PRECAST & PRESTRESSED CONCRETE BRIDGE UNITS
The purpose of this Instructional Memorandum is to set forth the minimum requirements of the fabricator’s Quality Control Program for the fabrication and inspection of precast/prestressed concrete bridge units. Approved producers and fabricators are listed in the Materials Approved Products Listing Enterprise (MAPLE). Apply this IM to both LRFD and LX beams except otherwise noted.
To ensure that all work performed will be in accordance with the contract documents by establishing management commitment to quality control, with trained, qualified, certified personnel and uniform production procedures.
In order to furnish precast/prestressed bridge units to projects administered by the Iowa Department of Transportation, the fabricator shall be placed on the approved producer/fabricator list (Appendix A) prior to the letting.
Each fabricator must submit a written application to the respective District Materials Engineer (DME). This application shall detail the fabricator’s Quality Control Program. NOTE: Fabricators with operations in more than one District shall apply to the appropriate DME for each site. (A sample application is attached to this IM.)
Prestressed concrete plant approval shall be dependent on a satisfactory inspection of the plant by both District Materials Engineer and the Prestressed and Precast Concrete Engineer after the plant’s quality control plan meets all the Iowa DOT requirements and recommendation by the District Materials Engineer (DME) responsible for inspection of the plant.
Each fabricator/producer shall have a plant specific Quality Control Procedure Manual modeled and detailed in accordance with the “Guidelines” for the fabrication of precast/prestressed bridge units intended for use on state, county and/or city projects. Guidelines of quality control for the fabrication of precast/prestressed bridge units are listed in Appendix F of this IM.
These guidelines are considered the principal factors in quality control and are the basis upon which each plant-specific procedure manual will be accepted and/or rejected. The plant-specific procedure manual shall detail fabrication procedures such as but not limited to: description of production lines, calculation procedure, tensioning procedures, concrete mixtures, approved mix designs, concrete placement and consolidation, detentioning procedures, curing procedures, repair and finishing procedures, handling, storage and shipping procedures. A sample of the forms used by the fabricator to document plant quality control inspection shall be approved by the DME and be included in the manual. A copy of this manual shall be submitted to the Iowa Department of Transportation for approval by the DME and the Prestressed & Precast Concrete Engineer.
The fabricator shall have a sufficient number of qualified, certified, capable personnel to perform the necessary quality control functions. This includes, but is not limited to, activities such as ensuring proper placement of steel reinforcement, placement and tensioning of strand, material identification and handling, concrete proportioning, mixing and consolidation, fabrication, marking, curing, and documentation. The quality control personnel shall be responsible for all phases of fabrication, for units being produced for state, county, and/or city projects.
Safety: To assure safety, the fabricator shall have a safety policy, safety program, safety manual and a designated safety officer responsible for enforcing the safety rules. Additionally, each fabricator shall comply with all applicable laws, rules, regulations and ordinances governing safety. The fabricator shall make adequate provisions satisfactory to the DME for the safety of the inspector, particularly at all sampling, tensioning and inspection locations. Any violation of the Safety Laws, Rules or Regulations may be considered sufficient grounds by the DME for suspending all inspection activities.
The fabricator’s written application shall detail the following:
1. A flowchart listing the chain-of-command to aid in problem solving and to facilitate communication between the Iowa DOT inspector and appropriate fabricator personnel. Included in the flowchart shall be a statement of management commitment to, and responsibility for, maintaining the Quality Control Program.
a. Quality control inspections shall be performed by QC and/or by personnel other than those responsible for production and thus, reporting directly to management.
b. Deviations from the established flowchart, in personnel that will affect the Quality Control Program, require prior approval from the DME (i.e., situations involving the temporary absence of personnel normally responsible for quality control inspection).
2. A statement that the fabricator will maintain qualified (certified) personnel.
3. Designation of how specification requirements are relayed to the responsible quality control personnel and which company representative is responsible for this task.
4. A statement that the approved plant-specific procedural manual will be adhered to maintained and updated as needed.
REMOVAL FROM THE APPROVED LIST
Significant and/or repeated non-compliance with the DOT contract documents will warrant a corrective action request (CAR) being submitted to the fabricator. The fabricator will have 20 working days to submit a corrective action plan for approval. Production may continue during this 20 day period with DOT inspection. If the corrective action plan is not approved, the fabricator will be in conditional status for 30 working days. During conditional status the fabricator shall hire an Iowa DOT approved consultant to inspect the fabrication. The DOT Materials Fabrication Inspector will oversee the fabricator and consultant. Products fabricated during this time will be approved for use based on acceptable consultant reports in conjunction with DOT review. Continued non-compliance will be considered grounds to remove the fabricator from the approved list. The ongoing project will be completed with consultant inspection and DOT review. Conditional status will be withdrawn with a satisfactory report from the consultant and Iowa DOT Fabrication Inspector at any time during the 30 day period.
Willful misrepresentation by the fabricator, intentional shipment of non-approved products or repeated placement on conditional status (three times in three years) will be considered grounds for removal from the approved list.
Any fabricator removed from the approved list may be considered for reinstatement by reapplying after the items of concern have been addressed.
