Design of Prestressed Concrete Bridges – A NYS DOT Training Course

 

Title: “Design of Prestressed Concrete Bridges – A NYS DOT Training Course”

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Location: Rensselaer Polytechnic Institute, Troy (NY), USA.

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Date: May 2007

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Instructors: Michael O’Rourke, Gianluca Cusatis, and David Wan

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Description: This two-days short course provided the participants with a basic knowledge on the design of prestressed concrete structures.  The main topics for the short course are listed below.

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1. Basic theory of prestressing concrete design, effects of prestressing force location with respect to the neutral axis, application of presstressing force by pretensioning or post-tensioning, proper application of each technique.

2. Review tensile and compressive properties of concrete, allowable stresses and ultimate concrete strength as per AASHTO and NYSDOT specifications, typical 28 day cylinder strengths for prestressed concrete bridges(currently 10 ksi).

3. Tensile stress-strain properties of steel, types of steel used for prestressing and need for high strength steel, relaxation of steel, allowable stress in steel before and after losses as per AASHTO and NYSDOT specifications.

4. Review standard AASHTO sections (voided slab, I shapes, box sections), and New England Bulb Tee sections. Typical range of spans for each type.

5. Review of ultimate strength analysis in ordinary reinforced concrete, ultimate and cracking moments in prestressed concrete as per AASHTO and NYSDOT specifications, design examples.

6. Importance of proper evaluation of prestress losses with reference to early prestressed concrete failures, prestress loss in pretensioned and post-tensioned sections due to elastic shortening of concrete, creep and shrinkage of concrete, and relaxation of prestressing steel. Additional loss of prestress in post-tensioned sections due to friction (curvature coefficient and wobble coefficient).

7. Review of shear force design in reinforced concrete, effects of prestressing and counter shear in prestressed concrete sections. Design shear capacity as per AASHTO and NYSDOT specifications, classical approach, modified compression field, and strut and tie approaches, design example.

8. Review deflection calculation in reinforced concrete, importance of deflection calculation for prestressed concrete sections, immediate and long term deflections, NYSDOT approach to long term camber estimation, camber calculation.

9. Design for horizontal shear transfer in composite prestressed beams as per AASHTO and NYSDOT specifications.

10. Design of a simple span composite pretensioned I-beam including flexural stresses at service loads, design for vertical and horizontal shear, and camber and deflection calculations.

11. Review development length concept in reinforced concrete design, transfer length and development length in pretensioned sections, end zone reinforcement.

12. Review of AASHTO load rating for prestressed bridges.

13. Design of draped and debanded strand.

14. Classification, causes and potential remedies for cracks in prestressed concrete bridges.