Human Comfort in the Internal Environment
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There are many factors that affect human comfort in the internal built environment. Human comfort is affected by thermal factors; physical factors and personal factors. Another factor that can affect human comfort is sound of the environment around them. The final factor that affects the human comfort is the visual of the room and the light intensity. There are ways to measure the physical factors that affect human thermal comfort, the sound comfort and the visual comfort.
The average temperature inside a building is 19-21 degrees and outside is -1 degrees, but there are two different thermal factors that affect the temperature of the room and human comfort; they are physical and personal factors. The physical factors include; air temperature, mean radiation temperature, relative humidity and air velocity. The air temperature inside of a building will change depending on the temperature outside the building, and the k-values of the materials used to build the walls and insulation. K-values are the values that all materials have which shows how good insulators the materials are, the lower the k-value the more affective the materials are at retaining heat. The u-value is what the overall heat resistance of the materials are. Air temperature is also affected by the people inside the building and they activity they are doing. The mean radiant temperature is also a factor affecting human comfort; the mean radiant temperature is the radiation that is coming into the building from windows and walls, balanced against the radiation given off by the human body. The relative humidity is another factor that affects the air temperature; the relative humidity is the percentage of water vapour saturation that is in the air. The final physical factor that affects human comfort is the air velocity; this is the movement of the air throughout a building or a room. This can be affected by the convection in the room, the warm air enters a room and rises to the ceiling, pushing the cold air downwards and draught also changes the air velocity, the cold air flows into the room and makes the temperature of the draught path colder that the room temperature.
Personal factors can affect the human comfort in a building, these include; age, gender, state of health, clothing and the level of activity. The age of a person greatly affects the temperature of a room; older people give off less heat then younger people. The gender of a person is a factor affecting the temperature they give off, with females giving off 85% less heat than males. Gender is also a factor that affects the temperature given off by people, females give off less heat than males, and they give off 85% of what the male body gives off. The state of health of the person also affects the heat that they give off and the temperature of the room, a person who is sick or has an illness gives off less heat that a person who is physically healthy. The clothing you are wearing also affects the temperature that you need to be comfortable, depending on the weight of the clothing you will need different temperatures to feel comfortable e.g. swimwear 29 degrees, light clothing 25 degrees, suit, jumper 22 degrees, coat, glove, hat 14 degrees. The level of activity you are doing also affects the heat that you give off and the temperature needed to feel comfortable. Sleeping 70W, watching TV 115W, office 140W, factory work 265W, lifting 440W.
Sound in the environment that a person occupies greatly affects their comfort in the building. Sound is a form of energy that is transmitted in pressure waves and changes depending on the pressure of the air in the room. Sound is the vibration of the particles in a wave that send the particles in all directions and spread out; this creates a pattern of refraction and compaction. Sound has two different sources and types where it can originate from, they are impact/structure-borne sound and air-borne sound. These are different as they are where the source of the sound comes from. Air-bone sound is sound which travels through the air before reaching a partition, meaning that the vibrations must have travelled through the air before they reach the partition. Main sources of air-borne noise are; voices, radios and musical instruments. Impact sound is vibrations that are generated on the partition and a continuous vibration can be classed as a series of impact noises in succession. Impact noise does not travel through air like air-borne noise does. The main sources of impact noise are; footsteps, slamming doors and vibrating machinery. It is important to know the difference between impact and air-borne noise as the methods that are used to prevent them are very different. However a single source could generate both air-borne and impact noise e.g. footsteps, on the floor below the origin, the sound would be impact as it is started on the partition, but in the room of the sound it travels through it before reaching the partition making it both air-born and impact. There are different ways of preventing both types of sound, so different installations must be put in to insulate from the type of sound. Air-born sound can be prevented by a mass of partitions e.g. thick walls as lightweight particles give very little resistance unless they are in layers. The main ways to prevent impact sound are by using vibration pads and soft covering on floors and walls. Sound reverberates, so if a sound suddenly stops the sound will not stop instantly. The time taken for the reverberation of a sound decays at different rates depending on the area of the exposed surfaces, sound absorption values of the materials used in the building, the distance between the surfaces and the sound and the frequency of the sound.
