Analysis of Building Material - Assignment Example

FAILURE MODES Name: Course: Instructor: Institution: City: Date Q1. Briefly discuss the main aspects of behaviour of plastics, steel, concrete and wood under normal conditions and under fire conditions. Plastic Plastics are organic polymers of high molecular mass. It is a material that comprises of synthetic or semi-synthetic organics that are malleable and can be transformed into solid objects of different shapes (Duron, 2008). According to Duron (2008), examples of plastics include polythene, polyurethane, nylon, polysulfone, phenolic, poly-ether-ether-ketone, and poly-vinyl-chloride. Plastics have the following features under normal conditions. They have low thermal conductivity for example, acrylic, Plastics under normal conditions can be easily fabricated Some plastics for example, acrylic, are transparent Plastics such as poly-ether-ether-ketone are excellent temperature resistance, excellent flexural and tensile features. Plastics such as Poly-vinyl-chloride, resists both acidic solutions and gases Plastics have low density Plastics have low thermal conductivity, however, exposure to large enough fire will make them burn and produce a liquid substance which on cooling turns into solid. Steel Steel is an alloy of iron and carbon, mainly used in construction since it is very strong (Brannigan, 2007). Brannigan (2007) stated that, steel has the following characteristics; Steel can be effectively connected by bolting and welding in order to form required building shapes or structures. Ductility. Steel can be strongly bent and stressed beyond its elastic limit and, but still consist of enough strength to resist failure. This feature makes steel the perfect building material. It is tough, light and can be molded or transformed into any shape, although it needs to be fireproofed. It only starts loosing strength at a very high temperature. Steel has the ability to resist for a long time, tension, compression and shear forces since it is very strong Steel can be easily put together if a cast is in place. Steel is very strong and ductile and only undergoes transformation or deformation under very high temperatures or when exposed to strong enough fire. Wood Wood is an organic, porous and fibrous structural material extracted from the stems or roots of trees and other woody plants (Duron, 2008). According to Duron (2008), it possesses the following properties; Wood also has defects such as splits, knots, and non-straight grain that concentrate stress. Wood, if properly portioned, its structures can be ductile especially when kept short. They are tough, fibrous, fire supporting, light and are cut and graded by human beings Wood can shrink, weak to shear, compression and tension forces If sheathing is nailed properly, the plywood sheathing of wood structures can make them tough and earthquake resistant. Light wood is highly susceptible to an abrupt collapse due to fire. Also, wood is a poor thermal conductor, however when exposed to fire it will burn into ashes. Their exposure to high ultra violet rays may also cause their deformation. .Concrete Concrete is a composite material consisting of mainly, water, aggregate, and cement. Also reinforcement materials such as rebar are sometimes added into the mixture in order to achieve the required properties of the final product (Brannigan, 2007). According to Brannigan (2007), properties of concrete include; Concrete is strong in terms of compression forces and very weak if subjected to shear and tension forces or high temperatures. A properly reinforced concrete can provide seismically resistant construction especially when the reinforcement is sufficient to resist the shear forces Expansion and shrinkage. Under normal conditions concrete has very low coefficient of expansion. However if provision for expansion is made or very large forces created, cracks can be experienced in some parts of the structure which cannot withstand high heat or temperatures. Elasticity. The modulus of elasticity of a concrete is relatively constant, but starts reducing at high stress level as matrix cracking develops. Concrete when exposed to fire or high temperatures may become very unstable and as a result, crack, sag or break into pieces Q2. Identify and discuss the different types of failure modes that can occur within structures. Types of failure modes According to Duron, (2008), failures in the building structures can either be strength or stiffness dominated. Stiffness failure occurs when displacement in a structure exceeds the laminate’s elongation to failure. On the other hand, strength dominated failure results when the stress unit exceeds the load carrying ability of the laminate. 1) Tensile failures Failure of a building material due to tensile is rare, due to filament reinforcement which makes them strong in tension along their primary axis (Brassell, & Evans, 2012). However they noted that fiber and resin strength properties vary highly in tension, therefore each should be closely analyzed for stress or strain, to ensure limited failure with off-axis loading scenarios. According to Brannigan (2007), in tensile failure, composite materials behavior is characterized of stress-strain curves P Q R Stress T Strain P and Q in the graph above represent tensile strength and elongation at break R shows tensile strength and elongation at yield S shows tensile stress and elongation at break T represents tensile stress and elongation at yield Definitions of Terms Applicable in Tensile Failures Strain is defined as the change in length per unit Elastic limit is the maximum stress that a material can withstand with temporary deformation Proportion limit is the maximum stress that a material can withstand with linear behavior Tensile strength is defined as the maximum tensile strength during the material test. Yield point is the point within the structure where increased strain occurs without increased stress Indicators of Tensile Failure a) Crazing Crazes are always seen as clean fractures extending from the building structure surface to the composite (Brannigan, 