COLLAPSE SAFETY MARGIN ANALYSIS OF SINGLE-LAYER SPHERICAL LATTICE SHELLS CONSIDERING CONSISTENT COLLAPSE PROBABILITY

A method is proposed to evaluate the collapse safety margin of single-layer lattice shells with the consideration of consistent collapse probability. With the assumed standard normal distribution for a collapse probability density function and the assumed exponential distribution for a seismic hazard function, the limit of 0.46% of 50-year consistent collapse probability for lattice shells is acquired through the integration of the two functions with a presumed collapse probability of 10% under major earthquakes. This limit is much lower than that suggested for ordinary building structures, i.e. 1%. The consistent collapse probability of large-span lattice shells is introduced to amend the pre-defined intensity of major earthquakes for large-span lattice shells. A new analytical method is proposed for the determination of the collapse margin ratio of lattice shells based on the amended intensity. The collapse resistance design combined with this method can account for earthquake intensities with various probabilities of exceedance, making lattice shells have a unified limit of collapse probability with different seismic fortification intensities. Spectral correction is also carried out through spectral parameters in the final determination of collapse safety margin. The incremental dynamic analysis performed on three example single-layer spherical lattice shells is used to analyze the influence of a rise-span ratio and a structural system on collapse safety margin and 50-year collapse probability. All shells meet the requirement of the limit of 50-year consistent collapse probability. Consistency can be observed between collapse safety margin and 50-year collapse probability.