外文翻譯----混凝土結構的耐久性

1、<p><b>　　附錄A 外文翻譯</b></p><p>　　Cellular Automata Approach to Durability Analysis of Concrete Structures in Aggressive Environments</p><p>　　Abstract: This paper presents a nove

2、l approach to the problem of durability analysis and lifetime assessment of concrete structures(under the diffusive attack from external aggressive agents.</p><p>　　The proposed formulation mainly refers to

3、beams and frames, but it can be easily extended also to other types of structures.</p><p>　　The diffusion process is modeled by using cellular automata.</p><p>　　The mechanical damage coupled to

4、 diffusion is evaluated by introducing suitable material degradation laws.</p><p>　　Since the rate of mass diffusion usually depends on the stress state , the interaction between the diffusion process and th

5、e mechanical behavior of the damaged structure is also taken into account by a proper modeling of the stochastic effects in the mass transfer . </p><p>　　To this aim, the nonlinear structural analyses during

6、 time are performed within the framework of the finite element method by means of a deteriorating reinforced concrete beam element. </p><p>　　The effectiveness of the proposed methodology in handling complex

7、 geometrical and mechanical boundary conditions is demonstrated through some applications.</p><p>　　Firstly, a reinforced concrete box girder cross section is considered and the damaging process is described

8、 by the corresponding evolution of both bending moment-curvature diagrams and axial force-bending moment resistance domains.</p><p>　　Secondly, the durability analysis of a reinforced concrete continuous T -

9、 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. </p><p>　　Introduction </p><p>　　Satis

10、factory structural performance is usually described with reference to a specified set of limit states, which separate desired states of the structure from the undesired ones.</p><p>　　In this context, the ma

11、in 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. </p><p>　　From a general point of

12、 view, a structure is safe when the effects of the applied actions S are no larger than the corresponding resistance R.</p><p>　　However, for concrete structures the structural performance must be considered

13、 as time dependent, mainly because of the progressive deterioration of the mechanical properties of materials which makes the structural system less able to withstand the applied actions.</p><p>　　As a conse

14、quence, 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 Ta should be able to account for such variability (Sa1Ja an

15、d Vesikari 1996; Enright and Frangopol 1998a, 1998b). </p><p>　　In this way, the designer can address the conceptual design process or plan the rehabilitation of the structure in order to achieve a prescribe

16、d design value Td of the structural lifetime. </p><p>　　In the following, the attention will be mainly focused on the damaging process induced by the diffusive attack of environmental aggressive agents, like

17、 sulfate and chloride, which may lead to deterioration of concrete and corrosion of reinforcement ( CEB 1992 ) .</p><p>　　Such process involves several factors, including temperature and humidity. </p>

18、<p>　　Its dynamics is governed by coupled diffusion process of heat, moisture, and various chemical substances. </p><p>　　In addition, damage induced by mechanical loading interacts with the environme

19、ntal factors and accelerates the deterioration process ( Saetta et al. 1993 , Xi and Bazant 1999 ; Xi et al . 2000 ; Kong et al . 2002 ) .</p><p>　　Based on the previous considerations, a durability analysis

20、 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 st

21、ructural behavior.</p><p>　　However, the available information about environmental factors and material characteristics is often very limited and the unavoidable uncertainties involved in a detailed and comp

22、lex modeling may lead to fictitious results.</p><p>　　For these reasons, the assessment of the structural lifetime can be more reliably carried out by means of macroscopic models which exploit the power and

23、generality of the basic laws of diffusion to predict the quantitative time-variant response of damaged structural systems. </p><p>　　This paper presents a novel approach to the durability analysis of concret

24、e structures under the environmental attack of aggressive agents</p><p>　　The proposed formulation mainly refers to beams and frames, but it can be easily extended also to other types of structures. </p&g

25、t;<p>　　The analysis of the diffusion process is developed by using a special class of evolutionary algorithms called cellular automata, which are mathematical idealizations of physical systems in which space and

26、time are discrete and physical quantities are taken from a finite set of discrete values.</p><p>　　In principle, any physical system satisfying differential equations may be approximated as a cellular automa

27、ton by introducing discrete coordinates and variables, as well as discrete time steps.</p><p>　　However, it is worth noting that models based on cellular automata provide an alternative approach to physical

28、modeling rather than an approximation.</p><p>　　In fact, they show a complex behavior analogous to that associated with differential equations, but by virtue of their simple formulation are potentially adapt

29、able 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).<

30、;/p><p>　　Noteworthy examples of cellular automata modeling of typical physical processes in concrete can be found in the ?eld of cement composites (Bentz and Garboczi 1992; Bentz et al. 1992,1994).</p>

