Wielokryterialna optymalizacja niezawodnościowa oraz szacowanie stanu technicznego konstrukcji prętowych z zastosowaniem teorii zbiorów rozmytych

• Autorzy: Niczyj J.
• Języki publikacji: PL

Abstrakty

EN

Optimum design as well as assessment of technical states of already civil existing structures are ones of the most important issues in engineering activities. Taking a decision on the effort state of the whole structure stands for a complicated problem, since it is difficult to proceed research related to an effort state or/and system damage. Information about the effort state of a structural member is often obtained on the basis of a visual evaluation or specialist's experiences. More frequently, in giving an opinion a verbal form is used. Such a linguistic qualification is defined as a qualitative valuation. In a decision problem, involved in expert computer codes for instance, linguistic information has to be expressed in terms of numerical data. Theory of fuzzy sets enables one to processing that linguistic information in order to make a decision that should be taken in complicated situations. Reliability-based multicriterion optimization is one of the more interesting engineering problems regarding structural designing and optimum decisions. This is because system properties and behaviour cannot be precisely observed, and statistical data related to uncertainties and imprecision data, related to, say, loading that the structure is subjected, are as a whole unavailable. A large number of optimum design problems define a set of constraints that are in conflict each other. On the other hand, the design constraints included in those problems are assumed as fuzzy (blurred) data. In many cases the values of required data can be given only in terms of their ranges, known as interval values. Also, their influences on taking a decision are expressed in the linguistic way only. Results followed from that interval analysis may be useful in qualitative assessments and taking decisions in order to improve utility states of the entire structure. It is shown in many examples of complex structures that the fuzzy sets may effectively be applied in a combination with the system reliability theory to estimate failure states. An original aspect of the work is thus the presentation of fuzzy failure probabilities with the help of fuzzy linguistic variables and interval analysis of fuzzy numbers. Operations on the intervals for each from the alpha-level of the fuzzy numbers are used. The alpha-level method allows one to calculate the probability of structural failure on various levels of uncertainties (fuzziness) of the system parameters. Descriptions of those uncertainties (inaccuracy) of the states of structural member damages in terms of the fuzzy sets enables one to estimate reliability of the existing structures in the case of insufficient system-parameter data. The alpha-levels method gives a parametric presentation of fuzzy design information and an evaluation of solutions on various levels in fuzzy analysis. An optimum solution depends on the value of the parameter alpha that denotes the achievement level through the allowable fuzzy quantities, as well as on the maximized value of the parameter lambda, which leads to general compromise solutions. In these solutions all the fuzzy objective functions and the fuzzy constraints are considered. Assessment of structural states is connected with the qualitative and quantitative evaluating. The fact that the last two evaluations are coupled is significant. An attempt to deal with the coupling aspect is introduced in Chapter 4 in the context of an original method, in which experimental research and expert evaluations of the structural effort states are combined to get various forms of a set of membership of function for appropriate visual evaluations. The expert evaluations are performed by questionnaire. To achieve agreement in those evaluations the method of fuzzy analysis of consensus in small groups is efficiently applied. As a result unique supports of linguistic values describing the technical state of structural members are given. These obtained evaluations are then assumed as a date-base in the next step of analysis. Effectiveness of the numerical algorithms worked-out is illustrated with the help of an optimum design problem of statically determinate and indeterminate trusses. Two conflict criteria defined for mass and displacement minima are defined in the objective functions. The system is subject to the stress and reliability constraints. It is assumed that the values of loading, admissible stresses and the probability of failure are described as fuzzy quantities. Chapter 9 shows reliability-based fuzzy multicriterion analysis of well-known aluminium 10-bar truss. An reliability scheme and same possible capacity forms of the truss are discussed. The probability of failure is computed basing upon a few dominant paths of failure that related to the margin of safety. The optimization techniques introduced in Chapters 8 and 9 stand for a new approach to optimum design analysis of truss systems. In this approach insufficient information taken into account can be leading to a more safe design point. All the solutions are obtained in these two chapters in the framework of the non-linear fuzzy programming. As shown by the author the calculations of the probability of failure and the determination of technical state of structure are based on visual assessments of the expert during the inspection process the problem formulated and solving algorithms presented in Chapters 10 are thus ones of the original aspects. A comparison of an technical state assessment of a structure through a long-time in intervals of repeated inspections is seemingly - by the author's knowledge - nonexisting in the literature. Moreover, it is particularity interesting when such a review is as most as specific the assessments were carried out for 7132 bars surfaces of the total length about 25000 m. More, the review is performed in the context of visual assessments, i.e. by linguistic values that are ones of the fuzzy variables. A comparison was made for the wooden roof of a hall in the 30-year interval, Chapter 11. The linguistic values followed from specific roofs trusses and obtained between two inspections, in 1964 and 1994, are compared via a number of histograms presented in this chapter. In author's opinion these histograms may stand for an inherent certification of the time state of either structural members or the entire structure whore at hand. These valuable data, when included in the recent data-base of structural states, and by periodical revives and comparisons (against previous states), enable the use in making proper decision.

Słowa kluczowe

PL

konstrukcja kratowa; konstrukcja prętowa; teoria zbiorów rozmytych; niezawodność obiektów technicznych

• Wydawca: Wydawnictwo Uczelniane Politechniki Szczecińskiej
• Czasopismo: Prace Naukowe Politechniki Szczecińskiej. Katedra Teorii Konstrukcji
• Rocznik: 2003
• Tom: Nr 581 (3)
• Strony: 3--229
• Opis fizyczny: Bibliogr. 441 poz., tabl., rys.

Twórcy

autor

Niczyj J.