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Performance Based Design Presentation By Deepak Bashetty

  1. 1. 1 DEPARTMENT OF CIVIL ENGINEERING MANIPAL INSTITUTE OF TECHNOLOGY Deepak S Bashetty Reg.No:060918003 PERFORMANCE BASED SEISMIC ANALYSIS OF RC BUILDINGS Under the Guidance of     Mr.S.VEERAMANI                                       Dr.KRISHNAMOORTHY Chief Engineering Manager (Civil) Professor, Engineering Design Research Centre Department of Civil Engineering (Building & Factories Sector) Manipal Institute of Technology, ECC Division L&T, Chennai – 600089 Manipal –576 104 External Guide Internal Guide
  2. 2. 2 Contents 1. Introduction 2. Methods of analysis 3. Modeling Approach 4. Details of Analysis 5. Result and Discussion 6. Conclusion 7. References
  3. 3. 3 Introduction
  4. 4. 4 Performance-based Design  The basic concept of performance based seismic design is to provide engineers with the capability to design buildings that have a predictable and reliable performance in earthquakes.  Thus the Performance-based seismic design is a process that permits design of new buildings or upgrade of existing buildings with a realistic understanding of the risk of life, occupancy and economic loss that may occur as a result of future earthquakes.
  5. 5. 5 Performance-based design begins with the selection of design criteria stated in the form of one or more performance objectives. Each performance objective is a statement of the acceptable risk of incurring specific levels of damage, and the consequential losses that occur as a result of this damage, at a specified level of seismic hazard.
  6. 6. 6 Performance Objectives Fully Operational, Operational Immediate-occupancy, life-safety and collapse-prevention
  7. 7. 7 Selecting Performance Present Generation Beer!Beer! Food! Operational Operational – negligible impact on building Beer!Beer! Food!Food! Joe’s Beer!Beer! Food!Food! Beer!Beer! Food! Joe’s Immediate Occupancy Immediate Occupancy – building is safe to occupy but possibly not useful until cleanup and repair has occurred Beer!Beer! Food!Food! Joe’s Beer!Beer! Food!Food! Beer!Beer! Food! Life Safety Life Safe – building is safe during event but possibly not afterward Collapse Prevention CollapsePrevention–building is onvergeof collapse, probabletotal loss
  8. 8. 8 Performance based design Performance Levels Building Damage States Immediate occupancy Life safety Collapse prevention Displacement parameter Force parameter Demand for specific hazard level
  9. 9. 9 A simple flow chart explaining the “Performance based design”
  10. 10. 10 Determination of Performance Point
  11. 11. 11 Generally, a team of decision makers, including the building owner, design professionals, and building officials, will participate in the selection of performance objectives for a building. Once the performance objectives are set, a series of simulations (analyses of building response to loading) are performed to estimate the probable performance of the building under various design scenario events. If the simulated performance meets or exceeds the performance objectives, the design is complete otherwise it has to be redesigned.
  12. 12. 12 Advantages of Performance Based Seismic Design Systematic methodology for assessing the performance capability of a building Design individual buildings with a higher level of confidence Design individual buildings to achieve higher performance and lower potential losses. Design individual buildings that fall outside of code-prescribed limits with regard to configuration, materials, and systems to meet the performance intended by present building codes Assess the potential seismic performance of existing structures and estimate potential losses in the event of a seismic event. Performance-based seismic design offers society the potential to be both more efficient and effective in the investment of financial resources to avoid future earthquake losses
  13. 13. 13 Differences between traditional approach and performance based approach 1) Conventional limit-states design is typically a two-level design approach having concern for the service operational and ultimate-strength limit states for a building, performance- based design can be viewed as a multi-level design approach that additionally has explicit concern for the performance of a building at intermediate limit states related to such issues as occupancy and life-safety standards. 2) The performance based analysis is based on quantifying the deformation of the members and the building as a whole, under the lateral forces of an earthquake of a certain level of seismic hazard. Traditional Approach-Force based Design has no measure of the deformation capability of members or of building.
