تعيين فركانس طبيعي تيرهاي فولادي با اتصال گيردار براي كنترل ارتعاش كف با استفاده از شبكه‌هاي عصبي مصنوعي

Determination of the Natural Frequency of the Moment Connections Steel Beams for Controlling Vibration of Floors by Artificial Neural Networks

- ارتعاش محسوس تيرهاي باربر فولادي در دهانه‌هاي بزرگ امري ناخوشايند در ساختمان‌هاست. حتي اگر محاسبات مربوط به اين تيرها از نظر مقاومت و معيارهاي كنترل تغيير شكل طبق آيين‌نامه به‌خوبي صورت گرفته باشد، با اين وجود ممكن است هنگام عبور افراد دچار نوساناتي شوند. مبحث دهم مقررات ملي ساختمان رابطه‌اي براي كنترل ارتعاش تيرهاي با اتصال مفصلي در حالت بهره‌برداري ارايه كرده است، اما براي تعيين فركانس تيرهاي با اتصالات گيردار روابطي را بيان نكرده است. از آنجا كه اين تيرها سهم قابل توجهي از قاب‌هاي ساختماني را به خود اختصاص مي‌دهند، كنترل ارتعاش آن‌ها از اهميت خاصي برخوردار است. روابط ارايه‌شده در تحقيقات سال‌هاي اخير براي تعيين فركانس تيرهاي گيردار داراي پيچيدگي‌هاي زياد است كه استفاده از آن‌ها براي كنترل ارتعاش سقف‌ها مشكل است. در اين مقاله، رابطه ارايه‌شده در آيين‌نامه طرح و اجراي ساختمان‌هاي فولادي ايران بررسي شده است. همچنين، با استفاده از تحليل ديناميكي، روش اجزاي محدود و شبكه‌هاي عصبي روابطي براي تعيين فركانس تير‌هاي دوسر گيردار و كنسول پيشنهاد شده است. مقايسه فركانس حاصل از روابط مورد نظر با داده‌هاي به‌دست آمده از شبكه عصبي با خطاي بسيار كم همراه بود كه حاكي از دقت بالاي روابط معرفي‌شده است. پيشنهاد مي‌شود براي محاسبه فركانس طبيعي تيرهاي كنسول و دوسر گيردار جهت كنترل ارتعاش سقف‌هاي ساختماني از روابط معرفي‌شده در اين مقاله استفاده شود.

Sensible vibration of steel beams in long spans is undesirable issue in the buildings. These beams may be vibrated during people passage, although the strength calculations of this beams to be performed, accurately and drift control index based on buildings codes to be considered. Frequency of beams is an essential property required for doing dynamic analysis and vibration control of floors. Extra vibration makes the residents worried and creates the fear of structural damage although such fear is usually unwarranted because of the small displacements and stresses which are actually produced. Nevertheless, perceptible vibration is usually considered to be undesirable because it affects people’s sense of well-being and their ability in carrying out tasks. Floors were traditionally designed to an Ultimate Limit State (ULS) in which designing for strength governed size of beams and thickness of deck. The concept of Serviceability Limit State (SLS) is to limit the maximum deflection of the floor and it is not set for avoiding the damage and collapse of structural members but for keeping away from the cracking of finishes. Instead of deflection, vibration serviceability has become a major concern in designing buildings for several reasons, such as changing the construction techniques, changing the occupancy of floors, sensitivity of some medical, scientific and micro-manufacturing equipment to vibration. Design guides from the American Institute of Steel Construction (AISC), Canadian Standards Association (CSA) and Iranian Design Code of Steel Buildings all offer methods of predicting and controlling natural frequency. These codes assert that the connected beams to large areas without beam partitions should be controlled based on shaking and vibration of kinetic loads (walking, elevator movement, etc). Iranian Steel Buildings Code has offered a formula for controlling of vibration of beams in building frames with pin connections in serviceability phase. However, this code has not presented criteria for beams include fixed connections. Since these beams have the considerable portion of building frames, their vibration control needs special attentions. The presented equations for determination of beams frequency are complicated and have been not used for control of buildings floor vibration. In this paper, the mentioned formula in forenamed codes has been discussed. The dynamic analysis, finite element method (FEM) and artificial neural networks (ANN) techniques have been adopted to constitute the frequency equations of the fix ends and cantilever steel beams. Comparison of resulted frequency from presented equations and ANN showed that the error is low. Furthermore, it is suggested that use proposed equations for determination of frequency of moment connection beams.