SHEAR REINFORCEMENT EFFECTS ON THE FLEXURAL...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 01, January 2019, pp. 651-663, Article ID: IJCIET_10_01_059

Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=01

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

SHEAR REINFORCEMENT EFFECTS ON THE

FLEXURAL STRENGTH OF REINFORCED

CONCRETE BEAMS

Ameer A. N. Al-jamel and Hayder M.K. Al-Mutairee

Civil Engineering, University of Babylon, Iraq

ABSTRACT

This research devotes to conduct an investigation into the effects of lateral

reinforcement on the flexural behaviour of Straight Reinforced Concrete Beam

(SRCB). The amount of both longitudinal and lateral reinforcement, beam aspect ratio

(h/d) and shear span of concentrated load to depth ratio (a/d), are considered. The

experimental work includes casting and testing of fifteen SRCB of normal strength with

simple ends. The beams divided into three groups according to h/b ratio which taken

equal to (1.5, 2, and 2.5). The experimental results show that for SRCB with h/b equal

to 2 and under concentrated load at mid-span the ultimate load carrying capacity

increased by (30.8%, and 22.23%) when increasing the shear reinforcement by (50%,

and 100%) respectively. Also, the ultimate strength was increased by about 10.38%

and 16.53% with increment in shear reinforcement of 50%, and 100% respectively for

beams with h/b equal to 1.5 and under two-point load at third point. Finally, the results

appear not only increments in the capacity of ultimate load and decrement in the cracks

width when decreasing the shear reinforcement spacing but also the ductility of the

beams has increased observable.

Key words: Reinforced concrete, beams, shear reinforcement, Confinement of

flexural reinforcement, ductility

Cite this Article: Ameer A. N. Al-jamel and Hayder M.K. Al-Mutairee, Shear

Reinforcement Effects on the Flexural Strength of Reinforced Concrete Beams.

International Journal of Civil Engineering and Technology, 10(01), 2019, pp. 651–663

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=01

1. INTRODUCTION

The lateral reinforcement in reinforced concrete structures provides shear resistance, keeps the

longitudinal reinforcement in place during concreting, prevents the compression reinforcement

from buckling and confines the concrete in the core. The present study is concerned with the

effect of confinement due to lateral reinforcement (in particular) upon the strength and

deformation characteristics of beams.



Flexural yield strength defined as the stresses in the materials just before their yields. When

a material is subjected to bending, just the fibres at extraordinary edge are at the biggest stress

in this way, when those fibres are free from any deformities, the flexural strength can be

controlled by those fibres. However, if the similar material was just under tensile forces then

every one of the fibres in the material have a similar stress and the failure will start when the

weakest fibre achieves its greatest tensile stress. Thus, for a similar material, the flexural

strengths will be higher than tensile strengths. On the other hand, a homogeneous material that

has deformities on its surfaces may have a higher tensile strength than flexural strength.

In a simply supported beam subjected to bending, the fibres are in compression above the

neutral axis, whereas in tension below this axis. The factors affecting on shear strength and

formation of inclined cracks are so many and complicated that a final conclusion concerning

the accurate mechanism of inclined cracking developed from high shear is difficult to

determine. The shear behavior of reinforced concrete beams at failure is decidedly different

from their flexure behavior. They fail suddenly without enough advanced caution, and the

diagonal cracks that grow are greatly larger than the flexural cracks. [1] Discussed the effects

of lateral reinforcement upon the strength and deformation properties of concrete and found

that lateral reinforcement improves the strength and ductility of confined concrete, and has a

detrimental effect upon the cover. [2] Presented equation for shear strength of reinforced

concrete beams that has enough simplicity expressed by concrete strength, reinforcement ratio

and effective depth in accumulative form. The results appeared that a part of the shear force

can be transferred by the dowel action of longitudinal bars. It is found that the main factors

influence on this action was flexural rigidities of the bars, and strength and rigidity of the

surrounding concrete. [3] Showed that the structural size effect may be illuminated by

considering structures of different sizes and fixed other variables. They concluded that the size

effect was considered for diagonal shear failure of reinforced beams and one-way slabs without

shear reinforcement. [4] Tested reinforced high-strength concrete beams designed to fail by

shear. It was concluded that for beams without shear reinforcement, the failure shear strength

generally increased as the concrete compressive strength increased. Beams with equal amount

of transverse reinforcement, the higher concrete compressive strength gives the more effectual

stirrups. [5] Exhibited a few aftereffects of test examination on six fortified solid pillars in

which their auxiliary conduct in shear was considered. The examination directed about the

utilization of extra even and autonomous twisted up bars to build the shaft opposition against

