Study On Application Of The Design Value Method In Construction Engineering Structure Design

In the 1980 s,reliability theory began to be widely used in the engineering structure design.Every country applied this approach one after another.Our country applied the partial safety factor method which introduced the partial safety factor into the design.These coefficients calibrated to be determined value make the design approach based on reliability theory more simplified and it is very easy to be accepted by designers with different professional qualities.But to the different structures,the approach also has flaws.There is a wide gap between reliability index by this method and objective reliability index.Taking steel structure as an example,reliability index check for steel structure is obviously low.With the development of computer technology,the emergence of calculation software and development of designer's professional qualities,however partial safety factors in the current design specification are also determined values.Comparing with optimized method which calibrates the partial safety factor in the current specification,the design value method has enormous advantages.Design value method establishes the function relationship between sensitivity coefficients and partial safety factors in theory.Through researching sensitivity coefficients,the wide gap between reliability index and objective reliability index can be efficiently controlled.The dissertation takes a comprehensive and deep study on the practical application of design value method based on reliability theory.Firstly,the paper researches optimized method and design value method in the current design specification and make clear that the wide gap between reliability index and objective reliability index.The advantages and disadvantages of these two methods can be reflected in the chart.Secondly,the paper analyzes the influential factors of reliability index computed by first order-second moment method.Research founds that change of sensitivity coefficients and load effect ratios have a significant impact on reliability index,then on this basis the paper analyzes theoretical relationships between these two variables.Because the process of reliability index calculation is complicated,the paper researches approximation relationship between these two variables.Finally,the real relationship between sensitivity coefficients and different load effect ratios of stressing state of the common structures are gained by calibrating different objective reliability index.The objective reliability index has been set as 3.2 and the theoretical relationship between these two variables is employed to fit calculating data and then the sensitivity coefficients calculated by fitting formula are brought into design value method,the gap between reliability index and objective reliability index can be kept in the bounds of ±1.0 and for different objective reliability index,the fitting formula can also be applied.Therefore,designers can set the partial safety factors independently for the different objective reliability index,which can improve the autonomy of designers.And on this basis the paper researches the calculation method of combination coefficients in design value method and the accuracy of the approach has been proved.