Prestress behaviour and ductility requirements in structures: solutions from a unified algebraic approach

This paper presents an algebraic approach that unifies both the elastic and limit theories of static structural analysis. This approach reveals several previously unpublished improvements, which are based on several dualities in the mathematical description. Firstly, we show a novel duality between the solutions to two different problems: the elastic solution to the internal forces of an externally loaded structure, and the nodal displacements induced by prestressing in one or several elements of the same structure. This duality is proven and discussed. The application of this solution to the limit state analysis is very productive, and includes the determination of the ductility requirements necessary to achieve full plastic behaviour, and the assessment of the prestress needed to limit or eliminate such requirements. The unified framework also allows to obtain the elasto-plastic deformed state at the beginning of the plastic structural collapse. We have also detailed the theoretical duality between two classes of structures—hyperstatic and hypostatic—which was derived from the linear algebra principles that define these solutions. Finally, we studied and exposed the dimensionality reduction of structural problems given by the singular value decomposition and the eigenvalues problem. An illustrative example that clearly illustrates all these points is provided.

Reforming Teacher Pension Plans: The Case of Kansas, the 1st Teacher Cash Balance Plan

The ongoing crisis in teacher pension funding has led states to consider various reforms in plan design, to replace the traditional benefit formulas, based on years of service and final average salary (FAS). One such design is a cash balance (CB) plan, long deployed in the private sector, and increasingly considered, but rarely yet adopted for teachers. Such plans are structured with individual 401(k)-type retirement accounts, but with guaranteed returns. In this paper I examine how the nation's first CB plan for teachers, in Kansas, has played out for system costs, and the level and distribution of individual benefits, compared to the FAS plan it replaced. My key findings are: (1) employer-funded benefits were modestly reduced, despite the surface appearance of more generous employer contribution matches; (2) more importantly, the cost of the pension guarantee, which is off-the-books under standard actuarial accounting, was reduced quite substantially. In addition, benefits are more equitably distributed between short termers and career teachers than under the back-loaded structure of benefits characteristic of FAS plans. The key to the plan's cost reduction is that the guaranteed return approximates a low-risk market return, considerably lower than the assumed return on risky assets.

Numerical and Experimental Modeling of Paper-Based Actuators

Microfluidic paper-based analytical devices (μPADs) have witnessed a great extent of innovation over the past decade, developing new components and materials assisting the diagnosis of different diseases and sensing of a wide range of biological, chemical, optical, and electrochemical phenomena. The novel paper-based cantilever (PBC) actuator is one the major components that allows autonomous loading and control of multiple fluid reagents required for the accurate operation of paper-based microfluidic devices. This paper provides an extensive overview of numerical and experimental modeling of fluidically controlled PBC actuators for automation of the paper-based assay. The PBC model undergoing hygro-expansion utilizes quasi-static 2D fluid loaded structure governed by the Euler–Bernoulli beam theory for small and moderately large deflections. The solution for the model can avail the response of paper-based actuators for response deflection θ, within 0° to 10° under the assumption of insignificant cross-sectional deformation. The actuation of PBC obtained using a quasi-static theory shows that our results are consistent with quantitative experiments demonstrating the adequacy of models.

Stabilization of black cotton soil using coconut fiber

Black cotton soil is a soil with low bearing capacity, swelling and shrinkage characteristics. Due to its peculiar characteristics, it forms a very poor foundation material. As black cotton soil is an expansive soil; it creates problem for lightly loaded structure than moderately loaded structure. Through this project, we are trying to study the improvements in the properties of soil by adding coconut fiber of varying percentages. Tests will be conducted to determine liquid limit and unconfined compression strength. Stabilization of soil is an effective method for improving the properties of soil. It has great significance in the future projects. Keywords: Soil stabilization, CBR, Atterberg limits

Design Optimization of a Composite Rail Vehicle Anchor Bracket

The rail transportation sector is currently seeking to decrease greenhouse gas emissions by incorporating composite materials that can reduce the mass of vehicles. During early adoption of composites in the rail transportation industry, these materials have predominantly been applied to simple design geometries and lightly loaded structures, have been optimized only through modification of composite thickness and composite layer shape, and have only been constrained with respect to a single mechanical performance metric. This study investigates the use of finite element analysis software in the simulation of fiber-reinforced composite materials applied to, and optimized for, a complex and heavily loaded rail vehicle anchor bracket. The research assesses the applicability of optimization methodologies to a complex and heavily loaded structure and advances established practices by constraining the solution with respect to multiple design requirements: manufacturing, compliance, and failure criterion. The optimization process successfully developed a composite structure with a predicted mass reduction of 33% compared to an existing steel design, and simultaneously met compliance, manufacturing, and failure criteria constraints.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

A Metamaterial based Monopole antenna for Satellite based Navigation Applications

A metamaterial-based monopole antenna which resonates at L (L1 and L5) and S band for the IRNSS applications is described. The antenna has a low profile and is nearly is four times smaller in size than a conventional patch antenna. The multifrequency behavior is realized using a reactively loaded structure for the monopole antenna resulting in operation at both monopole and dipole modes. The monopole resonates at S Band and the dipolar mode resonance at L5 band. The novelty of the configuration is in realizing an additional band by introducing small square slot in the loaded structure. Copper wires are used to balance the current between the two ground at the antenna and the CPW feed line. The performance of the antenna is evaluated using ANSYS HFSS.

Probabilistic fatigue analysis of existing steel structure

The paper deals with evaluation of possible fatigue damage of existing steel crane structure. It is possible to use the some traditional methods to solve the problem - a concept of fatigue S-N curves (which are mainly used for designing of a new structures) or the procedures based on linear fracture mechanics utilizing the Paris-Erdogan’s law (which are suitable for estimation of remaining lifetime). For the resistance assessment the relevant data of load effects caused by cyclically loaded structure operation are necessary for both concepts. For the prediction of fatigue damage over time, calibration functions for short edge cracks were derived based on the results of the experiment, and the acceptable size of the fatigue crack in damaged structural component under analysis was determined. Using the derived relationships, a stochastic analysis of the selected element was performed and the results are discussed.