The document provides information on methods of prestressing concrete, including pretensioning and post-tensioning. It discusses:
- Pretensioning involves stressing steel tendons before the concrete is cast around them.
- Post-tensioning involves stressing steel tendons after the concrete has cured using jacks, then grouting the voids.
- Both methods put the concrete in compression and increase its strength and durability compared to conventional reinforced concrete.
This document discusses prestressed concrete and provides details on:
- The definition and principle of prestressing concrete by applying compression prior to external loads
- Common prestressing methods like hydraulic, mechanical, electrical, and chemical prestressing
- Tests conducted on prestressed concrete components like post-tensioned splices and cast-in-place splices
- Advantages of prestressed concrete like reduced materials and increased strength
- Applications in bridges, buildings, water tanks, and more
- A case study on widening the Harrods Creek Arch Bridge using prestressed concrete
This document discusses different methods of prestressing concrete, including pretensioning and post-tensioning. Pretensioning involves stressing steel tendons before placing concrete around them, while post-tensioning involves stressing tendons after the concrete has cured using hydraulic jacks. Post-tensioning allows for longer spans, thinner slabs, and more architectural freedom compared to conventional reinforced concrete or pretensioned concrete. Common applications of post-tensioning include parking structures, bridges, and building floors and roofs.
Prestressed concrete is concrete that is placed under compression using tensioned steel strands, cables, or bars. This is done through either pre-tensioning or post-tensioning. In pre-tensioning, the steel components are tensioned before the concrete is poured, while in post-tensioning, the steel components are tensioned after the concrete has hardened. Prestressed concrete provides benefits over reinforced concrete like lower construction costs, thinner structural elements, and longer spans between supports.
This document provides an overview of different types of retaining walls, including gravity, cantilever, counterfort, sheet pile, and diaphragm walls. It discusses the key components and design considerations for gravity and cantilever retaining walls. Gravity walls rely on their own weight for stability, while cantilever walls consist of a vertical stem with a heel and toe slab acting as a cantilever beam. The document also covers lateral earth pressures, drainage of retaining walls, uses of sheet pile walls, and construction methods for diaphragm walls.
Prestressing Concept, Materilas and Prestressing SystemLatif Hyder Wadho
The document discusses prestressing concepts and materials used in prestressed concrete. It describes how prestressing applies an initial compressive stress to concrete prior to service loads to improve strength and durability. Common prestressing materials include high-strength steel strands/wires, which are assembled into tendons and anchored internally or externally before or after concrete casting for pre-tensioning or post-tensioning. Grout is also discussed for transmitting stress between steel and concrete.
This document discusses prestressed concrete, which uses tensioned steel cables or bars to put concrete members into compression and increase their strength. It describes three main methods: pre-tensioned concrete where the steel is tensioned before the concrete is cast; bonded post-tensioned concrete where steel is tensioned after casting to compress the concrete; and unbonded post-tensioned concrete where greased steel is used to allow individual adjustment. Applications include buildings, bridges, nuclear reactors and earthquake resistant structures. Advantages are lower costs, thinner members, and increased spans.
Pre-stressed concrete uses tensioned steel strands or bars to place concrete in compression before application of service loads. This counters the tensile stresses induced by loads and prevents cracking. There are two main methods: pre-tensioning applies tension before pouring concrete, while post-tensioning tensions strands after concrete curing. Pre-stressed concrete allows for smaller and lighter structures that resist loads, deflection, and cracking better than reinforced concrete.
This document discusses prestressed concrete and provides details on:
- The definition and principle of prestressing concrete by applying compression prior to external loads
- Common prestressing methods like hydraulic, mechanical, electrical, and chemical prestressing
- Tests conducted on prestressed concrete components like post-tensioned splices and cast-in-place splices
- Advantages of prestressed concrete like reduced materials and increased strength
- Applications in bridges, buildings, water tanks, and more
- A case study on widening the Harrods Creek Arch Bridge using prestressed concrete
This document discusses different methods of prestressing concrete, including pretensioning and post-tensioning. Pretensioning involves stressing steel tendons before placing concrete around them, while post-tensioning involves stressing tendons after the concrete has cured using hydraulic jacks. Post-tensioning allows for longer spans, thinner slabs, and more architectural freedom compared to conventional reinforced concrete or pretensioned concrete. Common applications of post-tensioning include parking structures, bridges, and building floors and roofs.
Prestressed concrete is concrete that is placed under compression using tensioned steel strands, cables, or bars. This is done through either pre-tensioning or post-tensioning. In pre-tensioning, the steel components are tensioned before the concrete is poured, while in post-tensioning, the steel components are tensioned after the concrete has hardened. Prestressed concrete provides benefits over reinforced concrete like lower construction costs, thinner structural elements, and longer spans between supports.
This document provides an overview of different types of retaining walls, including gravity, cantilever, counterfort, sheet pile, and diaphragm walls. It discusses the key components and design considerations for gravity and cantilever retaining walls. Gravity walls rely on their own weight for stability, while cantilever walls consist of a vertical stem with a heel and toe slab acting as a cantilever beam. The document also covers lateral earth pressures, drainage of retaining walls, uses of sheet pile walls, and construction methods for diaphragm walls.
Prestressing Concept, Materilas and Prestressing SystemLatif Hyder Wadho
The document discusses prestressing concepts and materials used in prestressed concrete. It describes how prestressing applies an initial compressive stress to concrete prior to service loads to improve strength and durability. Common prestressing materials include high-strength steel strands/wires, which are assembled into tendons and anchored internally or externally before or after concrete casting for pre-tensioning or post-tensioning. Grout is also discussed for transmitting stress between steel and concrete.
This document discusses prestressed concrete, which uses tensioned steel cables or bars to put concrete members into compression and increase their strength. It describes three main methods: pre-tensioned concrete where the steel is tensioned before the concrete is cast; bonded post-tensioned concrete where steel is tensioned after casting to compress the concrete; and unbonded post-tensioned concrete where greased steel is used to allow individual adjustment. Applications include buildings, bridges, nuclear reactors and earthquake resistant structures. Advantages are lower costs, thinner members, and increased spans.
Pre-stressed concrete uses tensioned steel strands or bars to place concrete in compression before application of service loads. This counters the tensile stresses induced by loads and prevents cracking. There are two main methods: pre-tensioning applies tension before pouring concrete, while post-tensioning tensions strands after concrete curing. Pre-stressed concrete allows for smaller and lighter structures that resist loads, deflection, and cracking better than reinforced concrete.
The document discusses different methods of post-tensioning concrete structures. It describes the Freyssinet system as the first introduced method using steel wires grouped into cables with a helical spring. The Magnel Blaton system stresses wires two at a time using sandwich plates and wedges. The Gifford Udall system uses single wires stressed independently with double-acting jacks and tube or plate anchorages. The Lee McCall system prestresses steel bars using threaded bars tightened with nuts against bearing plates.
The document discusses limit state design of reinforced concrete structures. It introduces limit states as conditions where the structure becomes unfit for use, including limit states of strength and serviceability. Limit state design involves characterizing loads and resistances as random variables and using partial safety factors on loads and resistances to achieve a target reliability. The document outlines the general principles of limit state design according to Indian Standard code IS 800, including defining actions, factors governing strength limits, and serviceability limits related to deflection, vibration and durability.
