What are some advantages? CBInS4 J' T$hLd!1dlU2}QF}JNL0RCg:"l9!A6FU2NOM'^h A residential post-tensioned concrete slab will typically be 8 inches thick and use 3000 psi concrete. Recently, weve had a few projects where our post-tension elongations came up longer than expected. Do those 18 tendons give him 27 kips per strand, or 27.1? Built in 1965, the existing uncoated steel strands corroded severely only 50 . Elongations have been used to assess the forces inside post tensioned tendons immediately after the post-tensioning operation. Building codes acknowledge such variability as a limitation and include tolerances for the elongation deviations between the calculated and measured values. The program is divided into three separate screens, which correspond to the three major areas of concern in the design of a post-tensioned member. Phone: +971.4.516.3208 & 3209, ACI Resource Center 107 0 obj <>stream HQk0+L[ucaVn{n[Wh\@{xOsszf7x*A|`4AA7WP+D6~/ex)y E9_.}QaR9Smmi ,C[H~YSy!>e&0QnMR 0000073686 00000 n (66)2-985-2357 , (66)88-8835646, (66)85-100-7766, (66)86. Even so, the specified tolerances are quite stringent and unrealistic for relatively short tendons. Invalid Email Address. 0000129015 00000 n Fax: 1.248.848.3701, ACI Middle East Regional Office EGb97+/fXL(5B,BL7K*,h}}g kU/ xYd@~/5Glo-6E{JTO JPe6-+!-D.(55`PRrO/[*w\E6pk"E.-d8QRoU%nVAIdIOPX n+[lvOH 36]%8!&Om_i$BzKOl_|^|zv| :2pT=+unt0h#(Gn;-A__HHJ$B`dxxtC?=j"Amj'^7?\+NGc^pdJ~=Y":BuJ"@`z4 k/^X`g=lkjKAR#HR{LatB7 &uCXQ'%(jv!-KNJz$46z Po9LtaXa)`MEsaFhK GQNMe[ &[pZ!MLm[U])HUHG+QZskay5% ~HXj$rn@/Y,pCSZ(#wf8 9M'R%5{?CAT>YQmwH, 0000134676 00000 n (REV 6-27-01) (FA 7-9-01) (1-02) PAGE 620. Please enter this 5 digit unlock code on the web page. f0 C)dC8w In this article [] Even so, the specified tolerances are quite stringent and unrealistic for relatively short tendons. 0000103577 00000 n ), a single tendon thats a bit long isnt a real issue. The paper discusses the history or background of specifications on the elongation tolerance for post-tensioning tendons with particular application to segmental concrete bridges. 0000050446 00000 n Add to cart. Listed below are seven causes of prestress losses: 1. The joints between the duct and the anchor shall be watertight. 0000071284 00000 n %PDF-1.5 % 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 This will also make the whole concrete . What is elongation in post tension? Relaxation . 0000002067 00000 n POST-TENSIONING. 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. 54 0 obj <> endobj However, the measured elongations are characterized by a high. 9BoLa05&&7Q;RW;:,f1CZ)6|`USDiegA#t1V4Ne.Iq@HCBZ4;yyuPxRO {LmoR> We(d>:aDQ+86QomL _VKx@)5)UtQ(@MS 0 Dx%TbSj)L$PB2zuHgSU1~PfU"lY$o( 9390gMaEoJ! 05w W 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. 453 0 obj <>stream Yx9~XZoe<< ked4$)KfW}!,*C%"V{Lt 7fPwkX7)+ 0Qq>qdK 51 0 obj <> endobj rY#DNDY1g zaDfc't4g1h!C$C\u=,B4ja,kD1!wt;;1YITv7FFIF ~TROks!z&X}d@r. 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. Contraction post-tension slab system. ]yZ;\}pR|\y_nBz]nnr 1lj>6exZ9,jw|1C|N>u:'juW6 ~Y^a4?t#eZa It is important to place the beam coils above the formwork brackets. In the early fifties, post-tensioning systems for the prestressing of concrete were developed by specialists, such as VSL in Switzerland. 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. This Manual will serve as a reference and guide to designers, inspectors and construction fhwa.dot.gov Introduction In South Africa, guidelines for post-tensioning are provided by SANS 2001-CC1 [1] . The focus of the following is a sequence of stressing and measurement of tendon elongation. Step one is to check to make sure the elongation from the shop drawings is accurate. After applying the additional pressure / elongation, if the Stressing result is within +/-5%, release the jack pressure slowly and then proceed for next stressing. 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. . POST TENSIONING MANUAL 6TH ED. jX=hLQkI>2pg2/ 0000150075 00000 n 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.