G. Zagari

A Mixed 4-Node 3D Plate Element Based on Self-Equilibrated Isostatic Stresses

A new mixed stress 4-node flat shell finite element, designed for the linear and nonlinear analysis of folded plate structures, is presented. The kinematics of the element is defined by 24 dofs with in- and out-of-plane displacements assumed to be quadratic, controlled by displacement and rotation parameters through an Allman like interpolation, and flexural rotations assumed to be bilinear. The assumed stress approximation, described within a local Cartesian frame aligned with the element orientation, is self-equilibrated and ruled by the minimum number of parameters. The element does not suffer from kinematical locking and rank defectiveness. Many numerical tests show the very good performance of the element.

Koiter asymptotic analysis of thin-walled cold-formed steel members

Abstract An imperfection sensitivity analysis of cold-formed steel members in compression is presented. The analysis is based on Koiter’s approach and Monte Carlo simulation. If the modes interaction is correctly accounted, than the limit load and the erosion of critical buckling load can be easily evaluated. Thousands of imperfection can be analysed with very low computational cost and an effective statistical evaluation of limit performance can be carried out. The analysis is done on pallet rack uprights in compression, based on an intensive experimental study carried out at the Politehnica University of Timisoara.

Imperfection sensitivity analysis of composite cylindrical shells using Koiter’s method

ABSTRACT The novel methodology for imperfection sensitivity analysis, presented in Barbero et al. [1], is here applied for the evaluation of limit load of composite cylindrical shells. Koiter’s perturbation method is used to calculate the imperfection paths emanating from mode interaction bifurcations, and the Monte Carlo method is used to test a large number of modes and all possible interactions among them. The computational cost is low because of the efficiency of Koiter’s method. The demands of Koiter’s method for accurate evaluations of higher order derivatives of the potential energy are met by a mixed, corotational element.

Structural solutions based on intensive use of steel for over-roofing of existing precast concrete panel buildings

An important segment of the Romanian urban population, similar to other Eastern European countries, lives in collective residential apartment buildings made using large prefabricated concrete panels. Most of these structures were built between 1960 and 1989 and present major issues concerning aesthetical aspects, lack of internal space, problems related to thermal comfort and, last but not least, weak energy efficiency. The presence of flat roofing system, generally with hydrothermal faults, represents an additional problem which leads to deficient living conditions of the last-storey inhabitants in many cases. Besides other ways of improving the conditions of such apartment houses, the over-roofing is welcome in order to both increase the habitable area and provide adequate roofing for the building. This article presents three types of over-roofing structural solutions, in two solutions, based on intensive use of steel, using (1) hot-rolled steel profiles, (2) rectangular hollow sections and (3) cold-formed steel profiles, respectively. In order to determine the optimum over-roofing system, the study analyses the structural design possibilities and particularly the connection between the new and old structural elements.