Post Tensioning[1]

POSTPOST--TENSIONING TENSIONING Principles and Principles and

Applications to Concrete Applications to Concrete ElementsElements

Prepared by:Prepared by:

Danny M. Francisco. C.E., G.E.Danny M. Francisco. C.E., G.E.Tel. 6770359 (Office)Tel. 6770359 (Office)Mobile: 0557124793Mobile: 0557124793Email: [email protected]: [email protected]

Objectives:Objectives:

1. To know the brief history of post1. To know the brief history of post--tensioning. tensioning.

2. To understand the basic principles of 2. To understand the basic principles of postpost--tensioning.tensioning.

3. To identify the components of post3. To identify the components of post--tensioning.tensioning.

4. To know the applications of post4. To know the applications of post--tensioningtensioning

HistoryHistory•• The first patent for prestressed concrete was The first patent for prestressed concrete was

issued to P.H. Jackson of San Francisco in 1886. issued to P.H. Jackson of San Francisco in 1886. He obtained a US patent for tightening steel tie He obtained a US patent for tightening steel tie rods in artificial stones (concrete blocks) and rods in artificial stones (concrete blocks) and concrete arches used for slabs and roofs.concrete arches used for slabs and roofs.

Shortly thereafter, in 1888, C.E.W. Doehring from Shortly thereafter, in 1888, C.E.W. Doehring from Germany also obtained a patent for prestressing Germany also obtained a patent for prestressing concrete slabs with metal wires. However, modern concrete slabs with metal wires. However, modern development of prestressed concrete is usually development of prestressed concrete is usually attributed to Eugene Freyssinet of France. attributed to Eugene Freyssinet of France.

In 1928, Freyssinet begun to use highIn 1928, Freyssinet begun to use high--strength strength steel wire for prestressing concrete.steel wire for prestressing concrete.

In 1940, Professor Gustav Magnel of Belgium In 1940, Professor Gustav Magnel of Belgium developed a system of curve, multideveloped a system of curve, multi--wire tendons in wire tendons in flexible rectangular ducts.flexible rectangular ducts.

The first use of postThe first use of post--tensioning in the US was on the tensioning in the US was on the Walnut Lane Bridge in Philadelphia in 1949. This Walnut Lane Bridge in Philadelphia in 1949. This landmark bridge had precast girders postlandmark bridge had precast girders post--tensioned tensioned with the Magnel system.with the Magnel system.

Ulrich FinsterwalderUlrich Finsterwalder-- German Civil Engineer German Civil Engineer

TieTie--Back AnchorageBack Anchorage

TieTie--Down AnchorageDown Anchorage

Over the years, there have been a number of significant Over the years, there have been a number of significant technological developments that have helped advance the technological developments that have helped advance the statestate--ofof--thethe--art of post tensioning and have contributed to its art of post tensioning and have contributed to its continued growth. These developments include:continued growth. These developments include:

1. Introduction of strand system1. Introduction of strand system

2. Development of ductile iron castings for single strand tendon2. Development of ductile iron castings for single strand tendonss

3. Introduction of the 3. Introduction of the ““loadload--balancingbalancing”” design methoddesign method

4. Introduction of 4. Introduction of ““bandedbanded”” tendon layout for 2tendon layout for 2--way slab systemway slab system

5. Segmental bridge construction5. Segmental bridge construction

6. Use of computers for analysis and design6. Use of computers for analysis and design

7. Formation of the Post7. Formation of the Post--Tensioning InstituteTensioning Institute

8. Improvements in corrosion resistance8. Improvements in corrosion resistance

•• In the United States, early bonded postIn the United States, early bonded post--tensioning tensioning system used highsystem used high--strength stressstrength stress--relieved steel wires, relieved steel wires, bars, or strand. The buttonbars, or strand. The button--headed tendon system headed tendon system used used ¼¼ inch wire bundled together, greased, and inch wire bundled together, greased, and wrapped with Kraft paper as sheathing. The wires ran wrapped with Kraft paper as sheathing. The wires ran through a stressing head and were through a stressing head and were ““button headedbutton headed”” to to anchor them. Machinery was used to coldanchor them. Machinery was used to cold--upset the upset the ends of the wires to create the buttonends of the wires to create the button--head anchors. head anchors. The postThe post--tensioning elongation was held with shims tensioning elongation was held with shims or a threaded nut. or a threaded nut.

•• The buttonThe button--headed tendon system had two major headed tendon system had two major problems. The first problem was that the tendons problems. The first problem was that the tendons had to be an exact length. Any deviation between had to be an exact length. Any deviation between the tendon length and the length between forms the tendon length and the length between forms required either a new tendon or moving the edge required either a new tendon or moving the edge forms before pouring the concrete. forms before pouring the concrete.

•• Second, because shims and stressing washer Second, because shims and stressing washer ended up on the outside edges of the constructed ended up on the outside edges of the constructed slab, they have to be covered with second slab, they have to be covered with second concrete pour.concrete pour.

•• The first strand tendon system The first strand tendon system –– developed by developed by Edward K. RiceEdward K. Rice and others at Atlas Prestressing and others at Atlas Prestressing CorporationCorporation-- used used ½½ inch severinch sever--wire prestressing wire prestressing strand and an anchorage assembly manufactured of strand and an anchorage assembly manufactured of coiled wire and a plate and anchored with two half coiled wire and a plate and anchored with two half wedge chucks. The strand was also greased andwedge chucks. The strand was also greased andwrapped with Kraft paper.wrapped with Kraft paper.

•• Since 1985, postSince 1985, post--tensioning usage tensioning usage has continued to grow at a rapid has continued to grow at a rapid pace, averaging 8.5% annual growth pace, averaging 8.5% annual growth as shownas shown..

•• In the last 50 years, prestressed concrete has grown In the last 50 years, prestressed concrete has grown to be a multibillionto be a multibillion--dollar industry in North America dollar industry in North America and is used in many different construction and is used in many different construction applications. Figure shows the relative usage of postapplications. Figure shows the relative usage of post--tensioning by market value.tensioning by market value.

Principles:Principles:•• PrestressingPrestressing

General:General:PrePre--stressing is a method of reinforcing concrete. Externally stressing is a method of reinforcing concrete. Externally applied loads induce internal stresses (forces) in concrete duriapplied loads induce internal stresses (forces) in concrete during ng the construction and services phases of a member. The concrete ithe construction and services phases of a member. The concrete is s prepre--stressed to counteract these anticipated stresses during the stressed to counteract these anticipated stresses during the service life of the member.service life of the member.

•• There are two commonly used methods of preThere are two commonly used methods of pre--stressing concrete. stressing concrete. One is called preOne is called pre--tensioning. The prefix tensioning. The prefix ““prepre”” means that the premeans that the pre--stressing steel is stressed before the concrete is cast. This mestressing steel is stressed before the concrete is cast. This method thod consists of first stressing highconsists of first stressing high-- strength steel strands or wires strength steel strands or wires between buttresses, and then casting the concrete around the between buttresses, and then casting the concrete around the steel. Once the concrete has reached a certain specified strengtsteel. Once the concrete has reached a certain specified strength, h, the steel is cut between the ends of the member and the the steel is cut between the ends of the member and the buttresses to transfer the prebuttresses to transfer the pre--stressing force to the concrete. This stressing force to the concrete. This process typically takes place at a precast plant and requires thprocess typically takes place at a precast plant and requires the e complete precomplete pre--tensioned concrete member to be trucked out to the tensioned concrete member to be trucked out to the job site and then assembled.job site and then assembled.

•• The other method of preThe other method of pre--stressing concrete is called stressing concrete is called postpost--tensioning. The prefix tensioning. The prefix ““postpost”” means that the premeans that the pre--stressing steel is stressed after the concrete is cast. stressing steel is stressed after the concrete is cast. Instead of stressing the highInstead of stressing the high--strength steel between strength steel between buttresses at a precast plant. The steel is simply buttresses at a precast plant. The steel is simply installed on the job site after the contractor forms up installed on the job site after the contractor forms up the member. The highthe member. The high--strength steel is housed in a strength steel is housed in a sheathing or duct that prevents it from bonding to the sheathing or duct that prevents it from bonding to the concrete. The steel is attached to the concrete at the concrete. The steel is attached to the concrete at the ends of the member by especially design anchorage ends of the member by especially design anchorage devices. Once the concrete has cured (hardened), the devices. Once the concrete has cured (hardened), the steel is stressed to induce forces in the concrete. Poststeel is stressed to induce forces in the concrete. Post--tensioning has all of the advantages of pretensioning has all of the advantages of pre--stressed stressed concrete while allowing the builder the freedom to concrete while allowing the builder the freedom to construct the member in any location, including its construct the member in any location, including its final position in the structure (castfinal position in the structure (cast--inin--place).place).

