Alteration and Strengthening of Existing Two Storey Structure to Four Storey Structure

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613

Alteration and Strengthening of Existing Two Storey Structure to Four Storey Structure Dutambodhi U. Gajbhiye1 Dr. Valsson Varghese2 1 M. Tech scholar 2Professor & hod 1,2 Department of Civil Engineering 1,2 K. D. K. C. E Nagpur Abstract— Due to the scarcity of space and change in utility of structure, vertical expansion of the structure has become essential. There can be many reasons such as ever increasing population, changes in the operating system, required improvement of safety margins etc. This will be managed by increasing the number of stories. But the existing structure may or may not be able to sustain the newly constructed stories. Since the load carrying capacity of existing structure reduces due to age and relaxation. The existing structure must be strengthened to sustain additional storey load.

During the design process various governing factors (like additional load, earthquake load, additional live load etc) will be considered.

Key words: Structure, Earthquake, Load Storey, Load Stories I. INTRODUCTION Jacketing is one of the most widely used worldwide technique for the strengthening of the structure. In this method, the R.C columns are strengthened by increasing stiffness and axial strength of an existing column. A durable material is fastened over concrete and gap is filled with grout. The section of an existing structural element is restored by encasing in new concrete.

The scope of this paper is to present the design for strengthening the existing two storey structure to bear the loads and moments of altered four storey structure.

The need to strengthen a structure may be required from the beginning of the construction of structure until the end of the life of the structure. During the construction phase, it may occur because of change in design, bad workmanship during construction, the addition of floor, change in utility etc.

The decision to strengthen must be made only after the inspection of the structure, its structural evaluation and a cost study of the different solutions.

The choice of strengthening method depends on the structural behaviour objectives. The strengthening may be achieved by increasing the resistance to lateral loads, improving the ductility, and an association of both.

Primarily, the strengthening techniques for reinforced concrete structures are adding of new structural elements and strengthening of the existing structural elements.

Strengthening an RC element basically involves the increase of strength and stiffness of the existing RC element.

II. STRENGTHENING TECHNIQUE In the strengthening of the foundation where the altered structure demands more size and depth of footing than the existing footing, the footing size and depth is increased by jacketing. Jacketing of columns consists of providing the additional longitudinal steel as required in the design for biaxial bending and axial compression. The axial and shear

strength of columns is increased with this type of strengthening. The lateral load capacity of the building is increased reasonably, In addition, the original geometry and function of the structure can be maintained. The jacketing of columns is generally made by two methods: (i) steel jacketing and (ii) reinforced concrete jacketing A. RC Jacketing Reinforced concrete jacketing can be employed as a repair or strengthening technique. Damaged regions of the existing elements should be repaired prior to their jacketing. There are two main objectives of jacketing of columns: (i) Increase in the shear strength of columns in order to accomplish a strong column and weak beam design and (ii) To improve the column's bending strength by the longitudinal reinforcement of the jacket made continuous through the slab system is anchored with the foundation.The new longitudinal reinforcement is passed through holes drilled in the slab and by placing new concrete joints. Rehabilitated cross sections are designed in this way so that the flexural strength of columns should be more than that of the beams.

Transverse steel above and below the joint has been provided.The longitudinal reinforcement usually is consolidated in the column corners because of the existence of the beams. It is advised that not more than 3 bars be bundled together. Windows are usually drilled through the slab to allow the steel to pass as well as to enable the concrete casting process.

Following are details for reinforced concrete jackets.  The compressive strength is greater by 5 N/mm2 or matches that of existing structure.  The properties of jackets are similar with that of jackets.  The minimum width of jackets should be 4cm for shotcrete and 10 cm for cast in-situ.  Four sided jacket should be the priority.  The behavior of composite column is monolithic  Its gives assurance of composite column to be monolithic.  The minimum area of longitudinal steel should be Af, where A is area of contact and f is in kg/cm2.  The spacing should not be greater than six times width of the new element.  The minimum steel provided should be in the range of 0.015 to 0.04.  Minimum 12 mm dia bar should be used in corners of jacket.  The transverse steel should be designed and spaced as per seismic design practice.  The minimum dia for lateral ties should not be less than 10 mm.  The hooks of ties should be bent at 135-degree.  Ties made up of multiple pieces should be used.

