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International Journal of Civil Engineering and Technology (IJCIET) Volume 6, Issue 9, Sep 2015, pp. 93-103, Article ID: IJCIET_06_09_009 Available online at http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication

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FLEXURAL AND SHEAR STRENGTH OF

NON-PRISMATIC REINFORCED HIGH STRENGTH CONCRETE BEAMS WITH

OPENINGS AND STRENGTHENED WITH

NSM-CFPR BARS

Prof. Dr. Mustafa B. Dawood and Reem Abd-Alraheem Nabbat Civil Engineering Dept. Collage of Engineering

University of Babylon

ABSTRACT:

These studies presents an experimental and theoretical investigation of flexural and shear behavior of High Strength Twelve reinforced concrete non-

prismatic beams with or without opening, strengthened by carbon fiber reinforced polymer (CFRP), tested as simply supported span subjected under

2 point loading. The openings in beams are frequently required to provide accessibility to accommodate essential service such as ducts and pipes. However, introducing an opening in non-prismatic reinforced concrete beams

can cause an abrupt deterioration in the flexural and shear capacity due to stress concentration at the corners of the openings. This research presents an

experimental and theoretical investigation for the use of carbon fiber reinforced polymer (CFRP) as a strengthening technique to upgrade the non-prismatic reinforced concrete beam with openings.

The experimental results showed that when non-prismatic beams are strengthened by carbon fiber bar, ultimate load is increased by (16% and

15%) for flexural and shear behavior respectively. Flexural behavior beams have openings where the ultimate load decrease by (11.2% and 33% ) for openings near support and openings near points load respectively, while for

shear behavior beams have openings, in which the decrease in ultimate load is (3% and 10% ) for opening in neutral-axis and upper of neutral-axis

respectively. When beams with openings are strengthened the ultimate load for flexural behavior beams is increased (23% to 35%), while shear behavior beam is increased (16% to 25%) compared with beams have opening.

Key words: Carbon Fiber Reinforced Polymer (CFRP), Flexural strength and Shear strength

Prof. Dr. Mustafa B. Dawood and Reem Abd-Alraheem Nabbat


Cite this Article: Prof. Dr. Dawood, M. B. and Nabbat, R. A.-A. Flexural and Shear Strength of Non-Prismatic Reinforced High Strength Concrete Beams

with Openings and Strengthened with NSM-CFPR Bars. International Journal of Civil Engineering and Technology, 6(9), 2015, pp. 93-103.

http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=9

1. INTRODUCTION

Non prismatic beams have been used in various structures including buildings and bridges since the first decades of the previous century, with an increasing application

as the structural engineering techniques were improved. With the beams being tapered, the architects would be able to create and implement novel aesthetic architectural designations, as well as the structural engineers who could seek for

optimum low weight - high strength systems through a redistribution of materials along the structural members [1].

There is a large need for strengthening of concrete structures all around the world and there can be many reasons for found strengthening, increased loads, design and construction faults, change of structural system, and so on. The need exists for

strengthening in flexure as well as in shear. Epoxy plate bonding with Carbon Fiber Reinforced Polymers, CFRP has been shown to be a competitive method for

strengthening of existing structures and increasing the load carrying capacity

The presence of web openings in such beam is frequently required reduce the element shear capacity to provide accessibility such as doors and windows, or to

accommodate essential services such as ventilating, pipes and air conditioning ducts. Enlargement of such openings due to architectural, mechanical requirements or

change in the building functions would reduce the element shear capacity [2].

2. EXPERIMENTAL PROGRAM

The experimental study consisted of two test groups. First group was designed to fail

in flexural and the second group designed to fail in shear.

The first group included six beams with and without openings. The beams has total

length (L) of 1500 mm ,the clear span (Ln) is 1350 mm ,the height at the mid span (H1) is 155 mm ,while the height at support (H2) is 220 mm and the width (b) is 150 mm. The flexure reinforcement of beams consisted of 2Ф12 mm tension bars at bottom, and 2Ф10

mm at top. To avoid shear failure, the beams were reinforced for shear with Ф6 mm closed stirrups spaced at 70 mm C/C as shown in Figure 1 show control beam F1.