•• Types of postTypes of post--tensioning system:tensioning system:•• In most postIn most post--tensioned construction, the pretensioned construction, the pre--stressing stressing

tendons are embedded in the concrete before the concrete tendons are embedded in the concrete before the concrete is cast. These internally postis cast. These internally post--tensioned systems can be tensioned systems can be either bonded or unbonded. In some bridge and retrofit either bonded or unbonded. In some bridge and retrofit applications, the postapplications, the post--tensioning tendons are mounted tensioning tendons are mounted outside the structural members. These are referred to as outside the structural members. These are referred to as external postexternal post--tensioning systems.tensioning systems.

•• In unIn un--bonded systems, the strand is kept unbonded to bonded systems, the strand is kept unbonded to the surrounding concrete throughout its service life. the surrounding concrete throughout its service life. In bonded systems, grout is injected in the ducts to In bonded systems, grout is injected in the ducts to bond the prebond the pre--stressing strand to the surrounding stressing strand to the surrounding concrete after it has been stressed. Once the grout concrete after it has been stressed. Once the grout has cured (hardened), the system behaves as an has cured (hardened), the system behaves as an integral system without any relative movement integral system without any relative movement between steel and concrete. Most of the internally between steel and concrete. Most of the internally grouted postgrouted post--tensioned systems are considered to be tensioned systems are considered to be bonded. Unbonded systems allow relative movement bonded. Unbonded systems allow relative movement between the strand and surrounding concrete between the strand and surrounding concrete throughout it service life. Most singlethroughout it service life. Most single--strand systems strand systems and all external postand all external post--tensioning systems fall under tensioning systems fall under this category.this category.

•• Unbonded PostUnbonded Post--Tensioning Systems:Tensioning Systems:•• The tendons in an unbonded system typically consist of The tendons in an unbonded system typically consist of

singlesingle--strand that coated with corrosionstrand that coated with corrosion--inhibiting coating inhibiting coating and protected by extruded plastic sheathing. This allows the and protected by extruded plastic sheathing. This allows the strand to move inside the plastic sheathing and prevent the strand to move inside the plastic sheathing and prevent the ingress of water. ingress of water.

•• The strands are anchored to the concrete using ductile iron The strands are anchored to the concrete using ductile iron anchors and hardened steel wedges. The tendon is anchors and hardened steel wedges. The tendon is supported by chairs and bolsters along its length to supported by chairs and bolsters along its length to maintain the desired profile. Figure shows the typical maintain the desired profile. Figure shows the typical components and construction sequence for an unbonded components and construction sequence for an unbonded system.system.

•• Depending on the exposure of the singleDepending on the exposure of the single--strand unbonded strand unbonded system, it can be classified as a standard or encapsulated system, it can be classified as a standard or encapsulated system. Encapsulated systems are required for aggressive system. Encapsulated systems are required for aggressive environment where there is a possibility of tendon exposure environment where there is a possibility of tendon exposure to chlorides or other deleterious substances. Encapsulated to chlorides or other deleterious substances. Encapsulated tendons are designed to prevent any ingress of water tendons are designed to prevent any ingress of water during and after construction. Figure shows an example of a during and after construction. Figure shows an example of a standard and encapsulated tendon.standard and encapsulated tendon.

•• Bonded PostBonded Post--Tensioning System:Tensioning System:•• Bonded postBonded post--tensioning systems consist of tendons with multi tensioning systems consist of tendons with multi

strands or bars. The strands or bars are placed in corrugated strands or bars. The strands or bars are placed in corrugated galvanized steel, high density polyethylene (HDPE) or galvanized steel, high density polyethylene (HDPE) or polypropylene (PP) ducts. Depending on the site conditions and polypropylene (PP) ducts. Depending on the site conditions and system used, the strands may be installed before the concrete issystem used, the strands may be installed before the concrete isplaced or the ducts may be installed without the strands. The placed or the ducts may be installed without the strands. The strands are then pulled or pushed through the ducts. Once the strands are then pulled or pushed through the ducts. Once the concrete has hardened, the tendons are stressed and ducts filledconcrete has hardened, the tendons are stressed and ducts filledwith grout. Inlets and outlets are provided at high/low points twith grout. Inlets and outlets are provided at high/low points to o ensure that the grout fills the ducts completely. Figure shows tensure that the grout fills the ducts completely. Figure shows the he components of a typical multi strand grouted system. The grout components of a typical multi strand grouted system. The grout provides an alkaline environment and protect the preprovides an alkaline environment and protect the pre--stressing stressing strands from corrosion. It also bonds the strands to the strands from corrosion. It also bonds the strands to the surrounding concrete.surrounding concrete.

Illustrations:Illustrations:

•• Concrete has a low tensile strength but is strong in Concrete has a low tensile strength but is strong in compression. The tensile strength of concrete is about compression. The tensile strength of concrete is about 10% of its compressive strength. As a result, plain 10% of its compressive strength. As a result, plain concrete members are likely to crack when loaded. concrete members are likely to crack when loaded.

•• Consider a beam of plain concreteConsider a beam of plain concrete

As the load increases, the beam deflects slight and then As the load increases, the beam deflects slight and then falls abruptly. Under load, the stresses in the beam will falls abruptly. Under load, the stresses in the beam will be compressive in the top, but tensile in the bottom. We be compressive in the top, but tensile in the bottom. We can expect the beam to crack at the bottom and break, can expect the beam to crack at the bottom and break, even with a relatively small load, because of concreteeven with a relatively small load, because of concrete’’s s low tensile strength. In order to resist tensile stresses or low tensile strength. In order to resist tensile stresses or counter the low tensile strength which plain concrete counter the low tensile strength which plain concrete cannot resist, it can be reinforced in two ways by using cannot resist, it can be reinforced in two ways by using steel reinforcing bars or by presteel reinforcing bars or by pre--stressing.stressing.

•• In the usual reinforced concrete beam, the In the usual reinforced concrete beam, the concrete cannot be used efficiently, certain forces concrete cannot be used efficiently, certain forces may be applied to the beams that result in a may be applied to the beams that result in a member in which all the concrete can resist the member in which all the concrete can resist the bending stresses. bending stresses.

•• Introducing a means of preIntroducing a means of pre--compressing the compressing the tensile zones of the concrete members to offset tensile zones of the concrete members to offset anticipated tensile stresses will reduce or anticipated tensile stresses will reduce or eliminate cracking and will produce a more eliminate cracking and will produce a more durable concrete member. By predurable concrete member. By pre--compressing a compressing a concrete element, so that when flexing under concrete element, so that when flexing under applied load, it will still remain in compression applied load, it will still remain in compression and achieving a more efficient design of the and achieving a more efficient design of the structure. structure.

•• The function of Prestressing (preThe function of Prestressing (pre--tensioning or tensioning or POSTPOST--TENSIONING) is to place the structure TENSIONING) is to place the structure under compression in those region where load under compression in those region where load causes tensile stresses. Compressive stresses causes tensile stresses. Compressive stresses introduced into areas where tensile stresses introduced into areas where tensile stresses under load will resist or annul these tensile under load will resist or annul these tensile stresses. stresses.

•• So the concrete now behaves as if it had a high So the concrete now behaves as if it had a high tensile strength of its own and, provided that the tensile strength of its own and, provided that the tensile stresses do not exceed the pretensile stresses do not exceed the pre--compression stresses, cracking cannot occur in compression stresses, cracking cannot occur in the bottom of the beam.the bottom of the beam.

•• Tension caused by the load will first have to Tension caused by the load will first have to cancel the compression induced by the postcancel the compression induced by the post--tensioning before it can crack the concrete. The tensioning before it can crack the concrete. The prepre--compression stresses can also be designed to compression stresses can also be designed to overcome the diagonal stresses. The normal overcome the diagonal stresses. The normal procedure is to design to eliminate cracking at procedure is to design to eliminate cracking at working loads.working loads.

•• However, bending is only one of the conditions However, bending is only one of the conditions involved. There is also shear. Vertical and involved. There is also shear. Vertical and horizontal shear forces are set up within a beam horizontal shear forces are set up within a beam and these will cause diagonal tension and and these will cause diagonal tension and diagonal compression stresses of equal intensity. diagonal compression stresses of equal intensity.

•• As concrete is weak in tension, cracks in a As concrete is weak in tension, cracks in a reinforced concrete beam will occur where the reinforced concrete beam will occur where the diagonal tension stresses are high, usually near diagonal tension stresses are high, usually near the support. In prethe support. In pre--stressed concrete, the stressed concrete, the compression stresses can also be design to compression stresses can also be design to overcome these tension stresses.overcome these tension stresses.

