Steel Braces in Series with Hysteretic Dampers for Reducing the Seismic Vulnerability of RC Existing Buildings: Assessment and Retrofitting with a Nonlinear Model

Abstract

In the present paper we analyze an innovative strategy for the retrofitting of a Reinforced Concrete (RC) building by the use of hysteretic dissipators. A device called Buckling Restrained Axial Damper (BRAD) is adopted which is used in series with a steel element to form the diagonal braces of the retrofitted structure. Such devices allow a significant improvement of the seismic behavior of the building by providing a better dissipation of the seismic input energy in the structure and thus ensuring a better performance of the RC structure in the elastoplastic range. In the paper the behavior of such devices is described and analyzed in detail. The advantages and disadvantages of their use in the retrofitting of RC structures is discussed. A nonlinear analysis is finally presented for the retrofitting of a RC existing building by a displacement based approach in order to verify the compatibility condition between the displacement capacity of the structure and the displacement demand according to the seismic codes. The performances of the use of the BRAD devices in the retrofitting of RC buildings is thus illustrated in detail.

Seismic vulnerability of an existing strategic RC building using non linear static and dynamic analyses

“…The advantage of these procedures with respect to linear procedures is that they directly take into account the effects of nonlinear material response and, hence, the calculated internal forces and deformations will be more realistic and closer to the values expected during an earthquake. Several methods exist: ATC 40, FEMA 273, FEMA 440, and EC8 [12][13][14]. They all consider that the nonlinear force-deformation characteristics of a building can be represented by a pushover curve which shows a building's resistance in terms of storey shear force versus top displacement.…”

Roof Isolation and Girder-to-Column Dissipative Connections in Seismic Design of Precast R/C Structures

“…T-ADAS dampers consist in the assembly of isosceles triangle-shaped steel plates vertically mounted on top of the supporting diagonal braces [35][36][37][38][39]. According to the symbols in Figure 11, the following typical dimensions of the plates were adopted [29,36,37]: h = 150 mm, t = 15 mm, and b = 150 mm.…”

“…Which gives a P y value of 16.9 kN, and by assuming maximum positive and negative displacements of the dampers approximately equal to the values obtained for the FV devices, tentatively rounded here to ±60 mm, the energy dissipated by a single plate in the maximum response cycle, E p,s , is equal to about 4.1 kNm. By observing that the energy dissipated in all the remaining cycles is approximately equal to 4 E p,s [39], the total energy dissipated by a plate, E p,t , is tentatively fixed at E p,t = 4 E p,s = 16.4 kNm. The sizing value of N p , N p,s , is thus obtained by dividing E d,t = 1500 kNm by E p,t = 16.4 kNm, obtaining a ratio of about 91, rounded to N p,s = 90.…”

Seismic Vulnerability of Existing RC Buildings and Influence of the Decoupling of the Effective Masonry Panels from the Structural Frames

“…After the assessment of the seismic vulnerability and before performing the proper retrofitting actions, see Cancellara and De Angelis [27][28], it may be convenient to examine the opportunity of decoupling the masonry panels from the structural frame, of course only for the masonry panels considered as effective. In such a case the structural frame may be considered as a bare structural frame without significant interactions with the masonry infills.…”