A Study on Strengthening of R.C.C Columns by Ferrocement Jacketing

IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 11 | May 2017 ISSN (online): 2349-784X

A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing Anagha.A.R PG Student Department of Civil Engineering Mar Athanasius College of Engineering, Kothamangalam, Kerala, India

Prof. Shibi Varghese Associate Professor Department of Civil Engineering Mar Athanasius College of Engineering, Kothamangalam, Kerala, India

Abstract This study is aimed to strengthening of deficient columns incorporating with different methods to reduce stress concentration at corners. Comparative study is carried out with column jacketed with and without steel fiber in mortar mix. In total, twenty seven reinforced concrete columns were loaded to ultimate loading. From the experimental investigation it is observed that improvement in ultimate load carrying capacity of the ferrocement jacketed columns in comparison to non-jacketed columns.

Four techniques and variations in those techniques are proposed to address the problem.

Keywords: Ferrocement, Jacketing, Strengthening, Steel angle, Wire mesh ________________________________________________________________________________________________________ I.

INTRODUCTION

Column is one the most important structural elements designed to support compressive load and transfer load to the foundation.

The strengthening of reinforced concrete columns through ferrocement jacketing is a commonly used effective technique because of its availability of raw material and low cost. Retrofitting with ferrocement confinement is the oldest and cost effective technique used to strengthen the concrete structures. The unique properties of ferrocement such as fire resistant, durability, low self-weight, water proof and crack resistant makes it an ideal material for wider applications. Confinement for square column by ferrocement by different type of techniques to strengthening of corners has also been studied by researchers. Result shows that strengthening of corners are practically more effective. This study aims to develop efficient techniques to overcome the drawback of conventional ferrocement jacketing.

II. EXPERIMENTAL PROGRAMME Experimental investigation of 27 square RC columns was done under concentric compressive load. Four types of jacketing techniques with and without steel fiber are taken into consideration. Such as; (i) square jacketing with single layer welded wire mesh without and with steel fiber(denoted as SL and SLSF) ,(ii) square jacketing with single layer welded wire mesh and rounded corner without and with steel fiber(denoted as RSL and RSLSF),(iii) square jacketing with single layer welded wire mesh and one extra layer of wire mesh at corner without and with steel fiber (denoted as SLOL and SLOLSF), and (iv) square jacketing with single layer welded wire mesh and steel angle at each corner without and with steel fiber(denoted as SLAL and SLALSF).

Fig. 1: Jacketing Techniques (1)SL,(2)RSL,(3)SLOL,(4)SLAL

Materials used Cement Ordinary Portland cement of 53 grade conforming to IS 2269(1987) was used in this investigation. It should be stored under dry condition for short period as possible.

Fine aggregate The fine aggregate used in this study was M sand. The specific gravity of fine aggregate was 2.75 and it belongs to zone II. IS 383:1970.

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A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing (IJSTE/ Volume 3 / Issue 11 / 022)

Coarse aggregate Both 12 mm and 20 mm size aggregate in the ratio 40:60 were used by conforming to IS 2386-1963.

Reinforcing wire mesh Welded wire mesh with an opening size of 12 mm and diameter of 0.9mm was used.

Steel fiber Hooked end steel fiber with length 30 mm diameter of 0.5mm and aspect ratio 60 was used.

Mortar mix Steel fiber at volumetric fractions of 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5,1.75 and 2% of the mixes were evaluated. Cement sand mortar of ratio 1:3 and water cement ratio 0.45 was used.

Compressive strength (28 days)

48

2

COMPRESSIVE STRENGTH (N/mm )

50

46

44

42

40

38

36 0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

% STEEL FIBER

Fig. 2: Compressive strength with varying percentage of steel fiber

At 1.25 % by volume of steel fiber gives higher compressive strength value 49.59 N/mm2.

Mix proportion The mix was designed as perIS10262:1982 .The compressive strength obtained after 28 days was recorded 29.61 N/mm2.

