Innovative bolted junction with high ductility for circular tubular element

• Design of the junction of tubular elements with high ductility.
• The joint avoids buckling collapses introducing a flexible element.
• The design solution has been demonstrated by FEM analysis and experimental tests.

This paper deals with the design of an innovative type of bolted junction that shows a high plastic range in the load displacement. The schematization studied and reported in this paper is generally valid for steel structures and can be applied where high ductility is required (for example structures subjected to earthquakes) or statically indeterminate structures. In this case due to the high ductility of the junction there is a redistribution of stress/load in the elements. For this implementation the bolted junction was studied and applied to the arches of a bridge (designed by the University of Brescia). The developed junction described in this paper will solve the problems described above and permit an adjustment of the arch length until a balanced configuration is reached. The design procedure includes a preliminary analytical computation using the most important buckling theories; subsequently it is carried out a numerical analysis which results are validated executing several experimental analyses on a scale model. The final scope is the design of an innovative junction for tubular elements with circular section which permits the modification of the post-buckling curve in order to increase the ductility of the entire junction. The geometric solution studied was verified numerically and experimentally tested on a scale model. The results show a meaningful increase in elastic plastic performance of the junction. Indicatively this innovative geometry increases the elastic plastic behavior on the experimental geometry approximately 2 times when compared with the junction of the tubular elements without the designed junction.