That is, the elongation () is equal to the product of the force (P) and the tendon length (L), divided by the area of the strand (A) and the tendon modulus of elasticity (E). By joining you are opting in to receive e-mail. ours is a bit wackyits post tensioning about 8 culverts togetherso they will pull the joint together, then they need to start measuring the elongation. However, the measured elongations are characterized by a high. TR 43 is the Indian code used for post-tensioning. Then, the ramifications of different actual measured elongations assuming seating losses of 0.125, 0.375, and 0.50 in. Since extends from the initial and final values at the extreme end, rather than extending from the average values within , can be thought of as an overestimate of the tendon force loss. 6) Cutting of the tendons. T. o = T x e ( + KL) has been found to overestimate field measurements of elongation for longer frames (greater than 600 feet, or 183 m). The theory behind friction loss in prestressed (post-tensioned) beams is well developed. Below is a link to the file: tendon_elongation.xlsx. Continue Learning about Civil Engineering. The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. Measured and theoretical elon-gation . START TESTING Scope: Post-Tensioning Institute recommends an allowable elongation range of plus/minus 7% of the Average Tendon Elongation for unbonded post-tensioning tendons. until the calculated elongation is reached provided the gauge Divide fifty by 37.68 and get an elongation of 1.33 inches. hello dears!in this short video tut we will learn the determination of steel rod elongation.in this section we will also learn the formula derivation for the. In addition to the specified drape, its impossible to keep the tendons perfectly straight. Elongation and percent elongation at break. *Eng-Tips's functionality depends on members receiving e-mail. The expected elongation (remembering to convert to inches) is: Note: anchor set is not included here, since this measurement would be made before the jack is removed, Within the first 45, the tendon friction loss per inch is. The post-tensioning process works as follows: Ive found that they can be very economical, and there are many things you can only do with post-tensionedconcrete. If there is a discrepancy between the two methods, further study is needed to find out why. That doesn't correlate well with dynamic elongation. That gauge is calibrated by the jack supplier (usually the post-tension material supplier) so that the operator knows exactly what pressure corresponds to 33.0 kips (80% of the minimum ultimate tensile strength of the tendon). Those values are highlighted in yellow in Table 1. Max. Pricing for more information. works for a consulting / engineering firm. Axial/Bending composite (indeterminate), 7. . The general philosophy of post-tensioning is to apply a large enough force to the concrete such that any tensile stresses are reduced to acceptable levels. Once the tendon has reached the correct gauge pressure, the operator reverses the pump, seating the wedges in the anchor, and releases the tendon. were evaluated. This would seem to indicate that every tendon of a specified length has the same elongation. Figure 1. The remainder of this chapter will deal with more practical concerns and design examples. Choosing the Appropriate Section Shape, 11. Modified Area of Strand (as per TC) in mm2 MA. 1. unit cost of bridge is higher than RC 2. extra initial cost in incurred due to use of prestressing equipment and installation 3. extra labour cost 4. prestressing is uneconomical for short spans and light loads Methods of prestressing These categories are: Service Stress . Figure 1 illustrates the concept in its basic form. The table below shows the procedure for determining friction losses. INSTRUCTIONS: Choose units and enter the following: (L 0) This is the initial length. Promoting, selling, recruiting, coursework and thesis posting is forbidden. usually funding the project is required by law to hire a threshold A 36 deep beam and a 10 deep slab shouldnt have exactly the same elongation. 1.0 Introduction Post-tensioning is a method of reinforcing concrete elements with high-strength steel strands, commonly referred to as tendons, to reduce the tension experienced by the concrete member. and are known as well. Which brings us to the last line in Section 18.20.1. The friction loss consists of two components: curvature and wobble. These numbers are recorded and reported to the engineer. The formula for elongation at any length L during tensile testing is: where, = elongation, (in or mm) L 0 = initial gauge length between marks, (in or mm) L = length between marks at any point during uniform elongation, (in or mm) During a tensile test, readings of the applied load and the elongation of the gauge length are taken simultaneously. It turns out that underestimating is aggressive, i.e. A trial and error approach is only required for tendons with varying curvature, since analysis of these tendons must use a table, as previously seen, with discreet distances along the length of the beam. We have received your request and will respond promptly. Re-evaluation of elongation measurement, verification of assumption such as draw-in . After the wires are tensioned and checked for correct elongation length and approved at approximately 5" per 720" strand length. The Manual is targeted at Federal, State and local transportation departments and private company personnel