Prestressed concrete structures and its applications By Mukesh Singh GhuraiyaMukesh Singh Ghuraiya
1. What is Prestressed??
2. Principle of Prestressed
3. Method of prestressing
4. Prestressed concrete structures
5. Advantages/application of Prestressed concrete
6. Disadvantages of Prestressed concrete
7. Comparison of RCC and Prestressed Concrete Flat Slabs
This document discusses losses in prestressed concrete, including short-term and long-term losses. It describes the differences between pre-tensioned and post-tensioned concrete. Losses include elastic shortening, friction, anchorage slip, creep, shrinkage, and relaxation. Total losses can be 15-20% of the initial prestress. Post-tensioned concrete experiences more types of losses but lower overall losses compared to pre-tensioned concrete. Proper design and materials are needed to minimize losses in prestressed concrete.
This document discusses different systems used for prestressing steel, which are grouped into four categories: mechanical, hydraulic, electrical/thermal, and chemical. It provides details on common tensioning devices within each category. Mechanical devices use weights, pulleys, and screw jacks. Hydraulic jacks ranging from 5-600 tonnes are widely used. Electrical/thermal heating of wires before concreting is another option. Chemical devices use expanding cement. The document also describes several popular prestressing systems including Freyssinet, Gifford Udall, Lee-McCall, Magnel Blaton, BBRV, and Baur Leonhardt.
This document discusses prestressed concrete bridges. It begins with definitions of prestressed concrete as concrete with internal stresses introduced to counteract external loads. It then provides a brief history of prestressed concrete, noting key innovators. Examples of prestressed concrete bridges in India are given, including the famous Pamban Road Bridge. The document goes on to explain the basic principles, terminology, types, and methods of prestressing, as well as the advantages and disadvantages of prestressed concrete.
Prestressed concrete is concrete that is placed under compression prior to service loads being applied through tensioning of steel tendons. This counteracts tensile stresses from loads to improve the performance of the concrete. Eugene Freyssinet is considered the father of prestressed concrete, developing techniques like high strength steel wires and conical wedges for post-tensioning in the 1930s-1940s. Prestressing can be through pre-tensioning or post-tensioning, depending on if the steel is tensioned before or after the concrete is cast. Popular post-tensioning systems include Freyssinet, Magnel Blaton, Gifford-Udall, and Lee-McCall methods. Prestressed concrete provides
Trusses are commonly used in buildings to span long distances and carry heavy loads. Steel trusses are preferred over wood trusses for their strength, simplicity of installation, and durability without risk of rotting. Various types of trusses include king post, queen post, Howe, Pratt, and fan trusses used in roofs, as well as north light trusses traditionally used for industrial buildings to maximize natural lighting. Larger spans may use tubular steel, quadrangular, or gusset plate connected trusses, while galvanized steel sheets are often used for roofing material.
This document discusses prefabricated modular structures. Some key points:
1. Prefabricated structures have standardized components that are produced off-site in a controlled environment and then transported for assembly. This allows for faster, more efficient construction.
2. Precast concrete offers advantages like higher quality, less weather dependency, and unlimited design possibilities compared to site-cast construction.
3. There are different precast systems like large panel, frame, and lift-slab. Precast components include walls, floors, beams, and more.
Post-tensioning is an effective alternative for earthquake-prone regions and dense populations in India. It has advantages over ordinary reinforced concrete like higher seismic resilience, less concrete usage, stiffer foundations, and faster construction. Post-tensioning involves threading steel tendons through ducts and tensioning them after concrete pouring. It provides better crack control, economy, quality, and efficiency. While widely used in other countries, post-tensioning is not yet common in India but has applications in slabs, buildings, and foundations.
Prestressed concrete uses high-strength steel tendons or cables to put concrete members into compression prior to stresses from service loads being applied. This counters the tensile stresses induced by loading and improves the behavior of the concrete. There are two main methods - pretensioning and post-tensioning. Pretensioning involves stressing steel tendons before concrete is cast, while post-tensioning stresses steel tendons after the concrete has hardened. Losses in prestress over time include elastic shortening, anchorage slip, friction, creep, shrinkage, and steel relaxation. Proper material selection and design can minimize these losses and optimize the performance of prestressed concrete.
Retaining walls are used at the Shraddha Vivanta Residency construction site in Mumbai for two main purposes. Cantilever retaining walls around 3.5 meters deep allow for a basement and four floors of stacked parking underneath the residential building. Additional retaining walls surround underground water tanks for suction and firefighting. The walls are located along the building perimeter and around the tank areas. Proper waterproofing of the retaining walls is important given their underground locations.
Prestressed concrete is a combination of steel and concrete that uses compressive stresses applied during construction to oppose tensile stresses that occur in use. There are three main types: pre-tensioned concrete uses steel tendons tensioned before concrete is placed; bonded post-tensioned concrete uses unstressed steel placed then tensioned after curing; and unbonded post-tensioned concrete provides freedom of movement between steel and concrete. Pre-tensioned concrete requires molds that can resist internal forces and calculations to account for losses over time. Prestressed concrete provides benefits like reduced cracking and corrosion, higher strength, and more economical construction for bridges compared to steel.
INDUSTRIAL TRAINING OF FLYOVER CONSTRUCTIONBhavek Sharma
The Public Works Department has a long history of infrastructure development in the state. It is responsible for constructing and maintaining roads, bridges, and government buildings. Originally, irrigation and public health engineering were also part of the PWD. Since its inception, the department has strived for excellence through continuous improvement and engineering milestones.
Principles of Earthquake resistant design of StructuresTarun kumar
This document discusses principles of earthquake-resistant building design and structural vibration control technologies. It explains that earthquake-resistant structures are designed to withstand expected earthquakes while minimizing loss of life and damage. This is achieved through methods ranging from ensuring adequate structural strength and ductility to using base isolation and vibration control systems. Base isolation allows a building to survive seismic impacts by installing flexible isolators between the structure and its foundation. Passive systems require no external power while active systems counterbalance earthquake forces using computer-controlled dampers. Hybrid systems combine aspects of passive and active control for reduced costs.
Prestressed concrete is a structural material that allows for predetermined, engineering stresses to be placed in members to counteract the stresses that occur when they are subject to loading.
Circular slabs are commonly used as roofs or floors with a circular plan, such as water tanks. They experience bending stresses in two perpendicular directions - radially and circumferentially. Reinforcement is provided as a mesh of bars with equal cross-sectional area in both directions. Near the edges, additional radial and circumferential reinforcement may be needed if edge stresses are significant. Circular slabs are analyzed based on elastic theory, and deflect into a saucer shape under uniform loads, developing tensile and compressive stresses on the convex and concave surfaces respectively. Reinforcement must be provided in both radial and circumferential directions near the convex surface.
Precast concrete construction involves casting concrete structural elements at a manufacturing facility rather than on site. This allows for rapid construction, high quality control, and easy incorporation of prestressing. Precast concrete provides advantages like speed of erection, durability, and economy, but also has disadvantages such as weight, limited flexibility in design, and need for skilled workmanship and lifting equipment on site. Common precast concrete elements include walls, slabs, beams, and structural framing using techniques like welded plates and rebar splicing.
The document discusses different types of joints used in concrete structures including construction joints, expansion joints, contraction joints, and seismic joints. It provides definitions and discusses the purpose, formation, location, and detailing of each joint type. Construction joints allow concrete to be placed continuously and provide limits for placements. Expansion joints allow for movement in the structure. Contraction joints create planes of weakness to control cracking. Seismic joints separate portions of buildings to improve performance during earthquakes.
