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Welcome to our Structural Engineering Blog! I’m Paul McEntee, Engineering R&D Manager at Simpson Strong-Tie. We’ll cover a variety of structural engineering topics here that I hope interest you and help with your projects and work. Social media is “uncharted territory” for a lot of us (me included!), but we here at Simpson Strong-Tie think this is a good way to connect and even start useful discussions among our peers in a way that’s easy to use and doesn’t take up too much of your time. Continue reading

Construction Referees: Evaluation Processes for Alternative Building Products

In a perfect world, every single product used in building would undergo a rigorous, independent evaluation process to determine its compliance with established safety codes and standards prior to its appearance in the market. “Alternative” building products and design methods are very much a reality of the construction industry, however. All the same, when Designers and building officials must decide whether to specify or approve such products, there are still review organizations and processes that help them evaluate whether or not the products meet the required safety standards to protect the public. In this post, Jeff Ellis, Simpson Strong-Tie Director of Codes and Compliance, delineates the process involved when an evaluation service entity, such as ICC-ES, issues an evaluation report (ER) for an alternative building product or method.

There are products used in many buildings that are not referenced by the codes or standards. These products can affect structural strength, stability, fire resistance and other building performance attributes, which can impact public safety, health, and general welfare. The International Building Code Section 104.11 (Alternative materials, design, and methods of construction and equipment) provides guidance on the approval process for the use of alternative products in the built environment. The code section identifies the building official as the evaluator and decision-maker. This is similar to a referee determining a player’s compliance with the rules.

The code section 104.11 indicates that the alternative material, design, and methods of construction shall be approved where the alternative complies with the intent of the code. The supporting data shall consist of valid research reports, and, in the absence of recognized standards, the building official shall approve the testing procedures. This is somewhat similar to asking the referee to write the rules during the game and expecting all referees to independently write and interpret the rules similarly for every game.

In the absence of publicly developed and majority-approved provisions, the building official is tasked with ensuring that the data provided is appropriate and adequately proves the alternative product meets code intent to protect public safety, no matter the product type or complexity. This contrasts with the robust code development process in which committees with balanced representation publicly develop and deliberate on provisions in order to protect public safety. The question arises whether the 104.11 requirement implies that a process should be used in the development of test and evaluation requirements for alternative products that is similar to the development of code and standard provisions: public debate, resolution of negative opinions, and a majority approval of the requirements. Requiring a similar code development process for alternative products makes sense.

Can the public and manufacturers afford the time and expense of a code-like evaluation process for alternative materials? Is the alternative product to be approved next time the same and are the building code requirements the same as they were the last time? Can the public and manufacturers expect the same rules from different referees every time? Some observers seem to believe that building officials and registered design professionals have plenty of time to consider the complexities of alternative products and design methods. However, we know that building officials and design professionals are already substantially tasked with the building systems that rely on code-recognized materials and methods.

Is there a solution that balances providing innovative and cost-effective alternative building product solutions to the building industry in a timely manner with providing a thorough product assessment that ensures consistency and public safety? Accredited building product certification companies, or evaluation service companies, that use publicly developed and majority-approved acceptance or evaluation criteria and publish an evaluation report with a product’s description, along with its design and installation requirements and limitations, provide such a solution. These evaluation service companies are a third-party resource that assist building officials in determining whether an alternative product meets code intent and should be approved for use in their jurisdiction.

One of a number of evaluation service companies is the ICC Evaluation Service. ICC-ES has been performing structural product evaluations for many years and is ANSI accredited to ISO/IEC 17065 (Conformity Assessment – Requirements for bodies certifying products, processes, and services) to provide building-code product certifications (ICC-ES). However, accreditation by itself mainly verifies that a certain process is implemented to ensure consistency and confidentiality. ICC-ES is one evaluation service that also has a public acceptance criteria process. This process includes an evaluation committee composed of building enforcement officials. The officials on the committee evaluate the proposed criteria, listen to expert and industry input, and only approve the criteria by a majority vote if products evaluated to those criteria will meet code intent. This is similar to the codes and standards development process — a transparent public process and a majority approval of requirements for many project types and conditions and not just an opinion of one or a couple of individuals.

