

Title of Thesis
Evaluation of Shear Strenth of High Strenght
Concrete Beams 
Author(s)
Attaullah Shah 
Institute/University/Department
Details Department of Civil Engineering / University of
Engineering & Technology, Taxila 
Session 2009 
Subject Engineering Civil 
Number of Pages 266 
Keywords (Extracted from title, table of contents and
abstract of thesis) Technology, Concrete, Shear,
Literature, Evaluation, Phenomena, Comparison, Beams, Steel,
Strenght, Reinforcement, Longitudinal 
Abstract In this thesis, the
shear properties of High Strength Reinforced Concrete (HSRC) beams
have been investigated on the basis of available research data an
experimental work at Structural Laboratories of University of
Engineering and Technology TaxilaPakistan. The shear capacity of
High Strength Reinforced Concrete (HSRC) beams is relatively less
investigated in the contemporary research, as most of the research
data available is based on the results from
normal strength reinforced concrete with compressive strength of
40MPa or less.
There is a general consensus amongst the researchers in the field of
Structural Engineering and Concrete Technology that the shear
strength of HSRC beams, unlike the Normal Strength Reinforced
Concrete (NSRC) does not increase, in the same proportion as the
increase in the compressive strength of concrete, due to brittle
behaviour of the High Strength Concrete. Hence the current empirical
equations proposed by most of the building and bridges codes for
shear strength of HSRC beams are less conservative as compared to
the Normal Strength Reinforced Concrete (NSRC) beams. This major
observation by the researchers is the main focus of this research.
An extensive literature review of the shear properties of Normal
Strength Reinforced Concrete (NSRC) beams and High Strength
Reinforced Concrete (HSRC) beams was undertaken.Additionally the
shear strength of disturbed region (DRegion) was also studied. In
disturbed region the ordinary beams theory based on Bernoulli’s
theorem is not applicable.In the literature review of disturbed
regions special emphasis was laid over Strut and Tie Model (STM),
which is an emerging analysis and design tool in the current
research in reinforced concrete.
The literature review was followed by the experimental work, which
comprised of 70 high strength reinforced concrete beams and 9 two
ways high strength concrete cobles. Beams were cast in two sets of
35 beams each, one set without web reinforcement and other with web
reinforcement. For each set of 35 beams five values of longitudinal
reinforcement and seven values of shear span to depth ratio were
selected to mainly study the behaviour of slender beams, where
typical shear failure can be anticipated.These beams were tested
under monotonic load at the mid span to examine the contribution of
various parameters like longitudinal steel, shear span to depth
ratio, and web reinforcement, on the shear capacity of HSRC beams.
It has been observed that the shear strength of beams has been
increased with the increase in longitudinal steel and shear
reinforcement but it has reduced with the increase in the shear span
to depth ratio The beams with low longitudinal steel ratio and no
web reinforcement failed mainly due to shear flexure cracks. However
the beams with longitudinal steel ratio of 1% and more failed mainly
due to beam action in shear tension failure.The beams with small
shear span to depth ratio and large values of longitudinal steel
ratio however failed due to shear compression failure.
The shear failure of HSC beams with large values of longitudinal
steel and shear span to depth ratio was however more sudden and
brittle, giving no sufficient warning before failure, which has been
observed as serious phenomena in the shear failure of HSC beams.
The addition of web reinforcement increased the shear strength of
all beams tested. The failure mode was also affected.The obvious
contribution of the minimum web reinforcement was avoiding the
sudden failure of the HSC beams.
These test results were also compared with the equations of some
international building and bridges codes and methods for shear
strength of HSRC beams.It has been noticed that these equations do
not provide equal level of safety in theshear design of HSRC
beams.Some of the codes are over conservative, while few others are
less conservative for the shear design of HSRC beams.Comparison of
the observed shear strength of tested HSRC beams with the results of
the codes equations used, reveal that most of these equations are
less conservative for shear design of HSRC beams at lower values of
longitudinal steel for both cases of beams with and without web
reinforcement, particularly for longitudinal steel ratio less
than1%. Hence additional care may be required for shear design of
HSRC beams at large values of shear span to depth ratios.
To analyze the behaviour of typical disturbed region in concrete
structures, the basic rationale of Strut and Tie Model (STM) was
used for the analysis and design of two way corbels.These corbels
were tested under monotonic loads applied at the overhanging portion
of the corbels. The actual shear capacities of these corbels were
compared with the theoretical shear capacities of the corbels worked
out with the STM. The actual and theoretical values of the shear
were falling close to each other.Their comparison reveals that STM
can be further tested as more simple and reliable tool for analysis
and design of disturbed region (DRegion) in concrete structures,
through more experimental research.
Further research work on shear properties of HSRC beams with higher
values of compressive strength of concrete in the beam region and
more experimental research on the disturbed region including pile
caps, deep beams, dapped ended beams and corbels has been
recommended at Engineering UniversityTaxila Pakistan. 
