Afram Keivani - Professor of Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran.
Mehdi Azizi - MSc of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran.
Hale Dasti - BSc of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran.

Moment resistant steel frame is one of the structural systems used to resist earthquake loads in buildings. Many existing steel structures with this system need retrofitting to overcome deficiencies and to resist seismic loads. In the present study, the seismic behavior of rigid frames with knee-type braces was investigated and the distribution of internal forces in frame elements such as beams and columns were discussed. Two types of structures, including moment frames and braced frames with knee-type braces in different positions of joints, for 11, 21 and 31 stories were designed per the Iranian Seismic Code, the Iranian Steel Structures Design Code and the Seismic Provisions. Dynamic analysis using 8 earthquake records for moment frames and braced frames were carried out to obtain dynamic responses. According to the analysis results, the distribution of internal forces such as bending moments, shear forces and axial loads for braced frames in beams and columns turned out to be different from moment frames. Comparing shear and moment diagrams in moment frames and braced frames showed that utilizing knee-type braces cause the moments and shear forces at fixed ends to decrease. It means that the joint forces in braced frames are dissipated by a group of elements that are restricted by knee elements which change the joint from a point joint to a zonal joint.

steel moment frames, knee braces, near-fault region, seismic design