Line geometry and 3D graphic statics

Budući da su sile koje djeluju na tijelo u prostoru, bilo da nas zanimaju uvjeti kretanja ili mirovanja (ravnoteže) toga tijela, vektorske veličine vezane za određene pravce djelovanja, tako da se sustav sila može povezati sa skupom pravaca u prostoru, u radu je ukratko prikazana matematička osnova pravčaste geometrije koja kao osnovni element uzima pravac. Primjenom pravčaste geometrije dokazana je poznata tvrdnja da se sustav sila u prostoru, ako su one u općemu položaju, može svesti na dvije sile na recipročnim pravcima. Prikazana je i vizualizacija te tvrdnje metodom prostorne grafostatike.The mathematical basis for the line geometry, with the line as its basic element, is presented in the paper because the forces that act on a body in space - whether we are interested in conditions of movement or immobility (balance) of that body - are vectorial values related to specific lines of action, so that the system of forces can be linked to the set of lines in space. The application of line geometry has proven the known claim that the system of forces in space, provided the forces are in a general position, can be reduced to two forces on reciprocal lines. The visualisation of this claim via the 3D graphic statics is also presented

Development of a new and modification of existing elastic clips for rails fastening

Jedan od problema sustava za pričvršćenje tračnica na podlogu (sustav pričvršćenja) koji se javlja s razvojem željeznica jest oštećenje elastičnih pritiskalica, čime se gubi konstrukcijski integritet između tračnice i podloge. Stoga postoji potreba za razvojem novih ili poboljšanjem postojećih pritiskalica. U radu je kroz dosadašnja istraživanja opisan doprinos i uloga pojedinih komponenata sustava pričvršćenja pri djelovanju raznih slučajeva opterećenja, a kao alatu čijom se promjenom parametara može utjecati na učinkovitost sustava pričvršćenja, posebno je usmjereno na pritiskalice. Detaljno je opisan postupak izrade numeričkih modela kojima je moguće provođenje parametarskih analiza za razvoj novih ili modifikaciju postojećih pritiskalica za pričvršćenje tračnica.One of the problems of railway fastening systems (fastening system) that occurs due to the development of railways is the damage of the elastic clips, which leads to the loss of structural integrity between the rail and the base. Therefore, there is a need to develop new clips or improve existing ones. The paper describes the contribution and role of each component of the fastening system in different loading cases. As a tool whose parameters can affect the efficiency of the fastening system, special attention is given to the clips. Finally, an example is briefly described for creating numerical models that can be used to perform parametric analyses in order to develop new clips or improve existing ones

Važnost znanstveno utemeljenih činjenica u kriznom komuniciranju: Dokazi iz zagrebačkog i petrinjskog potresa

Earthquakes are natural phenomena that can strongly affect the human population, infrastructure, and the environment. Croatia is part of a tectonically and seismically active area so its habitants and relevant institutions should be aware of possible hazardous events, which can be devastating. Therefore, crisis communication is extremely important, and in the event of natural disasters such as earthquakes, it must be clear, timely and concise. Scientific institutions dealing with earthquakes should also be involved in crisis communication. The information on two strong earthquakes in 2020 that shocked the area of Zagreb and Petrinja and the wide surrounding area, have shown how relevant institutions can deal with information on earthquakes and their consequences and share them publicly. This paper adopts a mixedmethods research design, combining both qualitative, and quantitative data on the Zagreb and Petrinja earthquakes from various sources of scientific and professional institutions in the field of geology, geophysics, seismology and civil engineering in Croatia. Empirical data suggest that interactive communication that strives to address local contextual concerns, explain actions, and provide honest, timely, accurate and reliable information is most effective. In the future, institutions have to find a way to react or share their information to help in the crisis.Potresi su prirodni fenomeni koji mogu snažno utjecati na zajednice, infrastrukturu i okoliš. Hrvatska je dio tektonski i seizmički aktivnog područja, tako da bi njezini stanovnici i nadležne institucije trebali biti svjesni mogućih opasnih događaja, koji mogu biti razorni. Stoga je krizna komunikacija izuzetno važna, a u slučaju prirodnih katastrofa poput potresa mora biti jasna, pravodobna i sažeta. Znanstvene institucije koje se bave potresima također bi trebale biti uključene u krizno komuniciranje. Podaci o dva snažna potresa 2020. godine koji su potresli područje Zagreba i Petrinje te širu okolicu, pokazali su kako se relevantne institucije mogu nositi s informacijama o potresima i njihovim posljedicama i javno ih dijeliti. Ovaj rad usvaja mješoviti dizajn istraživanja, kombinirajući i kvalitativne i kvantitativne podatke o potresima u Zagrebu i Petrinji iz različitih izvora znanstvenih i stručnih institucija iz područja geologije, geofizike, seizmologije i građevinarstva u Hrvatskoj. Empirijski podaci sugeriraju da je najučinkovitija interaktivna komunikacija koja nastoji riješiti lokalne kontekstualne probleme, objasniti radnje i pružiti iskrene, pravodobne, točne i pouzdane informacije. Ubuduće institucije moraju pronaći način da reagiraju ili podijeliti svoje informacije kako bi pomogle u krizi

Post-earthquake damage assessment of buildings – procedure for conducting building inspections

