Temblor Insights: Is the San Andreas “locked, loaded, and ready to go?”

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 theTom Jordan portrait 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 mediaand 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.

Source: http://www.latimes.com/local/lanow/la-me-ln-san-andreas-fault-earthquake-20160504-story.html
Source: http://www.latimes.com/local/lanow/la-me-ln-san-andreas-fault-earthquake-20160504-story.html

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:

The San Andreas (blue) is only the most prominent element of the 350 km (200 mi) wide plate boundary. Because ruptures do not repeat—either in their slip or their inter-event time—it’s essential to emphasize that these assessments are crude. Further, the uncertainties shown here reflect only the variation in slip rate along the fault. The rates are from Parsons et al. (2014), the 1857 and 1906 average slip are from Sieh (1978) and Song et al. (2008) respectively. The 1812 slip is a model by Lozos (2016), and the 1690 slip is simply a default estimate.
The San Andreas (blue) is only the most prominent element of the 350 km (200 mi) wide plate boundary. Because ruptures do not repeat—either in their slip or their inter-event time—it’s essential to emphasize that these assessments are crude. Further, the uncertainties shown here reflect only the variation in slip rate along the fault. The rates are from Parsons et al. (2014), the 1857 and 1906 average slip are from Sieh (1978) and Song et al. (2008) respectively. The 1812 slip is a model by Lozos (2016), and the 1690 slip is simply a default estimate.

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 quakeNicolas Ambraseysoverlapping 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.

This figure of North Anatolian fault quakes is from Stein et al. (1997), updated for the 1999 Mw=7.6 Izmit quake, with the white arrows giving the direction of cascading quakes. Even though 1939-1999 saw nearly the entire 1,000 km long fault rupture in a largely western falling-domino sequence, the earlier record is quite different. When we examined the inter-event times (the time between quakes at each point along the fault), we found it to be 450±220 years. Not only was the variation great—50% of the time between quakes—but the propagation direction was also variable.
This figure of North Anatolian fault quakes is from Stein et al. (1997), updated for the 1999 Mw=7.6 Izmit quake, with the white arrows giving the direction of cascading quakes. Even though 1939-1999 saw nearly the entire 1,000 km long fault rupture in a largely western falling-domino sequence, the earlier record is quite different. When we examined the inter-event times (the time between quakes at each point along the fault), we found it to be 450±220 years. Not only was the variation great—50% of the time between quakes—but the propagation direction was also variable.

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.

Ross Stein (ross@temblor.net), Temblor

You can check your home’s seismic risk at Temblor

References cited:

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

Simpson Strong-Tie® Strong-Wall® Wood Shearwall – The Latest in Our Prefabricated Shearwall Panel Line Part 1

calebphoto1This week’s post comes from Caleb Knudson, an R&D Engineer at our home office. Since joining Simpson Strong-Tie in 2005, he has been involved with engineered wood products and has more recently focused his efforts on our line of prefabricated Strong-Wall Shearwall panels. Caleb earned both his Bachelor’s and Master’s degrees in Civil Engineering with an emphasis on Structures from Washington State University. Upon completion of his graduate work, which focused on the performance of bolted timber connections, Caleb began his career at Simpson and is a licensed professional engineer in the state of California.

Some contractors and framers have large hands, which can pose a challenge for them when they’re trying to install the holdown nuts used to attach our Strong-Wall® SB (SWSB) Shearwall product to the foundation. Couple that challenge with the fact that anchorage attachment can only be achieved from the edges of the SWSB panel, and variable site-built framing conditions can limit access depending upon the installation sequence. To alleviate anchorage accessibility issues, we’ve required a gap between the existing adjacent framing and SWSB panel equal to the width of a 2x stud to provide access so the holdown nut can be tightened. Even so, try telling a framer an inch and a half is plenty of room in which to install the nut!

SWSB Edge Access

SWSB Edge Access

2x Gap for SWSB Installation

2x Gap for SWSB Installation

 

 

 

 

 

 

 

 

 

While the SWSB is a fantastic product with many great features and benefits from its field adjustability to its versatility with different applications and some of the highest allowable values in the industry, the installation challenges were real.

Back to the Drawing Board

Our goal was to develop a new holdown for the SWSB that would allow for face access of the anchor bolts, making the panel compatible with any framing condition, while maintaining equivalent performance. All we needed to do is cut a large hole in each face of the holdown without compromising strength or stiffness — piece of cake, right? Well, that’s exactly what we did. In the process, we addressed the needs of the architect, the engineer and the builder — and for bonus points, anchorage inspection is now much easier, which should make the building official happy too.

Introducing the Simpson Strong-Tie® Strong-Wall® Wood Shearwall

Simpson Strong-Tie® has just launched the Strong-Wall® Wood Shearwall (WSW) panel, which replaces the SWSB. The new panel provides the same features and benefits, and addresses the same applications as the SWSB; however, now it also features face-access holdowns distinguished by their Simpson Strong-Tie orange color.