2007). They are the first signs of surface tensile failures mostly experienced in plastic materials and coat finishes. Crazes are a combination of fibrils. b) Stress Whitening According to stress whitening mainly is highly experienced in plastic materials that are stretched near their yield point (Stroup, & Walton, 2004). Regions in a building structure with high stress appear to be whitish on the surface. Stress whitening rupturing of water tanks. c) Cracking According to Brannigan (2007), cracks in a building structure are as a result of stress and the environmental state. Cracking is usually accelerated by frequent rising temperatures, thermal and chemical environment and presence of strain and ultraviolet rays Cracking of structures can damage the elevators, cause leakage of gas and hazardous materials and results in collapsing of buildings 2) First Ply Failure First ply failure is a type of failure that takes place when the first ply or group of ply fails in different directions in laminate. The design limit load correlates to first ply failure. The total number of plies, relative stiffness of the plies and load sharing among the piles, determines the relationship between the first ply failure and overall failure of the laminate or structure (Brannigan, 2007). For example, in a structural laminate coated with gel, its surface is highly stressed region of laminate when subjected to flexural loading, although the gel will have the lowest stretch within the laminate. Therefore, the first to fail will be gel coated layer, but the laminate capability or strength of carrying the load will tend to remain unchanged. According to Duron (2008), tensile failure can cause collapse of the stairs, general cracking of the component structure, and damage to elevators, raptures to the water tanks and damage at the construction joints and at the partition joints 3) Compressive Failure According to Brannigan (2007), predicting of compressive failure is not easy since failure can occur at a very small scale such as, buckling or compression of individual fibres. Brannigan (2007) argued that, when compressive failure occurs in sandwich panels, the skin faces may be wrinkled or it may cause unstability of the panel. Classic beam theory is a theory used to explain this behavior and it states that, when the loaded face is in compression, the other face is in tension and as a result the core will experience some shear stress distribution profile. Brassell &, Evans (2012), postulated that, the type of compressive failure for example, that a sandwich laminate will first exhibit is a function of load span, skin to core thickness ratio, the relationship of core to skin stiffness and skin to core bond strength. Crimpling of the core is experienced when shear modulus is too low to transfer load between the skins (Stroup &, Walton, 2004.) They argued that due to this, the panel lacks the required moment of inertia, when the skins are required to resist the entire compressive load without the help from core and therefore it will fail a long thee core. Skin wrinkling is a type of buckling in which the structure skins tend to move away from core and buckle on their own. Sandwich skins can wrinkle symmetrically, anti-symmetrically and or on one side only. According to Brannigan (2007), compressive failure can lead to collapse of the stairs, general structure cracking, walls falling outside, damage to the elevators and poisonous gas or material leaks. . Q3. Discuss the signs of collapse and collapse hazards of different types of construction. Collapse of building structures is mostly as a result of structural deterioration, fire, natural disasters such as mudslides, hurricane tornado ,flooding, earthquakes, collusion impact for example from vehicles, explosions for example of flammable liquids and overloading of structural components (Brassell, & Evans,2012). A collapsing structure has the following signs; Falling or sliding plaster and a falling dust which may arise as a result of heavy winds and heavy rains or snow. Swinging doors and windows Unusual sound, wood crushing, creaking and groaning of the elements of component building structures Columns and walls out of plumb Vibrations. This may cracking of walls, sagging of floors or roof Sagging of floors and roofs which may be as a result of excessive loading on floors and roofs and heavy debris. Cracks in walls, floors, columns or foundations which may have been caused by extreme forces or earthquake Bulging and separating walls which may be effect of aftershocks anticipated to occur following an earthquake. Broken or missing structural elements for example windows and doors which may have been caused by high winds, heavy rains or snow According to Brassell & Evans (2012), collapse is very hazardous and may result into; i. Killing or severe injuries to the building occupants since the floors of a building structure are usually carried upwards and then collapse into a dense rubble pile making chances of survival to be minimal. ii. Exposure of human body to hazardous materials such as toxic gases, carbon monoxide, corrosive materials, radioactive materials iii. Collapse damages buildings. Involves partial or permanent removal of the roof and wall especially on a light frame building. It maybe structural or non-structural in nature and may cause permanent displacement of the building. This as a result may result into the owner incurring losses. iv. Due to flood, for example, structures maybe partly or completely moved off their foundations. References Brassell, L.D., & Evans, D.D(2012), Trends in Structural Collapse, National Institute of Standards and Technology, Gaithersburg, MD, Brannigan, F.L (2007). Building Construction, Third edition, National Building Protection Association, Quincy, Massachusetts, Duron, Z.H (2008). Early Warning Capabilities for Firefighters: Testing of Collapse Prediction Technologies, NIST GCR 03-846, National Institute of Standards and Technology, Gaithersburg, MD Stroup, D.W, & Walton, W.D (2004). Structural Collapse, National Institute of Standards and Technology, Gaithersburg, MD Read More