$;*mN-^/_h>s"_@P4.2=ate'` |`h8@2T&@_hX-sqKkNTpHPG/nh %%EOF Assuming that it provides no precompression or balanced load, he rechecks his calculations and looks for any slight overages in the nearby tendons to help. The PostTensioning Institute is a nonprofit trade . . "ts: %& ^#I2vUaiXf(Z 0000005747 00000 n Email Address is required Cost per Square Foot of Commercial Construction by Region, Type A vs. 3R.SYdaXN5}6;E%*{jg~A7v=-O$Q/h:P3SlmVv[b7QJ{_|9T{A(/w_t_~2EYn>}lSf'Gou ,d&Y^dPv;DR84=neMSm If elongation reached, but pressure not reached apply 5% additional If pressure reached, but elongation not reached apply 5% additional pressure. |y&BB:Z'\bB+FDCiZ|o[na#WNm}EZ"ys{rJzr Tendon Elongation Calculation - Beam. 5) Seating of the wedges. Date: 11/1/1992. Uz There are no good results from adjusting this valve in the field. vikramjain66. Cementitious grout is poured in to the duct . Cracks that do form are held tightly together. Southern California This . Based on the analysis of the data collected, a practical and rational tolerance between measured and calculated elongations is proposed. 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. I*lV&N'*ppNjR:)j->i&s'8W2$%cmoJ )r(^ezcN-fG]u2h8"'Z}l8RmZTr?o9gEnp||,+ nfgjY#[oVS^O_Ci,Mib}+j!+;q pV{k,~ 0000083967 00000 n ho! What happens when the tendons pull long? GD=~{FO. K&{k0X&/B9616~aUr-g_rRcIZuPlfD;. h'h8("8Xy_C=^:N2|AT*m@kQAA mN6pi]Wpf@%mm;66c>fbbK+x/y-h[$ycO^E`-5 'q.q)B?Ejpe[B,kt'5"1{CNS%Kg9'] _n3N5xTQwZ>47]S/~Oi:X;[*e>)H]{i~+L")y;Dh=4JY$1;=X#QVpq{Mp&_x;8x3iIa(PiW2Wg`$be&A#&,TFKC}a. The alternative to pre-tensioning is post-tensioning. 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. hn8`-E@a Kx&M/j$FHQgo3gl2e0c0?`q;x`,-LBpc8=lq9^Cxc#I^h"QydXtC}:l2Y]NFSoWj,SO([6dFl'Y|FsyMv:#E2O>@QqQMktW}VKap`0\r5tgQR=g3Yl"cb`*2Bq>eN 2p^CNaO8D}@ !L` ; > 08;g\`AQg-q'q:@lFlAO o 0000000016 00000 n The 6th Edition has been extensively expanded with 12 new chapters that give design guidance on modern applications of post-tensioning. Consider additional elongation tolerance and lower final effective force (PTI Tech Note 16) Look at percent over/under elongation carefully . . Phone: 1.248.848.3800, Home > Publications > International Concrete Abstracts Portal. 0000002247 00000 n when post-tensioning tendons are short. Potential energy is created by the combination of the stud's elongation and tension. kN\TDU&N9Y9Y]Q;jbd QH\w-1w%y'I@_W$k>$GRt WzlrK=LF0/cbh]]8FBsR3-[ IvEXe>H' ^ZU:`0:od&4h)!qR6Gx5O;F2!=+V-5 and do not adjust the pressure relief valve! 0000123131 00000 n 0000124488 00000 n We still check them theyre out of specification, after all but once you know the line that translates into permanent damage for the tendon (dont forget anchor set! POST TENSIONING MANUAL 6TH ED 1-15 - Free download as PDF File (.pdf), Text File (.txt) or read online for free. 0000125997 00000 n 0000073314 00000 n Americans with Disabilities Act (ADA) Info, ACI Foundation Scholarships & Fellowships. Then, once the concrete has strengthened, the ropes are tightly pulled or stretched and abutted against the outer edges of the concrete before the load is applied. 0000099617 00000 n In contrast, a typical piece of rebar will yield about 60,000 psi. W&\y Detailed discussions are presented on variations in the area and modulus of elasticity of 7-wire prestressing strand and variations in the values of tendon friction . 400 0 obj <> endobj 0000129279 00000 n 0000006802 00000 n Friction of the prestressing steel with the duct and loss due to misalignment of the duct. Home Articles Post-Tension Elongations: How Long is Too Long? 0 Your email address will not be published. 0000004826 00000 n 0000006378 00000 n Also, as explained earlier, the anchor set is a value that comes straight off the top of the elongation, instantly reducing the force in the tendon. Post-tension 'tendon' is a term used to define the complete assembly comprising of the sheath, pre-stressing strand, anchorages, corrosion-inhibiting coating or any grout around the steel wire or bar. measured elongation review". . *** Updated (10/21/2011) - In response to industry demand, we have updated our elongation report to include. Post tensioning are generally classified into 2 category, namely bonded and unbounded. Prestressing by post-tensioning is generally of the bonded type, i.e. 0000001436 00000 n x4HC$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$p6'Q6pJ"1(: ,!i& !@ !$"MvjuVt9sz&ss{>o(:u'%H|KGbV''B}~== . p* X5[E@m=OyMS3l.F{O*`v_9|$PIP| :K`;lCW'?JC B;.6>| P ost-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons. A post-tensioning tendon consists of strands, duct, and anchorages. The strand cables level usually reached the highest level in the form over the positions of the supports and lowest level between the supports so the tension force on the cables pulls pressing up the slab in the middle of the spans. JlJ&\E2"Lgqs^FJO171*[\vN{> 5rwaVHUO7Vfklw}NA=$:dqu:}8H?p>$79x(!Q;]AJE5D:G6 (RS8*("QeKy>k`! It's easy to ask that the installer re-pull the short tendons to ensure that the ram wasn't reversed early, or the wedges didn't slip unduly. Chloride Tolerance The chloride tolerance of galvanized reinforcement is >10x higher than black steel . The difference between 5 7/8 and 2 7/8 can be as insignificant as a typographical error. 