The alternative building product review process for ICC-ES is similar and has the following important components:

  • PUBLISHED CRITERIA: The accredited product evaluation service develops product acceptance criteria, with manufacturer and public input, which are publicly debated, revised and ultimately approved by a majority vote of a committee of building enforcement officials.
  • INDEPENDENT TESTING: The manufacturer contracts with an accredited independent third-party test laboratory to either perform or witness the product testing in accordance with the criteria.
  • THIRD-PARTY REVIEW: Registered design professionals with the accredited product evaluation service evaluate the testing and analyses performed and sealed by registered design professionals with the manufacturers or their representatives.
  • PUBLISHED RESULTS: The accredited product evaluation service publishes the evaluation report to their website. The report typically contains the product description, along with design and installation requirements and limitations.
  • CONTINUOUS COMPLIANCE: The manufacturer’s quality system is inspected at least annually by the accredited product evaluation service or an accredited third-party inspection agency to ensure that the product currently being manufactured is the same as that which was evaluated.

While the term “product evaluation” is sometimes used, so are “product certification” and “product conformity assessment.” ISO/IEC Guide 2:2004 defines “conformity assessment” as “Any activity concerned with determining directly or indirectly that relevant requirements are fulfilled.” Some “product certification” companies also provide “product listing” services for when testing and evaluation requirements for the product are already in code-referenced consensus standards, making the development of acceptance criteria unnecessary, thus simplifying the process.

A couple of previous Simpson Strong-Tie SE Blog posts on evaluation or code reports that you may find informative discuss steps to obtain an evaluation or code report and provide a checklist to determine adequacy of a report.

A mechanism is available to the building industry to safely provide innovative and cost-effective alternative building products in a timely manner. It implements a public and majority-approved alternative product acceptance criteria process. The process parallels the codes and standards development process and provides information that helps meet the “approved sources” requirement of building code section 104.11. This solution involves the building official referencing building product evaluation service reports based on acceptance criteria. It is a process that uses selected “referees” to write a set of majority-approved rules for the “game.” This robust evaluation process fosters consistency and helps ensure that an alternative product meets code intent, thus keeping construction costs reasonable and better protecting the public.

The article Construction Referees: Evaluation Processes for Alternative Building Products appeared first in Simpson Strong-Tie’s Structural Report newsletter. To sign up to receive Structural Report in your inbox, go to strongtie.com/subscribe.

NASCC 2018: Debuting Our Newest Yield Link Connection

This year the NASCC (North American Steel Construction Conference) will be in Baltimore, Maryland. The conference is the annual educational and networking event for the structural steel industry, which attracts attendees and exhibitors from all over the world. With more than 130 sessions this year, the conference will provide attendees the opportunity to learn the latest in research, design, technology and best practice in the steel industry.

Designers will hear updates on current specification, research and existing projects. With the construction industry facing labor shortage in both design and construction, this conference affords designers the chance to discover tools than can help improve productivity.

Builders can participate in discussions on best practice and learn from case studies. More than 240 exhibitors will showcase state-of-the-art equipment in the 70,000-square-foot exhibit space.

Simpson Strong-Tie (Booth #204) will debut the expansion of the successful all-bolted Yield-Link® connection. Stop by to see the latest in moment frame design, and cold-formed steel connectors such as the new steel header hanger and drift clips.

Drive a New Path: Resisting Uplift with Structural Fasteners

Structural screws are designed and tested to do hard work, but that doesn’t make them hard to use. In this post, Simpson Strong-Tie structural engineer Bryan Wert explains how the load-rated strength, versatility and easy installation of the code-listed Strong-Drive® SDWC Truss screw and SDWF Floor-to-Floor screw make it a cinch to create a continuous load path to resist wind uplift. Learn more during our May 2 webinar.

Winter’s finally shedding her blanket and unveiling springtime in Texas. There’s now a short window of picture-perfect weather where my purchases at Home Depot are no longer foam hose bib covers to protect outdoor faucets from freezing temperature, but aren’t quite yet tiki torches and floats for the pool for hot and humid summer days. I find myself in the garden center looking at the freshly delivered trees, shrubs and flowers, along with just about every other adult in my city. This year, my wife’s decided we need to surround our outdoor living space with hanging planters displaying perky red, purple, yellow and blue flowers.

Upon returning home to get started on the honey-do list I find that instead of simple screw-in hooks for the hanging planters, we’ve instead purchased extension arms with S-hook do-hickeys and — lucky me — they come with their own installation screws. I try installing the screws through the predrilled bracket into the wood cedar beam at my patio’s perimeter and the screw turns maybe two revolutions before refusing to embed further. Now I have to find a drill bit to match the undefined screws. At best, this will double my time for installation and at worst cost me a second trip to the store to replace the common Phillips-head screw as it cams out upon installation. In the end, I find myself somewhere in between — predrilling holes, then hand-driving each screw into place.

