Mechanisms of the Immune System: An Overview

Mechanisms of the Immune System: An Overview When the human body is attacked by microbes or pathogens, it defends itself using certain mechanisms. There are two types of mechanisms one which is non-specific and the other which is specific to the attack. The non-specific mechanism is similar no matter what attacks the body and is again sub divided into external and internal defences. The first line of defences The bodys first line of defense against pathogens is mostly physical. It involves sweat, skin, tears, mucus and stomach acid. Our skin and mucous membraneswhich line the body passages, are fairly effective in keeping most pathogens out of the body. They act like a protective barrier, defending against viral and bacterial invaders. The skin cannot be penetrated by bacteria or viruses under normal conditions. It has a pH range of 3-5 which is acidic enough to prevent the growth of bacteria. The clotting of blood near open wounds prevents an open space for antigens to easily enter the organism by coagulating the blood, and Lysozymes are an enzyme found in tears and saliva that have powerful digestive capabilities, and can break down foreign agents to a harmless status before they enter the body. Mucus in the nose traps pathogens, which are then washed away or destroyed by chemicals. The respiratory tract also has its own line of defense. Invading microbes and debris are trapped in layers of mucous or they are filtered by tiny hair like structures called cilia. The cilia move in waves, sweeping the debris towards the entrance where they can be extracted through coughing or sneezing, so dont hold your sneezes in!AndCorrosive acids in the stomach and protein digesting enzymes destroy most of the invading organisms carried in by food. The first line makes a very powerful line of defence, but sometimes intruders can find their way past this wall. Thankfully we have a second line on the inside! The second line of defence The 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 invading bacteria by certain blood cells. There are many phagocytic responses used in the body. When foreign particles penetrate the skin; like in cases of injury, certain leukocytes known as monocytes move to the blood tissues where they develop into eaters called macrophages. Using pseudopods, the macrophages engulf and destroy the bacteria with their enzymes. Another phagocytic response: white blood cells. Neutrophils are attracted to chemical signals sent off by cells that have been damaged by microbes. In the process of called chemotaxis, neutrophils move towards infected tissue. The neutrophils then engulf the microbe and release lysosomal enzymes that digest both the microbe and the leukocyte. The remaining fragments of protein, dead white blood and digested remainder are called pus. Tissue damage which is caused by physical damage also initiates an inflammatory response. An inflammatory response is a non-specific immune response which results in swelling, redness, heat and pain. Pus and inflammation are signs that the second line of defence is at work. That is how your body responds to a small localized injury. The body can also respond to severe injuries with a system-wide defence. Injured cells emit chemicals that simulate the production of phagocytic white blood cells and increase their release into the bloodstream. Bone marrow, the source of all blood cells is found in the inner spongy part of the upper leg bone, upper arm bone, breastbone and shoulder blades. A fever is a good example of the bodys system-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 such as 40 degrees Celsius. These conditions in the body make it difficult for the harmful bacteria to survive; so essentially, the fever helps you recover. People often take medication like aspirin to reduce fever; this however may actually prolong the infection. If the temperature is above 40 degrees Celsius however, it can be unsafe. Keep in mind human cells themselves cannot survive over 43 degrees Celsius. THE IMMUNE SYSTEM The immune system is made up of cells, protein, tissues and organs. It defends us from germs and bacteria every day. The immune system is usually very successful but sometimes when there is a problem we can get infections and illnesses. About the Immune System The immune system is the bodys defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system 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 involved 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-causing 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 contain hemoglobin which makes red bloodcells red. They have a life expectancy of 2-3 days 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 drop of blood! Leukocytes 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 also located in clumps of lymphoid tissue all around the body. They have asymetrical shapes which can change enabling them to get around all obstacles. The leukocytes circulate all around the body between the organs and nodes through the lymphatic vessels and the blood vessels. By doing so, the immune system works in a coordinated way to constantly 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 allow the body to remember and recognize previous 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 areasand kill intruders by ingestion. This process is called chemotaxis. Once the pathogen is swallowed 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). Some people have neutrophil difficiencies and as you can imagine it leads 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 simply help respond to infections. Eosinophils 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 better. They replenish Macrophages and also help against infection. Finally we have Macrophages. They are cells that eat