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Alteration and Strengthening of Existing Two Storey Structure to Four Storey Structure (IJSRD/Vol. 4/Issue 05/2016/341)

   

Due to monolithic behavior , adequate shear transfer mechanism is assured.

A relative moment between interface is prevented.

The bond between new and old concrete is by chipping and roughening old concrete.

Connectors may develop 80% of their yielding stress.

B. Steel Jacketing Steel plates are used steel jacketing. Following are the features of steel jacketing.  The thickness of steel plate should be at least 6 mm.  In the case of flexural columns, the height of jacket should be 1.2 to 1.5 times of splice length.  In the case of shear columns, the height of jacket should be equal to the full height of the column.  Rectangular or square jacket should be provided accordingly.  The gap between steel jacket and concrete column should be filled with 25 mm cementious grout.  An epoxy grout is used for installation of bolts through predrilled holes in the concrete jacket.  To stiffen and improve the confinement of splice anchor bolts are used.

III. DETAILS OF EXISTING TWO STOREY STRUCTURE A. Geometry 1) Length – 12.0 m 2) Width - 8.0 m 3) Floors- Ground + 1 floor 4) Frame – RCC frame 5) Size of Columns – 230 mm X 300 mm 6) Size of Beams – 230 mm X 400 mm 7) Slab Thickness – 125 mm 8) Wall Thickness – External walls 230 mm 9) Type of Infill wall – Conventional Red Bricks 10) Total no. of Columns – 12 B. Loadings Live Load – At all Floors 2.0 KN / sq.m Wall Load - 12.42 Kn/m (3.0 X0.23 X 20)

Fig. 2: 3D Layout of altered building.

IV. STAAD RESULTS FOR EXISTING G+1 STRUCTURE

COLUM N NO.

C1

C2

C4

C5

Fig. 1: Typical floor plan of existing building After complete analysis, the structure is designed for additional two storeys. The results are obtained as follows.

FLOOR LEVEL

Load on Col.

Pu kN 265.4 Below Plinth 7 179.7 Ground floor 0 First floor 56.02 485.9 Below Plinth 3 343.4 Ground floor 8 112.5 First floor 5 457.0 Below Plinth 8 321.6 Ground floor 8 105.4 First floor 9 776.1 Below Plinth 5 586.9 Ground floor 2 214.3 First floor 1 Table 1:

Momen t @X dir.

Mx kN-m

Momen t @Y dir.

My kN-m

10.30

8.71

14.98

11.73

15.96

12.42

9.96

0.00

18.92

0.00

22.74

0.00

0.81

8.56

1.39

14.90

1.40

17.68

0.39

0.00

1.39

0.00

1.68

0.07

V. STAAD RESULTS FOR STRENGTHING OF EXISTING G+1 STRUCTURE TO G+3 STRUCTURE

COLUM N NO.

C1

FLOOR LEVEL

Below Plinth

Load on Col. Pu kN 664.2

Momen t @X dir.

Mx kN-m 64.72

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Momen t @Y dir.

My kN-m 55.43

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Alteration and Strengthening of Existing Two Storey Structure to Four Storey Structure (IJSRD/Vol. 4/Issue 05/2016/341)

Ground floor

546.6

69.52

65.64

First floor

384.8

57.89

59.42

68.94

58.05

75.10 67.32

72.17 69.49

65.85

59.90

72.76 64.51

72.19 69.90

70.32

63.29

Below Plinth

C2

Ground floor First floor Below Plinth

C4

Ground floor First floor C5

Below Plinth

1034.

2 891.2 633.6 1014.

