HPFRCC for retrofitting of reinforced concrete members built with low-strength concrete

Bu çalışmada; düşük dayanımlı betonarme elemanların deprem yükleri altında davranışlarını iyileştirmek amacı ile kullanılabilecek bir malzeme geliştirilmesi hedeflenmiştir. Bu amaç için farklı özelliklerde Yüksek Performanslı Lif Donatılı Çimento Esaslı Kompozit (HPFRCC) numunelerin mekanik davranışı araştırılmıştır. Betonarme elemanların bu malzeme ile üretilecek ve kalınlıkları 20-50 mm arasında olması düşünülen ön üretimli HPFRCC ince plakların elamanların yüzeyine epoksi ve mekanik ankrajlar yardımıyla monte edilmesi ile güçlendirilmesi hedeflenmektedir. Bu plakaların mekanik özelliklerinin özellikle çekme dayanımlarının güçlendirilmesi düşünülen düşük dayanımlı panellere göre çok daha iyi olmasından dolayı güçlendirmede kullanılabileceği düşünülmüştür. Malzemenin mekanik özelliklerini geliştirmek amacı ile çeşitli parametrelerin etkilerinin incelendiği 27 adet standart silindir basınç (150×300 mm), 54 adet standart disk yarma-çekme (150×60 mm) ve 9 adet kiriş eğilme deneylerini (100×100×500 mm) kapsayan bir çalışma gerçekleştirilmiştir. Standart silindir ve standart disk yarma-çekme deneyleri sonuçları sıcak kürün çekme dayanımını arttırdığını göstermiştir. Liflerin az miktarda korozyona uğratılmasının mekanik özelikleri pratik olarak etkilemediği görülmüştür. Çelik lif oranının artışı çekme dayanımı, süneklik ve tokluk gibi mekanik özelikleri olumlu yönde etkilemesine karşın basınç dayanımı ve elastisite modülü gibi mekanik özelikleri pratik olarak etkilemediği görülmüştür. Eğilme deneyleri sonucunda çelik lif oranının % 4’e çıkması ile lifsiz numuneye göre tokluğunun çok büyük oranlarda ve net eğilme dayanımının yaklaşık altı kat arttığı görülmüştür. Anahtar Kelimeler: Betonarme, çelik lif, düşük dayanımlı beton, güçlendirme, HPFRCC.Improvements in concrete technology enabled engineers to produce special concretes with high strengths. However, as known high strength concrete exhibits a very brittle behavior. Many researchers have tried to change this brittle failure mode to a ductile type failure by adding various types of fibers in to the concrete. Consequently, different types of concrete with fibers were developed such as Fiber Reinforced Cementitious Composites (FRCC), Fiber Reinforced Concrete (FRC), Ductile Fiber Reinforced Cementitious Composites (DFRCC), High Performance Fiber Reinforced Cementitious Composites (HPFRCC) etc. Many researches on this topic have showed that fibers increased the ductility and energy dissipation capacity of the concrete members. In this research; the main goal is to develop a material that can be used to improve the behavior of reinforced concrete members built with low-strength concrete (f´c 10 MPa, in which f´c is the compressive strength of the concrete) under seismic loads. HPFRCC may be used for this purpose. The main idea is to produce precast thin panels made of HPFRCC and retrofitting reinforced concrete members by attaching these panels to the surface of the reinforced concrete members. It is clear that as the mechanical properties of the HPFRCC improve, the effectiveness of HPFRCC panels in retrofitting will also increase. In order to investigate the mechanical characteristics of the HPFRCC, two series of experimental studies were carried out. The first series of tests included compression tests of 27 standard cylinder specimens and tension tests of 54 standard splitting disc specimens. For compression tests nine sets and for each set three identical cylinder specimens were produced. For tension tests six standard splitting disc specimens were produced for each of nine sets. The diameter of cylinder is 150 mm and height is 300 mm. The diameter and height of the standard splitting discs are 150 and 60 mm, respectively. In the tests of the first series, the testing parameters included hot water curing, decomposition of steel fibers before adding them into mixture, corrosion and the amount of steel fibers. Second series of tests included flexural tests of beams with dimensions of 100×100×500 mm. The only parameter in beam tests is the amount of steel fibers. Three different mixtures and for each mixture there identical beams were produced. Compression tests of standard cylinder specimens were carried out either under static monotonic or cyclic axial compression loads by using Amsler machine with 5000 kN loading capacity. Two linear displacement transducers were used to measure axial deformations. To determine the elastic modulus, the specimens were subjected to one loading and unloading cycle in the linear range of the stress-strain curve before the full test and then elastic modulus was obtained from the slope of the linear best-fit line. During loading and unloading cycle axial deformations were measured both in the full length (300 mm) and in 150 mm at midheight of the specimens. For the tests of standard disc specimens a 1000 kN capacity Amsler machine was used. For the beam tests 100 kN capacity Instron 5500R machine was used. Fracture energy, bending strength and toughness of the specimens were obtained from load-displacement curves. Three point loading tests were carried out for beams and loading rates were 0.05 mm/minute and 0.1 mm/minute for the ascending and descending branch of load-displacement curves, respectively. The displacements were measured at the middle point of the beams. In the tests of specimens without steel fibers the loading rate was 0.0175 mm/minute during the entire test. The maximum target displacement was 10 mm, which corresponded to 2.5% drift ratio for specimens with steel fibers. For the tests of specimens without steel fibers, there was no maximum target displacement since the behavior was very brittle. The brittle failures occurred around 0.03% drift ratio. As results of the compression and splitting tension tests, the hot water curing was found to increase the tensile strength of concrete significantly. It was also found that small amount of the corrosion of steel fibers have no effect on the mechanical characteristics. It was clearly seen that as the amount of steel fibers increased, the mechanical properties such as tensile strength, toughness and ductility also increased while compressive strength and elastic modulus did not change. Results of beam tests showed that the bending strength and toughness increased significantly with increasing amount of steel fibers. Keywords: HPFRCC, low strength concrete, reinforced concrete, retrofitting, steel fibers

