Partially Prestressed Beams with Carbon Fiber Composite Strands: Preliminary Tests Evaluation


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Title: Partially Prestressed Beams with Carbon Fiber Composite Strands: Preliminary Tests Evaluation

Author(s): A.E. Naaman, K.H. Tan, S.M. Jeong, and F.M. Alkhairi

Publication: Special Publication

Volume: 138


Appears on pages(s): 441-464

Keywords: Beams (supports‘); carbon; composite materials; cracking (fracturing); deflection; fiber reinforced plastics; fibers; flexure; prestressing; prestressed concrete; prestressing steels; strains

Date: 9/1/1993

The use of fiber reinforced plastic reinforcement in reinforced and prestressed concrete structures is gaining increased attention. This paper describes the results of a preliminary experimental program in which strands made of carbon fiber composites (trade name CFCC - Carbon Fiber Composite Cable) were used as pretensioning reinforcement in two partially prestressed concrete T beams. The beams were ten foot in length and 12 inches in depth and contained, in addition to the carbon fiber strands, conventional reinforcing bars Experience gained with the stressing, anchoring, and releasing of CFCC strands is described. Relevant test results regarding load-deflection response, curvature, stress-increase in the reinforcement with increased load, cracking and crack widths, and failure modes are reported, and compared to results obtained from similar tests using prestressing steel strands. The load deflection response of beams prestressed with CFCC strands showed generally a trilinear ascending branch with decreasing slope up to maximum load. Deflections and crack widths were generally small but increased rapidly upon yielding of the non-prestressed steel reinforcement. The post-peak response was characterized by rapid step-wise decrease in load due to successive failures of the CFCC strands, and stabilization at about the load-carrying capacity of the remaining steel reinforcing bars. The presence of reinforcing bars helped the beams sustain large deflections before crushing of the concrete in the compression zone. Analytical predictions of the load-deflection response using a nonlinear analysis method were used and led to reasonable agreement with experimental results.