This document summarizes a presentation on prestressed concrete. It begins with an introduction to prestressed concrete and how it overcomes weaknesses in concrete in tension. It then describes the principles of prestressing by inducing compressive stresses with high-strength tendons before loads are applied. The document compares reinforced concrete with prestressed concrete and describes the methods of pre-tensioning and post-tensioning. It provides examples of prestressed concrete structures like beams, bridges and discusses advantages like reduced size and increased spans as well as disadvantages like higher material costs.
This document discusses prestressed and post-tensioned concrete. It covers topics like pretensioning and post-tensioning, stages of loading, partial prestressing, steel wires, strands and bars, fibre glass tendons, grouting, end anchorages, tensioning methods, post-tensioning systems using hydraulic jacks, bonded and unbonded systems, wedge action anchorages, time-dependent losses from creep, shrinkage, steel relaxation, anchorage, bending, friction, and tendon elongation. The document is split into two modules, with the second module focusing more on end anchorages and post-tensioning systems.
This document provides an introduction to prestressing in concrete structures. It defines prestressing as preloading a structure before design loads are applied to improve performance. The objectives of prestressing are to control or eliminate tensile stresses and cracking in concrete, control deflection, and allow use of high-strength materials. Benefits include improved concrete performance, longer spans, and innovative designs. Methods include pretensioning and post-tensioning. Post-tensioning involves tensioning tendons after casting and grouting the ducts. Different profiles and materials for prestressing steel are discussed. The Hognestad model is presented for modeling concrete stress-strain behavior.
The document discusses different methods of post-tensioning concrete structures. It describes the Freyssinet system as the first introduced method using steel wires grouped into cables with a helical spring. The Magnel Blaton system stresses wires two at a time using sandwich plates and wedges. The Gifford Udall system uses single wires stressed independently with double-acting jacks and tube or plate anchorages. The Lee McCall system prestresses steel bars using threaded bars tightened with nuts against bearing plates.
The document discusses limit state design of reinforced concrete structures. It introduces limit states as conditions where the structure becomes unfit for use, including limit states of strength and serviceability. Limit state design involves characterizing loads and resistances as random variables and using partial safety factors on loads and resistances to achieve a target reliability. The document outlines the general principles of limit state design according to Indian Standard code IS 800, including defining actions, factors governing strength limits, and serviceability limits related to deflection, vibration and durability.
Prestressed concrete structures and its applications By Mukesh Singh GhuraiyaMukesh Singh Ghuraiya
1. What is Prestressed??
2. Principle of Prestressed
3. Method of prestressing
4. Prestressed concrete structures
5. Advantages/application of Prestressed concrete
6. Disadvantages of Prestressed concrete
7. Comparison of RCC and Prestressed Concrete Flat Slabs
This document discusses losses in prestressed concrete, including short-term and long-term losses. It describes the differences between pre-tensioned and post-tensioned concrete. Losses include elastic shortening, friction, anchorage slip, creep, shrinkage, and relaxation. Total losses can be 15-20% of the initial prestress. Post-tensioned concrete experiences more types of losses but lower overall losses compared to pre-tensioned concrete. Proper design and materials are needed to minimize losses in prestressed concrete.
This document discusses different systems used for prestressing steel, which are grouped into four categories: mechanical, hydraulic, electrical/thermal, and chemical. It provides details on common tensioning devices within each category. Mechanical devices use weights, pulleys, and screw jacks. Hydraulic jacks ranging from 5-600 tonnes are widely used. Electrical/thermal heating of wires before concreting is another option. Chemical devices use expanding cement. The document also describes several popular prestressing systems including Freyssinet, Gifford Udall, Lee-McCall, Magnel Blaton, BBRV, and Baur Leonhardt.
This document discusses prestressed concrete bridges. It begins with definitions of prestressed concrete as concrete with internal stresses introduced to counteract external loads. It then provides a brief history of prestressed concrete, noting key innovators. Examples of prestressed concrete bridges in India are given, including the famous Pamban Road Bridge. The document goes on to explain the basic principles, terminology, types, and methods of prestressing, as well as the advantages and disadvantages of prestressed concrete.
Prestressed concrete is concrete that is placed under compression prior to service loads being applied through tensioning of steel tendons. This counteracts tensile stresses from loads to improve the performance of the concrete. Eugene Freyssinet is considered the father of prestressed concrete, developing techniques like high strength steel wires and conical wedges for post-tensioning in the 1930s-1940s. Prestressing can be through pre-tensioning or post-tensioning, depending on if the steel is tensioned before or after the concrete is cast. Popular post-tensioning systems include Freyssinet, Magnel Blaton, Gifford-Udall, and Lee-McCall methods. Prestressed concrete provides
Trusses are commonly used in buildings to span long distances and carry heavy loads. Steel trusses are preferred over wood trusses for their strength, simplicity of installation, and durability without risk of rotting. Various types of trusses include king post, queen post, Howe, Pratt, and fan trusses used in roofs, as well as north light trusses traditionally used for industrial buildings to maximize natural lighting. Larger spans may use tubular steel, quadrangular, or gusset plate connected trusses, while galvanized steel sheets are often used for roofing material.
This document discusses prefabricated modular structures. Some key points:
1. Prefabricated structures have standardized components that are produced off-site in a controlled environment and then transported for assembly. This allows for faster, more efficient construction.
2. Precast concrete offers advantages like higher quality, less weather dependency, and unlimited design possibilities compared to site-cast construction.
3. There are different precast systems like large panel, frame, and lift-slab. Precast components include walls, floors, beams, and more.
Post-tensioning is an effective alternative for earthquake-prone regions and dense populations in India. It has advantages over ordinary reinforced concrete like higher seismic resilience, less concrete usage, stiffer foundations, and faster construction. Post-tensioning involves threading steel tendons through ducts and tensioning them after concrete pouring. It provides better crack control, economy, quality, and efficiency. While widely used in other countries, post-tensioning is not yet common in India but has applications in slabs, buildings, and foundations.
Prestressed concrete uses high-strength steel tendons or cables to put concrete members into compression prior to stresses from service loads being applied. This counters the tensile stresses induced by loading and improves the behavior of the concrete. There are two main methods - pretensioning and post-tensioning. Pretensioning involves stressing steel tendons before concrete is cast, while post-tensioning stresses steel tendons after the concrete has hardened. Losses in prestress over time include elastic shortening, anchorage slip, friction, creep, shrinkage, and steel relaxation. Proper material selection and design can minimize these losses and optimize the performance of prestressed concrete.
Retaining walls are used at the Shraddha Vivanta Residency construction site in Mumbai for two main purposes. Cantilever retaining walls around 3.5 meters deep allow for a basement and four floors of stacked parking underneath the residential building. Additional retaining walls surround underground water tanks for suction and firefighting. The walls are located along the building perimeter and around the tank areas. Proper waterproofing of the retaining walls is important given their underground locations.
Prestressed concrete is a combination of steel and concrete that uses compressive stresses applied during construction to oppose tensile stresses that occur in use. There are three main types: pre-tensioned concrete uses steel tendons tensioned before concrete is placed; bonded post-tensioned concrete uses unstressed steel placed then tensioned after curing; and unbonded post-tensioned concrete provides freedom of movement between steel and concrete. Pre-tensioned concrete requires molds that can resist internal forces and calculations to account for losses over time. Prestressed concrete provides benefits like reduced cracking and corrosion, higher strength, and more economical construction for bridges compared to steel.
