Experimental Study On Mechanical Properties And Seismic Performance Of Adobe Building

Nowadays, there are lots of adobe buildings spread in small towns and villages of China. However, the technical standards of construction and design on theses adobe buildings are less developed. In general, adobe buildings are empirically constructed by local workers, and the qualities of them are unreliable. For this reason, they are heavily damaged in earthquakes, and the safety of peoples’lives and properties is threatened. Based on the National Technical R&D Program2006BAJ06B03, in order to research and develop the mechanical properties and seismic performance of adobe buildings, this thesis presents a study on the mechanical properties of adobe block and masonry and seismic behavior of adobe walls and house by experiments, theorical analyses and numerical computation. The conclusions are summarized as follows:(1) The results of axial compressive test show that the compressive strength of adobe block is influenced by fine grain content, dry density and aspect ratio. The increased of fine grain content also increases volumetric shrinkage ratio. The interal cracks caused by high volumetric shrinkage ratio probably decreased the compressive strength of adobe. In tests, adobe samples have low volumetric shrinkage ratio, no obvious cracks and high strength. It shows that physical modification of soil materials by mixing fine grained soil and sand is a good way to make adobes.(2) The results of monotonic and cyclic compressive tests and monotonic shear tests conducted on adobe prisms showed that the failure behavior of adobe prisms is similar to that of the plain clay and concrete masonry. The prisms under compression were predominately failed by splitting with vertical cracks. The failure mode of prisms under shear was shear bonding failure along the interface between adobe and soil mortar. The results of compressive tests show that the strength and stress-strain relations are influenced by the ratio of adobe and mortar strength. Under cyclic loads, the dispersing of the experimental results is effectively reduced, but the peak strain is increased heavily by residual strain. This character is different with the plain masonry. The results of shear tests show that shear strength increases with the increase of mortar strength; the descending part of load-displacement curve behaves brittle. (3) A series of pseudo-static tests on adobe solid walls and walls with different openings in plane were conducted to investigate the seismic performance of adobe walls. The results show that the failure modes of adobe walls which are similar to that of plain masonry are compression-shear and friction-shear failures. The ultimate strength and stiffness of adobe walls are influenced by vertical stress and aspect ratio. The strength, stiffness and energy dissipation of walls with openings are significantly reduced contrast to solid walls, but the ductility is improved. The formula of calculating bearing capacity is established with friction-shear equation. The calculated results agree well with the experimental data.(4) The results of in-plane pseudo-static tests of adobe walls show that the load-displacement curves and envelops curves in loading process behave linearly, but obvious residual deformations are found after unloaded. This character is different with the plain masonry. Based on the existing methods of calculation of in-plane stiffness, a revised elastic deep-beam method is presented to calculate adobe solid wall by introducing secan(?) modulus in view of initial vertical stress. Based on the revised rotational stiffness of adobe wall piers and secant modulus in view of initial vertical stress, a method calculating adobe walls with openings is presented. The results agree well with the experimental data.(5) An adobe house model was constructed to investigate the dynamic properties, failure patterns and seismic performance of adobe building by shaking table test. The results show that the natural frequency and damping ratio of single-story adobe model is15Hz-20Hz and4%-10%respectively. The failure behavior of model is similar to that of plain masonry.The ladder, horizonotal cracks found in walls and the vertical cracks found in connections of walls are the major crack patterns in tests. The deformability of model is better than that of plain masonry. When the story drift ratio was1/50, no cracks were found. When the story drift ratio was up to1/30-1/20, serious cracks were found, but the model was still not collapse. Based on the plasticity of adobe, a seismic design method for adobe building is presented.