invaders and are involved 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 neutral izes the invader so it becomes harmless and connot replicate and they preserve the antigen so that in the future it can be recognized and dealt with faster. The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes start out in the bone marrow and from there they either stay 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 intelligence system, they seek out their targets and send defenses to lock onto them and track 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 edge of each arm, the area where the anti-body combines with the antigen. Antigen markers are different depending on the virus, for example the antigen marker of the influenza virus is different from that of the HIV virus. Each antigen is accompanied by its own antibody, shape wise. The markers of an antigen are located on the membrane of the virus or bacterium. After each attachment of an antibody, the antibody-antigen combination makes it more 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 circulatory systems. This receptor site is designed to hold either a hormone or a specific nutrient. Specialized geometrical structures allow toxins and poisons to become attached to the receptor sites on cell membranes. After bring attached, the poison is ingested by the cell, which the receptor site mistakes for hormones or nutrients, absorbing the poison. Antibodies then interfere with the poison so that the structure created is not recognized by the receptor cell. Receptor sites are also used by viruses as entry ports. As the virus injects its hereditary material into the cell, it leaves an outer protein coat 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 Antigens As 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 membranes 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 cell`s 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 will be recognized as foreign, sending the Killer T-cells in. Immunosuppressant drugs such 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. Communication 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 repair and replace. As previously mentioned, helper T-cells must read a blue 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 characterize the invader. Most b and t cells produced die off within a few days; but memory B-cells remain. It can identify the enemy and quickly mobilize antibody-producing B-cells to defeat invading pathogens before they can establish 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 more 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. Under normal conditions these proteins are inactive. When invading microbes trigger them however they in turn work as messengers. The complement proteins gather and initiate an attack on the cell membranes of the foreign organism. The proteins will then form a protective 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 burst the cell. The tiny microbes become less soluble and more susceptible to phagocytes by leukocytes. All of these specialized cells are parts of the immune response system that offer the body protection against disease. This protection is called immunity. The Several Types of Immunity Innate Immunity Innate 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 sick 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 used have a limited repertoire of recognition. It is a first line of defense. Innate immunity includes the external barriers of the body, like the skin and mucous membranes, which are the first line of defense in preventing diseases from entering the body. If this outer defensive wall is broken, the skin attempts to heal quickly and the second line of defence becomes involved. Adaptive Immunity The second kind of protection is adaptive/active immunity, it develops throughout our lives. Adaptive immunity involves the lymphocytes and develops as people 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 Immunity Passive immunity isan immunity borrowed externally from another source and it is temporary. For example, antibodies in a mothers breast milk provide the baby with temporary immunity to diseases. This helps protect the baby against infections during childhood when the babys body is still in early stages of development and not very strong. Everyones immune system is different. Some people never seem to get infections,while others seem to 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 transplant The main challenge is the immune response of the recipient- their immune systems ability to distinguish between self and non-self. The donor organ is often identified as an invader by distinct markers on its cell membrane, MHC or Major histocompatibility complex. MHC is a protein fingerprint unique to each person so the recipient will make antibodies to destroy what it thinks is a foreign invader. To reduce rejections, attempts are made to match donor 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 term success. To help reduce rejection factor in deceased donor transplants, (because deceased donor transplants cannot usually have as close of an MHC as relatives) immunosuppressant drugs can be given, but it will also reduce the immune systems ability to fight off invading viruses and bacteria; placing these patients at risk of infections. Malfunctions of the immune system: Abnormal functions of the immune system can give rise to two types of problems: immune deficiency diseases and inappropriate 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. Allergies Allergies occur when the immune system mistakes harmless cells for harmful invaders. If youre allergic to peanuts, your body recognizes one of its proteins as dangerous. Although its safe, your body immobilizes the antibody strike force against it. Increased 