elastic shortening in prestressed concrete

Elastic shortening is the immediate shortening of the concrete member due to the application of prestressing. angular friction, so that the expression for the force in a tendon due to both angular The prestress loss due to elastic shortening in pretensioned members is taken as the concrete stress at the centroid of the prestressing steel at transfer, f cgp, multiplied by the ratio of the modulus of elasticities of the prestressing steel and the concrete at transfer. ): 136-137 Centrum Plaza, Golf Course Road, Sector 53, Gurgaon Haryana 122002, INTEGRAL WATERPROOFING & DURABILITY SOLUTIONS. 0000053708 00000 n the tensioning of any subsequent tendon will reduce the force in those already centre and the right-hand end if the prestress force is applied at the left-hand end. 0000050082 00000 n Answer: Option 2. 3. fill approximately 50% of the duct are shown in Table 4.2. 58, Xinhua West Street, Tongzhou District, Beijing, India (Kryton Buildmat Co. Loss due to elastic shortening (ElasticShort)a = (49.67 MPa) (350.64b mm2) = 17.41 kN Total loss due to elastic shortening (SumElasticShort)a = 17.41 kN x 11 tendons = 191.55 kN a Parameter. 0000050671 00000 n For most tendon profiles, s may be taken as the horizontal projection of the 1292 0 obj 3. More guidance in C.I. Thus the loss is 106.8 kN, which is 3.0% of the initial force. <>/Border[0 0 0]/Rect[243.264 211.794 412.896 223.806]/Subtype/Link/Type/Annot>> 3 as follows, Once the loss in prestress is calculated, the next step is to determine Tf by virtue of Eq. Stress in steel after loss . This is because elastic gains are not included and the result may be a reduction of compression in the beam bottom at mid-span. The loss of prestress in steel due to elastic shortening of concrete is approximated by: Qo 516 x1040 fs = n = (6) = 53 .664 MPa Ag 200 x300. Fig. The template calculates losses due to elastic shortening in post-tensioned members as stated in article 5.9.5.2.3b of the AASHTO LRFD Bridge Design Specifications 2012. 0000005285 00000 n which produce friction. 2) where Kes = 1.0 for pretensioned members. Elastic shortening of concrete (ES), (2) Creep of concrete (CR), (3) Shrinkage of concrete (SH), and (4) Relaxation of tendons (RE). Further information on friction during tensioning may be found in a report of the All symbols are defined in the text where they first appear. 1299 0 obj Although friction is a cause of loss of prestress force principally in post-tensioned startxref Find the maximum stress in concrete immediately after transfer, allowing only for elastic shortening of concrete If the concrete undergoes a further shortening due to creep; Question: 2. 0000044898 00000 n 4. This does not mean that there is no elastic shortening; it simply means that the elastic shortening is included as part of the stress equations and is not calculated separately. Pvt. . Combining Equations 4.1, 4.2 and 4.3 gives, If the tendons are closely grouped in the tensile zone, the loss due to elastic shortening Modulus of Elasticity of Concrete can be defined as the slope of the line drawn from stress of zero to a compressive stress of 0.45f'c. As concrete is a heterogeneous material. (ii) If the beam is tensioned from both ends, the minimum prestress force is at the previously, for no applied axial load the forces in the tendon and concrete must be 0000053255 00000 n 0000001396 00000 n Creep of concrete - 5%. The magnitude of this friction depends on the Because the concrete is usually stressed at such an early age, elastic shortening of the concrete and subsequent creep strains tend to be high. For the small angle , cos (/2) 1. View Notes - Ch3+Prestressed+Concrete+2017 from CEE 6523 at Georgia Institute Of Technology. An pass over deflectors or through diaphragms there is some loss of prestress. To be theoretically exact, net concrete section should be used up to the time of . TL-ES = 20 - 0.4(20) = 12% This issue I have is understanding why all the losses need to be considered at the time of prestress transfer, when the only losses that occur at that time are elastic shortening and maybe some anchor loss due to the chucks. acceptable approximation is to assume that the loss in each tendon is equal to the This paper does not cover the first event, elastic loss due to anchorage to the prestressing bed. Df pES = (E p/E ci)f cgp (S5.9.5 . readings. Creep strain = Ce x Elastic strain Elastic strain = (fc/Ec) fe is the stress in concrete at the level of steel. On this page: Overview Short-term losses this case an average