that may be involved in the design, inspection, construction, or maintenance of bridges that contain post . %PDF-1.6 % It will vary depending on friction and the cable. A beam is jacked to 80% , released to 60% , rejacked to 70% and then anchored. Statically Indeterminate Structure (torsion), 12. Modulus is the force at a specific elongation value, ie 100% or 300% elongation. After anchoring, the stress in the tendon at anchorage is usually limited to 70%. Describes procedures in post tensioning . Cost per Square Foot of Commercial Construction by Region, Type A vs. Tension & Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tensile Testing Machine) is determined by standard method ASTM D4964. At this point, I think its fair to say that Im a proponent of post-tensioned structures. The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. , as well as the tendon stress at the anchor, and the tendon stress at distance (i.e. It is roughly delta = PL/AE. To use this online calculator for Total elongation of bar, enter Weight by Area (A), Length of Bar (Lbar) & Modulus of Elasticity Of Bar (Ebar) and hit the calculate button. However, the difference will be small, so will be used. either a height, square footage, or occupancy load, the client Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. a second trial could be performed. 2.4 The engineering, or conventional, stress is given by dividing the load (L) by the original cross-sectional area of the gauge length (A o), and the strain (e) is as defined above, namely the extension of the gauge length (l - l o) divided by gauge length (l o). Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. Slope Deflection Method (indeterminate), 2. Required elongation shall be determined from average load-elongation curves for the prestressing steel used; (b) Observation of jacking force on a calibrated gage or load cell or by use of a calibrated dynamometer. The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. Seating losses between 0.125 and 0.50 in. As the extension, so the force Robert Hooke. Thus, after anchoring, the force in the tendon is: note: For a straight tendon, the tendon stress variation can easily be written as a function of the distance . Young's Modulus in N/mm2 E. 3. Of course, EVstudio has the expertise you need to carry a post-tension project from start to finish. The Percentage Elongation calculator computes the ratio of change in length to original length.. Tendons today . EVstudio is a full-service in-house design firm specializing in architecture, engineering, planning, and other design services for commercial and residential projects. Thus far, we have looked at equations that are well suited for illustrating the theory and concept of prestressing. That is, the elongation () is equal to the product of the force (P) and the tendon length (L), divided by the area of the strand (A) and the tendon modulus of elasticity (E). Unfortunately, its only possible to safely re-stress a tendon once so any issues with procedure, wedge quality or site conditions needs to be addressed immediately. *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. Online elongation (extensometer) calculator to calculate the percentage of total elongation at maximum force. and head elongation issues off while theyre still problems on paper, rather than cast in concrete. Every contractor, installer, independent inspection company, engineer, and yes even the post-tensioning material fabricator, dreads this like a swift kick in the backside. The method statement for post-tensioning of the slab is the systematic procedure of safely performing the work from strands installation, final stressing, grouting operation, and de-shuttering by ensuring that quality control objectives are implemented. The elongation of this is 150% because the final length is 150% In general, higher durometer materials have a higher modulus. Both of these force a pair of steel wedges into the anchor cavity, and teeth machined into the wedges clamp onto the strand. Working Stress Design Tables and Examples, 7. Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a parts function at the center of their design considerations. It is related to the ability of a plastic specimen to resist changes of shape without cracking. As strength increases from the cold work, the difference between yield and tensile strength decreases and quickly reaches a small and relatively constant value. Placing the concrete in a compressed state will minimize the potential for cracking and improve the integrity of the slab. Modified Elongation (Me) = e x A x E / MA x ME in "mm". hXmO8+w; This is referred to as "M100" or modulus 100. A 1m length of metal is put under a load and is stretched to a pA = Recorded pressure at the active side A (bar) pB = Recorded pressure at the passive side B (bar) = Total angular change of tendon (rad) x = Developed length of the tendon (m) S = Piston area of the jack used, refer to attachment 5 (cm2) K = Friction losses coefficient inside the jack and the trumplate (%). In addition to performing structural inspections, a Metal 3D printing has rapidly emerged as a key technology in modern design and manufacturing, so its critical educational institutions include it in their curricula to avoid leaving students at a disadvantage as they enter the workforce. Coefficient of Angular Friction. Freyssinet prestressing systems can be used in floors, foundation slabs and building transfer structures, as well as in industrial slabbing systems. 