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Papers by S A A D A L I A L T A A N

AL-Rafdain Engineering Journal (AREJ), 2006

AL-Rafdain Engineering Journal (AREJ), 2008

A numerical procedure based on the finite element method is developed for the geometric and mater... more A numerical procedure based on the finite element method is developed for the geometric and material nonlinear analysis of reinforced concrete members containing steel fibres and subjected to monotonic loads. The proposed procedure is capable of tracing the displacements, strains, stresses, crack propagation, and member end actions of these structures up to their ultimate load ranges. A frame element with a composite layer system is used to model the structure. An iterative scheme based on Newton-Raphson's method is employed for the nonlinear solution algorithm. The constitutive models of the nonlinear material behaviour are presented to take into account the nonlinear stress-strain relationships, cracking, crushing of concrete, debonding and pull-out of the steel fibres, and yielding of the reinforcement. The geometric nonlinearity due to the geometrical change of both the structure and its elements are also represented. The numerical solution of a number of reinforced fibrous concrete members are compared with published experimental test results and showed good agreement.

Properties of fresh and hardened high strength steel fibrous self-compacted concrete were studied... more Properties of fresh and hardened high strength steel fibrous self-compacted concrete were studied in this investigation. One reference high strength self-compacted concrete mixture is used, with five percent (by weight of cement) silica fume and eight percent of the cement replaced by limestone powder. Three steel fibers percentages by volume of concrete are used (0.4, 0.8, and 1.2). The used steel fibers were a shelled Harex type with irregular cross-section, equivalent diameter of 0.93 mm, and 32 mm long. Super plasticizer was used to improve the workability and flow ability of the mixes. The test results showed that the presence of steel fibers decrease the flow ability, and increase the time of spreading, segregation, and passing ability of the fresh concrete. For the three fibers percentages used, the properties of fresh concrete were within the recommended specifications for the self-compacted concrete. The test results showed that the self-compacted concrete exhibited an early strength development rate more than that for plain normal concrete due to the presence of the fine materials. As for normal concrete, the test results showed also that the increase in the splitting strength is more than the increase in the compressive strength due to the presence of the steel fibers and this attributed to the different failure mechnism of the two tests. The brittle mode of failure of the high strength unreinforced specimens changed to a ductile one due to the presence of the steel fibres.

Reinforced concrete members may be subjected to axial load, bending moment, shear and torsion. ... more Reinforced concrete members may be subjected to axial load, bending moment, shear and torsion. However the behaviour of these members under shear or combined shear and
torsion is a complex phenomenon.
In this study the softened truss model theory is applied for the analysis of fibre reinforced concrete deep beams and corbels. The theory is more promising than the strut and tie model which satisfies the equilibrium conditions and to some extent materials constitutive relationships. While this theory, considers the equilibrium, compatibility, materials constitutive relationships and the degrading effect of the diagonal tension cracks on the compressive strength of cracked reinforced concrete element when subjected to biaxial compression-tension stresses. The previously developed algorithms for the analysis were modified by incorporating the effect of short discrete steel fibres on the behaviour and strength of concrete subjected to shear.
Fibre reinforced concrete deep beams and corbels were analyzed using the adopted algorithm and materials constitutive relationships. The predicted effects of the shear span / depth ratio, volume fraction of steel fibres and the longitudinal steel ratio on the shear strength of fibre reinforced concrete deep beams and corbels showed good agreement with published experimental results.
Keywords: corbel, deep beam, reinforced concrete, shear, softened truss, steel fibres.

The present study consists of two parts, the first one look for producing self-compacting steel f... more The present study consists of two parts, the first one look for producing self-compacting steel fibrous concrete with reasonable flow, spread, and passing abilities, and resistance to segregation and shear. Ten percent of the cement was replaced by limestone powder with particle size less than 75μm to increase the fines fraction in the mix. The second part of the study, deals with the effect of adding steel fibres and the shear span / effective depth ratio on
the shear strength of self-compacted reinforced concrete beams. Twenty four beams were cast which were 1.0 m long, 150 mm wide, and with overall depth of 200 mm. Four volume percentages of steel fibres were used, 0, 0.35, 0.7 and 1.05 together with six shear span /effective depth ratios of, 1.50, 1.74, 1.98, 2.22, 2.46, and 2.69. The test results showed that the steel fibres have adverse effect on the fresh properties and this effect was reduced by using plasticizer that increased with the fibres percentages. On the other hand, the steel fibres improved the mechanical properties of the hardened concrete in compression and tension. All the beams failed in shear, and the test results showed that the presence of steel fibres increased the cracking shear stress and the shear strength and this increase depends on the
shear span / effective depth ratio and on the volume fraction of the steel fibres. The ratio of the cracking / shear strength increased from 0.4 to 0.8 as the shear span / effective depth ratio increased from 1.50 to 2.69. The strut and tie model, and some of the previously developed equations for predicting the shear strength of reinforced fibrous concrete slender beams can be used for predicting the shear strength of fibrous SCC deep and slender beams respectively.

