بررسی ضریب رفتار قاب خمشی بتن مسلح با شکل پذیری متوسط و ویژه با در نظر گرفتن اثرات نیروی محوری متغیر و برش

در این تحقیق ضریب رفتار قاب‌های بتن مسلح 2، 4 و 8 طبقه با شکل‌پذیری متوسط و ویژه بر اساس تحلیل غیرخطی دقیق پیشنهادی بررسی شده است. در ابتدا جهت صحت سنجی، مدل تحلیلی غیرخطی پیشنهادی این تحقیق با مدل‌های آزمایشگاهی موجود مقایسه شده است. نتایج صحت سنجی نشان می‌دهد مدل پیشنهادی از دقت بسیار بالایی برخوردار است. جهت به دست آوردن ضریب رفتار قاب‌های بتن مسلح 2، 4 و 8 طبقه اثر نیروی محوری متغیر، شکست برشی اعضا و همچنین کمانش میلگردهای طولی در تحلیل غیرخطی در نظر گرفته شده است. جهت محاسبه ضریب رفتار، دو معیار برای محاسبه تغییر شکل نهایی قاب‌ها در نظر گرفته شده است. معیار اول بر اساس جابجایی قاب‌ها متناظر با دوران نهایی و معیار دوم بر اساس جابجایی متناظر با 0.75 دوران نهایی عضو بحرانی در نظر گرفته شده‌اند. نتایج نشان می دهد که ضریب رفتار محاسبه‌شده قاب های خمشی بتن مسلح با شکل پذیری متوسط و ویژه براساس جابجایی متناظر با 0.75 دوران نهایی عضو بحرانی، به ضریب رفتار ارائه شده توسط استاندارد 2800 نزدیک‌تر می باشد. همچنین در قاب‌های بتن مسلح با شکل‌پذیری متوسط مقدار شکل‌پذیری با افزایش ارتفاع قاب‌ها کاهش یافته است که این نتیجه برای قاب‌های بتن مسلح با شکل‌پذیری ویژه صادق نیست.

Investigating the behavior factor of the intermediate and special RC moment resisting frame with considering the effect of variable axial load and shear

Today, most seismic design codes reduce the lateral elastic force by the behavior factor to design structures, so that by designing a structure based on elastic analysis, the effects of nonelastic behavior of the structure are applied. To obtain a behavior factor of structures, a nonlinear analysis is necessary. Research has shown that the nonlinear behavior of RC members depends on factors such as the effect of varying axial load, the effect of shear failure of the members and the effect of the buckling of the longitudinal bars. It is now generally accepted that axial load plays a dominant role in evaluating the seismic behavior of reinforced concrete columns. However columns, especially the exterior ones, can be subjected to varying axial loads depending on the lateral loads. Also the effects of shear on beams and columns are usually neglected in nonlinear analysis, which is carried out based on the flexural behavior of each element. In this research, the behavior factor of 2, 4, and 8 story reinforced concrete frames with intermediate and special ductility based on the proposed nonlinear analysis is considered. Initially, for verification, the proposed nonlinear analysis model was compared with existing experimental models. The verification results show that the proposed model has a very high accuracy. Designing and detailing of the 2, 4 and 8 story reinforced concrete structures are on the basis of the regulation of the Standard 2800 and the National building regulation chapter 9. In order to obtain the behavior of the 2, 4, and 8 story reinforced concrete frames, the effect of varying axial load, shear failure of the members and the buckling of the longitudinal bars are considered in nonlinear analysis. The behavior factor is mostly effected by ductility factor and over strength factor. The ductility factor has dependence with ductility of the reinforced concrete frames. To obtain ductility of reinforced concrete frames, ultimate deformation is needed. To calculate the frameschr('39') behavior factor, various criteria are used to calculate the ultimate deformation of frames. One of the criteria is the deformation correspond to the 0.75 percent of ultimate rotation in critical structure member. The other criteria is the deformation correspond to ultimate rotation of critical structure member. The results of the study and comparison of the obtained behavior factor with the proposed behavior factor of the reinforced concrete structures of Standard 2800 with intermediate and special ductility have shown that the calculated behavior factor for 2, 4 and 8 story reinforced concrete frames is bigger than the behavior factor in Standard 2800. Also the results indicate that the calculated behavior factor with the ultimate deformation correspond to the 75 percent of ultimate rotation in critical structure member is close to the proposed value of Standard 2800. In intermediate reinforced concrete frames, the amount of ductility factor and over strength factor decreased when the height of the reinforced concrete frames raised, which is not seen in concrete frames with special ductility.