This project deepened my appreciation for the full line of Simpson Strong-Tie® structural screws with either hex-head or 6-lobe drive-heads. The Simpson screws make driving easy, thanks to their proprietary SawTooth™ point that helps them start fast with reduced torque, and, the best part, require absolutely no predrilling.

One of the most exciting product groups in the growing Strong-Drive® line is the combination of the SDWC Truss screw and the SDWF Floor-to-Floor screw with TUW take-up washer. Models within these two lines of screws create a new and innovative method of creating a continuous load path for wind uplift resistance.

The Strong-Drive SDWC screw is suited for a plethora of fully tested and load-rated connection types. These include ledger-to-rim, sole-plate-to-rim and almost all connections needed to complete a load path to resist uplift forces. The SDWC is load rated for stud-to-bottom-plate or stud-to-top-plate connections, as well as fastening trusses and rafters to top plates. The fully threaded shank engages the entire length of the fastener providing a secure connection. It’s tested in accordance with ICC-ES AC233 (screw) and AC13 (wall assembly and roof-to-wall assembly), is code listed under IAPMO-UES ER-262 and meets 2012 and 2015 IRC® and IBC® code requirements for several common framing applications.

Where the SDWC Truss screw’s capabilities end, the Strong-Drive SDWF Floor-to-Floor screw’s begin. This screw’s designed to simplify the wind uplift–restraint floor-to-floor connection while providing superior performance over the life of the structure. The unique design of the SDWF enables it to attach upper and lower walls together from the top, spanning the floor system, and requires no predrilling to provide a secure connection within the continuous uplift load path of the structure.

The innovative take-up washer (TUW) plays a key role in the long-term performance of the SDWF when installed between the screw head and the sole plate of the upper floor. The specialized threaded portion under the head of the screw ratchets up through the matching threaded tabs of the TUW as the structure settles in response to shrinkage and construction loading. The interlock between the tabs of the take-up washer and the threads under the head of the SDWF prevents the screw from sliding back under load, providing a simple yet reliable means of shrinkage compensation up to 3/4″ per story.

As I sit back on my patio with a cold drink in my hand and admire my handiwork, I dare not tell my wife about the versatile, labor-saving SDWC and SDWF screws. Revealing the existence of these innovative wind uplift–resisting continuous load path screw connections might result in a much longer honey-do list that could even include deploying Strong-Drive® fasteners to build a whole new house. But while I won’t be telling my wife about it, if you’re an engineer, builder or code official interested in learning more about how to use fastener systems for uplift restraint, check out our upcoming one-hour webinar:

Drive a new path: Resisting uplift with structural fasteners

May 2 at 11:00 a.m. PT / 2:00 p.m. ET.

By attending this webinar, you should be able to:

  • Explain how a threaded fastener system works to establish a continuous load path for uplift restraint
  • Identify threaded fastener solutions for roof-to-wall, stud-to-plate and floor-to-floor connections
  • Describe the benefits of using Strong-Drive structural fasteners compared to traditional continuous load path connection methods
  • Recall design considerations when specifying fastening systems for resisting uplift

Continuing education credits will be offered for this webinar.

  • Participants can earn 1 professional development hour (PDH) or — by passing the accompanying test — 0.1 continuing education unit (CEU).

Timber Strong Gives Engineering Students Real-World Experience

Timber Strong

Structural engineering, like every other research field, advances by educating new generations of students in the principles and practice of the discipline. Knowing that, Simpson Strong-Tie has teamed with the Binational Softwood Lumber Council and the American Wood Council to co-sponsor and coordinate the Timber Strong Design-Build Competition, an annual design contest held at the ASCE Pacific Southwest Conference in Tempe, Arizona.

Engineering students will test their civil and environmental engineering skills this spring when they compete in the annual Timber Strong Design-Build Competition. Eighteen universities will send teams of students to Tempe, Arizona, to participate at the American Society of Civil Engineers (ASCE) Pacific Southwest Conference (PSWC).

The objective of the competition, taking place April 12–14, is to give students valuable real-world engineering design experience:

“…teams will prepare a project bid complete with a preliminary design, budget estimates, structural calculations and estimated carbon footprint. They’ll be expected to incorporate sustainability features such as rainwater capture systems or solar paneling on the rooftops. Teams will assemble their structure in real time within a 15′ x 15′ area and receive additional points for the fastest construction. Each entry will undergo a stress test.”

Simpson Strong-Tie™ is co-sponsoring the competition for the third time, alongside the Binational Softwood Lumber Council and Bosch Power Tools. This year, Simpson will donate up to $200 in materials for each team taking part in the competition, BSLC is providing$200 travel stipends and Bosch will supply cordless drills, screw guns and bits. The American Wood Council is coordinating the event.

Real-World Applications

Nearly 1500 civil and engineering students from universities in California, Nevada, Arizona and Hawaii compete at PSWC each year. Not only do those students gain hands-on experience, but they also help provide new insight into the real-world problems they will be facing as practicing professionals.

Tempe’s affordability and predictable climate are making it a popular destination for technology companies and startups. According to the East Valley Tribune, “Tempe had the highest tech rent growth of any submarket in the US over the past two years, at just under 30 percent.”

Job growth means a greater demand for housing and nonresidential building. That’s where the Timber Strong competition can play a role. Timber Strong’s sponsors are interested in using wood to develop sustainable housing for Tempe’s booming population. The competition’s white paper explains:

“While other natural resources are rapidly depleting due to this [housing] demand, wood is the only building material that grows naturally and is 100% renewable and outperforms other building materials in overall carbon footprint reduction.”

With greater growth, the importance of developing greater sustainability in our building and living practices only increases. That’s why wood engineering is so key to a sustainable future.

Simpson Strong-Tie is excited to support this important conference. We’ll post results from the competition on our Structural Engineering Blog.

Q&A About Fabric-Reinforced Cementitious Matrix

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

Simpson Strong-Tie engineering manager Brad Erickson, S.E., P.E., and Simpson Strong-Tie senior product manager Mark Kennedy, PMP, conducted an informative discussion of this new product solution. You can view the webinar in our Training Center and take a course to earn one hour of CEUs, PDHs and AIA LU/HSW credits. The course and webinar discuss installation steps, identify projects where FRCM would be ideal, and cite testing and industry standards associated with FRCM.

At the end of February’s webinar, we asked participants to submit further questions about this innovative product. We’ve answered some questions below and you can review all the FRCM webinar questions and answers here.

What is the cure time for overhead applications? When FRCM is applied to bridges and train tracks, how do we account for the vibrations’ effects on the cure process?

The initial set of the matrix takes approximately five hours, with the final set taking less than eight hours. For a project with potential vibration issues, it would be best to eliminate vibrations for the CSS-CM to achieve final set. If this closure would be an issue, a small field trial demo on this particular structure may be prudent to check how the vibrations affect the strength of the FRCM’s bond to the substrate.

If FRCM was used to strengthen a residential concrete foundation, could a two-part elastomeric coating be sprayed over it, and if so, how long should the FRCM be allowed to cure before being sprayed over?

Yes, an elastomeric coating could be placed on top of an FRCM installation. We would recommend waiting at least 28 days to allow the FRCM mortar to cure before applying the elastomeric coating. We would also recommend allowing the moisture content of the mortar to drop below 5% prior to applying elastomeric coating.

In practice how does one obtain the CSP profile? We find this difficult to obtain in the field.

Sandblasting, shotblasting and water-blasting could all provide a CSP 6-9 profile.

Could this be used in a soil nail wall in lieu of a shotcrete wall, or is it typically too thin? Anchoring the soil nails to the grid could be an issue, too.

FRCM should not be used as the primary structural system but could be used in combination with a reinforced concrete wall as a retrofit.

How many hours of training will the technician need to spray the matrix safely and properly, and what’s the cost associated with this training?

Training is provided at no cost and typically lasts about half a day.

What are the thickness limitations when using FRCM?

FRCM applications could be as thin as 1/2″ for one-layer grid installations or as thick as 3″ from the face of the substrate for up to four layers of grid. These dimensions do not include rock pockets or other voids in the substrate that can also be repaired with CSS-CM.

In view of the no-cover restrictions, how does this product meet fire-protection requirements?

We have a four-hour UL rating on our FRCM system. The matrix will also help the fire cover requirements of the rebar in the element being strengthened.

If surface preparation exposes existing reinforcement materials, or substantially reduces concrete cover for existing reinforcements, how do you provide the required concrete cover for the existing reinforcement?

The matrix of the FRCM system replaces the cover concrete removed during surface prep.

What surface preparation is required for fire-damaged concrete prior to FRCM application?

Demo to solid concrete and remediation to damaged rebar would be required prior to FRCM application.

Can’t you just prerake surfaces between layers?

That’s not required. Additional layers of matrix can simply be sprayed onto grid installed into previous layers of matrix.

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).

Q&A About MPBZ Moment Post Base

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

This past December, Simpson Strong-Tie hosted an interactive webinar in which product manager Emmet Mielbrecht and I discussed the development, testing, evaluation and applications of our new moment-resisting MPBZ moment post base. During the one-hour webinar, we explained the testing and evaluation criteria for new product development, test procedures, installation recommendations, allowable loads and the rotational stiffness of the connection. We also included a design example. In case you missed the discussion, you can watch the on-demand webinar and earn PDH and CEU credits here.

As part of the live webinar in December, Emmet and I led a lively Q&A session with the attendees. What follows is a curated selection of those questions and answers. Click here for more answers to participant questions. 

What is the most common ultimate failure mode?

It is concrete breakout.

How is wood shrinkage addressed?

We have evaluated wood shrinkage by testing, however, it is in review with ICC-ES. Additional information shall be made available upon approval from ICC-ES.

What was the actual strength of the concrete being used in the test (not the design value)?

It was 2500 psi, +/- 10 percent.

Breakout/pryout failure seems to govern allowable loads. Are there plans to test connection with adequate reinforcement to ignore breakout failure and achieve higher allowable moment loads?

Based on the overwhelming requests for higher loads we will be testing MPBX for:

  • Higher strength concrete
  • Reinforced concrete
  • Greater edge distances

Given overlap of steel, is one direction stronger than the other and Simpson uses the weak direction for tbl?

Yes, one direction is stronger than the other and the weak direction allowable loads are listed.

Technically, the stand-off tabs and side friction will also aid in the vertical load transfer, just extremely minimal.

Correct. Our tested loads are actually higher than the screw calculations. The code requires we use the lower of the two loads, so we use the SDS screws calculated capacity only.

Why is the 4×4 stiffer than 6×6?

The stiffness in the graphs is relative to the stiffness of the post. The 6×6 post is much stiffer, so the post base is less stiff as a percentage of the 6×6 post stiffness. The actual stiffness of the MPB66Z is stiffer than the MPB44Z.

Why a F1 value for wood? And you can use the higher wood values with a proper concrete design?

The F1 values listed in the allowable load tables are the lowest of concrete and wood assembly allowable loads.

Why aren’t uplift loads for the wood connection published?

The uplift loads are limited by the lesser of the wood or concrete capacity. We lumped those together under the concrete. This will be clarified in future publications.

Relative to deflection associated with rotation at the base is that considered elastic? In other words, when the load is removed will the deflection return to zero?

Yes. Deflection associated with rotation at the base due to applied loads within allowable load range is considered elastic.

Ready to learn more about MPBZ moment post base? See the rest of the Q&A questions here and you can watch the on-demand webinar and earn PDH and CEU credits 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.

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 17.2.3.4.3 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 (17.2.3.4.3(a)(i)(ii)).

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 (17.2.3.4.3(a)(iii)).

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
• SDC D
• 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 17.2.3.4.3(a)(i)(ii) 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 17.2.3.4.3(a)(iii) — 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 strongtie.com/SET3G.

What Building Professionals Need to Know About Construction Loading

This week’s post was written by Shawn Overholtzer, ICS Business Manager
at Simpson Strong-Tie. 

Understanding construction loading is important as it relates to the acceptable practices in terms of staging and storing construction materials prior to installation. What does “construction loading” mean? This term describes materials and people that are present during the course of construction. It refers to any construction material that is stacked and/or staged on the trusses for any length of time prior to the installation of said materials. This also includes those individuals that are working or walking on the trusses during the course of construction.

One of the most important concepts to understand is that before any construction materials can be loaded on roof or floor trusses, the trusses must be adequately restrained and braced. This must be done in accordance with BCSI-B1 and BCSI-B2. Loading material on trusses prior to adequate restraint and bracing can lead to failure, collapses, injury and even death. This is especially important when structural elements such as roof or floor trusses are involved.

The Truss Plate Institute, along with the Structural Building Component Association, provides guidelines (BCSI-B4) for the amount of material that can be stacked on a roof or floor along with the proper placement and orientation of this material, and the length of time the material can be staged. Additional guidelines include the following:

  • Do not position material so that it creates excessive load over a single truss or small group of trusses, but rather, place the material so that the load can be distributed over multiple trusses
  • Material should be placed perpendicular to the trusses.
  • Furthermore, it is optimal to position the material along interior or exterior supports or bearings.