•• Simple illustration #1: Simple illustration #1: •• Row of booksRow of books

•• Prof. Gustav Magnel, one of the pioneers of Prof. Gustav Magnel, one of the pioneers of prestressed concrete used this illustration and prestressed concrete used this illustration and simply explained to his students using stack of simply explained to his students using stack of books.books.

•• Illustration #2:Illustration #2:•• Figure 1.4 shows a plainly reinforced concrete Figure 1.4 shows a plainly reinforced concrete

simplesimple--span beam and a fixed cantilever beam span beam and a fixed cantilever beam cracked under applied load. cracked under applied load.

Reinforced concrete cracked under load (Fig. 1.4)Reinforced concrete cracked under load (Fig. 1.4)

•• Figure 1.5 shows the same unloaded beams with Figure 1.5 shows the same unloaded beams with prestressing forces applied by stressing high prestressing forces applied by stressing high strength tendons. By placing the prestressing low strength tendons. By placing the prestressing low in the simplein the simple--span beam and high in the span beam and high in the cantilever beam, compression is induced in the cantilever beam, compression is induced in the tension zones; creating upward camber. tension zones; creating upward camber.

PostPost--tensioned concrete before loading (Fig. 1.5)tensioned concrete before loading (Fig. 1.5)

•• While figure1.6 shows the two prestressed beams While figure1.6 shows the two prestressed beams after loads have been applied. The loads cause after loads have been applied. The loads cause both the simpleboth the simple--span beam and cantilever beam span beam and cantilever beam to deflect down, to deflect down,

•• creating tensile stresses in the bottom of the creating tensile stresses in the bottom of the simplesimple--span beam and top of the cantilever beam. span beam and top of the cantilever beam.

PostPost--tensioned concrete after loadingtensioned concrete after loading (Fig. 1.6)(Fig. 1.6)

•• The designer shall be able to balance the effects of load and The designer shall be able to balance the effects of load and prestressing in such a way that tension from the loading is prestressing in such a way that tension from the loading is compensated by compression induced by the postcompensated by compression induced by the post--tensioning. Figure 1.6 shows that tension is eliminated tensioning. Figure 1.6 shows that tension is eliminated under combination of Figures 1.4 and 1.5. Also construction under combination of Figures 1.4 and 1.5. Also construction materials (concrete and steel) are used more efficiently; materials (concrete and steel) are used more efficiently; optimizing materials, construction effort and cost. optimizing materials, construction effort and cost.

Fig. 1.4 Fig. 1.4

Fig. 1.5 Fig. 1.5

Fig. 1.6Fig. 1.6

•• One of the things that happen to a concrete, or a One of the things that happen to a concrete, or a masonry wall, is that they are subjected to forces masonry wall, is that they are subjected to forces that cause them to flex and bend. Examples of that cause them to flex and bend. Examples of this includes slabs on ground where the edges of this includes slabs on ground where the edges of the slabs are forced upward by swelling soil, the slabs are forced upward by swelling soil, elevated concrete slabs where gravity and other elevated concrete slabs where gravity and other applied loads pull down on the slab in between applied loads pull down on the slab in between supports, and walls that might be subjected to supports, and walls that might be subjected to lateral forces from wind or seismic activity. This lateral forces from wind or seismic activity. This bending creates high tensile forces that can cause bending creates high tensile forces that can cause the concrete and masonry to crack. This is where the concrete and masonry to crack. This is where the use of reinforcing is applied.the use of reinforcing is applied.

•• Illustration #3:Illustration #3:

•• Since steel has a high capacity to resist Since steel has a high capacity to resist tensile forces, it can be embedded in the tensile forces, it can be embedded in the concrete at the tension zones (the area concrete at the tension zones (the area that tensile failures could occur) allowing that tensile failures could occur) allowing the tensile forces to be handled by the the tensile forces to be handled by the reinforcing steel. Adding postreinforcing steel. Adding post--tensioned tensioned reinforcing combines the action of reinforcing combines the action of reinforcing the tension zones with the reinforcing the tension zones with the advantages of compressing the concrete or advantages of compressing the concrete or masonry structure.masonry structure.

•• Additional benefits are obtained when the postAdditional benefits are obtained when the post--tensioned reinforcing is installed in a draped tensioned reinforcing is installed in a draped profile instead of running in a straight line. A profile instead of running in a straight line. A typical draped profile in an elevated concrete typical draped profile in an elevated concrete slab would route the postslab would route the post--tensioned reinforcing tensioned reinforcing through a high point over the slabthrough a high point over the slab’’s supports, s supports, and through a low point in between those and through a low point in between those supports. Now, optimum efficiency is obtained supports. Now, optimum efficiency is obtained in the tension zones, the concrete is being in the tension zones, the concrete is being compressed, and the postcompressed, and the post--tensioned reinforcing tensioned reinforcing is creating an uplift force in the middle of the is creating an uplift force in the middle of the spans where it is needed the most.spans where it is needed the most.

•• Consider a beam with a force Consider a beam with a force P P applied at each end along the applied at each end along the beambeam’’s center line.s center line.

•• This force applies a uniform This force applies a uniform compressive stress across the compressive stress across the section equals to section equals to P/A.P/A.

•• Consider next a vertical load Consider next a vertical load WWapplied to the section and the applied to the section and the corresponding bending moment corresponding bending moment diagram applied to this alone.diagram applied to this alone.

•• The stress distribution from the flexure of the The stress distribution from the flexure of the beam is calculated from beam is calculated from M/ZM/Z, where , where MM is the is the bending moment and bending moment and ZZ is the section modulus. By is the section modulus. By considering the deflected shape of the beam, it considering the deflected shape of the beam, it can be seen that the bottom surface will be in can be seen that the bottom surface will be in tension. The corresponding stress diagram can be tension. The corresponding stress diagram can be drawn.drawn.

•• As previously discussed that concrete is strong in As previously discussed that concrete is strong in compression but not in tension. Only small tensile compression but not in tension. Only small tensile stresses can be applied before cracks that limit stresses can be applied before cracks that limit the effectiveness of the section will occur.the effectiveness of the section will occur.

•• By combining the stress distribution from the By combining the stress distribution from the applied preapplied pre--compression and the applied loading, compression and the applied loading, it can be seen that there is no longer any tension.it can be seen that there is no longer any tension.

•• In addition, the technique known as In addition, the technique known as ““load load balancingbalancing”” offers the designer a powerful offers the designer a powerful tool. In this, forces exerted by the pretool. In this, forces exerted by the pre--stressing tendons are modeled as stressing tendons are modeled as equivalent upward forces on the beam or equivalent upward forces on the beam or slab. These forces are then proportioned to slab. These forces are then proportioned to balance the applied downward forces. By balance the applied downward forces. By balancing a chosen percentage of applied balancing a chosen percentage of applied loading, it is possible to control deflections loading, it is possible to control deflections and also to make the most efficient use of and also to make the most efficient use of the beam or slab depth. the beam or slab depth.

Load Balancing by Prestressing Load Balancing by Prestressing

•• In order to use the load balancing technique, the In order to use the load balancing technique, the prepre--stressing tendons must be set to follow stressing tendons must be set to follow profiles that reflect the bending moment envelop profiles that reflect the bending moment envelop from applied loadings. Generally, parabolic from applied loadings. Generally, parabolic profiles are used.profiles are used.

Comparison between PostComparison between Post--tensioning and tensioning and Pretensioning:Pretensioning:

•• PostPost--tensioning can be done on the job site. From tensioning can be done on the job site. From reinforcing bars placement, installation of duct, reinforcing bars placement, installation of duct, steel form erection, concrete pouring, curing and steel form erection, concrete pouring, curing and postpost--tensioning of strands until erection or tensioning of strands until erection or placement.placement.

•• Bridge abutments and piers can be done Bridge abutments and piers can be done simultaneously while fabricating the postsimultaneously while fabricating the post--tensioned Itensioned I--girders (beams).girders (beams).

•• Pretensioning normally requires large open areas Pretensioning normally requires large open areas usually in a factory and being done between heavy usually in a factory and being done between heavy end anchorage, bulkheads or abutments. end anchorage, bulkheads or abutments.

•• Camber is the upward deflection in flexural Camber is the upward deflection in flexural members due to an eccentrically applied members due to an eccentrically applied prestressing force. Camber is divided into two prestressing force. Camber is divided into two categories i.e., initial camber and longcategories i.e., initial camber and long--term term camber. Initial camber is induced at transfer of camber. Initial camber is induced at transfer of the prestressing force at the time of release. It is the prestressing force at the time of release. It is the net upward deflection calculated by the net upward deflection calculated by algebraically summing the smaller downward algebraically summing the smaller downward deflection caused by the beam selfdeflection caused by the beam self--weight weight ((∆∆beam) and the larger upward deflection (beam) and the larger upward deflection (∆∆ps) ps) caused by the prestressing force applied at an caused by the prestressing force applied at an eccentricity eccentricity ‘‘ee’’ below the center of gravity of the below the center of gravity of the section.section.

