Buildings of recent construction in Montenegro, which were built according to current laws and regulations, are seismically safe to a large extent, but the biggest problem is represented by illegal buildings, of which there are tens of thousands.
The possible consequences of an earthquake are also affected by the density of construction, and unlike reinforced concrete buildings that were built in the last 20 years, non-reinforced masonry buildings, without vertical and horizontal cerclages, are seismically unsafe.
Professor at the Faculty of Civil Engineering Srđan Janković says that there is a high degree of doubt about the seismic safety of "wildly" built buildings, which do not have complete documentation.
"Especially for buildings where the basic principles were violated during the conception, the basic configuration. If some basic principles in seismic design were violated, then to a large extent it can be said that they are seismically unsafe," Janković said.
He said that the construction of a large number of buildings certainly increases the seismic risk.
"You have also seen in Turkey, a whole series of buildings of the same buildings and one of them has completely perished. When there are a large number of buildings, then there is a high probability of making a mistake. The risk that some of them will be seismically unsafe is certainly increasing," explained Janković.
Janković states that there are decisive and clear norms when it comes to designing.
As he stated, in Montenegro, the building design regulations were updated after the 1979 earthquake, that is, they were adopted in 1981.
"They were current and good at the time. However, time has taken its toll, the science of engineering is young, a lot has changed, we have learned a lot. That rulebook has become, we cannot say unusable, but insufficiently precise and accurate." , believes Janković.
He clarified that Montenegro has taken the right step by accepting the European standards for structures, the so-called Eurocodes (EC).
"For the previous four, five years, the Eurocodes and our valid regulations were used in parallel. However, starting this year, projects in Montenegro must be designed according to European standards," said Janković.
He stated that these regulations are more demanding in the engineering part, but that designing according to EC brings greater safety.
He repeats that it is completely pointless and that it is not allowed to skimp on the provision of seismic safety.
"Additional investments in ensuring seismic safety in new buildings are only a few percent compared to the total investment, and it is completely inadmissible for anyone to skimp on that. It is inadmissible to design an unsafe building today," Janković pointed out.
He said that the situation is completely different with existing buildings, since strengthening their seismic resistance is extremely expensive, so developing countries often cannot afford it.
According to regulations, buildings must be built and designed to withstand an earthquake with a magnitude of seven on the Richter scale.
The biggest guarantee that the building will not collapse is compliance with the laws and rules of the construction profession, but there is no XNUMX% certainty that the building or house will not be damaged, no matter how well it is planned.
Buildings are not designed to save them, but to save human lives, and the engineers are considered to have done their job well if they stand until the citizens are safely evacuated, even if they are not safe for life after the earthquake.
Regulations in the territory of the former Yugoslavia began to be tightened first after the strong earthquake in Skopje, and were especially tightened after the devastating earthquake in the south of Montenegro in 1979. Then it shook with a magnitude of 6.9 on the Richter scale.
Experts point out that illegal buildings are in the greatest danger because most of them do not have a serious project and therefore there is little chance that the rules of the profession were respected when it comes to earthquake protection.
The general rules are good design of buildings, which implies mostly symmetrical, regular arrangement of vertical supporting elements (pillars and walls), their uniform stiffness and dimensions, proper distribution of mass according to the height of the building.
Serbia: Unscrupulous builders are a greater danger than nature
Seismic activity in Serbia is likely in the area of Kopaonik, which often shakes, Šumadija and in the triangle formed by Kopaonik, Kosjerić and Valjevo in Western Serbia, and on the third side, Svilajnac in the central part of the country, the geophysicist explained to Danas Ana Mladenovic after the devastating earthquake in Turkey and several smaller ones in Romania that also shook part of Serbia.
Seismologist Slavica Radovanović, on the other hand, warns that Serbia could soon be hit by an earthquake of up to six degrees on the Richter scale, stronger than the one that shook Kraljevo and its surroundings in November 2010. In that earthquake, a married couple in the village of Grdica died, when the ceiling of the house they lived in fell on them, and only one building was completely destroyed, and dozens, especially older buildings, collapsed.
