1、蜂窩式無(wú)線(xiàn)通訊系統(tǒng)自動(dòng)控制方法來(lái)分析在惡劣環(huán)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(píng)估問(wèn)題的新穎的方法。這個(gè)被提到的假說(shuō)主要用于梁和框架，但是它也很容易擴(kuò)展到其它結(jié)構(gòu)類(lèi)型。通過(guò)使用蜂窩式無(wú)線(xiàn)通訊系統(tǒng)自動(dòng)控制來(lái)模仿這個(gè)散亂的過(guò)程。通過(guò)采用合適的材料降解法來(lái)評(píng)價(jià)散亂的機(jī)械損傷。由于質(zhì)量擴(kuò)散的速度通常取決于應(yīng)力狀態(tài)，已壞結(jié)構(gòu)的擴(kuò)散過(guò)程和力學(xué)特性也通過(guò)建立一個(gè)合適的質(zhì)量傳遞中的隨機(jī)效應(yīng)模型來(lái)考慮。為了這個(gè)目的，在這段時(shí)間的非線(xiàn)性結(jié)構(gòu)分析在 有限元框架 中 通過(guò)一個(gè)不斷惡化的鋼筋混凝土梁?jiǎn)卧姆椒▉?lái)完成。在處理復(fù)雜的幾何和力學(xué)邊界條件方面，所提到的一套

2、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(jìn)程通過(guò)相應(yīng)的彎矩曲率圖和軸力彎矩抵抗域來(lái)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(yīng)用于已建拱橋的分析和它的重要構(gòu)件的鑒定。 令人滿(mǎn)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(kāi)的極限狀態(tài)。在這方面，結(jié)構(gòu)設(shè)計(jì)的主要目的是在結(jié)構(gòu)的整個(gè)使用壽命過(guò)程中，對(duì)于每個(gè)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(lái)說(shuō)，作用效應(yīng)s小于或等于結(jié)構(gòu)抗力r時(shí)，結(jié)構(gòu)是安全的。然而，對(duì)于混凝土結(jié)構(gòu)，結(jié)構(gòu)性能必須被認(rèn)為是不定常的，主要是因?yàn)?材料力學(xué)性能的逐步惡化，這使結(jié)構(gòu)系統(tǒng)不足以承擔(dān)施加

3、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(shí)間而變，并且導(dǎo)致實(shí)際壽命的可靠評(píng)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(jì)者能夠解決概念設(shè)計(jì)過(guò)程或者設(shè)計(jì)結(jié)構(gòu)修復(fù)以使結(jié)構(gòu)壽命達(dá)到規(guī)定的設(shè)計(jì)值。接下來(lái)，注意力應(yīng)該主要集中在破壞過(guò)程，包括環(huán)境侵略性攻擊擴(kuò)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(guò)程包括一些因素，例如溫度和濕度。它的動(dòng)態(tài)受是由熱度，濕度和各種化學(xué)物質(zhì)組成。另外，破壞包括由機(jī)械載荷與環(huán)境因素的相互作用，加速惡了化過(guò)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(kuò)散過(guò)程和相應(yīng)的機(jī)械損傷，以及在擴(kuò)散、破壞、結(jié)構(gòu)狀態(tài)之間的耦合效應(yīng)

4、。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(xì)和復(fù)雜的模型中不可避免的不確定性可能導(dǎo)致虛構(gòu)的結(jié)果。基于這些原因，結(jié)構(gòu)壽命的評(píng)估可以通過(guò)宏觀模型來(lái)進(jìn)行而變得更可靠，模型是用來(lái)開(kāi)發(fā)擴(kuò)散基本規(guī)律的影響力和通用性而用于定量預(yù)測(cè)損壞結(jié)構(gòu)體系的時(shí)變反應(yīng)。這篇文章描述了一個(gè)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(gè)被提到的假說(shuō)主要用于梁和框架，但是它也很容易擴(kuò)展到其它結(jié)構(gòu)類(lèi)型。擴(kuò)散過(guò)程的分析通過(guò)使用一類(lèi)被稱(chēng)作細(xì)胞自動(dòng)機(jī)的特殊進(jìn)化算法來(lái)進(jìn)行，這種方法把實(shí)際系統(tǒng)數(shù)學(xué)理想化，在這種方法中，空間和時(shí)間是彼此分離的，物質(zhì)的量來(lái)源于一個(gè)有限集分離的價(jià)值。原則上，任何滿(mǎn)足不同平衡的物理系統(tǒng)通

