jacking force in prestressed concrete

Main-girder concrete shrinkage and creep effect on pier deformation. The initial jacking force was assumed as 7500 kN, and the optimal jacking forces of objectives I, II, and III can be obtained by several iterations with 5,332 kN, 6,975 kN, and 12,997 kN, respectively. Lengths of barrier or railing between joints. The maximum edge distance in the direction of the spacing = half of reinforcement spacing. The tendency of the distribution of standard deviations of prestress force per anchor head is now examined according to the change in the length of the structure, the curvature of the tendon, and the mean prestress force. f 18. If Regular longitudinal slab reinforcement may be utilized as part of the total longitudinal reinforcement required. j { 20 is the maximum spacing for the D18, D20 and D22 wire sizes. Camber at midspan after strand release (Estimated at 7 days). The same shear reinforcement bar size shall be used in a girder. Keunhee Cho, Jeong-Rae Cho, Young-Hwan Park, Sung Yong Park, Young-Jin Kim, Sung Tae Kim analyzed the data. p For Group 2 arrangements, the bottom two center strands are straight (two less draped strands). Girders shall be first designed assuming that the contractor will vary the joint filler supporting the panels on the girder flange. Taking the optimal stress of piers after ten years of bridge operation as the objective (objective III), control point 3 at the bottom of Pier 28# will have tensile stress, and a larger longitudinal displacement will occur, too. 2830 September 2005; pp. Temporary stresses immediately after transfer: #3 through #5 bars = 4.0 x Nominal Bar Diameter. to dimensions and leader notes as appropriate. jacking force exceeds the 75% limitation, some of the wires or strands in the tendon may be seriously overstressed. r The intersection points of the outside edge of slab and the centerline of each bent or fill face can be connected with chords. The A1 reinforcement shall resist the tensile force in a cracked section computed on the basis of an uncracked section. Objective II: the optimal stress state of piers considering both that after bridge completion and ten years of bridge operation. Recommended Adjustments for Using the Charts: Because the span limit charts were developed using older design criteria as noted above, increased span lengths are probable. (Minimum #6 Bars @ 12" cts.). j The higher cost of the smart strand compared to that of the conventional strand renders it unaffordable to replace all the strands by smart strands and results in the application of only a limited number of smart strands in the PSC structure. 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 \,l_{d}\geq 1.6{\Bigg (}f_{ps}-{\frac {2}{3}}f_{pe}{\Bigg )}d_{ps}}, Where: For girders that have excessive haunch or girder steps, create new B1 bars and adjust heights in one inch increments or provide #4 hairpin bars in accordance with EPG 751.10.1.14 Girder and Beam Haunch Reinforcement to ensure at least 2 inches of embedment into slab. The following charts provide span ranges (limits) for P/S I-girders based on girder spacing and standard roadway widths. If the dowel bars are not exposed to net tension a 15-inch embedment shall be used regardless of bar size. Hole (1-1/2") to be grouted with approved non-shrink grout meeting the requirements of ASTM C1107. Relaxation of steel Relaxation of steel is defined as the decrease in stress with time under constant strain. s Y. 0.50 Conventional concrete with the following compression strengths shall be used as required for I girders and bulb-tee girders. The use of contact sensors, like the load cell, to measure the prestress force would require them to be installed between the concrete structure and the anchor. Firstly, an expression for mechanical relationship between normal stress of piers and the jacking force was derived, and the effects of concrete shrinkage and creep and jacking force on deformation and stress of piers were analyzed. {\displaystyle \,d_{ps}} 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). Distribution of considered PSC structures per length and sag ratio. I Optional Concrete Charts Only Criteria used in determining maximum span lengths for greater conventional concrete strength: The dimensions, reinforcement and guidance shown are also applicable to squared bents. I b v ACI 318-14 [9] limits the maximum tensile stress of the tendon due to jacking force during prestressing to a value below 0.94fpy (where fpy = yield strength), 0.80fpu(where fpu = ultimate strength), and a proposed value by the manufacturer. When locating the stations in the preceding step, the distance between CL of intermediate bents are exactly the layout lengths specified on the file. = before composite action between slab and girder. Concept of the estimation of the prestress force distribution. This part corresponds to the first step in the