post tension elongation formula

, as well as the tendon stress at the anchor, and the tendon stress at distance (i.e. Young's Modulus in N/mm2 E. 3. The cables are pulled to 33,000 pounds, resulting in 8 inches of elongation in a 100-foot cable. inspector. cm. The jacking system will result in additional losses due to the seating of the wedges which anchor the post-tensioning strands. In addition to performing structural inspections, a Most suppliers put a stripe on the dial, so the operator only needs to observe the needle hit the stripe to know that the tendon is stressed correctly. The force is then checked by measur-ing strand elongation and comparing this measured value with a theoretical (calculat-ed) value. At their most basic, it's possible to estimate the elongation of a tendon using the formula = PL/AE. What does that mean? Pricing for more information. 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. If the duct were frictionless, then would equal the full length of the beam. Here is how the Total elongation of bar calculation can be explained with given input values -> 545.4545 = (6000000*2)/ (2*11000000). 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). The friction loss consists of two components: curvature and wobble. Advantages of Post Tensioned Floors. Copyright 1998-2022 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. In practice, the precise measurement of in the field should confirm the expected friction loss from theory ( 5%). 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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). 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stream Also Read: Post Tensioning, Methods, Advantages Your email address will not be published. hb```B ce`a02#[B s'( "P}S52s$*+}Q*&Af{=EJyhJYygK[5- %fwEW[K3cqb[>&%Qnb;vTttt400F%\4a0 Allowable Elongation = 93% of Avg. *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. hXmO8+w; The theory behind friction loss in prestressed (post-tensioned) beams is well developed. In general, the vast majority of tendon elongations fall within the 7% tolerance, with only occasional long or short pulls. Strut and Tie Methodology Regarding Shear, 6. such as pouring concrete and post tensioning. The Math / Science. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. Once the tendons have all been stressed, the installer (or inspector) measures how much the tendon stretched with a tape measure. Re-evaluation of elongation measurement, verification of assumption such as draw-in . 1) Casting of concrete. Once the tendon has reached the correct gauge pressure, the operator reverses the pump, seating the wedges in the anchor, and releases the tendon. Step one is to check to make sure the elongation from the shop drawings is accurate. Typical wobble values are rolled into whats called a wobble coefficient, an average deviation measured per foot of tendon. 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). Once the revised elongation report is complete, the engineer may have to additionally re-evaluate his calculations to reflect that there simply isnt as much compression or balanced load in the slab as he designed. In addition to the specified drape, its impossible to keep the tendons perfectly straight. 2.3 may be converted into the engineering stress-strain curve as shown in Fig. the maximum tendon stress) can be found directly for a straight tendon. If a building exceeds 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. A residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. 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. Every contractor, installer, independent inspection company, engineer, and yes even the post-tensioning material fabricator, dreads this like a swift kick in the backside. A 36 deep beam and a 10 deep slab shouldnt have exactly the same elongation. An extensometer is used to determine elongation and tensile modulus. The error is small enough though that this is considered acceptable practice. This allows one measure of strength . This is referred to as "M100" or modulus 100. hbbd```b``>"H .0DIQ0yLe &9`IK{@lm~-l If 1.05 times the calculated elongation is reached before the specified gauge pressure is attained, stop stressing and inform the Engineer. Below is a link to the file: tendon_elongation.xlsx. 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. Get informed, inspired and entertained at ENGINEERING.com. not having to answer to the GC. 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 . 