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HomeMy WebLinkAbout03 38 00 - Post-Tensioned ConcreteMidtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 1 SECTION 03 38 00 - POST-TENSIONED CONCRETE PART 1 - GENERAL 1.1 SECTION INCLUDES A. Materials, equipment and labor required to furnish and install all post-tensioning tendons. 1.2 RELATED SECTIONS 1. Section 03 30 00 – Cast-in-Place Concrete 1.3 REFERENCES A. ACI 318 – Building Code Requirements for Reinforced Concrete. B. ASTM A-416 -= Manufacture of Prestressing Steel. C. PTI Specification for Unbounded Single Strand Tendons, July 1993. D. Post-Tensioning Manual. E. Recommendations for Concrete Members Prestressed with Unbonded Tendons, ACI- ASCE Committee 423. 1.3 SUBMITTALS A. Prestressing Steel Mill Certificates: submit to the Architect/Engineer under the provisions of Division 1 and indicating. 1. Heat number and identification. 2. Location within structure (pour identification). 3, Ultimate tensile strength. 4. Yield strength as 1 percent extension under load. 5. Elongation at failure. 6. Modulus of elasticity. 7. Diameter and net area of strand. 8. Type of material (stress-relieved or low relaxation). 9. ASTM conformance. B. Jack Calibration Certificates: submit to Architect/Engineer under the provisions of Division 1 and indicating: 1. Jack designation. 2. Test date. 3. Calibration curve certified by a testing laboratory. 4. Gauge pressure corresponding to 80% of the ultimate strength of the strand. C. Caclulations: submit to Architect/Engineer under the provisions of Divison 1 and including: Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 2 1. Submit calculations showing all engineering required to fully design the post- tensioning system, including friction loss calculations, bursting reinforcement calculations, number of prestressing tendons, anchorage and coupling systems, tendon supports, and tendon stressing procedures, as required to fully comply with the final force and tendon profiles as shown on the structural drawings. The design shall be in accordance with the requirements of ACI 318. Submit tendon manufacturer’s data that documents the wobble and curvature friction coefficients used in the friction loss calculations. Clearly show on the shop drawings the values of wobble and curvature coefficients used in the design.. 2. Submit prior to shop drawing preparation. 3. Post-tensioning Supplier shall secure the services of a qualified professional engineer, licensed in the state where the project is located, to provide the design as specified above. Calculations shall be signed and sealed by the professional engineer and shall be submitted to Architect/Engineer for Owner’s record only. 4. Review of calculations and shop drawings by the Architect/Engineer will not relieve the Post-Tensioning Supplier of responsibility for final design as specified herein. 5. By offereing a proposal or entering into a contract for work of this Section, Post- Tensioning Supplier accepts the general design shown on the drawings as adequate for compliance with performance requirements at no additional cost to the Owner. 6. References to be used to calculate losses shall include: a. Friction loss-ACI 318. b. Anchorage seating loss- PTI Manual, Appendix A.3. c. Long-term losses (elastic shortening, creep, shrinkage, relaxation _ - Concrete International; June 1979- estimating Prestress Losses. D. Shop Drawings: submit to Architect/Engineer under the provisions of Division 1 and indicating. 1. Layout of all tendons and dimensions locating tendons in horizontal plane at all points. 2. Detail horizontal curvature of tendons at anchorages and at openings. 3. Number of tendons required for each beam and each slab. 4. Each post-tensioned beam shall be individually evaluated indicating the tendon profiles with tendon height at all support points. Method of tendon support shall be indicated. Anchorage details shall be detailed separately for each condition and referenced to each beam. 5. Support plan for slab tendons including method of tendon support and tendon height at all support points. All temperature tendons shall be supported directly by the slab main tendons. 6. Details of reinforcing steel at anchorages. 7. Placing sequence for all tendons. 8. Stressing sequence for all tendons. 9. Jacking force for tendons. 10. Calculated elongations for all tendons. E. Post-tensioning Component and System Compliances: Submit to Architect/Engineer under the provisions of division 1 the following: 1. Minimum sheathing compliance. 2. Coating compliance. 3. PT system compliance with PTI Specification of Unbonded Single Strand Tendons for aggressive environments. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 3 F. Stressing records: submit to Architect/Engineer within 24 hours after stressing using stressing record form and including: 1. Jack designation. 2. Jacking pressure. 3. Calculated elongation for each tendon. 4. Actual measured elongation for each jacking point and totals for each tendon. 5. Date of stressing operation. 6. Floor pour designation. 7. Signature of the contractor’s stressing personal. G. Non-shrink Grout Compliance: Submit to Architect/Engineer under the provisions of Division. H. Proof of plant certification per Article 1.4 1.4 QUALITY ASSURANCE A. Qualifications: 1. The post-tensioning tendons shall be fabricated at and shipped from a plant that is currently certified. a. Proof of plant certification is required and shall accompany each tendon shipment to the jobsite. b. The certification program shall meet or exceed the requirements of the Post-Tensioning Institute Plant Certification Program and shall be administrated by an independent agency of firm. c. Proof of PTI plant certification or a copy of the certification program for all plants applying materials to the job shall be submitted to the Architect/Engineer. 2. The post-tensioned materials shall be supplied by a firm which has been in the post-tensioning business for a minimum of 5 years. 3. The post-tensioning materials shall be supplied by firms that have successfully performed on at least five previous projects similar to the one involved in this contract. 4. Installer Certification: Post-Tensioning installation shall be performed by personnel certified by PTI’s “Level 1 Unbonded PT – Field Installation” program. Personnel shall maintain this certification throughout the duration of the project. 4. The post-tensioning contractor shall supply a minimum of 5 days of on-site technical assistance to assure that correct procedures for placement of tendons and tendon stressing are implemented. 5. Post-tensioning system shall be unbonded mono-strand system and shall confirm to all material and installation requirements of ACI 318 and of this Section. 6. The post-tensioning system shall provide a complete watertight encapsulation of the prestressing steel confirming to the PTI Specification of Unbonded Single Strand Tendons for aggressive environments. Unapproved corrosion protection systems shall be approved 14 days in advance of the bid date. Approved systems are as follows: a. VSL CP+ Monostrand Post-Tensioning System. b. Mono-strand Corrosion Protection System by Hayes Industries, Inc. c. Mono-strand Corrosion Protection System by General Technologies, Inc. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 4 1.5 DELIVERY, STORAGE, HANDLING A. Tendons shall be coiled and securely tied for shipping and handling. Coils shall be clearly identified as to grade, coil and heat number, and type (low relaxation). B. Equipment used to handle the tendons shall not cause damage to the tendon sheathing. C. During shipping, tendons shall be covered with a waterproof sheet. D. Adequate precaution shall be taken during loading to prevent damage in transit. E. All tendons shall be stored in weatherproof enclosures at the job site to insure that they remain dry until they are placed in the form work. PART 2 – PRODUCTS 2.1 PRESTRESSING STEEL A. The prestressing steel shall conform to the following: 1. One-half inch diameter, seven-wire, low relaxation strand for prestressed concrete manufactured in accordance with ASTM A-416, Grade 270. 2. Minimum ultimate tensile strength of 41,300 pounds. 3. Strand finish: Grade A, B, or C (PTI Specification for Unbonded Single Strand Tendons). 2.2 COATING A. The corrosion preventive coating material shall have the following properties. 1. Provide corrosion protection to the prestressing steel. 2. Provide lubrication between the strand and the sheathing. 3. Resist flow from the sheathing within the anticipated temperature range of exposure. 4. Provide a continuous nonbrittle film at the lowest anticipated temperature of exposure. 5. Be chemically stable and non-reactive with the pre-stressing steel, the sheathing material, and the concrete. 6. Shall meet all requirements of the PTI “Performance Specification for Corrosion Inhibiting Coating” as documented in PTI Specification for Unbonded Single Strand Tendons, for aggressive environments, including 1000 hour salt fog test. B. Minimum weight of coating material on a 0.50 inch diameter prestressing strand shall be 2.5 lb. of coating material per 1000 ft. of strand and shall extend over the entire tendon length. 