31、<p>　　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 the concrete matrix and steel bars in

32、terms of suitable damage indices.</p><p>　　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 struc

33、ture is also taken into account by a proper modeling of the stochastic effects in the mass transfer.</p><p>　　To this aim, the nonlinear structural analyses during time are performed within the framework of

34、the finite element method by means of a deteriorating reinforced concrete beam element (Bontempi et al. 1995;Malerba 1998; Biondini 2000).</p><p>　　The effectiveness of the proposed methodology in handling&l

35、t;/p><p>　　complex geometrical and mechanical boundary conditions is</p><p>　　demonstrated through some applications. Firstly, a reinforced</p><p>　　concrete box girder cross-section i

36、s 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 rein-f

37、orced 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.</p><p>　　Diffusion Proce

38、sses and Cellular Automata</p><p>　　Modeling of Diffusion Processes</p><p>　　The kinetic process of diffusion of chemical components in solids is usually described by mathematical relationships

39、that relate the rate of mass diffusion to the concentration gradients responsible for the net mass transfer (Glicksman 2000). The simplest model is represented by the Fick‘s first law, which assumes a linear relationship

40、 between the mass ?ux and the diffusion gradient. The combination of the Fick’s model with the mass conservation principle leads to Fick’s second law which, in the</p><p>　　where C=C(x, t)=mass concentration

41、 of the component and D=(x, t)=diffusivity coefficient, both evaluated at point</p><p>　　x=(x, y , z) and time t, and where ▽C=grad C. </p><p>　　Complexities leading to modifications of this sim

42、ple model may arise from anisotropy, multicomponents diffusion, chemical reactions, external stress fields, memory and stochastic effects. In the case of concrete structures, for example, the diffusivity coefficient depe

43、nds on several parameters, such as relative humidity,temperature, and mechanical stress, and the Fick’s equations must be coupled with the governing equations of both heat and moisture flows, as well as with the constitu

44、tive laws o</p><p>　　However, as mentioned, due to the uncertainties involved in the calibration of such complex models, the structural lifetime can be more conveniently assessed by using a macroscopic appro

45、ach which exploits the power and generality of the basic Fick’s laws to predict the quantitative response of systems undergoing diffusion. In particular, if the diffusivity coefficient D is assumed to be a constant, the

46、second order partial differential nonlinear Eq. (1) is simpli?ed in the following linear form:</p><p>　　where Despite of its linearity, analytical solutions of such an equation exist only for a limited numb

47、er of simple classical problems. Thus, a general approach dealing with complex geometrical and mechanical boundary conditions usually requires the use of numerical methods. In this study, the diffusion equation is effect

48、ively solved by using a special class of evolutionary algorithms called cellular automata.</p><p>　　蜂窩式無線通訊系統(tǒng)自動控制方法來分析在惡劣環(huán)境下混凝土結構的耐久性</p><p>　　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構耐久性分析和壽命評估問題的新穎的方法。</

49、p><p>　　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構類型。</p><p>　　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。</p><p>　　通過采用合適的材料降解法來評價散亂的機械損傷。</p><p>　　由于質量擴散的速度通常取決于應力狀態(tài)，已壞結構的擴散過程和力學特性也通過建立一個合適的質量傳遞中

50、的隨機效應模型來考慮。</p><p>　　為了這個目的，在這段時間的非線性結構分析在 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。</p><p>　　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。</p><p>　　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的彎矩—曲率圖和軸力—彎矩抵抗域

51、來描述。</p><p>　　其次，鋼筋混凝土連續(xù)T - 梁的耐久性分析被發(fā)展了。最后，所提到的方法應用于已建拱橋的分析和它的重要構件的鑒定。</p><p>　　令人滿意的結構特性通常被描述成參照特定的把結構的理想狀態(tài)與不理想狀態(tài)分開的極限狀態(tài)。</p><p>　　在這方面，結構設計的主要目的是在結構的整個使用壽命過程中，對于每個指定的極限狀態(tài)保證有足夠的結構性

52、能水平。</p><p>　　一般來說，作用效應S小于或等于結構抗力R時，結構是安全的。</p><p>　　然而，對于混凝土結構，結構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，這使結構系統(tǒng)不足以承擔施加的荷載。</p><p>　　因此，所需的作用效應S和結構抗力R可能隨時間而變，并且導致實際壽命的可靠評估的結構耐久性分析 Ta 應該能夠 需要

