Tension-only ideal dissipative bracing for the seismic retrofit of precast industrial buildings

Abstract

New precast frame industrial structures are seismically designed according to reliable modern criteria. However, most of the existing built stock hosting many workers and both regular and strategic industrial activities was designed and detailed neglecting the earthquake load or according to outdated seismic design criteria and regulations. Its seismic retrofit is a main challenge for the Engineering Community and a critical objective for institutional and private bodies. Among the envisaged solutions, the introduction of dissipative braces appears to be promising, although mostly inapplicable for these buildings, due to the brace lengths required by their typical large dimensions and the related proportioning against buckling. In this paper, an innovative seismic retrofitting technique based on monolateral dissipative bracing is investigated. The device proposed in this paper, yet in phase of preliminary design and testing, dissipates energy through friction in tension only while freely deforming in compression, which makes the issue related to compressive buckling irrelevant. A numerical analysis is carried out to investigate the efficiency of the proposed device in seismic retrofitting of precast industrial frame buildings with the aim to explore its feasibility and to better orient the definition of the slip threshold load range and the future development of the physical device. The simplified Capacity Spectrum Method (CSM) is employed for the global framing of the structural behaviour of the highly nonlinear retrofitted structures under seismic actions. A numerical tool is set to automatically apply the CSM based on the definition of few main parameters governing the seismic response of precast frame structures. The efficacy of the CSM is critically analysed through the comparison with the results of a set of nonlinear dynamic analyses. A smart simplified design process aimed at framing the most efficient threshold slip/yield load of the device given an existing structural configuration is presented with the application of the CSM through the identification of the most efficient performance indicator related to either displacement, shear force, equivalent dissipation of energy or a combination of them.

Design of Additional Dissipative Structures for Seismic Retrofitting of Existing Buildings

“…A novel retrofitting technique for precast concrete industrial frame buildings, based on tension-only monolateral dissipative devices mounted on steel braces, was proposed by Bruno Dal Lago [18]. These braces act as energy fuses and can provide additional stiffness and relevant hysteretic damping to the structural behavior during low-drift cycles.…”

“…According to an existing procedure [15,18] developed for the dimensioning of dissipative additional systems to be installed inside buildings (dissipative bracings), the energy dissipated by the S and ADS can be evaluated at each deformation value (Figure 4), and, according to A.K. Chopra [29], it can be evaluated by calculating ξ eq,S , that is, the equivalent viscous damping of the structure (as a function of the displacement, D); it can be expressed as follows:…”

Experimental and Numerical Investigation of a Dissipative Connection for the Seismic Retrofit of Precast RC Industrial Sheds

“…Global interventions are implemented by inserting in the structure particular devices, which either reduce the seismic input by separating the motion of the superstructure from the motion of the ground (namely seismic isolation systems), or increase the total energy dissipation capacity (namely energy dissipation devices) [15,16] by concentrating on special elements out of the vertical load bearing frame the dissipation of most of the energy transmitted by the earthquake [17,18]. Examples of application of energy dissipation systems to the retrofit of industrial frames can be found in references [16,[19][20][21][22].…”