Seismic retrofit of RC columns with sprayed basalt mesh reinforced GRC: Effects of stirrup spacing
Seismic retrofit of RC columns with sprayed basalt mesh reinforced GRC: Effects of stirrup spacing
Dosyalar
Tarih
2014
Yazarlar
Nasrinpour, Amin
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Deprem Mühendisliği ve Afet Yönetimi Enstitüsü
Institute of Earthquake Engineering and Disaster Management Sciences
Institute of Earthquake Engineering and Disaster Management Sciences
Özet
Türkiye dünyanın sismik yönden en aktif bölgelerinden birisidir. Can ve mal kaybına neden olan büyük magnitüdlü pek çok depreme maruz kalmıştır. Yakın dönemdeTürkiye de yaşanan depremler sonrasında çok sayıda betonarme bina hasar görmüştür. Mevcut yapı stokunun çok düşük beton basınç dayanımı, kolonlardaki yetersiz enine donatılar, etriyelerdeki detay zayıflıkları/yapım hataları ve bina kullanımının tasarımdaki amaca uygun olmaması gibi pek çok nedenlerle yetersiz deprem davranışına sahip olduğunu açığa çıkarmıştır. Birçok binada da mevcut haliyle hasar olduğu belirlenmiştir. Önceki yıllarda ABYYHY-1975 ve TS500-1984 yönetmeliklerine göre deprem esnasında yeterli davranışı göstermesi beklenen yapılar yeni tasarım yönetmelikleri olan DBYBHY-2007 ve TS500-2000 e göre yetersiz çıkmakta ve bu yapıların güçlendirilmesi gerekmektedir. Betonun sargılanması, yük taşıma kapasitesinin ve /veya sünekliğin arttırılması için kullanılan verimli bir yöntemdir. Kompozit güçlendirme sistemi betonarme elemanlara dıştan uygulanan bir güçlendirme sistemidir. Harici yapıştırmalı kompozit sistemler, yapı elemanlarının yük taşıma kapasitesini ve eğilme dayanımını artırır. Son 10 yıllık sürede pek çok araştırma, betonarme kolonlarda -sismik açıdan zayıf detaylandırılmış olanlar da dahil olmak üzere- TRMile sargılamanın gelecek vaat eden bir yöntem olduğunu göstermiştir. Bu çalışmayı diğer deneysel çalışmalardan ayıran yönü tekstilin karışım bileşeni olarak özel bir harçla (GRC) kullanımı ve özel uygulama (harcın tekstilin tamamını kaplayacak şekilde püskürtülmesi) tekniğidir. Bu kompozit malzeme Tekstille Güçlendirilmiş Harç (TRM) olarak bilinmekte ve çimento matrisinde reçine yerine cam liflerin bulunması daha yüksek modül sunmakta, bununla birlikte matris daha ucuz olan düşük modüllü tekstil kullanımına yol açmaktadır. bu malzemeler hafif, yüksek mukavemetli, liflerin dizilim yönleri değiştirilerek mukavemeti ayarlanabilen, beton ve çeliğin giremeyeceği yerlere girebilen, ince, uygulaması hızlı ve pratik, korozyona dayanıklı, uzun ömürlü yeni nesil malzemelerdir. Yeni bir malzeme ve dış donatı olarak TRM nin kullanımı yapı endüstrisi tarafından incelenmektedir. Bu çalışmada; zayıf ve iyi donatılmış betonarme kolonların sismik performansları ve aynı karakteristiklere sahip betonarme kolonlarda TRM nin eğilme davranışında ve enerji tüketme kabiliyetindeki etkileri deneysel olarak incelenmiş ve sonuçlar kolonların histeretik davranışlarını tahmin için önerilen modellerle teorik olarak karşılaştırılmıştır. Deneyler; dikdörtgen kesitli, sabit yüksek eksenel kuvvete sahip veçevrimsel yatay yüklemeye maruz 8 adet kolonda yürütülmüştür. Ek olarak, 4 adet kolon, kontrol numunesi olarak tasarlanmış ve diğerleri kontrol numuneleriyle aynı özelliklere sahip olmak üzere 3 kat Basalt Hasır Donatılı Püskürtme GRC (basalt textile reinforced mortar) ile sarılmış ve bütün tekstil katmanlarını kapatacak kadar cam lifli harç püskürtülmüştür. Numunelerde düşük dayanımlı beton ve düz