If the measured elongation are below the tolerance, another 5% of Stressing might be applied, or de-tension and stress again. p~k{7qvU!Xoigr)&8[?HU? This has been systematically observed on building proj- tensioned tendons immediately after the post-tensioning operation. 2. made up of steel strands housed in a duct, which is injected with cement grout after tensioning. In a post-tensioned beam, the tendons are stressed and each end is anchored to the concrete section after the concrete has been cast and has attained sufficient strength to safely withstand the prestressing force as shown in fig.2. However, the measured elongations are characterized by a high. endstream endobj 404 0 obj <>stream If you log in through your library or institution you might have access to this article in multiple languages. While it is an integral part of all post-tensioning operations, its results can be misun-derstood, leading to disagreements, finger-pointing, and The prestressing steel applied corresponds to international standards EURONORM 138-79, ASTM A 416-85, BS 5896. If the target was 50 KSI, you'd see values between 45-55 KSI. df41!Ph]nF Zm3,s,$(d! normal seating losses are a significant percentage of the calculated elongation. Second Floor, Office #207 . 0000125997 00000 n This video goes over the highlights of stressing unbonded Post Tensioned concrete. It's easy to ask that the installer re-pull the short tendons to ensure that the ram wasn't reversed early, or the wedges didn't slip unduly. It allows slabs and other structural members to be thinner. If the Engineer of Record cannot justify the tendons acceptability, hes forced to abandon it. P ost-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons. 0000006413 00000 n Post-tensioning is a method of reinforcement employing high-strength steel strands or bars, which enable the existence of longer clear spans, thinner slabs and in many cases of structural systems that would otherwise be impossible due to either site constraints or architectural requirements. After an initial pull of 3,000 pounds, the final jacking force read on the gauge is 25,500 pounds. retical elongation for a 400-foot-long strand, after initial tension of 3,000 pounds, is 30 inches. Post-Tension Elongations: How Long is Too Long? . 51 57 8^D%&]U)a=8Ash]ZT=tV^-:6 )zXs`[.th^GgJMUg7N`n/q*^%a6O$;LP**F4YSEUq|/-veQ\V5W 4, Q-X7^T#[d]w!aH2u>w],TqUM5aOv>@~R1? A Phone: 1.248.848.3800 %PDF-1.5 % Common procedure is to set that valve to prevent the pump from turning out more than about 90% of the tendons yield strength. Place additional wood brackets at these positions, if necessary, to distribute the load. The paper discusses the history or background of specifications on the elongation tolerance for post-tensioning tendons with particular application to segmental concrete bridges. 0000119393 00000 n The use of these equations in large-angle post-tensioning applications, such as hoop post-tensioning in cylindrical structures, may lead to unrealistic estimations of friction losses. In. This will also make the whole concrete . ACI World Headquarters 0000134933 00000 n The difference between 5 7/8 and 2 7/8 can be as insignificant as a typographical error. As concrete gains strength more slowly in colder temperatures, closely monitoring temperature is important to ensure the production of high-quality concrete that meets specifications. The PostTensioning Institute is a nonprofit trade . %PDF-1.6 % endstream endobj 58 0 obj <>stream and do not adjust the pressure relief valve! 114-S64 Elongation Tolerance for Short Tendons in Post-Tensioned Building Structures by Carol Hayek and Thomas H.-K. Kang Elongations have been used to assess the forces inside post- end. However, there are some important caveats to note here. Email Address is required ]}q+5[&j4O@s'~7p(Jr-TI'!(bEh%EI/HG=K-{+N[T-Rvd8[F-vT.NsfK8pA-&TkEc$q;1O0>M~tEF+XqIm.ukI/uj&|63'4BbRtXlg[ebc)hg,ki?u-Wju8(KY1UXB`3F4N f&: =^:sR<5H>&n)%G& JCfQ1 K'\S.vqABd 1{rN\yM-L$Q/Zbu^IJ-gbax%5%"D -@"&yBw3S^fuKlXGg*k+r424{dq(rH0eTKiXsDn_5>x@Gl_^W.H}vY3rDw @^Z:C 0000002067 00000 n fx)!j7y{@Q]~Z`S D-tQ8Ra]_}_Nlll'F~ D0K&"IC\![u{. It follows the Post-Tensioning Institute's Field Procedures Manuals for U. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. What if several tendons (especially tendons bundled together) are over-length? The cells or cavity containing the tendons . First, tensioning is more expensive and more complicated than torquing. Home Articles Post-Tension Elongations: How Long is Too Long? Which is certainly true in both directions and is why the calibrated gauge pressure is the first criteria for acceptance of the post-tensioning force. After applying the additional pressure / elongation, if the Stressing result is within +/-5%, release the jack pressure slowly and then proceed for next stressing. KfK.Y4.~W+cbrE\\+M&VJW&'K7*q2%)!i\-UcReIu i b%X|)*Z:.S &9.A0f#j#R6N7*Ah+k@3p/"0 The difference between 5 7/8 and 2 7/8 can be as insignificant as a typographical error. ; > 08;g\`AQg-q'q:@lFlAO o Detailed discussions are presented on variations in the area and modulus of elasticity of seven-wire prestressing strand and variations in the values . materials and method of fixation, . 0000129279 00000 n . This energy is stored when you tighten the nut and provides the clamping force on the flange. 0000071658 00000 n We still check them theyre out of specification, after all but once you know the line that translates into permanent damage for the tendon (dont forget anchor set! In this study, to resolve this issue, a statistical analysis is carried out using a large database of tendon elongations measured from actual projects of bonded post tensioned building structures. This acts as an additional factor of safety. In a bonded system, the tendons in the ducts are buried intside the concrete and grouted after stressing. ACI members have itthey are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them. HWn}W#;4&L3,r50y%f{s&-S`u9uzw They keep thorough notes showing both the gauge reading and the elongation. xref bT,3sT+:RF'5 juS7 Mv aTDH@:"(+? 0000039849 00000 n Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. Sale. That means your bolt scatter will be lower. Your email address will not be published. hlWyXO3U2.ZVqiZrT. $! 38800 Country Club Dr. . f0 C)dC8w 0000099617 00000 n 0000060414 00000 n ( 0000125829 00000 n Cost per Square Foot of Commercial Construction by Region, Type A vs. Post-Tensioned Concrete Design Table 1-1 List of Symbols Used in the ACI 318-08 Code cp Area enclosed by the outside perimeter of the section, in A g Gross area of concrete, in A 2 l Total area of longitudinal reinforcement to resist torsion, in A o Area enclosed by the shear flow path, sq-in A . In contrast, a typical piece of rebar will yield about 60,000 psi. The alternative to pre-tensioning is post-tensioning. This results in larger, column-free floor areas which greatly increase the flexibility of use . c2Knj%PNhL4UB+P9R"e ^B?5Y'RMcU[F w8#B|.pya W@!@~CF$$.,M26Q11 v;+}&*eE/d?VXI Phone: +971.4.516.3208 & 3209, ACI Resource Center Contraction post-tension slab system. ), a single tendon thats a bit long isnt a real issue. Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete. 0000072924 00000 n When tension is applied to steel tendons, they elongate in proportion to the tensile force, as predicted by Hooke's law. Southern California In Post-Tensioned Buildings: Design and Construction (2014), the author provides the details of the stress loss in the tendon and other considerations that govern the force in the tendon at stressing and long-term effects. Required fields are marked *. cuongnguyen. +`K,kv1!74[Y%GN](k1fdMv# |PG/=8(bAYQbb-4~C1]7;'RkcqmRLl7\aAy Post-tensioning During Cold Weather. Friction of the prestressing steel with the duct and loss due to misalignment of the duct. 0000006378 00000 n This value is used throughout the post-tensioning industry when calculating actual number of tendons required during shop drawing creation. hXmo6++w@&[wAD`[ww+;z#-c LXq`>K^1!8 The straight length of the duct adjacent to the anchorage shall be in accordance with the post-tensioning system. Uz p* X5[E@m=OyMS3l.F{O*`v_9|$PIP| :K`;lCW'?JC B;.6>| Post-tension 'tendon' is a term used to define the complete assembly comprising of the sheath, pre-stressing strand, anchorages, corrosion-inhibiting coating or any grout around the steel wire or bar. Elongation variation, post-tensioning, tendon, tension, friction, wobble. KmY@"[wXy85FAFkk 76 rfLg1RtqfKU-'$-n0=NeJvzLvS2dk]5R=PS,nY@m?==u(MN!vc70A+fq-N}3%WL6>RwgtcdD` Current design codes (ref. However, the measured elongations are characterized by a high degree of uncertainty and variability due to site tolerances, and that the calculated elongations are based on the ideal equations using theoretical parameters. 