11-IJAEST-Volume-No-2-Issue-No-1-SEISMIC-STRENGTHENING-OF-LOW-RISE-BUILDINGS-USING-BRICK-INSERTS-(RE by ISERP ISERP

Mr.R.Suresh Babu et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 1, 072 - 085

SEISMIC STRENGTHENING OF LOW RISE BUILDINGS USING BRICK INSERTS (RETROFIT) – EXPERIMENTAL INVESTIGATION ON 2D & 3D RC FRAMED STRUCTURES

could be reinforced with the added strength of masonry inserts. Finally it was suggested that, the existing columns with short-column mechanism could be strengthened with masonry inserts. By improving building strength with the above methods, the damage can be limited to within repairable limits and complete collapse of the building/loss of life can be avoided during an earthquake. The cost effectiveness of providing brick insert is very much cheaper than retrofit normally adopted to strengthen the structural elements and require simple construction method.

Abstract— Several literature and research papers were published in the topic of seismic retrofit of existing buildings. Attention has been focused on the existing building (designed without seismic loads) to prevent damages during future earthquake. A purpose of the study is to investigate seismic retrofit using brick inserts to upgrade the capacity of reinforce concrete frame with brick masonry infill wall and to addresses the buildings without following the details as stated in BIS 13920. The overall aim of study is by adding a small brick insert in the partial infilled RC structures, the structure could double its strength. An experimental investigation is conducted to study the effect of lateral behaviour of RC frames with partial-infill masonry panels (2D & 3D) viz. one with opening(frame 1) and other with masonry insert in the opening(frame 2). One-third scale, twobay two-storey RC frame (2D & 3D) designed for gravity loading is tested under in-plane lateral loading for 2D RC frames and push & pull load for 3D RC frame structures. A non-linear finite element analysis has been carried out using Ansys – 10. The results of experiment and analytical analysis were only marginal variations. In both 2D & 3D analysis of both frames, the columns in the bottom storey sustained critical shear damage with hinges in the column portions adjacent to the gap. The experimental results clearly indicated that the partial infill in RC frame leads to critical damages, which

Dr.R.Venkatasubramani HOD, VLBJCET, Coimbatore Coimbatore, India rvs_vlb@yahoo.com

Mr.R.Suresh Babu Research scholar – Anna University, Coimbatore Partner – PTK Architects, Chennai Chennai, India rsb@ptkarch.com

ISSN: 2230-7818

Keywords - Masonry Infill; Masonry Inserts; Captive Column effect; Retrofit; I INTRODUCTION Everyone is aware that earthquake occurred in Gujarat (Bhuj) - India in the year 2001 had several incidents of failure or complete collapse. Majority of the failure in the buildings are predominantly due to Captive column failure or soft storeyed building. After the revision in IS codes for seismic forces, we are able to take care of the proposed new buildings. But even many old buildings of similar nature still exists (built as per IS 456 detailed with SP 34) in highly earthquake prone areas throughout the country. Energy dissipation of these buildings are very poor for lateral loads mainly due to Captive column failure. By providing necessary masonry inserts in the partial infill opening shall increase the

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II MATERIALS AND METHODS LITERATURE REVIEW Previous experimental research on the behaviour of brick infilled RC frames(Achintya et.al. 1991:Yaw-jeng Ciou et.al.1999: Diptesh Das et.al. 2004: Ismail et.al 2004: Marina et.al:2006 have shown that the strudtural behaviour of the framed masonry wall subject to in – plane monotonic loading on partial fill masonry wall induce a short column effect aleads to severe failures of the column. Further experimental research of Mehmat Emin Kara et.al:2006 have shown that patially infilled non-ductile RC Frames exhibited significantly higher ultimate strength and higher initial stiffness than the bare frame. Prabavathy et.al(2006) have shown that infill panels can significantly improve the performance of RC Frames. Alidad Hashemi et.al(2006) have shown that infill wall changes the load path and the distribution of forces Kasim Armagan Korkmaz et.al(2007) shown that presence of nonstructural masonry infill walls can modify the global seismic behaviour of framed building to a larger extent. Umarani (2008) examined the behaviour of infilled frames (5 storey) for lateral loading. Test focused on the increase of energy dissipation over and above the base frames. Santiago pujol et.al(2008) shown that masonry infill walls were effective in increase the strength(by 100%) and stiffness (by 500%) of the original reinforced concrete structures. Salah El – Din Fahmy Taher et.al(2008) lower location of infill frames yields the higher strength, stiffness and frequency of the system

B) Details of Test Frame Test models was fabricated to 1:3 reduced scale following the laws of similitude by scaling down the geometric and material properties of the prototype for Frame (1) and Frame (2)(Ref. Fig.1).

