AC398 Now Includes Moment Evaluation of Cast-in-Place Post Bases

This week’s post was written by Jhalak Vasavada, Research & Development Engineer at Simpson Strong-Tie.

When we launched our new, patent-pending MPBZ moment post base earlier this year, the evaluation of the moment capacity of post bases was not covered by AC398 – or by any other code, for that matter. There wasn’t a need – there were no code-accepted connectors available on the market for resisting moment loads.

We proposed adding moment evaluation to the AC398 and presented our research to the ICC-ES committee in June. After a thorough review, which included a public hearing, the provision was approved. Here are some details about the revisions to this acceptance criteria.

What is AC398?

AC398 is the Acceptance Criteria for cast-in-place cold-formed steel connectors in concrete for light-frame construction.

Acceptance criteria are developed to provide guidelines for demonstrating compliance with performance features of the codes referenced in the criteria. ICC-ES develops acceptance criteria for products and systems that are alternatives to what is specified in the code, or that fall under code provisions that are not sufficiently clear for the issuance of an evaluation report.

The criteria are developed through a transparent process involving public hearings of the ICC-ES Evaluation Committee (made up entirely of code officials), and/or online postings where public comments were solicited.

How is the moment load evaluated?

The MPBZ moment post base is a cast-in-place post base designed to resist uplift, download, lateral and moment forces. This blog post in February describes how it works, how it was tested and includes a design example. Since the MPBZ falls under the specialty inserts category of cast-in anchorage, it is not covered by the provisions of chapter 17 of ACI 318-14. Therefore, the MPBZ was evaluated based on AC398 for anchorage to concrete.

Our engineers worked closely with ICC-ES and the American Wood Council to develop evaluation criteria for moment. This revision to the criteria for moment evaluation and testing was posted for public comments on the ICC-ES website, and then presented by our engineers at the ICC-ES committee hearing last June. The presentation included the design, use, testing and load rating of the MPBZ. Following the hearing, and a thorough review, the committee approved the proposed revision to AC398.

What are the revisions to AC398?

With reference to moment evaluation, a few of the key changes to AC398 are:

  1. Moment Anchorage Strength: Similar to tension and shear anchorage strength, the available moment anchorage strength shall be determined using the equation

Where F = applied horizontal test force used to determine moment strength (lbf)

D = vertical distance from top of concrete member to the applied lateral test force F (ft.) (moment arm)

Other terms are as previously defined for tension and shear anchorage strength equations.

  1. Rotation: Testing of moment base connectors subject to an applied moment shall include measurement and reporting of the connector rotation as determined by the relative lateral displacement of gauges positioned 1″ and 5″ above the top of the connector.
  2. Side Bearing: Testing of moment base connectors that rely on bearing of the wood member against the side of the connector to resist moment loads shall address wood shrinkage.

Learn more about the MPBZ in our free upcoming webinar.

Join us live on December 6 for an interactive webinar on the MPBZ moment post base, its evaluation, its testing and its applications. In this webinar, we will discuss MPBZ moment post base product features, product development, design examples and much more. Attendees will also have an opportunity to ask questions during the event. Continuing education units will be offered for completing this webinar. Register today here.

Upcoming free MPBZ webinar.

Join Simpson Strong-Tie R&D engineer Jhalak Vasavada, P.E., and Simpson Strong-Tie product manager Emmet Mielbrecht for a lively and informative discussion of this new product.

Introducing the New and Improved Simpson Strong-Tie Strong-Wall® Bracing Selector

This week’s post was written by Caleb Knudson, R&D Engineer at Simpson Strong-Tie.

It’s been said that the World Wide Web is the wave of the future. Okay, maybe this is slightly outdated news, as it’s been 25 years since Bill Gates penned his internet tidal-wave memorandum, but it’s a good lead-in to this week’s blog topic – web apps. More specifically, those apps that have been developed to address the wall-bracing requirements defined in the International Residential Code® (IRC). Designers and engineers have no doubt noticed that over the last several code cycles, the wall-bracing provisions in the IRC have become increasingly complex. To help navigate these requirements and calculate the required bracing length for a given wall line, Simpson Strong-Tie introduced the Wall-Bracing-Length Calculator (WBLC) a few years back, as discussed in an earlier blog post. I’ll also mention that the WBLC has since been updated to the 2015 IRC.

Those familiar with the wall-bracing provisions in the IRC know that there are twelve intermittent wall-bracing methods and four continuous-sheathing methods to address wall-bracing requirements. Each of these methods may be used in most applications, and, while some provide advantages over others, the code-based methods provide Designers with quite a bit of flexibility. However, there may be cases where the site-specific conditions are beyond the scope of the IRC, or there just isn’t enough available full-height wall space to accommodate the required wall-bracing length. These cases are most likely to occur at large window openings or at garage fronts.

Let’s take the following example of a house on Lake Washington – assuming the house is being designed in accordance with the IRC. Presumably, one might prefer to have unobstructed lake views, which of course means lots of large picture windows and not much room left for braced wall panels. Let’s also suppose you’ve got a brand-new Chris Craft that you’d like to protect against the weather when it’s not in the water – this means wide garage doors and, again, not much room for conventional wall bracing.

So what do we do now?

