 Open Access
 Total Downloads : 795
 Authors : Mohd Irfan, Dr. Abhay Sharma, Dr. Vivek Garg
 Paper ID : IJERTV3IS080489
 Volume & Issue : Volume 03, Issue 08 (August 2014)
 Published (First Online): 19082014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Strengthening Demand of Columns in A RCC Structure Due To Construction of An Additional Storey
Mohd Irfan, 
Dr. Abhay Sharma, 
Dr. Vivek Garg 
PG Scholar, 
Associate Professor 
Assistant Professor 
Civil Engineering Department 
Civil Engineering Department 
Civil Engineering Department 
NIT Bhopal, Madhya Pradesh, India. 
NIT Bhopal, Madhya Pradesh, India 
NIT Bhopal, Madhya Pradesh, India 
.Abstract – Generally the people construct the structure to fulfill their current needs but with the passage of time they realize that their demands have increased and there is a need for the addition/alteration of the current structure. This demand can be fulfilled by constructing a new storey. However, provision for additional load due to the new construction over existing structure was not made in the structural design of the old structure. Therefore, the construction of new storey requires the strengthening of the old structure. The present study investigates the structural behaviour of an RC frame under the additional load in the form of a new storey. The analysis of existing structure (two storey) and proposed structure (one additional storey constructed over existing two storey structure) is performed by using structural analysis software i.e. STAAD Pro. The analysis results of existing and proposed structure are compared to evaluate the increase in structural forces due to the construction of a new storey. The results indicates that the significant increase is found in the axial force and bending moment in columns. The weak and deficient columns are identified and strengthened for the additional loads and additional moments. The strengthening of columns is done by jacketing of the columns using four steel angles at corners, confined with the help of batten plates placed at equal spacing along the length of the column.
Keywords Concrete; Steel; Jacketing; Strengthening.

INTRODUCTION
Jacketing is one of the most commonly& popularly used practices to strengthen reinforced concrete columns. With this method, axial strength, bending strength, and stiffness of the column are modified. It should be noted that the success of this method depends on the monolithic behaviour of the composite element. The common practice consists of increasing the roughness of the interface surface and applying a bonding agent, generally an epoxy resin. Steel connectors are also sometimes applied. These involve expert workmanship, time, and cost. Regarding the added concrete mixture and due to the reduced thickness of the jacket, the option is usually a grout with characteristics of high strength concrete (HSC) and selfcompacting concrete (SCC). The common types of jackets are steel jacket, reinforced concrete jacket, FRP composite jacket, jacket with high tension materials like carbon fiber, glassfiber etc.
Purpose for jacketing:
To increase concrete confinement, to increase shear strength and to increase flexural strength
Fig1. Reinforcement mesh for jacketing
Fig2. 3D view of column jacketing

LITERETUREREVIEW
Eduardo N. B. S. JÃºlio et.al. conducted the study on the monolithic performance of the structure which was strengthened with jacketing. For this experimental investigations were done on seven models casted at the same time. The strength of concrete used was 20MPa and strength of steel was 400MPa .The dimensions of the old column was 0.2 x0.2 m2 and the thickness of reinforced concrete jacketing was 35mm. Three bars of 10mm diameter were used at each face with the reinforcing height of 0.90m for the column of height 1.35m. The transverse reinforcement used was 6mm diameter stirrups with a spacing of 150mm. The result was that all the models showed structural behaviour between the theoretical and experimented models. The stiffness and resistance of the strengthened column were much higher than the original column.
Aboutaha et. al. [1996] conducted the experiment to investigate the large rectangular column performance strengthened with a thin layer of steel jacket. The testing models in actual represented the structural design of 1960s in US. These columns were poor in confinement of concrete and also had a lap splices in reinforcement. Seven models were tested with different configurations of 6.3mm thick steel jacketing under the cyclic loading. The test results showed that there was less change in the stiffness but ductility of the reinforced member was increased significantly. There was also increase in the strength of the member because of the full flexural capacity developed.
Aviles et al. 1996, conducted a similar set of experiments on 18 column models. These models were retrofitted with a 1.2mm thick steel jacket connected with anchor bolts. At foundation level these models were found deficient. There was no increase in the strength and stiffness but there was an increase in the deformation capacity of the model.