Figure.1 Geometry of the frame model C) Testing Procedure : Lumped mass distribution was calculated and lateral loads were distributed as 80% for top storey & 20% for bottom storey. All applied lateral loads were divided accordingly. Frame (1) was tested of first increments of 10 kN base shear for each cycle and released to zero after each cycle. The deflections at all storey levels were measured at each increment and decrement of the load. The formation and propagation of cracks, hinge formation and failure pattern were recorded. This procedure was repeated for frame (2) with masonry insert.

A structure representing a multi-storeyed frame system is analysed and designed. The structure is modeled for experimental investigation by scaling down the geometric properties of the prototype using the laws of Geometric similitude.

stiffness of the building and increase in energy dissipation. Due to this the collapse of the building will delay and the structure became more safer. This remedy is evaluated without major alteration to structural elements and without affecting major existing functioning of the buildings.

III EXPERIMENTAL & ANALYTICAL INVESTIGATION ON 2D RC FRAME STRUCTURE

1) EXPERIMENTAL INVESTIGATION A) Modelling of Frames:

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D) Results: The results of various parameters like load Vs. deflection, stiffness degradation and ductility factor were considered for study of the captive column behaviour of the frame i) Loading And Load-Deflection Behaviour (P-∆): The frame was subjected to unidirectional lateral loading. The load was applied in increment of 10 kN base shear for each cycle and released to zero after each cycle. The deflections at all storey levels were measured using LVDT at each increment or decrement of load. The ultimate base shear of 73 KN was reached in the Eighth cycle of

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Top storey deflection versus base shear is shown in Fig.2. Load and top storey deflection is presented in Table 1. At the ultimate base shear the top storey deflection was found to be 47mm for frame (1) and 56mm for frame (2). Table.1: Load and Deflection for Frame 1 & 2

0 2 3.89 6 8.12 13.69 21.23 34.33 47

Load (KN)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

0 0.45 1 1.55 2.9 4.25 6.95 9.08 11.79 15.66 19.33 29 37 47 56

0 10 20 30 40 50 60 70 80

Frame (2) Deflect ion (mm)

Frame (1) Load Deflectio (KN) n (mm)

Figure. 2 Base shear hear Vs Top storey deflection for both frames

ii) Ductility: The ductility factor (µ) was calculated. For frame (1), the first yield deflection (∆y) for the assumed bi-linear load-deflection behaviour of the

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frame was found to be 6 mm for 30 KN base shear, while for frame (2), the same is found to be 11.79mm for 80 KN base shear. The ductility factor value µ = (∆1/∆y) for various load cycles of the frames was worked out and the variation of ductility factor for both frames with load cycles are shown in Fig.3. The ductility factor is found to be increasing more from 1.00 at third cycle to 7.833 at eighth cycle for frame (1). While for frame (2), the ductility factory is 1 at eighth cycle of loading and only 4.75 at fourteenth cycle of loading. This behaviour shows the reduction of ductility of frame due to the provision of masonry insert and is shown in Fig.4

loading and ultimate base shear of 140KN was reached in fourteenth cycle for frame 1 & 2 respectively.

Figure. 3 Ductility factor for both frames

iii) Stiffness Degradation: The stiffness of the partially-infilled frames for various load cycles is calculated and presented. The variation of stiffness with respect to load cycles is shown in Fig.4. For frame (1), it may be noted that stiffness decreases from 5 kN/mm in first cycle to 1.7 kN/mm in eighth cycle. A sudden reduction in stiffness takes place after the first crack occurrence in 30 kN load. For frame (2), the initial stiffness of frame is 20 kN/mm against 5 kN/mm for the first frame and stiffness is sustained for a longer duration until the development of first crack and is reduced to 2.5 kN/mm in fourteenth cycle. This behaviour shows that the initial stiffness of frame (1) is comparatively very low and flexural hinges and shear cracks are developed at an early stage of loading. For frame(2) with masonry insert, initial stiffness is increased and occurrence of flexural hinges and shear cracks in concrete and masonry takes place only after the eighth cycle. Also, it could be noted that the initial stiffness is

