Effect of openings in RC Infilled Frame Structure under Seismic Loads

Effect of openings in RC Infilled Frame Structure under Seismic Loads

Karam Singh Yadav Assistant Professor, UIT Allahabad

Dr. Partap Singh Professor,

NIT Jalandhar,

Abstract – Masonary infilled RC frames are the most common type of structures used for tall building constructions in the developing countries and also located in seismic regions. Window and door openings are important parts of infill walls for functional reasons. Currently, publications like FEMA-273 contain provisions for the calculation of stiffness of solid infilled frames mainly by modeling infill as a diagonal strut. However, such provisions are not provided for infilled frames with openings. Present study is an attempt to analyze the performance of RCC frame with infills panels with and without openings. In this paper building (G+4) is considered by modeling of frame and masonry Infills by STAAD PrO. Software and modelling of infills is done as per actual size of openings with the help of plate tool in software. The various models such as bare frame, infill frame and infill frame with opening are analyze and concluded that infill panels increase stiffness of the structure the increase in the opening percentage leads to a decrease on the lateral stiffness of inlled frame

Key words – Masonary infill wall, equivalent diagonal strut, RC Frame

METHEDOLOGY EQUIVALENT STRUT METHOD

In this method, the analysis is carried out by simulating the action of infills similar to that of diagonal struts bracing the frame. The infills are replaced by an equivalent strut of length D and width Wef

INTRODUCTION

The current design approach to tall-building design in most of the regions in the world requires the structural skeleton to resist vertical and lateral loads, under both the ultimate and serviceability loading conditions applied to the building. Non-structural components such as infill walls, facades and stairs are considered as non-load bearing components. These components are assumed to be detached from the primary structure in the design of high-rise buildings. However, because of different types of physical connections, interactions between the structural skeleton and the non-structural components do occur. Both structural and non-structural components participate in resisting structure movement.

In reality, the presence of infill wall changes the behavior of frame action into truss action, thus changing the

FIGURE 1

EQUIVALENT DIAGONAL STRUT MODEL

The width of the equivalent diagonal strut can be found by using number of expressions given by different investigators, are given below:

1. Holmes (1961)gave a formula for determination of width of diagonal strut are given below:

   = 1 3

2. Stafford Smith and Carter (1969) proposed a theoretical

   relation for the width of diagonal strut based on relative stiffness of infill and frame.

   lateral load transfer mechanism. The masonry can be of brick,

   1 0.445

   0.335(1 0.064

   concrete units or stones .Usually the RC frame is filled with

   = 0.58 ( )

   (. )

   )

   bricks as non-structural wall for partition of rooms.

   Where

   RC framed buildings are generally designed without

   considering the structural behavior of masonry infill walls present. These walls are widely used as partitions and

   h =

   4 sin 2

   4

   considered as non-structural elements. But they affect both the structural and non-structural performance of the RC buildings under lateral loads

3. Mainstone (1974) proposed a relationship for computing the width of the equivalent diagonal strut, is given by.

   = 0.175 (h Hinf) -0.4 D

   =

   =

   4 sin 2

   h 4

   Where

   h=Stiffness reduction factor

   Einf= Modulus of elasticity of the infill material, N/mm2 Ec= Modulus of elasticity of the frame material, N/mm2 Ic= Moment of inertia of column, mm4

   t = Thickness of infill, mm

   H = Centre line height of frames Hinf = Height of infill

   L = Centre line width of frames l = Width of infill

   D = Diagonal length of infill panel.

   = Angle between diagonal strut and beam

4. Pulay and Preistley (1992) suggested a conservative formula for design proposal , given by:

   W = 0.25D

5. FEMA (1998) provided a relationship for computing the width of the equivalent diagonal strut is given by:

= 0.175 ( Hinf)-0.4 D

Where: = h

ANALYSIS PROBLEM

A five storeyed building has been chosen for investigating the effect of openings in RC frame structure with masonry in-filled walls

TABLE – 1 STRUCTURAL DETAILS

Analytical Models

The present work has been divided into following four Cases. Case – 1 RC framed structure without masonry infill walls.

Case 2 RC framed structure with masonry infill walls.

Case -3 RC framed structure with masonry infill walls having

1. % openings.

   Case – 4 RC framed structure with masonry infill walls having 20 % openings.

   Openings in infill walls have been provided at periphery of uilding.

   Column C-1 is exterior and C-2 in interior column respectively as shown in plan.

   FIGURE 2

   PLAN OF THE BUILDING WITH LOCATION OF INFILL

   FIGURE 3

   ELEVATION OF RC FRAME STRUCTURE

   FIGURE 4

   ELEVATION OF BUILDING WITH INFILL WALLS

   FIGURE 5

   ELEVATION OF BUILDING WITH 11.11 % OPENING AT CENTRE

   2. STRESS- RESULTANTS

   20

   STOREY HEIGHT (m)

   STOREY HEIGHT (m)

   CASE – 1

   16 CASE – 2

   FIGURE 6

   ELEVATION OF BUILDING WITH 20 % OPENING AT CENTRE

   The above models have been analyzed with respect to

   1. nodal displacements and

   2. stress- resultants such as MX, MZ and FY in beams

   3. stress resultants in column

RESULTS AND DISCUSSION

Comparison of all analytical models with the help of graph and discussion of result.

1. NODAL DISPLACEMENTS

20

STOREY HEIGHT (m)

STOREY HEIGHT (m)

16

12

CASE – 1

8 CASE – 2

12 CASE – 3

CASE – 4

8

4

0

100 150 200 250 300 350

MOMENT Mz (kN-m) FIGURE 8

MAXIMUM MOMENTS MZ IN BEAMS PARALLEL TO X – DIRECTION ALONG – WITH STOREY HEIGHT FOR CASESS-1, 2, 3 AND 4 .

In Case – 2, maximum moment decreases by 50.91 % as compared to Case – 1 because of presence of infill walls. By providing 11.11 % and 20 % opening at centre in infill walls in Case – 3 and 4, maximum moments are increases by 0.2 % and 1.2 % respectively as compared to Case – 2. By increasing the openings from 11.11 % to 20 %, moment increases by 1 % in Case – 4 as compared to Case – 3.

20 CASE – 1

16

STOREY HEIGHT (m)

STOREY HEIGHT (m)

4 CASE – 3

CASE – 2

CASE – 3

CASE – 4

0

0 20 40 60 80

NODAL DISPLACEMENT (mm)

12 CASE – 4

8

FIGURE 7

MAXIMUM NODAL DISPLACEMENT ALONG – WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

Figure shows that, maximum nodal displacement decreases by 83.33 % in Case – 2 as compared to Case – 1.By providing

11.11 % and 20 % opening at centre, nodal displacement increases by 20.71 % and 64.87 % as compared to Case – 2 respectively. By increasing the opening from 11.11 % to 20

%, the nodal displacement increases by 36.58 % in Case – 4 as compared to Case 3

4

0

100 150 200 250 300 350

MOMENT Mx (kN-m)

FIGURE 9

MAXIMUM MOMENTS MX IN BEAMS PARALLEL TO Z – DIRECTION ALONG – WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

In Case -2 maximum moment decreases by 47.26 % as compared to Case – 1 due to presence of infill walls. By providing central openings 11.11 % and 20 % in Case – 3 and 4, moment increases by 4.48 % and 7.97 % respectively as compared to Case – 2. By increasing the openings with 11.11

% to 20 %, moment increases by 1.4 % in Case – 4 as compared to Case – 3.

20 CASE – 1 20

STOREY HEIGHT (m)

STOREY HEIGHT (m)

STOREY HEIGHT (m)

STOREY HEIGHT (m)

16 CASE – 2 16

CASE – 3

CASE – 1

CASE – 2

CASE – 3

12 12

CASE – 4

CASE – 4

8

8

4

4

0

0 50 100 150 200 250

MOMENT Mz (kN-m) FIGURE 10

MAXIMUM MOMENT MZ IN COLUMN C-1 ALONG – WITH STOREY

HEIGHT FOR CASES – 1, 2, 3 AND 4

In Case – 2, maximum moment decreases by 90.52 % as compared to Case – 1 due to presence of infill walls. By providing 11.11 % and 20 % opening at centre in Cases – 3 and 4 moments are increases by 26.77 % and 103.14 %

0

50 100 150 200

SHEAR FORCE Fy (kN)

FIGURE 12

MAXIMUM SHEAR FORCE FY IN BEAM IN X – DIRECTION ALONG- WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

The maximum shear force decreases by 51.67 % in Case – 2 as compared to Case 1. The maximum shear forces do not much differ in Cases – 3 and 4 as compared to Case – 2.

respectively as compared to Case -2. By increasing openings 20

from 11.11 % to 20 %, maximum moment increases by 60.23

% in Case – 4 as compared to Case- 3. 16

CASE – 1

CASE – 2

CASE – 3

CASE – 1

CASE – 2

CASE – 3

20

STOREY HEIGHT (m)

STOREY HEIGHT (m)

12

16

STOREY HEIGHT (m)

STOREY HEIGHT (m)

8

CASE – 4

CASE – 4

12 4

CASE – 1

CASE – 2

CASE – 3

CASE – 4

8

4

0

0 50 100 150 200

MOMENT Mz (kN-m) FIGURE 11

MAXIMUM MOMENT MZ IN COLUMN C-2 ALONG – WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

In Case – 2 maximum moment decreases by 84.6 % as compared to Case – 1 due to presence of infill walls. By providing opening 11.11% and 20% in Case – 3 and 4, moments are increases by 4 % and 49.1 % respectively as compared to Case – 2. By increasing the openings from 11.11% to 20%, maximum moment increases by 45 % in Case 4 as compared to Case 3.

