Top‐Level Belt Trusses Impact on Seismic Fragility of High‐Rise Braced Tube Steel Structures Subjected to Strong Near‐Fault Ground Motions

ABSTRACT

The seismic fragility assessment of high‐rise buildings, particularly those employing braced tube steel structural systems, requires comprehensive analysis of their dynamic response to intense near‐fault ground motions. These seismic events present unique challenges due to their distinctive characteristics, including distinct velocity pulses and considerable vertical ground motion component. Belt trusses represent a promising engineering intervention to enhance lateral stiffness, optimize load distribution, and mitigate seismic effects in high‐rise structures. This study investigates the quantitative impact of positioned belt trusses on the seismic fragility of high‐rise braced tube steel structures under near‐fault ground motions. A code‐designed 30‐story braced tube steel frame was analyzed in two configurations (i.e., with and without top‐level belt trusses) to assess the related influences on seismic performance and fragility characteristics. The methodology employed incremental dynamic analysis (IDA) using an ensemble of 14 ground motion records, specifically selected for their strong near‐fault, pulse‐type characteristics. Seismic fragility is quantified through nonlinear dynamic analysis using interstory drift ratios as the damage measure, with limit states defined based on established structural performance levels. This research results demonstrate that the integration of belt trusses not only enhances seismic performance under strong near‐fault ground motions but also significantly reduces the overall structural system fragility. Furthermore, the implementation of belt trusses promotes more efficient load distribution patterns and improves energy dissipation mechanisms throughout the structure, contributing to enhanced seismic resilience.