Structural reliability theory is concerned with the rational treatment of uncertainties in structural engineering and with the methods for assessing the safety and serviceability of civil engineering and other structures. It is a subject which has grown rapidly during the last decade and has evolved from being a topic for academic research to a set of well-developed or developing methodologies with a wide range of practical applications.

結(jié)構(gòu)可靠性理論與合理地處理結(jié)構(gòu)工程中不確定性因素有關(guān)，也與評(píng)價(jià)土木工程結(jié)構(gòu)和其他結(jié)構(gòu)的安全性和適用性的方法有關(guān)。結(jié)構(gòu)可靠性理論是在最近十年中迅速發(fā)展起來(lái)的一門(mén)學(xué)科，它已經(jīng)從學(xué)術(shù)研究的課題發(fā)展成為在實(shí)際中廣泛應(yīng)用的，比較可行的一整套方法。

Uncertainties exist in most areas of civil and structural engineering and rational design decisions cannot be made without modelling them and taking them into account. Most loads and other structural design parameters are rarely known with certainty and should be regarded as random variables or stochastic processes, even if in design calculations they are eventually treated as deterministic.?Some problems such as the analysis of load combinations cannot even be formulated without recourse to probabilistic reasoning.

大多數(shù)土木工程領(lǐng)域中都存在著不確定性因素，若不將它們模型化并加以考慮，就不可能有合理的設(shè)計(jì)決策。大多數(shù)的荷載和結(jié)構(gòu)的其他設(shè)計(jì)參數(shù)幾乎都不是確定性的量，它們都應(yīng)該被看作是隨機(jī)變量或隨機(jī)過(guò)程，即使在設(shè)計(jì)的計(jì)算中最后是按確定性的量處理的。像荷載組合分析這一類(lèi)問(wèn)題，如果不依賴(lài)于概率推理，甚至連公式也列不出來(lái)。

Until fairly recently there has been a tendency for structural engineering to be dominated by deterministic thinking, characterized in design calculations by the use of specified minimum material properties, specified load intensities and by prescribed procedures for computing stresses and deflections. This deterministic approach has almost certainly been reinforced by the very large extent to which structural engineering design is codified and the lack of feedback about the actual performance of structures. For example, actual stresses are rarely known, deflections are rarely observed or?monitored, and since most structures do not collapse the real reserves of strengths are generally not known. In contrast, in the field of hydraulic systems, much more is known about the actual performance of, say, pipe networks, weirs, spillways etc., as their performance in service can be relatively easily observed or determined.

直到最近，依然存在著用確定性的思想支配結(jié)構(gòu)工程的傾向，其特征是在設(shè)計(jì)的計(jì)算中利用規(guī)定的最低材料性能、規(guī)定的荷載強(qiáng)度和特定的步驟來(lái)計(jì)算應(yīng)力和撓度。由于結(jié)構(gòu)工程設(shè)計(jì)已編輯成規(guī)范，而且缺乏結(jié)構(gòu)實(shí)際性能反饋，這無(wú)疑在很大程度上加強(qiáng)了這種確定性方法的應(yīng)用。例如，實(shí)際的應(yīng)力幾乎是不知道的，撓度很難觀測(cè)或監(jiān)視，而且由于大多數(shù)結(jié)構(gòu)不會(huì)毀壞，實(shí)際的強(qiáng)度儲(chǔ)備一般是不知道的。反之，在水力學(xué)系統(tǒng)領(lǐng)域中，例如管路網(wǎng)絡(luò)，堤壩和溢洪道等的實(shí)際性能大多數(shù)是知道的，因?yàn)樗鼈冊(cè)谑褂弥械男阅鼙容^容易觀測(cè)或確定。

Most structural design is undertaken in accordance with codes of practice, which in many countries have legal status, meaning that compliance with the code automatically ensures compliance with the relevant clauses of the building laws. Structural codes typically and properly have a deterministic format and describe what are considered to be the?minimum standards for design, construction and workmanship for each type of structure. Most codes can be seen to be evolutionary in nature, with changes being introduced or major revisions made at intervals of 3-10 years to allow for; new types of structural form, the effects of improved understanding of structural behaviour, the effects of changes in manufacturing tolerances or quality control procedures, a better knowledge of loads, etc.