estimation of the prestress force distribution shown in Figure 15. However, camber, haunching and beam seat elevations shown on the plans should be based on the variable joint filler option. E This study verified that the individual strands pertaining to the same anchor could sustain different prestress forces and proposed a method enabling the estimation of the distribution of the prestress force in the anchor head in order to improve the applicability of the smart strands when present in limited number in PSC structures. The load from prestressing tendons can be defined only for bar elements in robot till now. tendon against the concrete. High strength concrete with compressive strengths up to fc =10 ksi (fci = 7.0 ksi) may be used with the permission of the Structural Project Manager or Structural Liaison Engineer. 41, no. Power comparisons of shapiro-wilk, kolmogorov-smirnov, lilliefors and anderson-darling tests. Per Sec 1029, precaster may position hold-down devices +/- 6 in. To consider the differences in the jacking effects of two piers of the PCCR bridges with asymmetric cantilever, the bottom and top of two piers were selected as control sections. r v + If this is the case, establish the tie point at the specified station and plot the skew line at the required angle. , shall be lesser of: V Estimation of Prestress Force Distribution in Multi-Strand System of Prestressed Concrete Structures Using Field Data Measured by Electromagnetic Sensor. The dowel bars and keys are required at fixed bents and shall be shown in the plan of beam showing reinforcement and in a section thru key detail (standard cell in MicroStation). 2 04, pp. 236240, 2008. G. G. Zhang and C. N. Wu, Discussion on jacking force design of continuous rigid frame bridg, Journal of China & Foreign Highway, vol. p This EM sensor device was used to measure the prestress force in each strand by attaching it to the head of the hydraulic jack (Figure 3). 8.6.3.1 Reinforced precast concrete piles Diameter or minimum dimension measured through the center should not be less than 8 in. Skews less than 40 degrees shall have girder ends coped on case by case basis. A mechanics model is shown in Figure 1. f With the jacking force increasing, the compressive stress on the outside of the curve raises, while the compressive stress on the inside of the curve decreases. Considering that the moment arm from the top of the thrust pier to the action line of the closure thrust is the longest and the transverse bending moment generated is also the largest, the main-girder normal stress at the cantilever root is displayed. ), = Total prestressing force of straight strand group just prior to transfer, (kips), = Distance between centerlines of bearing pads, (in. This page was last edited on 2 June 2022, at 10:45. The fabricator is responsible for determining the jacking force by adding the relaxation loss at transfer, jacking losses and seating losses to the Engineer-determined stress immediately prior to transfer. The ePub format uses eBook readers, which have several "ease of reading" features M. L. Xu and L. J. Luo, Control of pushing for closure of central span of Paidiao River Bridge No.1, Bridge Construction, no. For girders that have excessive haunch or girder steps, create new WWR and adjust heights in one inch increments or provide #4 hairpin bars in accordance with EPG 751.10.1.14 Girder and Beam Haunch Reinforcement to ensure at least 2 inches of embedment into slab. However, the closing jacking force does not transfer the normal stress from compressive to tensile, and the closing jacking force increases from 0kN to 10000kN while the normal stress only changes 1MPa. v Prestressing is a methdhod of reif iinforcing concrete. The use of all straight strands (none harped) may be considered when strength check of a hold-down device exceeds allowable. From Figures 14 to 16, it can be seen that the main-girder normal stress at the cantilever root of the central span has an obvious linear relationship with the jacking force. This bridge is a prestressed concrete continuous rigid-frame bridge with large spans, small curvature radius, asymmetry cantilevers and piers, and swivel construction. 1 For longitudinal displacement, a smaller pile numbers pointing to a greater pile number is taken as +; for lateral displacement, radially pointing to the center of circle along the curve is taken as +; for torsion angle, the counterclockwise rotation is taken as +.. i {;fK6g{!3'gqfa{X-J0VL)33i]S?k@P 8 fB(R[LM5AI\ o properly design prestressed concrete girders, designers must estimate the prestressing force that the strands apply on the concrete section, allowing . 7881, 2015. (2)The jacking force can also make the beam of curved continuous rigid-frame bridges produce transverse bending and torsional deformation. 03, pp. )== =QP,/gJ]JfhLY| Haunching shall be reported to the nearest 1/8 inch. + The debonded regions shall not be included when determining the nominal horizontal shear resistance. 