Wednesday, April 3, 2019
Mechanisms of the Immune System: An Overview
Mechanisms of the Immune System An OverviewWhen the compassionate trunk is attacked by seeds or pathogens, it defends itself exploitation certain mechanisms. in that location ar two personafuls of mechanisms atomic exit 53 which is non-specific and the separate which is specific to the attack. The non-specific mechanism is similar no exit what attacks the dust and is again sub divided into external and internal defences.The first limn of defencesThe physical grammatical locutions first business concern of defense against pathogens is roughlyly physical. It involves sweat, come up, tears, mucus and stomach acid. Our jumble and mucous membraneswhich line the body passages, be f broad expendly effective in keeping most pathogens proscribed of the body. They act akin a tutelary barrier, defending against viral and bacteriuml invaders. The shinny th infra mugnot be penetrated by bacteria or vir usances under normal conditions. It has a pH range of 3-5 which is acrid enough to save the growth of bacteria. The clotting of course near leave wounds prevents an open space for antigens to considerably enter the organism by coagulating the blood, and Lysozymes ar an enzyme ensn be in tears and saliva that ingest powerful digestive capabilities, and ass break d give birth contrary agents to a right emplacement before they enter the body. Mucus in the nose traps pathogens, which atomic number 18 wherefore washed a sort or sup demonstrateed by chemical substances.The respiratory folder as well has its own line of defense. Invading microbes and debris be detain in layers of mucous or they be filtered by tiny hair uniform complex body parts c on the wholeed cilia. The cilia move in waves, sweeping the debris towards the entrance where they scum bag be extracted finished coughing or sneezing, so dont hold your sneezes inAndCorrosive acids in the stomach and protein digesting enzymes abrogate most of the incursive organ isms machineried in by food.The first line makes a real powerful line of defence, just some snips intruders force out find their way past this w two. Thankfully we guide a randomness line on the insideThe second line of defenceThe second line of defence is immobilized when invaders enter in the body. A nonspecific internal defence mechanism is the process of phagocytosis the ingestion of trespassing(a) bacteria by certain blood electric cellphones. There be many a(prenominal) some other(prenominal) phagocytic chemical reactions employ in the body. When hostile particles penetrate the skin like in cases of injury, certain leukocytes know as monocytes move to the blood tissues where they phrase into eaters c all(prenominal)ed macrophages. Using pseudopods, the macrophages engulf and destroy the bacteria with their enzymes.Another phagocytic reaction white blood cells. Neutrophils be attracted to chemical signals move off by cells that cast been damaged by microbes . In the process of called chemotaxis, neutrophils move towards infected tissue. The neutrophils therefrom engulf the microbe and complete lysosomal enzymes that digest both the microbe and the leukocyte. The remaining fragments of protein, dead white blood and digested remainder argon called pus. create from raw stuff damage which is throwd by physical damage likewise initiates an rabble-ro apply response. An inflammatory response is a non-specific tolerant response which firmness of purposes in swelling, redness, heat and pain. ichor and inflammation are signs that the second line of defence is at work.That is how your body suffices to a small local anaestheticized injury. The body mess likewise respond to crack upe injuries with a placement- extensive defence. Injured cells emit chemicals that simulate the issue of phagocytic white blood cells and change magnitude their release into the bloodstream.Bone marrow, the source of all blood cells is found in the inne r spongy part of the hurrying leg rig out, upper arm bone, breastbone and shoulder blades.A febricity is a genuine fount of the bodys clay-wide response to infections. When infectious organisms spread through the body like in cold or flu, neutrophils and macrophages digest the invaders and release chemicals into the bloodstream. These chemicals cause your body to reset its thermostat to a higher temperature much(prenominal) as 40 degrees Celsius. These conditions in the body make it difficult for the bad bacteria to survive so es directially, the fever helps you recover. People practically fasten on medication like aspirin to down fever this however whitethorn actually prolong the infection. If the temperature is above 40 degrees Celsius however, it leave alone be unsafe. hold in mind human cells themselves screwingnot survive over 43 degrees Celsius.THE insubordinate SYSTEMThe insubordinate corpse is made up of cells, protein, tissues and organs. It defends us fro m germs and bacteria e truly day. The resistive strategy is usually very(prenominal) undefeated but sometimes when at that place is a problem we coffin nail get infections and illnesses. round the Immune SystemThe immune brass is the bodys defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune dodge