CONTENTS General Concepts 13 Introduction 13 Seismic Design and Analysis Concepts14 Basic Function of Design Codes 15 Earthquake Ground Motions 20 General Observations 20 Site Amplification and Modification by Presence of Structure 22 Actual Versus Effective Earthquake Motions 24 Design Response Spectra 29 Spectrum Concepts 29 Modification of Spectra for Large Periods or Low Frequencies 45 Dynamic Structural Analysis Procedures 49 Introduction 49 Building Properties and Allowable Ductility Factor for Analysis 52 Mass and stiffness 52 Damping and ductility 53 Modal Analysis Procedure 57 Structural idealization 59 Modal periods and shapes 59 Modal responses 60 Total responses 62 Application to inelastic systems 63 Combined earthquake design responses 64 Equivalent Lateral Force Procedure 64 Fundamental period of vibration 65 Lateral forces 67 Story forces 69 Deflections and drifts 70 Earthquake design responses 71 Special Design Considerations 73 Torsion 73 Distribution of Shears 74 Base or Overturning Moments 75 Vertical Compornt of Ground Motion 76 Combined Effects of Horizontal and Vertical Motions 76 Effects of Gravity Loads 77 Limitation and Choice of Lateral Force and Modal Analysis Methods 79 Applied Technology Council Provisions 84 Background 84 Basic Concepts of ATC-3 Provisions 86 Concluding Statement 97 Acknowledgment 98 Rferences 99