Displacement-based design procedure of damped braces for the seismic retrofitting of r.c. framed buildings

Abstract

The insertion of damped braces proves to be very effective for enhancing the performance of a framed building under seismic loads. For a widespread application of this technique suitable design procedures are needed. In this paper a design procedure which aims to proportion damped braces to attain a designated performance level of the structure, for a specific level of seismic intensity, is proposed. In particular, a proportional stiffness criterion, which assumes the elastic lateral storey-stiffness due to the braces proportional to that of the unbraced frame, is combined with the displacement-based design, in which the design starts from a target deformation. To check the effectiveness and reliability of the design procedure, a six-storey reinforced concrete plane frame, representative of a medium-rise symmetric framed building, is considered as primary structure. This, designed in a mediumrisk seismic region, has to be retrofitted as in a high-risk seismic region by the insertion of braces equipped with either metallic-yielding dampers or viscoelastic ones. Nonlinear dynamic analyses of unbraced and damped braced frames are carried out, under real (set A) and artificially generated (set B) ground motions, by a step-by-step procedure. Frame members and hysteretic dampers are idealized by bilinear models, while the viscoelastic dampers are idealized by a six-element generalized model describing the variation of the mechanical properties depending on the frequency, at a given temperature.

Direct design method based on seismic capacity redundancy for structures with metal yielding dampers

“…In view of this, scholars have proposed various design methods for structural systems with supplemental dampers. Based on the direct displacement-based design (DBD) procedure, Kim and Choi 12 proposed a design method for viscous dampers; furthermore, Di Sarno and Manfredi, 13 Lin et al, 14 and Mazza and Vulcano 15 proposed design methods for multiple types of EDDs. It should be noted that iterative procedures are required in these methods.…”

“…Substituting Equation 15 into Equation 14, the increment of external work, ΔW p,n , can be rewritten as Substituting Equation 15 into Equation 14, the increment of external work, ΔW p,n , can be rewritten as…”

“…28 In the existing design methods based on the CSM and DBD, a certain displacement is set as the performance design target. 12,[14][15][16] Some of these methods require iterations or graphical procedures, which make the method inconvenient. Moreover, because randomness is inevitable in ground motions, it is difficult to exactly satisfy the target displacement.…”

“…where ρ n is a scaling factor and A i is the distribution factor for P i , n . Substituting Equation 15 into Equation 14, the increment of external work, ΔW p,n , can be rewritten as…”

“…3 During an earthquake, metal yielding dampers can yield and enter the plastic stage ahead of a beam or column, thereby dissipating the input energy through their hysteretic behavior. Based on the direct displacement-based design (DBD) procedure, Kim and Choi 12 proposed a design method for viscous dampers; furthermore, Di Sarno and Manfredi, 13 Lin et al, 14 and Mazza and Vulcano 15 proposed design methods for multiple types of EDDs. Since Kelly 4 first proposed the metal yielding damper in 1972, scholars have conducted numerous studies on metal yielding dampers.…”