attacks organisms that invade body systems and cause disease.The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The cells knotted are white blood cells called leukocytes. Leukocytes are large opaque blood cells that engulf invading microbes and produce antibodies.They combine to seek out and destroy disease-ca use organisms or substances. All leukocytes are produced in bone marrow. There are approximately 6,000,000,000 leukocytes in the human body. They are rather colorless because they dont learn hemoglobin which makes red bloodcells red. They have a life expectancy of 2-3 classs and therefore the body is constanlty making large amounts of leukocytes all the time. Picture this there is half a million white blood cells per very rove of bloodLeukocytes are produced or stored in many locations in the body, including the thymus, spleen, and bone marrow. This is why they are called the lymphoid organs. Leukocytes are withal located in clumps of lymphoid tissue all well-nigh the body. They have asymetrical shapes which can heighten enabling them to get around all obstacles.The leukocytes circulate all around the body amidst the organs and nodes through the lymphatic vessels and the blood vessels. By doing so, the immune system works in a coordinated way to unceasingly monitor the body for germs or substances that might cause problems.There are 2 basic types of Leukocytes They are phagocytes and lymphocytes. Phagocytes are cells that chew up invading organisms and lymphocytes are cells that forgo the body to remember and reco gnize previous(prenominal) invaders and help the body destroy them.There are different types of phagocytes. The most common type is the neutrophil, it primarily fights bacteria. They are the most common type of white blood cell, neutrophils make up 50-70% of white blood cells in the body. They are the first to arrive at infected expansesand kill intruders by ingestion. This process is called chemotaxis. Once the pathogen is sw leaveed the neutrophil dies.The process of neutrophils killing bacteria involves them releasing a net of fibers which traps the cell. This is called neutrophil extracellular trap (N.E.T). whatsoever heap have neutrophil difficiencies and as you can imagine it touchs to severe problems and a compromised immune system.Other types of phagocytes are besophils, Eosinophils, Monocytes and Macrophages. Besophils are very rare in the body, they make up less than 1% of white blood cells. They d not do much as a result and manifestly help respond to infections. E osinophils help ingulf parasites and discharge destructive enzymes to damage invading cells. They also kill parasitic eggs and worms. Monocytes are also very rare in the body, the less monocytes in the body the reveal. They replenish Macrophages and also help against infection. Finally we have Macrophages. They are cells that eat invaders and are entangled in primary and innate immun response. For example they can be found in the lungs where they clean foreign debirs so they do not cause any problems. They usually remain stationed at specific posts in the body where foreign materials often enter. Anything that passes by the macrophages is scanned and if something is suspicious they engluf it. Once englufed the macrophage cereates an enzyme that neutralizes the invader so it becomes harmless and connot replicate and they preserve the antigen so that in the future it can be accept and dealt with faster.The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes pop off out out in the bone marrow and from there they either bind and mature into B cells or they leave for the thymus gland, where they mature into T cells. B lymphocytes and T lymphocytes have different functions. B lymphocytes are like the bodys military cognition system, they seek out their targets and send defenses to lock onto them and label them down. T cells on the other hand are like the soldiers, destroying the invaders that the intelligence systems (B cells) have identified.Antibodies are very specific Y-shaped proteins. For example an antibody produced against the influenza virus is not effective against HIV. These Y-shaped tails of the proteins are very similar, no matter which type of anti-body. Variation may only be produced in the outer(a) edge of severally arm, the area where the anti-body combines with the antigen. Antigen markers are different being on the virus, for example the antigen marker of the influenza virus is different from that of the HIV virus. E ach antigen is tended to(p) by its own antibody, shape wise. The markers of an antigen are located on the membrane of the virus or bacterium. later on each attachment of an antibody, the antibody-antigen combination makes it to a greater extent conspicuous, making it easy to be destroyed by wandering microphage.Antibodies prevent poisons and toxins from destroying cells with receptor sites, found on different cells. This might explain why some poisons affect the nervous system, while others affect digestive or circulative systems. This receptor site is somaed to hold either a hormone or a specific nutrient. Specialized geometrical bodily structures allow toxins and poisons to become attached to the receptor sites on cell membranes. After