چكيده فارسي :
در دهه هاي اخير تحقيقات گسترده اي در ارتباط با قطعات مستهلك كننده انرژي انجام شده كه در اين ميان ميراگرهاي ويسكوز، بخش مهمي از اين تحقيقات را به خود اختصاص داده اند. مطالعات انجام شده نشان مي دهد كه رفتار اين ميراگرها تنها با ثابت ميرايي آن ها قابل بيان نيست بلكه عواملي از قبيل رفتارِ سرعتي غيرخطي، سختي محوري هرچند ناچيز و اصطحكاك داخليِ ميراگر از عوامل مهم تاثيرگذار در رفتار اين سيستم هاي جاذب انرژي هستند. همچنين دامنه فركانسي اعمال بار، انعطاف پذيري غلاف پيراموني هسته ي ميراگر، تراكم پذيري مايع دروني آن، اثرات حرارتي نيز در تعيين مشخصه هاي رفتاري اين ميراگرها تاثير گذارند. در مطالعات تجربي كه تاكنون براي تعيين مشخصه هاي رفتاري اين ميراگرها صورت پذيرفته و همچنين ادبيات فني موجود، ارتباط موثري بين موارد ذكر شده با مكانيك رفتاري اين ميراگرها ديده نمي شود.در مطالعه حاضر اقدام به ساخت نمونه اي از ميراگر ويسكوزِ انقباض محوري، با ظرفيت نيرويي 500 كيلونيوتن و دامنه ي تغيير مكاني 150 ميلي متر شد. رفتار مكانيكي ميراگر جديد، تحت آزمايش هاي چرخه اي مورد بررسي قرار گرفت كه در نهايت مشخصه هاي رفتاري آن در فرم يك مدل ارائه شده است. ميراگر ساخته شده، طي چرخه هاي مختلف بارگذاري به طور متوسط داراي 10 كيلونيوتن نيروي اصطكاك اوليه است كه مي توان از آن به عنوان فيوز عملكردي ميراگر بهره گرفت. همچنين با توجه به نحوه ي ساخت ميراگر (عدم تقارن در ساخت بِلوزها) افزون بر نيروي ميرايي، نيروي اصطكاكي ثانويه اي، وابسته به فشار روغن به ميزان 50 كيلونيوتن وجود دارد كه باعث افزايش ظرفيت نيرويي ميراگر و بهبود منحني هاي رفتاري آن شده است.
چكيده لاتين :
New techniques in seismic design of structural systems are based on flexibility and energy dissipation approach. In this approach, the role of energy dissipaters is quite important. The behaviors of these devices and the way they dissipate energy have always been a concern for many researchers to improve the efficiency of these important parts of the structural systems. There has been a large number of investigations on behavioral aspects of energy dissipating devices capable of using in seismic design of structural systems. The concept of adding dissipating supplemental devices to a structure assumes that much of the energy imposed to the structure from a transient will be absorbed, not by the structure itself, but rather by supplemental damping elements. Among them, viscous devices have received considerable attention. The behavior of these energy dissipaters are dependent, not only on the relative velocity, but also on a large number of other parameters including relative displacement, compressibility of fluid, internal friction etc. The behavior of viscous devices are also dependent on the frequency of excitation and their thermal conditions. Determination of mechanical characteristics of these devices is usually based on experimental studies including cyclic tests in different amplitudes and frequencies. In this study, a new type of viscous dashpot in which the main body of the device has been made of contractible steel bellows (developed in IIEES) is chosen for experimental studies. The viscous device has the capacity of 500 kN and axial deformability of 150mm . The tests have been carried out using an actuator
capable of providing axial forces up to 300 kN in cyclic tests with displacement range of 120mm . Axial forces on dashpot and resulted deformations on the device during experiments have been used to find the relationships between applied forces and induced relative displacement and velocity on the device. According to the results, the dashpot shows a dominant viscous behavior. It also represents a small frictional behavior in order of 10 kN (on average). The device also shows a frictional feature that is proportional to its internal fluid pressure. This feature is due to a small asymmetry in manufacturing some parts of the device, but it can be used later to improve the behavior of contractible dashpots. To be able to develop a model for this device, the test results are used in the form of cyclic behavior and time series. The time series results show the fact that there is not a linear proportionality between forces and velocity experienced by the dashpot in all the range of excitation frequencies. In addition, according to the test results, damping constants for this device is also dependent on the excitation frequency. Different types of behavioral models have been examined for the device. The proper model is proposed based on the three element type Maxwell model. The model can be further improved to represent the pressure dependent frictional forces in this dashpot.