53、這種 變異。 </p><p>　　如此，設計者能夠解決概念設計過程或者設計結構修復以使結構壽命達到規(guī)定的設計值。</p><p>　　接下來，注意力應該主要集中在破壞過程，包括環(huán)境侵略性攻擊擴散劑，例如能夠導致混凝土惡化和鋼筋腐蝕的硫酸鹽和氯化物。</p><p>　　這種過程包括一些因素，例如溫度和濕度。</p><p>　　它的動態(tài)受

54、是由熱度，濕度和各種化學物質組成。</p><p>　　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。</p><p>　　基于先前的考慮，在惡劣的環(huán)境下混凝土結構的耐久性分析應該能夠包括擴散過程和相應的機械損傷，以及在擴散、破壞、結構狀態(tài)之間的耦合效應。</p><p>　　然而，關于環(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

55、模型中不可避免的不確定性可能導致虛構的結果。</p><p>　　基于這些原因，結構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構體系的時變反應。</p><p>　　這篇文章描述了一個在環(huán)境侵襲下混凝土結構耐久性分析的新穎方法。 </p><p>　　這個被提到的假說主要用于梁和框架，但是它也很容易擴

56、展到其它結構類型。</p><p>　　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)數學理想化，在這種方法中，空間和時間是彼此分離的，物質的量來源于一個有限集分離的價值。</p><p>　　原則上，任何滿足不同平衡的物理系統(tǒng)通過引入離散坐標系和變量，以及離散的時間步驟可近似為一個細胞自動機。</p><p>　　然而，值得指出

57、的是基于細胞自動機的模型提供了一個物理模型而不是一個近似可供選擇的方法。</p><p>　　事實上，它們表述了一個復雜的性能，類似于與微分方程相關聯(lián)，但是由于它們簡單的公式化的表述更有潛力適用于更復雜，更完整的系統(tǒng)，提供給整個系統(tǒng)一些突發(fā)的性質，只有通過它的本身動態(tài)自我包括。</p><p>　　值得注意的是， 在混凝土中，典型物理過程的元胞自動機模型的例子在水泥復合材料領域可以發(fā)現(xiàn)。&

58、lt;/p><p>　　基于這個演化模型，耦合擴散的機械損傷 通過引入混凝土和鋼筋有效抵抗區(qū)的降級理論，依據合適的損傷指數來評估的。</p><p>　　由于擴散的比率通常取決于應力狀態(tài)，損壞結構的擴散過程和機械性能之間的相互作用通常也通過一個合適的質量傳遞隨機效應的模型來考慮。</p><p>　　為了這個目的，在這段時間的非線性結構分析在有限元框架中通過一個不斷惡

59、化的鋼筋混凝土梁單元的方法來完成。</p><p>　　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的彎矩—曲率圖和軸力—彎矩抵抗域來描述。其次，鋼筋混凝土連續(xù)T - 梁的耐久性分析被發(fā)展了。最后，所提到的方法應用于已建拱橋的分析和它的重要構件的鑒定。</p><p>　　擴散過程和細胞自動機<

60、;/p><p><b>　　擴散過程模型</b></p><p>　　固體中化學成分擴散的動力學過程通常通過把大規(guī)模擴散率與造成網狀系統(tǒng)質量傳遞原因的濃度梯度聯(lián)系起來的數學關系來表述(Glicksman 2000)。</p><p>　　最簡單的模型是由Fick第一定律來描述的，這個定律假定質量轉移與擴散梯度之間是線性關系。Fick的模型與質量守恒

61、定律的結合產生了Fick第二定律，這個定律在各向同性介質中單個組合的情況下可以寫成一下形式：</p><p><b>　　其中：</b></p><p>　　C=C(x, t)=該組件的質量濃度</p><p>　　D=(x, t)=擴散系數</p><p>　　x=(x, y , z)</p><p

62、><b>　　時間 t</b></p><p>　　▽C=grad C. </p><p>　　導致這個簡單模型修改的復雜性可能產生于各向異性，多組分擴散，化學反應，外部的應力場，內存和隨機效應。例如，在混凝土結構而言，擴散系數取決于幾個參數，如相對濕度，溫度和機械應力,Fick’s方程,必須與熱和水分的流動方程,以及力學問題構成原理相結合。然而，像所提到的，由

63、于這些模型校準的不確定性，用宏觀的方法評估結構壽命更容易進行，它利用Fick’s定律的力量和通</p><p>　　用性預測進經受擴散的系統(tǒng)的定量反應。尤其，如果擴散系數D被假定為一個常數，二階非線性偏微分方程(1)被簡化成以下線性形式，</p><p>　　其中，盡管方程是線性的，但是這種方程的解析解只存在于一些有限的簡單經典問題中。因此，處理復雜幾何和力學邊界條件的一般方法通常需要使用