EARTHQUAKES AND EARTHQUAKE-RESISTANT DESIGN OF STRUCTURES. Er. K. S. BHARGAV LECTURER Department of Civil Engineering, GGSGP CHEEKA

Transcription

1 EARTHQUAKES AND EARTHQUAKE-RESISTANT DESIGN OF STRUCTURES by Er. K. S. BHARGAV LECTURER Department of Civil Engineering, GGSGP CHEEKA

2 SCOPE OF PRESENTATION EARTHQUAKE AND ITS CHARACTERIZATION EARTHQUAKE-RESISTANT DESIGN REPAIR & RETROFITTING OF STRUCTURES EARTHQUAKE ANALYSIS OF STRUCTURES ADVANCED TECHNOLOGIES

3 EARTHQUAKE An earthquake may be simply described as a sudden shaking phenomenon of the earth's surface due to disturbance inside the earth.

4 CLASSIFICATIONS AND CAUSES OF EARTHQUAKE Tectonic Earthquakes Non-tectonic Earthquakes

5 TECTONIC EARTHQUAKES Due to disturbances or adjustments of geological formations taking place in the earth's interior. Due to slip along geological faults. Less frequent. More intensive. More destructive in nature.

6 ELASTIC REBOUND THEORY

7 NON-TECTONIC EARTHQUAKES Due to external or surfacial causes such as: Volcanic eruptions Huge waterfalls Occurrence of sudden and major landslides Man-made explosions Impounding in dams and reservoirs Collapse of caves, tunnels etc. Very frequent, minor in intensity generally not destructive in nature.

8 EARTHQUAKE TERMINOLOGY Seismograms Focus or Hypocentre Epicentre Focal Depth Hypocentral Distance Epicentral Distance Isoseismal Coseismal

9 EARTHQUAKE WAVES P Waves: Primary waves, Longitudinal waves, etc. Speed 8 to 13 km/s S Waves: Shear waves, Transverse waves, etc. Speed 5 to 7 km/s L Waves: Long waves or Surface waves, etc. Speed 5 to 7 km/s

10 INTENSITY OF EARTHQUAKE Degree of destruction caused by it Severity of the shaking of ground MEASUREMENT OF EARTHQUAKE Magnitude Intensity - (MMI Scale) I to XII

11 MAGNITUDE OF EARTHQUAKE Related to the amount of energy released by the geological rupture. Measure of the absolute size of the earthquake, without reference to distance from the epicentre. Richter (1958) defined magnitude as the logarithm to the base 10 of the largest displacement of a standard seismograph situated 100 km from the focus. Largest magnitude of earthquake recorded = 8.9 Log10 E M (E = Energy in joules; M = Magnitude)

12 INTENSITY OF EARTHQUAKE Measure of the observed damage at a particular location Vary with distance from the epicentre and will depend on local ground conditions Measured on the scale of intensity which is Modified Mercalli Intensity (MMI). MMI is measured on Roman I to XII scale.

13 EARTHQUAKE FORCE Force due to earthquake is W F a W ( Seismic Coefficient) g W = weight of structure; g = acceleration due to gravity; a = peak earthquake acceleration. IS: provides the general principles and design criteria for earthquake loads.

14 (Before Earthquake) (After Earthquake)

15 BEFORE AN EARTHQUAKE 1. Store heavy objects near ground or floor. 2. Secure tall objects, like bookcases to the wall. 3. Secure gas appliances to prevent broken gas lines and fires. 4. Learn where your exits, evacuation route, and meeting places are. Know the safe spot in each room. 5. Keep emergency items, such as a flashlight, first aid kit and spare clothes, food in your car or office.

16 DURING AN EARTHQUAKE 1. If indoors, stay in the building. 2. Take shelter under solid furniture, i.e. tables or desks, until the shaking stops. 3. Keep away from overhead fixtures, windows, cabinets and bookcases or other heavy objects that could fall. Watch for falling plaster or ceiling tiles. 4. If driving- STOP, but stay in the vehicle. Do not stop on bridge, under trees, light posts, electrical power lines or signals. 5. If outside, stay outside. Move to an open area away from buildings, trees, power lines and roadways.

17 AFTER AN EARTHQUAKE 1. Check for injuries. Give first aid as necessary. 2. Check for safety hazards: fire, electrical, gas leaks, etc. and take appropriate actions. 3. Do not use telephones and roadways unless necessary so that these are open for emergency uses. 4. Be prepared for aftershocks, plan for cover when they occur. 5. Turn on your radio/tv for an emergency message. Evacuate to shelters as instructed. 6. Remain calm, try to reassure others. Avoid injury from broken glasses etc.

18 BASE ISOLATION Aseismic Design Philosophy Decouple the Superstructure from Ground with or without Flexible Mounting Period of the total System is Elongated A Damper Energy Dissipating Device provided at the Base Mountings. Rigid under Wind or Minor Earthquake

19 Advantages of Base Isolation Reduced floor Acceleration and Inter-storey Drift Less (or no) Damage to Structural Members Better Protection of Secondary Systems Prediction of Response is more Reliable and Economical. Non-isolated Base-isolated

20 Fixed base building Base-isolated building

21 SEISMIC BASE ISOLATION m N x N Period shift kn Acceleration Increasing damping m 2 x 2 k2 k1 m 1 x 1 Displacement Increasing damping Base isolator m b & x& g Period Figure 3.2 Concept of base isolation. 16

22 BASE ISOLATION SYSTEMS LRB System NZ System P-F System R-FBI System EDF System S-RF System Friction Pendulum System (FPS) High Damping Rubber Bearing