2010 PTI TECHNICAL CONFERENCE & EXHIBITION IMPROVED PERFORMANCE WITH TIGHT-RADIUS PLASTIC DUCT Larry B. Krauser General Technologies, Inc. Stafford, TX 1
WHY TIGHT-RADIUS (TR) DUCT What is tight-radius plastic duct? Corrugated plastic post-tensioning duct that can be bent to a tight radius while still achieving fib and FDOT wear resistance requirements through the use of specially formulated, proprietary composite, highperformance materials. 2
WHY TIGHT-RADIUS (TR) DUCT Why use tight-radius plastic duct? Light-weight, corrosion resistant materials with superior bonding properties. Prevents concrete spalling and deterioration due to expansion of corroding elements (metal or galvanized metal duct). Eliminates corrosion potential between highly stressed post-tensioning strand and galvanized metal pipe. 3
WHY TIGHT-RADIUS (TR) DUCT Excerpt from: Potential for Hydrogen Generation and Embrittlement of Prestressing Steel in Galvanized Pipe Voided Pile by Hart and Suarez The possibility of hydrogen embrittlement of prestressing strand in prestressed concrete using galvanized pipe cannot be discounted. Recognizing that alternative materials to galvanized pipe are available and that these have proven satisfactory, it is recommended that galvanized pipe not be used... 4
TIGHT-RADIUS (TR) DUCT 5
Duct Testing: fib Bulletin 7, Corrugated Plastic Ducts for Internal Bonded Post-Tensioning FDOT 462-4.2.5.5 Corrugated Plastic Duct Difference is primarily the residual plastic thickness after Wear Resistance testing. fib 0.040 in (1mm) for all sizes FDOT 0.060 in (1.5mm) for duct up to 3.35 in (85mm) FDOT 0.080 in (2mm) for duct over 3.35 in (85mm) 6
Duct Testing: 1. Dimensional Tolerance of Duct 2. Flexural Behavior of Duct 3. Flexibility of Duct 4. Lateral Load Resistance of Duct 5. Longitudinal Load Resistance 6. Leak Tightness of Duct System 7. Wear Resistance of Duct 8. Bond Behavior of Tendon 7
Wear Resistance of Duct The test confirms that the duct is resistant to wear caused by the prestressing steel during stressing when the tendon is bent to the minimum specified radius of curvature. 8
Tendon Profile 9
Wear Resistance of Duct Test Specimen Two strips cut out of production duct 1/8 of duct circumference (45 out of 360 degrees) Not less than 100 mm in length Contain a full rib/corrugation spacing Thickness recorded at six locations each Strips mounted into a supporting body 10
Wear Resistance of Duct Test Specimen 11
Wear Resistance of Duct CUT DUCT SAMPLES PRIOR TO TEST 12
Wear Resistance of Duct Procedure Strips mounted into a supporting body Length of strand stressed to 70% Clamp specimens around strand to force Q Move specimen 750mm (29.5 in) Maintain clamping force Do not allow specimen to rotate around strand Movement within 2 min. of applying clamping force Hold clamping force 3 min. after movement complete Measure remaining wall thickness 13
Wear Resistance of Duct Force Q simulates curvature of duct Calculated using Guaranteed ultimate tensile strength of strand Cross sectional area of strand Cable factor to account for effect of actual number of strands within one duct Length of specimen Minimum specified radius of curvature 14
Wear Resistance of Duct Calculations Cable Factor 15
Wear Resistance of Duct Procedure 16
Wear Resistance of Duct CLAMPED DUCT SAMPLES MOVING IN APPARTUS 750 mm 17
FDOT Bending Radius Test Same apparatus Procedure Strips mounted into a supporting body Length of strand stressed to 70% Clamp specimens around strand to force Q Do not move specimens to simulate wear Maintain force Q for a duration of 7 days Measure remaining wall thickness 18
Wear Resistance of Duct DUCT SAMPLES CLAMPED TOGETHER 19
Wear Resistance of Duct DUCT SAMPLES SHOWING WEAR FROM TEST 20
MINIMUM BENDING RADII PER FDOT Minimum Bending Radii (MBR) for GTI Corrugated Plastic Duct* Quantity of 0.6 Strands MBR for GTI Standard Duct (ft) MBR for GTI Tight-Radius Duct (ft) 48 mm 59 mm 76 mm 85 mm 100 mm 115 mm 130 mm 130 mm 5 7 12 15 19 27 31 37 10.9 13.7 14.2 17.1 19.7 24.6 26.4 28.3 7.8 9.8 10.2 12.3 14.7 15.7 15.1 17.3 * Based 0.06 residual thickness up to 85mm and 0.080 > 85mm duct 21
APPLICATION FOR TIGHT-RADIUS (TR) DUCT 22
APPLICATION FOR TIGHT-RADIUS (TR) DUCT Concrete Deviator Application at External Tendons 23
APPLICATION FOR TIGHT-RADIUS (TR) DUCT 24
APPLICATION FOR TIGHT-RADIUS (TR) DUCT 25
APPLICATION FOR TIGHT-RADIUS (TR) DUCT Stressing Blister Application 26
APPLICATION FOR TIGHT-RADIUS (TR) DUCT Stressing Blister Application 27
TIGHT-RADIUS (TR) DUCT 28
ADVANTAGES/BENEFITS OF TIGHT-RADIUS (TR) DUCT Eliminates corrosion potential between highly stressed pt strand and galvanized metal pipe. Allows use of light-weight, corrosion resistant materials with superior bonding at external tendon deviators. Provides material cost savings versus galvanized pipe. Permits use of light-weight material that is easy to transport, handle, and install. Allows a greater radius for tendons into stressing blisters increasing construction flexibilities. Provides positive connections to HDPE duct of external post-tensioning tendons. 29