EFFECT ON PERFORMANCE OF DIFFERENT STRUCTURES WITH SAME PLAN AREA UNDER SEISMIC LOAD USING STATIC AND DYNAMIC ANALYSIS

Transcription

1 EFFECT ON PERFORMANCE OF DIFFERENT STRUCTURES WITH SAME PLAN AREA UNDER SEISMIC LOAD USING STATIC AND DYNAMIC ANALYSIS KUNTA GAYATRI KIRAN 1 Dr. D. S. R. MURTY 2 (B.E + M.E)Integrated Dual Degree Civil Engineering With Specialization In Structural Engineering Andhra University College of Engineering (A) 1 Professor And Head of Department, Department of Civil Engineering Andhra University College of Engineering (A) 2 Abstarct The buildings considered here is (G+9) storey residential building located in different seismic zones and wind velocity id 5m/s. The study of these models is undertaken by analyzing, for each floor plan shape (T and L), first a regular rectangular floor plan with determined proportions ( initial models); and second, the initial regular floor-plan shapes was transformed into irregular T and L-shape floor plans, respectively. The design is carried out in both static and dynamic analysis. Model I is G+9 storey rectangular building. The plan dimension of the building is 3mx2m. The analysis carried out in three seismic zones III, IV,V. The buildings are designed with beams and columns made up of RCC. Height of each storey is 3m in typical storeys, bottom storey height is 2m and the total height of the building is 29m. Model II is a G+9 storey T-shape building. The plan dimension of the building is 4mx24m. The analysis is carried out in three seismic zones III, IV,V. The buildings are designed with beams and columns made up of RCC. Height of each storey is 3m in typical storeys, bottom storey height is 2m and the total height of the building is 29m. Model III is a G+9 storey L-shape building. The plan dimension of the building is 35mx24m.The analysis is carried out in three seismic zones III, IV,V. The buildings are designed with beams and columns made up of RCC. Height of each storey is 3m in typical storeys, bottom storey height is 2m and the total height of the building is 29m Page No:128

2 1. INTRODUCTION ETABS is an engineering software product that caters to multi-story building analysis and design. Modeling tools and templates, code-based load prescriptions, analysis methods and solution techniques, all coordinate with the grid-like geometry unique to this class of structure. Basic or advanced systems under static or dynamic conditions may be evaluated using ETABS. For a sophisticated assessment of seismic performance, modal and direct-integration time-history analyses may couple with P-Delta and Large Displacement effects. Nonlinear links and concentrated PMM or fiber hinges may capture material nonlinearity under monotonic or hysteretic behavior. Intuitive and integrated features make applications of any complexity practical to implement. Interoperability with a series of design and documentation platforms makes ETABS a coordinated and productive tool for designs which range from simple 2D frames to elaborate modern high-rises. 1.1 Loading, Analysis, and Design Once modeling is complete, ETABS automatically generates and assigns code-based loading conditions for gravity, seismic, wind, and thermal forces. Users may specify an unlimited number of load cases and combinations. Analysis capabilities then offer advanced nonlinear methods for characterization of static-pushover and dynamic response. Dynamic considerations may include modal, response-spectrum, or time-history analysis. P-delta effect account for geometric nonlinearity. Given enveloping specification, design features will automatically size elements and systems, design reinforcing schemes, and otherwise optimize the structure according to desired performance measures. Functions are defined to describe how a load varies as a function of period, time or frequency. Functions are only needed for certain types of analysis; they are not used for ststic analysis. A function is a series of digitalized abscissa-ordinate data pairs. There are two types of functions: 1.2 Response Spectrum Functions: Response spectrum functions are pseudo-spectral accelerations versus period functions for use in response spectrum analysis. In this program, the acceleration values in the function are assumed to be normalized; that is, the functions themselves are not assumed to have units. Instead, the units are associated with a scale factor that multiplies the function and is specified when you define the response spectrum case. 1.3 Time History Functions: These are loading magnitude versus time functions for use in time history analysis. The loading values in a time history function may be ground acceleration values or they may be multipliers for specified (force or displacement) load cases. Define as many named functions as necessary. They are not assigned to objects, but are used in the definition of Response Spectrum and Time History case. Page No:129

3 2. NECESSITY OF THE WORK Civil engineering structures are mainly designed to resist static loads. Generally the effects of dynamic loads acting on the structure are not considered. This feature of neglecting the dynamic forces sometimes becomes the cause of disaster, particularly in case of earthquake and severe wind action on structure. This has created a growing interest and need for earthquake wind resistant design of structures. Larger is the capacity of the structure to deform plastically without collapse, more is the resulting ductility and the energy dissipation. This causes reduction in effective earthquake forces. Plastically without collapse, more is the resulting ductility and the energy dissipation. To study the structural layout of the building and its necessity using advanced analysis tool when carrying out structural seismic response assessment. To assess the building s structural response under the seismic actions and propose respective repair and strengthening methodologies. This is to bring the earthquake damaged building back to its intended service while being able to sustain the code required seismic actions. To assess and design seismic retrofit solutions for existing buildings. Design new buildings that employ structural materials, systems, or other features that do not conform to current building code requirements. To assess the performance of buildings for specific owner requirements To investigate the earthquake resistance capacity of the individual element. 3. OBECTIVES OF THE STUDY To develop an analytical model for different structural systems. To carry out design analysis and design of the considered building using ETABS. To check the analysis results of ETABS for lateral stability as per IS code provisions for seismic and wind loads To provide a brief description to various components of members. Response spectrum analysis is adopted with SRSS (sum of square root of squares) for the directional combination in ETABS. Pushover analysis will provide adequate information on seismic demands imposed by the design ground motion on the structural system and its components. Identification of the critical regions in which the deformation demands are expected to be high and that have to become the focus through detailing. To perform dynamic analysis of buildings subjected to lateral loads. 4. SCOPE OF THE PRESENT STUDY The buildings considered here is (G+9) storey residential building located in different seismic zones and wind velocity is 5m/s. The study of these models is undertaken by analyzing, for each floor plan shape (T and L), first a regular rectangular floor plan with determined proportions ( initial models); and second, the initial regular floor-plan shapes was transformed into irregular T and L-shape floor plans, respectively. The design is carried out in both static and dynamic analysis. The buildings are designed with beams and columns made up of RCC. Height of each storey is 3m in typical storeys, bottom storey height is 2m and the total height of the building is 29m. Page No:13

4 5. ASSUMPTIONS OF THE WORK Certain assumptions have been made before the dissertation problem was intiated. They are as follows: The condition of the soil is considered to be of medium type. The wind forces and its effects on the buildings are considered as per IS (part3) The earthquake forces and its effects on buildings are considered as per IS The type of building considered is residential building 5.1 Method of Analysis For Seismic Analysis Of Buildings Depending on the nature of the considered variables, the method of analysis can be classified as shown in figure. Based on the type of external action and behavior of structure, the analysis can be further classified as linear static analysis, linear dynamic analysis, non-linear static analysis or non-linear dynamic analysis Analysis Process Method of Analysis Page No:131