PROPOSED WORK
The present study investigates the structural behaviour of an RC frame under the additional load in the form of a new storey. The analysis of existing structure (two storey) and proposed structure (one additional storey constructed over existing two storey structure) is performed by using structural analysis software i.e. STAAD Pro. The analysis results of existing and proposed structure are compared to evaluate the increase in structural forces due to the construction of a new storey. The results indicates that the significant increase is found in the axial force and bending moment in columns.
Methodology
The following sequence is adopted for strengthening the structure:

Analysis of the existing structure

Analysis of the new structure

Comparative study to evaluate the increase in column forces and identifying the weak zones

Strengthening of weak columns
Pictorial representation of the structure
Fig.3Isometric view of the proposed structure
Fig.4Plan of the structure
Fig.5 Member numbering at section AA
Fig.6 Member numbering at section BB
Fig.7 Member numbering at section CC Fig.8 Member numbering at section DD


DETAILS OF STRUCTURE
This paper presents the analysis and design of an existing structure (two storey) and proposed structure (additional storey constructed over existing two storey structure) RCC framed structure. The details of which are given below.
.TABLE1: Geometry of the Structure
S. No.
Description
Value
1
Area of building
408 2
2
Length
24 m
3
Breadth
17 m
4
Storey height
3.5 m
5
Height of the column below plinth level
1.5 m
6
Size of the column
300 mm x 300 mm
7 (a)
Size of beam for 6m span
200 mm x 500 mm
7 (b)
Size of beam for 4m span
200 mm x 400 mm
8
Thickness of slab
150 mm
9
Thickness of ouer walls
200 mm
10
Thickness of inner walls
100 mm
11
Support condition
fixed
Material properties Grade of concrete = M20 Grade of Steel = Fe415
Elasticity constant = 2.17 X 107kN/2
Dead load
Unit weight of concrete = 25 kN/3
Unit weight of masonry wall = 20 kN/3 Dead load of slab = 3.75 kN/2
Floor finish = 0.75 kN/2
Load of parapet wall = 2.6 kN/m Load of inner wall = 8.06 kN/m Load of outer wall = 14.26 kN/m Live load
Live load on floor = 4 kN/2 Live load on roof = 1.5 kN/2
Parameters for seismic load
TABLE2: Parameters for seismic load
S. No.
Parameter
Value
1
Location (ZONE II)
Zone Factor = 0.10
2
Response reduction factor
(Ordinary RC Moment Resisting Frame)
RF = 3
3
Importance factor (All General Building)
I = 1
4
Rock and soil site factor
(Medium soil)
SS = 2
5
Type of structure (RC Frame Building)
ST = 1
6
Damping ratio
DM = 0.05

FORCES IN COLUMNS
Analysis results of axial force Fx, bending moment My and bending moment Mz in columns obtained from Staad pro are presented below.