exploit attached, the poison is ingested by the cell, which the receptor site mistakes for hormones or nutrients, absorbing the poison. Antibodies indeed interfere with the poison so that the structure created is not recognized by the rece ptor cell. Receptor sites are also utilize by viruses as entry ports. As the virus injects its genic material into the cell, it leaves an outer protein show up in the entry port. The outer coat allows the virus to rest in different locations. For example the cold virus has the geometrical shape to allow it to attach the lung cells.How the Body Recognizes Harmful AntigensAs the T-cell scouts, it looks for foreign bodies posing a threat to its survival. The macrophages then attack the invader, engulfing it. As the macrophage presses the antigen into its cell membrane, it couples with the T-cell, also known as a helper T-cell. The T-cell then reads the shape of the antigen and releases a chemical messenger called lymphokine. The B-cells divide into clones because of the lymphokine. A second message is then sent from the helper T-cell to the B-cell, allowing the production of antibodies. A specific type of antibody is produced by each B-cell. Antibodies are attached to their cell mem branes by the time the B-cells enter the circulatory system.The Killer T-cell is an activated additional defender if the helper T-cell. These lymphokines go out for one purpose, which is to destroy. After being activated, the killer T-cells puncture through the cell membrane of the invader, which may differ from a protozoan parasite to a bacterium. Viruses are very different from the rest, as they hide within the structure of the cell. As the viral coat is found attached to the cells membrane, the T-cell attacks the infected cell. Killing the infected cell prevents the reproduction of the virus.Mutated cells are also destroyed by Killer T-cells. This process is extremely important as some of the altered cells may be cancerous. Getting cancerous virus or not depends on the success of the Killer T-cell. The bodys rejection of organ transplants depend on Killer T-cells. Antigen markers on the organ get out be recognized as foreign, sending the Killer T-cells in. Immunosuppressant drug s much(prenominal) as cyclosporine can slow down the Killer T cells. After the battle is done, and won, a different type of T-cell, the suppressor T-cell, signals the immune system to shut down. conference between Suppressor T-cells and Helper T-cells is vital, allowing the immune system to know how many antibodies to produce to contain the antigens. Phagocytes clean the area, removing the dead and injured cells, and tissue begins to fastness and replace.As previously mentioned, helper T-cells must read a blue thistle print of the invader before the B-cells can produce antibodies. This information is stored so that later infections can be destroyed before the microbe can cause any harm. Immunity is based on maintaining a good number of antibodies.Its believed that memory-B cells are generated during the infection to hold an imprint of the antigen or antigens that remember the invader. Most b and t cells produced die off within a few days but memory B-cells remain. It can ident ify the adversary and quickly mobilize antibody-producing B-cells to defeat invading pathogens before they can piss themselves. As long as the memory B-cell survives, a person is immune to the disease, which is why a person cannot catch chicken pox to a greater extent than once.Proteins also play a role in the bodys line of defence. When foreign organisms are present in the body, antimicrobial plasma proteins called complement proteins are activated. There are about 20 known types of complement proteins. chthonian normal conditions these proteins are inactive. When invading microbes trigger them however they in hug drug work as messengers. The complement proteins gather and initiate an attack on the cell membranes of the foreign organism. The proteins go out then form a preservative coating around the invader this seals the invading cell immobilizing it. A second group punctures the cell membrane, this causes water to rush in and let on the cell. The tiny microbes become les s soluble and more susceptible to phagocytes by leukocytes.All of these specialized cells are parts of the immune response system that purport the body fortress against disease. This protection is called immunity.The Several Types of Immunity subjective ImmunityInnate immunity is often called natural immunity, everyone is born with it, it is a general protection. It refers to basic resistance to germs or diseases that other species possess. For example, if a human has HIV their dog wont get HIV because it has innate immunity to that disease. Innate immunity works in both ways something that makes us uneasy wont get another species sick and something that gets another species sick wont get us sick. The Responses in innate immunity are Broad and non specific. The molecules use have a restrain repertoire of recognition. It is a first line of defense.Innate immunity allows the external barriers of the body, like the skin and mucous membranes, which are the first line of defense in preventing diseases from ledger entry