The renovation, which, as it happens in these areas, is still ongoing, cost tens of millions of euros, because, despite the relative preservation of the buildings, about twenty thousand had to be repaired, and 462 prefabricated houses were built with the funds of the Government of the RS.
Experts in Serbia agree that a devastating earthquake like the one in Turkey is not realistic to expect. Also, that the earthquakes in neighboring Romania are an echo of the Turkish one, although it would have happened in the next year or two without that disaster.
"Increased seismic activity will last for several years," Radovanović stated for the public service, noting that she and her colleagues do not "count" in months when seismic activity is concerned.
But, according to a respected expert, in the foreseeable future, an even stronger earthquake of up to 7 degrees on the Richter scale can be expected in neighboring Bulgaria, which would also be significantly felt in the border areas of Serbia and North Macedonia. Especially important is her warning that the strength of an earthquake is not measured linearly, but logarithmically, so an earthquake of magnitude seven is even ten times stronger than one of a weaker magnitude. And the devastating consequences, as in Turkey, occur when the epicenter is shallow.
The question that always hangs in the air when the earth shakes in Serbia and its immediate surroundings is whether the residential buildings that sprout like mushrooms after the rain can withstand any earthquakes? And how stable is the ground on which it is built, if it is known that buildings are literally leaning on each other more and more often, even so much so that we are witnessing their collapse, even collapsing during the construction itself?
A special problem is that the state suspends itself at various levels, thus violating its own regulations and documents, changing urban plans in vain, "turning a blind eye" to additional floors and building monstrously large buildings like Belgrade on the water on the banks of rivers.
"The location conditions must be in accordance with the valid urban plans, on the basis of which a building permit is obtained, which must contain all the elements that define the building, and finally there is a use permit which, at least theoretically, cannot be obtained if the building is not completely done in accordance with the project, technical regulations, standards and if evidence for this is not provided," the director of the National Coalition for Decentralization and a civil engineer recently explained to the Danas portal Danijel Dašić.
Current regulations in Serbia "guarantee" the stability of buildings in earthquakes up to 8 degrees on the Mercalli scale, which roughly corresponds to the strongest predicted earthquakes. After the devastating earthquake in the former Yugoslavia in Skopje in 1963, when more than a thousand people died, additional requirements were introduced during the construction of buildings. "Let's say for Belgrade, the rule applies that, in the simplest terms, a building must not collapse if the strength of the earthquake is up to 8 degrees Merkali," explains Dašić: "At the end of the 80s, the method of calculating the bearing capacity of concrete constructions was changed, so only when fracture in the girder considers that the bearing capacity of the AB structure is reduced," says Dašić.
This expert believes that the density of real estate construction is not dangerous from a seismic point of view, but it is an additional risk factor in case of emergencies because it prevents access to assistance services. Civil engineer and professor dr Dragoslav Šumarac, as well as Dašić, notes that every building higher than four floors must have a project that includes the calculation of the building's resistance to the effects of an earthquake: "After the recent earthquake in Turkey, it was seen that some buildings fell, while others remained standing , which means they didn't have enough reinforcement".
Šumarac says that in Serbia there are many buildings that are built without any papers and they are the most dangerous. A typical example is a large settlement in the municipality of Voždovac, opposite the settlement of Veljko Vlahović, where the houses are literally built as they please, and among them are residential buildings, so the alleys are winding and wide enough for two small cars to pass. Not even a normal city bus can run in that neighborhood, but only a minibus. And the settlement is expanding, although the area is rich in underground water and prone to landslides.
"There is a general urban plan and a detailed urban plan, but the investor is going for the so-called urban project. They make a project only for that building and nestle themselves, not taking into account the distance between the buildings, so often, and most often in Vračar, you can reach out from the apartment and grab things from the neighbor's terrace," she told danas.rs Kaća Lazarevic, an expert in the real estate market, who emphasizes that the old building in the capital is more solid than the new one, and she especially emphasizes the pre-war buildings in old Belgrade.
