§é d·n dµi t­¬ng ®èi øng víi lùc lín nhÊt

§é dÎo

Sè trÞ c¸c chØ tiªu ghi râ trong TCVN 6284: 1997.

Líp vá bäc ph¶i ®¸p øng ®­îc c¸c yªu cÇu :

§¶m b¶o tÝnh n¨ng c¬ häc trong kho¶ng nhiÖt ®é tõ -20^oC ®Õn 70^oC.

Cã ®é bÒn ®Ó kh«ng h­ háng khi chuyªn chë.

Kh«ng g©y ¨n mßn bª t«ng vµ thÐp vµ c¸c vËt liÖu chÌn kh¸c.

Cã kh¶ n¨ng chèng thÊm tèt.

Cã thÓ dïng líp b«i tr¬n vµ chèng gØ b»ng mì chèng gØ hoÆc h¾c Ýn chèng gØ.
Neo øng lùc tr­íc vµ bé nèi cèt thÐp øng lùc tr­íc:

CÇn ®èi chiÕu víi thiÕt kÕ ®Ó kiÓm tra xem nh÷ng neo vµ bé phËn nèi nµy cã phï hîp kh«ng. CÇn phï hîp vÒ tÝnh n¨ng kü thuËt vµ chñng lo¹i víi nh÷ng ®iÒu ghi trong thiÕt kÐ. Lùc ph¸ ho¹i cña neo vµ c¸c bé phËn nèi ph¶i ®­îc ghi lín h¬n lùc ph¸ ho¹i cña bã cèt thÐp øng lùc tr­íc. Khi kh«ng thÓ kiÕm ®­îc lo¹i ®¸p øng yªu cÇu nµy th× kh¶ n¨ng chÞu lùc cña nh÷ng bé nµy øng víi giíi h¹n ch¶y ph¶i ®¶m b¶o kh«ng bÐ h¬n 95% lùc ph¸ ho¹i cña bã cét thÐp øng lùc tr­íc.

èng dïng cho cèt thÐp ®¬n cã b¬m v÷a ph¶i cã ®­êng kÝnh lín h¬n ®­êng kÝnh cèt thÐp Ýt nhÊt lµ 6 mm. Víi nh÷ng èng chøa bã cèt thÐp ph¶i cã tiÕt diÖn ngang lín h¬n tiÕt diÖn ngang cña bã thÐp lµ 2 lÇn.

Tèi ®a hµm l­îng Cl ^- lµ 0,1 % khèi l­îng xi m¨ng.

Tèi ®a hµm l­îng SO₄ lµ 0,1 % so víi khèi l­îng xi m¨ng.
CÇn tiÕn hµnh c¸c thÝ nghiÖm ®Ó kiÓm tra :
C­êng ®é nÐn tiªu chuÈn cña v÷a kh«ng thÊp h¬n 30 MPa vµ c­êng ®é kÐo uèn tiªu chuÈn kh«ng thÊp h¬n 4 MPa.

§é t¸ch n­íc sau 2 giê kh«ng lín h¬n 0,02 vµ sau 24 giê th× hót hÕt.

§é co ngãt kh«ng qu¸ 0,003.

§é nhít kh«ng qu¸ 25 gi©y.

Nhµ thÇu cÇn lËp biÖn ph¸p chèng gØ vµ b¶o qu¶n vËt liÖu sö dông lµm øng lùc tr­íc th«ng qua c¸n bé t­ vÊn ®¶m b¶o chÊt l­îng vµ tr×nh chñ nhiÖm dù ¸n duyÖt.

(vii) Sai sè cho phÐp khi kiÓm tra gi÷a gi¸ trÞ øng lùc tr­íc thùc tÕ víi gi¸ trÞ qui ®Þnh lµ 5%. Cèt thÐp bÞ ®øt hay bÞ tuét kh«ng ®­îc qu¸ 3% tæng sè sîi cho mét tiÕt diÖn kÕt cÊu.

+ Víi kÕt cÊu mµ øng lùc tr­íc g©y nÐn däc trôc th× tÊt c¶ c¸c cèt thÐp cÇn ®­îc th¶ ®ång thêi.

+ Víi kÕt cÊu øng lùc tr­íc t¸c ®éng lÖch t©m th× cèt ë vïng chÞu nÐn Ýt h¬n ®­îc bu«ng th¶ tr­íc råi míi ®Õn c¸c cèt thÐp øng lùc tr­íc ë vïng chÞu nÐn nhiÒu h¬n.