donatı kullanılmıştır. Bütün kolonlarda paspayı 15 mm dir ve kolonların köşeleri 30 mmyarıçapında dairesel hale getirilmiştir. Etriyerler 60, 90, 120 ve 180 mm aralıklarlayerleştirilmiştir. Etriyelerin kanca açıları 90 derece ve kanca boyları 80 mm dir.Bu amaç doğrultusunda çalışmanın ilk bölümünde öncelikle çalışmanın amacı vekapsamı anlatılmıştır. Konunun devamında ilgili geçmişte yapılan çalışmalardan kronolojik sıraya göre bahsedilmiş, TRM malzeme ile güçlendirme yönteminin gelecekte çok sık kullanılacak bir yöntem olduğu vurgulanmıştır. İkinci bölümde, deney numunelerinin özellikleri, deney numunelerinin üretim aşamaları ve deney düzeneği açıklanmış, deneylerde kullanılan malzeme özellikleri belirtilmiştir. İç ve dıştan sargılanmış kolonların davranışı üçüncü bölümde analitik çalışma kapsamında sunulmuştur. Dördüncü bölümde, test sırasında gözlenmiş kolonların davranışı anlatılmıştır. Deney sonuçlarının detaylı şekilde anlatıldığı ve çeşitli grafikleri kullanarak sonuçları birbirile karşılaştırdığı beşinci bölümün sonrasında, altıncı bölümde deney sonuçları yorumlanmış ve değerlendirmeler anlatılmıştır. Teorik çalışmalar kapsamında elemanların yük kapasiteleri, yük-yerdeğiştirme (öteleme oranı) ilişkileri, hasar durumları ve deprem sırasında maruz kalacakları öteleme oranları tahmin edilmeye çalışılmıştır. Deney sonuçları dayanım, süneklik, enerji yutma kapasitesi, rijitlik, kalıcı deformasyonlar ve göçme modları bakımından değerlendirilmistir ve sonuçlar Basalt Hasır Donatılı Püskürtme GRC ile sargının ötelenme oranı ve çevrimsel deformasyon kapasitesi bakımından zayıf ve iyi detaylandırılmış kolonlarda çok etkili olduğunu göstermiştir.
For seismicityTurkey appears to be one of the most active regions on the earth exposed to large magnitude earthquakes, resulting in catastrophic consequences. Evaluating recent earthquakes in Turkey revealed that a remarkable number of existing buildings have poor seismic performance because of very low axial compressive strength of the concrete, inadequate lateral reinforcement in the columns, insufficient details in the stirrups or design/construction errors and change of the usage purpose of the facility. The existent buildings that are built using the old versions of Turkish Codes (i.e. ABYYHY 1975 and TS500-1984) which were expected to have sufficient performance under earthquake forces could not satisfy the seismic code requirements. As a result, the New Turkish Codes (i.e. DBYBHY 2007 and TS500-2000) took the fact that a lot of old buildings are not anyway acceptable into consideration as many requirements, so strengthening is required to improve the performance of the same structures to prevent from another disaster. All of mentioned reasons were caused New Turkish Seismic Code introduced a section to improve the performance of old structures to prevent disastrous consequences. To mitigate such risks, many retrofitting oriented studies on seismic behaviour substandard columns were conducted in last decades (Triantafillou et al 2006, Ludovico et al. 2008, Ilki et al. 2008, Bousias et al. 2009, Ilki et al. 2009, Sezen and Miller 2011 and Colajanni et al. 2014). Confinement of concrete is an efficient technique used to increase the load carrying capacity and/or ductility of a column and lateral pressure in the concrete case. Interpreting the results of the large amount of research made in the last decade on TRM jacketing as additional confinement, this method of structural