Simulation of Concrete Batch Plant Production

The decision-making process is a very essential part of any construction operation. Simulation can be used as a tool to assist construction managers in making informed decisions. In this paper, simulation is applied to concrete batching operations to analyze alternative solutions and resource management. Data are collected to define activity durations for the plant. A simulation model is constructed for the plant using the MicroCYCLONE simulation system. Based on sensitivity analysis, management tools are constructed to help the decision maker. These tools are a time-cost-quantity chart, a feasible region analysis, and a contour lines chart. Time-cost-quantity and contour lines charts are used for determining production time, production cost, and resources for a required distance from the plant. The feasible region chart is used for determining the range of alternative solutions that can be taken to minimize production time and cost of the available plant resources, according to the required transportation distance.     

Assessment of Life-Cycle Benefit-Cost of Composites in Construction

So far, composite materials have found only moderate acceptance in the construction industry. This has been due primarily to technical and economic barriers such as limited information on life-cycle costs and anticipated performance and benefits. To enhance the application of composites in construction, it is important to develop a model that allows life-cycle benefit-cost assessment based on limited available information. This paper presents such a life-cycle benefit-cost model for composites in construction that does not require monetary quantification of benefits for comparison of alternative materials. The model has been explained through an example application for highway bridge column rehabilitation. The example considers composite column wraps versus conventional steel jackets to illustrate the application of the model.     

Notched behavior of prepreg-based discontinuous carbon fiber/epoxy systems

The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC^®. Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/width ratio, and hole size yields fundamental information on the behavior of this material.     

The Halpin-Tsai equations: A review

The Halpin-Tsai equations are based upon the “self-consistent micromechanics method” developed by Hill. Hermans employed this model to obtain a solution in terms of Hill's “reduced moduli”. Halpin and Tsai have reduced Hermans' solution to a simpler analytical form and extended its use for a variety of filament geometries. The development of these micromechanic's relationships, which form the operational bases for the coniposite analogy of Halpin and Kardos for semi-crystalline polymers, are reviewed herein.     

Prediction and measurement of the thermal expansion coefficient of crystalline polymers

Among the increased structural demands now being made on both unfilled and reinforced plastics is that of dimensional stability under various performance environments. Crystalline polymers are heterogeneous materials consisting of two distinct phases and, as such, can be treated as molecular versions of engineering composites. This paper first outlines the general physical model whereby a crystalline polymer is considered to be a multi-ply laminate of unidirectionally reinforced plies. The calculational format is then detailed for the prediction of the stiffness and thermal expansion coefficient of an isotropic sheet of crystalline polymer and a sample calculation is given for quenched high density polyethylene. A data base is presented for the stiffness and thermal expansion coefficient of low and high density polyethylene having quenched, slowcooled, and annealed thermal histories. Comparison between experimental and predicted results yields good agreement in all cases to better than 25 percent. Implications and limitations of the predictive technique are discussed.