+ V× lý do nµo ®Êy mµ kh«ng thùc hiÖn ®­îc hai ®iÒu trªn th× nghiªn cøu ®Ó th¶ cèt thÐp theo tõng cÆp thanh ®èi xøng xen kÏ sao cho kh«ng g©y néi lùc bÊt lîi cho kÕt cÊu, ®¶m b¶o cho kÕt cÊu ®­îc an toµn.

+ NÕu èng kh«ng ph¶i lµ lo¹i gîn sãng th× víi cèt thÐp d¹ng cong hay th¼ng cã chiÒu dµi trªn 24 mÐt cÇn kÐo c¨ng ë hai ®Çu. NÕu ng¾n h¬n 24 mÐt th× chØ cÇn kÐo t¹i mét ®Çu.

+ ThÝ nghiÖm kiÓm tra ®é nhít ph¶i lµm 3 lÇn trong mçi ca b¬m.

+ ThÝ nghiÖm ®é t¸ch n­íc ph¶i lµm mçi ca mét lÇn.
* Qu¸ tr×nh c¨ng øng lùc tr­íc vµ b¬m nhåi v÷a, ng­êi t­ vÊn ®¶m b¶o chÊt l­îng ph¶i chøng kiÕn ®Çy ®ñ. CÇn l­u ý nh÷ng ®Æc ®iÓm thi c«ng cÇn ®¸p øng nh­ sau ®©y:
+ Tr­íc khi b¬m v÷a, d­êng èng ph¶i s¹ch vµ Èm.

+ B¬m v÷a theo qui tr×nh tõ èng b¬m d­íi thÊp lªn cao.

+ Khi gÆp c¸c èng ®øng vµ èng xiªn th× ®iÓm b¬m v÷a lµ ®iÓm d­íi thÊp nhÊt cña ®­êng èng.

+ CÇn theo dâi ®¶m b¶o ¸p lùc b¬m kh«ng qu¸ 1,5 MPa. VËn tèc b¬m duy tr× ë møc 6 m/1 phót. C¸c lç tho¸t khÝ cÇn më ®Ó h¬i bªn trong èng tho¸t ®­îc hÕt ra ngoµi, ®¶m b¶o v÷a lÊp ®Çy.

+ Ph¶i b¬m liªn tôc cho ®Õn khi v÷a tho¸t ra ë c¸c lç bè trÝ cao nhÊt còng nh­ c¸c lç ë ®Çu vµ cuèi trªn ®­êng èng. Sau ®ã nót c¸c lç tho¸t khÝ vµ duy tr× ¸p lùc b¬m 0,5 MPa trong 2 phót míi bÞt lç b¬m.
* V÷a ph¶i ®­îc lÊp ®Çy èng . NÕu nghi ngê v÷a kh«ng ®Çy hoÆc cã dÊu hiÖu kh«ng ®Çu èng , ph¶i phôt cho v÷a ra hÕt, b¬m n­íc thæi röa s¹ch , b¬m khÝ ®uái hÕt n­íc vµ lµm l¹i tõ ®Çu qu¸ tr×nh b¬m.
* ViÖc lËp hå s¬ ph¶i tiÕn hµnh ngay trong qu¸ tr×nh thi c«ng vµ theo tõng b­íc. Yªu cÇu cña hå s¬ lµ ®Çy ®ñ d÷ liÖu kü thuËt.
(3) C«ng nghÖ kh«ng b¸m dÝnh:
C«ng nghÖ kh«ng b¸m dÝnh chñ yÕu lµ c«ng nghÖ c¨ng sau nªn cÇn tu©n thñ c¸c qui ®Þnh cña c«ng nghÖ c¨ng sau. Tuy vËy cÇn nhÊn m¹nh:
* Ph¶i kiÓm tra cèt thÐp øng lùc ®¶m b¶o cho h×nh thøc bªn ngoµi ®¸p øng tÝnh nguyªn vÑn cña thanh hoÆc bã thÐp. NÕu vá bäc bÞ h­ háng ph¶i cã biÖn ph¸p kh¾c phôc. NÕu vá r¸ch nhiÒu, kh«ng cho sö dông.
* Khi ®Æt cèt thÐp kh«ng b¸m dÝnh ph¶i sö dông c¸c con kª b»ng thÐp ®Æt liªn kÕt chÆt chÏ víi cèt thÐp øng lùc ®Ó ®Þnh vÞ cao ®é cña cèt thÐp t¹i c¸c vÞ trÝ theo thiÕt kÕ. Kho¶ng c¸ch gi÷a c¸c con kª kh«ng xa qu¸ 1 mÐt hoÆc 60 lÇn ®­êng kÝnh bã hay thanh thÐp.
* Neo vµ c¸c phô kiÖn ®Çu, phô kiÖn cuèi cÇn ®­îc b¶o vÖ chèng gØ , chèng x©m thùc cña h¬i n­íc.
o 0 o
KÕt cÊu bª t«ng cèt thÐp lµ x­¬ng chÞu lùc chÝnh. CÇn ®­îc thi c«ng vµ kiÓm tra hÕt søc chÆt chÏ vµ tu©n thñ nghiªm ngÆt c¸c qui tr×nh khi kiÓm tra. KiÓm tra tr­íc vµ trong khi thi c«ng lµ biÖn ph¸p n©ng cao chÊt l­îng h÷u hiÖu.

