بررسي ارتعاشات ناشي از بارهاي قايم زلزله و حركت اجرام روي سازه‌ي پل و كاربرد ميراگرهاي لوله‌يي غيرفعال در آن

INVESTIGATING VIBRATION IN BRIDGE STRUCTURES CAUSED BY VERTICAL EARTHQUAKE EXCITATION AND MOVING MASS EMPLOYING PASSIVE PIPE DAMPERS

علي‌رغم اينكه در پل‌ها و تيرهاي موازي آن، طراحي براساس مولفه‌ي افقي تحريك لرزه‌يي صورت مي‌گيرد و از مولفه‌ي قايم آن صرف‌نظر مي‌شود، شواهدي در دست است كه برخي از مودهاي شكست در رابطه‌ي مستقيم با مولفه‌ي قايم زمين‌لرزه استهستند. اگرچه به‌طوركلي مولفه‌ي قايم در مقايسه با مولفه‌ي افقي زلزله، قدرت كمتري دارد، ؛ ولي بيشتر تاثير بيشتر آن در حوزه‌ي بسامدي به خصوصي واقع است كه مي‌تواند براي سازه‌هايي با بسامد طبيعي در اين حوزه‌ها بسيار مخرب باشد. در اين پژوهش، علاوه بر بررسي اثر مولفه‌ي قايم تحريك لرزه‌‌يي بر رويدر سازه‌ي پل، به بيان تاثير توام اين نيرو با بارهاي به‌صورت اجرام محرك و لزوم درنظرگرفتن اين آثار در طراحي پل‌ها و همچنين توجه به كاهش اين‌گونه اثرات آثار از طرق مختلف پرداخته شده است. در ادامه، با استفاده از يك سيستم ميراگر غيرفعال، سعي بر كاهش اثرات ذكرشده و كاربرد آن‌ها در سازه‌ي پل شده است. درنهايت، با بررسي و مقايسه‌ي نتايج، اقدام به كاهش مقاطع اين‌گونه سازه‌ها با حضور ميراگرها در جهت صرفه‌ي هر چه بيشتر اقتصادي شده است.

Dynamics of beam structures subjected to various loads have been investigated for over a century. The importance of such a problem arises in the structural design of bridges in which the nature of loading could affect the design parameters substantially. It has been observed that as a bridge structure is subjected to moving masses and earthquake loading, the dynamic deflection and stresses can be significantly higher than those observed in the static case. Although only the horizontal component of earthquake excitation is taken into account in the modeling of bridges and parallel beams sustaining the bridge deck loads. there exist several pieces of evidences showing that some of the failure modes are in direct relation to the vertical one. Generally, in comparison with the horizontal component of earthquake, however, the vertical one has less power and most part of its influence occurs in a particular frequency domain that could be so destructive to the structures with natural frequency in these domains. In addition, there are clearly many problems of great physical significance in which the load inertia is not negligible and can significantly alter the dynamic behavior of the system; therefore, moving mass is the another important and affective dynamic loads in design of these routine bridges. In this article, the seismic effect of vertical earthquake on the bridges is studied aiming to explore the necessity of simultaneous acts of this force and the moving masses. By proving the intensifying effects of these loads combination via the obtained results, by employing a passive damper system, it is attempted to decrease the mentioned influences on the studied structure. Dampers are used in two ways. and the best one is chosen based on its performance in suppression of the beam deflection. Finally, through analyzing and comparing the results, a simple algorithm is introduced for reducing the sectionsʹ dimensions of the bridge structures under this type of loading.