•• The components of camber due to selfThe components of camber due to self--weight and prestressing force.weight and prestressing force.

•• For straight tendon profile:For straight tendon profile:•• ∆∆beam =beam = 5wLs5wLs4 4

384EcI 384EcI •• ∆∆ps = ps = PeLs2PeLs2

8EcI8EcI•• The magnitude of initial camber is the The magnitude of initial camber is the

difference (difference (∆∆ps ps -- ∆∆beam) between the beam) between the above two values.above two values.

•• The three figures below illustrate the elastic components of The three figures below illustrate the elastic components of

beam camber and deflection immediately after released.beam camber and deflection immediately after released.

Load applied to the beam at released Load applied to the beam at released

Deflection due to beam weight Deflection due to beam weight

Camber due to prestressing force Camber due to prestressing force

Definition of commonly used terms:Definition of commonly used terms:•• Aggressive Environment Aggressive Environment –– An environment in which An environment in which

structures are exposed to direct or indirect application of structures are exposed to direct or indirect application of deicing chemicals, seawater, brackish water, or spray from deicing chemicals, seawater, brackish water, or spray from these water sources; and saltthese water sources; and salt--laden air as occurs in the laden air as occurs in the vicinity of seacosts. Aggressive environment also include vicinity of seacosts. Aggressive environment also include structures where stressing pockets are wetted or are structures where stressing pockets are wetted or are directly in contact with soils which contain chloride levels directly in contact with soils which contain chloride levels considered y the geotechnical engineer to be harmful to considered y the geotechnical engineer to be harmful to metals.metals.

•• Anchor Cavity Anchor Cavity –– The opening in the anchor or anchor block The opening in the anchor or anchor block designed to accommodate the strand passing through and designed to accommodate the strand passing through and the proper seating of the wedges. the proper seating of the wedges.

•• Anchor Nut Anchor Nut –– Threaded device that screws onto a threaded Threaded device that screws onto a threaded bar and transfers the force from the bar to the bearing bar and transfers the force from the bar to the bearing plate.plate.

•• Anchorage Anchorage –– A mechanical device comprising all A mechanical device comprising all components required to anchor the prestressing steel and components required to anchor the prestressing steel and permanently transfer the postpermanently transfer the post--tensioning force from the tensioning force from the prestressing steel to the concrete.prestressing steel to the concrete.

•• Anchorage Zone Anchorage Zone –– The portion of the member through The portion of the member through which the concentrated prestressing force is transferred to which the concentrated prestressing force is transferred to the concrete and distributed more uniformly across the the concrete and distributed more uniformly across the section. Its extent is equal the largest dimension of the section. Its extent is equal the largest dimension of the cross section. For anchorage devices located away from the cross section. For anchorage devices located away from the end of the member, the anchorage zone includes the end of the member, the anchorage zone includes the disturbed regions ahead of and behind the anchorage.disturbed regions ahead of and behind the anchorage.

The general expression for combined general and local The general expression for combined general and local zones.zones.

•• Anticipated set Anticipated set –– The expected movement of the wedges The expected movement of the wedges into the anchorage during the transfer of the prestressing into the anchorage during the transfer of the prestressing force to the anchorage device.force to the anchorage device.This is that set which was assumed to occur in the design This is that set which was assumed to occur in the design calculation of postcalculation of post--tensioning forces immediately after load tensioning forces immediately after load transfertransfer

•• AUTS AUTS –– Actual Ultimate Tensile Strength: The actual Actual Ultimate Tensile Strength: The actual breaking strength obtained in tests on a single breaking strength obtained in tests on a single representative strand or bar, breaking outside the representative strand or bar, breaking outside the anchorage. For multianchorage. For multi--strand or bar tendons, AUTS equals strand or bar tendons, AUTS equals the AUTS of a single tendon elements (strand, bar) times the AUTS of a single tendon elements (strand, bar) times the number of such elements in the tendon. Representative the number of such elements in the tendon. Representative samples must be from same coil of strands or the same bar samples must be from same coil of strands or the same bar from which strands or bars are cut and used in connection from which strands or bars are cut and used in connection efficiency tests.efficiency tests.

•• BackBack--Up Bars Up Bars –– Reinforcing bars placed in concrete in the Reinforcing bars placed in concrete in the anchorage zone to position the anchor and help in anchorage zone to position the anchor and help in distributing the loads. distributing the loads.

•• Banded Tendons Banded Tendons –– Group(s) of closely speced tendons in Group(s) of closely speced tendons in slabs placed together in a narrow strip, usually along the slabs placed together in a narrow strip, usually along the column line.column line.

•• Bar Bar –– Bars used in postBars used in post--tensioning tendons conforming to tensioning tendons conforming to ASTM A722, Standard Specification for Uncoated HighASTM A722, Standard Specification for Uncoated High--Strength Bar for Prestressing Concrete. Bars have a Strength Bar for Prestressing Concrete. Bars have a minimum ultimate tensile strength of 150,000 psi minimum ultimate tensile strength of 150,000 psi

(1035 Mpa).(1035 Mpa).

Type I Bar has a plain surface and Type II Bar has surface Type I Bar has a plain surface and Type II Bar has surface deformations. Postdeformations. Post--tensioning bars are hightensioning bars are high--strength steel strength steel bars, normally available from 16mm to 44mm (5/8 to 1bars, normally available from 16mm to 44mm (5/8 to 1--3/4in) diameter and usually threaded with coarse thread.3/4in) diameter and usually threaded with coarse thread.

•• Barrel Anchor Barrel Anchor –– A cylindrical metal device housing the A cylindrical metal device housing the wedges and normally used with a bearing plate to transfer wedges and normally used with a bearing plate to transfer the prestressing force to the concrete.the prestressing force to the concrete.

•• Barrier Cable Barrier Cable –– HighHigh--strength steel strand erected around strength steel strand erected around the perimeter of a structure and at open edges of ramps to the perimeter of a structure and at open edges of ramps to prevent automobiles and pedestrians from falling over the prevent automobiles and pedestrians from falling over the open sides.open sides.

•• Basic Bearing Plate Basic Bearing Plate –– Flat plate bearing directly against Flat plate bearing directly against concrete meeting the analytical design requirements. concrete meeting the analytical design requirements. Covered by this definition are square, rectangular, or round Covered by this definition are square, rectangular, or round plates, sheared or torch cut from readily available steel plates, sheared or torch cut from readily available steel plates, normally ASTM A36. plates, normally ASTM A36.

•• Bearing Plate Bearing Plate –– A plate which bears directly against the A plate which bears directly against the concrete and is part of an overall anchorage system. A steel concrete and is part of an overall anchorage system. A steel hardware that transfers the tendon force into a structure.hardware that transfers the tendon force into a structure.

•• Blowout Blowout –– A localized concrete failure which occurs during A localized concrete failure which occurs during or after stressing.or after stressing.

•• Bonded Tendons Bonded Tendons –– Tendon in which prestressing steel is Tendon in which prestressing steel is bonded to concrete either directly or through grouting.bonded to concrete either directly or through grouting.

•• Bursting Steel Bursting Steel –– Reinforcing steel used to control the tensile Reinforcing steel used to control the tensile bursting forces developed at the bearing side of the anchor bursting forces developed at the bearing side of the anchor as the concentrated anchor force from prestressed tendon as the concentrated anchor force from prestressed tendon spreads out in all directions.spreads out in all directions.

•• Cable Cable –– A term used by some to denote a prestressing A term used by some to denote a prestressing strand or a singlestrand or a single--strand tendon. strand tendon.

•• Camber Camber –– An upward deflection that is caused by the An upward deflection that is caused by the application of prestressing force. Camber is intentionally application of prestressing force. Camber is intentionally built in a structural element or form to improve appearance built in a structural element or form to improve appearance or to nullify the deflection of the element under the effect of or to nullify the deflection of the element under the effect of loads, shrinkage, and creep.loads, shrinkage, and creep.

•• Chair Chair –– Hardware used to support or hold postHardware used to support or hold post--tensioning tendons or reinforcing.tensioning tendons or reinforcing.

Bars in their proper position to prevent displacement Bars in their proper position to prevent displacement before and during concrete placement.before and during concrete placement.

•• Coating Coating –– Material used to protect the prestressing Material used to protect the prestressing steel from corrosion and reduce the friction. steel from corrosion and reduce the friction.

