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Major earthquakes have demonstrated that Natech events can be triggered by liquid overtopping in liquid storage tanks equipped with floating roofs. Thus, research on the dynamic behaviour of steel storage tanks with floating roofs is still required. In this paper, the seismic risk against liquid overtopping in a real steel storage tank with a floating roof was analysed using a simplified model that was validated by a refined finite element model based on the arbitrary Lagrangian-Eulerian approach. The simplified model utilizes the Lagrangian of a floating roof-fluid system and is capable of providing a response history of the floating roof. It was demonstrated that it could predict the maximum vertical displacement very accurately, while some differences were observed in the response history of vertical displacement. The computational time for a single response history analysis based on the simplified model amounted to a few minutes, which is significantly less demanding compared to hours required for response history analysis in the case of the refined FE model. The simplified model is thus appro-priate for the seismic fragility analysis considering the overtopping limit state. It is shown that the fragility curves are significantly affected by the liquid filling level. The risk for liquid overtopping is quite high in the case of a full tank. However, by considering the variation of filling level during the year, the overtopping risk was observed reduced by approximately 30%. Alternatively, the approximate fragility analysis for the liquid over-topping can be performed by utilizing the Eurocode formula for the vertical displacement of liquid. This approach is straightforward, but the formula does not account for the higher mode effects, which may result in overestimated seismic intensity causing overtopping, as discussed in the paper

The shear modulus, known as Gmax, is a key parameter for predicting the static and dynamic behavior of soils. Its value decreases by increasing the shear strain. This is because of reducing the soil’s stiffness as a result of increasing the shear deformation. The increasing of the shear modulus by increasing the shear strain is affected by some of the soil properties, such as the Void ratio (e), the Over consolidated ratio (OCR), the Normal stress (σ), the Plasticity index (PI), the Water content (ω%), the Shear strain rate, the Soil structure, and the Loading history, etc. In this paper, undrained, direct shear tests were conducted to study the effect of the plasticity index (PI) and the normal stress (σ) on the shear behavior and the shear modulus of remolded clays. The results show that the normalized shear modulus at a constant strain will generally increase as the σ and PI increase, and the common empirical equations for undisturbed soils at γ = 0~0.1 might be applicable for the disturbed soils too. Ljubljana se nahaja v plitvem sedimentnem bazenu zapolnjenim s kvartarnimi sedimenti. Območje sodi med seizmično najbolj aktivne v Sloveniji in ga je v preteklosti prizadelo več večjih potresov. Razmeroma mehki sedimenti pomembno prispevajo k ojačenju potresnega nihanja tal na tem območju, obstoječe potresne mikrorajonizacije v Ljubljanskem bazenu pa zaradi pomanjkanja geofizikalnih podatkov in podatkov iz vrtin niso zanesljive. Za dopolnitev mikrorajonizacije smo zato izvedli raziskave povprečne hitrosti strižnega valovanja v vrhnjih 30 m (Vs30) sedimentov na 30 točkah. Uporabili smo skupno modeliranje podatkov spektralnega razmerja horizontalnih in vertikalne (HVSR) komponente tri-komponentnih posamičnih meritev mikrotremorjev in disperzijskih krivulj pridobljenih s ploskovnimi meritvami mikrotremorjev analiziranih z metodama razširjene prostorske avtokorelacije (ESAC) in refrakcijskih mikrotremorjev (ReMi). Fazno-hitrostne disperzijske krivulje dobljene z obema metodama se zelo dobro ujemajo. Dobljene vrednosti Vs30 so večje v severnem in severo-vzhodnem delu mesta (300–600 m/s), kjer prevladujejo pleistocenski in holocenski glaciofluvialni sedimenti reke Save, predvsem prod in pesek. V južnem delu mesta (140–300 m/s) ustrezajo najnižje vrednosti Vs30 jezerskim in rečnim sedimentom Ljubljanskega barja. Pridobljeni rezultati se dobro ujemajo s porazdelitvijo različnih sedimentov v bazenu. V primerjavi z obstoječo mikrorajonizacijo, ki temelji na EC8 klasifikaciji, pa kažejo novi podatki na celotnem raziskanem območju na boljše seizmogeološke pogoje, na splošno za eno stopnjo boljšo vrsto tal po EC8 klasifikaciji. Ugotovljena prostorska porazdelitev Vs30 na območju Ljubljane predstavlja zato pomembno dopolnitev obstoječe mikrorajonizacije.