Strong-Wall Wood Shearwall

Strong-Wall Wood Shearwall

We’ve also updated the top connection, which now provides two options based on installer preference. The standard installation uses the two shear plates shipped with the panel which are installed on each side of the panel by means of nails. As an alternative, the builder can install a single shear plate from either side of the panel using a combination of Strong-Drive® SD Connector screws and Strong-Drive® SDS Heavy-Duty Connector screws.

woodshear4

Allowable In-Plane Lateral Shear Loads

I mentioned that one of our primary development requirements was to meet the existing allowable design values of the SWSB. Not only did we meet our target values, but we exceeded them by as much as 25% for standard and balloon framing application panels and up to 50% for portal application panels. I’ve included a table below showing the most commonly specified standard and portal application SWSB models and how the allowable wind and seismic shear values compare to those of the corresponding WSW model.

woodshear11

Grade-Beam Anchorage Solutions

I’d be remiss if I didn’t point out the grade-beam anchorage solutions we’ve developed for use with the Strong-Wall Wood Shearwall. The solutions have been calculated to conform to ACI 318-14, and testing at the Simpson Strong-Tie Tyrell Gilb Research Laboratory confirmed the need to comply with ACI 318 requirements to prevent plastic hinging at anchor locations for seismic loading. The testing consisted of 1) control specimens without anchor reinforcement, 2) specimens with closed-tie anchor reinforcement, and 3) specimens with non-closed u-stirrups. Flexural and shear reinforcement were designed to resist amplified anchorage forces and compared to test beams designed for non-amplified strength-level forces.

Significant Findings from Testing

We found that grade-beam flexural and shear capacity is critical to anchor performance and must be designed to exceed the demands created by the attached structure. In wind load applications, this includes the factored demand from the WSW. In seismic applications, testing and analysis have shown that in order to achieve the anchor performance expected by ACI 318 Anchorage design methodologies, the concrete member design strength needs to resist the amplified anchor design demand from ACI 318-14 Section 17.2.3.4. To help Designers achieve this, Simpson Strong-Tie recommends applying the seismic design moment listed below at the WSW location.

woodshear7

We also found that closed-tie anchor reinforcement is critical to maintain the integrity of the reinforced core where the anchor is located. Testing with u-stirrups that did not include complete closed ties showed premature splitting failure of the grade beam. In a previous blog post, we discussed our grade-beam test program in much greater detail as it applies to our Steel Strong-Wall panels.

Strong-Wall® Wood Shearwall

To support the Strong-Wall Wood Shearwall, Simpson Strong-Tie has published a 52-page catalog with design information and installation details. We’ve also received code listing from ICC-ES; the evaluation report may be found here. Now that you’re all familiar with the WSW, be sure to check out next week’s blog post where we’ll cover the basics of prefabricated shear panel testing and evaluation. In addition, to help Designers understand all of the development and testing as well as design examples using prefabricated shearwalls, Simpson Strong-Tie will be offering a Prefabricated Wood Shearwall Webinar on June 21, 2016, covering:

  • The different types of prefabricated shearwalls and why they were developed.
  • The engineering and testing behind prefabricated shearwalls.
  • Best practices and design examples for designing to withstand seismic and wind events.
  • Code reports on shearwall applications.
  • Introduction of the latest Simpson Strong-Tie prefabricated shearwall.

You can register for the webinar here.

Last but not least, we always appreciate hearing from you, whether you’re an engineer specifying our panels or in the field handling the installation. If there are applications that we haven’t addressed or additional resources that would be beneficial, please let us know in the comments below.

Impact Community Resilience as a USRC Member and Certified Rater

The U.S. Resiliency Council (USRC) recently launched its Building Rating System for earthquake hazards. The Rating System assigns a score of from one to five stars for three building performance measures: Safety, Damage (repair cost) and Recovery (time to regain basic function).

US Resiliency Council header

This first-of-its-kind building performance rating is based on decades of earthquake engineering research and observations of earthquake damage and recovery. It will become an important component of future sustainable and resilient community goals. The USRC will expand its building performance ratings to include other natural hazards such as hurricanes, tornadoes and floods in the coming years.

Building damaged by natural disaster

With the USRC rating system, users will receive reliable and consistent information about a building’s expected performance during an earthquake and the estimated speed of its recovery afterwards. They can use this information to help them make decisions about purchasing or leasing buildings in which they live, work or invest, or about financing or insuring these buildings. The USRC Rating System also allows businesses and communities to plan and prepare for disasters by giving them data on the likely performance of their building stock. With the support of its Sustaining Members, the USRC will play an important role in long-term strategic capital and disaster recovery planning for communities and businesses. With the USRC Rating System, owners can specify the desired level of performance for their important facilities, to ensure that they not only survive, but also continue operations after a disaster in accordance with their expectations.

The steps to obtain a USRC Verified or Transaction Rating are as follows.

