IJSRD - International Journal for Scientific Research & Development Vol., Issue, ISSN (online): - Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and Mohammed Khaja Moinuddin Professor Vishwanath. B. Patil P.G Student (Structural Engineering) Associate Professor, Department of Civil Engineering, P D A C E Gulbarga- Abstract RC framed high rise buildings are generally designed without considering the structural action of masonry walls present. These walls are widely used as partitions and considered as non-structural elements. But they affect both the structural and non-structural performance of the RC buildings during earthquakes. RC framed building with open first storey is known as soft storey, which performs poorly during earthquakes. A similar soft storey effect can also appear, at intermediate storey level if a storey used as a service storey. The soft storey located in the lower part of the high rise building especially the ground storey is undesirable as it attracts severely large seismic forces. At the same time, the soft storey located in the upper part of the high rise building does not significantly affect. To study the effect of masonry and its modeling technique with different soft storey level, s of R C framed building were analyzed with two different techniques of modeling of masonry with one type of shear wall when subjected to earthquake loading. Technique one is showing more strength and stiffness than two and an attempt is made to develop relationship between strength and stiffness ratios for linear trend line. Key words: Equivalent, Masonry, shear wall, soft storey. I. INTRODUCTION Tall buildings are the most complex built structures since there are many conflicting requirements and complex building systems to integrate. Today s tall buildings are becoming more and more slender, leading to the possibility of more sway in comparison with earlier high-rise buildings. Thus the impact of wind and seismic forces acting on them becomes an important aspect of the design. Improving the structural systems of tall buildings can control their dynamic response. In the present practice of structural design in India, masonry panels are treated as non- structural element and their strength and stiffness contribution are neglected. In fact the presence of wall changes the behavior of the frame action in to truss action, thus changing the lateral load transfer mechanism. Performance of buildings in the past earthquakes clearly illustrates that the presence of walls has significant structural implications. Therefore, we cannot simply neglect the structural contribution of walls particularly in seismic regions where, the frame interaction may cause significant increase in both stiffness and strength of the frame in spite of the presence of openings. Reinforced concrete (RC) structural walls, conventionally known as shear walls are effective in resisting lateral loads imposed by wind or earthquakes. They provide substantial strength and stiffness as well as the deformation capacity (capacity to dissipate energy) needed for tall structures to meet seismic demand. It has become increasingly common to combine the moment resisting framed structure for resisting gravity loads and the RC shear walls for resisting lateral loads in tall building structures. The consequence of the presence of a soft storey either in the ground storey or in the upper storey, may lead to a dangerous sway mechanism in the soft storey due to formation of plastic hinges at the top and bottom end of the columns, as these columns are subjected to relatively large cyclic deformations. The main Objectives of the present study is To know the effect of in the frame. To know proper modeling technique of masonry. To check the strength and stiffness of each storey. To know the effect of ground and intermediate soft storey. II. Description of structural model For the study different models of twenty one () storey building are considered the building has seven bays in X direction and five bays in Y direction with the plan dimension m m and a storey height of. m each in all the floors except th storey, height of th storey is m. The building is kept symmetric in both orthogonal directions in plan to avoid torsional response. The orientation and size of column is kept same throughout the height of the structure. The building is considered to be located in seismic zone V. The building is founded on medium strength soil through isolated footing under the columns. Elastic moduli of concrete and masonry are taken as MPa and MPa respectively and their poisons ratio as. and. respectively Response reduction factor for the special moment resisting frame has taken as. (assuming ductile detailing). The unit weights of concrete and masonry are taken as. KN/m and. KN/m respectively the floor finish on the floors is. KN/m. The live load on floor is taken as. KN/m. In seismic weight calculations, % of the floor live loads are considered. Thickness of slab, shear wall and masonry wall as.m,. m and.m respectively. III. MODEL CONSIDERED FOR ANALYSIS Following twelve () models are analyzed in ETABS. as special moment resisting frame using equivalent static analysis, response spectrum analysis. A. : Building modeled as bare frame. However, masses of the walls are included. All rights reserved by www.ijsrd.com
Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //) B. : Building has full brick masonry of mm thick in all the stories including ground storey and intermediate storey. C. : Building has no brick masonry in ground storey and has full brick masonry of mm thick in upper stories. V. MODELLING OF MASONRY INFILL IN ETABS A. As Four Noded Quadrilateral shell element In this technique the masonry is modelled as four noded quadrilateral shell elements (with in-plane stiffness) of uniform thickness of.mm. The four-node element uses an Iso-parametric formulation that includes both rotational and translational degrees of freedom. (Ref fig ) D. : Building has no brick masonry in intermediate storey ( th storey) and has full brick masonry in rest of the storeys. E. : Building has no brick masonry in ground storey, intermediate storey ( th storey) and has full brick masonry in rest of all storeys. F. : Building model is same as model further, L shaped shear wall (mm thick) in both x and y direction at corners and a core wall (mm thick) is provided at the centre. First set of models have been prepared while considering masonry as four noded quadrilateral shell element and second set is prepared while masonry is modelled as equivalent double diagonal. Fig. : Four Nodded Quadrilateral Element. B. As Equivalent Double diagonal The frames with unreinforced masonry walls can also be modelled as equivalent braced frames with walls replaced by equivalent diagonal. Many investigators have proposed various approximations for the width of equivalent diagonal. The width of depends on the length of contact between the wall & the columns (αh) and between the wall & the beams (αl). The formulations for αh and αl on the basis of beam on an elastic foundation has been used given by Stafford Smith (). Hendry () proposed the following equation to determine the equivalent or effective width w, where the is assumed to be subjected to uniform compressive stress. h = () L = π () w = () Fig. : Plan and Elevation of different building models with panel. Where Em is elastic modulus of masonry wall, Ef is elastic modulus of frame material, t is thickness of, h is height of and L is length of, Ic is moment of inertia of the column, Ib is moment of inertia of the beam and θ = tan- (h/l). Fig. : Elevation of different building models IV. MODELING OF FRAME MEMBERS, AND SHEAR WALL The frame elements are modelled as beam elements, slab is modelled as rigid (in-plane) diaphragm and shear wall is modelled with Mid-Pier frame. Fig. : Equivalent Double Diagonal. VI. ANALYSIS OF THE BUILDING Equivalent static and response spectrum analyses has been performed as per IS (part-) for each model using ETABS. software. Lateral load calculation and its distribution along the height is done. All rights reserved by www.ijsrd.com
T in (Sec) Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //) VII. FUNDAMENTAL TIME PERIOD Fundamental Time Period(Sec) Is Code - ETABS Analysis Mode Long Tran Long Tran Long Tran l No. i s i s i s.................................... Table : Comparison of time period between IS code method and using ETABS for various models.... No IS Code with Table : Comparison of Base shear with panel and double diagonal models for Equivalent Static Analysis. Fig. : Comparison of Base shear with panel and double diagonal models for Equivalent Static Analysis. Base shear (KN) no RSA (ETABS) RSA (ETABS) panel diagonal longi trans longi Trans........................ Table : Comparison of Base shear with panel and double diagonal models for Equivalent static Analysis. Fig. : Vs. Time period for different building models along longitudinal direction. VIII. COMPARISON OF BASE SHEAR Base Shear (KN) No ESA (ETABS) ESA (ETABS) Panel Diagonal Longi Trans Longi Trans........................ Fig. : Comparison of Base shear with panel and double diagonal models for Response Spectrum Analysis IX. STOREY DRIFT Storey Drift(mm) Storey Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux........................ All rights reserved by www.ijsrd.com
Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //).................................................................................................................................................................................................................................... Store y Table : Storey Drifts for various building models along Longitudinal direction Mode l X. STOREY DISPLACEMENT Storey Displacement (mm) Mode l Mode l Mode l Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux Ux................................................................................................................................................ All rights reserved by www.ijsrd.com
Storey Level Storey Level Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //).......................................................................................... Table Storey Displacement for various building models along longitudinal direction Fig. : Comparison of storey drift for different building models along longitudinal direction. Drift in mm Displacement in mm Fig. : Comparison of storey Displacement for different building models along longitudinal direction.......... XI. NON-DIMENSIONAL STRENGTH AND STIFFNESS PARAMETERS......... For purpose of calculating strength and stiffness of different storey level, the strength and stiffness ratio i.e. and are worked out, and have plotted as shown in (Fig to ).Further a linear trend line is drawn for normalized parameters in Microsoft Excel so as to know the best fitting of scattered points. And a co-relation is developed between them........ -. -... Fig. : Normalized strength and stiffness parameters for model ().... -. Qi = Vb. di d. R =. Qi = Vb. di d. R =. () Fig. : Normalized strength and stiffness parameters for model (). All rights reserved by www.ijsrd.com
Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //)... -. Qi = Vb. di d. R =. () Fig. : Normalized strength and stiffness parameters for model ()........ -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model ()........ -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model ()........ -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model ()........ -. Qi = Vb. di d. R =... () Fig. ; Normalized strength and stiffness parameters for model ().... -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model ().... -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model ()........ -. Qi = Vb. di d. R =... () Fig. : Normalized strength and stiffness parameters for model (). All rights reserved by www.ijsrd.com
Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //)... -. Figure Normalized strength and stiffness parameters for model ().... -. Qi = Vb. di d. R =. Qi = Vb. di d. R =... Fig. : Normalized strength and stiffness parameters for model (). XII. RESULTS AND DISCUSSIONS () () Table shows natural time period, for bare frame model, from ETABS, it is.% more than the IS code method. When the structural action of masonry is taken the fundamental natural time got reduced % when compare with bare frame model, When masonry is modelled as equivalent double, the time period is increased by.% as compared with panel model for model. [Ref table and Fig ] Seismic base shear obtained for double diagonal models are considerably higher than panel models for ESA and RSA in both the directions. [Ref table and Fig ] Storey drift drastically increased when a soft ground storey is exist, for model at ground storey level it is increased by.% in case of panel and.% in case of double diagonal as compared with.when a soft storey is at intermediate level it drift values are not much higher. Shear walls and central core wall drastically reduces the inter storey drift. [Refer table Fig ] (bare frame) model shows highest storey displacement values in all different building models model (full brick ) shows considerable reduction in storey displacement with a maximum reduction of.% in case of masonry panel and.% in case of double diagonal as compared with model and model shows.% and.% reduction in displacement value compared with model. [Refer table, Fig ] Thus it can be concluded that addition of and concrete shear wall act as drift and displacement controlled elements in RC buildings. Fig to shows the normalized Strength and stiffness ratios, R value for bare frame model is least as compared to all other models which shows the frame is very much flexible in nature and susceptible earthquake threatening. Ground soft storey model shows least strength and stiffness ratio at ground storey which leads to dangerous sway mechanism. Ground and intermediate soft storey models shows scattering of points and not fitting a good curve. and shows the best fit, which means it has got sufficient strength and stiffness to resist seismic loading. s with double diagonal are showing slightly lesser R values than models with panel which shows double diagonal models are flexible than masonry panel. XIII. CONCLUSIONS Fundamental time period decreases when the stiffness of masonry and concrete shear wall is considered. Double diagonal models are showing large time period as compared with panel model. Seismic base shear is considerably more for masonry and shear wall models as compared with bare frame model and storey drifts and joint displacements considerably reduces, Hence consideration of masonry and shear wall will increases strength and stiffness of structure when subjected to lateral seismic loading. s with soft stories have got highest storey drift values at soft stories levels, which leads to dangerous sway mechanism. Therefore providing shear wall is essential so as to avoid soft storey failure. A service storey of lesser height can be safer at higher altitude in a tall building as long as it is properly managed. Masonry panel models are showing much strength and stiffness as compared with double diagonal models, therefore masonry panel can be a good solution to model masonry. And therefore depending upon the importance of structure and type of design it has to be modeled. Double diagonal can be helpful for modeling openings in masonry walls. From the non-dimensional analysis it is observed that for full masonry and shear wall models, R value is nearly equal to, which means each storey has got sufficient strength and stiffness to resist lateral seismic loading. REFERENCE [] Jaswant N. Arlekar, Sudhir K. Jain And C.V.R. Murty. Seismic Response of RC Frame Buildings with Soft First Storeys. Proceedings of the CBRI Golden Jubilee Conference on Natural Hazards in Urban Habitat,, New Delhi.. [] Shaik Kamal Mohammed Azam And Vinod Hosur. Seismic behaviour of multi-storeyed buildings with soft intermediate storey. Journal of Structural Engineering Vol., No., August-September pp. -. All rights reserved by www.ijsrd.com
Importance of ing of Masonry and Effect of Soft Storey on Seismic Performance of R.C High Rise Building with Non Dimensional Strength and (IJSRD/Vol. /Issue //) [] Amit V. Khandve. Seismic Response of RC Frame Buildings with Soft Storeys. International Journal of Engineering Research and Applications (IJERA) Vol., Issue, May-Jun, pp.-. [] G V Mulgund et. al. Seismic Assessment of Masonry R C Framed Building with Soft Ground Floor. International Conference on Sustainable Built Environment (ICSBE-) Kandy, - December. [] Shaik Kamal Mohammed Azam and Vinod Hosur. Seismic Performance Evaluation of Multistoried RC framed buildings with Shear wall. International Journal of Scientific & Engineering Research Volume, Issue, January-. [] Dr. Vinod Hosur. Earthquake resistant design of building structures Wiley India Pvt Ltd. New Delhi. [] IS :. Indian Standard Code of Practice for plain and reinforced Concrete, Bureau of Indian Standards, New Delhi. [] IS (Part-I) : Criteria for Earthquake Resistant Design of Structures, Part-I General Provision and Buildings (Fifth Revision). Bureau of Indian Standards, New Delhi. [] Nikhil Agrawal, et.al Analysis of Masonry ed R.C. Frame with & without Opening Including Soft Storey using Equivalent Diagonal Method International Journal of Scientific and Research Publications, Volume, Issue, September [] ETABS Non-linear..Computers and Structures Inc, Berkeley. All rights reserved by www.ijsrd.com