Chóc c¸c b¹n thµnh c«ng./.

néi dung
1.PhÇn më ®Çu trang 2
2. Gi¸m s¸t thi c«ng vµ nghiÖm thu c«ng t¸c bª t«ng cèt thÐp 12
2.1 Mét sè quan niÖm míi vÒ bª t«ng cèt thÐp 12

2.2 Nh÷ng tiªu chuÈn liªn quan 26

2.3 Gi¸m s¸t vµ nghiÖm thu cèppha 26

2.4 Gi¸m s¸t vµ nghiÖm thu cèt thÐp 32

2.5 KiÓm tra qu¸ tr×nh thic«ng bª t«ng 44

2.6 KiÓm tra c«ng t¸c thi c«ng bª t«ng øng lùc tr­íc 53

This Chapter basically addresses construction procedures and operations from Shop Drawings, through tendon installation and stressing. Grouting is addressed in the next chapter. Information and details in these two Chapters may be used for guidance.

3.1 Shop Drawings


3.1.1 Drawings and Details


3.1.1.1 Purpose

To permit completion and to encourage further development in the field of post-tensioned bridge construction, in general, normal contract plans and specifications do not specify a particular manufacturer's post-tensioning system. The Engineer of Record usually selects the type, size, location and number of tendons, but the Contractor selects the anchorage system. All post-tensioning systems should have prior approval before being used.

All systems now in general use have been developed by independent companies and represent different methods by which the prestressing force is applied. Each offers certain advantages as compared to the others, but each will, when properly installed and stressed, accomplish the intended result.

A post-tensioning system proposed by a Contractor should be shown on shop drawings. These drawings should include details for the methods and materials used, including any rearrangement of or addition to reinforcing steel that differs from that shown on the contract plans. Shop drawings represent an important supplement to Contract Plans.

Shop drawings are normally reviewed by the Bridge Designer. The Designer normally checks them for completeness, contract compliance, clearances or interference of ducts and reinforcing steel. Despite the approval process, the Contractor remains responsible for the correctness of the shop drawings and ensuing construction.

Shop drawings are needed for integration of approved post-tensioning systems (i.e. post-tensioning supplier's information and details), reinforcement, post-tensioning, and other embedded items (including those for the Contractor's chosen "means and methods" of construction) for precast and cast-in-place components.

3.1.1.2 Typical Contents

Shop drawings from a Manufacturer of a Post-tensioning system typically address various details such as:

• 
  Dimensions, details and materials for all manufactured components.
  
• 
  For strand systems, dimensions and details of anchors, wedge-plates, wedges, for each size and tendon.
  
• 
  For bar systems, dimensions and details of anchor plates, anchor nuts, bars and couplers for each bar size.
  
• 
  Details of grout inlets and outlets at anchorages.
  
• 
  Size, type connection and sealing details of grout caps.
  
• 
  For each type of duct, dimensions, details, type of material, duct connectors and methods of connecting ducts to anchor cones (trumpets).
  
• 
  Details of means and methods of attaching intermediate grout inlets and outlets to the ducts, including sizes of grout pipes, materials, and shut-off valves.
  
• 
  Dimensions, clearances, force and stroke of stressing jacks for post-tensioning bars and strands, including single, mono-strand and multi-strand jacks as necessary.
  
• 
  Typical details of ancillary equipment such as power source, hydraulic lines, pressure gages for use with the stressing jacks.
  
