Silindirle sıkıştırılmış beton ağırlık barajların sismik performanslarının belirlenmesi için dinamik benzeri deney uygulamaları

TÜBİTAK MAG15.04.2014Su kaynaklarının verimli kullanılmasında en önemli yapılar barajlardır. Barajların, sismik etkiler altındaki davranışları deprem mühendisliğinde karşılaşılan en karmaşık problemlerden birisidir. Ülkemizde son yıllarda tercih edilen en önemli baraj tipi silindirle sıkıştıtılmış beton barajdır. Beton ağırlık barajların sismik davranışı laboratuvar ortamında birkaç sarsma tablası testi dışında deneysel olarak fazla incelenememiştir. Bu çalışma ile literatürde ilk defa dinamik benzeri deney yöntemi ile ölçekli baraj deneyleri gerçekleştirilmiştir. Çalışma kapsamında üç adet numunesi ardışık etki eden üç farklı deprem kaydı altında denenmiştir. Bu numunelerden ikisi farklı çekme dayanımlarına sahip SSB’den ve diğer numune ise geleneksel beton kullanılarak üretilmiştir. Tüm numuneler Türkiye’de tasarlanan en yüksek SSB baraj olan Melen Barajının 1/75 ölçekli halini yansıtmaktadır. Deneysel sonuçlar Türkiye'de tasarlanan en yüksek SSB ağırlık barajlardan birisinin sismik performansı hakkında da değerli deneysel veriler temin edilmesini sağlamaktadır. Ayrıca, baraj sismik performans belirlemesinde sıklıkla kullanılan nonlineer sonlu eleman modelleri ile gözlemlenen hasarın ne ölçüde tahmin edilebileceği de sunulmuştur.Dams are one of the most important structures for the efficient use of water resources. Dam- reservoir-foundation interaction problem under seismic loads is one of the most challenging problems in earthquake engineering. One of the most popular dam type in Turkey in the recent years is roller compacted concrete (RCC) dams. Testing of dams under simulated earthquake loads has only been limited to a few shake table tests. Pseudo dynamic testing method has been employed in this study for the first time in the literature. Three specimens tested in the course of this study were, two RCC specimens with two different concrete strengths and one conventionally vibrated concrete specimen. All the specimens were 1/75 scaled versions of Melen Dam, which is one of the most important RCC dams to be built in Turkey. The results of this study serve as means of observing the expected seismic performance of an actual dam under simulated earthquake loadings. The ability of numerical models in estimating the damage patterns observed in the tests are also evaluated in detail

Comparison of pseudo dynamic test results and numerical results of an RCC dam model

Inspired from the simplified single degree of freedom modeling approach used in the preliminary design of concrete gravity dams, a single degree of freedom pseudo dynamic testing method was devised for the seismic testing of a concrete gravity dam section. The test specimen was a 1/75 scaled section of the 120 m high monolith of the Melen Dam, one of the highest concrete gravity dams to be built in Turkey. First, the single degree of freedom idealization of the dam section was validated in the first stage of the study using numerical simulations including the dam-reservoir interaction. Afterwards, pseudo-dynamic testing was conducted on the specimen using three ground motions corresponding to different hazard levels. Lateral displacement and base shear demands were measured. The crack propagation at the base of the dam was monitored with the measurement of the crack widths and the base sliding displacements. A smeared crack finite element model of the test structure was analyzed for the prescribed ground motions. Load-deformation responses and crack patterns of the test and simulation results were compared. It was found that global response parameters such as displacements and forces were in reasonable agreement whereas accurate estimation of the actual crack lengths was found to be a challenging task

Cyclic Testing of Reinforced Concrete Double Walls

Reinforced concrete double walls are semi-precast structural elements constructed with factory-produced concrete shells on two exterior sides and cast-in-place concrete in the middle of the section. Their use has been limited in seismic zones due to the difficulty of connecting the adjacent double walls for monolithic action, and providing suitable seismic details in the presence of the lattice girder that is used to hold the concrete shells together. These limitations were overcome with the invention of discrete stainless steel connector ties with wave-shaped webs that can be used to connect the two concrete shells efficiently. This study presents experimental results on the reversed cyclic testing of reinforced concrete double walls constructed with the aforementioned ties, for the first time in the literature. Four experiments were conducted on double walls with rectangular, U-, and T-sections. Test results were evaluated in terms of strength, ductility, stiffness, and energy dissipation characteristics. The results obtained demonstrate the ability of double walls to sustain reversed cyclic displacement demands with significant ductility

