The Influence of Materials Properties on Structural Form and Behaviour - Essay Example

INFLUENCE OF MATERIALS PROPERTIES ON STRUCTURAL BEHAVIOR By of School and Introduction Throughout the human civilization history, many types of material have been used for construction of bridges, buildings, and roads among other structures, which include steel, concrete, wood, polymers, bituminous materials and fibrous composites. As far as civil engineering is concerned, the materials used in building have variable roles, meaning they ought to have corresponding properties (Van Kesteren, Stappers and Kandachar, 2005). For instance, structural materials are expected to have preferred mechanical characteristics, which include being waterproof materials that are both impermeable and resistant to water. In addition, the material for wall construction have to be insulated against heat and have good sound absorption, as well as being sufficiently durable considering that they are mostly affected by numerous external factors like rain, wind, frost and sun (Abeysundara, Babel and Gheewala, 2009). The basic properties for consideration in building material include the mechanical and physical properties, decorativeness, as well as the durability of the material. During the selection of materials to be used for engineering purposes, certain properties that include tensile strength, impact strength, as well as hardness is essential in indicating how suitable the selection for the material is, although the engineer has the obligation of ensuring that radiography together with other properties for the material are in line with required specifications (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). Considering the variable demands for metallic materials, there could be need for special surface treatment like hardening, in order to normalize the scope of service requirements. On the other hand, the material chemical properties, which include bonding energy, structure, and resistance to degradation by environmental factors, could equally affect material selection in engineering (Bevan and Woolley, 2008). Construction Material a) b) c) Figure for construction materials (a) concrete, (b) steel, (c) clay bricks (Rahman, Perera, Odeyinka and Bi, 2008) In the recent past, there has been an increase in popularity of plastics and polymeric materials in engineering. As much as these are inferior to majority of the metallic materials as far as temperature resistance and strengths are concerned, these have been used in corrosive environments as well as in other areas that require minimum wear, for example in small gear wheels that were initially manufactured from hardened steel, are currently produced from Teflon or nylon (Van Kesteren, Stappers and Kandachar, 2005). The performance of these materials is satisfactory; they are quiet and are in no need for lubrication. In this respect, therefore, prior to selection of material or even the designing of components, there is need for an individual to have sufficient knowledge of the process requirements, the limitations of operation like the non-hazardous and hazardous conditions, the continuous and the non-continuous operations, raw material availability together with the availability of spares and other alternate material (Rahman, Perera, Odeyinka and Bi, 2008). The Compositions of Materials Material composition includes mineral and chemical composition, all of which constitute the major factors for material properties. Chemical composition is the chemical constituents and they give the material different properties (Abeysundara, Babel and Gheewala, 2009). For instance, when the carbon content increases, it affects the hardness, strength and the toughness of carbon steel. Carbon steel rusts with a lot of ease, and there comes in place the stainless steel through addition of nickel, chromium, together with other chemical components to steel. Various inorganic non-metallic materials have different mineral composition (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). Minerals are monomer compounds that have specific chemical structure and components (Rahman, Perera, Odeyinka and Bi, 2008). The mineral composition forms an integral factor for properties of some materials used for building, among which are inorganic gel, natural stone and others. The micro-level structure observable using optical microscope is referred to as sub-microstructure or meso-structure. In this structure, the aspects of interest include she sizes, interface and shape of particles and grains, as well as the shape, size and distribution of the micro-cracks and pores (Abeysundara, Babel and Gheewala, 2009). For instance, the metallographic structure and size of metal grains could be analyzed, during which the determination of thickness of cement, concrete and the porous makeup could be effectively distinguished. Others include the timber wood fiber, line, catheter, resin, together with other observable structures. Micro-structure exhibits a significant level of influence on mechanical properties as well as the material durability (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). Refinement of grains is important in improving the strength, with an example being steel, which when mixed with vanadium, titanium, niobium, or other elements of alloy that can refine the grains forms a material with higher