value of cg should be assumed. Article 5.9.3 Page 1 of 3 10/2017 5.9.3 PRESTRESS LOSSES Elastic Losses or Gains, fpES fpES is the sum of all the losses or gains to the strand stress due to elastic shortening or extension caused by either internal (prestressing) or external (gravity) loads applied to the concrete section. The friction losses in the relatively shallow tendon in Example 4.2 are small, but in Elastic shortening 1297 0 obj Ultimate Strength of Prestressed Concrete: After designing a member to meet the stress . as measured by the actual force transmitted to the ends of the member via the tendons, 0000043468 00000 n <>/Border[0 0 0]/Rect[81.0 646.991 162.072 665.009]/Subtype/Link/Type/Annot>> <> Lubricated: P(x)=3531.2 exp [0.19(x/89.29+50104x)]. Transmission length when development length of section is given. The additional tensile stress at the level of average loss in all the tendons. 2. endobj of the deflector, and will usually be determined from tests on the particular deflection S5.9.5.2.3a-1. The prestress losses are defined as the loss of tensile stress in the prestress steel which acts on the concrete component ofthe prestressed concrete section. Assume =0.19 and k=50104 rad./m. the centre. 3. Thus, in Equation 4.1: The more frequently used symbols and those that appear throughout the book are listed below. In the case of post -tensioned members those losses occur only when a number of cables are progressively stressed one after another. being used and are generally in the range 50100104 rad/m. 0000022711 00000 n In members with many tendons, it is the usual practice to tension half the In this case the 4. This does not mean that there is no elastic shortening; it simply means that the elastic shortening is included as part of the stress equations and is not calculated separately. The total angular deviation in a parabolic curve may be conveniently determined 4.6. There are two basic mechanisms Elastic shortening is the loss of prestress force that takes place when the strand becomes shorter. PRESTRESSED CONCRETE- FLEXURAL ANALYSIS CONSIDERING SERVICE LOAD LIMIT STATE Structural Engineering CE-401, Civil Engineering Department, UET, Lahore. 0000022154 00000 n 0000021978 00000 n APPLICATIONS OF THE PRE-STRESSED CONCRETE: MEGA FLOOR,the Prestressed slab Shrinkage of concrete - 7%. type of duct-former used and the type of tendon. 3Q@[N 0000007676 00000 n The loss of prestress can be computed utilizing Eq. Then: The loss is now 198.3 kN, i.e. 0000045324 00000 n The advantages of high strength concrete in prestressed construction are as follows: 1. 2. <>/Border[0 0 0]/Rect[81.0 617.094 136.86 629.106]/Subtype/Link/Type/Annot>> 3-1 Part 3 Prestress Losses 3-2 Estimating Losses Elastic and time related effects for steel and concrete Loss = m.f c m - modular ratio and f c - prestress in concrete at the level of steel The advantages and disadvantages of post-tensioning are as follows: 1. 0000005286 00000 n Structural engineers typically . However, The loss of stress due to elastic shortening of concrete is maximum in pre-tensioned members. against deflectors, caused by friction between. cable at the two ends of the section are not equal. 0000004347 00000 n At the level of the prestressing tendons, the strain in the concrete must equal the change in the strain of the steel. number of tendons from one end and the remainder from the opposite end, resulting in hb```b``f`e`P.ag@ ~-r}tjhd_qMWY,Y'\ow8nK_rw\^"yk x:IpU|UZ*l|{-L|^HD&E|yg|{wt\E\:8$90.1\%k(G@l 6AAAC37bpPP~ ,Fg X0fdg0wt`. This sums up to be 15%. level of the centroid of the tendons. Thus the loss is 383.1 kN, which is 12.8% of the initial force. %PDF-1.4 % 4.2: 0000003350 00000 n 0000009289 00000 n 4.3(b); for the small angle , N=T. This is generally treated by considering it as additional endobj 0000008699 00000 n endobj Loss of prestress due to elastic shortening is a result of elastic shortening of a girder after release. 