An appeal may be made to the Review Board if the fabricator wishes to contest the conditional status. The Review Board will meet as needed for disciplinary actions and appeals involving approved producers.
Iowa DOT inspection of fabrication will be suspended until the conditional status is rescinded by the Review Board.
The Review Board will consist of the Iowa DOT Construction and Materials Engineer, the Iowa DOT Prestressed & Precast Concrete Engineer, and the Chief Structural Design Engineer.
Each Precast/Prestressed plant shall submit the updated quality control plan to District Materials Engineer at the end of every other calendar year. Precast/Prestressed plants without updated quality control plan at January 31st will be delisted from the approve list.
Any fabricator removed from the list may be considered for reinstatement by reapplying to the appropriate DME and the Review Board.
The Iowa DOT Office of Materials shall certify inspectors and Quality Control Technicians responsible for the inspection of precast/prestressed concrete bridge units.
Certification requirements are as follows:
1. Successful completion of the Iowa DOT training course (a score of at least 80% on the written test).
2. Experience of forty hours (of a variety of prestress work) assisting in quality control inspection at an approved plant. NOTE: The required forty hours must be documented and approved by the DME. A sample of Prestress Work History (40 hours) Form is attached to this IM.
Certification will be valid for a five-year period, after which the technician will retest to maintain certification.
The Quality Control Technician will be appointed by the producer and will be responsible for the quality control process and testing at each plant. The Quality Control Technician will have the following:
1. Knowledge of the plans, shop drawings and specification requirements.
2. Knowledge of the product manufacturing operations.
3. A valid DOT Level I PCC Certification or ACI Level I Certification.
If technicians perform aggregate gradation, they shall possess an Aggregate Level II Certification.
CERTIFICATION
Upon successfully completing the requirements for certification, the Program Director will issue a certificate and a pocket certification card. This certification is not transferable.
A written notice may be issued to the certified technician for any inadequacies performed during their duties. Upon receipt of two such notices, the certified technician may be given a three-month suspension. After three written notices, the certified technician is subject to decertification.
The certificate will become invalid for reasons such as:
1. Failure of the certificate holder to renew the certificate prior to regular expiration described above.
2. False or fraudulent use of information to secure or renew the certificate.
3. False or fraudulent actions or documentation by the certificate holder.
4. Not performing tests and technician’s duties properly and in accordance to specification.
Certifications will remain valid for five years (a three-month grace period will be allowed). If the individual has not renewed their certification within the 90-day grace period, she/he will be automatically decertified. The individual may obtain certification by taking the examination. If the individual does not take the examination within one year from the date of decertification, he/she must retake all applicable schools and pass the examinations. The responsibility for applying for recertification shall rest with the certified individual.
It shall be the responsibility of the individual to inform the Office of Construction and Materials of any address change.
Retesting will be required every five years regardless of work experience or performance. Failure of any certification test shall require the applicant to retake the applicable school and pass the test.
Detailed information on certification, decertification, and recertification is located in IM 213.
The fabricator shall initiate this meeting prior to the commencement of any fabrication. Representatives of both the fabricating plant and the DOT shall attend this meeting.
Items to be discussed are:
· Production schedule
· Applicable specifications, IMs, shop drawings, and design standards
· Approved mix designs
· Methods of testing and curing
· Materials testing, acceptance, and approval
· Material storage and handling
· Quality Control Program and certification requirements
· Fabrication errors, discrepancies, and repair methods
· Acceptance and approval of final products
· Cylinder strength requirements
· Initial camber reading
· Final inspection
· Shipping procedure and protection
· Documentation of the prefabrication meeting
· District Materials Engineer must be notified before combined pours with altered strand design patterns or with multiple size differentials.
· By mutual agreement, periodic scheduled meetings between the fabricator and the District Materials Engineer may be used in lieu of the prefabrication meeting.
All materials for use in precast/prestressed concrete fabrication shall meet the requirements of the Standard Specifications and the IMs.
· Cement - Cement shall be from an approved source (listed in IM 401, Appendix A) and shall meet the requirements of Section 4101 of the Standard Specifications. Monitor samples shall be at the rate of one sample per year per supplier.
·
Fly Ash - Fly Ash shall be from an approved source (listed
in IM 491.17, Appendix A) and shall
meet the requirements of Section 4108
of the Standard Specifications. Monitor samples shall be at the rate of one
sample per month year per supplier.
·
Ground Granulated Blast Furnace Slag (GGBFS) - Ground
Granulated Blast Furnace Slag shall be from an approved source (listed in IM 491.14, Appendix A) and shall meet the
requirements of Section 4108 of the
Standard Specifications. Monitor samples shall be at the rate of one sample per
month year per supplier.
· Concrete – Same mix shall be used on all beams in an individual span (camber issue) and in all exterior beams (color issue)
- Self consolidating concrete, if used shall meet the requirements of IM 445 Appendix D.