INDUSTRIAL TRAINING OF FLYOVER CONSTRUCTIONBhavek Sharma
The Public Works Department has a long history of infrastructure development in the state. It is responsible for constructing and maintaining roads, bridges, and government buildings. Originally, irrigation and public health engineering were also part of the PWD. Since its inception, the department has strived for excellence through continuous improvement and engineering milestones.
Principles of Earthquake resistant design of StructuresTarun kumar
This document discusses principles of earthquake-resistant building design and structural vibration control technologies. It explains that earthquake-resistant structures are designed to withstand expected earthquakes while minimizing loss of life and damage. This is achieved through methods ranging from ensuring adequate structural strength and ductility to using base isolation and vibration control systems. Base isolation allows a building to survive seismic impacts by installing flexible isolators between the structure and its foundation. Passive systems require no external power while active systems counterbalance earthquake forces using computer-controlled dampers. Hybrid systems combine aspects of passive and active control for reduced costs.
Prestressed concrete is a structural material that allows for predetermined, engineering stresses to be placed in members to counteract the stresses that occur when they are subject to loading.
Circular slabs are commonly used as roofs or floors with a circular plan, such as water tanks. They experience bending stresses in two perpendicular directions - radially and circumferentially. Reinforcement is provided as a mesh of bars with equal cross-sectional area in both directions. Near the edges, additional radial and circumferential reinforcement may be needed if edge stresses are significant. Circular slabs are analyzed based on elastic theory, and deflect into a saucer shape under uniform loads, developing tensile and compressive stresses on the convex and concave surfaces respectively. Reinforcement must be provided in both radial and circumferential directions near the convex surface.
Precast concrete construction involves casting concrete structural elements at a manufacturing facility rather than on site. This allows for rapid construction, high quality control, and easy incorporation of prestressing. Precast concrete provides advantages like speed of erection, durability, and economy, but also has disadvantages such as weight, limited flexibility in design, and need for skilled workmanship and lifting equipment on site. Common precast concrete elements include walls, slabs, beams, and structural framing using techniques like welded plates and rebar splicing.
The document discusses different types of joints used in concrete structures including construction joints, expansion joints, contraction joints, and seismic joints. It provides definitions and discusses the purpose, formation, location, and detailing of each joint type. Construction joints allow concrete to be placed continuously and provide limits for placements. Expansion joints allow for movement in the structure. Contraction joints create planes of weakness to control cracking. Seismic joints separate portions of buildings to improve performance during earthquakes.
This document summarizes a presentation on prestressed concrete. It begins with an introduction to prestressed concrete and how it overcomes weaknesses in concrete in tension. It then describes the principles of prestressing by inducing compressive stresses with high-strength tendons before loads are applied. The document compares reinforced concrete with prestressed concrete and describes the methods of pre-tensioning and post-tensioning. It provides examples of prestressed concrete structures like beams, bridges and discusses advantages like reduced size and increased spans as well as disadvantages like higher material costs.
This document discusses prestressed and post-tensioned concrete. It covers topics like pretensioning and post-tensioning, stages of loading, partial prestressing, steel wires, strands and bars, fibre glass tendons, grouting, end anchorages, tensioning methods, post-tensioning systems using hydraulic jacks, bonded and unbonded systems, wedge action anchorages, time-dependent losses from creep, shrinkage, steel relaxation, anchorage, bending, friction, and tendon elongation. The document is split into two modules, with the second module focusing more on end anchorages and post-tensioning systems.
This document provides an introduction to prestressing in concrete structures. It defines prestressing as preloading a structure before design loads are applied to improve performance. The objectives of prestressing are to control or eliminate tensile stresses and cracking in concrete, control deflection, and allow use of high-strength materials. Benefits include improved concrete performance, longer spans, and innovative designs. Methods include pretensioning and post-tensioning. Post-tensioning involves tensioning tendons after casting and grouting the ducts. Different profiles and materials for prestressing steel are discussed. The Hognestad model is presented for modeling concrete stress-strain behavior.
Brief Study about Prestressed Steel Concrete Composite GirderRohit kumar Mittal
In this presentation, introduction about different types of composite girder along with it's working is given.
This presentation tells about the fabrication procedure of the Prestressed Concrete Steel Composite Bridge. It also deals with different components of system design and different stages of analysis of Prestressed Concrete Steel Composite Girder.
It is also mentioned about finite element analysis procedure with elements selected for different materials, finite element analysis results, experimental investigation and examples with importance of such types of girder over other.
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.
The use of post-tensioning system in building offers numerous advantages such as economic savings, minimised floor-to-floor heights, increased column-free space, minimised foundations, in seismic areas, reduced weight and lateral load resisting systems, simplified slab design and construction etc.
The document provides information about prestressed concrete design. It discusses various topics related to prestress loss including immediate losses like elastic shortening, anchorage slip, and friction; and time-dependent losses like creep, shrinkage, and relaxation of steel. It describes the different types of prestressing systems and losses associated with pre-tensioning and post-tensioning. Methods to estimate total prestress losses including lump sum approximations and refined estimations are also presented.
Pre-stressed concrete is a combination of steel and concrete that takes advantage of each material's strengths. There are three main types of pre-stressed concrete: pre-tensioned concrete, bonded post-tensioned concrete, and unbonded post-tensioned concrete. Pre-tensioned concrete involves stressing steel reinforcement prior to placing concrete around it, while bonded and unbonded post-tensioned concrete involve stressing steel embedded in cured concrete. Pre-stressing concrete provides benefits like increased strength, reduced cracking and corrosion, and allowing for thinner members. The pre-stressing process requires careful planning and consideration of factors like creep, shrinkage, and stress losses over time.
1. Pre-stressed concrete uses steel tendons that are tensioned before or after the concrete is poured to put the concrete in compression and improve its strength.
2. There are two main types: pre-tensioned concrete, where tendons are tensioned before the concrete is poured, and post-tensioned concrete, where ducts are cast in and tendons are tensioned after the concrete cures.
3. Advantages of pre-stressed concrete include increased strength, reduced cracking and corrosion, higher span-to-depth ratios, and economic benefits. However, it requires experienced engineers and builders and sections can be brittle.
This document discusses the design and construction of a post-tensioned concrete slab. It begins with objectives to summarize experience with post-tensioning in building construction and discuss design and construction of post-tensioned flat slab structures. It then provides details on prestressed concrete principles, design of the PT slabs including thickness determination and prestress calculations, and execution steps like formwork, concrete pouring, prestressing, and grouting. Post-tensioning offers advantages over reinforced concrete like longer spans, thinner slabs, and improved seismic performance.
Prestressing Concept, Materials and Prestressing System - Section B, Group 1সাফকাত অরিন
This document provides an overview of prestressing concepts, materials, and systems. It discusses the basic concepts of prestressing including transforming concrete into an elastic material, combining high-strength steel with concrete, and achieving load balancing. The document describes the advantages and limitations of prestressing. It also summarizes the different types of prestressing in terms of the source of prestressing force, whether it is external or internal, pre-tensioned or post-tensioned, linear or circular, full or partial, and uniaxial, biaxial, or multiaxial. Finally, it discusses prestressing materials including concrete, aggregate, cement, water, admixtures, grout, and prestressing steel.