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Figure:4:Stiffness degradation curve for both frames

Figure.5.Test frame 1 with failure in the bottom and drift of the top storey (Constructed atVLBJCET, Coimbatore)

iv) Behaviour and Mode of Failure: a) Frame-1 without masonry insert: First crack was observed (horizontal hairline) at 30kN at the junction of loaded side of the beam and column at the bottom storey, where moment and shear forces are maximum while loading further, similar cracks were developed in the other bay columns and flexural cracks were developed from the junction of the loaded areas. Separation of infill occurred at the tension corners. At the ultimate failure load of 70 KN, crushing of loaded corner, widening of diagonal cracks in columns and infill, layer separation of brick infill were also observed. Width of the cracks was ranging from 3mm to 15mm in concrete and masonry. The crack pattern indicated a combined effect of flexure and shear failure. Also plastic hinges formation was observed first at loaded point and later to the middle column and finally at the leeward column. Captive column phenomenon was identified with the failure pattern of loaded column. It was also noticed that flow of diagonal crack from the loaded column adjacent to the opening was discontinuous, due to incomplete strut action (Fig.5). b) Frame-2 with masonry insert:

diagonal crack were initiated in the first (loaded) bay. Further, diagonal cracks were seen to flow through the brick infill. Separation of infill occurred at the tension corners. Due to the presence of insert, diagonal cracks were observed to flow from the loaded beam â&#x20AC;&#x201C; column junction to the diagonally opposite corner, clearly depicting the expected strut action (Fig.6). At ultimate load of 140 KN, plastic hinge formation and failure of frame at all bottom storey junctions were noticed. The width of the cracks was ranging from 2mm â&#x20AC;&#x201C; 10mm in concrete and masonry. The crack pattern indicated a combined effect of flexure and shear failure and the direction of flown crack showed the developed strut action through the brick infill, due to the presence of masonry insert

increased by 4.5 times due to the introduction of masonry insert and the stiffness is sustained for a longer duration of loading. The behaviour of frame for stiffness values is shown in Fig.4

First crack observed (inclined downwards and forwards) at only 80 kN, (against 30 kN for the frame without insert) at loaded side of the beam and column junction of the bottom storey where moment and shear forces were maximum While loading further, similar cracks were found to propagate in middle column beam junctions and

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Figure.6.Test frame 2 with failure in the bottom and drift of the top storey(Constructed atVLBJCET, Coimbatore)

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A crack in leeward column of the bottom storey at the base was also observed (Fig.7). Separation of infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends led to early crushing of the loaded corners (Fig.8).No crack was developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to short column effect.

Load – 80 KN , Deflection – 47.453 Figure.9 Ultimate Deformed Shape of the software Model For Frame 1

It is also evident from the propagation of cracks at bottom storey level of the eighth cycle (80 kN Base shear). Cracks in tension face of leeward column were developed after tenth cycle of loading. Also separation of infill from columns at highly stressed tension faces of column were seen at tenth cycle of loading. Further, shear flow was observed in frame 2 from the columns through the insert and brick infill, creating a largely visible crack (about 12mm wide), which is extended to the adjacent columns. This phenomenon is clearly exhibits the development of strut action through masonry insert.

Figure. 7.crack in leeward column

Figure:8 Crushing of the loaded Corners

2) FINITE ELEMENT ANALYSIS – ANSYS – 10: A comparative study was made between experimental and analytical values. Non-linear finite element analysis has been carried out using ANSYS-10 software for Frame (1) & (2). The deformed shape of the software model for ultimate load for Frame (1) and (2) is shown in Fig.9 &10

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Load – 140 KN , Deflection – 56.285 Fig.10 Ultimate Deformed Shape of the software Model For Frame 2 The results obtained from analytical by ANSYS10 for Frame (1) & (2) are compared with experimental results and the variation is mariginal. The experiments conducted on the two frames (with and without masonry insert) the following observations are drawn. 1) It is observed in frame with masonry insert that at a base shear of 80 kN, cracks are initiated at the junction of the loaded and middle end of the beam and column of the

