1. EAS 453 Pre-stressed Concrete Design Brief History, Basic Principles, Materials & Equipments of Pre-stressed Concrete 1Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM

2. A BRIEF HISTORY …..Design of pre-stressed concrete is usually left to specialist ; the unwary will either make mistakes or spend inordinate time trying to extract solutions from the various equations….Chris Bergoyne  analysis and design of pre-stressed concrete is a specialized field  concentrate on the basic principles of pre-stressing  fundamental aim of pre-stressed concrete is to limit tensile stresses and hence flexural cracking, in the concrete under working conditions and thus, the design is therefore based initially on the requirements under serviceability limit state (contradict to r.c structures)  subsequently considered are ultimate limit state criteria for bending and shear  in addition, deflections must be checked  stresses at service and at transfer  transfer stage – pre-stressed force is first applied to the immature concrete and no external load is applied, only self-weight 2Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM

3. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM3  In 1886, P.H. Jackson, an engineer of San Francisco obtained patents for tightening steel tie rods in artificial stones and concrete arches to serve as floor slabs  Around 1888, C.E.W. Doehring of Germany independently secured a patent for concrete reinforced with metal that had tensile stress applied to it before the slab was loaded.  Ever since the development of reinforced concrete by Hennebique at the end of 19 th century, it was recognized that steel and concrete could be more effectively combined if the steel was pre-tensioned, putting the concrete into compression  Cracking could be reduced, if not prevented altogether, which will increase stiffness and improve durability  In 1908, C.R. Steiner of U.S.A suggested the possibility of retightening the reinforcing rods after some shrinkage and creep of concrete had taken place

4. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM 4  In 1925, R.E. Drill of Nebraska tried high strength steel bars coated to prevent bond with concrete  Early attempts all failed because the initial pre-stress soon vanished leaving the structure to behave as it was reinforced  It was Freyssinet’s (Eugene) observations of the sagging of the shallow archers on 3 bridges that he had just completed in 1927 over the River Allier near Vichy which led directly to pre-stressed concrete  It had been assumed that concrete had a Young’s modulus which remain fixed but Freyssinet recognized that the deferred strains due to creep explained why the pre-stress had been lost in the early trials.  Freyssinet also correctly reasoned that high tensile steel had to be used, so that some pre-stress would remain after the creep had occurred

5. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM5  Also, high quality concrete should be used since this minimized the total amount of creep  In 1939, Freyssinet developed conical wedges for end anchorages (pre- stressing was not made possible before because of economical methods of tensioning and of end anchorage) and designed double acting jacks  In 1940, Professor Gustave Magnel of Belgium developed the Magnel system.  At about the same time work was underway on creep at BRE (British Research Establishment) in England. It was debatable which man should be given for the discovery of creep but Freyssinet clearly gets the credit for successfully using the knowledge to pre-stress concrete.

6. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM6  There are still problems associated with understanding how pre-stress concrete works, partly because there are more than one way of thinking about it. These different philosophies are to some extent contradictory, and certainly confusing to young engineers. The three philosophies are PERMISSIBLE STRESS DESIGN PHILOSOPHY, ULTIMATE STRENGTH PHILOSOPHY, LOAD BALANCING PHILOSOPHY.  PERMISSIBLE STRESS DESIGN PHILOSOPHY sees pre-stress as a way of avoiding cracking by eliminating tensile stresses ; the objective is for sufficient compression to remain after creep losses. This philosophy is derived directly from Freyssinet’s logic and primarily a working stress concept.

7. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM7  ULTIMATE STRENGTH PHILOSOPHY sees pre-stressing as a way of utilizing high tensile steel as reinforcement.  high strength steel have high elastic strain capacity  cannot be utilized when used as a reinforcement  if the steel is pre-tensioned, much of that strain capacity is taken out before bonding the steel to the concrete  structures designed this way are normally to be in compression everywhere under permanent load but allowed to crack under high live load  the idea derives directly from the work of Dischinger (1936) and Finsterwalder (1939)  primarily an ultimate load concept  extended to the idea of partial pre-stressing

