Seismic Fragility Functions for Sewerage Pipelines

Abstract

Fragility functions (or fragility curves when presented graphically) are a well established tool to assess seismic risk to infrastructures. Given a sustained level of ground motion intensity, seismic fragility functions of sewerage pipelines are used for predicting earthquake-induced physical damage to sewer pipes. However, existing fragility functions of sewerage pipelines refer to a limited number of pipe types and material categories. Therefore practitioners often draw upon fragility functions specifically defined for potable-water pressure pipelines available in the international literature, for foreseeing earthquake-induced failures on sewerage gravity and pressure pipelines. The discrepancies between existing fragility curves and the observed physical damage data collected after the Canterbury (NZ) Earthquake sequence in 2010-2011, evidence that the fragility functions defined for potable-water pipelines tend to underestimate the physical damage to sewerage gravity pipelines. This paper proposes fragility functions for sewer gravity and pressure pipelines, categorized by pipe materials and liquefaction zones. The proposed fragility functions are developed using maximum likelihood estimation by correlating peak ground velocity with damage ratio (defined as number of faults per km) for sewer gravity pipes and with repair rate, defined as number of repairs per km for sewerage pressurized pipelines.