What Are Non-Ductile Buildings?
Non-ductile buildings, often called “non-ductile concrete” or “non-ductile reinforced concrete” buildings, are a critical concern in earthquake-prone regions. These structures lack the flexibility to withstand seismic activity. This rigidity makes them highly susceptible to damage or collapse during an earthquake, posing significant risks to occupants, property, and communities.
This guide will explain what non-ductile buildings are, their vulnerabilities, and why retrofitting is essential for improving earthquake safety.
Ductile vs. Non-Ductile Concrete
The difference between ductile and non-ductile concrete is their ability to handle seismic forces.
Ductile Concrete
Ductile concrete is designed to flex and deform under stress without breaking. This flexibility allows a building to absorb and dissipate seismic energy, reducing the likelihood of catastrophic failure.
Types of ductile concrete include:
- Engineered Cementitious Composites (ECC): Known as “bendable concrete,” ECC contains polymer fibers and reduced aggregate volumes, enabling it to absorb large deformations without cracking.
- Fiber Reinforced Concrete (FRC): Made with cement, aggregates, and discrete reinforcement fibers, fiber-reinforced concrete has high tensile strength and deformation ability.
- Ultra-High Performance Concrete (UHPC): UHPC blends cementitious binders with micro-steel fibers, achieving high ductility and mechanical strength similar to steel.
Applications of ductile concrete include:
- Buildings: Used in modern high-rise and critical infrastructure for earthquake resilience.
- Bridge Decks: Enhances durability and performance under seismic stress.
- Repair and Rehabilitation: Strengthens older structures to improve ductility and seismic resistance.
Non-Ductile Concrete
In contrast to ductile concrete, non-ductile concrete is rigid and brittle. It lacks sufficient reinforcement, such as closely spaced steel ties or shear walls, to absorb and dissipate seismic forces. This inflexibility increases the likelihood of structural damage, including cracks, shearing, or even collapse during an earthquake.
Buildings constructed with non-ductile concrete are at significantly higher risk, and addressing these vulnerabilities is crucial to protecting lives and property.
How Do You Know if a Building Is Non-Ductile Concrete?
The most reliable way to confirm if a building is non-ductile is to schedule a seismic assessment. A structural engineer or seismic specialist can evaluate critical features, such as column strength, reinforcement details, and overall structural integrity.
However, there are three key indicators:
Construction Date
Buildings constructed before seismic codes improved in the late 1970s are more likely to be non-ductile. Structures built before 1977, when key seismic safety updates were implemented, are especially at risk.
Building Types
Non-ductile concrete is commonly found in:
- Apartments/housing
- Parking garages
- Mid-rise office buildings
- Schools, hospitals, and older retail centers
Structural Characteristics
Non-ductile concrete buildings share common structural flaws that make them vulnerable to seismic forces. These weaknesses include:
- Inadequate Reinforcement: Poorly spaced steel ties and insufficient rebar weaken the building’s ability to absorb seismic forces.
- Rigid Columns: Structural columns designed without flexibility are prone to cracking or breaking during earthquakes.
- Lack of Shear Walls: Without sufficient lateral support, these buildings cannot adequately resist lateral forces caused by ground shaking.
More than 1,300 non-ductile concrete buildings have been identified in Los Angeles alone, posing a serious risk during seismic events.
Non-Ductile Vulnerabilities During Earthquakes
Non-ductile buildings are particularly susceptible to damage or collapse during earthquakes due to their inability to bend or flex under stress. Their rigid construction and lack of reinforcement make them prone to severe structural failures, such as cracking, column shear, and even total collapse.
Historical earthquakes have shown the devastating impact of non-ductile buildings, including widespread property damage, injuries, and loss of life.
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A U.S. Geological Survey simulation estimates that a magnitude 7.8 earthquake in Southern California could lead to the full or partial collapse of 50 non-ductile concrete buildings, potentially endangering 7,500 occupants.
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The Importance of Retrofitting
These vulnerabilities highlight the importance of retrofitting to improve building resilience and reduce the risks associated with seismic activity.
Seismic retrofitting is a proven method for improving the safety of non-ductile buildings. Retrofitting involves strengthening key structural components, such as columns and walls, to enhance a building’s ability to withstand seismic forces.
Retrofitting Mandates
Several California cities have introduced retrofitting requirements to address the dangers of older non-ductile buildings:
- Los Angeles adopted a mandatory retrofit ordinance for non-ductile concrete buildings as part of Ordinance 183893, requiring owners to evaluate and strengthen structures built before January 13, 1977.
- Santa Monica’s Seismic Retrofit Ordinance, adopted in March 2017, mandates retrofitting for non-ductile concrete buildings. Owners must evaluate and strengthen these structures within a defined timeline.
- San Francisco mandates retrofitting for concrete tilt-up and non-ductile buildings, focusing on safety and resilience.
- West Hollywood’s seismic retrofit program includes provisions for non-ductile concrete structures. Owners are required to assess and retrofit these buildings to meet modern seismic safety standards.
- Burbank’s seismic retrofit efforts focus on both non-ductile concrete and soft-story buildings. Specific regulations for non-ductile structures are included in its broader seismic safety initiatives.
- Long Beach is in the process of developing mandatory retrofit ordinances targeting non-ductile concrete structures. The city has voluntary programs to encourage property owners to address vulnerabilities.
Building a Safer Future
The risks posed by non-ductile buildings are too significant to ignore. Property owners can protect lives, reduce liability, and safeguard communities by understanding their vulnerabilities and investing in seismic retrofitting.
Don’t wait until the next earthquake to act. Contact Saunders Seismic to discuss your retrofitting needs and take proactive steps toward earthquake safety. Our experienced team specializes in seismic upgrades for commercial and industrial buildings, ensuring your property is ready to face the challenges of the next big quake.