jacking force in prestressed concrete

{\displaystyle \,d_{v}} in., dividing the total initial force by this area results in a compressive stress over the total transformed area of 303.75/109 = 0 V Factored tensile force shall be less than or equal to the nominal tensile resistance. Type 7 and 8 girders, NU girders, and spread beams with top flanges exceeding a 4 percent cross-slope may experience sweep after form removal because of the unsymmetrical section and a resulting imbalanced prestressed load. y forces, shear walls and deep beams, beams with normal forces and torsional moments, and solutions dealing with membrane effects in slabs Simplifies the treatment of . Consequently, there is a need for a rational method enabling correlation of the measurement of the smart strand and the overall prestress force distribution. The finite element software MIDAS/civil was used to establish the calculation model of the bridge as shown in Figure 7. %%EOF r The following details satisfy the criteria for anchorage zone reinforcement in EPG 751.22.2.5 Pretensioned Anchorage Zones for up to the maximum number of bonded strands specified in EPG 751.22.2.5. = 384 Previous details showed the coping of the girders for the purpose of decreasing the length of the expansion device support piece. An additional spacing change (WWR piece) may be used in spans greater than 100 feet. This page was last edited on 2 June 2022, at 10:45. the display of certain parts of an article in other eReaders. Journal of Biomimetics, Biomaterials and Biomedical Engineering International Journal of Engineering Research in Africa If Note: The example shows Dimension A as greater than Dimension C. When Dimension A is less than Dimension C, modify detail to show this correctly keeping definitions of Dimensions A and C the same. Seating and friction losses bring stress in the tendon down to70% F pu = 189 ksi. The pier vertical normal stress reserve of the side span will decrease, and at last the tensile stress will even appear. R v The bridge has a total length 301m, and the span arrangement is 68+138+95m. The bridge curvature radius of the center upstream line is 350m, and the main-girder top and bottom flanges are 11m and 7m wide, respectively. Loss of Prestress (@ 0.4 L) PS force at transfer Po 279 k e 15.89 in o High-strength steel wires are stretched by a jacking mechanism that applies a force Q, as represented schematically in part a of the figure. {\displaystyle \,V_{c}=0.0316\beta b_{v}d_{v}{\sqrt {f'_{c}}}}, V MRTS73 Manufacture of Prestressed Concrete Members and Stressing Units . ( prestressed members follows. Dowel bars connect standard concrete diaphragms and beams on concrete girder bridges (standard fixed diaphragms are those with beam stirrups NOT extending up into the diaphragm). r 0.7 Concept of the estimation of the prestress force distribution. Main-girder concrete shrinkage and creep-induced pier-bottom normal stress. V hbbd```b``& , y"Y`B0nL_"`6 `v5n$/L q#30H0 ] d 7881, 2015. Tendons made up of strands are secured by steel wedges that grip each strand and seat firmly in a wedge plate. Developed device: (a) Electromagnetic (EM) sensor; (b) EM sensor device; (c) Schematic drawing of the composition of sensing device for the measurement of the prestress force distribution (EM sensor device + hydraulic jack). In addition, the closure jacking process can reduce the pier eccentricity and make the piers reach full-section compression for improving torsion stiffness [21, 22]. The designer needs to be aware of the fact that at an intermediate bent the distance between bearings on the approaching and leaving span sides will be different distances. The authors declare no conflict of interest. Measurement of forces in the cable stays of the apollo bridge; Proceedings of the 2nd Fib Congress; Naples, Italy. Investigate the possibility of using all straight strands when strength check of a hold-down device exceeds allowable. PLAN OF BEAMAnchor bolts and sole plates not shown for clarity. S E However, as shown in Figure 6, some strands exceed this stress limitation. 1, no. = c The standard " bearing plate will be anchored with four " x 4" studs for MoDOT shapes and eight x 5 studs for NU shapes. i endstream endobj 485 0 obj <>stream The minimum " fillet weld between the " bearing plate and 1" sole plate is adequate for all cases. Q. J. Alternate Bar Reinforcing Steel Details for NU Girders. Design shear blocks in accordance with LRFD 5.7.4.3. 