The Impacts of Natural Hazards » Tectonic Event Impacts on Buildings

What you'll learn this session

Study time: 30 minutes

How tectonic events affect buildings and infrastructure
The different types of building damage caused by earthquakes
How building design and materials influence vulnerability
Case studies of major earthquake impacts on buildings
Methods to improve building resilience against tectonic events

Tectonic Event Impacts on Buildings

When the ground shakes during an earthquake or when volcanic activity occurs, buildings face enormous stress. Understanding how tectonic events affect our built environment helps us design safer structures and reduce the loss of life and property.

Key Definitions:

Tectonic events: Natural hazards caused by movements in the Earth's crust, including earthquakes, volcanic eruptions and tsunamis.
Seismic waves: Vibrations that travel through the Earth's layers as a result of an earthquake.
Structural failure: When a building can no longer support its intended load and collapses partially or completely.
Liquefaction: Process where water-saturated soil temporarily loses strength during an earthquake and behaves like a liquid.

⊕ Primary Impacts

These are the immediate effects of tectonic events on buildings:

Ground shaking causing structural damage
Building collapse (partial or complete)
Foundation failure due to ground movement
Damage from falling debris
Fire outbreaks from damaged gas lines

⊕ Secondary Impacts

These occur as a result of the primary impacts:

Water damage from broken pipes
Electrical hazards from damaged wiring
Loss of shelter and displacement
Economic costs of rebuilding
Long-term infrastructure disruption

How Earthquakes Damage Buildings

Earthquakes generate different types of seismic waves that affect buildings in various ways. Understanding these mechanisms helps engineers design more resilient structures.

↭ Horizontal Forces

Seismic waves create side-to-side (lateral) forces that push buildings in alternating directions. This can cause:

Swaying and twisting
Wall separation from floors
Shear stress on load-bearing walls

↕ Vertical Forces

Up-and-down movements stress building foundations and can cause:

Column and beam failure
Foundation cracking
Floor collapse

↻ Resonance Effects

Buildings have a natural frequency of vibration. When this matches earthquake waves:

Amplified swaying motion
Increased structural stress
Higher risk of collapse

Building Vulnerability Factors

Not all buildings are equally vulnerable to earthquake damage. Several key factors determine how well a structure will withstand a tectonic event:

□ Building Design

The shape and design of a building significantly affect its earthquake resistance:

Symmetrical designs distribute forces more evenly
Irregular shapes create stress concentration points
Soft storeys (floors with fewer walls) are particularly vulnerable
Building height affects how it responds to seismic waves
Large openings in walls reduce structural integrity

□ Construction Materials

Different building materials respond differently to earthquake forces:

Unreinforced masonry (brick, stone) - brittle and prone to collapse
Reinforced concrete - stronger but heavy
Steel frames - flexible and ductile, generally perform well
Timber - lightweight and somewhat flexible
Adobe/mud brick - extremely vulnerable in earthquakes

Common Building Failures During Earthquakes

Understanding how buildings typically fail helps engineers develop better designs and retrofitting techniques:

╬ Pancake Collapse

When floors stack on top of each other as vertical supports fail. Often seen in concrete buildings with weak columns. Extremely deadly as it leaves few survival spaces.

╗ Soft Storey Failure

Occurs when one floor (often ground level with large openings for shops) is weaker than others above it. The weak floor collapses while upper floors remain intact.

╚ Corner Failure

Buildings often experience concentrated damage at corners and connections between walls. L or T-shaped buildings are particularly vulnerable to this type of damage.

Case Study Focus: 2010 Haiti Earthquake

The magnitude 7.0 earthquake that struck Haiti on January 12, 2010, caused catastrophic damage to buildings, with an estimated 250,000 homes and 30,000 commercial buildings destroyed or severely damaged.

Key building failure factors:

Poor construction quality and lack of building codes
Widespread use of unreinforced concrete
Inadequate steel reinforcement in concrete structures
Buildings constructed on steep slopes without proper foundations
Informal construction without engineering oversight

The Presidential Palace, considered one of Haiti's strongest buildings, partially collapsed, highlighting how even prominent structures were vulnerable due to construction deficiencies.

Earthquake-Resistant Building Techniques

Modern engineering has developed numerous approaches to make buildings more resistant to earthquake damage:

⌖ Structural Design Approaches

Base isolation: Special bearings that separate the building from ground movement
Shear walls: Reinforced walls that resist lateral forces
Moment-resisting frames: Flexible connections between beams and columns
Cross-bracing: Diagonal supports that prevent building distortion
Dampers: Devices that absorb seismic energy (like shock absorbers)

⌖ Building Code Improvements

Countries in earthquake-prone regions have developed strict building codes:

Japan's building code revisions after the 1995 Kobe earthquake
California's seismic requirements in the Uniform Building Code
New Zealand's performance-based design standards
Chile's successful implementation of seismic codes

Case Study Focus: 2011 Christchurch Earthquake

The February 2011 magnitude 6.3 earthquake in Christchurch, New Zealand, caused widespread building damage despite the country's strict building codes.

Key observations:

Modern buildings generally performed well, with few collapses
The CTV Building collapse (killing 115 people) was attributed to design and construction flaws
Unreinforced masonry buildings suffered extensive damage
Liquefaction caused foundation failures across the city
The earthquake led to further improvements in New Zealand's building codes

Comparing Building Performance in HICs and LICs

The impact of tectonic events on buildings varies significantly between High-Income Countries (HICs) and Low-Income Countries (LICs):

⊞ High-Income Countries

Enforced building codes and regulations
Use of earthquake-resistant design techniques
Regular building inspections
Resources for retrofitting older structures
Example: Japan's buildings withstood the 2011 magnitude 9.0 earthquake with relatively few collapses

⊟ Low-Income Countries

Limited enforcement of building standards
Use of cheaper, less resilient materials
Informal construction without engineering input
Lack of resources for maintenance and retrofitting
Example: Nepal's 2015 earthquake destroyed over 600,000 structures, many built with stone and mud mortar

Future Challenges and Solutions

As urban populations grow and climate change potentially affects geological stability, several challenges and solutions are emerging:

Retrofitting existing buildings: Many older structures need upgrading to meet modern seismic standards
Affordable earthquake-resistant housing: Developing low-cost solutions for LICs
Knowledge transfer: Sharing engineering expertise between countries
Community education: Teaching residents about building safety and evacuation
Innovative materials: Developing new construction materials with better seismic performance

By understanding how tectonic events impact buildings and implementing appropriate design and construction practices, we can significantly reduce the human and economic costs of these natural hazards.

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