The final factor that affects human comfort is light intensity. If the light levels are too low or too high then it will not be as suitable. Light travels in rays and bounces off objects and into the eye. The rays cannot bend so they must go in straight lines, but light can be refracted through certain materials which can bend the beam slightly. The light needs to be the right intensity so that the eyes don't have to strain too much if it is too dark or if the light is too bright it may blind. Light can be controlled by letting certain amounts of natural light through windows and also by the brightness of the artificial light from the light bulbs. Natural light can be controlled by using darkened windows and the artificial light can be controlled by having dimmers on the lights to change the intensity as the intensity of natural light changes. Glare can affect the human comfort, glare is a light intensity that is too high reflecting off a surface and reflecting into the eyes making it difficult to see detail or may cause visual discomfort.
P2- Describe how each factor is measured
There are methods that are used to measure the physical factors that affect human thermal comfort. To measure the physical factors, the instruments that are used are; thermometers, globe thermometer, hygrometer and anemometer. A thermometer is a device that is used to measure the temperature of a room, a thermometer includes a liquid that rises as the temperature does and on the side a scale that measures the temperature in °C and degrees °F. A globe thermometer is a device that measures radiant heat and consists of a thermometer sensor with a bulb located at the middle of a black copper bulb. The globe thermometers units' of measurement are °C. This can be used to calculate the mean radiant temperature providing that you know the air velocity and temperature. A hygrometer is an instrument that is used to measure that saturation of water vapour in the air of the surrounding environment. This instrument relies on the pressure, temperature, mass and mechanical or electrical change. By calibrating the device and calculating the other factors the humidity can be worked out. It measures its units in percentages. An anemometer is a device used to measure the speed of wind, but there is also an anemometer that measures the pressure of wind, it consists of three or four cups that revolve around a shaft at different speeds depending on the wind temperature and pressure. They are measure in meters per second.
Sound is measured using a sound level meter, this instrument analyses the sound that it picks up and uses electronics to convert the sound onto a digital scale. Sound level meter can pick up sound instantly or can be used to pick sound up over time and the average can be calculated.
The intensity of light in a room can be measured using a light meter. The light meter works using an electrical current which is generated by photosensitive electrons that detect the amount of light hitting the surface. This causes the electrons to react depending on the amount hitting the surface and is then converted into an electrical reading.
P3- State acceptable values for each factor
Each measurement has a range of acceptable values that affect the human comfort is the environment. The suitable range for temperature in a room is from 19°C- 21°C. This is also the same value with a globe thermometer. The acceptable value for the humidity of a room ranges from 40%-60%.
The units of measurement that sound is calculated in is decibels and the suitable range in a workplace is from 135dB-137dB maximum.
Light intensity is measured using Lux, the acceptable values for the intensity of light is 50- 100Lux.
P4- Interpret underpinning concepts relating to structures under load
Buildings have many different components that are used to keep the building steady and ensure that it is as structurally strong as possible. There are six different structural members that are used in buildings, they are; struts, ties, beams, columns, roof and frames.
In buildings the structural members are used to assist the buildings when they are holding a load or to help protect against loads. There are three different types of loads that are user upon a building, they are; dead loads, imposed loads and wind loads.
