Research on Engineering Structures and Materials

241-255

Authors: Hayri Baytan Ozmen, Mehmet Inel

Many earthquake prone countries have significant amount of existing deficient buildings to be evaluated for seismic actions. Although nonlinear methods are more preferable for assessment of existing buildings, most of the practicing engineers are unfamiliar to these methods. Therefore, linear methods seem to be in use in the near future for assessment of great number of deficient existing buildings in a reasonable time. In linear methods, nonlinear behaviour is taken into account by a single parameter: strength reduction factor (R) which is used to greatly reduce the elastic force demand accounting for the nonlinear behaviour. This study evaluates the use of R factors for different ductility and performance levels of buildings with respect to different soil site class. It is observed that the R factors: decrease with increasing periods, are more sensitive for higher performance levels, may change more than 30% with respect to number of story or transverse reinforcement amount, and may change 20% depending on the site class. However, effect of site class is generally smaller and a clear trend is not observed. Exemplary R values for different ductility, performance levels and number of stories are provided in the study.

279-296

Authors: H Ersen Balcıoğlu, Raif Sakin, Halit GÜN

Due to fiber reinforced polymer composite materials have a brittle structure, it is important to know their behavior under dynamic loads. Therefore, it is necessary to know the S-N curve that characterizes the fatigue life of the composite material, when selecting and sizing the material. In this study, fatigue behavior of glass/epoxy laminated composites was investigated under flexural loading. For this aim, computer controlled fixed end type flexural fatigue test machine was developed and glass/epoxy test samples were tested under flexural stress corresponding to 80%, 70%, %60, %50, and %40 of the static 3-point bending strength. In addition, the static strengths of the epoxy-laminated composites under tensile, compressive and flexural loads were also determined. It has been observed that the damage such as matrix and fiber cracks and delamination in the glass/epoxy laminated composites, which were exposed to flexural deformation. Also, it has been seen that, the developed fixed end type flexural fatigue test machine can be used to determine fatigue behavior of thin-walled composite materials.

151-160

Authors: Liang Ji, Xinzhi Liu, Houlei Zhang

Furfural residue is a detrimental waste generated in furfural production processes. Combustion is an efficient way to dispose furfural residue and drying is a necessary unit operation prior to combustion. In this paper, the properties of furfural residue, including particle size distribution, proximate analysis and pyrolysis process curves were presented. The flow and drying characteristics of furfural residue in a lab-scale single-shaft paddle heat exchanger were documented. The measurements show that the furfural residue contains high moisture (54.26%) and its as received basis lower heating value is 7301 kJ/kg. The high moisture content in furfural residue makes ignition and efficient combustion very difficult. It is feasible to use single-shaft paddle heat exchanger to dry furfural residue to moisture content of 15.94% which is advantageous for further combustion due to low moisture content. No agglutination and blockage were found. This preliminary experimental research provides reference for furfural residue drying unit design.

169-187

Authors: Daniel Helbig, Marcelo Langhinrichs Cunha, Caio Cesar Cardoso da Silva, Elizaldo Domingues dos Santos, Ignácio Iturrioz, Mauro de Vasconcellos Real, Liércio André Isoldi, Luiz Alberto Oliveira Rocha

