Browsing by Author "Temesgen, Abiy"

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    Site Response Analysis of Selected Sites of Adama City
    (Addis Ababa University, 2021-09) Temesgen, Abiy; Asrat, Worku (PhD); Atalay, Ayele (Prof.)
    The local soil deposits found in Adama area have the potential of seismic site amplification. Site response analysis of the study area is mainly motivated by the presence of thick local soil deposits in a seismic prone area. Compressional (P-wave), horizontally polarized shear (SH-wave) and surface waves was acquired at four sites in the study area. Multichannel Analysis of Surface Wave (MASW) and Micrometer Analysis Measurements (MAM) were used to evaluate the shear waves from the surface waves and refraction time term inversion, to evaluate shear waves from body waves. The Poisson's ratio and anisotropy of the site have been calculated using the P-wave, SV-wave and SH-wave results. Using the results of the average shear wave velocity for a depth of 30 m (VS30), the sites were characterized as site class C according to EN 1998:2015 and site class D according to National Earthquake Hazards Reduction Program (NEHRP). The geotechnical data collected from different private and government organizations have also been used to characterize additional five sites and to generate dynamic properties such as the modulus reduction and material damping curves. The input ground motions from the Pacific Earthquake Engineering Research Center (PEER) database were selected using several criteria such as magnitude, site conditions, and target spectrum. These are then scaled to the site PGA value of 0.15g as established based on Global Seismic Hazard Assessment Program (GSHAP). One-dimensional site response analyses have been conducted by adapting equivalent linear analysis (EQL), nonlinear analysis with Modified Kondner-Zelasko (MKZ) and General Quadratic/Hyperbaric (GQ/H) model at nine sites in the study area. The results have been presented in terms of peak ground acceleration (PGA) profiles, displacement profiles, strain profiles, and response spectra. The area shows an amplification between 1.30 and 3.73, 1.15 and 2.00, 1.25 and 2.36 in PGA value for EQL, MKZ and GQ/H models. The results indicate that the current code design spectra (EN 1998:2015) for the site class C underestimates the shaking intensity of the sites.
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    Study on Flexural Buckling Curves for Hot Finished Hollow Sections
    (AAU, 2018-03) Temesgen, Abiy; Shifferaw, Taye (PhD)
    This work focuses mainly on the resistance of members to flexural buckling according to Eurocode 3. The work provides the mathematical backgrounds to the equations and buckling curves presented in Eurocode 3. The work also attempts to reveal how material behavior and residual stress influence the flexural buckling resistance which is demonstrated through finite element (FE) simulations. The work presents modeling and analysis on hollow section columns in ABAQUS 6.14. Linear and non-linear buckling analyses of the hollow section columns, with the imperfections, are implemented in this work. Specifically, the imperfections considered in this study are material plasticity, initial bow and residual stress. It was found that mesh size influences buckling behavior. Elastic-plastic with a strain hardening slope of E/100 gives a little higher buckling load but did not significantly affect the results. Residual stresses influence buckling behavior. Both material behavior and residual stresses influence reduce when the column heights increases. The rectangular section has high buckling curve than that of square section with same slenderness ratio. The minor axis have high buckling curve when the ratio of height to width(h/b) of cross sections high but the major axis buckling have the same buckling curves given in Eurocode 3.