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Earthen architecture from the area of Slavonia and Baranja forms part of the cultural heritage of the Republic of Croatia. Earthen architecture also has a significant global impact, as 30% of the world's population lives in earthen houses. Walls made of rammed earth withstand gravity loads well, but their seismic resistance is very low. To date, a significant number of tests have been conducted on rammed earth walls subjected to simulated earthquake loads. However, the number of conducted out-of-plane seismic resistance tests of rammed earth walls is very modest. Numerical models of rammed earth walls, which represent the walls characteristic of the area of Slavonia and Baranja, were created using the computer program ANSYS. The thickness of the walls, the intensity of the vertical load and the mechanical properties of the material were varied. The obtained results suggest that the walls have sufficient seismic resistance for the reference seismic load expected in Karanac (Croatia).

Earth houses provide housing solution for around 30 % of the world's population. Building with soil is cheap and supports sustainable building. Albeit present, rammed earth (RE) houses in Croatia are mostly abandoned and heavily damaged due to an insufficiently raised level of awareness of their significance. In addition, current Croatian design standards do not recognize RE as a load-bearing element, and thus do not support the construction of new or reconstruction of existing earth houses. Project RE-forMS embodies the synergy of modern design of structural walls and traditional building with RE. Data and samples from existing earth houses will be collected through field surveys. The controlled cultivation and testing of agricultural crops will define the natural fibres for strategic reinforcement of RE walls. Properties of both RE samples from the field as well as improved RE mixtures reinforced with natural fibres will be determined in laboratories. Via experimental testing the thermal and seismic performance of RE walls and mock-up houses will be tested. Measured data will be used for studies through nonlinear numerical simulations. This project is transformational with expected impact on the preservation of cultural heritage, encouraging sustainable building and developing Croatian norms for design of RE houses.

Traditional houses in Eastern Croatia were usually built using local earthen material. Today, earthen architecture in Slavonia and Baranja is in deteriorating state. With no guidelines or standards for building and preserving earthen structures in Croatia, it is easy to presume that a part of Croatian cultural heritage will soon disappear. Moreover, poor seismic performance of earthen structures poses one of the biggest obstacles in finding proper ways of preserving existing and building new earthen architecture. It is, however, fair to assume that from the middle of the 19th century to today, earthen buildings encountered strong ground motions, but their seismic performance and possible fracture mechanisms are still unknown. Therefore, this paper deals with seismic risk assessment determined on a numerical model of a rammed earth structure.

Predstavljena je problematika djelovanja eksplozije na nadvožnjake iz različitih vidova istraživanja. Svjetski istraživači na temelju dostupnih normi i prijašnjih iskustava razvijaju poboljšane sustave stupova nadvožnjaka otpornih na djelovanje eksplozije. Kroz analitičku, eksperimentalnu i numerički analizu razjašnjavaju ponašanje najučestalijih oblika, kružni i pravokutni, stupova na djelovanje eksplozije. Također predlažu izvedbu složenih stupova ; sprezanje čelika i betona, oblačenje betonskih stupova čeličnim košuljicama, primjena betona visokih čvrstoća, betona ojačanih različitim tipovima mikro vlakana kao moguća rješenja povećanja otpornosti na djelovanje eksplozije u fazi projektiranja. Predstavljena istraživanja daju određena rješenja i rezultate ispitivanja koja pružaju uvid u složenost analiza i malu pouzdanost procijenjenih opterećenja što iziskuje daljnja istraživanja u ovom području. Slijedom toga i projekt BLAST analizira postojeće stupove te nastoji procijeniti moguću razinu oštećenja istih nakon djelovanja eksplozije i predložiti rješenja ojačanja stupova kako bi se izbjegle katastrofalne posljedice u slučaju takvih napada. Cilj je i predložiti postupak proračuna stupa izloženog višestrukoj (engl. Mulithazard) opasnosti. Trenutno se analiziraju eksperimentalni podatci postojećih stupova te kalibriraju numerički modeli koji će poslužiti kao temelj za daljnju parametarsku analizu i oformljivanje baze za prijedlog proračuna.

