外文翻譯----混凝土結(jié)構(gòu)的耐久性

1、附錄A外文翻譯Cellular Automata Approach to Durability Analysis of Concrete Structures in Aggressive EnvironmentsAbstract: This paper presents a novel approach to the problem of durability analysis and lifetime assessment of concrete structures(under the diffusive attack from external aggressive agents.The

2、 proposed formulation mainly refers to beams and frames, but it can be easily extended also to other types of structures.The diffusion process is modeled by using cellular automata.The mechanical damage coupled to diffusion is evaluated by introducing suitable material degradation laws.Since the rat

3、e of mass diffusion usually depends on the stress state , the interaction between the diffusion process and the mechanical behavior of the damaged structure is also taken into account by a proper modeling of the stochastic effects in the mass transfer .To this aim, the nonlinear structural analyses

4、during time are performed within the framework of the finite element method by means of a deteriorating reinforced concrete beam element.The effectiveness of the proposed methodology in handling complex geometrical and mechanical boundary conditions is demonstrated through some applications.Firstly,

5、 a reinforced concrete box girder cross section is considered and the damaging process is described by the corresponding evolution of both bending moment-curvature diagrams and axial force-bending moment resistance domains.Secondly, the durability analysis of a reinforced concrete continuous T - bea

6、m is developed. Finally, the proposed approach is applied to the analysis of an existing arch bridge and to the identification of its critical members.IntroductionSatisfactory structural performance is usually described with reference to a specified set of limit states, which separate desired states

7、 of the structure from the undesired ones.In this context, the main objective of the structural design is to assure an adequate level of structural performance for each specified limit state during the whole service life of the structure.From a general point of view, a structure is safe when the eff

8、ects of the applied actions S are no larger than the corresponding resistance R.However, for concrete structures the structural performance must be considered as time dependent, mainly because of the progressive deterioration of the mechanical properties of materials which makes the structural syste

9、m less able to withstand the applied actions.As a consequence, both the demand S and the resistance R may vary during time and a durability analysis leading to a reliable assessment of the actual structural lifetime T should be able to account for such variability (Sa1Ja and Vesikari 1996; Enright a

10、nd Frangopol 1998a, 1998b).In this way, the designer can address the conceptual design process or plan the rehabilitation of the structure in order to achieve a prescribed design value Td of the structural lifetime.In the following, the attention will be mainly focused on the damaging process induce

11、d by the diffusive attack of environmental aggressive agents, like sulfate and chloride, which may lead to deterioration of concrete and corrosion of reinforcement (CEB 1992 ).Such process involves several factors, including temperature and humidity.Its dynamics is governed by coupled diffusion proc

12、ess of heat, moisture, and various chemical substances.In addition, damage induced by mechanical loading interacts with the environmental factors and accelerates the deterioration process ( Saetta et al. 1993 , Xi and Bazant 1999 ; Xi et al . 2000 ; Kong et al . 2002 ).Based on the previous consider

13、ations, a durability analysis of concrete structures in aggressive environments should be capable to account for both the diffusion process and the corresponding mechanical damage, as well as for the coupling effects between diffusion, damage and structural behavior.However, the available informatio

14、n about environmental factors and material characteristics is often very limited and the unavoidable uncertainties involved in a detailed and complex modeling may lead to fictitious results.For these reasons, the assessment of the structural lifetime can be more reliably carried out by means of macr

15、oscopic models which exploit the power and generality of the basic laws of diffusion to predict the quantitative time-variant response of damaged structural systems.This paper presents a novel approach to the durability analysis of concrete structures under the environmental attack of aggressive age

16、ntsThe proposed formulation mainly refers to beams and frames, but it can be easily extended also to other types of structures.The analysis of the diffusion process is developed by using a special class of evolutionary algorithms called cellular automata, which are mathematical idealizations of phys

17、ical systems in which space and time are discrete and physical quantities are taken from a finite set of discrete values.In principle, any physical system satisfying differential equations may be approximated as a cellular automaton by introducing discrete coordinates and variables, as well as discr

