بررسي شاخص قابليت اعتماد تير طراحي شده بر اساس آيين نامه طراحي ساختمان هاي بتني ايران (مبحث نهم)

Reliabilitybased Evaluation of Beams Designed in Accordance with Iranian Design Code

آيين نامه طراحي ايران با اعمال ضرايب اطمينان جزئي در بار و مقاومت در صدد است تا سازه هاي طراحي شده را در محدوده ايمني مشخصي قرار دهد. با محاسبه شاخص قابليت اعتماد مي توان به بررسي ميزان ايمني سازه ها پرداخت. در اين مقاله شاخص قابليت اعتماد تير به عنوان عضو مهمي از سازه در نظر گرفته شده و چگونگي اثرگذاري مقادير مختلف پارامترها و ضرايب تغييرات اين پارامترها بر روي شاخص قابليت اعتماد تير بررسي مي شود. در انتها ضرايب اطمينان جزئي براي حالات مختلف ارائه مي شود. به منظور محاسبه شاخص قابليت اعتماد از يك روش جديد بر مبناي الگوريتم ژنتيك استفاده مي شود. اين روش جديد در مقايسه با روش هاي كلاسيك و روش هاي شبيه سازي همچون مونت كارلو كارايي بيشتري دارد. زيرا از يك سو به فرم رياضي تابع حالت حدي نياز ندارد و از سوي ديگر زمان محاسباتي نسبتاً كمي دارد.

Iranian design code like any other design code increases the reliability of a structure by means ofmultiplying the partial safety factors by load and resistant. The reliability index can be evaluated inorder to survey the reliability of structures. In this paper, the reliability index of a beam as an importantmember of a structure is considered and the effect of the values and coefficient of variation of designparameters on the reliability index is surveyed. Finally, the partial safety factors for different statesare proposed. In this paper, a new method based on genetic algorithm (GA) is used to calculate thereliability index. This new method has more efficiency in comparison with the classic methods and thesimulation methods such as Monte Carlo. This method does not require the mathematical form of thelimit state function and on the other hand, this method takes less computational time in comparison withsimulation methods. In structural construction, there are many different design parameters which arerandom variables. Probability distribution can be considered for each of these random variables. Fordifferent statistical data of design parameters, different partial safety factors are needed to optimumdesign of a beam. However, Iranian design code considers the constant partial safety factors for alldifferent conditions. In case that the exact and specific statistical data of design parameters are available,the structural reliability analysis can be applied for reaching an optimum design. The statistical data ofdesign parameters can be obtained by gathering the statistical data in any country and after that a reliabledesign code can be obtained based on these statistical data. Because of lack of statistical data of designparameters in Iran, five usual conditions were considered for data and then partial safety factors arecalculated.