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Fawad NajamSuivre

2 Apr 2016•0 j'aime•7,425 vues

2 Apr 2016•0 j'aime•7,425 vues

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Ingénierie

CE 72.32 (January 2016 Semester) Lecture 8 - Structural Analysis for Lateral Loads

Fawad NajamSuivre

CE 72.32 (January 2016 Semester): Lecture 1b: Analysis and Design of Tall Bui...Fawad Najam

CE 72.32 (January 2016 Semester) Lecture 2 - Design PhilosophyFawad Najam

CE 72.32 (January 2016 Semester) Lecture 7 - Structural Analysis for Gravity ...Fawad Najam

CE 72.32 (January 2016 Semester) Lecture 3 - Design Criteria Fawad Najam

Aitc step by-step procedure for pbd of 40-story rc building_overall (20141105)Ramil Artates

CE72.52 - Lecture1 - IntroductionFawad Najam

- 1. Dr. Naveed Anwar Executive Director, AIT Consulting Affiliated Faculty, Structural Engineering Director, ACECOMS Design of Tall Buildings AIT Hybrid Learning System
- 2. Dr. Naveed Anwar Executive Director, AIT Consulting Affiliated Faculty, Structural Engineering Director, ACECOMS Lecture 9: Structural Analysis for Lateral Loads Design of Tall Buildings
- 3. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • Analysis for Earthquake – Basic Elements of Seismology – The Seismic Analysis Problem – Forces generated by Earthquakes – Vertical and Horizontal Regularity – Seismic Analysis Methods • Analysis Using Equivalent Static Load • Analysis Using Response Spectrum • Analysis Using Acceleration Time History – Capacity Design Approach – Earthquake Analysis using ETABS and SAP 2000 Lecture Contents • Analysis for Wind – The Wind Analysis Problem – Bluff Body Aerodynamics – Wind Effects on Tall Buildings – Analysis Using Equivalent Static Load – Combining Response for Member Design 3
- 4. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Analysis for Earthquake 4
- 5. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Basic Elements of Seismology 5
- 6. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Earth Inside the EarthSource: Murty (2004) 6
- 7. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Dip Slip (normal or thrust) Strike Slip (right or left lateral) Four Basic Types of Faults A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. Source: Murty (2004) 7
- 8. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Theory of Continental Drift An earthquake is caused by the rebound of elastically strained rock. Elastic Rebound Theory Source: httap://www.seismo.unr.edu 8
- 9. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Plate Tectonics Source: Murty (2004) 9
- 10. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Convergence plate boundary: Subduction zone, etc. Divergence plate boundary: Plates diverges at mid-ocean ridges Transform fault: Plates move laterally past each other Earth’s 14 Lithospheric Plates and Their Movements Source: Murty (2004) 10 Earth’s Changing Landscape
- 11. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Waves Body Wave Surface Wave 11
- 12. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 12
- 13. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 13 Arrival of Seismic Waves at a Site Source: Murty (2004)
- 14. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 14 Basic Terminology Reducing illumination with distance from an electric bulb Electric Bulb Analogy Source: Murty (2004)
- 15. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Classifying the Earthquakes Terminology used to define earthquake Maximum Credible Earthquake (MCE) Maximum Design Earthquake (MDE) Safe Shutdown Earthquake (SSE) Contingency Level Earthquake (CLE) Ductility Level Earthquake (DLE) Operating Basis Earthquake (OBE) Maximum Probable Earthquake (MPE) Strength Level Earthquake (SLE) 15
- 16. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 16 • Maximum Credible Earthquake (MCE) – Earthquake associated with specific seismotectonic structures, source areas or provinces that would cause the most severe vibratory ground motion or foundation dislocation capable of being produced at the site under the currently known tectonic framework – Determined by judgment based on all known regional and local geological and seismological data – Little regard is given to its probability of occurrence, which may vary from less than a hundred to several tens of thousands of years Classifying the Earthquake
- 17. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 17 • Maximum Design Earthquake (MDE) – Represents the maximum level of ground motion for which the structure should be designed or analyzed. • Safe Shutdown Earthquake (SSE) – The maximum earthquake potential, for which certain structures, systems, and components, important to safety, are designed to sustain and remain functional (used in the design of nuclear power plants) • Contingency Level Earthquake (CLE) – Earthquake that produces motion with a 10% probability of exceedance in 50 years. For this event, the structure may suffer damage, however, life safety is protected. Classifying the Earthquake
- 18. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 18 • Operating Basis Earthquake (OBE) – EQ for which the structure is designed to resist and remain operational. – The OBE is usually taken as an: • EQ producing the maximum motions at the site once in 110 years (recurrence interval) • EQ with half the peak acceleration of SSE • EQ that produces motion with a 50% probability of exceedances in 50 years Classifying the Earthquake
- 19. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 19 • Maximum Probable Earthquake (MPE) – The maximum EQ that is likely to occur during a 100 year interval. • Strength Level Earthquake (SLE) – The maximum earthquake that is likely to occur during a 200 year interval – This earthquake is not anticipated to induce significant damage or inelastic response in the structural elements Classifying the Earthquake
- 20. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Seismic Analysis Problem 20
- 21. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Basic Equilibrium Equations • Linear-Static Elastic • Linear-Dynamic Elastic • Nonlinear - Static Elastic OR Inelastic • Nonlinear-Dynamic Elastic OR Inelastic 1FKu 2)()()()( tFtKutuCtuM 4)()()()()( tFtFtKutuCtuM NL 3FFKu NL 21
- 22. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Linear and Nonlinear • Linear, Static and Dynamic • Nonlinear, Static and Dynamic Non Linear Equilibrium FKu )()()()( tFtKutuCtuM )()()()()( tFtFtKutuCtuM NL FFKu NL 22
- 23. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Basic Analysis Types Excitation Structure Response Basic Analysis Type Static Elastic Linear Linear-Elastic- Static Analysis Static Elastic Nonlinear Nonlinear-Elastic- Static Analysis Static Inelastic Linear Linear-Inelastic- Static Analysis Static Inelastic Nonlinear Nonlinear-Inelastic- Static Analysis Dynamic Elastic Linear Linear-Elastic- Dynamic Analysis Dynamic Elastic Nonlinear Nonlinear-Elastic- Dynamic Analysis Dynamic Inelastic Linear Linear-Inelastic- Dynamic Analysis Dynamic Inelastic Nonlinear Nonlinear-Inelastic- Dynamic Analysis 23
- 24. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 24 • Non-linear Analysis – P-Delta Analysis – Buckling Analysis – Static Pushover Analysis – Fast Non-Linear Analysis (FNA) – Large Displacement Analysis • Dynamic Analysis – Free Vibration and Modal Analysis – Response Spectrum Analysis – Steady State Dynamic Analysis Special Analysis Types
- 25. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Comprehensive Equilibrium Equation )()()()()( tFtFtKutuCtuM NL • Cover all Static, Dynamic, Elastic, Non Elastic, Damped, Un-damped, Linear, Non-Linear cases and their combinations • Handles response for: – Basic Dead and Live Loads – Seismic, Wind, Vibration and Fire Analysis 25
- 26. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Comprehensive Equilibrium Equation FFKuuCuM NL Damping-Velocity Mass-Acceleration Stiffness-Displacement Nonlinearity External Force KuuCuM The basic variable is displacement and its derivatives 26
- 27. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Static Part Dynamic Part Static and Dynamic FFKuuCuM NL KuuCuM 27
- 28. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 28 • Static Excitation – When the excitation (load) does not vary rapidly with time – When the load can be assumed to be applied “slowly” • Dynamic Excitation – When the excitation varies rapidly with time – When the “inertial force” becomes significant • Most Real Excitation are Dynamic but are considered “Quasi Static” • Most Dynamic Excitation can be converted to “Equivalent Static Loads” Static versus Dynamic
- 29. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Linear and Non-Linear FFKuuCuM NL Linear Part Non-Linear Part KuuCuM 29
- 30. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Structure Stiffness - K Section Stiffness Member Stiffness Structure Stiffness Material Stiffness Cross-section Geometry Member Geometry Structure Geometry Linear Non-Linear 30
- 31. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Analysis FFKuuCuM NL Time History Analysis 0 KuuM EQNL FFKu Free Vibration Pushover Analysis EQFKu Equivalent Static Analysis EQFKu Response Spectrums Response Spectrum Analysis Acceleration Records guMKuuCuM 31
- 32. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar A SDOF System 32 Idealized SDOF system Un-damped free vibrations of SDOF system Damped free vibrations of SDOF system
- 33. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar A MDOF System 33 Representation of a multi- mass system by a single- mass system: (a) fundamental mode of a multi-mass system and (b) equivalent single-mass system.