intensity. The molecular and atomic structures of material which can be effectively studied using X-ray diffractometer, electron microscopy, and other reliable means are referred to as microstructure. The structure can be categorized into crystal and non-crystal structure. The crystal structure is constituted by a solid with particles, which include molecules, atoms or ions, packed in a particular regular order, with repeating patterns that extend in the three spatial dimensions (Van Kesteren, Stappers and Kandachar, 2005). This structure is characteristically made up of fixed geometric anisotropy and shape. The numerous mechanical crystalline material properties have relationship with the pattern of arrangement of the particles as well as their forces of bonding, which in this case are chemical bonds (Rahman, Perera, Odeyinka and Bi, 2008). The non-crystal structure, on the other hand, is the fuse mass that contains certain chemical constituents, which are rapidly cooled so that the particles fail to pack in a regular pattern, hence solidifying into solid of amorphous or vitreous body (Bevan and Woolley, 2008). The non-crystal structure does not have a fixed isotropy or geometry shape. This structure characteristically has chemical instability and easily reacts with other components and substances due to the rapid cooling process during its formation. The non-crystal is important because they function as adhesive within products made of burned clay and certain natural rocks. Physical Properties of Materials Density Density refers to the dry mass per unit volume for a given substance in absolute compact conditions. In this case, the volume under reference in the absolute compact conditions is the solid volume with no inner spore volume (Abeysundara, Babel and Gheewala, 2009). Apart from glass, steel and asphalt among other materials, majority of materials have pores in their natural state. While measuring the density of porous materials, there is need to grind the material into powder, and the powder dried till it attains fixed masses before measuring the solid volume using Lees density bottle (Bevan and Woolley, 2008). Apparent Density Apparent density refers to dry mass per volume for a given substance in its natural conditions. It is given in: Po=M/Vo, where Po is the apparent density, m is mass in dry conditions, whereas V, is volume in natural conditions. The volume of any substance under natural conditions is the solid volume together with the inner pore volume. For a regular-shaped material, the volume could be measured directly while an irregular shaped material would need measuring using drainage technique upon sealing all the pores available with wax (Bevan and Woolley, 2008). Among the most common uses of liquid drainage method is in measuring of sand aggregate volumes, which are used in concrete. However, the volume under measurement here is the solid volume together with closed pore volume with no addition of the volume for pores that are open to the outside. Considering the compact nature of sand stones with very few pores, there is very little volume for the pores opening to the outside (Bevan and Woolley, 2008). The volume using the liquid drainage technique is referred to as apparent density or virtual density. Bulk Density Bulk density is the per unit volume for any substance in conditions where granular or powdery materials are packed. Bulk density is obtained using volumetric container and the volumetric container size is dependent on the particle sizes (Van Kesteren, Stappers and Kandachar, 2005). In this case, bulk density could be referred to as the packaging density of the substance in dry conditions and the rest should be marked. The Solidity and Porosity Solidity is the degree at which a given volume of a material has its solid substances packed, and this refers to the ratio of solid volume to total volume. Solidity together with porosity demonstrates the compactness of a given material (Rahman, Perera, Odeyinka and Bi, 2008). The characteristics of pores and porosity, which are determined by connectivity, size and distribution, have a significant effect on the properties of the material (Abeysundara, Babel and Gheewala, 2009). In general, for a similar material, if the porosity is lower, there are fewer connected pores. In this respect, the strength increases, the absorption of water reduces, whereas frost resistance and permeability becomes better. However, this comes with an increase in conductivity. Mechanical Properties of Materials Strength refers to the highest amount of stress that a substance can effectively bear when under external forces with no destruction. Depending on the variable types of external forces, the strength is inclusive of compressive strength, tensile strength, bend strength, as well as the shear strength among others (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). The kinds of strength are influenced by static strength, which is often tested by use of destructive experiments on the basis of standard methods in place. Material strength depends on the structure and composition of the material. Strength reduces with the increase in porosity (Bevan and Woolley, 2008). Another important aspect of construction material is the strength grade which could be divided into several grades based on the ultimate strength of majority of the building material (Van Kesteren, Stappers and Kandachar, 2005). The brittle material grades, on the other hand, are divided on the basis of their comprehensive strength, and they include the stones, ordinary bricks of clay, concrete and cement, together with the plastic materials and the ductile material. Specific strength, however, refers to the strength of the material divided by the apparent density of the same. An increase in specific strength increases with the strength and lightness of the material (Abeysundara, Babel and Gheewala, 2009). In this respect, therefore, it is of great importance that materials that have high specific strengths are selected, or ensure that the specific strength is enhanced for the purpose of lifting the heights of buildings, reducing the structural weight as well as lowering the costs of the project. Elasticity and Plasticity Elasticity refers to the substance property where it can deform as a result of external forces and eventually return to the original shape upon the withdrawal of stress. When the deformation can be fully restored, the material is referred to as elastic. For example, E=2.1x1O5 MPa is the elastic modulus for low-carbon steel, whereas the elastic modulus for concrete has variable value, and its strength grades range between C15 and C60, whereas the elastic modulus E increases from between 1.55 x 104MPa and 3.65 x 1O4MPa (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). Plasticity Plasticity means the material deformation at the time when it is under non-reversible alteration in shape in line with the external forces, and this is referred to as plastic deformation. Building materials can never be purely elastic materials (Rahman, Perera, Odeyinka and Bi, 2008). Certain materials could only exhibit elastic deformation in instances where the stress is smaller, while plastic deformation occurs when stress surpasses the limits, and these include low-carbon steel (Abeysundara, Babel and Gheewala, 2009). When the external forces are exerted, certain materials are bound to undergo elastic and plastic deformation simultaneously. Brittleness and Toughness Brittleness is the material property that fractures upon encounter with stress but possesses minimal tendency to undergo deformation prior to rupture. The brittle materials characteristically have small deformation, poor ability to overcome impact and other load-related vibrations, high strengths of compression, as well as the low tensile strength (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). When vibrated or impacted by stress, materials are capable of absorbing a lot of energy which could lead to eventual deformation with no rupturing and this is referred to as toughness. Tough materials have characteristics of great deformation, increased tensile strength, increased strength of comprehension, and these include the construction wood, steel and rubber (Flórez, Castro-Lacouture, Sefair and Medaglia, 2009). Tough material ought to be used for structures that bear vibration and bearing, as observed in bridges, roads, beams and cranes. Fig.(a) Stress Strain Diagrams for Brittle, (b) For Ductile Materials The initial slope on the stress strain diagram demonstrates the material stiffness. The difficulty to deform the material increases with the steepness of the slope. In case the structural member is made by using materials that are stiffer, there will be reduction in its deflection (Van Kesteren, Stappers and Kandachar, 2005). Upon reaching the critical stress value, there will be a sudden failure with no warning, but the material has the ability to carry stress on extra deformation. In this case, the deformation capability is referred to as ductility, and it implies that the structural member is bound to undergo great level of deflection prior to failure, giving warnings to on and around the construction site (Bevan and Woolley, 2008). Hardness and Abrasive Resistance Hardness is the property exhibited by the material that offers resistance to in-ward pressure or the scratches of a hard object. Materials of variable degrees of hardness require variable methods of testing (Abeysundara, Babel and Gheewala, 2009). For instance the hardness of wood, steel and concrete could be tested using the pressing-in technique. An ideal example for this is the Brine11 Hardness (HB) test, which is expressed through pressure that is loaded on press mark for each unit area. Factors affecting choice of structural system The decision about structure is influenced by foundation condition, the column layout, building service integration together with the external wall constructions. The steel framed building design is inclusive of the structures, the building envelopes, finishes and services (Bevan and Woolley, 2008). In this respect, therefore, all elements ought to be coordinated in a firm dimensional system for the purpose of recognizing the modular nature demonstrated by the components in ensuring maximum standardization and repetition within the pre-determined layout (Rahman, Perera, Odeyinka and Bi, 2008). For example, the role of a structure in a multi-storey building is transmission of the load applied to the foundation. The principal loads exerted on this building are a resultant of wind and gravity, and all are applicable at each level of the floor and facades. The transmission of these loads is done by the structural from