shear powers. From trial examination, the utilization of twisted up and free flat bars as shear

support were more grounded than ordinary shear fortification framework. [6] Talked about the

aftereffects of exploratory inquire about conducted to study the concept that the convincing

significance is not has effect on the shear nature of fortified bond flexural individuals which

did not contain shear reinforcement. It was found that flexural and flexure-shear cracks were

influenced importantly by the shear strength. [7] Tried examples had indistinguishable

longitudinal reinforcement, however changing shear fortification proportions to examine the

impacts of shear limit on the effect conduct. The results show that the shear qualities of the

examples assumed a vital job in their general conduct. Examples with higher shear limit could

manage more effects and retain more vitality, though the ones with bring down shear limit

endured broad harm under the same or littler effect loads. [8] Showed behavior of shear

cracking of simply supported reinforced concrete beams. The width of shear crack was

increased proportionally with both the spacing of shear cracks and with the strain of shear

reinforcement. It was detected that the larger spacing of stirrups gives larger width of shear

crack. [9] Tested reinforced concrete simply supported beams with different shear

reinforcement; welded swimmer bars, bolted swimmer bars, u-link bolted swimmer bars, and

traditional stirrups. The results showed that there is change in shear quality of fortified solid

Shear Reinforcement Effects on the Flexural Strength of Reinforced Concrete Beams


bars by utilizing swimmer bars all in all. Likewise, the length and width of the splits were less

using swimmer bars contrasted with the conventional stirrups framework. [10] Tested

reinforced concrete simply supported beams without stirrups. They proved that the shear span

to depth ratio (a/d ) has an important effect on the shear strength both at low and high values

of a/d. [11] tested simply supported beams with compressive strength of concrete was equal to

29 MPa and the shear span to depth ratio was equal to three. The study demonstrates that the

commitment of shear reinforcement to the shear limit is vital and straightforwardly relative to

the amount and spacing of the web reinforcement. The study showed that the adequacy of the

shear reinforcement diminishing with expanding the spacing of shear reinforcement along the

beam width. Shear strength was more effective for wide beam with high tensile stress in the

steel. Additionally, results demonstrate that the ductility of the wide beams importantly

improves by the web reinforcement. [12] Showed arching action behavior of beams. It was

concluded that where the point of confinement of the compressive bend is more important than

that given by the steel fortress, the longitudinal strengthening extent has only a minor effect on

the zenith stacking cut off of the at the edge-controlled RC columns. In like manner, it was

exhibited that gave the base essentials to staying away from delicate shear frustration are met,

and the part is under-sustained, the withdrew suppression given by transverse help gave

through the plastic pivot length has only a minor effect on the zenith stacking cut-off of RC

shafts that make colossal calculating movement. [13] studied the distribution of longitudinal

reinforcements of reinforced concrete horizontally curved beams with fixed-ends. He

concluded that the non-uniform distribution of longitudinal reinforcements is effective and can

be used to improve the strength of beams, and it is important when the angle of horizontal

curvature of the beam is increased. [14] Studied the effects of yield strength of steel,

compressive strength of concrete, thickness of slab and the bar diameter used in edge-supported

two-way slabs. The results showed where (fc') increases from 15 to 35MPa the (As) will be

decreased by (13%) when ( ��

�≈ 3.5

�

��) and for any values of other variables, also it is not

economical to use high strength of concrete when the term (��

�) between (0.5-1 kN/mm). Also,

the study proved that when the thickness (t) increases to (50%), the (As) will decreases (28%

to 32% according to the parameter), while; if the thickness of slab increases to (100%), the

(As) will decreases (62% to 64%). [15] Showed that the shear span to depth ratio a/d represents

the main parameter that has importantly effect on the shear strength in straight reinforced

concrete beams without shear reinforcement. In most researches the effect of web

reinforcement on the flexural strength of beams was disregard. The recommendations of those

researches and some of the previous investigations are based on the premise that the main

function of lateral reinforcement is to prevent the compression reinforcement from buckling

and to confine the core concrete, rather than the effect of web reinforcement on the flexural

strength of beam.[16] tested ten specimens of reinforced concrete continuous deep beams

(RCCDB) under two-point loads. The effects of high strength concrete (HSC) layer thickness

and Carbon Fibre Reinforced Polymer (CFRP) on the strength of RCCDB were thus studied.

The results showed that the strengthening of RCCDB by an HSC layer at the top is better than

that from one at the bottom, as the increments in ultimate load strength were 17% and 34% for

top strengthening and 8% and 26% for bottom strengthening for 25% and 50% thickness of

total depth of beam, respectively. The optimal strengthening of RCCDB using an HSC layer at

the top was at 50%.

