Behaviour of tunnel lining strengthened by textile-reinforced concrete

In this paper, the effectiveness of textile-reinforced concrete (TRC), as a means of increasing the bending resistance of tunnel lining, was experimentally and analytically investigated. The short RC column strengthened by TRC on the side farthest from the axial load was designed to investigate the behaviour of tunnel lining strengthened by TRC. The parameters under study included the loading eccentricities, the number of textile layers and the preload ratio of the short RC columns. The experimental programme was composed of two control RC columns with different eccentricities. Five RC columns which were externally upgraded by TRC sheets were also analysed for their enhanced flexural capacity. Experimental responses of the reinforced concrete members strengthened in bending indicated that TRC substantially enhanced the bending resistance. Specifically, the gain increased with a concurrent increase in both the number of layers and eccentricity. The gain greatly worsened, however, with an increase in the preload ratio. An analytical method considering the non-linear behaviour of the materials was also proposed and validated through the test results. The study was extended analytically to include additional cases of TRC-strengthened specimens with some more parameters, including different concrete and steel types.     

Reliability assessment of reinforced concrete structures based on random damage model

A stochastic model is developed to describe the fracture behaviour of concrete fibres at micro-level, and a probabilistic relation between the fibre strain and the concrete damage variable is established. In this context, the concrete damage evolution can be quantified by two representative random variables. In this regard, the number of random variables employed in potential reliability assessment studies can be greatly reduced. The accuracy of the proposed method is verified by comparing the first- and second-order moments of the stochastic damage evolution with the corresponding closed form solutions. Further, the proposed method is applied to the non-linear analysis and reliability assessment of a five-story reinforced concrete frame, and the results show that it is quite efficient for stochastic response determination and reliability evaluation of complex structures.     

Reliability of prestressed concrete structures considering creep models

The reliability of prestressed concrete structures subject to viscoelastic behaviour is investigated regarding the creep model defined by the Eurocodes. A probabilistic phenomenological model is proposed for long-term creep strains on the basis of large database of creep tests. The uncertainties in the geometrical and mechanical parameters are modelled by random variables. The proposed model considers also the statistical fitting error in creep strain predictions. The reliability analysis is performed on a prestressed concrete deck, in order to show the large impact of time-dependent phenomena on the reliability of prestressed structures, and consequently the importance of considering appropriate viscoelastic models in the design of this kind of structures. Moreover, the errors related to creep models are shown to play a very important role in the structural safety assessment.     

Reliability of linear structures with parameter uncertainty under non-stationary earthquake

The present work aims towards the development of a general framework of time varying unconditional reliability evaluation of linear elastic multi degree of freedom structures with uncertain parameter subjected to the generalized earthquake ground motion, a non-stationary process both in amplitude and frequency content. The formulation is developed in double frequency spectrum to derive the generalized power spectral density function of the structural responses. The time varying reliability is evaluated using conditional crossing rate following the Vanmarcke’s modification. The perturbation based stochastic finite element method is utilized in deriving unconditional reliability. An idealized three dimensional dam structure subjected to El Centro (1940) earthquake is taken up to elucidate the proposed unconditional time varying reliability computation procedure based on the maximum top displacement and base shear criteria. The results are presented to compare the change in reliabilities of the uncertain system with that of deterministic system and associated variance of the reliability due to parameter uncertainty.     

Seismic vulnerability assessment of tilt-up concrete structures

This paper focuses on seismic vulnerability assessment for one-story tilt-up concrete structures. To capture the potential failure mechanisms, an analytical modelling approach using nonlinear properties is developed and verified with measured data from a shake table test documented in the literature. Nonlinear dynamic analyses using synthetic ground motions for Memphis, Tennessee, are performed to assess dynamic behaviour of the buildings. Then, probabilistic demand models for multiple limit states that represent potential failure mechanisms are developed with a Bayesian updating approach. These demand models are used in conjunction with appropriate capacity limits to develop fragility curves that provide a probabilistic measure of the seismic vulnerability of typical tilt-up concrete buildings. This study shows that the vulnerability of typical tilt-up structures in Mid-America is significant when seismic hazards are high. In addition, it is found that the aspect ratio of building geometry has a significant impact on the seismic performance and fragility estimates of tilt-up buildings.     

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.     

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.     

Evaluation of calibration efficacy under different levels of uncertainty

This paper examines how calibration performs under different levels of uncertainty in model input data. It specifically assesses the efficacy of Bayesian calibration to enhance the reliability of EnergyPlus model predictions. A Bayesian approach can be used to update uncertain values of parameters, given measured energy-use data, and to quantify the associated uncertainty. We assess the efficacy of Bayesian calibration under a controlled virtual-reality setup, which enables rigorous validation of the accuracy of calibration results in terms of both calibrated parameter values and model predictions. Case studies demonstrate the performance of Bayesian calibration of base models developed from audit data with differing levels of detail in building design, usage, and operation.     

