Material analysis reliability and chemical compatibility test.
Structural reliability is the probability measurement of structural reliability: the probability of structure accomplishing reserved function given by prescribed time and conditions, namely structural reliability. Structural reliability of "time period" refers to design reference period of 50 years, which considers the relations between various basic variables and time when calculating reliability degree, not to the service time of building structure. ‘Prescribed conditions’ means working conditions under normal design, normal construction and normal use which without influences of human errors. ‘Pre-determined function’ is all kinds of functions which is able to withstand under normal construction and normal use (security); good working performance under normal use (applicability); enough durability performance under normal maintenance (durability). It can maintain the necessary overall stability when accidents happen. The probability of structure accomplishing the predetermined function is called the reliable probability p↓s; the probability of structure failing to accomplish the predetermined function is called the failure probability P↓f. p↓f=1－Ps, the reliable indicator β is to measure the reliability of structural components. The relationship between it and failure probability is p↓f=ψ（－β）. According to the calibration results on the reliability level of normal design and construction structure and the consideration of long-term service experience and economic consequences, the ‘unified standards’ provides －β value: for security level I (important), ductile fracture, β = 3.7； brittle failure, β = 4.2; for security level II (general), ductile fracture, β = 3.2; brittle failure, β = 3.7; for the security level III (minor), ductile fracture, β = 2.7, brittle failure, β=3.2. The index above is adopted under static load condition. For the situation of dynamic load effect, the target reliability generally is lower than it, between about 1~2.
The factors which can influence the reliability of structure mainly are: loading and loading effect, materials strength, construction errors and force analysis. Since these factors are generally random, therefore, in order to ensure structure reliability, it is far from enough to emphasize design, to strengthen management, to control and acceptance over material structure and production is a must. To keep the structure normal condition use is also a part of the reliability. Considering the traditional habits and practical convenience, when conducting the structure design, not rely on β index but according to two kinds of limit state design requirements carry on the design by adopting load value, material design strength, geometric parameters standard values as well as all variety of practical expression of partial coefficient. Among it the partial factor reflects the structure reliability level marked by β.
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