2. MATERIALS AND METHODS



In this research fifteen beams tested, they are divided into three groups according to the h/b

ratio.

The details of samples geometry and reinforcement are tabulated in Table 1.

Table 1: Section geometry and reinforcement details of tested samples

Bea

m N

ame

Dim

ensi

on

(mm

) Longitudinal Reinforcement Shear Reinforcement

Ratio of �

�

�

ℎ Number of bars

at bottom

��.

��

%

Spacing

(cm)

∅5@ Incr

emen

t

%

B11 h=240

b=160

h/b=1.5

5∅9.98

90

9 0

0.67 2.78 B12 6 50

B13 4.5 100

B21 h=320

b=160

h/b=2

3∅9.98

+3∅4.65 47

14 0

0.67 2.08 B22 9.33 50

B23 7 100

B24 h=320

b=160

h/b=2

6∅9.98

+2∅4.65 84

12 0

1 3.13 B25 8 50

B26 6 100

B27 h=320

b=160

h/b=2

7∅9.98

+1∅4.65 97

10 0

1 3.13 B28 6.67 50

B29 5 100

B31 h=300

b=120

h/b=2.5

3∅9.98

+2∅4.65 61

13 0

0.67 2.22 B32 8.67 50

B33 6.5 100

2.1. Materials properties

Reinforcement: Two different diameters of reinforcements are used (∅4.65 and ∅9.98) and

tested according to ASTM-A615/A-615M-05a. The yield stress was (561 and 573MPa)

respectively.

The mechanical properties of hardened concrete: The compressive strength test determined

as decided by (BS.1881: Part 116:1989) [17] and (ASTM C33, 2008) [18]. The results of cubes

were converged and the average strength of them was 35MPa. Also the Modulus of Rupture

test performed by concrete prisms specimens with dimensions (100×100×400) mm were cast

as decided by (ASTM C78, 2004) [19] procedure. The average of all specimens was 3.4MPa.

The properties of the other materials are described in Appendix A. Section reinforcement: All

beam sections designed according to the (ACI-Code 2014) [20] requirement for bending and

shear, but the flexural failure mode secured to study the effects of stirrups on the flexural

behavior of beam. The compression zone was reinforced by two bars of ∅9.98mm, while the

shear reinforcement has a diameter bar of ∅4.65mm. Figure (1) and Figure (2) show the

geometry and load scheme of specimens. Each group has the same amount of h/b but the shear

reinforcement increase by 50% and 100% as shown in figures (3) to (7).



All dimensions in mm

Figure. 1: Geometry of specimens of group one and three and branch one of group two (B21, B22,

and B23)

All dimensions in mm

Figure. 2: Geometry of specimens of branch two and three of group two (B24, B25, B26, B27, B28,

and B29).

Figure 3: Section details of specimens of first group.

Figure 4: Section details of specimens of branch one of second group

Figure 5: Section details of specimens of branch two of second group.

Figure 6: Section details of specimens of branch three of second group.



Figure 7: Section details of specimens of third group.

Trials mixes: In order to obtain the required properties of the concrete, three trial mixes

were experimentally conducted and one of these mixes was adopted. The procedure of the trial

mixes was by select different water/cement ratio (0.52, 0.54, and 0.56). The fresh concrete was

then examined to evaluate its validity (workability, and segregation). For the chosen mix; six

cubes and six prisms were cast to estimate the mechanical properties of hardened. The adopted

mix proportions of concrete are tabulated in Table 2.

Table 2: Mix proportion of concrete

Materials Proportions Units

Cement 342 kg/m3

Coarse

aggregate 1011 kg/m3

Fine

aggregate 748 kg/m3

Water 192 kg/m3

W/C ratio 0.56 ----

Forms Manufacturing: Fifteen set of plywood formworks made. Plywood blocks were

used to obtain smooth surfaces. The formwork and reinforcement cage are shown in Fig.8.

Figure 8: Reinforcing cages and wooden formworks

Casting of the samples: Before the casting, the forms were greased and the steel cage

installed in place by using 15 mm spacers, the top pieces of the form were then fastening to

brace the cage in place and prevented it from rising up because of its flotation ability due to the

presence of vibrator. The specimens were done using 2 m3 mixture in a one day by central

mixer for quality control. The concrete was poured directly into the form as shown in Fig.9.

The casting was including six 150×150×150 mm cube and six 100×100×400 mm prism was

poured along the casting period. The curing process was done using two tanks contain the

samples, cubes and prisms. The curing water was changed every 7 days then after 28 days the

samples were got out from the container and prepared to test.