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to the gap in the bottom storey indicating a distinct “captive column effect” whereas frame with masonry insert strut action took place and diagonal crack flow clearly. Also after the localised separation of the infilled panel from the frame in the bottom storey, the stress flow is mostly along the line connecting the load point to the diagonal opposite corner support indicating the “diagonal strut” concept. Therefore, it could be evidently proven that the lateral strength of the RC frame is considerably increased due to the presence of masonry inserts. The partial masonry infill failed with a diagonal crack by shear along the mortar and/or bricks joints. In frame without masonry insert no crack is developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to captive column effect. But, it was noticed that the development of crack is postponed when the frame is provided with masonry inserts. The partial infill reduces the stiffness of the frame leading to critical damages. However, this could be improved to some extent by the provision of masonry inserts. In analytical study, it is noticed that a sudden increase in deflection after the base shear of 40 kN (nearly equal to experimental value of 40 kN) for Frame (1) and affect the base shear of 80 kN (nearly equal to experiemtnal value of 80 kN) for Frame (2). This proves the initiation of captive column behaviour adjacent to gap region. Analytical results by ANSYS-10 variations is very mariginal when compared to Experimental results

10)

11)

bottom storey where the moment and shear forces are maximum whereas in frame without insert, the first crack developed at 30 KN itself. The crack pattern indicated a combined effect of flexure and shear failure. However, it could be evidently seen that the shear carrying capacity of the frame is increased due to the presence of masonry inserts Separation of infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends lead to early crushing of the loaded corners. Diagonal cracks flown through the brick work where masonry inserts are provided showing clear strut action. While further loading of frames, further cracks are initiated and noticed are much dissimilar between a RC frame with partial infill and with masonry insert. The stiffness of the partially-infilled frame with and without insert for various load cycles is calculated and the variation of stiffness with respect to load cycles is plotted. The stiffness of the brick infilled RC frame with masonry insert is observed to be very high when compared to frame without insert. This shows greater increase of stiffness while introducing masonry insert. The ductility factor value µ = (∆ ((∆1/∆y) ∆1/ 1/∆ ∆y) y) for various load cycles of the frame is worked out for frames with and without insert and the variation of ductility factors and cumulative ductility factors for both frames with reference to load cycles is plotted. From the values, it may be noted that ductility factor for frame with masonry insert is reduced whereas cumulative ductility factor for both frames is more or less same. Cracks were developed in the leeward column (opposite to the loaded end) of the bottom storey at the base because of diagonal strut compression of the infill in the frame with masonry insert. The partial-infilled RC frame failed with hinges at the portion of columns adjacent

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12)

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IV EXPERIMENTAL AND ANALYTICAL INVESTIGATION ON 3D RC FRAME STRUCTURE 1) EXPERIMENTAL INVESTIGATION

A) Modelling of Frames: A structure representing a multi-storeyed frame system is analysed and designed. The structure is modeled for experimental investigation by scaling down the geometric properties of the prototype using the laws of Geometric similitude.

were applied and top storey deflections were measured at each increment and decrement of the load Using LVDT. Additional LVDT also placed at other levels to find the frame behavior. The formation and propagation of cracks, hinge formation and failure pattern were recorded. This procedure was repeated for frame (2) with masonry insert. D) Results: The results of various parameters like load Vs. deflection, stiffness degradation and ductility factor were considered for study of the captive column behaviour of the frame

i) Loading And Load-Deflection Behaviour (P-∆ (P∆): ): (P-∆):

he frame T was subjected to push and pull loading. The push and pull load was applied in increment of 5 kN base shear for each cycle and released to zero after each cycle. The deflections at top storey levels were measured using LVDT at each increment or decrement of load. The ultimate base shear of 105 KN was reached in the twenty first cycle of loading and ultimate base shear of 195KN was reached in thirty nine cycle for frame 1 & 2 respectively.