•• Confinement Reinforcement Confinement Reinforcement -- NonNon--prestressed prestressed reinforcement in the local zone. Confinement reinforcement in the local zone. Confinement reinforcement in the concrete ahead of tendon reinforcement in the concrete ahead of tendon anchorage is limited to the local zone. Confinement anchorage is limited to the local zone. Confinement reinforcement consists of spirals, orthogonal reinforcement consists of spirals, orthogonal reinforcing bars, or a combination of both. reinforcing bars, or a combination of both.

•• (Cont(Cont’’d) Confinement reinforcement:d) Confinement reinforcement:For basic bearing plates, confinement reinforcement is For basic bearing plates, confinement reinforcement is required in that volume of concrete in which compressive required in that volume of concrete in which compressive stresses exceed acceptable limits for unreinforced concrete stresses exceed acceptable limits for unreinforced concrete determine by rational analysis. For special bearing plate, determine by rational analysis. For special bearing plate, confinement reinforcement is system dependent as confinement reinforcement is system dependent as determined by tests on individual anchorages. Test block determined by tests on individual anchorages. Test block reinforcement, in the portion surrounding the special reinforcement, in the portion surrounding the special bearing plate and immediately ahead of it, must represent bearing plate and immediately ahead of it, must represent the confinement required in the local zone for that the confinement required in the local zone for that particular system.particular system.

•• Coupler Coupler –– A device designed to connect ends of two strands A device designed to connect ends of two strands together, thereby transferring the prestressing force from together, thereby transferring the prestressing force from end to end of the tendons.end to end of the tendons.The means by which the prestressing force maybe The means by which the prestressing force maybe transferred from one partialtransferred from one partial--length prestressing tendon to length prestressing tendon to another tendon.another tendon.

•• Creep Creep –– Time dependant deformation (shortening) of Time dependant deformation (shortening) of concrete under sustained stress (load).concrete under sustained stress (load).

•• Curvature Friction Curvature Friction –– Friction resulting from bends or curves Friction resulting from bends or curves in the specified prestressing tendon profile.in the specified prestressing tendon profile.

•• Distributed Tendons Distributed Tendons –– Single or group of tendons in a slab Single or group of tendons in a slab that are uniformly distributed, usually perpendicular to the that are uniformly distributed, usually perpendicular to the bonded tendons and spaced at a maximum of eight times bonded tendons and spaced at a maximum of eight times the slab thickness or 5 feet (1.5 M).the slab thickness or 5 feet (1.5 M).

•• Duct Duct –– A conduit (plain or corrugated) to accommodate A conduit (plain or corrugated) to accommodate prestressing steel for post tensioning installation.prestressing steel for post tensioning installation.

•• Eccentricity Eccentricity –– Distance between the center of gravity of the Distance between the center of gravity of the concrete crossconcrete cross-- section and center of gravity of the section and center of gravity of the prestressing steel at any point along the length of the prestressing steel at any point along the length of the member.member.

•• Effective Prestress Effective Prestress -- Stress remaining in prestressing steel Stress remaining in prestressing steel after all losses have occurred.after all losses have occurred.

•• Elastic Shortening Elastic Shortening –– The shortening of a member that The shortening of a member that occurs immediately after the application of the prestressing occurs immediately after the application of the prestressing force.force.

•• Elongation Elongation –– Increase in the length of the prestressing steel Increase in the length of the prestressing steel under the applied prestressing force. under the applied prestressing force.

•• Encapsulated System Encapsulated System –– A postA post--tensioning system that tensioning system that prevents the ingress of water into the tendon during all prevents the ingress of water into the tendon during all stages of construction, and isolates the strand and stages of construction, and isolates the strand and anchorage from contact with concrete.anchorage from contact with concrete.

•• Fixed End Anchorage Fixed End Anchorage –– An anchorage at the end of a tendon An anchorage at the end of a tendon where prestressing jack is not attached during stressing where prestressing jack is not attached during stressing operations. Fixedoperations. Fixed--end anchorages are typically attached end anchorages are typically attached from contact with concrete.from contact with concrete.

•• Friction Loss Friction Loss –– The loss of force in a prestressing tendon The loss of force in a prestressing tendon resulting from friction created between the strands and resulting from friction created between the strands and sheathing due to curvature and wobble during stressing. sheathing due to curvature and wobble during stressing.

•• General zone General zone –– The region in which the concentrated The region in which the concentrated prestressing force spreads out to a more linear stress prestressing force spreads out to a more linear stress distribution over the cross section of the structural member distribution over the cross section of the structural member (Saint Venant Region). It includes the local zone. The (Saint Venant Region). It includes the local zone. The general zone extends from the anchorage along the axis of general zone extends from the anchorage along the axis of the member for a distance equal to the overall depth of the the member for a distance equal to the overall depth of the member. The height of the general zone equal to the overall member. The height of the general zone equal to the overall depth of the member. depth of the member.

•• Grout Grout –– A mixture of cementitious materials and water, with A mixture of cementitious materials and water, with or without mineral additives, admixtures or fine aggregate, or without mineral additives, admixtures or fine aggregate, proportion to produce a pumpable consistency without proportion to produce a pumpable consistency without segregation.segregation.

•• GUTS GUTS –– Guaranteed Ultimate Tensile Strength: This is the Guaranteed Ultimate Tensile Strength: This is the tensile strength of the material that can be assured by the tensile strength of the material that can be assured by the Manufacturer. GUTS should not be confused with Manufacturer. GUTS should not be confused with ““fpufpu”” the the specified ultimate tensile strength (AASHTO LRFD). (The specified ultimate tensile strength (AASHTO LRFD). (The term term ““GUTSGUTS”” has been replaced by two definitions, has been replaced by two definitions, ““MUTSMUTS””and and ““AUTSAUTS”” by the Postby the Post--Tensioning Institute.) Tensioning Institute.)

•• HDPE HDPE –– Acronym for High Density Polyethylene plastic. Acronym for High Density Polyethylene plastic. HDPE has a minimum density of 0.941 gram per cubic HDPE has a minimum density of 0.941 gram per cubic centimeter in postcentimeter in post--tensioning. tensioning.

•• Initial Concrete Strength Initial Concrete Strength –– The strength of the concrete The strength of the concrete necessary for the postnecessary for the post--tensioning operation.tensioning operation.

•• Initial Prestress Initial Prestress –– The force in the tendon immediately after The force in the tendon immediately after transferring the prestressing force to the concrete. This transferring the prestressing force to the concrete. This occurs after the wedges have been seated.occurs after the wedges have been seated.

•• Inlet Inlet –– The opening used to inject grout into the duct. The opening used to inject grout into the duct.

•• Intermediate Anchorage Intermediate Anchorage –– An anchorage located at any An anchorage located at any point along the tendon length, which can be used to stress a point along the tendon length, which can be used to stress a given length of tendon without the need to cut the tendon. given length of tendon without the need to cut the tendon. Normally used at concrete pour breaks. Normally used at concrete pour breaks.

•• Jack Calibration Jack Calibration –– A chart showing the related gauge A chart showing the related gauge pressure to actual force applied to a tendon. pressure to actual force applied to a tendon.

•• Jack Gripper Plates Jack Gripper Plates –– Steel plates designed to hold the jack Steel plates designed to hold the jack grippers in place in the jack.grippers in place in the jack.

•• Jack Grippers Jack Grippers –– Wedges used in the jack to hold the strand Wedges used in the jack to hold the strand during the stressing operation. during the stressing operation.

•• Jack Jack –– A mechanical device (normally hydraulic) used to A mechanical device (normally hydraulic) used to apply force to a prestressing tendon.apply force to a prestressing tendon.

•• Jacking Force Jacking Force –– The maximum temporary force exerted by The maximum temporary force exerted by the jack on the tendon. the jack on the tendon.

•• Live End Live End –– Stressing End.Stressing End.

•• Local Zone Local Zone –– The local anchorage zone is the volume of The local anchorage zone is the volume of concrete surrounding and immediately ahead of the concrete surrounding and immediately ahead of the anchorage device where the concrete compressive stresses anchorage device where the concrete compressive stresses exceed acceptable values for unconfined concrete (concrete exceed acceptable values for unconfined concrete (concrete without confinement reinforcement). The local zone is without confinement reinforcement). The local zone is defined as a rectangular prism of concrete surrounding the defined as a rectangular prism of concrete surrounding the bearing plate and any integral confinement reinforcement. bearing plate and any integral confinement reinforcement. The transverse dimension of the prism are equal to those of The transverse dimension of the prism are equal to those of the bearing plate, including any integral confinement, plus the bearing plate, including any integral confinement, plus the supplierthe supplier’’s specified minimum edge covers. s specified minimum edge covers. The length of the local zone extends over the distance from The length of the local zone extends over the distance from loaded concrete surface to the bottom of each bearing loaded concrete surface to the bottom of each bearing surface of the anchorage device plus maximum dimension surface of the anchorage device plus maximum dimension of the bearing surface.of the bearing surface.