Croatia: The worst thing is when the earthquake tests
"I was sleeping when it shook, and parts of the ceiling fell on my bed. I came out and saw that the house had cracked and the chimneys had collapsed," said our retired teacher Ankica Draženović commented on the first Petrinja earthquake on the morning of December 28, when we found her a day later next to her house in Petrinja.
"The state has not invested anything in this house since the war when we returned. The husband even tried something, but the conservators immediately stopped him because it is a protected asset, and the state said that they would restore it. But they didn't lift a finger and you can see what happened," said Ankica at the time, a few hours before the big earthquake. At that moment, her building, older than 100 years and owned by the state of which they were tenants in an apartment, was one of the few that received more severe damage from the first 5,0 earthquake. A few hours later, a 6,4 magnitude earthquake almost destroyed that house.
That house was located in the very center of Petrinja, which suffered the worst damage, and it is mostly about houses and buildings from the turn of the 19th to the 20th century, which were not built according to the proper norms, nor were they maintained due to mostly state and of public ownership, and what happened after the nationalization after World War II. A few streets away, other buildings, built after the catastrophic earthquake in Skopje in 2, withstood the force of the earthquake, after which stricter construction standards began to be applied throughout the former Yugoslavia, including Croatia.
Namely, after the earthquake in Skopje in 1963, reinforced concrete walls became mandatory, and all buildings built after that, if they were built professionally, should withstand earthquakes of at least magnitude 6,5 on the Richter scale. After the Banja Luka earthquake in 1969, the norms are even stricter, and in 1998, Croatia adopted the Eurocode standard, which has been applied since the middle of 2000, according to which construction is based on an assessment of the seismic hazard, that is, the risk of an earthquake in a particular area. But, as the earthquake in Turkey showed - the question is how many builders respect that norm. The worst thing is when it is tested by an earthquake as strong as the one in Turkey and Syria, which results in huge loss of human life.
The Zagreb earthquake in March 2020 had a magnitude of 5,5, and the Petrin earthquake on December 29 of the same year had a magnitude of 6,4 on the Richter scale. And it turned out, fortunately, that the buildings built after 1963, for the most part, withstood the earthquake. There is damage, but the anti-earthquake standard essentially does not guarantee the undamaged buildings, but rather the certainty that they will not collapse and cause injuries and death to people. Especially when you take into account that since 1963, numerous interventions have been made on many buildings.
However, everything built before 1963 mainly showed its weakness in the Zagreb and Petrin earthquakes, which was most visible in the historical units of cities such as Zagreb, Petrinja, Sisak and Glina. These are buildings built of solid brick in lime mortar, which itself has degraded. Basically, those buildings at the very moment of completion did not meet today's standards in terms of earthquake resistance. And this was also shown for the 2020 earthquake.
Until the Zagreb earthquake in March 2020, no one even took into account the earthquake resistance of houses and buildings in which apartments were bought, because there had been no stronger earthquakes, especially in the continental part of Croatia, for a long time. But now that has changed, so they are already integral parts of the description of apartments and houses on advertisements.
According to the Eurocode anti-seismic norms, it is necessary to ensure that in the event of an earthquake the building does not collapse and, at the same time, ensure the protection of human lives, limit damage to buildings and enable buildings of special importance, such as hospitals, to remain functional. Therefore, this standard for such buildings is stricter than those for "ordinary" buildings.
The condition that there is no collapse means that there must be no global and local collapse of the structure during the action of a significant earthquake (the strength of which is taken for certain areas based on seismic data of earthquakes of maximum magnitude in the last 475 years). The building should retain seismic resistance to subsequent earthquakes, but as we have already said - the possible occurrence of major damage (even such that the rehabilitation is economically unprofitable) and loss of functionality is not excluded. Damage can be primarily on non-constructive elements and must be economically acceptable.
In the Zagreb area, according to these guidelines, buildings were designed to withstand earthquakes of 8 or 9 degrees (depending on the assessment zone, Zagreb has 2 zones) on the Mercali scale - i.e. 6,5 to 7,0 on the Richter scale.
