Betonarme bir binanın U şekilli metalik sönümleyiciler ile deprem performansının iyileştirilmesi
Seismic performance improvement of a reinforced concrete (RC) building using u-shaped metallic dampers
Yazar: HASAN TALHA ŞAHİN
Danışman: PROF. DR. OĞUZ CEM ÇELİK
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Deprem Mühendisliği Ana Bilim Dalı / Deprem Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Deprem Mühendisliği = Earthquake Engineering

Özet:
Mevcut yapı stokundaki betonarme binaların önemli bir bölümü çeşitli nedenlerden dolayı güncel deprem yönetmeliklerinde belirtilen performans seviyelerini sağlayamazlar. Yapının kullanım şeklinin değişmesi, yönetmeliklerin ve deprem tehlike haritalarının güncellenmesi, malzeme dayanım değerlerinin çeşitli dış koşullar nedeni ile düşmesi gibi nedenlerden dolayı mevcut betonarme yapılar güncel yönetmeliklerde belirtilen dayanım, rijitlik ve süneklik koşullarını karşılamayabilir. Bunlara ek olarak sünek olmayan detaylara sahip bir betonarme çerçevenin enerji yutma kapasitesi, çevrimsel yükler altında sınırlı olabilir. Bu türden sakıncalar, mevcut bina stoğunun hızlı bir şekilde güçlendirilmesi gerekliliğini ortaya koymaktadır.
Geleneksel güçlendirme (örneğin betonarme sisteme betonarme perde eklenmesi, betonarme elemanların mantolanması vb.) yöntemleri genellikle binaya kapsamlı müdahale gerektirir ve zaman alıcıdır. Bu çalışmada, önerilen güçlendirme yolu olarak bina mimari planına minimum müdahale ile deprem performans seviyesinin arttırılması önerilmektedir. Önerilen güçlendirme sistemi U şekilli çelik sönümleyici, rijit bir çelik kafes eleman ve disk ankrajlardan oluşmaktadır. U şekilli sönümleyici kiriş ortasında bulunan çelik kafes elemanın üstünde konumlandırılmıştır. Sönümleyicinin mevcut betonarme kirişe bağlantısı, özellikle düşük dayanımlı betonlarda kuvvetleri daha iyi aktarmak için özel olarak tasarlanmış disk ankrajlar ile gerçekleştirilmiştir; bilindiği kadarıyla, bu tarz bir uygulama ilk kez bu tez kapsamında ele alınmaktadır.
Önerilen güçlendirme modelinin etkinliğinin araştırılması amacı ile 6 Şubat 2023 tarihinde Kahramanmaraş (Nurdağı ve Ekinözü) depremlerinde (Mw=7.9 ve Mw=7.8) hasar alan betonarme bir konut binası kapsamlı bir biçimde ele alınmıştır. Konut binasında deprem sonucu oluşan hasarın tespit edilebilmesi için bina tez yürütücüsü tarafından yerinde incelenmiştir. Yapılan saha ziyareti sonucunda taşıyıcı sistem elemanlarında herhangi bir ciddi hasar gözlemlenmezken, yapısal olmayan elemanlarda ileri seviye hasar tespit edilmiştir. Bu yoğun hasarın açıklanabilmesi amacıyla çalışmanın devamında mevcut bina, zaman tanım alanında analiz yöntemi ile değerlendirilmiş olup analiz sonucunda binada oluşan hasar durumu ile saha ziyaretinde tespit edilen hasar durumunun birbiri ile tutarlı sonuçlar verdiği görülmüştür.
Çalışma kapsamında mevcut bina için önerilen güçlendirme modelinin uygulanması durumunda göreli kat ötelemesi oranının 1/150 (%0.67) değerini aşmayacağı gösterilmiştir; bu değer, Japonya'da bu türden güçlendirmelerde sıkça kabul gören bir tasarım hedefidir. Çalışma sonucunda güçlendirilmiş binanın göreli kat öteleme oranı azalmış ve taşıyıcı sistem elemanlarının depreme karşı performansının iyileştiği gözlemlenmiştir.

Abstract:
Some of the reinforced concrete (RC) building stock in Turkey does not meet the earthquake performance level specified in the current Turkish seismic code of TBDY-2018. Main reasons for this situation in Turkey are insufficient strength of structural materials used in building construction, poor workmanship, and lack of engineering services. Two widely accepted options are possible to make deficient buildings seismically reliable. These are demolition and reconstruction or retrofitting. Demolishing and rebuilding may not always be a good option when considering construction time, cost, and environmental impacts. Buildings that are suitable for retrofitting to make them earthquake-resistant could be a good option in terms of economy and environmental impact. There are many methods to be used in the retrofitting of buildings. The most commonly used method is conventional retrofitting, which involves adding a new RC element to the existing structure and increasing the size of the element (e.g. concrete jacketing). These methods would perform well especially in buildings with strength and stiffness issues. Apart from these, there are energy-dissipating systems that add stiffness and more importantly damping to the building, or only damping, reducing seismic demands. Retrofitting buildings with energy-dissipating systems is often less time-consuming than conventional retrofitting methods. With these systems, there is also less interference with building's architecture. Since architectural intervention would be minimized, it can be more economical than conventional retrofitting methods. Energy dissipating systems can be effectively used in schools, hospitals, industrial buildings, residences, bridges, data centers, historical buildings, and tall structures.
