مشخصات ديناميكي عرشه‌ي مركب اگزودرميك با استفاده از تابع پاسخ بسامدي

Dynamic Characteristics of Exodermic Composite Deck using the Frequency Response Function (FRF)

سيستم عرشه‌ي اگزودرميك از جديدترين عرشه هاي پل با شبكه‌بندي فولادي است، كه در طي دهه‌ي گذشته در پروژه‌هاي گوناگون به‌كار گرفته شده و ويژگي بارز آن كاهش قابل ملاحظه‌ي وزن سازه نسبت به عرشه‌هاي بتن‌آرمه‌ي معادل و همچنين افزايش سرعت اجرا با استفاده از عرشه‌هاي پيش ساخته‌ي اگزودرميك است. در اين مطالعه، بسامد ارتعاشي و نيز درصد ميرايي عرشه‌ي مركب اگزودرميك پل با برش گيرهاي پرفوبوند به‌طور آزمايشگاهي تعيين شده‌اند. بدين منظور، با تحريك يك نقطه از سازه و اندازه‌گيري مقادير شتاب و نيرو و تكرار آزمايش در چند مرحله، مقادير بسامد طبيعي و درصد ميرايي با استفاده از تابع پاسخ بسامدي و روش هاي پيك پيكينگ و برازش دايره‌ي نايكوييست تعيين شده‌اند، كه مطابقت مناسبي با مدل‌سازي به روش اجزا محدود داشته‌اند. همچنين نتايج آزمايشگاهي نشان مي‌دهند كه در بين مود هاي مختلف، مود اول غالب است.

Regarding the increasing demand for rapidly constructed bridges with lower dead load and cost, various types of structural system have been proposed for bridge decks. Due to the high tensile strength of steel and the remarkable compression strength of concrete at lower cost, steel-concrete composites are most commonly used in construction. In these composites, the concrete section can also enhance the fire resistance of the steel section. A convenient performance for steel-concrete composite structures can be achieved, provided the relative displacement of concrete and steel sections at their interface be prevented or, at least, reduced. Chemical adhesions, or bonds, interface friction and mechanical interlocking, do not provide sufficient resistance to heavy shear forces. Hence, to assure the shear transfer, various types of mechanical connector between the steel and the concrete, such as channels, reinforcing steel, headed shear studs and welded structural steel elements, have been considered. Exodermic deck systems are newly developed composite steel grid deck systems that have been used in various projects during the past decade. An eminent feature of this system is the considerable reduction in structural weight in ordinary reinforced concrete decks, and the reduction in construction time using the precast exodermic decks. The increase in the use of this system for deck bridges has made it necessary to identify its behavior; especially its dynamic behavior. In this research, natural frequencies, damping ratio and some physical properties, such as stiffness and effective mass, for exodermic deck bridges with alternatively perforated shear connectors, were determined experimentally. Towards this aim, by exciting a point on the structure and measuring input force and output acceleration, and then repeating it in more steps, the values of natural frequencies and damping ratios were determined. This was undertaken using the frequency response function (FRF), by employing peak picking and Nyquist circle fit methods, which suitably matched the finite element method. Also the experimental results show that the first mode is the most effective.