In the following Technical paper, Arvind Shah and Dr. Narendra Patel, state the important of precast prestressed concrete panels for mass housing stating various places where this technology has been used.Awareness, acceptance and availability are pnor requirements for any product to be used on a mass scale. Precast Prestressed Concrete buildings though widely used throughout the world has not found its proper place in Indian Construction Scenario. In spite of its great advantages like speed, quality and economy in construction it is yet to become popular with architects, engineers, builders and Government organisations on a regular basis. Though it has become standard product for construction of bridges, metro, mono rails and infrastructure projects because of its inherent advantages over conventional construction. It has not been commonly used in residential, commercial and industrial buildings where it has great potential. Shortage of skilled, semi skilled and unskilled labour has seriously affected progress of many important projects which has now made use of precast construction necessity as it benefits everyone, the owner, architects, engineers, contractors, tenants and end users. It is a step ahead of RMC concrete. This article describes use of large panel precast concrete panels for construction of some of the buildings where it has demonstrated its advantages over the conventional method of construction. Number of projects have been executed in India using precast prestressed concrete construction. Few projects are worth mentioning because of its pioneering nature, logistics and special requirements including one constructed in extreme cold climate of Leh Ladakh for MES while other in extreme hot climate of Kutch, Gujarat for UNICEF and other NGOs. Overview In India due to migration to urban areas, affordable mass housing is the requirement. For this precast technology is the most preferred solution. All over the world this technology is very widely used. Unfortunately in India due to lack of knowledge, experience and exposure this technology is not being used. This paper would like to remove certain doubts and apprehensions in the minds of professionals and authorities so that they can favourably consider adoption of this technology in their projects or consider as alternative. Some of the common expressed doubts and apprehensions are discussed below: Structures look temporary With the technological advancements, joints are well designed and properly connected so that the whole structure is integrated one. With superior joint ceiling materials and water proofing system these joints are well taken care of. Thousands of structures are already constructed throughout the world and are performing well for long time. Some of the most beautiful structures including "Sydney Harbour Opera" is constructed using this technology. Precast Components Have to Cater For Additional Stresses Due To Handling.Precast components have to be checked for stresses during handling but handling stresses and superimposed load stresses do not occur simultaneously. Normally stresses due to superimposed loads are governing the design and hence no additional provision for handling stresses is required. Not economical In normal in-situ construction concrete of grade M-25 is used while in precast prestressed concrete of grade M-50 and above is used without increasing material cost except a few Kg’s of cement and chemicals. Similarly high tensile steel used for prestressing is four times stronger than tor steel used for conventional construction. Thus more than double the strength is available with marginal increase in material cost that is where economy is realised. Thin sections are more rrone to corrosion As a matter of fact it is quite contradictory as precast members are manufactured in industrial manner with strict quality control and quality assurance system with far more superior concrete compared to cast in-situ concrete. Added to this pre-compression induced in the members makes it crack free. Because of these factors precast prestressed concrete members even thin are far more superior for corrosion resistants. Case Studies
Gujarat State Police Housing Corporation (GSPHCL)Gujarat State Police Housing Corporation (GSPHCL) wanted to construct check posts and out posts throughout the boarder of Gujarat for security reasons on urgent basis. GSPHCL wanted the structure to be strong, durable, impact resistance and maintenance free. Structures were to be constructed in the remotest part of Gujarat with quality and speed. Peculiarity • Distance between two extreme location: 1000 Km • Number of Structures: 52 • Size: About 300 sq ft approxMES staff quarters at Leh- Ladakh Military Engineering Services wanted to construct quarters for their officers in Leh where temperature goes up to -20°e. Logistics of the site conditions required that the entire project is to be completed only in the span of three months during summer working season. It was difficult to make good quality concrete in cold climate with limited local resources of men, materials and equipments. Moreover the quarters should be insulated against extreme cold. To meet these important criteria precast concrete insulated sandwich panels were used for wall and roof panels. They were cast at an established factory near Mumbai and kept ready for transportation to Leh. Precast elements were loaded at Pan vel (Mumbai) in train and transported up to Pathankot. From Pathankot precast elements were transported in MES trucks to Leh. Weight of the precast elements was kept