Estimation of Earthquake Input Energy, Hysteretic Energy and its Distribution in MDOF Structures

Current seismic codes for building design often utilize a force or a displacement-based approach in their implementation. In a force-based approach, a structure is designed to ensure it possesses sufficient strength to resist the maximum forces imparted to it by an earthquake. In a displacement-based approach, a target displacement is calculated or identified and the structure is proportioned to achieve a specified performance level, defined by strain or drift limits, under a specified level of seismic intensity. A third approach, which has gained momentum in the earthquake engineering community, is the energy-based approach. In this approach, a design is considered satisfactory if the capacity of a structure to absorb or dissipate energy exceeds its energy demand from an earthquake. In the present research, a new energy-based approach is proposed in which velocity index (VI), obtained as the product of two ground motion indexes - peak ground velocity (PGV) and cumulative absolute velocity (CAV), is used to normalize input energy spectra. The use of VI as a normalization factor not only allows for the creation of dimensionless input energy spectra, but can result in smaller values of coefficients of variation when compared to other normalization factors currently being used. Earthquake input energy spectra for four site classes (Site Class B, C, D and E as per IBC 2012 soil classifications) and four hysteretic models (bilinear plastic, stiffness degradation, bilinear flag and bilinear slip) are developed for five ductility levels (=1, 2, 3, 4, 5) using ground motion ensembles of 38, 42, 38 and 26 recorded at site classes B, C, D and E, respectively. For purpose of design, the normalized input energy spectra are divided into three regions - short period, intermediate period and long period - that are consistent with the customary design response spectra contained in various seismic codes and standards. A close examination of these spectra has shown that regardless of the hysteretic models used, the normalized seismic input energy decreases as ductility increases, and increases as the soil gets softer. For each site class, empirical ductility dependent input energy expressions are developed, and hysteretic to input energy ratio relationships are formulated. The proposed design input energy spectra are validated using six major earthquakes and are found to reasonably match the spectra generated using time history analysis. Since the input energy spectra are developed for single-degree-of-freedom (SDOF) systems, to facilitate the implementation of the proposed method in the design of multi-degree-of-freedom (MDOF) systems, simple expressions that relate earthquake input and hysteretic energies for MDOF system to its equivalent single-degree-of-freedom (ESDOF) systems are formulated. The energy relationships are verified using four (a three story, a five story, a seven story and a nine story) frames each subjected to six earthquakes wherein a very good estimate for the three- and five- story and a reasonably acceptable estimate for the seven-, and nine-story frames were obtained. A new method for distributing hysteretic energy over the height of moment resisting frames is also proposed. The new distribution scheme was used in determining the energy demand (hysteretic energy) component of an energy-based seismic design (EBSD). EBSD is a story-wise optimization design procedure developed using the relationship that exists between energy dissipating capacity and plastic analysis/design of structures. Finally, the entire process of determining the input energy for ESDOF systems to the distribution of hysteretic energy over the height of MDOF structures using the proposed EBSD design procedure is demonstrated using two design examples: a three-story one-bay frame and a five-story two-bay frame

Intensifying with high value trees in Africa RISING Ethiopia for food and nutrition security, income and climate resilient farming

United States Agency for International Developmen

Inflation and Money Growth in Ethiopia: is there a Threshold Effect?

This study analyses money growth - inflation nexus in Ethiopia using annual datasets covering the period 1970-2009. This period was considered due to data limitations. A significant aspect of the study is that it tries to identify the optimal level of money growth using Two Regime Threshold Model. The result from the two-regime threshold model reveals that there is indeed a threshold effect in the relationship between money growth and inflation and the optimal level of money growth is estimated to be 17% which has an important policy implication. Here, money supply creates inflationary pressures only when it exceeds 17%. A percentage increase in money supply above this threshold value is expected to cause 1.47 percent increase in annual inflation indicating that monetary factors are valid sources of inflation in Ethiopia. The results imply keep the money growth below 17%. Hence, a specific monetary policy measures that could be envisaged is controlling broad money supply (M2).Inflation; money growth; two regime threshold model; Ethiopi

Facilitate improving availability of quality planting material to intensify high value trees

United States Agency for International Developmen

Honey and beeswax value chains analysis: The case of Adwa and Ahferom Districts, Central Tigray, Ethiopia

Beekeeping is an appropriate and well-accepted farming activity which directly and indirectly contributes to smallholder income generation in Adwa and Ahferom districts. But there are a number of problems in honey and beeswax value chains that can be faced from production up to consumption. This study aimed at honey and beeswax value chain analysis in Adwa and Ahferom districts with specific objectives of describing and characterizing the different value chain functions, actors and service providers; identify factors affecting honey and beeswax value chain; and determine socio economic contribution of honey and beeswax value chain. Multistage sampling technique was used to identify the sample respondents. Data were collected from multiple sources including farmers, traders, processors and service providers by using semi structured interview, key informants interview, group discussion and field observation. Data were computed to descriptive statistics, probit regression models and triangulation. In this study there are multiple actors and service providers that directly and/or indirectly involve in the honey and beeswax value chains. The major factors that influence adoption of beekeeping technologies were age, education, extension service and total land size. From the result, there was significance mean difference in annual income between beekeepers and non beekeepers (p=0.001) with better income of the beekeepers. Benefit of beekeepers from white honey is higher than Amber/golden honey. The major problems in honey and beeswax value chains along each stage were shortage of modern beekeeping equipments, lack of beekeeping skill, lack of market linkage and lack of extension support. Generally, there are different value chain actors and service providers along the value chain. Honey and beeswax value chains used as source of food, income and employment moreover, total income of beekeepers was higher than non beekeepers. Honey and beeswax value chains were found to be influenced by different household, institutional and bio-physical factors despite its substantial economic and social values. Hence, addressing these constraints will be pertinent to maximize the benefits of honey and beeswax value chain