the body. If this outer defensive debate is broken, the skin attempts to heal quickly and the second line of defence becomes involved.Adaptive ImmunityThe second kind of protection is adaptive/active immunity, it develops throughout our lives. Adaptive immunity involves the lymphocytes and develops as stack are exposed to diseases or immunized against diseases through vaccination. With all kinds of diseases constantly exposed we adapt out bodies by taking vaccinations to become immune to them.Passive ImmunityPassive immunity isan immunity borrowed externally from another source and it is temporary. For example, antibodies in a mothers breast milk provide the babe with temporary immunity to diseases. This helps protect the baby against infections during childhood when the babys body is lighten in early stages of development and not very strong.Everyones immune system is different. Some people never seem to get infections,while others seem t o be sick all the time. As we grow older, we gradually become more immune to more germs as our immune system comes into contact with more and more of them.Matching tissues for organ transplantThe main challenge is the immune response of the recipient- their immune systems ability to distinguish between self and non-self. The bestower organ is often identified as an invader by manifest markers on its cell membrane, MHC or Major histocompatibility complex. MHC is a protein fingerprint bizarre to each person so the recipient impart make antibodies to destroy what it thinks is a foreign invader.To reduce rejections, attempts are made to match bestower MHC with that of the recipient as closely as possible. For living donor transplants, physicians usually look to close relatives because the MHC is genetically controlled. The better the match, the greater the chances of long bound success.To help reduce rejection factor in decedent donor transplants, (because deceased donor transpla nts cannot usually have as close of an MHC as relatives) immunosuppressive drugs can be splitn, but it will also reduce the immune systems ability to fight off invading viruses and bacteria placing these patients at endangerment of infections.Malfunctions of the immune systemAbnormal functions of the immune system can give rise to two types of problems immune deprivation diseases and in sequester attacks of the immune system against nonthreatening agents. Immune deficiency diseases may be caused by a foreign agent, such as the HIV virus which attacks t-cells, or a hereditary condition such as the severe combined immune deficiency SCID. Inappropriate or exaggerated immune response can also create problems. Hypersensitivity or response is where the immune system attacks normal cells in ones own body, which can destroy tissues and organs.AllergiesAllergies occur when the immune system mistakes harmless cells for harmful invaders. If youre allergic to peanuts, your body recognizes o ne of its proteins as dangerous. Although its safe, your body immobilizes the antibody suck up force against it. change magnitude tissue swelling, mucous secretion, and sometimes constricted air passages are all part of the immune response. Dust, ragweed and strawberries, do not pose any threat to life but the immune response can be so severe that it becomes life threatening. A sever food allergy is called an anaphylactic reaction which involves the respiratory and circulatory systems come with by hives, itching and swelling. When you eat a food to which youre allergic, the cells that believe they are in danger release histamine. It changes the cells of the capillaries, increasing permeability. The enlarged capillary causes the area to redden. White blood cells leave the capillary in search for the invader altering osmotic pressure. Proteins in extracellular fluids create another osmotic force to oppose it. Anaphylactic shock can occur very quickly and weakness, sweating and diff iculty breathing indicate the condition. Medial precautions include carrying a kit with adrenaline (Epipen).Autoimmune DiseaseThe immune system can make mistakes and launch an attack on the bodys own cells. Mutated T and B cells are capable of attacking the body but are usually held in check be suppressor T cells. The mischance of suppressor T cells can cause diseases such as arthritis and flea-bitten fever, all of which can scar the heart muscle. Drugs and serious infections can weaken suppressor T cells leaving the body vulnerable to autoimmune disease. The number of suppressor T cells also declines with age, and this explains the commonness of arthritis in the elderly.Stem cell researchThe answer for replacing damaged tissues may lie in stem cell research rather than transplantation. Stem cells can narrow down and develop into a miscellanea of different tissues such as epithelial tissue, muscle tissue or nerve tissue. Stem cells in the skin continuously replace cells that are sloughed off, give rise to a wide range of blood cells that protect against foreign invaders and identify human cells that have mutated, such as cancer cells. Stem cells are pluripotent cells that can give rise to different types of body cells.Pre pestle cover Advantages and Disadvantages formed Concrete Advantages and