AFRP retrofit of reinforced concrete columns against impact loading

Structures can be exposed to impact loads as a result of an explosion, falling objects, projectiles and vehicle collisions. Within the increasing threat of these impact sources, it is very important to protect the columns that are the vital members of the structural systems to ensure structural and personal safety. This study focuses on the performance of axially loaded reinforced concrete members subjected to impact loading. A dropped-weight test set-up developed to perform impact tests on reinforced concrete members. The test set-up was used to perform low elevation impact tests on reinforced concrete (RC) columns that targets to simulate vehicular impact against ground floor columns of low-rise buildings. Since, there is limited information about the transverse impact performances of RC columns; the main objective of this research is to assess the vulnerability of RC columns under transverse impact loads and to enhance their performances by using Aramid Fiber Reinforced Polymer (AFRP) sheets. The scope is limited to 300 mm square columns with 3 m height in low to medium rise buildings which were found to be more vulnerable to lateral impacts according to previous research conducted by the authors, (Gurbuz et al. 2010, 2011). This research provides fundamental knowledge on the behavior of RC columns under low elevation impact loading and also generates new information on impact strengthening of vulnerable concrete columns by AFRP sheets

The modified post-earthquake damage assessment methodology for TCIP (TCIP-DAM-2020)

Chapter 5Post-Earthquake damage assessment has always been one of the major challenges that both engineers and authorities face after disastrous earthquakes all around the world. Considering the number of buildings in need of inspection and the insufficient number of qualified inspectors, the availability of a thorough, quantitative and rapidly applicable damage assessment methodology is vitally important after such events. At the beginning of the new millennia, an assessment system satisfying these needs was developed for the Turkish Catastrophe Insurance Pool (TCIP, known as DASK in Turkey) to evaluate the damages in reinforced concrete (RC) and masonry structures. Since its enforcement, this assessment method has been successfully used after several earthquakes that took place in Turkey, such as 2011 Van Earthquake, 2011 Kutahya Earthquake, 2019 Istanbul Earthquake and 2020 Elazig Earthquake to decide the future of damaged structures to be either ‘repaired’ or ‘demolished’.Scopus - Affiliation ID: 6010507

