Effective with the December 2018 Letting 233 2019 Standard Spec ifications Section 503 Prestressed Concrete Members
503.1 Description
1.This section describes fabricating, furnishing, transporting, and erecting prestressed concrete girders, or other prestressed concrete members.
2.These specifications provide fo r prestressing concrete members by the pretensioni ng method. In this method, stress the reinforcing tendons initially, then place an d cure the concrete and release the stress from the anchorages to the concrete after developing spe cified concrete strength.
503.2 Materials
503.2.1 General
1.Furnish materials conforming to the following: Bar steel reinforcement ................................................................................................................................... 505
2.Use galvanized or epoxy-coated steel, stainless steel, or non- metallic materials for hardware incorporated into the finished structure.
503.2.2 Concrete
1.Furnish concrete as specified in 501. If the design ultimate stress, f' c, the plans show is 8000 psi or higher for a prestressed concrete I-type girder, extend 28-day strength requirements within 503 for that girder to 56 days.
2.Ensure concrete attains a minimum 28-day compressive strength of 6000 psi for prestressed I-type girders. Base tests on 6-inch b y 12-inch cylinders, or 4-inch b y 8-inch cylinders, provided the engineer develops and approves a correlati on factor. Mold concrete cylin ders in steel or plastic molds. Cure concrete cylinders according to AASHTO T23, except cure the cyl inders with the member until release strength is obtained, then cure the cylinders according to AASH TO T23. Maintain laboratory facilities and equipment according to AASHTO M201. Make 3 cylinders for ea ch line of prestressed members poured and test each cy linder according to AASHTO T22. Calibrat e cylinder-testing equipment at least annually according to AASHTO T67. Average the strengths of the 2 cylinders with the highest test results for each line and use the average to determine complian ce with the 28-day strength requirement. Ensure that neither of the 2 cylinders with the highest test results h as a strength less than 10 percent below the required strength.
3.Instead of the above acceptance procedure, the engineer will a llow early acceptance of the prestressed units, before the 28-day test, if 2 successive laboratory tests on standard test specimens, cured continuously with and in the same manner as the units, in dicate compressive strength in excess of the required 28-da y strength. Test the 28-day strength cylin ders and record the results to maintain continuity of the contractor's quality control records.
4.Have an HTCP-certified PCC Technician I sample concrete, perfo rm fresh concrete testing, and fabricate and cure cylinders. Hav e an HTCP-certified Concrete S trength Tester, working in a department-qualified laboratory, perform cylinder and core comp ression tests. Determine the compressive strength in psi fo r each cylinder according to AASH TO T22. Test each cylinder to failure. Use a compression machine that automatically records the date, time, rate of loading on a load vs. time plot, and maximum load for each cylinder. Include a printo ut of this information with the strength documentation for each cylinder tested. Notify the engineer imm ediately if concrete cylinder compressive strengths are less than the required 28-day strength. Keep neatly documented records of all cylinder testing on the day of the test and make them avail able to the engineer.
5.Furnish prestressed concrete me mbers cast from air-entrained c oncrete, except I-type girders may use non-air-entrained concrete. Use type I, IL, IS, IP, IT, II, or III cement. The contractor may replace up to 30 percent of type I, I L, II, or III cement with an equal weight of fly ash, slag, or a combination of fly ash and slag. Ensure th at fly ash conforms to 501.2.6 and slag conforms to 501.2.7 . Use only one source and replacement rate for work under a single bid item. U se a department-approved air- entraining admixture conforming to 501.2.2 for air-entrained concrete. Use only size No. 1 coarse aggregate conforming to 501.2.5.4 .
6.The contractor shall determine pr oportions for the mix within the following limitations: Water cementitious mat erial ratio, w/cm ....................... ............................................................... .... 0.45 or less[1] Cementitious mat erial content ................................. ............................................ 610-800 pounds per cubic yard Air content: Prestressed I- type girders .................................... ........................................................ 6.0 pe rcent maximum Other com ponents .............................................. ............................................................... ... 4.5 - 7.5 percent Slump ......................................................... ............................................................... .......... 8 inches maximum[2] Effective with the December 2018 Letting 234 2019 Standard Spec ifications [1] The water cementitious materia l ratio is the weight of the tot al added water plus the aggregate free water, divided by the combined weight o f the cement, fly ash, and slag . [2] Proportion the mix to provide a concrete of uniform quality and consistency with a slump no greater than necessary for proper place ment and consolidation.