12, pp. Measurement of forces in the cable stays of the apollo bridge; Proceedings of the 2nd Fib Congress; Naples, Italy. The EM sensor is a contactless sensor that was conceived based on the fact that the induced magnetic flux and current passing through the sensor experiences changes according to the stress state of the material [6]. Since the histogram of the prestress force shown in Figure 6 may exhibit various distributions according to the level of the design prestress force, the prestress force per anchor head is decomposed as follows in order to exclude the influence of the design prestress force. The use of the modified girders shall be discussed with Structural Project Manager or Structural Liaison Engineer. {\displaystyle \,\Delta _{IC}=\Delta _{g}+\Delta _{SS}+\Delta _{HS}}. `y u The finite element model had 881 units and 918 nodes in total. 1319. Z. Jing, Construction control of closure segment of asymmetric continuous rigid frame, Northern Communications, no. = The authors declare no conflict of interest. {\displaystyle \,\Delta _{ss-j}=\sum {\frac {F_{1-j}e_{1}}{8E_{ci}I_{tri}}}(L^{2}-4l_{0}^{2})}. Deformations along the span length can be approximately determined as a product of final camber at midspan times correction factors. 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. Distribution of residual prestress force excluding the mean prestress force from the prestress force of the strand: (a) Frequency distribution; (b) Density distribution. The return hydraulic pressure of the tensioning jack cannot exceed 10MPa. t Omit underlined portion of footnote (1) if prestressed panels are not used. Stage Design Criteria 1. d (c) 2'-6" unless skew requires wider diaphragm to accommodate coil tie rods. Step 2: Pumping grout. ( The dots indicate the distribution of the standard deviation and the solid line figures the linear trend line. Camber is an upward displacement caused by moment due to prestressing forces. However, the end spans need to follow the procedure for calculating length set forth in. G. Y. Tu, D. H. Yan, and K. B. Zhang, Calculation method and countermeasure for closure temperature influence in trussed CFST arch bridge, Engineering Mechanics, vol. 0.125 c The allowable stresses from ACI 31808 are shown on Figure A2. C. B. Yin, J. J. Wang, and C. Tang, Algorithms for the jacking force of high-temperature closure of a continuous rigid-frame bridge, Journal of Central South University of Forestry & Technology, vol. The prestress level was varied from 13% to 45% of the ultimate tensile strength of the prestressing tendon, and prestressing was performed by jacking one or . For self-weight of girder, In this study, a closure jacking force calculation algorithm for curved prestressed concrete continuous rigid-frame bridges with asymmetric cantilevers and piers was proposed. 08, pp. The main-girder concrete shrinkage and creep-induced pier-bottom normal stress during bridge operation period are shown in Figure 9, where the normal stress + is tension and is compression. f If the design requires a deviation from the preferred criteria then feasibility should be verified with a manufacturer. Shear stress on concrete shall be determined as: v 1.6 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. Temporary intermediate diaphragms/bracing are required for construction of the bridge deck. This will cause the slab thickness to vary due to camber of the girder, increasing load. Once the distance for CL bent to CL of bearing is calculated, the designer should offset lines by that dimension on either side of the CL of bent. 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. e holes are formed with galvanized sheet metal, the forms may be left in place. 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 . Three or less spacing changes (WWR pieces) are preferred for spans less than 100 feet. For fixed bearings, Transverse FT = 0.25(DL) and Longitudinal FL = (0.25)(segment weight) at bent. 4 Ag = area of gross concrete section at the cross section considered Ig = moment of inertia of gross concrete section at the cross section Considered Mg = bending moment due to self-weight of prestressed member and any other permanent loads in place at time of prestress In pretensioned members Pi typically is the prestress force level reflecting anchorage slip 12, pp. c adding effective prestressing force to prestressing loses will result in jacking force. Effective prestress force(P e | 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 987993, 2014. Therefore, the distribution of the prestress force in the anchor can be defined if the standard deviation is obtained. 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. DESIGN OF PRESTRESSED CONCRETE. The differences from uniform girder height details are highlighted.

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