In eastern Croatia, houses were traditionally built using soil as the building material. The construction of rammed earth houses is carried out in layers within the formwork, and the choice of suitable soil depends on several properties, such as particle size distribution and plasticity. Unfortunately, the construction and renovation of such houses is almost non-existent nowadays since there are no regulations and recommendations for construction in Croatia. With the aim of forming recommendations, soil samples were collected from existing houses in order to test the physical properties of the soil. The comparison of obtained results with those published in literature and published recommendations, showed that bulk density and Attbereg limits are within the limits of the published values. However, particle size distribution differs from most recommendations and published results. Further research on soil properties from existing houses is needed in order to make recommendations for the area of Eastern Croatia.

This paper presents original experimental research on soil-structure interaction conducted by authors. Small scale steel frame model was tested using shaking table. The model comprised two columns, a foundation beam representing strip foundations and a rigid beam connecting the top of the columns representing the superstructure mass. Model was tested as being fixed into the shaking platform and as placed on sand layer embedded into a container. Displacement time history was recorded using optical measurement system and compared for every tested case. Sand used in experimental research was local Drava sand. Experimental research is repeated for the case of dry and saturated sand. Results for all tested cases are shown and commented.

Earthen architecture, even though still very present today, lacks meticulous research, especially in Croatia. Therefore, the aim of this research is to gain new insight on seismic behaviour of rammed earth walls. To accomplish that, two rammed earth walls were built using traditional techniques. In addition to that, preliminary numerical models were made using ANSYS (v. 2020 R2) software to predict load required for demolition of walls by pull down method. It was observed that out of two walls, built with 10 cm difference in thickness, the thicker wall achieves higher out-of-plane bearing capacity, of around 16 kN, while the thinner wall achieves out-of-plane bearing capacity of around 10.5 kN. Moreover, contrary to the initial opinion, thicker wall exhibited plastic behaviour at lower horizontal displacement. Therefore, it was observed that the thinner wall endured 20 % higher interstorey drift (IDR) before experiencing plastic behaviour. However, further numerical modelling and experimental testing of rammed earth walls are necessary.

This paper presents new research in the field of nonlinear static seismic analysis and the N2 method for soil-structure systems. The rationale for this study stems from the inclusion of soil- structure systems in simplified displacement-based design methods. The conducted research comprises three parts, including original experimental investigations, the development of numerical models and the validation of results. A new methodology is presented that provides a step-by- step procedure for the implementation of the N2 method on soil-structure systems. Results of a dynamic shake-table test on a simplified scaled structural model founded on compacted dry sand are pre-sented, and a numerical model of the experiment is developed and calibrated with the inclusion of soil-structure interaction effects. This indicates one main significance of this paper, which is the variation between the experimental and the analytical model and how they can be compared. Lastly, a case study was conducted on a numerical model of a 3D steel building. The building was analysed using pushover analysis for a fixed base-case and by considering soil-structure interaction effects. The results of both observed cases were mutually compared and further examined by validating them with nonlinear dynamic analyses. A comparison was conducted considering the inter-story drifts, calculated according to the N2 method and time-history analyses. The results show good agreement when the N2 method is used for buildings on compliant soils. Overall, it was observed that a decrease in the inter-story drifts appears at ground level of the building. This research also provides a framework for future research in the examined field, for instance, on different types of buildings, building typologies and irregularities of the structural system.

Ponašanje tradicijskih kuća od nabijene zemlje do danas je nedovoljno istraženo, a većina postojećih zemljanih građevina je u vrlo lošem stanju. Zbog nedostatka normi i smjernica za projektiranje zemljanih kuća, projektanti su često primorani koristiti norme za projektiranje zidanih konstrukcija. Kako bi dobili saznanje o ponašanju tradicionalnih konstrukcija izgrađenih od nabijene zemlje, potrebno je utvrditi njihova osnovna mehanička svojstva. U ovom radu predstavljeno je laboratorijsko ispitivanje tlačne čvrstoće uzoraka prizme izrezanih iz većeg komada materijala prikupljenog na terenu. Prije ispitivanja provedena su preliminarna terenska istraživanja na području Istočne Hrvatske, u mjestu Aljmaš. Iz nekoliko zidova iste kuće od nabijene zemlje prikupljeni su materijali za pripremu ispitnih uzoraka. Provedbom ispitivanja uzoraka na tlak dobiveni su dijagrami odnosa sile i pomaka u smjeru tlačnog opterećenja. Na temelju najvećih tlačnih sila određene su tlačne čvrstoće, te je analiziran utjecaj udjela vlažnosti u materijalu na tlačnu čvrstoću.