7.Incorporate a department-approv ed high range water-reducing ad mixture conforming to ASTM C494, type G. Instead of a type G admixtu re, the contractor may use t ype F and type D admixtures in combination to achieve equivalent results.
8.Use a department-approved set ret arding admixture as specified in 501.2.3.2 at the recommended rate if the ambient air temperatur e is 70 F or higher. The cont ractor may use it if the ambient air temperature is less than 70 F.
9.The contractor shall not add more admixtures or water after mixing is complete.
10.Use admixtures that do not have significant chlorides or chlor ides added during manufacture.
11.Use admixtures compatible wit h all ingredients of the concrete mixture.
503.2.3 Pretensioning Reinforcement
1.Use high tensile strength, 7-wire strands of the nominal diame ter the plans show and conforming to ASTM A416, grade 270.
503.2.4 Plant Certification
1.Obtain prestressed concrete m embers from fabrication plants th at comply with the department's plant certification program for fabric ation of prestressed concrete members, unless the engineer agrees to accept these items according to the alternate procedures set fo rth in the department's plant certification program.
503.3 Construction
Revise 503.3 to require electronic submittal of shop dra wings, a quality certification form, and a progress report form.
503.3.1 General
1.Submit shop drawings to the engineer conforming to 105.2 with electronic submittal to the fabrication library under 105.2.2 . Certify that shop drawings con form to quality control standar ds by submitting department form DT2328 with each set of shop drawings . Department review does not rel ieve the contractor from responsibility fo r errors or omissions on shop drawings.
2.Ensure that the fabricator submit s a fabrication progress repor t on department form DT2336 electronically to the department’s fabrication library. Update this form weekly for each structure in fabrication.
503.3.2 Stressing Procedure
1.Ensure all the strands of a pretensioned girder are free from kinks or twists before starting tensioning operations. Ensure no strand unwinds more than one turn after s tarting tensioning operations. Tension all the strands 1500 pounds each before starting elongation readings, or as the contractor determines; however, the contractor shall no t use an initial load greater t han 4000 pounds. This initial tension in any strand shall not vary by more than 5 percent. Use equipment to produce the initial tensioning load that provides a way of accurat ely measuring the force. If applying the initial tensioning load by pressure jacks, equip them with a proper gaging system for the initial force.
2.If tensioning draped pretensioned strands in a horizontal posi tion, tension them to a less than required the design stress so that the in creased strain from jacking the drape in the strands results in a stress equal to the required design stress.
3.If tensioning the draped strand s in their draped position, sup port them by rollers at points of change in direction. Ensure the hold-up rollers between girders and at th e ends of the end girders have either bronze bushings or roller bearin gs, and are well lubricated. Us e free running rollers at the hold-down points that produce minimal friction. If stressing from one end results in a difference of more than 5 percent between the load calcula ted from elongation and the gau ge load then tension draped strands from both ends. The sum of elongation at both ends shall agree within 5 percent of that indicated by the jack gauges.
4.Provide to the contractor's project file details showing numbe r, spacing, and method of draping pretensioned strands.
5.The department will allow one splice per pretensioning strand provided the splices are positioned so only one splice occurs within a member. Ensure that spliced str ands have the same twist or lay. Make allowance for splice slippage in computing strand elongation. Effective with the December 2018 Letting 235 2019 Standard Spec ifications (6) The engineer may accept failure o f one wire in a 7-wire preten sioning strand if it attains 85 percent of the required tension load before failure, and the failed wire c onstitutes not more than 2 percent of the total area of strands in an individual beam or girder.
7.If using a jacking system equipp ed with an automatic release v alve that closes if the required prestressing force is reached, there is no requirement to measu re strand elongation for all horizontal strands; however, this measurem ent is required for the first an d last strand tensioned and for at least 10 percent of the remaining strands. If performing elongation computations, take into account strand anchorage slippage, horizontal mo vement of abutments, and any change in temperature of the prestressing steel between tens ioning and when concrete takes i ts initial set, if this change is expected to exceed 30 F.
