2014 RESEARCH NEEDS STATEMENT
AASHTO STANDING COMMITTEE ON RESEARCH
AMERICAN AASHTO SCOBS Technical Committee for Concrete Design (T-10)
TRB General Steel Bridges (AFF30)
NCHRP Problem Statement Outline
I. PROBLEM NUMBER:
To be assigned by NCHRP Staff
II. PROBLEM TITLE
Guidelines for Design and Construction of Curved Prestressed Concrete U- and I-Beams
III. RESEARCH PROBLEM STATEMENT
Curved steel girder bridges have received considerable NCHRP and FHWA research attention in the past 15 years. The research has resulted in LRFD Specification changes in 2004 and 2005 that unify the design of straight and curved beams. The concept of using curved precast concrete beams as an alternate to curved steel beams is unrecognized by most designers. Several projects in Florida, Pennsylvania, Colorado and Nebraska have demonstrated the cost effectiveness of such an alternate. Often the beams are made to a chorded alignment, rather than a true curve, and are post-tensioned, rather than pretensioned. However, pretensioning of truly curved box beams is being done in the Netherlands on a regular basis.
Many aspects of curved girder design and construction can benefit from further research and development of guidelines. Additional guidance on acceptable levels of torsion during the construction process, prior to placement of bracing or closing of the box is needed to ensure torsional stiffness is not lost during erection. Additional guidance would be very valuable on the implementation of other innovative materials, such as self-consolidating concrete, lightweight concrete, ultra-high performance concrete or non-ferrous tendons, or innovative methods, such as external tendons, thinner cross-sections or pretensioning only. Also, there needs to be guidance on the validity of the current live load distribution factors for curved concrete stringer bridges.
IV. LITERATURE SEARCH SUMMARY
Currently, very little work has been published on curved concrete girders. Only one paper has been recently published on pretensioned curved concrete I girders. This would be a system with a high cost-effectiveness in North American practice. Papers have been published in the PCI Journal on the Disney projects in California and Florida, and the curved U-girder systems used in Colorado. A significant amount of research has been published on curved steel I-girders and active research programs have existed at the University of Maryland and at the FHWA, Virginia Laboratory. This research will prove useful in global analysis of a bridge system. It provides some assistance in terms of structural performance of the girders and handling of the girders, but no assistance relative to production.
Some examples of literature on curved prestressed girders are:
1. “Precast Prestressed Concrete Horizontally Curved Bridge Beams- Special Report”, PCI Journal, Vol. 33, No. 5, Sept/Oct 1988.
2. W. Amorn, C. Tuan, M. Tadros, “Curved, Precast, Pretensioned Concrete I-Girder Bridges” PCI Journal, Vol. 53 , No. 4, Nov/Dec 2008.
3. C. Sun, S. Hennessey, M. Ahlman, M. Tadros, “Value Engineering Arbor Road Bridge with Curved Precast Concrete Girders”, PCI Journal, Vol. 52, No.2, March/April 2007.
4. PCI Bridge Design Manual Chapter 12, PCI, Chicago IL, 2011.
5. Itani, A.M., and Reno, M.L, “Chapter 15 – Horizontally Curved Bridges”, Bridge Engineering Handbook, edited by Chen, W.F. and Duan, L., CRC Press, 1999.
6. Endicott, W., “A Fast Learning Curve – Case Study of Colorado Curved Tub Bridge”, Ascent, Summer 2005, pp. 36-39.
7. “Curved Precast Concrete Bridges State-of-the-Art Report”, PCI, unpublished draft March 2011.
V. RESEARCH OBJECTIVE
This project should consider the most popular precast prestressed beam shape, the I-beam, as well as other shapes, such as U-beams and full boxes. The goal of the study is to develop guidelines for fabrication, design and construction of curved concrete girder bridges. Plant precasting/pretensioning, should be addressed along with post-tensioning. Side sway analysis, torsion design, and diaphragm requirements should be considered in the study.
Task 1 Conduct a literature review to determine current practice and identify areas requiring additional research
Task 2 Study the techniques used in Europe for design, production and construction of curved pretensioned concrete girders
Task 3 Identify potential production systems and processes and the advantages and disadvantages of these systems. Also identify barrier to implementation and solutions for these barriers.
VI. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD
Recommended Funding: $50,000 $500,000
Research Period: 12 36 months
VII. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION
There is a great urgency to reduce the traffic delays caused by bridge construction projects. Structural steel prices have been skyrocketing. Providing a concrete alternate to a steel curved girder bridge would greatly improve the cost effectiveness of the bridge. When guidelines are available, designers are encouraged to design curved concrete girder bridges. Implementation is thus expected to come very quickly, driven by economy.
This research addresses issues in several of the areas identified as program objectives in the 2013 Strategic Plan for Bridges and Structures developed by the AASHTO Highway Subcommittee on Bridges and Structures. The objectives addressed in this research are: Optimizing Structural Systems and Maintaining and Advancing the AASHTO Specifications.
VIII. PERSONS DEVELOPING THE PROBLEM STATEMENT
Maher K. Tadros
University of Nebraska
1110 South 67th Street
Omaha, NE 68182
Phone: 402 554 4842
IX. PROBLEM MONITOR
To be assigned by AASHTO to monitor the research, if programmed, from inception to completion. The monitor's final responsibility will entail recommendations to the Standing Committee on Research as to how the research results could be implemented.
X. DATE AND SUBMITTED BY – March 15, 2012
Carin L. Roberts-Wollmann
Virginia Tech
200 Patton Hall
Blacksburg, VA 24061
Phone: 540-231-2052
Sam Fallaha FDOT – Member AASHTO T-10
Assistant State Structures Design Engineer
FDOT- Structures Research Center
2007 E. Paul Dirac Drive
Tallahassee, FL 32310
Phone: 850-921-7111
Fax: 850-921- 7101