- 34. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Forces Generated by Earthquakes 34
- 35. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 35 Schematic Representation of Seismic Forces
- 36. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 36 Concept of 100% g (1g) Linear Viscous Damper
- 37. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Force Reversal 37 Bilinear Force–displacement Hysteresis Loop
- 38. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Inertial Forces 38 Effect of Inertia in a building when shaken at its base Flow of seismic inertia forces through all structural components Source: Murty, (2004) Inertia force and relative motion within a building
- 39. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 39 The natural period values are only indicative; depending on actual properties of the structure, natural period may vary considerably. Fundamental natural periods of structures differ over a large range. Source: Murty (2004) Free vibration response of a building: the back-and- forth motion is periodic.
- 40. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 40 Different Buildings Respond Differently to Same Ground Vibration Building Behavior during Earthquakes Source: Murty (2004)
- 41. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Vertical and Horizontal Regularity 41
- 42. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 42 Simple plan shape buildings do well during earthquakes Buildings with one of their overall sizes much larger or much smaller than the other two, do not perform well during earthquakes Identical vertical members placed uniformly in plan of building cause all points on the floor to move by the same amount. Source: Murty (2004)
- 43. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 43 Sudden deviations in load transfer path along the height lead to poor performance of buildings. Source: Murty (2004)
- 44. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 44 Rope swings and buildings: both swing back- and-forth when shaken horizontally. The former are hung from the top, while the latter are raised from the ground. Even if vertical members are placed uniformly in plan of building, more mass on one side causes the floors to twist. Source: Murty (2004)
- 45. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 45 Buildings have unequal vertical members; they cause the building to twist about a vertical axis Source: Murty (2004)
- 46. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 46 Vertical members of buildings that move more horizontally sustain more damage Pounding can occur between adjoining buildings due to horizontal vibrations of the two buildings Source: Murty (2004)
- 47. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar This is what earthquakes do … (Click to watch) 47
- 48. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Tragic Side… 48 On 8 October 2005, an earthquake of magnitude 7.6 hit Islamabad, Pakistan, killing 30, 000 and seriously injuring another 60, 000 people. Some structures collapsed next to others of the same age that remained intact. This zone was classified as to be considered as only moderate. UBC 97 was applied by private consultants. Courtesy: L. A. Prieto Portar (2008), University of Florida
- 49. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Kashmir Earthquake (Oct 8, 2005) Magnitude = 7.7 Death Toll > 80,000 49
- 50. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Haiti Earthquake (2010) Magnitude = 7.0 Death Toll: 100,000 ~ 200,000 50
- 51. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 51 Upper storeys of open ground storey buildings move together as a single block – such buildings are like inverted pendulums. Soft Story Mechanism Source: Murty (2004)
- 52. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 52 Open ground storey building - assumptions made in current design practice are not consistent with the actual structure. Source: Murty (2004)
- 53. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Soft Story Failures 53
- 54. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Analysis Methods 54
- 55. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 55 • Linear Static Procedures – Equivalent Static Analysis • Nonlinear Static Procedures – Capacity Spectrum Method – Displacement Coefficient Method – Various Other Pushover Analysis Methods • Linear Dynamic Procedures – Response Spectrum Analysis – Linear Response History Analysis • Nonlinear Dynamic Procedures – Nonlinear Response History Analysis Seismic Analysis Procedures
- 56. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 56 • Study the Geology of the Region • Study the Past EQ Records • Prepare General Soil Profile • Potential Site Amplification of Ground Motion • Estimation of Soil Shear Wave Velocity (SWV) • Soil Classification Based on SWV • Estimation of Soil Dynamic Properties • Collect Information about Existing Buildings • Estimate/Measure Time Period of Buildings • Classify the Buildings in Terms of Risk • Develop Design Response Spectra Seismic Hazard Analysis Process
- 57. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Hazard Curve Seismic hazard curve for Bangkok (Warnitchai & Lisantono, 1996) 57
- 58. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Typical Dynamic Analysis Typical Dynamic Analysis Free Vibration Response Response to Harmonic Forces Response to Periodical Loading Response to Impulse Loading Ambient Vibration Response Response to Direct Dynamic Force Response to Earthquake Excitation 58
- 59. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 59 • Definition – Natural vibration of a structure released from initial condition and subjected to no external load or damping • Main governing equation - Eigenvalue Problem • Solution gives – Natural Frequencies – Associated mode shapes – An insight into the dynamic behavior and response of the structure Free Vibration Analysis tt tt PuKucuM
- 60. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Mode Shapes • A mode shape is a set of relative (not absolute) nodal displacement for a particular mode of free vibration for a specific natural frequency • There are as many modes as there are DOF in the system • Not all of the modes are significant • Local modes may disrupt the modal mass participation 60
- 61. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Modal Analysis • The modal analysis determines the inherent natural frequencies of vibration • Each natural frequency is related to a time period and a mode shape • Time Period is the time it takes to complete one cycle of vibration • The Mode Shape is normalized deformation pattern • The number of Modes is typically equal to the number of Degrees of Freedom • The Time Period and Mode Shapes are inherent properties of the structure and do not depend on the applied loads 61
- 62. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Modal Analysis • The Modal Analysis should be run before applying loads any other analysis to check the model and to understand the response of the structure. • Modal analysis is precursor to most types of analysis including Response Spectrum, Time History, Push-over analysis, etc. • Modal analysis is a useful tool even if full Dynamic Analysis is not performed. • Modal analysis is easy to run and is fun to watch when animated. 62
- 63. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 63 • The Time Period and Mode Shapes, together with animation immediately exhibit the strengths and weaknesses of the structure. • Modal analysis can be used to check the accuracy of the structural model – The Time Period should be within reasonable range, • (Ex: 0.1 x number of stories seconds) – The disconnected members are identified – Local modes are identified that may need suppression Application of Modal Analysis
- 64. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 64 • The symmetry of the structure can be determined – For doubly symmetrical buildings, generally the first two modes are translational and the third mode is rotational – If the first mode is rotational, the structural is un-symmetrical • The resonance with the applied loads or excitation can be avoided – The natural frequency of the structure should not be close to excitation frequency Application of Modal Analysis
- 65. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Modal Analysis Results 65 Translationin Minordirection TranslationinMajor direction Torsional • T1=5.32 sec • 60% in Minor direction • T6=1.28 sec • 18% in Minor direction • T9=5.32 sec • 6.5% in Minor direction • T2=4.96 sec • 66% in Major direction • T7=0.81 sec • 5.2% in Major direction • T4=1.56 sec • 15% in Major direction T3=4.12 sec T8=0.65secT5=1.30 sec
- 66. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Eccentric and Concentric Response Mode-1 Mode-2 Mode-3 Symmetrical Mass and Stiffness Unsymmetrical Mass and Stiffness 66
- 67. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • Damper is an energy absorbing element • Viscous damper is the most common • Energy is lost by heat, friction, damages, etc. • Free vibration of a damped system dies out gradually Damped System 67
- 68. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Damped Dynamic Response 68 Easy to Remember: 1, 2, 4 Cycle for 10, 5, 2.5 0 1 2 3 4 5 6 7 0.02 0.04 0.06 0.08 0.1 NoofCyclestoReducePeakAmplitudeby50% Damping Ratio Effect of Damping (Approximate)
- 69. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Basic Dynamic for Ground Motion g g g g uuuu umumumum umkuucum mc m k ummgumF Fkuucum 2 2 2 2 2; 69
- 70. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • The input Variables are ground acceleration, damping ratio and circular frequency • The final unknown is displacement (and its derivatives) Ground Motion guuuu 2 2 70
- 71. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Modal Displacements 71
- 72. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 72 • Code based, Equivalent Static Methods – Uses single mode, single DOF approach • Modal Analysis – Determines the basic, inherent dynamic response indicators • Response Spectrum Methods – Linear, using modal combination and “Response Reduction Factor” – Nonlinear Static Pushover Methods • Time History Methods – Linear Time History method and “Response Reduction Factor” – Nonlinear Time History Analysis Estimating Seismic Response
- 73. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 73 Analysis Using Equivalent Static Load
- 74. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 74 • Model Code – IBC 2000 • International Building Codes • NEHRP Provisions • FEMA 368-369 Provisions • Incorporates most recent (1996) USGS Hazard Maps • Guidelines – ATC -40 • Applied Technology Council – FEMA • Federal Emergency Management Agency Model Codes and Guidelines
- 75. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Basic Notion • Convert the Seismic Excitation to an “Equivalent Static Force” applied at the base of the building, called the Base Shear. Then Distribute the Base Shear to various parts of the Building by using: V = W C ( from F = m a) • This formula is based on the assumption that the structure will undergo several cycles of inelastic deformation and energy dissipation without collapse. Force and displacements in the structure are derived assuming linear behavior. 75
- 76. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 76 • The old equation: V = (Z K C S I) W • The new equation: – I = Importance factor, for a specific occupancy category, from UBC Table 16-K – Cv = Velocity based ground response coefficient, for a specific seismic zone and soil profile, from UBC Table 16-R – R = Response modification factor, for a specific structural system, from UBC Table 16-N – T = Fundamental, period of vibration, from UBC Formula (30-8) or (30-10) The UBC-97 Form of Equation RT ICv s s C WCV
- 77. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 77 • Maximum Inelastic Displacement (Eq. 30-17) – ∆M = 0.7 R ∆s – ∆M = maximum inelastic displacement – R = overstrength factor – ∆s = design level displacement by design seismic forces • Drift Limit – For structures having a time period of < 0.7s, Drift limit = 0.025 x story height – For structures having a time period of ≥ 0.7s, Drift limit = 0.02 x story height – Actual time period calculated by Method B shall be used to calculate the design lateral force for story drift and neglect the 30% or 40% limitations in Section 1630.2.2. – Design base shear minimum limit formula (30-6) will also be neglected. Inelastic Displacement and Drift (UBC 97)
- 78. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The IBC-06 Form of Equation CsWV E DS S I R S C MSDS SS 3 2 SaMS SFS Fa = Site coefficient short period , Table 1615.1.2(1) Ss = Spectral accelerations for short periods, Maps R = The response modification factor, Table 1617.6 T I R S C E DI S EDSS ISC 044.0 E S I R S C 15.0 IE = The occupancy importance factor, Section 1616.2 Cs does not need to be greater than T = Fundamental period (in seconds) of the structure 11 3 2 MD SS 11 SFS VM FV = Site coefficient, 1 sec period, Table 1615.1.2(2). S1 = Spectral accelerations for a 1-second period, Maps Cs must be greater than 78
- 79. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 79 • W includes: – In areas used for storage, a minimum of 25% of the reduced floor live load (floor live load in public garages and open parking structures does not have to be included. – Where an allowance for partition weight or a minimum weight of 50 kg/m2 of floor area, whichever is greater. – Total operating weight of permanent equipment. – 20 % of flat roof snow load where the flat roof snow load exceeds 150 kg/m2 The IBC-06 Form of Equation
- 80. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • R is dependent on structural system and ranges from 1.5 to 8 (bad to good) • Fa is site modification for short period spectrum and ranges from 0.8 to 2.5 (good to bad) • Fv is a site modification for 1 sec period spectrum and ranges from 0.8 to 3.5 (good to bad) • I ranges from 1.0 to 1.5 (Normal to important) 80 The IBC-06 Form of Equation
- 81. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar IBC-2006: General Procedure • Maximum Considered Earthquake (MCE) based on 2005 USGS probabilistic hazard maps • Deterministic limits used in high seismicity areas where the hazard can be driven by tails of distributions • Hazard maps provide spectral accelerations for – T = 0.2 Sec called Ss – T= 1.0 Sec called S1 • Local soil conditions considered using site coefficients – Fa for short duration – Fv for longer duration • Develop the design spectrum using “S” and ‘F 81
- 82. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Overall Procedure • Step 1: Determine Seismic Zone Factor, Z • Step 2: Determine Seismic Source Type • Step 3: Determine Near Source Factor • Step 4: Determine Soil Profile Type • Step 5: Determine Ground Response Coefficients, Ca and Cv • Step 6: Determine Fundamental period, T 82