预应力混凝土空心平板的布筋形式分析

结合预应力混凝土空心平板在工程设计中的应用实例,采取两种不同的预应力筋布置形式,运用有限元进行建模计算,并对其结果进行比较,得出预应力筋均匀布置时最．大挠度稍大一点的结论。     

混凝土结构碳化寿命预测模型分析

混凝土碳化是影响结构耐久性的重要因素.根据碳化寿命准则,对现有混凝土结构碳化寿命预测模型进行分析比较,并用试验值或实测值验证.还对混凝土结构碳化寿命预测模型的影响因素进行了分析,对混凝土结构耐久性设计以及施工和维护期间应控制的影响因素提出了建议.     

型钢混凝土梁在特种结构中的应用初探

采用有限元计算、按规范传统公式计算及结合试验成果等方法,通过型钢混凝土梁和传统钢筋混凝土梁性能的对比分析,说明型钢混凝土梁在承载能力、裂缝、梁高以及施工方面的优越性,此外,为今后的研究提出一些建议,从而推动其在一些特殊的工业工程领域得到应用。     

剪力墙结构计算模型分析

比较全面地分析了目前国内外学者所采用的剪力墙结构计算模型,并重点介绍了多垂直杆元模型,用虎功原理推导了其单元刚度矩阵,应用这一模型计算了一片剪力墙的荷载一位移骨架曲线,并与试验曲线对比,表明了该模型具有较小的计算量和较好的计算精度。     

多层钢管混凝土组合框架结构抗震性能的比较研究

钢-混凝土组合结构能够充分发挥钢材和混凝土的优点,具有良好的抗震性能,越来越广泛地应用于高层建筑中.目前,应用较多的主要有钢管混凝土组合结构,为分析研究钢管混凝土组合结构的抗震性能,分别对2栋5层钢筋混凝土框架结构和钢管混凝土组合框架结构进行了地震反应弹塑性时程分析,并对多种地震波输入下的两类结构的加速度和位移反应进行了对比.理论计算分析结果表明:与钢筋混凝土结构相比,钢管混凝土结构具有较好的抗震性能.     

强震下钢框架动力时程分析模型应用对比分析

为比较几种有限元模型计算钢框架动力时程分析的精度以及效率,采用通用有限元软件ABAQUS,分别建立壳单元模型、多尺度模型、考虑损伤退化的纤维梁模型以及不考虑损伤退化的传统两折线模型,比较几种模型在计算结构变形、结构破坏形态等方面的特征,检验等效本构模型的计算精度,深入探讨考虑损伤退化对钢框架抗震性能的影响。同时,对比几种模型的计算效率,考察等效本构模型的改良作用。研究结果表明:在一开始损伤退化没有出现的时候,四种模型的计算结果基本一致。一旦由于塑性应变累积导致损伤退化的发生,考虑损伤退化的纤维模型、壳单元模型和多尺度模型的计算结果吻合良好,说明等效本构模型能够反映结构出现损伤对结构变形的放大作用。而没有考虑损伤退化的两折线杆系模型与三者的计算结果差别较大,计算得到的变形结果偏小,低估了结构的层间位移角和层位移,导致计算结果偏于不安全。计算效率上,等效本构模型的计算时间远小于壳单元模型和多尺度模型,比两折线模型略高,实现计算精度和计算效率的平衡。     

再生混凝土碳化预测模型参数及其敏感性分析

在现有再生混凝土碳化预测模型研究基础上,通过对比分析,给出了实用数学模型中的再生粗骨料影响系数建议值;采用数学回归分析方法,校订了经验模型中的拉应力影响系数;参数敏感性分析表明,再生混凝土碳化影响因素从大到小依次为保护层厚度、混凝土强度、湿度、温度、拉应力比、CO_2浓度。     

硫酸盐侵蚀环境下基于B3模型的混凝土抗压强度时效分析

基于B3模型,建立了持续荷载下混凝土抗压强度的时效模型.通过考虑持续荷载和硫酸盐共同作用对混凝土截面有效应力的影响,建立了持续荷载和硫酸盐共同作用下混凝土抗压强度的时效模型.经分析,持续荷载和环境因素是影响混凝土抗压强度时效水平主要的因素,而混凝土强度等级对强度时效水平的影响较小.     

A new model to simulate joint shear behavior of poorly detailed beam-column connections in RC structures under seismic loads, Part I: Exterior joints

A new model that can simulate the shear behavior of reinforced concrete connections in structures subjected to seismic loads is proposed. The model uses limiting principal tensile stress in the joint as the failure criteria so that due consideration is given to the axial load on the column. The spring characteristics are based on the actual deformations taking place in the sub-assemblage due to joint shear distortion. The model can be easily implemented in any commercial nonlinear analysis package and does not need any special element or subroutine. The model is more rational than the rotational spring models and at the same time being easier to implement in analysis than the multiple spring models. The formulations to obtain the spring characteristics are given in the paper. Currently the model is used to perform nonlinear static analysis for the joints, however, the same can be utilized for the nonlinear dynamic analysis too with an associated hysteretic rule. Highly promising results are obtained using the proposed model for the cases against which the model is validated. This paper focuses on the modeling of exterior joints. An extension to interior joints will be presented later.