ELAZIG GUNISIGI NEWSPAPER – July 2011
THE QUESTIONS YOU'VE ASKED - 1
Our country has been shaken by many devastating earthquakes in the past. Heavy loss of life and property has deeply affected us. Much has been written and said about earthquakes. In addition, a lot of hearsay about earthquakes and buildings has circulated. Some topics have become baseless obsessions, while important issues have been ignored. Earlier, at the request of our readers, I tried to answer some of these questions. Due to sincere and relevant requests, I wanted to share these questions and answers with you in a more comprehensive way. Through these questions, I have had the opportunity to understand the "commonly known wrongs and the wrongly known rights." I would like to thank all the readers who contributed with their questions. I hope this Q&A article will help settle some fundamental issues related to earthquakes, construction, and urban planning. (In the answers, I have tried to minimize the use of technical terms.)
QUESTION: Are multi-story buildings a risk factor during earthquakes? Do multi-story buildings collapse easily?
ANSWER: The number of stories in a building doesn't matter, as long as the building is designed and constructed according to relevant regulations and is constantly monitored. Whether a building is single-story or a high-rise, what matters is that it is designed and built with high seismic performance. The idea that multi-story buildings have inadequate seismic resistance originates from the existing stock of buildings with insufficient earthquake resistance. After destructive earthquakes, multi-story buildings are often brought to the forefront due to the higher number of casualties in these buildings. However, the rate of casualties in low-rise buildings can be the same. In other words, not just multi-story buildings but any building with insufficient earthquake resistance will cause loss of life.
QUESTION: Should buildings always have a "raft foundation" to be earthquake-resistant?
ANSWER: Raft foundations are one type of reinforced concrete foundation used in buildings. When choosing the foundation type for a building, the soil type, rather than the earthquake zone, plays a crucial role. In other words, even in a fourth-degree earthquake zone, if the ground strength is insufficient, a raft foundation may be used. Conversely, in a first-degree earthquake zone, if the ground strength is adequate, a raft foundation is not necessary, and a continuous foundation may be used instead. In first and second-degree earthquake zones, as well as in areas with high groundwater levels or alluvial (fill) soil, the risk of liquefaction exists. The foundation type is selected based on these conditions. Therefore, the notion that only raft foundations are earthquake-resistant is not completely accurate. The entire structure, from its foundation to its roof, must be designed with seismic resistance in mind. Every load-bearing element and system must have sufficient earthquake resistance.
QUESTION: Which is more earthquake-resistant: reinforced concrete frame structures or masonry structures?
ANSWER: Any structure that is designed and implemented according to standards will have the expected earthquake resistance. Masonry structures are generally required to be low-rise. If designed according to the rules, buildings with the same number of floors and floor plans will not cause loss of life during an earthquake. The advantage of reinforced concrete frame buildings is that their height, number of stories, and floor plans can be designed as needed. Masonry structures are more commonly used in rural areas today.
QUESTION: Is it appropriate to strengthen buildings to increase their earthquake resistance? Does strengthening work?
ANSWER: Just as certain diseases in humans can be treated within limits, building problems can also be treated within certain boundaries. This treatment is referred to as strengthening. First, the earthquake resistance of a building is assessed. If the building's seismic resistance is insufficient, strengthening projects are prepared using appropriate technical methods and calculations. If the cost of strengthening does not exceed 40% of the building's construction cost, a detailed project is prepared. If strengthening is not economically viable, the building's demolition is advised. The fact that buildings that were strengthened before the Düzce Earthquake of November 12, 1999, did not cause any loss of life proves that properly designed strengthening works are effective. Strengthening projects are specialized services and must be carried out by experienced and technical personnel.
QUESTION: Can only one apartment in a building be strengthened?
ANSWER: A building is a whole system. Weak elements within a system are strengthened. However, strengthening only one apartment in a building is not possible. If necessary, a strengthening project is prepared for the entire building.
QUESTION: What magnitude of earthquake can damage buildings?
ANSWER: The destructive power of an earthquake can be practically evaluated under three headings: magnitude, duration, and the distance between the earthquake's epicenter and the building. The larger and longer the earthquake, the more it will affect buildings. However, the impact also depends on the characteristics of the building. A building's earthquake resistance is determined through measurements and calculations, and each building has different seismic characteristics. Therefore, it is incorrect to use a single resistance value for an entire province or neighborhood. The earthquake resistance of each building must be assessed individually.
I will continue to answer the questions you are curious about as much as possible. If you have any questions, please feel free to send them to me via email at kealyamac@firat.edu.tr.