41, no. e In this study, a closure jacking force calculation algorithm for curved prestressed concrete continuous rigid-frame bridges with asymmetric cantilevers and piers was proposed. In addition, the p-value of F-statistic indicates the validity of the regressive line with a value smaller than 0.05. In this point, the jacking force makes the pier in the stress state coupling with bending, shear, and torsion under the maximum single cantilever condition of the main beam. t 27, no. Total initial camber at transfer due to self-weight of girder and prestressing forces shall be determined as: W9 horizontal wire sizes shall be used with D22 vertical wires. Firstly, the mechanics method was used to analyze the relationship between the CJF and normal stress of main-girder and the pier. ( In terms of numbers, 49 girders, 194 tendons, and 2761 strands were measured. The so-obtained distribution of the prestress force, together with the measurement of the limited number of smart strands included in the anchor, were then used to track the change in the distribution of the prestress force in the in-service PSC structure. Therefore, in the closure jacking process of a curved PCCR bridge, it is necessary to control the longitudinal, lateral, and torsion deformations of piers. Two full-scale prestressed concrete girders were fabricated and used for the friction loss experiment. 1319. Pier stress at each stage under different jacking forces (unit: MPa). = Therefore, main-girder and piers stress can be solved by the force method in the maximum single cantilever state with the action of the jacking force. ), = Total prestressing force of straight strand group just prior to transfer, (kips), = Distance between centerlines of bearing pads, (in. STRENGTH limit states, see LRFD Article 6.5.4.2 & 5.5.4.2 Dynamic load allowance shall be applied. The approved agency shall make a verified report identifying the members by mark and shall include such pertinent data as lot numbers of tendons used . 3 ) needs to be added to the dimension in the section near diaphragm or the dimension replaced with Varies. Prestressed Concrete Sources A listing of sources with accepted quality control plans. http://creativecommons.org/licenses/by/4.0/. (1) Height of shear block shall extend a minimum of 1 inch above the top of the sole plate (typ.). The shear force and the axial force can be neglected when calculating curved beam deflection. The results plotted in Figure 9 show good agreement for the data with high significance probability and clear disagreement for the data with low significance probability. Bar size = #4 min. Calibration and classification of force measuring systems . R Frequency histogram of prestress force measured in considered strands. d Besides, to fully consider the effect of the CJF on longitudinal and transverse bending of piers, four corner points of each control section were selected as stress control points, and the corresponding objective functions were established according to the objectives I, II, and III, and with the stress at control points as the constraint condition, the multi-objective linear programming algorithm by MATLAB Optimization Toolbox was used for calculation. {\displaystyle \,\Delta _{FC}=\Delta _{90}+\Delta _{S}+\sum \Delta _{C}}. f Concrete intermediate diaphragms are cast between the ends of simple-span precast girders at interior supports and make the girders continuous for loads applied after continuity is established. s When steel, such as prestressing strand, is stressed beyond its elastic limit or yield strength, some of its physical characteristics change. d Figure 10 plots the density histograms of the standard deviation per anchor head. This prestress force in the PSC structure is generally introduced by means of steel strand. 5 They adhere to concrete and form a composite material with it. As shown in Figure 9c, these 3 outliers correspond to the computation of a large standard deviation caused by the loose arrangement of some strands in the tendon. With the girder designed and the camber and haunching dimensions calculated, the girder should be checked assuming the contractor will use a constant 1 joint filler. Prestressing and measurement on construction sites. Creep is a time-dependent phenomenon in which deformation increases under a constant stress. The designer should consider using a value of NB that is less than the total number of blocks, because all blocks may not resist equal amounts of force. The following dimensions shall be detailed on the plan sheets for open concrete intermediate diaphragms. The minimum haunch may need to be increased for Type 7 and 8 girders, NU girders and spread beams. Long-term losses in the tendon are assumed to be 14 ksi. The following charts provide span ranges (limits) for P/S I-girders based on girder spacing and standard roadway widths. 