A tie is a structural component that is designed to carry tensile force on a building or high standing structure. They hold the building steady and help to resist high winds. Struts are used to distribute the weight throughout the building. The strut attaches to the roof and wall. The weight of the roof pushes down on the struts and transfers the weight onto the wall. This is the compressive force that is pushing against the weight of the structure. Beams are used to span between walls, they have both the forces of compression and tension acting upon them. They can be supported by columns. Columns are used to support a weight and transfer it vertically and downwards, they support the foundation and can be used to prevent beams from bending and breaking under the force. Beams are also used to keep the columns in place. They vary in size and are very important to the structure, if they are too long or too thin then the column may become distorted and will not work well. Walls are also a structural member. There are two different kinds of walls; they are load bearing and non-load bearing in fill panels. Load bearing walls are classed as structural elements as the force is safely carried to the foundations of the structure. They are built of stronger materials than normal walls; this makes the walls more solid and prevents the wall from breaking. The non-load bearing walls are made of cheaper, lighter materials as they are not needed for structural integrity. Frames are the final structural member. Frames are when all of the other structural members are linked together in a building. There are different kinds of frames depending on which structural members are linked together. Frames can be designed on computer software which makes the complex structures easier to make. However, they still need reviewing. There are three different types of frame structures, they are; grid skeleton, truss frame and portal frame.
The three different types of load are dead loads, imposed loads and wind loads. Dead loads are loads which are stationary and will not move throughout the life time of the building. They remain static and are never added to or removed from the structure. Imposed loads are another load that acts upon a building. Imposed loads are also known as dynamic loads. They are loads that change throughout the life of a building. Live loads can unpredictably change, so the supports that are used need to be placed for unpredictable changes. The final load that acts upon a building is wind load. The wind load can be also classed as a live load. They are unpredictable and can vary depending on where the building is and the exposure of the walls. The resistance of the walls needs to be designed to resist live loads that will change unpredictably.
A building will have different kinds of loads on it. There are two different kinds of load configurations, they are; point loads and uniformly distributed loads. The way that the buildings are strengthened for the different loads varies greatly to be as safe and efficient as possible. A point load is a weight that will act on a certain point on the floor; this is normally used for a heavy item that won't be moved. This is supported by a beam with greater or equal strength pushing upwards. However, a uniformly distributed load is for live loads that will move constantly and isn't too heavy. The uniformly distributed loads are evenly distributed loads throughout the structure. It is easier to design a building on the uniformly distributed load as this works for most loads that are in a building.
Buildings have many things that can change their forms and shapes. Stresses act on the structural members and materials that are used in the building. The different types of stresses are; compression, tension, shear, stress and strain. Compression is a vertical force that is formed when a downward force pushes down on the structure. Stress is the force, in newton's, that is acting upon a cross sectional area. Compression and tension usually act upon the same objects, such as a beam. Tension is when the fibres within the material are being pulled apart. The material is stretched and disfigured, making it weaker. When shear is acting upon a material the layers of the object shift and the object becomes weaker and stretched. This can pull apart materials which are connected by bolting and welding. Strain is not a force, but it is a measurement, it is the extension of length. Strain has no unit as it is ratio. There are three different types of strain; tensile strain, compressive strain and shear strain. Tensile strain is when the fore applied pulls a material from both ends, this stretches the material. Compressive strain is when the force applied crushes or compresses a material; this reduces the length of the material. Shear strain is the force applied which changes the shape of an object. However, the volume of the material stays the same.
P5- Predict simple structural behaviour from given data
Negative shear on a beam will force the right hand side of the beam upwards, distorting the shape and strength in the left half of the beam. Whereas, positive shear on a beam will force the left hand side upwards, this could result in the beam cracking or snapping.
Bending on a beam also affects the shape and effectiveness of a beam. Positive bending in a beam causes the beam to bend downwards and causes more pressure on the lower cross section of the beam; this is known as 'sagging'. But negative bending causes the beam to bend upwards, putting more pressure on the upper cross section of the beam; this is known as 'hogging'. These both cause distortion on the beam and make the beam unfit for its use.
P6 - Identify the main performance criteria relating to the specification of a range of vocationally relevant construction materials
There are many materials that can be used in a building. Each of the different materials has different uses and is suited to preventing certain things happening to the buildings structure and aesthetics. Three materials that are most commonly used as building materials are; timber, plastics and metals.