There are several areas of engineering that use thin plates as structural elements, among them, we can highlight their application in the construction of offshore structures, bridges, ship hulls, and aircraft fuselage. In some design situations, the plates may be subjected to compression stresses and, consequently, they may be under the effect of elastic and/or elasto-plastic buckling. The analysis of the buckling phenomenon presents significant differences between one-dimensional elements, such as beams and columns, and two-dimensional elements, such as plates. The buckling phenomenon is directly related to dimensional, constructive and/or operational aspects. In this sense, the presence of perforations in plates causes a redistribution of their stresses, affecting not only their resistance but also their buckling characteristics. In order to solve the problem of elasto-plastic buckling in thin steel plates with perforations, we used computational models developed in Ansys(R) software, which is based on the Finite Element Method (FEM). For the analysis, it was considered perforated plates with constant thickness h for the relationships H/L = 1.0 and H/L = 0.5, where H is the plate width and L is the plate length. For the volume fraction Ф, i.e., the ratio between the volume of the perforation and the volume of the plate, the following values were considered: 0.08; 0.10; 0.15; 0.20 and 0.25. In addition, the plates were considered to have centralized perforations with the following geometric forms: longitudinal oblong, transverse oblong, elliptic, rectangular, diamond, longitudinal hexagonal, and transverse hexagonal. The shape variation of each perforation type occurs through the ratio H0/L0, being H0 and L0 the characteristics dimensions of perforation. The Constructal Design method was employed to define the range of possible geometries for the perforated plates, allowing an adequately comparison about the von Mises stress distribution among the studied cases. The results show that the geometric shape variation, for all analyzed perforation types, leads to an optimum geometry.

219-230

Authors: Anunciação Jr.N. C, Anflor C.T.M, Goulart J.N.V

This paper focused on developing a methodology based on coupling the Genetic Algorithm (GA) and the Boundary Element Method (BEM) for predicting the mechanical properties of a soil if a previous displacement x frequency curve is known. The NSGA-II (Elitist Non-Dominated Sorting Genetic Algorithm) was chosen for optimizing a dynamic poroelastic problem. The revisited problem introduced by Cheng is the benchmark used to verify the numerical routine and to apply the proposed optimization procedure. The present methodology was shown to be able to predict the mechanical properties of the underground soil if a displacement x frequency curve is previously known.

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.

15-34

Authors: Pilade Foti, Aguinaldo Fraddosio, Salvatore Marzano, Gaetano Pavone, Mario Daniele Piccioni

Tensegrity structures are an innovative class of lightweight structures, which have gained the interest of researchers in many different fields, including but not limited to engineering. In particular, such interest is due to their aesthetic value, their large stiffness-to-mass ratio, the possible deployability, together to their reliability and controllability. Tensegrity structures, made of struts in compression and cables necessarily in tension, are innovative structures by itself: they are similar only in appearance to conventional pin-joint structures (trusses), and their mechanical behavior is strongly related to initial feasible self-stress states induced in absence of external loads. In particular, from a kinematical point of view, these self-stress states avoid the activation of possible infinitesimal mechanisms. In this paper, we study an innovative class of tensegrity beam-like grids, obtained by a suitable assembly of three elementary V-Expander tensegrity cells along a longitudinal axis (named x-axis) in the three-dimensional space. In particular, by means of a numerical study, we analyze the feasible self-stress states for seven tensegrity beam-like grids, with increasing degree of complexity, made by an arrangement of V-Expander elementary cells. Moreover, we analyze the influence on the feasible self-stress states of the addition of elements starting from the simplest V-Expander tensegrity configuration.

49-60

Authors: Agim Seranaj, Mihail Garevski

The Response Spectrum Analysis of the structures is based on the allowable ductility considered for that structure. In the case of multi-degree-of-freedom buildings, the required ductility cannot be the same with the allowable ductility; furthermore, the required ductility values are different for different storey. In the case of first soft/weak storey building, the required ductility of this storey is much higher compared to allowable ductility and impossible to achieve. Nowadays there are many cases of existing reinforced concrete structures with the possibility of soft/weak storey. Even new structures are required to have open space at ground floor level as the owners want them for shops or garages usage. This paper analysis the influence of base isolation to the required storey ductility of weak storey buildings. A five storey shear frame type structure is considered as the model. The elastic and elasto-plastic modeling of the structural elements and bilinear modeling of rubber isolators are used. Linear Response Spectrum analysis and Nonlinear Time History analysis are performed in order to determine the required storey ductility for the existing and new soft/weak storey buildings using the SAP2000 computer program. The analysis results show the reduction of the required storey ductility due to the application of base isolation not only in new structures, but in existing structures too. This means that the base isolation technique is a good alternative to be applied in buildings with first soft/weak storey structure.