Formulation of risk-targeted seismic action for the force-based seismic design of structures

A risk-targeted design spectral acceleration and the corresponding seismic design action for the force-based design of structures is introduced by means of two formulations. The first one called direct formulation utilizes the seismic hazard function at the site of the structure. Because the seismic action defined in the codes is often associated with a designated return period, an indirect formulation is also introduced. It incorporates a risk-targeted safety factor that can be used to define a risk-targeted reduction factor. It is shown that the proposed formulations give analogical results and provide an insight into the concept of the reduction of seismic forces for the force-based seismic design of structures if the objective is defined by a target collapse risk. The introduced closed-form solution for the risk-targeted reduction factor can be used to investigate how the target collapse risk, the seismic hazard parameters, the randomness of the seismic action, and the conventional parameters (ie, the overstrength factor and the deformation and energy dissipation capacity) affect the seismic design forces in the case of force-based design. However, collaborative research is needed in order to develop appropriate models of these parameters. In the second part of the paper, the proposed formulations are demonstrated by estimating the risk-targeted seismic design action for a six-storey reinforced concrete building. By verifying the collapse risk of the designed structure, it is demonstrated that the risk-targeted seismic action, in conjunction with a conventional force-based design, provided structure with acceptable performance when measured in terms of collapse risk.     

Equivalent-linear site response analysis on the site of the historical Trakošćan Castle,Croatia, using HVSR method

This paper presents a major extension of seismic vulnerability research project on the site of Trako??an Castle based on the initial horizontal-to-vertical-spectral-ratio (HVSR) results from Stanko et al. (2016). The estimated HVSR site frequencies and HV amplification at Trako??an Castle can only be used as an indication of the initial soil site frequency and amplification, so-called natural soil model, corresponding to the subsoil profile without the influence of an earthquake. The equivalent-linear (EQL) site response analysis has been carried out for different earthquake scenarios for a maximum input rock peak ground acceleration (PGA_ROCK) that corresponds to return periods of 95 (0.08 g), 475 (0.18 g) and 1000 years (0.31 g). The aim of the research is to evaluate structural seismic design responses and to determine type and degree of damage caused by local site effect, which is the result of an alluvial basin and topographic influences. The main objective of this research is the formation of local microseismic zones based on an EQL analysis: surface spectral acceleration and amplification maps at the predominant frequency. Based on the HVSR frequency response of the core structure of Trako??an Castle and the Tower itself (fundamental and higher frequency modes), maps of surface spectral acceleration and soil amplification at different frequencies (3, 5 and 10 Hz) are developed for different input PGA_ROCK levels (0.08, 0.18 and 0.31 g) to evaluate seismic response of the Castle. Observed amplifications are correlated with ground motion polarization and directionality of the ground motion from the alluvial basin to the hilltop. Shortening of predominant frequencies (lengthening of the period), particularly in the alluvial basin, has been observed with higher input PGA_ROCK in the EQL analysis. This effect is not manifested in the Trako??an hill, and predominant frequencies match HVSR frequencies. The use of certain geophysical survey methods at historical sites is a big problem, because terrain features (e.g. steep hills, mountains, ridges, slopes, cliffs) create lack of space and make it impossible to carry out geophysical investigation. Microtremor measurements at historical sites can overcome this limitation and provide local seismic response and vulnerability behaviour of historical monuments without destroying their authenticity. Also, computational modelling can greatly improve the results. The EQL site response analysis on the site of Trako??an Castle has confirmed and improved the results of seismic response and vulnerability based on HVSR method.     

Possibility for hydroenergetic utilization of relatively researched water streams

Small mountain water streams are lately more interesting from the aspect of hydroenergetic exploitation. Catchments area of smaller rivers and creeks are mostly not enough researched from hydroenergetic aspect, so the most difficult task for small hydropower plant designers is to determine hydroenergetic potential of discussed water streams, from short period of hydrological observations. Very often happens that existing measurement stations on discussed water streams are placed few kilometers from potentially place of water intake and the value of flow is drastically different on these two locations. In this work, two methods for determination of hydrological picture for the chosen location of water intake on discussed river are shown, correlation method and analogy method. Using these methods it is possible to use data that describes measured values of discharge from the old measurement stations, that is exists on the same or adjacent river, to determine flow duration curve on the place of interests. Results given from these two methods are compared with measured values of discharge and precipitation from last period that are collected from location of planed intake. Based on the good agreement of theoretical and measured values, it was concluded that these two methods can be also applied to the adjacent basins. Suggestion of hydroenergetic utilization of discussed water stream and its economic justification is also presented in this work.     