• 
  Jack calibration charts to show relationship between dial gage pressure and force delivered.
  

• 
  Duct profile and minimum clearances.
  
• 
  Details, types and locations of duct supports, connections to temporary bulkheads, and means of maintaining alignment and profile.
  
• 
  The method for installing strands, individually or in a complete bundle for each tendon.
  
• 
  The sequence in which tendons are stressed.
  
• 
  The end(s) from which tendons are stressed.
  
• 
  Assumed coefficient of friction (m) and wobble coefficient (k).
  
• 
  The estimated elongation and maximum jacking force for each tendon.
  
• 
  The estimated wedge set or seating loss.
  
• 
  Similar information for post-tensioning bar tendons.
  
• 
  When temporary post-tensioning bars are used to secure a precast match cast segment, the sequence and force to which each should be coupled and stressed around the cross-section.
  
• 
  The sequence and means by which temporary post-tensioning bar or strand tendons are de-tensioned and removed.
  
• 
  For all permanent installations, locations of grout inlets and outlets, details, direction of grouting and sequence in which tendons are grouted (See also Chapter 4).
  

Typical responsibilities associated with shop drawings include:

• 
  Contractor: Arrange for the preparation of the necessary shop drawings and other relevant information required by the Contract, see that shop drawings are submitted to the Engineer (usually the Designer) for review and approval, receive review comments, make revisions as necessary and carry out construction accordingly.
  
• 
  Contractor's Engineer: the person or firm who prepares calculations and shop drawings on behalf of the Contractor.
  
• 
  Engineer (Designer): Receive, log and review all submittals for compliance with the information conveyed on the plans and provide approval, reject, seek amendment or clarification as necessary. The Engineer may be a member of a state (Owner) agency or private firm engaged by that State or Owner.
  
• 
  CEI - Construction Engineering and Inspection: This is the person, firm or agency representing the interest of the State or Owner on the job-site (Resident Engineer).
  

Figure 3.1 - Typical Shop Drawing Approval Process for Post-tensioning

To ensure that the correct force is applied to each tendon, calculations are made to account for losses (friction, wobble, wedge-set and anchor friction) along the length of a tendon and to estimate the elongation as a check against the gauge pressure on the jack. Calculations are usually made by the Contractors Engineer or installer of the Post-Tensioning and should be checked by the Engineer (Designer or CEI). Key information, such as jacking force or gauge pressure and anticipated elongation, is extracted for stressing.

Stressing of a tendon may be performed from one or both ends. Stressing from both ends may be sequential, first from one end then the other, or simultaneous using two jacks. In some types of construction, it may only be necessary to stress from one end; for example, where tendons are relatively short, say up to about 50M (150 feet) and have relatively small friction loss. However, for long tendons, especially those within internal ducts set to a curved profile that passes continuously through three or four I-girder spans, friction loss may be so significant that it is essential to stress the tendon from both ends to ensure adequate force throughout.

Wedge-set should be taken into account for both the stressing end and dead end of a tendon. For long tendons, often the elongation may be greater than the travel on the jack. It is then necessary to take more than one pull of the jack. Each time the jack is released, the wedge-set occurs again at the jacking end. Since the load is picked up again upon re-gripping, the wedge set of individual pulls is not cumulative. Only the final wedge set affects the loss of tendon force. However, keeping account of cumulative elongations and wedge-sets during repeated pulls by a jack is always helpful for resolving unforeseen problems.

Stressing calculations are illustrated with two examples: first for a long tendon draped to a profile through four continuous spans and stressed sequentially from both ends; second for a deviated external tendon in an end span stressed from the expansion joint.

Various parameters for calculation of stressing forces and elongations are defined as follows:

• 
  Length of tendon (L)
  
• 
  Assumed area of tendon (A_S)
  
• 
  Modulus of Elasticity assumed (E_S)
  
• 
  Coefficient of friction between tendon and duct (µ)
  
• 
  Wobble coefficient (k)
  
• 
  Distance from jacking end to location of interest = x
  
• 
  Accumulated angle of curvature to point x = θ_X
  
• 
  Length of portion of tendon between two points "i" and "j", = X _{i j}
  
• 
  Wedge seating loss (W)
  
• 
  Friction in anchor (%)
  
• 
  Friction in jack (%)
  
• 
  P₀ = force at the jack
  

The force in the tendon (P_X) at each point of interest a distance "x" from the jack is determined from the formula:

P_X = P₀ .e ^{- ( µθ + kx )}

The total elongation is obtained by summing the increments of elongation for each portion of the tendon, based on the average of the force at the beginning and end of that portion: Elongation ΔL=∑ (Pav.X _{i j} / A_S1.E_S1) where Pav = average force over X _{i j}.