3) Placement of the anchorage block and jack. Elongation at break 3.5% in 24" gauge length 3.5% in 24" gauge length Maxi. . Anchorage slip as the strand wedges seat at the bearing plate. Based on the analysis of the data collected, a practical and rational tolerance between measured and calculated elongations is proposed. In. Once the concrete has gained strength to 2000 psi, typically within the 3 to 10 days recommended by PTI, the tendons are stressed. 0000098263 00000 n Copyright 2006-2022 EVstudio. bDWXiZ}>eXkf]W%R0*4: K;x"r+Mr`m,4UBr4K\ws^I| 1wU$&NSQxL"GDI/Qr?OwZp=-$Njr?zvj0 Reading time: 1 minute Post tension slab is a combination of conventional slab reinforcement and additional protruding high-strength steel tendons, which are consequently subjected to tension after the concrete has set. %PDF-1.4 % b`Z g 0 0"1 Advantages of Post Tensioned Floors. 0000106270 00000 n a.Bk;,H8&og 1K$n15P(%Fbza}r=2 .JBfu4$nA.K RvE%Q" D? Post-tensioning During Cold Weather. Abstract:Elongations have been used to assess the forces inside post tensioned tendons immediately after the post-tensioning operation. endstream endobj 55 0 obj <> endobj 56 0 obj <> endobj 57 0 obj <>stream uzti2i?yf'bx|y)o27W[-Vxom3x/qoF7`\pt/>Dc1]Mzl,1v8qZgb9l9 \p:qT~wtq,)KS #V~-8wK xUe-3RE Steel tendons used for post-tensioning typically have a tensile strength of 270,000 pounds per square inch (psi), are about 1/2 inch in diameter, and are stressed to a force of 33,000 pounds. Normal variations in seating losses in short tendons can often result in differences between measured and calculated elongation, which fall outside the range of 7% tolerance permitted in ACI 318-11, Section 18.20.1 . Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete. This has been systematically observed on building proj- tensioned tendons immediately after the post-tensioning operation. Post-tensioning is a method of reinforcing (strengthening) concrete or other materials with high-strength steel strands or bars, typically referred to as tendons . Midwest, Feedback via Email startxref #T1$]&`!Bl=SubNa & !zx[ o7]k}ENRfv;@:I9Wca3ttR:W{"uTsoS}\F.:KnS(ewKt'CJ(%R]pkPq~blM|&waRWHm[n;F:tu dW 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 [B3WB6#BUWWr(CEU% tdbFYU`~oMh{}im-5? This value is used throughout the post-tensioning industry when calculating actual number of tendons required during shop drawing creation. Post-tensioning applications include high rising buildings, office and apartment buildings, parking, structures, slabs-on-ground, bridges, sports stadiums, rock and soil anchors, and . Detailed discussions are presented on variations in the area and modulus of elasticity of seven-wire prestressing strand and variations in the values . The PT guys have two ways to measure cable tension, (1) direct measurement of force and (2) elongation. The following new Section is added after Section 460: SECTION B460 POST-TENSIONING B460-1 Description. ( 0000060414 00000 n This value comes from D = sL/AE where s = 189 ksi, L = 12 inches, A = 0.153 in 2, and E = 28,000 ksi. If the target was 50 KSI, you'd see values between 45-55 KSI. 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. The cells or cavity containing the tendons . Sale. suspension span, post-tensioned with 70-strand tendons. If the measured elongation are below the tolerance, another 5% of Stressing might be applied, or de-tension and stress again. The paper discusses the history or background of specifications on the elongation tolerance for post-tensioning tendons with particular application to segmental concrete bridges. 0000072924 00000 n Place additional wood brackets at these positions, if necessary, to distribute the load. Tendons today are seven high-strength steel wires wound together and placed inside a plastic duct. 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, elongation review is a critical part of an engineers acceptance of a post-tension slab, Virtual Reality Modeling for Client Walk-throughs, RAM Structural System: Integrated Gravity & Lateral Design, The Exciting Future of Bridge Inspections. It may even void the jacks calibration. Now, Ive said that we check every elongation, and that were very much aware of the upper edge of potential non-damaging elongations. 