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Thermal post-impact behaviour of closed-cell cellular structures with fillers
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, original scientific article

Abstract: The study describes the behavior of regular closed-cell cellular structure with gaseous fillers under impact conditions and consequent post-impact thermal conduction due to the compression of filler gas. Two dependent but different analyses types have been carried out for this purpose: (i) a strongly coupled fluid-structure interaction and (ii) a weakly coupled thermal- structural analysis. This paper describes the structural analyses of the closed-cell cellular structure under impact loading. The explicit code LS-DYNA was used to computationally determine the behavior of cellular structure under compressive dynamic loading, where one unit volume element of the cellular structure has been discretised with finite elements considering a simultaneous strongly coupled interaction with the gaseous pore filler. Closed-cell cellular structures with different relative densities and initial pore pressures have been considered. Computational simulations have shown that the gaseous filler influences the mechanical behavior of cellular structure regarding the loading type, relative density and type of the base material. It was determined that the filler's temperature significantly increases due to the compressive impact loading, which might influence the macroscopic behavior of the cellular structure.
Keywords: mechanics, cellular structures, closed cells, gas fillers, impact loading, fluid-structure interaction, dynamic loads, LS-DYNA, ANSYS CFX 10.0, computational simulations
Published: 31.05.2012; Views: 916; Downloads: 18
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Slip modeling in timber-framed walls with wood-based or fibre-plaster sheathing boards
Miroslav Premrov, Peter Dobrila, Branko Bedenik, Igor Špacapan, 2007, original scientific article

Abstract: The paper provides mathematical modelling for prefabricated timber-framed walls composed of a timber frame and two different types of sheathing boards. Since by wood-based boards (WBB) the tensile strength is similar to the compressive one, there are practically no cracks appearing in the boards. On the other hand, in case of fibre-plaster sheathing boards (FPB) the tensile strength is approximately 10-times lower than the compressive one and therefore cracks in the tensile diagonal boardćs direction usually appear. Based on analysis of experimental research results [1] special approximate mathematical models have been developed. The models enable simultaneously to consider the flexibility of mechanical fasteners in the connecting areas, as well as possible cracks appearing in the tensile area of the sheathing boards.
Keywords: civil engineering, timber structures, walls, CFRP strips, carbon fibre-reinforced polymer, mathematical modelling
Published: 31.05.2012; Views: 1233; Downloads: 26
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Analysis of composite T beam composed of timber, concrete and carbon strip
Matjaž Tajnik, Peter Dobrila, Miroslav Premrov, 2007, original scientific article

Abstract: This paper provides a mathematical model and numerical example of composite T-section composed of a concrete plate and a timber beam strengthened at the bottom tension side with a carbon fibre-reinforced polymer (CFRP) strip. Analysis is provided in accordance with the European standards for timber, steel and concrete structures. The tensile strength of the carbon strip as well as the compressive strength of the concrete plate are higher than the bending strength of the timber beam, therefore it is convenient to use such composition of material to gain a higher load bearing capacity. It has been shown that the inclusion of CFRP strip reinforcement on the increase of load carrying and bending stiffness capacity was not as high as expected. On the other hand, we realized the importance of variety of material grade and geometrical properties combinations between sub-components which can significantly improve load bearing capacity and stiffness of composed beam. Furthermore, the CFRP strip contribution to the bending resistance and stiffness of the element is presented as a function of the fastener spacing intervals between concrete plate and timber beam.
Keywords: composite structures, timber structures, carbon strip, load bearing capacity, modeling
Published: 31.05.2012; Views: 1209; Downloads: 51
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Cost estimation, optimization and competitiveness of different composite floor systems
Uroš Klanšek, Stojan Kravanja, 2006, original scientific article

Abstract: This paper presents self-manufacturing cost estimation, cost optimization and competitiveness of different composite floor systems: composite I beams, composite trusses produced from rolled channel sections and composite trusses made from cold formed hollow sections. Part 1 of this two-part series of papers presents the estimation of the self-manufacturing (direct production) costs for composite and steel structures. The self-manufacturing costs are proposed to be defined as the sum of the material, the power consumption and the labour costs. The material costs of the structural steel, concrete, reinforcement, the shear connectors, electrodes, the anti-corrosion, fire protection and top coat painting, the formwork floor-slab panels and gas consumption are presented in detail. The power consumption costs comprise costs of sawing the steel sections, edge grinding, drilling, welding, stud welding and vibrating the concrete. The labour costs (times) presented define the costs of metal cutting, edge grinding, preparation, assembling and tacking, welding, welding of shear connectors, steel surface preparation and protection, drilling, cutting, placing and connecting the reinforcement, concreting, consolidating and curing the concrete. New approximation functions are proposed for the calculation of some manufacturing times and material consumptions. As the discussed costs vary significantly around the world, the proposed cost expressions are given in the open form to be used for cost estimation in different economic conditions. A numerical example of the estimation of the self-manufacturing costs for a composite I beam floor system shows the suitability of the proposed approach. On the basis of the defined self-manufacturing costs, introduced in Part 1, the cost optimization and the competitiveness of different composite floor systems are discussed in Part 2.
Keywords: cost estimation, self-manufacturing costs, material costs, power consumption costs, labour costs, steel structures, composite structures, welded structures
Published: 30.05.2012; Views: 1373; Downloads: 18
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Shape optimization of truss-stiffened shell structures with variable thickness
Marko Kegl, Boštjan Brank, 2006, original scientific article