Information to be forwarded to the site engineer or inspector should include:

• 
  Tendon identification
  
• 
  Assumed area of strands (A_S)
  
• 
  Assumed modulus of elasticity (E_S)
  
• 
  Required jacking force, P jack
  
• 
  Wedge set (draw-in), W, assumed for each end of each tendon
  
• 
  Calculated elongation at each end, before release of the jack and wedge set for each end of the tendon, depending upon the ends to be jacked first and second
  
• 
  The anticipated total elongation, ΔL, before wedge set
  

• 
  A _r = actual area of strands
  
• 
  E _r = actual modulus from samples per strand LOT or per coil or (reel) of strand
  
• 
  Total target elongation = ΔL *(A _S*E _S) / (A _r*E _r)
  
• 
  Anticipated elongation at each end in proportion to the adjusted target elongation
  

Consider a four-span, spliced I-girder with a gradually curving tendon profile made up of several parabolic arcs as illustrated in Figure 3.2. It is necessary to calculate the expected elongation and final post-tensioning force, allowing for friction, wobble and wedge set. Two spans of the structure are shown and it is assumed to be symmetrical about the center pier. Being a long tendon, it must be stressed from both ends or else the total force loss will be too great. However, for on-site efficiency and resources, stressing is done first at one end then the other.

The calculation is made by considering each arc of the profile in turn and applying the above formula to determine the force at the beginning and end of each portion, commencing at the jack. For convenience, the calculation is made using a spreadsheet (Tables 3.1(a) and (b) at end of this Chapter). Also, for clarity, this example is shown in customary U.S. units at this time.

Figure 3.2 - Tendon profile in four-span I-girder

When stressed first from one end (A) (left hand end of Figure 3.2), the elongation is calculated to be 38.53 in. (Table 3.1 (a)). Two things should be observed. First, this elongation is greater than the available stroke of normal stressing jacks; so full elongation may require three or four separate pulls from this one end alone. Second, in Table 3.1(a), account is not taken of the initial wedge set at end (B) (the opposite end of the bridge). This anticipated wedge set occurs while end B is a non-stressing "dead end". In theory, it should be added to the total anticipated elongation for stressing from end A. For instance, if all of the elongation could be measured at end A, the apparent elongation at A would become 38.53 + 0.38 = 38.91 in. - if wedge set at end B is assumed to be, say, 0.38 in. However, in the field not all the force will be applied in one step at end A. In fact an initial load, usually 20%, is applied at A to remove slack and seat the wedges at end B. Elongations are only measured after this initial load. A correction is added for the initial 20% based upon that measured from 20 to 100% load.

The second stage of stressing is performed from end B. Consequently, it is necessary to calculate the anticipated (additional) elongation and final force at end B. After stressing from end A, the force in the tendon at end B is calculated to be 169.1 kips (Table 3.1(a)). Hence, when jacking at end B, the jack will not begin to move until the load exceeds this amount. The jack at B will pick up load at 169.1 kips and continue to the required jacking force of 308.0 kips.

However, because of loss due to friction and wobble, the effect of jacking at B will travel only so far along the bridge until it reaches a point where the force is equal to that from jacking at end A. In this case, because the bridge is symmetrical, this occurs at the middle pier. Consequently, the additional elongation at end B comes only from the increase in tendon force between end B and the middle pier. This elongation is calculated in Table 3.1(b) to be 6.36 in.

Figure 3.3 - Calculated tendon force after losses

38.53 (at A, from Table 3.1(a)) + 6.36 (at B from Table 3.1(b)) = 44.88 in.

The net elongation after wedge set at both ends is then:

44.88 - 0.38 (at A) - 0.38 (at B) = 44.12 in. (Table 3.1 (b)).

In the field, the elongation at B (6.36 in.) will be observed and measured at end B as taking place from the point to which the wedges have already been pulled in after stressing from end A. If a mark were made on the strand tails at end B before stressing from end A, it would move inwards at least by the amount of wedge set at B (0.38 in). In fact, it is likely to move more than this, especially if the wedges at B have only been initially seated "by hand". Fortunately, it is not necessary to know the initial wedge pull in at B due to load at A, because the actual elongation at B is measured from where the strand is at B only after loading from end A.