0000002696 00000 n When not using the transformed section properties option, the gross section properties method follow what has been industry practice for many years. f pES = f pES1 + f pES2 + f pES3 + f pES4 (1) where f pES1 remains unaltered. By submitting the form, you agree to our Terms and Conditions and Privacy Policy, Corporate Headquarters: 1645 East Kent Avenue, Vancouver, British Columbia, V5P 2S8 Canada, Calgary (Cementec): 13 Industry Way SE, Calgary, Alberta T3S 0A2 Canada, China: Room 1012, Block B, Tongzhou Wanda Plaza, No. Let T0 be the prestressing force that is applied at the centroid of the concrete section in a pretensioned member. article. endobj 6 can be equated: The above assumption implies that the concrete acts with the steel as a homogenous material and it already suggests that the concept of transformed section properties can be used. 0000056445 00000 n Ultimate prestress given bond length for prestressed tendon. Elastic shortening loss is induced, because the prestressing tendons are also shortened when a PSC member is subjected to compression induced by prestressing. analysis, the life of the prestressed concrete girder is divided into small steps, over which the strain in the concrete and steel are assumed to be constant. Tendon also shortens by same 0000005011 00000 n ends. This paper presents a synergic identification method to determine PF and moving load applied on a simply supported prestressed concrete beam via the dynamic responses caused by this, The proposed methodology aims to determine the following items: the suitable sleeper spacing for a given rail type, the wheel load distribution along successive sleepers, the, For these longer spans, continuity between the girder segments has the advantage of eliminating bridge deck joints, which leads to reduced maintenance costs and improved, The test model was left in the condition that the load cell was subjected to prestressing force (6.5 MN) during the test period. Calculate tensile force in steel immediately after transfer, Eq. "nc&Eu64QoV%hIC{> y^>_b&)i 8yEr|hunq. Losses in Prestressed Concrete. Any bending To recapitulate the above procedure the following steps are introduced: Consider the effect of loss of prestress due to elastic shortening as an element of the prestressing force, Eq. economical, case where the tendons are tensioned sequentially, after the first tendon curvature, as shown in Fig. Practically, however, gross section area is used instead. members, in pretensioned members there is some loss if the tendons are tensioned 0000014059 00000 n The change of the stress in concrete can be expressed as. 0 A prestressed concrete sleeper produced by pre-tensioning method has a rectangular cross-section of 300mm 250 mm (b h). The forms are stripped and the prestressing strands are released after adequate strength is. As a result, the concrete and strands shorten under the load. A prestressed concrete double-tee is an example of a post tensioned member. This is called elastic shortening of concrete. At the level of the prestressing tendons, the strain in the concrete The concre te undergoes ES when the prestressing force is transferred from the end blocks of the casti ng bed to the. For the first If values are not entered, the program assumes a set of defaults; however, the user must specify basic information about the beam for the design. 4.3Elastic shortening losses in pretensioned members, p. 16 4.4Post-tensioning losses during tensioning and transfer, p. 18 4.5Elastic shortening loss in post-tensioned members, p. 21 4.6Elastic gain under superimposed loads, p. 22 CHAPTER 5LONG-TERM LOSSES: SIMPLIFIED METHOD, p. 22 5.1Scope, p. 22 5.2Creep of concrete (f The value of a reflects the short-term losses due to elastic shortening, anchorage draw-in and friction.Total loss coefficient b accounts for the short term and long-term time-dependent losses due to concrete shrinkage and creep and steel relaxation. There is also a small amount of friction within the jack itself, between The change in strain (unit shortening) in the tendons as a result of losses can be expressed as, The increase of strain in concrete can be expressed as. must equal the change in the strain of the steel. When using transformed steel, Precast/Prestressed Girder shows ES equal to zero on the printout. Similarly to prestressed concrete, post-tensioned concrete loses tension in the tendons over time. . One is the curvature of the tendons to achieve a desired 0000003725 00000 n 4. Losses due to steel relaxation, elastic shortening of concrete, concrete shrinkage and concrete creep were considered. 1302 0 obj To know the accurate value of elastic modulus of a . Prestressed concrete bridges comprise a significant proportion of the bridge stock both in the United Kingdom and around the world. For the beam in Figure 4.7, determine the minimum effective prestress force if an In the more usual, and more grouted, the short-term prestress force is effectively held constant. portion of the curve, with radius of curvature rps1, the force in the tendon at point 2 is, where s1 is the length of the tendon to point 2. Assume the same values of and k as in Example 4.2. For pretensioned members, prestress loss is due to elastic shortening, creep of concrete, and steel relaxation. 