0.50 The lengths of the girders range between 39.5 m and 54.8 m, the tendon sag ratios vary from 0.0112 to 0.1420, and the number of strands per anchor head runs between 13 and 16; these measured details include most of the commonly used prestressing factors of the multi-strand systems. ) Relationship between the main-girder normal stress and the jacking force at central span cantilever root just after jacking process. Using these values, the distribution of the prestress force in the anchor can be estimated as a N(fm,2) normal distribution. The joint filler required for closed concrete intermediate diaphragms shall be shown in the plan of beam along with the bearings and girder chairs. The anchorage may be a simple steel bearing plate or may be a special casting with two or three concentric bearing surfaces that transfer the tendon force to the concrete. a In addition, the p-value of the F-statistic indicating the validity of the regressive line is smaller than 0.05 and shows that the regressive line is not valid. Prestressing strands shall be Grade 270 uncoated, low relaxation, seven-wire strands in accordance with AASHTO M 203 with the following design properties. The determination of the closure jacking force should be considered that piers maintain in optimal stress state after the bridge completion. 6 The return hydraulic pressure of the tensioning jack cannot exceed 10MPa. No limits are set for other types of prestressed girders however the Structural Project Manager or Structural Liaison Engineer shall be consulted prior to the design of any unusually long prestressed girder. I Girder regions requiring shear reinforcement. Moreover, the jacking force not only forces the pier to suffer longitudinal bending, but also causes the pier to suffer lateral bending and torsion bending, and it is mainly affected by the height of the pier, the radius of the curved beam, and the cantilever length of the curved beam. ) Since the EM sensor device must be attached to the hydraulic jack, the device was fabricated to be adaptable to the various jacks actually used on site. {\displaystyle \,Q=\textstyle \sum } According to Vlasov differential equation [19], the beamvertical displacement has no association with the bending moment Mz, so the following equations can be obtained:where and . d u 119123, 2011. Standard Specification for Low-Relaxation, Seven-Wire Steel Strand for Prestressed Concrete. to # 6 max. With a yield strength of 234.6 kN and ultimate strength 261 kN for a Grade 270 (1860) strand with a diameter of 15.2 mm, as specified in ASTM 416/416M [10], gives a maximum limit stress of 208.8 kN for the strand. Prestressed concrete beams of size 150 150 1000 mm were designed, and two bonded cold-drawn 7 mm steel wires were stressed at 70% UTS under service conditions before concreting. The pier-bottom normal stress is just listed, and the tensile stress is taken as +.. See the Structural Project Manager or Structural Liaison Engineer for full depth cast-in-place decks. The following dimensions shall be detailed on the plan sheets for concrete end diaphragms. ( r 7. This load shall be positioned at the 1/8 point from centerline of bearing pad. Assuming the force at transfer is 0.75*270 ksi the initial prestress force on the section is 0.75*270*1.5 = 303.75 kips. The last two columns of Table 1 arrange the mean of the mean prestress forces and the mean of the standard deviation of the prestress forces per anchor head by classifying the whole sets of measured data with respect to the girder length and tendon sag ratio. The reinforcement is that of the taller girder with additional #6 bars located under the shorter girder. Jacking stress is 80% of the tendon's ultimate strength (F pu) = 216 ksi. To that goal, this section examines the distribution pattern of the standard deviation per anchor head. v + d 3 increment spacing shall be used (i.e. A second anchor is secured against the member and the jacking force is released to transfer the load into the member as a precompression force. Here also, it is also concluded that the number of strands per anchor has practically no effect on the standard deviation. Specifically, the pier-top longitudinal displacement and torsion angle of Pier 27# will increase from 5.81mm and 0.54104rad just after bridge completion to 16.95mm and 2.29104rad in ten years of bridge operation, respectively, the lateral displacement will change from 0.07mm to 4.43mm. The one exception is that a closed-end diaphragm may be detailed in accordance with EPG 751.22.3.9.3 at finger plate expansion device connected to a steel girder series. Their elasticity modulus is Ep and Eb, and shear modulus is Gp and Gb. W 0.125 v For an explanation of post-tensioning terminology and acronyms,How to apply prestressed jacking force on strand | Post-tensioning | Post-tensioning jacking Process | What is post-tensioning jacking process? + W12 horizontal wire sizes shall be used with D31 vertical wires. 