Seismic Performance in Existing Buildings
Kenny Yip is a Senior Engineer based out of our Vancouver office. He is focused on structural engineering in existing buildings and recently sat down with us to discuss how seismic performance can be improved in older buildings.
Thanks for sitting down with us today, Kenny. Can you please tell us about yourself and your background in seismic?
I started my career as an entry-level structural engineer in Washington State and worked there for nine years before moving back to Vancouver at the end of 2007. After returning to Vancouver, I spent the first two years exclusively working on seismic upgrades on schools before joining another local consulting firm to work mostly on existing buildings. There I looked mostly at structural condition assessments, investigations, and remediation; seismic evaluations and retrofits; and insurance claims and forensic structural consultations.
Now that I’m with Entuitive, I’m looking forward to using my more than a decade of experience in existing buildings and seismic performance. I’m particularly looking forward to working closely with our Vancouver Building Envelope team, coordinating our structural and envelope efforts and delivering existing buildings performance together.
I have a strong interest in existing buildings. I enjoy investigating the causes of reported issues, identifying the structural weaknesses, and enhancing structural and seismic performance. I really hope I can play a role in helping Entuitive expand its market share in this area, particularly for our Vancouver office.
Why is seismic so important in Vancouver for existing buildings?
As you know, Vancouver is situated in a high seismic zone, so the seismic performance of a building is of particular importance here. There are a lot of old buildings in Vancouver. In fact, I have worked on buildings approaching 100 years old and beyond. Generally speaking, the older a building gets, the more seismic deficiencies it could have. This is either because the building codes didn’t exist at the time of construction or because the codes were not as stringent as they are today. Other factors like material strengths, omission of key elements (Photo 1), discontinuity in load path (Photo 2), workmanship (Photo 3), structural irregularities, and condition of elements (Photo 4), etc., will also play an important role in the overall seismic performance of a building.
Over the past decade working on existing buildings, I’ve seen many deficiencies prevailing in old buildings, particularly those constructed of masonry and wood. As a structural engineer, I think it is important to be able to identify what deficiencies a building has before proceeding with a retrofit.
The photo shown in this article is an example of a building envelope remediation project I worked on previously. The subject wall is an exterior load-bearing brick wall located on the 7th floor. The problem is that the mortar had lost most of its bonding characteristics (adhesiveness). The owner wanted to keep the brick wall as the walls below were also constructed of brick. It is apparent that both the in-plane and the out-of-plane resistances of the wall were very weak and thus required strengthening. A seismic upgrade of the wall was conducted during the remediation phase, which was deemed a cost-effective approach as both building envelope remediation and seismic upgrade can be done simultaneously.
The biggest gains in terms of cost-effectiveness are typically seen when the building is constructed of wood frame. Whenever such a building was stripped of its cladding, elements like studs, top plates, anchor bolts, and hold-downs (if existed) became exposed. This allowed me to review the conditions and connections of the framing members and verify the presence of essential hardware as well as the continuity of the load path, which otherwise would not have been discovered. It’s important to recognize what seismic deficiencies exist in a building. Only after we have developed a good understanding of the issues can we address them accordingly. In short, to enhance the seismic performance of a building is to ensure that the building has adequate Lateral Force Resisting Systems (LFRS) and that the continuity of a load path can be effectively maintained.
Are there any codes or legislation that we have to meet with respect to seismic performance?
Definitely! The type of code or legislation that’s applicable depends on where a building is and whether or not the building is new construction. If the building is new construction and situated in Canada, then the applicable building code should be one of the following: National Building Code of Canada (NBCC), Provincial Building Code such as BC Building Code (BCBC), or Vancouver Building By-law (VBBL). If you are talking about existing buildings, then there are reference documents that we can use to evaluate and upgrade the seismic performance of a building, including, but not limited to, the following:
- The Vancouver Building By-law, Part 11;
- The Seismic Retrofit Guidelines, 3rd Ed., by the Engineers & Geoscientists of British Columbia;
- ASCE/SEI 41-17 Seismic Evaluation and Retrofit of Existing Buildings;
- Methodology for Seismic Risk Screening for Existing Buildings in Canada: Structural Scoring System.
I know your focus is existing buildings but I’m wondering if there are changes in the considerations that Entuitive would need to consider for new structures?
For new construction it’s different. You design the major lateral force resisting systems to the current building code. You can do whatever you like if it meets the current code requirements.
When you are working on existing buildings; however, you need to do some investigation – either non-destructive or invasive. The latter is imperative if there are no construction drawings available.
Interesting. It seems like the scope and depth of our work on existing building seismic projects might be a lot larger than it is in a new structure or a new construction project?
I wouldn’t necessarily say that it is larger in terms of scope, but I think it is fair to say that the scope can often be more challenging. The current building codes are primarily developed to address new construction, in which many parameters like building materials properties are pre-defined, meaning that, we, as a designer, have full control of the building during the design stage, including the arrangement and selection of its SFRS. In other words, there are no, or very few, unknowns.
In contrast, we may have to deal with a lot of unknowns when working with existing buildings. For instance, the material properties may have changed over time due to deterioration, which can have a detrimental effect on the building’s (seismic) performance.
You mentioned that changing materials can create additional challenges when working on existing buildings. Does the type of material matter for seismic performance?
Yes, of course! We have four major materials – masonry, wood, steel, and concrete – and their seismic performance is quite different. Wood is a relatively light material, and its seismic performance is excellent because it’s lightweight and flexible; it can absorb a lot of energy during an earthquake. Masonry and concrete, on the other hand, are much heavier and considered brittle materials. Their seismic performance is generally not as good as wood, not to mention that wood is extremely sustainable and more environmentally friendly.
When you’re conducting a retrofit and assessing an existing building to improve seismic performance are there ever opportunities to integrate materials you think would work better?
Yes, whenever feasible I would go for wood for its high strength/weight ratio, excellent sustainability, and the lowest embodied energy. Sometimes, replacing bulky masonry partition walls with metal stud walls could be more cost-effective than simply upgrading them.
Are there any examples of current work on seismic performance projects that you’d like to share?
I joined Entuitive a couple of months ago and I’m pretty excited about this opportunity and believe I have a lot to contribute.
I’m already working with several colleagues on the BC Housing Reframed Project. Entuitive’s scope on the project is quite wide and includes seismic performance. I’m working with Hannah in our Vancouver office. When I joined the company, the project was already underway so I’m catching up.
In addition, I am currently working on another seismic retrofit project known as Gryphon Granville Presentation Centre located in Vancouver, which is required to be upgraded in accordance with Level S4 of the Vancouver Building Bylaw.
That’s great! Any previous experiences and lessons learned you’d like to share?
I once worked on a building envelope remediation project in Richmond, British Columbia. The project consisted of six 3-storey residential buildings. In my first field review, I noticed there was an omission of rim boards/blocking between the roof diaphragm and the perimeter exterior walls. I reported this in a subsequent field review report as a major seismic deficiency and strongly recommended to the owner that this deficiency be addressed by installing new rim boards and/or blocking so that lateral forces from the roof diaphragm could be properly transferred on to the shear walls and down to the foundations. Yes, this recommendation was ultimately accepted and implemented. I think open communication and discussion are the keys to success on any projects.
Is there anything else we should know about you or about seismic?
I look forward to collaborating closely with our Vancouver Building Envelope team to assist them with structural services relating to their remediation projects and continuing to deliver high quality seismic performance with Entuitive. I do believe that I have something meaningful to contribute to Entuitive. Thank you for having me today in this chat!
Thank you so much for sitting down with us today, Kenny. We learned a lot! If you would like to discuss seismic performance with Kenny, you can reach out to him here.