How do you calculate post tension elongation? Typical wobble values are rolled into whats called a wobble coefficient, an average deviation measured per foot of tendon. Also Read: Post Tensioning, Methods, Advantages The extensometer used shall have a gauge length of at least 100 mm. Max. I hope you find this information useful. Slope Deflection Method (indeterminate), 2. We have received your request and will respond promptly. This results in larger, column-free floor areas which greatly increase the flexibility of use . (L) This is the change in length.Percent Elongation (PE): The calculator return the ratio of elongation as a percent. Those values are highlighted in yellow in Table 1. Elongation is the percentage of the final dimension relative to Axial/Bending composite (indeterminate), 7. The friction loss consists of two components: curvature and wobble. Which brings us to the last line in Section 18.20.1. From equilibrium of the above force triangle. 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 EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. My post above related to post-tension slab on grade, not elevated slabs. Login. 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). 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. However, the measured elongations are characterized by a high. Thus far, we have looked at equations that are well suited for illustrating the theory and concept of prestressing. 742 0 obj <> endobj The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. Your email address will not be published. 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 Curvature friction losses occur from the intended angle changes of the draped tendon, and is essentially equal to ; the common formula for friction. 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 . average force in the tendon, determined from calculated force variation along the tendon, total length of tendon (total length of beam is adequate). You can get A 1m length of metal is put under a load and is stretched to a If no such limits exist it is recommended the values not exceed 0.200" per floor unless wall specific drift calculations are performed. Contribution of post-tensioning in the reduction of the effect of dead load on the member. The tendon shown in part (a) is in the shape of a simple parabola in each span. Elongation in mm e. 4. Once the tendons have all been stressed, the installer (or inspector) measures how much the tendon stretched with a tape measure. cm. 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. If the duct were frictionless, then would equal the full length of the beam. 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. We will solve for in the following way: For the reasons previously stated, is actually underestimated. In general, the vast majority of tendon elongations fall within the 7% tolerance, with only occasional long or short pulls. Allowable Elongation = 107% of Avg. 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. After the slab is poured the forms are wrecked (removed) and . Required fields are marked *. 0 The jacking system will result in additional losses due to the seating of the wedges which anchor the post-tensioning strands. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. Already a Member? A material with a higher percentage is a more ductile material, while a material with a lower percentage will be more brittle. At their most basic, it's possible to estimate the elongation of a tendon using the formula = PL/AE. (66)2-985-2357 , (66)88-8835646, (66)85-100-7766, (66)86. As tendons curve, the steel strand which is fairly stiff moves around in the grease. 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. . Of course, EVstudio has the expertise you need to carry a post-tension project from start to finish. Online elongation (extensometer) calculator to calculate the percentage of total elongation at maximum force. where: N = number of identical prestressing tendons. At this point, I think its fair to say that Im a proponent of post-tensioned structures. 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 and beam home custom built from the Post and Beam website. Working Stress Design Tables and Examples, 7. I think that elongations should be measured first, not put on the drawings so the PT guy thinks he has to match them. The Percentage Elongation calculator computes the ratio of change in length to original length.. This is referred to as "M100" or modulus 100. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. In practice, the precise measurement of in the field should confirm the expected friction loss from theory ( 5%). %%EOF 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 . If 1.05 times the calculated elongation is reached before the specified gauge pressure is attained, stop stressing and inform the Engineer. Statically Indeterminate Structure (torsion), 12. Every source of friction reduces the P in the elongation equation. 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. . Curvature friction losses occur from the intended angle changes of the draped tendon, and is essentially equal to ; the common formula for friction. 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. 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. 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. either a height, square footage, or occupancy load, the client Modified Elongation (Me) = e x A x E / MA x ME in "mm". Specifications: Post-Tension Concrete Cables. As the extension, so the force Robert Hooke. Strut and Tie Methodology Regarding Shear, 6. Note the . Allowable Elongation = 93% of Avg. INSTRUCTIONS: Choose units and enter the following: (L 0) This is the initial length. Prestressed concrete is a form of concrete used in construction. 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. Thus, the ratio can be said to be an overestimate of the relaxation (shortening) of the tendon within the distance , due to anchor set. This Manual includes state-of-the-art information relative to materials, post-tensioning systems, construction practices and grouting of post-tensioning tendons for bridges. This form is for Inspectors and Installers certified by the Post Tensioning Institute . 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 cables are pulled to 33,000 pounds, resulting in 8 inches of elongation in a 100-foot cable. It turns out that underestimating is aggressive, i.e. The error is small enough though that this is considered acceptable practice. So: what is an elongation report, and why are they important? Ive found that they can be very economical, and there are many things you can only do with post-tensionedconcrete. and can be a real nail-biter if the deck was just barely working to begin with, especially because the reinforcing steel is all in place. By joining you are opting in to receive e-mail. the initial dimension. This so-called anchorage set is usually about .25 inches. is underestimated as well. hb```B ce`a02#[B s'( "P}S52s$*+}Q*&Af{=EJyhJYygK[5- %fwEW[K3cqb[>&%Qnb;vTttt400F%\4a0 Check out our VIDEO for the basics in stressing post tensioning tendons. Here is how the Total elongation of bar calculation can be explained with given input values -> 545.4545 = (6000000*2)/ (2*11000000). Then, the ramifications of different actual measured elongations assuming seating losses of 0.125, 0.375, and 0.50 in. The gauge length shall be indicated in the test report. 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). 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). The theory behind friction loss in prestressed (post-tensioned) beams is well developed. For materials under tension, strain (e) is proportional to applied stress s. Where: E = Young's Modulus (lbf/in. Cost per Square Foot of Commercial Construction by Region, Type A vs. 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. *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. Pricing for more information. Jackson in the 1800s in San Francisco and refined to its contemporary form in the 1920s by Eugene Freyssinet in France. START TESTING Scope: At their most basic, it's possible to estimate the elongation of a tendon using the formula = PL/AE. This means when the material is subjected to this amount of stress, it will stretch by 1.33 inches. . 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. While post tensioning we use strand wire that is being joined by twisting around one and other to make a tendon, this tendon is to be inserted within a profile pipe called sheathing or duct after the concrete will achieve a specified compressive strength. 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 (%). 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