After release of the jack at B, the wedges are pulled in by the final wedge set of 0.38 in. at B. Consequently, as a check, the net total elongation after wedge set is given by (Table 3.1 (b)):

38.53 (net at end A) - 0.38 (set at B) + 5.98 (net movement at B) = 44.13 in (O.K.).

The force loss (dp) at each end is determined for the amount of anticipated wedge set as shown in Tables 3.1(a) and (b). For this example, the final, calculated Post-Tensioning force is summarized in Figure 3.3. The minimum force (228 kips) is at the center of the four span unit.

Required jacking forces and expected elongations are forwarded to the field for stressing operations. In the field these become the target forces and elongations of the field stressing report (Tables 3.3(a) and (b) at end of this Chapter).

It should be noted that in this example, no account has been taken for the elastic shortening of the structure under the axial compression force of the tendon. If this stressing is performed only on the girder before any deck slab has been cast and if the above tendon is the first of several, then the elastic shortening is estimated approximately as follows:

From Figure 3.3 the average force, P, in the girder is 264.6 kips. If the cross section area of the girder is A_C = 6.00 ft ² _, and assuming an initial modulus of elasticity of 4,500 ksi and total bridge length is L _B = 567 ft., the elastic shortening is given by x _EL = PL _B/ A_CE_C = 0.46 in.

This is relatively small. However, in the field, it would have the effect of increasing the measured elongations; approximately in proportion to the calculated elongation at each end. After a deck slab has been added, elastic shortening from a similar tendon would be much less.

It follows that stressing of a subsequent tendon of the same profile would result in the same elongations for that tendon. However, it also follows that elastic shortening caused by stressing of a second tendon reduces the effective force in the first tendon. Such reduction also occurs for the effect of all subsequent tendons stressed after earlier ones. The effect of such staged post-tensioning is normally taken into account by the Designer during design of the bridge. The Designer should consider the effects of elastic shortening in the design of post-tensioning forces.

3.1.2.2 Example 2 - External Deviated Tendon in End Span

Consider the external tendon in the end-span of a typical span-by-span bridge (Figure 3.4). In this case, the tendon is stressed from one end only (right hand end). It is necessary to calculate the anticipated force in the tendon after stressing, the elongation and effect of wedge set.

Friction between the tendon and duct can only occur at deviators and in those portions of duct in the diaphragms of pier or expansion joint segments where the tendon path curves to an anchor. In this example, there is a curve at the dead end only and none at the stressing end. Curvature friction, µ, applies at the deviators and the dead end diaphragm. There is no loss due to wobble in external tendons, so k = zero.

For the purpose of calculation, the tendon is considered in individual portions, either external or internal and the force loss is calculated according to the same formula as above, i.e:

P_X = P₀ .e ^{-( µθ + kx )}

Figure 3.4 - External Deviated Tendon in End Span

The effect of wedge set is not as easily determined as for a continuous, internal tendon of Example 1. Rather, it is necessary to determine if the effect of wedge set terminates within the first deviator (BC) or if it extends to the next deviator or beyond. This may be done by first making the assumption that the wedge set effect terminates at the first deviator and then calculating the force that should exist in the other portions of the tendon if this were the case, and comparing it to the original force at jacking before wedge set loss.

In this example, we find that the force in AB reduces significantly from 835 to 761 kips. It follows that the force in portion CD must be greater than that in AB but cannot be more than that due to friction loss through deviator BC. Hence the force in CD would have to be 761+ (835-819) = 775kips. But, because the original jacking force in CD of 819 kips is greater than 775, it follows that deviator BC alone cannot absorb all of the loss due to wedge set. Hence wedge set must also affect portion CD.

The calculation is repeated, this time assuming that the wedge set terminates in deviator DE. This time, we find that the force in AB is 792 kips and in CD is 807 kips. Because the difference in force in portions CD and EF (i.e. 807-797 = 10 kips) is less than the original friction loss of 22 kips across deviator DE, it follows that the effect of wedge set terminates at DE. The final force diagram after friction and wedge set loss jacking is then known (Figure 3.5). In this case, the final force is nearly uniform (approximately 800 kips) along the tendon.

Figure 3.5 - External Tendon Force after Friction and Wedge Set