Rational design methodology for fire exposed load bearing structures

The state-of-art of reliability studies in the area of fire-exposed structures or structural members is illustrated, taking examples from published papers concerning load-bearing building structures of steel, reinforced concrete, and wood. In parallel, trends are described in the present development of rational structural fire design methods, principally adapted to modern loading and safety philosophy for the non-fire state. Statistically derived results are presented for fire-exposed, insulated steel structures in office buildings, giving the breakdown of the total variance in maximum steel temperature and load-bearing capacity into component variances as a function of the insulation characteristics. The safety index and probability of failure are compared numerically for different fire design procedures. The data presented are examples of the information which is required as input in a qualified systems analysis of fire exposed load-bearing structures.     

现役混凝土结构的耐久性可靠度分析方法

针对现役的混凝土结构,综合考虑影响混凝土结构耐久性各种失效模型的相关性,基于概率网络估算技术的系统可靠度方法,提出钢筋混凝土构件和结构体系在多因素影响下的耐久性可靠度模型;并将此模型应用于现役混凝土结构的可靠度分析。     

可靠度在桥梁加固维修中的应用

由于影响混凝土强度的各种因素表现出不同程度的随机变异性,因此混凝土构件承载力也具有随机变异性。通过对加固补强后的混凝土强度数据进行收集和整理,用一次二阶矩法对结构可靠指标进行求解,进而得出结构的失效概率和可靠度。用严格的概率为加固补强后的混凝土结构构件的安全度和可靠度分析提供了理论依据。     

钢筋混凝土构件几何尺寸的调查和统计分析

本文根据大量实测数据,依据统计数学提供的方法进行分析,提出了钢筋混凝土结构构件几何尺寸变量的主要统计参数,研究了其概率分布形式,为研究钢筋混凝土结构构件的可靠度提供了分析依据,本文还根据统计分析的结果,对我国现行的国家标准(TJ 321-76)中有关构件几何尺寸允许偏差值的规定进行了对比分析,并对我国当前钢筋混凝土结构构件几何尺寸的实际质量水平作出了评价。     

Reliability evaluation of reinforced concrete beams

The purpose of this paper is to evaluate the time-invariant reliability of reinforced concrete beams designed under the provisions of the ACI Building Code. A wide range of practical design situations is considered. The beams are subjected to bending, shear, and torsion. The interaction between shear and torsion is considered via an elliptical failure surface defined in the shear-torsion stress space. No interaction is assumed between flexural resistance and resistance in both shear and torsion. Representative statistics and appropriate probability distributions of the basic resistance and load variables are selected from previous related work. The reliability analysis is performed using modern reliability methods, in which the formulation of the limit-state functions is consistent with the underlying design criteria. Reliability indices for various failure modes are compared and a system reliability analysis is performed to include all failure modes. It is found that the reliability indices are most sensitive to live load, model uncertainties, and material strengths. For the failure modes considered, the reliability indices are found to be rather insensitive to design parameter values, indicating that the ACI Building Code achieves its desired objective of uniform reliability across a wide range of design situations.     

混凝土受弯构件挠度控制可靠度分析

挠度控制是混凝土受弯构件正常使用极限状态设计中的重要内容,已有研究对混凝土受弯构件挠度控制的可靠度水平进行了分析和验证,但所采用的分析方法存在理论上的缺陷,且大多是以个别典型情况为例验证挠度控制的可靠度水平。为准确地揭示混凝土受弯构件挠度控制的可靠度水平,采用无量纲形式系统分析了各种情况下混凝土受弯构件挠度控制的可靠度水平,并分析了主要影响因素。结果表明,GB 50153-2008《工程结构可靠性设计统一标准》对钢筋混凝土受弯构件、不允许出现裂缝的预应力混凝土受弯构件的可靠度控制较为适中,对允许出现裂缝的预应力混凝土受弯构件的控制略显保守,可适当调整。可变作用效应的相对数值对构件挠度控制的可靠度影响显著,且可变作用效应相对越大,挠度控制的可靠度水平越高。     

