Piping Fragility Evaluation: Interaction With High-Rise Building Performance

Abstract

Many recent studies have emphasized the need for improving seismic performance of nonstructural systems in critical facilities in order to reduce the damage as well as to maintain continued operation of the facility after an earthquake. This paper is focused on evaluating system-level seismic fragility of the piping in a representative high-rise building. Piping fragilities are evaluated by incorporating the nonlinear finite-element model of a threaded Tee-joint that is validated using experimental results. The emphasis in this study is on evaluating the effects of building performance on the piping fragility. The differences in piping fragility due to the nonlinearities in building are evaluated by comparing the fragility curves for linear frame and nonlinear fiber models. It is observed that as nonlinearity in the building increases with increasing value of peak ground acceleration, the floor accelerations exhibit a reduction due to degradation/softening. Consequently, the probabilities of failure increase at a slower rate relative to that in a linear frame. It is also observed that a piping located at higher floor does not necessarily exhibits high fragilities, i.e., the fundamental building mode is not always the governing mode. Higher order building modes with frequencies closest to critical piping modes of interest contribute more significantly to the piping fragility. Within a particular building mode of interest, a good indicator of the amplification at different floor levels can be obtained by the product of mode shape ordinate and modal participation factor. Piping fragilities are likely to be higher at floor levels at which this product has a higher value.

Fragility Assessments of Multi-Story Piping Systems within a Seismically Isolated Low-Rise Building

“…Numerical simulations using a nonlinear building-piping model, with and without a bearing system, are often developed using the Open System for Earthquake Engineering Simulation (OpenSees). A nonlinear finite element model for the T-joint connections and bearings were experimentally validated with the experimental results and were incorporated step-by-step into the building-piping model [11][12][13]. A specified value of 2% damping ratio was used for steel structures, while the damping ratio 5% was used for concrete structures.…”

“…The ceiling tiles were characterized as an elastic material in OpenSees (Mazzoni et al [17]) to consider the interaction between the piping branches and the ceiling system. A detailed discussion on the reconciliation and validation of the components as well as the system-level piping models with their experimental results is presented in Ryu et al [13] and Ju et al [12]. System-level laboratory tests were also performed as shown in Figure 3b, and a finite element piping model with respect to each recognized failure was validated by Ryu et al [13] using the provided experimental data.…”

“…The ceiling tiles were characterized as an elastic material in OpenSees (Mazzoni et al [17]) to consider the interaction between the piping branches and the ceiling system. A detailed discussion on the reconciliation and validation of the components as well as the system-level piping models with their experimental results is presented in Ryu et al [13] and Ju et al [12].…”

Efficient Seismic Fragility Analysis for Large-Scale Piping System Utilizing Bayesian Approach

“…Recently, in contrast to the EPRI SOV method, according to the increase in the seismic intensity, nonlinear seismic response analyses were carried out in order to directly consider the characteristics of the integrated model of a building-piping coupled structural system. Based on these analysis results, a seismic fragility analysis was conducted using the statistical technique of maximum likelihood estimation (MLE) [22,23]. However, the problem arises that a piping seismic fragility analysis based on the nonlinear seismic response analysis of the building-piping coupled numerical model requires a number of nonlinear analyses to be performed to take into account the uncertainty of the earthquake and the model, which results in a large computational cost.…”