MEMBERS
553.01 Description
This work is the furnishing and placing of precast, prestressed concrete beams, slabs, piling, and other structural members.
553.02 Materials
553.02.1 Concrete
Furnish concrete in accordance with Section 551.
553.02.2 Reinforcing Steel
Furnish reinforcing steel in accordance with Section 555 and Subsection 711.01.1. Obtain the Project Manager’s written approval for reinforcing steel substitutions. State on the fabrication drawings showing reinforcing steel details the following or similar words: “All dimensions are out-to-out”.
553.02.3 Steel Rods and Bolts Furnish rods used as dowels and bolts in accordance with
Subsection 711.07.
553.02.4 Prestress Steel
Furnish high tensile strength steel wire in accordance with Subsection 711.11. Furnish the typical load-elongation curves for all shipments of prestress steel to the fabrication plant. Ensure all prestress steel used in the work is free of rust, corrosion, dirt, oil, spatter from welding or flame cutting, kinks, bends, nicks, broken wires, or other defects. Prestress steel is sampled in accordance with MT 111.
553.02.5 Enclosures
Use metallic enclosures, excluding aluminum, or forms using removable cores or ducts made of rubber or other approved material. Remove cores and ducts before installing the prestress steel. Use enclosures that are mortar tight and maintain their shape when subjected to loading. Use enclosures that are ¼-inch (6 mm) larger in internal diameter than the bar, cable, strand, or group of wires being enclosed. Equip cores or ducts with pipes or other connections for grout injection when pressure grouting is specified.
553.02.6 Structural Steel
Furnish structural steel in accordance with Subsection 711.02.
553.02.7 Elastomeric Bearing Devices
Furnish elastomeric bearing devices in accordance with Subsection 711.14.
553.02.8 Fiber Reinforced Pads for Bearing Plates
Furnish fiber reinforced pads in accordance with Subsection 711.16.
553.02.9 Deck Sealer
Furnish deck sealer for precast prestressed deck sections which is listed on the QPL and in accordance with Subsection 717.02. 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-2
553.02.10 Leveling Inserts
Furnish Leveling inserts for precast prestressed deck sections designed for a minimum working tension of 5,500 lbs. (24.4 kN) and have machine threaded ferrules. Use ¾-inch (19 mm) minimum diameter structural connection type leveling inserts.
553.03 Construction Requirements
553.03.1 Fabrication
Fabricate all prestressed concrete members using a manufacturing plant currently certified by the Prestressed Concrete Institute in the category applicable to the member being fabricated. The Department will make an exemption for new manufacturing plants that are of the same ownership as an existing certified plant, provided the new manufacturing plant operates under the same quality assurance and control programs as the certified plants, modified to address any production differences, and all fabrication is performed under the direct supervision of a quality assurance and control manager provided by an existing pre-qualified plant. Direct supervision means that the quality assurance and control manager is on site during all fabrication performed in the new fabrication plant and is responsible for the quality assurance and control activities. Furnish a copy of the plant’s current certification in the applicable category along with the fabrication drawings for the elements to be fabricated. For new manufacturing plants, submit and receive approval of any proposed modifications to the parent plant’s quality assurance and control program prior to beginning production. Allow 30 business days from the date submitted for Department review and approval. New manufacturing plants may operate under the parent plant’s quality assurance and control programs for a maximum of 18 months from the date of opening. Plants currently operating under this exemption may do so only until January 1, 2016. The fabricator may prestress by pretension or post-tensioning the member, subject to the contract requirements. Obtain written approval before changing the prestressing details.
553.03.2 Fabrication Drawings
Before casting members, submit fabrication drawings and designs calculations. Show complete details of the method, materials, and equipment proposed for use in prestressing. Include in the fabrication drawings the following information:
1.An erection layout of the members placed in the structure or structures with each prestress member assigned a production number. Mark each completed member with an assigned number.
