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Development of Simplified Design Guidelines for Reinforced Self-Consolidating Concrete Bridge Piers Confined with CFRP Grids


 
I.     RESEARCH PROBLEM STATEMENT

In a recent report to Congress, the Federal Highway Administration (FHWA) reported that 23 percent of the bridges are classified as structurally deficient. The U.S. Department of Transportation (USDOT) has estimated that $90.9 billion will be needed to repair the damage on existing bridges. Approximately 40 percent of the current backlog of highway bridge repair and rehabilitation costs is directly attributed to the corrosion of reinforced concrete bridge components. The FHWA aims at identifying and employing innovative technologies, materials and procedures to speed up both the design and construction phases for preserving, rehabilitating and reconstructing bridge systems. Innovative approaches for rapid constructing of long-lasting bridges, with minimal disruption to the community, need to be developed.

Carbon fiber reinforced polymer (CFRP) reinforcement was proven to provide a potential solution for corrosion-deteriorated bridges. Recently, CFRP grids have been successfully developed and implemented in the precast/prestressed industry. CFRP grids have been used in architectural concrete panels and double tees. The CFRP grids provide competitive alternative to the conventional steel reinforcement as small cover concrete is required, resulting in thinner and less expensive members especially in harsh and aggressive environments.

Self-consolidating concrete (SCC) is a specially proportioned hydraulic concrete that enables fresh concrete to flow easily into forms and around rebars without segregation. Recent research has shown that the use of SCC may provide the following benefits: (a) increased rate of production and safety; (b) fast concrete placement; (c) improved quality of the finished product; (d) reduced labor needs; (e) lower noise levels; and (f) less pumping pressure, thus reducing wear and tear of the pumps and the need for cranes to deliver concrete in buckets at the job site. Other long-term benefits include longevity of the bridges as they will be less likely to have large voids. 

The advantages of employing reinforced SCC in bridge piers confined with CFRP grids have not been investigated yet. Research on the applicability of using CFRP grids to confine the concrete core of bridge piers needs to be carried out. A comprehensive experimental program that includes testing of large-scale reinforced SCC bridge pier specimens confined with CFRP grids is lacking. Capacity, strength degradation, ductility, shear capacity, failure mechanism and long-term performance of reinforced SCC bridge pier specimens confined with CFRP grids should be experimentally investigated. Thorough analytical and parametric studies, to complement the experimental investigation, need to be carried out before recommending field implementation and widespread use of the system. Results of the experimental and analytical studies shall be used to establish simplified design guidelines for SCC bridge piers confined with CFRP grids.

 
 

II.    RESEARCH PROPOSED

The primary objectives of the proposed research are to clarify the long-term behavior of reinforced SCC bridge piers confined with CFRP grids and to provide rational and simplified design and construction guidelines. The following main tasks are proposed: a) conduct an international literature search to identify emerging technologies and applications for the use of CFRP grids in bridge structures; b) conduct an extensive experimental study to clarify the strength, ductility, shear capacity and failure mechanism of reinforced SCC bridge pier specimens confined with CFRP grids. Large-scale specimens will be tested under sequentially-increasing reversed cyclic loading to clarify the interaction between strength degradation and ductility; c) investigate the long-term behavior of the bridge piers through applying representative 50-year fatigue cycles; d) carry out analytical and parametric studies to establish the effect of the study variables; e) document all the research tasks, results, conclusions and recommendations; and f) produce rational and simplified design guidelines for implementation of reinforced SCC bridge piers confined with CFRP grids.

 
 

III.  PROBLEM FUNDING AND RESEARCH PERIOD

        Recommended Funding:          $500,000

        Research Period:                         36 Months

 
 

IV.   URGENCY, PAYOFF POTENTIAL, IMPLEMENTATION AND SUPPORT FOR BUSINESS NEEDS

Aging and deterioration of concrete bridges is a serious problem in the United States that often results in restrictive load ratings, costly repairs of structural members, and often early replacement of entire structures. Such infrastructure problems demand innovative and cost-effective techniques for preserving and reconstructing the concrete bridge systems.

The long-term benefit of this research is to provide experimental and analytical investigations for bridge piers employing: a) the advantageous SCC; and b) CFRP grids to confine the concrete core, to prevent the corrosion and to limit the structural deterioration. The study shall demonstrate the effectiveness of CFRP grids in SCC bridge piers under realistic fatigue loading. Several behavioral issues and limitations shall be examined and design guidelines shall be developed.

The precast and prestressed concrete industry shall benefit from the study findings to foster the widely-accepted Accelerated Bridge Construction (ABC) concept for transportation infrastructure. The study findings and recommendation shall assist State DOT’s and bridge engineers selecting competitive design and construction systems. The study findings and design guidelines shall be used to minimize maintenance costs, increase operational efficiency and make appropriate use of CFRP grids in sustainable bridge systems. The idea included in this statement has been endorsed by the West Virginia Department of Transportation.

