0 m c However, the prestress forces developed in the strands of the multi-strand system frequently adopted in PSC structures differ from each other, which means that the prestress force in the multi-strand system cannot be obtained by simple proportional scaling using the measurement of the smart strand. . Therefore, the final effective force in the tendon is 189 minus 14 = 175 ksi. Debonding strands shall be avoided at girder ends located underneath expansion joints. Threaded rods (coil tie rods) installed in coil inserts (coil ties) that are cast into the ends of prestressed girders are provided to aid in transferring forces from the diaphragms into the girder ends. MRTS73 Manufacture of Prestressed Concrete Members and Stressing Units . Max stress due to jacking force = min( 0.94 f py , 0.80 f pu ) Max . 116119, 2016. r n If this is the case, establish the tie point at the specified station and plot the skew line at the required angle. Alternate bar reinforcing steel details shall be provided for all NU girders for all spans. New Mexico Department of Transportation. 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. For full depth cast-in-place decks, a minimum haunch of one inch at the centerline of girder and 1/2 inch at the edge of the flange shall be provided to allow for construction tolerances and normal concrete variations. Normality test showed that the measured prestress force per anchor head was normally distributed. See EPG 751.22.3.7.1 Dimensions for location of the corresponding detail circles. 7 Field-measurement of the prestress force was conducted on a total of 24 types of structures with different levels of prestress, number of strands, curvature of tendon, and girder length, averaging 49 girders, 194 anchors, and 2716 strands. Z. J. Liu, Research on design and construction of long connecting, high pier, large-span and dissymmetry continuous rigid-frame bridge, Journal of Railway Engineering Society, vol. This study proposed a closure jacking force calculation algorithm for curved prestressed concrete . Deflection is a downward displacement due to external loads. This enables not only the measurement of the prestress force, but also reuse of the sensor, which is in alignment with the purpose of this study. = p The pier-top torsion angle and longitudinal displacement of Pier 28# change from 0.27104rad and 4.12mm to 2.33104rad and 5.98mm with the jacking force increasing from 0kN to 1000kN, respectively. 1 Slab longitudinal reinforcement that contributes to making the precast beam continuous over an intermediate bent shall be anchored in regions of the slab that can be shown to be crack-free at strength limit states. The mean can be easily obtained by dividing the prestress force indicated by the hydraulic jack by the number of strands inserted in the anchor. Start out by laying in the centerline (CL) of the survey curve. The pier-top longitudinal displacement, transverse displacement, and torsional angle show an obvious linear relationship with the CJF. Distribution of residual prestress force excluding the mean prestress force from the prestress force of the strand: (a) Frequency distribution; (b) Density distribution. Objective III: the optimal stress state of piers after ten years of bridge operation. u i The prestressed concrete plant fabrication inspector shall check the materials, equipment, tensioning procedure and construction of the prestressed members and prepare daily written reports. Gross properties may be used to calculate losses and is consistent with AASHTO LRFD 5.9.3.4. 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. Accordingly, the changed mean prestress force at the considered time becomes fm +f. Prestressing and measurement on construction sites. Green items are guidance and shall not be shown on plans. Figure 13 plots the distribution pattern of the standard deviation of the prestress force per anchor head with respect to the number of strands per anchor. in kips. ), Factored shear from Strength I load combination, (kips), Distance from extreme compression fiber to the centroid of tensile force in the tensile reinforcement, (in. Cracked Section Properties Two facts about the geometric prop-erties of cracked prestressed concrete members should be clearly understood. 2 Here also, it is also concluded that the number of strands per anchor has practically no effect on the standard deviation. Alternate Bar Reinforcing Steel Details for NU Girders. v j holes are formed with galvanized sheet metal, the forms may be left in place. If the dowel bars are not exposed to net tension a 15-inch embedment shall be used regardless of bar size. The section near the diaphragm shall be from the perspective of the shorter girders. {\displaystyle \,\Delta _{CR}=(\Delta _{SS-j}+\Delta _{HS-j}+\Delta _{g})\Psi +(\Delta _{SS-I}+\Delta _{HS-I})0.7\Psi }. s Building Code Requirements for Structural Concrete and Commentary. Figure 4 shows photographs of the EM sensor device attached to the hydraulic jack. Transport and Main Roads Specifications, July 2019 . hairpins placed parallel to the centerline of the beam, with #4 horizontal straight bars at the top of the hairpin to ensure proper alignment. 