When properly enforced, building codes are very effective for ensuring that buildings meet certain minimal requirements for strength and safety. Recent studies by the National Institute of Building Sciences (NIBS) have shown, however, that additional risk-mitigation measures can be beneficial even in proportion to the added costs. In the following post, Randy Shackelford, P.E., of Simpson Strong-Tie, shares some of the NIBS 2017 study benefit-cost results for two mitigation types — building beyond minimum code requirements, and federal mitigation grants. Continue Reading
Last year, I gave a presentation at the annual National Council of Structural Engineers Associations (NCSEA) Summit in Orlando, Florida, titled “Becoming a Trusted Advisor: Communication and Selling Skills for Structural Engineers.” As this was a summit for the leaders of the structural engineers associations from across the country, I wasn’t sure how many people would find it valuable to spend their time learning about a very nontechnical topic. To my surprise and delight, the seminar ended up being standing-room only, and I was able to field some great questions from the audience about how they could improve their selling and communication skills. In the many conversations I had with the conference attendees after my presentation, the common theme was that engineers felt they needed more soft-skills training in order to better serve their clients. The problem, however, was finding the time to do so when faced with the daily grind of design work.
When I started my first job as a design engineer at a structural engineering consulting firm straight out of school, I was very focused on improving and expanding my technical expertise. Whenever possible, I would attend building-code seminars, design reviews and new product solution presentations, all in an effort to learn more about structural engineering. What I found as I progressed through my career, however, was that no matter how much I learned or how hardworking I was, it didn’t really matter if I couldn’t successfully convey my knowledge or ideas to the person who really mattered most: the client.
How can an engineer be most effective in explaining a proposed action or solution to a client? You have to be able to effectively sell your idea by understanding the needs of your client as well as any reasons for hesitation. The importance of effective communication and persuasion is probably intuitive to anyone who’s been on the sales side of the business, but not something that occurs naturally to data-driven folks like engineers. As a result of recent legislation in California, however, structural engineers are starting to be inundated with questions from a group of folks who have suddenly found themselves responsible for seismically upgrading their properties: apartment building owners in San Francisco and Los Angeles.
Imagine for a moment that you are a building owner who has received a soft-story retrofit notice under the City of Los Angeles’ Ordinance 183893; you have zero knowledge of structural engineering or what this term “soft-story” even means. Who will be your trusted advisor to help you sort it out? The City of Los Angeles Department of Building and Safety (LADBS) has put together a helpful mandatory ordinance website that explains the programs and also offers an FAQ for building owners that lets them know the first step in the process: hire an engineer or architect licensed in the state of California to evaluate the building.
I’ve had the opportunity to be the first point of contact for a building owner after they received a mandatory notice, because it turns out some relatives own an apartment building with soft-story tuck-under parking. Panicked by the notice, they called me looking to understand why they were being forced to retrofit a building that “never had any problems in the past.” They were worried they would lose rent money due to tenants needing to relocate, worried about how to meet the requirements of the ordinance and, most importantly, worried about how much it was going to cost them. What they really wanted was a simple, straightforward answer to their questions, and I did my best to explain the necessity behind retrofitting these vulnerable buildings and give an estimated time frame and cost that I had learned from attending the first Los Angeles Retrofit Resource Fair in April 2016. With close to 18,000 buildings in the cities of San Francisco and Los Angeles alone that have been classified as “soft-story,” this equates to quite a number of building owners who will have similar questions and be searching for answers.
Submitting Building Plans with the Right Retrofit Product Solutions
Communicating with Your Building Tenants
Completing Your Soft-Story Retrofit
We encourage you to invite any clients or potential clients to attend this informative webinar, which will lay the foundation for great communication between the two of you. As part of the webinar, we will be asking the building owners for their comments, questions and feedback so we can better understand what information they need to make informed decisions, and we will be sure to share these with the structural engineering community in a future post. By working together to support better communication and understanding among all stakeholders in retrofit projects, we will be well on our way to creating stronger and more resilient communities!
For additional information or articles of interest, there are several resources available:
The Great ShakeOut Earthquake Drill is an annual opportunity for people in homes, schools and organizations to practice what to do during earthquakes and improve their preparedness. In a post I wrote last October about the Great ShakeOut, I reminisced about the first earthquake I had to stop, drop and cover for – the Livermore earthquake in January, 1980. This year got me thinking about how our evacuation drills work.
At Simpson Strong-Tie, we use the annual Great ShakeOut drill to practice our building evacuation procedures. Evacuation drills are simple in concept – alarms go off and you exit the building. We have volunteer safety wardens in different departments who confirm that everyone actually leaves their offices. There are always a few people who want to stay inside and finish up a blog post. Once the building is empty and we have all met up in the designated meeting area, we do a roll call and wait for the all-clear to get back to work.
Several years ago the alarms went off. While waiting for the drill to end, we were concerned to see fire fighters arrive and rush into the building. Realizing this was not a drill, there were some tense moments of waiting. The fire chief and our president eventually walked out of the building and our president was yelling for one of our engineers. Turns out the engineer (who shall remain nameless) was cooking a chicken for lunch. Yes, a whole chicken. The chicken didn’t make it – I’m not sure what the guilty engineer had for lunch afterwards. At least we received extra evacuation practice that year. We aren’t allowed to cook whole chickens in the kitchen anymore.
Simpson Strong-Tie is helping increase awareness about earthquake safety and encouraging our customers to participate in the Great ShakeOut, which takes place next Thursday on October 20. It’s the largest earthquake drill in the world. More than 43 million people around the world have already registered on the site.
On October 20, from noon to 2:00 p.m. (PST), earthquake preparedness experts from the Washington Emergency Management Division and FEMA will join scientists with the Washington Department of Natural Resources and the Pacific Northwest Seismic Network for a Reddit Ask Me Anything – an online Q&A. Our very own Emory Montague will be answering questions. The public is invited to ask questions here. (Just remember that this thread opens the day before the event and not sooner.)
Earthquake risk is not just a California issue. According to the USGS, structures in 42 of 50 states are at risk for seismic damage. As many of you know, we have done a considerable amount of earthquake research, and are committed to helping our customers build safer, stronger homes and buildings. We continue to conduct extensive testing at our state-of-the-art Tye Gilb lab in Stockton, California. We have also worked with the City of San Francisco to offer education and retrofit solutions to address their mandatory soft-story building retrofit ordinance and have created a section on our website to give building owners and engineers information to help them meet the requirements of the ordinance.
Last year, Tim Kaucher, our Southwestern regional Engineering Manager, wrote about the City of Los Angeles’s Seismic Safety Plan in this post. Since that time, the City of Los Angeles has put that plan into action by adopting mandatory retrofit ordinances for both soft-story buildings and non-ductile concrete buildings. Fortunately, California has not had a damaging earthquake for some time now. As a structural engineer, I find it encouraging to see government policy makers resist complacency and enact laws to promote public safety.
Participating in the Great ShakeOut Earthquake Drill is a small thing we can all do to make ourselves more prepared for an earthquake. If your office hasn’t signed up for the Great ShakeOut Earthquake Drill, we encourage you to visit shakeout.org and do so now.
Editor’s Note: This is a republished blog post with an introduction by Jeff Ellis.
This is definitely an attention-grabbing headline! At the National Earthquake Conference in Long Beach on May 4, 2016, Dr. Thomas Jordan of the Southern California Earthquake Center gave a talk which ended with a summary statement that the San Andreas Fault is “locked, loaded and ready to go.”
The LA Times and other publications have followed up with articles based on that statement. Temblor is a mobile-friendly web app recently developed to inform homeowners of the likelihood of seismic shaking and damage based on their location and home construction. The app’s creators also offer a blog that provides insights into earthquakes and have writtene a post titled “Is the San Andreas ‘locked, loaded, and ready to go’?” This blog post delves a bit deeper to ascertain whether the San Andreas may indeed be poised for the “next great quake” and is certainly a compelling read. Drop, cover and hold on!
Volkan and I presented and exhibited Temblor at the National Earthquake Conference in Long Beach last week. Prof. Thomas Jordan, USC University Professor, William M. Keck Foundation Chair in Geological Sciences, and Director of the Southern California Earthquake Center (SCEC), gave the keynote address. Tom has not only led SCEC through fifteen years of sustained growth and achievement, but he’s also launched countless initiatives critical to earthquake science, such as the Uniform California Earthquake Rupture Forecasts (UCERF), and the international Collaboratory for Scientific Earthquake Predictability (CSEP), a rigorous independent protocol for testing earthquake forecasts and prediction hypotheses.
In his speech, Tom argued that to understand the full range and likelihood of future earthquakes and their associated shaking, we must make thousands if not millions of 3D simulations. To do this we need to use the next generation of super-computers—because the current generation is too slow! The shaking can be dramatically amplified in sedimentary basins and when seismic waves bounce off deep layers, features absent or muted in current methods. This matters, because these probabilistic hazard assessments form the basis for building construction codes, mandatory retrofit ordinances, and quake insurance premiums. The recent Uniform California Earthquake Rupture Forecast Ver. 3 (Field et al., 2014) makes some strides in this direction. And coming on strong are earthquake simulators such as RSQsim (Dieterich and Richards-Dinger, 2010) that generate thousands of ruptures from a set of physical laws rather than assumed slip and rupture propagation. Equally important are CyberShake models (Graves et al., 2011) of individual scenario earthquakes with realistic basins and layers.
But what really caught the attention of the media—and the public—was just one slide
Tom closed by making the argument that the San Andreas is, in his words, “locked, loaded, and ready to go.” That got our attention. And he made this case by showing one slide. Here it is, photographed by the LA Times and included in a Times article by Rong-Gong Lin II that quickly went viral.
Believe it or not, Tom was not suggesting there is a gun pointed at our heads. ’Locked’ in seismic parlance means a fault is not freely slipping; ‘loaded’ means that sufficient stress has been reached to overcome the friction that keeps it locked. Tom argued that the San Andreas system accommodates 50 mm/yr (2 in/yr) of plate motion, and so with about 5 m (16 ft) of average slip in great quakes, the fault should produce about one such event a century. Despite that, the time since the last great quake (“open intervals” in the slide) along the 1,000 km-long (600 mi) fault are all longer, and one is three times longer. This is what he means by “ready to go.” Of course, a Mw=7.7 San Andreas event did strike a little over a century ago in 1906, but Tom seemed to be arguing that we should get one quake per century along every section, or at least on the San Andreas.
Could it be this simple?
Now, if things were so obvious, we wouldn’t need supercomputers to forecast quakes. In a sense, Tom’s wake-up call contradicted—or at least short-circuited—the case he so eloquently made in the body of his talk for building a vast inventory of plausible quakes in order to divine the future. But putting that aside, is he right about the San Andreas being ready to go?
Because many misaligned, discontinuous, and bent faults accommodate the broad North America-Pacific plate boundary, the slip rate of the San Andreas is generally about half of the plate rate. Where the San Andreas is isolated and parallel to the plate motion, its slip rate is about 2/3 the plate rate, or 34 mm/yr, but where there are nearby parallel faults, such as the Hayward fault in the Bay Area or the San Jacinto in SoCal, its rate drops to about 1/3 the plate rate, or 17 mm/yr. This means that the time needed to store enough stress to trigger the next quake should not—and perhaps cannot—be uniform. So, here’s how things look to me:
So, how about ‘locked, generally loaded, with some sections perhaps ready to go’
When I repeat Tom’s assessment in the accompanying map and table, I get a more nuanced answer. Even though the time since the last great quake along the southernmost San Andreas is longest, the slip rate there is lowest, and so this section may or may not have accumulated sufficient stress to rupture. And if it were ready to go, why didn’t it rupture in 2010, when the surface waves of the Mw=7.2 El Major-Cucapah quake just across the Mexican border enveloped and jostled that section? The strongest case can be made for a large quakeoverlapping the site of the Great 1857 Mw=7.8 Ft. Teton quake, largely because of the uniformly high San Andreas slip rate there. But this section undergoes a 40° bend (near the ‘1857’ in the map), which means that the stresses cannot be everywhere optimally aligned for failure: it is “locked” not just by friction but by geometry.
A reality check from Turkey
Sometimes simplicity is a tantalizing mirage, so it’s useful to look at the San Andreas’ twin sister in Turkey: the North Anatolian fault. Both right-lateral faults have about the same slip rate, length, straightness, and range of quake sizes; they both even have a creeping section near their midpoint. But the masterful work of Nicolas Ambraseys, who devoured contemporary historical accounts along the spice and trade routes of Anatolia to glean the record of great quakes (Nick could read 14 languages!) affords us a much longer look than we have of the San Andreas.
The idea that the duration of the open interval can foretell what will happen next loses its luster on the North Anatolian fault because it’s inter-event times, as well as the quake sizes and locations, are so variable. If this 50% variability applied to the San Andreas, no sections could be fairly described as ‘overdue’ today. Tom did not use this term, but others have. We should, then, reserve ‘overdue’ for an open interval more than twice the expected inter-event time.
However, another San Andreas look-alike, the Alpine Fault in New Zealand, has a record of more regular earthquakes, with an inter-event variability of 33% for the past 24 prehistoric quakes (Berryman et al., 2012). But the Alpine fault is straighter and more isolated than the San Andreas and North Anatolian faults, and so earthquakes on adjacent faults do not add or subtract stress from it. And even though the 31 mm/yr slip rate on the southern Alpine Fault is similar to the San Andreas, the mean inter-event time on the Alpine is longer than any of the San Andreas’ open intervals: 330 years. So, while it’s fascinating that there is a ‘metronome fault’ out there, the Alpine is probably not a good guidepost for the San Andreas.
If Tom’s slide is too simple, and mine is too equivocal, what’s the right answer?
I believe the best available answer is furnished by the latest California rupture model, UCERF3. Rather than looking only at the four San Andreas events, the team created hundreds of thousands of physically plausible ruptures on all 2,000 or so known faults. They found that the mean time between Mw≥7.7 shocks in California is about 106 years (they report an annual frequency of 9.4 x 10^-3 in Table 13 of Field et al., 2014; Mw=7.7 is about the size of the 1906 quake; 1857 was probably a Mw=7.8, and 1812 was probably Mw=7.5). In fact, this 106-year interval might even be the origin of Tom’s ‘once per century’ expectation since he is a UCERF3 author.
But these large events need not strike on the San Andreas, let alone on specific San Andreas sections, and there are a dozen faults capable of firing off quakes of this size in the state. While the probability is higher on the San Andreas than off, in 1872 we had a Mw=7.5-7.7 on the Owen’s Valley fault (Beanland and Clark, 1994). In the 200 years of historic records, the state has experienced up to three Mw≥7.7 events, in southern (1857) and eastern (1872), and northern (1906) California. This rate is consistent with, or perhaps even a little higher than, the long-term model average.
So, what’s the message
While the southern San Andreas is a likely candidate for the next great quake, ‘overdue’ would be over-reach, and there are many other fault sections that could rupture. But since the mean time between Mw≥7.7 California shocks is about 106 years, and we are 110 years downstream from the last one, we should all be prepared—even if we cannot be forewarned.
Sarah Beanland and Malcolm M. Clark (1994), The Owens Valley fault zone, eastern California, and surface faulting associated with the 1872 earthquake, U.S. Geol. Surv. Bulletin 1982, 29 p.
Kelvin R. Berryman, Ursula A. Cochran, Kate J. Clark, Glenn P. Biasi, Robert M. Langridge, Pilar Villamor (2012), Major Earthquakes Occur Regularly on an Isolated Plate Boundary Fault, Science, 336, 1690-1693, DOI: 10.1126/science.1218959
James H. Dietrich and Keith Richards-Dinger (2010), Earthquake recurrence in simulated fault systems, Pure Appl. Geophysics, 167, 1087-1104, DOI: 10.1007/s00024-010-0094-0.
Edward H. (Ned) Field, R. J. Arrowsmith, G. P. Biasi, P. Bird, T. E. Dawson, K. R., Felzer, D. D. Jackson, J. M. Johnson, T. H. Jordan, C. Madden, et al.(2014). Uniform California earthquake rupture forecast, version 3 (UCERF3)—The time-independent model, Bull. Seismol. Soc. Am.104, 1122–1180, doi: 10.1785/0120130164.
Robert Graves, Thomas H. Jordan, Scott Callaghan, Ewa Deelman, Edward Field, Gideon Juve, Carl Kesselman, Philip Maechling, Gaurang Mehta, Kevin Milner, David Okaya, Patrick Small, Karan Vahi (2011), CyberShake: A Physics-Based Seismic Hazard Model for Southern California, Pure Appl. Geophysics, 168, 367-381, DOI: 10.1007/s00024-010-0161-6.
Julian C. Lozos (2016), A case for historical joint rupture of the San Andreas and San Jacinto faults, Science Advances, 2, doi: 10.1126/sciadv.1500621.
Tom Parsons, K. M. Johnson, P. Bird, J.M. Bormann, T.E. Dawson, E.H. Field, W.C. Hammond, T.A. Herring, R. McCarey, Z.-K. Shen, W.R. Thatcher, R.J. Weldon II, and Y. Zeng, Appendix C—Deformation models for UCERF3, USGS Open-File Rep. 2013–1165, 66 pp.
Seok Goo Song, Gregory C. Beroza and Paul Segall (2008), A Unified Source Model for the 1906 San Francisco Earthquake, Bull. Seismol. Soc. Amer., 98, 823-831, doi: 10.1785/0120060402
Kerry E. Sieh (1978), Slip along the San Andreas fault associated with the great 1857 earthquake, Bull. Seismol. Soc. Am.,68, 1421-1448.
Ross S. Stein, Aykut A. Barka, and James H. Dieterich (1997), Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, Geophys. J. Int., 128, 594-604, 1997, 10.1111/j.1365-246X.1997.tb05321.x
They say you never forget your first love. Well, I remember my first earthquake, too. My elementary school had earthquake and fire drills often, but the Livermore Earthquake in January, 1980 was the first time we had to drop and cover during an actual earthquake. The earthquake occurred along the Greenville fault and over 20 years later, I was the project engineer for an event center not far from this fault. I don’t think that earthquake that led me on the path to become a structural engineer. I was only seven and was more focused on basketball and Atari games than future fields of study.
My favorite part about the Livermore Earthquake was the 9-day sleepover we managed to negotiate with my parents. I have a big family, so we had a large, sturdy dinner table. My brother Neil and I convinced my parents it would be better if we slept under the table, in case there was an aftershock. And, of course, we should invite our friends, the Stevensons, to sleepover because they don’t have as large a dinner table to sleep under at their house. And it worked! In our defense, there were a lot of aftershocks and an additional earthquake a few days later.
Each year, an earthquake preparedness event known as the Great ShakeOut Earthquake Drill takes place around the globe. The event provides an opportunity for people in homes, schools, businesses and other organizations to practice what to do during earthquakes.
Simpson Strong-Tie is helping increase awareness about earthquake safety and encouraging our customers to participate in the Great ShakeOut, which takes place next Thursday on October 15. It’s the largest earthquake drill in the world. More than 39 million people around the world have already registered on the site.
Earthquake risk is not just a California issue. According to the USGS, structures in 42 of 50 states are at risk for seismic damage. As many of you know, we have done a considerable amount of earthquake research, and are committed to helping our customers build safer, stronger homes and buildings. We continue to conduct extensive testing at our state-of-the-art Tye Gilb lab in Stockton, California, and next Wednesday, we’ll be performing a multi-story wall shake table test for a group of building officials at our lab. We are also working with the City of San Francisco to offer education and retrofit solutions to address their mandatory soft-story building retrofit ordinance and have created a section on our website to give building owners and engineers information to help them meet the requirements of the ordinance.
Our research is often in conjunction with academia. In 2009, we partnered with Colorado State University to help lead the world’s largest earthquake shake table test in Japan, demonstrating that mid-rise wood-frame buildings can be designed and built to withstand major earthquakes.
Earthquake articles like the one from The New Yorker also remind us how important it is to retrofit homes and buildings and to make sure homes, businesses, families and coworkers are prepared.
Like others in our industry, structural engineers play a role in increasing awareness about earthquake safety. We’d like to hear your thoughts about designing and retrofitting buildings to be earthquake resilient. Let us know in the comments below. And if your office hasn’t signed up for the Great ShakeOut Earthquake Drill, we encourage you to do so by visiting shakeout.org.
Have you ever been at home during an earthquake and the lights turned off due to a loss of power? Imagine what it would be like to be in a hospital on an operating table during an earthquake or for a ceiling to fall on you while you are lying on your hospital bed.
This week’s post comes from Marlou Rodriguez who is an R&D Engineer at our home office. Prior to joining Simpson Strong-Tie, Marlou worked as a consulting engineer. His experience includes commercial, multi-family residential, curtain wall systems and the design of seismic bracing for non-structural components. Marlou is a licensed professional Civil and Structural Engineer in California, and too many other states to list. He received his bachelor’s degree in Architectural Engineering from Cal Poly San Luis Obispo. Here is Marlou’s post.
I recently had the amazing opportunity to volunteer as a judge at The Tech Museum of Innovation’s The Tech Challenge 2015 in San Jose, Calif. My role involved evaluating projects designed by teams of students in grades 4-12 whose challenge was to build an earthquake-safe structure.
The museum’s annual Tech Challenge is a great event that excites young minds by introducing kids ages 8-18 to the science and engineering design process with a hands-on project based on solving a real-world problem. This year’s challenge was to build a scaled structure that supports live load and is earthquake safe. Simpson Strong-Tie was a sponsor of this year’s event and I was excited to be invited as a judge.
While The Tech Challenge is always focused on solving a real-world problem, no one could have anticipated how real this one would become. On the first day, April 25, I woke up to the horrifying news that a 7.8 magnitude earthquake had devastated Nepal. Thousands of lives were affected by this devastating earthquake. On that morning, this terrible tragedy thousands of miles away really highlighted how important this design challenge really is.
The Tech Challenge spans two days and is divided into three categories: elementary, middle and high school. The judging process consists of two phases. The first phase – a Pre-Performance Interview – gives students a chance to be creative in presenting their teams and designs. They discuss their roles within their team, describe how they chose their design and materials, and explain their method for solving problems and challenges. The second phase places their structures on a test rig and simulates three earthquake movements to test stability. Each structure was judged on its ability to:
Stay standing during all three seismic events
Return back to its original position
Perform with the least amount of drift or the horizontal movement at the top most part of the structure.
As an engineer, I have spent 20 years designing structures to withstand earthquakes. But when I was in elementary school years ago, my thoughts were focused on which parking lot with new curbs, banks and rails or empty pools I could skateboard in. These kids are spending their weekends thinking of how to come up with a system to vertically support a high-rise building and ways to laterally support the building while dissipating the seismic energy induced by the testing rig.
It was amazing to see the ideas the children had in their designs. There were structures with fixed bases, some with innovative base isolation systems and even a few with mass dampers attached to the top of the structure. The lateral systems chosen by the children consisted of moment frames, braced frames and solid core systems – closely resembling the systems used in most buildings today.
The design rules included:
Plan dimension of the building was limited to 16” square, while the base of the building could not exceed 20” square
Structure height could not exceed six feet
Floor-to-ceiling height had to be a minimum of 5 inches
Gravity weight of the structure could not exceed 7 lbs.
In addition, there were some size and length limitations for the supporting materials, based on grade levels, and an additional live load was added to the structure by using bolts that were inserted into drilled holes. Not only did the teams have to adhere to the rules, but they also had to calculate the area of living space within their structure. All of these rules, calculations and how they overcame the challenges had to be documented in a detailed journal.
One design that stuck out to me was developed by a team of elementary school children. I had the pleasure of conducting their pre-performance interview. They had a typical rectangular building with an interior compression member made of stacked plastic PVC pipes. The lateral system comprised of some tension wires that were attached to the top of the building at the interior PVC column. The tension wires were angled as they went through the floors and finally attached to the four corners at the base. The central PVC column bear on the base but was not directly attached to the base. This was a form of base isolation. The four tension wires attached to the four corners of the building were turned toward the central PVC column and attached via a spring. The spring acted as a way for the central column to return to its original position. The design was very interesting and had some innovative features built into it. I could only imagine how it would have performed in the device performance phase of the event, since I wasn’t able to observe that part.
Earthquakes occur all over the world. These natural occurring events profoundly affect and change people’s lives. Although there are a lot of buildings that withstand earthquakes, there are still a lot of failures of existing buildings. Structural engineers learn from these failures and develop building codes and innovative products to resist future earthquakes. These future scientists, engineers and innovators that I had a pleasure of meeting are truly amazing kids. What struck me was how well these children were able to document their thought process and how they developed their final design. It makes me believe the future of this world is in great hands. I can’t wait to come back next year to judge another challenge.
Thanks for reading our blog – have a nice holiday weekend!
I have a special place in my heart for old buildings. Every college design course I took was related to new design. Concrete, steel, or wood design, the design problem was invariably part of a new building. I thought structural engineers designed new buildings. When I showed up for my first day of work wearing dress pants, a button-down shirt and a tie, I was handed a flashlight, tape measure, a clipboard and a Thomas Guide map (no Google maps back then) and sent to do as-built drawings for a concrete tilt-up that we were retrofitting.
In San Francisco, thousands of building owners are already required by law to seismically retrofit multi-unit (at least five) soft-story, wood-frame residential structures that have two or more stories over a “soft” or “weak” story. These buildings typically have parking or commercial space on the ground floor with two or more stories above. As a result, the first floor has far more open areas of the wall than it actually has sheathed areas, making it particularly vulnerable to collapse in an earthquake.
San Francisco’s ordinance affects buildings permitted for construction before Jan. 1, 1978. Mandatory seismic retrofit program notices requiring that buildings be screened were sent out in September, 2013, to more than 6,000 property owners. It is anticipated that approximately 4,000 of those buildings will be required to be retrofitted by 2020.
“When we look at the demographic of these buildings, they house approximately 110,000 San Franciscans. It’s paramount that we have housing for people after a disaster. We know we will see issues in all types of buildings, but this is an opportunity for us to be able to retrofit these buildings while keeping an estimated 1100,000 San Franciscans in their homes and, by the way of retrofit, allowing them to shelter in place after a disaster,” according to Patrick Otellini, San Francisco’s chief resilience officer and director of the city’s Earthquake Safety Implementation Program. “This exponentially kick starts the city’s recovery process.”
One solution to strengthen such buildings is the Simpson Strong-Tie® Strong Frame® special moment frame. Its patented Yield-Link™ structural fuses are designed to bear the brunt of lateral forces during an earthquake, isolating damage within the frame and keeping the structural integrity of the beams and columns intact.
“The structural fuses connect the beams to the columns. These fuses are designed to stretch and yield when the beam twists against the column, rather than the beam itself, and because of this the beams can be designed without bracing. This allows the Strong Frame to become a part of the wood building and perform in the way it’s supposed to,” said Steve Pryor, S.E., International Director of Building Systems at Simpson Strong-Tie. “It’s also the only commercially-available frame that bolts together and has the type of ductile capacity that can work inside of a wood-frame building.”
Another key advantage of the Simpson Strong-Tie special moment frame is no field welding is required, which eliminates the risk of fire in San Francisco’s older wood-framed buildings.
To learn more about San Francisco’s retrofit ordinance, watch a new video posted on strongtie.com/softstory. For more information about the Strong Frame special moment frame, visit strongtie.com/strongframe.
Imagine that it’s 4:30 a.m. and suddenly you’re awakened by strong shaking in your home. Half asleep, you hang on to your bed hoping that the shaking will stop soon. All of a sudden, the floor gives away and you fall. You think, “What just happened? How could this have possibly occurred? Am I alive?”
These could have been the thoughts of Southern California residents living in one of the many apartment buildings, which collapsed on January 17, 1994, during a 6.7 magnitude earthquake. The Northridge Earthquake brought awareness to buildings in our communities with a structural weakness known as a soft story, a condition that exists where a lower level of a multi-story structure has 20% or less strength than the floor above it. This condition is prevalent in buildings with tuck-under parking and is found in multistory structures throughout San Francisco, Los Angeles and other cities (see Figure 1). These structures are highly susceptible to major damage or collapse during a large seismic event (see Figure 2).
Soft story retrofits help to strengthen our communities and make them more resilient to major disasters. There are several resources available to structural engineers that need to retrofit weak-story buildings. Some of these resources are mentioned in our September 18 blog post.
During the 2014 SEAOC Convention held in Indian Wells on September 10-13, speakers discussed different methods, analysis and research that address the behavior of various materials and construction types during seismic events along with approaches to retrofit historically poor performing structures. This information can be viewed from the convention’s proceedings available at www.seaoc.org.
On October 20, 2014, the Structural Engineers Association of Southern California (SEAOSC) will be hosting their 4th annual Strengthening Our Cities BAR Summit in downtown Los Angeles. This event brings together many different stakeholders in our built environment, including public officials, building owners and managers, business owners, insurance industry representatives, emergency managers and first responders, and design professionals.
Many prestigious thought leaders, including USGS Seismologist Dr. Lucy Jones will be speaking at the summit, discussing such topics as tools and analysis methods for retrofitting vulnerable buildings and the Building Occupancy Resumption Program (BORP).
Expect a great day full of useful information about ways to strengthen our communities and prepare for major earthquakes as well as opportunities to network with like-minded peers. For additional information and to register, visit www.barsummit.org. We also hope you’ll visit our booth. We look forward to speaking with you there.
Steve Pryor, S.E., has been with Simpson Strong-Tie for 17 years and currently serves as the International Director of Building Systems. Prior to joining the company, Mr. Pryor was a practicing structural engineer in California. While at Simpson Strong-Tie, he developed the Tyrell T. Gilb Research Laboratory, one of the world’s premier large-scale structural systems test facilities. The lab has the capability to simulate both wind and seismic effects on light-frame structures via both quasi static/cyclic and dynamic test machines that can apply vertical and lateral loading simultaneously. A recognized expert in the structural response, analysis and testing of light-frame buildings, Mr. Pryor participates on several state and national building code committees. He was the primary industry technical consultant for the highly successful NEESWood Capstone seismic testing in Miki, Japan, which tested a full-scale seven-story mixed-use steel/wood structure, the largest building ever tested on a shake table.
We all know that earthquakes physically shape the landscape here in California, but they shape careers as well. Earthquakes I felt while growing up in California’s southern San Joaquin Valley got me thinking about engineering as a career while in high school. When the Loma Prieta earthquake struck on October 17, 1989, like many of you I was watching the World Series live on television and thus got to see the earthquake live as well. I was in my senior year of college at the time, studying Civil Engineering with a structural emphasis. This earthquake cemented the direction I would take in my career. I wanted to be a structural engineer, and I wanted to design buildings that would not fall down in earthquakes.
After Loma Prieta hit, I was relieved when I finally got through to my family and realized everyone was okay. If an earthquake like that happened again today, I would get an alert on my cell phone and know within minutes exactly where it happened, how big it was, and how deep it was. I would also be able to look at the USGS ShakeMap online to get a feel of ground-level damage potential and locations. But in 1989, none of this information was available so over the course of the next few days along with the public, I learned about what had happened in the Bay Area.
After graduating in 1990, several great mentors guided me as I pursued the art of earthquake-resistant structural engineering. I began to realize that earthquakes are like a great predator of the built environment: occasionally they take down healthy buildings in their prime, but they particularly focus on the old and the weak amongst our building stock; buildings with known (and sometimes unknown) deficiencies that if improperly designed or left unretrofitted cause them to fall prey to the earthquake. After several years of practicing structural engineering, and after obtaining my P.E. and S.E., it was with some irony that I came to work at Simpson Strong-Tie in 1997. I became part of a team of dedicated people working to provide structural solutions to new and existing buildings in an effort to keep them from falling prey to the next earthquake. I was now a Bay Area resident, living in the shadows of the same seismic hazards that had manifest themselves on October 17, 1989, and which had shaped my career choice.
While there were many different types of structural weakness on display as a result of the Loma Prieta earthquake, soft- or weak-story wood-frame structures commanded much of the attention. These multi-story wood light-frame structures have an inherent weakness at the ground floor because the area open for parking also cuts down on the area available for shear walls, and thus the available lateral strength. Without the requisite lateral strength in these weak stories, many buildings suffered heavy damage and even collapse. And all of this from an earthquake that was centered about 56 miles south of San Francisco. One can only imagine what would happen if a similar earthquake occurred much closer.
In response to this threat, the City of San Francisco has embarked on a groundbreaking mandatory retrofit ordinance that will hopefully allow many of the city’s residents who live in these structures to “shelter in place” after the next “big one.” What buildings are affected by this ordinance? Wood-frame buildings built or permitted prior to January 1, 1978 with two or more stories over a soft- or weak-story that contain five or more dwelling units.
There are many questions that automatically pop up in response to this. How well does my building have to perform in order to enable me to shelter in place? Could I possibly shelter in place with a yellow tag on my building, or does it have to be green tagged? There is debate on this issue. What constitutes the “big one” – is it the “expected” more frequent earthquake, or is it the extremely rare, very large earthquake? The engineering criteria of the retrofit ordinance points toward it being the “expected” earthquake. Can these retrofits be done (economically) and will they make a difference? Absolutely. How can you say that? We’ve tested them.
Simpson Strong-Tie was a proud sponsor and contributor to an ambitious project known as NEES-Soft. Led by Dr. John W. van de Lindt of Colorado State University, the project culminated with shake table testing of a full-scale four-story weak-story building on the outdoor shake table at the University of California San Diego in the summer of 2013. Constructed to be like a real San Francisco weak-story structure, the building offered a fantastic platform to test various retrofit technologies. One of the retrofit technologies tested was the Simpson Strong-Tie Strong Frame® special moment frame. Designed according to one of the engineering approaches (FEMA P-807) permitted in the City of San Francisco’s retrofit ordinance, the Strong Frame special moment frame performed extremely well, and we were able to conclusively demonstrate the improved performance of the building. Check out this link to understand some of the unique features that make this frame especially well suited for seismic retrofits of wood-frame structures. And don’t forget that any retrofit frame or wall is only one part of the complete load path needed for a successful retrofit!
The Strong Frame special moment frame did not materialize overnight in response to the new retrofit ordinance. The work on it and the other lateral force resisting products we manufacture began years earlier. It turns out that there are a whole bunch of people at our company, professional engineer or not, who are constantly thinking about this and share the same desire that developed in me back in 1989: let’s make products that help buildings not fall down in earthquakes. How can we help you on your project? Let us know – we’d love to hear from you.