5 Linear static analysis or equivalent static analysis can be used for regular structures with limited height. Linear dynamic analysis can be performed in two ways, either by the Response Spectrum Method or by the Elastic Time History Method. The significant difference between linear static and linear dynamic analysis is the level of the forces and their distribution along the height of the structure. Non-Linear static analysis is an improvement over linear static or dynamic analysis in the sense that it allows inelastic behavior of the structure 5.2 Linear Elastic Dynamic Analysis Dynamic analysis is an alternative procedure to the equivalent lateral force method performed to obtain the design lateral forces at each floor level along the height of the building and its distribution to individual lateral load resisting elements. Dynamic analysis should be performed to obtain the design seismic force and its distribution to different levels along the height of the buildings and to the various lateral load-resisting elements, for the following buildings: Regular buildings: Those greater than 4m height in zones IV and V, and those greater than 9m in height in zones II and III. Irregular buildings: All framed buildings higher than 12m in zones IV and V, and those greater than 4m in height in zones II and III. 5.2 Methods of Dynamic Analysis Dynamic analysis may be performed either by the Response Spectrum Method or by the Time History Method. However, in either method, the design base shear (V ) is compared with a base shear (V ), calculated using a fundamental period Tn. Where V is less than V, all the response quantities, e.g., member forces, displacement, storey forces, storey shears, and base reactions, should be multiplied by V /. 5.3 Response Spectrum Method In the response spectrum method, the peak response of a structure during an earthquake is obtained directly from the earthquake response (or design) spectrum. This procedure gives an approximate peak response, but this is quite accurate for structural design applications. In this approach, the multiple modes of response of a building to an earthquake are taken into account. For each mode, a response is read from the design spectrum, based on the modal frequency and the modal mass 5.4 Inelastic Time History Analysis or Nonlinear Response History (NRH) Analysis In NRH analysis the reduced stiffness in nonlinear range is considered and the force deformation is not a single valued function. It depends on direction of motion as well. The inelastic time history analysis is the most accurate method to predict the force and deformation demands at various components of the structure 5.5 Nonlinear Static Analysis or Pushover Analysis The static pushover analysis is becoming a popular tool for seismic performance evaluation of existing and new structures. The expectation is that the pushover analysis will provide adequate information on seismic demands imposed by the design ground motion on the structural system and its components Page No:132

6 Table-1 General description and parameters Rectangular structure T-shape structure L-shape structure Plan dimension 3mx2m 4mx24m 35mx24m Total height of the building 29m 29m 29m Typical story height 3m 3m 3m Bottom story height 2m 2m 2m Height of parapet 1.m 1.m 1.m Size of beam 4mmx6mm 4mmx6mm 4mmx6mm Size of column 6mmx75mm 6mmx75mm 6mmx75mm Thickness of slab 15mm 15mm 15mm Wind speed 5m/s 5m/s 5m/s Soil condition Medium soil Medium soil Medium soil Damping ratio 5% 5% 5% Live load at all floors 3. kn/m 3. kn/m 3. kn/m Grade of concrete M25 M25 M25 Grade of reinforcing steel Fe415 Fe415 Fe415 Density of concrete 25kN/m 25kN/m 25kN/m Density of reinforcement bars 77kN/m 77kN/m 77kN/m Code used for RCC design IS 456:2 IS 456:2 IS 456:2 Page No:133

7 Rectangular shape structure Fig-1 Fig-2 Mode Shape Pushover Analysis Results for Rectangular shape structure in different seismic zones The resulting pushover curve for the three seismic zones of building is shown in Fig-1. The curve is initially linear but starts to deviate from linearity as the beams and columns undergo inelastic actions. When the building is pushed into the inelastic range, the curve become linear again but with a smaller slope. The curve could be approximated by a bilinear relationship 25 Fig-3 Base shear in X-direction Base Shear (kn) Page No:134

8 Fig-4 Base shear in Y-direction Base Shear (kn) Fig-5 Comparison of story drifts for Rectangular shape structure in different seismic zone Displaceme nt (mm) No of stories Page No:135

9 T- Shape structure Fig-6 Fig-7 Mode Shape Pushover Analysis Results of T- shape structure in different seismic zones The resulting pushover curve for the three seismic zones of building is shown in Fig 5. The curve is initially linear but starts to deviate from linearity as the beams and columns undergo inelastic actions. When the building is pushed into the inelastic range, the curve become linear again but with a smaller slope. The curve could be approximated by a bilinear relationship Base Shear (kn) Fig-8 Base shear in X-direction Displacement (m) Base Shear (kn) Fig-9 Base shear in Y-direction Page No:136

10 Fig-1 Comparison of story drifts of T-shape structure in different seismic zones Displaceme nt (mm) No of stories L-shape structure Fig-11 Fig-12 Mode Shape Pushover Analysis Results of L-shape structure in different seismic zones The resulting pushover curve for the three seismic zones of building is shown in Fig. The curve is initially linear but starts to deviate from linearity as the beams and columns undergo inelastic actions. When the building is pushed into the inelastic range, the curve become linear again but with a smaller slope. The curve could be approximated by a bilinear relationship Page No:137

11 Fig-13 Base shear in X-direction 25 2 Base Shear (kn) Fig-14 Base shear in Y-direction Base Shear (kn) ZONEV Page No:138

12 Fig-15 Comparison of story drifts of L-shape structure in different seismic zones Displaceme nt (mm) No of stories Spectral Acceleration for different shape structures in seismic zonev The response spectrum analysis was carried out for the seismic zone V and their respective design spectrum showing spectral acceleration co efficient varying with period is shown in figure 5. The acceleration experienced by the buildings is least in rectangular structure and highest in T-shape structure as evident from the graph below. Spectral Acceleration Cofficient (Sa/g) PERIODS (S) T-SHAPE L-SHAPE RECTANGULAR Fig-16 Time History Analysis Results for different shape structures in seismic zonev Page No:139

13 2 15 Base Force (FX) kn T-SHAPE L-SHAPE RECTANGULAR Time (sec) Fig-17 Base Force VS time CONCLUSIONS The major objective of the present study was to understand the effect of the reinforced concrete building structure in different seismic zones. From the analysis results, it has been observed that the base shear increases with the increase seismic zone of the building. Time period and displacement of the structure increases with the increase in seismic zone. It has also been observed that spectral acceleration is increases and spectral displacement is increased as with the increase seismic zone.. The response spectrum analysis was carried out for the three seismic zones and their respective design spectrum showing spectral acceleration co efficient varying with period is shown in figure 5. The acceleration experienced by the buildings is least in seismic zone III and highest in zone V as evident from the graph below. The peak acceleration co efficient for zone III, IV & V is.16,.24, and.36 respectively. The Time History analysis was carried out for the three seismic zones. The base force is more in seismic zone V and least in seismic zone III. Time history method of analysis when used shall be based on an appropriate ground motion and shall be performed using accepted principles of dynamics. The performance of reinforced concrete frames was investigated using the pushover Analysis. These are the conclusions drawn from the analysis: The pushover analysis is a relatively simple way to explore the non-linear behavior of Buildings. When earthquake load is applied, it was found that structure in seismic zone V has more base shear compared to seismic zone III and IV. But the percentage increment is acceptable. The results obtained in terms of demand, capacity spectra shows real behavior of structures. It was also found that storey displacements are higher in seismic zone V than in seismic zone III and IV Pushover analysis showed actual nonlinear behavior of the structure which helps in performance based seismic design of structure. Page No:14