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. For Group 1 arrangements, all strands in the center two columns are harped. The NU girders shall use conventional concrete with the following compression strength. The prestressing force may be assumed to vary linearly from zero at the point where bonding commences to a maximum at the transfer length. c The minimum reinforcement is #6 bars at 12-inch centers. Since concrete has no tensile strength, rebar provides this essential strength for the load transfer. g s This means that the unquantifiable skill and practice of the technician has a larger influence on the standard deviation relative to the distribution of the prestress force per anchor than the factors considered in this study. d 2018144. t For a calculated seismic vertical reaction or an anticipated foundation settlement resulting in a net tensile reaction, use the development length of dowel bars into beam and into diaphragm based on dowel bar size. High strength concrete may increase costs due to production modifications necessary to obtain the required strength. In the case of pre-tensioning the anchor holds the strands until after the concrete has gained sufficient strength; the strands are then released, transferring the prestressing force to the concrete. In terms of numbers, 49 girders, 194 tendons, and 2761 strands were measured. m See Bridge Standard Drawings for details. Deformations along the span length can be approximately determined as a product of final camber at midspan times correction factors. 0.50 Cho K., Park S., Cho J.-R., Kim S., Park Y.-H. Estimation of prestress force distribution in the multi-strand system of prestressed concrete structures. This indicates that large distortion is generated by the 3 outliers. The following dimensions shall be detailed on the plan sheets for open concrete intermediate diaphragms. ) Calculate the stresses in the concrete at transfer and at service. Note that barrier and railing are usually discontinuous over the bents. Measurement of forces in the cable stays of the apollo bridge; Proceedings of the 2nd Fib Congress; Naples, Italy. In this study, a closure jacking force calculation algorithm for curved prestressed concrete continuous rigid-frame bridges with asymmetric cantilevers and piers was proposed. T End diaphragms transfer loads at the end of slab to the girders and serve to tie girders together to better enable the bridge cross section to function as a unit. i L 119123, 2011. x Keunhee Cho and Jeong-Rae Cho wrote the paper. After several iterations, when the relative error of the jacking force calculated in the previous and last two calculations meets the expectation, the calculation can stop and the optimal jacking force can be obtained. When the . L 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. Notably, if the jacking force changes concrete creep secondary interior force, the pier stress is not completely in a linear correlation with the jacking force, but the jacking force can be modified through iteration. a Relationship between the pier-bottom stress and the jacking force after bridge completion. (2)The parameter can be calculated based on the numerical simulation model of the bridge, and the stress of j-th pier during the jacking process and at a time point in the bridge operational state under the action of no jacking force is denoted. y The shear center of each section is coinciding with the centroid, and the calculation satisfies the plane cross-sectional assumption and the rigid cross-sectional assumption [18]. 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. e is generated due to the deviation of the jacking force from the section centroid [2], where e is the vertical deviation distance. {\displaystyle \,V_{n}} Camber at midspan after erection (Estimated at 90 days). Then, and can be obtained. ) u E @article{Chen2022ACJ, title={A Closure Jacking Force Calculation Algorithm for Curved Prestressed Concrete Continuous Rigid-Frame Bridges with Asymmetric Cantilevers and Piers}, author={Chuang Chen and Xuyiling Wang and Qidong Lin and Yinhui Wang}, journal={Mathematical Problems in Engineering}, year={2022} } DESIGN OF PRESTRESSED CONCRETE. 02, pp. The following sections, except those specified as modified, shall be preferred because of their familiarity to local precast plants. Therefore, in order to determine the jacking force, the effect of torque on the piers can be ignored, and it just only needs to consider the effect of jacking force on the longitudinal and transverse bending of piers. endstream endobj startxref Stay connected and subscribe to get the latest news. Factored tensile force shall be less than or equal to the nominal tensile resistance. Moreover, this study also intends to propose a method enabling correlation of this distribution with the smart strand. Concrete shear blocks shall be used when 4 anchor bolts per bearing are insufficient, or for preventing loss of support on beams and stub bent footings. Spans over 90 feet require two intermediate diaphragms per span. 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. d Mean and standard deviation of prestress force per anchor head based on structural factors of considered PSC structures. L I Girders, Bulb-Tee Girders, and NU Girders with Alternate Bar Reinforcing Steel, NU Girders with Welded Wire Reinforcing Steel. C 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. Total initial prestress force equals the number of strands multiplied by the required initial prestress force per strand. V Jacking force in prestressed concrete | Post-tensioningWatch also:Concrete Pouring for Post-tensioning flat slab- :https://www . a ), = 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. The following details are required for closed concrete intermediate diaphragms and shall be provided on the plan sheets for intermediate bents as shown below. By summarizing the literature [1117], it can be found that the concrete shrinkage and creep can be fully developed after ten years of bridge operation, and there are two main methods to determine