How engineers check if a building is safe after an earthquake

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MANILA, Philippines – Whenever earthquakes hit, debris from collapsed or damaged infrastructure is one of the most dangerous hazards. Even when structures remain standing after the main tremor, aftershocks can still make them life threatening.

Because of this, identifying infrastructure that is unsafe is an important part of disaster response. Local governments are in charge of conducting post-earthquake assessments that can identify these unsafe structures, but they are often overwhelmed by this monumental task.

This is where the Association of Structural Engineers of the Philippines (ASEP) comes in.

ASEP is a professional organization of structural engineers in the Philippines. Their president, Dr. Rodolfo Mendoza Jr., told Rappler that they have long been deploying volunteers to conduct post-earthquake rapid safety assessments on all types of infrastructure, including buildings, bridges, ports, and harbors.

They also work with engineers from the government and the Philippine Institute of Civil Engineers Incorporated but their organization often leads these assessment efforts because of their expertise. In fact, ASEP has been actively seeking ways to continuously improve these efforts, even creating an application to speed up inspections.

So, how do experts like those from ASEP check if buildings and other infrastructure are safe for use? Here’s what you need to know and learn about their process.

What is the process of a post-earthquake rapid safety assessment?

Rapid assessments are purely visual, but they are done with the professional judgment of an engineer. ASEP also developed a standardized form for buildings to make sure assessments are uniform, which is based on the Applied Technology Council’s form used in the United States.

The first step in these assessments is to check whether damages are structural or non-structural.

Structural damage involves the key skeleton of a structure, such as the foundation of a building, its posts, columns, beams, and floor. These parts are essential to the overall integrity of the building, which means substantial damage to them may result in a total collapse.

Non-structural damage, on the other hand, involves components like ceilings and partition walls. While they don’t contribute to overall structural integrity of the structure, they can still pose hazards.

For buildings, engineers use ASEP’s form to rate damage to specific areas as “none,” “minor, “moderate,” or “severe.” Key conditions to observe include the following:

Collapse, partial collapse, or building off foundation
Building or story leaning
Damage to walls and parapets
Ground slope movement
Structural damage to columns, beams, roof
Falling hazards

For other types of infrastructure, there is no standardized form, but engineers instead give general comments that describe the damage. These are conducted based on specialty, such as bridge engineers inspecting bridges and port designers assessing ports and harbors.

Based on their observations, engineers then give the government their recommendations on what type of access should be allowed. The assessed structure is then officially classified into one of three categories:

Inspected, which means the building is safe to occupy
Restricted use, which means some areas may be safe to occupy for a specific period of time
Off limits, which means the building is not safe to occupy at all

Once the government decides on the type of access to be given, placards declaring the assessments are placed outside the building.

Further action can also be recommended, such as the barricading of specific areas or conducting detailed evaluations. But these evaluations must be carried out by professional engineers separate from the rapid assessment team.

If the building is owned by the government, engineers from the Department of Public Works and Highways or from a third party can conduct the assessment and succeeding repairs.

For private owners, they must also find a professional engineer to assess their properties. Mendoza said ASEP members can do this, but on their own account and separate from the organization.

How can a non-engineer know whether a home is safe after an earthquake?

Mendoza said there are three main ways for ordinary citizens to check if a building is safe to enter after an earthquake:

Make sure there is no falling hazard or loose debris, including unsecured furniture like cabinets
Check if there are large cracks that were not present before the earthquake
Check if the building is tilting, even subtly, which can be seen if soil begins to settle and reveal parts of the building’s foundations

Based on ASEP’s past assessments, the majority of earthquake casualties were caused by the collapse of non-structural elements like ceilings and partition walls. He also emphasized that loose appliances and furniture can also pose life-threatening risks if they fall or topple over, so they should be secured.

What can we learn from post-earthquake assessments?

Mendoza said that ASEP’s assessments over the years reveal a common pattern on how structures fare during earthquakes. In general, buildings that followed the National Building Code (NBC) consistently sustained little to no damage after an earthquake, while those that collapsed often had issues complying with the code.

ASEP also has a structural code that supplements the NBC, which is called the National Structural Code. It contains more provisions on how to make buildings earthquake-resilient.

ASEP, together with the Philippine Institute for Volcanology and Seismology and the Japan International Cooperation Agency, created a 12-point checklist back in 2014 that regular citizens can use to know if their home is ready for disasters.

But Mendoza said it’s not enough to have a building design that is compliant with these standards. It’s important that the construction is conducted by competent contractors who follow the agreed-upon plan diligently, down to the proper dimensions and materials.

He also emphasized that professional engineers should be involved at every step of the process. This includes quality control once the building is completed, which he said should be conducted by another engineer separate from the contractor.

Aside from that, proper maintenance should be done regularly. Whenever homeowners notice damage to their buildings, they should get these repaired right away so that this damage will not further weaken the structure whenever an earthquake strikes. – Rappler.com

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