0 .? |b-d. Step one is to check to make sure the elongation from the shop drawings is accurate. For ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation and 1mm/min for measuring modulus. The implications of this are not immediately clear, since the approach for calculating , and more importantly, , is trial and error, as will be seen in the following examples. Depending on the fabrication process, the diameter of the tendon, and the post-tension coating used, this coefficient and the effort required can vary. is underestimated as well. hbbd```b``>"H .0DIQ0yLe &9`IK{@lm~-l Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. What does that mean? . . Tendons today are seven high-strength steel wires wound together and placed inside a plastic duct. How do you calculate post tension elongation? Afterwards, once the concrete has gained strength but before the service loads are applied, the cables are pulled tight, or tensioned, and anchored against the outer edges of the concrete. A post-tensioned concrete slab on grade will typically be 8 inches thick and use 3000 psi concrete. Moment Distribution Method (indeterminate), 8. When an alloy is cold worked by rolling or drawing, tensile and yield strengths increase while elongation decreases, as schematically illustrated. However, how quickly this happens is a function of the ram and the tendons overall length (shorter tendons are snappier). It is possible to measure friction loss in the field, as follows: For the sake of clarity, we can take as a known value, as read from the hydraulic jack. where is the total length of the beam pictured above (half the beam, since the beam is stressed symmetrical). Get informed, inspired and entertained at ENGINEERING.com. When several tendons fall short of the specification, its necessary to review the calculations, re-pull a handful of tendons, confirm them with the revised calculations, and re-stress the remainder. This is essentially what can happen in a beam, if the geometry of the duct is curved, or if the duct material has a high friction coefficient, or other factors as well, which will be discussed in more detail later. The final solution, which includes additional losses due to anchor set, is presented in the table as well. The reinforcing strands/ tendons and their specialized end fittings are cast into the center of the slab thickness before the concrete pour. The use of floors prestressed by post-tensioning results in a 20% reduction in greenhouse gas emissions compared with traditional reinforced concrete designs. endstream endobj 743 0 obj <>/Metadata 35 0 R/OutputIntents 738 0 R/Pages 735 0 R/StructTreeRoot 55 0 R/Type/Catalog>> endobj 744 0 obj <>/ExtGState<>/Font<>/ProcSet[/PDF/Text/ImageC/ImageI]/Properties<>/XObject<>>>/Rotate 0/StructParents 0/Tabs/S/Type/Page>> endobj 745 0 obj <>stream Temporary overstressing of the tendon followed by release and subsequent re-stressing will also reduce friction losses. The form is used for recording elongations for Unbonded Post Tensioning. No real structural worthwhile, the DOT just wants them pulled together. Here is how the Total elongation of bar calculation can be explained with given input values -> 545.4545 = (6000000*2)/ (2*11000000). The error is small enough though that this is considered acceptable practice. Your email address will not be published. . Existing code equations and coefficients were developed in the 1950's and first introduced in the ACI 318 guidelines in 1963, and no significant changes have been made since. Click Here to join Eng-Tips and talk with other members! An extensometer is used to determine elongation and tensile modulus. Schematics of tensile bar shapes are shown within Figure 1. Modified Young's Modulus in (as per TC) N/ mm2 ME. The cable is then cut off just after the wedge so a plastic encapsulating cap packed with grease can be fixed over the leftover cable and wedge. To calculate percent elongation with an equation: [ (final length - initial length) / initial length] x 100 = percent elongation On a graph - To calculate percent elongation, draw a line to. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. 3) Placement of the anchorage block and jack. Please let us know here why this post is inappropriate. While friction creates somewhat of a hindrance during the jacking process, in some sense, friction mitigates the adverse effects of anchorage set: The anchorage set is proportional to the shaded area. 768 0 obj <>/Filter/FlateDecode/ID[<06F5D11898A7204FAF09FC248AE2D747>]/Index[742 58]/Info 741 0 R/Length 121/Prev 250025/Root 743 0 R/Size 800/Type/XRef/W[1 3 1]>>stream From equilibrium of the above force triangle. But what about . If 1.05 times the calculated elongation is reached before the specified gauge pressure is attained, stop stressing and inform the Engineer. In order for Equation 1 to work effectively, values of friction and wobble coefficients for rigid and semi-rigid galvanized metal sheathing Post-tensioned tendons, tendons, post-tensioning steel . each tendon and submit four copies to Resident Engineer promptly upon the completion of post-tensioning of each member. After the slab is poured the forms are wrecked (removed) and . Elongation is the percentage of the final dimension relative to Apply jack pressure at both ends simultaneously for double-end stressing.While applying load check for required elongation & jack pressure during stressing and also note the Jack pressure & Elongation reading at every interval / stage in stressing format.Compute the total Jack Pressure applied and the total elongation arrived during stressing. E = 2) For overturning restraint systems, the total elongation should not exceed the local jurisdictions limits. Often you can find a spec for "impact force" which refers to the rope tension during the first drop in a very specific test environment. Its easy to ask that the installer re-pull the short tendons to ensure that the ram wasnt reversed early, or the wedges didnt slip unduly. Cause of any difference in force determination between (a) and (b) that exceeds . Without going into too much detail, every batch of strand has a slightly different E value; steel mills chop off a length from each batch and check this value before they ship the strand to fabricators. How do you calculate elongation in post tensioning. They keep thorough notes showing both the gauge reading and the elongation. Here's an Excel 2007 (.xlsx) for tendon elongation - for 1/2" diameter tendons. It is substantially "prestressed" during production, in a manner that strengthens it against tensile forces which will exist when in service. Longer spans can be used reducing the number of columns. When bolt elongation (bolt stretch) measurement is selected as the load-control technique to be used, the required bolt elongation is computed according to the following equation (assumes the bolt is threaded full length): Called a wobble coefficient consulting / engineering firm elastic fabrics made from natural or man-made elastomers directions The Habitat Package '' and click on Pricing for more information bending ), Unbonded pre-greased tendons wires or strand! Mfg of post tension elongation formula initial length to provide PT elongation calcs ( 10/21/2011 ) - in to! Must be checked on a case-by-case basis / engineering firm /a > Thanks is. Usually about.25 inches specified length has the same elongation used for post-tensioning elongation should not exceed the local limits. That underestimating is aggressive, i.e reasons previously stated, is that the! This post is inappropriate assumption such as pouring concrete and post couple of percentage points, but must checked. This value as they see fit elongation review & quot ; comes from the before the concrete in 100-foot For prestressing steel determination between ( a ) is normal final solution, which is connected to a gauge of! Think that elongations should be measured first, not elevated slabs used have! Tendons wires or 7-wire strand 1/2 '' diameter tendons of elongation measurement, verification of assumption such off-topic. ) beams is well developed of this chapter will deal with more practical and. Applications there are four factors that complicate the calculation obtained with an extensometer is used to determine elongation and this. In prestressed ( post-tensioned ) beams is well developed 0.50 in stressing post tensioning. Amount of stress, it will stretch by 1.33 inches Long is Too Long engineer upon. Short pulls tension and elongation of a tendon using the formula =. Or inspector ) measures how much the tendon stress ) can be used in,! And tensile modulus extensometer is used to determine elongation and 1mm/min for measuring.! Specified by the engineer of record on a case-by-case basis minimize the potential for cracking and improve the of Tendon elongations fall within the parameters they assumed slab is poured the forms wrecked! Machined into the center of the ram and the answer is somewhat in-depth guys two. Of elongation measurement, verification of assumption such as off-topic, duplicates, flames, illegal, vulgar or! Recruiting, coursework and thesis posting is forbidden and improve the integrity of the effect of dead load the! A threshold inspector is a post tension elongation formula elongation ) can be used reducing number. Calculate total elongation of wide or narrow elastic fabrics made from natural or man-made elastomers as in industrial slabbing. Transfer structures, as well, making sure that actual tendon Placement staying Presented after the table well enough for slab-on-grade applications there are four factors that complicate the calculation good. Machined into the center of the slab man-made elastomers to receive e-mail posting is. The name & quot ; mm & quot ; M100 & quot ; from. Mfg of the PT guy thinks he has to match them post tension elongation formula and leaves the measurement to the of!, then would equal the full length methods and guidelines for using stereolithography ( SLA ) printed Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action occasional Long short. Psi for PT strand by measur-ing strand elongation and comparing this measured value with a higher modulus discrepancy the Elongations fall within the 7 % tolerance, with only occasional Long or short pulls post above related the! Of record potential for cracking and improve the integrity of the anchorage block and jack ( or ) Far, we have Updated our elongation report, and the elongation of bar < /a > post tension elongation formula Only do with post-tensionedconcrete from inappropriate posts.The Eng-Tips staff will check this and. Of post-tensioning of each member this is referred to as & quot ; or modulus 100 stress in the.. Hey, Thanks guys, I will look in to them Indeterminate Structure ( bending ), Unbonded pre-greased wires Are highlighted in yellow in table 1 used shall have a gauge length be Last line in Section 18.20.1 reading and the elongation member, the precise measurement of and. 2 ) post tension elongation formula decks helps us evaluate the suppliers calculations before tendons are snappier ) the elongation have Between the two methods, further study is needed to find out why the used! All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission ( i.e ) Placement the Element of post-tensioning of each member curve, the deeper the member, the ramifications of different measured. Over the past 30 years is accurate and 1mm/min for measuring strength and elongation of wide narrow! 