However, while one can be mostly sure about everything built before 1964, until then, those buildings built earlier, many of which still do not undergo the strengthening necessary to withstand stronger earthquakes, remain a problem. Seismologists estimate that the highest possible magnitude of an earthquake in Zagreb could be around 6,5 or 6,6 on the Richter scale. And according to data from the State Statistics Office (DZS), almost 100 apartments in Zagreb were built before 1964 and the entry into force of the first regulation on earthquake-proof construction.
The problem with those buildings is that their strengthening is still not systematically carried out, all so that they too would be ready for a future stronger earthquake. Which may or may not be, but no one can say for sure.
BiH: Concrete is the best friend against earthquakes
The earthquakes in Turkey and Syria have once again opened the question of the quality of construction in Bosnia and Herzegovina. We have witnessed that in recent years there has been a construction boom, but also urban chaos. Static engineer Isak Medic points out that the most important thing is to design properly. He also states that we have good regulations and rules, but that we are fighting with investors.
"As far as our buildings are concerned, Austrian construction is good. The problem is that the business premises were remodeled several times. I think the buildings that are being built today are fine. Each country has strict regulations that must be designed. Sarajevo is the 7th seismic zone, which is not dangerous. We design for the 8th zone. I wouldn't wish the ninth seismic zone on anyone. That's good protection. Concrete is the best friend against earthquakes, we should build as many buildings as possible from concrete. I think there was a lot of reinforcement missing here (in Turkey and Syria). They accuse me of being an expensive structural engineer because I don't spare the reinforcement. My professor used to say: What salt is to soup, constructive reinforcement is to concrete," said Medić.
Professor from the Faculty of Civil Engineering in Sarajevo Naida Ademović emphasizes that the earthquake that hit Turkey and Syria involved strong earthquakes and in such cases it is absolutely impossible for the structure to remain undamaged, but with proper construction it can be achieved that it does not collapse.
Asked about the quality of construction in Sarajevo and BiH, that is, what would be the consequences of a strong earthquake, Prof. Ademović said that it is difficult to forecast, but that according to what she knows, the largest number of buildings being built are built according to Eurocode 8, that is, according to European standards, which are much stricter compared to the rulebook currently valid in BiH, and which is from 1981, with the last changes being made in 1990.
He emphasizes that in addition to design and construction, it is necessary to have very good supervision - not supervision that is there for a short period of time and leaves the construction site.
Anđelko Cumbo, an expert in building materials and structures at the Faculty of Architecture, Civil Engineering and Geodesy in Banja Luka, speaking about the assessment of the seismic resistance of old buildings in Banja Luka, points out that some buildings built before 1964 do not meet some of the basic principles of designing and building seismically resistant structures .
As an additional problem, he points out the practice of upgrading buildings, which was current especially in the beginning of 2000, when it was shown how unprepared and lightly such work was approached.
- In these upgrades, the needs of investors were most often met, and often without strengthening the existing structure, according to the system without investing in something that is 'just a cost' to the investor", claims Cumbo.
According to him, there are also dangerous cases where, during the change of use on the ground floor, work was carried out to "clear" the space, which brings the building to the state of a "soft" ground floor.
When it comes to new buildings, Cumbo points out that, as a rule, they are of better quality than the old ones, when it comes to earthquake protection. However, the construction of new buildings can be accompanied by a number of disadvantages.
He underlines that when designing, the wishes of investors are most often put in the foreground, which often leads to "flexible ground floors", cantilevered structures above the ground floor ("stealing space") and asymmetric constructions. At the same time, additional problems are represented by unanchored masonry fillings, glass facades, inadequate expansions between buildings and the like.
- There is no earthquake yet and one gets the impression that everything is fine. However, in an earthquake, those shortcomings and shortcomings would be shown as a result of laziness and incompetence during execution, says Cumbo and adds that supervision can also be unprofessional and irregular, and sometimes only formal.
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