Thankfully, the International Residential Code provides some guidance. Section R301.1.3 states that when a building, or portion thereof, is outside the scope of the IRC, the element(s) may be designed in accordance with accepted engineering practice. The code goes on to state that the extent of the design shall be such that the engineered element(s) are compatible with the performance of conventional methods prescribed in the code. That creates some additional options for our tool box. We could design a site-built shearwall; however, due to aspect-ratio limitations defined in the Special Design Provisions for Wind and Seismic (SDPWS), we still may not be able to get the lake views and wide garage we want. The next option, and one we’ll focus on here, is the code-approved prefabricated Simpson Strong-Tie® Strong-Wall® shearwall.

In an earlier blog post, as previously mentioned, we introduced the Strong-Wall Bracing Selector (SWBS) and defined just how we determine equivalence to conventional bracing methods. We further described the benefit of using the selector in conjunction with the Wall-Bracing-Length Calculator (WBLC). To refresh your memory, when Designers start with the WBLC to determine required wall-bracing-lengths for up to seven parallel wall lines, they can export those bracing lengths as well as project and jobsite information directly to the SWBS with the click of a button. The SWBS will then provide a list of Strong-Wall panels that provide an equivalent bracing length, evaluate their anchorage requirements, and return a list of pre-engineered anchor solutions for a variety of foundation types.

On to the present: We just launched the Strong-Wall Bracing Selector web app version 2.0, and there are a few new features worth noting.

First, I’ll mention that all Strong-Wall solutions have been evaluated according to the 2015 I-Codes. Next, and hopefully this doesn’t come as too much of a surprise, the original wood Strong-Wall shearwall (SW) is being phased out with guaranteed availability through December 31, 2018. In light of this planned obsolescence, we have removed the SW solutions from the latest version of the bracing selector.

Here’s the good news – and this is big: We’ve now added the new Strong-Wall wood shearwall (WSW) to the app and recommend this as a replacement for the SW in all applications. In the interim, while the original wall is still available, version 1.0 of the bracing selector app may be used if an SW bracing solution is required.

Lastly, we’ve provided the Designer with a bit more flexibility and control over the Strong-Wall bracing solutions provided by the app. If you recall, version 1.0 provided a solution using the minimum possible number of Strong-Wall panels to satisfy the bracing length requirement. We’ve changed that in version 2.0; Designers may still select a solution using the minimum number of panels, but they may also select the exact number of Strong-Wall panels to satisfy their wall-bracing-length requirements. Typically, it’s desirable to address the bracing requirement with the minimum number of Strong-Wall shearwall panels possible. Sometimes, however, it may be advantageous to increase the number of panels used, in order to decrease the Strong-Wall panel width used for a solution or to reduce anchorage requirements, i.e., lesser footing dimensions and anchor embedment depths. Stated a little differently, we’re providing the option to find the right balance between the braced wall panel design and the anchorage design – i.e., the Goldilocks zone for prescriptive wall bracing.

So now that we’ve reviewed just why a Designer may need to specify a Strong-Wall shearwall in prescriptive applications and how the Wall-Bracing-Length Calculator and Strong-Wall Bracing Selector web apps help to navigate this process, we’re interested to see what you think. Is there any additional functionality that you’d like to see in the future, or are these apps just right for your design needs? Let us know in the comments below.

Q&A About CFS Designer™ Software

I recently had the pleasure of presenting a webinar with Rob Madsen, PE, of Devco Engineering on our CFS Designer software, “Increase Productivity in Your Cold-Formed Steel Design Projects.” The webinar took place on September 28, and a recording is available online on our training website for anyone who wasn’t able to join us. Viewing the recording (and completing the associated test) qualifies for continuing education units and professional development hours. The webinar covers how to use the CFS Designer software to design complex loading conditions for beams, wall studs, walls with openings, and stacked walls using cold-formed steel studs, tracks, built-up sections, and even custom shapes. We received some excellent questions during the webinar, but due to time constraints were only able to answer a few during the live webinar. Rob and I did get a chance to answer all the questions in a Q&A document from which I’d like to share some excerpts. The complete Q&A webinar list can be accessed here, or through the online recording.

Where can I download the CFS Designer program?

Please visit to download a free 14-day trial version of the software or to purchase a license. Webinar attendees should check their email for a special discount code. There are different licensing options based on the number of users.

Is the price for the software an annual subscription fee or is it a one-time purchase price? Is there any maintenance cost?

There’s no annual maintenance fee or subscription fee. You pay only a one-time fee for the license. CFS Designer is based on an update-and-upgrade program. All updates to the program are free to licensed users and occur every few months to correct software bugs and add functionality. Upgrades, which include new design modules and updated code information, will require an additional purchase. Simpson Strong-Tie anticipates releasing upgrades on a two-year cycle, and the next upgrade has a projected release of early 2019. If you elect not to upgrade your version of the software, the current version you have will still work, but will not have the new upgrade features.

Is CFS Designer fully compliant with AISI S100-12?

CFS Designer is compliant with AISI S100-12. You can also access earlier versions of the AISI Specification in CFS Designer by selecting Project Settings/Code and selecting the version.

Are load inputs in ASD or LRFD? Do the load combination factors have to be applied prior to entering loads in the program? Should factored or unfactored loads be input?