大多數(shù)的結(jié)構(gòu)是按照實(shí)用的規(guī)范進(jìn)行設(shè)計(jì)的，這些規(guī)范在許多國(guó)家有著法律上的地位，這意味著遵照規(guī)范就自動(dòng)遵循了建筑法令的有關(guān)條款。結(jié)構(gòu)規(guī)范通常有標(biāo)準(zhǔn)的確定格式，并對(duì)各種結(jié)構(gòu)的設(shè)計(jì)、施工和工程質(zhì)量應(yīng)當(dāng)具有的最低標(biāo)準(zhǔn)作了描述?？梢哉J(rèn)為，大多數(shù)規(guī)范實(shí)質(zhì)是在發(fā)展的，考慮到新型結(jié)構(gòu)的出現(xiàn)，對(duì)結(jié)構(gòu)性能的進(jìn)一步了解，制造的容許偏差或質(zhì)量控制方法的變化，對(duì)荷載的進(jìn)一步了解等，每隔3～10 年就要對(duì)規(guī)范作一些修改或作出重大的修訂。

The lack of information about the actual behaviour of structures combined with the use of codes embodying relatively high safety factors can lead to the view, still held by some engineers as well as by some members of the general public, that absolute safety can be achieved. Absolute safety is of course unobtainable; and such a goal is also undesirable, since absolute safety could be achieved only by deploying infinite resources.

由于缺乏有關(guān)結(jié)構(gòu)的實(shí)際性能資料，加之使用安全系數(shù)比較高的規(guī)范，從而使得一些工程師及某些公眾仍然堅(jiān)持認(rèn)為絕對(duì)安全是可以達(dá)到的。絕對(duì)安全當(dāng)然是不可能得到的；這樣的目標(biāo)也是不符合需要的，因?yàn)榻^對(duì)安全只有調(diào)用無(wú)限多的資源才能達(dá)到。

It is now widely recognized, however, that some risk of unacceptable structural performance must be tolerated. The main object of structural design is therefore to ensure, at an acceptable level of probability, that each structure will not become unfit for its intended purpose at any time during its specified design life. Most?structures, however,have multiple performance requirements,commonly expressed in terms of a set of serviceability and ultimate limit states, most of which are not independent; and thus the problem is much more complex than the specification of just a single probability.

但是，現(xiàn)在普遍認(rèn)為，必須容許不令人滿意的結(jié)構(gòu)性能所造成的某種風(fēng)險(xiǎn)。因此，結(jié)構(gòu)設(shè)計(jì)的主要目標(biāo)是，在可接受的概率水平上，保證每一結(jié)構(gòu)在規(guī)定的設(shè)計(jì)使用期間內(nèi)能夠滿足預(yù)期的用途。然而，大多數(shù)結(jié)構(gòu)具有多種性能要求，這些要求通常由一組適用性和主要的極限狀態(tài)來(lái)表示，它們大多數(shù)不是相互獨(dú)立的；因此，這個(gè)問(wèn)題比僅僅是一種可能性的情況要復(fù)雜得多。

There is a need for all structural engineers to develop an understanding of structural reliability theory and for this to be applied in design and construction, either indirectly through codes or by direct application in the case of special structures having large failure consequences, the aim in both cases being to achieve economy together with an appropriate degree of safety. The subject is now sufficiently well developed for it to be included as a formal part of the training of all civil and structural engineers, both at undergraduate and post-graduate levels. Courses on structural safety have been given at some universities for a number of years.

所有的結(jié)構(gòu)工程師都需要了解結(jié)構(gòu)可靠性理論，并把它應(yīng)用到設(shè)計(jì)和施工中去，無(wú)論是通過(guò)規(guī)范間接應(yīng)用它，還是對(duì)具有嚴(yán)重破壞后果的特殊結(jié)構(gòu)直接應(yīng)用它，兩者都要達(dá)到既經(jīng)濟(jì)又具有適當(dāng)安全度的目的。日前，這門(mén)學(xué)科正良好地得到充分發(fā)展，它已經(jīng)被列為土木和結(jié)構(gòu)工程師在大學(xué)和研究生階段正式的學(xué)習(xí)內(nèi)容。許多年來(lái)，一些大學(xué)已經(jīng)開(kāi)設(shè)了結(jié)構(gòu)安全制度課程。