ITEM 515 PRESTRESSED CONCRETE BRIDGE MEMBERS
515.01 Description
515.02 Fabricator Approval Procedure
515.03 Levels of Fabricator Qualification
515.04 General
515.05 Fabricator Documentation Responsibility
515.06 Shop Drawings
515.07 Pre-Fabrication Meeting
515.08 Materials
515.09 Materials Approval
515.10 Casting Beds
515.11 Cold Weather Operations
515.12 Equipment
515.13 Inspection Facilities
515.14 Construction Methods
515.15 Concrete
515.16 Release of Prestressing Strands
515.17 Transportation, Storage, and Erection
515.18 Method of Measurement
515.19 Basis of Payment
515.01 Description. This work consists of preparing shop drawings and manufacturing, testing, fabricator performed quality control and documentation, and transporting, storing, and erecting prestressed concrete bridge members.
515.02 Fabricator Approval Procedure. Select fabricators that are pre-qualified and evaluated by the Laboratory according to Supplement 1079.
515.03 Levels of Fabricator Qualification. There are three levels of fabricator qualification. The Laboratory will classify each fabricator at the highest level of fabrication it is qualified to perform.
|
Level |
Description of Capabilities |
|
1 |
Straight strand prestressed box beam members |
|
2 |
Straight strand prestressed I-beam members |
|
3 |
Draped strand prestressed I-beam members |
515.04 General. Produce all members according to Item 511, except as otherwise specified herein.
515.05 Fabricator Documentation Responsibility. The
fabricator shall keep and maintain records for each project bid line number
concerning:
A. Fabricator approval.
B. Shop drawing approval.
C. Material test reports.
D. Welding qualifications.
E. Quality control inspection.
At the Department’s request, the fabricator shall provide access to the above records for audit, inspection, and copying. Retain the documentation for at least 5 years from the date of final shipment from the fabrication shop.
Document quality control activities that
thoroughly inspect fabrication, and verify that fabrication conforms to the
specification requirements. Quality control activities include material
quality checks, dimensional checks, weld inspections, strand tensioning
procedures, release procedures, and concrete release and final strengths. The Department’s evaluation of the
fabricator’s performance, using forms defined in Supplement 1079,
includes validation of the fabricator’s actual records of inspection. This validation is intended to assure that
rating of an individual component reflects the overall quality of all
components.
515.06 Shop Drawings. Provide shop drawings conforming to 501.04 and the following requirements.
Include details, dimensions, size of materials, piece mark diagrams for field connection and erection of steel members, and other information necessary for the complete fabrication and erection of the prestressed members.
515.07 Pre-Fabrication Meeting. At least 7 days after the Department receives shop drawings, conduct a pre-fabrication meeting at the fabricator’s facilities, or another location agreed to by all parties. The fabricator and its quality control specialist, the inspector, and the Contractor, or its designated representative, shall attend the meeting. The purpose of this meeting is to review fabrication issues, including information on shop drawings, inspection, hold points, unique fabrication items, and special processes. The fabrication quality control specialist shall conduct the meeting and record and distribute meeting minutes that document all issues discusses. Begin fabrication after the pre-fabrication meeting is complete and all issues are resolved.
The time of the meeting shall be agreeable to all parties, but no earlier than 7 days after receipt by the Director of the Contractor’s accepted shop drawings. Office of Material Management may waive the pre-fabrication meeting if accepted by the Fabricator and the Contractor. If Contractor submitted shop drawings do not comply with the requirements of 515.06, no pre-fabrication meeting can be scheduled or waived.
515.08 Materials. Furnish materials conforming to:
Reinforcing steel........................................................... 509
Concrete.................................................................. 515.15
Aggregate*............................................................... 703.02
Air-entraining admixture.......................................... 705.10
Chemical admixtures for concrete............................ 705.12
Prestressing steel..................................................... 711.27
Transverse tie rods.................................................. 711.01
* For fine aggregate, use natural sand for members without a separate wearing course. Modify coarse aggregate as follows:
Do not allow more than 0.4 percent deleterious materials.
For gradation, use No. 57, 6, 67, 68, 7, 78, or 8 size coarse aggregate.
515.09 Materials Approval. The fabricator is responsible of controlling, testing, and validating material requirements for all materials either incorporated into the prestressed fabricated item or supplied under Item 515 as component parts of the fabricated items. The fabricator shall provide supporting documentation to the inspector at the time of final inspection.
The Department will not sample materials at the fabricator’s shop for Department approval; however, the Department may randomly sample materials to check the fabricator’s performance.
515.10 Casting Beds. Use casting beds constructed of steel or concrete that are set above grade to ensure that the beds remain above the accumulation of water as a result of curing operations. Design beds and abutments capable of safely resisting all forces applied to them without appreciable movement or deflection. These forces include compression and eccentric forces due to end-jacking operations, forces at hold down points when draped strands are used, and downward forces due to the dead weight of the members.
515.11 Cold Weather Operations. Conform to the requirements of this subsection if the ambient air temperature is below 50 °F (10 °C). Heat mixing water, aggregates, or both as necessary to produce a concrete temperatures from 50 to 70 °F (10 to 21 °C) when placed. Do not allow water heated above 150 °F (66 °C) to directly contact the cement. Do not place concrete that contacts forms, reinforcing steel, prestressing strand, or other hardware materials with temperatures less than 32 °F (0 °C). If casting bed temperature is less than 30 °F (-1 °C), tension the prestressing strand to provide the design tension at 50 °F (10 °C).
515.12 Equipment. Provide hydraulic jacks of sufficient capacity and stroke to tension strands. Use either single or multiple strand tensioning. Provide tensioning jacks equipped with automatic cutoff valves and equipped with gages with a minimum diameter of 6 inches (150 mm) and 500-pound (2 kN) increments. Calibrate gages for the jacks with which they are to be used. Have a graph or table showing the calibration available for the inspector. Calibrate jacks according to a method acceptable to the Laboratory, at least once every 6 months or as ordered by the Director. Maintain calibration documentation as part of the project’s QC inspection records.
Design the jacking system to ensure uniform stress in all strands. If simultaneously tensioning multiple strands, use approved types of dynamometers to equalize the initial stress on all strands before applying the full tensioning load with the master jack Provide dynamometers with sufficient capacity to ensure that the desired readings are in the middle to upper range.
515.13 Inspection Facilities. The fabricator shall provide the inspector office accommodations conforming to the following requirements:
A. Minimum floor area of 120 square feet (11 m2).
B. Minimum ceiling height of 7 feet (2.1 m).
C. Adequate working and storage facilities, lighting, electrical outlets, and ventilation.
D. Heat capable of maintaining a temperature of not less than 68 °F (20 °C).
E. Telephone with direct access to an outside trunk line for the inspector’s exclusive use.
515.14 Construction Methods. Use metal forms capable of producing members within the tolerances shown on the plans. Forms made of material other than metal may be used for bulkheads and voids. Ensure that the surfaces of the forms in contact with the concrete are smooth and the joints between panels are tight. The soffit form shall have a plane surface at right angles to the vertical axis of the members and have the two bottom edges beveled 3/4 inch (19 mm) with a triangular strip built into the forms. Increase the length of the forms for elastic shortening and normal concrete shrinkage, and design the forms to accommodate this movement.
Use water-resistant forms, constructed of a material that resists breakage and deformation during placement of concrete, for voids in box beams. The form material shall not excessively increase the dead load of the beams.
Prevent the release agent from contacting the prestressing strands or reinforcing steel.
Install and assemble reinforcing steel according to the approved shop drawings. If authorized, weld reinforcing cages using welders qualified to AWS D1.4. Do not weld epoxy coated or galvanized reinforcing steel unless approved by Office of Material Management. Repair all coating areas damaged by welding according to the coating manufacturer’s instructions. Reject reinforcing steel with a loss of cross-section of reinforcing caused by welding. Accurately place strands in the positions shown on the shop drawings. Do not use strands with kinks, bends, nicks, broken wires, scale, loose rust, or other defects. The Contractor may use slightly rusted reinforcing steel provided the rust is not sufficient to cause visible pits. Before placing the concrete, carefully clean the strands of all dirt, grease, oil, or other foreign matters. Do not splice strands within a member.
Tension strands uniformly to the stress indicated on the shop drawings. If multiple stands are stressed simultaneously, use dynamometers to equalize the initial stress on all strands before applying full tension load with master jack. Measure the required stress in the strands using the jacking equipment gages, and check the measured stress by the elongation of the strands. If the stress from the gages and the measured elongation are not within a 5 percent tolerance of the design, stop stressing the strands and determine the reason for the differences. The quality control specialist shall keep a record of all jacking forces and elongations. Secure the strands by suitable anchorage devices capable of developing at least 85 percent of the ultimate strength of the strands. The anchorage shall not allow the strand to slip after the tensioning operation.
If using draped strands, the loss of stress due to friction shall not exceed 5 percent. The quality control specialist shall measure the loss due to friction by a procedure approved by the Laboratory. Tension the strands at both ends. Place hold-down points within 3 inches (90 mm) of the locations shown on shop drawings and within 12 inches (0.3 m) of the locations shown on the plans.
515.15 Concrete. The fabricator shall submit the concrete mix designs to Office of Material Management along with test data confirming the mix conforms to the required 28-day strength while cured with the method to be used for beam fabrication.
Mix the concrete according to Item 499, except that 499.03 does not apply. The plastic air content of the concrete before placement shall be 6 ± 2 percent. Add an approved corrosion inhibiting admixture at the approved dosage.
Maintain the slump according to the manufacturer’s submitted mix design. No slump will be allowed which causes segregation of the mix. Provide a specified water-cement ratio with the mix design and maintain production of the concrete within that limit at all times. If a slump increase is required to conform to the mix design slump, add a chemical admixture conforming to 705.12, Type F or G. Do not use calcium chloride or admixtures containing calcium chloride.
Proportion the concrete materials to provide a minimum cylinder strength of 5500 pounds per square inch (38 MPa), or plan specified strength, in 28 days. Make at least two cylinders for samples from both the first and last loads placed on each casting bed, each day. Determine strength, for both strand release and final shipping, by testing a group of cylinders, which consists of one cylinder from every sample location. Each group of cylinders shall have an average strength of what is specified in the shop drawings, and no individual cylinder shall have less than 95 percent of the specified strength. If producing more than 200 feet (60 m) of beam on the same bed, make at least two additional cylinders for each additional interval up to 200 feet (60 m). The quality control specialist shall determine the sample location for the additional cylinders (generally from the load placed in the middle of the additional beam length).
Provide a concrete mix design which will achieve 2000 coulombs or less @ 90 days when tested per AASHTO T277. Use samples for the test that were mixed without corrosion inhibitors and that were cured with the same methods that will be used to produce the prestressed concrete bridge members. Do not apply additional cure to samples that have reached the required design strength. Submit the test results when submitting the concrete mix design to the Office of Materials Management.
The inspector may require additional cylinder samples from any location that does not appear to conform to mix design or placement requirements. Include these additional cylinders in the group of cylinders for determining strength.
The fabricator may place concrete in the bottom flange of a box beam before placing the interior forms and reinforcement for the upper portion of the member, provided continuous placement is not interrupted for more than 45 minutes.
Screed the top surfaces of non-composite members and finish the surface with a burlap drag or other means to provide a uniform surface with a gritty texture suitable for waterproofing. Screed the top surface of composite members and finish the surface with a wire broom, in a transverse direction and penetrating the finished surface approximately 1/4 inch (6 mm).
Immediately after final concrete placement, accelerate the cure by covering the concrete with an enclosure suitable to contain live steam or radiant heat. Until applying the steam or radiant heat, maintain an ambient temperature inside the enclosure of at least 50 °F (10 °C). The allowable temperature rise and range of the plastic concrete before initial set shall not be greater than 10 °F (5 °C) per hour; shall not have a total rise of greater than 40 °F (22 °C), and shall not exceed a maximum temperature of 100 °F (38 °C).
Start initial application of the steam or heat from 2 to 4 hours after final concrete placement. If using retarders, start applying the steam or heat from 4 to 6 hours after final concrete placement. If determining the time of initial set according to ASTM C 403, these time limits do not apply.
During the initial application of live steam or radiant heat, the ambient temperature within the curing enclosure shall increase at an average rate not to exceed 40 °F (22 °C) per hour until reaching the curing temperature. Do not allow a maximum curing temperature to exceed 160 °F (71 °C). The fabricator may use a maximum curing temperature of 180 °F (82 °C) if the fabricator can document to the Department that delayed ettringite or alkali silica reaction is not at issue. Maintain the maximum temperature until the concrete has reached the required release strength. De-tension the strands immediately upon completing the accelerated curing.
A. Curing with Low-Pressure Steam. Do not apply live steam directly onto the concrete forms if it causes localized high temperatures.
B. Curing with Radiant Heat. Apply radiant heat using pipes circulating steam, hot oil, or hot water, or using electric heating elements. Minimize moisture loss by covering all exposed concrete surfaces with plastic sheeting, 705.06, or by applying a liquid membrane curing compound, 705.07, to all exposed concrete surfaces. Before bonding field-cast concrete or other materials in the finished structure, remove the curing compound from the shear faces of composite members and other surfaces.
Neatly fill cavities in the exposed surface of beams with nonshrink grout. Clean the concrete, and apply and cure the grout according to the manufacturer’s published recommendations. Reject beams with honeycombing that impairs the member’s performance.
515.16 Release of Prestressing Strands. Do not release prestressed strands until the concrete reaches a minimum strength of 4000 pounds per square inch (28.0 MPa), or plan defined release strength. Determine strength by testing pairs of concrete cylinders (made according to AASHTO T 23 and cured by the same method used to cure the beam) according to AASHTO T 22. Test cylinders in the fabricator’s laboratory. Both tested cylinders shall meet or exceed the required strength of 4000 pounds per square inch (28.0 MPa), or plan defined release strength. Notify the inspector in advance of the testing. The inspector may observe the cylinder testing. A-rated fabricators are not required to provide notification.
Before releasing prestressed strands, loosen or remove forms and hold-downs that restrict either horizontal or vertical movement of prestressed members. Release the strands immediately upon completing accelerated curing. Burn or heat release all strands simultaneously at selected exposed points between anchorages, and follow an approved pre-determined pattern, to equalize the forces being transferred to the various areas of the cross-section of the member. For heat release, use a low-oxygen flame to uniformly heat at least a 4 inches (100 mm) long section of strand.
515.17 Transportation, Storage, and Erection. Do not ship prestressed members until the concrete obtains its 28-day design strength and until receiving the inspector’s approval.
Transport, store, and erect the members in an upright position. Apply approximately the same points of support and direction of reactions during transportation and storage as those applied when the members are in their final position. During storage, provide unyielding horizontal supports capable of maintaining the members in a vertical position. If it is necessary to transport the members in a position other than vertical, obtain the Director’s written approval. At the Directors discretion, repair or replace members damaged by improper handling, storing, transporting, or erecting.
Use lifting devices capable of withstanding the required loads to lift and erect the members. Accurately place the prestressed beams during erection to ensure a uniform load on all bearings. Place box beams to ensure a correct fit of the keyways and to ensure proper grouting of the keyways. Use keyway grouts, 705.22, approved by the Office of Material Management. Mix, install, and cure the grout according to the manufacturer’s published recommendations to obtain a design compressive strength of 5000 pounds per square inch (34.5 MPa).
Do not allow vehicular load on an individual prestressed concrete box beam until the grout in the keyway obtains the specified design strength of 5000 pounds per square inch (34.5 MPa).
If erection of prestressed members requires placing cranes or launching devices on previously erected spans, submit erection procedures for approval according to Item 501.
515.18 Method of Measurement. The Department will measure Prestressed Concrete Bridge Members by the number of members.
The Department will measure the intermediate diaphragms by the number of each placed.
515.19 Basis of Payment. Payment for prestressed concrete beams include all inserts, sleeves, fittings, reinforcing steel fully or partially encased in the members, and all transverse tie rods necessary to complete this work.
The Department will pay for concrete diaphragms, steel diaphragms, and bearing plates or pads, or other expansion materials, as separate items.
The Department will not pay for repaired or replaced members damaged by improper handling, storing, transporting, or erecting.
The Department will pay for accepted quantities at the contract prices as follows:
Item unit Description
515 Each Prestressed Concrete Non- Composite Box
Beam
Bridge Members, Level 1
515 Each Prestressed Concrete Composite Box
Beam
Bridge Members, Level 1
515 Each Straight Strand
Prestressed Concrete Bridge
I-Beam
Members, Level 2
515 Each Draped Strand
Prestressed Concrete Bridge
I-Beam
Members, Level 3
515 Each Intermediate Diaphragms