confinement is highly successful and efficient for columns, including the ones, which are poorly detailed located in seismic regions. The two elements making this research unique is the usage of Basalt textile with special mortars (GRC) as a mix component and applying to system by a special method (spraying the mortar until covering all textile) which is a composite material known as Textile Reinforced Mortar (TRM). A new technique for the use of lower modulus textile is offered due to the existence of Glass fibers in the cement matrix (instead of resin) which is less expensive. The construction industry started to use Textile Reinforced Mortar (TRM) reinforcement currently, experimenting and exploring the material for further use. In the experimental process, seismic performance of poor and well detailed RC columns and effectiveness of TRM for improving flexural behavior and energy dissipation capacity of the same characteristic reinforced concrete columns are experimentally investigated and compared with theoretical models which are used to estimate the hysteretic behavior of columns. The test specimens were cantilever typecolumns, representing half a column in a real building frame. A total of eight rectangular columns of dimensions 300 x 200 x 1500 mm along with a stub of dimensions 700 x 700 x 450 mm were constructed. All columns are reinforced with four longitudinal bars Ф14 placed symmetrically as longitudinal reinforcement. The transverse steel reinforcement was given by stirrups Ф8. All specimens were subjected to cyclic lateral and constant high-axial loads. At the specimen designing phase, columns were expected to fail in flexural behavior before reaching their shear strength. In addition, four of the columns were designed as reference group and others, which had the same characteristics, were confined by three layers of Basalt mesh sprayed with Glass Fiber Reinforced Concrete until covering all textile layers. Characteristics of the specimens are low strength concrete with plain longitudinal reinforcement bar. Corners of all columns were rounded about 30 mm and clear cover thickness of columns were 15 mm. Transverse reinforcement bars with hook angles of 90° and hook length of 80 mm at both ends were examined. Stirrups were placed at a variable spacing of 60 mm, 90 mm, 120 mm and 180 mm. For this purpose, primarily in the first chapter of the thesis, purpose and scope of the study was explained. In continuation of the work done in the past about the subject, a summuraised literature review was mentioned and TRM composites as a significant retrofitting method in the future are emphasized. In the second chapter, properties of the test specimens, material properties, manufacturing steps of the test specimens and experimental setup are indicated. A summuraised analytical study at the third chapter of thesis discusses about internal and external confinement in columns. The forth chapter describes the behavior of columns that was observed during the test. Into the fifth chapter, a variety of experimental and theoritical results are described in detail and are compared by using graphics. At the end, the sixth chapter discusses conclusions and reccommondations related with thesis. Experimental results indicated that Basalt mesh jacketing, especially with sprayed GRC is quite effective as it increases the drift ratio and cyclic deformation capacity of poor and well detailed RC columns causing more energy dissipation.