1323 0 obj (2) Elastic shortening losses Because all tendons will be simultaneously tensioned the elastic shortening of concrete will not affect tendons since it will be taking place at the same time as tensioning and no loss of prestress force will take place. 2 one wire post-tensioned beam. 001188 193000000 = = = . McGraw-Hill Dictionary of Architecture and Construction. mid-length friction losses using such tendons are small. Subscribe to our eNewsletter Stay connected and subscribe to get the latest news. . 6. Losses from elastic shortening and long-term effects, including creep, shrinkage, and relaxation, are computed for tendons which are modeled as objects, and may be specified for those modeled as loads. endobj concrete. profile, and the other is the inevitable, and unintentional, deviation between the Assuming n = 6, compute the stresses in the concrete and steel immediately after transfer. 898 0 obj <> endobj xref 898 55 0000000016 00000 n Determine the loss of prestress force due to elastic shortening of the beam shown in Elastic Shortening of Concrete, posttensioned If only a single tendon, the concrete shortens as that tendon is jacked against the concrete. The variation between the actual centrelines of the tendon and duct is known as the type of duct used, the roughness of its inside surface and how securely it is held in then superimposed to give the total effective prestress force. 0000000936 00000 n 0000007766 00000 n The prestress losses are defined as the loss of tensile stress in the prestress steel which acts on the concrete component ofthe prestressed concrete section. Assume that po=1239 N/mm2, Ap=2850 mm2 and m=7.5 for the concrete at. Elastic shortening produces the most significant effect on prestress losses. =3321.6 kN. What we are trying to quantify is the change in the strain. Please note also that the area of concrete is equal to the gross area minus the area of steel, Ac=Ag-As. where: N = number of identical prestressing tendons. 4.2 ELASTIC SHORTENING Consider a pretensioned member with an eccentric prestress force P o transferred to it as shown in Fig. centre of the beam. Type of wire/strand Bonded Grouted duct Unbonded Steel tube Unbonded HDPE tube 0000011355 00000 n Because the concrete shortens when the Prestressing force (in full or in part)is applied to it, the tendon already attached to concrete also shorten.Elastic Shortening occure When the tendons are cut and the prestressing force is transferred to the member, concrete undergoes immediate shortening due to prestress. 0000007021 00000 n members with tendons of large curvature the losses may be so large that the member In practice, the 0000002449 00000 n Since there is friction between the cable and the pulley, the forces in the 3. Therefore the stress in concrete, c, can be determined by substituting Eq. As the tendons that are bonded to the adjacent concrete simultaneously shorten, they lose part of prestressing force that they carry. (i) The total angular change for the full length of the tendon is given by, The minimum prestress force occurs at the right-hand end of the beam: Prestressed concrete is a method for overcoming concrete's natural weakness in tension. Nevertheless, the post-tensioned concrete still has more tensile strength and efficiency than traditional concrete . Figure 4.4 Tendon with several curvature changes. y This is presented in Eq. Admin April 09, 2020. Prestress loss due to the elastic shortening in pretensioned girders can be computed using Eq. Relaxation of Steel - 3%. Tendon also shortens by same amount, which leads to the loss of prestress. The prestress loss due to elastic shortening in pretensioned members is taken as the concrete stress at the centroid of the prestressing steel at transfer, fcgp, multiplied by the ratio of the modulus of elasticities of the prestressing steel and the concrete at transfer. force in post-tensioned members at transfer is not constant owing to friction. In case of post-tensioned members, there will be no loss of pre-stress due to elastic deformation if all the wires are simultaneously tensioned. In post-tensioned beams, for single tendon, there is no need to calculate elastic shortening loss because it is compensated in jacking (not so for several tendons jacked in sequence). inside of the ducts during tensioning. 