•• Material Certification Material Certification –– Documentation from manufacturer Documentation from manufacturer that confirms that the quality of material supplied meets all that confirms that the quality of material supplied meets all project requirements.project requirements.

•• Modulus of Elasticity Modulus of Elasticity –– Ratio of stress to corresponding Ratio of stress to corresponding strain for tensile or compressive stresses below strain for tensile or compressive stresses below proportional limit of material.proportional limit of material.

•• Monostrand Monostrand –– One singleOne single--strand.strand.

•• Multistrand Multistrand –– More than one singleMore than one single--strand in a tendon. strand in a tendon.

•• MUTS MUTS –– Minimum Ultimate Tensile Strength: When Minimum Ultimate Tensile Strength: When measured as a force, for a single strand or bar breaking measured as a force, for a single strand or bar breaking outside of the anchorage or the multiple of those single outside of the anchorage or the multiple of those single strand or bar forces for multistrand or bar forces for multi--strand or bar tendons; strand or bar tendons; MUTS is the force equal to the nominal crossMUTS is the force equal to the nominal cross--sectional area sectional area of strand , or bar, times their nominal ultimate tensile of strand , or bar, times their nominal ultimate tensile stress.stress.

•• NonNon--Aggressive Environment Aggressive Environment –– All environments not All environments not specifically defined as aggressive, including enclosed specifically defined as aggressive, including enclosed buildings. buildings.

•• Outlet Outlet –– Opening to allow the escape of air, water, grout Opening to allow the escape of air, water, grout and bleed water from the duct during grouting operation. and bleed water from the duct during grouting operation.

•• P/T Coating P/T Coating –– material used to protect against corrosion material used to protect against corrosion and reduce friction between prestressing steel and and reduce friction between prestressing steel and sheathing. For unbonded application P/T coating should sheathing. For unbonded application P/T coating should meet or exceed the performance criteria outlined in the PTI meet or exceed the performance criteria outlined in the PTI Specifications for Unbonded Strand Tendons. Specifications for Unbonded Strand Tendons.

•• Pocket Former Pocket Former –– A temporary device used at the stressing A temporary device used at the stressing end to provide a cavity that can be grouted after the end to provide a cavity that can be grouted after the prestressing operation is complete.prestressing operation is complete.

•• PostPost--Tensioning System Tensioning System –– This is the proprietary system This is the proprietary system where the necessary hardware (anchorage, wedges, where the necessary hardware (anchorage, wedges, strands, bars, couplers, etc.) is supplied by a particular strands, bars, couplers, etc.) is supplied by a particular manufacturer or manufacturers of postmanufacturer or manufacturers of post--tensioning tensioning components and may also include ducts and local zone components and may also include ducts and local zone reinforcement. reinforcement.

•• PostPost--tensioning tensioning –– Method of prestressing in which steel is Method of prestressing in which steel is tensioned after concrete has hardened.tensioned after concrete has hardened.

•• Potable Water Potable Water –– Water defined by EPA (Environmental Water defined by EPA (Environmental Protection Agency) to meet drinking water standards.Protection Agency) to meet drinking water standards.

•• Prestressed Concrete Prestressed Concrete –– Structural concrete in which internal Structural concrete in which internal stresses are introduced to reduce potential tensile stresses stresses are introduced to reduce potential tensile stresses in concrete resulting from applied loads.in concrete resulting from applied loads.

•• Prestressing Steel Prestressing Steel –– HighHigh--Strength steel, most commonly Strength steel, most commonly 77--wire strand, used to impart prestress forces to wire strand, used to impart prestress forces to concrete.concrete.

•• The steel element of a postThe steel element of a post--tensioning tendon, which is tensioning tendon, which is elongated and anchored to provide the necessary elongated and anchored to provide the necessary permanent prestressing force.permanent prestressing force.

•• Pretensioning Pretensioning –– A method of prestressing in which the A method of prestressing in which the tendons are tensioned before the concrete has been tendons are tensioned before the concrete has been placed.placed.

•• Profile Profile –– The path of a tendon in concrete from end to The path of a tendon in concrete from end to end.end.

•• Pump Pump –– A hydraulic pump used to provide hydraulic A hydraulic pump used to provide hydraulic pressure to the stressing jack.pressure to the stressing jack.

•• Reference Point Reference Point –– The painted mark placed on a tendon The painted mark placed on a tendon tail used to measure the elongation of a tendon after tail used to measure the elongation of a tendon after stressing.stressing.

•• Seating Loss Seating Loss –– The relative movement of the wedges into The relative movement of the wedges into the anchor cavity during the transfer of the prestressing the anchor cavity during the transfer of the prestressing force to the anchorage resulting in some loss of force to the anchorage resulting in some loss of prestressing force.prestressing force.

•• Set Set –– The total movement of point on the strand just The total movement of point on the strand just behind the anchoring wedges during load transfer from behind the anchoring wedges during load transfer from the jack to the permanent anchorage. the jack to the permanent anchorage.

•• Set movement is the sum of slippage of wedges with Set movement is the sum of slippage of wedges with respect to the anchorage head and the elastic respect to the anchorage head and the elastic deformation of the anchor components.deformation of the anchor components.

•• Sheathing Sheathing –– A material encasing prestressing steel to A material encasing prestressing steel to prevent bonding of the prestressing steel with the prevent bonding of the prestressing steel with the surrounding concrete, provide corrosion protection, and surrounding concrete, provide corrosion protection, and contain postcontain post--tensiong coating.tensiong coating.

•• Slab Bolster Slab Bolster –– Continuous hardware used to support or Continuous hardware used to support or hold posthold post--tensioning tendons in place prior to and during tensioning tendons in place prior to and during concrete placement. concrete placement.

•• Special Bearing Plate Special Bearing Plate –– Any hardware that transfers Any hardware that transfers tendon anchor forces into the concrete but does not tendon anchor forces into the concrete but does not meet analytical design requirements. Covered by this meet analytical design requirements. Covered by this definition are devices having single or multiple plane definition are devices having single or multiple plane bearing surfaces, and devices combining bearing and bearing surfaces, and devices combining bearing and wedge plate in one piece. They normally require wedge plate in one piece. They normally require confinement reinforcement.confinement reinforcement.

•• Split Pocket Former Split Pocket Former –– A temporary twoA temporary two--piece device used piece device used at the intermediate end during casting of the concrete to at the intermediate end during casting of the concrete to provide an opening in the concrete, allowing the provide an opening in the concrete, allowing the stressing equipment access to the anchor cavity.stressing equipment access to the anchor cavity.

•• Stage Stressing Stage Stressing –– Sequential stressing of tendons in Sequential stressing of tendons in separate steps or stages in lieu of stressing all the separate steps or stages in lieu of stressing all the tendons during the same stressing operation.tendons during the same stressing operation.

•• Strand Slippage Strand Slippage –– Slippage or relative movement of Slippage or relative movement of strand with respect to wedges during force transfer. See strand with respect to wedges during force transfer. See seating loss.seating loss.

•• Strand Strand –– HighHigh--strength steel wires helically placed strength steel wires helically placed around a center wire. For bonded tendons typically a 7around a center wire. For bonded tendons typically a 7--wire strand.wire strand.

•• Stressing End Anchorage Stressing End Anchorage –– The anchorage at the end of a The anchorage at the end of a tendon where the prestressing jack is attached to the tendon where the prestressing jack is attached to the tendon during stressing operations.tendon during stressing operations.

•• Stressing Equipment Stressing Equipment –– Consists normally of a jack, pump, Consists normally of a jack, pump, hoses, and a pressure gauge.hoses, and a pressure gauge.

•• Stressing Force Stressing Force –– See jacking force.See jacking force.

•• Stressing Pocket Stressing Pocket –– The void created by the pocket former The void created by the pocket former between the stressing anchor and the edge of the concrete between the stressing anchor and the edge of the concrete to allow access for stressing equipment. After stressing, this to allow access for stressing equipment. After stressing, this void is filled in with an approved grout to provide protection void is filled in with an approved grout to provide protection for the tendon end.for the tendon end.

•• Stressing Record Stressing Record –– A permanent record of the actual tendon A permanent record of the actual tendon elongations after stressing produced by the Inspector.elongations after stressing produced by the Inspector.

•• Stressing End Stressing End –– The end of the tendon at which the The end of the tendon at which the prestressing force is applied. prestressing force is applied.