Investigations and Researches Related to the Restoration of Şah Sultan Mosque

Eyüp İlçesi’nde Bahariye Mevkii, Haliç kıyısında yer alan Şah Sultan Camii, Yavuz Selim’in kızı Şah Sultan tarafından H.963/M.1555’de yaptırılmıştır. Geniş programlı bir külliyenin parçası olan cami, zaman içerisinde değişikliklere uğramış, 18. yüzyılın sonlarında ve 1835 yılında II. Mahmud döneminde onarılarak 16. yüzyıldaki görünümünü kaybetmiştir. Külliyeyi oluşturan diğer yapıların büyük bölümü bu süreçte iz bırakmadan ortadan kalkmıştır. Şah Sultan Camii günümüzde yaklaşık 16.50x13.70m boyutlarında harim ve giriş bölümünde yer alan ahşap son cemaat yeri ile kıble yönünde bulunan 1812 tarihli türbeden ibarettir. 1953 ve 1971 yıllarında yapıyı özgün durumundan epeyce uzaklaştıran iki restorasyon geçiren yapı, 2013 yılında yeniden restorasyon kapsamına alınmıştır. Bu makalede restorasyon uygulaması öncesinde gerçekleştirilmekte olan yapısal analizleri ve bu analizlere bağlı olarak belirlenen müdahale önerilerini ele almaktadır

Flexural retrofit of support regions of reinforced concrete beams with anchored FRP ropes under reversed cyclic loading

Many studies have been conducted for enhancing the positive moment capacity of the mid-span areas of reinforced concrete (RC) beams strengthened with fiber reinforced polymer (FRP) reinforcement under monotonic increasing loads. However under seismic actions, the support regions of beams may also require retrofitting. In such cases, retrofitting should be effective under reversed cyclic flexural actions. According to the best knowledge of authors, there is no study investigating this important issue in the literature. Therefore, the present study focuses on retrofitting of beam support regions under reversed cyclic flexural moments. As the initial stage of a more comprehensive testing program, three full-scale RC beam-column-slab sub-assemblages were tested. The sub-assemblages also included a part of transverse beams perpendicular to the main beam tested. One specimen was tested as a reference specimen while the remaining two specimens were tested after being retrofitted with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) ropes with two different details in terms of anchorage of the CFRP ropes into joint region. The anchorage of CFRP ropes was provided by NSM application over the slab next to the column in one of the specimens, while CFRP rope was anchored by epoxy adhesive within the joint core by embedding it through a drilled hole on the column in other specimen. The effectiveness of the proposed anchoring methods was investigated through experimentally. The findings of the study indicated that the specimen retrofitted with NSM anchoring method achieved a remarkable enhancement in flexural capacity, whereas, anchoring through embedment of the CFRP rope within the epoxied drilled hole was not that successful

Retrofit of damaged reinforced concrete members by using steel corners and plates

Bu çalışmada daha önce sabit eksenel yük ile yön değiştiren tekrarlı eğilme etkileri altında denenmiş betonarme numuneler epoksi enjeksiyonu ve tamir harcı ile onarıldıktan sonra boyuna doğrultuda çelik korniyer ve lamalar ile, enine doğrultuda ise çelik lamalar ile güçlendirilmiştir. Onarılmış ve güçlendirilmiş numuneler aynı yükleme şartlarında tekrar denenmiş, uygulanan onarım ve güçlendirme tekniğinin numune davranışına katkısı dayanım, süneklik, eğilme rijitliği ve enerji yutma kapasitesi açılarından değerlendirilmiştir. Güçlendirilmiş betonarme kesitler için analitik moment-eğrilik ilişkileri elde edilmiş ve bunların deneysel sonuçlar ile uyumlu olduğu görülmüştür. Deneysel ve analitik çalışmaların sonucunda, incelenen bu ekonomik onarım ve güçlendirme tekniğinin hasarlı betonarme kesitlerin performanslarını önemli ölçüde geliştirdiği görülmüştür. Anahtar Kelimeler: Betonarme, dayanım, enerji, güçlendirme, onarım, süneklik. There are large numbers of damaged buildings that need repair/strengthening in Turkey. Consequently, experimental and analytical work on the behaviour of damaged reinforced concrete members, which are repaired/strengthened by different techniques, is vitally important. In this study, specimens tested before under the combined effects of axial and reversed cyclic flexural loads, are repaired and strengthened by steel corners and plates. The repaired and strengthened specimens are then tested in the same conditions as original specimens and the contribution of the repair and strengthening technique on strength, ductility, stiffness and energy dissipation are investigated. Then analytical moment-curvature relationships are obtained by using fiber element approach and it is seen that the analytical results are in good agreement with the experimental data. In the analytical study, confinement effect for concrete, strain hardening and Bauschinger effects for reinforcing steel can be taken into account. At the end of experimental and analytical studies, it is seen that the investigated economical repair and strengthening technique is highly effective on improving the behaviour of reinforced concrete sections, which were damaged previously.Keywords: Ductility, energy, reinforced concrete, repair, retrofit, strength