08, pp. i For composite design, the design cross-section should include the entire width of the roadway and the structurally continuous portions of railings, sidewalks, and median barriers. in post-tensioned we cast concrete then tendons are inserted inside ducts placed before concreting and then The bursting resistance of anchorage zones provided by vertical reinforcement (i.e., B2 bars and the D31 wires of WWR6) in the ends of prestressed girders at the service limit state shall be taken as: The required vertical reinforcement shall be provided within the following end regions: The number of strands bonded in the anchorage zone is limited by the standard bursting reinforcement of EPG 751.22.3.4.3 Anchorage Zone Reinforcement and the 20 ksi resistance stress limit. This makes the CJF more difficult to determine for curved PCCR bridges. i Note that barrier and railing are usually discontinuous over the bents. 2 which is known as f pi or the jacking stress f pj, and then estimating the amount of stress the strand will lose due to the time-dependent deformations (prestress loss f p). However, this assumption relates to the distribution of the prestress force of individual strands and does not mean that the distribution of the prestress force per anchor head is normal. V. Vlasov, Thin-walled Elastic beam, National Science Foundation, Washington. ( Prestressing force immediately prior to transfer, = Deflection due to self-weight of girder, = Camber due to prestressing straight strands, = Camber due to prestressing harped strands, = Camber at 7 days after strand release with creep, = Time - dependent camber due to creep at 7 days, = Camber at 90 days after strand release with creep, = Time - dependent camber due to creep at 90 days, Deflection due to concentrated loads (haunch, diaphragms, etc. | Jacking process | Immediately force at jacking | force on strand and tendon | Design of prestressed concrete at jacking | loss of prestressed concrete at Jacking | Post-tensioning work at site when jacking | jacking force |jacking force in prestressed concrete |jacking forces | jacking forces suspensionvia YouTube Capture Strand arrangements shall start at the bottom row and then move up for the most efficient design. Since only a very small portion of the data failed the normality test, it can be assumed reasonably that the distribution of the prestress force per anchor head follows the normal distribution. Using the following data, calculate (a) the total loss of stress in the wires, (b) The jacking force required at the left end: Coefficient of friction for curvature effect = 0.55 Friction coefficient for wave effect = 0.003/m. 1 The top flange height and overall height may be increased if required but any deviation from the standard sections shown shall be discussed with Structural Project Manager or Structural Liaison Engineer. p DESIGN OF PRESTRESSED CONCRETE. p f According to the DIN Technical Report 159, 4.2.3.2.3 [10], the concrete strength f cm,min (t 0) must at least be equal to 1.5 times the maximum concrete compressive stress at the time of transmitting the prestressing force whilst amounting to at least 25 N/mm. Check clearance from fill face of integral end bents to bottom flanges of NU girders. See EPG 751.11.3.6 Girder/Beam Chairs for additional girder chair details. These joints are placed perpendicular to the centerline of the roadway through the intersection point of the centerline bent and the inside edge of barrier or railing. ), = Eccentricity between centroid of harped strands (CHS) and center of gravity of transformed non-composite section (CGB) at the end of girder as shown in Figure below, (in. Group 2 arrangements are not provided in diagrams below for Type 6, 7 and 8 girders, but may be derived similarly to how specified for the smaller girders. v Since both density distribution and normal