· Fine Aggregate - Fine Aggregate shall be from an approved source and shall meet the requirements of Section 4110 of the Standard Specifications. The fabricator shall perform certified gradation testing at a minimum frequency of one test per week per source during production of certified project items. If the fabricator is using aggregate producer gradations, use “Producer Quality Control Testing Frequency” shown in Table 1 of Materials IM 209
· Coarse Aggregate - Coarse Aggregate shall meet the requirements of Section 4115 of the Standard Specifications, and shall be Class III durability aggregate. The fabricator shall perform certified gradation testing at a minimum frequency of one test per week per source during production of certified project items. If the fabricator is using aggregate producer gradations, use “Producer Quality Control Testing Frequency” shown in Table 1 of Materials IM 209.
· Admixtures - Admixtures shall be from an approved source and shall meet the requirements of Section 4103 of the Standard Specifications.
· Steel and Iron Products – All reinforcing steel, iron products, and coatings shall meet the requirements of IM 107.
· Strand for Prestressing - Strand for prestressing shall be from a domestic source and shall be the size, grade, and type specified in the contract documents. The fabricator shall provide certified Mill Test Reports and load-elongation curves. Prestressed strand may be accepted by certification, and monitored by sampling and testing at the rate of one sample per heat. Sample size is 6 ft. length of strand with copies of certified Mill Test Reports. All strands shall be free of contamination (dirt, mud, oil, paint, wax, etc.) that may prevent bonding between the strands and the concrete. Strands shall be free from nicks, kinks, and excessive rust. Rusting is generally acceptable if the rust is light and if pitting is not evident. Strand shall conform to the requirements of AASHTO M203 M (ASTM A416, Grade 270, ASTM A416M, Grade 1860), seven-wire prestressing strand. Strand suppliers shall provide the following certification:
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"The materials itemized in this shipment are certified to be in compliance with the applicable AASHTO and/or ASTM requirements and Iowa Department of Transportation Standard Plans and Specifications, IMs and meet the Buy America requirements as described in IM 107 for all steel, iron products and coatings."
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Authorized Signature and Date |
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Audit results from the National Transportation Product Evaluation Program (NTPEP) are required for plant approval. Upon satisfactory review the manufacturing mill will be placed on the approved list in Appendix C of this IM.
· Wire Failure-Prestressing Strands-During stressing of seven-wire prestressing strands for a single beam or one line of beams cast with a common strands, the number of individual wire failure shall not exceed 2% of the total number of wires. The permissible number of wire failure shall be rounded to the next lowest whole number. No individual strand shall have more than one wire failure.
Example - D 100, No. of 7-wire strands = 28, total number of wires = 196, 2% of total number of wires = 3.92, max allowable No. of strands with one wire failure = 3.
· Uncoated Reinforcement - Steel reinforcement for precasting/prestressing shall be grade 60 (ASTM A615) and shall be from an approved source and shall be accompanied by a Mill Test Certification and shall comply with the requirements of Section 4151.03 of the Standard Specifications. Monitor sampling will be done at a minimum rate of one sample of the most common bar per manufacturer per year. Rusting is generally acceptable if the rust is light and if pitting is not evident.
· Epoxy-Coated Steel Reinforcement for precasting/prestressing shall meet the requirements of ASTM A615, Grade 60, IM 451.03B, Article 4151.03B of the Standard Specifications and the following requirements:
a. Measurement of epoxy coating thickness (acceptance)
b. Visual observation of the coated bars and stirrups for uniform coating and cracking (verification)
c. The QA Inspector shall submit one sample of coated bar and stirrup for testing by Central Laboratory at a frequency of one sample per size, per year, per manufacturer (coater).
· Alternative Top Transverse Bar Placement for Bulb Tee Beams – The six 5a bars in the top of the beam as shown in the beam detail sheets may be replaced by four 0.6-in diameter strands. The strands shall be located 2” from the top of the beams to the centers of the strands. Spacing of the strands across the width of the top flange shall be as shown on the beam standards. The 4c1 bars shall be placed on top of the strands.
· Sole Plates, Steel & Masonry Curved Sole Plates - Acceptance shall be on the basis of approved shop drawings, acceptable workmanship, and fabrication inspection reports which shall include mill certification, type and steel grade, and galvanizing checks. ASTM A852, Grade 70 is required. ASTM A514, Grade B or ASTM A709, Grade 70W structural steel may be substituted for ASTM A852, Grade 70.
· Protection Plates - Acceptance shall be on the basis of approved shop drawings, and acceptable workmanship. Protection plates can be used at the discretion of the producer/fabricator. Protection Plates shall be made of ASTM A36 and shall be fully galvanized in accordance with the requirements of ASTM A121 (See Appendix H & H1 for details).
· Inserts/Hangers – Acceptance shall be on the basis of approved shop drawings, which shall include the manufacturer’s design, spacing and installation requirements. Inserts/hangers can be used in prestressed beams (1) upon request by the contractor as an aid to stripping floor forms, (2) shall be coated using one of the following methods:
1. Electroplating in accordance with ASTM B633, service condition SC4, required coating thickness of 1.0 mil. Classification and coating suffix FE / Zn 25
2. Mechanical galvanizing in accordance with ASTM B695, Type 1, Class 50. Minimum coating thickness shall be 2 mils.
· Neoprene Bearing Pads - Neoprene bearing pads will be accepted from an approved manufacturer on the basis of certification with monitor sampling and testing in accordance with IM 495.03 and Article 4195.02 of the Standard Specifications.
