状态定义方法。     

浅论钢筋混凝土结构抗火设计

现就钢筋混凝土结构抗火性能的研究进行了综合述评，分析了火灾下钢筋混凝土力学性能的劣化过程，针对现阶段的研究状况，对需要深入探讨的课题提出了建议。     

碳纤维布补强钢筋混凝土梁的动态性能分析

为了研究碳纤维布补强钢筋混凝土梁的动力性能,采用分离式方法建立了碳纤维布补强钢筋混凝土梁的有限元模型,并利用有限元方法对此模型进行了模态分析,得出了补强后钢筋混凝土梁的振动模态,其结果与试验值吻合,并将其与素混凝土梁和未补强钢筋混凝土梁的结果进行比较,发现在梁未开裂前,3种形式梁的自振频率差别不大,在此基础上对其进行了简谐集中荷载作用下的动力响应分析,得出在简谐集中动荷载作用下粘贴碳纤维布补强钢筋混凝土梁底部开裂的极限动荷载幅值-频率曲线.提出,在简谐集中荷载作用下,使补强梁开裂之动载幅值随激励的频率可分为两种区域:其一为在该梁各阶固有频率的约±10%区域是共振区,在此区域开裂荷载幅值很小,接近于零;另一区域为非共振区,在此区域开裂荷载的幅值稍小于静力开裂荷载.     

施工期钢筋混凝土结构安全分析的探讨

结构在施工过程中的平均风险率远高于使用期,对施工期钢筋混凝土结构进行安全分析与控制,就必须对施工期间荷载在部分完成的结构和支撑系统之间的传递进行分析与研究。本文通过具体的工程案例比较发现：现行的钢筋混凝土结构设计规范和施工规范不能对施工期钢筋混凝土结构的受力进行合理分析,因而无法对施工期结构的安全进行有效的控制。国内目前推广应用的部分施工期结构安全计算软件尚不能很好地对施工期钢筋混凝土结构进行受力分析,而清华大学土木工程系与北京第七建筑工程公司合作开发出一套人机交互的“施工期钢筋混凝土结构安全分析与控制软件-SAC”,能对施工期整个阶段每次施工步骤对各楼层受力的影响进行分析,具有一定的科学性。     

冲击载荷作用下钢筋混凝土结构动力响应仿真及损伤机理

为了进一步考察钢筋混凝土在受到荷载冲击时的动态响应结果,以期为今后工程钢筋混凝土应用提供指导,借助于专业有限元分析软件,采用仿真模型进行研究,在改变冲击荷载能量(钢球速度和质量)以及钢筋混凝土性能参数(抗压强度和配筋率)条件下,考察钢筋混凝土柱的柱中水平位移。结果显示,钢筋混凝土受到不同载荷冲击时,柱中水平位移不同,并且配筋率和轴心抗压强度对会影响水平位移。结论:为了提高钢筋混凝土,可以适当提高混凝土抗压能力,但不宜超过50 MPa,配筋率为0.019时比较经济,并且要结合工程实际情况来优化。     

Analytical models for the nonlinear seismic analysis of reinforced concrete structures

This paper discusses the analytical techniques for nonlinear dynamic analysis of reinforced concrete structures. The paper reviews the strain-rate effect, damping, and the hysteretic behaviour of structural members. Three classifications of analytical models of RC structures are reviewed, and their applications to the different types of structural systems discussed. The three groups are: (1), simple models; (2), line element models; (3), finite element models. A large portion of this paper discusses different hysteresis and analytical line element models of RC members and their application to structural systems.     

Finite element reliability analysis of chloride ingress into reinforced concrete structures

For many reinforced concrete structures corrosion of the reinforcement is an important problem since it can result in maintenance and repair actions. Further, a reduction of the load-bearing capacity can occur. In the present paper the Finite Element Reliability Method (FERM) is employed for obtaining the probability of exceeding a critical chloride concentration level at the reinforcement bars, both using Monte Carlo Simulation (MCS) and the First Order Reliability Method (FORM). The chloride ingress is modelled by the Finite Element Method (FEM) and the diffusion coefficient, surface chloride concentration and reinforcement cover depth are modelled by stochastic fields, which are discretized using the Expansion Optimum Linear Estimation (EOLE) approach. The response gradients needed for FORM analysis are derived analytically using the Direct Differentiation Method (DDM). As an example, a bridge pier in a marine environment is considered and the results are given in terms of distributions of time for initiation of corrosion.     

Bar fracture modeling in progressive collapse analysis of reinforced concrete structures

Reliable evaluation of progressive collapse resistance of structures requires substantiated methods and techniques for analyzing the response of critical elements subjected to large deformations. Steel bar fracture is a significant event that can lead to progressive collapse of reinforced concrete (RC) structures. Given the sudden discontinuity associated with bar fracture, modeling of such an event in a continuum domain analysis is challenging. In this paper a method is proposed for finite element modeling and analysis of RC elements that accounts for bar fracture. It is demonstrated that such a modeling technique is capable of developing catenary action. Analytical results based on the proposed method show good agreement with experimental data. The underlying cause for a drop in beam vertical resisting force following the peak force is identified and explained.     

考虑材料耐久性的在役混凝土结构可靠度研究

基于近年来大量的相关研究文献，从混凝土结构的材料耐久性和在役结构的荷载特点出发，按结构可靠性分析的常规步骤，对在役混凝土结构可靠性研究的成果和应用作了概括性介绍，并对不同的方法做了比较分析，以期为在这方面的进一步应用和发展提供参考。并指出基于信息更新的在役结构可靠性研究将是该领域今后一个新的研究方向。     

In-situ condition monitoring of reinforced concrete structures

Performance of concrete structures is significantly influenced and governed by its durability and resistance to environmental or exposure conditions, apart from its physical strength. It can be monitored, evaluated and predicted through modeling of physical deterioration mechanisms, performance characteristics and parameters and condition monitoring of in situ concrete structures. One such study has been conducted using Non-destructive testing equipment in the city of Bhopal and around located in India. Some selected parameters influencing durability of reinforced concrete (RC) structures such as concrete cover, carbonation depth, chloride concentration, half cell potential and compressive strength have been measured, for establishing correlation among various parameters and age of structures. Effects of concrete cover and compressive strength over the variation of chloride content with time are also investigated.     

Collapse simulation of reinforced concrete frame structures

Study of collapse‐resisting properties of structures has attracted widespread attention because of frequently occurring earthquakes and extreme events (e.g. blast) around the world. The developments in computational methods have enabled researchers to numerically simulate the collapse of structures under different kinds of loadings and provide reliable assessments of the collapse performance of structures. The dynamic nature of structural collapse requires a direct integration algorithm to solve the equations of motion of the numerical simulation model. A major concern in such simulations is the computational efficiency, which stems from the need to use a small time step size in both implicit algorithm and explicit algorithm. In this paper, modeling techniques to simulate typical failure mechanisms in reinforced concrete frame structures combined with the application of the recently developed explicit, unconditionally stable, parametrically dissipative KR‐α integration method to investigate collapse simulation are presented. A fiber beam‐column element is used to model the frame members, where the material nonlinearities, especially material softening, are simulated by a plastic damage model combined with a failure criterion. Numerical examples are presented to illustrate the proposed collapse simulation technique. The results indicate that the proposed technique provides an accurate result and has exceptional computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd.