Effect of modeling of infill walls on performance of multi story rc building

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Effect of modeling of infill walls on performance of multi story rc building

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 243 EFFECT OF MODELING OF INFILL WALLS ON PERFORMANCE OF MULTI STORY RC BUILDING Dr. Suchita Hirde* , Ms. Dhanshri Bhoite** * Professor, Dept. of App. Mechanics Govt. College of Engineering Karad 415124 India ** PG student, (Civil- Structure), Govt. College of Engineering, Karad 415 124, India ABSTRACT Buildings with masonry infill wall RC frames are the most common type of structures used for multistory constructions in the developing countries. In several moderate earthquakes, such buildings have shown excellent performance during earthquake. While analysing such multi storey frames using structural engineering software, normally the multistory frames are modeled as bare frame. The infill walls are not modeled in software and its resistance is not considered to lateral forces. Hence in this paper attempt has been made to study the effect of modeling of such infill walls on the performance of multi storey reinforced concrete framed building. Nonlinear static pushover analysis of multi storey frame is carried out considering it as bare frame. Then the pushover analysis of same frame is carried out by modeling the infill walls for throughout the height and for modeling the infill walls excluding ground storey so as to make it as soft storey, since the soft storey feature is very common in multi storey building to provide the parking place. The results of bare frame analysis and frame with infill effects are compared in the form of capacity spectrum curve, performance point and hinge formation at performance point and conclusion are made. It is seen that the masonry infill contribute significant lateral stiffness, strength, overall ductility and energy dissipation capacity. Keywords: Nonlinear static pushover analysis, performance point, performance level, plastic hinges, bare frame, masonry infill, soft storey INTRODUCTION In a country like India, use of reinforced concrete framed structure is very common in multi storey building construction. The masonry infill walls which are constructed after completion of reinforced concrete frames are considered as non-structural elements. Although they are designed to perform architectural functions, masonry infill walls do resist lateral forces with substantial structural action. In addition to this infill walls have a considerable strength and stiffness and they have significant effect on the seismic response of the structural system. From the literature review it has INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), pp. 243-250 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2013): 5.3277 (Calculated by GISI) www.jifactor.com IJCIET © IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 244 been seen that many research papers are available to understand the behavior of soft storey. However there is little work carried out by researcher related to finding vulnerability of existing RCC building with soft storey using pushover analysis. The concept of pushover analysis is rapidly growing in the area of seismic evaluation now a day. It gives the capacity curve of the building from which lateral load carrying capacity of the buildings can be calculated. Hence for the safety of the structure during earthquake, it is important to assess performance level of the building and to suggest retrofitting schemes for deficient buildings. There is a general agreement among the researchers that infilled frames have greater strength as compared to frames without infill walls. The presence of the infill walls increases the lateral stiffness considerably. Due to the change in stiffness and mass of the structural system, the dynamic characteristics change as well. Structural engineering software are used to analyze multi storey buildings. But while analyzing such structures using software the multistory building are modeled as bare frames without infill walls. The dead load of wall is simply applied as an external dead load. Hence in this study three different models of an eight storey building symmetrical in the plan are considered to find the effect of modeling of such infill walls on performance of the building. Following three different models are investigated in the study. Model I: Multi storey frame modeled as bare frame without infill Model II: Multi storey frame with infill excluding ground story so as to make it as soft story. Model III: Multi storey frame with masonry infill throughout the height of the building. These models of 8 storey building are modeled and pushover analysis (Nonlinear static analysis) is carried out using SAP 2000 software. The purpose of pushover analysis is to evaluate the expected performance of structural systems by estimating performance of a structural system by estimating its strength and deformation demands in design earthquakes by means of static inelastic analysis, and comparing these demands to available capacities at the performance levels of interest. A plot of total base shear versus top displacement in a structure is obtained by this analysis that would indicate any premature failure or weakness. The analysis is carried out upto failure, thus it enables determination of collapse load and ductility capacity. This type of analysis enables weakness in the structure to be identified. This type of analysis is useful to take decision for retrofitting of structure. Based on these results this paper explores the beneficial effects of masonry infill walls on seismic behavior of RC frame buildings. MODELING OF MULTI STOREY BUILDING The study is carried out on 8 storey reinforced concrete moment resisting frame building having symmetrical plan layout as shown in figure 1. Building is kept symmetric in both orthogonal directions in plan to avoid torsional response under pure lateral forces. Plinth height is 1.2m and story height is 3.1m for each floor level. The building is considered to be located in seismic zone V and intended for residential use. The building is founded on medium strength soil. Elastic moduli of concrete and masonry are taken as 28500 Mpa and 3500Mpa respectively and their poisons ratio is 0.2. The unit weights of concrete and masonry are taken as 25.0 KN/ m3 and 20.0 KN/ m3 . The floor finish on the floor is 1 KN/ m2 . The roof treatment is taken as 1.5 KN/ m2 . The live load on the floor is taken as 3 KN/ m2 and that of the Roof is taken as 1.5 KN/ m2 . In the seismic weight calculations only 25% of the floor live load is considered. Size of beam for peripheral beams is considered as 300x500mm and internal beams as 300x600mm. Size of exterior columns is considered as 450x450 mm while internal column size is 550x550mm. Figure 2 shows the 3 D model of bare frame, Fig. 3 shows the 3 D model of multistory frame with masonry infill excluding ground floor (i.e. soft storey) and Fig.4 shows 3 D model of multistory frame with masonry infill throughout the height.
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 245 Figure 2: Model I – Bare frame Figure 3: Model II – Multi storey frames (without infill) with soft storey Figure 1: Plan of Building Figure 4: Model III – Multi storey frame with full masonry infill
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 246 PUSHOVER ANALYSIS The pushover analysis provides an insight into the structural aspects, which control the performance during earthquakes. It also provides data on the strength and ductility of a building. It is widely accepted that, when pushover analysis is used carefully, it provides useful information that cannot be obtained by linear static or dynamic analysis procedures. Due to its simplicity, the structural engineering profession has been using the nonlinear static procedure (NSP) or pushover analysis. Modeling for such analysis requires the determination of the nonlinear properties of each component in the structure, quantified by strength and deformation capacities, which depend on the modeling assumptions. Pushover analysis is carried out from either user-defined nonlinear hinge properties or default-hinge properties, available in some programs based on the FEMA-356 and ATC-40 guidelines. While such documents provide the hinge properties for several ranges of detailing, programs may implement averaged values. In this study, for pushover analysis, beams and columns are modeled with concentrated plastic hinges for flexure and shear at the column and beam faces, respectively. Beams have both moment (M3) and shear (V2) hinges, whereas columns have axial load and biaxial moment (PMM) hinges and shear hinges in two directions (V2 and V3). COMPARISON OF PERFORMANCE OF VARIOUS FRAMES Pushover analysis of frames shown in figure 2, 3 and 4 is carried out. Comparison between the performance point in terms of base shear and roof displacement obtained from the nonlinear static analysis and hinge formation pattern of the three models. EFFECT OF MODELING OF INFILL OF WALLS ON BASE SHEAR AND ROOF DISPLACEMENTS Effect of modeling of infill of walls on base shear and roof displacements is presented in table 1. Table 1: Comparison of performance of three models in terms of base shear and roof displacement Building (8 storied) Performance Point Seismic performa nce level X direction (kN, mm) Y direction (kN, mm) Base shear Roof Displacement Base shear Roof Displacement Bare frame 1518.249 194 1507.6362 187 LS-CP Open ground soft story 8072.274 79 7815.3 83 LS-CP Full masonry infills 12003.252 69 10458.648 71 B It is observed that the performance level of the bare frame and open ground soft story structure are in LS-CP range (i.e. life safety to collapse prevention range) whereas full infill masonry structure is in elastic range. Roof displacement for bare frame is greater than frame with masonary infill and open ground soft story.
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 247 Figure.5 and figure 6 show the comparison of pushover curve of three models in X direction and in Y direction. These curves clearly represent that the performance of bare frame is modified after modeling infill walls. Figure 5: Comparison of pushover curve for three models in X direction Figure 6: Comparison of pushover curve for three models in Y direction
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 248 EFFECT OF MODELING OF INFILL WALLS ON HINGE FORMATION PATTERN Figure 7, figure.8 and figure 9 shows the formation of hinges in structure at performance level. Figure 7 shows the formation of hinges in model I: bare frame structure by considering push load in X and Y directions. Figure 8 shows the formation of hinges in model II i.e. model with masonry infill with soft bottom storey in X and Y directions and figure 9 shows the formation of hinges in model III with full masonry infill in X and Y directions From the pushover curve shown in figure 5 and figure 6, it has been observed that the performance of structure with masonry infill wall is improved after modeling the masonry infill walls as compared to bare frame. Performance of bare frame is modified from LS-CP range i.e. life safety to collapse prevention range to B range i.e. operational range after modeling the infill walls in structure. In case bare frame, as observed in figure 7 more number of beams are in life safety range and plastic hinges are concentrated at middle storeys. Figure 7: Formation of hinges in model I: Bare Frame in X direction and Y direction Figure 8: Formation of hinges in model II: Soft story structure in X direction and Y direction
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 249 Figure 9: Formation of hinges in model II: Full infill frame structure in X direction and Y direction The response of open ground soft story building in terms of plastic hinge properties is also in collapse level due to formation of hinges some in life safety range, some in collapse prevention range and some are at C (effective cracking) range which is not acceptable criteria for hinges in column. From figure 8, it is very clear that since the columns of the soft storey are in LS range, this building will get sever damages during earthquake. In case of full masonry structure shown in figure 9, all the hinges are in B range (i.e. operational range) which is acceptable criteria for hinges. The plastic deformation in case of masonry infill in columns and beams is within limit i.e. linear range but it is crosses collapse (C) level in case of masonry strut. CONCLUSION The Effect of modeling of masonry infill on the response of multi-storied building under seismic loading is illustrated using three different models. The presence of full masonry infill panels modifies the stiffness, performance of structure and formation hinges in elastic range i.e. all hinges are formed operational. The total storey shear force increases considerably as the stiffness of the building increases in the presence of masonry infill. In case of soft story at open ground floor the mode of failure is by soft story mechanism (formation of hinges in LS, CP and C range in ground floor columns). The lateral load resisting mechanism of the masonry infill frame is essentially different from the bare frame. The bare frame acts primarily as a moment resisting frame with the formation of plastic hinges at the joints under lateral loads. In contrast, the infill frame behaves like a braced frame resisted by a truss mechanism formed by the compression in the masonry infill panel and tension in the column. The plastic hinges are confined with the joint in contact with the infill panel. It is seen that the existing building with open ground story is deficient due to formation of plastic hinges at ground floor column at collapse level and in need to have retrofitting measures to prevent collapse of such buildings during earthquake.. The present study will be very useful to Civil Engineers to understand the effect of the modeling of infill walls on the performance of multi storey framed reinforce concrete building. It is also useful to understand the contribution of infill walls in formation of plastic hinges in beams and columns in multistory frame.
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 4, Issue 4, July-August (2013), © IAEME 250 REFERENCES [1] ATC 40, (1996), “Seismic Evaluation and Retrofit of Concrete Buildings”, Vol.1 & 2, Applied Technology Council, Redwood City, CA, USA, Report No. SSC 96-01. [2] FEMA 356, 2000, Prestandard and Commentary for the Seismic Rehabilitation of Buildings, Federal Emergency Management Agency, Washington, D. C. [3] Fardis M. N., Panagiotakos T. B., 1997, “Seismic Design And Response of Bare And Masonry Infilled Reinforced Concrete Buildings Part II: Infilled Structures”, Journal of Earthquake Engineering, Imperial College Press, Vol. 1, No. 3, pp. 475-503. [4] Dolsek M., Fajfar P., 2008, “The Effect of Masonry Infills on the Seismic Response of a Four-Storey Reinforced Concrete Frame-A Deterministic Assessment”, Science Direct, Engineering Structures, Vol. 30, pp. 1991-2001. [5] Sattar S., Liel A. B., “Seismic Performance of Reinforced Concrete Frame Structures with and without masonry Infill Walls”, Department of Civil, Environmental and Architectural Engineering, University of Colorado. [6] Kormaz K. A., Demir F., Sivri M., 2007, “Earthquake Assessment of R/C Structures with Masonry Infill Walls” International Journal of Science and Technology, Vol. 2, No. 2, pp. 155-164. [7] IS 1893 (Part I): 2002, Criteria for Earthquake Resistant Design of Structures, Part I General Provisions and Buildings, Bureau of Indian Standards, New Delhi. [8] IS 456, 2000, Code of Practice for Plain and Reinforced Concrete, Bureau of Indian Standards, New Delhi. [9] Agarwal P., Shrikhande M., 2007, “Earthquake Resistant Design of Structures”, Prentice Hall of India Pvt. Ltd. New Delhi. [10] Chopra A. K., “Dynamics of Structures”, Earthquake Engineering Research Institute, Berkeley, California. [11] Reddy M. K., Rao D. S. P., Chandrasekaran A.R., 2007, “Modeling of RC Frame Buildings with Soft Ground Story”, Indian Concrete Journal, Vol. 81, No.10, pp. 42-49. [12] Mohammed J. Abed, K. Nasharuddin, M. A. Alam, Zakaria CM and Moatasem M. Fayyadh, “Damaged RC Beams with Circular Web Opening Repaired using Different Configurations of Bonding Steel Plate”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp. 70 - 83, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [13] Vidula S. Sohoni and Dr.M.R.Shiyekar, “Concrete–Steel Composite Beams of a Framed Structure for Enhancement in Earthquake Resistance”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 1, 2012, pp. 99 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [14] Shaikh Zahoor Khalid and S.B. Shinde, “Seismic Response of FRP Strengthened RC Frame”, International Journal of Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp. 305 - 321, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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