Ashour, 2000 - Efeitos Do Comprensão... Experimento de Comparação de Vanalli

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Engineering Structures 22 (2000) 1145–1158 www.elsevier.com/locate/engstruct Effect of the concrete compressive strength and tensile reinforcement ratio on the flexural behavior of fibrous concrete beams Samir A. Ashour * , Faisal F. Wafa, Mohmd I. Kamal Civil Engineering Department King Abdulaziz University, Jeddah, Saudi Arabia Received 18 January 1999; received in revised form 22 April 1999; accepted 4 June 1999 Abstract Twenty seven reinforced concrete beams were tested to study the effects of steel fibers, longitudinal tensile reinforcement ratio and concrete compressive strength on the flexural behavior of reinforced concrete beams. Concrete compressive strengths of 49, 79 and 102 MPa and tensile reinforcement ratios of 1.18, 1.77 and 2.37% were used. The fiber contents were 0.0, 0.5 and 1.0% by volume. The results show that the additional moment strength provided by fibers was not affected by the amount of tensile reinforcement ratio. However, the concrete compressive strength influenced the fiber contribution significantly. The flexural rigidity increases as the concrete compressive strength and steel fiber content increases. The transition of effective moment of inertia from uncracked to fully cracked sections depends strongly on the considered variables. A previously propose d formu la in the literatu re for the estimation of the effect ive moment of inertia is modified to conside r the effect of reinforcement ratio and concret e compressive strengt h as well as fiber content. © 2000 Publish ed by Elsevi er Science Ltd. All right s reserv ed. Keywords: Beams (supports); Compressive strength; Cracking; Deflection; Flexural strength; Flexural rigidity; High-strength concrete; Moment of inertia; Reinforced concrete; Steel fibers; Tensile reinforcement ratio 1. Introd uction The maximum potentiality of high-strength concrete (HSC) cannot be realized fully in structures due to the britt leness of the material and the serviceab ility prob- lems ass oci ate d wit h the res ult ing red uce d cross-sec - tional dimension. Addition of fibers to high-strength concrete converts its brittleness into a more ductile behavior. Whe n concre te cracks, the ran domly ori ent ed fibe rs arrest bot h microc rac kin g and its pro pag ati on, thus improving strength and ductility. Addition of fibers only slightly influences the ascending portion of the stress- strain curve but leads to a noticeable increase in the peak strain (strain at peak stress) and a significant increase in ductility [1,2]. Researches conducted on the flexural behavior of fiber rei nfo rce d con cret e (FRC) bea ms hav e bee n concen- * Corre spon ding author. Tel.: +966-2-695-2488; fax: +966-2-695- 2179. E-mail address: [email protected] (S.A. Ashou r). 0141-0296/00/$ - see front matter © 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0141 -0296 (99)00 052-8 trated on the prediction of the ultimate flexural strength and the load deformation behavior in terms of various material parameters [3–15]. Less attention was given to the flexural rigidity of FRC beams in the service load range. Several methods have been proposed for calculat- ing the deflections of reinforced concrete flexural mem- bers subjected to short and long-term loadings [16–20], howeve r, tho se met hods dea l mai nly wit h non fibr ous concrete, and differences may exist for FRC beams. The deter minat ion of short -term deflection requires the estimation of the moment of inertia, I , of the beam which depends on the degree of cracking that has taken place in the member. For loads below the cracking load, comput ati on of defl ection may be based on the gro ss concr ete section, I g . Howeve r, as the load increases above the cracking load, the member will crack at dis- crete intervals because the tensile strength of the concrete has been exceeded, and all tensile stress is carried by the steel reinforcement. The neutral axis will fluctuate between cracks causing variation of the curvatures along the member length and reducing the flexural rigidity of the section. The value of I changes along the beam span

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Ashour, 2000 - Efeitos Do Comprensão... Experimento de Comparação de Vanalli