Item Cement Fine aggregate Coarse aggregate water

Table – 1 Mix proportion Mix proportion 1 2.05 3.43 0.5

By weight(kg/m3) 350 718 1438 175

Specimen preparation RC columns were cast satisfying the condition of short column (l/b<12). The cross sectional dimensions of the columns are 150 mm X 150mm and the height of column was 500 mm. The column consists of 4 nos. of 10 mm diameter longitudinal bars with 6mm diameter lateral ties at 100 mm c/c spacing. Workability of concrete was tested by slump test. Column specimens were then cast and it was demoulded after 24 hours of casting.

Ferrocement jacketing Ferrocement with closely spaced and uniformly distributed reinforcement provided ductility to the brittle concrete .RC column were jacketed after 7 days of casting. Final size of jacketed specimen was 174mm including 12mm ferrocement jacket. The cement sand proportion of the mortar used for jacketing work was 1:3. All strengthened columns were cured in water after completing work for 28 day from the date of casting.

Testing of specimen A total 27 RC column specimen were cast in this study .The test were conducted by using compression testing machine with a capacity of 5000kN. Dial gauges within the accuracy of 0.01mm were fixed to the loading set up to measure the deflection of

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A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing (IJSTE/ Volume 3 / Issue 11 / 022)

column. Axial and lateral deflection were noted from the dial gauges at every load increment of 50 KN. The ultimate load and corresponding deflection were noted for each column specimen.

III. RESULTS AND DISCUSSIONS The experimental results of the tested column specimens are discussed in the following sub sections.

Ultimate load carrying capacity Test result shows that the ultimate load carrying capacity of different type of ferrocement jacketed columns is higher than that of conventional ferrocement jacketing techniques. The ultimate load carrying capacity of RSL and RSLSF type column specimen has higher value than SL type column specimen. Because of rounded corner it reduces the stress concentration at corners. By using steel fiber in mortar, only slight increase in ultimate load is observed. SLOLSF type column specimen has higher ultimate load value than RSLSF type specimen. This is because of effective stress transferring through the middle face of column. In SLAL type column specimen, due to steel angle at corners reduces the stress concentration at corners and has high ultimate load carrying capacity. In SLAL type specimen percentage of steel in cross section of column is large as compared to other techniques. The increased load carrying capacities obtained are 31.55%, 35.2%, 42.124%, 64.769% for SL, RSL, SLOL and SLAL type square column specimen and 33.42%, 37.06%, 43.062%, and 66.07% for SLSF, RSLSF, SLOLSF, and SLALSF type column specimen respectively.

1 2 3 4 5

Specimen type NJ SL RSL SLOL SLAL

Sl. NO 1 2 3 4 5

Specimen type NJ SLSF RSLSF SLOLSF SLALSF

Sl.NO

Table â&#x20AC;&#x201C; 2 Average ultimate axial and lateral deflection of tested specimen without steel fibers Ultimate load Ultimate axial %Increment in axial Ultimate lateral (kN) deflection(mm) deflection deflection(mm) 618.79 2.94 814.02 3.85 26.53 0.56 836.61 4.19 42.52 0.92 879.44 4.61 56.8 1.08 1019.58 4.42 50.34 1.02 Table -3 Average ultimate axial and lateral deflection of tested specimen with steel fibers Ultimate load Ultimate axial %Increment in axial Ultimate lateral (kN) deflection (mm) deflection deflection (mm) 618.79 2.94 825.61 3.64 23.8 0.38 848.12 3.85 30.95 0.65 890.45 4.22 43.53 0.77 1027.6 4.09 39.12 0.68

%Increment in lateral deflection

76.92 107.69 83.92

%Increment in lateral deflection 71.05 102.63 78.94

Deflection response Lateral deflection was measured at the mid height of the tested specimen. The axial and lateral deflection values are shown in table 1and table 2 by using dial gauges. It is clear from the table that SLOL has higher axial and lateral deflection values. The deflection is maximum were the maximum stress occurs just before the failure of column. Increment in lateral deflection in case of SLOL, SLAL, and RSL type specimen are 107.69%, 83.92% and 76.92% respectively. Increment in lateral deflection in case of SLOLSF, SLALSF and RSLSF type column specimen are 102.63%, 78.94% and 71.05% respectively. Load Vs. deflection curve of each type of tested specimen are shown in Fig. 3 and Fig. 4.

