دانلود رایگان مقاله انگلیسی بررسی رفتار برشی پرتوهای بتنی پیش تنیده توسط بتن تقویت شده با الیاف - اشپرینگر 2018

Abstract

Failure due to shear is brittle in nature, and inherent lesser concrete tensile strength is a main contributing factor. During loading before the shear reinforcement could start functioning, cracking in concrete starts. Use of fibers in concrete had proven improved impact on tensile strength of concrete. Active reinforcement role initiates after concrete cracking starts. This paper investigates into the shear behavior of fiber reinforced, pretensioned concrete I-section beam specimens. A total of six beam specimens were cast. Two types of fibers, steel fibers and polypropylene fibers were used in five different proportions. For comparison, one control specimen was also cast without inclusions of fibers in concrete. Concrete mix ratio, prestress force, shear span-to-depth ratio and shear and flexural reinforcement details were kept constant in all specimens. Specimens were subjected to four-point loading to ensure that all specimens fail due to excessive shear force. During tests, deflections and strains were also measured. It was concluded that shear strength of beams was improved using steel fiber reinforced concrete (SFRC) as compared to polypropylene fiber reinforced concrete (PPFRC). SFRC beam containing 0.65% fiber depicted 50.71% improvement in ultimate failure load, 67% improvement in first cracking load and 36% improvement in ultimate deflection as compared to control beam.

4 Conclusions

Following conclusions were drawn based on experimental results of normal prestressed and fiber reinforced prestressed concrete beam specimens subjected to four-point loading:

1. First crack load can be increased more using SF as compared to hybrid or PF. However, first crack load would reduce if excessive amount of SF is used. Fig. 17 Crack patterns of P4 beam Fig. 18 Crack patterns of beam P5 Fig. 19 Crack patterns of P6 beam

2. Using SF, ultimate load of beams can be improved appreciably. Hybrid fibers also give good results but PF do not give appreciable results in this concern.

3. Steel fibers and hybrid fibers would improve deflection, i.e., give enough indication before failure as compared to polypropylene fiber.

4. Use of fibers improves ductility index. However, this improvement is more pronounced in SF and hybrid fibers as compared to PF.

5. Due to usage of fibers, crack width is much reduced. SF, hybrid fibers and PF all show good reduction, but SF would give best results.

6. SFRC prestressed beam with optimum fiber percentage is recommended in overall, as it performed better in terms of load, deflection, crack width compared to other beams investigated in the research. However, by increasing SF percentage above optimum value, adverse results may be obtained. In this investigation, when SF percentage was increased to 0.85%, the behavior was not improved.

7. Increasing SF percentage above 0.65% as 0.85% in P4 has not shown noticeable improvement in yield load or yield displacements.