Structural element

About: Structural element is a research topic. Over the lifetime, 3154 publications have been published within this topic receiving 34754 citations. The topic is also known as: structural member.

Statistical and structural approaches to texture

Abstract: In this survey we review the image processing literature on the various approaches and models investigators have used for texture. These include statistical approaches of autocorrelation function, optical transforms, digital transforms, textural edgeness, structural element, gray tone cooccurrence, run lengths, and autoregressive models. We discuss and generalize some structural approaches to texture based on more complex primitives than gray tone. We conclude with some structural-statistical generalizations which apply the statistical techniques to the structural primitives.

Size-dependent elastic properties of nanosized structural elements

Abstract: Effective stiffness properties (D) of nanosized structural elements such as plates and beams differ from those predicted by standard continuum mechanics (Dc). These differences (D-Dc)/Dc depend on the size of the structural element. A simple model is constructed to predict this size dependence of the effective properties. The important length scale in the problem is identified to be the ratio of the surface elastic modulus to the elastic modulus of the bulk. In general, the non-dimensional difference in the elastic properties from continuum predictions (D-Dc)/Dc is found to scale as αS/Eh, where α is a constant which depends on the geometry of the structural element considered, S is a surface elastic constant, E is a bulk elastic modulus and h a length defining the size of the structural element. Thus, the quantity S/E is identified as a material length scale for elasticity of nanosized structures. The model is compared with direct atomistic simulations of nanoscale structures using the embedded atom method for FCC Al and the Stillinger-Weber model of Si. Excellent agreement between the simulations and the model is found.

Effect of fire on concrete and concrete structures

Abstract: The behaviour of concrete in fire depends on its mix proportions and constituents and is determined by complex physicochemical transformations during heating. Normal-strength concretes and high-performance concretes microstructurally follow similar trends when heated, but ultra-high-performance concrete behaves differently. A key property unique to concrete amongst structural materials is transient creep. Any structural analysis of heated concrete that ignores transient creep will yield erroneous results, particularly for columns exposed to fire. Failure of structural concrete in fire varies according to the nature of the fire; the loading system and the type of structure. Failure could occur from loss of bending or tensile strength; loss of bond strength; loss of shear or torsional strength; loss of compressive strength; and spalling of the concrete. The structural element should, therefore, be designed to fulfil its separating and/or load-bearing function without failure for the required period of time in a given fire scenario. Design for fire resistance aims to ensure overall dimensions of the section of an element sufficient to keep the heat transfer through this element within acceptable limits, and an average concrete cover to the reinforcement sufficient to keep the temperature of the reinforcement below critical values long enough for the required fire resistance period to be attained. The prediction of spalling – hitherto an imprecise empirical exercise – is now becoming possible with the development of thermohydromechanical nonlinear finite element models capable of predicting pore pressures. The risk of explosive spalling in fire increases with decrease in concrete permeability and could be eliminated by the appropriate inclusion of polypropylene fibres in the mix and/or by protecting the exposed concrete surface with a thermal barrier. There are three methods of assessment of fire resistance: (a) fire testing; (b) prescriptive methods, which are rigid; and (c) performance-based methods, which are flexible. Performance-based methods can be classified into three categories of increasing sophistication and complexity: (a) simplified calculations based on limit state analysis; (b) thermomechanical finite element analysis; and (c) comprehensive thermohydromechanical finite element analysis. It is only now that performance-based methods are being accepted in an increasing number of countries.