COMPARISON STUDY OF DESIGN STRENGTH IN STEEL DESIGN CODES OF DIFFERENT COUNTRIES

摘要

Limit state method and partial factor format are widely used in steel structure design codes of different countries,such as Europe,USA,Canada,Australia and China.The partial factor for resistance(γM)is one significant aspect in partial factor format.In this paper,partial factor for resistance in different steel structure design codes [GB50017(draft),ANSI/AISC360-10 and Eurocode 3] was compared.Firstly,the definition and classification of limit state were given.It is shown that the ultimate limit state mainly considers strength,stability and fracture problems while serviceability limit state focuses on deformation,vibration and local damage.Secondly,the expression of partial factor for resistance and its value in each code were compared.In Europe and China,partial factor for resistance which value is greater than or equal to 1 is used.In USA,resistance factor(φ)which value is less than or equal to 1 is used.φ is the inverse of γM and these factors are the same in essence.The factors used in Europe and USA are classified by different members or failure modes while that of China is classified by steel grades and thickness.Then,the calculation process of partial factor for resistance was introduced.It is seen that the assumption of probability distribution that actions and resistance obey,the formulae which are used to calculate the reliability index β,the target value of β and survey details of each code are quite different.Finally,on this basis,a case study was carried out to analyze the safety level of axial tension and compression members designed by these three codes,using a method called design value criterion.The results show that the safety level of GB50017(draft)is the lowest and the safety level of Eurocode 3 is a little higher than ANSI/AISC360-10.