8.Equip prestressing sy stems with accurately calibrated gauges for measuring the loads produced. Ensure gauges are accurate to w ithin 2 percent and are equipped with a gauge dial read to the nearest 250 pounds of prestressing force. Use a department-appr oved testing laboratory to calibrate the gauge, and furnish a certifi ed calibration curve for each g auge. If gauges do not read loads directly in pounds, provide a chart tabulated in increments of at least 250 pounds for converting the readings to pounds. Calibrate the gauges with the gauges in place on the jacking system, completely assembled in the manner used i n the prestressing operation.
9.For gaging, use loads between 1/4 and 3/4 of the total graduat ed capacity of the gauge, unless calibration data clearly establish consistent accuracy over a w ider range.
10.Re-calibrate gaging devices at least once a year; however, if the gaging system gives erratic results, or if the gauge and elongation meas urements indicate significan tly different stresse s, then re-calibrate the jack and the gauges.
11.Measure the stress induced in t he prestressing element by both jacking gauge pressure and by elongation of the prestressing steel. If these measurements dif fer, use the gauge pressure to indicate the true stress in the prestres sing steel. There is an allowabl e master tolerance of +/- 5 percent between the actual gauge pressure and elongation and the calculated value of each. Additionally, there is a more restrictive 5 per cent tolerance for algebraic c omparison of the variation of gauge pressures to the variation of e longations. If the difference be tween gauge pressure and elongation exceeds 5 percent, carefully check the entire operation, determ ine, and correct the source of error before proceeding further.
12.Mark each anchor (dead, live, and splice) and visually check f or slippage in excess of that assumed in the calculations. Perform random measured checks.
13.During prestressing operations , provide the safety measures and means necessary to prevent accidents in the event the pres tressing steel, hold down device s, abutments, and beds break, or the grips slip.
14.Tension the prestressing elements to provide the required pres tress the plans show.
15.Perform transfer of prestress to concrete after the concrete develops the minimum required strength for transfer determined by the test cylinders.
16.Use the minimum required concr ete strength at tr ansfer of pres tress that the plans show.
503.3.2 1 Placing and Fastening Steel
1.Place steel units in the position the plans show and hold firmly during concrete placing and setting as specified in 505.3 .
2.Maintain distances from the forms by using stays, ties, hanger s, or other enginee r-approved supports. Separate layers of units by suit able devices. The contractor sh all not leave wood blocks in the concrete.
3.Position wires, wire groups, parallel-lay cables, and any othe r prestressing elements, correctly in the enclosures. Provide suitable horizontal and vertical spacers, if required, to hold the wires in true position in the enclosures.
4.Ensure that prestressing steel is free of dirt, grease, wax, s cale, rust, oil, or other foreign material that may prevent bonding between t he steel and the concrete.
503.3.3 Concrete Operations
503.3.3 1 Placing Concrete
1.Handle and place the concrete as specified in 502, except as specified otherwise below.
2.Place and consolidate concrete i n lifts in a way that prevents segregation, provides uniform consolidation throughout the memb er, and minimizes visible lift lines and dried concrete deposits along formed surfaces. Ensure not more than one hour elapses be tween placing successive lifts. Effective with the December 2018 Letting 236 2019 Standard Spec ifications (3) Consolidate the concrete in gi rders by internal, external, or both internal and external vibration. Avoid displacing reinforcing, conduits , or wires. Ensure that concret e is free from honeycombing throughout the member, free from voids aro und reinforcement and inserts, a nd free from excessive bug holing along formed surfaces.