DisadvantagesJump to Advantages of formed Concrete device Disadvantages of formed Concrete Construction1.1 Introductionprecast cover is a form of wind, where cover is cast in a reusable mould or form which is then cured in a controlled environs, transported to the twirl site and lifted into place. By producing formed cover in a controlled surround ( formed plant), the formed cover is provides the opportunity to properly cure and be closely monitored by plant employees. There are many different types of precast cover forming systems for architectural applications, differing in size, function and cost. The advantages of using precast cover is the increas ed select of the material, when formed in controlled conditions, and the reduced cost of constructing large forms used with cover poured on site. It is used mainly in the construction of makes with repetitive design and elements, such as schools and apartments.Every construction material system has its own characteristics which influence the layout, span length, construction depth, perceptual constancy system, etc. This is also the case for precast concrete. Not only in comparison to steel, wood, masonry structures, but also with respect to cast unaffected concrete. Precast concrete members may be solid or may contain hollow centre of attentions. Many precast components have thinner cross sections than cast in situ concrete. Precast concrete may be either normal or lightweight concrete. Theoretically, all joints between the precast units could be made in such a way that the completed precast structure has the same concept as a in-situ one. However, this is a wrong approach one, which is very crowd intensive costly. If the full advantages of precast concrete are to be realized, the structure should be conceived according to its specific design philosophyLong spans, appropriate stability concept, simple details,etc. Designers should from the very beginning of the project consider the possibilities, restrictions advantages of precast concrete, its details, constrainr, transport, erection service stages before completing a design in precast concrete.Architectural precast concrete provides architects with an exciting medium when conniving facades for a wide range of buildings, from healthcare facilities to memoryping malls, commercial share buildings to sports stadiums.1.2 History of IBSConcept of IBS in not new and can be traced back to as early 1624. In 1624, panellised timber houses were shipped from England to the new gag rule in North America. In 1851 Crystal Palace in Hyde Park, capital of the United Kingdom and 1889 Eiffel Tower, Paris are the well-known examples of buildings which uses the mode of precast in constructing the structure of the building itself.1.3 Precast building systemPrecast building system is divided into 3 main partsPrecast concrete put inPrecast concrete wallPrecast concrete account1.3.1 precast cover FRAMEDescriptionPrecast concrete frames involve an create-in structure being fabricated off-site. In addition, structural components can be supplied for incorporation into a structure on-site. Frames can simultaneously achieve both structural and decorative design strikements. A variety of mixes, colours and finishes can be used too. The precast frame is composed of precast tower and beam.ProcessPrecast concrete frames are cast in the same way as precast concrete cladding, but as they are designed as structural elements they have heavier reinforcement than readd for non-structural cladding. urbane connections are required between columns and beams to transfer considerable forces without affe cting the optic appearance of the frame.1.3.2 PRECAST CONCRETE WALLDescriptionMany precast concrete walls are cast in a flat lay at the building site. But they are unruffled sort out as precast, not sitecast. When the concrete is strong enough, the wall panels are lifted and hardened in the desired positions for the building. This method is commonly known as tilt-up construction. right away such walls are lifted and placed with cranes, so that moulding can make repeated use of single forms.Some wall units are cast in factories, where the form, attribute of materials, and finishing can be more controlled. Because of their large size and weight, these walls cannot be transported to long distance from the factory. Thus, their use is limited to a short distance from the precast factory.Precast units for ceiling and floor structures are usually prestressed. However, precast wall units are usually courtlyly reinforced with inert steel bars. Precast wall are used for internal e xternal walls, lift shafts, central cores etc. Precast wall systems are by and large used in house servant construction, both for undivided housing for apartments. The solution can be considered as the industrialized from of cast in-situ walls or classical brick or block masonry walls.1.3.3 PRECAST CONCRETE FLOOR SLABPrecast concrete floor slab is the most fully alike(p) precast concrete elements. They are used for making floor and roof slabs. The principle advantages of precast floors are rush along of construction, absence of scaffolding, large variety of types, large span capacity, economy.Precast floors can also be class