Placing the concrete in a compressed state will minimize the potential for cracking and improve the integrity of the slab. . . Moment Distribution Method (indeterminate), 8. Advantages of Post Tensioned Floors. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. Cause of any difference in force determination between (a) and (b) that exceeds . is the friction loss, and since we know that friction is , we can say that: where the term is associated with wobble. How do you calculate post tension elongation? 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. Your email address will not be published. The Math / Science. Statically Indeterminate Structure (bending), Unbonded pre-greased tendons wires or 7-wire strand, Unbonded mastic-coated tendons wires or 7-wire strand. Already a member? The procedure for determining anchor set losses is presented after the table. 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. Modified Elongation (Me) = e x A x E / MA x ME in "mm". The error is small enough though that this is considered acceptable practice. Online elongation (extensometer) calculator to calculate the percentage of total elongation at maximum force. Prestressed concrete is a form of concrete used in construction. So: what is an elongation report, and why are they important? the calculated elongation for each tendon length was based on a seating loss of 0.25 in. Every contractor, installer, independent inspection company, engineer, and yes even the post-tensioning material fabricator, dreads this like a swift kick in the backside. Schematics of tensile bar shapes are shown within Figure 1. That doesn't correlate well with dynamic elongation. The equation . Expressed in pounds per square inch (psi) or megapascals (MPa), modulus is most widely used for testing and comparison purposes at 100% elongation. the maximum tendon stress) can be found directly for a straight tendon. Axial/Bending composite (indeterminate), 7. . (L) This is the change in length.Percent Elongation (PE): The calculator return the ratio of elongation as a percent. A variety of applications. %%EOF 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] 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). Describes procedures in post tensioning . The elongation of this is 150% because the final length is 150% In the early fifties, post-tensioning systems for the prestressing of concrete were developed by specialists, such as VSL in Switzerland. 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. We have been asked to provide PT elongation calcs. Click Here to join Eng-Tips and talk with other members! In practice, the precise measurement of in the field should confirm the expected friction loss from theory ( 5%). document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); 5335 W. 48th Ave. Suite 300Denver, CO 80212. Already a Member? Tendon Wobble. If a building exceeds Once the tendon has reached the correct gauge pressure, the operator reverses the pump, seating the wedges in the anchor, and releases the tendon. Related Related Related 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. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Suppliers monitor this value as well usually, its 1/4, but for a very short tendon, it might go as high as 3/8. 5) Seating of the wedges. 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. The table below shows the procedure for determining friction losses. After the slab is poured the forms are wrecked (removed) and . Statically Indeterminate Structure (axial), 5. 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). depends on the size and material of the beam and post! Every post-tension project has a list of elongations. 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. threshold inspector will oversee certain activities during building 2) Placement of the tendons. 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. Tendons today . 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 0 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. The name "Post-Tension" comes from the . Even though post-tensioning is a mature technology, it is still a fantastic tool for the design engineer as it enables the active definition of the internal load path in concrete structures by superposing a favorable state for the internal stresses. Modified Young's Modulus in (as per TC) N/ mm2 ME. 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. From equilibrium of the above force triangle. At their most basic, it's possible to estimate the elongation of a tendon using the formula = PL/AE. The extensometer used shall have a gauge length of at least 100 mm. final length of 1.5m. As anyone familiar with my post-tension elevator speech will know, the key element of post-tensioning is pulling on the tendons. However, the measured elongations are characterized by a high. varies between .0001 and .002 per foot. Min. Post-tensioned tendons, tendons, post-tensioning steel . 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. 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 program is divided into three separate screens, which correspond to the three major areas of concern in the design of a post-tensioned member. However, the difference will be small, so will be used. Cost per Square Foot of Commercial Construction by Region, Type A vs. Temporary overstressing of the tendon followed by release and subsequent re-stressing will also reduce friction losses. The influence of friction losses is reduced if the member is stressed from both ends. EVstudio is a full-service in-house design firm specializing in architecture, engineering, planning, and other design services for commercial and residential projects. 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. A threshold inspector is a certified building inspector who Measured and theoretical elon-gation . If no such limits exist it is recommended the values not exceed 0.200" per floor unless wall specific drift calculations are performed. 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. Note the . 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 . As tendons curve, the steel strand which is fairly stiff moves around in the grease. The difference between 5 7/8 and 2 7/8 can be as insignificant as a typographical error. At their most basic, its possible to estimate the elongation of a tendon using the formula = PL/AE. 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. Elongation and percent elongation at break. When an alloy is cold worked by rolling or drawing, tensile and yield strengths increase while elongation decreases, as schematically illustrated. A material with a higher percentage is a more ductile material, while a material with a lower percentage will be more brittle. 2) s = stress (psi) 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. ASME PCC-1. The tendon shown in part (a) is in the shape of a simple parabola in each span. This so-called anchorage set is usually about .25 inches. Threshold inspectors 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. 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. 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. Registration on or use of this site constitutes acceptance of our Privacy Policy. The force is then checked by measur-ing strand elongation and comparing this measured value with a theoretical (calculat-ed) value. Divide fifty by 37.68 and get an elongation of 1.33 inches. Keywords: elongation variation, post-tensioning, tendon, tension, friction, wobble, elongation limits. Jackson in the 1800s in San Francisco and refined to its contemporary form in the 1920s by Eugene Freyssinet in France. Our long history of elevated post-tension decks helps us evaluate the suppliers calculations before tendons are shipped . Thanks. He would provide a value of Modulus of Elasticity for the strand you are using. 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. Thus far, we have looked at equations that are well suited for illustrating the theory and concept of prestressing. How do you calculate elongation in post tensioning. . 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. For ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation and 1mm/min for measuring modulus. The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. Post Tensioning manual - Free download as Word Doc (.doc), PDF File (.pdf), Text File (.txt) or read online for free. Post-tension tendons are stressed using a hydraulic ram, which is connected to a gauge. Elongation in mm e. 4. Which brings us to the last line in Section 18.20.1.
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