2.A tentative fabrication schedule.
3.The proposed mix design, including admixtures.
4.The prestress steel manufacturer’s name and the applicable specifications.
5.Details of the method and sequence of stressing including the numbered or lettered layout to be followed to stress the member. Show complete details of the proposed method for tensioning the draped strands. Include in the details gauge and elongation readings for initial, intermediate, and final tensioning, as well as the deflection sequence, where applicable.
6.Complete details, including anticipated camber, tensioning forces (initial and final), and required concrete strengths (transfer and 28-day).
7.A complete detensioning procedure for the castings.
8.Details of items to be incorporated into the beam, such as chairs, inserts, hold-downs, etc., listed by source, type, size or capacity, and supplier. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-3
9.Show all items incidental to the beams, such as bearing plates, rocker assemblies, anchor bolts, etc., if supplied by the beam fabricator. Include the specification and grade of all steel items.
10.All information and data required for fabrication.
11.Show the tack welding procedures.
12.Detail the use of all external weights or hold-downs if used. If weights are not required, note it on the fabrication drawings.
13.Show the finish for all steel members incorporated in the beams. For galvanized items, identify the applicable specification. For painted items specify paint type, manufacturer and recommended dried film thickness for each coat applied in the shop. Also identify surface preparation for each item to be painted. For paint requirements, refer to Section 612.
14.Submit welder certifications and welding procedure specifications for all welding done to any member incorporated into the beam. For welding requirements see Subsections
556.03.1 and 556.03.10
; and
15.For precast prestressed deck sections:
a.Show the location of the leveling inserts; and
b.Drawings of the proposed leveling system. Show all changes from the prestressed details in the contract. Submit shop of welding procedures and design calculations. Ensure the submittal includes all information required to check the structural accuracy and fabrication procedures for the structure. Structural shop drawings must be designed and stamped by a professional engineer registered and licensed to conduct engineering in the State of Montana. Do not begin fabrication until the Department approved drawings are received by both the plant and the Department Inspector. Coordinate the fabrication schedule with the Department Inspector.
553.03.3 Design of Concrete Mixtures
The prestressed girder concrete must have a minimum ultimate compressive strength of 4,000 psi (27.6 MPa) at transfer of prestress and 5,000 psi (34.5 MPa) at 28 days. The actual required strengths are specified in the contract. Furnish a concrete mix design that produces concrete meeting the specified compressive strengths before use. Approved changes to the mix design may be permitted during fabrication. Use a concrete design of between 6.5 to 8.0 sacks of cement per cubic yard (350 - 450 kg/m
3.of concrete. Establish the Class Pre concrete slump range between 1 and 4½ inches (25 and 115 mm). The high and low limits of the range may not exceed 1½ inches (38 mm). The range may be changed with the Engineer’s approval.
553.03.4 Forms
Use steel side and bottom forms. End bulkhead forms may be steel or plywood. Form joints and strand exits through bulkhead forms that are mortar tight. Check the grade and alignment of side forms before casting. Check the beam bed alignment for displacement while placing the concrete. 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-4 Construct beam bed forms to limit movement to not exceed ¼-inch (6 mm) from a straight line in any 50-foot (15.25 m) length of the bed. Use clean forms that are free from warp, bulge, and other defects. Do not exceed a maximum offset of 1⁄16-inch (2 mm) where form sections are joined. Treat the form facing with a bond breaker before each casting. Form treating materials that stain or react with concrete are not permitted. Apply form oil or other bond breaker materials without contaminating the prestress strand and reinforcing steel. Clean soiled strand or reinforcing with a non-contaminating solvent. Chamfer all exposed concrete edges, excluding the beam top, with an enclosed angle of less than 120°. Use chamfer strips having no irregularities and maintain smooth joints with the chamfer tightly fitted against abutting forms. Fit forms with a grade strip or other positive control to establish the nominal depth of the beam. Use forms that can be removed from the member without damaging the concrete. Identify production form dimensions that vary from the contract beam dimensions on the fabrication drawings.