Available evidence classifies traditional earth architecture as Croatia’s treasure as they embody authenticity and uniqueness. Thereunto, Baranja’s earth houses are presented as the best realizations of traditional Croatian rural architecture. Although present in Croatia, earth houses are often relinquished, damaged, or in an adverse state. The Act on Protection and Preservation of Cultural Goods defines the traditional earth house as an immovable cultural good which, as such, needs to be protected from disappearing. Nevertheless, until today there has been no conducted research on traditional Croatian earth architecture to assess their behaviour and performance. Croatia is situated in an earthquake- prone area, thus the design of all load-bearing structures has to be done in accordance with standards from the HRN EN 1998 series. In this paper, the seismic behaviour and dynamic properties of a typical Croatian earth house were investigated. The paper consists of three main parts. The first part is dedicated to the description of the geometry and materials of a typical traditional Croatian house. The second part presents numerical model developed using the ANSYS software package, which allowed assessment of the dynamic properties and seismic capacity of the house. The third and last part of the paper provides a discussion on results considering the nonlinear behaviour of the traditional earth house.

Zemljane kuće rješavaju pitanje stanovanja za 30% svjetske populacije. Hrvatske tradicijske zemljane kuće se svrstavaju u narodno bogatstvo. Međutim, takve kuće su u Hrvatskoj nerijetko napuštene i u vrlo lošem stanju. Razlog tome se može naći u nedostatnom znanju o građenju zemljom te nedostatku odgovarajućih normi za projektiranje. Kako bi razvoj normi za projektiranje kuća od nabijene zemlje bio moguć, potrebno je provesti opsežna istraživanja koja obuhvaćaju eksperimentalna ispitivanja i numeričke studije. U radu je dan pregled eksperimentalnih ispitivanja provedenih na zidovima od nabijene zemlje te karakterističnih mehanizama sloma. Svi radom obuhvaćeni zidovi su ravni i opterećeni u svojoj ravnini.

Oslonci i potresno opterećenje za projektiranje konstrukcija obično su matematički izvodi podataka dobivenih iz profila tala sa slobodnom površinom. Ovo istraživanje je vođeno pretpostavkom da pritisak od konstrukcije na tlo može promijeniti rezonantna svojstva tla i tako preusmjeriti projektiranje konstrukcija. Istraživanje je provedeno na setu od 10 stvarnih profila tla; na 21 studiji slučaja i koristeći dvije metode za korekciju profila brzina posmičnih valova s ciljem uključivanja kontaktnog pritiska. Analitički dobiveni rezultati su uspoređeni s pandanima dobivenim iz eksperimenta provedenog u centrifugi., The supports and seismic actions for structural design are usually mathematical derivatives of the data collected from soil profiles with free-field conditions. This study is based on the premise that the pressure exerted by the structure onto the soil can change resonant properties of soil and thus redirect structural design. The research was conducted on a set of 10 real soil profiles, and involves 21 case studies and the use of two methods for correction of shear wave velocity profiles in order to include contact pressure. Analytically obtained results are compared with the corresponding results obtained by means of a centrifuge experiment, Unterstützung und Erbebenbelastung für die Projektierung von Konstruktionen sind in der Regel mathematische Ableitungen von Daten, die aus den Bodenprofilen mit freien Oberflächen erhalten werden. Diese Untersuchung basiert auf der Annahme, dass der Druck der Konstruktion auf den Boden die Resonanzeigenschaften des Bodens verändern und somit die Projektierung der Konstruktionen umlenken kann. Die Untersuchung wurde an einem Set von 10 realen Bodenprofilen durchgeführt; anhand von 21 Fallstudien und zwei Methoden werden Scherwellengeschwindigkeitsprofile mit dem Ziel korrigiert, den Anpressdruck zu berücksichtigen. Die analytisch erhaltenen Ergebnisse wurden mit den aus dem Zentrifugenexperiment erhaltenen Gegenstücken verglichen.

