ارزيابي مكانيكي يك اتصال نيمه صلب فولادي جديد

Mechanical Evaluation of a Novel Semi-rigid Steel Connection

امروزه اتصالات نيم صلب نقش ارزنده اي در سازه هاي فولادي بر عهده دارند. يكي از عواملي كه نشان دهنده ميزان صلبت در اتصالات مي باشد منحني لنگر- چرخش است. از اين رو مي توان در محاسبات اجزاء محدود براي به دست آوردن نمودارهاي منحني لنگر- چرخش كه اثر غيرخطي در پاسخ اتصالات را نشان ميدهد پارامترهاي مختلف روي رفتار اتصالات مورد ارزيابي قرار بگيرند. در اين مطالعه خواص مكانيكي و رفتاري يك اتصال نيمه صلب جديد مورد بررسي قرار گرفته اند. نتايج حاصله نشان مي دهد كه با تغييراتي از قبيل تغيير در تعداد پيچ ها يا كاهش لاغري ورق هاي بالايي و پاييني قابليت پوشش رده هاي مختلف مقاومتي را در اين اتصال جديد دارد. همچنين اين اتصال توانايي جذب انرژي و تحمل تغييرشكل هاي زياد در مقايسه با ساير اتصالات نيمه صلب هم رده ي مقاومتي را دارد. امروزه اتصالات نيم صلب نقش ارزنده اي در سازه هاي فولادي بر عهده دارند. يكي از عواملي كه نشان دهنده ميزان صلبت در اتصالات مي باشد منحني لنگر- چرخش است. از اين رو مي توان در محاسبات اجزاء محدود براي به دست آوردن نمودارهاي منحني لنگر- چرخش كه اثر غيرخطي در پاسخ اتصالات را نشان ميدهد پارامترهاي مختلف روي رفتار اتصالات مورد ارزيابي قرار بگيرند.

With regard to the increase of computing power in the past decade، finite element methods have been used to obtain the graphs of rotational moment curves which reflect non-linear effect in connections response. Using finite element methods the effect of different parameters on connections behavior can be investigated. In this study، several common semi-rigid connections are modeled and their behavioral properties are briefly reviewed and then providing the details related to a new semi-fixed connection، its behavioral properties like its hardness، ultimate capacity and ductility is investigated and is compared to other modeled connections. In this study، to perform non-linear analyses of connection، finite element software Abaqus is used. One capability of this software is different analyses like non-linear analysis which is very applicable. In this modeling، it has been tried to have inter-component interactions according to reality as much as possible. Bolted connections are modeled exactly and the interaction among the bolt surface and hole is modeled as a hard friction with friction coefficient 0.3 with the ability of separating after loading. Also، fillet welds are modeled as a prism with triangular section. Where a groove weld is applied، since the strength in this type of welding is like base metal، two connection parts are stuck together. To mesh the element، C3D8R element is used. To modeling the behavior of high strength bolts A10.9، the polyline elasto-plastic stress-strain curve has been used. The force is applied to samples according to the loading protocol presented by ATC-SAC which in fact is a replacement of real earthquakes. The proposed connection n1 has the most rigidity values among semi-rigid connections. Reducing the number of connection bolts has more reducing impact on connection rigidity value، so that with the half thickness of upper and lower sheets، rigidity rate is reduced only 9%، but with the half number of bolts، rigidity rate is reduced about 64%. Also the connection n3 have lowest rigidity rate and its rigidity amount is in the class of bolted connection in seat angle to web angle. In connections with high strength، the connection strength is highly related to girder strength and during creating plastic joint، this joint is formed in girder، while in connections with low strength، joint is formed in connection so it can be said that except joint connection state which are not applied in flexural resisting frames، four modes of rigid connection with high strength، semi-rigid connection with high strength، rigid connection with low strength and semi-rigid connection with low strength can be used in flexural resisting structures. Connection ductility is a key parameter for semi-rigid connections in which deformations are concentrated in connection members. Results show that the used mechanism in this connection has the ability of covering different classes of strength with the changes such as reducing the number of bolts or reducing the thickness of upper and lower sheets. Also this connection has the ability of absorbing energy and tolerating many deformations compared to other semi-rigid connections with same-class strength.