553.03.5 Placing Reinforcing Steel
Place and secure all reinforcing steel as shown in the contract before placing concrete. Fasten all bars at all intersections with adjacent bars. Do not tack weld reinforcing steel if the reinforcing bar is a stress-carrying member. Welding non-stress reinforcing bars may be permitted with the Engineer’s approval. Reinforcing steel welds not shown on the approved tacking detail or fabrication drawings are prohibited. For convenience, additional reinforcing steel may be tied in for securing inserts, void ducts, etc., or may be secured by tack welding. Protect the tensioning strand from weld spatter using wet burlap or other protective covering. Replace all strands with weld spatter at Contractor expense. Provide the distance between the reinforcing and side forms using approved stays, ties, or chairs. Do not use precast mortar blocks, pebbles, pieces of broken stone or brick, metal pipe, or wooden blocks. Provide clearance between the beam stirrups and the beam bed using metal chair supports with stainless steel or other approved, corrosion-resistant legs. Use reinforcing steel in the ends of prestressed beams to provide clearance for the paving notch block out, void ducts, embed plates and anchorages, and inserts without interfering with the reinforcement spacing. Reinforcement in the prestressed member will be inspected in place and approved by the Inspector before the concrete is placed. Concrete placed before inspection may be rejected.
553.03.6 Prestressing Equipment
Use approved jacking equipment for prestressing. Equip hydraulic jacks with pressure gauges. Have a certified testing laboratory calibrate each jack and gauge combination as a unit with the cylinder extension in the approximate position that it will be in at the final jacking force. Have a certified calibration chart for each jack. Other types of jacks may be used with proving rings or other approved devices calibrated by a qualified testing laboratory. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-5 Calibrate jacking equipment once each year and after each repair. Re-calibration may be required if any jack or gauge gives erratic results or if the difference between the gauge reading and elongations exceed allowable limits. Equip tensioning systems with hydraulic gauges that prevent the gauge pointer from fluctuating until the jacking load is released from the tendon. The gauge must read loads directly in pounds (Newtons) or have a chart to convert the dial reading into pounds (Newtons). Ensure the gauge readings are accurate to within ± 2%. Locate the gauges to provide the operator and Inspector a clear view of elongation measurements and gauge readings. Use gauge dials graduated in increments not exceeding 100 pounds (700 kPa) pressure. The gauge range or load cells must not use the lower 10% of the manufacturer’s rated capacity in determining the jacking stress, unless calibration data establishes accuracy within the 2% requirement at the lower range. Ensure the end anchorages and prestressed member stressing blocks can maintain the required tension in all prestressed tendons until the concrete has been placed and reached transfer strength. Equip the end anchorages and stressing blocks to detect deflection while prestressing. The Inspector will check for deflection. Provide the equipment to determine concrete compressive strengths at the location the prestressed members are manufactured. The test equipment may be mechanical or hydraulic, capable of applying and measuring the required load. Error for loads within the loading range of the test equipment may not exceed an error of ± 1.5%. Have a certified calibration diagram covering the entire use range with the equipment at all times. The indicated load of the testing equipment does not have to be corrected by calculation or by the calibration diagram to obtain values when the values are within the required variation of + 1.5%. Certify the concrete strength testing equipment every 2 years; after each repair or adjustment of the equipment; when a non-portable machine has been moved; and whenever accuracy is in question.