Identfying Masonry Buidings That are Under High Seismic Risk

Masonry has been one of the most popular construction materials for centuries as it provided economical solutions for sheltering problems worldwide. Turkey, as a country with significant portion of its land in seismic zones, has a masonry building stock in the order of millions, most of which built in the twentieth century. In addition to the complications associated with anisotropic and composite nature of masonry buildings, the accurate estimation of seismic demands with simple yet accurate analytical tools is an extremely challenging task. A comprehensive research project was initiated at Middle East Technical University comprising of in-situ material strength determination from ten existing masonry buildings, two building tests including forced vibration and lateral load testing, and numerical simulations for calibration and modelling of existing masonry buildings. Making use of these experimental and simulation results, available seismic assessment techniques based on linear elastic analysis were refined. More specifically, lower bound material strength values, effective pier stiffness models and performance limit states for masonry walls were proposed. The overviews of the proposed revisions, which are currently under consideration by the committee, are presented in this paper

Seismic behavior of double walls with continuity reinforcement

The conventional precast construction has deficiencies especially related to its connections between structural elements. Hence, its use in earthquake zones has been limited. However, the seismic performance of these systems can be improved by a semi-precast system, namely the double wall system. In this structural system, both precast and cast-in-situ concrete elements are utilized during the construction period, i.e. precast concrete shells are benefitted as a formwork to place cast-in-situ concrete. In this way, monolithic building elements, which finally show the same effectiveness as cast-in-situ concrete walls and slabs can be constructed. In this study, reversed cyclic test results for the double walls are reported. The main objective of the experimental program is to compare the seismic response of two double walls, one cast monolithically, the other one composed of two walls constructed side-by-side and having monolithically cast concrete at the central region along with the continuity reinforcement between the two separate wall elements. Test results demonstrate that the use of continuity reinforcement between adjacent double walls ensure monolithic response with increased stiffness and energy dissipation characteristics

Identifying Masonry Buildings That Are under High Seismic Risk

Masonry has been one of the most popular construction materials for centuries as it provided economical solutions for sheltering problems worldwide. Turkey, as a country with significant portion of its land in seismic zones, has a masonry building stock in the order of millions, most of which built in the twentieth century. In addition to the complications associated with anisotropic and composite nature of masonry buildings, the accurate estimation of seismic demands with simple yet accurate analytical tools is an extremely challenging task. A comprehensive research project was initiated at Middle East Technical University comprising of in-situ material strength determination from ten existing masonry buildings, two building tests including forced vibration and lateral load testing, and numerical simulations for calibration and modelling of existing masonry buildings. Making use of these experimental and simulation results, available seismic assessment techniques based on linear elastic analysis were refined. More specifically, lower bound material strength values, effective pier stiffness models and performance limit states for masonry walls were proposed. The overviews of the proposed revisions, which are currently under consideration by the committee, are presented in this paper

Lateral load testing of an existing two story masonry building up to near collapse

Laboratory testing, although necessary to understand failure mechanisms of individual masonry walls, spandrels or small scale building models, cannot fully mimic the real system behavior of masonry structures. In order to observe the performance of an existing two story masonry structure, cyclic lateral load testing up to near collapse was conducted. The test building was sliced approximately in the middle through the reinforced concrete slabs of both stories and one side was strengthened with the objective of obtaining a strong reaction wall. The other side of the structure was taken as the test structure with a floor plan of approximately 10 m x 10 m. Hydraulic actuators attached at the slabs of both stories were employed to impose one way cyclic displacement excursions. Flexural and shear deformations on a number of walls were measured and crack propagations were monitored. The structure was tested up to a lateral strength drop of approximately 20 % from the ultimate load, which occurred at a drift ratio of about 0.60 %. The failure of the walls in the building, which were mostly failed in a diagonal tension mode, was concentrated on the first story. Results of this valuable test provide important data on the performance of an actual masonry building and were employed to assess the applicability of various stiffness and strength and simplified load-deformation models in the literature

In Situ Lateral Load Testing of a Two-Story Solid Clay Brick Masonry Building

The seismic behavior of unreinforced masonry (URM) structures has usually been investigated by conducting laboratory tests. Such efforts, although useful in order to understand the response of single walls or subassemblages, cannot fully mimic the in situ seismic response of masonry buildings. In this study, in situ lateral load testing of a two-story full-scale URM building was conducted. First, forced vibration tests were performed to determine the vibration frequencies of the building. Afterwards, the building was tested by reacting against a braced steel frame built behind the test building and imposing one-way cyclic displacements. The building was pushed until 20% loss of lateral load capacity, which corresponds to a drift ratio of approximately 0.8%. The diagonal tension cracking of the walls was followed by sliding of the second-story concrete slab over the walls. A three-dimensional nonlinear finite-element analysis of the test building was conducted to simulate the behavior of the test building. The results showed that upon careful selection of the contact cohesion at the slab-wall interfaces, the numerical model provided reasonable estimations of the global structural behavior in terms of load-deformation response