Analytical model of composite floors with steel fibre reinforced concrete slab subjected to fire

Under fire, membrane action plays an important role in the performance of slabs subjected to large deflections. In this paper, a new model is proposed based on a proper approximation of horizontal displacements for a simply sup­ported composite slab. The novelty of the proposed approach consists in a special treatment of the system of shape func­tions for the “in-plane” displacements. Moreover, a load applied to the slab is divided into two components, so that one component is balanced by the membrane forces, while the second one is transmitted by the bending forces (including transfer of shear and moment). The deflection due to thermal elongations is replaced by the identical deflection caused by a fictitious load. Unknown parameters are calculated using the principle of virtual displacements. The effectiveness of the model is validated by the results obtained from experiments.

A Unified Method of Modeling a 3-Phase Induction Motors

Many textbooks on electro-mechanical machines introduce the induction motor using a transformer circuit model connected to a fictitious load resistor, the value of which changes as a function of the slip speed. The method is essentially a power based analysis, which yields some neat, quick results. The developed torque is calculated in terms of the power developed in that fictitious resistor. Although clever in its simplicity, the method fails to provide much physical insight into how the developed torque comes about. One is just expected to trust the circuit model. The approach described in this paper is based on theory of Lorentz force and Faraday’s Law used successfully to explain the operation of DC commutator machines. The method is readily understood and it provides direct insight into how the torque is developed. The paper will introduce a torque angle, which can be useful in visualizing how the machines work. It will also be shown that the traditional transformer model of the motor can be derived from the new analysis.

A BEM-BASED MESHLESS METHOD FOR ELASTIC BUCKLING ANALYSIS OF PLATES

In this paper, a BEM-based meshless method is developed for buckling analysis of elastic plates with various boundary conditions that include elastic supports and restraints. The proposed method is based on the concept of the Analog Equation Method (AEM) of Katsikadelis. According to this method, the original eigenvalue problem for a governing differential equation of buckling is replaced by an equivalent plate bending problem subjected to an appropriate fictitious load under the same boundary conditions. The fictitious load is established using a technique based on BEM and approximated by using the radial basis functions. The eigenmodes of the actual problem are obtained from the known integral representation of the solution for the classical plate bending problem, which is derived using the fundamental solution of the biharmonic equation. Thus, the kernels of the boundary integral equations are conveniently established and evaluated. The method has all the advantages of the pure BEM. To validate its effectiveness, accuracy as well as applicability of the proposed method, numerical results of various problems are presented.

Numerical Approaches to the Nonlinear Stability Analysis of Single Layer Reticulated and Grid-Shell Structures

The paper illustrates the characteristics of a procedure for evaluating the buckling and post-buckling behaviour and the influence of imperfections on reticulated and grid-shells structures. The presentation is composed by two steps: firstly, a simple way to comprehend the effects of initial imperfections by means of an “equivalent” fictitious load vector, acting on the ideal design structure, is presented. The fictitious load's characteristics are evaluated so to qualitatively reproduce the behaviour of an unknown structure, affected by an arbitrary distribution of small geometry variations with respect to the design structure. The second step allows to detect exactly the position of critical points and to trace the secondary equilibrium paths by means of a perturbation technique. Numerical examples illustrate the characteristics and performances of the approaches and suggest practical applications.