Structural behaviour of fibers as part of shear reinforcement in reinforced concrete slab

• Main Author: Baarimah, Abdullah Omar Obaid
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://umpir.ump.edu.my/id/eprint/29009/1/Structural%20behaviour%20of%20fibers%20as%20part%20of%20shear%20reinforcement%20in%20reinforced.pdf; http://umpir.ump.edu.my/id/eprint/29009/

Due to the brittle behaviour of plain concrete in tension, shear failure of the slab is generally catastrophic. An increase in the thickness of the slab is recommended in many instances to increase the shear capacity of the slab and avoid such failure in the slab. Hence, this study investigated the behaviour of fibers as a part of shear reinforcement in reinforced concrete slabs. The main objective was to investigate the potential effect of single and hybrid fibers added with reinforced concrete (RC) slabs with and without a reduction in the slab thickness and its potential to serve as part of shear reinforcement. Moreover, the optimum ratio of hybrid fiber (kenaf and steel) in RC slabs was as well studied. The experimental work focuses on three parameters, which include the thickness of the slab, types of fibers and volume fraction of fiber (Vf). Two series of slabs with different dimensions were designed in accordance with the Eurocode 2 for the experimental study. The first series of the slab was designed to fulfil shear capacity characteristic, while the second series of the slab was designed with 17% less thickness than required, intended to be failed in shear. The difference in the slab thickness was to cater for the potential of the fibers and serve as part of shear reinforcement in the RC slab. Both series of slabs were added with the single fibers (steel fiber and kenaf fiber separately) using different volume fraction of fiber such as Vf = 0%, Vf = 1% and Vf = 2%. However, the volume fraction considered was Vf =1% with ratios 0.75:0.25, 0.50:0.50 and 0.25:0.75 for the slab with hybrid kenaf-steel fiber. The RC slab without fiber Vf = 0% and no reduction in thickness was taken as the control slab. A total number of thirty-two slabs were constructed and tested to fail under the four-point bending test. The results show that the addition of single and hybrid fibers to RC slabs have a significant contribution to improve the structural performance of the FRC slabs such as load-carrying capacity (32 and 27%), ductility (87 and 50%) and energy absorption (250%) for the second series of slabs with Vf = 2% of steel fiber and Vf = 0.5:0.5 of hybrid fiber, respectively. Fibers were found more effective in controlling the crack propagation and altering the failure mode of the slab from brittle to a more ductile manner. In addition, it was observed that the inclusion of single fibers and hybrid were able to fully compensate for the loss in concrete shear capacity due to thickness reduction which had the potential of serving as part of shear reinforcement in RC slabs except for the kenaf fiber which was probably due to insufficient treatment. Furthermore, these findings show that the optimum ratio of hybrid fiber at Vf = 0.5:0.5 produced the best structural performance in RC slabs such as load-carrying capacity (41 and 27%), ductility (29 and 50%) and energy absorption (200 and 250%) for the first and second series of slabs, respectively compared to control slab. Moreover, this ratio of hybrid fiber recorded the similar behaviour of structural performance to the steel fiber at Vf =1%, especially in strength and ductility which improved to 19 and 50% in the second series of the slab compared to control slab. Overall, this investigation demonstrated a significant enhancement of the structural performance of RC slabs with the addition of single and hybrid fibers.