Search

Many of the existing reinforced concrete (RC) structures in Turkey built prior to 1999 have deficient design details due to their non-seismic design or construction flaws. In particular, the beam-column joints (BCJs) experience high shear forces during such events, mainly due to inadequate design detailing of transverse reinforcements as well as inadequate lap splicing. Severe damage or total collapse of structures often occurred. To enhance the performance of such deficient joint systems, several strengthening techniques such as reinforced concrete and steel jacketing, as well as fiber-reinforced polymer (FRP) wrapping, have been proposed. In this study, new shear strengthening techniques were developed using carbon-fiber-reinforced polymer (CFRP) to retrofit these insufficient BCJs. The effectiveness of various CFRP wrapping methoclologies was investigated experimentally. One control specimen was constructed according to provisions specified by the 1975 Turkish Building Design Code, whereas four other specimens were constructed with deficiencies observed in the practice. Moreover; three additional specimens were constructed to develop alternative shear strengthening techniques via CFRP wrapping. The quasi-static tests were carried out by applying constant axial load and reversed-cyclic lateral load at the top of the column. Comparative analysis of control and CFRP-strengthened specimens' results showed that significant improvements in the lateral load and the energy dissipation capacities were achieved by using the proposed CFRP-strengthening techniques.

The research presented in this study involves full-scale experimental evaluation of carbon fiber-reinforced polymer (CFRP) rehabilitation for existing beam-column joints designed for gravity load with common pre-1970s deficient reinforcement details when subjected to cyclic loading. Numerous studies have demonstrated effectiveness of externally bonded fiber-reinforced polymer (FRP) materials for retrofitting the deteriorating RC structures. Although these materials are widely used in bridges, their applications in buildings have been somewhat limited. In particular, the experimental investigations on external FRP retrofit of deficient beam-column joints have not thoroughly been investigated and they are mainly on scaled-down specimens. The failure of these subassemblies, which possess lack of shear reinforcement within the joint core and shortly embedded positive beam reinforcement, would possibly result in catastrophic collapse of reinforced concrete frame structure during an earthquake event. Recognizing the urgent need to upgrade these structural subassemblies, the current investigation uses CFRP retrofit techniques to enhance the performance of such deficient joints. Experimental variables studied entail the developed CFRP retrofit configurations, and magnitude of the applied column axial load. Comparative analysis of the lateral loads versus drift hysteresis loops, stiffness degradation, and total dissipated energy curves of three as-built and three corresponding CFRP-retrofitted RC joints revealed that significant improvement in the shear capacity of the upgraded joints occurred. More importantly, the slippage of short embedded beam positive reinforcement into the joint was substantially controlled due to the developed CFRP retrofit. The results demonstrate the effectiveness of CFRP retrofit configurations in enhancing the structural performance of actual size connections.

Amerika Birleşik Devletleri'nde, 1970 öncesinde yapılan betonarme binalar incelendiğinde, kolon?kiriş birleşim noktalarının deprem etkisi altında en kritik bölgeler olduğu gözlenmiştir. Kolon etriyelerinin geniş aralıklarla yerleştirilmesi, kolon-kiriş birleşim bölgesinde etriye bulunmaması, kolon donatısı bindirme boyunun kısa olması ve kiriş donatılarının yetersiz ankraj edilmesi, birleşim noktalarındaki ortak detaylandırma hatalarıdır. Bu araştırma, döşeme ve yükleme yönüne dik yönde yer alan kirişlerin etkisi altında, belirtilen birleşim noktalarının davranışını incelemektedir. Bu yetersizliklere sahip birleşim noktaları için, CFRP ile sargılama teknikleri geliştirilmektedir.CFRP sargılama ile güçlendirmenin, kolon-kiriş birleşim noktası davranışına etkisi, dört, 2/3 oranlı, betonarme kolon-kiriş birleşim noktası numunesi üretilip, sabit eksenel yük altında, tersinir yatay kuvvetler ile test edilerek incelenmiştir. Bu numunelerden üçü, döşeme ve yükleme yönüne dik yönde yer alan kirişlere sahipken, biri sadece yükleme yönüne dik yönde yer alan kirişlere sahiptir. Döşemesiz numune ve döşemeli numunelerden biri kontrol numunesi olarak, CFRP uygulanmadan test edilmiş, kalan iki numune ise, CFRP ile güçlendirildikten sonra test edilmişlerdir.Deneysel sonuçlar göstermiştir ki, kesme ve burulma kuvvetleri altındaki deformasyonlar, özellikle döşemeli numunelerde oldukça kritik seviyelerdedir. Yetersiz ankraj edilmiş kiriş donatılarının sıyrılması, kontrol numunelerinde gözlenen bir diğer önemli sorundur. CFRP ile güçlendirilmiş numuneler, taşıma gücü bakımından oldukça üstün bir performans sergilemişlerdir. Kiriş donatılarındaki sıyrılma problemi başarıyla çözülmüş, kirişler ve kolonlar sarılarak, kesme ve burulma dayanımları arttırılmıştır. Güçlendirilmiş numunelerin enerji sönümleme kapasitelerinde de artış gözlenmiştir. Under seismic action, the most critical part of R/C structures, which were built in the United States before 1970, is beam-column joints. Common deficiencies of these joints could be summarized as; widely spaced column ties, no transverse reinforcement in joint region, inadequate lap splicing in column and insufficient embedment length of positive beam reinforcement in the joint. This research investigates the actual behavior of such joints with an inclusion of transverse beams and a floor slab. Moreover, CFRP wrapping methodologies are developed to improve the seismic behavior of such deficient joints.In order to investigate the effect of CFRP retrofitting on the behavior of exterior beam-column joints, four 2/3-scaled reinforced concrete beam-column subassemblies were produced and tested under constant axial load and reversed cyclic loading. Three of the specimens had floor slabs and one specimen had only transverse beams (without the slab). The specimen that had no floor slab and one of the other specimens with floor slab were tested as control specimens without the CFRP application. The remaining two specimens with floor slabs were retrofitted with CFRP sheets and then tested.Experimental results demonstrated that torsional cracks on the transverse beams and shear deformations within the joint core turned out to be critical especially when the floor slab was included. Slippage of the positive beam reinforcement in the joint region was another significant deficiency observed in the control specimens. CFRP retrofitted specimens exhibited superior behavior in terms of load carrying capacities. Slippage of the positive beam reinforcement was successfully prevented. Beams and columns were also confined by CFRP sheets and their performance was enhanced in terms of shear and torsional strength. 158

