Project Performance Evaluation using EVA Technique: Kotay Bridge Construction Project on Kayto River in Afghanistan

The objective of the study is the assessment of an operating bridge project in terms of its performance by the evaluate project performance (EVA) technique. To apply the EVA technique, cost and schedule baselines and an update record of performed work with spent money is prepared for the project. The data is taken directly from site office of the project. Kotay bridge construction project is selected for case study. Project tracking is achieved by taking EVA technique to assess the Kotay bridge construction project performance in the last five months, and to find out the cost and time overruns if they exist. The Estimation at Completion (EAC) and To-Complete Performance Index (TCPI) are found as well to know how efficiently are used the remaining financial resources. The study revealed that CPI and SPI are both less than 1.0, which means that the project could not be performed well. Cost & time overruns are clearly indicated as well

The eigenvalues of isolated bridges with transverse restrains at the end abutments

This paper examines the eigenvalues of multi-span seismically isolated bridges in which the transverse displacement of the deck at the end-abutments is restricted. With this constraint the deck is fully isolated along the longitudinal direction, while along the transverse direction the deck is a simple supported beam at the end abutments which enjoys concentrated restoring forces from the isolation bearings at the center piers. For moderate long bridges the first natural period of the bridge is the first longitudinal period, while the first transverse period is the second period, given that the flexural rigidity of the deck along the transverse direction shortens the isolation period offered by the bearings in that direction. This paper shows that for isolated bridges longer than a certain critical length, the first transverse period becomes longer than the first longitudinal period despite the presence of the flexural rigidity of the deck. This critical length depends on whether the bridge is isolated on elastomeric bearings or on spherical sliding bearings. This result is also predicted with established commercially available numerical codes only when several additional nodes are added along the beam elements which are modeling the deck in-between the bridge piers. On the other hand this result can not be captured with the limiting idealization of a beam on continuous distributed springs (beam on Wrinkler foundation) –a finding that has practical significance in design and system identification studies. Finally, the paper shows that the normalized transverse eigenperiods of any finite-span deck are self-similar solutions that can be represented by a single master curve and are independent of the longitudinal isolation period or on whether the deck is supported on elastomeric or spherical sliding bearings

The Contribution of Agricultural Sector on Economic Growth of Nigeria

Agriculture is a panacea for economic growth (Gunner Myrdal, 1984). The battle for long-run economic growth is either won or lost in the agricultural sector. However, how this path births economic prosperity has been the subject of debates among economist and development scholars. This study empirically examines the impact of agricultural sector on the economic growth of Nigeria, using time series data from 1981 to 2013. Findings revealed that Real Gross Domestic Product (RGDP), agricultural output and oil rents have a long-run equilibrium relationship. Vector Error Correction Model (VECM) result shows that, the speed of adjustment of the variables towards their long run equilibrium path was low, though agricultural output had a positive impact on economic growth. It was recommended that, the government and policy makers should embark on diversification and enhance more allocation in terms of budgeting to the agricultural sector. Keywords: Agriculture, economic growth, time series, cointegration and vector error correction model (VECM). JEL Classifications: O13, Q32, Q3

Critical Buckling Loads of the Perfect Hollomon's Power-law Columns

In this work, we present analytic formulas for calculating the critical buckling states of some plastic axial columns of constant cross-sections. The associated critical buckling loads are calculated by Euler-type analytic formulas and the associated deformed shapes are presented in terms of generalized trigonometric functions. The plasticity of the material is defined by the Hollomon's power-law equation. This is an extension of the Euler critical buckling loads of perfect elastic columns to perfect plastic columns. In particular, critical loads for perfect straight plastic columns with circular and rectangular cross-sections are calculated for a list of commonly used metals. Connections and comparisons to the classical result of the Euler-Engesser reduced-modulus loads are also presented.Comment: 15 page

A DEM model for visualising damage evolution and predicting failure envelope of composite laminae under biaxial loads

A two dimensional particle model based on the discrete element method (DEM) is developed for micromechanical modelling of fibre reinforced polymer (FRP) composite laminae under biaxial transverse loads. Random fibre distribution within a representative volume element (RVE) is considered for the micromechanical DEM simulations. In addition to predicting the stress-strain curves of the RVEs subjected to transverse compression and transverse shear stresses against the experimental testing results and other numerical modelling results, the DEM model is also able to capture the initiation and propagation of all micro damage events. Fibre distribution is found to more significantly influence the ultimate failure of composite laminae under transverse shear, while it has much less effect on the failure under transverse compression. The failure envelope of composite laminae under biaxial transverse compression and transverse shear is predicted and compared with Hashin and Puck failure criteria, showing a reasonable agreement. The predicted failure envelope is correlated with the damage evolution and the quantitative analysis of failure events, which improves the understanding of the failure mechanisms

Superlattice Growth via MBE and Green’s Function Techniques

A model has been developed to simulate the growth of arrays consisting of a substrate on which alternating layers of quantum dots (QDs) and spacer layers are epitaxially grown. The substrate and spacer layers are modeled as an anisotropic elastic half-space, and the QDs are modeled as point inclusions buried within the half-space. In this model, the strain at the free surface of this half-space due to the buried point QDs is calculated, and a scalar measure of the strain at the surface is subsequently determined. New point QDs are placed on the surface where the previously calculated scalar strain measure is a minimum. Following available DFT results, this scalar strain measure is a weighted average of the in-plane strains. This model is constructed under the assumption that diffusional anisotropy can be neglected, and thus, the results are more in agreement with results from experiments of growth of SiGe QDs than experiments involving QDs of (In,Ga)As

New Bending Algorithm for Field-Driven Molecular Dynamics

A field-driven bending method is introduced in this paper according to the coordinate transformation between straight and curved coordinates. This novel method can incorporate with the periodic boundary conditions in analysis along axial, bending, and transverse directions. For the case of small bending, the bending strain can be compatible with the beam theory. Consequently, it can be regarded as a generalized SLLOD algorithm. In this work, the bulk copper beam under bending is analyzed first by the novel bending method. The bending stress estimated here is well consistent to the results predicted by the beam theory. Moreover, a hollow nanowire is also analyzed. The zigzag traces of atomic stress and the corresponding 422 common neighbor type can be observed near the inner surface of the hollow nanowire, which values are increased with an increase of time. It can be seen that the novel bending method with periodic boundary condition along axial direction can provide a more physical significance than the traditional method with fixed boundary condition

The role of rock joint frictional strength in the containment of fracture propagation

The fracturing phenomenon within the reservoir environment is a complex process that is controlled by several factors and may occur either naturally or by artificial drivers. Even when deliberately induced, the fracturing behaviour is greatly influenced by the subsurface architecture and existing features. The presence of discontinuities such as joints, artificial and naturally occurring faults and interfaces between rock layers and microfractures plays an important role in the fracturing process and has been known to significantly alter the course of fracture growth. In this paper, an important property (joint friction) that governs the shear behaviour of discontinuities is considered. The applied numerical procedure entails the implementation of the discrete element method to enable a more dynamic monitoring of the fracturing process, where the joint frictional property is considered in isolation. Whereas fracture propagation is constrained by joints of low frictional resistance, in non-frictional joints, the unrestricted sliding of the joint plane increases the tendency for reinitiation and proliferation of fractures at other locations. The ability of a frictional joint to suppress fracture growth decreases as the frictional resistance increases; however, this phenomenon exacerbates the influence of other factors including in situ stresses and overburden conditions. The effect of the joint frictional property is not limited to the strength of rock formations; it also impacts on fracturing processes, which could be particularly evident in jointed rock masses or formations with prominent faults and/or discontinuities