A Simplified Analytical Approach for CLT-Based Seismic Retrofit of Existing Reinforced Concrete Structures

Reinforced concrete (RC) framed buildings characterize the built heritage of many countries. Many of these buildings were built between 1950 and 1970, when seismic codes and guidelines were scarce and not mandatory, and therefore the design was based exclusively on gravity loads. The absence of specific seismic details combined with little awareness of the consequences of the interaction between the RC frame and the masonry infill has resulted in buildings highly vulnerable to seismic excitation. The need to bring the seismic safety of existing RC buildings up to a satisfactory level has led to the development of a wide range of retrofit systems and solutions. This paper focuses on a retrofit method that involves the complete or partial replacement of the masonry infills with structural timber panels. Previous stages of the research have shown that this solution can considerably improve the seismic performance of RC frames. However, to maximize the effectiveness of the intervention, the retrofit design must be precisely tailored to the characteristics of the existing frame. The aim of the present study is to propose a straightforward and reliable analytical method capable of predicting the behaviour of the retrofitted system and guiding the design of the optimal retrofit configuration. The proposed analytical method was successfully validated on the results of nonlinear static analyses performed on models of single-storey single-bay frames, and on the results of testing performed on a full-scale RC frame that was subjected to in-plane cyclic loading up to collapse.