Abstract: This paper presents an effective approach to shape optimal design of statically loaded elastic shell-like structures. The shape parametrization is based on a design element technique. The chosen design element is a rational Bézier body, enhanced with a smoothly varying scalar field. A body-like designelement makes possible to unify the shape optimization of both pure shells and truss-stiffened shell structures. The scalar field of the design element is obtained by attaching to each control point a scalar quantity, which is an add-on to the position and weight of the control point. This scalar field is linked to the shell thickness distribution, which can be optimized simultaneously with the shape of the shell. For linear and non-linear analysis of shell structures, a reliable 4-node shell finite element formulation is utilized. The presented optimization approach assumes the employment of a gradient-based optimization algorithm and the use of the discrete method of direct differentiation to perform the sensitivity analysis.Four numerical examples of shell and truss-stiffened shell optimization are presented in detail to illustrate the performance of the proposed approach.
Keywords: mechanics of structures, shape optimization, shells, trusses, Bézier body, numerical methods, optimum design
Published: 30.05.2012; Views: 1142; Downloads: 73
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Planar structures
Miroslav Premrov, Matjaž Tajnik, 2008, independent scientific component part or a chapter in a monograph

Keywords: timber structures, timber trusses, frames
Published: 31.05.2012; Views: 971; Downloads: 29
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Timber frame houses
Miroslav Premrov, 2008, independent scientific component part or a chapter in a monograph

Keywords: timber structures, timber frame buildings, frames
Published: 31.05.2012; Views: 1199; Downloads: 36
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Improvement of the statical behaviour of pressure controlled axial piston pumps
Darko Lovrec, Edvard Detiček, 2009, original scientific article

Abstract: The control of pressure by means of variable displacement pumps is one of the most important tasks in the field of pump control, which is influenced by the properties of the pumps. Looking for a suitable control concept with good static behaviour, a method is tested which tunes the parameters of a controller. Instancing a variable displacement axial piston pump controlled bya 3/2 proportional valve the improvement will be achieved by fuzzy logic on the one hand and a non-linear approach - adaptation of gain of the classical controller - on the other.
Keywords: servo hydraulic, variable displacement pump, pressure control, conventional control structures, fuzzy control structures, nonlinear control structures
Published: 31.05.2012; Views: 951; Downloads: 28
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On fracture behaviour of inhomogeneous materials - a case study for elastically inhomogeneous bimaterials
Otmar Kolednik, Jožef Predan, G.X. Shan, N.K. Simha, Franz Dieter Fischer, 2005, original scientific article

Abstract: This paper presents a case study, examining the influence of a sharp bimaterial interface on the effective crack driving force in a fracture mechanics specimen. The inhomogeneity of the elastic modulus in linear elasticand non-hardening and hardening elastic-plastic bimaterials is considered. The interface is perpendicular to the crack plane. The material properties and the distance between the crack tip and the interface are systematically varied. The effect of the material inhomogeneity is captured in form of a quantity called "material inhomogeneity term",▫$C_inh$▫. This term can be evaluated either by a simple post-processing procedure, following a conventional finite element stress analysis, or by computing the J-integral along a contour around the interface, ▫$J_int$▫. The effective crack driving force,▫$J_tip$▫, can be determined as the sum of ▫$C_inh$▫ and the nominally applied far-field crack driving force, ▫$J_far$▫. The results show that ▫$C_inh$▫ can be accurately determined by both methods even in cases where ▫$J_tip$▫-values are inaccurate. When a crack approaches a stiff/compliant interface,▫$C_inh$▫ is positive and ▫$J_tip$▫ becomes larger than ▫$J-far$▫. A compliant/stiff transition leads to a negative ▫$C_inh$▫, and ▫J_tip$▫ becomes smaller than ▫$J_far$▫. The material inhomogeneity term, ▫$C_inh$▫, can have the same order of magnitude as ▫$J_far$▫. Based on the numerical results, the dependencies of ▫$C_inh$▫ on the material parameters and the geometry are derived. Simple expressions are obtained to estimate ▫$C_inh$▫.
Keywords: mechanics of structures, fracture toughness, inhomogeneous materials, J-integral, crack driving force, interface, material force
Published: 01.06.2012; Views: 838; Downloads: 10
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Optimum design of plane timber trusses considering joint flexibility
Simon Šilih, Miroslav Premrov, Stojan Kravanja, 2005, original scientific article

Abstract: The paper presents the optimization of metal-plate-connected plane timber trusses with special emphasis on joint flexibility. The optimization was performed by the non-linear programming approach. Since various truss design parameters such as type of truss configuration, span/depth ratio, number and type of diagonal and vertical members and type of joint connections simultaneously affect each other, it is proposed that all of these parameters should be considered simultaneously in a single mathematical model. An optimization model for cost optimization of timber trusses was thus developed. The economic objective function for minimizing the structure's self-manufacturing costs was defined, subjected to the design, stress and deflection (in)equality constraints. The finite element equations were as the equality constraints defined for the calculation of the internal forces and the deflections of the structure. The stiffness matrix of the structure was composed by considering fictitiously decreased cross-section areas of all the flexibly connected elements. Constraints for the dimensioning of the timber members were determined in accordance with Eurocode 5 in order to satisfy the requirements of both the ultimate and the serviceability limit states. The cross-section dimensions and the number of fasteners were defined as independent optimization variables. A numerical example demonstrates the applicability of the optimization approach presented as well as the influence of the fasteners' flexibility on the optimal self-manufacturing costs.
Keywords: civil engineering, timber structures, trusses, fasteners, flexibility, optimization, non-linear programming
Published: 01.06.2012; Views: 1360; Downloads: 75
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