The document discusses the benefits of exercise for both physical and mental health. It notes that regular exercise can reduce the risk of diseases like heart disease and diabetes, improve mood, and reduce feelings of stress and anxiety. The document recommends that adults get at least 150 minutes of moderate exercise or 75 minutes of vigorous exercise per week to gain these benefits.
This document discusses methods of prestressing concrete, including pretensioning and post-tensioning. Pretensioning involves stressing steel tendons before concrete is poured around them. Post-tensioning involves stressing steel tendons inserted into voids in cured concrete using jacks. Both methods put the concrete in compression and improve its tensile strength. Common applications include building floors/roofs, bridges, and parking structures.
Pre-stressed concrete uses tensioned steel cables or rods to put concrete members under compression and increase their strength. It allows for longer spans than reinforced concrete. There are three methods: pre-tensioned concrete uses tensioned tendons before pouring concrete; bonded post-tensioned concrete uses tendons tensioned after pouring; unbonded post-tensioned concrete uses individually coated tendons without bonding to the concrete. Prestressed concrete has advantages like less cracking and material efficiency but also disadvantages like higher costs.
This document discusses prestressed concrete, which uses steel that is tensioned to put concrete in compression and increase its strength. There are two main types: pre-tensioned concrete, where steel is tensioned before the concrete is poured; and post-tensioned concrete, where steel is tensioned after the concrete has hardened. Post-tensioned concrete can be bonded or unbonded. Prestressed concrete allows for longer spans, thinner sections, and increased strength over traditional reinforced concrete. It has applications in buildings, bridges, parking structures, and other structures.
Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons. Post-tensioning applications include office and apartment buildings, parking structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and water-tanks.
>>>Published by Post-Tensioning Institute
This document provides information about prestressed concrete, specifically focusing on post-tensioning methods. It defines post-tensioning as a method of reinforcing concrete with high-strength steel strands called tendons. After the concrete cures, the tendons are tensioned using hydraulic jacks and wedged into place to transfer pressure to the concrete. There are benefits to post-tensioning like allowing longer spans, thinner structures, and reduced cracking compared to conventional reinforced concrete. The document discusses bonded and unbonded post-tensioning methods and provides examples of applications like buildings, bridges, and parking structures.
This document discusses prestressed concrete and defines key terms like pretensioning and post-tensioning. Pretensioning involves stretching steel tendons before concrete is poured, while post-tensioning stretches steel inserted into hardened concrete. The document covers advantages of prestressing like reduced cracking and member sizes. It also discusses design considerations like prestress losses from shrinkage, creep, and relaxation. Both pretensioning and post-tensioning methods are outlined, along with tendon types like bars, wires, and strands.
This document provides an outline for lectures on prestressed concrete, including basic concepts, materials, flexural analysis, design considerations, shear/torsion, loss of prestress over time, composite beams, and deflections. Key points covered include how prestressing controls cracking by applying compressive stresses to concrete before service loads; common prestressing methods of pre-tensioning and post-tensioning; estimating stresses in uncracked concrete beams using elastic theory; and accounting for various load stages in analysis and design.
The document discusses stress ribbon bridges. It begins by explaining that a stress ribbon bridge is a tension structure similar to a suspension bridge, with suspension cables embedded in the deck which follows a catenary arc. Unlike simple suspension bridges, the ribbon is stressed in compression which adds stiffness. Supports provide upward thrusting arcs to change the grade between spans. Stress ribbon bridges are typically reinforced concrete with steel tensioning cables to prevent excessive flexing from vehicle traffic. Fewer than 50 have been built worldwide due to their rare design.
Comparison of reinforced concrete and prestressed concreteSpice Shuvo
This document compares reinforced concrete and prestressed concrete. Reinforced concrete uses steel reinforcement embedded in concrete to increase its tensile strength. Prestressed concrete applies compression to concrete before loading to counteract tensile stresses when in use. For construction, reinforced concrete requires steel bars and formwork while prestressed concrete uses steel tendons stressed after the concrete reaches strength. Prestressed concrete allows for thinner sections, reduced self-weight, and less deflection compared to reinforced concrete. However, it requires higher quality materials and specialized equipment. In summary, the document outlines the key differences in material composition and behavior between the two composite concrete materials.
This document provides an overview of prestressed concrete presented by Sayan Saha from Silliguri Institute of Technology. It introduces prestressed concrete as a method to overcome concrete's weakness in tension. The principle is that compressive stresses induced in concrete by high-strength steel tendons before loading will balance tensile stresses during use. There are two main methods: pre-tensioning where tendons are stressed before concreting, and post-tensioning where tendons are stressed after concrete curing. Advantages include reduced member thickness, deflections, weight, and cracking, while disadvantages require specialized equipment, technical knowledge, and skilled labor.
This document provides an overview of post-tensioning, including:
- Typical applications like suspended slabs, foundations, and cantilevered structures
- The two main types are bonded and unbonded post-tensioning
- Advantages include material savings, quicker construction, and increased performance, while disadvantages include complexity and potential corrosion issues
- The construction process involves placing ducts, casting concrete, tensioning tendons, and anchoring them
- Real-life projects in Morocco and Malaysia utilized post-tensioning for large structures like malls and transit systems.
Prestressed concrete uses tensioned steel tendons to put concrete structures into compression and improve their strength. There are two main types - pre-tensioned concrete where the tendons are tensioned before the concrete is poured, and post-tensioned concrete where the tendons are tensioned after the concrete has cured. Prestressed concrete allows for longer spans, uses materials more efficiently, and results in stronger, crack-resistant structures.
Here are the key steps in concrete frame construction:
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.
5. Curing - After concreting, the concrete elements
This document discusses long span structures, which are buildings with unobstructed column-free spaces greater than 15-20 meters used for stadiums, arenas, and pools. Steel is commonly used due to its ability to span large distances. Prestressed concrete is also used, which involves pre-tensioning or post-tensioning tendons to put concrete into compression and improve its strength. Pre-tensioning tensions tendons before pouring concrete, while post-tensioning does so afterwards. Segmental and composite construction are also discussed as methods to achieve long spans.
Prestressed concrete ,post tensioning ,pre tensioning, where normal concrete can not be used and need of more strength is required this type of concrete are used. Metal bars are replaced by the tendoms which are generally used to create tension in concrete. So because of that beam bends in upward direction and when load is applied it come in normal conditon.
Post-tensioning is a technique for reinforcing concrete structures. The prestressing steel cables inside the sleeves or plastic ducts are positioned in the forms before placing the concrete. As the concrete gains strength, the cables are stressed to design forces before the application of the service load and are anchored att the outer edge region of the concrete.
Prestressed concrete uses high-strength steel tendons to place concrete in compression before loading. This counters the tensile stresses from loads and allows for longer spans and lighter structures. There are two main methods: pretensioning, where tendons are tensioned before concrete is poured, and post-tensioning, where tendons are tensioned after concrete cures. Prestressed concrete has advantages like reduced cracking, increased load capacity, and smaller deflections under loads.
Pre stressed concrete- modular construction technologyAnjith Augustine
This document provides an overview of pre-stressed concrete, including its history, types (pre-tensioning and post-tensioning), materials, applications, advantages, and tensioning devices. Some key points include: pre-stressed concrete was developed in the 1930s-1940s and the first pre-stressed concrete bridge was built in India in 1948; it uses high-strength steel tendons to put concrete under compression and improve its tensile strength; common applications include bridges, buildings, and other structures; and advantages are increased strength, reduced cracking, and lighter/thinner designs.
