What Triggers a Seismic Upgrade/Retrofit to an existing building?

With an increased focus on resiliency as well as emphasis on the reuse of existing buildings, understanding when a building requires a seismic retrofit is becoming ever more important and can often not be so simple an answer…

I was recently traveling to an existing office campus which a client of ours was considering purchasing. As part of our review and due diligence for our client we were performing a general structural review of the building, but we were also asked to consider the implications of some changes they were considering to the building. And the question was raised, “Will this trigger a seismic retrofit to my building?”

This is a common question among Developers, Owners and Architects when it comes to potential changes to existing buildings. So, what is a seismic retrofit? The definition can be as simple as new construction in an existing building that increases or enhances a buildings capacity to withstand earthquakes.

Here are a few key triggers:

• A mandatory Building Code Ordinance,
• A building alteration,
• A building addition,
• An occupancy change,
• A change of use,
• Voluntary upgrade,
• Repair and retrofit after an earthquake.

Let’s briefly examine each of these:

Mandatory Building Code Ordinance

Many cities over time have enacted mandatory, Building Code required seismic retrofits via an Ordinance. The 1980’s in Los Angeles saw a mandatory program for upgrading dangerous unreinforced masonry (URM) buildings and recently the City of Portland has sought to do the same. These ordinances are enacted to upgrade buildings which at one time were built to current Code standards but are now understood to be potentially hazardous and it is deemed to be in the publics best interests that these buildings be renovated.

Building Alteration

At first glance a building alteration may seem a sure thing for a full or partial building retrofit and, in many cases, it may be a good thing to do for the building. However, the Building Code may not require a retrofit for every alteration. An alteration could be many things that often falls under the umbrella of a “tenant improvement”. Consideration of how the changes affect the building lateral system are key to understanding the extent of any retrofits required. What may appear to be significant demolition to interior spaces of the building could in fact be removal of non-structural elements and not impact the buildings lateral system and therefore not require a retrofit (and vice versa).

Building Addition

Additions to existing buildings are generally thought of as adding space. Again, this typically would be thought of as triggering building retrofits. Often, we want to examine whether it makes sense from a structural perspective to connect the new and existing structures together or whether to isolate them. A seismic separation in the right location may avoid potential upgrades to an existing building while allowing the new building addition to be designed to current structural code requirements.

Occupancy Change

An occupancy change can many times require building retrofits. In Chapter 16 of the Building Code, different types of structures are assigned to “Risk Categories” to associate certain buildings with greater risk a higher force level of seismic design. For example, an existing office building that is being converted into a K-12 educational facility with an occupant load over 250 people would require a higher risk category (RC III) than the building was originally designed. Therefore, it would require a seismic upgrade of the entire building to meet the increased seismic design forces required for these types of structures.

Change of Use

A change of use could occur for example when a space becomes storage rather than office space. In addition to likely requiring floor upgrades to support the added live load weight, the Building Code requires a certain percentage of the storage weight we added to the seismic mass of the building and could trigger a seismic upgrade.

Voluntary Upgrade

With each new Building Code, new standards are introduced which improve the design and methods to which we develop new structures. Older buildings can improve their seismic performance and resiliency in many cases by upgrading. A voluntary upgrade can enhance the structural seismic integrity of a building. There can be full building seismic upgrades, but these upgrades are often targeted at specific elements of a building to provide the greatest improvement for the work performed.

Repair and Retrofit after an Earthquake

It has been some time since a significant earthquake along the west coast required major repairs, but with each shaking come repairs and retrofits that are needed. These may range from emergency repairs and retrofits needed immediately to long term repair and retrofits to put buildings back into operation.

Summary

Seismic retrofits are an important tool in the Structural Engineers toolbox in helping to maintain and improve our existing building stock. Projects may have one or more of the triggers noted above and careful consideration of each is necessary to provide feedback to Owners, Developers, Architects and others on how to proceed on a given development. This feedback on potential seismic retrofits can significantly affect the course of a project! If you have a question or are interested in learning more about seismic retrofits or about any of our projects, please feel free to contact Craig Chamberlain at (310) 853-7180 or email NCInfo@nishkian.com.

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