0

0 500 1000 1500 2000 2500

AXIAL FORCE FX (kN) FIGURE 13

MAXIMUM AXIAL FORCE FX IN COLUMN C-1 ALONG – WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

Maximum axial force decreases by 2.01 % in Case – 2 due to presence of infill walls as compared to Case – 1. Maximum axial forces increase by 0.85 % and 1.38 % in Cases – 3 and 4respectively as compared to Case – 2, because of presence of

11.11 % and 20 % opening at centre in infill walls respectively.

20

CASE – 1

16 CASE – 2

STOREY HEIGHT (M)

STOREY HEIGHT (M)

CASE – 3

12

CASE – 4

8

4

0

0 500 1000 1500 2000 2500 3000

REFERENCES

1. Ahmed K. H., Sayed F. K. A., Ahmed M.H. and Al- Mekhlafy N. (2013), Equivalent Strut Width for Modeling R.C. Infilled Frames, Journal of Engineering Sciences, Vol.41, No.3, pp. 851-866.

2. Albanesi S., Albanesi T. and Carboni F. (2004), The Influence of Infill Walls in R.C. Frame Seismic Response, High Performance Structures and Materials, Vol. 2, pp. 776 782.

3. Decanini L., Mollaioli F., Mura A. and Saragoni R. (2004), Seismic Performance of Masonry Infilled RC Frames, 13th World Conference on Earthquake Engineering Vancouver, B.C., Canada.

4. FEMA 273 (1997), Guidelines for the Seismic Rehabilitation of Buildings, Federal Emergency Management Agency.

5. IS: 1893-2002, Criteria for Earthquake Resistant Design of Structure (part 1), Bureau of Indian Standards, New Delhi.

6. IS: 456- 2000, Plain and Reinforced Concrete – Code Practice,

   Axial force FX

   (kN)

   Bureau of Indian Standards, New Delhi.

7. Meharbi A.B. and Shing P. B. (2003), Seismic Analysis of Masonry-

   FIGURE 14

   MAXIMUM AXIAL FORCE FX IN COLUMN C-2 ALONG – WITH STOREY HEIGHT FOR CASES – 1, 2, 3 AND 4

   The maximum axial force decreases by 7.27 % in Case – 2 due to presence of infill walls as compared to Case -1. Maximum axial force increases 2.62 % and 3.51 % in Cases – 3 and 4respectively as compared to Case – 2. By increasing openings from 11.11 % to 20 %, the maximum axial force increases by 0.83 %in Case – 4 as compared to Case – 3.

   CONCLUSION

   The results of the present study having following conclusions

   1. By introducing infill walls, the maximum nodal displacement at roof level decreases about 80 %; Maximum moment and maximum shear force in beams decreases approximately 50 %; maximum moment MZ in interior column decreases about 80 % respectively; Maximum axial force FY in interior column decreases nearly 7 % as compared to RC frame structure means in general, infill panels increase stiffness of the structure.

   2. By providing openings of 11.11 % and 20 % , the maximum nodal displacement at roof level increases by about 20 % and 64 % respectively; maximum moments of beams MZ parallel to X- direction increases about 0.5

   % and 1.5 % respectively; maximum moment MX in beams parallel to Z direction increases approximately 5

   % and 8 % respectively; theeffects in maximum shear forces FY of beams are insignificant; maximum moment MZ in interior column increases about 4 %and 50 % respectively; maximum axial forces FY in interior column increases nearly 3 % and 4 % as compared to RC frame structure with infill walls means the increase in the opening percentage leads to a decrease on the lateral stiffness of inlled frame.

   Infilled Reinforced Concrete Frames,The Masters Seminary Journal, Vol.1,pp. 81-94.

8. SamoilaD. (2013), Masonry Infill Panels – Analytical Modeling and Seismic Behavior, IOSR Journal of Engineering (IOSRJEN), Vol. 1, pp. 30-39.

9. Wakchaure M.R. and Ped S. P. (2012), Earthquake Analysis of High Rise Building with and Without In filled Walls,International Journal of Engineering and Innovative Technology (IJEIT), Vol. 2,pp.89-94.

AUTHOR INFORMATION

Karam Singh Yadav, Assistant Professor, Department of Civil Engineering, UIT, Allahabad

Dr. Partap Singh, Professor, Department of Civil Engineering, NIT Jalandhar