  1. Select Rating type The building owner or building jurisdiction determines the desired USRC Rating: Transaction or Verified.
  2. Select Certified Rating ProfessionalThe building owner selects and contracts with a USRC Certified Rating Professional (CRP) to complete a seismic evaluation of the building. Owners can search for CRPs and see what the requirements are for individuals to be USRC-certified at www.usrc-portal.org.
  3. Perform detailed evaluation and determine preliminary Rating The CRP performs a seismic engineering evaluation of the subject building using one of the USRC-approved evaluation methodologies, which include ASCE 41 and FEMA P-58, and translates their findings into a three-dimensional rating using the USRC translation matrix. A simplified version of the translation matrix for an ASCE 31/41 assessment is shown below:USRC translation matrix
  4. Submit evaluation and Rating to USRC The CRP’s evaluation report, proposed Rating and application fee are submitted to the USRC along with a request for either a Transaction or a Verified Rating.
  5. USRC performs review and issues Rating The USRC reviews the submission for completeness. The USRC will then either issue a Transaction Rating certificate, or one of its USRC Certified Rating Reviewers will perform a technical review before issuing a Verified Rating certificate.

Becoming a USRC Certified Rating Professional or Reviewer:

The minimum requirements for becoming a USRC Certified Rating Professional include an educational background in structural engineering, five years of relevant building evaluation experience as a licensed Professional Engineer and professional references.

The minimum requirements for becoming a USRC Certified Rating Reviewer includes either holding a Structural Engineering license followed by five years of relevant experience, or a Professional Engineering License followed by 10 years of relevant experience.

Details of the application process and other requirements for certification are provided on both the USRC website, www.usrc.org, and the USRC portal, www.usrc-portal.org. The cost to become a USRC Certified Rating Professional or Reviewer is $600 for individuals with a $100 annual renewal fee. Individual and corporate members have discounts on certification.

Building Inspector Looking At New Property

USRC Membership

The U.S. Resiliency Council is a growing 501(c)(3) nonprofit organization with the vision of a world in which building performance in earthquakes and other natural hazards is better understood by building owners, tenants, financial institutions and communities. Corporations, organizations and individuals who are stakeholders in the built environment and who have a passion for improving the resiliency of our nation, have the opportunity to support the USRC through sustaining memberships. With the help of its sustaining members, the USRC will encourage:

  • Increasing market demand for better-performing buildings
  • Fostering collaboration among diverse stakeholders and technical experts
  • Promoting integrity, stability, consistency and transparency of rating systems
  • Educating and advocating for safe buildings and a better public understanding of building performance

USRC Membership List

USRCs members include many of the largest and most respected professional A/E firms and engineering professional societies in the country. Membership is open to all companies, individuals, communities and other stakeholders in the built environment. Information on joining the USRC can be found at the USRC website www.usrc.org.

What contributions from engineers are necessary to help create more resilient communities? Let us know in the comments below.

Shrinkage Compensation Devices

Over the weekend, I had the pleasure of watching my daughter in her cheer competition. I was amazed at all the intricate detail they had to remember and practice. The entire team had to move in sync to create a routine filed with jumps, tumbles, flyers and kicks. This attention to detail reminded me of the new ratcheting take-up device (RTUD) that Simpson Strong-Tie has just developed to accommodate 5/8″ and ¾” diameter rods. The synchronized movement of the internal inserts allows the rod to move smoothly through the device as it ratchets. The new RTUDs are cost effective and allow unlimited movement to mitigate wood shrinkage in a multi-story wood- framed building. When designing such a building, the Designer needs to consider the effect of shrinkage and how to properly mitigate it.

Our SE blog post on Continuous Rod Restraint Systems for Multi-Story Wood Structures explained the importance of load path and  the effects of wood shrinkage. This week’s blog post will focus on the importance of mitigating the shrinkage that typically occurs in multi-story light-frame buildings.

Shrinkage is natural in a wood member. As moisture reaches its equilibrium in a built environment, the volume of a wood member decreases. The decrease in moisture causes a wood-framed building to shrink.

The IBC allows construction of light-framed buildings up to 5 and 6 stories in the United States and Canada respectively. Based on the type of floor framing system, the incremental shrinkage can be up to ¼” or more per floor. In a 5-story building, that can add up to 1-¼” or more and possibly double that when construction settlement is included.

rods1

Typical Example of gap forming between nut and plate when wood shrinkage at top level occurs without shrinkage device.

The Simpson Strong-Tie Wood Shrinkage Calculator is a perfect tool to determine the total shrinkage your building can experience.

Wood Shrinkage Calculator

Wood Shrinkage Calculator

In order to accommodate the shrinkage that occurs in a multi-story wood-framed building, Simpson Strong-Tie offers several shrinkage compensating devices. These devices have been tested per ICC-ES Acceptance Criteria 316 (AC316) and are listed under ICC-ES ESR-2320 (currently being updated for the new RTUD5, RTUD6, and ATUD9-3).

AC316 limits the rod elongation and device displacement to 0.2 inches between restraints in shearwalls. This deflection limit is to be used in calculating the total lateral drift of a light-framed wood shearwall.

rod3

3 Part Shearwall Drift Equation

The 0.2-inch allowable limit prescribed in AC316 is important to a shearwall’s structural ability to transfer the necessary lateral loads through the structure below to the foundation level. This limit assures that the structural integrity of the nails and sill plates used to transfer the lateral loads through the shearwalls is not compromised during a seismic or wind event. Testing has shown that sill plates can crack when excessive deformation is observed in a shearwalls. Nails have also been observed to pull out during testing.  Additional information on this can be found here.

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Sill Plates Cracked due to excessive uplift at ends of shearwall.

rods5

Nails pull out due to excessive uplift at ends of shearwall.

In AC316, 3 types of devices are listed.

  • Compression-Controlled Shrinkage Compensating Device (CCSCD): This type of device is controlled by compression loading, where the rod passes uninterrupted through the device. Simpson Strong-Tie has several screw-type take-up devices, such as the Aluminum Take-Up Device (ATUD) and the Steel Take-Up Device (TUD), of this type.
rods6

ATUD (CCSCD)

  • Tension-Controlled Shrinkage Compensating Device (TCSCD): This type of device is controlled by tension loading, where the rod is attached or engaged by the device and allows the rod to ratchet through as the wood shrinks. The Simpson Strong-Tie Ratcheting Take-Up Device (RTUD) is of this type.

rod7

RTUD (TCSCD)

  • Tension-controlled Shrinkage Compensating Coupling Device (TCSCCD): This type of device is controlled by tension loading that connects rods or anchors together. The Simpson Strong-Tie Coupling Take-Up Device (CTUD) is of this type.
CTUD (TCSCCD)

CTUD (TCSCCD)

Each device type has unique features that are important in achieving the best performance for different conditions and loads. The following table is a summary of each device.

rods9The most cost-effective Simpson Strong-Tie shrinkage compensation device is the RTUD. This device has the smallest number of components and allows the rod unlimited travel through the device. It is ideal at the top level of a rod system run or where small rod diameters are used. Simpson Strong-Tie RTUDs can now accommodate 5/8″ (RTUD5) and ¾” (RTUD6) diameter rods.

How do you choose the best device for your projects? A Designer will have to consider the following during their design.

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RTUD Assembly

Rod Tension (Overturning) Check:

  • Rods at each level designed to meet the cumulative overturning tension force per level
  • Standard and high-strength steel rods designed not to exceed tensile capacity as defined in AISC specification
    • Standard threaded rod based on 36 / 58 ksi (Fy/Fu)
    • High-strength Strong-Rod based on 92 / 120 ksi (Fy/Fu
    • H150 Strong-Rod based on 130 / 150 ksi (Fy/Fu)
  • Rod elongation (see below)

 Bearing Plate Check

  • Bearing plates designed to transfer incremental overturning force per level into the rod
  • Bearing stress on wood member limited in accordance with the NDS to provide proper bearing capacity and limit wood crushing
  • Bearing plate thickness has been sized to limit plate bending in order to provide full bearing on wood member

 Shrinkage Take-Up Device Check

  • Shrinkage take-up device is selected to accommodate estimated wood shrinkage to eliminate gaps in the system load path
  • Load capacity of the take-up device compared with incremental overturning force to ensure that load is transferred into rod
  • Shrinkage compensation device deflection is included in system displacement

 Movement/Deflection Check

  • System deformation is an integral design component impacting the selection of rods, bearing plates and shrinkage take-up devices
  • Rod elongation plus take-up device displacement is limited to a maximum of 0.2″ per level or as further limited by the requirements of the engineer or jurisdiction
  • Total system deformation reported for use in Δa term (total vertical elongation of wall anchorage system per NDS equation) when calculating shearwall deflection
  • Both seating increment (ΔR) and deflection at allowable load (ΔA) are included in the overall system movement. These are listed in the evaluation report ICC-ES ESR-2320 for take-up devices

 Optional Compression Post Design

  • Compression post design can be performed upon request along with the Strong-Rod System
  • Compression post design limited to buckling or bearing perpendicular to grain on wood plate
  • Anchorage design tools are available
  • Anchorage design information conforms to AC 318 anchorage provisions and Simpson Strong-Tie testing

In order to properly design a continuous rod tie-down system for your shearwall overturning restraint, all of the factors listed above will need to be taken into consideration.

A Designer can also contact Simpson Strong-Tie by going to www.strongtie.com/srs and filling out the online “Contact Us” page to have Simpson Strong-Tie design the continuous rod tie-down system for you. This design service does not cost you a dime. A few items will be required from the Designer in order for Simpson Strong-Tie to create a cost-effective rod run (it is recommended that on the Designer specify these in the construction documents):

  • There is a maximum system displacement of 0.2″ per level, which includes rod elongation and shrinkage compensation device deflection. Some jurisdictions may impose a smaller deflection limit.
  • Bearing plates and shrinkage compensation devices are required at every level.
  • Cumulative and incremental forces must be listed at each level in Allowable Stress Design (ASD) force levels.
  • Construction documents must include drawings and calculations proving that design requirements have been met. These drawings and calculations should be submitted to the Designer for review and the Authority Having Jurisdiction for approval.

More information can be obtained from our website at www.strongtie.com/srs, where a new design guide for the U.S., F-L-SRS15, and a new catalog for Canada, C-L-SRSCAN16, are available for download.

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US Design Guide F-L-SRS15 and Canadian Catalog C-L-SRSCAN16

California Has Funding for $3,000 Grants for Home Retrofits

Are you an engineer working with California clients whose homes were built before 1979 on a raised foundation?

Evident earthquake damage

Earthquake damage sustained by a two-story building over a cripple wall system after the Mexicali Earthquake (M7.2).

If you are, these clients may be among the 1.2 million California homeowners eligible for a seismic home retrofit. The state of California has approved the continuation of an initiative known as Earthquake Bolt + Brace (EBB). In its second year, this program plans to make as many as 1,600 grants to selected homeowners, nearly three times the number given the previous year. The EBB grant program provides up to $3,000 to homeowners residing in more than 150 California zip codes. Check to see whether your clients live within one of these communities here.

Simpson Strong-Tie has several different resources to assist you in helping your clients understand how to mitigate seismic risks to houses with raised foundations. The Seismic Retrofit Details sheet provides various ways to retrofit the cripple wall system using prescriptive methodologies, which can be adapted for engineered solutions. The picture below highlights the use of the Simpson Strong-Tie universal foundation plate (UFP) to attach the boltless sill plate of the cripple wall to the concrete stemwall. This simple step can help prevent the house from sliding off its foundation. The picture also reveals plywood sheathing used to reinforce the weak cripple wall system. Additional resources for retrofit can be found here.

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Retrofit with UFP foundation plate in Napa, California

To help your clients better understand the impact these simple steps can have in preventing structural damage in an earthquake, click here to watch the story of a Napa business women who had purchased a structure with a raised foundation for her business and retrofitted it just prior to the 2014 M6.0 Napa earthquake, which caused considerable damage to many similar structures.

Let your clients know that the time to apply is very limited if they think they qualify for a retrofit grant. Registration for the 2016 EBB program ends on February 20. To register or learn more about the program, visit www.earthquakebracebolt.com.

When you finish a retrofit for one of your clients, we want to hear how it went. Let us know in the comments below.

Great ShakeOut Earthquake Drill

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.

We’re also providing resources on how to retrofit homes and buildings, and have information for engineers at strongtie.com/softstory and for homeowners at safestronghome.com/earthquake.

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.

Soft Story Building with seismic damage.

Seismic damage to a soft-story building in San Francisco.

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.

Understanding and Meeting the ACI 318 – 11 App. D Ductility Requirements – A Design Example

If you’re one of the many engineers still confused by the ACI 318 – 11 Appendix D design provisions, this blog will help explain what’s required to achieve a ductile performing anchorage. Most building codes currently reference ACI 318 – 11 Appendix D as the required provision for designing a wide variety of anchor types that include expansion, undercut, adhesive and cast-in-place anchors in concrete base materials. This blog post will focus on section D.3.3.4.3(a) for an anchor located in a high seismic region. We’ll go over what these requirements are with a simple design example.

Ductility is a benefit in seismic design. A ductile anchor system is one that exhibits a meaningful degree of deformation before failure occurs. However, ductility is distinct from an equally important dimension called strength. Add strength, and a ductile steel element like the one shown in Figure 1 can now exhibit toughness. During a serious earthquake, a structural system with appreciable toughness (i.e., one that possesses both strength and ductility in sufficient degree) can be expected to absorb a tremendous amount of energy as the material plastically deforms and increases the likelihood that an outright failure won’t occur. Any visible deformations could help determine if repair is necessary.

Figure 1 – ½" mild steel threaded rod tensilely loaded to failure (starting stretch length = 8d)

Figure 1 – ½” mild steel threaded rod tensilely loaded to failure (starting stretch length = 8d)

Let’s start off with a simple example that will cover the essential requirements for achieving ductility and applies to any type of structural anchor used in concrete. We’ll arbitrarily choose a post-installed adhesive anchor. This type of anchor is very common in concrete construction and is used for making structural and nonstructural connections that include anchorage of sill plates and holdowns for shear walls, equipment, racks, architectural/mechanical/electrical components and, very frequently, rebar dowels for making section enlargements. We’ll assume the anchor is limited to resisting earthquake loading in tension only and is in seismic design category C – F. Section D.3.3.4.2 requires that if the strength-level earthquake force exceeds 20% of the total factored load, that the anchor be designed in accordance with section D.3.3.4.3 and D.3.3.4.4. We will focus on achieving the ductility option, (a), of D.3.3.4.3.

To understand anchor ductility we need to first identify the possible failure modes of an anchor. Figure 2 shows the three types of failure modes we can expect for an adhesive anchor located away from a free edge. These three failure modes generically apply to virtually any type of anchor (expansion, screw, cast-in-place or undercut). Breakout (Nb) and pullout (Na) are not considered ductile failure modes. Breakout failure (Nb) can occur very suddenly and behaves mostly linear elastic and consequently absorbs a relatively small amount of energy. After pullout failure (Na) has been initiated, the load/displacement behavior of the anchor can be unpredictable, and furthermore, no reliable mechanism exists for plastic deformation to take place. So we’re left with steel (Nsa). To achieve ductility, not only does the steel need to be made of a ductile material but the steel must govern out of the three failure modes. Additionally, the anchor system must be designed so that steel failure governs by a comfortable margin. Breakout and pullout can never control while the steel yields and plastically deforms. This is what is meant by meeting the ductility requirements of Appendix D.

Figure 2 –Three possible failure modes for an adhesive anchor loaded in tension

Figure 2 – Three possible failure modes for an adhesive anchor loaded in tension

Getting back to our design example, we have a single post-installed 5/8” diameter ASTM F1554 Gr. 36 threaded rod that’s embedded 12” deep, in a dry hole, in a concrete element that has a compressive strength of 2,500 psi. The concrete is 18” thick and we assume that the edge distance is large enough to be irrelevant. For this size anchor, the published characteristic bond strength is 743 psi. Anchor software calculations will produce the following information:

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The governing design strength is compared to a demand or load combination that’s defined elsewhere in the code.

Here’s the question: Before proceeding with the remainder of this blog, judging by the design strength values shown above, should we consider this anchorage ductile? Your intuition might tell you that it’s not ductile. Why? Pullout clearly governs (i.e., steel does not). So it might come as a surprise to learn that this adhesive anchor actually is ductile!

To understand why, we need to look at the nominal strength (not the design strength) of the different anchor failure modes. But first let’s examine the equations used to determine the design strength values above:

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The above values incorporate the notation φ (“phi”) and a mandatory 0.75 reduction factor for nonductile failure modes (Ncb ,Na) for applications located in high seismic areas (seismic design category C–F). The φ factor is defined in section D.4. However, manufacturers will list factors specific to their adhesive based on anchor testing. The mandatory 0.75 reduction comes from section D.3.3.4.4 and is meant to account for any reduction associated with concrete damage during earthquake loading. The important thing to remember is that the nominal strength provides a better representation of the relative capacity of the different failure modes. Remove these reduction factors and we get the following:

ductility6

Now steel governs since it has the lowest strength. But we’re not done yet. Section D.3.3.4.3.(a).1 of Appendix D requires that the expected steel strength be used in design when checking for ductility. This is done by increasing the specified steel strength by 20%. This is to account for the fact that F1554 Gr. 36 threaded rod, for example, will probably have an ultimate tensile strength greater than the specified 58,000 psi. (Interestingly, the ultimate strength of the ½” threaded rod tested in Figure 1 is roughly 74 ksi, which is about 27% greater than 58,000 psi.) With this in mind, the next step would be to additionally meet section D.3.3.4.3.(a).2 such that the following is met:

ductility7

By increasing the steel strength by 20%, the nominal strength of the nonductile failure modes (Ncb ,Na) must be at least that much greater to help ensure that a ductile anchor system can be achieved. The values to compare finally become:

 

ductility8Now steel governs, but one more thing is required. As shown in Figure 3, Section D.3.3.4.3.(a).3 of Appendix D also requires that the rod be made of ductile steel and have a stretch length of at least eight times the insert diameter (8d). Appendix D defines a ductile steel element as exhibiting an elongation of at least 14% and a reduction in area of at least 30%. ASTM F1554 meets this requirement for all three grades of steel (Grade 36, 55 and 105) with the exception of Grade 55 for anchor nominal sizes greater than 2”. Research has shown that a sufficient stretch length helps ensure that an anchor can experience significant yielding and plastic deformation during tensile loading. The threaded rod shown in Figure 1 was tested using a stretch length of 4” (8d). Lastly, section D.3.3.4.3.(a).4 requires that the anchor be engineered to protect against buckling.

Figure 3 – Stretch length

Figure 3 – Stretch length

Appendix D doesn’t require that an anchor system behave ductilely. Three additional options exist for Designers in section D3.3.4.3. Option (b) allows for the design of an alternate failure mechanism that behaves ductilely. Designing a base plate (or support) that plastically hinges to exhibit ductile performance is one example. Option (c) involves a case where there’s a limit to how much load can be delivered to the anchor. Although option (c) under D.3.3.4.3 falls under the tensile loading section of Appendix D, the best example would apply to anchorage used to secure a wood sill plate or cold-formed steel track. We know from experiments that the wood crushes or the steel yields and locally buckles at a force less than the capacity of the concrete anchorage. Clearly energy is absorbed in the process. The most commonly used option is (d), which amplifies the earthquake load by Ωo. Ωo can be found in ASCE 7 – 10 for both structural and nonstructural components. The value of Ωo is typically taken to be equal to 2.5 (2.0 for storage racks) and is intended to make the anchor system behave linear elastically for the expected design-level earthquake demand.

These same options exist for shear loading cases. However, achieving system ductility through anchor steel is no longer an option for shear loading according to ACI 318 – 11, because the material probably won’t deform appreciably enough to be considered ductile.

While factors such as edge-distance and embedment-depth restrictions make achieving ductility difficult for post-installed anchors, it should come as some consolation that in many cases the Designer can achieve ductile performance for cast-in-place anchors loaded in tension through creative detailing of reinforcing steel (section D.5.2.9) to eliminate breakout as a possible failure mode. This has been explored in some detail in two previous Simpson Strong-Tie blogs titled “Anchor Reinforcement for Concrete Podium Slabs” and “Steel Strong Wall Footings Just Got a Little Slimmer.”

 

Seismic Bracing Requirements for Nonstructural Components

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.

One of the last things you want is to experience serious electrical, mechanical or plumbing failures during or after a seismic event. During the 1994 Northridge earthquake, 80%-90% of the damage to buildings was to nonstructural components. Ten key hospitals in the area were temporarily inoperable primarily because of water damage, broken glass, dangling light fixtures or lack of emergency power.

Complete loss of suspended ceilings and light fixtures in the 1994 Northridge Earthquake. (FEMA 74, 1994)

Complete loss of suspended ceilings and light fixtures in the 1994 Northridge Earthquake. (FEMA 74, 1994)

Broken sprinkler pipe at Olive View Hospital in Sylmar, California after the 1994 Northridggde, Earthquake. (FEMA 74, 1994)

Broken sprinkler pipe at Olive View Hospital in Sylmar, California after the 1994 Northridggde, Earthquake. (FEMA 74, 1994)

ASCE 7 has an entire chapter titled Seismic Design Requirement of Nonstructural Components (Chapter 13 of ASCE 7-10) that is devoted to provisions on seismic bracing of nonstructural components. Unfortunately, not a lot of Designers are aware of this part of the ASCE. This blog post will walk Designers through the ASCE 7 requirements.

Nonstructural components consist of architectural, mechanical, electrical and plumbing utilities. Chapter 13 of ASCE 7-10 establishes the minimum design criteria for nonstructural components permanently attached to structures. First, we need to introduce some of the terminology that is used in Chapter 13 of ASCE 7.

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  • Component – the mechanical equipment or utility.
  • Support – the method to transfer the loads from the component to the structure.
  • Attachment – the method of actual attachment to the structure.
  • Importance Factor (Ip) – identifies which components are required to be fully functioning during and after a seismic event. This factor also identifies components that may contain toxic chemicals, explosive substances, or hazardous material in excess of certain quantities. This is typically determined by the Designer.

Section 13.2.1 of ASCE 7 requires architectural, mechanical and electrical components to be designed and anchored per criteria listed in Table 13.2-1 below.

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Architectural components consist of furniture, interior partition walls, ceilings, lights, fans, exterior cladding, exterior walls, etc. This list may seem minor compared to structural components, but if these components are not properly secured, they can fall and hurt the occupants or prevent them from escaping a building during a seismic event. The risk of fire also increases during an earthquake, further endangering the occupants.

Failure of office partitions and ceilings during the Northridge 1994 Earthquake. (FEMA 74, 1994)

Failure of office partitions and ceilings during the Northridge 1994 Earthquake. (FEMA 74, 1994)

Damage to overloaded  storage racks during the 1994 Northridge Earthquake. (FEMA 74, 1994)

Damage to overloaded storage racks during the 1994 Northridge Earthquake. (FEMA 74, 1994)

Section 13.5 of ASCE 7-10 includes the necessary requirements for seismic bracing of architectural components. Table 13.5-1 provides various architectural components and the seismic coefficients required to determine the force level the attachments and supports are to be designed for.

Mechanical and electrical components consist of floor-mounted and suspended equipment. It also includes suspended distributed utilities such as ducts, pipes or conduits. These components are essential in providing the necessary functions of a building. In a hospital, these components are required to be fully functioning both during and after a seismic event. A disruption of these components can make an entire hospital building unusable. In order for hospitals to properly service the needs of the public after a seismic event, fully functioning equipment is essential.

Failed attachments to a chiller after the 1994 Northridge Earthquake. (FEMA 74, 1994)

Failed attachments to a chiller after the 1994 Northridge Earthquake. (FEMA 74, 1994)

Section 13.6 of ASCE 7-10 provides the requirements of seismic bracing for mechanical and electrical components. Table 13.6-1 provides a list of typical components and the coefficients required to determine the force level the attachments and supports are to be designed for.

Chapter 13 lists some typical requirements for which components are to be anchored and supported under specific conditions:

  1. Section 13.1.4 item 6c: Any component weighing more than 400 pounds.
  2. Section 13.1.4 item 6c: Any component where its center of gravity is more than 4 feet above the floor.
  3. Section 13.6.5.6 has specific electrical conduit size and weight requirements.
  4. Section 13.6.7 has specific size and weight requirements for suspended duct systems.
  5. Section 13.6.7 has specific size and weight requirements for suspended piping systems.

The chapter also has some general exceptions to the rules:

  1. 12 Inch Rule: When a distributed system such as conduit ducts or pipes are suspended from the structure with hangers less than 12 inches in length, seismic bracing is not required.
  2. If the support carrying multiple pipes or conduits weighs less than 10 pound/feet of lineal weight of the component, the seismic bracing of the support does not have to be considered.
Example of a support with multiple pipes and the hanger rod length. These exceptions do have limitations, which that are clearly listed in Ssections 13.6.5.6, 13.6.7 and 13.6.8.

Example of a support with multiple pipes and the hanger rod length.

These exceptions do have limitations that are clearly listed in Sections 13.6.5.6, 13.6.7 and 13.6.8.

These systems may not seem important in the structural systems of a building, but they are essential in allowing the building to function the way it was designed to serve the public. It is also important that occupants are able to escape a damaged building after a seismic event. Obstacles such as bookcases blocking exit doors or falling debris may prevent occupants from leaving a building after a seismic event.

It is important that Designers are aware of these code requirements and take the time to read and understand what is needed to provide a safe structure.

 

Report Back from Nepal – Assessing Seismic Damage from April/May Earthquakes

 Dr. H. Kit Miyamoto assessing damage in Nepal.

Dr. H. Kit Miyamoto assessing structural damage in Nepal.

This week’s post comes from Dr. H. Kit Miyamoto, S.E. Kit is CEO of Miyamoto International, a structural engineering firm and president of the nonprofit, Miyamoto Global Disaster Relief. He also is a California Seismic Safety Commissioner.

As soon as news spread that 7.8-magnitude and 7.3-magnitude earthquakes struck Nepal in April and May of this year, earthquake structural engineering experts from our firm, Miyamoto International, hopped on planes from three countries to offer assistance. We do this in hopes that our expertise and technical advice might help stricken communities recover; help them to build better and ultimately help save lives.

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Dr. H. Kit Miyamoto on site. Evidence of massive damage is present in the background.

While structural engineers are not first responders, we are well equipped to assess whether it is safe for people to return to homes, businesses, schools and critical-services buildings. We also can help people understand why some buildings stand while others collapse. This information is essential. It is the only way to protect people from future tragedy.

On touch down in Nepal, we found the airport filled with frightened people leaving the country. It is always a bit sobering to see people leaving while you head in.  We struck out for the hotel we could only hope was still standing. Once there, we found the building to be structurally sound, although uneasy guests opted to sleep in the courtyard, leaving us, the structural engineers, the only ones sleeping inside.

I expected the devastation in Kathmandu to be much greater than it was – we all did. Yet because the epicenter was about 50 miles from the capital, the quake’s power was partially dissipated by distance and the Kathmandu Valley’s soft river soil, which likely saved many lives and structures.

Nepal’s Minister of Education asked our team to examine some of the schools in remote areas.  We drove into a village to a horrible find: a large, three-story school reduced to a rubble pile of brick, concrete and broken desks. What we found were columns made of bricks without any reinforcement. This is something I saw in schools in Sichuan, China in 2008, where poor construction practices left tens of thousands of school children vulnerable to disaster. And yet, I have to say that Nepal was lucky. Although more than 7,000 of the country’s schools were severely damaged or destroyed, the quake hit midday on a Saturday when students were not in school. Had the quake hit in the middle of a school day, tens of thousands of students would have died.

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A look inside the collapsed school.

Driving out beyond the city, we found rural areas in the central and western regions particularly devastated, with entire villages destroyed and further isolated by road damage, closures, rugged terrain and the threat of landslides. As is the case in much of the world, unreinforced masonry construction presented the biggest problem. In rural Nepal – where traditional homes are made of stone, mud and wood – we found up to 90 percent of the structures destroyed. Whole villages were gone.

DSC_0306

Absolute devastation of a rural village.

Around the world, the experts involved in construction – from the engineer and contractor to the building inspector – have to invest in constructing safe buildings. No corruption. No excuses. Build as if your children are attending that school or living in those homes and we will begin to have seismically resilient cities.

Many of the newer high-rise buildings in Kathmandu have also exhibited crippling damage and we have assessed more than 30 of these to date. Even when building codes are adhered to, a big gap exists between what code provides and what society expects. Even in places like Los Angeles and San Francisco, people don’t understand that. At one meeting in Kathmandu, luxury condo owners were stunned and angry to learn that the building they bought into met standards, but was still too heavily damaged to occupy. These buildings are not usable now. The financial loss is enormous.

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An aerial view of the earthquake damage. 

We have to understand that people don’t have to die in earthquakes. Earthquakes don’t kill people; buildings kill people. Or more precisely, poorly constructed buildings. This is tragic and avoidable because we know how to design seismically strong buildings. When an earthquake strikes, our disaster response efforts include “knowledge transfer,” during which we train engineers, masons and contractors on simple seismic techniques that save lives and help communities “build back better.” Our profession has disaster-resilient solutions for new construction and retrofits.

At Miyamoto International, our mission is to save lives and positively impact economies through our work. In China, 169,000 lives were lost, including tens of thousands of students in 7,000 classrooms. In 2010 in Haiti, more than 200,000 people died. In Nepal, the earthquake killed more than 8,600 people. It doesn’t have to be this way.  Building seismically resilient cities is possible. It is achievable. We can save lives.

Kids + Structural Engineering = The Tech Challenge!

Our future is in good hands.

Our future is in good hands.

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.

Teams with their structures.

Teams with their structures.

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.

A design from an elementary school team.

A design from an elementary school team.

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.

Structure designed by the elementary school team.

Structure designed by the elementary school team.

Close up of the base isolation of the team’s structure.

Close up of the base isolation of the team’s structure.

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!