The current software is all in ASD (allowable strength design). The next upgrade version will feature up to eight stories of stacked x-bracing and shearwalls, which will be in LRFD. Everything else will be in ASD. The stacked x-brace and shearwalls will be LRFD because of the ACI requirements for concrete. We will also make it much more clear in this version which input is ASD and which is LRFD.

What is a web stiffener? How would you use one at a stud, header, or jamb?

A web stiffener is typically a stud or track piece that is used to support the wall stud or joist from crippling at a point load or bearing support. There are different ways to design a stiffener at different locations. Some examples include using a cut piece of stud or track attached to the stud or using a clip attached to the beam. Essentially, a web stiffener is a member that is added to the stud to help stiffen the stud from crippling.

Does this program take into consideration the cold work of forming in the design/analysis?

Yes, per AISI the program’s Project Settings default is to include cold work of forming in the design and analysis.

We generally try to size our cold-formed members to avoid the need for web stiffeners, just to save on construction and material costs. Something that helps quite a bit with the web bending and crippling calc is the bearing length. Are there code requirements for bearing lengths, or is this simply based on how much bearing we anticipate the member to have at its supports?

There are no specific code requirements for calculating bearing length for web crippling; the calculation is usually based on engineering judgment and connection detailing to determine how much bearing there will be at the support. A reasonable bearing length may be the length of the connection clip you are using for the attachment. Since web crippling is a “bearing” phenomenon, where attachments are made through the web, provided the attachment is not isolated near a flange, you may not need to consider web crippling. For stud-to-track types of connections, it’s common to use the track leg length as the bearing length.

Does this software give any stud-to-stud connection calculation like stud tearing and shearing? Checks?

The studs are designed per the AISI code for shear, moment, web crippling, axial load, and the related code-required interactions. Net-section rupture near connections is not checked by the CFS Designer™ software.

What is the difference between flexural bracing and axial bracing?

Flexural bracing is bracing that is used to increase the moment capacity of the stud, and axial bracing is bracing that is used to increase the axial capacity of the stud. These might be the same for your design, but we have given the user the ability to designate different spacings.

Do you have recommendations for how to properly terminate bridging at the end of the wall?

We agree that termination of bracing is often overlooked by engineers and should definitely be considered in design. Accumulation of bridging forces should also be considered. AISI S100-12, D3.3 and AISI S240-15 D3.4 provide methods of estimating brace forces. Simpson Strong-Tie has provided some suggestion in our cold-formed steel typical details sheets that show our SFC clip as one method to properly terminate a line of bridging.

Can the kicker connection be used on the underside of concrete fill over metal deck?

Yes! The SJC kicker connection has been tested and code listed to support diagonal brace loads. Simpson Strong-Tie has also provided a wide range of anchorage solutions for the kicker application that include connecting to the underside of concrete fill over metal deck. Concrete over metal deck may be normal weight or sand-lightweight with f’c of 3,000 psi minimum and 2.5″ minimum slab height above upper flute. Minimum deck flute height is 1.5″ (distance from top flute to bottom flute). Please visit for more information and design tables.

Why do some engineers use steel posts welded to a base plate for low wall applications?

For walls that are not top-supported, some Designers use a welded steel post at a certain spacing and infill with cold-formed steel studs and a top track. Simpson Strong-Tie has developed an innovative moment-capacity connection called the RCKW rigid kneewall kit, which can support many of these same conditions using cold-formed steel studs and eliminate the need for structural steel.

Are there any plans to expand the software capabilities?

We have a long list of enhancements and additions for the software and will continue to make the software more efficient, more user friendly, and with additional design capabilities.

Thanks again to everyone who joined us for the webinar and sent us questions. For complete information regarding specific products suitable to your unique situation or condition, please visit or call your local Simpson Strong-Tie cold-formed steel specialist at (800) 999-5099.

Introducing the Building Strong Blog

Building Strong Blog

This week we want to let you know about a new resource, the Building Strong blog. It’s very different from the SE Blog in that it ranges beyond the topics important to structural engineers to cover issues and various perspectives that help construction professionals of all disciplines design and build safer, stronger structures as efficiently as possible. We developed the new industry blog to highlight issues and topics that are of special interest to construction and building professionals. Through semi-monthly articles, the blog will cover topics ranging from rising labor costs to innovative technologies and the changing landscape of the building industry.

The Building Strong blog will cover topics on:

  • Safety, codes, and compliance
  • Residential and commercial construction
  • Decks and outdoor living
  • Building resilience
  • Emerging trends and industry insights
  • Collaborations and giving
  • Pro tips

We’re excited to offer the Building Strong blog. If you enjoy the SE Blog, this new content will give you a fresh take on timely topics affecting our industry. Check it out today!

What You Need to Know About Differences in Wind-Speed Reporting for Hurricanes

This week’s post was written by Darren Conrad, PE. Engineering Manager, Truss at Simpson Strong-Tie.

With Hurricane Irma wrapping up, the cleanup after Hurricane Harvey’s devastation underway in Houston and more big storms already churning in the Atlantic, it seems like a good time to discuss hurricanes and high wind. There is a great deal of good information out there to help us better understand hurricanes and their impact on people, structures and other property. To improve awareness of wind speeds and their measurement, this article will discuss a commonly misunderstood aspect of hurricane wind-speed reporting.

When a storm is approaching, you will hear meteorologists report wind speeds. They often refer to storm categories. These categories attempt to generalize expected damage to structures based on the wind speed of the storm. The wind speed for a given storm is a measure of the severity of the storm and the danger it poses to life and property. But how do meteorologists determine the wind speed that they are reporting? It seems so concrete and certain, but anyone who has been outside during a storm or windy day knows that wind isn’t constant at any one location over a period of time. It varies continuously in magnitude and direction over time. So how can something so variable be the subject of knowledge that is precise enough to be useful? How do we understand wind-speed measurements and make sure that when comparing them we are doing so in such a way that they are comparable? That is a great question.

The good news is that even though wind is variable, we have a commonly accepted way to measure wind speed and know something about a wind field or event that is occurring at a time and place. This is done by averaging measured wind speeds over specified lengths of time, or picking the highest average wind speed that occurs for a specified averaging interval from a longer period of time. A great resource for understanding how wind speeds are measured and reported can be seen here. From this explanation, it can be seen that a reported wind speed is meaningless without a specified averaging time. The shortest averaging intervals will yield the highest reported wind speeds. The longer averaging times will capture more peaks and lulls and yield lower reported wind speeds. The most common averaging intervals used to report wind speeds are three seconds, one minute and two minutes. Some countries even use a ten-minute averaging interval for reporting wind speeds. So the question arises, which average is correct? And the answer is, none of them and all of them. They are just different ways of looking at measured wind data. That is not very comforting, but one thing we can know is that none of them can be truly interpreted or compared without understanding this idea of averaging time. To make it more confusing, meteorologists and building codes do not use the same averaging interval when reporting or specifying wind speeds. This can lead to misunderstandings.

In general, you will hear meteorologists report sustained wind speeds when covering an approaching hurricane. They might also mix in some peak gusts, but for the most part they focus on sustained wind speeds. Sustained wind speeds for tropical cyclones use a 60-second averaging time. Sustained wind speed is also used by the Saffir-Simpson scale to roughly quantify the likely damage that the wind from a storm might cause typical buildings and other structures. There are criticisms of the accuracy of the Saffir-Simpson scale method, but it is widely used by the public to generalize about the severity of tropical cyclones; therefore, it is likely that the public might and commonly does attempt to compare reported sustained wind speeds to building-code-specified three-second-gust wind speeds to determine if their house or structure will withstand the storm. There is danger in making that comparison.

We need to be careful when comparing the reported sustained wind speed for a storm with the three-second-gust design wind speeds referenced in building codes and design standards. They are not the same and need to be converted before they can be compared for equivalence. After seeing the following example, one could easily see the possibility of the public or a public official comparing the sustained wind speeds reported by the weatherman to the wind speeds used by building codes and design standards and drawing conclusions that may underestimate the force and effect of the storm.

Let’s take a hypothetical situation where a building jurisdiction has adopted a wind speed of 130 mph three-second-gust design wind speed for structures built in that jurisdiction. There are various methods to convert wind speeds between different averaging times, and many factors that may need to be considered when doing that. One method for converting is the Durst method referenced in ASCE 7. Another more recent method recommended by the World Meteorological Organization provides a pretty straightforward conversion between sustained wind speed and three-second-gust wind speeds for near-surface applications. So for the sake of simplicity, we will use it for this example. If we convert a reported sustained wind speed of 130 mph to a three-second-gust average wind speed using this method, it equates to a three-second-gust wind speed for Off-Sea of 160 mph (Off-Sea is appropriate for an approaching hurricane). The adopted130 mph three-second-gust wind speed converts to 105 mph sustained wind speed. This difference could lead individuals in the path of the storm to underestimate its severity if they are not aware of the difference between averaging intervals for wind speeds. They could see the sustained wind speed of 130 mph being reported by the weather service when the storm is over open water and assume that their structure, or structures in their jurisdiction, will stand up fairly well. This would be a serious underestimate, since those structures would need to be designed to resist a 160 mph three-second-gust wind speed using ASCE 7 in order for that to be true. To say that a different way, one might think that their structure was designed for a Category 4 storm (130 mph sustained), when in fact it was actually designed for a Category 2 storm (105 mph sustained) using the Saffir-Simpson scale. Hurricane Irma at its maximum sustained wind speed of 185 mph would equate to a 227 mph three-second-gust wind speed using this conversion method. From a roof anchorage, lateral design and load path design perspective, the difference between 130 mph and 160 mph can be substantial, especially when the building is located on flat open terrain where Exposure C or Exposure D are appropriate assumptions for the design.

There is a lot more background and detail to this very complicated discussion, but the general point is to know your averaging times when comparing reported wind speeds, so as not to underestimate a storm’s force. If a storm is headed your way, hopefully you have already selected the proper hurricane tie for your structure; you have a well-defined and properly designed continuous load path; and you are protecting your exterior openings from windborne debris. Remember, the objective is not to protect the window or door product itself. Unless you are in the insurance business, you are preventing the breach of the opening to keep wind from pressurizing the structure, increasing loads on the structure and potentially causing catastrophic failure.

Know how to secure your structure against high winds, and be safe.

Q&A About Advanced FRP Strengthening Design Principles

Our thoughts go out to everyone affected by Hurricane Harvey and this disaster in Texas. To help with relief efforts we are donating $50,000 to the American Red Cross Disaster Relief Fund. Employees at our Houston warehouse are safe and the employees from our McKinney branch will be doing as much as they can to help with relief efforts.

This week’s post was written by Griff Shapack, PE. FRP Design Engineer at Simpson Strong-Tie.

On July 25, 2017, Simpson Strong-Tie hosted the second interactive webinar in the Simpson Strong-Tie FRP Best Practices Series, “Advanced FRP Design Principles,” in which Kevin Davenport, P.E. – one of our Field Engineering Managers – and I discussed the best practices for fiber-reinforced polymer (FRP) strengthening design. The webinar examines the latest industry standards, proper use of material properties, and key governing limits when designing with FRP and discusses the assistance and support Simpson Strong-Tie Engineering Services offers from initial project assessment to installation. Watch the on-demand webinar and earn PDH and CEU credits here.

During the live webinar, we had the pleasure of taking questions from attendees during the Q&A session. Here is a curated selection of Q&A from that session:

While I see how you improve the flexural capacity of a beam, how do you increase its shear capacity to match new moment strength?

ACI 440.2R recommends checking the element for shear if FRP is used to increase flexural strength. U-wraps can be used to provide shear strengthening of a beam.

Are there any “pre-check” serviceability checks (deflection, vibration, etc.) similar to the ACI 440 strength check that you recommend when considering the use of FRP?

ACI 440.2R contains a few serviceability checks on the concrete, rebar and FRP that can be performed once you have designed a preliminary strengthening solution.

Are these strengthening limits for gravity loads only? What about for a seismic load combination?

Yes, the strengthening limits are just for gravity loading. Seismic loading does not require an existing capacity check as it is highly unlikely for the FRP to be damaged during a lateral event.

Did Simpson Strong-Tie perform load tests on FRP repaired timber piles?

We are currently testing our FRP products as applied to timber piles at West Virginia University. We have also implemented a full-scale testing program on damaged timber piles at our own lab using our FX-70® fiberglass jacket system.

Will any of your seminars cover FRP and CMU? Seismic applications?

Yes, these are topics we are considering for future webinars.

The 0.6 limit for compressive stress can be very limiting. Can this value be evaluated on a case-by-case basis? The Euro code allows higher limits on compressive stress?

Our designers will report this value, along with the section addressing this check from ACI 440.2R, to the EOR and discuss whether the EOR would like to proceed with the FRP strengthening on his or her project.

Which engineer (EOR or Delegated Engineer) is responsible for specifying the scope of special inspections?

We provide a draft FRP specification to the EOR to use in their final determination of the special inspection requirements for a project. It’s in the owner’s best interest to hire a qualified special inspection agency on an FRP installation project.

For complete information regarding specific products suitable to your unique situation or condition, please visit or call your local Simpson Strong-Tie RPS specialist at (800) 999-5099.

Introducing Fabric-Reinforced Cementitious Matrix (FRCM)

February 14 marks the third interactive webinar in the Simpson Strong-Tie Composite Strengthening Systems™ Best Practices Series: “Introducing Fabric-Reinforced Cementitious Matrix (FRCM).

Join Simpson Strong-Tie engineering manager Brad Erickson, S.E., P.E., and Simpson Strong-Tie senior product manager Mark Kennedy, PMP, for an informative discussion of this new product solution. Attendees will have the opportunity to ask questions during the live event.

Continuing education credits will be offered for this webinar.
Participants can earn one professional development hour (PDH) or 0.1 continuing education unit (CEU).

Meet the First Simpson Strong-Tie Engineering Excellence Fellow with Build Change

Introducing James P. Mwangi, Ph.D., P.E., S.E. – our first annual Simpson Strong-Tie Engineering Excellence Fellow with Build Change. James Mwangi will write a quarterly blog about his experience throughout the Fellowship.

I’m delighted to have been asked to contribute this post and feel honored to be the first-ever Simpson Strong-Tie Engineering Excellence Fellow with Build Change. It’s my hope that this post will inform you about my professional background, why I applied to the Fellowship and how I think the Fellowship can benefit people and the structures they live, work and go to school in.

I grew up in Kenya and went through my basic education and my undergraduate coursework in civil engineering there. I worked for the government of Kenya as a junior roads engineer before proceeding to Nigeria for my masters in structural engineering. I returned to Kenya and worked for the government as a junior structural engineer. I joined the faculty of civil engineering shortly after that as a lecturer.

Central Kenya – including Nairobi, where I lived – is subject to moderate seismic activity, and I felt several earth tremors growing up. This puzzled me from a very young age, and I always wanted to learn how buildings behaved during these events. Since I didn’t acquire this understanding during my undergraduate or my master’s studies, I headed to California in 1988 for doctoral work in structural engineering at UC Davis. I didn’t have to wait long for first-hand experience of the effects of major seismic activity, because the Loma Prieta earthquake happened hardly a year after my arrival. This earthquake helped shape my career by giving me the opportunity to visit the destruction sites in the San Francisco Bay Area. Through my professors at Davis, I led a very successful Caltrans-funded project on full-scale testing of repair methods (steel jacketing and epoxy injection) of pile extensions that we harvested from a bridge that collapsed along Highway 1 in Watsonville. From completing my doctoral studies at UC Davis, I joined Buehler and Buehler Structural Engineers (B&B) in Sacramento. The 1994 Northridge earthquake happened while my steel moment frame school building in Milpitas was undergoing review by DSA. When we realized that no DSA engineer would sign off on this system from the field observation of the behavior of steel moment frames, I had to redesign the building over a weekend with a steel-braced frame system to meet the client’s schedule. At B&B, I was able to design building structures of wood, steel, masonry and concrete ranging in use from public schools, hospitals, and other essential service facilities to commercial buildings.

Since 2003, I have been a university professor, having joined the Architectural Engineering department (ARCE) at Cal Poly, San Luis Obispo, where I teach both undergraduate and graduate design courses in timber, masonry, steel and concrete. As a certified disaster safety worker in the governor’s office of emergency services, I have participated in the Structural Assessment Program in Paso Robles following the 2003 San Simeon earthquake; in Port-au-Prince following the Haiti earthquake of 2010; in Napa following the Napa earthquake of 2014; and in Kathmandu following the Nepal earthquake of 2015. I have contributed my experience from these deployments to the profession by serving in the technical activities committee of The Masonry Society (TMS) and also representing the seven western states in the TMS Board of Directors.

After my two-week building assessment in Haiti in 2010, I returned to Haiti for a year with the Mennonite Central Committee (MCC), participating in capacity building and safe building-back-better workshops targeting homeowners, contractors, engineers, architects and government officials. It was during this time that I first met Build Change as we shared information on our projects in Haiti. Since then, I’ve led a group of ARCE students to Haiti and Nepal every summer, and we have made it part of our itinerary to visit Build Change projects in each of the countries.

As a structural engineer, I have used Simpson Strong-Tie (SST) products throughout my career here in the US. I’ve not only used the SST products to teach my timber and masonry design courses at Cal Poly but have also supervised ARCE senior projects where we have used SST products. One of these projects led to a naming of one of our design laboratory rooms as The Simpson Strong-Tie Laboratory. It was only natural, then, that when I saw the advertisement for the Simpson Strong-Tie Engineering Excellence Fellowship, I couldn’t believe that two organizations with whom I have worked so closely as an individual and as a teacher were teaming up to create such a great opportunity. My familiarity with the two organizations, along with the fact that I already had a sabbatical leave approved from Cal Poly for the year of the Fellowship, made it a must for me to apply for the Fellowship. Natural disasters only cause human devastation where naturally occurring events (earthquakes, hurricanes, etc.) are not mitigated. The missions of the two organizations – BUILD Disaster-Resistant Buildings and CHANGE Construction Practice Permanently, alongside Simpson Strong-Tie’s No-Equal commitment to creating structural products that help people build safer, stronger homes and buildings –added to my desire to apply for the Fellowship.

Build Change projects involve helping local governments provide safe school buildings and other structures so their communities can better withstand damaging natural events, whether hurricanes, tornadoes or earthquakes. Where possible, we’ll use Simpson Strong-Tie products for the repair or retrofit of roofs, walls and anchorage. Build Change currently has projects in Indonesia, the Philippines, Nepal, Haiti and Colombia, all of which are located in areas susceptible to high winds and earthquakes. Indonesia is the fourth most populous country in the world. It’s my hope that I’ll be able to participate in projects in each of these countries, and I certainly believe that Build Change and Simpson Strong-Tie together can help millions of people live in better structures, built from better local, sustainable materials, which will be safe from strong winds and earthquakes.

If you’d like more information about the fellowship or my involvement over the next year, I can be reached at

Top 10 Changes to Structural Requirements in the 2018 IBC

This blog post will continue our series on the final results of the 2016 ICC Group B Code Change Hearings, and will focus on 10 major approved changes, of a structural nature, to the International Building Code (IBC).

  1. Adoption of ASCE 7-16
    • The IBC wind speed maps and seismic design maps have been updated.
    • A new section has been added to Chapter 16 to address tsunami loads.
    • Table 1607.1 has been revised to change the deck and balcony Live Loads to 1.5 times that of the occupancy served.
  2. New and Updated Reference Standards
    • 2015 IBC Standard ACI 530/ASCE 5/TMS 402-13 will be TMS402-16.
    • ACI 530.1/ASCE 6/TMS 602-13 will be TMS 602-16.
    • AISC 341-10 and 360-10 have both been updated to 2016 editions.
    • AISI S100-12 was updated to the 2016 edition.
    • AISI S220-11 and S230-07 were updated to the 2015 edition.
    • AISI S200, S210, S211, S212 and S214 have been combined into a new single standard, AISI S240-15.
    • AISI S213 was split into the new S240 and AISI S400-15.
    • ASCE 41-13 was updated to the 2017 edition.
    • The ICC 300 and ICC 400 were both updated from 2012 editions to 2017 editions.
    • ANSI/NC1.0-10 and ANSI/RD1.0-10 were all updated to 2017 editions.
  3. Section 1607.14.2 Added for Structural Stability of Fire Walls
    • This new section takes the 5 psf from NFPA 221, so designers will have consistent guidance on how to design fire walls for stability without having to buy another standard.
  4. Modifications of the IBC Special Inspections Approved
    • Section 1704.2.5 on special inspection of fabricated items has been clarified and streamlined.
    • The Exception to 1705.1.1 on special inspection of wood shear walls, shear panels and diaphragms was clarified to say that special inspections are not required when the specified spacing of fasteners at panel edges is more than 4 inches on center.
    • The special inspection requirements for structural steel seismic force-resisting systems and structural steel elements in seismic force-resisting systems were clarified by adding exceptions so that systems or elements not designed in accordance with AISC 341 would not have to be inspected using the requirements of that standard.
  5. Changes Pertaining to Storm Shelters
    • A new Section 1604.11 states that “Loads and load combinations on storm shelters shall be determined in accordance with ICC 500.”
    • An exception was added stating that when a storm shelter is added to a building, “the risk category for the normal occupancy of the building shall apply unless the storm shelter is a designated emergency shelter in accordance with Table 1604.5.”
    • Further clarification in Table 1604.5 states that the type of shelters designated as risk category IV are “Designated emergency shelters including earthquake or community storm shelters for use during and immediately after an event.”
  6. Changes to the IBC Conventional Construction Requirements in Chapter 23
    • The section on anchorage of foundation plates and sills to concrete or masonry foundations reorganized the requirements by Seismic Design Category (SDC) and added a new section on anchoring in SDC E. It also states that the anchor bolt must be in the middle third of the width of the plate and adds language to the sections on higher SDCs saying that if alternate anchor straps are used, they need to be spaced to provide equivalent anchorage to the specified 1/2″- or 5/8″-diameter bolts.
    • The second change permits single-member 2-by headers, to allow more space for insulation in a wall. 
  7. Modification to the Requirements for Nails and Staples in the IBC
    • ASTM F1667 Supplement One was adopted that specifies the method for testing nails for bending-yield strength and identifies a required minimum average bending moment for staples used for framing and sheathing connections.
    • Stainless-steel nails are required to meet ASTM F1667 and use Type 302, 304, 305 or 316 stainless steel, as necessary to achieve the corrosion resistance assumed in the code.
    • Staples used with preservative-treated wood or fire-retardant-treated wood are required to be stainless steel.
    • The new RSRS-01 nail was incorporated into TABLE 2304.10.1, the Fastening Schedule. The RSRS nail is a new roof sheathing ring shank nail designed to achieve higher withdrawal resistances, in order to meet the new higher component and cladding uplift forces of ASCE 7-16.
  8. Truss-Related Code Change
    • The information required on the truss design drawings was changed from “Metal connector plate type” to “Joint connection type” in recognition that not all trusses use metal connector plates.
  9. Code Change to Section 2304.12.2.2
    • A code change clarifies in which cases posts or columns will not be required to consist of naturally durable or preservative-treated wood. This change makes the requirements closer to the earlier ones, while maintaining consistency with the subsequent section on supporting members.
    • If a post or column is not naturally durable or preservative-treated, it will have to be supported by concrete piers or metal pedestals projecting at least 1″ above the slab or deck, such as Simpson Strong-Tie post bases that have a one-inch standoff.
  10. Code Change to IBC Appendix M
    • A code change from FEMA makes IBC Appendix M specific to refuge structures for vertical evacuation from tsunami, and the tsunami hazard mapping and structural design guidelines of ASCE 7-16 would be used rather than those in FEMA P-646.

Once the 2018 IBC is published in the fall, interested parties will have only a few months to develop code changes that will result in the 2021 I-Codes. Similar to this last cycle, code changes will be divided into two groups, Group A and Group B, and Group A code changes are due January 8, 2018. The schedule for the next cycle is already posted here.

What changes would you like to see for the 2021 codes?

The New Way to Connect with Strong Frame®

The April SE blog article, What Makes Strong Frame® Special Moment Frames So Special, explained the features and benefits of the Yield-Link® structural fuse design for the Strong Frame® special moment frame (SMF) connection. In this blog, I will be introducing the Yield-Link end-plate link (EPL) to the Strong Frame connection family.

What is the EPL?
The EPL connection (Figure 1) is the latest addition to the Strong Frame Strong Moment Frame (SMF) solution. The new EPL connection can accommodate a W8X beam which is approximately a 33% reduction in beam depth from a W12X beam. The frame is field bolted without the need for field welding which means a faster installation. The snug-tight bolt installation requirement means no special tools are required. The EPL SMF connection has the same benefit of not requiring any additional beam bracing as the T-Stub connection. The frame can be repaired after a large earthquake by replacing the Yield-Link connection. Since the shear tab bolts will be factory installed, installation time for the frame is reduced by 25% making the EPL connection one of the most straightforward connections to assemble.

Figure 1: New Yield-Link EPL connection

Why Did We Develop the EPL?
The development of the EPL came from strong interest and numerous requests to offer a solution with more head room for clearance of retrofit projects or enhancement for new construction using a shallower beam profile. The original T-stub link design has the shear tab welded to the column flange. The geometry of the shear tab meant that a W12X beam is required to accommodate the Yield-Link Flange. In Figure 2, you can see that a shallower beam profile will bring the Yield-Link flange closer to each other and limit the attachment of the shear tab. A new connection was needed.

Figure 2: Yield-Link flange interference with shear tab

Figure 3: 3 Bolt configuration with notched flange plate. (The 3rd bolt is on opposite side of beam.) The asymmetric layout produced uneven force distribution in the bolts.

How Did We Develop the EPL?
Multiple configurations were studied, including a notched flange plate with 3 bolts (Figure 3) to avoid interference with the shear tab connection to the column. In the end, a compact end plate link combining the shear tab and Yield-Link stem in a single connection was the final design. However, many questions loomed over the prototype. How will the single end plate design perform in a full scale test? Will the new configuration change the limit state? These questions needed to be studied prior to launching an expensive full-scale test program with multiple samples and configurations. Numerous Finite Element Analysis (FEA) models were studied and refined prior to full scale testing of a prototype. Modeling included ensuring the stem performs as a fuse (Figure 4) as discussed in the April blog and the integrity of the shear tab is maintained in the compact design. Figure 5 shows a graph comparing the analytical model to the actual full scale test. The full scale test with a complete beam and column assembly was performed to the requirements under AISC 341 Section K. The full scale test passed the requirements for the SMF classification as can be seen in Figure 6 for the specimen with 6-inch columns and 9-inch beam.

Figure 4: Equivalent Plastic Strain Plot of Yielding-Link Stem

Figure 5: Full Scale Test vs. Analytical model

Figure 6: Moment at Face of Column vs. Story Drift

Where Can I Get More Information?
The EPL is now recognized in the ICC-ES ESR-2802 code report as an SMF. EPL solutions are also offered in the Strong Frame Moment Frame Selector Software. Want to see how the new connection and member sizes can expand your design options? Visit to download the new Strong Frame Design Guide or contact your Simpson representative for more information.

Keep Your Roof On

He huffed, and he puffed, and he blew the roof sheathing off! That’s not the way kids’ tale goes, but the dangers high winds pose to roof sheathing are very real. Once the roof sheathing is gone, the structure is open and its contents are exposed to the elements and much more vulnerable to wind or water damage. It is a storyline that we meet all too often in the news.

About two years ago, the ASTM subcommittee on Driven and Other Fasteners (F16.05), addressed fastening for roof sheathing in high-wind areas by adding a special nail to ASTM F1667-17 – Standard Specification for Driven Fasteners: Nails, Spikes and Staples. The Roof Sheathing Ring-Shank Nail was added to the standard as Table 46. Figure 1 illustrates the nail and lists its geometrical specifications. This is a family of five ring-shank nails that can be made from carbon steel or stainless steel (300 series). Specific features of these nails are the ring pitch (number of rings per inch), the ring diameter over the shank, the length of deformed shank and the head diameter. Also, note B specifies that the nails shall comply with the supplementary requirement of Table S1.1, which tabulates bending yield strength. In this diameter class, the minimum bending yield strength allowed is 100 ksi.

Figure 1. Roof Sheathing Ring-Shank Nails (ASTM. 2017. Standard Specification for Driven Fasteners: Nails, Spikes and Staples, F1667-17. ASTM International, West Conshohocken, PA.)

The IBHS (Insurance Institute for Business and Home Safety) discusses roof deck fastening in its Builders Guide that describes the “FORTIFIED for Safer Living” structures. The IBHS FORTIFIED program offers solutions that reduce building vulnerability to severe thunderstorms, hurricanes and tornadoes. Keeping the roof sheathing on the structure is critical to maintaining a safe enclosure and minimizing damage, and roof sheathing ring-shank nails can be part of the solution. As Figure 2 from IBHS (2008) shows, every wood-frame structure has wind vulnerability.

Figure 2. Hurricane, high wind and tornado regions of the US (IBHS. 2008. Builders Guide, Fortified for Safer Living. Tampa, FL. 81 pp.)

More importantly for the wood-frame engineering community, the Roof Sheathing Ring-Shank Nails are being included in the next revision of the AWC National Design Specification for Wood Construction (NDS-2018), which is a reference document to both the International Building Code and the International Residential Code. You will be able to use the same NDS-2018, chapter 12 withdrawal equation to calculate the withdrawal resistance for Roof Sheathing Ring-Shank Nails and Post Frame Ring-Shank nails. The calculated withdrawal will be based on the length of deformed shank embedded in the framing member. Also, Designers need to consider the risk of nail head pull-through when fastening roof sheathing with ring-shank nails. If the pull-through for roof sheathing ring-shank nails is not published, you will be able to use the new pull-through equation in the NDS-2018 to estimate that resistance.
Simpson Strong-Tie has some stainless-steel products that meet the requirements for Roof Sheathing Ring-Shank Nails. These will be especially important to those in coastal high-wind areas. Table 1 shows some of the Simpson Strong-Tie nails that can be used as roof sheathing ring-shank nails. These nails meet the geometry and bending yield strength requirements given in ASTM F1667. See the Fastening Systems catalog C-F-2017 for nails in Type 316 stainless steel that also comply with the standard.

Table 1. Simpson Strong-Tie collated nails made from Type 304 stainless steel that comply with F1667-17 specifications for Roof Sheathing Ring-Shank Nails.

Improve your disaster resilience and withstand extreme winds by fastening the sheathing with roof sheathing ring-shank nails. You can find Roof Sheathing Ring-Shank nails in ASTM F1667, Table 46, and you will see them in the AWC NDS-2018, which will be available at the end of the year. Let us know your preferred fastening practices for roof sheathing.