9 873.4 619.7 1603.

8

1418.

78.21 78.96 9 1010.

First floor 70.04 76.59 7 Table 2: For this design load and moment the design are carried out for strengthing the G+1 stucture to G+3 stucture for the structure modification due to the future utilite.

For the design of column SP 16 has been referred and considered.

Ground floor

Fig. 3: Ground and first floor

Column No C1 C2 C4 C5

Column size a b 350 450 350 450 350 450 350 450

Second and Third floor Column size Main Bars Stirrups Main Bars Stirrups a b 6no ɸ 12 + 8 no ɸ 12 ɸ 8 @ 150 c/c 300 450 10 no ɸ 16 ɸ 8 @ 150 c/c 6no ɸ 12 + 10 no ɸ 16 ɸ 8 @ 150 c/c 300 450 6 no ɸ 16 ɸ 8 @ 150 c/c 6no ɸ 12 + 8 no ɸ 12 ɸ 8 @ 150 c/c 300 450 12 no ɸ 16 ɸ 8 @ 150 c/c 6no ɸ 12 + 8 no ɸ 12 ɸ 8 @ 150 c/c 300 450 6 no ɸ 16 ɸ 8 @ 150 c/c Table 3: Schedule of Columns for Altered Structure Footing size Reinforcement Footing Depth Length Width Along –x Along –y No (mm) (mm) (mm) (mm) (mm)  12 @  12 @ F1 2100 2100 500 120 c/c 120 c/c  12 @  12 @ F2 2400 2400 600 120 c/c 120 c/c  12 @  12 @ F4 2550 2550 550 120 c/c 120 c/c  12 @  12 @ F5 2800 2800 700 120 c/c 120 c/c Table 3: Schedule of Isolated Footing for Altered Structure

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Alteration and Strengthening of Existing Two Storey Structure to Four Storey Structure (IJSRD/Vol. 4/Issue 05/2016/341)

Fig. 4: Cross-section of Footing after strengthening

[3] Oliveto G. and Marletta M. (2005), “Seismic retrofitting of reinforced concrete buildings using traditional and innovative techniques” ISET Journal of Earthquake Technology, Paper No. 454, Vol. 42, No. 2-3, JuneSeptember 2005, pp. 21-46.

[4] Brena F. and Alcocer M. (2009), “Seismic Performance Evaluation of Rehabilitated Reinforced Concrete Columns through Jacketing” ATC & SEI 2009 Conference, Paper No.572,pp. 1-12.

[5] Kaliyaperumal G. and Sengupta A.K.(2009), “Seismic retrofit of columns in buildings for flexure using concrete jacket.” ISET Journal of Earthquake Technology, Paper No. 505, Vol. 46, No. 2, June 2009, pp. 77–107.

[6] Waghmare P.(2011), “Materials and Jacketing Technique for Retrofitting of Structures” International Journal of Advanced Engineering Research and studies,Vol.I/IssueI/October-December,15-19.

[7] Julio E, Branco F and Silva V (2003), “Structural rehabilitation of Columns with Reinforced Concrete Jacketing” John Willey & Sons, Ltd.

Fig. 4: Cross-section of Column after strengthening VI. CONCLUSIONS Many of the studies have been carried out for various strengthening techniques. and this study deals with concrete jacketing method of strengthening. it can be found and observed that when the utility of structure changes during its lifespan, the structure can be modified to sustain or face the present day demands. there is further need for studies and research on this subject.

ACKNOWLEDGMENT The journalist would like to prompt their sincere thanks to the KDK college of Engineering for giving guidance and technical support to get done this research.

REFERENCES [1] Agarwal P. and Shrikhande M. (2011), “Earthquake Resistant Design of Structures.”PHI Learning Private Limited, New Delhi.

[2] Gomes A. and Appleton J.(2000)“Strengthening design of concrete beams by the addition of steel plates” Department of Civil Engineering, IST, Technical University of Lisbon, Portugal.

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