混凝土受弯构件裂缝控制的可靠度分析

裂缝控制是混凝土构件正常使用极限状态设计中的重要内容,我国对混凝土构件裂缝控制的可靠度水平进行分析和验证,但这些工作采用的分析方法存在理论上的缺陷,且多数是以个别典型情况为例验证裂缝控制的可靠度水平,结论并不全面。为全面、准确地揭示我国混凝土构件裂缝控制的可靠度水平,以混凝土受弯构件为研究对象,采用无量纲的形式系统分析了各种情况下我国混凝土构件裂缝控制的可靠度水平,并分析了主要的影响因素。结果表明：我国目前对三级钢筋混凝土受弯构件可靠度水平的控制较为适中,对其他构件可靠度水平的控制偏于保守。     

Reliability-based condition assessment of deteriorating concrete bridges considering load redistribution

A wide variety of models have been proposed for estimating the reliability of highway bridges. For reinforced concrete bridges subjected to environmental attack, time-variant reliability methods have to be used. In this study, the condition of reinforced concrete girder bridges is assessed using a time-variant system reliability approach in which both load and resistance are time-variant quantities. Several system models are considered, including failure of any girder (series system) and failure of a specified number of adjacent girders (series-parallel system). Adaptive importance sampling is used to determine the cumulative-time system failure probability. An existing reinforced concrete T-beam bridge located near Pueblo, Colorado, is investigated. The influence of resistance degradation and post-failure load redistribution is included. A comparison of reliability estimates for several system models is given, including the influence of correlation among initial girder strengths. The results can be used as a guide for the selection of system models for bridge reliability analysis, identification of critical girders in a bridge system, and for the development of optimal reliability-based maintenance strategies for reinforced concrete highway bridges.     

国内外钢筋混凝土构件受剪承载力可靠度的对比分析

对我国、美国、欧洲和加拿大混凝土规范中钢筋混凝土构件受剪承载力的可靠度进行对比分析。分析中作用、材料强度和几何尺寸采用相关研究报告或相关文献提供的概率分布和统计参数,受剪承载力计算模式不定性统计参数采用国内外415个无腹筋和178个有腹筋钢筋混凝土构件受剪承载力的试验结果与计算结果的分析值。结果表明,对于无腹筋和有腹筋构件,我国规范受剪承载力的可靠指标均大于加拿大规范,小于美国和欧洲规范,其中,对于无腹筋构件,欧洲规范最大,对于有腹筋构件,美国规范最大。除集中荷载作用下我国、美国、欧洲和加拿大的无腹筋构件和均布荷载作用下我国的无腹筋构件受剪承载力的可靠指标不能满足目标可靠指标要求外,其他基本上能满足要求。     

A new look at reliability of reinforced concrete columns

This paper presents an investigation on reliability of reinforced concrete columns. For short columns, the fiber model is used for generating failure surfaces and strain and stress histories of both steel and concrete fibers under proportional and sequential loads. Two failure criteria, one based on the collection of peak-load points, the other based on prescribed maximum concrete strains are presented. For slender columns, failure surfaces are generated using a method proposed in 1991 by Ba ant et al. (ACI Structural Journal, 1991, 88, 391–401). The reliability estimation of short and slender columns under random loads is formulated by Monte Carlo simulation in the load space. In this space, isoreliability contours for both deterministic and nondeterministic columns under different load paths and load correlations are plotted. It is demonstrated that these factors may have substantial effects on the reliability of reinforced concrete columns. Therefore, the results of this study can be used to support the consideration of load path and load correlation in the development of improved evaluation and design specifications for reinforced concrete columns.     

