الفهرس 
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Abstract
This thesis presents the results of a research study on the shear behavior of Ultra High
Strength Concrete (UHSC) beams. The study aims to investigate the shear behavior of UHSC
and verify the applicability of current code provisions to determine the minimum shear
reinforcement of higher concrete strengths. Seven UHSC beams were cast and tested under
two concentrated vertical loads to study their shear behavior. Furthermore, three High
Strength Concrete (HSC) and three Normal Strength Concrete (NSC) were cast and tested to
evaluate the adequacy of ECP minimum shear reinforcement requirements. Three main
factors were studied to investigate the behavior of the tested beams. These factors are:
• Concrete Compressive Strength (fcu).
• Amount of transverse reinforcement (ρw).
• Amount of steel fiber (Vf).
The scope of the study consisted of an experimental investigation and finite element
analysis. The experimental program was conducted at the Properties and Testing of Material
Laboratory of the National Housing & Building Research Centre. The results of the
experimental program were presented and discussed.
The theoretical phase included a numerical study to investigate the shear behavior of
the tested beam specimens. In the first section of this phase, the experimental results were
used to calibrate the finite element models. Then in the second section, the calibrated model
was used to estimate some complex data to be measured experimentally.
7.2 Conclusion
The following conclusions were drawn from the results of the research program:
1. Shear capacity and midspan deflection in UHSC beams increased with the increase in
the volume fraction of steel fibers by 29% and 43%, respectively.
2. The use of steel fibers led to (a) an enhanced inclined cracking pattern (multiple
cracks), (b) more ductile shear failure, and (c) an increase in the stiffness of the beam.
Chapter (7) Summary & Conclusions
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3. Increasing the concrete strength caused an increase in the shear capacity of beams
with and without stirrups. For example, for specimens with identical shear
reinforcement spacing, increasing the concrete strength from 48 MPa to 83 MPa
caused an increase in the shear capacity by about 14%, while increasing the concrete
strength from 83 MPa to 128 MPa caused an increase in the shear capacity by about
25%.
4. The beams with a more significant amount of stirrups (that is, lower spacing of
stirrups) failed with the formation of diagonal cracks with closer widths. On the other
hand, beams with fewer shear stirrups (that is, higher spacing of stirrups) failed with
the formation of diagonal cracks with wider spacing. Further, in the case of stirrups
with lower spacing, the shear load capacity and midspan deflection of UHSC beams
were higher.
5. Diagonal crack width has been influenced by both the amount of shear reinforcement
and concrete compressive strength. As a result, the diagonal crack widths for
specimens with identical shear reinforcement spacing are almost similar, although
shear strength and the number of cracks.
6. Test results indicated that adding steel fibers enhanced cracking loads, ultimate loads,
shear strength, and the ductility of the studied beams. For example, adding 1% fibers
by volume increased the cracking load by about 25% and the ultimate load by about
31% over the reference beam.
7. It was found that a combination of web reinforcement and fibers resulted in obtaining
the benefit of both high capacity and ductility. This combination resulted in a
significant increase in the ultimate loads by 25% over those of the reference beam
specimen. The addition of transverse shear reinforcement can modify the failure mode
from a brittle shear to a ductile flexural failure mode.
8. By adding steel fiber to beams with transverse shear reinforcement, redaction in crack
width has been observed by 80%. In addition, the fibers appeared to be effective in
delaying the formation of cracks.
9. Comparing the experimental results with the equations used for calculating the
ultimate shear capacity of UHSC beams given in ACI 318-19 [45] and the Egyptian
code for concrete structures ECP 203-17 [58], it was found that the ACI code
equations give preferable calculated shear capacity than Vn calculated using the ECP
203-17 equations. The ECP needs reassessment to include the effect of higher
concrete compressive strength.
10. The ECP 203-17 [58] requirements for minimum shear reinforcement are not
satisfactory when UHSC and HSC are used. Test beams having ECP 203-17
minimum shear reinforcement had less reserve shear strength than the others, and the
crack width observed at the stage of shear cracking was beyond the allowable
serviceability limits.
11. The equation proposed in this paper requires approximately 35% more minimum
shear reinforcement than ECP 203-17. Beams designed using this equation had a
significant increase in reserve shear strength index by 53% than beams having ECP
Chapter (7) Summary & Conclusions
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203-17 minimum shear reinforcement, and crack width remained below the allowable
serviceability limits (< 0.30 mm). Specimens having the minimum shear
reinforcement following the proposed equation satisfied the criteria set in this study.
12. In respect of reserve strength is the most important parameter in determining the
minimum shear reinforcement (which depend on concrete tensile strength). It would
be more reasonable and rational to derive the equation by equating the magnified
cracking shear strength to the ultimate shear strength. When this is done, the
following equation is obtained, where the coefficient C is related to reserve strength.
𝐴𝑣𝑚𝑖𝑛
𝑏𝑤𝑠
= 𝐶
𝑓𝑡
𝑓𝑦
13. The finite element program gives conservative values for the diagonal shear cracking
loads concerning the experimental diagonal shear cracking loads.
14. There is a good agreement between the failure loads obtained from the finite element
analysis and those obtained from the experimental results for the all-beam specimens.
15. There is a good agreement between the deformations obtained experimentally and
theoretically.
16. The predicted stirrups strain values are well correlated to the experimental values. At
the same time, the FEM underestimate longitudinal steel strain values for UHSFC
beam specimens. However, the curves show good agreement with the experimental
findings for the rest of the beam specimens.
7.3 Recommendations for Future Research
1. Studying the behavior of UHSC beams under pure torsion stresses and the combined
effect of direct shear and torsion.
2. Studying the effect of using UHSC on the long-term deformations of beams.
3. Studying the behavior of UHSC beams under the effect of cyclic loading.