The document discusses India's energy sector and provides details on various energy sources like renewable energy, non-renewable energy, coal, oil and gas. It summarizes the key points of the National Energy Policy which aims for energy independence through rationalization of costs and subsidies while boosting renewable energy. The policy targets installing 175 GW of renewable energy capacity by 2022 and transitioning from coal to clean energy. It also outlines India's expected energy needs and scenarios for 2040 with electricity demand rising 4.5 times and clean energy sources accounting for 13.5% of production compared to 78% from coal, oil and gas.
This document summarizes techniques for seismic retrofitting of existing structures. It defines seismic retrofitting as modifying structures to make them more resistant to earthquakes. Common retrofitting techniques discussed include adding new shear walls, steel bracing, jacketing columns and beams, using innovative materials like fiber reinforced polymers, base isolation using elastomeric bearings or sliding systems, and installing seismic dampers. The document also discusses retrofitting performance objectives, codes and guidelines, and provides examples of retrofitted structures.
The document provides information on methods of prestressing in concrete, including pretensioning and post-tensioning. It discusses:
- Pretensioning involves stressing steel tendons before the concrete is cast around them.
- Post-tensioning involves stressing steel tendons after the concrete has cured using jacks, then grouting the voids.
- Both methods put the concrete in compression and increase its strength and durability compared to conventional reinforced concrete.
Green concrete is a type of concrete that uses less energy and causes less harm to the environment during production compared to conventional concrete. It incorporates waste materials like recycled concrete aggregates as partial replacements for cement or standard aggregates. Using materials like fly ash also reduces the carbon dioxide emissions associated with cement production. Green concrete provides benefits like improved durability, strength, and workability while reducing the construction industry's environmental impact through lower CO2 emissions and higher waste reuse.
Piles are deep foundations used to transfer structural loads through weak or wet soils to stronger soils below. Piles can be classified based on function (end bearing, friction, tension), material (concrete, timber, steel), or installation method (driven, cast-in-place). Key factors in pile design include soil properties, load types, and groundwater conditions. The ultimate load capacity of a pile considers end bearing and side friction, while the allowable load uses a factor of safety. Dynamic testing and soil parameters can be used to estimate pile capacities.
The document discusses wastewater treatment and its various stages. Wastewater treatment involves applying engineering techniques to change the physical, chemical, or biological properties of water so that it can be disposed of safely or reused. It goes through various stages including pre-treatment to remove solids, primary treatment where gravity is used to separate solids from water, secondary treatment using bacteria and algae to break down organic matter, and final treatment to further remove solids before being disposed or reused. The sludge from treatment is also processed, stabilized, and applied to agricultural fields. Monitoring is done at the plant and by government agencies to ensure safety.
Green concrete is a type of concrete that uses less energy and causes less harm to the environment during production compared to conventional concrete. It incorporates waste materials like recycled concrete aggregates as partial replacements for cement or standard aggregates. Using materials like fly ash also reduces the carbon dioxide emissions associated with cement production. Green concrete provides benefits like improved durability, strength, and workability while reducing the construction industry's environmental impact through lower CO2 emissions and higher waste reuse.
Piles are deep foundations used to transfer structural loads through weak soil layers to stronger soil strata below. There are different types of piles based on function (load bearing, non-load bearing), material (concrete, timber, steel), and installation method (driven, cast-in-place). Load bearing piles can be end bearing piles that rest on a hard layer or friction piles that transfer load through side friction. Factors like soil conditions, water table, and cost determine the suitable pile type for a given foundation. Load capacity is estimated through testing, soil parameters, or dynamic/static formulas.
The document discusses wastewater treatment processes. It describes how wastewater treatment involves applying engineering techniques to change the physical, chemical, or biological properties of water so it can be disposed of safely. The treatment process includes pre-treatment to remove solids, preliminary treatment using screens and grit chambers, primary treatment using sedimentation to remove solids, secondary treatment using biological processes like trickling filters to further reduce organic matter, and final clarification before water is disposed of or reused. Sludge produced from treatment is stabilized and applied to agricultural fields. The wastewater treatment plant monitors water quality through testing.
The document discusses wastewater treatment and its various stages. Wastewater treatment involves applying engineering techniques to change the physical, chemical, or biological properties of water so that it can be disposed of safely or reused. It goes through various stages including pre-treatment to remove solids, primary treatment where gravity is used to separate solids from water, secondary treatment using bacteria and algae to break down organic matter, and final treatment to further remove solids before being disposed or reused. The sludge from treatment is also processed, stabilized, and applied to agricultural fields. Monitoring is done at the plant and by government agencies to ensure safety.
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Sri Guru Hargobind Ji - Bandi Chor Guru.pdfBalvir Singh
Sri Guru Hargobind Ji (19 June 1595 - 3 March 1644) is revered as the Sixth Nanak.
• On 25 May 1606 Guru Arjan nominated his son Sri Hargobind Ji as his successor. Shortly
afterwards, Guru Arjan was arrested, tortured and killed by order of the Mogul Emperor
Jahangir.
• Guru Hargobind's succession ceremony took place on 24 June 1606. He was barely
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• As ordered by Guru Arjan Dev Ji, he put on two swords, one indicated his spiritual
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• He had a long tenure as Guru, lasting 37 years, 9 months and 3 days
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PRESTRESSED CONCRETE
1. Seminar Presentation on
METHODS OF PRESTRESSING
IN CONCRETE
Submitted To-
Mr. S.C.Verma
Department of civil engg.
COER
Submitted By-:
Abhishek Jain
Civil Engg.
Section – E (T1)
Roll No.-03
3. PRESTRESSED CONCRETE
PRINCIPLE – Using high tensile strength
steel alloys producing permanent pre-
compression in areas subjected to Tension.
A portion of tensile stress is counteracted
thereby reducing the cross-sectional area of
the steel reinforcement .
METHODS :- a) Pretensioning
b)Post-tensioning
PRETENSIONING :- Placing of concrete
around reinforcing tendons that have been
stressed to the desired degree.
POST-TENSIONING :- Reinforcing tendons
are stretched by jacks whilst keeping them in
serted in voids left pre-hand during curing of
concrete.
These spaces are then pumped full of grout to
bond steel tightly to the concrete.
STEEL BARS BEING
STRETCHED BY JACKS
4. POST - TENSIONING
WHAT IS POST-TENSIONING?
Post-tensioning- is a method of reinforcing
(strengthening) concrete or other materials with high-
strength steel strands called tendons.
Post-tensioning allows construction that would
otherwise be impossible due to either site constraints
or architectural requirements.
Requires specialized knowledge and expertise to
fabricate, assemble and install.
After adequate curing of concrete, reinforcing
tendons (placed in side the voids of the structure) are
tensioned/stretched by jacks on the sides & grouts
filled with appropriate mix.
Applications – a) Structural members beams,
bridge-deck panels, Roof –Slabs, Concrete Silos Etc.
6. BENEFITS
Concrete is very strong in compression but weak
in tension,
This deflection will cause the bottom of the beam
to elongate slightly & cause cracking.
Steel reinforcing bars (“rebar”) are typically
embedded in the concrete as tensile
reinforcement to limit the crack widths.
Rebar is what is called “passive” reinforcement
however; it does not carry any force until the
concrete has already deflected enough to crack.
Post-tensioning tendons, on the other hand, are
considered “active” reinforcing.