This paper studied the breakout capacity of cast-in-place single short-headed anchor bolts embedd... more This paper studied the breakout capacity of cast-in-place single short-headed anchor bolts embedded in both normal and high strength steel fibrous reinforced concrete. Concrete strength ranged from 27.4 to 58 MPa, four volume fractions of steel fibres (0.4%, 0.8%, 1.2%, and 1.6%), two aspect ratios (19.63, 36.36), three anchor diameters (8, 10, and 12 mm), and four embedment depths (25, 37.5, 50, and 62.5 mm) were used. The majority of the specimens were failed by concrete cone failure and the cone breaks into pieces in some cases (concrete failure), while the other specimens were failed by yielding or fracture of the bolts (steel failure). The tests results showed that the concrete angle cone is increasing with the embedment depth, the fibre reinforcing index and decreasing with the concrete strength. The breakout capacity of the anchors were increased by the addition of steel fibres to concrete and the size of the cones failure in fibrous concrete were smaller than the cones in plain concrete specimens. Based on the experimental results, an expression is proposed to estimate a variable concrete cone angle, which is then used to predict the breakout capacity of single headed anchors embedded in normal and high strength fibrous concrete and showed good agreement with the test results. A regression equation based on the observed breakout capacities is also proposed to predict the breakout capacity, and both methods showed the same degree of accuracy.

This investigation studied the effect of steel fibres on the developed stress in headed bars. On... more This investigation studied the effect of steel fibres on the developed stress in headed bars.
One concrete mix is used with a weight proportions of (1:1.7:3:0.45;cement:sand:gravel
and water cement ratio respectively) and gave a minimum cylinder strength of 37.5 MPa.
The variables included three bars sizes (10, 12 and 16 mm), embedment depths(50, 55, 60,
65, 95 and 100 mm,) three plane dimensions of a 10 mm thick square steel head (20×20,
25×25 and 30×30 mm) welded to the bars, and the steel fibres volume percentage (0.4,0.8
and 1.2). The steel fibres were of the Harex type with irregular cross section, 16 mm long
and an equivalent aspect ratio of 19.64. The test results showed that the developed stress
in the bars increased with the embedment depth and with the steel fibres percentage
considerably, while the used dimensions of the square steel head does not affect the steel
stress significantly. The failure mode of the concrete specimens was sudden and brittle
while that of the fibrous concrete specimens showed a gradual and ductile mode of failure.

Fresh and hardened properties of steel fibrous self-compacted concrete were studied in this inve... more Fresh and hardened properties of steel fibrous self-compacted concrete were
studied in this investigation. One reference self-compacted concrete mix is
used with ten percent of the cement replaced by limestone powder. Three steel
fibres percentages by volume of concrete are used (0.35, 0.7, and 1.05). The
used steel fibres were a shelled Harex type with irregular cross-section,
equivalent diameter of 0.78 mm, and 16 mm long. Super plasticizer was used
to improve the workability and flow ability of the mixes. The test results
showed that the presence of steel fibres decrease the flow ability, and increase
the time of spreading, segregation, and passing ability of the fresh concrete.
For the fibres percentages used, the fresh properties were within the
recommended specifications for the self-compacted concrete. The test results
showed, an early strength development rate more that for plain normal
concrete due to the presence of the fine materials. As for normal concrete, the
test results showed also that the increase in the splitting strength is more than
the increase in the compressive strength due to the presence of the steel fibres.
The splitting strength of the cylindrical specimens is about eighty four percent
of that for the cubic specimens. The brittle mode of failure of the plain unreinforced specimens changed to a ductile one due to the presence of the steel
fibres.

This investigation studied the effect of steel fibres on the pull out capacity of short- headed ... more This investigation studied the effect of steel fibres on the pull out capacity of
short- headed anchor bolts embedded in high strength concrete. The studied
variables in experimental programme included testing short headed anchors
embedded in 72 pull-out specimens, with three embedment depths ( 25 , 37.5 ,
and 50 mm), three compressive strengths ( 45 , 53 , and 58 MPa), four steel
fibres volume percentages ( 0.0 , 0.4 , 0.8 , 1.2 ) and two anchor diameters (10,
and 12 mm). The steel fibres used were of the shelled type (Harex) with
irregular cross-section type with an aspect ratio of 36.34. The test results
showed that the embedment depth has the major effect on the pullout capacity.
The pullout capacity increases also with the addition of steel fibres and with
the square root of the concrete compressive strength, which is an indirect
measurement of the tensile strength of concrete. The brittle type of failure of
the unreinforced specimens changed to a ductile one with the presence of the
steel fibres. For all the specimens, the failure angle ranged between (20-30
o
)
with the horizontal plane.