5、過(guò)引入離散坐標(biāo)系和變量，以及離散的時(shí)間步驟可近似為一個(gè)細(xì)胞自動(dòng)機(jī)。然而，值得指出的是基于細(xì)胞自動(dòng)機(jī)的模型提供了一個(gè)物理模型而不是一個(gè)近似可供選擇的方法。值得注意的是， 在混凝土中，典型物理過(guò)程的元胞自動(dòng)機(jī)模型的例子在水泥復(fù)合材料領(lǐng)域可以發(fā)現(xiàn)。事實(shí)上，它們表述了一個(gè)復(fù)雜的性能，類(lèi)似于與微分方程相關(guān)聯(lián)，但是由于它們簡(jiǎn)單的公式化的表述更有潛力適用于更復(fù)雜，更完整的系統(tǒng)，提供給整個(gè)系統(tǒng)一些突發(fā)的性質(zhì)，只有通過(guò)它的本身動(dòng)態(tài)自我包括。基于這個(gè)演化模型，耦合擴(kuò)散的機(jī)械損傷 通過(guò)引入混凝土和鋼筋有效抵抗區(qū)的降級(jí)理論，依據(jù)合適的損傷指數(shù)來(lái)評(píng)估的。由于擴(kuò)散的比率通常取決于應(yīng)力狀態(tài)，損壞結(jié)構(gòu)的擴(kuò)散過(guò)程和機(jī)械性能之間

6、的相互作用通常也通過(guò)一個(gè)合適的質(zhì)量傳遞隨機(jī)效應(yīng)的模型來(lái)考慮。為了這個(gè)目的，在這段時(shí)間的非線(xiàn)性結(jié)構(gòu)分析在有限元框架中通過(guò)一個(gè)不斷惡化的鋼筋混凝土梁?jiǎn)卧姆椒▉?lái)完成。在處理復(fù)雜的幾何和力學(xué)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(jìn)程通過(guò)相應(yīng)的彎矩曲率圖和軸力彎矩抵抗域來(lái)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(yīng)用于已建拱橋的分析和它的重要構(gòu)件的鑒定。擴(kuò)散過(guò)程模型擴(kuò)散過(guò)程和細(xì)胞自動(dòng)機(jī)固體中化學(xué)成分?jǐn)U散的動(dòng)力學(xué)過(guò)程通常通過(guò)把大規(guī)模擴(kuò)散率與造成網(wǎng)狀系統(tǒng)質(zhì)量傳遞原因的濃度梯度聯(lián)系起來(lái)的數(shù)學(xué)關(guān)系來(lái)表述(glic

7、ksman 2000)。 最簡(jiǎn)單的模型是由fick第一定律來(lái)描述的，這個(gè)定律假定質(zhì)量轉(zhuǎn)移與擴(kuò)散梯度之間是線(xiàn)性關(guān)系。fick的模型與質(zhì)量守恒定律的結(jié)合產(chǎn)生了fick第二定律，這個(gè)定律在各向同性介質(zhì)中單個(gè)組合的情況下可以寫(xiě)成一下形式：其中：c=c（x, t）=該組件的質(zhì)量濃度d=（x, t）=擴(kuò)散系數(shù)x=(x, y , z)時(shí)間 tc=grad c. 導(dǎo)致這個(gè)簡(jiǎn)單模型修改的復(fù)雜性可能產(chǎn)生于各向異性，多組分?jǐn)U散，化學(xué)反應(yīng)，外部的應(yīng)力場(chǎng)，內(nèi)存和隨機(jī)效應(yīng)。例如，在混凝土結(jié)構(gòu)而言，擴(kuò)散系數(shù)取決于幾個(gè)參數(shù)，如相對(duì)濕度，溫度和機(jī)械應(yīng)力,ficks方程,必須與熱和水分的流動(dòng)方程,以及力學(xué)問(wèn)題構(gòu)成原理相結(jié)合。然而

