Simpson Strong-Tie® SET-3G™ Adhesive Offers a Ductile Solution for Post-Installed Anchorage near a Concrete Edge

Designing post-installed anchorage near a concrete edge is challenging, especially since the ACI provisions for cracked-concrete anchorage went into effect. In the following post, one of our field engineers, Jason Oakley, P.E., explains how SET-3G™ and Anchor Designer™ software from Simpson Strong-Tie make it easier to design a ductile anchor solution.

Engineers often provide holdown anchoring solutions near a concrete edge to help prevent overturning of light-frame shear walls during a seismic (or high-wind) event. Sometimes a post-installed anchor must be used if the cast-in-place anchor was mislocated or misinstalled, or is located where a retrofit or addition is needed. Since the cracked-concrete anchorage design provisions went into effect more than a decade ago, it has been challenging for engineers to offer a near-edge post-installed anchoring solution. This is especially true for structures subject to earthquake loads in seismic design category (SDC) C through F. Simpson Strong-Tie’s new SET-3G epoxy is the first anchoring adhesive in the industry to offer exceptionally high bond-strength values that permit ductile anchorage in concrete near an edge. This blog post will cover a specific example that focuses on Chapter 17 of ACI 318-14 to design a threaded rod, anchored with SET-3G adhesive, used to secure a holdown located 1 3/4″ away from a single concrete edge (Figure 1).

Figure 1. Design Example for SET-3G Adhesive Anchor Used to Secure a Holdown near a Single Concrete Edge

Before proceeding with our design example, some background information will be helpful. Section of ACI 318-14 provides four options for designing anchorage in concrete base material. This post will address the two most commonly chosen options for holdown anchorage, (a) and (d). Information on options (b), (c) and more can be found in one of our previous blog posts.

Option (a) requires the anchor system to behave in a ductile manner. To accomplish this, we must meet the following ACI 318-14 requirements:

1) Both the nominal concrete breakout and adhesive bond (pullout) strengths must be great enough by a certain margin to allow a ductile steel insert to exhibit sufficient axial plastic deformation before rupture (

2) The insert must be classified as ductile. A threaded rod conforming to ASTM F1554 Gr. 36 is one example of an insert that meets the ACI 318 requirements to qualify as a ductile steel element (see Ch. 2, definition for steel element, ductile).

3) The insert must have enough stretch length to achieve a meaningful level of axial deformation under tensile loading (

In many cases, engineers have used option (d), which requires that the earthquake force be amplified by an over-strength factor, Ωo. Option (d) makes ductility irrelevant by ensuring that the anchor system behaves in a linear elastic way during an earthquake. For light-frame shear wall construction, Ωo is 3, but it can be reduced to 2.5 for a structure having a flexible diaphragm. Unfortunately, choosing option (d) often results in an amplified earthquake force far greater than the post-installed anchor design strength. This has caused some engineers to resort to expensive solutions such as anchoring through an existing footing into a new reinforced footing underneath.

Anchor Design Software Can Help
The free Simpson Strong-Tie Anchor Designer software for ACI 318 makes it easy to design a ductile anchor system using SET-3G anchoring adhesive. Figure 2 is a screen shot of our design example. Here is a list of some input information, some of which is shown in the calculation summary and 3D-model tab of the software:
• Strength-level tensile demand load: Nu = 7,700 lb.
• Anchor: 5/8″-diameter ASTM F1554 Gr. 36 threaded rod (Fu = 58,000 psi)
• Embedment depth: 12 1/2″
• Single-edge distance: 1 3/4″ (typical for 2×4 stud wall)
• Concrete strength: f’c = 3,000 psi normal-weight concrete
• Cracked concrete
• Hole condition: dry

Figure 2. Simpson Strong-Tie Anchor Designer Software SET-3G Design Example Summary Output

