Earthquake and Its Effects on Residential Structural Design

Are you a structural engineer, architect, or designer looking to understand the effects of earthquakes on residential structures?

At its core, creating a safe and secure home for families requires an understanding of the environmental risks that can potentially impact its structures. This is especially true when it comes to designing a residential structure in earthquake-prone areas.

In this blog post, we will discuss the effects of earthquakes on building design and key structural considerations for you to consider for designing safe and reliable residential homes.

Introduction

An earthquake is a natural event that occurs when the Earth's tectonic plates move, causing the ground to shake and vibrate. Earthquakes are caused by the release of energy stored in the Earth's crust and can range in intensity from slight, barely perceptible tremors to significant, devastating events that can cause widespread damage and destruction.

The intensity of an earthquake is usually measured using the Richter Scale. Based on their location and depth, earthquakes can also be classified into different types, such as shallow, intermediate, and deep-focus earthquakes.

Figure 1: A damaged building in downtown Napa, California, after the 6.0 magnitude earthquake on August 24th, 2014 (Reference)

In general, earthquakes can cause damage to residential buildings (Figure 1) and other types of structures, including collapse, which can result in injury or death to the occupants.

To ensure the safety of residential structures during an earthquake, engineers and architects use seismic load analysis methods that determine the strength and stability of the building and its components.

Effects of Earthquakes on Residential Buildings

The movement of tectonic plates inside the lithosphere typically causes earthquakes when the rock on one side of a fault abruptly shifts relative to the rock on the other side of the fault, releasing a substantial quantity of energy in the form of seismic waves that can cause surface damage.

Earthquakes with significant ground-shaking intensities can devastate residential buildings (Figure 2) by inducing demand, causing minor to major cracks and increasing the buildings' probability of failure.

Figure 2: An illustration of building sway under earthquake-induced shaking intensities.

The earthquake effects on a residential building can vary widely depending on several factors, including the earthquake's magnitude, the distance from the epicenter, and the type of soil on which a building is constructed.

How Do Earthquake Impact Building Structural Elements

In general, designing buildings to withstand seismic forces requires a comprehensive understanding of the likely points of failure and the load paths that the building will be subjected to during an earthquake.

Connections between Structural Elements

The most critical areas of a building in terms of seismic performance are typically the connections between structural elements, such as beams and columns. These connections must be designed to be strong and flexible, allowing the building to move without breaking.

Overall Structural System of the Building

Other key considerations in seismic design include the overall structural system of the building, including the type of foundation and the type of structural system used, as well as the materials used in construction.

Load Paths of the Building

Additionally, load paths must be carefully considered to ensure that the forces generated by an earthquake are distributed throughout the building in a way that minimizes damage.

Residential buildings that are not adequately designed and constructed to withstand seismic activity are particularly vulnerable to damage. Additionally, old structures may be more susceptible to damage than newer ones due to the lack of newer construction techniques and technologies that improve their seismic resistance.

Key Considerations When Designing Residential Buildings in Earthquake-Prone Areas

Under earthquakes, the building is expected to possess a range of cracks in its structural (i.e., beams, columns, bracings, and slabs) and non-structural (i.e., walls, ceilings, floors, and electrical, plumbing, and heating systems) components. Accordingly, it is important to consider separating structural and non-structural components when designing buildings to withstand seismic forces.

The non-structural components, such as windows and curtain walls, can be particularly vulnerable to damage during an earthquake. To reduce damage, engineers should consider incorporating squishy materials, such as rubber or other flexible materials, into the design of these components. This can help absorb some of the earthquake's energy, reducing the likelihood of damage.

Additionally, in some cases, it is important to consider incorporating movement mechanisms, such as seismic isolation and base isolation systems, into the design of the building. These systems allow the building to move in a controlled manner during an earthquake, reducing the likelihood of damage to both structural and non-structural components.

On the other hand, while cracks in structural sections can be a concern in seismic design, as they can weaken the overall strength and integrity of the building, the point of the design is not necessarily to prevent cracks from occurring but rather to design a path for the cracks to follow that minimizes damage to other parts of the building. This is known as controlled cracking. By designing a specific path for cracks to follow, engineers can ensure that the building remains stable and that the load is distributed to minimize damage to other parts of the building.

Conclusion

In conclusion, it is important for structural engineers, architects and designers to understand how earthquake impacts your residential structural design. Guidelines such as ASCE 7-16 outline the steps for determining the forces a building or structure will experience during an earthquake and evaluate the building's ability to withstand those forces.

If you want to understand more how seismic analysis is done according to ASCE 7-16 requirements, check out this article!