Prestessing Manual

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STATE OF CALIFORNIA DEPARTMENT OF TRANSPORTATION ENGINEERING SERVICES

PRESTRESS MANUAL
A GUIDE FOR FIELD INSPECTION OF CAST-IN-PLACE POST-TENSIONED STRUCTURES

JANUARY 2005

Revision 1 05/05

TABLE OF CONTENTS Topic INTRODUCTION SAFETY PRESTRESS WORKING DRAWINGS PRESTRESSING DUCTS PRESTRESSING STRANDS/BARS ANCHORAGE DEVICES STRAND WEDGES PRESTRESSING JACKS PRESTRESSING OPERATION a. b. c. d. Preparation for Stressing Inspection Field Inspection Overstressing of Prestressing Steel Elongation Measurements and Calculations Page 1 2 3 5 8 15 16 17 20 20 21 27 28 30 35 35 36 42 42 43 51 57 64 74

GROUTING OPERATION APPENDIX A – PRESTRESSING SYSTEMS a. b. c. d. New System Proposals Presently Used Systems Soil Anchors Girder Strengthening

APPENDIX B – PRESSURE CELL APPENDIX C – INSPECTION CHECKLIST APPENDIX D – POST-TENSIONING LOSSES AND ELONGATIONS APPENDIX E – EXAMPLE CALCULATIONS APPENDIX F – CALIFORNIA TEST # 541 (FLOW CONE METHOD)

California Prestressing Manual
INTRODUCTION

January 2005

A large percentage of the bridges built in California are prestressed, post-tensioned type structures. As a bridge engineer working for the Divisions of Structure Construction, you should understand the construction principles relating to prestressed, post-tensioned bridge construction. This Prestress Manual has been compiled to provide the field engineer with the necessary information and the background to perform three basic duties: 1. 2. 3. Check the contractor’s working drawings. Provide thorough and complete inspection during the construction of the bridge with respect to the prestressing operation. Understand and enforce Section 50 titled “Prestressing Concrete” of the Standard Specifications and any pertinent references. The information included herein is to be considered as both a reference and guideline for structure representatives and assistant structure representatives. This manual should be reviewed both prior to working drawing review and during the prestressing operation. This manual should be available to the field engineer during the post-tensioning operation. This manual, along with good communication between the structure representative, Structure Design, Materials Engineering and Testing Services (METS), and the contractor, will provide a finished product consisting of sound structural integrity with a minimal amount of construction related problems.

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California Prestressing Manual
SAFETY

January 2005

The prestressing operation can be a potentially dangerous one. Due to the tremendous forces involved, if a failure occurs, there is a good possibility that high velocity projectiles will be produced. The field engineer should always stay alert and be aware of the contractor’s operations. General “common sense” rules to be practiced around and during the prestressing operation are as follows: 1. 2. Stay clear of the area when the contractor is unpacking the strands. Securing bands may spring in any direction when released, causing injury. Before the contractor begins the stressing operation, check all of the high-pressure hoses for leaks and/or poor condition. Worn or damaged hoses are to be replaced only with hoses that can withstand the high pressures involved. 3. Never stand behind, along side, or directly above the prestressing jack during the stressing operation. Never stand behind the “dead” end of the tendon during the stressing operation. Use caution around tendons until after they are grouted. For additional information and safety requirements, refer to Cal/OSHA Construction Safety Orders, Section 1721. 4. 5. Always be aware of the contractor’s operation and equipment during the stressing operation. The pressure cell indicator box is an expensive piece of equipment. Do not leave the box unattended, and make sure the contractor does not damage it with his equipment. After verifying gage pressures, the pressure cell and readout box should be relocated to a safe location away from...
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