0000132541 00000 n 0000004323 00000 n There are no good results from adjusting this valve in the field. Elongations have been used to assess the forces inside post-tensioned tendons immediately after the post-tensioning operation. Elongation result should be checked and verified by the engineer before cutting excess strand. The focus of the following is a sequence of stressing and measurement of tendon elongation. endstream endobj 405 0 obj <>stream 0000073686 00000 n Americans with Disabilities Act (ADA) Info, ACI Foundation Scholarships & Fellowships. 0000134676 00000 n ho! The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. Even so, the specified tolerances are quite stringent and unrealistic for relatively short tendons. 400 0 obj <> endobj bDWXiZ}>eXkf]W%R0*4: K;x"r+Mr`m,4UBr4K\ws^I| 1wU$&NSQxL"GDI/Qr?OwZp=-$Njr?zvj0 Invalid Email Address. Post-tensioning applications include high rising buildings, office and apartment buildings, parking, structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and . So, barring typographical errors on the shop drawings, what causes over-elongation? %%EOF 0000000016 00000 n 0000129015 00000 n In post-tensioned construction, hollow concrete masonry units are laid conventionally and prestressing tendons are either placed in the concrete masonry cells or in the cavity between multiple wythes. Relaxation . %PDF-1.4 % A post-tensioning tendon consists of strands, duct, and anchorages. Please enter search criteria and search again, Elongation Tolerance for Short Tendons in Post-Tensioned Building Structures, bonded; elongation; measurement; post-tensioned building structures; short tendons; tolerance; unbonded. suspension span, post-tensioned with 70-strand tendons. Install prestressing steel, which may be strands, wires or bars, through preformed voids or ducts in the concrete or in external 0000129798 00000 n Even so, the specified tolerances are quite stringent and unrealistic for relatively short tendons. when post-tensioning tendons are short. 0000112125 00000 n 0000098263 00000 n If, after careful checking, the slab doesnt meet the engineers criteria, the tendon may have to be replaced. 1. stiffness in increased because we can consider uncracked inertia 2. we can support higher bending moments 3. we can reduce the hight of the bridge and the self weight can be reduced 4. they show better behavior under corrosion 5. effective solution is high strength concrete combined with greater amount of tendons . These categories are: Service Stress . 0 3. Bridges, including major cast-in-place and precast . 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. For instance; A 1m length of metal is put under a load and is stretched to a final length of 1.5m The . 0000072126 00000 n 0000018542 00000 n Cracks that do form are held tightly together. The strand cables level usually reached the highest level in the form over the positions of the supports and lowest level between the supports so the tension force on the cables pulls pressing up the slab in the middle of the spans. 0000005671 00000 n Elongation at break 3.5% in 24" gauge length 3.5% in 24" gauge length Maxi. 0000002538 00000 n Prestressing by post-tensioning is generally of the bonded type, i.e. 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. Hlo0+&z`T,1q:LkpMm However, I mostly concentrated on short pulls in that article. when post-tensioning tendons are short. 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 . Advantages of Post Tensioned Floors. The purpose of filling with grout is to introduce compatibility between the prestressed concrete and tendons. I*lV&N'*ppNjR:)j->i&s'8W2$%cmoJ )r(^ezcN-fG]u2h8"'Z}l8RmZTr?o9gEnp||,+ nfgjY#[oVS^O_Ci,Mib}+j!+;q pV{k,~ 0000071284 00000 n All Rights Reserved. Based on the analysis of the data collected, a practical and rational tolerance between measured and calculated elongations is proposed. The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. 