First storey columns
The axial force Fx, bending moment My and bending obtained from analysis of case 1 (existing structure) and case 2 (proposed structure) are presented and compared in Table3, 4 and 5.
Axial Force Fx in first story columns
The axial force Fx for the columns of first storey which are obtained from analysis of case 1 and case 2 are tabulated and compared in Table 3.
TABLE3. Comparison of axial force Fx in first storey columns due to additional storey.
Col. No.
Axial force Fx ( kN )
Increase in Axial Force Fx ( kN )
%
Increase
Case 1 (Existing
Structure)
Case 2 (Proposed
Structure)
101
328.51
575.62
247.11
75.22
102
400.88
588.21
187.33
46.73
103
254.03
443.36
189.33
74.53
104
276.31
467.53
191.22
69.20
108
365.38
645.90
280.52
76.78
109
478.18
703.01
224.83
47.02
110
292.12
485.21
193.09
66.10
111
351.97
507.00
155.03
44.05
115
215.79
481.69
265.90
123.22
116
350.81
562.40
211.59
60.31
117
80.44
144.34
63.90
79.44
118
85.27
110.61
25.34
29.72
122
302.81
633.75
330.94
109.29
123
472.82
642.92
170.10
35.98
124
243.64
450.00
206.36
84.70
125
307.43
460.49
153.06
49.79
130
68.84
133.35
64.51
93.71
131
15.47
16.17
0.70
4.52
Bending Moment My in first storey columns
The bending moment My for the columns of first storey which are obtained from analysis of case 1 and case 2 are presented and compared in Table4.
Col. No.
Bending Moment My
Increase in Bending Moment My
( kNm )
%
Increase
(Existing Structure)
(Proposed Structure)
101
35.45
78.28
42.83
120.82
102
30.21
21.98
8.23
27.24
103
34.78
30.94
3.84
11.04
104
34.77
31.08
3.69
10.61
108
64.38
86.61
22.23
34.52
109
62.48
13.71
48.77
78.06
110
57.94
77.05
19.11
32.98
111
55.24
76.94
21.70
39.28
115
42.99
61.96
18.97
44.13
116
48.66
5.49
43.17
88.72
117
0.21
0.54
0.33
157.14
118
3.37
0.83
2.54
75.37
122
39.61
1.94
37.67
95.10
123
1.03
0.37
0.66
64.08
124
39.92
16.36
23.56
59.02
125
16.34
13.05
3.29
20.13
130
34.15
51.18
17.03
49.87
131
1.94
2.03
0.09
4.64
TABLE4 Comparison of bending moment My in first storey columns due to additional storey
( kNm )
Case 1 Case 2
Bending Moment Mz in first storey columns
The bending moment Mz for the columns of first storey which are obtained from analysis of case 1 and case 2 are presented and compared in Table5.
TABLE5 Comparison of bending moment Mz in first storey columns due to additional storey
56.94
Col. No.
Bending Moment Mz (kNm )
Increase in Bending
Moment Mz ( kNm )
%
Increase
Case 1 (Existing Structure)
Case 2 (Proposed Structure)
101
64.95
36.31
28.64
44.10
102
62.06
80.87
18.81
30.31
103
38.92
18.02
46.30
104
37.04
55.18
18.14
48.97
108
33.93
33.83
0.10
0.29
109
22.76
80.77
58.01
254.88
110
2.11
1.89
0.22
10.43
111
0.25
0.00
0.25
100.00
115
33.37
33.21
0.16
0.48
116
24.31
80.33
56.02
230.44
117
36.99
55.62
18.63
50.36
118
36.02
56.16
20.14
55.91
122
34.19
70.35
36.16
105.76
123
63.37
81.65
18.28
28.85
124
34.54
67.24
32.70
94.67
125
61.87
78.27
16.40
26.51
130
1.27
1.89
0.62
48.82
131
22.41
36.01
13.60
60.69
Table 3, 4 and 5 indicates that there is an increase in axial force Fx and bending moment My and Mz in most of the columns.

Critical value of axial force Fx (703.01 kN) is found in column no 109 of case2 which is 76.78% higher than the critical value of axial force Fx (478.18 kN) in column no109 of case 1.

Critical value of bending moment My (86.61 kNm) is found in column no108 of case2 which is 34.52% higher than the critical value of bending moment My (64.38 kNm) in column no108 of case 1.

Critical value of bending moment Mz (80.77 kNm) is found in column no 109 of case2 which is 24.35% higher than the critical value of bending moment Mz (64.95 kNm) in column no 101 of case 1.