Masonry buildings subjected to settlements: half-scale testing, detailed measurements, and insights into behaviour

Industry procedures to assess the risk of settlement-induced damage to masonry buildings ignore key aspects of the problem, such as the influences of building weight, façade openings, and floor structures. Experimental data are needed to characterise the influence of these aspects on damage. This paper describes tests on three brick masonry half-scale building models subjected to settlements. The use of scaling rules in choosing the model materials and kentledge, the settlement apparatus, and the cross-validation of displacement and strain measurements are presented. Comparative evaluation of building responses show that: (i) the distribution of building weight and the resulting in-situ stresses play a key role in determining compliance to settlements, (ii) openings make the structure vulnerable to cracking and (iii) floor slabs stiffen and strengthen the building and prevent the formation of damage in the upper floors, leading to a concentration of damage at the ground storey

Structural assessment of the 13th century great mosque and hospital of Divrigi: A world heritage listed structure

. The Great Mosque and Hospital of Divrigi is located in the central eastern part of Turkey, in Divrigi, Sivas. The historical facility consists of a monumental mosque and a two-story hospital, which are adjacent to each other. The structure dates back to 13th century Mengujekids period and has been listed by the UNESCO as a World Heritage since 1985. Great Mosque and Hospital of Divrigi is particularly notable for its monumental stone portals that are decorated with three-dimensional ornaments carved from stone. The structural system of the monument consists of multi-leaf stone masonry walls and stone piers that support the roof structure which consists of stone and brick arches and vaults. The structure is located about 90 km away from the North Anatolian Fault Line, that has been causing several destructive earthquakes. Consequently, the structure is prone to destructive seismic activities. In this study, after a brief introduction on the structural system and current condition of the structure, the structural performance of the Great Mosque and Hospital of Divrigi is investigated through site observations and structural analyses. For this purpose, linear and nonlinear 3D finite element models of the structure are developed and the structure is examined under the effects of vertical loads and seismic actions. In the light of the analyses results, recommendations for potential interventions are outlined for further preservation of the structure

Mevcut binalar için güçlendirme yöntemleri geliştirilmesi

TÜBİTAK MAG01.05.2005Bugün ülkemizde ve diğer ülkelerde yaygın olarak uygulanan "sistem iyileştirmesi" yöntemi, dayanımı ve rijitliği yetersiz çerçevelerin bazı gözlerinin betonarme dolgu ile doldurularak yeni bir yatay yük taşıyıcı sistemi olmuşturulması olarak tanımlanabilir. Ülkemizde bugün karşılaşılan en önemli sorunlardan biri de hasar görmemiş ve kullanılmakta olan çok sayıda zayıf binanın depreme dayanıklı duruma getirilmesidir. Bu binaların güçlendirilmesinde, "sistem iyileştirmesi" yönteminin kullanılması elbette mümkündür. Ancak sözü edilen yöntemde dolgu duvarların oluşturulmasında beton kullanılacağından, binaların boşaltılması gerekmektedir. Çok sayıda binanın boşaltılması ve binada yaşayanların eşyaları ile birlikte başka bir konuta yerleştirilmesi pratik bir çözüm değildir. Bu proje kapsamında, depreme dayanıklı olmayan ve halen kullanılmakta olan binaların boşaltılmadan güçlendirilmesini sağlayacak yöntemler geliştirilmiş ve bunların gerekli dayanım ve rijitliği sağladığı deneysel ve analitik olarak kanıtlanmıştır.In the system behavior improvement technique, the general philosophy is to introduce a new lateral load resisting system, which will increase the lateral strength and the lateral stiffness of the existing system, which is generally a non-ductile frame with inadequate lateral stiffness. Various techniques based on this principle have been developed and applied in the past. Among them, the most widely used technique is the formation of new stiff walls through infilling some bays of the existing frame with reinforced concrete infills. Use of infilled frames as a method of seismic behavior improvement for existing structures is presently a very common application in Turkey. All these techniques are applicable at the cost of a certain discomfort to the occupants and, the application of these techniques in the rehabilitation of undamaged buildings may not very practical. With this project, the development of new strengthening techniques was achieved. Experimental and anaylical studies have been done to proove the effectiveness of newly developed strengthening techniques. In this study, rapid and yet reliable rehabilitation methodologies for Turkey have be developed