For seismicityTurkey appears to be one of the most active regions on the earth exposed to large magnitude earthquakes, resulting in catastrophic consequences. Evaluating recent earthquakes in Turkey revealed that a remarkable number of existing buildings have poor seismic performance because of very low axial compressive strength of the concrete, inadequate lateral reinforcement in the columns, insufficient details in the stirrups or design/construction errors and change of the usage purpose of the facility. The existent buildings that are built using the old versions of Turkish Codes (i.e. ABYYHY 1975 and TS500-1984) which were expected to have sufficient performance under earthquake forces could not satisfy the seismic code requirements. As a result, the New Turkish Codes (i.e. DBYBHY 2007 and TS500-2000) took the fact that a lot of old buildings are not anyway acceptable into consideration as many requirements, so strengthening is required to improve the performance of the same structures to prevent from another disaster. All of mentioned reasons were caused New Turkish Seismic Code introduced a section to improve the performance of old structures to prevent disastrous consequences. To mitigate such risks, many retrofitting oriented studies on seismic behaviour substandard columns were conducted in last decades (Triantafillou et al 2006, Ludovico et al. 2008, Ilki et al. 2008, Bousias et al. 2009, Ilki et al. 2009, Sezen and Miller 2011 and Colajanni et al. 2014). Confinement of concrete is an efficient technique used to increase the load carrying capacity and/or ductility of a column and lateral pressure in the concrete case. Interpreting the results of the large amount of research made in the last decade on TRM jacketing as additional confinement, this method of structural confinement is highly successful and efficient for columns, including the ones, which are poorly detailed located in seismic regions. The two elements making this research unique is the usage of Basalt textile with special mortars (GRC) as a mix component and applying to system by a special method (spraying the mortar until covering all textile) which is a composite material known as Textile Reinforced Mortar (TRM). A new technique for the use of lower modulus textile is offered due to the existence of Glass fibers in the cement matrix (instead of resin) which is less expensive. The construction industry started to use Textile Reinforced Mortar (TRM) reinforcement currently, experimenting and exploring the material for further use. In the experimental process, seismic performance of poor and well detailed RC columns and effectiveness of TRM for improving flexural behavior and energy dissipation capacity of the same characteristic reinforced concrete columns are experimentally investigated and compared with theoretical models which are used to estimate the hysteretic behavior of columns. The test specimens were cantilever typecolumns, representing half a column in a real building frame. A total of eight rectangular columns of dimensions 300 x 200 x 1500 mm along with a stub of dimensions 700 x 700 x 450 mm were constructed. All columns are reinforced with four longitudinal bars Ф14 placed symmetrically as longitudinal reinforcement. The transverse steel reinforcement was given by stirrups Ф8. All specimens were subjected to cyclic lateral and constant high-axial loads. At the specimen designing phase, columns were expected to fail in flexural behavior before reaching their shear strength. In addition, four of the columns were designed as reference group and others, which had the same characteristics, were confined by three layers of Basalt mesh sprayed with Glass Fiber Reinforced Concrete until covering all textile layers. Characteristics of the specimens are low strength concrete with plain longitudinal reinforcement bar. Corners of all columns were rounded about 30 mm and clear cover thickness of columns were 15 mm. Transverse reinforcement bars with hook angles of 90° and hook length of 80 mm at both ends were examined. Stirrups were placed at a variable spacing of 60 mm, 90 mm, 120 mm and 180 mm. For this purpose, primarily in the first chapter of the thesis, purpose and scope of the study was explained. In continuation of the work done in the past about the subject, a summuraised literature review was mentioned and TRM composites as a significant retrofitting method in the future are emphasized. In the second chapter, properties of the test specimens, material properties, manufacturing steps of the test specimens and experimental setup are indicated. A summuraised analytical study at the third chapter of thesis discusses about internal and external confinement in columns. The forth chapter describes the behavior of columns that was observed during the test. Into the fifth chapter, a variety of experimental and theoritical results are described in detail and are compared by using graphics. At the end, the sixth chapter discusses conclusions and reccommondations related with thesis. Experimental results indicated that Basalt mesh jacketing, especially with sprayed GRC is quite effective as it increases the drift ratio and cyclic deformation capacity of poor and well detailed RC columns causing more energy dissipation.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014
Anahtar kelimeler
Sütunlar,
Betonarme yapı,
Yapısal tasarım,
Standartlar,
Deprem dayanıklılık tasarımı,
Yapılar,
Betonarme,
Deprem etkileri,
Columns,
Reinforced concrete construction,
Buildings,
Specifications,
Structural design,
Standards,
Earthquake resistant design,
Buildings,
Reinforced concrete,
Earthquake effects