Predesign of steel frames with semi-rigid joints

It is well known that real solutions of steel joints in framed structures are far away from the conservative assumption that joints behave like pure hinges and/or full rigid connections. Applying semi-rigid philosophy in the design requires consideration of joint characteristics (M- relationship) in the global analysis. The main parameters describing M- curve are the moment resistance Mj.Rd and initial stiffness Sj.ini. In EC3, part 1-8, there are procedures to determinate joint properties, but calculation of them is very troublesome and time consuming. Using regression analysis, simple formulas for Mj.Rd and Sj.ini, possible for hand calculator, were obtained for end-plate bolted as well as welded beam-to-column connection. The distribution of internal forces in the frame depends on, and changes with the changes of joints stiffness, which in turn depend on beam and column sections. To help designers avoid many recalculation and speed up their design work there is a need to supply design tools, like "good guess" assessment, simple formulas, tables, design guidelines, which enable designer to assess preliminary members and joints properties. Based on the wide analysis of many frames with various types of joints, such design tools were developed and are presented in the paper.