Figure.11 Geometry of the 3D frame model 1&2 B) DETAILS OF TEST FRAME

Test models was fabricated to 1:3 reduced scale following the laws of similitude by scaling down the geometric and material properties of the prototype for Frame (1) and Frame (2)(Ref. Fig.11). C) Testing Procedure :

Lumped mass distribution was calculated and lateral loads were distributed as 75% for top storey & 25% for bottom storey. All applied lateral loads were divided accordingly and applied as push and pull method. Frame (1) was tested of first incremental Push load of 5 KN and released to zero and a pull load of 5 KN and released to zero. The deflections at top storey levels were recorded. Further an incremental load of 5 KN(Push and Pull)

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The push pull curve for top storey displacement versus base shear for both frames is represented in Fig.12 & 13. Load and top storey deflection is presented in Table 2. At the ultimate base shear the top storey deflection was found to be 58.24mm for frame (1) and 71.15mm for frame (2). Table.2: Load and Deflection for Frame 1 & 2 Frame (2) Frame (1) Load Deflectio Load (KN) n (mm) (KN) 0 5 0 -5 0 10

0.00 0.75 0.08 -0.66 -0.02 1.60

0 5 0 -5 0 10

Deflecti on (mm) 0.00 0.27 0.02 -0.19 -0.01 0.54

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0.22 -1.67 -0.39 2.74 0.92 -2.51 -0.44 3.91 1.04 -3.17 -0.72 5.06 0.22 -4.84 -0.48 6.17 0.13 -5.67 -0.59 7.24 0.71 -6.69 -0.71 8.48 0.75 -6.81 -0.74 9.61 1.04 -8.68 -0.84 10.97 1.05 -9.64 -0.89 12.23 1.24 -10.44 -0.92 13.85 1.35 -12.80 -1.16

0 -10 0 15 0 -15 0 20 0 -20 0 25 0 -25 0 30 0 -30 0 35 0 -35 0 40 0 -40 0 45 0 -45 0 50 0 -50 0 55 0 -55 0 60 0 -60 0

14.84

0.08 -0.40 -0.04 0.82 0.12 -0.67 -0.07 1.16 0.36 -0.98 -0.12 1.55 0.36 -1.30 -0.19 1.91 0.45 -1.38 -0.24 2.34 0.42 -2.15 -0.28 3.02 0.41 -2.78 -0.36 3.59 0.47 -3.69 -0.36 4.35 0.54 -3.56 -0.41 6.53 0.58 -5.78 -0.38 8.21 0.57 -7.33 -0.38 10.049

0 -10 0 15 0 -15 0 20 0 -20 0 25 0 -25 0 30 0 -30 0 35 0 -35 0 40 0 -40 0 45 0 -45 0 50 0 -50 0 55 0 -55 0 60 0 -60 0

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Frame (1) Deflectio n (mm)

Load (KN) 0 -65 0 70 0 -70 0 75 0 -75 0 80 0 -80 0 85 0 -85 0 90 0 -90 0 95 0 -95 0 100 0 -100 0 105

1.35 -13.62 -1.15 16.17 1.43 -16.31 -1.25 17.34 1.47 -17.13 -1.26 22.81 1.89 -21.12 -1.50 24.05 1.77 -23.30 -1.55 29.79 1.93 -24.71 -1.55 33.88 1.83 -35.29 -1.88 44.42 1.98 -40.26 -1.84 58.24

Load (KN) 0 -65 0 70 0 -70 0 75 0 -75 0 80 0 -80 0 85 0 -85 -85 0 90 0 -90 0 95 0 -95 0 100 0 -100 0 105 0 -105 0 110 0 -110 0 115 0 -115 0

Frame (2) Deflecti on (mm)

Frame (2) Load Deflecti (KN) on (mm)

Frame (1) Load Deflectio (KN) n (mm)

0.67 -10.32 -0.47 12.31 0.69 -12.49 -0.50 14.07 0.77 -14.66 -0.53 17.40 0.70 -15.87 -0.52 19.02 0.68 -20.27 -0.62 21.76 0.79 -23.19 -0.62 25.02 0.83 -21.64 -0.68 27.20 0.86 -24.73 -0.64 30.49 0.83 -25.12 -0.62 32.15 0.98 -30.62 -0.73 33.82 0.97 -33.66 -0.76 35.53

120

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Frame (2) Deflecti on (mm)

175 0 -175 0 180 0 -180 0 185 0 -185 0 190 0 -190 0 195 195

60.97 2.13 -60.81 -2.12 63.09 2.70 -65.89 -2.20 65.72 2.93 -55.88 -2.56 67.63 3.04 -61.93 -2.47 71.15

