Giammaria Gabbianelli

Reliable estimation of floor accelerations and floor response spectra (FRS) is essential for the seismic design of non-structural elements, particularly in timber buildings where damping, stiffness, and diaphragm behavior remain highly uncertain. This paper presents a comprehensive assessment of FRS in a full-scale residential timber building, combining unique in-situ seismic testing, numerical modeling, and comparisons with simplified code-based design approaches. The study is based on a field-testing program conducted within the PASFIT project on a multi-story timber building instrumented to record floor accelerations, displacements, and interstory drifts under seismic excitations representative of the local hazard. A finite element model developed in MIDAS Gen was subjected to the same input motions, and floor accelerations and response spectra were extracted for direct comparison with experimental data. Sensitivity analyses were performed to investigate the influence of effective stiffness and equivalent viscous damping, identifying parameter combinations that best reproduce the observed response at different shaking intensities. The field results and the calibrated numerical model are then used as benchmarks to evaluate several international code-based FRS formulations, including European and North American approaches. Results show that time-history analyses can closely reproduce the experimentally measured floor spectra when appropriate damping and stiffness assumptions are adopted, while simplified code-based methods exhibit varying levels of conservatism and accuracy, particularly in the spectral plateau. Although code provisions are intended for design use and calibrated to perform well on average across multiple ground motions, the comparisons provide valuable insight into their ability to capture observed amplification trends and key governing parameters.

The importance of nonstructural elements in the overall seismic performance of buildings highlights the need for accurate and precise calculations of their seismic demand and response. Currently, building codes and other guideline documents suggest values and modelling approaches to consider the inherent damping of the structural system. However, these recommendations were developed focusing only on the structural response, neglecting the effects they can have on the nonstructural seismic demand. In addition, bad design practices along with misinterpretations of damping formulations can lead to erroneous evaluation of the seismic demand on nonstructural elements, and therefore, to under- or overestimate their seismic capacity. This study evaluates the impact of diverse inherent structural damping modelling assumptions on the seismic demand of nonstructural elements through the evaluation of different floor response spectra. The results were obtained from an archetype reinforced concrete framed structure subjected to non-linear time history analyses using several seismic intensity levels. The inherent damping in the archetype building was modelled following commonly used assumptions such as mass proportional damping, stiffness proportional damping, and Rayleigh damping, considering also the use of initial or tangent stiffness, and two different levels of equivalent viscous damping, The results show that the modelling assumptions of the inherent damping can have significant effects on the floor response spectra, hence, on the seismic demand of nonstructural elements, exhibiting mean differences between the maximum and minimum response parameter of up to three times the minimum value.

Industrial plants are vulnerable to different natural hazards, which can cause significant damage, economic losses, and loss of functionality, generating what is called a Natural Hazard Triggering Technological Disaster (Na-Tech event). Considering the different possible hazard sources, earthquakes can subject industrial plants to demanding scenarios, making it important to better understand and characterize their seismic response. Among the different components of industrial plants, piping systems represent a key element as they transport liquids and gases among different equipment and reservoirs. Any induced damage to piping systems can lead to leakage and loss of containment of hazardous substances, causing floods, fires, and explosions, starting a cascade effect along the industrial plant. This study evaluates the seismic response of diverse configurations of industrial steel piping systems through experimental tests. Twelve piping specimens composed of different geometrical layouts (i.e., straight, Omega, and V loops) and joint mechanisms (i.e., welded and flanged joints) were subjected to cyclic axial loads and seismic inputs, measuring displacements, deformations, forces, and acceleration in key points. The results show that some configurations, especially those with flanged connections, can exhibit larger seismic demands in terms of local deformations and acceleration response.

Liquid-storage tanks are critical components in industrial plants, especially during seismic events. Tank failures can cause significant economic losses, operational disruptions, and environmental damage. Therefore, accurate design and performance evaluation are essential to minimize these risks. However, past earthquakes have highlighted the need for a better understanding of tanks’ seismic behavior. This requires selecting the appropriate seismic input and ground motion records to properly simulate tank responses. This study examines the seismic behavior of various tank types using different earthquake record sets, including both far-field and near-field events. The tanks were modelled with varying geometries, such as diameter–height ratios, wall thickness, liquid height, and radius. Time-history analyses were conducted to generate fragility curves and evaluate the seismic performance of the tanks based on specific limit states. The findings show that the choice between far- and near-field records significantly influences seismic response, particularly in terms of fragility curve variation. The fragility curves derived from this analysis can serve as valuable tools for risk assessments by governments and stakeholders, helping to improve the safety and resilience of industrial plants.