Figure 1 Details of Tested Beams

Flexural and Shear Strength of Non-Prismatic Reinforced High Strength Concrete Beams with Openings and Strengthened with NSM-CFPR Bars


The second beam is (F2) same to F1 but strengthen with carbon bar in tension zone grooved at bottom face as shown in Figure 2.

Figure 2 Section and Bottom view of (F2)

The third beam (F3-O1) has two openings in the shear zone with dimension (150*70) mm. The location of its openings were (275) mm from the edge of the beam to the center of the openings as shown in Figure 3.

Figure 3 Section of Beam (F3-O1)

The fourth beam (F4-O1-S) is same to (F3-O1) but strengthen with carbon sheet in bottom face as shown in Figure 4.

Figure 4 Bottom view of (F4-O1-S)

The fifth beam (F5-O2) has two openings in shear zone with dimension (150*70) mm. The location of openings were (350) mm from the edge of beam to the center of opening as shown in Figure 5.

Figure 5 Section of Beam (F5-O2)

The sixth beam (F6-O2-S) is same to (F5-O2) but strengthen with carbon sheet in

the tension zone at bottom face; also the openings were strengthened with CFRP as shown in Figure 6.

Carbon Bar

Carbon Sheet



Figure 6 Section of Beam (F6-O2-S)

The second group included six beams with and without openings. The beam has a total length (L) of 1500 mm, the clear span (Ln) is 1350 mm, the height at the mid

span (H1) is 240 mm, the height at the supports (H2) is 140 mm and the width (b) is 150 mm. The flexure reinforcement of beams consisted of 3Ф12 mm bars at bottom, and 2Ф10 mm at top, the beams were reinforced for shear resistance with Ф4 mm

closed stirrups spaced at 55 mm C/C as shown in Figure 7.

Figure 7 Section of Control beam (S1)

The second beam (S2) is same to (S1) but strengthen in shear zone with inclined carbon bar with angle (45°) and space between bars are (55)mm as shown in Figure 8.

Figure 8 Section of beam (S2)

The third beam (S3-O1) has one opening in flexure zone with dimensions

(150*80) mm. The location of opening is at the center of the beam as shown in Figure 9.

Carbon bar

Carbon Sheet



Figure 9 Section of beam (S3-O1)

The fourth beam (S4-O1-S) is same to (S3-O1) but strengthen with carbon bar in the shear zone and the opening was strengthened with CFRP as shown in Figure 10.

Figure 10 Section of beam (S4-O1-S)

The fifth beam (S5-O2) has one opening in flexure zone with a dimension (150*80) mm. The location of the opening is (100) mm from the top of beam to the

center of opening as shown in Figure 11.

Figure 11 Section of beam (S5-O2)

The sixth beam (S6-O2-S) is same to (S5-O2) but strengthen with carbon bar as shown in Figure 12.

Figure 12 Section of beam (S6-O2-S)

Carbon Sheet

Carbon Bar

Carbon Sheet

Carbon Bar



3. MATERIALS

In the experimental program, (ф4, 6, 10, 12 mm) hot-rolled, deformed, mild steel bars

are employed as tension reinforcement for both, flexure and shear beams. Modified Portland cement (Type I) from Iraq plant named Kubaise. Crushed gravel from Al-

Nibaey region with maximum size of (14 mm). Natural sand from Al-Akhaidher region in Iraq with maximum size of (4.75 mm) and fineness modulus of (2.501). High-range water-reducer superplasticizer (Viscocrete) [3].

Table 1 Concrete Mix

High strength concrete Parameter

0.28 Water/cement ratio

140 Water (kg/ )

500 Cement (kg/ )

625 Fine aggregate(kg/ )

1065 Coarse aggregate(kg/ )

5* Superplasticizer (L / )

50 Silica fume (kg/ )

1 litter /100 kg cement

4. TEST MEASUREMENT AND INSTRUMENTATION

A hydraulic universal test machine (MFL system) was used to test the beam specimens. The deflections were measured by means of (0.01 mm) accuracy dial

gauge (ELE type) and (50 mm) capacity. Strain of concrete measured used demic point and dial gauge (ELE type) with accuracy of (0.002 mm) and (10 mm) capacity.

