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. If 1.05 times the calculated elongation is reached before the specified gauge pressure is attained, stop stressing and inform the Engineer. endstream endobj startxref |b-d. *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. 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. 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. 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. As tendons curve, the steel strand which is fairly stiff moves around in the grease. Post-tension cables are steel, flexible cables made from several strands of steel wire intertwined with each other in order to form a thicker steel "wire" which we call the Post-Tension cable. Each span has a listed high and low point designed to balance dead loads. each tendon and submit four copies to Resident Engineer promptly upon the completion of post-tensioning of each member. can be considered a form of quality control seeing that the are Elongation in mm e. 4. The formula for percent elongation is: This is referred to as "M100" or modulus 100. The error is small enough though that this is considered acceptable practice. 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). Schematics of tensile bar shapes are shown within Figure 1. In order for Equation 1 to work effectively, values of friction and wobble coefficients for rigid and semi-rigid galvanized metal sheathing While a properly-placed tendon will never have kinks or other sharp bends, this movement does increase the amount of effort required to stretch the tendon. 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. the calculated elongation for each tendon length was based on a seating loss of 0.25 in. The jacking system will result in additional losses due to the seating of the wedges which anchor the post-tensioning strands. 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. 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). Also Read: Post Tensioning, Methods, Advantages 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. Post-tensioned tendons, tendons, post-tensioning steel . However, the difference will be small, so will be used. If there is a discrepancy between the two methods, further study is needed to find out why. Contribution of post-tensioning in the reduction of the effect of dead load on the member. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. Although there are exceptions, percent elongation . . Working Stress Design Tables and Examples, 7. EVstudio is a full-service in-house design firm specializing in architecture, engineering, planning, and other design services for commercial and residential projects. Thanks. 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 . In the early fifties, post-tensioning systems for the prestressing of concrete were developed by specialists, such as VSL in Switzerland. This so-called anchorage set is usually about .25 inches. We can measure , say with a tape measure, and then solve for from the above equation. However, theres one point that I think all structural engineers agree on: while post-tensioning is a great tool to have available, reviewing the elongation reports is a pain. Which brings us to the last line in Section 18.20.1. 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. That doesn't correlate well with dynamic elongation. Those values are highlighted in yellow in Table 1. This usually comes out to be only a couple of percentage points, but must be checked on a case-by-case basis . When an alloy is cold worked by rolling or drawing, tensile and yield strengths increase while elongation decreases, as schematically illustrated. . The procedure for determining anchor set losses is presented after the table. For ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation and 1mm/min for measuring modulus. This Manual includes state-of-the-art information relative to materials, post-tensioning systems, construction practices and grouting of post-tensioning tendons for bridges. Elongation Tolerance ACI Structural Journal - post-tensioned concrete Both of these force a pair of steel wedges into the anchor cavity, and teeth machined into the wedges clamp onto the strand. 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. 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. The influence of friction losses is reduced if the member is stressed from both ends. It will vary depending on friction and the cable. After the slab is poured the forms are wrecked (removed) and . 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. 3) Placement of the anchorage block and jack. You can get 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 Measured and theoretical elon-gation . START TESTING Scope: Our long history of elevated post-tension decks helps us evaluate the suppliers calculations before tendons are shipped . Slope Deflection Method (indeterminate), 2. Specifications: Post-Tension Concrete Cables. The loss due to elastic shortening in post-tensioned members is computed as follows: fpES = N - 1 Ep fcgp (5.9.5.2.3b-1) 2N Eci. This form is for Inspectors and Installers certified by the Post Tensioning Institute . 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. were evaluated. My post above related to post-tension slab on grade, not elevated slabs. 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. For materials under tension, strain (e) is proportional to applied stress s. Where: E = Young's Modulus (lbf/in. The final solution, which includes additional losses due to anchor set, is presented in the table as well. Then, the ramifications of different actual measured elongations assuming seating losses of 0.125, 0.375, and 0.50 in. 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 force is then checked by measur-ing strand elongation and comparing this measured value with a theoretical (calculat-ed) value. Post-tension tendons are stressed using a hydraulic ram, which is connected to a gauge. The theory behind friction loss in prestressed (post-tensioned) beams is well developed. 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. So: what is an elongation report, and why are they important? is underestimated as well. I hope you find this information useful. The name "Post-Tension" comes from the . What does that mean? Fastener and Screw / Bolt Design, Formula & Calculations . Ive found that they can be very economical, and there are many things you can only do with post-tensionedconcrete. After the wires are tensioned and checked for correct elongation length and approved at approximately 5" per 720" strand length. 2.3 may be converted into the engineering stress-strain curve as shown in Fig. 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). It is substantially "prestressed" during production, in a manner that strengthens it against tensile forces which will exist when in service. Divide fifty by 37.68 and get an elongation of 1.33 inches. Step one is to check to make sure the elongation from the shop drawings is accurate. It is related to the ability of a plastic specimen to resist changes of shape without cracking. hired by the developers and not the general contractor, therefore Tendon Drape. New Tennis Court Construction: Post-tension cable lay-over. where is the total length of the beam pictured above (half the beam, since the beam is stressed symmetrical). Material suppliers watch their elongation reports carefully and adjust this value as they see fit. 