Probabilistic model for failure initiation of reinforced concrete interior beam-column connections subjected to seismic loading

The results of previous experimental tests indicate that reinforced concrete interior beam column joints may exhibit significant strength and stiffness loss under earthquake loading, and the results of post-earthquake reconnaissance indicate that joint failure may result in structural collapse. Thus seismic evaluation and design of reinforced concrete frames requires accurate prediction of the potential for joint failure. This paper presents a binomial logit model, developed using data from 110 experimental tests, which define the probability that a reinforced concrete interior beam-column building connection, with a specific set of design parameters, will exhibit either a non-ductile joint shear failure prior to beam yielding or a ductile failure that initiates with beam yielding. The calibrated model identifies the relative importance of various design parameters in determining the connection’s response mechanism. The model can be used by an engineer designing a new connection, constructed of normal or high-strength materials, to estimate the likelihood of joint failure initiation. The model can also be used by an engineer evaluating an existing structure to estimate the likelihood of joint failure, determine the factors that most significantly affect this likelihood, and, thereby, develop a suitable and efficient retrofit strategy.     

Structural reliability of concrete bridges including improved chloride-induced corrosion models

A structural deterioration reliability (probabilistic) model has been used herein to calculate probabilities of structural failure. New reinforced concrete corrosion initiation, corrosion rate and time-variant load models are proposed. Three durability design specifications are considered in a lifetime reliability analysis of a RC slab bridge. Time-variant increases in loads are considered also. It was found that the application of de-icing salts causes significant long-term deterioration and reduction in structural safety for poor durability design specifications. A reduced cover or increased water-cement ratio increases failure probabilities. When compared to the case of “no deterioration”, it was observed also that the probability of failure only marginally increased for good durability design specifications. The approaches described herein are relevant to other physical infrastructure also.     

运营公路隧道衬砌正常使用极限状态模糊随机可靠度分析

该文基于运营公路隧道衬砌正常使用极限状态的特征,针对钢筋混凝土偏心受压构件的最大裂缝宽度极限状态开展了研究。建立了考虑衬砌结构抗力模糊性及荷载效应随机性的正常使用极限状态下模糊随机可靠度分析方法,并对某海底隧道海域Ⅲ级（Ⅳ类）围岩下衬砌结构最大裂缝宽度的可靠度进行了计算。计算结果表明：（1）在考虑结构安全重要性系数、结构的使用环境及荷载条件等因素前提下,模糊失效准则的边界应根据规范规定的允许裂缝宽度值确定;（2）某海底隧道海域Ⅳ类围岩下左洞某断面衬砌拱顶处出现最大宽度裂缝时的失效概率pf=0.194,小于50%,可以满足使用要求;（3）某海底隧道海域Ⅳ类围岩下左洞某断面衬砌拱腰处出现最大宽度裂缝时的失效概率pf=0.322,小于50%,可以满足使用要求。     

Modelling of probability of failure of concrete columns

This paper predicts the probability of failure or short and long columns of square reinforced concrete for deterministic and probabilistic loads. The effect of various parameters; width, length of column, effective length coefficient, percentage of steel, axial load, grade of concrete and random numbers; on the probability of failure of the column is studied. The material, geometric parameters and the load are treated as probabilistic. The results for short columns show that the rate of decrease of probability of failure is a maximum with increase in width, while it increased to a maximum with increase in loads, whereas for long columns the length of column had the predominant effect.     

钢筋混凝土桥梁受弯构件最大裂缝宽度的可靠度研究

基于结构可靠度理论和《公路钢筋混凝土及预应力钢筋混凝土桥涵设计规范》JTGD 62-2004关于最大裂缝宽度的规定,对钢筋混凝土桥梁受弯构件按正常使用极限状态设计的可靠度进行了计算分析,并对比研究了作用效应比、计算模式不定系数、钢筋弹性模量、配筋率、钢筋直径和截面尺寸等随机变量对最大裂缝宽度可靠指标的影响程度.研究表明:最大裂缝宽度计算公式的可靠度基本满足设计要求,可变作用与永久作用的效应比对最大裂缝宽度的可靠度影响很大,而其他因素对最大裂缝宽度的可靠度影响较小.     