503.3.3 1.1 Tolerances
1.Cast prestressed concrete members to plan dimensions within th e following applicable tolerances: PRESTRESSED CONCRETE I-TYPE GIRDERS Depth of the flange, web, and f illets ......................... ............................................................... .................. +/- 1/4" Depth overall ................................................. ............................................................... ................... +1/2" to -1/4" Width of flanges and fill ets .................................. ............................................................... .............. +3/8" to -1/4" Width of web .................................................. ............................................................... ................... +3/8" to -1/4" Length of beam ................................................ ..................................... +/- 1/8" per 10', up to a max of +/- 1 1/2" Deviation from square of exposed beam ends Horizontally. ................................................. ............................................................... ........................ +/- 1/4" Vertically. ................................................... .................................................... +/- 1/8" p er foot of beam depth Side inserts, spacing between centers and from centers to beam ends ................................................... +/- 1/ 4" Bearing plates, spac ing between centers ....................... ....................... the greater of +/- 1 /8" per 10', or +/- 1/2" Bearing plates, spacing from center s to beam ends ............................................................................ ..... +/- 1/4" Bearing plate or bearing area, deviation from plane ........... ............................................................... ..... +/- 1/16" Stirrup bars, projecti on above top of beam .................... ............................................................... ... +1/4" to -3/4" Stirrup bars, longi tudinal spacing ............................ ............................................................... ...................... +/- 1" End of stirrup bars from end of beam .......................... ............................................................... ........... 2" or less Horizontal alignment, deviation fr om a straight line, "sweep" . ............................... 1/8" per 10' of member length Camber, differential between adjac ent beams ................... ........................ 1/8" per 10' of s pan up to a max of 1" Center of gravity of d raped str and group ...................... ............................................................... ............. +/- 1/4" Center of gravity of draped st rand group at end of beam ....... ............................................................... ... +/- 1/2" Position of hold-down poi nts for draped strands ............... ............................................................... ............ +/- 6" Position of hand ling devices .................................. ............................................................... ....................... +/- 6"
503.3.3 2 Curing
1.Steam cure concrete members as specified below or cure by othe r methods identified by the contractor's fabrication quality control plan. Protect the surf aces of members exposed during curing from moisture loss until release strength is obtained. The cont ractor shall not use curing compound for this purpose. 503.3.3.2.1 Steam Curing
1.If steam curing, enclose the conc rete member in a chamber or e nclosure, with at least 12 inches between the member and the enclo sure. If using tarpaulins for e nclosures, use at least 2 layers and arrange them to form a tight enclo sure that leaks as little steam as possible. Use low-pressure steam and do not allow steam jets to spr ay directly on the concrete o r on the forms. Maintain the relative humidity at approximately 100 pe rcent within the enclosure.
2.Maintain the concrete temperature at or near the pouring tempe rature until the initial set, according to AASHTO T197, before allowing the temperature to r ise. The rate of temperature rise of the concrete shall not exceed 40 F per hour.
3.During curing maintain the inte rnal concrete temperature betwe en 50 F and 160 F. Ensure that the temperature of the concrete in di fferent locations within the h ousing does not vary more than 20 F at any time.
4.Place a minimum of 3 engineer-approved continuous recording th ermometers in each line. Provide the engineer with complete temperature record charts for the curing period, including the heat-up and cool-down times. If the temperature records indicate that steam control produces rates or temperatures that do not conform to those specified, modify pro cedures to obtain specified results.
5.Continue steam curing until the concrete develops the required strength for transfe r of prestress. The contractor may then discontinue steaming and uncover the beam. Cure the test specimens used to determine the above strength as specified in 503.3.3.3 .
6.If steam-curing girders, relea se the prestressing strands imme diately after steam curing. Cut or release strands in a sequence tha t minimizes eccentricity of pr estress force in the beam. Effective with the December 2018 Letting 237 2019 Standard Spec ifications (7) If the contractor wants to remov e the forms before completing the steaming, the contractor may uncover the beam one side at a time and for as much length as r equired to remove the form sections. Immediately replace the covering after removing each form secti on. During this operation, the contractor shall not expose the forms and beam surface for more than 30 minutes.
503.3.3 3 Test Cylinders for Release of Pretensioned Steel
1.Make test cylinders for determin ing the time for releasing the pretensioned steel. Make 6-inch by 12- inch test cylinders and mold them i n suitable steel or plastic molds. Cure the test cylinders with the represented concrete member until removal for capping and testi ng. Ensure that at least 2 cylinders have strengths above the minimum specified required strength, or average above the specified minimum with the lower not more than 5 percent below this strength, before releasing the tension. Make these test cylinders in addition to the cylinders designat ed in 503.2.2 for determining the 28-day strength.
503.3.3 4 Surface Finish
1.The manufacturer of prestress con crete girders or other member s shall notify the engineer of the following: - All honeycomb deep enough to ex pose the prestressing steel. - Defects that may affect bond length or transfer length. - Any area that the manufacturer believes to be detrimental.
