الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Hybrid reinforcement schemes are a combination of steel bars and FRP bars, this
combination was widely used as a longitudinal reinforcement in concrete beams. Using this
combined reinforcement was an effective method to overcome the structural defects resulting
from using FRP bars as longitudinal reinforcement in concrete beams. FRP is a good alternative
to steel as it has higher tensile strength, less weight, and higher corrosion resistance. However,
there are two main defects of FRP material that form an obstacle to using it in R.C. structures.
FRP has linear stress-strain behavior until failure without yielding meaning that it has no
ductility. Moreover, the elasticity modulus of FRP bars is about only 20% of that of steel bars
leading to decreasing the element stiffness and increasing deflection which affect the
serviceability requirements. Using hybrid schemes significantly enhanced the stiffness and
ductility of beams compared with FRP-reinforced beams, but this enhancement depended on
the ratio of steel reinforcement in hybrid schemes. So, another alternative should be found to
be able to decrease the steel portion in hybrid schemes without decreasing the ductility or
stiffness of the beams. In the present work, the effect of steel fiber inclusion on the flexural
behavior of beams reinforced with hybrid schemes is studied.
Seven half-scale beams were experimentally tested until failure under static loading.
The main parameters used in this study were the steel fibers volume ratio, the portion of GFRP
reinforcement in the hybrid schemes, and the total longitudinal reinforcement ratio. The
experimental program was divided into three groups, group (A) represented the control
specimen reinforced with steel bears only and beams reinforced with hybrid schemes without
adding steel fibers to the concrete matrix. group (B) represents the beams reinforced with
different ratios of hybrid schemes including a 0.50% steel fibers volume ratio. group (C)
represents the beams reinforced with different ratios of hybrid schemes including a 1.00% steel
fibers volume ratio. All specimens had a rectangular section with 150 mm in width and 250
mm in depth. The web reinforcement of all specimens was 8@100 mm and the compression
reinforcement was 210.
The experimental results showed that using steel fibers in the concrete matrix of beams
reinforced with hybrid schemes significantly enhanced the initial stiffness, ductility factors,
and toughness of tested beams. The first cracking load and load-carrying capacity were slightly increased. The improvements in load-carrying capacity were 13% and 21% for the steel fiber
volume ratio of 0.50% and 1.00% respectively, and the enhancement in stiffness was 17% and
21% for the steel fiber volume ratio of 0.50% and 1.00% respectively. The increase in ductility
factor was 65% and 132% for steel fiber volume ratio of 0.50% and 1.00% respectively. The
values of GFRP strain were increased by adding steel fibers to concrete beams leading to
increasing the tensile stress in GFRP bars and therefore increasing the flexural strength.
A non-linear finite element analysis (NLFEA) was performed to simulate the flexural
behavior of RC beams reinforced with hybrid schemes. The load-deflection responses and
crack patterns of experimental specimens and numerical models were compared. The
comparison showed a good agreement between the experimental and numerical results.
A simple formula was developed to predict the ultimate flexural strength of fibrous
concrete beams reinforced with hybrid schemes. This formula was developed based on
equilibrium conditions and idealized stress- blocks given by empirical equations. The
computed flexural capacities resulting from the proposed formula were compared with
experimental flexural capacities for specimens in this work and 41 other specimens from the
literature. This comparison was made to measure the accuracy of the proposed formula to be
used as a powerful tool in the analysis and design of R.C. beams reinforced with hybrid
schemes. A very good correlation was achieved for different concrete compressive strengths,
longitudinal reinforcement ratios, and different cross-sectional dimensions.