  14. 14. 14 3) The deformation or strains are better quantities to assess damage than stress or forces. Since the deformation are expected to go beyond the elastic values. 4) The performance based analysis gives the analyst more choice of ‘performance’ of the building as compared to the limit states of collapse and serviceability in a design based on limit state method. 5)Traditional based design uses Elastic behavior where as Performance based design uses inelastic behavior
  15. 15. 15 Methods of analysis
  16. 16. 16 Methods of analysis Generally for analyzing the structure the following analysis methods are used depending upon the requirements. 1) Linear static procedure 2) Linear dynamic procedure 3) Nonlinear static procedure 1. Pushover analysis 2. Capacity spectrum method 4) Nonlinear dynamic procedure 1. Time history Analysis Push-over and Time History analyses tools to perform non-linear analysis are considered.
  17. 17. 17  pushover analysis is the one which is suitable for the performance based seismic design, because elastic analyses are insufficient, therefore they cannot realistically predict the force and deformation distributions after the initiation of damage in the building.  Inelastic analytical procedures become necessary to identify the modes of failure and the potential for progressive collapse.  Inelastic time-history analysis are most realistic analytical approach for evaluating the performance of a building. However, the inelastic time-history analysis is usually too complex and time- consuming in the design of most buildings.
  18. 18. 18 What is Push-Over Analysis? • Push-over analysis is a technique by which a computer model of the building is subjected to a lateral load of a certain shape (i.e., parabolic, inverted triangular or uniform). • Building is pushed in one horizontal direction. The intensity of the lateral load is slowly increased and the sequence of cracks, yielding, plastic hinge formations, and failure of various structural components is recorded. • Proportion of applied force on each floor is constant , only its magnitude is increased gradually (i.e., Load pattern may be 1st mode shape, parabolic, uniform, inverted triangular etc.). • Material nonlinearity is modeled by inserting plastic hinge at potential location.
  19. 19. 19 Continued… • A series of iterations are usually required during which, the structural deficiencies observed in one iteration, are rectified and followed by another. • This iterative analysis and design process continues until the design satisfies a pre-established performance criteria. • The performance criteria for push-over analysis is generally established as the desired state of the building given a roof-top or spectral displacement amplitude. • Push over analysis requires a large number of assumptions and member response curves are to be provided to the program before it can analyze.
  20. 20. 20 VB Δroof Δroof VB Continued…Continued…
  21. 21. 21 Why Push-Over Analysis? • Static Nonlinear Analysis technique, also known as sequential yield analysis, or simply "push-over" analysis. • To get the performance level of structure in case of seismic load. • Elastic analysis cannot predict failure mechanism and account for redistribution of forces during progressive yielding. • The use of inelastic procedure for design and evolution is an attempt to help engineer better understand how structures will behave when subjected to major EQ, where it is assumed that the elastic capacity of the structure will be exceeded.
  22. 22. 22 What is Time History Analysis? • Time History analysis is a step by step analysis of the dynamical response of a structure to a specified loading that may vary with time. • The performance analysis may be – Linear – Non-linear
  23. 23. 23 Why Linear Time History Analysis? • To get the variation of forces at each time step and to get the maximum response under the the particular time history. • To verify the design of structure. If forces in the member are within the design forces, then no need to do Non- Linear time history analysis. • If the forces are exceeding the design forces, then Non-Linear time history analysis is required to understand the performance of structure.
  24. 24. 24 Why Non-Linear Time History Analysis? • Elastic analysis cannot predict failure mechanism and account for redistribution of forces during progressive yielding. • Certain part may yield when subject to major earthquake. • To get the performance level of structure in case of seismic load. • The use of inelastic procedure for design and evolution is an attempt to help engineer to better understand how the structures will behave when subjected to major EQ.
  25. 25. 25 Pushover Analysis Procedure Create 2D/3D Model Assign end offsets Design Structure Assign Hinge properties Beams – M3, V2 Columns –PMM, V2 Define Static Pushover Cases Gravity Pushover (Force controlled) Lateral Pushover (Displacement controlled) Define Load case (Lateral Load at centre of mass) Analyze Run analysis, Run Now Establish Performance point Base shear Vs Roof Displacement Sequential Hinge Formation
  26. 26. 26 Performance Analysis Create Model as Designed Define Time History Function Define Linear Time History cases Analyze Check Member Forces ≤ Design Force Define Non linear Time History Case Assign Plastic Hinges (Material Nonlinearity) Define Geometric Nonlinearity Analyze Results Check the performance of the structure and if required, redesign YESYES NoNo  Material nonlinearity is modeled by inserting plastic hinge at potential location.
  27. 27. 27 Modeling
  28. 28. 28 Modeling of Beams and Columns • 3D Frame Elements • Cross Sectional dimensions, reinforcement details, material type • Effective moment of inertia (As per ATC 40) Beams Rectangular 0.5 Ig T-Beam 0.7 Ig L-Beam 0.6 Ig Columns 0.7 Ig
  29. 29. 29 Modeling approach Lp = 0.5H Location of hinges in beams and columns: • Beam & column elements - nonlinear frame elements with lumped plasticity - defining plastic hinges at both ends of the beams and columns. lcolumn Dcolumn lbeam Dbeam Moment and shear hinge Axial-moment and shear hinge L = Critical distance from critical section of plastic hinge to point of contra flexure fye = yield strength of transverse reinforcement dbl= diameter of transverse reinforcement
  30. 30. 30 Modelling Approach • Plastic hinge is defined in terms of Force-deformation behaviour of the member. • Values are depend on type of element, material properties, longitudinal and transverse steel content - axial load level on the element. • For beam, flexural hinge is assigned • For Column, axial and flexural hinges are assigned • A-unloaded condition, B-effective yield, C-ultimate strength, D- residual strength and E-maximum deformation Force-deformation Relationship of a Typical Plastic Hinge
  31. 31. 31 EXAMPLE-1
  32. 32. 32 Description of Structure Building Type RC frame without brick infill Concrete compressive strength Yield Strength of reinforcement – 25 MPa – 415 MPa Number of stories Ground + 5 Storey Plan dimensions 16 m × 12 m Building height 24.775 m above plinth level Type of footing Raft footing (fixed) •Seismic performance - inter-storey drift ratio, ductility, maximum base shear, roof displacement and plastic hinge formation.
  33. 33. 33 Column Dimensions and Area of Longitudinal Reinforcement Column Label Cross Section mm x mm Acol (mm2 ) 1 & 9 300 x 500 5892 2 & 10 300 x 500 4020 3 & 11 300 x 400 3216 4 & 12 300 x 300 3080 21& 23 300 x 300 1232 24& 26 300 x 300 905 27& 29 300 x 300 905 5 650 x 650 14784 6 600 x 600 12744 7 550 x 550 10620 8 500 x 500 7856 22 450 x 450 6372 25 300 x 300 4928 28 300 x 300 804 Acol = Area of longitudinal reinforcement in column The beam in all storey levels is of size 300mm x 600mm with tension and compression reinforcements of 3885mm2 and 2412mm2 respectively. The column dimensions and area of longitudinal reinforcement (Acol) details are presented in Table
  34. 34. 34 Details of Analysis • Pushover Analysis  Gravity analysis is an Force controlled.  Pushover analysis is a Displacement controlled.  Behaviour of structure characterized by capacity curve (base shear force Vs. roof displacement) • Time-History Analysis  Step by step analysis of the dynamical response of structure to a time varying load.  7 sets of strong ground motion in the magnitude range of 6.5-7.5 were selected.  The peak displacement from NTH is not correspond to ultimate displacement from pushover analysis.  To facilitate comparison the ground motion records scaled according to peak roof displacement =target displacement
  35. 35. 35 Input Ground Motions EQ No. Year Earthquake Recording Station Magnit ude PGA in g EQ. Scale Factor DBE MCE 1 1979 El Centro Array #7 7.0 0.338 0.45 0.785 2 1999 Duzce Turkey 7.1 0.348 0.8 1.15 3 1971 San Fernando Old Ridge 6.5 0.268 1.7 1.9 4 1995 Kobe KJM 6.9 0.343 0.35 0.5 5 1976 Friuli Tolmezzo 6.5 0.315 0.95 1.2 6 1994 Northridge Arleta 6.7 0.344 0.6 1.0 7 1989 Loma Prieta Gilroy #2 7.1 0.322 0.35 0.515
  36. 36. 36 Base shear • Maximum base shear - 571kN - 10% of seismic weight - displacement corresponding to base shear - 1.02m. • Displacement ductility - 2.32. • Base shear values - DBE & MCE levels from Pushover analysis - 116 kN & 171kN • From NTH - 151kN & 51kN. • Results from NTH are 23% & 32% higher than pushover analysis.
  37. 37. 37 Target Displacement • Represent the maximum displacement likely to be experienced during the design earthquake • Performance levels are calculated based on equation from FEMA 356. C0 = Modification factor to relate spectral displacement of an equivalent SDOF system to the roof displacement of building MDOF system C1 = Modification factor to relate expected maximum inelastic displacements to displacements calculated for linear elastic response C2 = Modification factor to represent the effect of pinched hysteretic shape, stiffness degradation and strength deterioration on maximum displacement response C3 = Modification factor to represent increased displacements due to dynamic P- ∆ effects Te = Effective fundamental period of building, sec Sa = Response Spectrum Acceleration at effective fundamental period and damping ratio of building g 4 T SCCCC 2 2 e a3210t π =δ
  38. 38. 38 Performance Point • Intersection of capacity & demand spectrum. • Performance assessed for two levels of performance - Life Safety (LS) under Design Basis Earthquake (DBE) & Collapse Prevention (CP) under Maximum Considered Earthquake (MCE). • Base shear, roof displacement, spectral acceleration, spectral displacement, effective time period and effective damping - performance point - shown. • Displacement @ performance point in DBE level - 123mm greater than target displacement 119mm. • Displacement @performance point in MCE level - 171mm lesser than target displacement 177mm.
  39. 39. 39 Demand Vs Capacity Spectrum DBE Level MCE Level Demand SpectrumDemand Spectrum Capacity SpectrumCapacity Spectrum
  40. 40. 40 • Important indicator of building performance. • 3rd storey level- the largest interstorey drift values -0.58% and 0.85% at both DBE and MCE levels. • Interstorey drift ratio - increased with increase in storey level up to first 4 stories - thereafter - reverse trend at both levels of earthquake. • DBE level - pushover analysis over-estimated - interstorey drift ratio - lower storey levels - underestimated - upper storey levels. • MCE level -pushover analysis -over-estimated - interstorey drift ratio - all storey levels. Interstorey Drift htStoreyHeig ntfloorsntofadjaceDisplaceme izontallativedHorRe ydriftInterstore =
  41. 41. 41 0 1 2 3 4 5 6 7 0.00 0.20 0.40 0.60 0.80 1.00 Interstorey drift in % StoreyLevel DBE MCE (a) Results from Pushover Analysis at DBE & MCE Levels 0 1 2 3 4 5 6 7 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Intersotrey drift in % StoreyLevel NTH-DBE NSP-MCE NSP-DBE NTH-MCE (b) Comparison between Pushover & Time-history Results at DBE & MCE Levels 0 1 2 3 4 5 6 7 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Interstorey Drift Ratio in % StoreyLevel Elcentro Duzce San Fernando Friuli,Italy Kobe Northridge LomaPrieta Average 0 1 2 3 4 5 6 7 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Interstorey Drift Ratio in % StoreyLevel Elcentro Duzce San Fernando Friuli,Italy Kobe Northridge LomaPrieta Average (a) Results from Time-history Analysis at DBE Level (b) Results from Time-history Analysis at MCE Level Figure 8.6 Interstorey Drift Ratios from Time – history Analysis Figure 8.5 Interstorey Drift Ratios
  42. 42. 42 Plastic Hinge Pattern • Pushover analysis • Outer columns at all storey level yielded first • Beams showing hinges in yielding stage at one end only in the DBE level • Beams in the MCE Level at all the storey levels except topmost showing hinges in yielding stage. • Time History Analysis • More number of hinges at yielding in beam ends model compared to pushover analysis at both DBE and MCE levels. • At MCE level middle columns in upper stories also yielded; but in the pushover analysis not showing hinges in any column.
  43. 43. 43 Plastic Hinge Pattern at DBE Level (a) Pushover Analysis (b) Time History Analysis
  44. 44. 44 Plastic Hinge Pattern at MCE Level (a) Pushover Analysis (b) Time History Analysis
  45. 45. 45 Plastic Hinge Pattern • Pushover analysis  At final step (frame roof pushed up to 4% of height of frame) - hinge formation started with yielding in outer columns at all stories  and yielding of few beam ends in upper stories.  Middle columns in the upper stories start yielding with simultaneous yielding of base columns.  Beams experienced less number of hinges than columns but shows significant damage or failure stage.
  46. 46. 46 Conclusions • Base shear from time history analysis are 23% and 32% higher than pushover analysis at DBE and MCE levels. • Roof displacement at DBE and MCE levels indicates that frame satisfies the requirement for Life Safety performance at DBE level and not satisfies the requirement for Collapse Prevention performance at MCE level. • From analyses the middle storey experience the maximum interstorey drift ratio at both levels. • Pushover analysis over estimate the interstorey drift ratio compared with time history analysis
  47. 47. 47 • No significant difference of plastic hinge pattern at DBE and MCE levels from both analyses • Time-history analysis shows more number of beam hinges at both levels. • From time history analysis at MCE level, middle column shows yielding but not in pushover analysis. • The behaviour of frame designed for gravity load shows column side sway mechanism. Conclusions
  48. 48. 48 EXAMPLE-2
  49. 49. 49 Description of Structure A regular four storeyed (G+3), five storeyed (G+4), six storeyed (G+5) and a seven storeyed (G+6) building were considered in the present study. All the buildings are rectangular in plan with same plan dimensions and storey height. The plan view and sectional elevation of a G+3 building is shown in Figure.
  50. 50. 50 Figure: Comparison of Variation of Fundamental Time Period using Time History Analysis Figure :Comparison of Variation of Roof Displacement using Time History Analysis Results
  51. 51. 51 • Analysis results shows that, hinges will be formed earlier in frames of structures without strut action than frames of structures with strut action • It is observed that, in all the cases, the fundamental time period of the structure with strut action is considerably less than the structures without strut action. • Figure, compares the roof displacement of G+3, G+4, G+5 and G+6 frames with and without strut action. • The graph shows that roof displacement get considerably (50%) reduced with strut action.
  52. 52. 52 CONCLUSIONS From the pushover and time-history analyses of 2D RC frames with infill, the following conclusions are drawn: • It is found that the fundamental time period of the structure get considerably reduced due to strut action. This will alter the response of the structure to lateral loads. • In addition strut action will considerably reduce the roof displacement. This will increase the safety level of the structure. • Hence it is recommended to model infill stiffness using equivalent diagonal struts for any lateral load analysis.
  53. 53. 53 References 1. Ali M. Memari, Shahriar Rafiee, Alireza Y. Motlagh and Andrew Scanlon (2001), “ComparativeEvaluation of Seismic Assessment Methodologies Applied to a 32-Story Reinforced Concrete Office Building”, Journal of Seismology and Earthquake Engineering, Vol. 3 ,No.1, 31-44. 2. Andreas J. Kappos, Alireza Manafpour (2001), “Seismic design of R/C buildings with the aid of advanced analytical techniques”, Engineering Structures, 23, 319–332 3. Chung C. Fu and Hamed AlAyed, “Seismic Analysis of Bridges Using Displacement-BasedApproach”, 1-20. 4. Federal Emergency Management Agency, Prestandard and Commentary for the Seismic Rehabilitation of Buildings (FEMA 356), Washington D.C. November 2000.