1.05 -36.92 -0.83 36.92 0.99 -35.63 -0.80 37.95 1.08 -41.47 -1.00 40.00 1.30 -44.96 -0.96 41.20 1.40 -37.90 -1.08 43.66 1.53 -41.76 -1.07 45.22 1.48 -42.94 -1.14 47.72 1.93 -49.08 -1.38 51.78 1.96 -51.04 -1.55 54.42 2.12 -52.99 -1.71 57.65 2.08 -52.01 -1.69

0 -120 0 125 0 -125 0 130 0 -130 0 135 0 -135 0 140 0 -140 0 145 0 -145 0 150 0 -150 0 155 0 -155 0 160 0 -160 0 165 0 -165 0 170 0 -170 0

Load (KN)

Frame (2) Load Deflecti (KN) on (mm)

Figure. 12 Push and Pull curve for Frame 1

Figure. 12 Push and Pull Curve for Frame 1

Figure. 13 Push and Pull Curve for Frame 2

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initial stiffness is increased and occurrence of flexural hinges and shear cracks in concrete and masonry takes place only after the Fifteenth cycle. Also, it could be noted that the initial stiffness is increased by 2.8 times due to the introduction of masonry insert and the stiffness is sustained for a longer duration of loading. The behaviour of frame for stiffness values is shown in Fig.15

ii) Ductility: The ductility factor (µ) was calculated. For frame (1), the first yield deflection (∆y) for the assumed bi-linear load-deflection behaviour of the frame was found to be 8.48 mm for 40 KN base shear, while for frame (2), the same is found to be 14.06mm for 75 KN base shear. The ductility factor value µ = (∆1/∆y) for various load cycles of the frames was worked out and the variation of ductility factor for both frames with load cycles are shown in Fig.14. The ductility factor is found to be increasing more from 1 at eighth cycle to 6.86 at twenty first cycle for frame (1). While for frame (2), the ductility factory is 1 at fifteenth cycle of loading and only 5.05 at thirty nine cycle of loading. This behaviour shows the reduction of ductility of frame due to the provision of masonry insert and is shown in Fig.4

Figure:15:Stiffness degradation curve for both frames

iv) Behaviour and Mode of Failure: a) Frame-1 without masonry insert:

Figure. 14 Ductility factor for both frames

iii) Stiffness Degradation: The stiffness of the partially-infilled frames for various load cycles is calculated and presented. The variation of stiffness with respect to load cycles is shown in Fig.15. For frame (1), it may be noted that stiffness decreases from 6.7KN/mm in first cycle to 1.8 KN/mm in twenty first cycle. A sudden reduction in stiffness takes place after the first crack occurrence in 40 kN load. For frame (2), the initial stiffness of frame is 18.69 KN/mm against 6.7 kN/mm for the first frame and stiffness is sustained for a longer duration until the development of first crack and is reduced to 2.74 KN/mm in Thirty nine cycle. This behaviour shows that the initial stiffness of frame (1) is comparatively very low and flexural hinges and shear cracks are developed at an early stage of loading. For frame(2) with masonry insert,

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First crack was observed (horizontal hairline) at 40kN at the junction of loaded side of the beam and column at the bottom storey, where moment and shear forces are maximum while loading further, similar cracks were developed in the other bay columns and flexural cracks were developed from the junction of the loaded areas. Separation of infill occurred at the tension corners. At the ultimate failure load of 100 KN, crushing of loaded corner, widening of diagonal cracks in columns and infill, layer separation of brick infill were also observed. Width of the cracks was ranging from 3mm to 17mm in concrete and masonry. The crack pattern indicated a combined effect of flexure and shear failure. Also plastic hinges formation was observed first at loaded point and later to the middle column and finally at the leeward column. Captive column phenomenon was identified with the failure pattern of loaded column. It was also noticed that flow of diagonal crack from the loaded column adjacent to the opening was discontinuous, due to incomplete strut action (Fig.16).