according to their manufacture into totally partially precast floors. Totally precast floors are composed of units, which are totally cast at the plant. After erection, the units are connected to the structure the longitudinal joints are grouted.In some cases a cast in-situ structural topping screed is added.Partially precast floors are composed of a pre cast part a cast in-situ part. Both parts are working together at the terminal stage to achieve the composite structural capacity. The main totally precast floor roof types are described hereafter.Pre cast hollow core slabMost widely used type of pre cast flooringhighly efficient design and production1.4 Advantages of Precast Concrete ConstructionSome of the advantages of using precast concrete construction are as follows1.4.1 bring down Construction Time and CostPrecast concrete construction will save valuable time and helps to reduce the risk of project stick around and possible monetary losses. Precast design and production of elements can be started while the construction site is under survey or earthworks. intersection are also unaffected by weather conditions due to the controlled environment of the casting area. withal, the tradition of large precast panels will reduce the time taken to complete the structural works. Therefore, other trades such as motion-picture sh ow and electrical wiring can begin work sooner.In pompous construction method, time-consuming works such as formworks, scaffoldings and readiness are needed to produce a structural element. In precast concrete construction method, structural elements are produced in manufacturing plants while other activities at the construction site proceed. When the structural elements are needed, they are immediately sent to the site and assembled continuously, forming the structural frame and enclosing the building. In precast concrete manufacturing plants, modernistic machineries are utilized with several technicians attending to certain production process. This greatly reduced the number of unskilled requirements.1.4.2 High prize and painterly value of productsPrecast products are manufactured in a casting area where critical factors including temperature, mix design and stripping time can be closely checked and controlled and this will discover that the quality of precast products are b etter than cast-in-situ concrete. A huge sum of money will be saved by not having to do rectification works. also due to factory-controlled prefabrication environment, many combinations of colours and textures can be applied easily to the architectural or structural pieces. A vast range of sizes and shapes of precast components can be produced, providing a great deal of flexibility and offer fresher looks to the structures.1.4.3 Cleaner and safer construction sitesUsage of precast elements eliminates or greatly reduces conventional formworks and props. Precast construction also lessens the problem of site wastages and the tie in environmental problems. The prefabricated products also provide a safe working computer programme for role players to work on. Workers and materials are also greatly reduced at the construction sites. Using Just-in-Time principles, the precast elements are kept at the factory cubic yard until the site is ready for installation. Also, as elements are pro duced in the plant and mostly designed to be repetitive, minimal wastage will be drawd at both factory and construction sites.1.4.4 Greater unobstructed spanThe routine of prestressed precast solutions such as the Hollow Core slabs and Double-T beams offer greater unobstructed span than the conventional reinforced concrete elements. Having lesser beams and columns, will provide larger open space. It is very ideal for the construction of places of worship, warehouses, halls, car parks, shops and offices.1.4.5 Lower total construction costAll of the above change the construction processes and increase productivity, quality and safety. As a result, the total cost of construction are reduced. More often than not, most of the opponents of precast construction only use the costs of materials in comparing the in-situ and precast construction without realising that there are hidden costs to the traditional methods. Also a contributing factor to the low usage is the fact that Malaysia ha s unceasingly been able to source cheap moils from neighbouring countries. Therefore, the persistence players are very loth(p) to change to the new construction methods. As a result, the country is go about by problems of low quality, productivity and safety in the construction industry due to high dependency of manual labour. The country also suffers from the run of monies as well as social problems. If the labour supply experience sudden reduction while demand remains the same, labour costs will definitely be increased and produce more problems to the industry.1.4.6 Increased Quality of Structural ElementsPrecast concrete elements produced in plants using modern techniques and machineries. Raw materials such as concrete, sand, and reinforcement bars are under high level of quality control. Formworks used are of higher quality than those used at construction sites. This allows truer shapes and better finishes in