BASICS OF DYNAMICS AND ASEISMIC DESIGN MUTHUMINALR ASSISTANT PROFESSOR CIVIL DEPARTMENT

OBJECTIVE: The main objective of this Subject is to provide a basic knowledge over the reaction of structures due to the action of dynamic loads

Elements Of Seismology Response Of Structures To Earthquake UNITS COVERED Theory Of Vibrations Multiple Degree Of Freedom System Elements Of Seismology Response Of Structures To Earthquake Design Methodology

THEORY OF VIBRATIONS Concept of inertia and damping Types of Damping Difference between static forces and Dynamic excitation Degrees of freedom SDOF idealization Equations of motion of SDOF System for mass as well as base excitation Free vibration of SDOF system Response to Harmonic excitation Impulse and response to unit impulse Duhamel integral

Introduction to dynamics Structural analysis is mainly concerned with finding out the behaviour of a structure when subjected to some action. This action can be in the form of load due to the weight of things such as people, furniture, wind, snow, etc. or some other kind of excitation such as an earthquake, shaking of the ground due to a blast nearby, etc. Dynamic analysis for simple structures can be carried out manually, but for complex structures finite element analysis can be used to calculate the mode shapes and frequencies.

Importance of dynamics The importance of Structural Dynamics is to find the behaviour of a structure when subjected to some action. This can be done by means of dynamic loads or vibration.

Types and sources Periodic Loading i. Sinusoidal Loading ii. Stepped Loading iii. Complex Variation Loading

Types of analysis Equivalent static analysis Response spectrum analysis

Types of structural vibration Free vibration Forced vibration Damped vibration Undamped vibration

Types Of Damping Viscous damping Coulomb damping Structural damping Active damping Passive damping

Degrees of freedom Single degree of freedom Two degree of freedom

Single degree of freedom Deals with analyzing the structure which has been provided with a single mass connected to a spring

Two degree of freedom This deals with analyzing the system provided with two masses which is connected to the spring

Elements of seismology Causes of Earthquake Geological faults Tectonic plate theory Elastic rebound Epicenter Hypocenter Primary, shear and Raleigh waves Seismogram Magnitude and intensity of Earthquakes Magnitude and Intensity scales Spectral Acceleration Information on some Disastrous earthquakes

Elements of seismology Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions).

Indian codes IS 1893 (Part I), 2002, Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision) IS 4326, 1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision) IS 13827, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Earthen Buildings IS 13828, 1993, Indian Standard Guidelines for Improving Earthquake Resistance of Low Strength Masonry Buildings IS 13920, 1993, Indian Standard Code of Practice for Ductile Detailing of Reinforced Concrete Structures subjected to Seismic Forces IS 13935, 1993, Indian Standard Guidelines for Repair and Seismic Strengthening of Buildings

Indian seismicity

Faults

Types of waves

Intensity

Magnitude

RESPONSE OF STRUCTURES OF EARTHQUAKE Response and design spectra Design earthquake concept of peak acceleration Site Specific response spectrum Effect of soil properties and damping Liquefaction of soils Importance of ductility Methods of introducing ductility into RC structures.

Response spectrum The representation of the maximum response of idealized single degree freedom systems having certain period and damping, during earthquake ground motion. The maximum response is plotted against the undamped natural period and for various damping values, and can be expressed in terms of maximum absolute acceleration, maximum relative velocity, or maximum relative displacement.

Response history analysis It is an analysis of the dynamic response of the structure at each increment of time, when its base is subjected to a specific ground motion time history. The response of a structure to ground vibrations is a faction of the nature of foundation soil; materials, form, size and mode of construction of structures; and the duration and characteristics of ground motion.

Modal analysis

Types of liquefaction Flow Liquefaction Cyclic Mobility Flow Liquefaction is a phenomenon in which the static equilibrium is destroyed by static and dynamic loads in a soil deposits with low residual strength Cyclic mobility is a liquefaction phenomenon, triggered by cyclic loading, occurring in soil deposits with static shear stresses lower than the soil strength.

Effects of liquefaction 1. Loss of bearing strength 2. Lateral spreading 3. Sand boils 4. Flow failures 5. Ground osculation 6. Flotation 7. Settlement

Methods to reduce liquefaction 1. Avoid liquefaction – susceptible soils 2. Build liquefaction – resistant structures 3. Shallow foundation aspects 4. Deep foundation aspects 5. Improve the soil 6. Drainage techniques 7. Verification improvements

Soil structure interaction

Design methodology IS 1893, IS 13920 and IS 4326 – Codal provisions – Design as per the codes Base isolation Techniques Vibration control measures Important points in mitigating effects of earthquake on structures.