Seismic response of concentrically braced steel frames with INERD (Innovative energy dissipative) connections

Abstract

Concentrically braced frames are capable of undertaking the drift problems with economical solutions under sligth and moderate earthquakes. However, this type of frames are known to have limited ductility capacity under severe earthquakes. This study is focused on an innivative concept that can minimize the ductility problems of concentrically braced steel frames by introducing bending pin elements at the ends of braces, called INERD connections. In fact, the purpose of utilizing INERD connections is to restrict the inelastic deformations to the connections instead of braces developing a lower quantity of force than the buckling resistance. Therefore, the braces and accordingly the columns are protected against buckling. In order to exhibit the behavior of frames with innovative connections compared to conventional frames, nonlinear time history analysis is performed for all case studies by using the open source program OpenSEES. The case studies consist of four storey and six storey concentrically X-braced steel frames, both including a conventional frame and three frames with INERD connections having different yield strength. The analysis are carried out by utilizing three earthquake records; El Centro (Imperial Valley 1940), Kobe (1995) and Kocaeli (1999). Each earthquake is scaled with appropriate scale factor so that all of them has four different peak ground accelerations ; 0.2g , 0.4g , 0.8g , 1.2g , in order to capture the behavior of frames under different severity of strong ground motions. The top displacements, interstory drift ratios, axial forces of first story braces, devices and columns are recorded. The analytical results indicate that frames with INERD connections prevent buckling of braces while they do not create serviceability problems. In fact, they exhibit better performance than the conventional frames at higher PGA values.