CJF: the first method is to offset the influence of concrete shrinkage and creep for ten years after bridge completion; the second method is to offset half of concrete shrinkage and creep for ten years after bridge completion, or the effect of concrete shrinkage and creep for three years after bridge completion, or half of concrete shrinkage and creep for the thirty years after bridge completion. Therefore, the closure jacking force will only influence the pier stress, and insufficient and excessive jacking force will generate tensile stress only for piers. Flexure capacity of girders shall be determined as the following. Using the same spacing scenario (i.e. Four or less spacing changes are preferred for spans up to 100 feet. A dead-load torque of the curved girder was applied through node torque. If straight strands are required below the harped strands the designer shall first attempt to locate these straight strands in the second row. In prestressed concrete, prestress is the permanent force in the member, causing compressive stress at the level of steel. For precast concrete, the clear distance between parallel bars in a layer shall not be lesser than: Minimum Spacing of Prestressing Strands 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 . 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 . 90 s e The prestressing levels per strand are between 164 kN and 200 kN, which includes the range actually found in real structures. H = height of shear block and shall extend to about an inch (+/-) above the top of the sole plate. Considering that the prestress force measured by the smart strand has changed by f from the prestressing stage to a definite time, it is reasonable to assume that the distribution curve of the prestress force has also translated by f during that period. e The force method equations can be written as follows: When a unit unknown force X1=1 acts on the basic structure and , the beam internal force is, When a unit unknown force X2=1 acts on the basic structure and , the beam internal force is. o E The nominal horizontal shear resistance of the interface plane shall be taken as specified in LRFD 5.7.4.3. e Therefore, it is necessary to carry out the pushing on the mid-span girder before bridge closure so as to improve the pier stress state after the bridge formed. The excess unknown forces X1 and X2 are used to replace the vertical support constraint and horizontal radial constraint of supports. = f The shear force and the axial force can be neglected when calculating curved beam deflection. For the sake of clarity only the keys (not the dowel bars) are shown in the plan of beam (plan showing joint filler). Open concrete diaphragms allow clearance for jacks required for future bearing rehabilitation and therefore should be used at girder ends with bearing assemblies (laminated neoprene, Type N PTFE, Pot and Disc bearings). Thus, the constrained multi-objective achieving problem in solving the jacking force can be solved using the multi-objective linear programming method, and the optimal jacking force can be calculated according to the following procedure:(1)The control section of pier and the pier allowable stress in the construction stage is determined according to relevant specifications or concrete material performance tests. The minimum thickness of the top flange and the overall height at the minimum point shall match the top flange thickness and height of the girder or spread beam used in design. Coping may be permitted with approval of the Structural Project Manager or Structural Liaison Engineer. e + 31, no. Spacing between each pretressing strand shall not be less than the larger of: Designers shall first attempt to use one of the strand arrangements specified in EPG 751.22.3.2.1 through EPG 751.22.3.2.5. An analysis of variance test for normality (complete samples). The following allowable modification of material properties listed in order of increasing costs may be considered if required by design. The differences from uniform girder height details are highlighted. The minimum " fillet weld between the " bearing plate and 1" sole plate is adequate for all cases. b Conventional concrete with the following compression strengths shall be used as required for I girders and bulb-tee girders. {\displaystyle \,v_{u}\geq 0.125f'_{c}} 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. L. S. Yao, Curved Beams, China Communications Press, Beijing, China, 1989. v Jacking stress is 80% of the tendon's ultimate strength (F pu) = 216 ksi. The data are available from author Chuang Chen (email: chenchuang@nit.zju.edu.cn). r Before the bridge closure, the closure jacking force (CJF) needs to be determined firstly, which plays an important role in mid-span deflection controlling and the whole bridge stress state. The pattern of the distribution of the standard deviation does not show particular tendency according to the increase of the structure length. + in., dividing the total initial force by this area results in a compressive stress over the total transformed area of 303.75/109 = I-Girders, Solid Slab Beams, Voided Slab Beams, Box Beams, Double-Tee Girders, Deck Panels and Miscellaneous Prestress Units, see Sec 1029. hmOH|qHJ". = First, normality test is conducted to determine if the distribution pattern of the prestress force per anchor head follows the normal distribution for the whole set of anchors. ) 14811486, 2018. Total deformation after slab is poured can be determined as the sum of theoretical camber of girder after erection (90 days) and deflections due to slab and concentrated loads (haunch, diaphragms, etc.) Losses