The structural engineer is concerned about vibration of the structure in reaction to ground shaking at its foundation, which is taken into consideration by codal provisions of several seismic-resistant design codes. These rules, on the other hand, do not include any provisions for other impacts, which may even outnumber those caused by vibration, because the process for estimating them and the measures required for design are outside the scope of structural engineering. Even so, the structural engineer must be aware of the various seismic dangers in order to advise the customer on the possibility for damage when choosing sites in such zones. As a result, the first phase in the design process for a future construction should be an assessment of the suitability of the site chosen, taking into account the risk of any of the following types of damage.
The following are the various ‘Direct’ and ‘Indirect’ seismic effects:Effects that are immediate:
• Surface faulting, soil vibration (or seismic wave impacts), ground cracking, liquefaction, ground lurching, differential settlement, lateral spreading, and landslides are all examples of ground failures.
(A) Damage due to surface faulting:
The damage to structures and facilities near fault scarps ranges from entirely wrecked dwellings to foundation ruptures, foundation slab tilting, and wall collapse. Houses can also be damaged in minor ways.
(B) Damage due to liquefaction:
Internal seismic waves can cause significant damage due to soil instability in the affected area. The soil response is influenced by the mechanical properties of the soil layers, the depth of the water table, and the intensity and duration of ground shaking. If there are any loose granular materials in the area, the ground vibrations caused by the earthquake may condense them. This will result in significant ground surface settling and differential settlements. Furthermore, soil compaction may result in the creation of excessive hydrostatic pore water pressures large enough to produce liquefaction of the soil, causing settlement, tilting, and rupture of structures. Most codes’ seismic-resistant design rules only ensure that structures are designed and built in a way that protects them from damage caused by the structure’s potential vibratory response to ground shaking. However, it is probable that not all of these cases will be successful. In some regions, the only remaining alternative is to restrict the construction of any structures.
(C) Damage due to ground shaking:
Integrated field inspection and post-earthquake studies of structural damage caused by earthquake shaking is one of the most efficient ways to gain expertise in seismic response in order to improve the state of the art and practise in seismic-resistant design and construction. In addition to the soil conditions indicated above, such comprehensive inspections and analysis revealed that a structure’s seismic performance is highly dependent on the kind of foundation, structure configuration, structural material, and design and construction detailing.
(D) Damage due to sliding of superstructure on its foundation:
The entire structure-foundation system should act as a unit, and the superstructure should be appropriately linked or attached to the foundation, according to one of the basic rules in seismic-resistant design and construction of structures.
• Vibrations carried by the structure from the ground.
(E) Damage due to Structural Vibration:
I. Wood-Framed Structures:The inertia forces arise during a structure’s vibratory reaction to earthquake ground shaking, the intensity of which is determined by the product of mass and acceleration. As a result, it’s critical to keep the structure’s mass to a bare minimum. Among the classic structural materials – timber, masonry, concrete, steel, and aluminium – timber is clearly the most efficient earthquake-resistant material for low-rise buildings. However, correct lateral bracing and linking of all components together from the roof to the base must be adhered to.
Concrete structures, part two:Concrete is a relatively heavy substance with a high compressive strength. Steel reinforcement is supplied in constructions because of its low tensile and flexural strengths. Seismic-resistant construction can benefit from such reinforced concrete. The use of lightweight aggregate concrete offers a major advantage in seismic regions, as it overcomes its comparatively poor strength per unit weight when regular weight aggregates are employed. members with care: the amount and precise detailing of reinforcing steel plays an essential influence in a reinforced concrete structure’s seismic reaction.
Steel constructions, third:Steel is produced in steel factories that have strict quality control. Steel has about the same rigidity per unit weight as any other traditional construction material. However, it has much higher strength, ductility, and toughness per unit weight than concrete and masonry materials. As a result, the slenderness of steel structural members typically exceeds that of other structural members by a large margin. As a result, buckling becomes a severe issue. The risk of buckling increases dramatically as the steel’s yield strength increases. Furthermore, when stretched in the inelastic region, the plate elements utilised to produce the structural forms are prone to local buckling.
