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1. Seismic fragility analysis using nonlinear autoregressive neural networks with exogenous input

   https://doi.org/10.1080/15732479.2021.1894184  

   Sheikh, Imran A. ; Khandel, Omid ; Soliman, Mohamed ; Haase, Jennifer S. ; Jaiswal, Priyank ( January 2021 , Structure and Infrastructure Engineering)

   null (Ed.)

   Rapidly growing societal needs in urban areas are increasing the demand for tall buildings with complex structural systems. Many of these buildings are located in areas characterized by high seismicity. Quantifying the seismic resilience of these buildings requires comprehensive fragility assessment that integrates iterative nonlinear dynamic analysis (NDA). Under these circumstances, traditional finite element (FE) analysis may become impractical due to its high computational cost. Soft-computing methods can be applied in the domain of NDA to reduce the computational cost of seismic fragility analysis. This study presents a framework that employs nonlinear autoregressive neural networks with exogenous input (NARX) in fragility analysis of multi-story buildings. The framework uses structural health monitoring data to calibrate a nonlinear FE model. The model is employed to generate the training dataset for NARX neural networks with ground acceleration and displacement time histories as the input and output of the network, respectively. The trained NARX networks are then used to perform incremental dynamic analysis (IDA) for a suite of ground motions. Fragility analysis is next conducted based on the results of the IDA obtained from the trained NARX network. The framework is illustrated on a twelve-story reinforced concrete building located at Oklahoma State University, Stillwater campus. 

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2. An earthquake-source-based metric for seismic fragility analysis

   https://doi.org/10.1007/s10518-018-0341-9  

   Radu, Alin ; Grigoriu, Mircea ( February 2018 , Bulletin of Earthquake Engineering)

   The seismic fragility of a system is the probability that the system enters a damage state under seismic ground motions with specified characteristics. Plots of the seismic fragilities with respect to scalar ground motion intensity measures are called fragility curves. Recent studies show that fragility curves may not be satisfactory measures for structural seismic performance, since scalar intensity measures cannot comprehensively characterize site seismicity. The limitations of traditional seismic intensity measures, e.g., peak ground acceleration or pseudo-spectral acceleration, are shown and discussed in detail. A bivariate vector with coordinates moment magnitude m and source-to-site distance r is proposed as an alternative seismic intensity measure. Implicitly, fragility surfaces in the (m, r)-space could be used as graphical representations of seismic fragility. Unlike fragility curves, which are functions of scalar intensity measures, fragility surfaces are characterized by two earthquake-hazard parameters, (m, r). The calculation of fragility surfaces may be computationally expensive for complex systems. Thus, as solutions to this issue, a bi-variate log-normal parametric model and an efficient calculation method, based on stochastic-reduced-order models, for fragility surfaces are proposed. 

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3. Incremental dynamic analysis and FEMA P695 seismic performance evaluation of a cold‐formed steel–framed building with gravity framing and architectural sheathing

   https://doi.org/10.1002/eqe.3245  

   Leng, Jiazhen ; Buonopane, Stephen G. ; Schafer, Benjamin W. ( January 2020 , Earthquake Engineering & Structural Dynamics)

   The objective of this paper is to present incremental dynamic analysis (IDA) and seismic performance evaluation results for a two‐story cold‐formed steel (CFS)–framed building. The archetype building was designed to current U.S. standards and then subjected to full‐scale shake table tests under the U.S. National Science Foundation Network for Earthquake Engineering Simulation (NEES) program. Test results showed that the building's stiffness and capacity were considerably higher than expected and the building suffered only nonstructural damage even at excitations in excess of Maximum Considered Earthquake levels for a high seismic zone. For the archetype building, three‐dimensional finite element models at different modeling fidelity levels were created using OpenSees. The models are subjected to IDA using the far‐field ground motion records prescribed in Federal Emergency Management Agency (FEMA) P695. Seismic performance quantification following the FEMA P695 procedure shows that if the modeling fidelity only follows the state‐of‐the‐practice, ie, only includes shear walls, unsafe collapse margin ratios are predicted. State‐of‐the‐art models that account for participation from CFS gravity walls and architectural sheathing have overall performance that are consistent with testing, and IDA results indicate acceptable collapse margin ratios, predicated primarily on large system overstrength. Neglecting the lateral force resistance of the gravity system and nonstructural components, as done in current design, renders a safe design in the studied archetype, but largely divorced from actual system behavior. The modeling protocols established here provide a means to analyze a future suite of CFS‐framed archetype buildings for developing further insight on the seismic response modification coefficients for CFS‐framed buildings.

    

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4. A new perspective on seismic intensity measures (IMs)

   Grigoriu, M. ( August 2019 , SEMC 2019)

   The usefulness of current intensity measures (IMs) and fragilities are assessed in a setting in which the probability law of the seismic ground acceleration process is known. It is shown that typical demand parameters and IMs are weakly dependent so that fragilities defined as functions of these measures provide limited information for seismic design. 

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5. A new perspective on seismic intensity measures (IMs)

   Grigoriu, M. ( August 2019 , SEMC 2019)

   The usefulness of current intensity measures (IMs) and fragilities are assessed in a setting in which the probability law of the seismic ground acceleration process is known. It is shown that typical demand parameters and IMs are weakly dependent so that fragilities defined as functions of these measures provide limited information for seismic design. 

   more » « less