· Coil Ties and Hold Downs - Will be accepted per the manufacturer’s certification once per year per size.
· Water - Water shall meet the requirements of Article 4102.01 and will be sampled once per year.
· A copy of reports of approved materials, cement certifications, Mill Test Reports for steel reinforcement, etc., shall be kept on file by the fabricator and be available for examination by the engineer for one calendar year after the prestressed units are incorporated into a project.
· An independent registered professional engineer shall design casting beds and approve the equipment. The design shall be stamped, approved and signed by the registered professional engineer who designed the casting beds. Annual safety inspection to verify the adequacy of the bed(s) (vertical movement) shall be performed and documented by the producer. A copy of the safety inspection shall be submitted to the State of Iowa upon request. Calculation shall be submitted to the Iowa Department of Transportation should there be any anticipated change(s) in the maximum intended loading.
· Plan dimensions and specification values are to be considered as the target value to strive for and comply with as the design value from which deviations (within tolerances) are allowed. If any plan or specification changes are implemented, then the revised values shall govern.
· Casting beds, forms and bulkheads shall meet the requirements of Article 2407.03 of the Standard Specifications. Casting beds shall be checked for line and grade at a frequency of at least once per year or as often as necessary. This check shall be performed and documented by the fabricator. Casting beds, forms, and bulkheads that are not mortar tight shall be sealed or repaired prior to reuse.
· Forms shall be straight and true to the line. Form joints shall be comparable and even with each other.
· Weighing and proportioning equipment shall meet the requirements of Article 2001.20 of the Standard Specifications except that a vibrator will not be required on the cement batch hopper. Batching and proportioning equipment and scales shall be calibrated at least once a year. The Engineer may order a verification calibration test or check as necessary to ensure continued compliance.
· Mixing equipment shall meet the requirements of Article 2001.21 of the Standard Specifications.
· Stressing equipment shall be in accordance with Article 2407.03.A.3 of the Standard Specifications and shall be calibrated at a frequency of at least once per year or when is determined necessary. Calibration of the jacking system shall compare the indicated force applied by the system, to the force indicated on a calibrated load cell, dynamometer, or proving ring.
· When artificial heat is used to obtain temperatures above 100°F the temperature of the interior of the concrete shall be recorded by a system meeting the requirements of Article 2407.03.D of the Standard Specifications.
· Keep the maximum curing temperature of the concrete to 155°F. During curing record the temperature of the interior of the concrete using a system meeting the requirements of Article 2407.03.D of the Standard Specifications when the concrete temperature is above 100°F.
· Concrete temperature shall be uniform throughout the curing process and shall not vary by more than 40°F through the entire casting bed. Temperature probe locations shall be randomly located within 100 ft. throughout the length of the line (each line).
· Concrete shall not be placed without the written permission of the engineer when:
a. Ambient temperature is below 35°F Article 2407.03.C)
b. Plant approval by the engineer is required for cold weather placement.
· Automatic moisture measuring-equipment for aggregate shall comply with the requirements of IM 527.
· Testing equipment shall have sufficient capacity for the testing involved. Cylinder breaking equipment shall be calibrated at a minimum frequency of once per year.
· Jack calibration/tensioning equipment calibration shall be performed by an independent certified, approved laboratory and witnessed by Iowa DOT.
· Plant calibration shall be performed once a year and/or as needed by an independent certified, approved laboratory and witnessed by Iowa DOT.
DOT INSPECTOR KNOWLEDGE & DUTIES
The inspector's main functions are to monitor production, report findings and assist in quality improvement wherever possible. This is done to ensure that the Quality Control Program provided by the fabricator is functioning and is adequate to produce acceptable products.
The inspector is the liaison between the contracting authority and the fabricator. Good communications are important to maintain a good working relationship between the inspector and fabricator.
The inspector should be familiar with Standard Specification Article 1105.06, which describes the authority and duties of the inspector. He/she will not direct the fabricator's activities, but will have the authority and responsibility to question and, where necessary, reject any operation not in accordance with contract documents.
There are many phases included in the process of fabricating precast prestressed concrete products. While all phases are important to the overall quality of the product, there are several that the Agency inspector should make every effort to personally witness or perform:
· Verify tensioning calculations and tensioning production records as soon as possible after tensioning.
· Visually inspecting the product as soon as possible after casting.
· Approve repairs.
· Provide final inspection after repair and finish work is completed including excessive lateral sweep.
· Review fabricator’s documentation and prepare fabrication report.
An Iowa DOT inspector shall monitor the remaining phases as needed (as deemed necessary by the District Materials Engineer).
· Location of hold-ups and hold-downs, strand pattern, bed condition
· Placement of end plates, trueness of forms, insert type and location
· Tensioning operations
· Steel reinforcement and placement
· Concrete placement, making strength specimens, concrete operations
· Curing operation
· Compressive strength determination
· Detensioning operations
· Camber at release
· Finishing and repair operations
· Storage of units
· Loading and transporting (Overhang requirements; padding required if chains used for tie-downs.)
The Quality Control Technician shall check and document the following:
PRE-POUR
· Identify and document materials requiring outside fabrication inspection.