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. The use of floors prestressed by post-tensioning results in a 20% reduction in greenhouse gas emissions compared with traditional reinforced concrete designs. Slope Deflection Method (indeterminate), 2. Insert the values into the equation: Elongation = P * L / (A * E) In the example, multiple ten times five to get fifty and multiple 3.14 times twelve to get 37.68. Login. varies between .05 and .50. These categories are: Service Stress . During post-tensioning, it is usually permitted to stress the tendon temporarily to a maximum of about 80% of the specified tensile strength of the tendon. Choosing the Appropriate Section Shape, 11. $2 The reinforcing strands/ tendons and their specialized end fittings are cast into the center of the slab thickness before the concrete pour. The elongation of this is 150% because the final length is 150% The primary source of tendon curve is the profile specified by the engineer of record. 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). Tensile strain, or the elongation of a bar per unit length, is determined by: For the equations described above we may adequately expressed by Hooke's Law for elastic materials. Depending on the fabrication process, the diameter of the tendon, and the post-tension coating used, this coefficient and the effort required can vary. .? They keep thorough notes showing both the gauge reading and the elongation. P = L = Ae = which is the rod effective net area from AISC. 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. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. measured elongation review". Elongations have been used to assess the forces inside post-tensioned tendons immediately after the post-tensioning operation. As strength increases from the cold work, the difference between yield and tensile strength decreases and quickly reaches a small and relatively constant value. TR 43 is the Indian code used for post-tensioning. Specifications: Post-Tension Concrete Cables. 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. Thus far, we have looked at equations that are well suited for illustrating the theory and concept of prestressing. The stages are shown schematically in the following figures.After anchoring a tendon at one end, the tension is applied at the other end by a jack.The . Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. . Latest news, games, resources, videos and job postings for engineers.job postings for engineers. 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. The equation . 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 Working Stress Design Tables and Examples, 7. In a tensile test, uniform elongation is the percentage the gauge length elongated at peak load relative to the initial gauge length. In general, higher durometer materials have a higher modulus. INSTRUCTIONS: Choose units and enter the following: (L 0) This is the initial length. 7 percent for post-tension construction shall be ascertained and corrected. Make elongation measurements at each stressing location to verify that effective force has been properly achieved. At their most basic, its possible to estimate the elongation of a tendon using the formula = PL/AE. Axial/Bending composite (indeterminate), 7. For ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation and 1mm/min for measuring modulus. Tension & Elongation of Elastic Fabrics (Constant-Rate-of-Extension Type Tensile Testing Machine) is determined by standard method ASTM D4964. For a slab-on-grade job, this can be as simple as a spreadsheet that takes tendon slab length and multiplies it by 0.08; for an elevated deck project, every tendon has a listed elongation which is calculated by the detailer and approved by the engineer. and head elongation issues off while theyre still problems on paper, rather than cast in concrete. A threshold inspector is a certified building inspector who %%EOF . After initially tensioning the strand to re-move slack, an operator applies the final prestressing force, which is read from a hy-draulic gauge mounted on the tensioning jack. *Eng-Tips's functionality depends on members receiving e-mail. Wobble friction losses occur from unintended angle changes, which essentially depends on an empirical wobble coefficient . As anyone familiar with my post-tension elevator speech will know, the key element of post-tensioning is pulling on the tendons. Thats a good question, and the answer is somewhat in-depth. P*f`yA(k.1U2debcnb:4ENMgL3Lc8 #i A@wsfg`010 Q ` n Change in length = Strain X Original length Change in length = 0.000354 X 3000 = 1.062 mm Now every thing is known, put values in percentage elongation formula and find the percentage elongation as a result of pulling force; Percentage Elongation = (1.062 x 100)/ 3000 Percentage Elongation = 0.0345% About The Author From equilibrium of the above force triangle. It turns out that underestimating is aggressive, i.e. The circular pocket at the edge is grouted with corrosion inhibitor. When the pump reverses, two things happen: the tendon starts to slide back into the concrete, and the ram deploys a tool called the seating plunger. The table below shows the procedure for determining friction losses. 