Northern Adriatic phytoplankton response to short Po River discharge pulses during summer stratified conditions

A 275‐km‐long transversel Northern Adriatic profile from the mouth of the Po River (Italian Adriatic coast) to the Kvarner region (Croatian coastal island area) was investigated in three successive case studies in August 2008, 2009 and 2010. The short Po River pulses in August result in the surface advection of riverine water, nutrients and phytoplankton from the western to the eastern side of the Adriatic. This surface spreading exhibits inter‐annual variability depending on the riverine discharge in the preceding period. The Po River discharge pulse in August 2010 in particular resulted in an extraordinary tongue‐like advection of riverine water, nutrients, and phytoplankton towards the Eastern Adriatic coast. The phenomenon was detected using both satellite imagery and classical oceanographic measurements. In the advective water, toxic dinoflagellates were most abundant in August 2010, when the influence of the Po was greatest.     

Refined δ<Superscript>13</Superscript>С trend of the Dal’nyaya Taiga series of the Ura uplift (Vendian,southern part of Middle Siberia)

New data were obtained on δ¹³С_carb and δ¹⁸O variations in the sequence of deposits of the Dal’nyaya Taiga series at the western and eastern flanks of the Ura anticline. The summary δ¹³С curve was plotted in view of the correlation of sequence–stratigraphic data of the basin analysis. A series of positive anomalies was found within the succession. Alternatives for global chemostratigraphic correlation of the Dal’nyaya Taiga series of the Ura uplift were considered.     

Mechanisms of landslides in over-consolidated clays and flysch

In this report, we present the situation in Slovenia, Europe with regard to natural hazards, emphasizing land-sliding problems. Furthermore, we shortly present the University of Ljubljana and the Faculty of Civil and Geodetic Engineering as the new member of the ICL that was selected to be the World Center of Excellence on Landslide Risk Reduction for the period of 2008–2013 with the project entitled “Mechanisms of landslides in over-consolidated clays and flysch” in the Activity scale and targeted region as “National.” Some preliminary results of this project are shortly presented at the end.     

A web‐based methodology for the prediction of approximate IDA curves

A web‐based methodology for the prediction of approximate IDA curves, which consists of two independent processes, is proposed. The result of the first process is a response database of the SDOF model, whereas the second process involves the prediction of approximate IDA curves from the response database by using n‐dimensional linear interpolation. Such an approach enables user‐friendly prediction of the seismic response parameters with high accuracy. In order to demonstrate the capabilities of the proposed methodology, a web application for the prediction of the approximate 16th, 50th and 84th fractile responses of an RC structure was developed. For the presented case study, the response database was computed for a set of 30 ground motion records and the discrete values of six structural parameters. Very good agreement between the computed and the approximated IDA curves of the four‐storey RC building was observed. Copyright © 2012 John Wiley & Sons, Ltd.     

Small-scale patterns of meiofauna in a bryophyte covered tufa barrier (Plitvice Lakes,Croatia)

Meiobenthic fauna is complex and essential part of the stream benthos and it is known as intermediaries from bacteria to higher trophic levels. However, the dynamics and mechanisms regulating this community at small-scale largely have been neglected. This study was carried out to determine meiofaunal dynamics in a small scale-patterns influenced by flow velocity and other abiotic and biotic factors. We examined meiofauna within bryophytes on a tufa barrier in Plitvice Lakes National Park using a detailed taxonomic approach of various meiofaunal groups and their feeding guilds. We choose three microhabitats (slow, medium, fast) differing significantly in flow velocity above bryophytes. Bdelloid rotifers were the most abundant group in microhabitat with highest flow velocity, while in other two microhabitats nematodes and monogonont rotifers prevailed in abundance. Data on environmental variables and main meiofaunal taxa and feeding guilds were analyzed using redundancy analysis. This analysis indicated that microfilter feeding guild (e.g. bdelloid rotifers) was strongly affected by interaction of flow velocity and POM fractions. Other feeding guilds were influenced by temperature, oxygen and/or pH and did not prefer high flow velocity. Suction-feeder nematodes and microfilter-feeder rotifers were dominant on temporal and spatial scale, indicating their good adaptations on frequently disturbed conditions that prevailed on bryophyte covered tufa barrier. Our results provide comprehensive survey of diversity, density as well as trophic structure of meiofauna in aquatic bryophytes. Differences in meiofaunal composition and density between three microhabitats suggest that the meiofauna is relevant indicator of environmental changes even at small-scale pattern.