【正文】 where γf is a multiplier (or partial safety factor) and is a characteristic load which, if defined in statistical terms , is given by where is the value of the most unfavourable load with a 50 per cent probability of its being exceeded once in the expected life of the structure δ is the standard deviation of the distribution of the .maximum loading k is a coefficient depefldin8 on a selected probability of maximum loadings being greater than It is usual to take the characteristic load as that which will have a 5 per cent probability of being exceeded during the lifetime of the structure.④In many situations, however,statistical data are not available and the characteristic loads have to be based on nominal values given in codes of practice or other factorγf is a function of severalpartial coefficients. which takes account of the possibility of unfavourable deviation of the loads from the characteristic external loads ,thus allowing for abnormal or unforeseen actions which takes account of the reduced probability that various loads acting together will a11 be simultaneously at their characteristic values. which is intended to allow for possible modification of the load effects due to incorrect design assumptions (for example, introduction of simplified support conditions, hinges, neglect of thermal and other effects which are difficult to assess) and constructional discrepancies such as dimensions of crosssection, deviation of columns from the vertical and accidental eccentricities.Similarly , design strengths of materials, R* , are defined by R * ﹦where Rmks is the characteristic strength of the material Rm is the arithmetic mean of test results s is the standard deviation k is a coefficient depending on the probability of obtaining results less than The characteristic strength of a material is usually taken as the 95 per cent confidence limit of the material strength in a relevant test series. The reduction coefficient γm isa function of two coefficients which is intended to cover possible reductions in the strength of the materials in the structure as whole as pared to the characteristic value deduced from the control test specimen which is intended to cover possible weakness of the structure arising from any cause other than the reduction in the strength of the materials allowed for by coefficient γm1, including manufacturing tolerances. Additionally , ISO 2394 allows for the introduction of a further coefficient which may be applied either to the design values of loadings or material strengths. This coefficient is in turn a function of two partial coefficients which is intended to take account of the nature of the structure and its behaviour , for example, structures or parts of structures in which partial or ple