553.03.7 Pre-tensioning
Hold the prestressing elements in position using jacks when stressing. Keep a record of the jacking force and the elongations. Multiple units may be cast in a continuous line and stressed at one time. Leave a space between the ends of the units to permit cutting of the strands. Furnish strand in coils, reel-less packs, or on reels. Stringing may be performed by pulling single or multiple strands. Pull to gradually relieve strand rotation on coil or reel-less packs. Strand with gripped points are not permitted within the lengths to be stressed. Bring all prestress tendons to the uniform initial tension on the approved fabrication drawings. Initial tension is the minimum force required to equalize stresses and eliminate slack in the strand. Submit alternate initial loading proposals for approval. The initial load may be applied by the jack used for single strand tensioning or by any other approved method that provides a definite, uniform load. Regardless of the method used, measure the initial load within ± 100 pounds (450 N). Compute elongation measurements for initial tensioning but do not use as a measurement of the initial force. Once initial tensioning is complete, reference mark the strand as directed. The mark must provide an accurate measurement of elongation by final tensioning. Measure the induced stress by gauge and check it by elongation, load cell, or both. The results must agree within 5%. Do not permit jacking stress to exceed 75% of the specified minimum ultimate tensile strength of the prestressing steel. Measure the strand elongation to 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-6 within 1% of the theoretical elongation or ⅛-inch (3 mm), whichever is smaller. If a discrepancy between measured elongations and gauge readings exceeds 5%, check and correct the entire operation before proceeding with the work. All uplift devices, hold-down devices, and strand openings in end bulkheads must have rounded, smooth surfaces at all contact points with the strand. Take gauge readings, elongation measurements, and make calculations for elongation and include allowances for operational losses for the tensioning system used. These allowances must include losses for strand slippage, anchor movement, friction, strand rotation, and other forces acting on the strand. If the temperature difference between the strand at the time of tensioning and the concrete at the time of pouring exceeds 30 °F (16 °C), correct the computed elongation measurements for the temperature differences. Provide the elongation calculations to fabrication and inspection personnel at the beginning of production to ensure all allowances for the method of tensioning have been considered.
553.03.8 Final Tensioning
A.Single Strand Tensioning. After the initial load is applied and the reference marks are established, individually pull the strands to the final load. Tension each strand to the load required by the gauge reading. The elongation measurement must be within ± 5% of the load indicated by the gauge reading. If the load indicated by gauge reading doesn’t agree with the measured elongation within the required tolerance, discontinue tensioning and inspect the bed for restrictions that could affect the accuracy of the applied load. If the measurements agree, three more strands may be tensioned. If elongation measurement and gauge readings are within the required tolerance, the remaining strands may be tensioned. As some variation in the modulus of elasticity and the cross-sectional area of a strand does exist, the strand tensioning may be accepted, if the difference between the load determined by elongation and that indicated by the gauge does not exceed 5%. A maximum 10% of the total number of straight strands for any one line of casting will be accepted on this basis. If the difference between the elongation load and gauge readings exceeds the limits, discontinue tensioning, and correct the problem.
B.Multiple Strand Tensioning. Mark each strand, once pre-loaded and seated in the anchorage, at both end anchorages to determine elongation and slippage. The Inspector will establish references to verify parallel movement. Measure the stressing force by the gauge system and check it by the elongation measurement. Use 2 load cells to verify the applied design load and check the uniformity of pull. Place one load cell on each side of the line of pull, preferably on the outermost strands of an upper row of straight strands. If the hydraulic gauge and the load cells agree with the elongation measurements within ± 5%, the strands are acceptably tensioned. If the gauge reading is within 5% but either or both of the load cells exceed that limit, re-tension the strands including pre- loading. Locate and place the load cells on the strands nearest to those previously gauged. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-7 If, upon re-tensioning, the load cells are within the 5% tolerance, no excess strand slippage has occurred, and the movable anchorage has traveled the required distance, the tensioning may be accepted. If the difference between the gauge readings, load cell readings, and elongation measurements exceed the tolerance limit, stop tensioning, and correct the problem. Lubricate the jacking ram or rams, guide rods, and movable anchorage rails to minimize friction and run the ram through its length of travel at least four times before tensioning the strand.
