ارزيابي شاخص خرابي و كاهش مقاومت قاب خمشي بتن‌آرمه با استفاده از روش سطح پاسخ

Evaluation of Nonlinear Behavior of Moment-Resisting Reinforced Concrete frame using the Response Surface Method

بررسي تاثير پارامترهاي مختلف در رفتار سازه، همواره مورد توجه پژوهشگران بوده است. اما بررسي هم‌زمان اين پارامترها نياز به تحليل آماري مناسب دارد. در اين نوشتار، تاثير هم‌زمان نسبت ابعاد ستون‌ها، آرماتور طولي، خاموت‌ها، و ضريب محصورشدگي بتن در رفتار غيرخطي يك ساختمان قاب خمشي بتن‌آرمه‌ي 5 طبقه، تحت جابه‌جايي رفت‌ و ‌برگشتي با استفاده از نرم‌افزار غيرخطي IDARC تحليل و با استفاده از روش سطح پاسخ مدل‌سازي شده است. نتايج نشان مي‌دهد كه بررسي جداگانه‌ي عوامل، به دليل حذف اثرات متقابل، نتيجه‌ي مطلوبي به‌دست نمي‌دهد. در محدوده‌ي رفتار خطي، شاخص خرابي تابعي از نسبت ابعاد ستون، آرماتور طولي، و ضريب محصورشدگي است. اما در محدوده‌ي رفتار غيرخطي، فقط تابعي از آرماتور طولي و نسبت ابعاد ستون است. نسبت ابعاد ستون، آرماتور طولي، و ضريب محصورشدگي در ميزان تغييرات سختي جانبي سازه تاثيرگذارند، ولي فاصله‌ي خاموت‌ها تاثيري در آن ندارد. روابط به‌دست‌آمده، قابليت تخمين شاخص خرابي را به طراح سازه مي‌دهد.

In recent years, there has been an increasing interest in studying the effect of different parameters on the nonlinear behavior of moment resisting reinforced concrete structures. However, it seems that simultaneous evaluation of some parameters needs a comprehensive statistical analysis. This paper describes a logical investigation into the seismic behavior of a five storey moment resisting reinforced concrete structure under cyclic lateral load, using an inelastic analysis computer program named IDARC. The response surface method was used for the experimental design and analysis of the interaction effect of 4 factors: column dimension ratio, longitudinal and shear reinforcement, column confinement and effectiveness coefficient, on the overall damage index and stiffness degradation of the structure. Using the central composite design method, each 4 factors were defined over 5 levels. 25 IDARC models were analyzed and 4 responses obtained: Damage index at drifts equal to 1.5%, 3% and 4% of the structure height, and the tangent of stiffness degradation in a linear area, were taken from each model. A computer program, named; Design Expert 7, was used for statistical analysis. Results show that in linear areas, the drift equals 1.5% of the structure height. The overall damage index is affected by the column dimension ratio, longitudinal reinforcement and the column confinement effectiveness coefficient. However, in nonlinear areas, where the drift equals 4% of the structure height, the damage index is affected by the column dimension ratio and longitudinal reinforcement. In linear areas, the effect of shear reinforcement, and, in nonlinear areas, the effect of shear reinforcement and the column confinement effectiveness coefficient, on the overall damage index of the structure, is negligible. Furthermore, results show that the stiffness degradation of the structure is affected by the column dimension ratio, longitudinal reinforcement and the column confinement effectiveness coefficient. However, the effect of shear reinforcement on the stiffness degradation of the structure is negligible. The presented numerical model can be used for prediction of the damage index.