5. pre stressed & pre-cast members
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This document discusses the concept and principles of pre-stressing concrete. Pre-stressing involves applying compression to reinforced concrete to reduce tensile stresses and prevent cracking. There are two main methods - pre-tensioning where tension is applied before pouring concrete, and post-tensioning where tension is applied after curing. Pre-stressed concrete has advantages like needing less material, being lighter, and resisting corrosion and deflection better than reinforced concrete. However, it is more technically complex and expensive. Common applications include bridges, buildings, water tanks, and offshore platforms.
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Prestressed concrete
At the beginning of the twentieth century, “Prestressed Concrete” soon became the single most significant new direction in structural engineering according to Billington (2004).
This unique concept gave the engineer the ability to control the actual structural behavior while forcing him or her to dive more deeply into the construction process of the structural material. It gave architects as well as engineers a new realm of reinforced concrete design pushing not only the structural but also the architectural limits of concrete design to a level that neither concrete nor structural steel could achieve. Ordinary reinforced concrete could not achieve the same limits because the new long spans that “Prestressed Concrete” were able to achieve could not be reached with reinforced concrete. Those longer spans required much deeper members, which quickly made reinforced concrete uneconomical. Additionally, steel structures weren’t able to create the same architectural forms that the new “Prestressed Concrete” could.
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The concept of Prestressed Concrete appeared in 1888 when P.H. Jackson was granted the first patent in the United States for Prestressed Concrete design as a method of Prestressed construction in concrete pavement.
Jackson’s idea was perfect, but the technology of high strength steel that exhibited low relaxation characteristics was not yet available. This was the reason Prestressed Concrete was not used as building material in the early years. For example, metallurgists had not yet discovered high strength steel, which combined the needed high compressive forces in a minimal amount of steel with low relaxation characteristics that minimized creep and post-stress deformations in the prestressing steel; therefore, the idea hibernated until Freyssinet reexamined it in the early twentieth century, the first to actively promote prestressed concrete.
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1. Excavation and foundation work - This involves excavating the land and laying the foundation system such as raft or pile foundations.
2. Erection of formwork - Formwork is erected to give shape to the concrete elements like columns, beams, slabs, etc. It is designed to bear the pressure of wet concrete.
3. Reinforcement cage - Steel reinforcement bars are cut, bent and assembled into cages and placed accurately in position in the formwork.
4. Concreting - Concrete is poured, compacted and finished after placing the reinforcement cages in position.
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Prestresses concrete
Prestressed concrete is a method that applies compressive force to reinforced concrete in order to counteract tensile forces. This prevents cracking and allows concrete to be treated as an elastic material. There are two main methods: pre-tensioning, where tendons are tensioned before casting, and post-tensioning, where tendons are tensioned after casting using ducts. Prestressed concrete enables longer spans, reduces material usage, and improves durability compared to reinforced concrete. However, it requires higher quality materials and specialized equipment, which increases costs.
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Pre-stressed concrete uses tensioned steel strands or bars to place concrete in compression and improve its tensile strength. There are two main methods - pre-tensioning, where steel is tensioned before concrete is poured, and post-tensioning, where steel is tensioned after concrete has cured. Pre-stressing counters the effects of tensile stresses from loads and prevents cracking, allowing concrete to act as an elastic material. It provides advantages over reinforced concrete like reduced size, weight, and cracking as well as improved corrosion resistance and shear strength.
Pre-stressed Concrete
Pre-stressed concrete uses tensioned steel strands or bars to place concrete in compression and improve its tensile strength. There are two main methods - pre-tensioning and post-tensioning. Pre-tensioning tensions the strands before the concrete is poured, while post-tensioning tensions strands inside ducts after the concrete has cured. This compression counteracts tensile and flexural stresses from loads to reduce cracking and increase strength, allowing pre-stressed concrete to be lighter and more durable than reinforced concrete. It is commonly used in bridges, buildings, tanks, and other structures.
UNIT-1 PSC.pptx
This document provides information on a syllabus for a course on prestressed concrete. It outlines the course objectives which are to understand the principles, necessity, techniques, losses, and analysis and design of prestressed concrete members. The course outcomes are for students to acquire knowledge on the evolution of prestressing, prestressing techniques, and skills in analyzing and designing prestressed structural elements per code provisions. The syllabus then outlines 5 units that will be covered which include introduction, methods and systems, losses of prestress, flexure, shear, transfer of prestress, composite beams, and deflections. Relevant textbooks and codes are also listed.
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Village as a focal point of planning and development
Village can serve as a focal point for planning and development when it has certain key characteristics and facilities. A village becomes a focal point as it develops surrounding facilities that help it grow. Basic village facilities include a post office, administration buildings, shops, religious buildings, schools, and agriculture. For a village to be suitable for development, it needs a measurable population and to be surrounded by other development. Planning and development of villages should consider input from local communities and monitor progress against objectives.
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This document discusses standards and requirements for open space and different land uses. It provides guidelines for open space percentages based on population size ranging from 0.5-7% for over 500,000 people to 0.5-2% for 25,000-49,000 people. Requirements are outlined for housing, commercial, and industrial land uses. Housing requires accessibility, infrastructure, and being away from industry. Commercial needs to be central with accessibility and infrastructure while industry requires accessibility, loading areas, and separation from residences.
Process of planning and designing a new town
The document discusses the process of planning and designing a new town. It outlines the key steps: (1) identifying problems/objectives, (2) gathering information, (3) analyzing information, (4) determining alternative plans, (5) selecting a plan, (6) detailing sequencing and timing, and (7) checking progress. New towns are purposefully planned to provide housing, facilities, and recreational areas as self-sufficient communities to ease overcrowding in existing cities. Examples of new towns in India include Navi Mumbai, New Town Kolkata, and Lavasa near Pune.