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. 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. Typically, the deeper the member, the higher the losses. 5. Young's Modulus in N/mm2 E. 3. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. By joining you are opting in to receive e-mail. However, the shortening due to anchor set is in fact a known value, based on the type of jack used. Already a Member? 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. At their most basic, its possible to estimate the elongation of a tendon using the formula = PL/AE. Modified Young's Modulus in (as per TC) N/ mm2 ME. Post-tensioning was first patented by P.H. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. No real structural worthwhile, the DOT just wants them pulled together. not having to answer to the GC. Already a member? Elongation = 1.07 x (Avg.El.) Of course, EVstudio has the expertise you need to carry a post-tension project from start to finish. A spacing of 3 to 4 feet on center in a crossed grid pattern is typically used on most residential post tensioned slabs in the San Antonio area. *Eng-Tips's functionality depends on members receiving e-mail. 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. In reality, would turn out to be less than the full length. %PDF-1.6 % Related Related Related A 36 deep beam and a 10 deep slab shouldnt have exactly the same elongation. inspector. Once the tendon has reached the correct gauge pressure, the operator reverses the pump, seating the wedges in the anchor, and releases the tendon. But what about . Statically Indeterminate Structure (torsion), 12. If the duct were frictionless, then would equal the full length of the beam. final length of 1.5m. However, the measured elongations are characterized by a high. 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. 7 percent for post-tension construction shall be ascertained and corrected. File sharing on the ENG-TIPS Forums is outsourced to ENGINEERING.com. and are known as well. This spreadsheet program provides for the design and analysis of post-tensioned concrete one-way beam and slab systems and two-way flat plate slab systems. The form is used for recording elongations for Unbonded Post Tensioning. : 3-5 This compression is produced by the tensioning of high-strength "tendons" located within or adjacent to the concrete and is done to improve the performance of the concrete in service. Tendons today . 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] depends on the size and material of the beam and post! These numbers are recorded and reported to the engineer. P*f`yA(k.1U2debcnb:4ENMgL3Lc8 #i A@wsfg`010 Q ` n Online elongation (extensometer) calculator to calculate the percentage of total elongation at maximum force. The cables are pulled to 33,000 pounds, resulting in 8 inches of elongation in a 100-foot cable. Elongation and percent elongation at break. Copyright 1998-2022 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. Modulus is the force at a specific elongation value, ie 100% or 300% elongation. Freyssinet prestressing systems can be used in floors, foundation slabs and building transfer structures, as well as in industrial slabbing systems. 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): Jackson in the 1800s in San Francisco and refined to its contemporary form in the 1920s by Eugene Freyssinet in France. After anchoring, the stress in the tendon at anchorage is usually limited to 70%. 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. The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. The Percentage Elongation calculator computes the ratio of change in length to original length.. 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. Home Articles Reviewing Elongation Reports. Check out our VIDEO for the basics in stressing post tensioning tendons. 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%. Every contractor, installer, independent inspection company, engineer, and yes even the post-tensioning material fabricator, dreads this like a swift kick in the backside. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. From equilibrium of the above force triangle. We have been asked to provide PT elongation calcs. . the maximum tendon stress) can be found directly for a straight tendon. (66)2-985-2357 , (66)88-8835646, (66)85-100-7766, (66)86. fcgp = sum of concrete stresses at the center of gravity of prestressing tendons due to the prestressing force after jacking and the self-weight of the member at . . Threshold inspectors 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. While it is an integral part of all post-tensioning operations, its results can be misun-derstood, leading to disagreements, finger-pointing, and The Math / Science. 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. Post Tensioning manual - Free download as Word Doc (.doc), PDF File (.pdf), Text File (.txt) or read online for free. The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. Pulled to force P, the tendon exerts a uniform uplift (PT) shown in part (b). However, how quickly this happens is a function of the ram and the tendons overall length (shorter tendons are snappier). Here is how the Total elongation of bar calculation can be explained with given input values -> 545.4545 = (6000000*2)/ (2*11000000). Once the tendons have all been stressed, the installer (or inspector) measures how much the tendon stretched with a tape measure. Bolt Elongation Formula and Calculator per. required elongation shall be determine from average load-elongation curves for prestressing steel . Elongation = 0.93 x (Avg.El.) 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 document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); 5335 W. 48th Ave. Suite 300Denver, CO 80212. A beam is jacked to 80% , released to 60% , rejacked to 70% and then anchored. the initial dimension. A 1m length of metal is put under a load and is stretched to a 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. We will solve for in the following way: For the reasons previously stated, is actually underestimated. 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. The table below shows the procedure for determining friction losses. The elongation of this is 150% because the final length is 150% Post-Tensioning Friction & Anchor Set Losses, 6. Suppliers monitor this value as well usually, its 1/4, but for a very short tendon, it might go as high as 3/8. INSTRUCTIONS: Choose units and enter the following: (L 0) This is the initial length. The use of floors prestressed by post-tensioning results in a 20% reduction in greenhouse gas emissions compared with traditional reinforced concrete designs. Below is a link to the file: tendon_elongation.xlsx. The equation . threshold inspector will oversee certain activities during building Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. This test covers the measurement of tension and elongation of wide or narrow elastic fabrics made from natural or man-made elastomers. In a tensile test, uniform elongation is the percentage the gauge length elongated at peak load relative to the initial gauge length. This method consists of determining the extension at maximum force on the force-extension curve obtained with an extensometer. Max. The circular pocket at the edge is grouted with corrosion inhibitor.
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