0000004826 00000 n The Manual is targeted at Federal, State and local transportation departments and private company personnel that may be involved in the design, inspection, construction, or maintenance of bridges that contain post-tensioning tendons. What happens when a tendon is over the line? Building codes acknowledge such variability as a limitation and include tolerances for the elongation deviations between the calculated and measured values. Step one is to check to make sure the elongation from the shop drawings is accurate. What happens when the tendons pull long? Date: 11/1/1992. Step one is to check to make sure the elongation from the shop drawings is accurate. 0 Built in 1965, the existing uncoated steel strands corroded severely only 50 . Add to cart. Tendon elongation during stressing (D) is typically considered to be 0.081 inches per foot of concrete. 426 0 obj <>/Filter/FlateDecode/ID[<52E6B974CD58B0459493BD4438105C12><8E9E88EA1056F24E993B78BB31D78C05>]/Index[400 54]/Info 399 0 R/Length 118/Prev 275052/Root 401 0 R/Size 454/Type/XRef/W[1 3 1]>>stream This manual contains updated information on the current practices in the use, design, and construction of post-tensioned structures. hbbd``b`$A !$:l'5H8 H$RAHHJ >&F iCg\ N5 It is critical that only the jack supplier adjust this valve! For that reason, elongations have always been used as a way to assess the post-tensioned forces within the tendons because the tendon force is directly proportional to the elongation through a known equation. _ e-,FC8H- vJT 0000007084 00000 n What is Post Tensioning[2] ABAMELA. 71 0 obj <>/Filter/FlateDecode/ID[<623A578A69BA82C539DC842F59108376><82263C54187F944DAC72704F2143DEB6>]/Index[54 38]/Info 53 0 R/Length 89/Prev 174833/Root 55 0 R/Size 92/Type/XRef/W[1 2 1]>>stream 0000072665 00000 n Dubai, UAE Every contractor, installer, independent inspection company, engineer, and yes even the post-tensioning material fabricator, dreads this like a swift kick in the backside. When there is permanent stress and elongation in the post-tension cables, a compressive force is created on the concrete. 0000003097 00000 n 0000002247 00000 n Title No. A residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. endstream endobj startxref 6) Cutting of the tendons. Do those 18 tendons give him 27 kips per strand, or 27.1? a.Bk;,H8&og 1K$n15P(%Fbza}r=2 .JBfu4$nA.K RvE%Q" D? Since the usual concern with elongation reports is understressed tendons, the occasional long tendon isnt a cause for great concern. ]=PFQd9P# z?J0U5\17}AykS34\^xPRz5M1}&PA -5lLd~ Normal variations in seating losses in short tendons can often result in differences between measured and calculated elongation, which fall outside the range of 7% tolerance permitted in ACI 318-11, Section 18.20.1 . Help us help you by always stressing to calibrated gauge pressure . Post-tensioning, or PT, has become increasingly popular over the past few years, as the technology has been perfected with better materials and construction methods has made this system a preferred one. !zx[ o7]k}ENRfv;@:I9Wca3ttR:W{"uTsoS}\F.:KnS(ewKt'CJ(%R]pkPq~blM|&waRWHm[n;F:tu dW The report should contain the theoretical elongation, provided by the designer, measured elongation as well as the percentage of variation. 2) Placement of the tendons. 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. Copyright 2006-2022 EVstudio. The paper discusses the history or background of specifications on the elongation tolerance for post-tensioning tendons with particular application to segmental concrete bridges. With tensioning, you're typically going to see +/- 10% accuracy. This hybridisation helps achieve the formation of a much thinner slab with a longer span devoid of any column-free spaces. 0000001986 00000 n Furnish, install, stress and grout prestressing tendons. Please enter this 5 digit unlock code on the web page. Check out our VIDEO for the basics in stressing post tensioning tendons. Introduction In South Africa, guidelines for post-tensioning are provided by SANS 2001-CC1 [1] . 0000073314 00000 n Does the slab work with 143 psi of precompression in this bay, rather than 160 psi specified? What is elongation in post tension? MattChuo. hb```f``2g`a`jgd@ A+sgl{Q@ iv4 */J( h @Q(.8]HxG[ecx>300Q{:{l. endstream endobj 401 0 obj <>/Metadata 37 0 R/OutputIntents 396 0 R/Pages 395 0 R/StructTreeRoot 80 0 R/Type/Catalog>> endobj 402 0 obj <>>>/Font<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI]/Properties<>/PR1<>/PR2<>>>/XObject<>>>/Rotate 0/StructParents 0/Tabs/S/Type/Page>> endobj 403 0 obj <>stream (66)2-985-2357 , (66)88-8835646, (66)85-100-7766, (66)86. 