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The evaluation of the seismic performance of non-structural elements (NSEs) has gained special relevance in the last decades from the earthquake engineering community as a result of several aspects. The losses estimated following the seismic events that have occurred in urban regions in the last two decades, repeatedly showed that the NSE losses often exceed that of the structural components. This issue is partly due to the fact that the investment associated to the NSEs is on average higher than the cost of the structure, and partly due to the higher vulnerability of NSEs at lower seismic intensities if compared to their structural counterpart. Additionally, in the performance-based seismic design and assessment framework, the harmonization between the performance of both non-structural and structural elements plays a fundamental role, since a non-acceptable NSE performance level can completely compromise the global performance and functionality of a facility. Several methodologies have been developed to seismically design and analyze NSEs in the last decades. However, a complete comprehensive methodology to quantify the performance of NSEs is still not available due to the multitude of NSE typologies and to the difficulties to consider all the involved parameters, such as the prediction of a seismic demand representative of the different possibilities of building seismic-force-resisting systems (SFRSs) containing the NSEs. For building structures, the FEMA P695 methodology has been developed. It provides a standardized and objective methodology that defines how to calibrate seismic performance factors (SPFs), namely the response modification factor (R), the system overstrength factor (Ω0), and the deflection amplification factor (Cd), for new SFRSs proposed for inclusion in model building codes in the United States. Nowadays, a proper equivalent methodology for NSEs is not yet available. The main objective of the ongoing research is to develop a standardized framework to evaluate performance and quantify SPFs for new and existing NSEs systems. The FEMA P695 methodology will be used as a reference guide in the development of the framework, by adapting the general organization of the performance evaluation process for NSEs evaluation. As an initial step, a proposal of the framework was developed, and its application has been demonstrated through an illustrative example, which deals with the evaluation of the behavior factor (qa) of suspended piping restraint installations (Figure 1) to be designed according to the Eurocode 8.
Figure 1. Archetype selected for illustrative example of the framework. Units in millimeters
The flowchart of the proposed framework is presented in Figure 2. The various phases of the framework phases coincide with those of the FEMA P695 methodology, with the exception of an additional phase entitled “Establish Seismic Demands”. This additional phase is required because the determination of the seismic demand on NSEs is far less trivial if compared to the one of a building SFRS, in the sense that the dynamic interaction between the building’s SFRS, the ground motion and the NSEs leads to the seismic demand on the NSEs being dependent on the dynamic response of the structural system.
The information required to move forward with the illustrative example consisted in the design requirements for NSEs from Chapter 4 of Eurocode 8 and the experimental data generated by Perrone et al. (2019) in order to characterize the response of the suspended piping restraints under monotonic and reverse cyclic loading. The supporting structures considered for the determination of the seismic demand consisted in the 100 reinforced concrete frame buildings generated in a study performed by Perrone et al. (2019). The cyclic response of the suspended piping restraint trapeze installation is presented in Figure 3.
Figure 3. Numerical and Experimental cyclic load-displacement response for the considered suspended piping restraint trapeze installation
Figure 2. Flowchart of the proposed general framework for the quantification of seismic performance factor for non-structural elements
After conducting each of the performance evaluation phases presented in Figure 2, the following behavior factors were obtained:
were Ta corresponds to the fundamental period of the NSE, and T1 to the fundamental period of the supporting structure.
The proposed framework addresses all the main phases that have a direct impact on the global nonlinear response of a non-structural system, allowing for an accurate assessment of its performance. Additionally, the proposed framework was proven flexible enough in order to be able to use different design equations to achieve similar performance objectives. It also demonstrated that some design variables difficult to evaluate accurately could be eliminated from the design process. Finally, the approach proposed for the definition of the seismic demands requires a large number of analyses, thus a simplified procedure should be developed.
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