C.Tensioning Draped Strands. Draped, pre-tensioned strands may be tensioned by partial jacking at the stressing block and subsequent depressing or uplifting to the deflected position or by tensioning to the initial and final loads with the tendons held in the final design position using pins, rollers, or other devices. Use low-friction devices at all points of slope change of the draped strand. When draped strands are partially tensioned in the straight condition and then depressed to the final design position, determination of the final load is made as follows:
1.Before starting the tensioning operation, place a load cell at the dead end anchorage on one of the strands to be deflected in each line of beams.
2.The Inspector will select the strand to which the load cell will be placed.
3.Once tensioning is complete, the load cell reading must be within ± 6% of the final design load. Should the load cell reading exceed the allowable tolerance, use additional deflecting jacks to distribute friction and restraint at the deflection points or, if necessary, revise the entire method for applying the final design load within tolerances. If the tensioning of draped strands indicates readings within the tolerances, the Inspector may require load cells for occasional checks. If tensioning of the draped strands is performed by partial tensioning and uplift or, by tensioning in the draped position, submit the method for approval before use. Strand splicing using approved devices is permitted. One splice is allowed on any one strand between anchorages. Splices must not fall within a beam. For single strand tensioning, the number of strands spliced is not restricted. When multiple strand tensioning is used, the number of strands spliced may not exceed 10% of the total number of strands in the casting line, or all the strands must be spliced. Use only one manufacturer’s strand in any one tensioning operation. Use the same direction of twist of strand wires in all spliced strands. One wire failure in 7 wire strands may remain in the casting, subject to the following: For beams with:
a.Less than 20 strands ................................... No wire breaks permitted
b.20 to 39 strands ........................................... 1 wire break permitted
c.40 to 59 strands ........................................... 2 wire breaks permitted
d.60 or more strands ...................................... 3 wire breaks permitted Should wire breaks exceed these limits, or more than one wire break in any individual strand, remove and replace that strand or strands. Locate all wire breaks allowed to remain in the casting, and securely wrap the broken ends with tie wire to prevent unraveling. 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-8 The Fabricator may be ordered to check the prestressing steel in a tensioned member for loss of prestress before placing concrete. The Project Manager will approve the checking method for loss of prestress. Re-tension all strands showing a loss of prestress exceeding 3% of the original computed jacking stress. Except as permitted in Subsection 553.03.5, do not weld, flame-cut, or ground welding equipment to the bed or forms after the prestress strand has been tensioned.
553.03.9 Placing Concrete
A.General. Batch and mix concrete in accordance with Subsection 551.03.3, except as provided below:
1.Provide master batch sheets for review before production.
2.A timing device that locks the discharge gates of a stationary mixer is not required, however, the mixer must not be emptied until the materials have been mixed the specified time.
3.Ready-mix delivery slips are not required unless specifically requested. The batching operation and equipment may be inspected at any time. The work will be stopped for failure to use approved procedures or equipment.
B.Method and Manner. Place concrete in accordance with Subsection 552.03.4 and the following. Obtain the Project Manager’s approval before placing concrete in large members. Concrete may be placed in the member in a single lift if satisfactory results are obtained, or in multiple horizontal lifts provided cold joints are not formed. Remove and replace concrete containing cold joints. When concrete is placed in layers, place the first lift to fill the form slightly above the juncture of the bottom flange and the beam web. Compact the concrete immediately after pouring with high-frequency mechanical vibrators operating at a minimum 4,500 impulses per minute. Apply vibration internally, externally, or a combination of both methods to flush the mortar to the surface of the forms. Vibrate succeeding concrete layers to extend into the previously placed layer. Use vibrators to thoroughly consolidate the concrete to a plastic mass without causing segregation. Do not permit vibrator heads to contact reinforcing steel, prestressing steel, or other embedded items to aid consolidation. Slowly insert and remove internal vibrators from the concrete. Have one additional vibrator available at the site at all times during concrete pours.