18、ete time steps.However, it is worth noting that models based on cellular automata provide an alternative approach to physical modeling rather than an approximation.In fact, they show a complex behavior analogous to that associated with differential equations, but by virtue of their simple formulatio

19、n are potentially adaptable to a more detailed and complete analysis, giving to the whole system some emergent properties, self-induced only by its local dynamics (von Neumann 1966; Margolus and Toffoli 1987; Wolfram 1994, 2002; Adami1998).Noteworthy examples of cellular automata modeling of typical

20、 physical processes in concrete can be found in the field of cement composites (Bentz and Garboczi 1992; Bentz et al. 1992,1994).Based on such an evolutionary model, the mechanical damage coupled to diffusion is then evaluated by introducing a degradation law of the effective resistant area of both

21、the concrete matrix and steel bars in terms of suitable damage indices.Since the rate of mass diffusion usually depends on the stress state, the interaction between the diffusion process and the mechanical behavior of the damaged structure is also taken into account by a proper modeling of the stoch

22、astic effects in the mass transfer.To this aim, the nonlinear structural analyses during time are performed within the framework of the finite element method by means of a deteriorating reinforced concrete beam element (Bontempi et al. 1995;Malerba 1998; Biondini 2000).The effectiveness of the propo

23、sed methodology in handling complex geometrical and mechanical boundary conditions is demonstrated through some applications. Firstly, a reinforced concrete box girder cross-section is considered and the damaging process is described by the corresponding evolution of both bending moment-curvature di

24、agrams and axial force-bending moment resistance domains. Secondly, the durability analysis of a rein-forced concrete continuous T-beam is developed. Finally, the proposed approach is applied to the analysis of an existing arch bridge and to the identification of its critical members.Diffusion Proce

25、sses and Cellular AutomataModeling of Diffusion ProcessesThe kinetic process of diffusion of chemical components in solids is usually described by mathematical relationships that relate the rate of mass diffusion to the concentration gradients responsible for the net mass transfer (Glicksman 2000).

26、The simplest model is represented by the Ficks first law, which assumes a linear relationship between the mass flux and the diffusion gradient. The combination of the Ficks model with the mass conservation principle leads to Ficks second law which, in the case of a single component diffusion in isot

27、ropic media, can be written as follows:(一 WC?)= (1)where C=C(x, t)=mass concentration of the component and D=(x, t)=diffusivity coefficient, both evaluated at pointx=(x, y , z) and time t, and where C=grad C.Complexities leading to modifications of this simple model may arise from anisotropy, multic

28、omponents diffusion, chemical reactions, external stress fields, memory and stochastic effects. In the case of concrete structures, for example, the diffusivity coefficient depends on several parameters, such as relative humidity,temperature, and mechanical stress, and the Ficks equations must be co

29、upled with the governing equations of both heat and moisture flows, as well as with the constitutive laws of the mechanical problem (CEB 1992; Saetta et al. 1993; Xi and Bazant 1999; Xi etal. 2000).However, as mentioned, due to the uncertainties involved in the calibration of such complex models, th

30、e structural lifetime can be more conveniently assessed by using a macroscopic approach which exploits the power and generality of the basic Ficks laws to predict the quantitative response of systems undergoing diffusion. In particular, if the diffusivity coefficient D is assumed to be a constant, t

31、he second order partial differential nonlinear Eq. (1) is simplified in the following linear form:go whereDespite of its linearity, analytical solutions of such anequation exist only for a limited number of simple classical problems. Thus, a general approach dealing with complex geometrical and mech

32、anical boundary conditions usually requires the use of numerical methods. In this study, the diffusion equation is effectively solved by using a special class of evolutionary algorithms called cellular automata.蜂窩式無線通訊系統(tǒng)自動控制方法來分析在惡劣環(huán)境下混凝土結(jié)構(gòu)的耐久性摘要：這篇文章描述了一種解決在外部荷載作用下混凝土結(jié)構(gòu)耐久性 分析和壽命評估問題的新穎的方法。這個被提到的假說主