Conveniently, the design strength value for each of the following failure modes — steel, concrete breakout and adhesive bond (pullout) — is summarized on the left. The 3D-model tab shows the anchor located 1 3/4″ away from a single edge with all other edges assumed to be infinite. Note that the adhesive bond (pullout) design strength governs. Before proceeding further, try to answer the following question: Is this anchor system ductile?
To see whether this anchor system is ductile, we first must determine the nominal strength for each failure mode. The nominal strength provides a better representation than the design strength of the relative expected tensile limit of each failure mode. To qualify an anchor system as ductile, section of ACI 318- 14 requires that the following relative strength conditions be met:

1.2 Nsa < Ncb and Na

The nominal steel strength, Nsa, is multiplied by 1.2 to account for the possibility that the ultimate tensile strength of the insert (threaded rod in our case) could be larger than expected. This check is important as it helps to increase the probability that non-ductile failure modes — namely, concrete breakout (Ncb) and adhesive bond (Na) — will not occur. The nominal strength for each failure mode can be calculated backwards from the design strength as follows:

Because the steel failure mode governs (1.2Nsa = 15,732 lb.) and the steel in this design example is ductile (ASTM F1554 Gr. 36), the anchorage is considered ductile. It’s important to note that the nominal strength does not include the material reduction factor, φ, which is 0.75 for steel and 0.65 for breakout and adhesive bond. It also does not include the 0.75 reduction factor for anchorage located in SDC C – F. This reduction factor accounts for the possibility of increased cracking and spalling in the concrete caused by seismic activity.

Next, the threaded rod must have a stretch length of eight times the nominal diameter of threaded rod (8d) according to — or, in our case, 5″. In our example, the sill plate is 1 1/2″ thick and the distance between the anchor nut and HDU5 base, SO, is 1 3/8″. SO will vary according to the holdown model and is published in the Simpson Strong-Tie Wood Construction Connectors catalog. To meet the 8d stretch length, the holdown will need to be raised 5″ – 1 1/2″ – 1 3/8″ = 2 1/8″ above the 2x sill plate (Figure 1). If the anchor needs to be extended with a coupler nut to reach the holdown, then the 8d stretch length should (1) only apply where the threaded rod is continuous and (2) never include the length of the coupler nut. Simpson Strong-Tie HDU holdowns can be raised up to 6″ (2 1/2″ for the DTT1 and 4 1/2″ for the DTT2) above the concrete surface (measured to the holdown nut) without having to consider additional rod elongation.

A nice feature of the Anchor Designer software is that it performs the ductility check and conveniently shows the results, highlighting in bold font which failure mode governs (Figure 3). The software will show you whether the anchor system, based on the design information entered by the user, is ductile or not.

Figure 3. SET-3G Ductility Check

We see that the anchor system, rated for a governing design strength of 7,727 lb. (adhesive bond), can resist the demand load of 7,700 lb. Dead load is not addressed here, but it should be included in the design because it reduces the net uplift force, Nu.

Next, we must choose a holdown. Since ASD values are listed for Simpson Strong-Tie holdowns, we must convert our demand load to an ASD level load. To simplify, we assume 100% seismic loading.

ASD level tensile demand load = 7,700 x 0.7 = 5,390 lb.

Figure 4 shows a list of predeflected holdowns that can be found in the Wood Construction Connectors catalog. For a DF/SP wood post, we find that the HDU5 is the best choice. This holdown is rated for 5,645 lb., exceeding the design load of 5,390 lb.

Figure 4. Simpson Strong-Tie Predeflected Holdowns
(HDU5 highlighted in yellow)

There you have it! A ductile anchor solution near a concrete edge is possible because SET-3G adhesive achieves some of the highest bond-strength values on the market. Ever since the building code started referencing the ACI anchorage design provision more than 10 years ago, engineers have been struggling to make concrete anchorage work for holdowns located near an edge. But now engineers have the option of designing with an adhesive anchor for a more cost-effective solution.

Additional information about Simpson’s newest adhesive, SET-3G, can be found at

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 by watching our free webinar.

On December 6 we hosted an interactive webinar on the MPBZ moment post base, its evaluation, its testing and its applications. In this webinar, we discussed MPBZ moment post base product features, product development, design examples and much more. Attendees had an opportunity to ask questions during the event and you can find answers to those questions here.

Watch a 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 MPBZ.

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.

What Structural Engineers Need to Know About the New OSHA Silica Dust Standards

This week’s post was written by Todd Hamilton, PE. ICI Field Engineer at Simpson Strong-Tie.

In March of 2016, the United States Department of Labor issued new OSHA standards on how crystalline silica dust should be handled in various workplaces including within the construction industry. The changes are intended to limit workers’ exposure to and inhalation of silica dust on the jobsite. These regulations will replace the current standard, which was issued in 1971. Compliance with the new rules will be required on construction jobsites starting September 23, 2017, and will be enforced through OSHA from that time forward.

Crystalline silica is a naturally occurring mineral that is found in sand, sandstone, shale and granite, and since some of these materials can be found on jobsites on their own or as a component of a construction material such as concrete and mortar, changes to how workplaces contain and dispose of silica dust will affect the way our industry operates. Some of the processes performed on a construction jobsite that can expose workers to crystalline silica dust are drilling, grinding and sawing concrete and masonry; jackhammering; and sand blasting. Inhaling crystalline silica can lead to long-term illness and early death. Illnesses caused by inhaling silica dust include silicosis, lung cancer and chronic obstructive pulmonary disease (COPD).

The new OSHA standards do the following:

  • Reduce the permissible exposure limit (PEL) for respirable crystalline silica to 50 micrograms per cubic meter of air, averaged over an eight-hour shift. Previous PEL was 250 micrograms per cubic meter of air, averaged over an eight-hour shift.
  • Require employers to use engineering controls (such as water or ventilation) to keep worker silica exposure within the PEL; provide respirators when engineering controls cannot adequately limit exposure; limit worker access to high-exposure areas; develop a written exposure-control plan; offer medical exams to highly exposed workers; and train workers on silica risks and how to limit exposure.
  • Provide medical exams to monitor highly exposed workers and give them information about their lung health.
  • Provide flexibility to help employers – especially small businesses – protect workers from silica exposure.

Beyond that, the OSHA standards offer three methods an employer can use to demonstrate compliance:

  • A list of common jobsite activities and the required engineering control method, plus the additional respiratory protection (if needed) to meet the 50 PEL.
  • For activities/protection methods not included in the preceding list, the use of credible third-party assessment is allowed to show that the exposure level is < 50 PEL. This includes data from universities, trade associations, etc. that can be used provided they are based on conditions similar to, or more inherently hazardous than, the employer’s current conditions.
  • Manufacturers can generate their own data on their workers’ exposure level using an air-monitoring system.

Visit the US Department of Labor’s OSHA website for more in-depth information and useful links.

All these new requirements directly affect contractors onsite, but it’s also important for structural engineers to have an understanding of them. Beyond that, there are some key things that structural engineers should consider when specifying products such as post-installed anchors where the installation process includes drilling concrete, which does generate crystalline silica dust. Back in 2006 when Acceptance Criteria 308 was adopted, it made a lot of changes to how adhesive anchors are tested and qualified, but it also required that the manufacturers’ printed installation instructions (MPII) be published as part of the code report. This tied the published data in the code report to the installation procedures that could be used to achieve those data. And with the adoption of ACI 335.4 in 2015, the requirement for the MPII to be included in the code report continues. Therefore, with MPIIs being a part of the code report, a structural engineer needs to understand the importance of having an installation method that accounts for silica dust generated during the installation process and verify that the MPIIs include an installation process which utilizes a high-efficiency dust-collection system.

To get a better understanding of how these high-efficiency dust-collection systems work, let’s look at the Simpson Strong Tie Speed Clean™ DXS dust extraction system. This system was developed through a partnership with Bosch. Here is a video that clearly explains the system and its method:

So as structural engineers, we should consider what the MPII says when we are specifying a product.  Does it have an installation procedure, such as the Simpson Strong-Tie/Bosch DXS, that properly controls the crystalline silica dust generated? Does the code report lock the contractor into a specific brand of vacuum? Some code reports may only allow the use of a specific brand and model of vacuum and drills that can be used, which in some cases could require the purchase of new tools.

The new OSHA standard is very beneficial to installers because it will protect them from potential long-term health hazards. When it comes to anchor installation, the new regulations, along with compliant technologies such as the Speed Clean DXS, will eliminate the blow-brush-blow installation method that creates a lot of harmful airborne crystalline silica dust and is also often a source of installation error. Even though it will take time and effort for contractors and engineers to come to grips with the full ramifications for their projects, the new regulations are a positive development for the construction industry.

Why Fire-Rated Hangers Are Required in Type III Wood-Frame Buildings

One of the first mixed-use designs I worked on as a consulting structural engineer was a four-story wood-frame building over two levels of parking. Designing the main lateral-force-resisting system with plywood shearwalls was a challenge for this project that required new details to meet the high design loads. The high overturning forces were resisted using the Simpson Strong-Tie® Strong-Rod™ anchor tiedown system, which incorporates high-strength rods, bearing plates and shrinkage compensation devices.

At the time, these construction details using Strong-Rod systems and high- load shearwall diaphragms were new, innovative concepts. However, this method of construction rapidly became commonplace as intense demand for housing fueled the trend toward denser, mixed-use developments in downtown areas. I discussed the trend toward taller, denser developments in this post.

A more recent trend in wood-frame construction has been the shift to Type III wood-frame construction, which allows designs up to five stories. To help educate designers on some of the nuances of Type III wood-frame construction and provide guidance on meeting the associated code requirements, we reached out to Bruce Lindsey, the South Atlantic Regional Director for WoodWorks. Bruce wrote a two-part article entitled Fire Protection Considerations with Five-Story Wood-Frame BuildingsPart 1 and Part 2. This post will go into more detail on connecting the floor system to the two-hour fire-rated exterior walls and discuss our new DG series joist hangers that are specially designed for this application.

As a structural engineer, I was aware of fire requirements mostly because I needed to account for the weight of fire sprinklers, added layers of gypsum board, fire-proofing on steel, or concrete slab thickness in my design. While the increased loads can affect the vertical- and lateral-force-resisting systems, I seldom needed to change the details and connections in my designs.

The exterior walls in Type III wood-frame construction require fire-retardant-treated (FRT) lumber with two layers of gypsum board to provide a two-hour fire rating. There are many established fire-rated floor and wall assemblies available. The challenge, as discussed in Part 2 of Mr. Lindsey’s post, is detailing the intersections between the floor and wall systems. Connecting the floor framing to the exterior walls in Type III construction requires careful detailing to transfer the vertical loads without compromising the two-hour fire rating of the wall assembly.

Below is a summary of some of the possible fire wall connections as discussed in Mr. Lindsey’s previous blog posts.

A solid header on top of the wall that has adequate thickness to provide a two-hour rating through its charring capability. The cost and availability of solid rim board material should be considered.

A continuous 2x ledger or blocking to provide one hour of fire resistance. The second hour of resistance is provided by ceiling gypsum board. Some jurisdictions object to this detail over concerns about a fire starting within the floor cavity.

Some jurisdictions interpret the two-hour exterior wall requirement as applying only to the wall and not the floor. In such jurisdictions, designers can sometimes use standard platform framing in Type III construction.

A variation where the ledger can be installed over two layers of gypsum board. Simpson Strong-Tie has tested and published values for ledger connections over gypsum board using our SDWH and SDWC fasteners. The testing of these fasteners was discussed in our Spanning the Gap post from earlier this year.

In this detail, one hour of fire resistance is provided by a single layer of gypsum board running the full height of the wall with a hanger installed over the gypsum board. The second hour of resistance is provided by the ceiling gypsum board.

A variation of this detail is our DU/DHU series of drywall hangers that are installed over two layers of gypsum board. These were addressed in this post.

Designs using hangers or ledgers installed over gypsum board can create construction sequencing challenges. Since the gypsum board needs to be installed before the framing, the contractor will need to coordinate between the trades.

A new solution that eliminates sequencing issues for Type III construction is our series of DG/DGH/DGB fire wall hangers, which are designed to easily install on a two-hour wood stud fire wall. These top-flange hangers feature enough space to allow two layers of 5/8″ gypsum wall board to be slipped into place after the framing is complete.

These new fire wall hangers were tested in accordance with ICC-ES AC13 and ASTM D7147, which I discussed in How We Test – Part I: Wood Connectors. These standards do not explicitly detail how to test a hanger installed on a wood stud wall, so we collaborated closely with ICC Evaluation Services to develop a test setup that meets the intent of the standards.

All three of our new fire wall hangers have been tested according to ASTM E814 and received F (flame) and T (temperature) ratings for use on either or both sides of the fire wall. These ratings verify that the DG/DGH/DGB hangers do not reduce the two-hour fire wall assembly rating.

Our testing and load tables address installation of 2×4 or 2×6 stud walls constructed of Douglas fir (DF), southern pine (SP), spruce-pine-fir (SPF) or hem-fir (HF) lumber.

DG Hanger

DGH Hanger

DGB Hanger

Drywall Notch Detail

If you are working on a Type III wood-frame construction project, check out our Fire Wall Solutions page, which has product profiles with links to further information about the new DG hanger series, as well as our DU/DHU series of drywall hangers and fire wall fastener solutions using Strong-Drive® SDWS Timber screws.

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.

What’s New in the ACI 440.2R-17?

The wait is over. The ACI 440.2R-17 Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures is now available. The following post will highlight some of the major changes represented by this version of the document.

It’s been a long road and countless committee hours to get from the last version of ACI 440.2R-08 to this document. While there are multiple smaller changes throughout the document, the most notable update is the addition of Chapter 13 – Seismic Strengthening.


The new seismic chapter addresses the following FRP strengthening scenarios:

  • Section 13.3 – Confinement with FRP
    • This section includes all of the following: general considerations; plastic hinge region confinement; lap splice clamping; preventative buckling of flexural steel bars.
  • Section 13.4 – Flexural Strengthening
    • The flexural capacity of reinforced concrete beams and columns in expected plastic hinge regions can be enhanced using FRP only in cases where strengthening will transfer inelastic deformations from the strengthened region to other locations in the member or the structure that are able to handle the ensuing ductility demands.
  • Section 13.5 – Shear Strengthening
    • To enhance the seismic behavior of concrete members, FRP can be used to prevent brittle failures and promote the development of plastic hinges.
  • Section 13.6 – Beam-Column Joints
    • This section covers a great deal of recent research on the design and reinforcement of beam-column joints.
  • Section 13.7 – Strengthening Reinforced Concrete Shear Walls
    • This section provides many recommendations for FRP strengthening of R/C shear walls.

Simpson Strong-Tie Can Help

We recognize that specifying Simpson Strong-Tie® Composite Strengthening Systems™ (CSS) is unlike choosing any other product we offer. Leverage our expertise to help with your FRP strengthening designs. Our experienced technical representatives and licensed professional engineers provide complimentary design services and support – serving as your partner throughout the entire project cycle.

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.

Upcoming Free Webinar: Advanced FRP Design Principles

Join us live on July 25 for the second interactive webinar in the Simpson Strong-Tie FRP Best Practices Series: Advanced FRP Design Principles. In this webinar we will highlight some very important considerations during the FRP design processes. This will include topics such as the latest industry standards, proper use of material properties, and key governing limits when designing with FRP. Attendees will also have an opportunity to pose questions to our engineering team during the event. Continuing educations units will be offered for attending this webinar. 

Learn more: Webinar – Introducing Fabric-Reinforced Cementitious Matrix (FRCM)

In this free webinar we dive into some very important considerations including the latest industry standards, material properties and key governing limits when designing with FRCM.

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

How Are DECK-DRIVE™ DWP Screws Load-Rated?

Experiential learning — has it happened to you? Certainly it has, because experiential learning is learning derived from experience. It happens in everyday life, in engineering and in product development, too. For example, experience has taught us that after a product is launched, our customers will find applications for the product that were never expected or listed in the product brief. Also, experience has shown us that larger fasteners tend to be placed in applications that have greater structural and safety demands.

When the larger Deck-Drive™ DWP screws were manufactured, we decided that they should be marketed as “load-rated” screws because they were big enough to support physically large parts and would be expected to provide structural load resistance.

So what is a “load-rated” screw? To Simpson Strong-Tie, a load-rated screw is a threaded fastener that has controlled dimensions and physical properties, as well as validated connection properties.  Load-rated fasteners are also subject to the same quality inspection that would occur if they were undergoing an evaluation report.

The products in the focus of this blog are Deck-Drive DWP Wood stainless-steel tapping screws. They are made from stainless steel (Types 305 and 316) and are particularly interesting because they have a box thread design feature. What is a box thread and what are its benefits? A box thread is a thread that is square rather than round. It is formed by rolling (not a trivial tooling challenge) like a standard thread. The box thread is preferred for some applications in part because of the low torque required to install the screw; that is, the installation demand is low relative to standard threads of the same pitch (number of threads per inch). You can easily see the box thread by looking from the point of the screw toward the head. The square corners of the box thread rotate at a defined angle, giving the threaded length a twisted appearance. The box thread is also used on the Timber-Hex SS screws. See Figure 1 for an illustration.

Figure 1. Phone photo showing box thread on a DWP screw (No.12, 4 inches long). These screws have a flat head, and this size has a T-27, six-lobe drive recess.

When we load rate a fastener, ICC-ES AC233 (Acceptance Criteria for Alternate Dowel-type Threaded Fasteners, 2015) is the guiding document. Essentially, we do everything that would be done if the product was going into an evaluation report. The testing uses representative products and is witnessed by a third party, and every test report is reviewed and stamped by a professional engineer. The DWP screws that are fully load rated are No. 12 and No. 14 that are three to six inches long. This means that we have evaluated by test the shear and tensile strengths, bending yield strength, head pull-through resistance, withdrawal resistance and certain logical lateral shear configurations of these models. The connection properties are developed in at least three species combinations of wood representing a range of specific gravities. Each cell in the connection load matrix is a reference allowable value based on a mean of at least 15 tests that is subject to a precision of five percent at a 75-percent confidence level. Table 1 is snipped from the prepublication spreadsheets.

While we were working on the No. 12 and No. 14 screws, we also realized that No. 10 DWP screws often require withdrawal loads because they are used in decks and docks to fasten the decking to the structural frame. You can see in Table 1 that the withdrawal loads were included for No. 10 DWP screws and the related properties, because uplift resistance is often engineered for those applications.

What is the test method for each property in the load table? See Table 2 for the test method used for each property and the related data for that property. The reference allowable shear loads shown in Table 1 represent more than 1,200 individual tests, and each test includes wood specific gravity, moisture content and continuous load-displacement data from start of test to past ultimate load.

Table 1. Reference allowable properties for the DWP load-rated screws.

Table 2. Test methods used to evaluate the properties of load-rated screws per ICC-ES AC233.

Load rating screws is a big job, and it creates an elevated continuous quality-monitoring obligation. However, our experience has taught us that the engineering community needs information and reference properties that can be relied on when specifying, and thus working with load-rated screws makes it possible to put your stamp on a design with confidence.

We look forward to hearing from you about load-rated fasteners, because we learn from you every time you contact us.