- 83. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Overall Procedure • Step7: Classify the Structural System and determine the Response Modification Factor, R • Step 8: Determine the Occupancy Categories and Importance Factor, I • Step 9: Determine the Seismic Response Coefficient, Cs • Step 10: Determine the Base Shear • Step 11: Vertical Distribution of Base Shear into Lateral Forces 83
- 84. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Calculation of seismic response coefficient , where I R S C DS S factoronmodificatiresponseTheR periodshortatparameteronacceleratiresponsespectraldesignDSS factorimportanceoccupancyTheI 84
- 85. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Upper limit of seismic response coefficient, • Lower limit of seismic response coefficient, R = response modification factor SD1 = design spectral response acceleration parameter at a period of 1s TL = long-period transition period T = fundamental period of building I = importance factor L D S TT I R T S C for1 L LD S TT I R T TS C for 2 1 01.0SC 85
- 86. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Buildings and structure for which the 1-second spectral response, S1 , is equal to or greater than 0.6 g, the value of the seismic response coefficient, Cs , shall not be taken as less than: R = response modification factor S1 = spectral response acceleration parameter at a period of 1s I = importance factor IR S CS / 5.0 1 86
- 87. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Computing Time Period, T: – The fundamental period of the building, T , in the direction under consideration shall be established using the structural properties and deformational characteristics of the resisting elements in a properly substantiated analysis • Or – Shall be taken as the approximate fundamental period, Ta. The calculated fundamental period, T, shall not exceed the product of the coefficient for upper limit on calculation period, Cu, and the approximate fundamental period , Ta. 87
- 88. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Approximate fundamental period N = number of stories h = height in feet stories)12exceedingnot(buildings1.0 NTa x nt hCTa 88
- 89. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Equivalent Lateral Load Procedure • Vertical distribution of seismic forces: • The lateral force, (kip or kN) , induced at any level: where – Cvx =Vertical distribution factor. – k = A distribution exponent related to the buildings period as follows: • For buildings having a period of 0.5 second or less, k = 1 • For buildings having a period of 2.5 seconds or more, k = 2 • For building having a period between 0.5 and 2.5 seconds or more, k shall be 2 or shall be determined by linear interpolation VCF vxx n i k ii k xx vx hw hw C 1 89
- 90. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Hazard Maps for Determining Ss, S1 90
- 91. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 91 • Adjust Maximum Considered Earthquake (MCE) values of Ss and S1 for local site effects – SMs = Fa x Ss – SM1 = Fv x S1 • Calculate the spectral design values – SDS = 2/3 x SMS – SD1 = 2/3 x SM1 Design Spectral Values
- 92. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Site Classification Characteristics • Soil conditions at the site should be determined. • They modify the ground motion • Based on the site soil properties, the site shall be classified as either Site Class A, B, C, D, E or F in accordance with Table 1613.5.2 • When the soil properties are not known in sufficient detail to determine the site class, Site Class D shall be used unless the building official or geotechnical data determines that Site Class E or F soil is likely to be present at the site 92
- 93. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Site Classification Characteristics 93
- 94. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Site Coefficients • To adjust maximum considered earthquake spectral response acceleration according to soil conditions SMS =Fa Ss SM1 = Fv S1 94
- 95. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Site Coefficients 95
- 96. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Design Category • The structure must be assigned a seismic design category. • Determines the permissible structural systems • Determines limitations on height and irregularity. • Determines those components of the structure that must be designed for seismic • loads, and the types of analysis required. • The seismic design categories, designated A through F • They depend on the seismic use group and the design spectral acceleration coefficients, SDS and SD1. The structure is assigned the more severe of the two values taken from these tables 96
- 97. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Seismic Design Category 97
- 98. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 98 • Seismic Design Category are used to select: – Type of analysis • Very Simplified • Equivalent Lateral Load Procedure • Response Spectrum • Time-history – Type of design and detailing • Special Detailing • Intermediate Detailing • Ordinary Detailing – Many other checks/requirements Why Seismic Design Categories?
