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.

A simple alternative to the conjugate gradient (CG) method is presented; this method is developed as a special case of the more general iterated Ritz method (IRM) for solving a system of linear equations. This novel algorithm is not based on conjugacy, i.e. it is not necessary to maintain overall orthogonalities between various vectors from distant steps. This method is more stable than CG, and restarting techniques are not required. As in CG, only one matrix-vector multiplication is required per step with appropriate transformations. The algorithm is easily explained by energy considerations without appealing to the A-orthogonality in n-dimensional space. Finally, relaxation factor and preconditioning-like techniques can be adopted easily.

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Original scientific paper When the decision has been made to seismically strengthen a building, in order to mitigate possible damaging effects of an earthquake, choice of seismic strengthening is entirely left to the expert. The choice is often made without any specific analyses of the need and implementation possibilities, but depends completely on the expert's knowledge and experience. The article presents the development of the innovative approach to strengthening technique selection for existing buildings that incorporates all important elements that influence the strengthening selection process. The presented model is simple, quick, precise, allowing analytically supported decision making. Although the developed model is designed particularly for masonry buildings, decision support model for strengthening technique selection is adaptable to any building type. Keywords: decision support model; existing buildings; innovative approach; masonry; seismic strengthening technology Metodologija odabira tehnologije seizmičkog ojačanja zidanih zgradaIzvorni znanstveni članak Kada je donesena odluka o potrebi za ojačanjem zgrade u cilju preventivne zaštite od potresa, kao pravilom, odabir ojačanja prepušten je stručnjaku. Odabir ojačanja se najčešće provodi bez konkretnih analiza mogućnosti i potreba za određenim pothvatom, već isključivo prema nahođenju i prošlom iskustvu stručnjaka. U članku se predstavlja proces razvoja inovativnog pristupa izboru tehnologija ojačanja postojećih zgrada, a kojim se uzimaju u obzir svi bitni elementi koji mogu utjecati na izbor ojačanja. Predstavljeni model je jednostavan, brz i precizan, te dozvoljava donošenje odluka na osnovu analitički dokazanih činjenica. Unatoč tomu što je model izrađen isključivo samo za zidane zgrade, model za izradu potpore odlučivanja pri odabiru tehnologije ojačanja je prilagodljiv bilo kojem tipu građevina.Ključne riječi: inovativan pristup; model za odabir tehnologije; postojeće zgrade; tehnologije seizmičkih ojačanja; ziđe

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