Fragility assessment of a RC structure under tsunami actions via nonlinear static and dynamic analyses

Current guidelines for design and assessment of buildings under tsunami actions do not explicitly state how to apply tsunami loads to buildings and which analysis methods to use in order to assess the structural response to the tsunami loads. In this paper, a reinforced concrete (RC) moment-resisting frame, which is designed as a tsunami evacuation building, is selected as a case study and subjected to simulated 2011 Tohoku tsunami waves. To assess tsunami impact on the model building, different nonlinear static analyses, i.e. constant-height pushover (CHPO) and variable-height pushover (VHPO), are compared with nonlinear dynamic analysis. The results of VHPO provide a good prediction of engineering demand parameters and collapse fragility curves obtained from the dynamic analysis under a wide range of tsunami loading. On the other hand, CHPO tends to overestimate interstorey drift ratio (IDR) and underestimate column shear by about 5–20%. It provides a larger fragility, i.e. about 10% in median value, for global failure and a smaller fragility for local shear failure. On the basis of these results, it is recommended that VHPO be used in future fragility analysis of buildings subjected to tsunami. However, pushover methods might not be adequate in cases where the tsunami inundation force time-histories are characterised by a “double-peak”, which subjects the structure to a two-cycle load. Finally, it is found that tsunami peak force is better correlated to IDR than flow velocity and inundation depth for the considered structure. This suggests that the peak force would be a more efficient intensity measure than the other two in the development of tsunami fragility curves

Tsunami fragility curves of a RC structure through different analytical methods

Recent tsunami events have stimulated research activity into tsunami fragility functions which have been largely based on empirical data. However, empirical fragility functions are biased because the influence of earthquake and tsunami damage are difficult to separate. We develop a new theoretical framework to assess the structural performance of a building due to tsunami inundation by drawing on recent experimental and theoretical progress at UCL on building. Different nonlinear static analyses, i.e. constant-height pushover (CHPO) and variable-height pushover (VHPO), are compared with nonlinear dynamic analysis in assessing the fragility curves of a case study structure for a set of realistic tsunami wave traces. The results of VHPO provide a good prediction of collapse fragility curves obtained from the dynamic analysis under a wide range of tsunami time-histories. On the other hand, CHPO provides a larger, i.e. about 10% in median value, fragility in case global failure is considered and a smaller fragility for local shear failure. On the basis of these results, it is recommended that VHPO be used in future fragility analysis of buildings subjected to tsunami

Stochastic coupled simulation of strong motion and tsunami for the 2011 Tohoku, Japan earthquake

© 2016 The Author(s)This study conducts coupled simulation of strong motion and tsunami using stochastically generated earthquake source models. It is focused upon the 2011 Tohoku, Japan earthquake. The ground motion time-histories are simulated using the multiple-event stochastic finite-fault method, which takes into account multiple local rupture processes in strong motion generation areas. For tsunami simulation, multiple realizations of wave profiles are generated by evaluating nonlinear shallow water equations with run-up. Key objectives of this research are: (i) to investigate the sensitivity of strong motion and tsunami hazard parameters to asperities and strong motion generation areas, and (ii) to quantify the spatial variability and dependency of strong motion and tsunami predictions due to common earthquake sources. The investigations provide valuable insights in understanding the temporal and spatial impact of cascading earthquake hazards. Importantly, the study also develops an integrated strong motion and tsunami simulator, which is capable of capturing earthquake source uncertainty. Such an advanced numerical tool is necessary for assessing the performance of buildings and infrastructure that are subjected to cascading earthquake–tsunami hazards

Inelastic seismic shear in multi-storey cantilever columns

Seismic shear magnification in the columns of multi-storey precast structures entering far into inelastic domain is addressed in the paper. Such structures consist of an assemblage of cantilever columns connected with ties. Considering analogy with cantilever walls, it has been expected that during inelastic response the actual shear forces in multi-storey cantilever columns could be considerably higher than the forces foreseen by traditional equivalent elastic analytical procedures (equivalent lateral force or modal spectrum). A parametric study of a set of realistic three-storey structures/columns was performed. These structures were designed according to Eurocodes and shear forces were determined by the equivalent elastic (modal spectrum) analysis. Average values of the shear forces obtained by the inelastic response analysis were compared to those of the traditional (modal spectrum) procedure. They were also compared to magnified shear forces predicted using the shear magnification factor ε suggested in Eurocode 8 for RC ductile walls. In parallel, modelling issues related to the inelastic response analysis of multi-storey cantilever columns were also discussed. Very large seismic force magnifications (up to 3 times and more) were observed. Therefore it is essential to account for this phenomenon in the seismic (capacity) design of cantilever columns in multi-storey precast buildings. It was demonstrated that for this purpose the expression given in Eurocode 8 to account for seismic shear magnification in ductile cantilever walls could be used with some minor modifications