distribution are in good agreement, the distribution of the measured prestress force can be assumed to follow the normal distribution. Jacking Force for Prestressing Concrete Jacking force (Pjk) is the force used at the field to stress a tendon. A y Using the same spacing scenario (i.e. Shear blocks shall be detailed parallel to the centerline of roadway. ( Once the concrete is sufficiently strong, the tendons are stressed by jacking against the concrete. Cho et al. = Figure 7 redraws Figure 6 in term of the residual prestress force from which the influence of the mean prestress force is removed. for prestressed concrete, it's standard practice to measure force in the strand by two inde-pendent methods. Even if the overall average of the mean prestress force per anchor head does not exceed the criterion, the prestress force of some individual strands exceeds the limit stress criterion. f Design of Superstructure Prestressed Concrete Bridge Design Example Task Order DTFH61-02-T-63032 5-28 lump sum estimate, (2) a refined estimate, and (3) the background necessary to perform . c r The details are appropriate for bulb-tee and NU girders by substituting the appropriate reinforcing details from above. Max stress due to jacking force = min( 0.94 f py , 0.80 f pu ) Max . Green items are guidance and shall not be shown on plans. r H x Using the same shear reinforcement wire size for all of the spans is preferred but not required for girders of different spans lengths. Regular longitudinal slab reinforcement may be utilized as part of the total longitudinal reinforcement required. f With approval of the Structural Project Manager or Structural Liaison Engineer, closed concrete diaphragms may be used at bents free to expand longitudinally over the beam cap, completely separated by joint filler. The distribution of the prestress force in the tendon in the PSC structure can vary according to the length and curvature of the tendon, following the effect of the friction of the tendon. Razali N.M., Wah Y.B. Initial prestress force(P i ) is the force after transfer and is equal to jacking force reduced due to the instantaneous shortening of the concrete. Six spacing changes may be used for spans greater than 100 feet. The pier normal stress and the jacking force always show an obvious linear relationship in three states of jacking construction process, bridge completion, and ten years of bridge operation. ), = Prestressing force in the strand just prior to transfer, (ksi). F To that goal, a special electromagnetic (EM) sensor device, adaptable to various hydraulic jacks, was fabricated to measure the prestress force of each individual strand in the anchor head. F 48 Closed diaphragms at fixed bents allow for a change in girder heights within a continuous girder series (not to exceed next available girder height and only when specified on design layout or by the Structural Project Manager). = Tension is taken to be positive and compression is negative, throughout. Four or less spacing changes are preferred for spans up to 100 feet. Therefore, proper CJF is very crucial in controlling the piers stress state. [Oe?~0W$}wLA/Fgih1ZiX!o;&JAer &97r(x6n_`jRWn>yQ m B;DkS. EPG 751.22 illustrates the general design procedure for prestressed concrete I girders (Type 2, 3, 4 and 6), bulb-tee girders (Type 7 and 8) and NU girders (NU 35, 43, 53, 63, 70 and 78) using AASHTO LRFD Bridge Design Specifications except as noted. SERVICE I and SERVICE III Limit states shall be investigated at each stage. The use of G1 bars at 6-inch spacing shall be extended for the first 10 feet and then at 12-inch spacing for the remaining length of welded wire-reinforced NU girders. 6, 9, 12, 15, 18, 21 and 24) except when less than 6 spacing is required for the first set. in reply to: s304948LCUYF. Consider using the same section for all spans. X. M. Sonh, H. Melhem, L. J. Chrng et al., Optimization of closure jacking forces in multispan concrete rigid-frame bridges, Journal of Bridge Engineering, vol. The prestressing force may be assumed to vary linearly from zero at the point where bonding commences to a maximum at the transfer length. 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. Debonding a strand consists of wrapping the unnecessary strand(s) with a polyethylene plastic sleeve that prevents interaction of the strand with the concrete during casting and release which prevents any prestress force transfer. While the first launch was for a weight of 660t with a jacking force of 107t, the final launch was 31,400t with a jacking force of 2,600t. i A Deflection and camber calculations shall consider all internal loads (i.e., prestressing, concrete creep, and shrinkage) and external loads such as dead loads and live loads. (3)The concrete stress is prevented from exceeding the allowable value during the construction process. 