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 accompanied 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 extracellu lar fluids create another osmotic force to oppose it. Anaphylactic shock can occur very quickly and weakness, sweating and difficulty breathing indicate the condition. Medial precautions include carrying a kit with adrenaline (Epipen). Autoimmune Disease The 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 failure of suppressor T cells can cause diseases such as arthritis and rheumatic 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 research: The answer for replacing damaged tissues may lie in stem cell research rather than transplantation. Stem cells can differentiate and develop into a variety 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. Precast Concrete: Advantages and Disadvantages Precast Concrete: Advantages and Disadvantages Jump to: Advantages of Precast Concrete Construction  | Disadvantages of Precast Concrete Construction 1.1 Introduction Precast concrete is a form of construction, where concrete is cast in a reusable mould or â€Å"form† which is then cured in a controlled environment, transported to the construction site and lifted into place. By producing precast concrete in a controlled environment (precast plant), the precast concrete is provides the opportunity to properly cure and be closely monitored by plant employees. There are many different types of precast concrete forming systems for architectural applications, differing in size, function and cost. The advantages of using precast concrete is the increased quality of the material, when formed in controlled conditions, and the reduced cost of constructing large forms used with concrete poured on site. It is used mainly in the construction of buildings 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, stability 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 in-situ concrete. Precast concrete members may be solid or may contain hollow cores. 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 labour intensive costly. If the full advantages of precast concrete are to be realized, the structure should be conceived according to its specific design philosophy: Long 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, manufacturer, transport, erection service stages before completing a design in precast concrete. Architectural precast concrete provides architects with an exciting medium when designing facades for a wide range of buildings, from healthcare facilities to shopping malls, commercial office buildings to sports stadiums. 1.2 History of IBS Concept 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 settlement in North America. In 1851 Crystal Palace in Hyde Park, London and 1889 Eiffel Tower, Paris are the well-known examples of buildings which uses the method of precast in constructing the structure of the building itself. 1.3 Precast building system Precast building system is divided into 3 main parts: Precast concrete frame Precast concrete wall Precast concrete floor 1.3.1 PRECAST CONCRETE FRAME Description Precast concrete frames involve an entire 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 requirements. A variety of mixes, colours and finishes can be used too. The precast frame is composed of precast column and beam. Process Precast 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 required for non-structural cladding. Elegant connections are required between columns and beams to transfer considerable forces without affecting the visual appearance of the frame. 1.3.2 PRECAST CONCRETE WALL Description Many precast concrete walls are cast in a flat position at the building site. But they are still classified as precast, not sitecast. When the concrete is strong enough, the wall panels are lifted and placed in the desired positions for the building. This method is commonly known as tilt-up construction. Today such walls are lifted and placed with cranes, so that casting can make repeated use of single forms. Some wall units are cast in factories, where the form, quality 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 roof and floor structures are usually prestressed. However, precast wall units are usually conventionally reinforced with inert steel bars. Precast wall are used for internal external walls, lift shafts, central cores etc. Precast wall systems are mostly used in domestic construction, both for individual 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 SLAB Precast concrete floor slab is the most fully standardized precast concrete elements. They are used for making floor and roof slabs. The principle advantages of precast floors are speed of construction, absence of scaffolding, large variety of types, large span capacity, economy. Precast floors can also be classified 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 precast part a cast in-situ part. Both parts are working together at the final stage to achieve the composite structural capacity. The main totally precast floor roof types are described hereafter. Pre cast hollow core slab Most widely used type of pre cast flooring highly efficient design and production 1.4 Advantages of Precast Concrete Construction Some of the advantages of using precast concrete construction are as follows: 1.4.1 Reduced Construction Time and Cost Precast concrete construction will save valuable time and helps to reduce the risk of project delay and possible monetary losses. Precast design and production of elements can be started while the construction site is under survey or earthworks. Production are also unaffected by weather conditions due to the controlled environment of the casting area. Also, the usage of large precast panels will reduce the time taken to complete the structural works. Therefore, other trades such as painting and electrical wiring can begin work sooner. In conventional construction method, time-consuming works such as formworks, scaffoldings and curing 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, modern machineries are utilized with several technicians attending to certain production process. This greatly reduced the number of unskilled requirements. 