Cyclic Behavior of Bolted Flange Plate Moment Connection

Understanding the exact real performance of rigid connections in steel moment frames is very important. Not paying enough attention in connection design process may lead to not only local connection damages but also other structural members' failure or even building collapse. According to seismic requirements of the tenth topic of national building regulations of Iran, clear span to depth ratio of beam (L/D) in the prequalified bolted flange plate moment connection shall be limited to 7 and 9 or greater respectively for intermediate moment frames and special moment frames and the beam flange thickness shall be limited to 30 millimeters too. Although the beam depth is limited to 1000 millimeters in this type of prequalified moment connection, due to architectural limitations and urbanism requirements, it is usually unacceptable to design such deep beam in the conventional residential buildings. So, in spite of its wide use and practical utility because of exceeding the clear span to depth ratio or beam flange thickness limitations, applying this kind of moment connection in steel moment frame structures is sometimes impossible specially in big span structures. To study the effect of these limitations on cyclic behavior of aforementioned rigid connection towel samples in L/D of 6, 7, 9, 12 and beam flange thickness of 20, 30, 35 were considered and modeled in a finite element software. First of all, the moment connection designed to have enough strength. Then, in term of ductility, the moment connection acceptance criterion is to count the rotation corresponding to related inter story displacement of 0.04 and 0.02 in special moment frames and intermediate moment frames respectively. The results show that applying this type of connection in special moment frames in L/D of 7 and beam flange thickness up to 35 millimeters provides required ductility, and thus, is acceptable. In addition, the moment connection in L/D up to 12 which it's flange thickness limited to 30 millimeters has enough ductility to pass seismic requirements of the tenth topic of national building regulations. In intermediate steel moment frames, applying bolted flange plate connection in clear span to depth ratio of beam up to 12 and the beam flange thickness up to 35 millimeters fulfills the seismic requirements. Comparison between models was shown that although by increasing the beam flange thickness and decreasing clear span to depth ratio of beam, the strength of connection is improved up to 37%, the connection ductility is reduced and so, the connection capacity is decreased. The von Mises stress distribution in samples show that the plastic hinges are almost located on the last row of bolts from column faces. The maximum stress in beams which observed in distance range of 20 to 100 centimeters from column faces has exceeded the yield stress and shows protected zone. As expected, the beams failure mode is top or bottom plate buckling. As a research suggestion, it seems that it is possible to combine these three limitations (clear span to depth ratio of beam, beam section flange thickness, and beam section depth) to gain a more comprehensive and useful phrase.