C.Concreting in Adverse Weather Conditions. Perform concrete work in accordance with Subsection 551.03.6 when the ambient air temperature falls below 40 °F (4 °C), except that the placement temperature for steam-cured Class Pre concrete must be between 50 and 90 °F (10 and 32 °C) at placement. When the ambient temperature before concrete is placed is 35 °F (2 °C) or less, pre- heat forms to a minimum 50 °F (10 °C) removing all frost, snow, and ice from the forms and components to be embedded in the concrete. Do not permit the concrete temperature to exceed 90 °F (32 °C). Cover open buckets of concrete with wet burlap mats or other approved coverings, when necessary, to prevent slump loss or premature drying.
553.03.10 Curing
Water-cure or steam-cure prestressed concrete members in accordance with Subsection
551.03 7
. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-9
553.03.11 Transfer of Prestress
Prestressed strands may be released when the concrete has:
1.Reached the minimum compressive strength for transfer of prestress.
2.The cure cycle is complete; and
3.Restrictive forms are removed. If delays are anticipated, maintain the temperature in the curing enclosure at a minimum 50 °F (10 °C) until transfer of prestress. Use positive, external hold-downs or weights to offset the uplifting forces in the member when the hold-down strands are released, when required. Use a method of harped and straight strands release to hold the lateral eccentricity of prestress to a minimum. Detail the bed release and the strand-cutting pattern on the fabrication drawings. Changes to the release procedures shown on the approved drawings are not permitted except by written request and the Engineer’s written approval. Cast cylinders to determine prestressed transfer strengths using MT 101 and MT 111 as modified below: • Cast and cure the release cylinders under the exact conditions the prestressed members were cured. • The concrete sample for each cylinder will be selected at random from different batches. Once the cure cycle is complete, test the release cylinders in accordance with AASHTO T
22.Test 3 cylinders to determine the prestressed transfer strengths for each round of beam castings. The average strengths of the 3 cylinders must equal or exceed: F'r + 0.35S Where: S = the standard deviation of the strengths for the 3 cylinders F'r = the required concrete transfer strength as specified in the contract Test all 3 cylinders within 30 minutes. Furnish the number of release cylinders required to perform these tests. The Contractor may cast additional back-up test cylinders. Should the release strengths not be reached, and all back-up cylinders are broken, put the casting through at least one additional complete cure cycle. The Engineer may direct other tests to determine release strengths. Test compression specimens using AASHTO T 22. While testing, apply the last ½ of the load at a rate between 1,200 to 3,000 psi (8.28 - 20.7 MPa) per minute. The Inspector will witness the Fabricator’s casting and testing of release cylinders.
553.03.12 Post-tensioning
Begin tensioning of the prestress reinforcing steel when the concrete cylinders representing the member to be prestressed reach the compressive strength shown on the approved fabrication drawings. Stress the prestress reinforcing steel, using jacks, to the specified tension with the stress transferred to the end anchorage. Measure the tension and elongation at all times. 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-10 Make a record of gauge pressures and elongation while post tensioning and submit it for review.
553.03.13 Bonding Steel
Bond post-tensioned steel to the concrete unless otherwise specified. Clean all dirt, loose rust, grease, or other deleterious material from all pre-stress reinforcing steel. Flush all conduits with water and blow them out with compressed air after post-tensioning. Remove rubber sheaths used as enclosures, then flush and blow out the voids as described above. Once cleaned, pressure-grout the conduit or void using a pressure not exceeding 100 psi (690 kPa). Continue grouting until a steady flow of grout exits from the pipe outlet. Close the outlet, then the inlet with the grout under pressure. Maintain the final grout pressure at between 50 to 100 psi (345 - 690 kPa).