33、要用于梁和框架，但是它也很容易擴展到其它 結(jié)構(gòu)類型。通過使用蜂窩式無線通訊系統(tǒng)自動控制來模仿這個散亂的過程。通過采用合適的材料降解法來評價散亂的機械損傷。由于質(zhì)量擴散的速度通常取決于應(yīng)力狀態(tài)，已壞結(jié)構(gòu)的擴散過程和力 學特性也通過建立一個合適的質(zhì)量傳遞中的隨機效應(yīng)模型來考慮。 為了這個目的，在這段時間的非線性結(jié)構(gòu)分析在 有限元框架中 通過一個不斷惡化的鋼筋混凝土梁單元的方法來完成。在處理復雜的幾何和力學邊界條件方面，所提到的一套方法的效果被證明是有用的。首先，鋼筋混凝土箱形梁橫截面被考慮，所造成的破壞性進程通過相 應(yīng)的彎矩一曲率圖和軸力一彎矩抵抗域來描述。其次，鋼筋混凝土連續(xù)T -梁的耐久性分析

34、被發(fā)展了。最后，所提到 的方法應(yīng)用于已建拱橋的分析和它的重要構(gòu)件的鑒定。令人滿意的結(jié)構(gòu)特性通常被描述成參照特定的把結(jié)構(gòu)的理想狀態(tài)與不理想狀態(tài)分開的極限狀態(tài)。在這方面，結(jié)構(gòu)設(shè)計的主要目的是在結(jié)構(gòu)的整個使用壽命過程中，對 于每個指定的極限狀態(tài)保證有足夠的結(jié)構(gòu)性能水平。一般來說，作用效應(yīng)S小于或等于結(jié)構(gòu)抗力R時，結(jié)構(gòu)是安全的。然而，對于混凝土結(jié)構(gòu)，結(jié)構(gòu)性能必須被認為是不定常的，主要是因 為材料力學性能的逐步惡化，這使結(jié)構(gòu)系統(tǒng)不足以承擔施加的荷載。因此，所需的作用效應(yīng)S和結(jié)構(gòu)抗力R可能隨時間而變，并且導 致實際壽命的可靠評估的結(jié)構(gòu)耐久性分析Ta應(yīng)該能夠需要這種 變異。如此，設(shè)計者能夠解決概念設(shè)計過程或

35、者設(shè)計結(jié)構(gòu)修復以使結(jié)構(gòu)壽命達到規(guī)定的設(shè)計值。接下來，注意力應(yīng)該主要集中在破壞過程，包括環(huán)境侵略性攻擊擴散 劑，例如能夠?qū)е禄炷翋夯弯摻罡g的硫酸鹽和氯化物。這種過程包括一些因素，例如溫度和濕度。它的動態(tài)受是由熱度，濕度和各種化學物質(zhì)組成。另外，破壞包括由機械載荷與環(huán)境因素的相互作用，加速惡了化過程。 基于先前的考慮，在惡劣的環(huán)境下混凝土結(jié)構(gòu)的耐久性分析應(yīng)該能夠 包括擴散過程和相應(yīng)的機械損傷，以及在擴散、破壞、結(jié)構(gòu)狀態(tài)之間 的耦合效應(yīng)。然而，關(guān)于環(huán)境因素和材料特性的可用信息通常是非常有限的，并且 在詳細和復雜的模型中不可避免的不確定性可能導致虛構(gòu)的結(jié)果。 基于這些原因，結(jié)構(gòu)壽命的評估可以通過宏觀模型來進行而變得更可 靠，模型是用來開發(fā)擴散基本規(guī)律的影響力和通用性而用于定量預測 損壞結(jié)構(gòu)體系的時變反應(yīng)。這篇文章描述了一個在環(huán)境侵襲下混凝土結(jié)構(gòu)耐久性分析的新穎方法。這個被提到的假說主要用于梁和框架，但是它也很容易擴展到其它 結(jié)構(gòu)類型。擴散過程的分析通過使用一類被稱作細胞自動機的特殊進化算法來 進行，這種方法把實際系統(tǒng)數(shù)學理想化，在這種方法中，空間和時間 是彼此分離的，物質(zhì)的量來源于一個有限集分離的價值