These goals shall comply with AASHTO’s initiatives to develop and apply sustainable materials, structural systems, and technologies that reduce life-cycle costs, and extend the useful life of bridge structures. The study objectives are closely-aligned with the Grand Challenges identified by the 2005 AASHTO Highway Subcommittee on Bridges and Structures in their Strategic Plan Report for Bridge Engineering. This includes: Challenge 2, Optimizing Structural Systems through the use of newer and emerging materials including FRP and SCC; Challenge 3, Accelerated Bridge Construction through fostering the Precast and Prestressed Industry; Challenge 4, Advancing the AASHTO Specifications through developing design guidelines; and Challenge 6, Contributing to National Policy through focusing on sustainable bridge projects.

 
 
V.   Literature Search Summary

Shahawy et al. (2000) tested standard concrete cylinders wrapped with carbon fiber fabrics. The results varied depending on the number of carbon layers applied. For an unconfined concrete strength of 41.4 MPa the confined strength of cylinders was increased to 70 MPa for the 1-layer wrap and 110 MPa for the 4-layer wrap. The ultimate strain for the 1-layer wrap was 0.007 and for the 4-layer wrap was 0.016. Xiao and Wu (2000 and 2003), Lam and Teng (2004), Li et al. (2002), Harries and Kharel (2002) and Li and Hadi (2003) tested concrete cylinders wrapped with FRP composites and reported that the strength of FRP confined concrete was increased compared to the unconfined concrete. The reported increase was dependant on the type and amount of the FRP composites. Pantelides et al. (1999) wrapped a bridge pier with carbon fiber composites and tested it in situ. Another unwrapped pier was also tested. The pier wrapped with carbon was able to accommodate lateral movements two times larger than the unwrapped pier. Many other researchers worldwide reported several advantages when testing bridge pier specimens wrapped with FRP materials. Mirmiran et al. (1998) tested round and square FRP tubes filled with concrete in compression. The round tubes increased the peak axial stress by as much as 2.5 times the peak axial stress of unconfined concrete and reached an axial strain of 12 times the axial strain at peak stress of unconfined concrete. Few confinement models have been developed to accurately predict the stress-strain curve of concrete (Li and Hadi 2003; Campione and Miraglia 2003; Li et al. 2003; Xiao and Wu 2000, 2003; Fam and Rizkalla 2001). Most models of FRP confined concrete employ a bilinear curve for the stress-strain relationship.

In an effort to address the problem of corrosion of bridge deck reinforcement due to deicing salts, Rahman et al. (2000) used heavy CFRP composite grids (exceeding 0.5” thickness) as reinforcement in a section of concrete deck manufactured in the laboratory. Satisfactory behavior of the carbon grid was reported. Benmokrane et al. (2000) also researched the use of two-dimensional grids to replace the conventional steel welded wire fabric for bridge decks. Yost et al. (2001) tested CFRP grid as reinforcement in concrete beams and reported that the use of the grid as flexural reinforcement resulted in brittle failure due to the rupture of the CFRP grid. Light carbon grids have been investigated primarily for crack control in concrete structures. Harries and Gassman (2003) conducted tests on reinforced concrete basin knockout panels and reported that the grid reduced cracking of the panel significantly. Shao et al. (2003) used carbon grids to control plastic shrinkage cracking in concrete and concluded that the plastic shrinkage cracks were reduced by 50 to 65 percent. Frankl et al. (2008) studied the behavior of prestressed concrete sandwich panels reinforced with CFRP shear grids to achieve the composite action between the two concrete wythes. The panels were subjected to gravity loads and reversed-cyclic lateral loading to simulate 50-year service life of the structure. Frankl et al. reported many positive features of the system and recommended its implementation in architectural panels.

 
 
 
 
 
 
 
 
 

VI.   Person(s) Developing the Problem Statement

Dr. Wael Zatar
Professor, College of Information Technology and Engineering

Program Director, Sustainable Transportation Infrastructure Systems

Nick J. Rahall II Appalachian Transportation Institute
112 Gullickson Hall, One John Marshall Drive
Marshall University
Huntington, WV 25755-2586

Tel:               (304) 696-6043

Fax:              (304) 696-5454

E-mail:         zatar@marshall.edu
 
Dr. Sami Rizkalla

Distinguished Professor of Civil Engineering and Construction

Director of the Constructed Facilities Laboratory

Department of Civil, Construction, and Environmental Engineering

North Carolina State University

Raleigh, NC 27695-7908

Tel:               (919) 513-4482
Fax:              (919) 513-1765
E-mail:         sami_rizkalla@ncsu.edu
 
 
VII. Date and Submitted by
February 19, 2010
Issam E. Harik

Sponsoring Committee:AKB10, Innovative Highway Structures and Appurtenances
Source Info:Dr. Wael Zatar and Dr. Sami Rizkalla
Date Posted:02/19/2010
Date Modified:02/20/2010
Index Terms:Concrete bridges, Self compacting concrete, Carbon fibers, Fiber reinforced polymers, Bridge maintenance, Structural analysis, Corrosion, Precast concrete, Prestressed concrete bridges, Guidelines, Bridge design,
Cosponsoring Committees: 
Subjects    
Highways
Design
Materials
Research
Bridges and other structures

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