•• Temperature Tendons Temperature Tendons –– Tendons used to resist Tendons used to resist shrinkage and temperature stresses.shrinkage and temperature stresses.

•• Tendon Group Tendon Group –– More than one strand of Prestressed More than one strand of Prestressed steel tied together to form a tendon. steel tied together to form a tendon.

•• Tendon Support System Tendon Support System –– The required support bars, The required support bars, chairs, bolsters, and other accessories required to chairs, bolsters, and other accessories required to maintain the tendon profile. Tendon Tail maintain the tendon profile. Tendon Tail –– The excess The excess strand beyong the stressingstrand beyong the stressing--end anchor.end anchor.

•• Tendon Tendon –– In postIn post--tensioned applications, the tendon is a tensioned applications, the tendon is a complete assembly consisting of anchorages, prestressing complete assembly consisting of anchorages, prestressing steel, and sheathing with poststeel, and sheathing with post--tensioning coating for tensioning coating for unbonded applications or ducts with grout for bonded unbonded applications or ducts with grout for bonded applications. A single or group of prestressing elements applications. A single or group of prestressing elements and their anchorage assemblies, which impart a and their anchorage assemblies, which impart a compressive force to a structural member. Also included are compressive force to a structural member. Also included are ducts, grouting attachment and grout. The main stressing ducts, grouting attachment and grout. The main stressing element is usually a high strength steel member made up of element is usually a high strength steel member made up of a number of strands, wires or bars. a number of strands, wires or bars.

•• Thixotropic Thixotropic –– The property of a material that enables it to The property of a material that enables it to stiffen in a short time while at rest, but to acquire a lower stiffen in a short time while at rest, but to acquire a lower viscosity when mechanically agitated. The process is viscosity when mechanically agitated. The process is reversible.reversible.

•• Threshold Inspector Threshold Inspector –– This is a term employed by certain This is a term employed by certain states to define a qualified professional engineer who states to define a qualified professional engineer who inspects structures of certain defined parameters, and who inspects structures of certain defined parameters, and who also inspects the postalso inspects the post--tensioning tendons.tensioning tendons.

•• Ultimate Strength Ultimate Strength –– The tension force or stress that is The tension force or stress that is required to fail a steel element in tension.required to fail a steel element in tension.

•• Unbonded tendon Unbonded tendon –– Tendon in which prestressing steel is Tendon in which prestressing steel is prevented from bonding to concrete and is free to move prevented from bonding to concrete and is free to move relative to concrete. The prestressing force is permanently relative to concrete. The prestressing force is permanently transferred to concrete at the tendon ends by the transferred to concrete at the tendon ends by the anchorages only. anchorages only.

•• Water reducing Admixture Water reducing Admixture –– An admixture that either An admixture that either increases the slump of freshly mixed grout without increases the slump of freshly mixed grout without increasing the water content or maintains the slump with increasing the water content or maintains the slump with reduced amount of water due to factors other than air reduced amount of water due to factors other than air entrainment.entrainment.

•• Wedge Plate Wedge Plate –– The hardware which holds the wedges of a The hardware which holds the wedges of a multistrand tendon and transfers the tendon force to the multistrand tendon and transfers the tendon force to the bearing plate.bearing plate.

•• Wedges Wedges –– Pieces of tapered metal with serrations, Pieces of tapered metal with serrations, which bite into the prestressing steel (strand) during which bite into the prestressing steel (strand) during transfer of the prestressing force.transfer of the prestressing force.

•• Wedge Set Wedge Set –– See seating loss.See seating loss.

•• Wobble friction Wobble friction –– The friction caused by the The friction caused by the unintended deviation of the tendon.unintended deviation of the tendon.

•• Wire Wire –– A single, small diameter, high strength steel A single, small diameter, high strength steel wire, typically the basic component of strand. wire, typically the basic component of strand.

•• Yield Strength Yield Strength –– The stress at which a material The stress at which a material exhibits a specific limiting deviation from exhibits a specific limiting deviation from proportionality of stress to strain.proportionality of stress to strain.

Anchor assembly

Banded Tendons

Barrier Cable

Barrel Anchor

Bearing Plate

General zone

Local Zone

Stressing End Anchorage

Wedge Plate

Temperature Tendons

•• Materials used in PostMaterials used in Post--tensioningtensioning::

•• Prestressing Steel:Prestressing Steel:•• Strand Strand –– The most commonly used prestressing The most commonly used prestressing

material in not only North America is a 7material in not only North America is a 7--wire carbon wire carbon steel strand. Sevensteel strand. Seven--wire has a center wire enclosed wire has a center wire enclosed tightly by six helically wound outer wires. Strand tightly by six helically wound outer wires. Strand conforming to ASTM A416 Grade 270 has a minimum conforming to ASTM A416 Grade 270 has a minimum ultimate strength of 279 ksi (1860MPa). Grade 250 is ultimate strength of 279 ksi (1860MPa). Grade 250 is also available (with an ultimate strength of 250 ksi) also available (with an ultimate strength of 250 ksi) for use, for barrier cable applications. ASTM A416 also for use, for barrier cable applications. ASTM A416 also sets forth other requirements for strands, such as sets forth other requirements for strands, such as strand size, tolerances, workability, bending, fatigue, strand size, tolerances, workability, bending, fatigue, stress corrosion and hydrogen embrittlement, and stress corrosion and hydrogen embrittlement, and bond.bond.

•• For each grade, there are two types of steel: low For each grade, there are two types of steel: low relaxation and stress relieved (normal relaxation). relaxation and stress relieved (normal relaxation).

•• Almost all of the prestressing strand supplied today is low Almost all of the prestressing strand supplied today is low relaxation steel. Up until 1970relaxation steel. Up until 1970’’s, stresss, stress--relieved strands were relieved strands were common; however they are rarely used today. Relaxation is common; however they are rarely used today. Relaxation is defined as the reduction in force over time in a highly stresseddefined as the reduction in force over time in a highly stressedtendon at a given elongation. Low relaxation strand must conformtendon at a given elongation. Low relaxation strand must conformto the Supplement I requirements of ASTM A416, which limit to the Supplement I requirements of ASTM A416, which limit relaxation loss after 1000 hours of testing to 2.5% at 70% of relaxation loss after 1000 hours of testing to 2.5% at 70% of minimum ultimate tensile strength (MUTS) or 3.5% at 80% of minimum ultimate tensile strength (MUTS) or 3.5% at 80% of MUTS.MUTS.

•• Stress relieved strand, in contrast, is not subject to any relaxStress relieved strand, in contrast, is not subject to any relaxation ation loss limit under ASTM A416. Relaxation losses for such tendons loss limit under ASTM A416. Relaxation losses for such tendons typically run at 4.5%, 8%, and 12% of the initial stress in the typically run at 4.5%, 8%, and 12% of the initial stress in the free free tendon (i.e., strand is not associated with a concrete element) tendon (i.e., strand is not associated with a concrete element) for for an initial stress equal to 0.6, 0.7, and 0.8 of MUTS, respectivean initial stress equal to 0.6, 0.7, and 0.8 of MUTS, respectively. ly.

•• Minimizing relaxation loss reduces overall prestress losses, andMinimizing relaxation loss reduces overall prestress losses, and as as a result enables the designer to take advantage of a higher finaa result enables the designer to take advantage of a higher final l prestressing force after all other losses have occurred.prestressing force after all other losses have occurred.

•• If a structure is exposed to an aggressive If a structure is exposed to an aggressive environment, the designer may elect to specify a environment, the designer may elect to specify a corrosion protective coating for the strand such corrosion protective coating for the strand such as epoxy coating or hot dip galvanizing. Epoxyas epoxy coating or hot dip galvanizing. Epoxy--coated strands shall conform to ASTM A882, coated strands shall conform to ASTM A882, Standards Specification for EpoxyStandards Specification for Epoxy--Coated SevenCoated Seven--Wire Strand. Galvanized strand shall conform to Wire Strand. Galvanized strand shall conform to ASTM A475ASTM A475--98, Standard Specification for Zinc98, Standard Specification for Zinc--Coated Steel Wire strand. Neither epoxyCoated Steel Wire strand. Neither epoxy--coated coated or galvanized strand are widely used in general or galvanized strand are widely used in general postpost--tensioning applications in the United States. tensioning applications in the United States. The designer should evaluate the local availability The designer should evaluate the local availability of these materials before specifying.of these materials before specifying.

