Failure Mode and Drift Control of MRF-CBF Dual Systems

Abstract

Abstract:In this paper, a new method for designing moment resisting frame (MRF) -concentrically braced frame (CBF) dual systems failing in global mode is presented. Starting from the analyses of the typical collapse mechanisms of such structural typology subjected to seismic horizontal forces, the method is based on the application of the kinematic theorem of plastic collapse. Beam and diagonal sections are assumed to be known quantities, because they are designed to resist vertical loads and horizontal forces, respectively. Therefore, the column sections are the only unknowns of the design problem. Column sections are obtained by imposing that the equilibrium curve corresponding to the global mechanism has to lie below all the equilibrium curves corresponding to the undesired collapse mechanisms within a displacement range compatible with the local ductility supply of dissipative elements. Such procedure has been applied to design several MRF-CBF dual systems and has been validated by means of non-linear static analyses aimed to check the actual pattern of yielding.

High strength steel in chevron concentrically braced frames designed according to Eurocode 8

“…More recently, Tenchini et al [2] confirmed this result highlighting the limited benefit in using HS steel for seismic application in moment resisting frames (MRFs) compared to using solely MC steel, because the design of MRFs is conditioned by the need to guarantee lateral stability and to satisfy the performance limits in terms of story displacements. On the contrary, when the seismic design is associated to Theory of Plastic Mechanism Control (TPMC) [3][4][5][6][7][8][9][10][11][12][13][14][15], the HS steel has provided adequate seismic performance where it is possible to see a reduction of the steel weight compared to frames in complacent with European code. In fact, in order to ensure a collapse mechanism of global type, this approach provides a plastic http://dx.doi.org/10.1016/j.engstruct.2016.06.001 0141-0296/Ó 2016 Elsevier Ltd. All rights reserved.…”

Theory of Plastic Mechanism Control of Seismic-Resistant MR-Frames with Set-Backs

“…Conversely, the actual behavior is elasto-plastic so that structures exhibit significant lateral displacements before failure, and second order effects cannot be neglected in the design procedure. To this scope, a linearised mechanism equilibrium curve can be used to represent the structural behavior [1,7]:…”

“…By properly solving the 3n s design conditions provided by Eq. (9) [1,7], the sum of column plastic moments, reduced due to the contemporary action of axial forces, required to prevent the development of undesired collapse mechanisms is obtained for each storey. The final step consists in distributing such sum among the storey columns.…”

“…It is universally recognized that failure mode control is a fundamental requirement for designing seismic resistant structures, because local failure modes, such as partial and soft-storey mechanisms, lead to damage concentration and, as a consequence, to the premature collapse of structures. For this reason, the development of a collapse mechanism of global type [1][2][3][4][5][6][7][8][9][10] is promoted by modern seismic codes by means of simplified design rules. The first studies on this topic have been carried out mainly with reference to reinforced concrete frames and, in particular, in New Zealand where the capacity design procedure has been in use since 1980 [13][14][15].…”

MRFS Designed According to the Theory of Plastic Mechanism Control vs Code Rules

“…In particular, it consists on the extension of the kinematic theorem of plastic collapse to the concept of mechanism equilibrium curve. This design approach was successively extended to a large variety of structural typologies [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In 2015 TPMC was developed also with reference to the reinforced concrete frames [38][39][40].…”