Wood Wood is an organic, porous and fibrous structural material extracted from the stems or roots of trees and other woody plants (Duron, 2008). According to Duron (2008), it possesses the following properties; Wood also has defects such as splits, knots, and non-straight grain that concentrate stress. Wood, if properly portioned, its structures can be ductile especially when kept short. They are tough, fibrous, fire supporting, light and are cut and graded by human beings Wood can shrink, weak to shear, compression and tension forces If sheathing is nailed properly, the plywood sheathing of wood structures can make them tough and earthquake resistant.

Light wood is highly susceptible to an abrupt collapse due to fire. Also, wood is a poor thermal conductor, however when exposed to fire it will burn into ashes. Their exposure to high ultra violet rays may also cause their deformation. .Concrete Concrete is a composite material consisting of mainly, water, aggregate, and cement. Also reinforcement materials such as rebar are sometimes added into the mixture in order to achieve the required properties of the final product (Brannigan, 2007). According to Brannigan (2007), properties of concrete include; Concrete is strong in terms of compression forces and very weak if subjected to shear and tension forces or high temperatures.

A properly reinforced concrete can provide seismically resistant construction especially when the reinforcement is sufficient to resist the shear forces Expansion and shrinkage. Under normal conditions concrete has very low coefficient of expansion. However if provision for expansion is made or very large forces created, cracks can be experienced in some parts of the structure which cannot withstand high heat or temperatures. Elasticity. The modulus of elasticity of a concrete is relatively constant, but starts reducing at high stress level as matrix cracking develops.

Concrete when exposed to fire or high temperatures may become very unstable and as a result, crack, sag or break into pieces Q2. Identify and discuss the different types of failure modes that can occur within structures. Types of failure modes According to Duron, (2008), failures in the building structures can either be strength or stiffness dominated. Stiffness failure occurs when displacement in a structure exceeds the laminate’s elongation to failure. On the other hand, strength dominated failure results when the stress unit exceeds the load carrying ability of the laminate. 1) Tensile failures Failure of a building material due to tensile is rare, due to filament reinforcement which makes them strong in tension along their primary axis (Brassell, & Evans, 2012).

However they noted that fiber and resin strength properties vary highly in tension, therefore each should be closely analyzed for stress or strain, to ensure limited failure with off-axis loading scenarios. According to Brannigan (2007), in tensile failure, composite materials behavior is characterized of stress-strain curves P Q R Stress T Strain P and Q in the graph above represent tensile strength and elongation at break R shows tensile strength and elongation at yield S shows tensile stress and elongation at break T represents tensile stress and elongation at yield Definitions of Terms Applicable in Tensile Failures Strain is defined as the change in length per unit Elastic limit is the maximum stress that a material can withstand with temporary deformation Proportion limit is the maximum stress that a material can withstand with linear behavior Tensile strength is defined as the maximum tensile strength during the material test.

Yield point is the point within the structure where increased strain occurs without increased stress Indicators of Tensile Failure a) Crazing Crazes are always seen as clean fractures extending from the building structure surface to the composite (Brannigan, 2007).

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