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b) Frame-2 with masonry insert:

First crack observed (inclined downwards and forwards) at only 75 kN, (against 40 kN for the frame without insert) at loaded side of the beam and column junction of the bottom storey where moment and shear forces were maximum While loading further, similar cracks were found to propagate in middle column beam junctions and diagonal crack were initiated in the first (loaded) bay. Further, diagonal cracks were seen to flow through the brick infill. Separation of infill occurred at the tension corners. Due to the presence of insert, diagonal cracks were observed to flow from the loaded beam â&#x20AC;&#x201C; column junction to the diagonally opposite corner, clearly depicting the expected strut action (Fig.17). At ultimate load of 195 KN, plastic hinge formation and failure of frame at all bottom storey junctions were noticed. The width of the cracks was ranging from 2mm â&#x20AC;&#x201C; 10mm in concrete and masonry. The crack pattern indicated a combined effect of flexure and shear failure and the direction of flown crack showed the developed strut action through the brick infill, due to the presence of masonry insert

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Figure.17.Test frame 2 with failure in the bottom and drift of the top storey(Constructed atVLBJCET, Coimbatore)

Figure.16.Test frame 1 with failure in the bottom and drift of the top storey (Constructed atVLBJCET, Coimbatore)

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A crack in leeward column of the bottom storey at the base was also observed (Fig.18). Separation of infill occurred at the tension corners and the high stress concentration at the loaded diagonal ends led to early crushing of the loaded corners (Fig.19).No crack was developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to short column effect. It is also evident from the propagation of cracks at bottom storey level of the Fifteenth cycle (75 kN Base shear). Cracks in tension face of leeward column were developed after twenty first cycle of loading. Also separation of infill from columns at highly stressed tension faces of column were seen at tenth cycle of loading. Further, shear flow was observed in frame 2 from the columns through the insert and brick infill, creating a largely visible crack (about 12mm wide), which is extended to the adjacent columns. This phenomenon is clearly exhibits the development of strut action through masonry insert.

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Figure 18.crack in leeward column

Figure.19 Crushing of the loaded Corners

A comparative study was made between experimental and analytical values. Non-linear finite element analysis has been carried out using ANSYS-10 software for Frame (1) & (2). The deformed shape of the software model for ultimate load for Frame (1) and (2) is shown in Fig.20 &21

2) FINITE ELEMENT ANALYSIS – ANSYS – 10:

Load – 195 KN , Deflection – 70.448

Fig.21 Ultimate Deformed Shape of the software Model For Frame 2

The results obtained from analytical by ANSYS10 for Frame (1) & (2) are compared with experimental results and the variation is mariginal.

Load – 105 KN , Defle Deflection – 59.432

Figure.20 Ultimate Deformed Shape of the software Model For Frame 1

ISSN: 2230-7818

The experiments conducted on the two frames (with and without masonry insert) the following observations are drawn. 1) It is observed in frame with masonry insert that at a base shear of 75 kN, cracks are initiated at the junction of the loaded and middle end of the beam and column of the bottom storey where the moment and shear forces are maximum whereas in frame without insert, the first crack developed at 40 KN itself. The crack pattern indicated a combined effect of flexure and shear failure. However, it could be evidently seen that the shear carrying capacity of the frame is increased due to the presence of masonry inserts 2) Separation of infill occurred at the tension corners and the high stress concentration at

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Mr.R.Suresh Babu et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 1, 072 - 085

10)

11)

that the lateral strength of the RC frame is considerably increased due to the presence of masonry inserts. The partial masonry infill failed with a diagonal crack by shear along the mortar and/or bricks joints. In frame without masonry insert no crack is developed in the columns, beams and in the infill of top storey clearly depicting that the frame has failed only by hinges in columns due to captive column effect. But, it was noticed that the development of crack is postponed when the frame is provided with masonry inserts. The partial infill reduces the stiffness of the frame leading to critical damages. However, this could be improved to some extent by the provision of masonry inserts. In analytical study, it is noticed that a sudden increase in deflection after the base shear of 40 kN (nearly equal to experimental value of 40 kN) for Frame (1) and affect the base shear of 75 kN (nearly equal to experiemtnal value of 75 kN) for Frame (2). This proves the initiation of captive column behaviour adjacent to gap region. Analytical results by ANSYS-10 variations is very mariginal when compared to Experimental results

