شناسايي مفصل خميري در تير ساده تحت اثر زلزله با محاسبه‌ي دياگرام انحنا

DETECTION OF THE PLASTIC HINGE IN SIMPLE BEAM DURING AN EARTHQUAKE BY OBTAINING CURVATURE DIAGRAM

در اين نوشتار، روش جديدي براي شناسايي خرابي تير دو سر مفصل ارايه شده است، كه در آن با استفاده از ابزار تغييرات انحنا در طول تير حين زلزله به شناسايي مفاصل خميري ايجادشده‌ در تير پرداخته شده است. در اين نوشتار ابتدا سعي شده است كه خرابي از نوع ترك مصنوعي (ترك ايجادشده در تير قبل از اعمال بارگذاري) با استفاده از ابزارهاي موجود در روش‌هاي پردازش سيگنال و همچنين روش تغييرات بردار انحنا خرابي از نوع مفصل خميري شناسايي شود. در ادامه، روش مذكور بسط و گسترش داده شده و از آن براي شناسايي خرابي از نوع مفصل خميري در يك تير در طول بارگذاري زلزله استفاده شده و در نهايت، دقت روش ذكرشده و مزيت‌هاي آن نسبت به روش‌هاي موجود پردازش سيگنال نظير تبديل موجك بيان شده است.

This paper presents a new method for detecting damage of simply-supported beam. This method is based on the using deference of curvature vectors. The plastic hinges throughout the beam, were determined during an earthquake using deference of curvature vectors. At first, artificial crack applied in the form of cuts in some parts of the flange and web section of a simple steel beam was detected by obtaining different mode shapes vectors and performing Continuous wavelet transform. Then, the same artificial crack was detected in the beam that was exposed to a net bending of 30 KN M using difference between slope vectors in the damaged and undamaged beam. Then, an undamaged beam was modeled, and plastic zones were created by applying push loads, and not artificial cracks, to the beams and created plastic hinges under the push load were detected. An important point to consider is that the damage caused by an earthquake to a structure is mostly nonlinear so it is necessary to detect plastic hinges after an earthquake in order to improve the structure. The modeled beam was exposed to the accelerations of Chichi earthquakes (1999), and the curvature vectors of the beam were calculated using the accelerometers output data at each time step. In this paper a criterion is developed by which we can easily identify the critical time step. The plastic hinges were detected through curvature vectors at the critical steps. A sudden increase in curvature values at the critical step and the observation concerning the values exceeding the yielding curvature are used as indicators of the formation of a plastic hinges. Moreover, the proposed method determines the length and depth of plastic hinges as well as their location in the beam. Finally, the accuracy and advantage of the mentioned method were compared to the conventional signal processing methods such as Continuous wavelet analysis.