ELAZIG GUNISIGI NEWSPAPER - April 2010
COMMONLY KNOWN MISTAKES
For many years, our country has experienced many earthquakes. The heavy loss of life and property has deeply affected our country. A lot has been said and written about earthquakes. Also, through word of mouth, many rumors about earthquakes and buildings have circulated. Some issues have become unnecessary obsessions, while important topics have been ignored. This week, I’ve compiled some questions I received from the readers of Günışığı newspaper. I wanted to share these questions and answers with you because, from these questions, we found an opportunity to understand the “commonly known mistakes” and the “mistaken truths.” I would like to thank all the readers who contributed with their questions. I hope this Q&A article will help put some pieces in place regarding earthquakes and buildings. (Effort has been made to use the fewest technical terms in the answers.)
QUESTION 1: Is the height of buildings a risk factor during an earthquake? Do tall buildings collapse easily?
ANSWER 1: The number of floors of a building does not matter for earthquake resistance as long as the building has been designed and constructed according to the relevant rules and is continuously monitored. Whether the building is a single-story or a skyscraper, what matters is that it is designed and built with high earthquake resistance. The misconception that tall buildings are less resistant to earthquakes comes from the existing stock of buildings with inadequate earthquake resistance. After destructive earthquakes, tall buildings are often highlighted because they tend to result in higher numbers of casualties. However, the ratio of casualties is similar in low-rise buildings as well. In other words, it’s not the number of floors or just the tall buildings, but all buildings with insufficient earthquake resistance that cause loss of life.
QUESTION 2: Should buildings definitely have “raft foundations” to be earthquake-resistant?
ANSWER 2: A raft foundation is one of the types of reinforced concrete foundations used in buildings. When selecting the type of foundation for a building, it is not the earthquake zone, but the soil type that is important. For example, if the soil's bearing capacity is not sufficient in an area located in a fourth-degree earthquake zone, a raft foundation may be used. Similarly, in a first-degree earthquake zone, if the soil's bearing capacity is adequate, a continuous foundation, not a raft foundation, may be used. In first- and second-degree earthquake zones and areas with a high water table and alluvial soils (fill), due to the risk of liquefaction (the risk that the soil will behave like liquid under the effect of earthquake forces), the foundation type is selected considering these conditions. Therefore, the approach that a building must have a raft foundation to be earthquake-resistant is incorrect. The building, from its foundation to its roof, is a whole. Each structural element and the entire system must have adequate earthquake resistance.
QUESTION 3: Which is more resistant to earthquakes, reinforced concrete frame buildings or masonry buildings?
ANSWER 3: Any building designed and constructed according to standards is as earthquake-resistant as intended. Masonry buildings must be low-rise. Buildings with the same number of floors and floor plans, made according to the rules, will not cause any casualties in an earthquake. The advantage of reinforced concrete frame buildings is that their height, number of floors, and floor plans can be customized. Masonry buildings are more commonly used as rural structures today.
QUESTION 4: Is it appropriate to strengthen buildings to increase their earthquake resistance? Does strengthening work?
ANSWER 4: Just as human diseases can be treated within certain limits, building defects can also be treated within certain limits. This treatment is called strengthening. First, the earthquake resistance of a building is determined. If the earthquake resistance of the building is insufficient, strengthening projects are prepared with appropriate techniques and calculations. If the cost of strengthening does not exceed approximately 40% of the building’s construction cost, the project is prepared in detail. If strengthening is not economically feasible, it is recommended that the building be demolished. The fact that structures that could be strengthened before the Düzce Earthquake on November 12, 1999, did not cause loss of life in the earthquake shows that well-designed projects work. Strengthening projects require expertise and should definitely be carried out by experienced technical personnel.
QUESTION 5: Can just one apartment in a building be strengthened?
ANSWER 5: A building is a whole system. The weak elements in the system are strengthened. However, it is not possible to strengthen only one apartment in a building. If necessary, a strengthening project is prepared for the entire building.
QUESTION 6: What magnitude of earthquake will cause damage to buildings?
ANSWER 6: The destructive power of an earthquake can be practically categorized under three headings: its magnitude, duration, and the distance of the earthquake's epicenter from the building. The larger the magnitude and the longer the duration of the earthquake, the more effective it will be on structures. However, the effect here is related to the characteristics of the building. A building’s earthquake resistance is determined after appropriate measurements and calculations, and each building has different earthquake resistance characteristics. Therefore, it is not correct to use a single resistance concept for a city or a neighborhood. The earthquake resistance of each building should be determined individually.
QUESTION 7: Where is the safest place in a house during an earthquake?
ANSWER 7: This question needs to be answered in two parts. In an earthquake-resistant house, you should avoid falling objects, and the location in the building (except for balconies) does not matter. The problem arises in buildings with insufficient earthquake resistance. These buildings move according to various parameters under earthquake forces. Therefore, I believe a general recommendation on where to be inside a house during an earthquake is not appropriate. Frankly, the best approach is to make your building earthquake-resistant before the earthquake hits.
QUESTION 8: What is the earthquake safety level of the existing building stock in Elazığ?
ANSWER 8: So far, no assessment of the earthquake resistance of the general buildings in Elazığ has been made. In fact, determining this situation is part of urban transformation. The first step of urban transformation is to create a structural earthquake risk map of the city center. With this map, the actual condition of the buildings will be revealed, and this result will lead to necessary steps being taken. This question can be answered by considering the studies carried out by the Department of Civil Engineering at Fırat University in our province and region. In these studies, it has been observed that a significant portion of the buildings constructed before the year 2000 have insufficient earthquake resistance. In the April 7, 2010 issue of the Günışığı newspaper, the structural earthquake resistance of our city was expressed with photographs.