27, no. 8 Although CJF can affect the longitudinal and transverse bending and torsional deformation of piers simultaneously, it cannot eliminate all deformations synchronously. Losses include relaxation, creep and shrinkage, but exclude elastic shortening. Confinement reinforcement (i.e., D1 bars or G1 bars spaced with WWR4) shown in the figure above shall be placed to confine the prestressing strands in the bottom flange for a minimum distance of 1.5d from the end of beam. H These sections have been entered into the beam section libraries of in-house design software. Moreover, this study also intends to propose a method enabling correlation of this distribution with the smart strand. Per Sec 1029, precaster may position hold-down devices +/- 6 in. For fixed bearings, Transverse FT = 0.25(DL) and Longitudinal FL = (0.25)(segment weight) at bent. For investigating maximum absolute deflection, all design lanes shall be loaded, and all supporting components should be assumed to deflect equally. d The section near the diaphragm shall be from the perspective of the shorter girders. fy = yield strength of shear reinforcement not to exceed 60 ksi. Copyright 2022 Chuang Chen et al. a The following maximum haunch at the centerline of the girder is allowed when prestressed panels are used: A maximum haunch of 3 1/2 inches is allowed for all girders when only the cast-in-place option is used. If the resistance provided by extending the vertical shear reinforcement is inadequate then, in lieu of increasing shear reinforcement, additional U bars may be provided as shown for a Type 7 girder in EPG 751.22.3.4 Girder Reinforcement. t The view before and after girder rotation is shown in Figure 4. {\displaystyle \,d_{ps}} However, the latter factors relative to the technician cannot be quantified. The recently developed smart strand can be used to measure the prestress force in the PSC structure from the construction stage to the in-service stage. 25, no. Sumitro S., Jaroevi A., Wang M.L. Consult SPM or Liaison on replacing "skew angle" with actual value for curved bridges. If the offset is greater than half the girder bottom flange width, see Structural Project Manager. The same shear reinforcement bar size shall be used in a girder. Without considering the effect of the jacking force on concrete creep, a linear relationship between the vertical normal stress of the j-th pier and the jacking force at one time point after bridge completion can be established as follows:where is the stress of the j-th pier at one time point after bridge completion; is the jacking force at the i-th position; is the stress variation of the i-th position of the j-th pier at one time point after bridge completion under the unit jacking force; is the stress of the j-th pier under the dead load; and is the stress of the j-th pier under the live load. c EM sensor device attached to hydraulic jack. The use of the modified girders shall be discussed with Structural Project Manager or Structural Liaison Engineer. L. Qin, J. F. Chen, H. Y. Hu et al., Study of incremental launching schemes for closure of Beipanjiang River Bridge, World Bridges, vol. Transmission and anchorage of prestress. 2 Stage Design Criteria 1. Normality test of residual prestress force per anchor head. Since the tendons may be intertwisted, the distribution can also be influenced by the number of tendons and the level of prestress. H = height of shear block and shall extend to about an inch (+/-) above the top of the sole plate. The following limit states shall be considered for P/S Girder design: See LRFD Table 3.4.1-1 for Loads and Load Factors applied at each given limit state. 1.6 = The number of strands per anchor runs around 1316, which constitutes a relatively small number of samples. See Structural Project Manager for preference on modifying this detail when either the end bent or intermediate bent is not applicable for the span. The optimal solution obtained with the multi-objective linear programming method is closely related to the objective function, but at present, there is no unified standard or theoretical basis for the control of closure jacking, and there is no unified objective.

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