Procjene oštećenja i uporabljivosti građevina u Hrvatskoj, iskočile su u prvi plan nakon potresa u Zagrebu 22. ožujka 2020. S obzirom na manjkavosti pripremne faze, pri čemu nije provedena edukacija stručnjaka prije potresa, nego u hodu, procjene su sadržavale dozu subjektivnosti i interpretacije na temelju znanja, iskustva, ali i intuicije pojedinaca. U radu je detaljno prikazana metodologija koja može pomoći u brzim procjenama te kod detaljnih inženjerskih pregleda koji se moraju napraviti prije obnove. Prikazana metodologija se može iskoristiti u slučaju novoga razornog potresa koji se može dogoditi već sutra.Assessments of building damage and usability were of primary importance after the Zagreb earthquake of 22 March 2020. Due to deficiencies of preparatory phase, where education of experts was not carried out before the earthquake, but later on, the assessments contained certain subjectivity and interpretations, based on knowledge and experience, but also on intuition of individuals. Detailed methodology, which should improve rapid assessments and detailed engineering inspections to be performed before reconstruction, is highlighted in the paper. This methodology may be utilized if another devastating earthquake occurs, which could happen already tomorrow

Zagreb earthquake of 22 March 2020 – preliminary report on seismologic aspects and damage to buildings

U radu su opisane bitne značajke i glavne posljedice potresa magnitude 5,5 koji je u jeku pandemije virusa COVID-19 zadesio Zagreb i okolicu. Premda je potres, seizmološki gledano, bio umjerene magnitude, prouzročio je gubitak jednoga života i veliku materijalnu štetu. Napravljen je pregled stanja prije trešnje te prikaz lokacije, seizmičke aktivnosti i organizacije pregleda zgrada. Grubo su razvrstani podaci o oštećenjima, s težištem na povijesnoj jezgri i četvrtima blizu epicentra. Na kraju su istaknute nužne aktivnosti koje je odavno trebalo provesti, s nadom da će ih ovaj potres potaknuti.Significant characteristics and main consequences of the 5.5 magnitude earthquake that struck Zagreb and its surroundings in the midst of the COVID-19 pandemic are presented in the paper. Although, from the seismologic aspect, the earthquake was of moderate magnitude, it caused the loss of one life and considerable material damage. An overview of the situation before the quake is given, and information about the location, seismic activity, and organisation of building inspection activity, is presented. The data on damage are roughly classified, with the focus on historic core of the city and districts situated close to the epicentre. A strong emphasis is placed on indispensable activities that should have been carried out a long time ago, in the hope that they will be prompted by this earthquake

Increasing efficiency of iterative application of the force density method

The method for reducing total computational time during iterative application of the force density method, intended to attain prescribed force values in cables or prescribed lengths of cable segments, is described in the paper. In each step of the iterative procedure, linear systems are solved with the accuracy that takes into account differences between the calculated and required values. The rule that prevents excessively fast increase in accuracy, while maintaining it high enough not to compromise the convergence of the iterative process, is proposed

Increasing efficiency of iterative application of the force density method

U radu je opisan postupak skraćivanja trajanja proračuna pri iteracijskoj primjeni metode gustoća sila kojom se u fazi nalaženja oblika prednapete konstrukcije od užadi postižu tražene vrijednosti sila ili duljine odsječaka kabela. U svakom se iteracijskom koraku linearni sustavi jednadžbi rješavaju s točnošću koja u obzir uzima razlike izračunanih i traženih vrijednosti. Predloženo je pravilo koje sprečava prebrzo povećavanje točnosti, održavajući je istodobno dovoljno velikom da se konvergencija ne naruši.The method for reducing total computational time during iterative application of the force density method, intended to attain prescribed force values in cables or prescribed lengths of cable segments, is described in the paper. In each step of the iterative procedure, linear systems are solved with the accuracy that takes into account differences between the calculated and required values. The rule that prevents excessively fast increase in accuracy, while maintaining it high enough not to compromise the convergence of the iterative process, is proposed

Seismic Retrofitting of Dual Structural Systems—A Case Study of an Educational Building in Croatia

On 29 December 2020, a devastating Mw6.4 earthquake struck near the town of Petrinja, Croatia. The main earthquake was preceded by a Mw4.9 foreshock the day before. The earthquakes caused extensive damage to buildings, especially historic buildings made of unreinforced masonry but also to buildings of other typologies and to critical infrastructure. Today, recovery efforts in Croatia focus primarily on reconstruction and seismic retrofitting. Family homes and public, cultural, educational, and other facilities are top priorities. In this paper, a comprehensive study of existing building in the educational sector is presented as a case study. The seismic performance of the building is evaluated using numerical methods, first for the as-built condition and then for the retrofitted building. For each condition, the collapse mechanisms of the building were determined and critical structural elements were identified. The presented retrofit strategy of the dual structural system consisting of RC frame system and masonry walls aims to reduce the displacements of the RC frame system to a level sufficient to prevent the early brittle failure of the concrete. Additionally, the discrepancies when using different modelling approaches are discussed

Damage Evaluation and Seismic Assessment of a Typical Historical Unreinforced Masonry Building in the Zagreb 2020 Earthquake: A Case Study—Part I

The city of Zagreb, the national capital and economic hub of Croatia, is situated in a seismically active region and hosts a significant array of historical buildings, from the medieval to Austro-Hungarian periods. These buildings possess varying but generally high degrees of vulnerability to seismic loading. This was highlighted in the Zagreb earthquake of 22 March 2020, emphasizing the need for seismic retrofitting in order to preserve this architectural heritage. In this paper, the seismic capacity of one such unreinforced masonry building is considered through a number of analysis methods, including response spectrum, pushover, and out-of-plane wall failure analyses. Given the advantages and disadvantages of the individual methods, their applicability and value in a seismic analysis is considered. Ambient vibration measurements before and after the Zagreb 2020 earthquake, used for model calibration, are also presented. Conclusions are drawn from each individual analysis and later compared. In conclusion, no single analysis method considers all relevant failure modes, and a combination of nonlinear static or dynamic analysis and out-of-plane analysis is recommended. Due to the large volume of the material, it is published in two parts, with ground motion record selection, dynamic analysis, and a comparison of the results published in part two