14 When earthquake load is applied, it was found that irregular structure in seismic zone V has more base shear compared to rectangular structure. But the percentage increment is acceptable. The results obtained in terms of demand, capacity spectra shows real behavior of structures. ACKNOWLEDGEMENT I am extremely fortunate to work under the guidance of Prof.D.R.S.MURTY, Professor & Head of the Department, Department of Civil Engineering, ANDHRA UNIVERSITY for giving me an opportunity to work in the area of Deign of Buildings in different seismic zones. He provided an insight of the project and extended his extraordinary guidance and support during the entire course of work. REFERENCES 1) PUSHOVER ANALYSIS OF A 19 STORY CONCRETE SHEAR WALLBUILDING Rahul RANA1, Limin JIN2 and Atila ZEKIOGLU 2) COST MODELING OF REINFORCED CONCRETE BUILDINGS DESIGNED FOR SEISMIC EFFECTSV.Thiruvengadam1 J.C.Wason2 Lakshmi Gayathri3 3) COST MODELING OF FOUNDATIONS OF REINFORCED CONCRETE BUILDINGS DESIGNED FOR SEISMIC EFFECTS V. Thiruvengadam1, J. C. Wason2 and K. I. Praseeda3 1Professor, Dept. of Building Engineering and Management, School of Planning and Architecture, New Delhi. 4) International Journal of Innovative Research in Science, Engineering and Technology (An ISO 3297: 27 Certified Organization) Vol. 4, Issue 1, October 215 Copyright to IJIRSET DOI:1.1568/IJIRSET Seismic Demand Study on RC Structural Systems using Pushover Analysis An Overview S.Devi 1, Dr.G.Nandini Devi 2 5) International Journal of Innovative Research in Science, Engineering and Technology (An ISO 3297: 27 Certified Organization) Vol. 4, Issue 8, August 215, copyright to IJIRSET DOI:1.1568/IJIRSET , Comparative Static and Dynamic Study on Seismic Analysis of Uniform and Non Uniform a. Column Sections in a Building b. Santosh Kumar Adhikari1, Dr K. Rajasekhar 2 6) SEISMIC ANALYSIS AND DESIGN OF BUILDING STRUCTURES WITH i. SUPPLEMENTAL LEAD DAMPERS b. Xi LIN1, Peter J MOSS2 And Athol J CARR3 7) Pushover Analysis of Medium Rise Multi-Story RCC Frame With and Without Vertical Irregularity Mohommed Anwaruddin Md. Akberuddin*, Mohd. Zameeruddin Mohd 8) Pushover Analysis of Structures with Plan Irregularity Prof. Milind V. Mohod 9) Earthquake Resistant Design of Structures S.K.duggal 1) Analysis and Design of Multi Storied Building by Using Etabs Software 11) Methods for Earthquake Analysis Helge Dørheim 12) Earthquake Analysis of Multi Storied Residential Building - A Case Study E. Pavan Kumar1, A. Naresh2, M. Nagajyothi3, M. Rajasekhar4 13) Pushover Analysis of Reinforced Concrete Structures S. C. Pednekar P. G. Student Department of Civil Engineering Datta Meghe College of Engineering Airoli, Navi Mumbai H. S. Chore Professor and Head Department of Civil Engineering Datta Meghe College of Engineering Page No:141

15 Airoli, Navi Mumbai S. B. Patil Assistant Professor Department of Civil Engineering Datta Meghe College of Engineering Airoli, Navi Mumbai 14) Non-Linear Static Analysis (Pushover Analysis) A Review Nishant Rana, Siddhant Rana 15) Non-Linear Static Analysis of Multi-Storied Building Srinivasu. A1, Dr. Panduranga Rao. B2 16) NON LINEAR STATIC PUSHOVER ANALYSIS OF IRREGULAR SPACE FRAME STRUCTURE WITH AND WITHOUT T SHAPED COLUMNS Govind M1, Kiran K. Shetty2, K. Anil Hegde3 17) COMPARATIVE STUDY OF RC FRAMED STRUCTURES USING SPECTRA BASED PUSHOVER ANALYSIS Pavan Kumar N1, Avinash Gornale2, Gargi G S3, B G Naresh Kumar4 18) SEISMIC RESPONSE OF BUILDINGS WITH RE - ENTRANT CORNERS IN DIFFERENT SEISMIC ZONES Shreyasvi C1, B. Shivakumaraswamy2 19) Seismic analysis of RC regular and irregular frame structures Arvindreddy1, R.J.Fernandes2 THE STATE OF THE ART IN SEISMIC HAZARD ANALYSIS I.D. Gupta Central Water & Power Research Station Khadakwasla, Pune ) PERFORMANCE-BASED SEISMIC DESIGN OF 3D R/C BUILDINGS 21) USING INELASTIC STATIC AND DYNAMIC ANALYSIS Andreas J. Kappos and Georgios Panagopoulos Department of Civil Engineering Aristotle University of Thessaloniki Thessaloniki, Greece 22) NIST GCR Nonlinear Structural Analysis For Seismic Design A Guide for Practicing Engineers Gregory G. Deierlein Andrei M. Reinhorn Michael R. Willford 23) ADVANCED SEISMIC ANALYSIS METHODS AND APPLICATION TO EARTHQUAKE DAMAGED BUILDINGS STRENGTHENING DESIGN Zheng Ping Wu1 Page No:142