2.The engineer responsible for inspection at the prestress concrete manufacturing plant will consult with the manufacturer to determine t he corrective action required to repair the member. The prestress manufacturing plant is responsible for rejecting prestress memb ers that cannot be effectively repaired. The engineer is responsible for acceptance.
3.Provide a sack rubbed surface fi nish on the exposed surfaces of prestressed concrete girders as specified in 502.3.7.5 before shipping from the plant. Provide a wire brush or stiff broom finish on surfaces to be bonded. Provide a smooth trowelled finish on the top surface of the top flanges of bulb tee girders, except for the bonding region centered over the we b.
4.After the sack rubbed finish adequ ately cures, apply engineer-approved gray-pigmented concrete sealer for non-trafficked surfac es uniformly to sack rubbed and smooth trowelled surfaces using the manufacturer’s recommended rate and procedures. Apply sealer an d allow adequate time for sealer to dry before shipping prestressed concrete members from the plant . Add 503.3.3.4(5) to specify fillin g precast voids created for trans port, erection, or deck forming.
5.Fill exposed voids created for tr ansport, erection, or deck for ming. For voids with a surface opening greater than 2 inches in diamet er, dry and uniformly coat void surfaces with an epoxy bonding agent conforming to ASTM C881 type II and following the bondi ng agent manufactu rer's recomme ndations. Epoxy bonding agent is not required for voids with a surface opening of 2 or less inches in diameter. Fill with an engineer-approved non- shrink grout immediately aft er applying the bonding agent, unless the grout manufacturer recommends otherwise.
503.3.4 Transportation, Sto rage, and Erection
1.Transport, handle and store the prestressed girders in an upri ght position, and ensure that points of support, and direction of the reac tions with respect to the gir der are approximately the same during transportation, storage, and erect ion as when the girder is in its final position. The maximum overhang from the point of support to the end of girder during storage, handling, and transporting shall not exceed the depth of the girder unless the engineer allows a lar ger overhang.
2.Handle, store and erect prestressed units in a way that preven ts cracking or other damage to the unit. Discard and replace units damag ed by improper handling or stori ng.
3.Do not transport or erect prest ressed girders before they attain a minimum 28-day compressive strength, determined from test c ylinders made, cured, and teste d as specified in 503.2.2 . The engineer may allow delivery and erection o f girders before their accepta nce, pending strength tests, if the contractor provides in writing that it accepts re sponsibility f or their removal and replacement in the event of rejection due to deficient strength.
4.The contractor shall not place fl oors on girders until the spe cified tests made on representative test cylinders indicate they achiev ed their minimum 28-day strength.
5.If, during the prestressed gird ers erection, the contractor el ects to use a crane on the girders before placing and curing the concrete s lab for the span, then the con tractor shall submit details of the proposed temporary flooring, the strutting between the girders, and information about the crane used to the engineer for prior approval. Effective with the December 2018 Letting 238 2019 Standard Spec ifications (6) Clean the exposed surface of sta inless steel bearing plates on girders before setting the girder on the opposing bearing surface. Ensure that bearing surfaces are clea n and free of materials that could adversely affect the functi on of the sliding bearing.
503.4 Measurement
1.The department will measure the Pr estressed Girder bid items by the linear foot acceptably completed.
503.5 Payment
1.The department will pay for measured quantities at the contrac t unit price under the following bid items: ITEM NUMBER DESCRIPTION UNIT 503.0100 - 0199 Prestressed Girder (type) (inch) LF
2.Payment for the Prestressed Girder bid items is full compensat ion for providing girders, including concrete, grout, morta r, reinforcement steel, tie bars, anchor plates, and other embedded metal; for casting and curing concrete; fo r jacking and prestressing; for handling, hauling and erecting; and for discarding and replacing units damaged by improper handling or storage.
3.The department will accept prestressed concrete members with 2 8-day concrete cy linder strengths below the required 28-day compres sive strength, as specified in 503.2.2, based on a pay reduction, if the 28-day concrete cylinder st rength provided is greater than the engineer-determined design strength of the individual member. The department will reduce p ayment for an accepted member with 28-day concrete cylinder strength less than the required 28-day compressive strength by the greater of $500, or 20 percent of the contra ct unit price applied to the m easured length of the member.