Timber is one of the most common materials used in a building. It is very versatile and can be used for many things. Timber has been used in buildings for thousands of years.
Timber is strong because of the direction of the grain. If it is split across the grain it is much stronger than splitting down the grain. But if the timber is split perpendicular to its grain it will be much weaker. Timber is a very rigid material and has and does not bend unless under very high amounts of stress and would snap if too much weight and pressure is put upon it. Timber is a porous material as it has pockets of air; this means that it can absorb water. Timber materials are hydroscopic, meaning that they easily absorb large amounts of water from the air. Because of moisture movement, this means that if hydrated timber goes from a cold place to a heated house then the timber would shrink, become distorted and crack. Timber has no thermal or electrical conductivity, meaning that it has high resistivity. Timber does not conduct electricity or heat. This means that is can be used to stop the flow of electricity and heat. Timber has a very low U-value, so it is a very good material to insulate with. Timber is also a very durable and strong material. However, it is not fireproof, meaning that if it is exposed to fire it will burn.
Because timber is inconsistent, it must be stress graded so that it can be set to different uses. There are many different uses for timber; floor joists, ceiling joists, roof rafters, hip rafters and roof trusses. TRADA literature is responsible for grading the timber, their uses and the average span of the timber.
Metal has multiple uses in construction because of its diversity. The metal that is used the most in construction is mild steel. Steel is very strong and can cope well many different situations; steel can also have a small high of elasticity in it depending on its size and width. Steel can normally take a high amount of stress and will return to its original shape, meaning that steel has a high elastic limit. Steel has no prosperity, meaning that is has no air gaps in it and cannot absorb water. Steel is a water proof material and can be used to store water, block an area or route of water or to protect something from water e.g. steel roof sheeting. When steel is heated it will expand. Steel, like any other metal, is a very good conductor of thermal and electrical energy. This meant that metals can be used as electrical wiring and radiators. Steel, because of its density, allows it to be a durable material. But it may rust if it is not maintained. Metal is used a lot in construction; lead roof lining, stainless steel wall tiles, steel frames and galvanised roof straps.
Plastics are another material that is frequently used lots in construction. Plastics are complex compounds that are produced by polymerisation. Plastics are malleable, so they can be altered and moulded into any shape and used for many different things. . Plastic is very resilient and does not degrade. They are also very versatile and most plastics are water proof and cheap. Plastic is not a very strong material and, but plastic has high elasticity, so it will begin to deform quicker but will return to its original shape. Plastic is not a very porous material and will resist water well, making it a good material to stop the flow of water. This also means that the moisture movement within plastic would not change as because it has no air pockets that can fill with moisture. Although plastic has a high electrical resistivity, it has a very high thermal conductivity, making it a good material to insulate wiring, but also a good material to distribute heat. Plastics are not very durable as they can scratch easily and can become weathered, so are often used inside and covered.
Plastics are used in many different parts of construction; PVC window frames, to cover and watertight gaps.
P7- Describe the production process and/or manufacturing process for two vocationally relevant construction materials
All materials that are used in construction must go through a specific production process to make them as strong and pure as possible. This is so that they will last longer and many will be recyclable.
Timber has a very specific process that makes it as strong as it can and as resilient as possible.
When trees are cut down for timber they are selected and only certain trees may be cut down from certain areas. After the trees are cut down they must be replaced so that the population of trees stays steady. When trees are cut down they are very moist, so they must dry the timber out. They do this by using a certain method. This method is air/ kiln drying. After this is done, the moisture of the tree is reduced greatly and the timber becomes stronger. Many different timber products can then be produced by from the timber after the moisture percentage drops below 20%.
There are two different categories for timber, they are hardwood and softwood. Hardwoods are stronger than soft woods because the hardwoods contain two types of cells. There are cells that transfer sap and cells that provide strength to the tree. There are many different trees that produce hardwood, they are; oak, beech, ash and walnut. Softwood trees are weaker and normally include trees such as Douglas fir.