Second storey columns
The analysis results of axial force Fx, bending moment My and bending moment Mz for the columns of second storey for case 1 (existing structure) and case 2 (proposed structure) are presented below.
Axial Force Fx in second story columns
The axial force Fx for the columns of second storey which are obtained from analysis of case 1 and case 2 are presented and compared in Table6.
TABLE6 Comparison of axial force Fx in second storey columns due to additional storey
Col. No.
Axial force Fx ( kN )
Increase in Axial Force
Fx ( kN )
%
Increase
Case 1 (Existing
Structure)
Case 2 (Proposed
Structure)
201
129.53
338.56
209.03
161.14
202
180.35
389.88
209.53
116.18
203
87.73
265.32
177.59
202.43
204
87.61
277.47
189.86
216.71
208
178.86
412.45
234.59
131.78
209
200.41
505.01
304.60
151.99
210
113.55
299.79
186.24
164.02
211
123.43
312.77
189.34
153.40
215
90.92
292.86
201.94
222.11
216
149.46
346.22
196.76
131.65
217
35.63
91.54
55.91
156.92
218
53.26
67.91
14.65
27.51
222
111.97
350.00
238.03
212.58
223
176.98
398.88
221.90
125.38
224
84.74
271.21
186.47
220.05
225
119.64
281.41
161.77
135.21
230
50.00
85.41
35.41
70.82
231
36.45
114.11
77.66
213.06
Bending Moment My in second storey columns
The bending moment My for the columns of second storey which are obtained from analysis of case 1 and case 2 are presented and compared in Table7.
TABLE7 Comparison of bending moment My in second storey columns due to additional storey
Colum n No.
Bending Moment My ( kNm )
Increase in Bending
Moment My ( kNm )
%
Increas e
Case 1 (Existing Structure)
Case 2 (Proposed Structure)
201
50.22
81.34
31.12
61.96
202
61.79
42.48
19.31
31.25
203
50.64
37.32
13.32
26.30
204
42.00
37.43
4.57
10.88
208
36.19
76.21
39.31
108.33
209
55.45
71.57
16.12
29.07
210
29.91
79.05
49.14
164.29
211
54.22
79.65
25.43
46.90
215
22.47
58.49
36.02
160.30
216
35.53
6.13
29.40
82.75
217
0.09
1.34
1.25
**
218
8.54
2.62
5.92
69.32
222
20.92
52.31
31.39
150.05
223
1.63
0.22
1.41
86.50
224
25.39
53.02
27.63
108.82
225
20.97
16.25
4.72
22.51
230
26.52
45.32
18.80
70.89
231
25.93
37.91
11.98
46.20
Bending Moment Mz in second storey columns
The bending moment Mz for the columns of second storey which are obtained from analysis of case 1 and case 2 are presented and compared in Table9.
TABLE8Comparison of bending moment Mz in second storey columns due to additional storey
Col. No.
Bending Moment Mz ( kNm )
Increase in Bending moment
Mz ( kNm )
%
Increase
Case 1
(Existing Structure)
Case 2
(Proposed Structure)
201
52.88
42.19
10.69
20.21
202
35.68
70.79
35.11
98.40
203
19.36
52.04
32.68
168.80
204
24.92
50.38
25.46
102.17
208
63.86
53.34
10.52
15.80
209
35.01
36.91
1.90
5.43
210
29.01
1.61
27.40
94.45
211
0.55
0.00
0.55
100.00
215
48.95
40.51
8.44
17.24
216
30.17
82.06
51.89
171.99
217
25.29
49.01
23.72
93.79
218
25.64
49.25
23.61
92.08
222
50.34
41.07
9.27
18.41
223
59.46
85.91
26.45
44.48
224
37.24
38.15
0.91
2.44
225
51.66
80.28
28.62
55.40
230
6.99
3.75
3.24
46.35
231
6.23
6.07
0.16
2.57
Table 6, 7 and 8 indicates that there is an increase in axial force Fx and bending moment My and Mz in most of the columns.

Critical value of axial force Fx (505.01 kN) is found in column no 209 of case2 which is 152% higher than the
Column location
Case 1
Case 2
200
505
703
478
803
1200
1000
800
600
400
200
0
1151
Axial force Fx ( kN )
Fig9. Comparison of maximum axial force Fx in columns at different storey
Comparison of maximum values of bending moment My in columns at different storey.
The maximum values of bending moment My is compared for the columns of below plinth level, first storey and second storey due to additional storey.
Bending moment My ( kNm )
78 80
80
critical value of axial force Fx (200.41 kN) in column no 209 of case 1.

Critical value of bending moment My (79.65 kNm) is found in column no 211 of case2 which is 28.90% higher than the critical value of bending moment My (61.79 kNm) in column no 202 of case 1.

Critical value of bending moment Mz (85.91 kNm) is found in column no 223 of case2which is 34.52% higher than the critical value of bending moment Mz (63.86 kNm) in column no 208 of case 1.
70
60 48
50
40 33
30
20
10
0
64 62
Case 1
Case 2
Comparison of maximum values of axial force Fx at different storey.
The maximum values of axial force Fx is compared for the columns of below plinth level, first storey and second storey due to additional storey.
Column location
Fig 10. Comparison of maximum bending moment My in columns at different storey
Comparison of maximum values of bending moment Mz in columns at different storey.
The maximum values of bending moment Mz is compared for the columns of below plinth level, first storey and second storey due to additional storey.
Bending moment Mz ( kNm )
100
80
60
40
20
0
82 86
65 64
45
30
Case 1
1= 2206 2
Strengthening requirement for additional moment
Additional moment = 58.01 kNm Assuming Cyy = 20 mm and thickness of angle section = 10 mm Moment of Inertia = A x 1302
Extreme fiber distance from CG = y = 160 mm M = f x = 58.01 x 106 = 150 x x 1302
Case 2
y
2 = 36612
Therefore,
160
Column location
Fig 11. Comparison of maximum bending moment Mz in columns at different storey