the application points to foundations (Bevan and Woolley, 2008). In essence, it is expected that it combines efficiency of the structure with the least impact on economy as well as other building functions. Choosing of the structural column grid gives the definition of the column position and has significant importance in decision design. The definition of the structural grid is provided by the column position together with the main beams that span in between (Chan and Tong, 2007). Health and Safety Among the most common safety hazards are crashes by motor vehicles, falls from heights, evacuation accidents, machines, electronics, as well as falling objects striking people. Of the major health hazards on construction sites are solvents, noise, asbestos, and other activities of manual hardening (Bevan and Woolley, 2008). In the construction industry, falls from heights constitute the most common form of health hazard hence the need for fall protection in the activities taking place on runaways, ramps, excavations, holes, hoist areas, leading edge work, formwork, unprotected edges and sides, roofing, wall openings, all running and walking surface, residential construction, and the overhand bricklaying work among others (Bevan and Woolley, 2008). Protection from falls could be effected using safety net, guardrail, and personal fall arrest, warning line and positioning device systems. All employees should undergo training in order to understand ideal means of using the systems in use as well as for identification of hazards. Motor vehicle crashes constitute other important safety hazard at the sites of construction. There is need to practice caution while at the construction sites particularly when operating the motor vehicles and other equipments on the site ((Chan and Tong, 2007). Motor vehicles must have emergency brake system, service brake system, as well as the parking brake system (Van Kesteren, Stappers and Kandachar, 2005). All vehicles should be equally equipped with a warning system that is audible in case the operator opts to use such. In addition, the vehicles are fitted with doors and windows, the power windshield wipers, together with clear views of the site when observed from rear window (Abeysundara, Babel and Gheewala, 2009). The job site equipments should be fitted with light and reflectors for use at night. As much as the regulations are characteristically very broad as far as the definition of how various states ought to create and implement health and safety plans, the set regulations dictate particular requirements regarding how agencies need to plan for the significant projects (Rahman, Perera, Odeyinka and Bi, 2008). In this case, the significant projects are those with higher likelihood of causing sustained impact in work zone, which is greater than what is virtually tolerable as dictated by the engineering judgment or state policy. There is need for the agencies to create Temporary Traffic Control and Traffic Management Plans in order to address the safety concerns of the time (Chan and Tong, 2007). The use of personal protective equipments remains paramount, and among these are steel-toe boots and hard hats which are the most common (Chan and Tong, 2007). Upon conducting risk assessment, it may be determined on whether or not other protective equipments like goggles, gloves and the high-visibility clothing are necessary. Figure: hazard warnings at construction sites (Bevan and Woolley, 2008). There is a close link between decision making on construction material and the product service life. For instance, a contemporary architect could choose on the basis of performance attributes of the models in place, and this implies that their choices are not based on material but rather on material tools or systems (Van Kesteren, Stappers and Kandachar, 2005). It is also believed that limitation of the products or material performance to system specifications impedes the important qualities inherent in the product or material. The model that measures material selection together with the sustainability of the same is of significant impact on the sustainability construct from the architect’s perception. References Abeysundara, U.G.Y., Babel, S. and Gheewala, S. A., 2009. Matrix in life-cycle perspective for selecting sustainable materials for buildings in Sri Lanka. Build. Environ, 44, pp. 997-1004 Bevan, R. and Woolley, T., 2008. Hemp Lime Construction: A Guide to Building with Hemp Lime Composites; IHS BRE Press: Watford, UK Chan, J.W.K. and Tong, T.K.L., 2007. Multi-criteria material selections and end-of-life product strategy: Grey relational analysis approach. Mater. Des, 28, pp. 1539-1546. Flórez, L.; Castro-Lacouture, D.; Sefair, J.A. and Medaglia, A.L., 2009. Optimization model for the selection of materials using the LEED green building rating system. Build. Environ, 44, pp. 1162-1170. Rahman, S.; Perera, S.; Odeyinka, H. and Bi, Y. A. 2008. Conceptual Knowledge-based Cost Model for Optimizing the Selection of Materials and Technology for Building Design. In Proceedings of the 24th Annual ARCOM Conference, Cardiff, UK, Dainty, A., Ed.; pp. 217-225. Van Kesteren, I.E.H., Stappers, P.J. and Kandachar, P.V., 2005. Representing Product Personality in Relation to Materials in a Product Design Problem. In Proceedings of the 1st Nordic Design Research Conference, Copenhagen, Denmark Read More