the loaded diagonal ends lead to early crushing of the loaded corners. Diagonal cracks flown through the brick work where masonry inserts are provided showing clear strut action. While further loading of frames, further cracks are initiated and noticed are much dissimilar between a RC frame with partial infill and with masonry insert. The stiffness of the partially-infilled frame with and without insert for various load cycles is calculated and the variation of stiffness with respect to load cycles is plotted. The stiffness of the brick infilled RC frame with masonry insert is observed to be very high when compared to frame without insert. This shows greater increase of stiffness while introducing masonry insert. The ductility factor value µ = (∆1/∆y) for various load cycles of the frame is worked out for frames with and without insert and the variation of ductility factors and cumulative ductility factors for both frames with reference to load cycles is plotted. From the values, it may be noted that ductility factor for frame with masonry insert is reduced whereas cumulative ductility factor for both frames is more or less same. Cracks were developed in the leeward column (opposite to the loaded end) of the bottom storey at the base because of diagonal strut compression of the infill in the frame with masonry insert. The partial-infilled RC frame failed with hinges at the portion of columns adjacent to the gap in the bottom storey indicating a distinct “captive column effect” whereas frame with masonry insert strut action took place and diagonal crack flow clearly. Also after the localised separation of the infilled panel from the frame in the bottom storey, the stress flow is mostly along the line connecting the load point to the diagonal opposite corner support indicating the “diagonal strut” concept. Therefore, it could be evidently proven

ISSN: 2230-7818

12)

V CONCLUSION For existing buildings with short column in earthquake prone areas needs this easy method of providing masonry insert to improve the base shear capacity. Many of the existing captive columns have poor seismic detailing. Due to short dowels and little transverse reinforcement, risk of brittle shear failure in such members is very high. Therefore, it is important to develop efficient techniques to strengthen shear critical columns and increase their energy dissipation capacity. Wrapping concrete columns with a proper strengthening material can be an effective solution. . The various method of improve the strengthening of existing building and the costs are prescribed.

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Mr.R.Suresh Babu et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 1, 072 - 085

Cost/Sqm 4)

External

Internal

Introducing masonry insert in the opening

Rs.750/-

Rs.1500/-

Beam column joint strengthening using carbon fibres

Rs.10000/-

Rs.12000/-

Beam column joint strengthening using GFRP

Rs.7500/-

Rs.8750/-

Introducing longitudinal and shear reinforcement and micro concrete pack up

Rs.17000/-

Rs.19700/-

6) 7)

expanded steel meshes", Structural Engineering and Mechanics, Vol. 21, No.3, pp. 333-50 (2005). Galal, K.E., Arafa, A., and Ghobarah, A., (2005), “Retrofit of RC square short columns" Engineering Structures Journal, Vol. 27, No 5, pp. 801-813 Melhmet Mehmet Emin Kara, Altin Sinan, (2006), “Behavior of reinforced concrete frames with reinforced concrete partial infills”, ACI structural journal, 2006, vol. 103, no5, pp. 701-709 FEMA 306, “Evaluation of earthquake damaged concrete and masonry wall buildings”, Applied Technology Council, USA “NEHRP guidelines for the seismic rehabilitation of buildings. FEMA Publication 273”, Multidisciplinary Center for Earthquake Engineering Research (MCEER), USA Dr.C.V.R. .C.V.R. Murthy (2005) on Key notes on seismic resistance buildings.

Si.No Technique

Therefore, cheaper and affable solutions involving easily available ilable materials and simple construction techniques such as masonry inserts must be given much consideration during construction.

From the studies, the width of diagonal strut transferring the shear is approximately found to be 0.10 times the length of the diagonal of infill. Therefore, a minimum width of insert based on the above criteria may be provided as described. References:

1) Yaw-Jeng Chiou, Jyh-Cherng Tzeng, and YuhWehn Liou, (1999), (1999), “Experimental and Analytical Study of Masonry Infilled Frames”, Journal of Structural Engineering, Vol. 125, No. 10, October 1999, pp. 1109-1117 2) Murtthy , C.V.R., and Das, Diptesh., (2000), “Beneficial Effects of Brick Masonry In Fills In Seismic Design of RC Frame buildings" Engineering Structures Journal, Vol. 21, No 4, pp. 617-627 3) R. Morshed and M.T. Kazemi, (2005), "Seismic shear strengthening of R/C beams & columns with

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