· Identify potential fabrication or production problems and notify Iowa DOT inspectors.
· Verify that all materials incorporated meet the requirements of the contract documents.
· Review concrete placement documents for strand locations.
· Check tension calculations.
· Measure elongation and gauge pressure during tensioning.
· Check hold-down and insert locations.
· Check stress distributions.
· Check steel placement.
· Check strand position.
· Check condition of pallet (level, holes, gaps, and other deformities).
· Determine moisture of aggregates.
· Check form condition and placement (oil, line alignment level, and tightness)
CONCRETE PLACEMENT
· Check on use of an approved mix design and batching operations (sequence).
· Ensure appropriate placement and proper vibration techniques.
· Measure and record concrete temperature.
· Ensure test cylinders are properly made.
· Ensure test cylinders are properly cured.
· Ensure appropriate finish.
· Ensure appropriate curing operations.
POST-POUR
· Check temperature and record during curing process.
· Ensure concrete strength has been met prior to releasing the line.
· Ensure proper detensioning procedure.
· Check unit for defects and obtain approval for repairs.
· Identify and store cylinders with the respective units.
· Check beam ends for fabrication in accordance with the plans.
· Ensure exterior sides of facia beams are grouted.
· Measure and record overall dimensions of beam.
· Measure and record camber at release and compare to design camber. (See camber measurement procedures.)
· Check and/or measure and record lateral sweep before shipping. (See sweep measurement procedures.)
· Ensure proper cylinder cure. (Cylinders must remain moist throughout the entire cure process and until testing.)
1. For release strength, see the requirements of Article 2407.03 of the Standard Specifications, and contract documents and/or as indicated on the plans.
2. For 28-day strength, see the requirements of Article 2407.03 of the Standard Specifications and/or as indicated on the plans. Prestress units cannot be shipped until the unit is minimum 14 days old. Prestressed piles may be shipped when the piles are 7 days old and attain 28-day strength.
3. Prestress units cannot be shipped until the 28-day strength is attained.
4. Beams must be at least 28 days old before the floor is placed, unless a shorter curing time is pre-approved by the engineer.
5. For each release and shipping strength a set of three (3) cylinders representing three different portions of the line cast (each end and the center) shall be cast. The average of three (3) cylinders shall be used to determine the minimum strength requirements for either release or shipping.
For either release or shipping strengths the set of cylinders tested shall meet the following requirements:
a. The average strength of the specimens tested shall be equal to or greater than the minimum strength required.
b. No individual cylinder of the set tested shall have a compressive strength less than 95% of the specified strength.
c. If both conditions a. & b. are not met after the appropriate curing period, another set of specimens representing the line shall be tested.
DEBONDED PRESTRESSING STRANDS
When detailed in the bridge plans, sheathing of prestressing strands to provide debonding shall meet the following requirements:
1. Use slit sheathing with high density polyethylene or polypropylene plastic.
2. The sheathing must have a minimum wall thickness of 0.025 inch, and an inside diameter exceeding the maximum outside diameter of the prestressing strand by 0.025 inch to 0.140 inch.
3. Extend the tubular debonding material (sheathing) through the header for all debonded prestressing strands.
4. After strands have been stressed, tie and tape the debonding material at the terminus located at the inside of the member. The tape must be strong enough to hold the sheathing closed.
5. The sheathing and tape must not react with the concrete, coating, or steel.
6. Additional slit tubular sheathing may be used to repair minor defects such as breakages or punctures in the installed sheathing, rectifying an improperly debonded strand, or incorrect debonded length of a strand.
7. The slit sheathing must maintain its integrity during the placement of fresh concrete without opening the seam. Tape and tie to ensure mortar tightness of the sheathing tube.
8. Do not tie reinforcing bars to debonded prestressing strands within the limits of the sheathing material.
9. All costs for material and labor for furnishing and installing the debonding material shall be included in the cost for the prestressed beam bid item.
Releasing of beams with debonded strands shall be as follows:
1. If strands are not released as a unit, the following release sequence shall be used.
a. Release draped strands and hold downs per IDOT Standard Specification 2407.03.H
b. Release bonded strands.
c. Debonded strands shall be released last with the shortest debonded strands released first and the longest debonded strands to be released last.
2. Any beam cracking noted during release shall be reported to the engineer for evaluation.
3. To measure the extent of debonding, strands shall be marked at a known distance from the end of the beam to measure the amount of retraction after cutting. Other methods to determine the extent of debonding may be considered with the approval of the Engineer.
4. All debonded strands shall be cutoff flush with the beam ends and shall not be embedded into the pier or abutment diaphragm concrete.
5. Seal openings between debonded strands and sheathing with 100% silicone sealant within fourteen calendar days of detensioning, before coating of the beam ends per I.M. 491.19 (if required in the bridge plans) and cure per the manufacturer’s recommendations.
When detailed in the bridge plans, sheathing of prestressing strands to provide debonding shall meet the following requirements:
1. Use slit sheathing with high density polyethylene or polypropylene plastic.
2. The sheathing must have a minimum wall thickness of 0.025 inch, and an inside diameter exceeding the maximum outside diameter of the prestressing strand by 0.025 inch to 0.140 inch.