8. A BRIEF HISTORY Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM8 LOAD BALANCING PHILOSOPHY introduced by T.Y. Lin in 1963 (T’ung Yen Lin) uses pre-stressing to counter the effect of the permanent loads. The sag of the cables causes an upward force on the beam, which counteracts the load on the beam …these 3 PHILOSOPHIES all have their champions, and heated debates take place between them as to which it is almost fundamental……  In 1945, pre-stress concrete began to acquire importance, perhaps due to the shortage of steel in Europe during the War. A pre-stress member, when compared with an equivalent reinforced concrete member, requires less concrete and about 1/5 to 1/3 of the amount of steel.  Although France and Belgium led the development of pre-stress concrete, England, Germany, Switzerland, Holland Russia and Italy quickly followed.

9. BASIC PRINCIPLES Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM9 …Pre-stress concrete : concrete in which there have been introduced internal stresses of such magnitude and distribution that the stresses resulting from given external loadings are counteracted to a desired degree…ACI Committee of Pre- stress Concrete 1. Principles  Pre-stressed can most easily defined as pre-compressed concrete. This means that a compressive stress (through tensioning a ‘reinforcement – wire strand for example) is put into a concrete member before it begins its working life  The compressive stress is positioned to be in areas where tensile stresses will develop under working load  Why we are concerned with area with tensile stresses? Simple reason – concrete is week in tension

10. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM10 Consider a beam of plain concrete carrying a load As the load increases, the beam deflects slightly and then fails abruptly. Under load, the stresses in beam will be compressive in the top fibres but tensile in the bottom fibres. Top fibre (compression) Bottom fibre (tension)

11. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM11  We can aspect the beam to crack at the bottom and break, even with relatively small load, because of concrete’s low tensile strength. There are 2 ways of countering this low tensile strength:  using reinforcement – reinforced concrete where reinforcement in the form of steel bars is placed where tensile stresses will develop under load  the reinforcement absorbs all the tension (assumption) and by limiting the stress in the reinforcement, the cracking of the concrete is kept within acceptable limits  pre-stressing – the compressive stresses introduced will resist these tensile stresses  the concrete now behaves as if it had a high tensile strength of its own and provided the tensile stresses do not exceed the pre-compression stresses, cracking cannot occur at the bottom of the beam

12. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM12 An everyday example of the fundamental principle of pre-stressing is used by a person moving several bricks. As an alternative to stacking them vertically, one on top of the other and supporting them underneath, they can be lifted and moved in a horizontal stack by exerting pressure with a hand at each hand The tensile strength of the row of bricks is zero, but as long as sufficient pressure is applied, the whole row can be lifted together. Bricks arrange horizontally PP

13. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM13  If the pressure is applied at near the top, it will be found that the unit is not very stable and will tend to open at the bottom (this can be further explain in the topic concerning ‘deflection’). With the pressure applied at mid height, it will be possible to stack bricks on top, so the unit is also carrying a load.  The more load we put on, the more pressure we need to exert at each end. P P Neutral Axis

14. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM14  Elimination or significant reduction or changing a tensile zone to a compressive zone will definitely control cracking. With cracking reduced or eliminated, a pre-stressed section is considerably stiffer than the equivalent reinforced section.  Pre-stressing may also impose internal forces which are of opposite sign to the external loads (hence totally opposite the nature of deflection due external load) and may therefore significantly reduce or eliminate deflections  As for now, we can conclude, from basic principles that pre-stress structures :- i. can sustain more loads although lighter ii. stiffer due to less (or no) cracks iii. significantly, lesser deflection iv. close pores in concrete

15. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM 15  With service load behavior improved, the use of high strength steel and high strength concrete becomes both economical and structurally economical. However, only steel which can be tensioned with large initial elastic strain (elongated significantly and return to its original position without yielding) is suitable for pre-stressing concrete hence it is a necessity. δ (downward) W kN/m P δ (upward)

16. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM16 2. Method of pre-stressing  Pre-stress is usually imparted to a concrete member by highly tensioned steel (wire, strand or bar) reacting on the concrete. The high strength pre-stressing steel is most often tensioned by hydraulic jacks  The tensioning operation may occur before or after the concrete is cast, accordingly, pre-stressed members are classified either pre-tensioned or post-tensioned.

17. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM17 a. Pre-tensioned concrete  As the word implies, first the pre-stressing reinforcements are initially tensioned between fixed abutments and anchored.  Second, with the formwork in place, the concrete is cast around the highly stressed steel and cured  Third, when the concrete has reached its required strength, the wires are cut or otherwise released from the abutments. As the highly stressed steel attempts to contract, the concrete is compressed.  Pre-stress is imparted via bond between the steel and the concrete  Pre-tensioning is usually carried out in factory where permanent stressing beds have already been constructed.  The most effective method is the long-line production – a number of similar units are produced at the same time Stage 1 Stage 2 Stage 3

18. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM18  Steel – usually wire for small units and strand for larger units are tensioned between anchor plates (thick with holes through which the wires or strands can be passed and anchored) at opposite ends and supported by large steel sections embedded in a block of concrete.  In a very long stressing beds, sometimes intermediate blocks with preformed pockets with temporary steel joist were placed to give a shorter stressing bed if necessary.  Fixed abutment – the anchor plate bears directly onto the steel joist  Jacking end – where jacking begins  Upon attaining required force, the wire is then anchored and the jack released  Operation repeated for remaining wires  To achieve full compaction, vibrators are used internal or external or both.  Curing is necessary – sometimes by steam curing  When concrete attain sufficient strength (at transfer), the struts are replaced by jacks which can be slowly released  Cut the wire safely at the ends of the units

19. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM 19  b. Post-tensioned concrete  The use of straight tendons is not efficient when it comes to larger units. Effectiveness of the pre-stressing force is a function of the force multiplied by the eccentricity.  The maximum effective pre-stress is required at positions where maximum bending occurs and conversely minimum effective pre-stress where the minimum bending occurs  With a constant pre-stressing force, this can be achieved by varying the eccentricity of the force so that, at any section along a beam, the pre- stressing effect will counteract the loading effect  If the tendons are within the concrete section, they will be positioned in a curved profile (some how like the bending moment diagram) and this can be done by fixing preformed ‘duct’ (sesalur) either flat or circular to the required profile  For the duct to be in positioned (and to avoid floating when pouring concrete), it is usually fixed to the reinforcement cage

20. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM20  With the mould assembled, the concrete is placed while the steel tendons are still unstressed during the concrete pour.

21. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM21  It is then essential that the unstressed units are properly cured, to avoid shrinkage cracking during  When the concrete has achieved sufficient strength, the steel tendons are tensioned by anchoring one end of the tendon and jacking against the face of the anchorage at the other end or by jacking both ends simultaneously  Jacking by using single-strand jack or multiple-strand jack

22. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM22  In post-tensioning, it is important to verify the extension in the tendon as well as the load as the movement in the duct cannot be seen  Checked for irregularities in the rate of extension for a given rate of loading that may be due to tendon becomes ‘locked’ some where along the duct (making the amount of extension decrease)  When the design has been reached, the extension is recorded and has reached the calculated value, the tendon can be anchored off  Load should never be increased beyond the specified value, particularly in an attempt to achieve the required extension  With all the tendons stressed and anchored off, the ducts are normally filled with a colloidal cement grout under pressure. The hardened grout is mainly to prevent corrosion of the tendons.  Grout – also provides a bond between the tendons and concrete

23. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM23  Different stressing systems use different equipment  At the end of post-tensioned units, the tendons apply a large force (termed bursting force – in later chapter by PM Dr Ir Md Azlin) through an anchorage of relatively small area. The effect is like driving a wedge into a block of wood, unless this bursting force can be contained until it has dispersed over the section, the end of the unit will break up

24. Materials & Equipment Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM24  The behavior of a PC member throughout the full range of loading depends on the properties and behavior of the constituents materials.  In order to satisfy the design objectives of adequate structural strength, the ultimate strengths of both concrete and steel need to be known.  Factors affecting material strength and the non-linear behavior of each material in the overload range must also be considered  The concrete and the pre-stressing cables form 2 systems which are externally connected, in theory. However, we can study them as separate properties

25. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM25  a. Concrete  A concrete mix for pre-stressed work should be workable when it is fresh and strong when it has hardened.  As we know, workability of fresh concrete is increased by increase water content and good grading of aggregates.  However, the strength of hardened concrete, which increase in age, is increased by a reduced water/cement ratio  Strength of concrete – important and very relevant to PC as the strength of the concrete in the member when the pre-stress is applied is a very important factor and generally referred to as the ‘initial’ or ‘transfer’ condition.  It takes about 0.25 of water cement ratio to completely hydrate the cement but larger ratio is needed for workability  In PC, the water/cement ratio is about 0.4 (desirable to use as little water as possible because un-use water in the hydration process cause voids and increase permeability)  The use of chemical admixtures and superplasticizers to improve one or more properties in common nowdays.  However, any admixture must never be used is calcium chloride and codes of practice prohibit its use

26. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM26  b. Strength of concrete  In structural design, the quality of concrete is usually controlled by the specification of a minimum concrete compressive strength at 28 days (f cu )  In practice, the concrete used in PC construction is usually of better quality and higher strength compared to ordinary RC  Values often 30-40 MPa but in some countries, concrete strength of more than 100 MPa has successfully being used  Why need high strength concrete in PC ?  forces imposed are relatively large and the use of HSC keeps section dimension to a minimum  Advantage over the anchorage zone of post-tensioned members where bearing stress are high  In pre-tensioned members, HSC having higher bond strength facilitates the transfer of pre-stress  Higher compressive strength means higher tensile strength thus delay/prevent the onset of cracking in a member  Stiffer, higher elastic modulus, lower elastic deformation (one type of loss of pre-stress)  Lesser creep effect hence smaller pre-stress loss and smaller long term deformations  Creep – defined as the ‘inelastic deformation due to the sustained (compressive) stress’, concrete reduced in length hence reduce the stress in steel

27. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM27  c. Steel used for pre-stressing  The shortening of concrete due creep and shrinkage caused shortening in pre-stressing steel.  Can be significant – result in loss of pre-stress of about 150 – 300 MPa  Early attempts to pre-stress concrete of low strength steel failed because the entire pre-stressing force was rapidly lost due to time- dependent deformations of the poor quality concrete used at that time  The steel used in pre-stressing work is usually in the form of cold-drawn, stress relieved high tensile round wires or stress relieved strands or high strength alloy steel bars  Twisted wires – termed as strand (lembar)

28. Useful terms: Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM28  Cable : a group of tendon  Tendon : a stretched element used in concrete member to impart pre- stress to the concrete. May consist of individual hard-drawn wires, strands or bars  Wire : reinforcement of solid section complying with the requirements of BS 2691 superseded by BS 5896 : Part 2 and generally supplied in coil form. Diameter varies from 2 mm – 8 mm. In general use, the smallest diameter should be 4 mm  Bars : reinforcement of solid section complying with the requirements of BS 4486 and generally only supplied in straight lengths. Diameter 12mm – 40mm, plain or deformed  Strands : a group of wires spun in helical form around a common longitudinal axis complying with the requirements of Euronorm 138-79 or BS 5896 : Part 3 (Super Grade). Normally strand of ‘low relaxation’ is used (smaller loss of initial stress). In Malaysia, normally 2 sizes are used - 13 mm (0.5 inch) or 15 mm (0.6 inch) diameter

29. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM29  d. Strands  Two basic types of pre-stressing strand are available having 7 or 19 wires  Choice depends mainly on the degree of flexibility and strength required  7-wire strand more popular (easier to manufacture)  Nominal diameter 6.4 – 18 mm (7-wire) and 18 -32 mm (19-wire)  To form a 7-wire strand, 6 wires are helically wound to form a single layer about a straight inner core wire  After formation, 7-wire is subjected to heat treatment  To reduce the percentage of voids, the strands are drawn through a machine to compress it. This ‘compacted’ strand has low relaxation criteria

30. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM30  Construction of 19-wire is more complicated, comprising of  an inner layer of 9 helical wires laid on a straight core wire with outer layer of nine thicker wires OR  7-wire strand with an outer layer of 12 wires of 2 different diameters  Compaction of 19-wire strand is not practical  Usage of 19-wires has decreased  Example Seale 19 wire and Warrington 19 wire

31. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM31  e. Fiberglass Tendons  Manufactured by drawing fluid glass into fine filaments.  Has been under investigation for some years but has not yet commercially applied  Extensive research was conducted by U.S. Army Corps of Engineers both as reinforcement (fiberglass rods) and pre-stressed elements (fiberglass tendons)  Possess certain superior qualities such as having typical ultimate tensile strength of 6500 N/mm 2 as values as high as 35,000 N/mm 2 for individual silica fibers of 0.003 mm. (take note that strength for silica fibers varies inversely as the diameter of the fiber)  Fiberglass laminated with epoxy resins have appeared to be superior  Another advantage – low modulus of elasticity ranges from 41,000 N/mm 2 to 69,000 N/mm 2.  High stress and low modulus of elasticity – leads to very small loss of pre-stress  Other advantage – resistance to acids and alkalies and able to withstand high temperature

32. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM32  f. Auxillary Materials – Grouting (Post-tensioned)  Used as bonding agent between tendon to the concrete after tensioning  Cement grout is injected – also serves to protect the steel against corrosion  Entry for the grout into the cableway is provided by means of holes in the anchorage head or pipes buried in the concrete members  The injection can be applied at one end of the member until it is forced out of the other end  For longer members, it can be applied at both ends until forced out of a center vent  Normally use OPC or high-early-strength cement with water + commercial additives to ensure sound grouting  Sometimes (in US), fly ash and pozzolans are occasionally added as filler materials.  Grouting under pressure is desirable, grouting pressure generally ranges from 550 to 700 kPa, normally maximum pressure specified is 1700 kPa.  After the grout has discharged from the far end, that end is plugged and pressure is again applied at the injecting end to compact the grout  PCI specified minimum temperature for grouting 1.7 C.

33. Equipment Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM33  a)Pre-tensioning  The most important item of equipment consists of the temporary grip which hold the wires or strand during, and after tensioning. Typical grip consist of a barrel and wedge  Method of tensioning may vary  Wedge is generally in 2 or 3 pieces with a collar and wire clip to keep them in the same relative position ie. concentric position  The wedge has grooves on the surface in contact with the tendon. May be used many times but should be carefully examined each time before use

34. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM34  At the fixed anchorage, the grip are forced onto unstressed tendon close to the anchor plate  While at the stressing end the grip is only placed on the unstressed tendon against the anchor plate. The jack is then positioned on the tendon and stressing begin.  When the required load and extension have been reached, the wedge is forced onto the tendon, the stressing jack is released  The tendon tries to pull through the wedge, it forces the wedge onto itself and firmly grip

35. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM35  b)Post-tensioning  The equipment required for post-tensioning depends upon which system is being used.  If classified by the method adopted to anchor the tendons – 2 (either threaded nut such as BBRV, Dividag and Macalloy OR wedge such as for VSL, CCL, PSC  If classified under ‘Tendon System’ – based on development of 5 original systems :   Coyne System – usually used for anchorage of retaining walls and dams in bed rock   Freyssinet System – essential feature is the conical shape of the anchorage   Magnel System – tensioning wires in pairs   Roebling System – stranded cables   Bar System – ends of the bar have screw treads  Note ** - The Magnel and Roebling systems are only of historical importance 

36. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM36 OrganizationSystemTendon BBRV Pre-stressingBBRVWire (M) CCL System LtdCabco Multiforce Force (S) (M) (S) Dividag Stressed Concrete LtdDywidag Single Bar Dywidag Multiple Bar Bar (S) Bar (M) Losinger System LtdVSL(M) Maccaloy PrestressingMacalloyBar (S) PSC EquipmentMonoGroup MonoStrand (M) (S) M = multiple stressing S = single stressing

37. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM37  i. BBR V and BBR CONA  Designed by 4 Switzerland engineers – Birkenmaier, Brandestini, Ros & Voight in 1949  Classed as a threaded nut system consist of a lock nut which bears against a steel bearing plate and transfer the compression into the concrete  Basic element consist of steel cylinder with a number of machined axial holes to accommodate the separate wires  Anchoring of each wire is by means of a preformed button head with 2 typical examples on the types of anchorage as shown below  Basic element is treaded internally to receive a draw bar for jacking and externally to receive the locking nut (for smaller version of anchorage)  The button heads are formed at both ends of the wire after the wire has been passed through the anchor head  Normally 7 mm wires are used with number of wires varies from 8 – 163 giving jacking force of 340 kN to 7900 kN

38. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM38  ii.Dividag  This system uses an alloy steel bar as the tendon.  2 types of bar – smooth or threaded  The force is transmitted to the end bearing plate by means of a nut which screws onto the end s of the bar  Figure below shows the bell type and the solid plate type of anchorages  Smooth bar – available diameters 12.2, 26, 32 & 36 mm and always stressed singly  Threaded bar – available diameters 15,16, 26.5, 32 and 36 mm, usually stressed singly although the 16 mm bar for example can be stressed in the multiples of 3-9.  Jacking force ; 130 – 960 kN (single) and 630 – 2020 kN (multiple)  During the stressing operation, as the bar is being stretched by the jack, the anchor nut is continuously screwed down and then transfer the load to the anchorage once the jack is released

39. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM39  iii.Macalloy  Only use smooth bar system with threads rolled on the ends of the bars.  Force is transferred to the concrete by means of the threaded nut bearing against steel washers onto a solid steel distribution plate  Bars of 20, 25, 32 & 40 mm are available  Always stressed singly but can arranged in cables of 1,2,3 or 4 giving a stressing forces ranging from 230 kN to 3500 kN  Figure below shows solid steel distribution plate, ribbed cast iron sleeve and a tapped steel plate (at a dead end anchorage)  With all threaded-nut systems, the load can be applied at intervals to suit construction or design requirement  Advantage – the loss is completely positive hence there is no loss of pre-stress on transfer of the load from the jack to the nut.

40. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM40  ivPSC  using Freyssinet 12-wire system  develop single and multiple stressing, all systems use wedges  stressing anchorage consists of an iron guide, forged steel anchor block and 3-piece wedges to anchor the strand  Strands are arranged in a circular pattern and the holes in the anchor block are not only tapered but drilled at an angle in relation to the tendon pattern  2 types of dead end – looped anchorage (strand passes around a metal saddle) or swage & capped anchorage (ends of the strand have swaged grips) – quite similar to VSL system  Single jack – Titan jacks  Multiple – ‘S’, ‘T’ (small and intermediate forces) and ‘K’ (large forces) range jack  ‘K’ range – 1000 kN to 14,000 kN

41. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM41  v.SCD  Stressed Concrete Design Limited have 2 basic systems, circular and rectangular  Circular system – strands are arranged in a circular pattern and anchored by means of a taper hole barrel with 3-piece wedge  Individual stressing (Monogrip) – Multiple (Multigrip)  7 – strand diameter (12.7, 15.2 & 18 mm) – Dyform  19 – strand diameter (15.2 mm & 18 mm) – Dyform  Rectangular system – development from Magnel – Blaton system, the modern system is a series of blocks with 3 tapered circular holes  Stressed individually  Wide range of forces available from 1200 (single 13 mm strand) up to 4000 kN (27 nos – 13 mm strand

42. Dr. NORAZURA MUHAMAD BUNNORI (PhD), USM42  vi.VSL   Use VSL multiple strand stressing in circular pattern  All strands are stressed simultaneously and are anchored by means of wedges forced into the tapered holes  Transmit force to the concrete by means of a steel bearing plate  Figure below shows a typical stressing anchor  When the required force has been reached, the strands pull the wedges into the tapered holes  Dead end – use loop round curved plate and led back to the stressing end (U TYPE) or the ‘onion type’ (H anchorage) which is completely embedded in the concrete (Others ‘P’ and ‘L’ type dead end anchorage)  Number of strand varies from 1 – 55 (13 mm) and (1-37) (15 mm)  Jacking force ranging from 110 kN to 11500 kN