# Performance-Based Seismic Design
## 2 An Overview of Published Papers  
The contributions gathered in this Special Issue reflect the growing interest in Performance-Based Seismic Design (PBSD) as a comprehensive and adaptable approach to earthquake-resistant construction. The published studies showcase innovative methodologies, advanced numerical modeling, and experimental validations, with a focus on optimizing both new and existing structures to achieve predefined seismic performance levels. Covering a range of structural typologies--including reinforced concrete (RC) frames, steel moment-resisting frames (MRFs), hybrid systems, and cold-formed steel structures--these studies offer valuable insights into seismic retrofitting strategies, energy dissipation mechanisms, and the calibration of simplified design procedures. A recurring theme across these contributions is the need for the seismic performance enhancement of existing buildings, particularly in highly seismic regions where outdated structures pose significant risks. Addressing this challenge, [PERSON] and [PERSON] propose an innovative cold-formed steel exoskeleton system as a lightweight yet highly effective retrofitting solution for RC multi-story buildings [41]. Their study introduces the Resisto 5.9 Tube system, which not only improves the seismic safety of vulnerable structures but also enhances their energy efficiency by integrating thermal insulation into the exoskeleton. Through nonlinear static analyses, the authors demonstrate a substantial increase in seismic performance, highlighting how external reinforcement strategies can provide cost-effective and minimally invasive retrofit solutions. This integrated approach aligns with contemporary trends in sustainable engineering, where seismic resilience and energy efficiency are pursued simultaneously. Another significant research focus within this Special Issue is the development of advanced energy dissipation mechanisms. [PERSON] et al. introduce a refined design procedure for steel frames equipped with viscoelastic dampers, addressing a critical gap in the current literature [42]. While previous studies have established the efficacy of these passive control devices, their interaction with higher-mode vibrations has often been overlooked. The proposed methodology accounts for these effects, offering a more accurate prediction of internal forces in bracing systems. By validating their approach through nonlinear dynamic analysis, the authors provide a practical framework for improving the seismic response of steel moment-resisting frames (MRFs), ensuring both damage mitigation and post-earthquake functionality. The simplification of PBSD methodologies is another key aspect explored in this collection of studies. [PERSON] et al. present a performance-based assessment framework aimed at streamlining seismic vulnerability evaluations for steel moment-resisting frames [43]. Their method leverages a trilinear non-dimensional pushover curve, allowing engineers to quickly assess the structural capacity without the need for computationally expensive nonlinear dynamic analyses. By validating their approach through comparisons with Incremental Dynamic Analysis (IDA) and Eurocode-based provisions, the authors highlight the high reliability and practical applicability of this simplified procedure. Such developments are crucial for large-scale seismic risk assessment, particularly in urban areas where the rapid screening of vulnerable structures is a priority. Moving beyond traditional seismic-resistant systems, [PERSON] et al. explore the seismic performance of hybrid moment-resisting-eccentrically braced dual frames (MRF-EBF) equipped with detachable links [44]. By integrating dissipative fuses, these systems are designed to sustain severe earthquakes while facilitating post-earthquake reparability. Through extensive pushover analyses, the study demonstrates how hybrid configurations enhance energy dissipation and structural redundancy, significantly reducing the likelihood of progressive collapse.