3. Extend the tubular debonding material (sheathing) through the header for all debonded prestressing strands.
4. After strands have been stressed, tie and tape the debonding material at the terminus located at the inside of the member. The tape must be strong enough to hold the sheathing closed.
5. The sheathing and tape must not react with the concrete, coating, or steel.
6. Additional slit tubular sheathing may be used to repair minor defects such as breakages or punctures in the installed sheathing, rectifying an improperly debonded strand, or incorrect debonded length of a strand.
7. The slit sheathing must maintain its integrity during the placement of fresh concrete without opening the seam. Tape and tie to ensure mortar tightness of the sheathing tube.
8. Do not tie reinforcing bars to debonded prestressing strands within the limits of the sheathing material.
9. All costs for material and labor for furnishing and installing the debonding material shall be included in the cost for the prestressed beam bid item.
Prestressed/Precast units shall be free from honeycomb, surface defects, surface voids, bug holes and oil stain. Bug holes can be accepted if they are less than 1/2” in diameter (as measured by a DOT template) and not in a concentrated form (shot gun appearance).
Honeycomb and surface defects (exterior and interior beams) shall be filled and finished in accordance with the requirements of Article 2407.03.L of the Specifications. Bug Holes smaller than 1/2 in. in diameter need not to be filled unless it’s in a concentrated form. NOTE: For definition of honeycomb, bug holes and surface defects please refer to Appendix G of this IM.
Handling and storage shall be done in accordance with the requirements of Article 2407.03K of the Standard Specifications.
The Prestressed units shall be fabricated as per the plans and the bridge standards. No alterations or coring of the Prestressed units are allowed without the approval of the Precast and Prestressed Engineer or the Bridge Engineer.
The top of each beam will have a tined finish (grooves), except for a smooth strip, approximately two inches wide, continuously along one side of the beam. Grooves will be 1/4 inch in depth, spaced at not more than one inch center to center and will have a width of 1/8-inch ± 1/16-inch.
The outer surface of “Exterior Girders” shall have a surface finish in accordance with the requirement of Article 2407.03.L of the Standard Specifications. The finished surfaces shall be free of surface defects, oil stain and shall have a uniform color.
When required by the plans, beam-ends shall be coated and sealed at the prestressed fabrication plant with an approved gray or clear epoxy listed in MAPLE (IM 491.19, Appendix B).
The overhang shall not exceed 5 percent of the length of the beam and/or as indicated in the contract documents.
IDENTIFICATION
Each unit must have legible identification. Identification must remain in place and legible until the final project is accepted by Owner. Pieces with fading identification must be re-marked before any of the information becomes illegible.
Identification must include all of the following marked on the web approximately mid span between the beam end and the first diaphragm location:
a. Producer’s Name and Plant Location
b. Unique Beam Number (schema designed so no two beams from any plant can ever have the same number)
c. Fabrication Date MM-DD-YYYY
Identification must include the word “EXTERIOR” clearly visible at each end of the exterior face of the facia girder.
Identification must include the acceptance mark of the QA inspector prior to shipping. Prestressed/precast units that are not marked as accepted by the QA Inspector shall be rejected at the project site and cannot be incorporated into the project.
Initial camber due to prestress shall be measured after lifting and resetting the beam within three hours after detensioning and separation of the beam. After lifting, the beam may be reset on the precasting bed or in a holding area or storage yard. The beams with initial camber within 30% of designed release camber are considered as compliant camber. The compliance will be expired at the end of 120 days from the casting date of the beam. The 120 days is the time for the full designed camber, consisting of the initial camber and after losses camber, to develop. The theoretical 120 days of age is based upon the support of the PPC beam in storage being at L/30 after initial camber measurement. Beam support locations during storage will not be directly addressed at this time however it does have an effect on beam camber growth.
Camber of the beams shall be verified after delivery to the project. Beams cannot be accepted without specific approval of the project engineer after delivery to the project.
Initial Camber Measurement Procedure:
Fabricators shall use the survey equipment such as levelling instrument or equivalent to take elevation readings at the beam ends and beam midpoint to the nearest hundredth of a foot (0.01 feet). Survey shots are based on the top of the beam top flange and the fabricators are required to produce a flat surface across the full width of the top flange at the center line of the bearing locations and at midspan. The following steps shall be taken to ensure correct camber measurement.
1) Cast concrete and screed top surface.
2) Provide a level and smooth surface in the plastic concrete of the beam top at midspan and at the center line of bearing locations from which to measure camber. Surfaces shall span the entire width of the beam, measure at least 3.5 inches long centered at the required locations, and be flush with the top of the form edges. These surfaces may be troweled into the beam top, formed into the top by clamping a rigid material to the forms spanning the full width of the beam, or in another manner agreed upon by the Engineer
3) Allow concrete beam to cure.
4) Remove material used to create camber measurement locations (if used) and forms and detension beams.
bed or on blocking in a holding area or in the storage yard and measure the elevation of the beam using survey equipment at the flat surfaces of the top of the top flange. Beams must be supported at the beam ends for survey shots.
6) Take the average of the end elevation readings and subtract from midspan elevation reading to determine initial camber.
