TBDY 2018'e göre sismik yalıtımlı yapının tasarlanması
Design of seismic isolated structure according to TBDY 2018
Yazar: MURAT YALÇIN ALBAŞ
Danışman: DR. ÖĞR. ÜYESİ PINAR ÖZDEMİR ÇAĞLAYAN
İstanbul Teknik Üniversitesi / Deprem Mühendisliği ve Afet Yönetimi Enstitüsü / Deprem Mühendisliği Ana Bilim Dalı / Deprem Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Deprem Mühendisliği = Earthquake Engineering

Özet:
Türkiye Alp-Himalaya deprem kuşağında yer almaktadır ve ülkemizin yüz ölçümünün neredeyse yarısı birinci derece deprem kuşağındadır. Ayrıca ülkemizdeki nüfusun yarısından fazlası aktif deprem fayları üzerinde kurulan şehirlerde yaşamaktadır. Bu sebeplerden dolayı ülkemizde depreme dayanıklı yapı tasarımı konusu oldukça önemlidir. 

Ülkemizdeki olan büyük depremler araştırıldığında, bu depremler sonucu çok sayıda can ve mal kaybı yaşandığı, yapıların büyük hasar aldığı ve çoğunun depremden sonra kullanılamaz hale geldiği görülmüştür. Depremlerin sebep olduğu can ve mal kayıplarını, göçen veya kullanılamaz hale gelen yapıların sayısını en aza indirebilmek için yapıların depreme dayanıklı şekilde tasarlanması çok önemlidir.

Depreme dayanıklı yapı tasarımında birçok yöntem vardır ve bunların en etkili sonuç verenlerinden birisi de sismik izolasyon yöntemidir. Sismik izolasyon yönteminde temel amaç yapı ile yapının oturduğu zemin arasına sismik yalıtım birimleri yerleştirip yapının periyodunu arttırarak, deprem etkisinden dolayı yapıya etkiyen kuvvetleri en aza indirmektir.

Bu tez çalışmasında sismik izolasyonun tarihçesi, sismik izolasyon tekniği ile inşa edilen yapılar, sismik izolasyon tekniğinin teorik esasları, günümüzde kullanılan yalıtım birimi çeşitleri ve izolatörlerin mekanik özelliklerinden bahsedilip, örnek bir uygulama yapılmıştır.

Örnek uygulamada sismik izolasyonun yapı üzerindeki etkilerini göstermek amacıyla 4 katlı konut binasının inşa edileceği yer belirlenmiş ve bu yere göre AFAD veri tabanından elde edilen spektral veriler kullanılarak tasarımda kullanılacak olan yatay elastik tasarım spektrumları oluşturulmuştur. Bir sonraki adımda ise bölgede daha önce gerçekleşmiş olan bir depremin parametreleri (faya uzaklık, kaynak mekanizması vs.) kullanılarak 11 adet deprem kaydı PEER veri tabanı vasıtasıyla seçilmiştir. Daha sonra sabit temelli modelin titreşim analizi yapılarak yapı hâkim periyodu elde edilmiştir. Yapıda kullanılacak kurşun çekirdekli kauçuk yalıtım biriminin ön tasarımı yapılarak, modellemede kullanılacak yalıtım birimi parametreleri elde edilmiş ve modeller bu veriler ışığında oluşturulmuştur. Ardından yalıtımlı modellerin modal analizi yapılarak yapı hâkim periyotları belirlenmiştir. Yapı hâkim periyotları kullanılarak uygun genlik aralıklarında seçilen deprem kayıtları ölçeklenmiş olup, ölçek çarpanları her iki doğrultuda aynı olacak şekilde kayıtlara etkitilmiştir. Son olarak tüm modellerin zaman tanım alanında doğrusal olmayan yöntem kullanılarak dinamik analizi yapılmış ve elde edilen sonuçlar grafikler üzerinden karşılaştırılmıştır.

Çalışma sonucunda elde edilen sonuçlar göstermiştir ki sismik yalıtım uygulaması yapıya etki eden kuvvetleri, ivmeleri ve yapı deplasmanlarını olumlu yönde etkilemiştir. Ayrıca depreme dayanıklı yapı tasarımında sismik yalıtım birimlerinin kullanılabileceği anlaşılmıştır.

Abstract:
Turkey is located in Alpine-Himalayan seismic belt and almost half of our country's acreage is in the first degree seismic zone. Also, half of the population in our country live in cities which are built on active fault lines. Therefore, earthquake resistant structural design is a significant matter in our country. Earthquake which is one of the major disasters for our country, inflicts heavy damage on the structure, even causes them to collapse, because of the fault lines breaking and Ashifting shape on the ground levels. When constructional engineering is carried out by ignoring regulations and structures are built with only visual and aesthetic concerns, earthquake forces cause major disasters on buildings.