碳纤维布加固混凝土构件正截面受弯承载力分析

根据碳纤维布加固钢筋混凝土构件受弯性能的试验研究 ,对受弯破坏形态、极限状态和设计要求进行了讨论。利用基于平截面假定的正截面受弯承载力的计算理论 ,分析了配筋率、加固量及二次受力等因素的影响。在此基础上提出了正截面受弯承载力的实用计算方法 ,计算结果与试验结果吻合较好 ,并具有一定的可靠性 ,可供设计参考。     

Spatial variability of pitting corrosion and its influence on structural fragility and reliability of RC beams in flexure

A stochastic process for assessing the effect of spatial variability of pitting corrosion on structural reliability and fragility is developed for singly reinforced simply supported reinforced concrete (RC) beams in flexure. A distribution of pitting corrosion is inferred from existing literature. The RC beam is discretised into a series of elements and maximum pit depths are generated for each reinforcing steel bar in each element. The analysis considered various member spans, loading ratios, bar diameters and number of bars in a given cross-section. Comparisons made with general corrosion showed that pitting corrosion is more critical for smaller diameter reinforcing steel bars. It was also found that up to a three-fold increase in 50-year probabilities of failure were observed if spatial variability of pitting corrosion are included in the analysis when compared to probabilities of failure based on the mid-span limit states only. This strongly suggests that the inclusion of spatial variability of pitting corrosion can lead to significant decreases in structural reliability for flexural RC members.     

钢筋混凝土构件承载能力极限状态可靠度分析

采用考虑随机变量分布类型的一次二阶矩法,推导了承载能力极限状态控制设计的钢筋混凝土受弯构件可靠指标计算的一种近似方法,并对混凝土受弯构件承载能力极限状态的可靠度进行了全面的计算和分析。     

型钢混凝土剪力墙变形指标限值研究

为更好地评估型钢混凝土(SRC)剪力墙的抗震性能,对SRC剪力墙的破坏形态划分准则、性能状态划分方法及各性能状态的变形限值进行研究。基于收集的56片SRC剪力墙低周往复加载试验结果,以剪跨比和弯剪比为控制参数,将SRC剪力墙划分为弯曲控制和剪切控制两类破坏形态,分别提出对应的划分准则。根据DBJ/T 15-151—2019《建筑工程混凝土结构抗震性能设计规程》,将SRC剪力墙划分为7个抗震性能状态。依据试验中试件的骨架曲线,定义3个关键性能点,提出SRC剪力墙各性能状态的变形指标限值的确定方法。对56片剪力墙的试验数据进行回归分析,依据回归结果建立SRC剪力墙的变形指标限值体系,并进行可靠性分析。结果表明：所给出的破坏形态划分方法能够较好地预测构件破坏形态,建立的SRC剪力墙变形指标限值体系的保证率在合理的范围之内,其中性能点1（无损坏）和性能点5（比较严重损坏）的失效概率均小于设定的最大失效概率(35%),性能点6（严重损坏）的失效概率为31%(弯曲控制)和41%(剪切控制)。     

A Refined Methodology for Durability‐Based Service Life Estimation of Reinforced Concrete Structural Elements Considering Fuzzy and Random Uncertainties

Abstract: A reliable method for service life estimation of the structural element is a prerequisite for service life design. A new methodology for durability‐based service life estimation of reinforced concrete flexural elements with respect to chloride‐induced corrosion of reinforcement is proposed. The methodology takes into consideration the fuzzy and random uncertainties associated with the variables involved in service life estimation by using a hybrid method combining the vertex method of fuzzy set theory with Monte Carlo simulation technique. It is also shown how to determine the bounds for characteristic value of failure probability from the resulting fuzzy set for failure probability with minimal computational effort. Using the methodology, the bounds for the characteristic value of failure probability for a reinforced concrete T‐beam bridge girder has been determined. The service life of the structural element is determined by comparing the upper bound of characteristic value of failure probability with the target failure probability. The methodology will be useful for durability‐based service life design and also for making decisions regarding in‐service inspections.