## 5 Conclusions  
This paper evaluates the effectiveness of a recently proposed methodology for seismic damage identification by investigating a set of existing ductile, multistory, planar steel frames with an X- or V-bracing structural system. One of these frames is presented here in detail. It is a ductile six-story, steel X-braced frame with four equal spans and a taller first floor, wherein single or multiple X-braces are arranged in a staggered or single configuration across the floors of the frame. The proposed damage identification methodology employs a hybrid technique, called the \"\(M\) and \(P\)\" technique, which integrates the instrumental monitoring of the structure (M) with pushover analysis (P). According to this technique, in order to identify damage in a steel frame after the end of a post-seismic sequence, (a) a multi-channel network of accelerometers is installed to detect the structure's fundamental eigenfrequency through ambient vibrations; (b) the capacity curves and the eigenfrequency (key) diagram of the structure in the nonlinear range are developed by performing pushover and stepping modal analyses using two floor-force patterns to account for the influence of higher modes on the seismic behavior; (c) the inelastic seismic roof displacement \(u_{\text{top},i}\) of the structure, at the \(i\) inelastic step, is revealed in the eigenfrequency diagram by inserting the field-monitored fundamental eigenfrequency; (d) seismic damage is identified at the final step of the pushover analysis, where the target roof displacement is set equal to \(u_{\text{top},i}\); (e) the stepping stiffness matrix \(\mathbf{k}_{i}\) and the damage stiffness matrix \(\mathbf{\Delta k}_{i}\) are calculated at the same \(i\)-inelastic step, revealing the location and magnitude of seismic damage to the floors of the structure and confirming the observed seismic damage at the target displacement \(u_{\text{top},i}\) of the pushover analysis. The main aspects of the hybrid \"\(M\) and \(P\)\" technique and the key conclusions are summarized below:  
_Integration of monitoring and pushover analysis_: Provides a straightforward and robust framework that combines structural health monitoring with pushover analysis for identifying damage in existing steel-braced frame structures after seismic events or other dynamic causes (e.g., wind loads). _Damage localization_: Dynamic properties (i.e., eigenfrequencies) detected in near-real-time through monitoring enable the accurate identification of damage without prior knowledge of the excitation forces. _Critical indicator of damage state_: The monitored fundamental eigenfrequency in the field is a key indicator of the structure's damage state and is directly linked to the inelastic roof displacement of the structure in the eigenfrequency key diagram established through pushover analysis. Direct interconnection of parameters: The inelastic roof displacement, damage stiffness matrix, and eigenvalues of the structure are directly related to the field-measured fundamental eigenfrequency. Damage stiffness matrix compatibility: The damage stiffness matrix reflects the stiffness degradation at the inelastic step corresponding to the identified roof displacement and is fully compatible with the damage image of the structure at the same step, as obtained from pushover analysis. Accurate damage estimation: The interconnected nature of the parameters in the \"\(M\) and \(P\)\" technique ensures accurate estimation of both the location and magnitude of seismic damage within the floors of multistory steel-breaced frames. Thus, the present methodology for seismic damage identification provided a highly reliable assessment of seismic damage in the existing six-story, planar, steel X-breaced frame under investigation. The effectiveness of the \"\(M\) and \(P\)\" technique for damage identification has been validated in regular in-plan RC buildings with a frame structural system or with a dual structural system equivalent to a wall system, as per EN 1998-1.