پديد آورندگان :
عموزاده، عاطفه موسسه ي آموزش عالي علوم و فناوري آريان، بابل , فدوي اميري، محمدرضا دانشگاه شمال، آمل , زارع حسين زاده، علي دانشگاه علم و صنعت , قدرتي اميري، غلامرضا دانشگاه علم و صنعت
كليدواژه :
پايش سلامتي سازه ها , شناسايي آسيب , پاسخ تاريخچه ي زماني , تبديل موجك , مدل رفتاري سختي دو خطي
چكيده فارسي :
هدف اصلي اين مقاله، تشخيص آسيب هاي رخداده در سازه ها در حين وقوع زلزله ميباشد. اين كار، با پردازش سيگنال هاي مربوط به پاسخ تاريخچه زماني سازه به كمك تبديل موجك و واكاوي ضرايب جزئيات بدست آمده، صورت مي پذيرد. بر اين اساس، معيوب بودن كل سازه و لحظه رخداد آسيب، با ظهور تغييرات ناگهاني در ضرايب مذكور، تشخيص داده مي شود. همچنين، محل آسيب، از طريق بررسي بيشينه مقادير متناظر با تغييرات بوجود آمده در ضرايب موجك، تعيين مي گردد. بمنظور بررسي كارآيي روش ياد شده در شناسايي آسيب ها، سناريوهاي آسيبي مختلفي بر روي سه مثال عددي تحت زلزله هاي نورثريج و ال- سنترو، مطالعه شده است. در اولين مثال، كاهش يكنواخت سختي، بعنوان آسيب رخداده در يك قاب برشي 4 طبقه، در نظر گرفته شده است. مثال دوم، به شناسايي آسيبهاي احتمالي در يك تير ساده، با در نظر داشتن پاسخ هاي تاريخچه زماني متناظر با درجات آزادي انتقالي اختصاص يافته است. در آخرين مثال، جهت بررسي آسيب هايي با مكانيزم پيچيده تر، سختي سازه ي آسيب ديده بصورت مدل رفتاري متناظر با سختي دو خطي، تعريف و روش مذكور، جهت شناسايي آسيب ها پياده سازي شده است. نتايج بدست آمده، حاكي از توانايي روش مطالعه شده در تشخيص آسيب ديدگي سازه ها تحت اثر زلزله و قابليت بالاي آن در تعيين محل و زمان رخداد آسيب ها، بدون نياز به اطلاعات سازه اوليه، مي باشند.
چكيده لاتين :
Structural damage identification can be considered as the main step in Structural Health Monitoring (SHM). There are many different methods which use structural dynamic responses for damage prognosis. Although some of them are concentrated on solving an inverse problem for damage identification, others suggest a direct procedure for defect detection. Despite the good performance of these methods in damage identification, researchers are attempting to find efficient and simple methods for damage identification with high level of accuracy. This paper presents a reference-free method for structural damage identification under earthquake excitation. Damages are defined by some changes in the special instants during an earthquake occurrence, and structural time history responses are used as an input signal for discrete wavelet analysis. Finally the “detail coefficients” are inspected for determination of the damage characteristics including the appearance, the time sequence, and the location of damage(s). Although the peak values in the detail coefficients can show the existence and time sequence of damage, these peak values must be inspected for determining the damage location and finding the maximum value. As a result, the element associated with a signal which has the maximum peak value, can be considered as the damaged element. Applicability of the presented method is demonstrated by studying three numerical examples. The first is devoted to damage identification in a four-story shear frame. It is assumed that all of the stories are equipped by sensors for recording structural responses. Three different damage scenarios with single and multiple damage cases are studied under two samples of earthquake records, namely El-Centro (1940), and Northridge (1994) earthquakes. In addition, the effects of using different wavelet mother functions and different input signals, such as displacement and velocity responses, are investigated in this research. Obtained results emphasize on the applicability of the presented method in damage identification. In the second example, a simple concrete beam is considered with ten elements for simulating two different damage scenarios. In this case, applicability of the method is inspected by considering only the transitional degrees of freedom (DOF) as the equipped DOFs by sensors. This can be interpreted as using limited number of sensors. In addition, the displacement time histories are used for damage identification. In order to reach a clear strategy in damage localization, two rules are proposed for judging about elements’ health. The rules are based on seeking maximum values of the wavelet coefficients in the damaged instants. Obtained results show the reliable performance of the presented method in finding time sequence of damage occurrence and damage location. In the third example, applicability of the presented method is investigated in the presence of complex damage models by defining bilinear stiffness reduction. Although the damage can cause some reduction in the effective stiffness of damaged structures of this case, the reduction is different in positive and negative displacements. Two different damage scenarios are simulated on a single DOF structure under different excitations, namely earthquake excitations and generated White Noise excitation. Obtained results reveal the robustness of the presented method in damage prognosis in the presence of complex damage models.