When steel is produced it can go through one of two processes which strengthen and purify the steel and make it as strong as possible.
The UK steel industry uses two different processes to manufacture steel. The arc furnace is use, this is powered by electricity. The other method is the basic oxygen converter. There are three raw materials that are used to make steel, they are; fluxes, molten iron and coke.
The arc process uses raw materials that are cold to start with. A vessel is filled with lots of recycled scrap steel. Electric probes are dropped into the vessel and the lid is shut. When the power is turned on arcs from between the probes and melts the mixture. Other metals are added as the process goes on so that the best quality steel can be produced. Oxygen is blown into the mixture so that the steel can be purified.
The second method that is used to create mild steel is the oxygen convertor. This process uses molten iron, produced in a blast furnace. The molten iron is poured into a vessel and scrap steel is added. Oxygen is then blown into the mixture by a lance, this purifies the steel and the impurities float to the surface of the mixture. The bi-product of this process, slag, is then scraped off the top. The purified steel is then taken to be processed into ingots, billets or is continuously poured and rolled into shape.
P8- Describe the important features and properties of construction-related materials
There are many different criteria that affect the materials and whether or not the materials are effective. The specifications which affect these are whether it is fit for purpose, aesthetics, the costs, resistance to degradation, ease of installation and use, environmental implications, sustainability and recycling potential, COSHH considerations and compatibility of the materials. All of these factors will affect the decision of which materials to use.
Fit for purpose
Materials usually have a standard or specification set by and recognised standards body. All materials have a set 'fit for purpose'; these are recognised worldwide and are the quality standards. This is so that the materials can be purchased globally with the same specifications.
The appearance of a material is very important to the architects, designers and the client. The look of the material can also be linked in with the texture of the material and the materials that are used with it. Light can also be a large factor in the appearance of materials. The look of the material may change in different lights and different temperatures. The traditional materials that were being used are less popular and the newer, greener materials are becoming more popular and are seen as more attractive.
Costs of materials are also a very important factor in the decision of what will be used. If the budget of the project is low or running out then the materials would have to be cheaper. Higher quality materials are also more costly than materials that are a lower quality. However, more expensive materials will prove to be cheaper in the long term over a longer time as they will not need to be replaced changed or repaired often.
Resistance to degradation
Materials quality and density is linked with the resistance of the material. If the material is used in a busy area then it will need to be a more dense material. Degradation can be a result of many things;
Sunlight's harmful UV rays
Age of the material
Design is a very important factor in the resistance of material. The placements of certain things that help the materials resist certain factors. Material selection takes many factors into account, the environment, location and the usage.
Ease of installation or use
A material that would need tradesman to install would be more costly than a material that could be installed and used by anyone. If a material is also easily maintained, it will be cheaper and more desirable. If a material needs replacing it may cost a lot more if a tradesman in needed again. A cheaper material may also have large costs when it needs to be replaced or repaired at the end of its life span.
Issues involving greener materials are becoming more important with new buildings. Whether a material is environmentally friendly is a large factor in material selection. The amount of carbon produced in the manufacturing of the material and the embedded energy must both be taken into consideration when deciding on a material. Materials which are wholly or partially recycled should be considered over other materials so that the effect of global warming can be reduced.
Sustainability and recycling potential
Materials should now include elements of sustainable materials and should be designed with regards with the environment so that valuable resources are not use up in the process. Timber products are a good material as they are produced from trees, which can be re-grown and will not run out, the waste materials can be used for different products and can be recycled into other products after it has been used and needs to be changed.
The control of substances hazardous to health is very important when choosing materials to build with. This is important as it takes into account:
- Chemicals used in the production of the material
- Chemicals used to treat the materials
- Chemical additive part of a material
Many materials include chemicals which are harmful, so they need a trained operative to install the materials. Products like solvents are being replaced in use as the solvents are harmful to the environment in its use in modern products and also the production process. Manufacturer's data sheets are also read so that the chemicals used are safe and acceptable and if not then the chemicals should be changed so that it is less harmful to the environment.