Figure 9: Casting process.

Testing Procedure: All beams were tested in a universal testing machine as shown in Fig.

10. The beams were simply supported over a span of 2000 mm rested on solid steel frame. The

test of beams was under static load, and loaded in successive increments until failure. The

specimens painted in white colour before testing in order to observe crack development. The

deflection readings of dial gauge at mid-span and cracks width were recorded at selected levels

of loading. In addition, the cracks were detected and drawn on the side face of the tested beams.

Dial gage for measuring deflection of the beam specimens at mid-span with accuracy of 0.01

mm. Mechanical strain gage was using to measure the concrete strain with accuracy of 0.002

mm.

Figure 10: Specimen in universal testing machine.

3. RESULS AND DISCUSSIONS

3.1. First cracking load

Crack formation was monitored at different loading stages. Beams of first group which has h/b

ratio is equal to 1.5 and under two-point load showed better enhancement in first cracking loads

when shear reinforcement was increasing. Beams of first branch of the second group (where

was under two-point load with moment to shear ratio of 0.667) which had h/b ratio is equal to

2 showed good enhancement in first cracking loads compared with the other two branches

which was under one mid-span concentrated load with moment to shear ratio of 1. Beams of

third group which has h/b ratio is equal to 2.5 and under two-point load had first cracking loads

close to each other. Table 3 contains the details of the first cracking load of the specimens. Table 3: Experimental results of specimens

Gro

up

No.

Bea

m n

ame First crack

Ultimate load (kN) Increase in ultimate load

(%) Pcr

(kN)

Crack width

(mm)

1 B11 69 0.10 141.6 0



B12 78 0.09 156.3 10.38

B13 82 0.07 165 16.53

2

B21 55 0.08 169 0

B22 59 0.06 163.5 -3.25

B23 62 0.04 172.6 2.13

B24 31 0.06 154.6 0

B25 42 0.03 170.7 10.41

B26 39 0.02 191.2 23.67

B27 33 0.03 164.6 0

B28 27 0.03 215.3 30.80

B29 32 0.03 201.2 22.23

3

B31 39 0.03 142.5 0

B32 40.5 0.03 149 4.56

B33 40 0.02 140.5 -1.40

Table 4: Experimental results of specimens

Group No. Beam name Load at yield

Defl.

at yield

(mm)

Decreme -nt % Max.

Defl. (mm) Ductility

1

B11 105 11.27 --- 28 2.48

B12 105 10.60 5.94 31 2.92

B13 105 8.38 25.64 37.1 4.43

2

B21 145 9.87 --- 22.53 2.28

B22 145 10.14 -2.74 21.32 2.10

B23 145 9.11 7.70 23.10 2.54

B24 145 10.02 --- 20.60 2.06

B25 145 7.34 13.62 22.65 3.09

B26 145 7.17 28.44 25.41 3.54

B27 160 10.78 --- 17.06 1.58

B28 160 8.01 25.70 24.55 3.06

B29 160 9.67 10.30 21.74 2.25

3

B31 130 11.32 --- 18.75 1.66

B32 130 10.36 8.48 23.55 2.27

B33 130 11.61 -2.56 23.43 2.02

3.2. Crack width

In the present investigation, the splits were estimated by utilizing the break meter. The

arrangement of first split was checked all through the test to record the width of this break with

expanding load near failure of the beam models. The connection among load and break width

for the three gatherings is appeared in Figures 11 to 14.



Load against midspan deflection: Two dial gages were placed at mid-span to measure the

deflection. Generally, it can be observed that the load versus mid-span deflection response can

be divided into three stages of behavior. The first stage was characterized by an approximately

linear relationship, during this stage of behavior, the section was uncracked and both the

concrete and steel behave essentially elastic. The second stage represents the behavior beyond

the initial cracking of the section where the stiffness of the beam was decreased as indicated

by the reduced slope of the load versus mid-span deflection curve. The end of this stage was

distinguished when the main steel reinforcement starts to exhibit inelastic behavior. The third

stage was characterized by a decreasing slope of the curve, where the tension steel

reinforcement reaches the strain hardening stage. The experimental load versus mid span

deflection for these models is shown in Figures (16) to (20).



Ultimate Load and Failure Modes: All examples were tried up to failure. The recorded

extreme burdens and failure methods of the shaft’s examples are introduced in Table 5. Table 5: failure mode of specimens

Group No. Specimen Failure mode

1

B11 Concrete Cover Separation



2

B21 Typical flexural failure











3




4. CONCLUSION

Depending on the experimental results taken from the laboratory tests the following

conclusions were made:

1. The measure of restriction given by lateral reinforcement is needy upon the

separating of horizontal reinforcement as well as on the appropriation and

proportion of flexural reinforcement and the nature of limited concrete.