 When we dive into some of the biggest earthquakes in our country, we see significant amounts of life and property loss, major damages on buildings and most of them are uninhabitable post-earthquake. In order to minimize the number of life and property losses and collapsed or inhabitable buildings caused by earthquakes, it is critical to design earthquake resistant structures.
 
 There are various methods in earthquake resistant structural design and one of the most effective methods is the seismic isolation. The main goal in the seismic isolation method is minimizing the earthquake forces impacting the structure by placing seismic insulation units between the structure and the ground which the structure is on which will lead to increasing the structure period. One of the advantages of the seismic insulation units use is that this system decreases the frequency of the structure. The building which has less frequency is now able to relatively move as a rigid body pipe. Which means that the movements caused by the earthquake force happens within the insulation system levels. Another benefit of the insulation systems is that the accelerations on the structure caused by the earthquake are reduced. As the accelerations on the structure are reduced, so are the shear force on the structure. Also, axial forces are reduced on the structure which means that on the designing phase, upper structures can now be built by smaller pillars and beams which are beneficial in terms of architectural purposes.
 
 In this thesis study, the history, structures which are built by seismic isolation method, the theoretical facts of seismic isolation, the types of insulation units and the mechanical features of the isolators are touched upon, also a model practise made in accordance with the Turkey Building Earthquake Code (TBEC) 2018. As the practise is carried out, lead rubber bearing was used as the insulation unit. The reason why this type of a unit was used is; it shows a rigid behavior under the vertical load, it shows a very flexible behavior under the horizontal loads and also there is no need for an additional system in the structure for damping.
 
 In the model practise, in order to showcase the seismic isolation's effects on the structure, a location where a four-storey residence building is planned to be built was determined. And horizontal elastic design spectrums were formed which are to be used in the building phase. These spectrums were formed by using the spectral data taken from the Disaster and Emergency Management Presidency (AFAD) database. In the next step, by using the parameters (how far it is to the fault line, source mechanism, etc.) of an earthquake that happened before in the district, 11 earthquake records were picked by using the PEER database. The pre-designing of the lead rubber bearing which is going to be used in the structure was made. Then, the insulation parameters which are planned to be used in the model were obtained and the models were formed within the light of these data. When the pre-designing of the insulation unit was being made, these steps were followed respectively: Firstly, the parameters of the rubber were found such as the shear modulus of the rubber, the rubber hardness value and the yield strength and via the pack program, the total weight was obtained. Later on, respectively, the lead core diameter, the lead core total space, the insulation unit characteristic strength, total rubber space, insulation system active section rigidity, lower and upper limit values according to the Turkey Building Earthquake Code (TBEC) 2018, insulation system characteristic strength and rigidity multiplied with the lower and upper values, insulation unit active rigidity, insulation unit active period, active damping percentage and damping scaling factor, calculating the biggest movement in the insulation system level, and the insulation level vertical rigidity were calculated step by step. The values found the result of these calculations were used and in accordance with the regulations the shape-shifting limits of the insulation unit and its vertical stability was checked to see if it is suitable.
 
After that, the modal analysis of the insulated models was completed and their predominant periods were determined. By using the predominant periods, earthquake records were scaled within the suitable amplitude margins and the scale factors were influenced on the records as the same in both directions. Finally, the dynamic analysis of all models was completed by using a non-linear method in the time history area and the results were compared on graphics.  

As a result, it was found that the predominant period of a structure with a stable foundation is 0,43 seconds, and in an insulated structure for the earthquake ground motion-1, it is 1,88 seconds and for earthquake ground motion-2, it is 1,38 seconds. When the insulation unit design is being carried out, the results gained are very close to the aimed period values. 

When the story shifts in the structure are viewed, the biggest shifts are in the insulation levels in an insulated structure and in the insulation system a significant increase in the story shifts was observed because of the isolators.

When the inter-story drifts are compared, in the seismic insulated models, the story drifts are very close to each other and it moves like a rigid pipe, but in the models with no insulation, these drifts are not spread homogeneously.

When we take a look at the accelerations on the stories the accelerations impacting the isolated structure are less than the stable foundation structure and the biggest acceleration value is on the isolation level. This can be seen clearly on the acceleration value chart. The structure in which the lead rubber beared insulation unit was placed, the acceleration reaching to the top earthquake ground motion-1 percentage is approximately decreased by 77\%, and for the earthquake ground motion-2 it was decreased by 79\%. 

If we view the structure in terms of the shear force which impacts the stories, the shear force on the ground floor was decreased in the isolated structure compared to the stable foundationed structure. For earthquake ground motion-2 it is 43\%, and for earthquake ground motion-1 it was decreased by 58\%.

The results that are found by the study illustrates that seismic insulation affects the forces on the structure, accelerations and the structure displacements positively. It is also understood that the seismic insulation units can be used in the earthquake resistant structural designs. Our country is built on active fault lines which means in order to prevent the structural damages and collapses caused by earthquakes, it can be told by this thesis that seismic insulation units are remarkably beneficial.