Role of accidental torsion in seismic reliability assessment for steel buildings

[[abstract]]This study investigates the role of accidental torsion in seismic reliability assessment. The analyzed structures are a 6-story and a 20-story regular steel office buildings. The eccentricity in a floor plan was simulated by shifting the mass form the centroid by 5% of the dimension normal to earthquake shaking. The eccentricity along building heights was replicated by Latin hypercube sampling. All that allowed considering a more realistic distribution of live load mass and the accidental torsion. The fragilities for immediate occupancy and life safety were evaluated using 0.7% and 2.5% inter-story drift limits. Two limit-state probabilities and the corresponding earthquake intensities were further compared. The effect of ignoring accidental torsion and the use of code accidental eccentricity were also assessed. The results show that accidental torsion may play a minor role in seismic reliability assessment. However, the fragilities for low-rise buildings and at small drift limits may be underestimated if ignoring the accidental torsion effects. On the other hand, the code recommendation of 5% mass eccentricity at all floors may provide conservative estimates. Moreover, the trend will increase in high-rise buildings at small drift limits