As a result, in earthquake-resistant design, the compactness requirements for the cross section of the crucial regions of structural components are more strict than in normal design. Furthermore, another issue in establishing efficient seismic-resistant design is field-connection of structural elements.Consequential Phenomena (or Indirect Effects):
Tsunamis, for example.
Seiches ,Landslides , Natural disasters (floods), Explosions
Landslides, tsunamis, fires, and fault rupture are all disastrous repercussions of earthquakes. The most property damage and personal injuries are caused by intense ground shaking.Eight of the ten most expensive earthquakes in the last century occurred in California, due to the collapse of buildings, roads, and infrastructure. According to the USGS, there is a 72 percent chance that a magnitude 6.7 or bigger earthquake will affect the San Francisco Bay area over the next 30 years. In the same timeframe, Southern California has a 60% chance of experiencing an earthquake with a magnitude of 6.7.
WHICH ARE THE DANGERS OF EARTHQUAKES? Ground shaking, ground rupture, landslides, tsunamis, and liquefaction are all examples of earthquake damage. Fire damage caused by earthquakes is the most significant secondary effect.
The most recent big earthquakes in Southern California were the Ridgecrest earthquakes, which struck on July 4 and 5, 2019 with magnitudes of 6.4 and 7.1, respectively. The second quake, measuring 7.1 on the Richter scale, lasted 12 seconds and was felt by over 30 million people from Sacramento to San Diego. More than 6,000 houses lost electricity as a result of the storm.
After the Northridge earthquake, there was a 25-year “calm period” before the Ridgecrest earthquakes. Northridge, a 6.7 magnitude earthquake, killed 58 people, injured over 9,000 others, and cost the economy more than $49 billion.
HOW DO EARTHQUAKES AFFECT THE ENVIRONMENT?Earthquake devastation starts with the earth’s intense shaking, which can break the earth, cause landslides, and convert the earth’s surface to liquid. The devastating tremors of big cities.
Ground tremors and structural collapse The trembling of the ground during an earthquake is known as ground shaking. Other risks, like as liquefaction and landslides, are triggered by the shaking. Seismic waves travelling beneath houses, roads, and other structures cause the majority of earthquake damage.Rupture of the surface and displacement of the ground Surface rupture is the most dangerous type of earthquake hazard. Vertical or horizontal movement on either side of a ruptured fault might induce it. Structures, roads, railways, and pipelines can be severely damaged by ground displacement, which can affect enormous amounts of land.LandslidesLandslides and mudslides can be triggered by earthquakes, especially in locations where the soil is saturated with water. Landslides can cause people, plants, animals, buildings, and automobiles to collide with cascading boulders and debris. They can also cause roadblocks and power outages.
LiquefactionDuring an earthquake, the shaking from the shaking can transform loose soil into a liquid.Buildings, bridges, pipelines, and roadways can all be harmed by liquefaction, which can cause them to sink into the ground, collapse, or dissolve.TsunamisA tsunami is a sequence of very lengthy waves caused by an earthquake that occurs deep under the Pacific Ocean’s surface. Large tsunamis that rise from the ocean floor are hazardous to people’s health, property, and infrastructure. Tsunami destruction has long-term consequences that can be felt well beyond the coast.FiresEarthquake-caused fires are the second most common danger, according to earthquake damage statistics. Electrical and gas lines become loosened as the earth shakes, resulting in earthquake fires. The gas has been turned on.
Earthquake Earthquake Earthquake Earthquake Earthquake Earthquake Earthquake Earthquake Earth This animated gif depicts how an earthquake’s sudden release of pressure and seismic waves can produce earth shaking and ground displacement, which appears as cracks in the ground dirt in this case. Liquefaction can also happen, causing the soil to become liquid. Other hazards and sorts of damage, such as a house shifting off its foundation, are frequently caused by ground shaking.Rupture of the Surface Image: Rupture of the Surface An earthquake’s vibrations can cause ground displacement and surface rupture. Other risks, as well as damage to roads and buildings, may result from the surface breach. The surface rupture in this case resulted in huge fissures and the collapse of a paved road. This could result in injuries or even death.