Because it is prestressed, the steel is effective as
reinforcement even though the concrete may not
be cracked .
Post-tensioned structures can be designed to
have minimal deflection and cracking, even
under full load.
Post –Tensioned Structure
7. ADVANTAGES/APPLICATIONS
Post-tensioning allows longer clear spans, thinner
slabs, fewer beams and more slender, dramatic
elements.
Thinner slabs mean less concrete is required. It
means a lower overall building height for the same
floor-to-floor height.
Post-tensioning can thus allow a significant
reduction in building weight versus a conventional
concrete building with the same number of floors
reducing the foundation load and can be a major
advantage in seismic areas.
A lower building height can also translate to
considerable savings in mechanical systems and
façade costs.
Another advantage of post-tensioning is that beams
and slabs can be continuous, i.e. a single beam can
run continuously from one end of the building to
the other.
Reduces occurrence of cracks .
Freezing & thawing durability is higher than non
prestressed concrete.
This innovative form is result of
post tensioning.
Bridge decks
8. Post-tensioning is the system of choice for parking structures
since it allows a high degree of flexibility in the column layout,
span lengths and ramp configurations.
In areas where there are expansive clays or soils with low
bearing capacity, post-tensioned slabs-on-ground and mat
foundations reduce problems with cracking and differential
settlement.
Post-tensioning allows bridges to be built to very
demanding geometry requirements, including complex
curves, and significant grade changes.
Post-tensioning also allows extremely long span bridges to be
constructed without the use of temporary intermediate
supports. This minimizes the impact on the environment
and avoids disruption to water or road traffic below.
In stadiums, post-tensioning allows long clear spans and very
creative architecture.
Post-tensioning can also be used to produce virtually crack-free
concrete for water-tanks.
The high tensile strength & precision of placement gives
maximum efficiency in size & weight of structural members.
Applications of various prestressed techniques enable quick
assembly of standard units such as bridge members,building
frames, bridge decks providing cost-time savings.
9. CONSTRUCTION
In slab-on-ground construction, unbonded tendons
are typically prefabricated at a plant and delivered to
the construction site, ready to install.
The tendons are laid out in the forms in accordance
with installation drawings that .
After the concrete is placed and has reached its
required
strength, usually between 3000 and 3500 psi
(“pounds per
square inch”), the tendons are stressed and
anchored.
The tendons, like rubber bands, want to return to
their original length but are prevented from doing so
by the anchorages.
The fact the tendons are kept in a permanently
stressed
(elongated) state causes a compressive force to act
on the
concrete.
The compression that results from the post-tensioning
counteracts the tensile forces created by subsequent
applied loading (cars, people, the weight of the
beam itself when the shoring is removed).
This significantly increases the load-carrying capacity
of the concrete.
Since post-tensioned concrete is cast in place at the
job site, there is almost no limit to the shapes that can
be formed.
Limitations of Prestressing
The limitations of prestressed concrete are few and really
depend only upon the imagination of the designer and the
terms of his brief. The only real limitation where
prestressing is a possible solution may be the cost of
providing moulds for runs of limited quantity of small
numbers of non-standard units.
11. PRESTRESSED CONCRETE
Prestressed concrete, invented by Eugene
Frevssinet in 1928 is a method for overcoming
concrete’’s natural weakness in tension . It can
be used to produce beams , floors or bridges with
a longer span than is practical with ordinary
reinforced concrete.
It can be accomplished in three ways: pre-
tensioned concrete, and bonded or unbonded.
Pre-tensioned concrete
Pre-tensioned concrete is cast around already tensioned
tendons.
This method produces a good bond between the tendon
and concrete, which both protects the tendon from
corrosion and allows for direct transfer of tension.
The cured concrete adheres and bonds to the bars and
when the tension is released it is transferred to the
concrete as compression by static friction.
However, it requires stout anchoring points between
which the tendon is to be stretched and the tendons are
usually in a straight line.
Thus, most pretensioned concrete elements are
prefabricated in a factory and must be transported to the
construction site, which limits their size.
Pre-tensioned elements may be balcony elements, lintels
, floor slabs, beams or foundation piles.
12. Bonded post-tensioned concrete
Bonded post-tensioned concrete is the descriptive term for a
method of applying compression after pouring concrete and the
curing process (in situ).
The concrete is cast around a plastic, steel or aluminium curved
duct, to follow the area where otherwise tension would occur in
the concrete element.
A set of tendons are fished through the duct and the concrete is
poured. Once the concrete has hardened, the tendons are
tensioned by hydraulic jacks.
When the tendons have stretched sufficiently, according to the
design specifications they are wedged in position and maintain
tension after the jacks are removed, transferring pressure to the
concrete.
The duct is then grouted to protect the tendons from corrosion.
This method is commonly used to create monolithic slabs for
house construction in locations where expansive soils create
problems for the typical perimeter foundation.
All stresses from seasonal expansion and contraction of the
underlying soil are taken into the entire tensioned slab, which
supports the building without significant flexure. Post-stressing
is also used in the construction of various bridges.
The advantages of this system over unbonded post-tensioning
are:
DECK STEEL LAYING
13. Large reduction in traditional reinforcement
requirements as tendons cannot destress in
accidents.
Tendons can be easily 'weaved' allowing a
more efficient design approach.
Higher ultimate strength due to bond
generated between the strand and concrete.
No long term issues with maintaining the
integrity of the anchor/dead end.
Unbonded post-tensioned
concrete
Unbonded post-tensioned concrete differs
from bonded post-tensioning by providing
each individual cable permanent freedom of
movement relative to the concrete.
To achieve this, each individual tendon is
coated with a grease (generally lithium
based) and covered by a plastic sheathing
formed in an extrusion process.
The transfer of tension to the concrete is
achieved by the steel cable acting against
steel anchors in the perimeter of the slab.
The main disadvantage over bonded post-
tensioning is the fact that a cable can
destress itself and burst out of the slab if
damaged (such as during repair on the slab).
The advantages of this system over bonded
post-tensioning are:
14. External Prestressing
This refers to the case where prestressing tendons are
placed outside the concrete section and the
prestressing force is transferred to a structural member
through end anchorages or deviators. Advantages of
external prestressing include the possibility of
monitoring and replacing tendons, ease in concreting
and hence better concrete quality and the use of
narrower webs. External prestressing is being
increasingly used in the construction of new bridges
and is a primary method for the strengthening and
rehabilitation of existing structures.
At NUS, a three-year project on the application of
external prestressing in structural strengthening has
been completed, and this has resulted in design charts
being developed for such applications. Works were
also carried out on the use of fibre-reinforced polymer
(FRP) reinforcement as external tendons in both simply
supported and continuous beams.
15. • Fallingwater is comprised of a series of concrete cantilever
“trays” 30-ft. above a waterfall. Previous efforts failed to
permanently address excessive deflections of the cantilever
and repair the cracks. After a thorough design review, the
owner and engineer selected an external post-tensioning
solution for its durability, aesthetics and structural
unobtrusiveness.
• Construction plans called for strengthening of three support
girders spanning in the north-south direction with multistrand
post-tensioning tendons consisting of multiple 0.5” diameter
strands.
• Thirteen strand tendons were placed on each side of two
girders. One 10-strand tendon was placed on the western side
of the third girder (access on the eastern side of this girder
was not available). Eight monostrand tendons, 0.6” diameter,
were slated for the east-west direction.