8、，像所提到的，由于這些模型校準(zhǔn)的不確定性，用宏觀的方法評(píng)估結(jié)構(gòu)壽命更容易進(jìn)行，它利用ficks定律的力量和通用性預(yù)測(cè)進(jìn)經(jīng)受擴(kuò)散的系統(tǒng)的定量反應(yīng)。尤其，如果擴(kuò)散系數(shù)d被假定為一個(gè)常數(shù)，二階非線(xiàn)性偏微分方程（1）被簡(jiǎn)化成以下線(xiàn)性形式，其中，盡管方程是線(xiàn)性的，但是這種方程的解析解只存在于一些有限的簡(jiǎn)單經(jīng)典問(wèn)題中。因此，處理復(fù)雜幾何和力學(xué)邊界條件的一般方法通常需要使用數(shù)值方法。在這項(xiàng)研究中，通過(guò)使用一類(lèi)特殊的進(jìn)化算法稱(chēng)為細(xì)胞自動(dòng)機(jī)的方法有效地解決了擴(kuò)散方程。細(xì)胞自動(dòng)機(jī)首次是在19481950被neumann and ulam首次引進(jìn)的，接下來(lái)其他的研究人員在許多科學(xué)領(lǐng)域應(yīng)用它。起初，涉及到對(duì)圖靈機(jī)的自

9、我復(fù)制問(wèn)題的研究，細(xì)胞自動(dòng)機(jī)在20世紀(jì)70年代離開(kāi)實(shí)驗(yàn)室，并在學(xué)術(shù)界隨著conway發(fā)明的著名游戲流行 。基本上，他們代表了簡(jiǎn)單的物質(zhì)系統(tǒng)數(shù)學(xué)理想化，在這一系統(tǒng)，空間和時(shí)間是不分離的，物理量取自一個(gè)離散值的有限集合。事實(shí)上，如前所述， 通過(guò)引入離散坐標(biāo)和變量，以及離散時(shí)間的步驟，任何滿(mǎn)足微分方程的物理系統(tǒng)可近似作為細(xì)胞自動(dòng)機(jī)。因此，合理地說(shuō)，基于細(xì)胞自動(dòng)機(jī)的模型提供了一個(gè)可供選擇和更廣泛的物理模型而不是近似值的方法 。他們表現(xiàn)出復(fù)雜的行為，類(lèi)似于復(fù)雜的微分方程，但是，在這種情況下，根據(jù)簡(jiǎn)單的規(guī)則從簡(jiǎn)單的實(shí)體之間的相互作用出現(xiàn)8cellular automata approach to dura

10、bility 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 proposed formulation mainly refers to be

11、ams 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 rate of mass diffusion usually depends on

12、 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 during time are performed within the fr

13、amework 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 , a reinforced concrete box girder c

14、ross 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 - beam is developed. finally, the prop

15、osed approach is applied to the analysis of an existing arch bridge and to the identification of its critical members. introduction satisfactory structural performance is usually described with reference to a specified set of limit states, which separate desired states of the structure from the unde

16、sired 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 effects of the applied actions s

17、 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 system less able to withstand t

18、he 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 ta should be able to account for such variability (sa1ja and vesikari 1996; enright and frangopol 1998a, 199

19、8b). 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 induced by the diffusive at

20、tack 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 process of heat, m

21、oisture, 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 considerations, a du

22、rability 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 information about env

23、ironmental 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 macroscopic m

24、odels 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 agentsthe

25、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 physical s

26、ystems 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 discrete ti

27、me 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 formulation are

28、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 physi

29、cal processes in concrete can be found in the eld 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 the con

30、crete 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 stochastic e

31、ffects 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 proposed me

32、thodology in handlingcomplex geometrical and mechanical boundary conditions isdemonstrated through some applications. firstly, a reinforcedconcrete box girder cross-section is considered and the damaging process is described by the corresponding evolution of both bending momentcurvature diagrams and

33、 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 processes and c

34、ellular 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). the simple

35、st model is represented by the ficks first law, which assumes a linear relationship between the mass ux 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 isotropic media,

36、 can be written as follows: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, multicomponents diffusion, ch

37、emical 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 coupled with the governin

38、g 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 baant 1999; xi etal. 2000). however, as mentioned, due to the uncertainties involved in the calibration of such complex models, the structural lifetime c

39、an 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, the second order partial

40、 differential nonlinear eq. (1) is simplied in the following linear form:where despite of its linearity, analytical solutions of such an equation exist only for a limited number of simple classical problems. thus, a general approach dealing with complex geometrical and mechanical boundary conditions

41、 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.short history, formal definition, and emergingproperties of cellular automatacellular automata were firstly introdu

42、ced by von neumann and ulam in 19481950 (von neumann 1966) and subsequently developed by other researchers in many fields of science (see for reviews: margolus and toffoli 1987; adami 1998; wolfram 2002).originally related to the study of self-replication problems on the turings machine, cellular au

43、tomata left laboratories in the 1970s and became popular in the academic circles with the now famous game of life invented by conway (gardner 1970). basically, they represent simple mathematical idealizations of physical systems in which space and time are discrete, and physical quantities are taken from a finite set