2.3 SHEATHING A. The sheathing shall confirm to the following: 1. Be formed by a continuous extrusion process which applies a seamless polyethylene or polypropylene jacket to the prestressing steel. 2. Prevent the intrusion of cement paste and the escape of the coating material. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 5 3. Be chemically stable without embrittlement or softening over the anticipated exposure temperature range. 4. Be non-reactive with concrete, steel and the coating. 5. Have a minimum thickness of 0.040 inches of high density polyethylene or polypropylene. 6. Be of a light color so coating leaks at damaged sheathing locations can be easily detected. Black and dark brown sheathing is not allowed. Sheathing shall be of a uniform, opaque color. 2.4 COUPLERS A. Couplers shall confirm to the PTI Specification of Unbonded Single Strand Tendons, section 3.4. B. Couplers shall be coated with the same corrosion preventive coating used on the strand and shall be enclosed in sleeves which permit the necessary movements during stressing. 2.5 ANCHORAGES A. Anchorages shall confirm to the PTI Specification for Unbonded Single Strand Tendons, sections 3.1 3.2, 3.3, and 3.6. B. Anchorages shall include design features permitting a watertight connecting of the sheathing to the anchorage and a watertight closing of the wedge cavity for stressing and nonstressing anchorages. C. Anchorages shall be protected by a fusion-bonded epoxy coating confirming to ASTM A775 or be plastic-encased. D. All prestressing steel shall be secured at the ends by acceptable anchoring devices which shall be of such mature that wires will not king, break down, or otherwise by damaged. E. Anchorage devices shall hold the prestressing steel without slip of more than ¼ inch at lead equal to the applied load in the strand of prestressing. F. The maximum concentrated bearing stress in the concrete shall not exceed that permitted by ACI 318. 2.6 GROMMET A. The grommet shall provide a minimum concrete cover to the anchorage of 2”. 2.7 ACCESSORIES A. Tendons shall be supported by tying to reinforcing steel and to standard reinforcing steel accessories. B. Reinforcing bars and high chairs shall confirm to Section 03 30 00. 2.8 GROUT A. A non-shrink, non-metallic grout containing no chlorides (or other chemicals known to be deleterious so the prestressing steel) shall be used to grout the anchorage recesses. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 6 B. An approved product is “Sonogrout” manufactured by Sonneborn. PART 3 – EXECUTION 3.1 FABRICATION A. Tendons shall be manufactured in such sequence and quantity as to avoid lengthy storage at the jobsite. B. Tendons shall be clearly identified as called for on the placing drawing for easy placement. C. All prestressing steel within every group or in the same member shall be of the same heat where practical. Mill certificates for material fabricated shall be kept by the post- tensioning supplier. 3.2 FORMWORK A. Forms shall be drilled to receive tendons at edges of slab and at construction joints. B. Formwork shall be designed taking into account the possibility of the member lifting off the formwork during stressing. C. Do not remove any formwork except that required to allow stressing until tensioning operations are completed. D. Forms of scaffolding shall be extended beyond the tendon terminal to provide space for the stressing operations. E. Construction Joints 1. Construction joints through post-tensioned beams are not allowed. 2. Construction joints shall be located in the slabs at the quarter points of the slab span where tendons are at slab mid-depth. 3. Slab construction joints shall be located at the first quarter point of the slab span measured in the direction of uniform tendon stressing. F. Refer to Section 03 03 00 for additional requirements. 3.3 INSTALLATION A. Tolerances: Maximum permissible deviation from detailed placement. 1. Prestressing tendons and anchorages. a. + 1.8” – slab tendons and anchors b. +1/4” – beam tendons and anchorages B. Broken strands and strands showing severe fabrication defects shall be removed and replaced. C. Post-tensioning tendons shall have a parabolic profile and shall conform to the control points shown on the drawings. Tendons shall be supported at a maximum spacing of 4 feet. D. Uniform slab tendons shall be supported at midspan with a slab bolster. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 7 E. Slight deviation in spacing of the slab tendons is permitted where required to avoid openings and inserts which are specifically located. The maximum horizontal sweep of tendon shall be 1 in 6 in. F. Tendons shall clear openings and drains by a minimum of 4 inches. G. Tendons shall be placed normal to anchorage plates. H. Tendons shall be firmly supported to prevent displacement during concrete placement. Slab tendons, support bars and high chairs shall all be tied to one another. I. Anchorages shall be secured to the forms with ring shank nails. J. Wrap bare strand at all anchorages so there is no more than 1” of unsheathed strand immediately behind the anchor and at all sheathing tears. Use a flexible, polyethylene, non-porous waterproof tape. K. Welding of support bars or any welding in the vicinity of the tendons will not be allowed nor shall the tendons or anchorages be used as a ground for any welding. L. Placement of mild steel reinforcement shall be coordinated with placement of post- tensioning tendons. Proper tendon location has priority. M. Install post-tensioning system per the supplier’s requirements to result in a complete watertight encapsulating of the prestressing steel. 3.4 CONCRETE PLACEMENT A. No concrete shall be poured in post-tensioned members until placement of tendons and conventional reinforcement have been reviewed by the Engineer. 1. For all floor pours, roof pours and mats; the installation of all reinforcement shall be completed by noon of the day prior to casting the concrete. B. Concrete shall be placed in such a manner as to insure that the position of post- tensioning tendons and conventional reinforcement remains unchanged. If tendons remove out of the designed positions, they shall be adjusted to the correct position before proceeding with placing operations. C. Concrete shall be placed in conformance with the requirements as outlined in Section 03 30 00. 3.5 STRESSING A. Stressing of tendons may commence when concrete has obtained a compressive strength of 3000 psi per the field-cured cylinders. Stressing of all tendons shall be done within 72 hours after casting of concrete. If the concrete does not reach 3000 psi compressive strength at 72 hours, partial stressing of all tendons is required. B. All tendons shall be stressed by means of hydraulic jacks, equipped with accurate reading calibrated hydraulic pressure gauges to permit the stress in the prestressing shall be computed at any time. A certified calibration curve from a recognized testing laboratory shall accompany each jack. If inconsistences between the measured elongation and the jack gauge reading occur, the jack gauges shall immediately be recalibrated. Midtown West 17070 Carmel, Indiana September 15, 2017 03 38 00 - 8 C. In order to ensure that proper calibration is maintained, care shall be exercised in the handling of all stressing equipment. Adequate power shall be available to avoid power drop at the equipment. D. There shall be a minimum of two properly calibrated jacks at the job at all times. E. Safety precautions shall be taken to prevent workers from standing over or behind the jacks when tendons are being tensioned. F. The maximum tendon jacking force shall not exceed 80 percent of the ultimate strength of the strand. G. Measure and record the elongation for each individual tendon. Present the data in a tabular form. H. Tendon measured elongation must agree within 7% with the tendon calculated elongation. If inconsistencies esceeding + 7% occur, the cause of the inconsistency shall be determined and resolved. I. Excess tendon strand shall not be cut until the Stressing Records have been approved. J. No material shall be stored in post-tensioned members before final prestension is accomplished. At no time shall the weight of the storage material placed on the member, after prestressing is completed and concrete has obtained its specified 28 day strength, exceed the total design load of the member. 3.6 FORM REMOVAL A. Full shoring shall be left in place until the stressing operations on each floor pour have been completely performed. 3.7 GROUTING ANCHORAGE RECESSES A. After tensioning is completed and stressing records have been approved, cut off the excess tendon strand approximately 1 inch away from the face of the wedges with torch or hydraulic shear. 1. If a plastic-encased anchorage with threaded cap is used, a hydraulic shear must be used to cut the tendon. B. Complete the installation of the watertight encapsulation system by coating the end of the strand and then by installing the corrosion protection cap. C. Repair any damage to anchorage prior to grouting to ensure a watertight system. D. Fill recess flush with grout. E. The grouting shall be completed within one week after stressing has been done. END OF SECTION 03 38 00