Perspectives 01.27.2020

Designing to Protect Life and Property: Strategies for Earthquake Design

By Yanel de Angel

Harnessing existing and new professional networks for earthquake relief

It is imperative to design buildings to protect life, first and foremost. However, we must also design to protect property, so we’re not forced to rebuild after major event shocks. In recent years, we’ve been reminded of this imperative almost monthly. On January 6, 2020, the southern part of Puerto Rico woke up to a magnitude 6.4 earthquake that shook the entire island. The tremors began in December with a magnitude 5.0 earthquake, which at the time felt like a warning. Throughout January, after shocks have continued to cause fragile buildings to collapse. Despite the catastrophic impact on lives, property, infrastructure, and economic disruption–not to mention the emotional toll–civilians and nongovernmental organizations continue to rise, providing much needed support.

After Hurricane Maria made landfall in September 2017, networks of multidisciplinary professionals from all over the globe, including diaspora communities, academic institutions, private sector, and nonprofit organizations, learned to organize themselves and collaborate to provide relief. These collaborations led to a groundswell of activities, all requiring strong partnerships to avoid redundancy and to achieve more impactful outcomes. ResilientSEE-PR was one of those initiatives that sprung from the humanitarian crisis need in Puerto Rico. Our hurricane relief efforts focused on mid- to long-term strategies. Today, we continue those commitments with a renewed focus on earthquake relief. We are harnessing the networks developed in the last couple of years to be intentional about all stages of relief, design, and reconstruction.

AIA PR leaders and volunteers on site
The President of AIA Puerto Rico, architect Eugenio Ramirez (blue shirt) with architects and engineers colleagues performing Safety Assessments in neighborhoods affected by the earthquake.
Courtesy of AIA Puerto Rico

Design Professionals are well positioned to contribute at different stages of relief.

Whereas hurricane paths can be mapped in advance, earthquakes strike without warning. Our building codes consider many strategies to project life and property but the realities on executions can vary. In the case of Puerto Rico, many assembly buildings such as schools were built before modern seismic codes were adopted and while retrofit programs were in place, not all buildings had appropriate techniques incorporated. Layered on this, is the fact that most of the housing stock in the island is informal construction. Vulnerable populations can’t afford professional designers and builders, many municipalities lack funds to have planning and code-enforcing departments, and construction trade schools have closed due to a collapsing economy.

Short Term: Disaster Relief Training for Design Professionals

The AIA Disaster Relief Program is a national network of architects to help communities before and after a disaster. This training allows architects to have disaster response processes and protocols aligned with federal frameworks. Volunteers that are SAP trained (Safety Assessment Program) are deployed in an organized manner and in coordination with local AIA chapters in need of help. Today, AIA Puerto Rico has deployed trained professionals to assess and tag houses in the southern neighborhoods of the Island. This allows families to understand what homes are safe, need repairs or have major structural damages. Why is this important as a short-term action? It removes the uncertainty many families face. For example, there are families camping in their back yards or in temporary shelters because they fear the houses will collapse with aftershock tremors. A trained professional can let them know if the house is strong and safe to be inhabited. Some architects and engineers in the field have seen houses that are safe and if those families knew it, they could resume normalcy. This puts less stress in shelters and allows relief efforts to focus on those needing reconstruction or relocation. We are helping set new training sessions for design professionals, so we can deploy brigades when the local AIA chapter activates the regional SAP certified professionals to help assess more than 700 buildings.

Multifamily residential structural failure
A multifamily residential building with parking spaces at ground level suffered structural damages visible in some of the columns. In this case, the building did not collapse.
Courtesy of AIA Puerto Rico
Private residence structural failure
A private residence has significant structural damage in most perimeter columns. While the house has not collapsed, there are no structural bracing elements to offer rigidity. The homeowners have added temporary support and bracing elements. It is not clear if this house could be repaired to withstand future seismic activity.
Courtesy of AIA Puerto Rico

Medium to Long Term: Educate and Design for Risk and Reconstruction

In coordination with other organizations, such as Enterprise Community Partners with whom we developed KEEP SAFE: A Guide for Resilient Housing Design in Island Communities and Communities Together: A Guide for Resilient Community Center Design in Island Communities, we are crafting webinars and short training modules that can be push out quickly through social media. There will also be on-site training with more hands-on components. These are meant to educate professionals, community leaders and the general public; and will cover a range of subjects:

  • Assessment of Home for Reentry: Protecting Life/Protecting Property
  • Finding Assessment Professionals
  • Fortified Home: Structural and Non-Structural Failures for Concrete and Wood Buildings

Given what professionals are seeing in the field (images resembling those in structural textbooks) there are some techniques that should be prioritized, such as:

Wood Construction: playing up the inherent flexibility and lightweight properties of wood that reduce seismic inertia.

  • Building appropriate ductile connections that do not fracture (quality of nails and connections are critical).
  • Providing code-compliant minimum fastening requirements.
  • Allowing for redundant load paths so if one connection fails, another one takes on the seismic load.
  • Calibrating wood elements for the right strength and stiffness with an eye on overall assembly stiffness and heavy bracing for shear walls to resist lateral distortion. (Wood can’t be used as retaining walls).
  • Designing strong concrete foundations adequately design for the soil type. Foundations should be anchored to wood columns by metal elements and fasteners.
  • Including Hold Down Connectors to resist overturning moments.
  • Connecting wood frame diaphragms to framing members.
  • Designing wood-frame sheer walls at strategic locations.
  • Bracing the wall line support to continues foundations that are in the same vertical plane.
  • Creating portal frames with hold-downs: door and windows with full-length header.
  • Using the right sheathing attachments as regulated by charts in the building code.

 

Multifamily residential structural failure
A multifamily residential building suffered structural damages at the column-slab-façade interface. In this case, the building did not collapse and adjacent load bearing walls are in good condition.
Courtesy of AIA Puerto Rico

Concrete Construction: offering the right rigidity within flexible tolerances.

  • Avoiding short column effect by calibrating reinforcement and openings around columns so they can resist deformation.
  • Avoiding partial collapse of bearing walls by reinforcing upper floors connections to columns and foundations.
  • Enforcing adequate column details so they can resist flexural yielding with the right stirrups and anchorage to slab.
  • Providing the right cross ties in the formwork.
  • Avoiding insufficient use of materials such as thin concrete cover of rebar, slender columns supporting roof, lack of bracing elements, and designs that can represent displacement of principal beams.
  • Creating roof diaphragms that are flexible and can resist deformation, provide bracing and redundancy.
  • When appropriate integrating foundation isolators that allow ground to move horizontally while upper levels sway preventing collapse.