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. The program is divided into three separate screens, which correspond to the three major areas of concern in the design of a post-tensioned member. threshold inspector will oversee certain activities during building final length of 1.5m. (66)2-985-2357 , (66)88-8835646, (66)85-100-7766, (66)86. the calculated elongation for each tendon length was based on a seating loss of 0.25 in. These numbers are recorded and reported to the engineer. We have received your request and will respond promptly. Related Related Related However, the shortening due to anchor set is in fact a known value, based on the type of jack used. The post-tensioning process works as follows: Pulled to force P, the tendon exerts a uniform uplift (PT) shown in part (b). In reality, would turn out to be less than the full length. Statically Indeterminate Structure (torsion), 12. It has been a while since I did that, but I recall values between 28e6 and 29e6 psi for PT strand. varies between .05 and .50. My post above related to post-tension slab on grade, not elevated slabs. Check out our VIDEO for the basics in stressing post tensioning tendons. PX8/e|mHmp'mRnux3Lp`B:%Bpzo[Ks{' JTB sZ '%7Lre@LZIPA sb\,A?.VLY30sp#!a #?GNtO;@q4bve_f4]G5Y'E'AY)q4,/.g>b9vXTw$q-F!TapwVFw$[0iWdO9S)ii1y|U9fAWLrKgD#4G9rZebDFjWO ]@5Q0&9.Ts2>=d[U9;:9iiOg%%?i,{p-K@AMQ/Z`8D%T N,{T@CrPJ] . Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. Freyssinet prestressing systems can be used in floors, foundation slabs and building transfer structures, as well as in industrial slabbing systems. How do you calculate post tension elongation? While this is true in theory and works well enough for slab-on-grade applications there are four factors that complicate the calculation. We have been asked to provide PT elongation calcs. Material suppliers watch their elongation reports carefully and adjust this value as they see fit. 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. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); 5335 W. 48th Ave. Suite 300Denver, CO 80212. This Manual includes state-of-the-art information relative to materials, post-tensioning systems, construction practices and grouting of post-tensioning tendons for bridges. Keep records of elongation and of tension applied to each tendon and submit four copies to the COR promptly upon the completion of post-tensioning of each member. Statically Indeterminate Structure (axial), 5. Post and beam homes is around $135 per square foot. hired by the developers and not the general contractor, therefore Temporary overstressing of the tendon followed by release and subsequent re-stressing will also reduce friction losses. Click Here to join Eng-Tips and talk with other members! Elongation Tolerance ACI Structural Journal - post-tensioned concrete 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. hey, thanks guys, I will look in to them. Post-tensioned tendons, tendons, post-tensioning steel . This usually comes out to be only a couple of percentage points, but must be checked on a case-by-case basis . The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. Post-Tensioning Friction & Anchor Set Losses, 6. It is sufficiently accurate to calculate the tendon force only at the ends of each parabolic segment (for a draped tendon in a continuous beam) and then assume that the force varies linearly between these points. . were evaluated. Stage Elongation: When calculating the first stage elongation, it is common practice to break the force coefficient diagram into two parts, identified as areas A and B in the above diagram. But what about . varies between .0001 and .002 per foot. For materials under tension, strain (e) is proportional to applied stress s. Where: E = Young's Modulus (lbf/in. This method consists of determining the extension at maximum force on the force-extension curve obtained with an extensometer. can be considered a form of quality control seeing that the are SNP POST TENSION CO.,LTD.110/18 Moo 2 Mahasawat, Bangkruai, Nonthaburi, Thailand 11130 Tel. Both of these force a pair of steel wedges into the anchor cavity, and teeth machined into the wedges clamp onto the strand. ASME PCC-1. 4) Applying tension to the tendons. We always indicate elongations on the drawings. Structural engineering general discussion Forum, http://files.engineering.com/getfile.aspx?folder=3bf254a4-e593-4113-a347-27, Low-Volume Rapid Injection Molding With 3D Printed Molds, Industry Perspective: Education and Metal 3D Printing. 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. Suppliers monitor this number as well, making sure that actual tendon placement is staying within the parameters they assumed. Modified Elongation (Me) = e x A x E / MA x ME in "mm". 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. a second trial could be performed. Suppliers monitor this value as well usually, its 1/4, but for a very short tendon, it might go as high as 3/8. 