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- 50-1.03A(2) Epoxy-Coated Strand
- 50-1.03B(2) Post-Tensioned Members
- 50-1.03B(2)(b) Losses Reserved 50-1.03B(2)(c) Anchorages and Distribution
- 50-1.03B(2)(d) Bonding and Grouting
- 50-1.03B(2)(d)(ii) Grouting Equipment
- 50-1.03B(2)(d)(iii) Mixing and Proportioning
- 50-1.03B(2)(d)(iv) Placing
- 50-1.03B(2)(d)(v) Weather Conditions
- 50-1.03B(2)(d)(vi) Curing
- 50-1.03B(2)(d)(vii) Grout Storage
- 50-1.03B(2)(d)(ix) Secondary Grouting
- 50-1.03B(2)(d)(x) Vertical Tendon Grouting
- 50-1.03B(3) Pretensioned Members
- 50-1.03B(3)(b) Debonding Prestressing Strands
50-1.03 CONSTRUCTION50-1.03A General50-1.03A(1) GeneralIf authorized, you may: 1. Apply a portion of the total prestressing force to a PC member before the member has obtained the concrete strength shown 2. Move the member after applying the portion of prestressing force
After final fabrication of the strand, do not perform any electric welding on the prestressing steel. If electric welding is performed on or near members containing prestressing steel, attach the welding ground directly to the steel being welded. 50-1.03A(2) Epoxy-Coated StrandCover epoxy-coated strand with an opaque polyethylene sheeting or other suitable protective material to protect the strand from exposure to sunlight, salt spray, and weather. For stacked coils, drape the protective covering around the perimeter of the stack. The covering must be adequately secured and allow for air circulation around the strand to prevent condensation under the covering. Cut epoxy-coated strand using an abrasive saw. Patch all visible damage to the epoxy coating caused by shipping, job site or casting site handling, installation, or cutting of ends under ASTM A882/A882M.
50-1.03A(3) DuctsAccurately place prestressing ducts. Securely fasten the ducts in place to prevent movement of the ducts during concrete placement. After installation, cover the duct ends and vents to prevent water or debris from entering. Support ducts vertically and horizontally during concrete placement at a maximum spacing of 4 feet. If prestressing strand is installed using the push-through method, use guide caps at the front end of each strand to protect the duct from damage. 50-1.03A(4) VentsPlace vents at the following locations: 1. Anchorage areas at both ends of the tendon 2. Each high point 3. 4 feet upstream and downstream of each crest of a high point 4. Each change in the cross section of duct
50-1.03B Prestressing50-1.03B(1) GeneralTension the prestressing steel using hydraulic jacks. The force in the prestressing steel must be the value shown in the shop drawings. After seating, the maximum tensile stress in the prestressing steel must not exceed 75 percent of the minimum ultimate tensile strength shown. 50-1.03B(2) Post-Tensioned Members50-1.03B(2)(a) GeneralIf requested, for verification of the force in the prestressing steel, furnish the resources necessary to install and support the Department's testing equipment at the prestressing steel location and to remove the equipment after the testing is complete. Conduct the tensioning process such that the force being applied and the elongation of the prestressing steel can be measured at all times. The maximum temporary tensile stress in the prestressing steel of post-tensioned members must not exceed 75 percent of the specified minimum ultimate tensile strength of the prestressing steel. If steam curing is used for PC members, do not install prestressing steel for post-tensioning until the steam curing is completed. Do not tension the prestressing steel of post-tensioned members until (1) at least 10 days after the last concrete has been placed in the member and (2) the concrete has attained the compressive strength described. Distribute the prestressing force of post-tensioned bridge girders with an approximately equal quantity in each girder and place the force symmetrically about the centerline of the structure. In slabs, distribute the prestressing force uniformly across the slab. Sequence the stressing of post-tensioned bridge girders such that no more than 1/2 of the prestressing force in any girder is applied before an equal force is applied in the adjacent girders. The maximum temporary force variation between girders must not exceed the prestressing force of the largest tendon used in all girders. Do not apply an eccentric force about the centerline of the structure that exceeds 1/6 of the total prestressing force at any time during the prestressing.