There are many types of energy-dissipating systems. The most commonly used ones are viscous, viscoelastic, friction type, metal yielding type, and tuned mass dampers. Some of these systems may require periodic maintenance after they are installed in the building. In the second part of the study, studies on metallic dampers and retrofitting with metallic dampers are overviewed. Widely used metallic dampers in previous studies vary in size, material properties, and configurations. In general, it was found that the shape, geometry, and material strength of the selected metallic damper, as well as the way the damper is connected to the existing building element, changes the reinforced concrete frame performance. Additionally, under seismic effects, force directions in metallic dampers may vary depending on the observed deformation shape in the damper. Nowadays, U-shaped dampers are used alone or in combination with rubber-type base isolation systems. In addition, some studies have investigated the effectiveness of configurations including U-shaped dampers between RC frames.
In this thesis, a retrofitting model with a U-shaped metallic damper and rigid steel members is proposed. U-shaped steel dampers are located above the rigid steel micro frame. The proposed retrofitting model is positioned between RC frame beams in subsequent floors. When using the proposed model in building retrofitting, only the infill wall in the part to be retrofitted is removed. Apart from this, no other architectural elements need interventing. Note that necessary precautions should be taken regarding mechanical and electrical elements before retrofitting. The U-shaped metallic damper is a relatively simple energy-dissipating device to manufacture compared to other alternative energy dissipators such as buckling restrained braces (BRBs), viscous dampers, or rubber isolators. In addition, the steel members and disc anchors used in the retrofitting model are very simple to manufacture and install. Due to these features, the proposed retrofitting system aims to be produced quickly and to retrofit many vulnerable buildings.
To better examine the performance of the proposed retrofitting model under earthquake loads, a residential building damaged (mostly architectural) by the February 6,2023 Kahramanmaraş earthquakes (Mw=7.9 and Mw=7.8) was taken as a case study. To determine the accuracy of the numerical model to be created, a site visit was made by the thesis advisor to observe damage to the existing building as a result of the earthquake. Major nonstructural damage was observed on the infill walls and architectural elements of the building. It was observed that the architectural damage was concentrated especially on the third, fourth, and fifth floors of the building. On the other hand, concrete cracks of medium sizes were observed in the structural system of the building that could have opened and closed during the earthquake, but no serious damage was observed. After reconstruction of the infill walls and repair of the minor damage to the structural system, the building may have been reused without any problem. Unfortunately during the writing of this thesis, an information regarding the demolition of the building has been received. After this stage, seismic performance of the existing building was evaluated with nonlinear time history analyses. TBDY-2018 was used in the assessment. In TBDY-2018, the earthquake acceleration records selected for evaluation and retrofitting are matched according to the period of the structure and analyzed. The earthquake records used in this study were taken from the earthquake stations close to the location of the building, and the earthquake records were directly impacted on the structure without matching to observe the structural damage caused by the real earthquake records in the numerical model.
As a result of the time domain analyses using real earthquake records, it was concluded that the damage distribution observed in the numerically modeled structure and the damage distribution observed as a result of the field visit were similar. The earthquake performance of the existing building's columns, beams, and shear wall elements under actual earthquake records was examined according to TBDY-2018. As a result of the analyses, it was determined that the existing structure met the controlled damage (CD) performance level.
To better improve the earthquake performance of the existing building and at the same time to reduce non-structural damage in future earthquakes, alternative retrofit schemes are suggested such as asymmetric partial retrofitting until the 6th story and complete asymmetric and symmetric retrofitting along the height of the building. Relative story drift ratios observed in the retrofitted building under earthquake effects are targeted to be 1/150 (%0.67) based on the Japanese Seismic Guideline (JBDPA, 2001). As a result of the analyses performed on the retrofitted building, the damage condition of the reinforced concrete columns, beams, and shear wall elements in the structure has improved.
Some of the studies on energy-dissipating systems include the reliable connection of these systems to existing elements. Cracks that will occur during the earthquake at the points where the retrofitting elements are connected to the structural system prevent the retrofitting component from operating at sufficient capacity, thus reducing the energy dissipated during the earthquake. In addition, the cracks formed to reduce the capacity of the existing structural elements. In this thesis, disc anchors were alternatively used for the connection of the U-shaped damper to the beam to minimize interference with the structure. The analyses and proposal details reveal that such retrofit application would be viable solution to be implemented in the seismically vulnerable substandard RC multi-story building stoch in mega cities of Turkey especially in Istanbul, Izmir, and Bursa.