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. Elongations have been used to assess the forces inside post-tensioned tendons immediately after the post-tensioning operation. However, there are some important caveats to note here. If, after careful checking, the slab doesnt meet the engineers criteria, the tendon may have to be replaced. 0000003097 00000 n document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); 5335 W. 48th Ave. Suite 300Denver, CO 80212. As I explained earlier, post-tension stressing pumps are calibrated before they reach the jobsite to a pressure corresponding to 33.0 kips. This results in larger, column-free floor areas which greatly increase the flexibility of use . 0000071658 00000 n 0 Extreme fiber bending stresses will form only if stressing results in a change in slab curvature. In post-tensioning method, tendons are coated with grease or . The EOR normally specifies the initial tension required and leaves the measurement to the technicians in the field. "f'Ctr 0000106469 00000 n yF-KMjY+l$&h.7riCaJp%56eFK Did he need 18 tendons, or just 17.6? The Post Tensioning workers use many sized bar chairs that locate the strand cables at there correct profiles. Keywords: elongation variation, post-tensioning, tendon, tension, friction, wobble, elongation limits. All Rights Reserved. endstream endobj 404 0 obj <>stream This hybridisation helps achieve the formation of a much thinner slab with a longer span devoid of any column-free spaces. KmY@"[wXy85FAFkk 76 rfLg1RtqfKU-'$-n0=NeJvzLvS2dk]5R=PS,nY@m?==u(MN!vc70A+fq-N}3%WL6>RwgtcdD` At best, its a dirty, labor-intensive process thats prone to false starts; at worst, its invasive and dangerous. 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. 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. 2) Placement of the tendons. The straight length of the duct adjacent to the anchorage shall be in accordance with the post-tensioning system. Elongation result should be checked and verified by the engineer before cutting excess strand. 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 arrangement enables strand loads to be transferred to the concrete structure by bonding, which allows for passive reinforcement to be optimised and significantly reduced. retical elongation for a 400-foot-long strand, after initial tension of 3,000 pounds, is 30 inches. 91 0 obj <>stream when post-tensioning tendons are short. 0000129798 00000 n AcH%;R/Vb>(-II?sB3#Ncaic&:I=.Syoed8rD$`:b1qf'w ~EJfLKYwosd 0dwuuwEB|[x{w_n|lpvo?|r ?s{3YQQ)fKs,?gz1ghrN)@/Ym7Frq{4/sr%l(+#RyKta3Ca~l9}vdX5fXG#u*hUe2 y2@Sexs'3>2dG%Q7;{i+[%0=C=ENic+RcB8R1Idy^N@7_Qw^GJI However, the measured elongations are characterized by a high degree of uncertainty and variability due to site tolerances, and that the calculated elongations are based on the ideal equations using theoretical parameters. 0000006207 00000 n It is critical that only the jack supplier adjust this valve! Current design codes (ref. 0000002538 00000 n As youll recall from my post earlier this year, elongation review is a critical part of an engineers acceptance of a post-tension slab. ACI members have itthey are engaged, informed, and stay up to date by taking advantage of benefits that ACI membership provides them. endstream endobj 405 0 obj <>stream 4) Applying tension to the tendons. Help us help you by always stressing to calibrated gauge pressure . df41!Ph]nF Zm3,s,$(d! materials and method of fixation, . @Zef`Tfdx0Qqc&2v+M9/`zDL1=Fa_LcA=e@`0"@A! bbL EVstudio is a full-service in-house design firm specializing in architecture, engineering, planning, and other design services for commercial and residential projects. 0000119393 00000 n If the Engineer of Record cannot justify the tendons acceptability, hes forced to abandon it. Post-tensioning tendons, which are prestressing steel cables inside plastic ducts or sleeves, are positioned in the forms before the concrete is placed. However, I mostly concentrated on short pulls in that article. 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 . . Since the usual concern with elongation reports is understressed tendons, the occasional long tendon isnt a cause for great concern. 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 made up of steel strands housed in a duct, which is injected with cement grout after tensioning.

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