What is Seismic Load? Explain different types of Seismic Load in details with example of Wind load.

Seismic load refers to the force or shaking that a structure experiences during an earthquake. It is a critical consideration in the design and analysis of buildings, bridges, and other structures located in seismically active regions. Seismic load calculations consider factors such as the intensity and duration of ground shaking, the type of soil, the structure’s weight, and its dynamic characteristics.

Here are the different types of seismic load with examples:

1. Inertial Load: Inertial load is the force generated due to the acceleration and deceleration of a structure during an earthquake. It is directly related to the mass of the structure and its dynamic response to ground motion. Inertial load calculations involve determining the seismic acceleration and applying it to the mass of the structure to calculate the force it experiences. The design of the structure, including its lateral load-resisting systems, foundations, and connections, should be able to withstand the inertial loads.
2. Ground Motion: Ground motion refers to the movement of the ground during an earthquake. It includes various types of shaking, such as horizontal and vertical displacements, rotations, and vibrations. Ground motion is characterized by parameters such as peak ground acceleration (PGA), spectral acceleration, and response spectrum. Engineers use historical earthquake records, geological data, and site-specific studies to determine the expected ground motion at a particular location. The design of the structure considers the ground motion characteristics to ensure it can withstand the resulting seismic forces.
3. Shear Load: Shear load is the lateral force exerted on a structure due to the lateral ground motion during an earthquake. It causes the structure to deform or shift horizontally. Shear load is significant in the design of lateral load-resisting systems, such as shear walls, moment frames, and braced frames, which are designed to resist the shear forces generated during an earthquake. These systems provide stiffness and strength to counteract the lateral loads and keep the structure stable.
4. Torsional Load: Torsional load refers to the twisting or rotational forces experienced by a structure during an earthquake. It can occur when the ground motion is not uniform or when the structure’s configuration is asymmetrical. Torsional loads can cause irregularities and additional stresses on the structure, particularly in tall buildings with varying floor plans or irregular shapes. Proper design considerations, such as the distribution of mass and stiffness, are crucial to minimize torsional effects and ensure the structure’s stability.
5. Soil-Structure Interaction: Soil-structure interaction refers to the interaction between the soil and the structure during an earthquake. The properties of the underlying soil significantly influence the seismic response of a structure. Different soil types, such as rock, sand, or clay, have varying dynamic characteristics and amplification effects on ground motion. The analysis of soil-structure interaction involves considering the interaction between the structure and the underlying soil to determine the structure’s response and design appropriate foundation systems.

Seismic load calculations are essential for designing structures that can safely withstand the forces and shaking generated during an earthquake. Structural engineers consider local seismic codes, building regulations, geological studies, and site-specific data to accurately determine the expected seismic loads. They then design the structure’s components, including the lateral load-resisting systems, foundations, and connections, to withstand the calculated seismic loads and ensure the safety and resilience of the structure during an earthquake.