By Edwin T. Dean, PE, SE
Having completed the initial designs for the innovative CoreFirst system, we at Nishkian Dean believe that it is a viable alternative to doing nothing and accepting fate when it comes to the next earthquake that may devastate Oregon buildings and put occupants in harm’s way. There is little argument that a full seismic strengthening of a building is the best solution, but for many building owners, it is simply not an expense that they can afford. If a full seismic upgrade is not a financially viable option, an alternative that would potentially provide a robust sanctuary to shelter occupants as the building around them shakes apart during a seismic event is a good one.
The CoreFirst system functions as a seismic shelter erected within an existing building, providing improved life safety during a seismic event without the need to retrofit the building to current seismic standards. Coupled with an earthquake early-warning system that can provide more than 60 seconds to evacuate, CoreFirst both alerts building occupants and provides a safe place to congregate during an earthquake.
Composed of a one or two-story steel special moment frames oriented in both principal directions, the CoreFirst system includes a steel grating plank platform at each level to provide protection from debris and existing building failure. The moment frames are isolated from the existing structure, ensuring that they only resist load generated by the seismic weight of the CoreFirst shelters. While the moment frames are not tied to the building’s existing seismic-force-resisting system, they are designed with a large reserve capacity for additional lateral load, with the added benefit of potential use as a component of a future comprehensive seismic upgrade of the building.
The shelters are designed so that their floor levels are located below the floor structure of the existing building. These floor levels are framed out with infill gravity framing supporting steel planks or channels that form a debris shield, preventing debris from falling through the floor of the existing structure into the shelter’s protective zone. The platforms are designed for a floor live load of 100 psf, a roof live load of 20 psf, and a vertical seismic load of 50 psf (representing both the dynamic load of debris falling on the platform and the static load of accumulated debris). Ultimately, all the gravity load is supported by the moment frames.
The moment frames are designed to the requirements of a Risk Category IV structure, which primarily impacts the drift limit, or the typical governing limit state for steel moment frames. Based on the seismic weight of the frames and grating platforms, seismic loads are generated for the frame per the equivalent lateral force procedure of ASCE 7. To enable the potential use of the frames as a component of a future full seismic upgrade of the building, additional seismic load is assigned at each level of the moment frames. It is not always possible to predict what shape a future seismic upgrade would take, and what loads the moment frames might need to carry, but a conservative load is estimated by assuming that a certain tributary area is assigned to the moment frames based on their location in the building. The total lateral load the frames are designed for is indicated on the construction drawings for future reference.
Footings are also designed for the additional seismic load described above. Because the frames are isolated from the main structure, they have very little dead load to resist overturning. As a result, there are three footing options:
1) Very large isolated footings with enough weight to prevent overturning
2) A mat footing designed to resist overturning
3) Small isolated footings/pile caps utilizing helical piles to resist uplift and downforce
The seismic gap required around all interfaces between the shelters and the existing structure is determined by estimating the maximum seismic drift of the building (based on the drift limits for the building’s structural system at the time it was constructed), determining the maximum seismic drift of the moment frames, and calculating the resulting maximum drift in any direction for both cases by combining the maximum drift in one direction with 30% of that drift in the orthogonal direction. The sum of the two maximum drifts is the minimum required seismic gap.
We believe that building owners could benefit from this affordable system. If you have any questions about CoreFirst, please contact us at the Nishkian Dean office or visit the CoreFirst website. We are happy to discuss this innovative system!
Edwin T. Dean, PE, SE is Vice President and Managing Principal of Nishkian Dean a structural engineering consulting firm in Portland, Oregon.
By Edwin T. Dean, PE, SE
Unreinforced masonry (URM), or the use of stone or brick masonry for structural walls, was a common approach in Portland building construction from the late 1800s to as recently as the 1950s. These buildings range in size from small one-story residences to large 10- or 12-story buildings, most with wood-framed floors with some structural steel or cast-iron components. Many of these buildings are historically registered and represent a valuable part of the City’s cultural heritage. Several are public buildings used for government operations or public schools. The characteristic of concern for this type of building construction is that they are extraordinarily vulnerable to earthquake damage, where even moderate ground shaking could result in partial collapse.
Earthquake occurrences in other West Coast cities, such as Loma Prieta in 1989 in the San Francisco Bay Area and Northridge in 1994 near Los Angeles, have demonstrated that this type of construction is susceptible to devastating collapse and associated loss of life and property damage. There were many URM buildings that were damaged in these events, including those that had been seismically strengthened. This damage represented a very significant economic cost, though fortunately not a large number of deaths and URMs did not represent the deadliest type of buildings. These cities now have URM mandates: in the Bay Area, this was largely put into place after the Loma Prieta event, and in Los Angeles it had been implemented prior to the Northridge event.
The Portland metro area has so far been spared from a major earthquake in recent history, though geoscientists believe that large damaging earthquakes are possible. Beginning in the 1980s, the building codes have progressively increased the seismic design requirements in recognition of the potential for such natural disasters. The rate at which URMs have been retrofitted to resist earthquakes on par with current code requirements has been slow.
The City of Portland’s Unreinforced Masonry (URM) Building Policy Committee (Committee) estimates that since 1995, roughly 8% of URMs have been demolished. Of those that remain, about 5% have been fully retrofitted and about 9% have been at least partially upgraded. At that rate, it could take almost another 100 years for the URM building inventory in Portland to be either strengthened or demolished. Based on the risks posed by URM buildings to public safety, the Committee is proposing a tiered retrofit approach, requiring URM upgrades to buildings over a defined period of time. See our prior blog article, Portland Poised to Mandate URM Building Seismic Strengthening, for more background information on this.
The Committee proposal to require seismic strengthening of URM buildings is a tiered approach based on the buildings’ use and occupancy. The only exceptions to these recommended requirements are for one- and two-family homes and URM buildings that were previously seismically strengthened to an acceptable defined standard.
The Committee has defined four categories or classes of URMs with differing levels of seismic strengthening requirements and time horizons to complete them. The classes range from 1 to 4 with Class 1 for Critical Buildings and Essential Facilities and Class 4 for Low-Occupancy structures. In between these, Class 2 is for Schools and High-Occupancy structures (Churches and Theaters), and Class 3 is for is the largest class of building (approximately 2/3 of all URMs) and covers every other URM building not in the other classes. The City has compiled a detailed inventory of the buildings and the classification that they would fall under. The timeframe for implementation of the seismic strengthening varies by Class, but generally requires a seismic assessment in 3 or 5 years and strengthening implementation in 10 to 20 years.
Step 1 – A seismic assessment (ASCE 41-13) with a schematic seismic upgrade strategy including detailed cost estimates must be completed within three or five years.
Step 2 – Parapets, cornices and chimneys must be braced, and the roof must be attached to walls within 10 years.
Step 3 – All floors must be attached to walls and the roof must be sheathed within 15 years.
Step 4 – A complete retrofit must be performed within 20 years.
Separately, the Portland Bureau of Emergency Management and Bureau of Development Services commissioned Goettel & Associates, Inc. to prepare a Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance. The report was published on November 23, 2016, and concluded, “The benefit-cost results indicate that the benefits of the URM building seismic retrofits current under consideration exceed the retrofit costs for the defined “typical building” for each URM Class of buildings.” The Committee intends to present their codified recommendations for mandatory seismic strengthening of URM to City Council for adoption. The City Councils adoption of the mandatory ordinance will start the clock and require building owners to either strengthen their URM buildings, demolish them, or face growing fines and the eventual loss of the use of their buildings.
Cost to Implement
The implementation of this mandatory ordinance will have a significant financial impact on the building owner. The objective of such an ordinance from the City’s perspective would be to reduce the life-safety risk these buildings pose to the occupants and those people who may be nearby these buildings in the event of an earthquake. The benefit-cost analysis demonstrated that there was a net benefit to the seismic strengthening; however, those benefits are not directly correlated to the financial return of the building. The Committee in its recommendations were not able to identify anything more than $5M in available Urban Renewal Area (URA) capital funds to assist building owners with the high costs of implementing the seismic strengthening. There are also possible State and Federal tax exemptions or credits and funding from the State Seismic Rehabilitation Grant Program (SRGP) for schools and emergency service facilities and potentially the sale of Floor Area Ration (FAR) transfers to another site. Additionally, the current Committee recommendations do not provide any material relief to buildings with “special considerations,” meaning those with occupants needing affordable housing, schools, religious or non-profit users, or historic structures. The Committee report does not identify the total cost to implement the required mandate. The cost-benefit study identifies the current costs to seismically retrofit or strengthen the four classes of building types on a square-foot basis in Table 15 of their report. Combining these square foot costs with the building areas contained in the inventory list provides the following total costs:
Table 1: Estimated Total Retrofit Costs Based on BDS Inventory
|URM Class||UPGRADE||Cost per Square Foot||No. of Buildings||AREA in Square Foot||TOTAL||AVG per Building|
|Class 1||Immediate Occupancy||$111.45||10||49,329||$5,487,717||$549,772|
|Class 2||Damage Control||$82.62||92||3,253,423||$268,797.808||$2,921,715|
|Class 3||Life Safety||$68.77||220||8,379,527||$576,260,072||$2,619,364|
|Class 4||Modified Bolts Plus||$51.00||1,339||10,915,945||$556,713,195||$415,768|
This would indicate that the cost to implement this mandate, if all the buildings are strengthened, to be on the order of $1.4 billion. However, this amount is an oversimplification. Faced with these costs, which in many cases exceeds the economic value of the property, it is reasonable to assume that many building owners will either abandon the properties or opt to have the buildings torn down until market conditions favor the cost of rebuilding. This will particularly impact buildings at the lowest economic value, such as those being used for affordable housing. The mandate will also allow the seismic assessments to be performed and permit the seismic strengthening to be implemented over a period of up to 20 years, assuming that building owners will wait as long as possible to seismically strengthen their buildings. When this is factored in, and the time-value of the construction costs at a 4% annual escalation are accounted for in the total cost to implement this regulation, the total costs rises to approximately $4.6 billion. Again, this assumes that all the recommended buildings will be strengthened and the reality is that many will not due to the financial restraint.
“total cost to implement this regulation, rises to approximately $4.6 billion”
The URM Building Policy Committee will continue meetings and prepare final recommendations. These recommendations will be taken up by the Portland City Council, possibly as soon as the fall of 2017. At that point, the Council will need to decide if it will implement the recommendations, or some aspects of the recommendations, as an ordinance mandating seismic strengthening of URM buildings, or continue with the status quo as required by Title 24.85. Nishkian Dean will continue to monitor the development of this important issue that affects many of our clients.
Edwin T. Dean, PE, SE is Vice President and Managing Principal of Nishkian Dean a structural engineering consulting firm in Portland, Oregon.
 City of Portland Policy Committee, DRAFT Unreinforced Masonry (URM) Building, Policy Committee Report, dated October 2016, pg. 8
 Kenneth A. Goettel, Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance, City of Portland, November 23, 2016, pg. iv
 Religious facilities would be provided relief from completing steps 3 & 4.
 Kenneth A. Goettel, Benefit-Cost Analysis of the Proposed Seismic Retrofit Ordinance, City of Portland, November 23, 2016, Table 15, pg. 31
The Los Angeles Times proclaimed the start of a “New Frontier” for earthquake safety: a phenomenon kicked off by the city of Santa Monica, which recently adopted the most comprehensive seismic retrofit ordinance in the nation.
An Owner’s desire to evaluate the seismic performance of an existing building varies. Some national, regional and local Owner’s simply have a genuine concern for knowing the seismic vulnerability of their buildings. Other reasons Owners perform evaluations can include an adopted City Ordinance, a policy trigger for analysis or modification of the building, a requirement for a financial transaction, or buildings with State employee tenants requiring special analysis, just to name a few.
We are currently performing dozens of these evaluations on projects throughout California, efficiently utilizing the ASCE standard ASCE/SEI 41-13. Copyrighted in 2014 by the American Society of Civil Engineers, the standard was developed and written to combine the previously adopted standards ASCE 31 and 41 into a single document for the Seismic Evaluation and Retrofit of Existing Buildings. Whereas past retrofit designs often did not align with evaluations due to having documents with differing criteria for evaluations versus design, this single document coalesces both evaluation and design of existing building retrofits providing one coordinated methodology. Seismic evaluation is defined as an approved process or methodology of evaluating deficiencies in a building that prevent the building from achieving a selected Performance Objective. Seismic retrofit is defined as the measures taken to improve the seismic performance of a building by the correction of deficiencies identified in the evaluation relative to a selected Performance Objective.
The initial step in the process is to assist the client in establishing or selecting a Performance Objective which is a combination of a desired Structural and Non-Structural Performance Levels paired with Seismic Hazard Level(s). The chart below demonstrates the different Performance Level terminology:
Following the establishment of a Performance Level, the Seismic Hazard is established based on the seismicity at the building site determined by historical data, with consideration of proximity to known faults and their activity as well as the specified Seismic Hazard Level(s).
Evaluation procedures based upon the selected Performance Objective, level of seismicity and building type are identified in the following flowchart:
Each Tier of evaluation becomes more detailed and complex. The Tier 1, Screening Procedure, is a quick checklist of structural and non-structural components of the building. A Tier 2, Deficiency-Based Evaluation procedure, utilizes more involved checks of the building to provide a deeper understanding of the building’s design. A Tier 3, Systematic Evaluation Procedure, provides a full building review including linear and non-linear / performance based analysis and design options.
The final step in the review process is to prepare an evaluation report to communicate the results of the evaluation to the owner, local jurisdiction or agency requesting the evaluation. Depending upon the availability of information and the scope of the evaluation, the extent of the report may range from a letter to a detailed document.
If the seismic evaluation suggests that a seismic retrofit is warranted, the next step is to perform the design for the retrofit. A Seismic Retrofit design will utilize the evaluation report to identify the seismic deficiencies relative to the selected Performance Objective. One or more of the following strategies to retrofit the deficiencies may be considered:
Nishkian Chamberlain has extensive experience in seismic retrofit projects and is currently working with building owners to assist in identifying the impact that retrofitting in accordance with the City Ordinances will have on their building assets. We are currently working as part of an advisory council to evaluate over 50 buildings for one client that is proactively looking to understand the overall vulnerability of their portfolio.
Should you need the assistance of a trusted advisor to guide you through the uncertainty of the City Ordinances, evaluate an existing building or make additions/modifications to an existing building, contact us at NCInfo@Nishkian.com or give us a call at 310.853.7180 for cost effective, creative seismic retrofit solutions. You can also go to our Contact page to connect with any one of our offices in your region.
Since the passing of the LA City’s Ordinance in October of 2015 to improve the seismic safety and community resilience of the City by requiring retrofit of over 15,000 soft story and non-ductile concrete buildings, the City of Santa Monica (approximately 16 miles west of LA) appears to be the next major city to adopt a similar but more expansive building type ordinance.
The Santa Monica City Council, on February 14, 2017, tentatively approved, unanimously, to adopt the nation’s most extensive seismic retrofitting effort, which could require safety improvements to as many as 2,000 earthquake-vulnerable buildings. For the ordinance to be approved, the City Council will need to pass the law a second time in the next month. If the measure receives that affirmation, the proposal will become law 30 days later.
Santa Monica’s safety rules would go beyond what Los Angeles has done by requiring not only wood-frame apartments and concrete buildings to be retrofitted, but also Concrete Tilt-Up, Unreinforced Masonry and Steel-frame structures.
Of the roughly 2,040 buildings, about 1,700 of them are suspected to be wooden apartment buildings with carports on the ground floor, known as soft-story buildings, one such complex collapsed in the 1994 Northridge earthquake, killing 16 people on the ground floor in the predawn darkness.
About 200 are suspected vulnerable brick buildings, also known as unreinforced masonry, in which bricks can come spilling out of walls, striking occupants and passersby and triggering the collapse of the roof. 60 suspected brittle concrete buildings were listed, holding residences, hotel rooms and office space. 30 Concrete Tilt-up buildings susceptible to failure at interconnection between the roof and the wall could cause the wall to pull away from the building resulting collapse of the roof. And finally, 80 steel moment-frame buildings, with the tallest a 13-story condominium and two 12-story office buildings, that could be vulnerable in an earthquake.
Santa Monica’s proposed law gives owners of steel buildings the most time to retrofit once an order is given to evaluate the structure — 20 years. Brittle concrete buildings will have a deadline of 10 years; wooden apartment buildings, six years; tilt-ups, three years; and brick buildings, two years.
Other Southern California cities are also looking to strengthen their seismic safety laws. West Hollywood and Beverly Hills are both considering mandatory retrofit laws, and elected leaders are now casting the issue as not one of cost, but of public safety. Stricter retrofit ordinances are also becoming law up and down the west coast.
Nishkian Chamberlain has extensive experience in seismic retrofit projects and is currently working with building owners to assist in identifying the impact that retrofitting in accordance with the City Ordinances will have on their building assets. We are currently working as part of an advisory council to evaluate 50 of 200 buildings for one client that is proactively looking to understand the vulnerability of their portfolio.
Should you need the assistance of a trusted advisor to guide you through the uncertainty of the City Ordinances and provide cost effective, creative seismic retrofit solutions, contact Craig Chamberlain at CChamberlain@nishkian.com. You can also go to our website at www.nishkian.com to connect with any one of our offices in your region.
By Dave Beh
Structural engineers design the primary structure to withstand seismic forces, as a minimum, as outlined by the design code. However, during an earthquake people can be injured and costly damage can result by falling non-structural components such as; kitchen hoods, bookcases or mechanical/electrical equipment. The code also requires seismic anchorage for certain non-structural components but these can sometimes get overlooked by designers/owners/plans examiners that simply don’t yet have the information or are unaware of the requirements.
The City of Portland is laced with seismic faults and is vulnerable to the looming Cascadia subduction zone earthquake, which could have a magnitude as high as 9.0. Despite this risk, Portland has one of the highest concentration of unreinforced masonry (URM) buildings in the Pacific Northwest. URM buildings are particularly vulnerable to potential catastrophic collapse in earthquakes. To alleviate this risk, the Portland Bureau of Emergency Management (PBEM) convened a series of committees to propose new URM seismic retrofit standards, which are currently under deliberation with the goal of passing the new standards in the City Council in 2017.
Originally constructed as a medical office building, this four-story, semi-circular structure will be the new home to Nova Academy located in Santa Ana, California. In order to meet the increased design criteria required to convert the existing building to a school building, a series of fluid viscous dampers were installed into the structure to supplement the existing pre-Northridge steel moment frame system.
Over the past few months, major earthquakes have shaken areas around the world. The 7.8-magnitude earthquake that struck Ecuador on April 16 has killed at least 659 people, and more than 27,732 others were injured. The quake, Ecuador’s worst in decades, destroyed or damaged about 1,500 buildings, triggered mudslides and left some 20,500 people sleeping in shelters, according to the government. Japan was also hit with a series of earthquakes last month killing at least 49 people and injured about 3,000 others in total. Severe damage occurred in Kumamoto and Ōita Prefectures, with numerous toppled buildings, collapsed bridges and shredded structures into pile of debris.
The reconstruction of the F&H Building on 211 East Main Street was a major contribution to the revitalization of downtown Bozeman, its place in the community and local economy. The process of rebuilding also played a major part of the healing process for downtown Bozeman. Seven years ago in the morning of March 5, 2009, a gas main explosion and fire rocked the snow-covered downtown Bozeman, destroyed five historic buildings and businesses on the north side of the 200 block of East Main Street, and killed one young woman. Eleven months after the explosion, two Bozeman businessmen submitted plans to build a new three-story structure, which would fill more than fifty percent of the gaping hole and rebuild. Rockin R Bar owners, Ralph Ferraro and Mike Hope, named the new building the “F&H Building.”
Renters and apartment owners must equally share the financial burden of earthquake retrofitting, the Los Angeles City Council agreed Wednesday, January 13, 2016, capping a more than year-long debate that allows the city to begin implementing the most comprehensive mandatory seismic laws in the nation.
Following many housing studies and heated meetings with landlord and tenant groups, city staff proposed a compromise that the City Council unanimously voted to move forward: Owners can pass half the retrofit costs to tenants through rent increases over a 10-year period, with a maximum increase of $38 per month.
Aging and historic structures bring a style of their own into the skyline as they mesh with the sleek lines and polished surfaces of modern construction. Old age, poor or nonexistent drawings, past renovations, and other unknown conditions mean bringing these structures up to current code represents a unique challenge. The design team should be aware of the most up to date code standards and how they can be utilized in the project jurisdiction. American Society of Civil Engineers (ASCE) 41-13 is one such code that deserves attention.
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. 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.
As structural engineers, and with the recent large earthquakes around the world, the latest earthquake disaster movie moving out of theaters–and yesterday’s 4.0 magnitude earthquake that jolted East Bay residents awake, we get a lot of questions about what to do during an earthquake. We have gotten this question from family members and friends, and even a stranger at a bar who overheard our conversations. Surprisingly, I have been able to use a scene in the movie San Andreas to better illustrate the answer this question: duck, cover, and hold.
It has been shown that the number one cause of harm during an earthquake in the U.S. is falling objects. These are items like lights, signs, ceiling tiles, and broken glass. To avoid getting hurt by these objects, it is the consensus of the engineering society to duck, cover, and hold. Specifically, get under a surface, cover your head, and hold on to the legs of the surface. This way you will be well hidden from falling objects, and the surface won’t roll or slide away from you in the event of large shaking.
After an extensive 16-month renovation and seismic retrofit the Joseph Phelps Vineyards Guest Center re-opened its original winery building to visitors this summer. Originally designed by renowned architect John Marsh Davis in 1973 the majority of the historic building’s interior was removed, an interior floor was added, and the old building seismically upgraded. The Phelps family and the executive team collaborated with Baldauf Catton Van Eckartsberg (BCV Architects), Brandenburger Associates AIA, Cello & Maudro Construction Company (General Contractor), and Nishkian Monks to repurpose the interior winery spaces, enhancing the guest experience, while maintaining the building’s existing redwood exterior design.
Timing and logistics were key challenges as work occurred with hundreds of guests visiting the winery campus located in California’s Napa Valley. The architects focused on creating lighter spaces and installing modern utilities, while preserving the classic character of the structure. One of the primary challenges of the project was the seismic reinforcement and safety of the 40 year old structure.
A recent article in The New Yorker entitled “The Really Big One: An earthquake will destroy a sizable portion of the coastal Northwest. The question is when.” has caused a media storm with outlets across the country now talking about, what was for many, a previously little-known fault line, the Cascadia Subduction Zone, and its anticipated impact on the Pacific Northwest.
The Cascadia Subduction Zone refers to a fault line just off the Oregon/California/Washington coastlines, paralleling a series of volcanic mountains called the Cascade Range, where the North American and Juan De Fuca tectonic plates meet in the Pacific Ocean. These tectonic plates are so tightly wedged against one another and the pressure is so intense that when they eventually slip along its length, scientists are anticipating a 9.0, or higher, magnitude earthquake accompanied by a potentially 45-foot tall tsunami that will batter the north Pacific coastline from California to Canada. And, according to those same scientists, we are 315 years into a 243-year recurrence cycle.
The Cascadia Subduction Zone, an area where tectonic plates off the coast of Oregon typically grind and slip to relieve pressure, have become “locked.” All of this pressure building along the fault line must be released at some point, which has significant implications for risk of major earthquake in the Pacific Northwest.
In response to this, Oregon’s Seismic Rehabilitation Grant Program (SRGP) was initiated by Oregon Emergency Management to fund earthquake retrofitting and seismic upgrade efforts for schools, higher-education institutions, and emergency services buildings.
The most obvious threat from earthquakes is physical damage to vulnerable buildings. Buildings can be built to withstand strong earthquake shaking, but because of the increased costs associated with such enhancements, most are not. Many people believe that modern Building Codes ensures that our buildings will not be severely damaged in earthquakes. Current Building Codes, however, are designed to maximize life-safety, and not to minimize building damage. These standards mean that while buildings are designed to remain standing and protect occupants from collapse, they are not designed to necessarily remain usable or prevent damage after strong earthquakes. A strong earthquake in Los Angeles could cause some older buildings to collapse, but would leave many more standing but unusable or in need of repairs, which would close businesses, deny residents access to goods and services, and devastate our economy.
“Resilience by Design” presents the recommendations of the Mayoral Seismic Safety Task Force (headed by Dr. Lucy Jones of the United States Geological Survey as his Science Advisor for Seismic Safety). These recommendations address the city’s greatest vulnerabilities from earthquakes with significant and attainable solutions to:
Earthquakes versus hurricanes…which natural disaster proves to be more damaging to buildings? This is an interesting question to compare and contrast. Each event affects buildings in fundamentally different ways, yet there are some striking similarities, as well. Let’s examine them.
Earthquakes are strong ground movements that result from ruptured crustal faults. And although regions that are seismically active and prone to earthquakes are largely known and geoscientists have mapped at least the potential for strong ground motions throughout the United States, earthquakes are unpredictable. The strength of the ground shaking below a particular building is a function of the distance from the rupture (both depth and distance along the surface), the type of soil the building sits on, and, of course, the size of the rupture/the extent to which the fault fractures during the event. The ground accelerations manifest themselves in forces within the building (remember from science class, F = ma where “m” is the mass of the building and “a” is the ground accelerations). Some of the strongest ground accelerations mapped by the USGS can be found in:
More and more discussions these days are focusing around the resiliency of our communities. How well are the cities in which we live prepared to react to emergencies? In the Structural Engineering community here on the West coast, we tend to think of these related to our response to earthquakes, but this can also related to hurricanes, flooding, tsunamis, fires or other significant events. Community resilience has to do with many different things from our building structure survival to emergency response teams to communication lines to water distribution and other lifeline critical elements.
One major aspect to the community resiliency discussion is the ability of our existing building stock to survive a disaster. An effort is underway to better track and categorize how safe each and every building is that we live, work and play in every day. A relatively new organization, The U.S. Resiliency Council (http://www.usrc.org/) is working to address this topic. This group is developing a system to measure the risk and resiliency of our existing building stock. Ratings will benefit Owners, Lenders, tenants and government jurisdictions by increasing the value of well-designed buildings and providing a means for quantifying risk. See the chart below of an example of how these ratings could be posted on a building.
The U.S. Geological Survey’s (USGS) Working Group on California Earthquake Probabilities estimated in 2007 that there is a 63% probability of at least one magnitude 6.7 or greater quake, capable of causing widespread damage, striking the San Francisco Bay region before 2030. There is a 67% probability of a similarly sized earthquake striking the Southern California region within the same period (http://www.scec.org/ucerf2/).
Seismic retrofitting a building in California is a great way to reinforce the long term durability of a building before the next earthquake hits. It also makes the structure safer by protecting the occupants from potential loss of life. A retrofitted structure can generally withstand more movement than a non-retrofitted structure and this will help business owners protect their assets, reduce liability and lower the risk of catastrophic loss.
Nestling high in the foothills of Mount Everest lies the village of Phortse, a community of Sherpas working together to develop their village. One of the ongoing community project work is the Khumbu Climbing Center, a project of the Alex Lowe Charitable Foundation. In 2003 the Alex Lowe Charitable Foundation launched the Khumbu Climbing Center to teach basic mountaineering and climbing skills to Sherpas who often make their living guiding on Mount Everest with little or no climbing experience. The climbing center project is being built in honor of Alex Lowe who was widely considered one of the finest all-around mountaineers when he was killed by an avalanche in Pakistan in 1999. The building will be the first structure in this region to be engineered professionally to reduce structural damage from an earthquake and prevent roof collapse due to heavy snow load. Also unique to the region is the building’s passive solar design considerations. The building will be heated entirely by passive heating techniques. The Alex Lowe Charitable Foundation collaborated with the community of Phortse, Montana State University, architect and MSU professor Michael Everts, and structural engineer Ty Monks, P.E., LEED A.P. of Nishkian Monks PLLC in Bozeman, Montana to design and build this new school located in the rural hillsides of Nepal. Once completed, the 3,000-square-foot (279 square meters) building will house classrooms for teaching technical climbing and rescue skills, an indoor training wall, a library, storage room for gears, solar showers, and community center.
The 6.0-magnitude earthquake that struck at 3:20 am on Sunday, August 24, 2014 near American Canyon in the San Francisco Bay Area has once again brought attention to earthquake preparedness. According to various local reports, the earthquake injured about 200 people and caused at least $1 billion in damage and losses. San Francisco Business Times’ Chris Rauber reported that overall damages could hit as high as $4 billion.
The Napa Valley earthquake was the first significant test of the Bay Area’s preparedness since the 1989 Loma Prieta earthquake. In the 25-years since the devastating Loma Prieta earthquake, great strides have been made in encouraging seismic retrofitting. However, there are still far too many vulnerable buildings in our seismically active regions. If you’re a long-time resident in California or the Pacific Northwest chances are that you’ve seen firsthand the dangers that older “soft story” type structures and unreinforced masonry buildings pose. We cannot stress enough that retrofitting older structures is crucial to saving lives before the next “big one” hits. Nishkian engineers have extensive experience in seismic upgrades and retrofitting, and keep up to date with ever changing building codes and state-of-the-art solutions to address these challenges. If you have any questions about seismic upgrades and your building, please contact any of our offices.
Earlier this year we wrote about several cities across the state of California that were in the process of enacting new legislation regarding retrofit of certain types of older buildings. While San Francisco passed legislation specifically for soft-story structures, Los Angeles and Santa Monica have been working to put new legislation in place. Here we’ll discuss the latest progress in the City of Santa Monica.
On February 11th, 2014 the City of Santa Monica put their latest Seismic Retrofit Plan in motion. At this council meeting the Department of Planning and Community Development was allocated $105,000 to launch the first of three phases of a comprehensive seismic safety program that will address building vulnerabilities within the City of Santa Monica.
Currently, in the City and County of San Francisco, there are over 24,000 children attending private K-12 schools. These schools play a vital role in San Francisco communities and in the education of future generations. As such, the buildings that make up these schools play an important role in protecting students. Private schools in general are held to a lower building code standard than public schools. Plans for public school are required to be reviewed by the Division of State Architect and designed by a licensed structural engineer, while private schools are only designed by a licensed professional engineer. The inspection and material testing requirements are also much more lenient in private school building construction than in public schools. These requirements, coupled with an aging building population, can result in lower seismic safety of private school building.
The Private Schools Earthquake Safety Working Group started meeting in late 2012 to discuss and explore the current state of private school’s building seismic safety. The Working Group was made up of parents, school faculty, engineers, city officials, and concerned citizens who met for over a year to assess the best course of action in regards to the seismic safety of buildings. The Working Group’s recommendation to the City of San Francisco is to implement a mandatory seismic evaluation ordinance for all private schools within the City and County of San Francisco.
On the U.C. Berkeley campus, directly adjacent to the California Memorial Stadium, sits Maxwell Family Field. The existing multi-use playing field has been temporarily removed in order to build a two story parking structure and new elevated field in its place. The project will provide an updated sports field and 450 much needed parking spaces to the UC Berkeley campus. Pacific Union Development Company, with architect Gould Evans, contractor Build Group, and Nishkian Menninger, has created plans that allow this structure to be built on this challenging site.
Long ago, the site was once a creek bed. During the development of the campus, the creek was turned into a set of large culverts, and filled in to provide a flat surface. This type of loose fill makes building a seismically safe structure more difficult. Similar to the challenges of building on bay mud in San Francisco, the ground could liquefy during an earthquake, resulting in amplified forces on the structure. This condition is exacerbated by the presence of the Hayward fault, which runs just a few hundred feet away from the site.
Located in the Crow’s Nest development at Sugar Bowl Ski Resort in Tahoe, California this 5,600-square-foot, three-story, unique ski-in/ski-out chalet is truly a one-of-a-kind custom home. Nishkian Monks PLLC participated in the project as the structural engineer of record, working directly with San Francisco-based architectural firm Baldauf Catton Von Eckartsberg/BCV Architects, and general contractor Mt. Lincoln Construction of Truckee, California. Situated in the Sierra Nevada mountain range where maximum expected design snow depth is 16 feet – equating to 380 pounds per sq.ft. of snow weight, construction of this luxury residential building posed challenges due to the site and program constraints. Additionally, the site is located at one of Sugar Bowl’s highest reaches – higher than many of the resort’s ski lifts, and situated in a region of high seismicity. BCV Architects challenged Nishkian Monks with designing a multi-folded, double sloping plane roof with oversized overhangs out of wood framing that could support the extreme roof snow loads. Through numerous design iterations and collaboration with BCV, Nishkian Monks successfully achieved a structural design for BCV’s striking exposed wood purlin roof. The roof purlins were arranged in such a fashion so as to emanate from the center of the chalet when viewing the house from any side.
After the Northridge Earthquake in 1994, seismic retrofit was on the minds of many Californians. Within several years of that event, the Santa Monica City Council introduced new Retrofit Ordinances to address and mitigate vulnerabilities of these existing, older buildings. The City Council ordered its staff to locate potentially vulnerable types of wood, concrete, masonry or steel framed buildings and require the owners to strengthen or demolish them.
At nearly the same time, the Los Angeles City Council discussed mandatory retrofitting for soft-story apartments as well. Hal Bernson, the city councilman who proposed the measure back then, said in an interview that property owners fought him “tooth and nail.” In the end, the proposal never passed.
With the recent 20th anniversary of the Northridge Earthquake, retrofitting of these at-risk structures is again being discussed. At the forefront of these discussions are cities such as Santa Monica, Los Angeles and San Francisco. And requirements for retrofitting are beginning to be passed this time around.
Twenty years ago today on January 17, 1994 at 4:31am, a 6.7 magnitude earthquake of about 10 seconds centered in the Northridge area shook much of Southern California awake. The Northridge Earthquake would soon register over 1,000 aftershocks with the strongest ground motion recorded reaching some 220 miles from the epicenter. The quake also caused more than 11,000 landslides which blocked roads and damaged and destroyed structures. It is recorded as one of the costliest natural disasters to hit the United States with over $40 Billion in damages sustained.
As a result of the quake, many changes occurred in building codes, public awareness, preparation and public policy. One of the causes of loss of life was the collapse of the Northridge Meadows Apartment Building which contained a “soft story”, where the first story (consisting of parking) lacked shear walls or lateral force resisting elements along one edge of the building. During the earthquake, this level gave way and was crushed under the weight of the second and third floor apartments. 16 people tragically lost their lives in this one building.
Do you remember seismic zones? Depending on how long you have been involved in the building industry you may or may not remember seismic zones. May be you had experience with Zone 4 rated components or even today we get asked to design to Zone 3 or other seismic Zone requirements.