An adequate seismic protection of steel storage tanks of industrial, chemical and petrochemical plants is essential since potential consequences of failures, besides the economic losses, can be catastrophic for the environment and for people living nearby. Among the most common damages suffered by steel tanks in recent earthquakes, there are the elephant‐foot‐buckling of the perimeter wall and the tanks’ uplift or overturning. Due to the uncertainties related to the estimation of the mechanical properties of filled tanks and related seismic loads (i.e. dynamic overpressures generated by the content), conventional design approaches may lead to unsafe or, on the contrary, oversized solutions. Among effective alternatives, base isolation through Curved Surface Slider isolators (CSSs) offers some valuable advantages like high load bearing and displacement capacity with compact dimensions, independence of the oscillation period on the supported mass, and minimisation of torsional effects. Despite being neglected by most common commercial FEM codes, as a drawback, recent studies pointed out that the initial peak of friction force at CSSs’ motion breakaway can lead to significantly increased lateral deformations and accelerations of the superstructure. Within this framework in this study, a refined numerical model is developed in OpenSees FEM code, and an exhaustive parametric study is carried out to investigate the effect of the breakaway on isolated tanks providing some useful insights for the selection of the most suitable isolators.

A large portion of aging existing buildings are susceptible to significant structural damage during earthquakes and suffer from poor energy performance. When considering how to improve the seismic performance and energy efficiency of these structures, retrofitting has been shown to be a more attractive alternative compared to complete demolition and reconstruction. Not only is retrofitting generally preferable from an economic perspective, but it also typically has lower levels of social and environmental impact as well. Together, these three aspects (economic, social, and environmental) form the so-called three pillars of sustainability. Recently, research efforts have begun to focus on developments in combined and integrated seismic and energy retrofit frameworks and techniques, showing that investing in combined retrofitting schemes is often more cost effective than conducting either energy-efficiency or seismic retrofitting alone. As new national and transnational policies place greater emphasis on the environmental impact of the built environment, it is crucial that combined retrofit schemes be evaluated in a comprehensive manner that allows for the selection of optimal schemes when a range of key sustainability-related decision variables (DVs) are considered. This study investigated the selection of a life cycle assessment (LCA)-based optimal combination of seismic and energy-efficiency retrofit schemes for an existing reinforced concrete case-study building in Italy. The seismic performance of the retrofit schemes was evaluated using detailed nonlinear time-history analysis and the Pacific Earthquake Engineering Research Centre’s performance-based earthquake engineering (PEER-PBEE) framework, and the resulting economic costs and environmental impacts were incorporated into the LCA methodology. A detailed energy assessment was performed for each retrofit scheme so that the costs and environmental impacts associated with the operation of the building could be included in the LCA. Subsequently, the characteristics of each retrofit scheme were evaluated for a range of additional DVs, which encompassed the three pillars of sustainability. Finally, a multicriteria decision-making process was used to evaluate the optimal combination of seismic and energy retrofit schemes for several locations exhibiting different combinations of seismicity and climatic conditions. The results of this study provide insight into which combinations of seismic and energy efficiency retrofit measures can produce optimal solutions within the constraints set by decision makers and illustrate how assessments of both seismic and energy retrofit interventions can be implemented in the future.

The evaluation of retrofitting alternatives through multi-criteria decision making (MCDM) approaches allows an optimal selection based on a ranking system. This rank depends on evaluation parameters that assess particular aspects of the retrofitting options and influence the selection of the most advantageous alternative. Moreover, when integrating uncertainty of the input parameters into the procedure, the outcome may be altered and the rank order notably different with respect to a deterministic MCDM implementation. This paper examines an MCDM approach applied to four retrofit alternatives proposed for a case-study building, starting from a deterministic perspective. Subsequently, the MCDM method is extended to consider random variables, in order to compare and understand the influence of uncertainty of the input parameters in the selection of retrofit alternatives for the same building. To ensure that accurate and representative data was used in the stochastic implementation, an ad-hoc survey was developed to collect the views from relevant parties involved in the field of seismic retrofitting interventions, particularly those with an academic/research or practice/industry background. The outcomes of the study are believed to serve as useful guidelines and as a future reference for practitioners in the field of structural retrofitting, on how to select the most convenient retrofit alternative for an existing building.

Modern society requires that structures exhibit greater levels of resilience, especially under earthquakes. The seismic resilience of buildings is thus gaining increased attention as a particular, beyond-code approach. Seismically retrofitted buildings behave satisfactorily under expected earthquake scenarios; however, this does not guarantee operativity after a seismic event. This study critically reviews several methods currently available in the literature that quantify the seismic resilience level of buildings from different perspectives. An existing reinforced concrete school building, retrofitted according to four distinct strategies, is first evaluated in terms of seismic resilience levels. The overview and critical analysis of available resilience assessment frameworks determine the most suitable parameters to measure the seismic resilience for buildings. Subsequently, this metric is incorporated as an additional decision variable into an integrated seismic and energy retrofitting set of strategies. A multicriteria decision-making analysis is performed to select the optimally combined seismic and energy retrofitting alternative under social, technical, environmental evaluation, and seismic resilience aspects. We show how resilience impacts the preference for integrated seismic and energy retrofitting strategies, especially when this metric is considered as an annualized expected value.