  54. 54. 54 Contd… 5. IS 456-2000, Indian Standard Plain and Reinforced Concrete - code of practice, Bureau of Indian Standards. 6. IS 1893 (Part 1) – 2002, Indian Standard Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards. 7. Mehmet Inel, Hayri Baytan Ozmen, (2006) “Effects of plastic hinge properties in nonlinear analysis of reinforced concrete buildings”, Engineering Structures, 28, 1494–1502. 8. SAP2000. Linear and nonlinear static and dynamic analysis and design of structures. Ver.10.0. Berkeley (CA, USA): Computers and Structures, Inc. 9. Sashi K. Kunnath and Erol Kalkan (2004), “Evaluation of Seismic Deformation Demands using Nonlinear Procedures in Multistory Steel and Concrete Moment Frames”, ISET Journal of Earthquake Technology, Paper No. 445, Vol. 41, No. 1, March 2004, pp. 159-181 10. ATC 40 (1996), “Seismic Evaluation and Retrofit of Concrete Buildings”, Applied Technology Council, USA, Vol.1.
  55. 55. 55
  56. 56. 56 Moment curvature relationship for singly reinforced sections
  57. 57. 57 Finding Mcr & Φcr Values ( ) bc cr cr bt tstt ckcr cr cr yE f yyD ydmA D ybDbDI ff y If M = += −+      −+= = = φ 2 2 3 2 7.0
  58. 58. 58 Finding M-Φ values • Assume ec • Find k1& k2 for corresponding ec • Assume initially a value for kd , now • Compare the assumed kd & the calculated kd. If matching take that value , otherwise try with new kd. ( ) sstck sss cs fAbkdfkk Ef kd kdd = = − = 31 ε εε
  59. 59. 59 Finding M-Φ values (cont…) ( )kdkdbkdfkkM ck 231 −= kd cε φ= εc < εo < εu εo < εc < εu η εc /εo εo /εc k1 η - η2 /3 1 - η/3 k2 (1/3 −η/12)/(1−η/3) (6−4η + η2 )/(12 − 4 η)
  60. 60. 60 Stress block 0.002 0.0035 kd fc k2kd T C=C3fckbkdC1
  61. 61. 61 Stress block parameters 002.00 002.0002.0 2446.0 2 ≤<               −      = c cc ckc ff ε εε  0035.0002.01 002.0 25.01446.0 2 ≤<               −−= c c ckc ff ε ε 
  62. 62. 62 Section considered for calculating M- Φ relationship Assumed 25 mm clear cover All dimensions in mm
  63. 63. 63 εc M Φ start 0 0 cracked 8033504.196 9.74069E-07 0.0005 8283594.419 4.05201E-06 0.001 15378489.83 7.84424E-06 0.0015 21200915.35 1.13588E-05 0.002 25649262.16 1.45742E-05 0.0025 27587840.7 1.85134E-05 0.003 28996952.56 2.22161E-05 0.0035 29959200.87 2.59188E-05 M-Φ values for the section considered M in Nmm & Φ in rad/mm M-Phi 0 5000000 10000000 15000000 20000000 25000000 30000000 35000000 0 0.000005 0.00001 0.000015 0.00002 0.000025 0.00003 Phi M
  64. 64. 64 Comparison of M-Φ values for different pt values. M in Nmm & Φ in rad/mm M-Phi 0 5000000 10000000 15000000 20000000 25000000 30000000 35000000 0 5E-06 0.00001 1.5E-05 0.00002 2.5E-05 0.00003 3.5E-05 0.00004 4.5E-05 Phi M 0.25% 0.50% 0.75% 0.96%

Editor's Notes

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    The damage evaluation procedures are performance-based; that is, they measure acceptability (and changes in acceptability) on the basis of the degree to which a structure achieves one or more performance levels for the hazard posed by one or more hypothetical future earthquakes. A performance level typically is defined by a particular damage state for the components of a building. Commonly-used performance levels, in order of decreasing amounts of damage, are Collapse Prevention, Life Safety, and Immediate Occupancy. Hazards associated with future hypothetical earthquakes commonly are defined in terms of ground shaking intensity with a certain likelihood of being exceeded over a defined time period, or in terms of a characteristic earthquake likely to occur on a given fault. The combination of a performance level and a hazard defines a Performance Objective. For example, a common Performance Objective for a building is that it maintain Life Safety for ground motion with a ten percent chance of exceedance in fifty years.