This paper deals with the tensile behaviour and strength of cast-in-place short headed anchor bol... more This paper deals with the tensile behaviour and strength of cast-in-place short
headed anchor bolts embedded in both normal concrete (NC) and steel fibre reinforced
concrete (SFRC). Four volume fractions (v
f=0.4%, 0.8%, 1.2%, and 1.6%), two aspect
ratios (lf/ df=19.63, 36.33), three bolt diameters (db=8, 10, 12mm), and four embedment
depths (hef=25, 37.5, 50, 62.5mm) were used. More than (108) specimens were tested
under monotonic tensile loading. Only (90) specimens were failed by large concrete
failure cone exceeding the dimensions of the specimen and the cone breaks into pieces in
most cases (concrete failure), while the other specimens were failed by yielding or
fracture of the bolts (steel failure). Tests results showed that breakout capacity (
u
P ) of
the anchors were significantly enhanced by the addition of steel fibers to concrete and the
size of the failure cone in (SFRC) specimens were smaller than the size of failure cones
in (NC).

In this paper, the finite element method is used to study the nonlinear behaviour o... more In this paper, the finite element method is used to study the nonlinear behaviour of
beam-column fibrous reinforced concrete joints under short–term monotonic loading.
Concrete is represented by eight nodded isoparametric elements and the reinforcement was
represented by axial two noded bar elements embedded in the concrete elements. Strain
hardening approach, has been employed to model the compressive behavior of the fibrous
concrete. In tension a continuous function is used to model fibrous concrete in the pre-peak
and post – peak states. Material nonlinearities due to cracking of concrete, crushing of
concrete in compression, debonding and pull – out of fibers and yielding of reinforcement
have been taken into account. A smeared fixed crack approach of the cracked concrete in
tension is assumed. An incremental – iterative scheme based on Newton – Raphson’s method
is employed for the nonlinear solution algorithm and a displacement criterion is adopted for
checking the convergence of the solution. Several previously published test results for fiber
reinforced concrete beam-column joints were analyzed and the numerical results showed
good agreement with the published experimental results.

This study was carried out to determine the influence of the randomly oriented discrete steel fi... more This study was carried out to determine the influence of the randomly oriented discrete
steel fibres on the bearing capacity of plain concrete through testing concentrically loaded
150mm square prisms. The concrete strength, ratio of total areato loaded area, height of
prisms, dimensions and fibre percentage were varied throughout the investigation.
It was found that the bearing capacity increases with the concrete strength and the ratio of
the total to loaded area both for the plain and for the fibrous concrete.
It was also found that the bearing capacity ofsteel fibrous concrete was significantly higher
than that of unreinforced concrete, and showed ductile mode of failure and retained their
integrity also at failure. It was also found that the bearing capacity of fibrous concrete
increases with the aspect ratio of the used fibres.
Prediction of the bearing capacity both for the plain and fibrous concrete using the limit
theorems of perfect plasticity showed fair agreement with the experimental results.

The brittle nature of concrete leads to a brittle shear failure, which the designers try always... more The brittle nature of concrete leads to a brittle shear failure, which the
designers try always to avoid by making the flexural strength of the member less than
the shear strength. The addition of steel fibers to concrete converts the brittle
characteristics of concrete to a ductile one, such fibers are uniformly distributed and
randomly oriented throughout the volume of the concrete. The steel fibers are suitable
as shear reinforcement especiallyin thin members such as slabs and thin webs, where
the use of shear reinforcement is not possible.
An incremental- iterative method whichutilizes the equations of equilibrium,
compatibility of deformations and materials constitutive relationships is employed to
find out the complete response of beams under increasing shear loads. The method
gives detailed information about the flexural and shear stresses in concrete, steel
stresses, cracks initiation and propagation and failure loads. The results obtained such
as failure load and failure pattern showed good agreement with some published
experimental results.

The present study aimed at evaluating the adequacy of the strut and tie model which was proposed ... more The present study aimed at evaluating the adequacy of the strut and tie model which was proposed by the ACI
Code (318-11), AASHTO, FIB recommendations and an Equation proposed by Narayanan and Darwish for
predicting the shear strength of fibre reinforced concrete deep beams. The four methods were applied to 68 fibre
reinforced concrete deep beams whose geometrical, materials and experimental results were previously
published. The collected test results cover a wide range of the variables that affect the shear strength of fibre
reinforced concrete deep beams, like the shear span to effective depth ratio which varied from 0.29 to 1.91,
concrete compressive strength from 18.2 to 54.9 MPa and steel fibres volume percentage from 0.25 to 1.25. Ten
of the beams were loaded with one concentrated load at the midspan section and the others were loaded with
two points loads. The ACI Code (318-11), AASHTO LRFD, FIB recommendations underestimated the shear
strength of the investigated fibre reinforced concrete deep beams. Since these recommendations are for
conventional reinforced concrete deep beams, the effect of steel fibres has to be incorporated in the materials
properties affecting the shear strength of fibre reinforced concrete deep beams. On the other hand the equation
proposed by Narayanan and Darwish overestimated the shear strength of the investigated fibre reinforced
concrete deep beams. A realistic prediction method is therefore required so that it can be used as a design guide.

AL-Rafdain Engineering Journal (AREJ), 2006

AL-Rafdain Engineering Journal (AREJ), 2008