STRENGTHENING OF COLUMNS The columns of first storey and second storey are
strengthened for the additional load and moment estimated from theabove tables.
Total area required (1 + 2) = 58672
Area required for each section = 5867/4 = 1466 2
Angle section provided = ISA 80 x 80 x 10 Total area provided = 4 x 1502 = 6008 2
b) Strengthening of second storey
The second storey columns are strengthened for critical value of additional axial load and bending moment obtained from Table 4 due to construction of new storey.
Strengthening requirement for additional axial load Maximum increase in axial load = 304600 N Permissible stress = 150 N/2
Additional area required for Fe250 grade steel
a)Strengthening of first storey columns
= Load = 304600
The first storey columns are strengthened for critical value
of additional axial load and bending moment obtained from
Permissible Stress
1= 2030 2
150
Table 3 due to construction of new storey.
Strengthening requirement for additional axial load Maximum increase in axial load = 330940 N Permissible stress = 150 N/2
Additional area required for Fe250 grade steel
Strengthening requirement for additional moment Maximum increase in bending moment = 51.89 kNm Assuming Cyy = 20 mm and
thickness of angle section = 10 mm Moment of Inertia = A x 1302
Assuming thickness of the angle section = 10 mm
Extreme fiber distance from CG = y =160 mm
= Load
Permissible Stress
= 330940
150
M = f x = 51.89 x 106 = 150 x x 1302
y
2 = 3275 2
Therefore,
160

CONCLUSIONS
In present work the effect of additional forces due to construction of new storey on existing structure is studied.
Total area required (1+ 2) = 5305 2
Area required for each section = 5305/4 = 1326
Angle section provided = ISA 75 x 75 x 10 Total area provided = 4 x 1402 = 5608 2
The axial force and bending moment in columns are compared to investigate the need of strengthening of columns. Comparison of column forces due to construction of additional storey over existing structure is presented in Table5.
TABLE5 Comparison of column forces due to construction of additional storey over existing structure.
13.16 803.32
(31) – (9)
Structural component 
Variation of forces in existing structure 
Variation of forces in structure with additional storey 
% Variation in forces due to additional storey 
i) Axial force Fx (kN) 

a) Below plinth level (Member no.) 
5.46 1150.51 (31) – (9) 
0.58 43.21 

b) First storey (Member no.) 
15.47 478.18 (131) – (109) 
16.17 703.01 (131) – (109) 
4.52 47.01 
c) Second storey (Member no.) 
36.45 200.41 (231) – (209) 
67.91 505.01 (218) – (209) 
86.31 151.98 
ii) Bending moment My (kNm) 

a) Below plinth level (Member no.) 
0.04 32.57 (16) – (1) 
0.18 48.31 (30) – (8) 
3.50 48.32 
b) First storey (Member no.) 
0.21 64.38 (117) – (108) 
0.37 86.61 (123) – (108) 
76.19 34.52 
c) Second storey (Member no.) 
0.09 61.79 (217) – (202) 
0.22 81.34 (223) – (211) 
144.44 31.63 
iii) Bending moment Mz (kNm) 

a) Below plinth level (Member no.) 
0.05 29.91 (4) – (24) 
0.03 43.77 (10) – (2) 
40.00 46.33 
b) First storey (Member no.) 
0.25 64.95 (111) – (101) 
1.89 81.65 (110) – (123) 
# – 25.71 
c) Second storey (Member no.) 
0.55 63.86 (211) – (208) 
1.61 85.91 (210) – (223) 
192.72 34.52 
Note:
* Value within the bracket indicates member no.
** Negative sign indicates decrease in the value.
# Indicates insignificant value.
The main findings of this study are mentioned below:

The construction of additional storey causes substantial increase in axial force in all the columns. The increase in critical value of axial force is found to be about 50% in columns below plinth level and first storey and 152% for second storey columns.

The construction of additional storey causes substantial increase in bending moment in all the columns. The increase in critical value of bending moment is found to be about 30% in columns below plinth level and first storey and about 50% for second storey columns.
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