0000038860 00000 n The force P(x) in a curved tendon at an intermediate point along the curved 2%, and is usually covered by the calculated duct friction losses, which tend to be 1300 0 obj 0000008730 00000 n Numerical examples show that the variability in the prestress losses exceeds the loss calculated by deterministic methods. 0000009375 00000 n conservative. along the member than if all the tendons had been tensioned from the same end. The magnitude of this loss will depend upon the details The first takes place as the Thus, f pES calculated by Eq. using the properties of the parabola shown in Fig. "Pre-stressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose those found when in use." It is a combination of steel and concrete that takes advantages of the strengths of each material. modified by the self weight of the member. As the tendons that are bonded to the adjacent concrete . 0000003659 00000 n 3 multiple wire pre-tensioned beam with sequential cutting of wires. 0000027926 00000 n =2 tan1(4dr/L), The radius of curvature is given by 4.1. #Types of Losses in pre tensioning#losses in post tensioning, # Detail about losses due to elastic shortening of concrete, #Demonstration on successive post . endobj system being used. 0000000016 00000 n rps=(d2y/dx2)1=L2/8dr, Table 4.2 Coefficients of friction for different tendon types. kN L A sl p p 68.9 21 .3 100 0.64 P A E 0. Elastic Shortening - Kryton International Inc. Media Contact Us Elastic Shortening in prestressed concrete, the shortening of a member that occurs immediately on the application of forces induced by prestressing. 0000045759 00000 n 0000027749 00000 n Question: The loss of prestress due to elastic shortening of concrete is least in: 1 one wire pre-tensioned beam. 0000013230 00000 n Provide the answer in percentage. can be assumed to be equal to the strain in the concrete at the same level, even though 1294 0 obj At the supports: III. 0000056164 00000 n Solution. LOSS OF PRE-STRESS. as shown in Fig. 0000007551 00000 n the piston and the jack casing, which causes the load applied to the tendon to be Please not that the total force, T0, did not change the value during transfer and only the component due to elastic shortening was introduced. The prestress loss or gain due to elastic shortening or ex- tension occurs at five events (Fig. xref (after elastic shortening loss) is 169 kips. influences of the tendons, or groups of tendons, should be determined separately and 0000015486 00000 n For unbonded members, the prestress force will vary with the The prestress losses are defined as the loss of tensile stress in the prestress steel which acts on the concrete component ofthe prestressed concrete section. 0000012633 00000 n hVPT>u]\` . endobj 4.4, may be described using Equation 4.6. PSTRS14 is a MS-DOS based system in which a text file is input with material properties, loading and design considerations for a prestressed concrete beam. This relatively high time-dependent shortening of the concrete causes a significant reduction in the tensile strain in the bonded, pre-stressing steel and a relatively high loss of pre-stress. X? 0000034758 00000 n Figure 4.3 Friction in a cable. <<>> <>stream 22 ksi (152 MPa) for bars. (Wobble, Elastic shortening, Long term creep, Anchor seating loss) Wobble. Stay connected and subscribe to get the latest news. . 0000002943 00000 n tendon, for no applied axial force on the section this must equal the force in the 0000001599 00000 n Jeffrey Luin. loading on the member, but in practice this effect is ignored. In the case of a post-tensioned member, a group of strands are sequentially tensioned duct-by-duct using a multi-strand jack. In the case of pretensioned tendons, it is usually assumed that the total force is In post-tensioned members there is friction between the prestressing tendons and the fpES= (Ep/Eci)fcgp (S5.9.5.2.3a-1) Immediate Losses Elastic Shortening of Concrete In pre-tensioned concrete, when the prestress is transferred to concrete, the member shortens and the prestressing steel also shortens in it. 1293 0 obj CSI Software calculates prestress loss according to the friction and anchorage loss parameters specified. 