4.If the 28-day concrete cylinder str ength for the prestressed c oncrete member falls below the engineer- determined design strength of t he individual member, obtain cor es from each member according to AASHTO T24, test according to AASHTO T22, and evaluate for stre ngth comparison. Obtain the engineer's approval for the core sample locations. If the avera ge of 3 core strengths per member satisfies the design strength, and if none of the core strength s are less than 10 percent below the design strength, the engineer will accept t he member based on t he pay reduction defined above for deficient 28-day concrete cyli nder strengths. The contractor may perform coring and testing, or an independent testing a gency that the engineer a pproves may perfo rm coring and testing. The engineer will observe coring and testing done by the contra ctor. Costs a ssociated with taking, analyzing, and testing cores are the cont ractor’s responsibility. Effective with the December 2018 Letting 239 2019 Standard Spec ifications Section 504 Culverts, Retaining Walls, and Endwalls
504.1 Description
1.This section describes providi ng culverts whether defined as a culvert or bridge under 101.3 , retaining walls, and endwalls. This work does not include providing pipe culverts.
504.2 Materials
1.Furnish steel reinforcement conforming to 505 . Revise 504.2 to specify different concrete material requirements for cast in place vs precast structures.
2.For cast in place structures, furnish grade A, A-FA, A-S, A-T , A-IS, A-IP, or A-IT air-entra ined concrete conforming to 501 as modified in part 7 . Where the contract specifies or the engineer allows, the contractor may use high early s trength concrete. Provide QMP fo r concrete as follows: - For culverts and retaining walls as specified in 715 for class I structure concrete. - For endwalls as specified in 716 for class III ancillary concrete.
3.For precast structures, conform to ASTM C1577 . Manufacture in a plant lis ted under precast concrete fabricators on the department's APL. Conform to the specified ASTM ma terials requirements for the structure specified except as follows: - Use concrete with 565 pounds or m ore cementitious material per cubic yard. - The contractor may use cement conforming to 501.2.1 or may substitute for portl and cement a t the time of batching conforming to 501.2.6 for fly ash, 501.2.7 for slag, or 501.2.8 for other pozzolans. In either case the maximum total supplementary cementitious content is limited to 30 percent of the to tal cementitious content by weight. - For wet cast use air-entrained concrete with 7.0 percent +/- 1.5 percent air content.
504.3 Construction
504.3.1 General
1.Construct culverts, retaining walls, and endwalls conforming to 502.3 .
504.3.2 Placing Concrete
1.For constructing concrete box c ulverts, unless specified other wise, place the curtain walls, base slab, and the barrel sidewalls as a single unit to an approximate hei ght of 6 inches and allow to set before constructing the remaining culvert. If constructing the sidewal ls and top slab of box culverts as a monolith, allow not less than one hour or more than 3 hours to elapse between completing placement of the sidewalls and beginning placement of the top slab.
504.3.3 Removing Falsework and Applying Load
1.For culvert spans less than 12 feet, the engineer may allow fa lsework removal based on one of the following: - Absent compressive strength in formation, the mi nimum equivalent days specified in 502.3.10.1 . - With compressive strength information, a strength of 2000 psi or greater.
2.For culvert spans of 12 feet and greater, the engineer may all ow falsework removal after 7 equivalent days as defined in 502.3.10.1 .
3.The contractor may backfill culverts, retaining walls, and end walls that have attained the specified compressive strength or upon expiration of the minimum times as specified in 206.3.13 . Do not apply additional loads on culverts until attaining a compressive stre ngth of 3500 psi or, absent compressive strength information, for at least 21 days.
504.3.4 Name Plates
504.3.5 Curing
1.Cure concrete in culverts, ret aining walls, and end walls by any of the methods specified in 502.3.8 .
2.Cure retaining wall parapets with pigmented cure and seal conf orming to 502.2.11 . If applying architectural or other surface treatments, use a curing method compatible with those treatments.
504.4 Measurement
1.The department will measure the several bid items that constit ute the completed and accepted structure according to the prov isions of the contract for those bid items and in the units the contract specifies. All work i ncluded within the sc ope of this contract but not listed as bid items in the proposal is incidental to the work.
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Source: Wisconsin Standard Specifications for Highway and Structure Construction, 2019 Edition. Pages 242–247 of 601. View official source ↗