1.4.2 High quality and aesthetical value of products Precast 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 ensure that the quality of precast products are better 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 sites Usage of precast elements eliminates or greatly reduces conventional formworks and props. Precast construction also lessens the problem of site wastages and the related environmental problems. The prefabricated products also provide a safe working platform for workers 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 yard until the site is ready for installation. Also, as elements are produced in the plant and mostly designed to be repetitive, minimal wastage will be experienced at both factory and construction sites. 1.4.4 Greater unobstructed span The usage 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 costs All of the above simplify the construction processes and increase productivity, quality and safety. As a result, the total costs 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 has always been able to source cheap labours from neighbouring countries. Therefore, the industry players are very reluctant to change to the new construction methods. As a result, the country is faced 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 outflow 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 prob lems to the industry. 1.4.6 Increased Quality of Structural Elements Precast 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 better 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 Structural Elements Prestressed precast concrete components have high structural strength and rigidity, which are important to support 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. Dense 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 concrete 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 Concrete Some of the drawbacks of using precast concrete construction are as follows: 1.5.1 High Capital Cost A 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 high-rise 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 suitable are large stadiums, halls, factories, awrehouses, airports and hangars. The scale of the construction projects using precast concrete must be large enough to ensure sufficient profit to offset the initial capital cost. 1.5.2 Sophisticated Connection Works The behaviour 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 leakage problem can be avoided. Skilled and well-trained labours are required to ensure proper connection is produced during erection stages, which lead to additional cost. 1.5.3 Transportation, Handling Difficulties and Modification Limitation Workers must be careful when handling precast concrete components to avoid damage. Precat components are manufactures in plants, which are not always situated in the area of the construction sites. Precast components must 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, portable 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 w alls cannot be demolished for renovation purposes, as this will affect the stability of the entire precast structure. 1.6 Precast Concrete Construction in Malaysia The usage of precast building system is gaining popularity in Malaysia because of its many advantages such as high quality structural finishes, less labour force, shorter time of completion 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 fulfill 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 Building Systems) in Malaysia has many advantages if it is compared to the traditional cast in situ system. Production 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 concrete curing and concrete formwork removal can be reduced resulting in shorter completion time of construction. Besides that, precast system requires lesser amount of labour force. 1.6.1 Development of IBS in Malaysia IBS in Malaysia has begun in early 1960s when Ministry of Housing 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 construction 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-ris es, 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, City 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 private companies in Malaysia have teamed up with foreign expert from Australia, United States and Japan 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 reported 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 disappointing with only 20% completed houses reported due to use of conventional construction method. 1.6.2 IBS as Mass Construction Method The 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. Lacking 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 image of IBS buildings. 1.6.3 Characteristics of IBS Industrial production of components though prefabrication. Reduced labour during prefabrication of components and site works. Modern design and manufacturing method using CAD/CAM. Systematic Quality Control i.e ISO 9000. Open Building System i.e permitting hybrid applications. 1.6.4 Why IBS Budget Speech 2005: The Government is determined to ensure that every Malaysian 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 dependence of foreign workers 1.6.5 Social Problems Currently 75 foreign workers out of 100 construction workers. There are 318,000 foreign workers in Malaysian Construction Industry Let 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 year It shows the High outflow of Ringgit 1.6.6 Types of IBS The construction method can be classified into 4 categories: