4-52 Section 430
ERECTING PRESTRESSED CONCRETE MEMBERS
430-1 Description
Furnish and erect precast -prestressed concrete bridge members other than piling. Furnish, galvanize, place and paint, as applicable, bearing components, anchor bolts, washers, nuts, structural and reinforcing steel, miscellaneous hardware, bearing assemblies and all other materials; handle, transport and stor e materials; furnish erection drawings; set bearings and anchorage; grout and erect and install the bridge members and all other items necessary to complete the erection in accordance with the contract. When used in this section, the term “ prestressed concrete ” refers to precast, pretensioned, prestressed concrete.
430-2 Materials
Refer to Division 10. Item Section Bearing Plate Assemblies 1072 -3 Elastomeric Bearings 1079 -2 Grout, Type 3 1003 Organic Zinc Repair Paint 1080 -7 Precast -Prestressed Members 1078 Structural Steel 1072
430-3 Handling and Storage
Take special care in handling, transporting and storing prestressed members. Members damaged while handled or transported will be rejected unless repaired to the satisfaction of the Engineer. Handle members at the bearings or at pick -up points designated in the plan s unless using other methods approved in writing. Transport prestressed concrete bridge girders in a horizontal upright position. Provide support and bracing for each girder during transportation and storage that matches girder support locations in the final position within the structure.
430-4 Methods and Equipment
Use methods and equipment to install prestressed members that result in safe and satisfactory installation.
430-5 Bearings and Anchorages
Supply elastomeric bearings, when required by the plans, meeting Section 1079. Set steel sole plates level in exact position with full and even be aring on the bearing pad. Accurately set anchor bolts in accordance with Subarticle 420 -12(A). When welding the sole plate to the embedded plate in the girder, use temperature indicating wax pens or other suitable means, to ensure that the temperature of t he sole plate does not exceed 300 °F. Temperatures above this may damage the elastomer. Before welding, grind the galvanized surface of the portion of the embedded plate and sole plate that require welding. After welding, repair damaged galvanized surface s in accordance with
Article 1076 — 7.
4-53 430-6 Erection and Installation
A.General Erect prestressed concrete members by methods that satisfy the handling requirements specified in A rticle 430 -3. Perform field welding in accordance with Article 1072- 18 only when required in the plan s. When concrete is cast in contact with prestressed members, thoroughly clean and wet the surface of the prestressed member which contacts the fresh concr ete for at least 2 hours just before casting the fresh concrete. After casting and finishing all concrete, thoroughly clean the prestressed members.
B.Cored Slabs and Box Beams Prior to setting cored slabs or box beams , check the top of cap with a straightedge to ensure full and even bearing of the bearing pads. Correct any deviations by grinding or other approved methods before setting prestressed members . When erecting prestressed cored slabs and box beams , use meth ods that ensure a tight fit between adjacent slabs. The post tensioning system shall use 0.6 inch diameter strands. T ransverse post tensioning strands shall be tension ed to a final load of 43,950 lbs. Strands shall be g reased and placed in a non-corros ive 0.6 inch diameter, 1/16 inch minimum wall thickness black polyethylene pipe meeting ASTM D2239. Cut and remove the black polyethylene pipe and thoroughly clean off all grease from the strands in the area of the recesses at the ends of the strands where the strand vise is located and grout is applied. Position the jack and tension along the same axis as the strand. Utilize a double acting jack which tensions the strand and properly seats the wedges after achievi ng tension. Ensure an approved testing facility calibrates the jack within 12 months of the testing date and provide the Engineer a certificate of calibration. Tension the strands in the diaphragm nearest mid- span first to approximately 50% of the final tension load. Proceed to tension strands to 50% in the adjacent diaphragms. Continue the tensioning operation in a systematic manner along the length of the span until all strands are tensioned to approximately 50% . After all tensioning in a span is com pleted to approximately 50% of the final tension load, fill the shear key with an approved Type 3 grout . After the grout has cured and reaches design strength, complete the tensioning of each strand to 43,950 lbs, utilizing the same systematical order. Prior to release of the jack on each strand, hold the pressure for 2 minutes to ensure no loss in tension occurs. Finally, cut ends of strands and grout the recesses at the ends of the transverse strands and dowel holes with an approved Type 3 grout. Flame cutting of the strands is not allowed. After tensioning , grouting and curing, obtain approval before placing material and equipment on the cored slab or box beam spans. Support cranes or other equipment exceeding the legal load limit on mats. Submit to the Engineer for review a detailed drawing for the mats that are intended for use on the spans and a complete description of the equipment that is intended for placement on the mats. Supply and construct mats at no additional cost to the Department.
430-7 Painting
Clean, by hand or with power tools, and paint with 2 coats of non -aerosol organic zinc repair paint all ungalvanized steel surfaces or damaged coated surfaces , not encased in concrete in accordance with Section 442. Provide a minimum dry thickness of each coat of paint of 1.5 mils.
430-8 Measurement and Payment
__" Prestre ssed Concrete Girders will be measured and paid as the number of linear feet of prestressed concrete girders estimated in the plan s as being necessary to complete the project.
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 188–189 of 857.