Out-of-plane seismic performance of plasterboard partition walls via quasi-static tests

Internal partitions, as many nonstructural components, should be subjected to a careful and rational seismic design, as is done for structural elements. A quasi-static test campaign aimed at the evaluation of the out-of-plane seismic performance of Siniat plasterboard internal partitions with steel studs was conducted according to FEMA 461 testing protocol. Four tall, i.e. 5 m high, specimens were selected from the range of internal partitions developed in Europe by Siniat, a leading supplier of plasterboard components in Europe. Under the specified testing protocol, a significant nonlinear pinched behaviour of the tested specimen was observed. The pinched behaviour was caused by the damage in the screwed connections, whose cyclic behaviour was strongly degrading. Both stiffness and strength of the specimens are significantly influenced by the board typology and the amount of screwed connections. Finally, it was concluded that Eurocodes significantly underestimate the resisting bending moment of the tested specimens

SEISMIC FRAGILITY ASSESSMENT OF MEDICAL COMPONENTS

Shake table tests on a full scale three-dimensional model of a consultation room has been carried out at the University of Naples, Federico II ,Italy . The sample room con-tains a number of typical medical components, which are either directly connected to the panel boards of the perimeter walls or are simple free-standing elements. System identifica-tion was firstly carried out in order to identify the modal properties of the tested components. Selected ground motion records were scaled to detect different limit states for the medical de-vices. Fragility analysis has also been carried out; in so doing, the fragility curves have been evaluated according to a systemic approach. Simplified yet reliable finite element models of the experimentally tested sample components are defined upon the laboratory outcomes through the computer platform routinely used for practical applications. The implemented numerical model is capable to simulate the variations of natural frequency as provided by the experimental tests, in case the component is shaken along the two horizontal directions. The main finding of the present analytical study is therefore that simple models are able to ade-quately simulate the dynamic properties of the tested cabinets

The Emilia Earthquake: Seismic performance of precast reinforced concrete buildings

On 20 and 29 May 2012, two earthquakes of MW5.9 and MW5.8 occurred in the Emilia region of northern Italy, one of the most developed industrial centers in the country. A complete photographic report collected in the epicentral zone shows the seismic vulnerability of precast structures, the damage to which is mainly caused by connection systems. Indeed, the main recorded damage is either the loss of support of structural horizontal elements, due to the failure of friction beam-to-column and roof-to-beam connections, or the collapse of the cladding panels, due to the failure of the panel-to-structure connections. The damage can be explained by the intensity of the recorded seismic event and by the exclusion of the epicentral region from the seismic areas recognized by the Italian building code up to 2003. Simple considerations related to the recorded acceleration spectra allow motivating the extensive damage due to the loss of support

Disease-Modifying Therapies and Coronavirus Disease 2019 Severity in Multiple Sclerosis

Objective: This study was undertaken to assess the impact of immunosuppressive and immunomodulatory therapies on the severity of coronavirus disease 2019 (COVID-19) in people with multiple sclerosis (PwMS). Methods: We retrospectively collected data of PwMS with suspected or confirmed COVID-19. All the patients had complete follow-up to death or recovery. Severe COVID-19 was defined by a 3-level variable: mild disease not requiring hospitalization versus pneumonia or hospitalization versus intensive care unit (ICU) admission or death. We evaluated baseline characteristics and MS therapies associated with severe COVID-19 by multivariate and propensity score (PS)-weighted ordinal logistic models. Sensitivity analyses were run to confirm the results. Results: Of 844 PwMS with suspected (n = 565) or confirmed (n = 279) COVID-19, 13 (1.54%) died; 11 of them were in a progressive MS phase, and 8 were without any therapy. Thirty-eight (4.5%) were admitted to an ICU; 99 (11.7%) had radiologically documented pneumonia; 96 (11.4%) were hospitalized. After adjusting for region, age, sex, progressive MS course, Expanded Disability Status Scale, disease duration, body mass index, comorbidities, and recent methylprednisolone use, therapy with an anti-CD20 agent (ocrelizumab or rituximab) was significantly associated (odds ratio [OR] = 2.37, 95% confidence interval [CI] = 1.18-4.74, p = 0.015) with increased risk of severe COVID-19. Recent use (<1 month) of methylprednisolone was also associated with a worse outcome (OR = 5.24, 95% CI = 2.20-12.53, p = 0.001). Results were confirmed by the PS-weighted analysis and by all the sensitivity analyses. Interpretation: This study showed an acceptable level of safety of therapies with a broad array of mechanisms of action. However, some specific elements of risk emerged. These will need to be considered while the COVID-19 pandemic persists