5. TEST PROCEDURE

Tests were carried out by using universal testing machine with capacity of 2000 kN. The universal testing machine is a closed loop servo hydraulic testing system

controlled manually, the heart of the universal testing machine is a custom installed 4 m high frame, this frame has a high degree of stiffness and can be modified to

accommodate different configurations of beams as well as other structural elements. The experiments were executed in load control with manually data monitoring. All of the non-prismatic beams were statically tested to fail in one loading cycle. The

supports, as well as the loading point measured 100 mm in width. The load was slowly applied, in a load-control manner at a rate of 0.5 kN/s, in successive

increments up to failure. The applied load increment was initially 5 kN which was then increased to 10 kN intervals until specimen failure. At each increment, the load was held constant so that deflection and mechanical strain gauge reading could be

taken. After the readings were taken, the test beam was inspected for any new or extended cracks. These observations were recorded on the beam using felt tipped

markers. Once the readings and observations were taken, the loading was then increased by the next increment and the procedure was repeated. Test was terminated at the onset of one of the following;

Substantial drop in the value of the total applied load.

Excessive deformations and cracks widening under the same load level.

Concrete crushing.

Carbon

Bar



6. EXPERIMENTAL RESULTS

6.1. Flexural Beams Results

The test results of this group including (ultimate and cracking loads) are given in

Table 2.

Table 2 Ultimate and Cracking Loads of flexural behavior of Tested Beams

6.1.1. Deflections of flexure beam

Load-deflection curves of the tested beams at mid span at all stages of loading up to

failure were constructed and shown in Figures (13).

Figure 13 Load-deflection curves of the tested beams at mid span



Figure 14 Crack Pattern of Flexural Beams

6.2. Shear Beams Results

All beams of this group were designed to fail in shear. Photographs of the tested beams are shown in Figure (15). The test results of this group including (ultimate and cracking loads) are given in Table 3.



Table 3 Ultimate and Cracking Loads of shear behavior of Tested Beams

6.2.1. Deflections of shearbeam

Load-deflection curves of the tested beams at mid span at all stages of loading up to

failure were constructed and shown in Figures (16).

Figure 15 Crack Pattern of Shear Beams



Figure 16 Load-deflection curve

7. CONCLUSIONS

The presence of openings in the non-prismatic beams near interior support decreases

the ultimate load by about (12.56%), while the beams have openings near interior point load decreases the ultimate load about (59.44%) when compared with beam without openings.

The CFRP sheet technique gives a better performance in comparison with near surface mounted (NSM) in Flexure beams

The presence of opening in the non-prismatic beam located at mid span over neutral axis decreases the ultimate load about (10.75%) and (2.84%) for beam with opening in neutral axis, when compared with beam without openings.

The strengthening by CFRP, decreases the crack width and increases number of cracks, this is one of the several advantages of using the CFRP.

The first cracking load obtained from numerical data show results lower than the experimental data recorded with a difference about (10.78%) as an average of Flexure beams and (4.86%) as an average of Shear beams



The cracking patterns at the final loads of the finite element models compared well with the observed failure modes of the experimental tested beams.

REFERENCES

[1] ACI Committee-363. State of the Art Report on High Strength Concrete (ACI 363R-92). American Concrete Institute, Detroit, 1997.

[2] Al-Dolaimy, A. Structural Behavior of Continuous Reinforced Concrete Beams with Openings and Strengthened by CFRP Laminates. M. Sc. Thesis, College of Engineering, University of Babylon, IRAQ, 2011.

[3] Iraqi Specification, No.5. Portland cement, Baghdad, 1984.

[4] Said, M. and Elrakib, T. M. Enhancement of Shear Strength and Ductility for Reinforced Concrete Wide Beams due to Web Reinforcement. International Journal of Civil Engineering and Technology, 4(5), 2013, pp. 168–180.

[5] Hans I. A., Arturo, T. and Alejandro, G. Behavior of reinforced concrete haunched beams subjected to cyclic shear loading. Elsevier Ltd., 2013.

flexural and shear strength of non-prismatic …€¦ · non prismatic beams have been used in...

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