A fragility-oriented approach for seismic retrofit design

Abstract

This study proposes a practical fragility-oriented approach for the seismic retrofit design of case-study structures. This approach relies on mapping the increase of the global displacement-based ratio of capacity to life-safety demand ( CDRLS) to the building-level fragility reduction. Specifically, the increase of CDRLS due to retrofitting is correlated with the corresponding shift in the fragility median values of multiple structure-specific damage states, observing that a pseudo-linear trend is appropriate under certain conditions. Accordingly, a practical approach is proposed to fit such a (structure-specific) linear trend and then use it by first specifying the desired fragility median and subsequently finding the corresponding target value of CDRLS that must be achieved through retrofit design. The validity of the proposed approach is illustrated for an archetype reinforced concrete (RC) structure not conforming to modern seismic design requirements, which has been retrofitted using various techniques, namely, fiber-reinforced polymers wrapping of columns and joints, RC jacketing, and steel jacketing.

Direct loss‐based seismic design of reinforced concrete frame and wall structures

“…A non-exhaustive list of examples may include procedures targeting displacement as a decision variable, such as direct displacement-based design 8 or yield point spectra 9 ; methods targeting seismic fragility (e.g., refs. [10,11]), both used for new design or retrofit; procedures targeting the mean annual frequency of exceeding a given DS, such as the yield frequency spectra approach 12 , the probabilistic displacement-based design 13,14 , or the risk-targeted force-based design 15 ; procedures targeting losses, discussed in more details below; resilience-based methods 16 . A review of different possible performance-based design approaches is given in refs.…”

“…The effect of these parameters provides changes in the vulnerability curve within a ground motion intensity range characterised by high frequency (according to the hazard curve). Clearly, according to Equation (11), this has a high impact on the final loss estimation. Contrarily, parameters related to the extensive and complete damage states produce a minor sensitivity to EAL, as easily inferred from Equation (11).…”

“…Clearly, according to Equation (11), this has a high impact on the final loss estimation. Contrarily, parameters related to the extensive and complete damage states produce a minor sensitivity to EAL, as easily inferred from Equation (11).…”

“…For each selected seed, run the capacity spectrum method (CSM 46 ) using spectra for each DS demand (code-based, as per Figure 3B, or site-specific ones) and disregard the cases not meeting the code-based seismic demand for any DS (i.e., 𝜇 𝑑𝑒𝑚,𝐷𝑆𝑖 > 𝜇 𝐷𝑆𝑖 ). In addition, calculate the frequency of exceeding the complete damage DS, by integrating the complete damage fragility with 𝜆 𝐼𝑀 , analogously to Equation (11), and disregard the cases above a conventionally-established threshold (e.g., between 10 −5 and 10 −447 ). The seed SDoFs meeting the target EAL, the complete-damage reliability bound, and complying with the code-based displacement check are equally valid candidate design SDoFs.…”

Effect of Retrofit Interventions on Seismic Fragility of Italian Residential Masonry Buildings

“…After developing seismic vulnerability analyses of the existing built heritage, the scientific community has started investigating the effectiveness of single retrofit interventions or extensive risk mitigation strategies [25][26][27]. To do this, the impact of possible retrofit interventions on risk mitigation must be estimated.…”