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| dc.contributor.author | Yibekal, Kassahun Arega | |
| dc.date.accessioned | 2022-03-04T06:53:30Z | |
| dc.date.available | 2022-03-04T06:53:30Z | |
| dc.date.issued | 2021-11 | |
| dc.identifier.uri | http://ir.bdu.edu.et/handle/123456789/13132 | |
| dc.description.abstract | Local site conditions and foundation configurations have a great deal to do with damages to structures built on the flexible ground during earthquakes. Hence, the investigation on the energy transfer mechanism from soil to buildings during earthquakes is critical for the seismic design of multi-story buildings and for retrofitting existing structures. Most building code provisions recommend simplified model for SSI (Soil-Structure Interaction) problems, which ignores significant characteristics of SSI and local site effects including material and geometrical nonlinear responses, soil layering and inhomogeneity. However, they acknowledge the need for site specific studies for structures on liquefiable and soft soils subject to strong levels of shaking. The importance of considering SSI in seismic design of buildings with basement stories built (to be built) on liquefiable and soft soil is recognized by the modern seismic design community, which is very much moving towards PBD (Performance-Based Design) principles. Conventionally, soil-structure interaction effects were ignored in seismic design of structures, since they were believed to only have favorable effects. However, recent studies and case histories show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Moreover, local site conditions have a significant influence in the distribution of damage on surface structures associated to earthquakes. Most building codes of practice including EBCS (Ethiopian Building Code of Standards) lack any structural analysis procedures for including the effect of basements with SSI during seismic excitation. In addition, traditional force/stress-based design approach, which is not good damage indicator, has no measure of the deformation capability of members or buildings. Furthermore, existing International seismic design standards and codes do hardly provide any straight forward tools for engineers to account for soil-pile-structure interaction (i.e., foundation types and local site conditions) effects in relation to PBD. Accordingly, the need for research into soil-structure interaction towards PBD principles is greater than ever. So, the SSI analysis of fifteen-story reinforced concrete moment resisting building with two basement stories supported by different foundation configurations built on liquefiable and dense Nevada sand soil under PBD framework is the main focus of this research. The current study tried to answer questions such as (1) Does SSI has always beneficial effects? (2) How does soil liquefaction provide protection to surface buildings? (3) Do basement stories have only space functionality? On the way to response for the above three research questions, a numerical model of fifteen-story moment resisting building with two basement stories at prototype scale was developed with different foundation configurations and soil conditions using FLAC3D. The building was assumed to be founded on two types of typical Nevada sand soil profiles. The results of numerical validation analysis revealed a reasonably well agreement between measured and computed values. Moreover, this study exhibited results that illustrate detrimental effects of SSI. For instance, in the current case although the performance level of the fixed base building is in the life safe zone (i.e., inter-story drift less than 1.5%), performance level of buildings supported by piled-raft foundation, raft foundation with basement stories and raft foundation without basement stories are all shifted to the near collapse level (i.e., inter story drifts is between 1.5% and 2.5%), due to the influence of SSI. Furthermore, the present study demonstrated the contribution of basement stories for overall structural integrity. For example, for the model excited by 1995 Kobe near field earthquake, the generated base shear on the structure supported by shallow foundation with basement stories is less on average by 23% than that of structure supported by piled-raft foundation. In addition, the study also showed beneficial effects of liquefiable soil layer. For example, in comparison to structures supported by raft foundation on uniform dense Nevada sand, the maximum developed base shear and inter story drift on structure supported by raft foundation on layered soil decreases in average by 21%, and 4.5% respectively. In the meantime, this study implied the necessity of performing inelastic responses study for the structural components including piles in SSI system as substantial plastic hinges are formed around the pile head and the mid height of the building. Likewise, from liquefaction and soil hysteretic analysis, the study concluded that the rate of strain reversal of the input excitations is more critical than their peak strain amplitude variations. At large, as revealed in this study liquefaction has positive effects on structural response which is totally against to the anticipation. So, the study signposted necessity of performing full SSI and nonlinear site-specific response analysis for particular site, loading, structure and foundation conditions in addition to use codes and guidelines. Keywords: Liquefaction, Fluid-Mechanical Interaction, Large-strain, Finn-Byrne model, Performance level, Finite Difference, Soil-Structure Interaction | en_US |
| dc.language.iso | en_US | en_US |
| dc.subject | CIVIL AND WATER RESOURCE ENGINEERING | en_US |
| dc.title | Seismic Soil-Structure Interaction and Liquefaction Coupling Effects on Buildings: Performance-Based Design | en_US |
| dc.type | Thesis | en_US |
