Fragility Evaluation in Building-Piping Systems: Effect of Piping Interaction with Buildings

Many studies assessing the damage from 1971 San Fernando and 1994 North Ridge earthquakes reported that the failure of nonstructural components like piping systems was one of the significant reasons for shutdown of hospitals immediately after the earthquakes. This paper is focused on evaluating seismic fragility of a large-scale piping system in representative high-rise, midrise, and low-rise buildings using nonlinear time history analyses. The emphasis is on evaluating piping's interaction with building and its effect on piping fragility. The building models include the effects of nonlinearity in the performance of beams and columns. In a 20-story building that is detuned with the piping system, critical locations are on the top two floors for the linear frame building model. For the nonlinear building model, critical locations are on the bottom two floors. In an eight-story building that is nearly tuned with the piping system, the critical locations for both the linear frame and nonlinear models are the third and fourth floors. It is observed that building nonlinearity can reduce fragility due to reduction in the tuning between building and piping systems. In a two-story building, the nonlinear building frequencies are closer to the critical piping system frequencies than the linear building frequency; the nonlinear building is more fragile than the linear building for this case. However, it is observed that the linear building models give excessively conservative estimates of fragility than the nonlinear building models.