Compatibility is also a factor which affects the material choice. If certain materials are not compatible with each other and may react badly to each other, this can cause types of corrosion and would be costly in maintenance and replacement. Ways that this can be avoided is by applying finishes to the surfaces that will protect them from chemicals given off in reactions.
The properties of a material have a large effect on the decision of the material that will be used. Different materials have different strengths and will be better suited in certain situations. The properties that are taken into account are; strength, elasticity, porosity and water absorption, thermal and moisture movement, thermal and electrical conductivity/resistivity, thermal transmittance, durability, workability, density, specific heat capacity and viscosity.
The strength of a material is the amount of tension, stress or weight that a material will be able to endure before the materials limit is reached and begins to deform. Materials strength vary depending on the type of material.
Elasticity is the amount of stress that a material can take before it reaches its elastic limit and the material becomes distorted and its dimensions are altered permanently. The elasticity of a material will also vary depending on the production and the nature of the material.
Porosity and water absorption
Porosity is the amount of air pockets or pores that are within a material. The density of a material is closely linked with porosity. If a material is heaver per unit volume then it will have fewer pores inside. The porosity of a material is tested by weighing the material then leaving the material in water for a set amount of time and re-weighing the material. This will provide a measurement, which can be shown as percentages, of the amount of water that the material absorbed.
Thermal and moisture movement
Thermal movement is changes in materials depending on the time of year. All materials contract with cold and expand with heat. Many materials have high rates of expansion and contraction, so predictions of joints must be provided for in the brickwork or concrete. These joints would allow for expansion and contraction and helpful in areas with changing climates.
Moisture movement is the ability for materials to absorb water from the air. Materials that can absorb a lot of moisture from the air may expand and deform. But if placed into a warm area, they can shrink and become distorted.
Thermal and electrical conductivity/resistivity
The thermal and electrical resistivity is the materials ability to block the passage of electric and thermal energy. Thermal and electrical conductivity is closely linked in materials. Materials that are good conductors of heat are usually good conductors of electricity. However, plastics don't conduct electricity but are good conductors of heat. Any metal can conduct electricity.
Thermal transmittance is the U-value of a material. The U-value of materials tells you how effective the material is at stopping heat. If a U-value is lower it is more efficient at stopping the passage of heat.
Durability is the materials resistance to any form of damage that can occur to the surface of the material. This is also linked to the life cycle of the materials. Denser materials are very durable and can withstand large amounts of surface damage, making them more hard wearing than materials that are less dense. Materials durability also depends on whether the material is looked after correctly and if it has the right forms of varnish and protection.
Workability is how easily a material can be produced and formed. The workability of materials has many factors that affect it. If a material has too much or too little of what is needed to make it then the material will be harder to work with and form into the right shapes and sizes without any imperfections.
The density of a material is how heavy it is in comparison to its size. Density is also the degree of how compact the material is. Denser materials are more durable and usually have a longer life span. Density is expressed as:
Density = Mass
Specific heat capacity
Specific heat capacity is the change in the number of joules in a material or substance without the material changing its state. This is closely linked with thermal capacity, which is how much heat can be stored in a material. Thermal capacity is expressed as: Thermal capacity = Mass X Specific capacity
The amount of heat needed to cause a change in the temperature of a material's specific mass is expressed as: Quantity of heat = MCΔT
Viscosity is the resistance of a liquid to flow. Viscosity is closely linked with materials workability. If the substance is thicker then it will be harder to use and apply. Because of gravity the viscosity of a material has to be right for the application of the material.
P9- Explain how construction materials can deteriorate in use
All materials have a life span and will eventually need replacement. There forms of deterioration that may speed up the process or affect the material. They are; corrosion, electrolytic action, fungal attack, insect attack, frost attack, chemical and sulphate attack, efflorescence, ultraviolet attack, stress fatigue and the role of water in failure mechanisms.