•The monostrand tendons were stressed in the east-west
direction and then the multistrand tendons were stressed in the
north-south direction and grouted with a high quality, low-bleed
cementitious grout mixture.
•VSL’s scope of work also included welding steel cover plates,
attaching structural steel channels, injecting epoxy grout,
doweling reinforced cast in place concrete blocks and the
installation of near surface mounted carbon fiber rods.
Challenged with maintaining Fallingwater’s original setting,
furnishings and artwork, the project was successfully
completed in six months.
The lower and upper terraces cantilever
over the stream below. The temporary
structural steel shoring was placed beneath
the main level terrace.
Frank Lloyd Wright's Fallingwater
Mill Run, Pennsylvania
APPLICATIONS
16. Cline Avenue Bridge
Gary, Indiana
The Cline Avenue Bridge (SR 912) is a predominately cast-in-place post-tensioned
structure located in Gary, Indiana. The bridge mainline is over 6,000 LF, has two
adjacent segments nearly 35 feet wide each, and contains four connecting ramps. An
inspection and analysis team was assembled to perform a thorough investigation of
the bridge. The team concentrated on the existing post-tensioning system and
interior and exterior concrete cracks. The engineer retained VSL to assist with the
inspection of the tendons.
VSL approached the Cline Avenue project with a guideline that outlines a statistically
sound method of sampling the tendons. A statistical sample pool (which consisted of
the mainline structure and the ramps) was defined by referencing the American
National Standard Institute’s (ANSI) guideline “Sampling Procedures and Tables for
Inspection by Attributes as published by the American Society for Quality Control
(1993).”
The probable void locations throughout the structure’s mainline segments and ramps
were initially identified by VSL to appropriately distribute the sampling population.
Such areas consisted of high points, areas approaching and leaving the high points,
and couplers.
Using non-destructive Ground Penetrating Radar (GPR) and field layout drawings,
VSL located existing post-tensioning tendons. Once the layout was performed,
specific tendons throughout the bridge and ramp structures were sampled by drilling
into the duct and exposing the tendon for visual inspection. The use of a borescope
allowed for detailed visual inspection of the tendon and also captured video footage
to share with the owner and the engineer. After review of each inspection, VSL
placed epoxy in the borescope hole to protect the tendons from air and moisture
intrusion. When voids were encountered, the project team observed and documented
the condition of the strand based on the PCI Journal guideline, “Evaluation of Degree
of Rusting on Prestressed Concrete Strand.” VSL used vacuum grouting technology
to fill the void, thereby protecting the previously exposed strand.
The tendon inspection data was analyzed with other findings (such as crack survey
findings) to determine what type of rehabilitation was required. VSL’s goal to
establish a statistically sound sample of physically inspected tendons that provided
valid data as to the current state of the existing PT system was accomplishedGrouting of void using VSL’s specialized vacuum grouting equipment
17. 85th Street Bridge
Valley Center, Kansas
The 85th Street North Bridge is a seven span post-tensioned
haunched slab bridge with a typical span of 26 meters for the
middle five spans, and 20 meters at the ends. This 170 meter
long bridge accommodates two lanes of traffic reaching over
the Wichita Valley Center Floodway. VSL post-tensioning
systems utilized for this project include 5-19 longitudinal
tendons as well as 6-4 transverse tendons.
Post-tensioned haunched slab bridges are noted for ease of
construction. Once the geometry of the bridge falsework has
been obtained, prefabricated spacer frames are set into
place. The spacer frames serve as templates for profiling the
longitudinal post-tensioning tendons and aid in the placement
of the remaining conventional reinforcement. Transverse
tendons maintain mid-depth placement along the geometry of
the haunched slab and provide the minimum pre-
compression over the length of the structure.
The fi nished product has several advantages over
conventionally reinforced concrete. Dead loads are balanced
by the use of longitudinal post-tensioning reducing the
sustained loading and associated creep. Corrosion
resistance is increased due to the encapsulation of the post-
tensioning reinforcement. Through the use of transverse
post-tensioning, added compression improves the longevity
of the structure by adding resistance to de-icing methods
such as salt and magnesium chloride. Post-tensioned
haunched slab bridges allow for a larger span to depth ratio
than that of conventionally reinforced haunched slab bridges.
The labor and material savings on mild reinforcement is
another clear advantage to using post-tensioning for this
application.
Overlooking the 85th Street Bridge prior to concrete placement
18. Colorado Convention Center
Expansion
Denver, Colorado
The Colorado Convention Center Expansion
project is a 1.4 million square foot expansion of
the existing facility. This was a multi-level
project, which included a 1,000-car attached
parking garage.
The garage above the street was constructed
using precast tees and columns with a cast-in-
place topping slab. In order to maintain regular
spacing for the columns in the precast section
of the garage and still maintain an
unobstructed path for the road and light rail,
large post-tensioned transfer girders were
required to support several of the columns
above. The transfer girders allowed for the
placement of columns required for the precast
design despite the restricted column locations
at the street level.
Post-tensioning the transfer girders resulted in
smaller dimensions than a conventional
reinforced concrete design, an important factor
given the girders are over 7 feet high and up to
7 feet wide and a larger section would not fit
within the space constraints of the building.
The girders could not be stressed until after the
precast garage was fully erected and the
topping slab poured on the truck dock.
Temporary columns were placed under the
girders to support the load until stressing.
The effective post-tensioning force required for
the beams ranged from 2176 to 5457 kips. A
multistrand bonded system was installed
19. The Seward Silo project involved the post-tensioning of three
interconnected ash silos that are part of the Seward Re-Powering
Project in Seward, Pennsylvania. The overall project involved the
construction of a new, state-of-the-art 208 MW power plant designed to
burn low-grade coal that can not be burned in ordinary coal plants. This
is a design-build project with Drake-Fluor Daniel as the
owner/construction manager until the completed plant is turned over to
Reliant Energy, the ultimate owner.
T.E. Ibberson Company was contracted to build three 187’-6” tall,
interconnected, in-line silos; two 82’-4” diameter fly ash silos and one
64’-8” diameter bed ash silo. The silos were built using the slip-form
method of construction and are believed to be the first interconnected
silos in the world built using post-tensioning as the primary
circumferential reinforcement.
VSL’s work was performed from November 2003 through February
2004, during the second coldest winter on record locally. Significant
snowfall and subzero temperatures made progress challenging, yet with
a strong focus on safety, both cold-related and otherwise, the job was
completed with no incidents. The job required close coordination
between the various trades working in close proximity and constant
communication between parties working above and below VSL’s work
locations to phase the work to avoid having personnel under an active
work zone.
The strand installation, stressing and grouting operations were
completed successfully, with cold-weather grouting made possible
through a variety of heating methods.
Seward Silo
20. THE BICYCLE WHEEL
Bicycle wheel as we know it today - each is
associated with an application of prestressing to
a structural system.
The first and most obvious is the tensioned
spokes - the rider's weight is carried from the
forks to the ground not by hanging off the top
spokes, but by reducing the pretension in the
lower spokes - only a couple of spokes are
carrying the load at any one time.
The second is the pneumatic tyre, where the
compressive load is carried to the ground by
reducing the tension in the sidewall. The air
pressure in the tyre does not change when the
load is applied.
The final prestressing system is the tyre cord,
which is shorter than the perimeter of the rim.
The cord is thus in tension, holding the tyre on
the rim, which enables the pretension in the
sidewalls to be reacted