7) Record initial camber value from step 6.
8) Submit initial camber of each beam to the District Materials Engineer.
DECISION PROCESS FOR PRETENSIONED PRESTRESSED CONCRETE BEAM CAMBER Pretensioned Prestressed Concrete Beam design includes designed initial camber at release and camber after losses. The total PPC beam camber (ie: initial camber at release and after losses) is designed to theoretically occur when the PPC beam reaches 120 days of age. The theoretical total PPC beam camber at 120 days of age is based upon the support of the PPC beam in storage being at L/30 after initial camber measurement.
Steps in Decision Making Process for PPC beam camber:
· If the deck haunches are all within the allowable limits, no further action is required and the contractor can proceed with setting the deck forms for the bridge.
· If the beam seat elevations and the PPC beam initial cambers are within the associated tolerances and the PPC beams are no greater than 120 days of age, but there are still areas of excess haunch after deck grade adjustments, the additional costs resulting from supplemental haunch reinforcing and additional haunch concrete will be paid by the Contracting Authority.
· If the PPC beam initial cambers are out of tolerance, but the beam seat elevations and PPC beam final cambers are within the associated tolerances, but there are still areas of excess haunch after deck grade adjustments, the additional costs resulting from supplemental haunch reinforcing and additional haunch concrete will be paid by the Contracting Authority.
· If the beam seat elevations or PPC beam initial cambers are outside the associated tolerances and the PPC beam final cambers are out of tolerance which results in areas of excess haunch after deck grade adjustments, the additional costs resulting from supplemental haunch reinforcing and additional haunch concrete will be the responsibility of the contractor.
· If the PPC beam: 1) is older than 120 days, 2) final camber does not comply with the +/- 30% camber tolerance which results in supplemental haunch reinforcing/additional haunch concrete, and 3) delivery was not delayed by the Contracting Authority: the costs for supplemental haunch reinforcing and additional haunch concrete will be the responsibility of the contractor.
1. Sweep shall be measured when the beam is not influenced by any differences in surface temperatures from face-to-face or side-to-side.
2. A beam should be able to meet the sweep tolerance without any external influence (temperature, sun) or any applied force of any kind.
3. The determination of sweep compliance shall be made no earlier than 48 hours and not until after the sweep correction techniques have been fully completed and the beam has been freed. The corrected beam must remain straight, in straight line parallel to the centerline of the beam and must comply with specification requirements of L/80 (Table 2407.03-3). For sweep determination, beam must be completely free. If the beam is checked on the bed, lifting and resetting shall be required.
NOTE: “L” is the entire beam length in feet (meters).
The following procedures shall be followed in the event of prestressed concrete beams having developed sweep in excess of the allowable specification requirement tolerance of L/80. The procedures described in this section apply only to a uniform sweep with single lateral curvature producing a maximum offset at mid-point of the beam length.
A. Beams with excessive sweep greater than L/80 shall be corrected at the fabricator’s plant prior to shipping to the project site.
B. The fabricator may either tilt or lean the beam. This procedure will not require any prior approval.
C. A force may be applied to induce a maximum corrective lateral deflection as outlined below:
Beam Type and Size (English) Sweep (inches)
C 55 - C 80 L/80
D 80 - D 95 3L/160
D 100 - D 110 L/40
LXC 55 - LXC 80 L/80
LXD 80 - LXD 105 3L/160
LXD 110 - LXD 120 L/40
This procedure will not require any prior approval.
D. If a force is to be applied other than what is outlined in paragraph “C”, then this force needs to be predetermined and pre-approved by the Office of Bridges and Structures.
E. If approved, the intended force indicator must be carefully applied and must be monitored by means of a dial or a digital gauge. The monitor inspector shall make sure that the applied force does not exceed the predetermined limits. If the force exceeds the predetermined limits, then the beam shall be rejected.
F. A beam with twisted upper flange or lower flange shall not be accepted.
G. If approval is required for the jacking force, a written request shall be made to the District Materials Engineer. The District Materials Engineer will forward to the Office of Bridges and Structures for review and approval and with a copy to Central Materials.
H. Sweep in prestressed beam shall be measured at the web mid-point utilizing a cotton or nylon string tied to beam ends with sufficient tension. A conventional tape measure or a ruler may be used to measure the sweep.
*For further information, consult the “Sweep Correction/Conversion Verification Table,” listed below.