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Planning concept of Chandigarh city.
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Neighbourhood city
The document discusses the concept and principles of neighborhood planning. Neighborhood planning aims to give communities direct power to develop a shared vision for their neighborhood and shape development in their local area. It involves planning for housing, businesses, transportation, renewable energy, and other infrastructure. The purpose is to create safe, healthy neighborhoods where residents have walking access to schools, shops, work, and recreation. Sustainable principles of neighborhood planning include thorough preparation, building on neighborhood assets, involving residents, building neighborhood capacity, transparency, and democratic decision-making.
Neighborhood planning
The neighborhood is defined as a combination of two or more mohallas according to the National Reference Manual. It can also be defined as the smallest unit which serves the local community and encourages neighborhood spirit. Characteristics of a neighborhood include a secondary school, mosque, and population of around 25,000 people. Neighborhood planning was conceived as a means to insulate communities from increasing traffic and gives residents power to develop a shared vision and shape local development. Elements of neighborhood planning include facilities, sector size, street systems, boundaries, and layout of buildings. The goals are to foster socialization, support a safe environment, provide safety and share public amenities.
Modern city islamabad
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Modern city brasilia
Brasilia is the purpose-built capital of Brazil, located in the center-west region. It was founded in 1960 to serve as a new, more centrally located capital instead of Rio de Janeiro. Brasilia has a planned, sector-based design and is a center of government, hosting the branches of the federal government and over 100 foreign embassies. While initially planned for 500,000 people, Brasilia's population has grown faster due to internal migration and now numbers over 2.5 million.
Layout plan of housing
This document discusses housing layout plans and public facilities. It describes basic building forms like blocks, towers, and courtyard apartments. Blocks are wider than they are tall with apartments arranged along a central corridor. Towers have a vertical form and centralized zone. Courtyard apartments provide side open spaces like communal courtyards. Rectilinear street grids create uniform blocks and intersecting streets, while cul-de-sacs are closed roads with one inlet/outlet. Public facilities provided by the government include services that cannot be supplied to individual homes, and satisfy community needs for safety, communication, recreation, education, health, culture and administration.
Layout plan of housing blocks and public facilities and services
This document discusses layout patterns for housing blocks and public facilities and services. It defines layout as an arrangement or plan, especially the schematic arrangement of parts or areas. It then describes common layout patterns like rectilinear/gridiron layouts with uniform blocks and right angle streets, cul-de-sacs which limit through traffic, and radiocentric, star, and ring patterns. It also defines public facilities and services as infrastructure financed by the government like roads, transportation, utilities, schools, hospitals and discusses their significance for quality of life.
Layout of roads and streets
The document discusses the layout of roads and streets. For roads, it describes the information needed in schematic layouts submitted for review, including general project details, interchange and alignment locations, profiles, typical sections, and traffic volumes. For streets, it emphasizes that layout is important for travel and connecting neighborhoods. New developments should encourage walking, cycling and public transit by prioritizing people over traffic and creating well-connected, safe and accessible places. Quality design considers accessibility, efficient use of space, and integrating with neighboring areas through scale, density and access.
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Landscaping involves modifying the visible features of an area of land through living elements like plants, natural elements like landforms, and abstract elements like weather. Landscaping is important for making yards beautiful and enhancing the environment. Objectives of landscaping include maintaining urban landscape character, preserving trees and grass, and enhancing public spaces. Open spaces are undeveloped land accessible to the public, such as parks, playgrounds, and vacant lots. They provide recreation and beautify neighborhoods. Guidelines for open spaces recommend they be adequately sized, accessible, well-designed, protected from wind, have amenities, access to sunlight, lighting, and be open and safe for public use.
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5. pre stressed & pre-cast members
- 6. CONCEPT OF PRE-STRESSING : 1- The concept of pre stressing was invented many years ago when metal brands were wound around wooden pieces to form barrels. 2-The metal brands were tighten under tensile stress which creates compression between the staves allowing them to resist internal liquid pressure
- 7. PRINCIPLE OF PRE-STRESSING : Pre-stressing is a method in which compression force is applied to the reinforced concrete section. The effect of pre stressing is to reduce the tensile stress in the section to the point till the tensile stress is below the cracking stress.Thus the concrete does not crack. It is then possible to treat concrete as a elastic material.The concrete can be visualized to have two compressive force i . Internal pre-stressing force. ii . External forces These two forces must counteract each other. PRE-STRESSED CONCRETE METHODS There are two basic methods of applying pre-stress to a concrete member Pre-tension concrete – most often used in factory situations Post-tension concrete (bounded & unbounded) – site use
- 14. ADVANTAGES & DIS-ADVANTAGES ADVANTAGES : Need less materials Smaller and lighter structure No cracks Use the entire section to resist the load Better corrosion resistance Good for water tanks and nuclear plant Very effective for deflection control Better shear resistance DISADVANTAGES COMPAREDTO RC: Need higher quality materials More complex technically More expensive Harder to re-cycle APPLICATION: Bridges Slabs in buildings WaterTank concrete Pile thin Shell Structures Offshore Platform Nuclear Power Plant Repair and Rehabilitations
- 16. Precast concrete means a concrete member that is cast and cured at a location other than its final designated location.The use of reinforced concrete is a relatively recent invention, usually dated to 1848 when jean- Louis Lambot became the first to use it. Joseph Monier, a French gardener, patented a design for reinforced garden tubs in 1868, and later patented reinforced concrete beams and posts for railway and road guardrails.