50-1.03B(2)(b) LossesReserved 50-1.03B(2)(c) Anchorages and DistributionThe ends of post-tensioned prestressing steel must be secured with a permanent type anchoring system. You may omit steel distribution plates or assemblies if you use an anchorage device of a type that is sufficiently large and that is used in conjunction with a steel grillage embedded in the concrete that effectively distributes the compressive stresses to the concrete. If loop tendon anchorages are used, enclose the anchorages in ducts for their entire length. Where the end of a post-tensioned assembly is not to be covered by concrete, recess the anchorage system such that the ends of the prestressing steel and all parts of the anchorage system are at least 2 inches inside of the end surface of the members. After post-tensioning, fill the recesses with concrete and finish flush. The concrete used to fill the recess must be the same as that used for the structure. The load from the anchorage system must be effectively distributed to the concrete such that: 1. Concrete bearing stress directly underneath the plate or assembly does not exceed 3,300 psi 2. When the prestressing steel is tensioned to 95 percent of its specified ultimate tensile strength: 2.1. Bending stress in the plate material or assembly material does not exceed the yield point of the material 2.2. No visible distortion is evident in the anchorage plate 50-1.03B(2)(d) Bonding and Grouting50-1.03B(2)(d)(i) GeneralBond the post-tensioned prestressing steel to the concrete by completely filling the entire void space between the duct and the prestressing steel with grout. Ducts, vents, and grout caps must be clean and free from water and deleterious materials that would impair bonding of the grout or interfere with grouting procedures. Compressed air used for cleaning must be clean, dry, and free from oil or contaminants. Prevent the leakage of grout through the anchorage assembly by positive mechanical means. Before starting daily grouting activities, drain the pump system to remove any water from the piping system. Break down and thoroughly clean the pump and piping system after each grouting session. After completing duct grouting activities: 1. Abrasive blast clean and expose the aggregate of concrete surfaces where concrete is to be placed to cover and encase the anchorage assemblies 2. Remove the ends of vents 1 inch below the roadway surface 50-1.03B(2)(d)(ii) Grouting EquipmentGrouting equipment must be: 1. Capable of grouting at a pressure of at least 100 psi 2. Equipped with a pressure gauge having a full-scale reading of not more than 300 psi 3. Able to continuously grout the longest tendon on the project in less than 20 minutes Grout must pass through a screen with clear openings of 1/16 inch or less before entering the pump. Fit grout injection pipes, ejection pipes, and vents with positive mechanical shutoff valves capable of withstanding the pumping pressures. If authorized, you may substitute mechanical valves with suitable alternatives after demonstrating their effectiveness. Provide a standby grout mixer and pump.
Proportion liquids by weight or volume to an accuracy of 1 percent. Mix the grout as follows: 1. Add water to the mixer followed by the other ingredients. 2. Mix the grout with mechanical mixing equipment that produces a uniform and thoroughly mixed grout without an excessive temperature increase or loss of properties of the mixture. 3. Do not exceed 5 gal of water per 94 lb of cement or the quantity of water in the manufacturer's instructions, whichever is less. 4. Agitate the grout continuously until the grout is pumped. Do not add water after the initial mixing.
Inject grout from the lowest point of the duct in an uphill direction in one continuous activity maintaining a one-way flow of the grout. You may inject from the lowest anchorage if complete filling is ensured. Before injecting grout, open all vents. Pump the grout at a rate of 16 to 50 feet of duct per minute. Conduct grouting at a pressure range of 10 to 50 psi measured at the grout inlet. Do not exceed maximum pumping pressure of 150 psi at the grout inlet. As grout is injected, continuously discharge grout from the vent to be closed. Do not close any vent until free water, visible slugs of grout and entrapped air have been ejected, and the consistency of the grout flowing from the vent is equivalent to the injected grout. Close the vents in sequence in the direction of flow starting with the closest vent. Before closing the final vent at the grout cap, discharge at least 2 gal of grout into a clean receptacle. After closing all vents, bleed all high point vents. Lock a pressure of 5 psi into the duct by closing the grout inlet valve. 50-1.03B(2)(d)(v) Weather ConditionsIf hot weather conditions will contribute to quick stiffening of the grout, cool the grout by authorized methods as necessary to prevent blockages during pumping activities. If freezing weather conditions are anticipated during and after the placement of grout, provide adequate means to protect the grout in the ducts from damage by freezing. 50-1.03B(2)(d)(vi) CuringDuring grouting and for a period of 24 hours after grouting, eliminate vibration from Contractor-controlled sources within 100 feet of the frame in which grouting is taking place, including from moving vehicles, jackhammers, large compressors or generators, pile driving activities, soil compaction, and falsework removal. Do not vary loads on the span. For PC concrete members, do not move or disturb the members after grouting for 24 hours. If the ambient temperature drops below 50 degrees F, do not move or disturb the members for 48 hours. Do not remove or open valves until grout has set and cured for at least 24 hours.