Sweep Correction
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CONVERSION VERIFICATION TABLE C/D BEAMS |
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Beam ID |
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Length |
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Allowed Correction |
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C |
55 |
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56.00 |
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0.70 |
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IN |
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C |
59 |
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60.17 |
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0.75 |
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IN |
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C |
63 |
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64.33 |
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0.80 |
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IN |
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C |
67 |
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68.50 |
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0.86 |
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IN |
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C |
71 |
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72.67 |
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0.91 |
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IN |
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C |
75 |
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76.83 |
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0.96 |
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IN |
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C |
80 |
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81.00 |
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1.01 |
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IN |
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D |
80 |
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81.00 |
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1.52 |
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IN |
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D |
85 |
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86.00 |
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1.61 |
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IN |
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D |
90 |
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91.00 |
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1.71 |
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IN |
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D |
95 |
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96.00 |
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1.80 |
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IN |
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D |
100 |
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101.00 |
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1.89 |
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IN |
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D |
105 |
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106.00 |
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1.99 |
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IN |
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D |
110 |
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111.00 |
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2.78 |
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IN |
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CONVERSION VERIFICATION TABLE LXC/LXD BEAMS |
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Beam ID |
Length |
Allowed Correction |
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LXC |
55 |
56.00 |
0.70 IN |
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LXC |
59 |
60.17 |
0.75 IN |
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LXC |
63 |
64.33 |
0.80 IN |
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LXC |
67 |
68.50 |
0.86 IN |
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LXC |
71 |
72.67 |
0.91 IN |
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LXC |
75 |
76.83 |
0.96 IN |
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LXC |
80 |
81.00 |
1.01 IN |
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LXD |
80 |
81.00 |
1.52 IN |
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LXD |
85 |
86.00 |
1.61 IN |
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LXD |
90 |
91.00 |
1.71 IN |
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LXD |
95 |
96.00 |
1.80 IN |
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LXD |
100 |
101.00 |
1.89 IN |
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LXD |
105 |
106.00 |
1.99 IN |
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LXD |
110 |
111.00 |
2.78 IN |
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LXD |
115 |
116.00 |
2.90 IN |
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LXD |
120 |
121.00 |
3.03 IN |
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Sweep Correction - Field Procedures
For Beams that have developed sweep at the project site, only the applied force method described above may be used. The beam tilt or lean method may NOT be used in the field.
The precast and prestressed beam fabricator is required to maintain a file containing all required documentation for a minimum of seven years from the time the products are shipped for incorporation into a project.
Production records shall include as a minimum, the following data for each precast or prestress unit:
· Approved mix used
· Tensioning calculation
· Elongation measurements and gauge pressure
· Air temperature, at time of concrete placement
· Concrete temperature
· Curing temperature
· Release and shipping cylinder strengths
· Release and 28-day or shipping camber
· Fabrication Approval Date
· Dimensional check
· General appearance
· Repairs made
· Irregularities and remarks
The units are to be reported on Form #820905.
Certifications
The producer of precast and prestressed concrete beam units shall furnish, on each shipment day, a certified bill of materials or invoice which identifies the county, project number, contractor, and number of pieces. The certification of compliance shall be signed by a designated, responsible company representative and shall be stated as follows:
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"The materials itemized in this shipment are certified to be in compliance with the applicable AASHTO and/or ASTM requirements and Iowa Department of Transportation Standard Plans and Specifications, IMs and meet the Buy America requirements as described in IM 107 for all steel, iron products and coatings." |
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Authorized Signature and Date |
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One copy of the above-described document shall be forwarded to the Project Engineer on the day the item is delivered to the project. In addition, one copy shall be sent to the District Materials Engineer.
The producer of precast and prestressed concrete beam units shall furnish the follow up certification if the beam suffers any damage during shipment and the certification shall state as follows:
“The damaged beam in this shipment was repaired as per DOT approved repair plan and per Iowa Department of Transportation specifications and IMs.”
Units shall be in full compliance with the specification requirements at the time of shipment to the project. Units with noncompliant initial camber are allowed to ship to the project. Units shall be inspected and stamped before leaving the fabricator yard.
Final acceptance of the units shall be at the project site by construction personnel.
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PRECAST & PRESTRESSED CONCRETE BRIDGE UNITS |
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FABRICATOR APPROVAL APPLICATION |
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1. Has a current Plant Procedures Manual been approved by the DME? (Yes or no. If no, please explain.) |
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2. I agree to the following statements: Production operations will adhere to the Plant Procedures Manual. Updates and changes will be approved by the DME before use. (Yes or no. If no, please explain.) |
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3. Will Plant Quality Control forms be maintained during the course of production and be available for review by Iowa DOT personnel? (Yes or no. If no, please explain.) |
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4. Which company representative (position or name) will be responsible for distributing current, applicable specifications to production and quality control personnel? |
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5. Do quality control personnel inspect all phases of manufacturing (i.e., materials used, mixes, tensioning, pouring, curing, finishing, yardage and shipping)? (Yes or no. If no, please explain.) |
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6. Are the personnel responsible for quality control inspection Iowa DOT-certified? (Yes or no. If no, please explain.) |
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7. Please attach a flowchart of your company chain of command (See attached example.) including names, business addresses and phone numbers of appropriate management personnel to contact for problem resolution. |
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Indicate the District(s) for which you are seeking approval below. |
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Authorized Company Signature |
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DME Recommendations |
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DME Signature |
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Approval (Yes or No) Remarks |
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Materials Engineer Signature |
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Date |
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TECHINICAL TRAINING & CERTIFICATION PROGRAM |
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PRESTRESS WORK HISTORY |
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CERTIFICATION NO. |
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ACI NO. |
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WORK HISTORY |
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LOCATION OF PLANT |
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SUPERVISOR (Certified Prestress Technician) |
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REMARKS: |
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PLEASE FORWARD TO DISTRICT MATERIALS ENGINEER |
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