•• BarsBars –– Prestressing bars are highPrestressing bars are high--strength steel bars that strength steel bars that are coldare cold--stressed to not more than 80% MUTS and then stressed to not more than 80% MUTS and then stress relieved to produce the desired mechanical stress relieved to produce the desired mechanical properties. They have a minimum ultimate tensile strength properties. They have a minimum ultimate tensile strength of 150 ksi (1036 MPa). Prestressing bars are rolled from of 150 ksi (1036 MPa). Prestressing bars are rolled from properly heat ingot properly heat ingot –– or strandor strand--cast steel. They can be cast steel. They can be manufactured as a smooth round (Type I) or with manufactured as a smooth round (Type I) or with deformations similar to a common reinforcing bar (Type II). deformations similar to a common reinforcing bar (Type II). Deformed prestressing bars have deformations that are Deformed prestressing bars have deformations that are arranged in a thread pattern permitting the use of screwarranged in a thread pattern permitting the use of screw--on couplers and nuts. Plain round bars must be threaded on couplers and nuts. Plain round bars must be threaded before they can be used with nut/bearing plate anchoring before they can be used with nut/bearing plate anchoring system. Bars used in postsystem. Bars used in post--tensioned structures Bars for tensioned structures Bars for Prestressed Concrete, including must meet the Prestressed Concrete, including must meet the requirements of ASTM A722, Specifications for Unbonded requirements of ASTM A722, Specifications for Unbonded HighHigh--Strength Supplementary Requirements S1 and S2. Strength Supplementary Requirements S1 and S2. These requirements include chemical composition, These requirements include chemical composition, dimension, and tensile properties.dimension, and tensile properties.

•• WiresWires –– Wires used for prestressing generally Wires used for prestressing generally conform to ASTM A421, Uncoated Stressconform to ASTM A421, Uncoated Stress--Relieved Relieved Wire for Prestressed Concrete. Rods are used to Wire for Prestressed Concrete. Rods are used to manufacture wires by open hearth or elastic manufacture wires by open hearth or elastic furnace process. Heat treatment is then used to furnace process. Heat treatment is then used to stressed relieve the wires so that the desired stressed relieve the wires so that the desired mechanical properties are achieved. Wires are mechanical properties are achieved. Wires are manufactures with various crossmanufactures with various cross--sectional shapes sectional shapes and surface conditions: round versus oval, and surface conditions: round versus oval, smooth versus indented, ribbed or crimped. ASTM smooth versus indented, ribbed or crimped. ASTM A421 also has a supplement for lowA421 also has a supplement for low--relaxation relaxation wires. Wires are rarely used for postwires. Wires are rarely used for post--tensioning tensioning applications in the United States; however, they applications in the United States; however, they are still used to a greater degree in other parts of are still used to a greater degree in other parts of the world.the world.

Types of Prestressing tendons: Typical shapes and commonly available

diameters.

Properties of Prestressing SteelProperties of Prestressing Steel

•• Mechanical Properties: Certain mechanical Mechanical Properties: Certain mechanical properties of prestressing steel must be known to properties of prestressing steel must be known to properly design a postproperly design a post--tensioned structure. ASTM tensioned structure. ASTM specifications identify requirements for: MUTS specifications identify requirements for: MUTS fpu; yield limit fpy, modulus of elasticity Ep; and fpu; yield limit fpy, modulus of elasticity Ep; and the total elongation under load. In most cases, the total elongation under load. In most cases, the design strength of unbonded tendon fps will the design strength of unbonded tendon fps will substantially less than the yield limit fpy. For substantially less than the yield limit fpy. For bonded construction, the designstrength will be bonded construction, the designstrength will be greater than or equal to fpy. Typically mechanical greater than or equal to fpy. Typically mechanical properties for lowproperties for low--relaxation strands, wires, and relaxation strands, wires, and bars are shown in the table below.bars are shown in the table below.

Prestressing Steel

fpu

ksi (MPa)

fpy

ksi (MPa)

Ep

ksi (MPa)

% Elongation [Gauge Length] Relaxation

Low-Relaxation 7-Wire strand

Grade 270 per ASTM A416/416M

270 (1860) 0.90 fpu 28,500 (196,50

0)

3.5 [24 in (610

mm)]

[2.5% @ 70% MUTS] or

[3.5% @ 80% MUTS]

Stress-Relieved Wire

per ASTM A421/421M

235 - 250 (1620 -1725)

0.85 fpu 29,000 (200,00

0)

4 [10 in (250

mm)]

Low-Relaxation Wire

per ASTM A421/421M

235 - 250 (1620 -1725)

0.90 fpu 29,000 (200,00

0)

4 [10 in (250

mm)]

[2.5% @ 70% MUTS] or

[3.5% @ 80% MUTS]

Prestressed Bars Grade 150 per ASTM A722

150 (1035)

Type I: 0.85 fpu Type II:

0.80 fpu

29,700 (205,00

0)

4 [20 bar dia.] 7 [10 bar dia.]

•• The typical values shown in the table are often The typical values shown in the table are often used for design purposes; however, the actual used for design purposes; however, the actual material properties for the prestressing steel material properties for the prestressing steel supplied to the project may vary and may exceed supplied to the project may vary and may exceed specification minimums. specification minimums.

•• Knowing the actual properties can be important Knowing the actual properties can be important during inspection and future rehabilitation. For during inspection and future rehabilitation. For example, when evaluating outexample, when evaluating out--ofof--tolerance tolerance elongations during stressing, the design engineer elongations during stressing, the design engineer should compare the actual values (e.g. the should compare the actual values (e.g. the modulus of elasticity) as given on the suppliermodulus of elasticity) as given on the supplier--provided mill certificates and the value assumed provided mill certificates and the value assumed in design. In many instances, the difference may in design. In many instances, the difference may explain the observed elongation.explain the observed elongation.

•• Ductility Ductility –– Ductility is an essential property Ductility is an essential property of a prestressing material. Standard of a prestressing material. Standard specifications prescribe ductility specifications prescribe ductility requirements, which are usually expressed requirements, which are usually expressed as a minimum percent elongation in the as a minimum percent elongation in the gauge length under total load. For ASTM gauge length under total load. For ASTM A416 prestressing strand, the minimum A416 prestressing strand, the minimum elongation is specified as 3.5% using gauge elongation is specified as 3.5% using gauge length of not less than 24 inches (610mm). length of not less than 24 inches (610mm). For ASTM A722 prestressing bars, the For ASTM A722 prestressing bars, the minimum percent elongation after rapture is minimum percent elongation after rapture is 4% and 7% for type I and type II 4% and 7% for type I and type II prestressing bars, respectively.prestressing bars, respectively.

•• Static and Fatigue Testing Static and Fatigue Testing –– Tendons in Tendons in prestressed concrete structures and ground prestressed concrete structures and ground anchors normally do not experience stress anchors normally do not experience stress cycling significant enough to cause fatigue cycling significant enough to cause fatigue problems. For those applications where problems. For those applications where fatigue is a concern, such as postfatigue is a concern, such as post--tensioned tensioned bridge and cablebridge and cable--stayed bridges, fatigue stayed bridges, fatigue resistance can be increase by proper resistance can be increase by proper material selection and anchorage design. material selection and anchorage design. Tendon fatigue will depend on the type of Tendon fatigue will depend on the type of structure and whether the tendon is bonded structure and whether the tendon is bonded or unbonded. The strandor unbonded. The strand--wedge connection wedge connection is the most sensitive part of a tendon in is the most sensitive part of a tendon in regards to fatigue resistance.regards to fatigue resistance.

•• Where fatigue is a possible concern, the design Where fatigue is a possible concern, the design engineer should confirm that the intended postengineer should confirm that the intended post--tensioning system has been dramatically tested tensioning system has been dramatically tested and qualified in accordance with the PTI and qualified in accordance with the PTI Acceptance Standards for PostAcceptance Standards for Post--Tensioning Tensioning Systems for bonded tendons and in accordance Systems for bonded tendons and in accordance with the postwith the post--tensioning project specifications for tensioning project specifications for unbonded tendons. For unbonded systems on unbonded tendons. For unbonded systems on bridges, AASHTO requires that a representative bridges, AASHTO requires that a representative anchorage and coupler specimen, as well as anchorage and coupler specimen, as well as tendon, be dynamically tested without failure, tendon, be dynamically tested without failure, 500,000 cycles from 60 to 66 percent of MUTS, 500,000 cycles from 60 to 66 percent of MUTS, and 50 cycles from 40 to 80 percent MUTS.and 50 cycles from 40 to 80 percent MUTS.

Application of PostApplication of Post--tensioningtensioning•• Today, postToday, post--tensioning is used for a wide range of tensioning is used for a wide range of

applications including:applications including:

Prepared by:Prepared by:

Danny M. Francisco. C.E., G.E.Danny M. Francisco. C.E., G.E.Tel. 6770359 (Office)Tel. 6770359 (Office)Mobile: 0557124793Mobile: 0557124793Email: [email protected]: [email protected]