Mostovi postaju zanimljive mete terorističkih napada zbog njihove lake dostupnosti, ali i katastrofalnih posljedica prilikom rušenja. U prošlosti stupovi mostova nisu dimenzionirani da podnesu velika horizontalna opterećenja te njihovim urušavanjem, most gubi nosivost i dolazi do rušenja cijele konstrukcije. Promatran je pretpostavljeni scenarij napada na nadvožnjak na osječkoj obilaznici, kada je eksploziv postavljen i detoniran u automobilu u neposrednoj blizini stupa. Određena je trenutna nosivost stupa na djelovanje eksplozije koristeći analitički program SBEDS koji se temelji na analizi sustava s jednim stupnjem slobode (engl. SDOF – Single Degree of Freedom). Programom su dobivene krivulje koje povezuju djelovanje tlaka i impulsa na stup i razinu oštećenja stupa. Razine oštećenja ovise o duktilnosti i kutu rotacije armiranobetonskog elementa. Na temelju dobivenih krivulja određena je razina oštećenja stupa s obzirom na pretpostavljeni scenarij napada.

I nakon dva stoljeća postoje otvorena pitanja o utjecaju međudjelovanja tla i konstrukcije na ponašanje cjelokupnog sustava. Koristeći jednostavne pristupe modelianja sustava tlo konstrucija i djelovanja potresne sile, provedena je parametarska studija utjecaja veličine temelja na ponašanje plitko temeljene zgrade. Deset temelja različitih tlocrtnih dimenzija korišteno je za usporedbu katnih pomaka te perioda osciliranja čeličnog okvira. Pokazano je da modeliranjem temelja te uključivanjem tla u numeričke modele dolazi do smanjenja katnih pomaka, dok se periodi osciliranja sustava tlo konstrukcija povećavaju u odnosu na upeti model.

A frequent dilemma in seismic design of buildings founded on soft soils is how to include soil compliance in numerical models. Although various international building codes propose methods for soil-structure interaction (SSI) modeling, common engineering practice is to model and design buildings as being fixed into the ground. Different codes propose different methods for including SSI effects into the seismic design of buildings and they are mostly based upon impedance functions. Impedance functions serve as an efficient replacement for demanding soil models under buildings. Since codes from around the world use different expressions and different models for soil modeling, numerical research and parametric study on a scaled model of a two- dimensional frame is conducted in order to determine the efficiency of each tested method. To verify the efficiency of the tested methods, a numerical model was developed in which a frame model was subjected to nonlin-ear static pushover analysis. Results obtained from the numerical analysis are compared to the results obtained on the experimentally tested frame at the Laboratory for experimental mechanics at the Faculty of Civil Engineering and Architecture Osijek.

Reinforced concrete buildings represent the largest share of the world’s building’s stock. Although such buildings are usually designed to endure extreme loadings, their structural elements can deform and manifest cracks. Large cracks can point out problems related to structural health. For instance, hairline cracks can cause reinforcement corrosion. In addition, many existing cracks can be hidden by façade or can be difficult to determine due to inaccessibility to the structural element. Thus, many cracks cannot be easily detected by simple visual inspection of the building. Following the idea on how simple burglar alarm circuits and home security systems work we have proposed a sensor for monitoring occurrence of cracks in reinforced concrete buildings. The detector was experimentally tested in a centrifuge using a small-scale mock-up representing a real reinforced concrete system. This paper, inter alia, demonstrates scaling rules for centrifuges and how those rules are applied to a model used to mimic behaviour of real large scale reinforced concrete structures. Different small scale models comprising beams and slabs are made of gypsum mixtures. All the models were tested in the laboratories of the Faculty of Civil Engineering Osijek using a 0, 40 m in radius centrifuge. The off-the shelf detector showed good potential in discovering crack occurrence on structural parts in buildings.

European norms propose several different approaches for seismic design of buildings. One of the approaches considered fast, accurate but simple as well is N2 method. Although N2 method is commonly used by academic community, it still consists limitations regarding soil- structure interaction. When building is designed it is considered fixed into the ground which does not accurately present buildings on shallow foundations founded on soft soil. When determining dynamic properties of buildings changes (longer fundamental period of oscillations, increased damping) are evident when soft soil under the structure is included, yet, there are no proposed method for this problem in the European norms. Within the experimental research underway in Osijek soil structure interaction effects are observed. First part of the experimental research is presented in this paper which includes determination of model and its behavior when fixed into the ground. Also, further research ideas are presented.