precast components. Precast components have higher density and be tter crack control, offering better protection from harsh weathers and sound insulation. High density is achieved by using vibrating table or external vibrators placed on formworks. Precast concrete also provide better fire resistance for reinforcement bars. When compared to in situ concrete, this reduces the amount of long-term movement, which needs to be recognized in building design.1.4.7 Increased Durability and Load Capacity of StructuralElements Prestressed precast concrete components have high structural strength and rigidity, which are important to jut heavy loads. This allows shallow construction depth and long span in structural components. Fewer supporting columns or walls result in larger floor space, which allow more flexibility in interior design. bleak precast and prestressed concrete components are cast-in with smooth steel, concrete or fiberglass. This result in components with smooth surfaces which resist moisture penetration, fungus and corrosion. High density c oncrete reduces the size and quantity of surface voids thus resisting accumulation of dirt and dust. Precast concrete components are more durable to acid attack, friction, corrosion, impact, abrasion, and other environment effects. Precast concrete structures have longer service years and require minimal repairs and maintenance.1.5 Disadvantages of Precast ConcreteSome of the drawbacks of using precast concrete construction are as follows1.5.1 High Capital CostA large amount of resources must be invested initially to set up a precast concrete plant. Sophisticated machineries are expensive and require heavy investment. Percast concrete is mainly used in construction of multistorey buildings and flats, which are atleast 5 storeys high. Precast concrete is also utilized in construction of housing estates where the design of houses is uniform. Other projects where precast concrete is fit are large stadiums, halls, factories, awrehouses, airports and hangars. The scale of the construct ion projects using precast concrete must be large enough to ensure sufficient profit to offset the initial capital cost.1.5.2 Sophisticated Connection WorksThe behavior of connections determines the performance of precast concrete structures. When assembling of precast concrete structures, connections between precast components must be supervised and done properly. This way, the intended behaviour of a connection (simple, semi-rigid, or rigid) can be achieved. Apart from that, a good sound insulation can be provided and water outpouring problem can be avoided. Skilled and well-skilful labours are required to ensure proper connection is produced during erection stages, which lead to additional cost.1.5.3 Transportation, Handling Difficulties and fitting LimitationWorkers must be careful when handling precast concrete components to avoid damage. Precat components are manufactures in plants, which are not always fit(p) in the area of the construction sites. Precast components mus t be carried from the plants to the sites using trailers. Usually, precast components are large and heavy, creating difficulties in transportation. Upon arrival at the sites, take-away cranes or tower cranes will lift the precast components into place for erection. Usually, to increase the speed of construction, several cranes are used requiring large space. Proper construction planning and site management is a must. Workers be well trained to ensure that precast components are positioned and connected properly to avoid cases where the columns, beams, walls, or slabs are not well aligned, dislocated or out of plane. Precast concrete system is not flexible when future modification is taken into account. For example, the walls of a flat built using load bearing precast walls cannot be demolished for renovation purposes, as this will affect the stability of the entire precast structure.1.6 Precast Concrete Construction in MalaysiaThe usage of precast building system is gaining popular ity in Malaysia because of its many advantages such as high quality structural finishes, less labour force, shorter time of uttermost and saves cost. In the construction industry today, the usage of cast in-situ method is not so practical and effective especially when it is in a large scale construction. Therefore, the usage of precast components is the best alternative to forgather the needs in large scale constructions. The precast concrete concept is ideal to suit the future demands of higher specifications and performance for the commercial, industrial, civic and domestic buildings.Precast building system or commonly known as IBS (Industrialized make Systems) in Malaysia has many advantages if it is compared to the traditional cast in situ system. labor of precast components such as beams, columns and slabs were done in the factory thus ensuring high quality control for each component. Structures of precast building can be quickly erected on site and the delays due to concre te curing and concrete formwork removal can be reduced resulting in shorter culmination time of construction. Besides that, precast system requires lesser amount of labour force.1.6.1 Development of IBS in