Seismic performance assessment of concentrically braced steel frame buildings with high strength tubular steel columns

In the paper, an analytical and experimental study aimed at supporting new design criteria for the exploitation ofsteel circular hollow columns made of HSS and subjected to exceptional loads, like earthquakes is presented. Infact, there is an increasing interest in the use of hollow sections of High Strength Steels (HSS). The ambitioustargets are to enhance the structural performance of concentrically braced steel frame buildings with tubular columns,and to reduce weight and, at the sametime, construction costs. The paper initially describes an experimentalstudy of the seismic behaviour of substructures representing a concentric braced frame of a prototypestructure: a steel building with concentric bracings for offices, meetings or exhibitions. The prototype structurewas designed in accordance with the capacity design criterion, i.e. by assuming that breaking of connectionsand buckling of beams and columns must be preceded by yielding of the diagonals in tension. The bracebeam-to-column joints represent the critical component. The objective of the test programme was to characterizethe connection behaviour under monotonic, cyclic and random loads. In detail, five tests were carried out onspecimens with standard braces and two tests on specimens with weakened braces. Experimental results areshown as force-interstorey drift ratio diagrams. Then, a numerical calibration of a model of these joints was successfullyaccomplished. After the calibration of the numerical models, in order to evaluate the global responseunder seismic loading, a numerical analysis of the reference building was performed with the OpenSeesprogramme. Both pushover and dynamic nonlinear time-history analyses were carried out. Experimental andnumerical results show that performance-based design approaches can be reasonably extended to concentricallybraced frames (CBFs) with high strength tubular steel columns.