ظرفيت برشگيرهاي نبشي

Angle Shear Connectors Capacity

دانش كنوني مهندسي در ارتباط با رفتار و ظرفيت برشگيرها بيشتر به اطلاعات به دست آمده از آزمايش هاي برون راني و آزمايش تير مختلط محدود مي شود. با در نظر گرفتن اين موضوع كه آزمايش هاي عملي وقت گير و هزينه بر است، تهيه ي مدلي كامپيوتري كه بتواند رفتار و ظرفيت برشگير را پيش بيني كند لازم و ضروري است. با توجه به اين كه تاكنون رفتار برشگير نبشي مدفون شده در بتن به شكل جدي مورد بررسي قرار نگرفته است، در اين مقاله يك مدل كامپيوتري به منظور تعيين ظرفيت برشي برشگير نبشي تحت بارهاي مونوتونيك ارايه شده است. براي اين منظور، چند آزمايش برون راني برشي در مورد برشگير نبشي در نرم افزار آباكوس شبيه سازي شد. نتايج به دست آمده از مدل عناصر محدود با نتايج آزمايش هاي عملي مقايسه شد. اين مقايسه نشان داد كه مدل با تقريب خوبي مي تواند نتايج آزمايش برون راني نبشي را پيش بيني كند. با استفاده از مدل به دست آمده، يك مطالعه پارامتري بر روي برشگير نبشي انجام گرفت. در اين مطالعه اثر پارامترهايي مانند مقاومت بتن، ارتفاع، ضخامت، عرض بال و طول برشگير بر رفتار و ظرفيت برشگير نبشي مورد بررسي قرار گرفت. در ادامه به منظور كارايي بهتر برشگير نبشي، رابطه اي براي محدود كردن طول برشگير نبشي پيشنهاد شد. در پايان با استفاده از نتايج مطالعه پارامتري انجام شده و آزمايش هاي عملي موجود، رابطه اي براي پيش بيني ظرفيت برشگير نبشي ارايه شده است.

The steel-concrete composite beams are increasingly used in bridge and building construction in recent years. In this system, a shear connection between steel and concrete should be provided to effectively transfer the shear forces and to make the two materials act as a single unit. The mechanical shear connectors provide this means. They are the essential component of any composite beam system. Many studies have been performed on shear connectors and many different steel shapes have been suggested for connectors. The steel studs and channels are the most popular code accepted connectors. However, economic considerations continue to motivate the development of new products. Present knowledge of the capacity and behavior of the shear connectors are mainly limited to the data obtained from the push-out or beam tests with the latter being more expensive and accurate. Therefore, analytical procedures that can predict the nonlinear response and the capacity of the composite beams are necessary when the experimental resources are not available. In this study a three-dimensional FE model using the computer code ABAQUS is developed to simulate the push-out tests of angle shear connectors. The main objective of this study is to investigate the behavior and to find the ultimate strength of angle shear connectors in a solid slab. In order to obtain dependable results from the FE analysis, all components of the connection should be correctly modeled. There are four parts in this model: concrete slab, shear connector, steel beam and the rigid base. Because of symmetry, only a quarter of the push-out specimen is modeled.Nonlinear material and large displacement capability are employed. The load-slip behavior, capacity and maximum displacement at failure obtained from the finite element model were validated against available push-out test results. The results show the FEM can predict the capacity of the angle shear connectors with adequate precision. Using the FE model, a parametric study was conducted to evaluate the effect of variations in angle dimensions and concrete strength. The parametric study reveals that: ? The capacity of angle connector increases with increasing concrete strength. ? The flange width has no measurable effect on angle connector capacity and its behavior. ? The height of the angle has no considerable effect on load-displacement behavior of the connector. ? The capacity of angle connector increases whereas the maximum slip decreases with increasing angle thickness. ? The stress value is not constant along the angle length and it decreases from the center of the angle towards the edges. The shorter the length of the connector, the lower the stress change. Therefore, long angle shear connectors become ineffective. An equation is suggested to predict the angle effective length. Finally, an equation is proposed to predict the ultimate shear strength of the angle connectors.