553.03.14 Concrete Surface Finish
Perform the concrete finish work immediately after de-tensioning. Give the exterior surfaces of exterior members and the entire bottom flange of all girders to the juncture with the beam web an ordinary finish as specified in Subsection 552.03.11(D) . All other beam surfaces may be left with the surface created by the forms, if the surfaces are true, even, and free of stone pockets, depressions, or surface projections. Point with mortar and strike off even with the surrounding surface, all air holes in the concrete measuring ½-inch (13 mm) or more in any direction. Repair rough, uneven, and non-uniform concrete surfaces using power grinders, carborundum stones, brushhammers, or other approved equipment and then apply an ordinary finish. Match the appearance of the surface adjacent to the repair. Apply an ordinary finish to the entire adjoining surface of the member if a match is not possible. Repair rock pockets identified for repair. Chip rock pockets back to sound concrete, clean, and permit inspection before patching. Rock pockets affecting the member’s strength will be further evaluated before repair. Notify the Inspector of all members having the prestress strand exposed for 8 inches (200 mm) or more on any one strand or any exposure of multiple strands before repair. Provide an ordinary finish on beam ends not embedded in concrete. The Contractor may use approved epoxy or quick-setting grout products, provided the colors blend with the surrounding surface. Before finishing the beam ends, cut the strands back a minimum of ½-inch (13 mm) and fill the depressions with an approved epoxy. When beam ends are to be embedded in concrete, the ends may be left rough, and strands cut back to extend a maximum 1-inch (25 mm) beyond the surface of the concrete. Cut the strands in the area of the paving notch flush with the concrete surface. Screed and rough float the top surface of prestressed girders to the required depth of the member, bringing grout to the surface, and covering all aggregate. Clean all projecting reinforcing stirrups of mortar and other foreign materials before starting the cure cycle.
553.03.15 Workmanship and Tolerances
All tolerances are applied to the theoretical positions and dimensions shown in the contract and approved fabrication drawings. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-11 The tolerances from the plan and theoretical dimensions listed in Table 553-1 are the maximum acceptable cumulative deviations. The Project Manager will verify that the girders are within the allowable tolerances when the girder’s alignment is not influenced by temporary temperature differences between the girder’s surfaces. Tolerances in other manufacturing sequences cannot accumulate to supersede any individual tolerance. Members having dimensions outside the tolerance limits may be rejected. TABLE 553-1 TOLERANCES FOR PRESTRESSED CONCRETE MEMBERS Element Tolerance Length of beam, end-to-end, measured at centerline of beam, top or bottom flange ± ¾-inch (19 mm) Centerline-to-centerline of end bearing plates ⅛-inch per 10 feet (3 mm per 3 m), but no greater than ½-inch (13 mm) Depth of flanges, fillets, and web ± ¼-inch (5 mm) Depth overall + ½ to -¼-inch (13 to 5 mm) Width of flanges, fillets, and web + ⅜ to -¼-inch (10 to 5 mm) Beam ends - deviation from square or specified skew horizontal ± ¼-inch (5 mm), vertical ⅛-inch per foot (3 mm per 300 mm) of beam height or ½-inch (13 mm), whichever is less Side insert, center-to-center and center to beam end ± ½-inch (13 mm) Horizontal alignment (deviation from a straight line parallel to centerline of the member) ⅛-inch per 10 feet (3 mm per 3 m) of beam length but not greater than 1-inch (25 mm) Camber differential between adjacent beams measured at release of prestress (to be applied only to identical members cast in same line) ⅛-inch per 10 feet (3 mm per 3 m) of span to a maximum of 1-inch (25 mm) Stirrup bars (specified projection above beam top) ± ½-inch (13 mm) Tendon position ± ¼-inch (5 mm) in center of gravity of strand group and individual tendons Position of deflection points for deflected strands ± 6-inch (150 mm) Position of handling devices along centerline of beam ± 6-inch (150 mm) Centerline of bearing plates to end of beam ± ¼-inch (5 mm) Bearing plates (deviation from a plane perpendicular to the vertical axis of the beam) ± 1⁄16-inch (2 mm) Stirrup bars (longitudinal spacing) ± 1-inch (25 mm) Position of post-tensioning ducts ± ¼-inch (5 mm) 553 – PRESTRESSED CONCRETE MEMBERS 2020 EDITION V5.1 553-12
553.03.16 Storage and Transportation
Exercise care during transporting, storing, hoisting, and handling of the precast units to prevent cracking or damage. Transport precast girders and slabs in an upright position, with the points of support and directions of the reactions with respect to the members being approximately the same during transport and storage as when the members are in the final planned position. Lift the beams using the lifting eyes. During lifts, use spreaders between slings to eliminate the horizontal component of the lifting force from being applied to the beam. A spreader is not required when the angle between the sling and the top of the beam exceeds 45°. Do not move prestressed members from the casting yard until the concrete has reached the 28 day strength and the Project Manager has been notified of the intent to transport the beams. Replace units damaged by improper storing, handling, or transporting at Contractor expense.