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. No real structural worthwhile, the DOT just wants them pulled together. The load- elongation curve of Fig. Keywords: elongation variation, post-tensioning, tendon, tension, friction, wobble, elongation limits. The equation for calculating tendon elongations is shown as follows: PL = AE When jacking to 202.5 ksi, and using a strand nominal area of 0.153 in Elongation and percent elongation at break. This results in larger, column-free floor areas which greatly increase the flexibility of use . Max. A beam is jacked to 80% , released to 60% , rejacked to 70% and then anchored. Threshold inspectors This would seem to indicate that every tendon of a specified length has the same elongation. Our long history of elevated post-tension decks helps us evaluate the suppliers calculations before tendons are shipped . To visualize the idea of friction loss, imagine if at midspan, there was so much friction in the duct, that the latter half of the span had no prestressing force whatsoever, as shown below. Although there are exceptions, percent elongation . Already a Member? Please let us know here why this post is inappropriate. The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. After anchoring, the stress in the tendon at anchorage is usually limited to 70%. 5. 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. Further, these. 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): 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 (%). As the extension, so the force Robert Hooke. Type B in Residential Design, Interpreting Truss Shop Drawing Dimensions, Construction Types V-A and V-B in the International Building Code, Electrical Panel Locations- A guide for placement, Virtual Reality Modeling for Client Walk-throughs, RAM Structural System: Integrated Gravity & Lateral Design, The Exciting Future of Bridge Inspections. Find: ratio throughout the tendon, ignoring anchor set, Phenomenological and Micromechanical Models, 5. Elongation in mm e. 4. A material with a higher percentage is a more ductile material, while a material with a lower percentage will be more brittle. . where: N = number of identical prestressing tendons. usually funding the project is required by law to hire a threshold Make elongation measurements at each stressing location to . I think that elongations should be measured first, not put on the drawings so the PT guy thinks he has to match them. 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. While it is an integral part of all post-tensioning operations, its results can be misun-derstood, leading to disagreements, finger-pointing, and Modified Area of Strand (as per TC) in mm2 MA. the initial dimension. By joining you are opting in to receive e-mail. Close this window and log in. It is related to the ability of a plastic specimen to resist changes of shape without cracking. Elongation = 1.07 x (Avg.El.) Every post-tension project has a list of elongations. of the initial length. . Post-tensioning Pretensioning Post-Tensioning Steel tendons are stressed after the concrete has been placed and gained sufficient strength at the construction Bonded PT Unbonded PT site NPCA 1 fThe Precast Show 2014 Pre-Tensioning: Pre-Tensioning: Precast elements are transported to the site. The "elongation" specification that comes with ropes is usually a static elongation value, something like an 80kgf load. 0 . is the friction loss, and since we know that friction is , we can say that: where the term is associated with wobble. 2) s = stress (psi) The influence of friction losses is reduced if the member is stressed from both ends. For example, if the gauge length at peak load measures 61 mm and the initial gauge length was 50mm, uniform elongation is (61-50)/50 = 22%. The gauge length shall be indicated in the test report. How do you calculate elongation in post tensioning. The formula for calculating the average tensile force under the anchor is: PP=P (1-e- (KX+))/ (KX+) Among them, P is the tensile force at the tensile end of the prestressed anchor steel. Note the . 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. Moment Distribution Method (indeterminate), 8. The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. Elongation at Break, also known as fracture strain or tensile elongation at break, is the ratio between increased length and initial length after breakage of the tested specimen at a controlled temperature. So: what is an elongation report, and why are they important? Coefficient of Angular Friction. Modulus is the force at a specific elongation value, ie 100% or 300% elongation. Thus, the ratio can be said to be an overestimate of the relaxation (shortening) of the tendon within the distance , due to anchor set. 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. A variety of applications. The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field.

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