EARTHQUAKE RESISTANT BEHAVIOR OF CONFINED AUTOCLAVED AERIATED CONCRETE (AAC) BLOCK MASONRY WALL

Abstract

Masonry structure is widely used due to its low cost and construction easiness especially in developing countries. These structures are extremely vulnerable during earthquake and the main cause of casualties. It is, thus, urgent to improve their seismic performance in order to reduce future casualties and to protect existing buildings. Collapse of unreinforced masonry walls causes a large number of human causalities due to a strong ground motion. The seismic resistance of structure can be possible either by increasing the capacity of the building or by decreasing the weight of building. The seismic force induced in the structure is directly proportional to the weight of the building. Heavier the structure larger the seismic force. So different techniques are thought, one is decreasing the mass of the structure by reducing the unit weight of the material used in the building. AAC blocks are around 50% lighter than normal brick. Its unit weight range 7 to 9 kN/m3. It is said that its strength to weight ratio is high. So this thesis mainly focus on the ultimate capacity of AAC block masonry wall. Further the ultimate capacity of hollow block masonry wall has already studied by many researchers which is similar to AAC block in sense that the hollow block weigh about 50% the solid concrete block. So, in this thesis work comparison between concrete hollow block masonry wall and AAC block masonry wall panel is done which gives clear idea about the structural capabilities of two different options for brick masonry wall constructions. In order to investigate the material properties of concrete block masonry wall, three layer block elements were tested on compression, shear and tension. To simulate the experimental results of composite block masonry wall, Norio[2] , finite element simulation software ABAQUS was used. Simplified micro model is prepared for simulation of the experimental results. Blocks and frame are modeled as finite elements C3D8R. CDP material model was used for the finite elements in the model. The interface was modelled as the interaction properties traction separation. The properties were depicted from experiment from three layer block tests. Reinforcement was modeled as 3d truss element. Material non-linearity were included in all the materials used. The geometric nonlinearity were also considered during the simulation of the model. During the simulation of the model the iteration are performed using Newton- Rapson Method by default. The analytical results obtained by ABAQUS analysis are compared with the experimental results Norio[2]. After the validation of analyzed results with experiment material properties are modified for concrete block masonry and replaced with AAC block masonry. Then the ultimate capacity curve plot is obtained for Confined AAC block masonry. The results obtained is compared with the concrete hollow block masonry. vi In conclusion, ABAQUS finite element analysis verified with (confined concrete block masonry) experimental results. Material properties for AAC block(Sand Based) and bond mortar are determined with the help of Khwopa Engineering College laboratory. The Finite element method can also be used to depict the non-linear analysis of structure having discontinuities in the material properties. The nonlinear curve for confined AAC block masonry wall was drawn. The behavior of nonlinear curve was found similar to confined concrete block masonry. The seismic resisting behavior of composite AAC block masonry wall are understood. Besides the structural point of view AAC blocks are environment friendly. AAC block use sand and cement with aluminum powder which are baked in oven. AAC block use less material than conventional concrete block. The manufacture process require less heat and electric power. Also use of sand replace fertile soil which is degrading in present context in Nepal specially in Kathmandu valley and other Cities. Therefore AAC blocks can be good alternative to concrete and clay brick.