0000005323 00000 n Because elastic shortening in pretension amounts to maximum loss. The frictional force is equal to N, The solution of this is, where To and Tf represent the initial and final cable tensions respectively for a length, The variation in tension in a tendon inside a duct undergoing several changes of <>/ProcSet[/PDF/Text]>>/Rotate 0/Type/Page>> tendon, so that, For the portion of the tendon 23, the initial force is P2, and the final force P3 is given, This process can be repeated for all the changes in curvature along the length of the Where these Determine the elastic shortening loss of a pretensioned prestressed concrete (simply supported L=15m, H=900mm, B=300mm) given that, fpi=1100MPa, f'ci=40MPa, Eps=200GPa, and the total area of the straight profile tendons is 140 sq mm. For a post-tensioned member the change in strain in the tendons just after transfer Prestressing strands are initially tensioned with hydraulic jacks at solid abutments, which causes them to stretch slightly . This effect is small, however, of the order of Thus, for the tendon profile in Fig. Problem 1. 0000005939 00000 n 0000006577 00000 n in prestressed concrete, the shortening of a member that occurs immediately on the application of forces induced by prestressing. r=471 mm. 0000001622 00000 n <<6A04720DC7A5B2110A008034C051FE7F>]/Prev 311131>> <>/Border[0 0 0]/Rect[494.328 609.894 549.0 621.906]/Subtype/Link/Type/Annot>> If (x/rps+kx) < 0.2 then Equation 4.8 may be simplified to, Values of k should be taken from technical literature relating to the particular duct 0000024138 00000 n 0000015740 00000 n 3. Prestressed Concrete calculators give you a list of online Prestressed Concrete calculators. The triangle of forces 0000032109 00000 n tendons tensioned simultaneously, there is no elastic shortening loss, since jacking wo=9.97 kN/m; Ac=4.23105 mm2; Ic=9.361010 mm4; The gradual reduction of this introduced compressive stress in a prestressed member due to various reasons is called losses of prestress. many large bridge decks tendons curve in the horizontal plane as well, and the friction 1296 0 obj the tendon and the deflector. 0000006814 00000 n 0000013123 00000 n Elastic Shortening -Pre-tensioned Members: When the tendons are cut and the prestressing force is transferred to the member, concrete undergoes immediate shortening due to prestress. from both ends, although the prestress force at the centre support is the same in both equal. For pretensioned members, and for post-tensioned members once the ducts have been 7. The forms are stripped and the prestressing strands are released after adequate strength is added to the casting bed. You can unsubscribe at any time. will proceed until the desired prestress force is reached. Elastic Gains Elastic shortening Exceeding stress limit for Precast Top - Negative Moment Envelope condition at Bearing location Expansion joint Export and Import of reactions from Conspan to RCPier. To use this online calculator for Strain in Concrete due to Elastic Shortening, enter Initial strain ( pi) & Residual strain ( po) and hit the calculate button. This is because the area and moment of inertia of the cross-section includes the transformed steel, as specified in Reference 6, Design of Prestressed Concrete Structures, Chapter 5 p. 126-132. 0000014148 00000 n 4.3(a). transferred to the member at one time and that the elastic shortening loss is mcg. Many modern bridges now employ external post-tensioned tendons. 0000013412 00000 n 5 into Eq. Creep of concrete Friction Anchorage slip There will be losses due to sudden changes in temperature. 0000003864 00000 n DESIGN OF PRESTRESSED CONCRETE. After the transfer, this force can be divided into two components as follows: where T=final tensile force in the tendons just after elastic shortening has occurred and s is the loss of prestress times area of steel. 0000052966 00000 n Losses caused by elastic shortening of the prestressed concrete member are also calculated. Loss in prestress = creep strain x Es 4. . 0000049798 00000 n 4.1. f` :&c`.1t:sg`.b`4>SF 0 For the beam in Example 4.1 determine the prestress loss due to friction at the 1298 0 obj The value of cg in Equation 4.4 should reflect the fact that, in general, a member, deflects away from its formwork during tensioning and the stress at any section is elastic shortening 1. Hence there is creep strain in the member. increases), and the loss for the last tendon is zero, so that the average loss is mcg/2. 0000005712 00000 n The tendons can be curved, which makes it suitable for large structures. where k is a profile coefficient with units of rad./m. S5.9.5.2.3a-1. Elastic deformation of concrete: An elastic shortening of the concrete takes place because of the application of pre-stress in concrete. position during concreting. For pretensioned members, when the prestress in the steel is transferred from the bulkheads to the concrete, the force, which was resisted by the bulkheads, is transferred to both the steel and concrete.

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