- 99. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Response Modification Coefficient • It reduces the design loads to account for the damping and ductility of the structural system. An abbreviated set for values for R is found in Table below. 99
- 100. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 100 • Typical Values 3.0 Ductile steel frames (Special Case) 2.5 Ductile concrete frames 2.5 Ordinary concrete frames 2.5 RC shear walls 2.5 Reinforced masonry shear walls 2.5 Unreinforced masonry shear walls 2.0 Ordinary steel frames Over Strength Factor (Ω0)
- 101. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Flow Chart 101
- 102. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • Ss and S1, mapped MCE spectral accelerations are 0% to 300% and 0% to 100% in the map. • For example, if the map value is 125%g, it should be input as 1.25g Using ETABS For EQ Static Analysis (IBC 2006) 102
- 103. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • UBC-97 Summary: UBC-97 versus IBC2006 • IBC-2000 RT ICv s s C WCV CsWV R IS I R S C EDS E DS S RT IS T I R S C DI E DI S Cv = 0.05 to 0.5 I = 1.0 to 1.5 R = SDS = 0.13 to nearly 1.0 IE = 1 to 1.5 R = 4 to 8 SD1 = 0.05 to nearly 0.5 103
- 104. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Analysis Using Response Spectrum 104
- 105. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar What are Response Spectra? • For a ground acceleration at particular time, for a given time period and damping ratio, a single value of displacement, velocity and acceleration can be obtained • The output of the above (u, v, a) equation are the dynamic response to the ground motion for a structure considered as a single DOF • A plot of the “maximum” response for different ground motion history, different time period and damping ratio give the “Spectrum of Response” guuuu 2 2 105
- 106. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Response Spectrum – A picture is worth a concept 106 Graphical description of a response spectrum
- 107. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar What is Response Spectrum? 107
- 108. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar The Overall Picture … 108 Combined DVA response for El Centro ground motion, β = 2%
- 109. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Response Spectrum Generation 109
- 110. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Spectral Parameters • Spectral Displacement Sd • Pseudo Spectral Velocity Sv • Pseudo Spectral Acceleration Sa 2 2 dt ud uva dt du uv u dva dv SSS SS 2 110
- 111. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Spectra for Different Soils 111
- 112. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar How to Use Response Spectra • For each mode of free vibration, the corresponding Time Period is obtained. • For each Time Period and specified damping ratio, the specified Response Spectrum is read to obtain the corresponding Acceleration • For each Spectral Acceleration, the corresponding velocity and displacements response for the particular degree of freedom is obtained • The displacement response is then used to obtain the corresponding stress resultants • The stress resultants for each mode are then added using some combination rule to obtain the final response envelope 112
- 113. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar • ABS SUM Rule Add the absolute maximum value from each mode. Not so popular and not used so much used • SRSS Square Root of Sum of Squares of the peak response from each mode. Suitable for well separated natural frequencies • CQC Complete Quadric Combination is applicable to large range of structural response and gives better results than SRSS. N n no rr 1 0 Modal Combination Rules N n no rr 1 2 0 N i N n niino rrr 1 1 00 113
- 114. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Response Spectrum Analysis n i imi m g w M 1 2 1. Develop the Mathematical Model of the Structure 2. Determine Mode Shapes by Eigen Value Analysis 3. For Each Mode m, determine: n i imi m g w L 1 Eq Participation Factor Modal Mass 114
- 115. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar Response Spectrum Analysis n i iwW 1 g M L W m m m 2 WM gL PM m m 2 Effective Weight Participating Mass Where; 115
- 116. Design of Tall Buildings: Hybrid Learning System, Dr. Naveed Anwar 4. Determine the Number of Modes to be Considered to represent at least 90% of the participating mass of Structure 5. Determine the Spectral Acceleration and Seismic Design Coefficients for each mode: a. For Design response spectrum (UBC) determine Sam for Tm b. Determine modal Seismic design coefficient I = Importance Factor; R = Response Modification Factor Response Spectrum Analysis R I SC amm