553.03.17 Placing
Place precast, prestressed structural members as specified. Place piling in accordance with Section 559 .
553.03.18 Bearing and Anchorage
Place masonry bearing plates in accordance with Subsection 565.03.2. Place anchor bolts in accordance with Subsection 552.03.13.
553.03.19 Precast Prestressed Deck Sections
A.Fabrication Control. Schedule fabrication so that camber differences between adjacent deck sections are minimized. Measure camber on each deck section immediately after transfer of prestress forces. At transfer of prestress, the difference in camber between adjacent deck sections of the same design must not exceed ¼-inch (6 mm) per 10 feet (3 meters) of span length or a maximum difference of ¾-inch (19 mm), whichever is less.
B.General. Locate the leveling inserts so that the specified camber corrections are achieved. Center the leveling inserts over the beam’s web, install a minimum of ⅛-inch (3 mm) below the finished deck surface and cast into the member. Fill all insert holes with a non-shrink epoxy grout in accordance with Subsection 713.04 .
C.Leveling. Adjust by use of a leveling beam and jack assembly. Attach the leveling beam to the inserts and jack the deck sections to within ⅜-inch (10 mm) at the center of the span prior to placement of the weld tie connections and diaphragms. More than one leveling beam and jack assembly may be necessary to adjust adjacent sections. If the prescribed tolerance between deck sections cannot be attained by the approved leveling system, shim the bearings of the deck sections so that the required tolerance is met throughout the span.
D.Acceptance. Remove any grease, oil, or other contaminants on the deck surface by sandblasting. After sandblasting, power-wash the entire deck surface to remove concrete swarf, dirt, dust, and other debris. Allow the deck to dry until it is visibly dry with no ponding or dark areas indicating moisture in the concrete surface. Apply deck sealer by spray until refusal to the cleaned, dry deck. Refusal means that additional spray applications remain on the surface of the concrete and do not soak in. Ensure that a minimum of 28 calendar days have passed from the time the deck is cast to the application of the deck seal. Prevent chloride contamination of the deck during all stages of construction. 2020 EDITION V5.1 PRESTRESSED CONCRETE MEMBERS – 553 553-13
553.04 Method of Measurement
Precast, prestressed concrete members, excluding piling, are measured by the foot (meter) for each specified type and/or size, installed and accepted. Prestress beams are measured by the foot (meter) from centerline bearing to centerline bearing along the beam centerline. Precast prestressed deck sections are measured by foot (meter) for each type installed and accepted.
553.05 Basis of Payment
Payment for the completed and accepted quantities is made under the following: Pay Item Pay Unit Precast Member Foot (m) Prestress Member Foot (m) Prestressed Beam – (Type) Foot (m)
Referenced in this section
Sections that cite this one
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Source: Standard Specifications for Road and Bridge Construction, 2020 (v5.1) Edition. Pages 333–346 of 611. View official source ↗