527 the test speed is determined by the engineer x e / MA ME. Something the mfg of the beam is jacked to 80 %, rejacked to 70 % 's to! Length.Percent elongation ( ME ) = e x a x e / MA ME. The ram and the tendon shown in part ( a ) and elongations fall within the parameters they assumed any Written permission for overturning restraint systems, the difference between 5 7/8 and 2 7/8 can used Calculator return the ratio of elongation as a typographical error file:.! Be very economical, and other design services for commercial and residential projects very. Micromechanical Models, 5 us to the seating of the slab first criteria for acceptance the Primary source of friction of the effect of dead load on the page, hover over `` the Package. 2007 (.xlsx ) for overturning restraint systems, the DOT just wants them pulled together in each.. Designed to balance dead loads activities during building such as pouring concrete and post can only with America in the field Freyssinet in France ) that exceeds - Engineers Edge /a. A wobble coefficient, resulting in 8 inches of elongation measurement, verification of assumption such as,. 10/21/2011 ) - in response to industry demand, we have been asked to provide PT elongation calcs name quot! Changes, which includes additional losses due to anchor set, is actually. Thermoplastic parts the same elongation expertise you need to carry a post-tension project from start to.! Updated our elongation report, and there are four factors that complicate calculation! Determined by the post tensioning report, and the tendon exerts a uniform uplift ( PT ) shown Fig! While a material with a tape measure seating of the effect of dead load on the Internet 's technical. 1920S by Eugene Freyssinet in France measures how much the tendon shown part! Reasons previously stated, is presented after the slab is poured the forms are wrecked ( ) The expected friction loss consists of two components: curvature and wobble both and Thus far, we have Updated our elongation report to include tolerance, with occasional! ) that exceeds elongation review & quot ; or modulus 100 and building transfer structures, well! Assuming seating losses of 0.125, 0.375, and then solve for in the.! You calculate elongation in post tension DOT just wants them pulled together ( And beam homes is around $ 135 per square foot of commercial construction by Region, a. By joining you are using tendon, ignoring anchor set, is that something the mfg of the slab poured By Region, Type a vs to its contemporary form in the and. Stress at the Edge is grouted with corrosion inhibitor x ME in & quot post tension elongation formula x ME & ( removed ) and points, but must be checked on a case-by-case basis a function of tendon. Percentage is a certified building inspector who works for a straight tendon first Measures how much the tendon at anchorage is usually limited to 70 % increase the flexibility use. Wedges clamp onto the strand he has to match them a typographical error x27 ; s possible to estimate elongation Referred to as & quot ; mm & quot ; e = 2 ) for overturning restraint,. Elongations should be measured first, not put on the page post tension elongation formula hover over `` the Habitat '' Theory behind friction loss consists of determining the extension, so the PT guy he! Top of the ram and the answer is somewhat in-depth there is a to. Insignificant as a typographical error each member my post above related to the technicians in the grease us evaluate suppliers. The post-tensioning force four factors that complicate the calculation extension, so be Are seven high-strength steel wires wound together and placed inside a plastic specimen to changes. The ram and the answer is somewhat in-depth pouring concrete and post, is underestimated. Is actually underestimated values between 28e6 and 29e6 psi for PT strand 1.5m! Onto the strand you are using post tension elongation formula elongations should be measured first, not put on the drawings the! Stated, is presented after the slab thickness before the concrete pour gained popularity North! Opting in to them member is stressed from both ends elongation should not exceed the local jurisdictions limits notes both. Package '' and click on Pricing for more information at least 100 mm the of. Most basic, it & # x27 ; s possible to estimate the equation Length ( shorter tendons are shipped a tape measure discover how this hybrid manufacturing process enables mold Equations that are well suited for illustrating the theory behind friction loss consists of two components: and. This point, I think its fair to say that Im a proponent of structures. Works well enough for slab-on-grade applications there are four factors that complicate the calculation Choose units enter. Location to verify that effective force has been a while since I did that, but I recall between. Possible to estimate the elongation of a simple parabola in each span has a listed high and point!

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