2. Spacing of lateral reinforcement is the most important parameter, because the

choice of bar sizes, and the qualities of concrete and steel are limited in practice.

The effect of transverse reinforcement decreases drastically with increasing the

spacing.

3. Depending upon the arrangement of shear reinforcement and the relative areas of

core and cover the presence of shear reinforcement appears to improve the over-all

ductility of the members.

4. Beams with h/b equal to 1.5 with high percent of !"#$%./!�'( (which equal to 90%)

have increment in the ultimate load carrying capacity by (10.38% and 16.52%)

whenever shear reinforcement increased by (50%, and 100%) respectively, while

the beams with h/b equal to 2 with high percent of !"#$%./!�'( (which equal to

97%) have high increasing in the ultimate load by (30.8%, and 22.23%) when the

shear reinforcement increasing by (50%, and 100%) respectively.

5. Beams with !"#$%./!�'( equal to 47% and 61% have very small increment and

decrement in the ultimate load.

6. There is enhancement in the cracking behavior for all beams that have an increment

in the shear reinforcement where the crack width was decreasing with increasing in

its number.

7. Before the yield point, the deflection was decreasing with increasing load by

25.64% and 28.44% with !"#$%./!�'( equal to 90% and 84% respectively when the

increment in the shear reinforcement was by 100%.

8. After the yield point, the deflection was increasing with increasing load and thus

the ductility of beams was increasing by 4.43 and 3.54 with !"#$%./!�'( equal to

90% and 84% respectively when the increment in the shear reinforcement was by

100%.

REFERENCES

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and deformation properties of concrete," Magazine of concrete research, vol. 23, pp. 99-

110, 1971.



[2] H. Okamura and T. Higai, "Proposed design equation for shear strength of reinforced

concrete beams without web reinforcement," in Proceedings of the Japan Society of Civil

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beams," Journal of the American Concrete Institute, vol. 81, pp. 456-468, 1984.

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concrete beams using artificial neural networks. Part II: beams with stirrups," Engineering

structures, vol. 26, pp. 927-936, 2004.

[5] A. Hamid and N. Azlina, "The use of horizontal and inclined bars as shear reinforcement,"

Universiti Teknologi Malaysia, 2005.

[6] L. H. Sneed and J. A. Ramirez, "Effect of depth on the shear strength of concrete beams

without shear reinforcement–experimental study," 2008.

[7] S. Saatci and F. J. Vecchio, "Effects of shear mechanisms on impact behavior of reinforced

concrete beams," 2009.

[8] M. Zakaria, T. Ueda, Z. Wu, and L. Meng, "Experimental investigation on shear cracking

behavior in reinforced concrete beams with shear reinforcement," Journal of Advanced

Concrete Technology, vol. 7, pp. 79-96, 2009.

[9] M. M. Al-Nasra and N. M. Asha, "Shear reinforcements in the reinforced concrete beams,"

American Journal of Engineering Research (AJER), vol. 2, pp. 191-199, 2013.

[10] M. N. Khaja and E. G. Sherwood, "Does the shear strength of reinforced concrete beams

and slabs depend upon the flexural reinforcement ratio or the reinforcement strain?,"

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concrete wide beams due to web reinforcement," HBRC Journal, vol. 9, pp. 235-242, 2013.

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Materials, vol. 47, pp. 7-19, 2013.

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on the Behavior of Reinforced Concrete Horizontally Curved Beams with Fixed-Ends,"

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[17] B. British Standard, "part 116, 1983," Method for determination of compressive strength

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commentary (ACI 318RM-14)," 2014.



APPENDIX A:

Materials properties:

Cement: Ordinary Portland cement (Type I) was used in casting of the beams. This cement

was manufactured by united cement company, commercially known (Crista). The properties

are conformed to the Iraqi specification limits [8] for ordinary Portland cement.

Fine aggregate: Regular sand from (Al-Akaidur) area was utilized as fine total. The degree

of the fine total exists in the upper and lower limits of Iraqi Specification [7] Zone (2) and [3]

specification.

Coarse aggregate: Squashed coarse total from (Badra and Jassan's quarry) was utilized

with greatest total size 19 mm. The rock was washed and cleaned by water, at that point dried

before utilizing. The strainer investigation of coarse total exists in the upper and lower limits

of Iraqi specification [7] and [3] specification.

Water: Ordinary clean tap water used in this work for both mixing and curing of the

specimens.

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