50-1.03B(2)(d)(viii) BlockagesIf the grouting pressure reaches 150 psi, close the inlet and pump the grout at the adjacent vent that has just been or is ready to be closed as long as a one-way flow is maintained. Do not pump grout into a succeeding outlet from which grout has not yet flowed. When complete grouting of the tendon cannot be achieved by the steps specified, stop the grouting. 50-1.03B(2)(d)(ix) Secondary GroutingPerform secondary grouting by vacuum grouting. The vacuum-grouting process must be able to determine the size of the void and measure the volume of grout filling the void. Vacuum grouting equipment must consist of: 1. Volumeter for the measurement of void volume 2. Vacuum pump with a capacity of at least 10 cfm and equipped with a flow meter capable of measuring the amount of grout being injected
Remove the standpipe after the grout has hardened. For vertical tendons in excess of 100 feet high or if grouting pressure exceeds 145 psi, inject grout at a higher vent from which grout has already flowed to maintain one-way flow.
50-1.03B(3)(a) GeneralAnchor the prestressing steel at stresses that will result in the ultimate retention of jacking forces at least equal to those shown. If prestressing steel for pretensioning is placed in the stressing bed and is to be exposed to the elements for more than 36 hours before encasing in concrete, protect the steel from contamination and corrosion using authorized measures. Do not cut or release prestressing steel in pretensioned members until the concrete in the member has attained a compressive strength of at least the value shown or 4,000 psi, whichever is greater. If epoxy-coated strand is used, do not cut or release the steel until the temperature of the concrete surrounding the strand is less than 150 degrees F and falling. If requested, check individually-tensioned strands using authorized methods and equipment for loss of prestress not more than 48 hours before placing concrete for the members. Strands showing a loss of prestress of more than 3 percent must be retensioned to the original computed jacking force. If prestressing steel in pretensioned members is tensioned at a temperature appreciably lower than the estimated temperature of the concrete and the prestressing steel at the time of initial set of the concrete, the calculated elongation of the prestressing steel must be increased to compensate for the loss in stress. The maximum temporary tensile stress in the prestressing steel of pretensioned members must not exceed 80 percent of the specified minimum ultimate tensile strength of the prestressing steel. Cut and release the prestressing steel in pretensioned members in such an order that lateral eccentricity of the prestress force is a minimum. Cut off pretensioned prestressing steel flush with the end of the member. After cutting the steel, clean and paint the exposed ends of the steel and a 1-inch strip of adjoining concrete as follows: 1. Wire brush or abrasive blast clean to remove all dirt and residue on the metal and concrete surfaces. 2. Immediately after cleaning, apply 1 coat of organic zinc-rich primer to the surfaces except apply 2 coats to surfaces that will not be covered by concrete or mortar. Do not use aerosol cans. Mix the paint thoroughly when applying and work into any voids in the prestressing steel. 50-1.03B(3)(b) Debonding Prestressing StrandsWhere debond prestressing strands are shown, debond the strands by encasing the strands in plastic sheathing along the entire length shown and sealing the ends of the sheathing with waterproof tape. Distribute the debonded strands symmetrically about the vertical centerline of the girder. The debonded lengths of pairs of strands must be equal. Do not end debonding at any one cross section of the member for more than 40 percent of the debonded strands or 4 strands, whichever is greater. Thoroughly seal the ends with waterproof tape to prevent the intrusion of water or cement paste before placing the concrete. Directory: esc esc -> Biblical Eschatology Presentation by: D. Paul Beck May 4, 2016 Ground Rules esc -> Mikael Håfstrӧm Screenplay by Miles Chapman and Arnell Jesko esc -> Escort affinity Program for Audi Club Members esc -> Preliminary entry form pistol esc -> Application form esc -> Request from Asian and Pacific Training Centre for Information and esc -> Constitution of the engineering student council university of maryland esc -> Subdisciplines of Earth Science Geology; study of the earth Download 6.74 Mb. Share with your friends:
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