Research on Engineering Structures and Materials

79-89

Authors: Agim Seranaj, Erald Elezi, Altin Seranaj

The first reinforced concrete spatial structures date from 1920. These types of structures faded near 1970’s because of the high costs in formwork and labor work, but also from calculations difficulties. The technological evolution of formworks, as well as the advance of software industry for civil engineering, has helped to reach new levels of expertise during the structural design process. The scope of this analytical study is the use of structural openings to create new lighter, sustainable and architectural forms of structures, and using algorithms for form finding process. The paper includes structure cyclic analysis due to finding the appropriate position and geometrical form of the openings considering stresses, deformations and boundary conditions of specific cases. Optimizations are made using advanced optimization algorithms of form finding and topological optimization (ATOM – Abaqus Topology Optimization Module ®) and FEM for static analysis. Based on the analysis data of the examples presented on this paper with the use of advanced software, we conclude that spatial shells in 21-st century should be considered as the next engineering challenge in conjunction to architectural trends for free, irregular and diverse forms. In this article a theoretical study of the issue is made, including data from examples of optimization of shells with advanced algorithms using step by step sensitivity analysis. As a result of all data taken from the optimizations is concluded that using latest optimization algorithms, sensitivity analysis sums up to 40 % less stressed structures, and up to 30-40% lighter ones by creating structural openings.

103-125

Authors: Moein Hosseini, Fatemeh Farhatnia, Soheil Oveissi

The present study investigates buckling in functionally graded material (FGM) beams when exposed to a temperature rise. The proposed FGM beams have arbitrary edge supports that are modeled by rotational and translational springs. The mechanical properties are assumed to vary continuously across the thickness direction according to a simple four-parameter power law. To obtain the critical value of temperature, the governing equilibrium equations are extracted based on Timoshenko beam theory, using the assumption of Von-Karman nonlinearity for the physical neutral surface concept. The equations are further solved by Fourier series expansion via Stokes’ transformation technique. Numerical examples are provided to demonstrate the accuracy and reliability of the proposed method. The influence of two models of metal-ceramic distribution across the thickness (symmetrical and unsymmetrical ones) on the response of the beam in thermal buckling of FG beam is investigated. It is observed that, the critical buckling temperature rises more for symmetrical model of FGM beam with respected to unsymmetrical one. Also, increasing the translational and rotational spring coefficient makes the beam stiffer; consequently, the critical buckling temperature is increased.