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Shake Table Test on Masonry Structures Retrofitted by Shotcrete

Ghezelbash, Amir Hossein | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52563 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Mohtasham Dolatshahi, Kiarash
  7. Abstract:
  8. In order to investigate the behavior of unreinforced masonry buildings and the effects of shotcrete retrofit, a half-scale one-story masonry building was constructed and tested on the shake-table of Earthquake Research Center at Sharif University of Technology (SUT), Iran. The project was jointly founded by SUT and Ecole Polytechnique Fédérale de Lausanne (EPFL), with the support of The Organization for Development, Renovation, and Equipping of Schools of I.R Iran (DRES). The 3.7×3.7×2 [m] specimen was modeled after a typically built classroom, with eccentric window openings on one wall and a door opening on the opposite wall. The walls were constructed using half-scale 10.5×5.0×2.9 [cm] clay bricks and 0.5 cm of 1:1:3 (cement: lime: sand) mortar joints, with a one-and-a-half brick configuration in thickness. Composite concrete slab and steel beams were used for the roof. First, the unreinforced specimen was subjected to seven steps of a shake-table test to identify the failure modes and the weak points. In this step, focused investigations were made on the interaction between perpendicular walls and the effects of opening eccentricity. Afterward, the damaged specimen was rehabilitated by applying a layer of steel mesh and shotcrete on the interior face of two of the walls and the exterior face of the other walls. Three different connections, namely interior-to-interior, exterior-to-exterior, and interior-to-exterior shotcrete connections, were designed to link the shotcrete layers of the intersecting walls. Furthermore, the shotcrete was connected to the roof slab through a set of previously installed hooks. A releasable connection was designed in order to restrain the shotcrete layer to the steel foundation, allowing further comparison of the failure modes before and after opening the connection. Finally, a nine-step shake-table test was carried out to push the repaired specimen to the point of collapse. The ground-motion used in the tests belonged to a local earthquake and was scaled based on Cauchy similitude law. Comparing the crack pattern of the rehabilitated (RM) and unreinforced (URM) specimens demonstrated the efficiency of the shotcrete layer in countervailing the damages and changing the crack propagation paths. Other than that, the drift ratios and roof torsion, obtained from the instrument outputs, showed a significant performance improvement for the RM specimen in terms of ultimate strength and displacement capacity. The fundamental frequencies of the specimen, extracted from instrument outputs, exhibited significant contribution of the shotcrete layer in deferring the damages to higher excitation levels. Moreover, satisfying composite action was observed between the shotcrete layer and the masonry thanks to the hooks employed to fasten the steel grid to the walls. However, in two corners of the specimen, the shotcrete layer was delaminated from the wall and acted as a separate component without participating in the load-bearing mechanism. The shotcrete-to-roof and shotcrete-to-shotcrete connections all remained undamaged during the RM test. The exception was the interior-to-exterior shotcrete connection in which notable damage was observed on the masonry face of the internally shotcreted walls. The RM specimen showed rocking movements only after the shotcrete-to-foundation connection was released in the seventh step of the test
  9. Keywords:
  10. Retrofit ; Shaking Table Test ; Shotcrete Concrete ; Masonry Buildings ; Construction Materials

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