Search results

Implicit solutions in viscoplastic analysis of structures are very often avoided due to the fact that they lead to non‐symmetric systems of equations. On the other hand, structures such as soils have a marked non‐associate behaviour that has to be taken into consideration. Here the implicit solutions are formulated in a way that, even for non‐associate models, the system of equations is kept as symmetric. Apart from an ‘exact’ formulation of the algorithm other possibilities are considered and tested in the numerical examples given.

A model for the analysis of plain and reinforced concrete structures is developed in the present work. In the plain concrete the localisation of the microcracking within a small band is formulated in terms of constant fracture energy. In the reinforced concrete the model considers the cracking localisation in the element, according to the expressions of Model Code 1990. The objective of this model is to approximate the tension stiffening effect observed in the reinforced concrete elements submitted to tensile stresses. The reinforcing steel is analysed with an element overlapped to the concrete element, having equivalent nodal displacements. Numerical examples are presented and compared with experimental and other numerical results.

The aim of this paper is to obtain the analytical solution for the optimal design of reinforced concrete sections under ultimate design. The equilibrium equations of the section under bending moment and axial force in rupture are derived. The ultimate conditions are considered either in the steel or in the concrete according to the concrete design codes. The definition of the strains and stresses in the materials is based on the use of Heaviside functions. With this definition the equilibrium equations are described by unique equations. The optimization can then be developed with any design variables in the geometric definition, as area of the reinforcement and location. The optimization is developed with yielding of tensile steel and crushing of concrete. Although this is the current situation in reinforced concrete design, future developments of the model can include other steel and concrete conditions. Cost optimization and variable materials strength ratio are possible applications of the model. The interest of the model is the use of closed form unique equilibrium equations in the optimization of reinforced concrete sections. Numerical examples of the optimization of a rectangular section with minimum reinforcing steel area and economic bending moment are presented. The originality of the paper is the use of Heaviside functions in the definition of the ultimate strains in the reinforced concrete section. Unique equations for the objective function and restrictions are derived. The paper is useful for the design of reinforced concrete. The equations derived can be implemented into computer programs.

The initial stiffness method has been extensively adopted for elasto‐plastic finite element analysis. The main problem associated with the initial stiffness method, however, is its slow convergence, even when it is used in conjunction with acceleration techniques. The Newton‐Raphson method has a rapid convergence rate, but its implementation resorts to non‐symmetric linear solvers, and hence the memory requirement may be high. The purpose of this paper is to develop more advanced solution techniques which may overcome the above problems associated with the initial stiffness method and the Newton‐Raphson method.

In this work, the accelerated symmetric stiffness matrix methods, which cover the accelerated initial stiffness methods as special cases, are proposed for non‐associated plasticity. Within the computational framework for the accelerated symmetric stiffness matrix techniques, some symmetric stiffness matrix candidates are investigated and evaluated.

Numerical results indicate that for the accelerated symmetric stiffness methods, the elasto‐plastic constitutive matrix, which is constructed by mapping the yield surface of the equivalent material to the plastic potential surface, appears to be appealing. Even when combined with the Krylov iterative solver using a loose convergence criterion, they may still provide good nonlinear convergence rates.

Compared to the work by Sloan et al., the novelty of this study is that a symmetric stiffness matrix is proposed to be used in conjunction with acceleration schemes and it is shown to be more appealing; it is assembled from the elasto‐plastic constitutive matrix by mapping the yield surface of the equivalent material to the plastic potential surface. The advantage of combining the proposed accelerated symmetric stiffness techniques with the Krylov subspace iterative methods for large‐scale applications is also emphasized.

This paper addresses revolutionary changes in the education, fertility and market work of U.S. families formed in the 1870s–1920s: Fertility fell from 5.3 to 2.6; the graduation rate of their children increased from 7% to 50%; and the fraction of adulthood wives devoted to market-oriented work increased from 7% to 23% (by one measure).

These trends are addressed within a unified framework to examine the ability of several proposed mechanisms to quantitatively replicate these changes. Based on careful calibration, the choices of successive generations of representative husband-and-wife households over the quantity and quality of their children, household production, and the extent of mother’s involvement in market-oriented production are simulated.

Rising wages, declining mortality, a declining gender wage gap, and increased efficiency and public provision of schooling cannot, individually or in combination, reduce fertility or increase stocks of human capital to levels seen in the data. The best fit of the model to the data also involves: (1) a decreased tendency among parents to view potential earnings of children as the property of parents and (2) rising consumption shares per dependent child.

Greater attention should be given the determinants of parental control of the work and earnings of children for this period.

One contribution is the gathering of information and strategies necessary to establish an initial baseline, and the time paths for parameters and targets for this period beset with data limitations. A second contribution is identifying the contributions of various mechanisms toward reaching those calibration targets.

This chapter proposes semiparametric estimation of the relationship between growth rate of GDP per capita, growth rates of physical and human capital, labor as well as other covariates and common trends for a panel of 23 OECD countries observed over the period 1971–2015. The observed differentiated behaviors by country reveal strong heterogeneity. This is the motivation behind using a mixed fixed- and random coefficients model to estimate this relationship. In particular, this chapter uses a semiparametric specification with random intercepts and slopes coefficients. Motivated by Lee and Wand (2016), the authors estimate a mean field variational Bayes semiparametric model with random coefficients for this panel of countries. Results reveal nonparametric specifications for the common trends. The use of this flexible methodology may enrich the empirical growth literature underlining a large diversity of responses across variables and countries.

This paper presents an alternative approach to evaluating the overall efficiency and performance of Taiwanese container ports. Specifically, a parallel activity with series structure concept in the form of data envelopment analysis (MNDEA) is used to construct a model that applies to three different activities: harbor management, stevedoring and warehousing operations. We will further divide each activity into two process types, production processes and services processes. We will also adopt a Delphi survey approach and use the Analytic Network Process (ANP) to identify these processes’influence dependence and their degree of importance for the MNDEA model setting. An empirical application demonstrates the performance of Taiwanese container ports by using MNDEA with window analysis techniques via the directional distance functionThe results demonstrate that the application is effective in indicating and/or suggesting resource-adjustments, while considering which undesirable output levels and shared inputs were involved. The results also present directions for possible improvements in workplace efficiency.