First short introduction to soil-structure interaction (SSI)and N2 method, a performance-based seismic design approach, was given. Introduction of soil-structure interaction effects into the N2 method was suggested through modification of response spectrum functions. Response spectra derived from shallow founded inverted pendulums and fixed-base counterparts were developed and compared. Numerical modeling was conducted using SASSI2000 and SHAKE2000, while experimental results obtained from tests conducted in centrifuges and on shaking tables were used for calibration. Also, the influence of foundation contact pressure on response spectrum-based design was investigated. And penultimately, results from comparison of free-field and foundation input motions from experiments are shown and discussed. Finally conclusions are provided.

Vibrations induced by machinery, traffic and other stochastic frequency-rich sources may cause deformations and cracks on both structural and non-structural elements but also fatigue related problems. Moreover, vibrations in buildings may cause discomfort for people and animals. On the other hand, wind turbines may often be found in urban areas surrounded by buildings or placed a top of a building. Although the turbines support green engineering and production of clean energy, they also produce vibrations that may negatively influence the behaviour of both structures and living beings. This paper aims to investigate effects of vibrations generated by small-scale wind turbines placed on buildings in urban areas. A platform for this research is a soil-structure-wind turbine system, where the structures selected for this case study are typical buildings that can be found in city of Osijek. The aim of this research is to set the stage for a small-scale wind turbine that will harvest green energy in Osijek in near future. Numerical analysis was performed using software SAP2000, while program SeismoSignal was employed for interpretation of analysis results. Parametric analysis provides results in the light of displacement response spectrums and acceleration response spectrums taken from characteristic structural elements on different floors compared with code-based thresholds. In addition, parametric study provides transfer functions calculated by dividing output (structural vibration) and input (vibration of the top of the turbine) signals pointing out amplified frequencies by structural members.

N2 je brza nelinearna statička metoda za projektiranje zgrada otpornih na potres. Rad predstavlja značajke i ograničenja metode, njezin razvoj te mogućnosti primjene na različitim tipovima zgrada. Istaknute su razlike između klasične N2 metode i njezinih proširenja. Također, dana je usporedba N2 metode i sličnih proračunskih pristupa. Ustanovljeno je da se rezultati dobiveni proračunima uz primjenu N2 metode dobro slažu s rezultatima dobivenim uz primjenu znatno složenijih metoda. Na kraju su dane smjernice za daljnje istraživanje., The N2 method is a fast nonlinear static method for the seismic design of buildings. This paper presents main properties and limitations of the method, its development over time, and possibilities of its application for different types of buildings. Differences between the traditional N2 method and its extensions are highlighted. Comparison of the N2 method with similar design approaches is also provided. The results obtained by calculations based on the N2 method are found to be in good agreement with the results obtained by much more complex methods. Guidelines for further research are given in the final part of the paper., N2 ist eine schnelle nicht lineare statische Methode für die Planung von erbebensicheren Gebäuden. Die Abhandlung stellt die Merkmale und die Grenzen der Methode, deren Entwicklung sowie die Möglichkeiten der Anwendung an verschiedenen Gebäudetypen vor. Hervorgehoben werden die Unterschiede zwischen der klassischen N2 Methode und deren Erweiterungen. Des Weiteren wird ein Vergleich der N2 Methode und ähnlicher Berechnungsansätze dargelegt. Es wurde festgestellt, dass die Ergebnisse, die durch die Berechnung durch Anwendung der N2 Methode erhalten wurden, gut zu den Ergebnissen passen, die man durch die Anwendung wesentlich komplexerer Methoden erhalten hat. Am Ende werden Richtlinien für weitere Untersuchungen gegeben.

The very beginnings of the N2 method started in late 1980s. Since then the method has been developing by many researchers. The N2 method is a nonlinear static method implemented in European norms and it is considered as a useful tool in seismic design of buildings. In this paper, the N2 method results are compared to the results obtained from the Blind Test Challenge conducted in Portugal in 2012. Within the challenge a 3D reinforced concrete frame model was experimentally tested using bi-directional shaking table. Data comprising displacement time history records was available to the authors and used in this research. The N2 method was applied to the concrete 3D frame model. Using the method target displacement was determined and compared to displacements recorded during the experiment.