Sismik yetersizliği bulunan döşemeli ve döşemesiz betonarme köşe birleşimlerin sismik etki altındaki davranışının belirlenmesi ve uygun bir güçlendirme tekniğinin geliştirilmesi üzerine yapılan bir deneysel çalışmadır. Bu çalışma kapsamında 1970 öncesi Amerikan kodlarına gore dizayn edilmiş 4 adet 2/3 ölçekli numune test edilmiştir. Numuneler deprem yönetmeliklerinden önce inşa edilen yapılarda bulunan sünek olmayan detaylandırma karakteristiklerini simule edebilecek şekilde dizayn edilmişlerdir. Bu nedenle bazı tipik detaylandırma yetersizliklerini bulundurmaktadırlar; 1) birleşim bölgesinin hemen üstünde kolon donatısında bindirmeli ekler, 2) aralıkları geniş kolon etriyeleri, 3) etriyesiz kolon-kiriş birleşim bölgesi, ve 4) kolona yeteri boyda ankrajlanmamış süreksiz kiriş alt donatısı. Döşemeli betonarme köşe birleşimlerindeki bu yetersizliklerin aşılarak numunelerin güçlendirilmesi amacıyla muhtemel mafsallaşma bölgelerine CFRP sarılmıştır. Numuneler sabit 700 kN eksenel yük (kolon eksenel yük kapasitesinin %30'u) altında, tersinir tekrarlı periyodik yanal yüklere tabi tutularak, test edilmiştirDeney sonuçlarına göre, yukarıda belirtilen yetersizliklere sahip betonarme köşe birleşimleri mesnetteki aşırı kesme etkisi ve kiriş alt donatılarının sıyrılması nedenleriyle gevrek çökmelere maruz kalmışlardır. Bu çalışma kapsamında test edilen güçlendirme teknikleri, gevrek davranışı geciktirmeyi ve sınırlandırmayı başarmıştır. CFRP uygulaması aynı zamanda numunelerin yatay yük-kat ötelenmesi davranışını, enerji sönümleyebilme potansiyellerini ve rijitlik kaybı karakteristiklerini geliştirmiştir. An experimental study was conducted on seismically deficient RC corner connections with and without floor slab in order to examine the behavior under seismic action and to develop proper strengthening techniques. Four 2/3 scale specimens were tested which were designed according to pre 1970?s USA design codes. The specimens were designed to simulate non-ductile detailing characteristics of pre-seismic codes construction. Therefore, they contained some typical detailing deficiencies; 1) lapped splices of column reinforcement just above the joint region, 2) widely spaced column ties, 3) no transverse reinforcement within the beam-column joint, and 4) discontinuous positive beam reinforcement with a short embedment length into the column. Carbon fiber reinforced polymers (CFRP), which were placed around potential hinging zones, were used to strengthen the specimens with floor slab in order to overcome these deficiencies. The specimens were tested under constant axial load, with a magnitude of 700 kN (30% of axial load capacity of the column), and reversed cyclic lateral load.The test results showed that RC corner connections with above mentioned deficiencies were subjected to the brittle joint shear and bond-slip failures under seismic action. The tested strengthening techniques were successful in delaying and limiting the joint shear and bond-slip failures. CFRP application also improved lateral load versus drift response, energy dissipation potential and stiffness degradation characteristics of deficient subassemblies. 145