Pin-supported walls as seismic retrofit for existing RC frames: feasibility and preliminary design

Abstract

The seismic retrofit of the existing building heritage represents an urgent issue to be faced and innovative solutions which allow to overcome renovation barriers are needed. In this scenario, pin-supported (PS) walls represent an eligible solution, enabling linearization of the deformation of the frame along its height and inhibiting soft storey collapse mechanisms. The PS wall can be connected to the existing building from outside, thereby avoiding disruption to occupants or their relocation, which are acknowledged as the main barriers to the renovation nowadays. Suitability of PS wall solutions in the seismic retrofit of the existing building stock has been investigated herein, particularly in the case of existing reinforced concrete (RC) buildings, preliminarily focusing on 2D RC frames. The paper shows the weaknesses and strengths of the PS wall solution in relation to the specific features of the considered buildings. An analytical closed-form formulation is proposed and applied as a preliminary tool to evaluate the load distribution in the existing frame and in the PS wall after the retrofit considering the first mode of vibration of the retrofitted system. The results show that, in some conditions, the application of PS walls may be detrimental to the structural response. Along with the evaluation of the effectiveness of the retrofit solution, the proposed formulation allows a preliminary design of the retrofit system. Finally, a series of finite element model analyses have been carried out for validation purposes showing a good agreement between the proposed analytical formulation and the numerical results.

Pin-supported walls as seismic retrofit for existing RC frames: performance improvement through link removal

“…A complete linearization of the deformed shape of the retrofitted system is inherently assumed in the proposed analytical model, thus considering a lateral stiffness ratio (χ) at least equal to 0.3 in the following applications. The interested reader is referred to Casprini et al (2022) for further details and for the background of the analytical method presented in this paper. Herein the 1st link removal is investigated in order to improve, when necessary, the efficacy of a PS wall solution.…”

“…Pin-supported (PS) walls represent a possible innovative seismic retrofit solution for existing reinforced concrete (RC) buildings (Belleri et al 2016;Casprini et al 2022;Wada et al 2011;Wada 2018), particularly for those designed before the enforcement of modern antiseismic regulations and seismic zonation, featuring low-ductility structural detailing and structural irregularities, which represent a wide portion of the existing heritage (Marini et al 2017). The introduction of a stiff pin-supported wall (also referred to as "hinged walls" or "rocking cores") able to linearize the lateral deformation of the existing frame along its height (MacRae et al 2004), allows spreading the ductility demand, thus inhibiting soft storey collapse mechanisms.…”

“…The introduction of a stiff pin-supported wall (also referred to as "hinged walls" or "rocking cores") able to linearize the lateral deformation of the existing frame along its height (MacRae et al 2004), allows spreading the ductility demand, thus inhibiting soft storey collapse mechanisms. Although the first examples of PS walls as retrofit systems are quite recent (Wada et al 2011;Qu et al 2012), its application has increased in the last decade in several countries (Balducci and Castellano 2015;Gioiella et al 2017). Some research studies deal with finite element simulations to investigate the behaviour and effectiveness of 2D wall-frame retrofitted systems (Qu et al 2015) or to define preliminary design criteria (Blebo and Roke 2015), while others focus on analytical formulations able to derive the dynamic characteristics of the system (Bozdogan and Öztürk 2016), or the displacement and force demand under several lateral load configurations (Sun et al 2017;Zhou et al 2021).…”

“…Based on these preliminary considerations, a closed-form analytical method able to assess the suitability of this solution in relation to the actual configuration and geometrical properties of the existing structures was proposed (Casprini et al 2022). In this method, differently from most approaches proposed in the former mentioned research works, the frame 1st storey lateral stiffness was set as a key parameter to understand the behaviour of the retrofitted system.…”

“…In this paper, the analytical procedure developed by Casprini et al (2022) (i.e., with links at each floor level) is extended for the case of the 1st link removal, providing a closed-form solution to estimate the load distribution in the PS wall and the system capacity in terms of strength, both considering a linear and nonlinear behaviour of the frame elements. The postretrofit deformation demand should be then compared with the capacity of the existing elements; in this paper, such comparison is carried out through nonlinear pushover analyses.…”