Strengthening of RC Beam with Steel Plate as Shear Reinforcement

Strengthening of RC Beam with Steel Plate as Shear Reinforcement

1Anandhi.L, 2Ramamoorthy.S, 3Dr.K.Dhanasekar

1,2Assistant Professor, Associate Professor, Civil Department ,Agni College of Technology

3Professor, Civil Department,Panimalar Engineering College

Abstract: In this study, galvanised steel plates are used to improve flexural and shear performance of reinforced concrete. The purpose of this work is to present the results of a study carried out to characterize the structural behavior of RC beams with enrolled steel plate. Further, the study aims to evaluate the ability of predicting the ultimate shear capacity of concrete beams. In order to improve its flexural strength and brittleness, a technique of placing steel plate as shear reinforcement will be introduced to the concrete. This study is also aims to improve the strength of reinforced concrete by providing enrolled steel plate along with stirrups by gas welding. From experimental investigations that the strengthened beams exhibited more strength and ductility comparison to the control beams. The results indicate that internally encased galvanised steel plate can be effectively used to rehabilitate or strengthen concrete beams, and analytical methods needed to describe their behaviour are available based on the strain compatibility conditions.These tests should provide information regarding the ability of the internally encased galvanised steel plates to withstand aggressive environments and cyclic loads.

Key Words: RC Beams, Flexural Strength, galvanised steel plates,Welding

1. INTRODUCTION

   It was learnt that steel plates were encased in the reinforced concrete. Some scientists are discussed about the combination of both hot rolled steel and cold formed steel plates were used in the reinforced concrete and to determine the shear behaviour of concrete. In this work, it is proposed to use these steel plates in concrete and to determine the shear and flexural behavior of concrete.

2. EXPERIMENTAL INVESTIGATION

1. TEST RESULTS

   2.1.1Test on cement

   Table 1 Test for Specific gravity of cement

   S.No	Description	Trial- 1	Trial- 2	Trial-3
   1	Empty weight of bottle, w1	109 g	110 g	109 g
   2	Weight of bottle + cement, w2	173 g	179 g	151 g
   3	Weight of bottle +cement + diesel, w3	412 g	420 g	393 g
   4	Weight of flask + diesel, w4	359 g	362 g	358 g
   5	Specific gravity, Gc	3.11	3.21	3.15

   Percentage of water	Depth of penetration (mm)
   25%	3
   30%	6
   35%	8

   Average specific gravity of cement, Gc= 3.15 Table 2 Test for consistency of cement

   Consistency of cement = 30%

   Table 3 Test for setting time of cement

   S.No.	Initial setting time (mins)	Final setting time (mins)
   1	27	540
   2	25	520
   3	28	555
   Average	26	538

   S.No	Trial No.	Trial- 1	Trial- 2	Trial- 3
   1	Weigh of empty bottle, w1	650 g	652 g	649 g
   2	Weight of bottle + sand w2	1235 g	1450 g	1400 g
   3	Weight of bottle + sand +water w3	1811 g	1950 g	1920 g
   4	Weight of bottle +water w4	1450 g	1455 g	1452 g
   5	Specific gravity Gs	2.61	2.63	2.65

   Table 4 Test for Specific gravity of sand

   Average Gs= 2.63

   IS sieve designation	% retained	% passing	Cumul% retained	Remarks
   4.75mm	0.2	99.8	0.2	As per IS 383-1970 it is conformed to zone III
   2.36mm	0.4	99.4	0.6
   1.18mm	9.8	89.6	10.4
   600m	24.9	64.7	35.3
   300m	55.5	9.2	90.8
   150m	8.1	1.1	98.9
   75 m	0.5	0.6	99.4

   Table 6 Test Results of Fine Aggregate

   Description	Result obtained	As per IS 383- 1970
   Specific gravity	2.61	2.55 minimum
   Bulk density	1653.06kg/ m3	–
   Surface moisture	0.11%	–
   Water absorption	1%	–

   Inference

   The properties of fine aggregate satisfy the allowable limits of IS 383: 1970.

   1. Coarse Aggregates test

      Table 7 Sieve Analysis of Coarse Aggregate

      IS sieve designa tion	% retained	% passing	Cumul % retained	Remarks
      80mm	0	100	0	As per IS 383-1970 it is conformed to 20mm size
      40mm	0	100	0
      20mm	46.6	53.4	46.6
      10mm	53.4	0	100
      4.75mm	0	0	100

      Table 8 Specific gravity of Coarse Aggregate Test

      Description		Weight of sample
      Weight of empty pycnometer (w1)	=	625gm
      Weight of pycnometer + C.A (w2)	=	825gm
      Weight of pycnometer + C.A + water(w3)	=	1620gm
      Weight of pycnometer + water (w4)	=	1492gm

      td>

      Values

      S.No.	Description
      1	Specific gravity	2.70
      2	Bulk density	1350kg/m3
      3	Surface moisture	0.086%
      4	Water absorption	0.5%

      The test results of coarse aggregates are given in Table Table 9 Test Results of Coarse Aggregate

      Inference

      The properties of coarse aggregate satisfy the allowable limits of IS 383 : 1970

   2. TEST ON CUBE

      Table 10 Compression test on concrete cube

      Day	S.No.	Compressive load (kN)	Compressive strength (MPa)
      7th day	1	394	17.5
      	2	400.5	17.8
      	3	391.5	17.4
      	Average		17.6
      14th day	1	535.5	23.8
      	2	513	22.8
      	3	544.5	24.2
      	Average		23.6

   3. CASTING OF TEST SPECIMENS Casting of Specimen

      Beam moulds of size 1100mm x 150mm x 150mm were used for casting the rectangle RC beam. The fresh mix of concrete waspoured into the mould and the top surface was finished smooth with trowel.

      Welding of Plate

      The steel plates were encased on all the four side faces of the beam reinforcement. The thickness of galvanised steel plate, which were encased on RC beams is 2mm respectively. The width of the plate was 60mm and the width of the beam was 150 mm. The length of plate was in three proportions and they were 750mm, 500mm, 250mm and the length of the beam is 1100 mm. The galvanised steel plates were placed on the reinforcement by means of gas welding.

   4. RESULTS AND DISCUSSION

FIGURE 1 Load Deflection Behaviour of Reference Beam

FIGURE 2 Load-Deflection Behaviour of Strengthened beams with 2mm plate encasedat the ends

FIGURE 3 Load Deflection Behaviour of Strengthened beams with 2 mm plate encased at the midspan

FIGURE 4 Load -Deflection Behaviour of strengthened beam with 2mm plate encased at 3/4th span of the beam

CONCLUSION

• From experimental investigations that the strengthened beams exhibited more strength and ductility comparison to the control beams. The results indicate that internally encased galvanised steel plate can be effectively used to rehabilitate or strengthen concrete beams, and analytical methods needed to describe their behaviour are available based on the strain compatibility conditions.

• Also it can be inferred from observations that lesser the thickness of the plate used, greater is the ductility and lesser is the stiffness.Also marked improvements in the strength are observed when the steel plates are internally encased

• More investigations have to be carried out in the future to address the problem of the diagonal cracks due to internal stress developed.

• Also shear failure is one more aspect whose has to be studied with respect to the failure mode of the strengthened beam in light of the expected flexural failure.

• Before this type of strengthening procedure is safely applied, further studies involving the durability of these internally encased galvanised steel plate reinforced beams are needed. These tests should provide information regarding the ability of the internally encased galvanisedsteel plates to withstand aggressive environments and cyclic loads.

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