0000005213 00000 n As youll recall from my post earlier this year, elongation review is a critical part of an engineers acceptance of a post-tension slab. 0000129515 00000 n 0000029538 00000 n This arrangement enables strand loads to be transferred to the concrete structure by bonding, which allows for passive reinforcement to be optimised and significantly reduced. b`Z g 0 0"1 This value . yF-KMjY+l$&h.7riCaJp%56eFK 0000129857 00000 n Your email address will not be published. W&\y For a 55% tolerance, the measured elongation should be between 281 2 and 311 2 inches. In practically all constructions, the post-tensioning is fine-tuned to balance a fraction of the member's self-weight, typically 50% to 80% - not more than the member's total weight at stressing. 0000123131 00000 n About half the time (in my experience) the yield strength is higher than nominal, or the strand is just a little bit oversized both of which help justify leaving the tendon as-is. The following new Section is added after Section 460: SECTION B460 POST-TENSIONING B460-1 Description. In todays market, it is imperative to be knowledgeable and have an edge over the competition. f{&u2J. CBInS4 J' T$hLd!1dlU2}QF}JNL0RCg:"l9!A6FU2NOM'^h measured elongation review". Post tensioning are generally classified into 2 category, namely bonded and unbounded. Post-tensioning, which is a form of prestressing, has several advantages over standard reinforcing steel (rebars): It reduces or eliminates shrinkage cracking-therefore no joints, or fewer joints, are needed. GD=~{FO. +dj7.JrS}"@KHh((lU(-ldT\e\,zh~|/&y\e})j9)\8vwin8=(Kl\L7I p~6/5|R5{USHO,|j~R J>VZ 94R!Cwu6HN~|OJq=m>]AL!m KDvMiFhBKJ(4. 1OM>v$pm?m?}k7l@hbo%R]XP"0p% ? 0000006802 00000 n Also, as explained earlier, the anchor set is a value that comes straight off the top of the elongation, instantly reducing the force in the tendon. Yx9~XZoe<< ked4$)KfW}!,*C%"V{Lt 7fPwkX7)+ 0Qq>qdK PT Detailing. Elongation Tolerance ACI Structural Journal - post-tensioned concrete This is 80% of the yield strength of the tendon essentially, the most the strand can be stretched without permanently deforming, while still leaving a factor of safety. Cementitious grout is poured in to the duct . 0000005593 00000 n Here are some primary advantages of post-tensioned floors over conventional reinforced concrete in-situ (cast in site) floors may be following: Longer Spans. Q/Ml//-]Z,>G56 Lw!ZCCet'G Sm`/>P6KK(Vv)v&RYm?ur80S$yfMB)-)xr>2ttw[Rr.IXGJi>Yk/+Eys!kUtd687[pn^yxJc?0t55ENS1t?SK*jG!jn+K_^luD*hl1\ l RLQZVpVbi }Q#14qdZpK>Z#N>yE+F6dq 3R.SYdaXN5}6;E%*{jg~A7v=-O$Q/h:P3SlmVv[b7QJ{_|9T{A(/w_t_~2EYn>}lSf'Gou ,d&Y^dPv;DR84=neMSm Elongation is the percentage of the final dimension relative to the initial dimension. As I explained earlier, post-tension stressing pumps are calibrated before they reach the jobsite to a pressure corresponding to 33.0 kips. Thats why the factor of safety is 20% (instead of 15%), and why almost all post-tensioning pumps are equipped with a pressure-relief valve. 0000083967 00000 n The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts. Listed below are seven causes of prestress losses: 1. xb```f``} Ab,g8;74```{Q(i6ye CE7o_. L>NiXSvUJEG"W+7Ke5W3#7@^qd9iB@DNnvX"!c wEBKdUZ'!}\l ;KeJKK _I,g ( q]\\4W56It@8Bj vf Qf`3H# |L.L"d"#0Mr %`f*UNc2[C6w %%EOF hbbd```b``A$dY`RLr`]`vB.9`0)"Y[@$7$/H-~83H8`(:?cs x4HC$j?l_cp-x `>l.HDN\e:cw`pzl2H8t`nqz(|%Cd1PC;F_ GL}F]'(twp9 ykE0dt>!Va3l0^mX3`hc(nctpd}d>#,9#.fS0}x!3}~{Y:TAl9Tz~f8a}`l:q^4CQH2&>|;:9OB#H0*E/W*qdl=mc-Bem3$p6'Q6pJ"1(: ,!i& The form is used for recording elongations for Unbonded Post Tensioning. 4x +g^qtWMu4+EVN;3c^#6"cjFsTM9 '_eG~oKv4]36lK\c ?=c+hgjL|E9:4(2hOmI(onxzA/emeXO1>xYq S" J2#\qVo/?Om_!Bx`D^_M~7/yyy}|=5gQgG_\5*B]~G;0Y0~j gGK[Z.$;*mN-^/_h>s"_@P4.2=ate'` |`h8@2T&@_hX-sqKkNTpHPG/nh Hence, the slab will not lift off the form support. 0 *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. 0000003664 00000 n POST-TENSIONING. This . 0000132803 00000 n 3) Placement of the anchorage block and jack. This Manual will serve as a reference and guide to designers, inspectors and construction fhwa.dot.gov The Post Tensioning workers use many sized bar chairs that locate the strand cables at there correct profiles. Assuming that it provides no precompression or balanced load, he rechecks his calculations and looks for any slight overages in the nearby tendons to help.

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