Flexural Cracking Evaluation Using Fiber Optic Sensors in High Strength Composite Beams Reinforced With Prestressed Prisms

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Title: Flexural Cracking Evaluation Using Fiber Optic Sensors in High Strength Composite Beams Reinforced With Prestressed Prisms

Author(s): E. G. Nawy and B. Chen

Publication: Special Publication

Volume: 154

Issue:

Appears on pages(s): 21-40

Keywords: beams (supports); cracking (fracturing); crack width and spacing; high-strength concretes; loads (forces); prestressing; prisms; strains; reinforced concrete; stabilization; stresses; Materials Research

Date: 5/1/1995

Abstract:
This paper covers analytical and experimental investigation of high- strength concrete beams reinforced with high-strength prestressed concrete prisms as main reinforcement. Fiber optics technology has been developed and used in this investigation to measure the flexural crack widths developed throughout the full loading history of the specimens. Thirteen beams, 8 in. x 12 in. (200 x 300 mm) is cross section and having a 9.0 ft (2.74 m) span were tested to failure. The embedded prestressed prisms had a length of 9 ft, 6 in. (2.90 m) and cross-sectional dimensions ranging between 1.5 in. x 3.0 in. (38 mm x 76 mm) and 4.5 in. x 3.0 in. (114 mm x 76 mm). The prisms were prestressed with 7-wire, 3/8 in. (10 mm) diameter, 270 ksi (1860 MPa) tendons. Concrete strength in both the prisms and the beams was in excess of 14,000 psi (100 MPa) using silica fume as a partial cementitious replacement, as well as a high-range water reducer (superplasticizer) to attain the desired workability and compressive strength. A study of the extensive data accumulated in this research program, supported by the National Science Foundation, resulted in expressions for the evaluation of flexural crack widths in ultra-high-strength concrete composite beams. Test results also showed that the embedded prisms delayed the development of cracks, while the additional use of non-prestressing steel significantly reduced the crack spacing in the beams and limited the crack width at the onset of prism cracking.