include relaxation, creep and shrinkage, but exclude elastic shortening. Cho et al. Allow about 1/2 in. 22, no. The jacking force significantly affects the normal stress and deformation on piers in the state of bridge completion and ten years after bridge operation, while it has relatively small effect on the maximum principal stress of piers. After jacking to the full, required force, the force in the tendon is transferred from the jack to the end anchorage. The main-girder of T-frame (small T-frame) is 59m in height (changing according to 1.8-degree parabola) with 13 segments through symmetric cast-in-place cantilever method. It is permissible for the reinforcing bars and or the strands to come in contact with the materials used in forming A.B. V However, the latter factors relative to the technician cannot be quantified. Moreover, apart from these factors, the distribution of the prestress force in the tendon is also subordinate to the skill and practice of the technician. Qualified Labs Producers with Accepted QC Programs/Qualified Labs The jacking force can also make the beam of curved continuous rigid-frame bridges produce transverse bending and torsional deformation. F. Zhang and Y. Wang, Studies on closure jacking force and closure temperature of the continuous rigid frame bridge with Vshaped pier, in Proceedings of the 2018 7th International Conference on Sustainable Energy and Environment Engineering (ICSEEE 2018), Atlantis Press, Shenzhen, China, November 2018. The distance between these chords and their partner curves need to be calculated at five-foot intervals beginning at the center point of each chord. ) Stage Design Criteria 1. Accordingly, the evaluation of the extent of the influence on the distribution of the prestress force was done only for the factors that can be quantified. 4 fy = yield strength of shear reinforcement not to exceed 60 ksi. In the present study, a method estimating the force distribution in all the tendons of a prestressed concrete (PSC) girder installed with one smart strand is proposed. v From Figure 8, it can be noticed that main-girder concrete shrinkage and creep can force Pier 27# and Pier 28# clockwise and counterclockwise rotation, respectively. Length of WWR sections should be based on shear and confinement requirements before adjusting height to avoid multiple short sections. 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. Muhammed.OPERA. s This research was supported by a grant from a Strategic Research Project (Development of Smart Prestressing and Monitoring Technologies for Prestressed Concrete Bridges) funded by the Korea Institute of Construction and Building Technology. {\displaystyle \,d_{v}={\Bigg (}d_{e}-{\frac {a}{2}}{\Bigg )}\geq largerof{\begin{cases}0.9d_{e}\\0.72h\end{cases}}}, The horizontal shear between the girder and slab shall be determined as specified in LRFD 5.7.4.4. 0.125 Seating and friction losses bring stress in the tendon down to70% F pu = 189 ksi. c = This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (, optical fiber sensor, electromagnetic sensor, prestress, smart strand, multi-strand system, Distribution of residual prestress force excluding the mean prestress force from the prestress force of the strand: (, Comparison of the distribution of prestress force per anchor head and the normal distribution: (, Distribution of standard deviation of prestress force per anchor head: (. 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. Report on the plans the required number of strands by design and the total initial prestress force using EPG 751.50 Standard Detailing Notes H2c1.3. g {\displaystyle \,d_{v}} b d The corresponding stress results in the state of just after bridge completion and ten years of bridge operation are shown in Table 1, and pier-top displacement results are shown in Table 2. ), = Initial concrete modulus of elasticity based on, = Moment of inertia of transformed non-composite section computed based on, = Eccentricity between centroid of straight strand group (CSS) and center of gravity of transformed non-composite section (CGB) as shown in Figure below, (in. Especially, the lateral stress of Pier 27# side span even transforms from compressive to tensile in three years. 8.6.3.1 Reinforced precast concrete piles Diameter or minimum dimension measured through the center should not be less than 8 in. {\displaystyle \,d_{ps}} 5 Consider using the same number of draped strands for all spans and debond where needed. d V This device was used to measure the distribution of the prestress force in a construction site having real PSC girders. = 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. 3136+46, 2010. holes. 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 These will later be useful in laying in the wings and end bents. Lengths of barrier or railing between joints. {;fK6g{!3'gqfa{X-J0VL)33i]S?k@P 8 fB(R[LM5AI\ ( a The method can make multiple bridge piers (the stress state including multiple sections and multiple parts) simultaneously reach the optimal stress state, and can overcome the traditional method that can only control the bending effect of bridge piers in one direction. The more frequently used symbols and those that appear throughout the book are listed below. Short spans (<40 ft.) are to use straight strands only for all girders greater than 2'-8" tall. Power comparisons of shapiro-wilk, kolmogorov-smirnov, lilliefors and anderson-darling tests. Girder regions requiring shear reinforcement. 8 HV]kA}_gaf)[Aq> &$tMW{=5]{]G&KeeBd. = 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].
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