minimum to handle precast elements during transportation and erection. Precast elements were directly erected from the trucks over the strip footing cast at site. The unique feature of this project was that precast elements were transported by train and trucks for a distance of about 2000 Kms. and erected in a short period using locally available equipments in remote area with extreme climatic conditions.School buildings for UNICEF in KutchAfter devastating earthquake in Kutch UNICEF, JICA, Rotary International and other NGOs wanted to construct schools in Kutch immediately after the earthquake in the shortest possible time. 800 classrooms were to be constructed in arid and remotest area in Kutch at about 200 locations where at many places even water was not available. For this project double tee elements were selected for wall and roof panels to keep the weight of the structure minimum in the earthquake Zone V region and to minimise transportation and erection cost. Wall panels were RCC precast while roof panels were precast prestressed. To complete the project in the shortest possible time initially precast elements were transported by road from Mumbai to Kutch about distance of 1000 Kms. Precast elements were directly erected from trucks on the strip footing constructed at site. There were different arrangements of school rooms at various locations depending upon the sites at each location. Schools were in clusters of two classrooms to 10 classrooms at one location. Standard module of 6mtr.x 12mtr. for each classroom was usedMultistoried building for MHADA Maharashtra Housing and Area Development Authority (MHADA) wanted to construct multistoried buildings for High Income Group (HIG) in Mumbai in the shortest possible time. The project involved construction of six buildings 8-storeyed high consisting of 168 flats covering about 1,20,000 Sq.ft. area. Each building is 16.5 mtr. long, 16.6 mtr. wide and 24 mtr. high with a stilt floor at the ground level for parking vehicles. The building consisted of precast columns, prestressed floor beams and hollow core slabs. The structure was designed as a coupled shear wall with frame action. Columns for the buildings were cast and erected in two pieces. Lower column was erected up to 4Y2 storey while upper column was 3Y2 storey long. In the first stage building was erected up to 4Y2 storey and the upper 3Y2 storey was erected in the second stage. The entire 8- storeyed building was erected in 45 days. The buildings where constructed in 1987 and are performing well till now. (Fig.1 and 2). Low cost houses in Mumbai A reputed developer in Mumbai wanted to construct large number of low cost houses for accommodating project affected people in the shortest possible time. The main consideration for acceptance of large panel precast concrete technology was to rehouse the people so that sale building can be constructed in the shortest possible time. Rehabilitation buildings were to be constructed at several locations in Mumbai. All the precast elements above plinth level such as walls, floor slabs, staircases, water tanks, etc. were precast in the factory with strict quality control and quality assurance system. Precast elements were transported about 70 km from the factory and erected at site using telescopic gantry. Fig.3 shows transportation of precast elements. 5-storeyed building consisting of 50 tenements were erected and completed in 30 days. Totally about 2,00,000 sq ft area was constructed in one year. Similar type of buildings have been constructed for City and Industrial Development Corporation (CIDCO) and MHADA.Similar system was adopted by Narmada Project Authorities for construction of their staff quarters and office buildings at various locations along Narmada Canal.Conclusions There is a growing realiaation that providing mass housing using industrialised construction is the only way of fulfilling the ambitious state and national housing plans. Careful planning would ensure efficient use of time and national resources. The authors also are of the opinion that the precast panel type industrialised construction is the best solution if the mass housing programme and infrastructure targets are to be met. It is possible to construct about 20 houses every day using this system with one module. Advantages of this technology are given in the table 1. For the successful execution of such projects, careful planning, design and detailed working drawings are essential. Similarly, preparation of working programme and careful design of the casting stacking yard and transport and erection scheme are equally important. To gain maximum economic advantage of industrialised construction, assured continuous demand in the industry is very essential. To make large panel precast system widely acceptable in the Indian construction sector, the authors feel that all government tenders should provide for an alternate design with large panel construction. This will encourage the use of this system through new entrepreneurs. Moreover, at least 20 per cent of the government sponsored housing programme should be constructed using large panel precast system, which will result in substantial economy in the initial cost of construction and in the case of life cycle costing too.To popularise this technology positive attitude and open mind set is required with professional and Government Authorities.The development of these technologies lies on the policies by the Government, thus it will be a wait and watch game for the industry if the policies support the sector or they still go their way