Earthquake Engineering

substructure

the part of the structure below ground level, including the foundation and basement, which supports the entire building and transfers loads to the soil.

superstructure

everything above ground level, encompassing floors, walls, columns, beams, and the roof, providing enclosure, support, and functionality to the building.

Base isolation

aims to reduce the seismic demand instead of increasing the capacity. Controlling ground motion is impossible, but we can modify the demand on structure by preventing/reducing the motions being transferred to the structure from foundations.

Base Isolation System

Also known as seismic base isolation which is one of the most popular means of protecting a structure against earthquake forces.

Base Isolation System

a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure’s integrity.

➢ Elastomeric Rubber Bearing

➢ Rubber and Ball Bearing

➢ Sliding Bearing

➢ Spring Bearing

➢ Curved Slider Bearings or Pendulum Bearings

➢ High Damping Bearings

Bearing Base Isolation System

Bearing

Spring

Types of Base Isolation System

Elastomeric Rubber Bearing

Bearings formed of horizontal layers of synthetic or natural rubber in thin layers bound between steel plates. These bearings are capable of supporting high vertical loads with very small deformations. These bearings are flexible under lateral loads. Steel plates prevent the rubber layers from bulging. Lead cores are provided to increase damping capacity as plain elastomeric bearings does not provide significant damping. They are usually soft in horizontal direction and hard in vertical direction.

Rubber and Ball Bearing

For isolation applications in machinery isolation, roller and ball bearing are used. It includes cylindrical rollers and balls. It is sufficient to resist service movements and damping depending on the material used

Sliding Bearing

a predefined coefficient of friction can provide isolation by limiting acceleration and forces that are transferred. Sliders are capable of providing resistance under service conditions, flexibility and force- displacements by sliding movement. Shaped or spherical sliders are often preferred over flat sliding systems because of their restoring effect. Flat sliders provide no restoring force and there are possibilities of displacement with aftershocks.

Curved Slider Bearings or Pendulum Bearings

These bearings feature a concave, curved sliding surface that allows the structure to move horizontally during an earthquake, dissipating energy through friction while the curvature brings the structure back to its original position. The pendulum bearing is a type of curved slider bearing.

Springs

Steel springs are most likely used in mechanical applications as in roller bearings. It is not adopted in structural applications because it is flexible in both vertical and horizontal directions. This will increase service deflections

Passive-control devices

have no feedback capability between them, structural elements and the ground.

Active-control devices

incorporate real-time recording instrumentation on the ground integrated with earthquake input processing

Hybrid-control devices

have combined features of active and passive control systems.

Earthquake Resistant Structures

a set of technical means aimed at mitigating seismic impacts in building and non-building structures.

Earthquake Resistant Structures

can be classified into 3, active, passive or hybrid

➢ STRUCTURAL HAZARDS

➢ LIQUEFACTION

➢ LANDSLIDES AND SLOPE FAILURES

➢ RETAINING WALL FAILURES

➢ LIFELINE HAZARDS

➢ TSUNAMI

Types of Earthquake Hazards

Structural Hazards

One of the deadliest hazards associated with earthquakes is structural collapse. Unreinforced Masonry (URM) is typically recognized as the most dangerous type of structure in an earthquake.

Structural Hazards

Falling objects from buildings such as bricks, parapets and statues can also be deadly.

Liquefaction

now recognized as one of the most expensive hazards associated with earthquakes. Though it is rarely deadly, it often wreaks havoc on infrastructures.

Liquefaction

a critical aspect of geotechnical earthquake engineering

Landslides and Slope Failures

are often triggered by earthquakes. Sometimes they can be caused by liquefaction, but other times they occur on marginally stable slopes. Slope failures range in size from localized failures to massive slides.

Landslides and Slope Failures

Engineering Geologists and Geotechnical Engineers often perform seismic slope stability evaluations.

Retaining Wall Failures

Collapse of a Retaining Wall. The common signs for retaining wall failure are often cracking, tilting, bulging, bowing or buckling.

Retaining Wall Failures

Seismic loads on retaining walls can be very high. Geotechnical and Structural Engineers must design retaining structures to withstand the anticipated dynamic loads induced during an earthquake.

Lifeline Hazards

Considered perhaps as the most “expensive” hazard associated with earthquakes, damage to lifeline systems like roads, bridges, water lines, gas lines, electric lines, etc. can cause massive disruptions to society which may lead to additional hazards such as fire or epidemic.

Tsunami

One of the most feared and deadly hazards associated

with earthquakes are tsunamis. In the past 10 years alone, tsunamis have

claimed close to half a million lives

Tsunami

Engineering for tsunamis and seiche is still relatively new field and many advances have been developed since the Great Indian Ocean Tsunami of 2004

Focus / Hypocenter

The point of generation of an earthquake.

Epicenter

The point on the earth surface directly above the focus.

Focal Depth

The depth or the focus from the epicenter.

Focal Distance (Epicentral Distance)

The distance from the epicenter to any point of interest.

M.F. Reid in 1906

Proposed the Elastic Rebound Theory

Earthquakes

are vibrations of the earth caused by the rupture and sudden movement of rocks that have been strained beyond their elastic limit. If a strained rock breaks, it then snaps into a new position and, in the process of rebounding, generates vibrations called SEISMIC WAVES. The rocks on opposite sides of the fault move with respect to each other, typically distances ranging from millimeters to many meters. Earthquakes.

Elastic Rebound Theory

States that strain energy builds up on rocks as they are forced in different directions. Rocks on either side of a fault undergo elastic strain as they are stressed by tectonic forces. When stress exceeds the strength of the rock, it breaks, and the rocks abruptly slip past one another along the rupture. When slippage and rapture occur along the fault, the stored energy is released as seismic waves that radiate out in all directions, and that causes EARTHQUAKE

Earthquake

occur when energy stored in

elastically strained rocks is suddenly released

Solids – Iron and Nickel

Inner Core of the Earth

Liquid – Iron and Nickel Alloyed with silica

Outer Core of the Earth

Flowing Ability (IGNEOUS ROCKS)

Mantle

Basalt and Granite

Crust

16,000 kg/m³ / 5,500 C

Density and Temperature of Inner Core

12,000 kg/m³ / 5,000 C

Density and Temperature of Outer Core

5,000 - 6,000 kg/m³ / 1,200 C

Density and Temperature of Mantle

1,500 kg/m³ / 25 C

Density and Temperature of Crust