NJ SL RSL SLOL SLAL

1100 1000 900 800

LOAD (kN)

700 600 500 400 300 200 100 0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

AXIAL DEFLECTION (mm)

Fig. 3: Comparison of NJ, SL, RSL, SLOL, SLAL

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A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing (IJSTE/ Volume 3 / Issue 11 / 022)

NJ SLSF RSLSF SLOLSF SLALSF

1100 1000 900 800

LOAD (kN)

700 600 500 400 300 200 100 0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

AXIAL DEFLECTION (mm)

Fig. 4: Comparison of NJ, SLSF, RSLSF, SLOLSF,SLALSF

Failure pattern It is seen that because of short column, non-jacketed column fails by crushing and jacketed column fails from ferrocement jacket.

In SL and SLSF column specimen because of stress concentration at corners steel fibers in mortar reduce the length and width of crack. In RSL and RSLSF type column specimen cracks occurs towards the middle face of column extending towards the corners. In SLOL and SLAL type column specimen, mainly cracks are visible at the middle face. In these two cases reduces the stress concentration at corners and middle face is more effective in stress transferring.

NJ

SL

RSL

SLOL

SLAL

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A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing (IJSTE/ Volume 3 / Issue 11 / 022)

SLSF

RSLSF SLOLSF Fig. 5: Failure pattern of different ferrocement jacketing techniques

SLALSF

Comparison of jacketed column with and without steel fibers The ultimate load carrying capacity of a column jacketed with steel fibers increased to 2 % compared to column jacketed without steel fibers. Test result shows that by adding steel fibers axial and lateral deflection decreases. Below graphs shows that after loading up to initial crack there is no much difference in deflection of column jacketed with and without steel fibers .After initial crack deflection decreases because of the tensile strength of steel fibres.

Fig.6: Comaprison of SL and SLSF

Fig. 8: Comaprison of SLOL and SLOLSF

Fig.7: Comaprison of RSL and RSLSF

Fig. 9: Comaprison of SLAL and SLALSF

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A Study on Strengthening of R.C.C Columns by Ferro Cement Jacketing (IJSTE/ Volume 3 / Issue 11 / 022)

IV. CONCLUSION          

From the experimental investigation of ferrocement jacketed RC square columns under concentric load, the following concluding remarks could be made: Ferrocement confinement improves the ultimate load carrying capacity of RC column.

Ferrocement confinement increases the ultimate deflection and ductility of RC column.

Strengthening of RC square column by rounded corners is more effective than strengthening the column with sharp corners.

It is concluded that column strengthened with steel angle at corner with steel fiber (SLALSF) increases 66.07% of ultimate load carrying capacity than RC column.

The ultimate load carrying capacity of SL, RSL, SLOL, SLAL type specimens is increased to 31.55%, 35.2 %, 42.124 % and 64.769 %.

The ultimate load carrying capacity of SLSF, RSLSF, SLOLSF, SLALSF type specimens is increased to 33.42 %, 37.06 %, 43.902 % and 66.07 %.

Crack patterns of tested columns also confirm that type SLSF, RSLSF, SLOLSF and SLALSF type is more effective than SL, RSL, SLOL and SLAL. Adding 1.25 % fiber content to the mortar used in the jacket has a significant effect in decrease in both axial and lateral deflection. This content may be the ideal fiber content.

All the ferrocement jacketing techniques in this study are effective to overcome the drawbacks of conventional square ferrocement jacketing of square RC column.

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