MalaysiaIBS in Malaysia has begun in early 1960s when Ministry of lodgement and Local Government of Malaysia visited several European countries to learn about precast concrete construction and evaluate their housing development program. After their successful visit in 1964, the government had started first project on IBS aims to speed up the delivery time and built affordable and quality houses. Precast concrete construction started in Malaysia with the production of 7 blocks of 17-storey flat, 4 blocks of 4-storey flat and 40 units of shop house opposite the Kuala Lumpur General Hospital at the intersection of Jalan Pekeliling and Jalan Pahang. This project used the Larsen-Nielson system from Denmark. The second construction project, which used precast concrete, was the construc tion of 6 blocks of 17-storey flat, 3 blocks of 18-storey flat and 66 units of shop house along Jalan Rifle, Penang. This project used the Frenchs Estior system. Since then, numerous precast structures such as high-rises, car parks, warehouses, factories, housings and retail units have been built all over the country. Some latest examples are the Telekom Headquarter in KL, townhouses in Cyberjaya, urban center Square in Johor Bahru, Putra Mosque in Putrajaya and Metal Pak Factory in Shah Alam.Today, the use of IBS as a method of construction in Malaysia is evolving. Many confidential companies in Malaysia have teamed up with foreign expert from Australia, United States and lacquer to offer precast solution to their project. In addition, more and more local manufacturers have established themselves in the market. Precast, steel frame and other IBS were used as hybrid construction to build national landmark such as Bukit Jalil Sport Complex, LRT and Petronas Twin Tower. It was repo rted that at least 21 of various manufacturers and suppliers of IBS are actively promoting their system in Malaysia. Nevertheless, the government of Malaysia still feels that the usage of IBS is low despite the possible potential.From the survey conducted by CIDB of Malaysia in 2003, the usage level of IBS in local construction industry stands at 15%. The total registered IBS contractors in Malaysia stand for 1,993 in year 2007 and registered IBS manufacture in Malaysia until 2007 is 138 producing 347 IBS products available in the market.Most of the local developed products are based on traditional materials such as reinforced concrete and the most innovative materials are based on imported technology. previously in the RMK-7, the country intend to construct about 800,000 units of houses for its population using the IBS and 58,500 units planned for the low medium cost houses. However the achievements are spoil with only 20% completed houses reported due to use of conventional cons truction method.1.6.2 IBS as Mass Construction MethodThe term IBS is often misinterpreted with negative meaning as it is always linked with industrialized buildings that were built in 1960s. These buildings are normally associated with prefabricated mass construction method, low quality buildings, leakages, abandoned projects, unpleasant architectural appearances and other drawbacks. Due to the poor architectural design, the old prefabriacted buildings have given the pbulic bad impression about precast concrete.There have been quiet a number of cases where the use of IBS had lead to such drawbacks. For example, in the case of Pekeliling Flats in Kuala Lumpur and Taman Tun Sardon, Gelugor, Penang. These 2 early prefabricated flats were constructed in mass to produce low cost accomodation for lower income groups.However, the design was very basic and not considering the service aspects like the need for wet toilets and bathrooms. absent in this design consideration leads to problems of leakage that becomes the common issue with precast buildings. In addition, in many cases the low cost housings are not maintained properly, thus contributing further to the poor catch of IBS buildings.1.6.3 Characteristics of IBSIndustrial production of components though prefabrication.Reduced labour during prefabrication of components and site works. juvenile design and manufacturing method using CAD/CAM.Systematic Quality comptroller i.e ISO 9000.Open Building System i.e permitting hybrid applications.1.6.4 Why IBSBudget dialect 2005The Government is determined to ensure that every Malayan will have access to affordable homes. During the period 1971-2003, the Government constructed 490,000 units of low-cost houses. The government intends to provide an additional 100,000 units of affordable homes to be implemented through the Industrialised Building System (IBS).This system will ensure quality, save cost, create a safer and cleaner working environment as well as reduce the d ependence of foreign workers1.6.5 Social ProblemsCurrently 75 foreign workers out of 100 construction workers.There are 318,000 foreign workers in Malaysian Construction IndustryLet say one foreign worker gain RM400 per month RM400.00 x 12 months = RM5,000 per year, 318,000 x RM5,000 = RM 1.59 Billion per yearIt shows the High outflow of Ringgit1.6.6 Types of IBSThe construction method can be classified into 4 categories
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment