An article released in the New Yorker in 2015 by Kathryn Schulz brought great attention to the issue of seismic risk to buildings and infrastructure in the Pacific Northwest region. The Really Big One walks through research into the Cascadia subduction zone and the dangers that exist in the region if a large earthquake were to hit.
While research into seismic upgrades for existing buildings as well as changes to the building code for new construction were previously underway, the article caught the attention of local building departments, building owners and users, as well as contractors and engineering firms – and for good reason. As Oregon’s 2019 report card determined, should an earthquake such as the one described hit our area, many buildings, roads and bridges will be perilously unprepared.
Perlo’s projects often include seismic retrofits triggered either by code requirements, changes in occupancy, building owner preference or a host of other reasons. We spent some time discussing seismic upgrades with Jason Sahlin of VLMK Engineering + Design to look at the many reasons an upgrade might be done, and what it takes to complete this kind of work.
What triggers seismic upgrades?
Seismic upgrades to existing buildings may be triggered by a number of things, including:
- Change in occupancy
- Significant renovation work triggering code upgrades
- Building code changes
- Volunteer upgrades by ownership
- Local jurisdiction requirements, for instance, Portland’s Title 24.85
- Roofing replacements
- Original building construction methods, like URM (Unreinforced Masonry, “Red Brick or Concrete Block”)
Note that vintage era buildings are particularly prone to seismic damage, especially those constructed of unreinforced masonry.
“Owners should be familiar with how a seismic event may affect their properties,” says Jason. Seismic upgrades are geared towards saving lives in the event of an earthquake – something building occupants typically appreciate.
What types of buildings need seismic upgrades?
Recently constructed buildings are built up to or above current building codes, which includes requirements for seismic considerations. Older buildings, however, may have deficiencies. Some of the building types likely to be insufficient include:
- Unreinforced masonry (URM), red brick or concrete masonry.
- Unreinforced concrete buildings, often consisting of cast in place unreinforced elements.
- Older tilt-up concrete buildings with limited out of plane wall anchorage elements.
While this list isn’t exhaustive, these are the most typical building types in the Pacific Northwest that may need to be upgraded.
“Unreinforced masonry is the worst-case scenario. These building types often have no reinforcing elements, they’re just stacked brick and mortar,” says Jason. In a significant earthquake, these buildings are most prone to damage and potential collapse. Many landlords have proactively worked to upgrade their URM buildings in this area.
If you’re a building owner and would like to know how well prepared your building is for a large seismic event, it’s best to engage a structural engineer to investigate and determine what upgrades would be advisable.
What do seismic upgrades involve?
The particular upgrades for each building will be dependent on the construction type, the age of the structure, and the access available to complete the work. Some typical upgrades are summarized below:
Unreinforced Masonry (URM)
This type of building has an exterior structure of stacked clay bricks and mortar and are the most challenging to upgrade. They can also be made up of concrete masonry blocks. Steel reinforcing is either absent or minimal.
- Seismic improvements for clay masonry vary but may include the installation of steel/wood stud shear walls at the interior. This provides an internal lateral system that is secured to the brick exterior. Interior structural steel frame systems can also be incorporated.
- Seismic improvements for concrete masonry can include providing steel reinforcing into the interior of the wall to upgrade the seismic resistance of the structure. Like unreinforced masonry buildings, added interior shear walls or other lateral resisting elements may be a consideration.
On these structures, the connection between the tilt walls and the roof structure is what most often fails in the event of an earthquake. In past large earthquake events, these buildings have been left with the walls standing while the roof collapsed. Seismic upgrades typically include the addition of strapping between the roof diaphragm and walls, and perhaps the addition of clips at the top of the tilt walls that allow for more movement between the panels. These upgrades are often added during the process of re-roofing, but can be completed at other times, as well.
Unreinforced Concrete Buildings
Like URM buildings, older unreinforced concrete buildings were often constructed with no, or very minimal steel reinforcing. Upgrade improvements can be similar to those under the URM designation.
These options are just the tip of the iceberg in terms of what seismic upgrades may be required for any given building. Fiber reinforced polymer or steel strong backs that tie the building walls to the roof diaphragm may be options, as well. It’s best to consult a structural engineer to evaluate each individual building.
What does the construction schedule look like?
Similar to how variable the construction work is, so is the timeline to complete it. The size of the building, the extent of the structural upgrades required, the occupancy status of the building and what interior finishes that need repair will all play a part in determining the length of time required to accomplish the upgrades.
Some of the factors that are considered when building the construction schedule for seismic upgrades are:
- Extent of the work required.
- Footprint and number of stories.
- Ability to access each area of work.
- Occupancy of the building.
- Level of interior and exterior finishes that must be maintained/repaired.
The best method to determine the schedule length is to involve a contractor early in the preconstruction process. A skilled contractor can complete selective investigative demolition to determine existing conditions, walk through phasing needs and evaluate the constructability of engineered designs. In partnership with the engineer, the contractor can develop an accurate and realistic schedule for the work that considers all the factors involved.
Funding sources for seismic upgrades
Much of the funding for seismic upgrades comes from private money or loans. In the case of schools, however, there are grant programs available. Sometimes local jurisdictions will create funding sources for landlords to access for upgrading their buildings.
Unfortunately, seismic upgrades can be very expensive to complete. When the upgrades can be made in coordination with other construction work, it may reduce the costs. For instance, school projects to update finishes or infrastructure often include elements of seismic upgrade work in areas where work will already be occurring. Or, in the case of roofing replacements where the roofing is going to be removed as a course of regular maintenance, additional strapping and nailing can be completed for seismic improvements at the same time.
Final costs are dependent on all of the factors outlined here, like type of upgrades, phasing requirements, accessibility, etc. No two projects are likely to be the same and will vary widely, even on a cost per square foot basis.
How do you get permits for seismic upgrades?
The permit process for seismic upgrades is very similar to that of other building permits. The work must be designed by a structural engineer. Depending on whether the upgrades are mandatory or voluntary will dictate the ultimate approach. Mandatory upgrades will often require full code compliance with the adopted code. Voluntary upgrades can allow for phased code compliance and approval to address the most critical failure concerns.
The designs for seismic upgrades aren’t black and white because they are so specific to each building. In order to balance function of the design and cost of the work, no design will be the same from building to building.
It is recommended that any upgrade be coordinated with the governing jurisdiction ahead of application for permit. Having conversations with the permit reviewers at the building department ahead of permit submission typically goes a long way towards speeding up the review process.
Seismic upgrades to existing buildings are important for preventing the loss of life in the event of a large earthquake. However, they can be quite complex to design and build. Acquiring both the engineering and construction teams to investigate the design very early in the process is the best way to approach the work to maximize improvements and minimize cost.
If you’re considering a seismic upgrade, we encourage you to contact Jason Sahlin and his team at VLMK or our estimating teams here at Perlo.
Visit VLMK’s website: https://www.vlmk.com/