Corrosion is a process which happens mainly on metals. When the material is in contact with air and water rust will start to form and this will run down the material and turn it into an orange colour which stains.
Certain metals which come into contact with water may have an electrolytic action. This is when one of the metals may corrode. Materials for roofing and other forms of protection from rain do not corrode due to electrolytic action so that long term corrosion can be avoided.
Timber based materials are the most prone to fungal attack. Fungal attack can come in two forms, which are dry rot and wet rot. Dry rot is caused by fungal attack, but wet rot is the natural degradation of a material that is too moist. If a timber material starts to degrade due to rot it will become weak and could fail to carry loads required. However, dry rot can spread through other materials and can be very bad for any material that it passes onto. The only way to fix dry rot is to remove the infected materials and fungus.
Insect attacks occur mainly on timber materials. The insects burrow into the timber and eat the material from the inside. This affects the strength of timber greatly and will eventually cause the timber to crumble to a powder.
Frost attack occurs when the temperature drops below freezing. The water vapour on materials will solidify and form ice crystals. The frost can affect external brick work and cause shelling off. If the material is porous then the water vapour inside the material will also freeze and expand causing the materials to become structurally weaker and to break outwards.
Chemical and sulphate attacks
Chemical attacks occur on stone materials. This is most common in the form of acid rain. This gradually wears away the surface of the stone and removes any features. Chemical attacks can also occur from the burning of fuels at they contain high amounts of chemicals that can be harmful. In busy built up areas chemicals will layer up on materials and will cause discolouration and damage.
Sulphate attacks occur mainly on materials that have sulphates which can react with concrete cement. Sulphate attacks can occur where water absorbs sulphates from the ground and reacts with cement foundations and can weaken the buildings.
Efflorescence is the effect of water moving through a material. The water absorbs the salt from the inside of the materials and when the water evaporates it leaves the salt crystals on the surface of the building. This is obvious to the eye and but can be removed or will clear when all of the salts are dissolved or washed away.
Ultraviolet attacks are cause by the UV radiation in the sun's rays discolouring and bleaching the materials. This is obvious to see but can be prevented f the materials are treat correctly.
Stress fatigue is caused by constant large amounts of stress on a material that is structurally important. This can cause a permanent deformation of the material. Stress fatigue is rare in materials but can also be caused form forces from the wind. Roofs must be built so that they can withstand the stress of the wind and the weights above them.
Role of water in failure mechanisms
Large amounts of water can cause failures in systems that are put in place to prevent water. Guttering may break with high amounts of rain and could cause water to leak into the building and cause internal damage. Water is not very viscous so it can seep through very small gaps and cracks. Water can also cause visual staining due to the dirt that is in the air.
P10- Explain the preventative and remedial techniques used to prevent deterioration of construction materials
The use of stainless steel
Full painting programme
Metal breakdown and loss
Use metal which are similar and will not react with each other
Wet and dry rot
Removal and replacement of infected timber
Prevent moisture entering timber
Structure of timber eaten away
Woodworm chemical treatment
Timber treatment using pressure impregnated chemicals
Shelling of outer surface of brick work
Use class A or B engineering bricks below damp-proof course
High specification facing brickwork
Motor joint maintenance
Breakdown of limestone
Replacement of stone with harder material
Treatment of surface stone
Breakdown of chemical bonds of cement
Use sulphate-resistance cement
Re-pointing using sulphate-resistance cement mortar
Formation of salt crystals
Wash down and remove salt
Surface treatment with chemicals
Quality specification on bricks
Known source of sands
UV fixed colours resistant to UV light
Metal fracture and failure
Over design on fixings
Factors of safety
High strength stainless steel fixings
Role of water in failure mechanisms
Dirt build up
Use of weather drips
Overhangs to direct water
Regular maintenance of guttering overflows and downpipes
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