To view the figures and tables associated with this article, please refer to the flipbook above.
Two summers ago, I had the opportunity and pleasure to present on “Post-Elastic Design” at the 12th Annual Structural Engineers Association of Alabama (SEAoAL) Code Conference & XPO in Homewood, Alabama. To narrow the subject, I chose to discuss many of the seismic ordinances (cantilevering brick parapets, concrete tilt-ups, soft-story buildings, etc.) enacted in California over several decades to improve the expected performance of building structures in future earthquakes based on performance observed in past earthquakes.
The intent of my presentation was to demonstrate that the prescriptive force-based design criteria provided in these ordinances and similarly in various editions of the Uniform Building Code improve performance, but in my opinion, not to the degree that the ordinance authors may have intended. My conclusion for the attendees was that following post-elastic performance-based design concepts is a far better way to develop ordinances, retrofit existing structures, and design new buildings. By that I mean, first, defining a performance goal or objective for the structure and then secondly, back-figuring appropriate design criteria.
I came to this conclusion about performance-based design after reviewing the ordinances and thinking (or you might say “discovering”) that the design criteria would work well for some structures in some locations and not so well for other structures in other locations, mainly because all structures are different (to some degree all structures are prototypes) and respond to earthquakes differently.
To be crystal clear, I am not being critical of the ordinance authors as I am certain they were doing the best they could with the information and analytical tools available at the time. Today, it is difficult to remember what it was like before cell phones with cameras, or before the internet, let alone when hand calculators were the new thing, displacing slide rules. I wasn’t “in the room” (not many alive today were) so it is difficult or impossible to ascertain today what the authors’ specific motivations were and what conflicting political pressures they were under. They were probably thinking about post-elastic concepts based on observed earthquake damage, but they also lived during the allowable stress/force-based design era. It is definitely worth one’s time to read any or all of the excellent Oral History Series books published by the Earthquake Engineering Research Institute (EERI) focusing on the legends in the field to get a glimpse into their thinking.
What I am advocating for is another approach going forward. This applies to the building code itself, future seismic retrofit ordinances and the evaluation of structures previously retrofitted following the provisions of past ordinances.
What Would It Be Like If There Was No Building Code?
I was in my first year (around 1980) of graduate school at the University of California before I took a class that required that I buy a copy of the Uniform Building Code. Prior to that, the structural engineering classes had focused on the theoretical basics of mechanics of materials, statics, structural analysis with a few material-specific design classes for concrete, prestressed concrete, steel and wood. There was no class on masonry.
After graduation, I was lucky enough to land a job at a prestigious firm in San Francisco, starting in early 1982. That is when I learned that the Uniform Building Code—that book I hardly knew anything about—would become one of the most important books to possess, in addition to the AISC Steel Construction Manual, ACI 318 and the NDS for wood. Our firm’s mix of work was diverse and involved design of new buildings, seismic retrofits usually as part of major renovations, structural studies of existing buildings, and construction engineering (for which I learned there is NO building code, not even today). We were proudly not a “design shop.”
We had happy hour on most Friday afternoons starting around 5 pm. We usually put a few beers, sometimes a bottle of rye whiskey (left over from the previous year’s Christmas party), a tin of mixed nuts, and a deck of playing cards on the lunchroom table and chatted. We discussed current events or weekend plans, and sometimes a project. But, if we did talk shop, the conversation eventually turned to the question posed by the older engineers in the room, namely “what would have happened if there was no building code?” The very thought scared the younger engineers. I suspect the older engineers knew the effect that the question would have, like pulling a cat’s tail.
The younger engineers would ask:
- Are you suggesting a society with no engineering rules?
- Who would protect public safety?
- Wouldn’t some buildings collapse?
The responses from the more experienced crowd included:
- The engineers who have enough knowledge and experience to convince a client that they can be trusted with a design commission will get more work. Others won’t.
- Maybe some buildings might have structural problems, but the designers of those buildings wouldn’t get future clients. The system will naturally correct itself.
- Doctors, lawyers, and airline pilots don’t have codes.
- Wouldn’t we all be better off, eventually?
We were reminded that California did not have a building code before 1927 and that if we walked along Market Street or around the Financial District in San Francisco, we would see many dozens of buildings that were designed and built without a “code,” several of which even survived the 1906 San Francisco earthquake. We were also reminded that there never has been a “building code” for construction engineering, since it is considered the “contractor’s means and methods.” That scared me a bit more since I was involved in that line of our firm’s practice. I came away with the conclusion that I just had to do it right and not make mistakes, since there was no code to defend me, nor to limit me as well.
The larger takeaway for us (maybe intended, maybe not) was that it was important to understand how buildings responded under earthquake excitation, and what aspects of various designs worked better and what should be avoided. I was really thankful to my mentors for making me a critical thinker and teaching me that I really needed to be a “professional,” which meant that I had to continuously learn about buildings whether by walking around and observing, reading journals, staying abreast of recent developments, engaging in engineering laboratory research, discussing engineering with more experienced engineers, or by learning from earthquakes and other natural hazards.
The most important thing I learned, and still employ today, is to first establish the required loads/design criteria, then configure and design a structure with appropriate load paths (avoiding irregularities to the extent possible) and the best materials and configurations available, and then check to make sure I have complied with the building code. It is never the other way around. As we all know, building codes only establish the minimum requirements for a design and are by their nature backward looking in that they are written based on past experiences. They are imperfect at best and subject to varying interpretations even by those working within the same city jurisdiction or entity.
I recognize that we are never going to go back to the pre-1927 era, since the building code is necessary to reassure the general public. The reality is too many well-intentioned people are involved in research, writing codes and standards, selling codes and standards (every three years for example), reviewing design documents, checking structural calculations (sometimes), and issuing permits for it to be anything else.
The evolving field of performance-based design may be the best we can hope for. In the past, and currently, this is called the “alternative means of compliance” provision. I have worked on a few performance-based design projects and find it quite exciting to look at the building as a whole (rather than a bunch of parts) to determine how it will perform in an earthquake. Sometimes it is discovered that the building can be economized and made less expensive. Sometimes certain aspects may need to be strengthened or stiffened, but the end result is that the engineer needs to be a real engineer and think hard about how the building is going to perform. I do not think prescriptive building code provisions can ever achieve this result or allow us to sleep comfortably at night. ■
This article is Part 1 of a four-part series. Part 2 will appear in the March issue of STRUCTURE.
About the Author
John A. Dal Pino is a Principal with Claremont Engineers, Inc. in Oakland, California. He serves as the Chair of the STRUCTURE Editorial Board (jdalpino@claremontengineers.com).