It is imperative not to overload trusses, because this can have long-term effects on their structural performance. Even after the loads from building materials have been removed, the deflection or sagging in the roof or ceiling often remains.

As a component manufacturer, you have probably heard or read all of this information before. It’s important that component manufacturers are educated in the best practices and guidelines defined within the BCSI. However, it cannot end there. These guidelines have little value if they are not correctly implemented on the jobsite.

How can you, as the component manufacturer, help promote jobsite safety and ensure that trusses retain their structural integrity? First, it’s vital that you send BCSI summary sheets with your jobsite packages. Second, use this as an opportunity to educate your customer, contractors and sub-contractors. Third, ensure that your staff is familiar with current information and facilitates preconstruction meetings with your customers. A little upfront work can save a lot of headache and cost throughout the construction process. Simpson Strong-Tie is committed to offering sound structural solutions and providing education to help people design and build safer, stronger structures.

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Good Ideas Come from Many Places — “Necessity Is the Mother of Invention”

You never know where the next great product idea or innovation is going to come from — some of our best new ideas originate with the customers who use our current products. At Simpson Strong-Tie, we welcome any inspiration that can help us serve our customers’ needs even better. With so much competition, however, and because so much research and testing are entailed in developing each new product, the criteria that an idea must meet to gain eventual acceptance are necessarily quite rigorous. In this post, Steve Rotzin, Manager of Intellectual Property and Legal Services at Simpson Strong-Tie, outlines some of these criteria for your consideration.

All of us, at one time or another, dream up a product idea of some sort. My wife was once sanding the tongue-and-groove boards of our living room ceiling and she thought of a very cool idea of gloves that had Velcro on them and users could interchange sandpaper of various grit on any finger of the glove. If you’ve ever sanded anything, this actually made a lot of sense especially for complex shapes and tough to reach spots. I researched it and found out that someone had already thought of it and “patented it.”

We are no different here at Simpson Strong-Tie Company. We are constantly thinking of ways to make the very best products, incorporating innovative features to make the installation as easy and cost effective as possible. We also strive to exceed the performance requirements of the application in order to help build the strongest, safest possible structures. While these ideas are something we think about day in and day out, we also know you think about solutions as well. It’s you who encounter circumstances where our parts may not work as needed or fail to meet a specific need or application. These are the times we receive ideas from customers hoping we might adopt or develop an idea to meet their needs.

Annually, we receive a number of ideas from outside the company, even though they’re not something we actively solicit. The truth is that product ideas from consumers, especially ideas that come from consumers who work in the construction industry, are often relevant and timely. To make it easier for you to share feedback and ideas, we’ve set up a process whereby anyone who has an idea they’d like to share, can submit it to us for evaluation.

Here are some tips to help your product idea receive our fullest consideration, :

  1. Do Your Research — Has someone invented this before? You might be surprised by how many ideas have come and gone. Ideas that we think are novel and have never been attempted by anyone else have often been manufactured, sold and put out to pasture years before we thought of them. So do some research. Also, just because you don’t see the exact same thing doesn’t mean the elements which could be patented, or protected, in your device haven’t been claimed before in someone else’s patent.
  2. Protect Yourself — Make sure you’ve taken steps to ensure you are protected. Did someone else help you? Could someone else claim ownership? Have you filed for a provisional application with the United States Patent and Trademark Office? We cannot offer legal advice, but seeking legal advice from a patent professional is always a good idea.
  3. Cost Considerations — When we receive ideas, often those ideas overlook cost. Yes, they serve a need, but they’d probably never be manufactured or purchased because they would cost several times more than the market will bear. You can build a better mousetrap, but that doesn’t mean anyone will buy it. Be sure you’ve considered how much steel or material your product is using. Also, consider that things like “door hinges” and secondary manufacturing processes are steps that add cost and most likely will make the product too expensive to the end user. A product that significantly increases a structure’s overall volume or thickness isn’t advisable, either. Those are just a few factors you may want to consider.
  4. Approvals — Please consider what approvals your product might require. Products that arrive at Simpson Strong-Tie with ICC code reports, UL listing, IAPMO or other approvals or that are already patented receive the highest attention.
  5. How to Submit — if you’re still interested in submitting to Simpson, please visit strongtie.com/ideas. Print the documents, fill them out and return them to the name at the bottom of the form. Please be sure you’ve included pictures or drawings of your product or application.
  6. Timing — It may take some time for us to review your idea. Simpson does review most ideas, and those ideas that have all the elements discussed above usually receive the quickest response. If you have any questions, you are welcome to reach out to us.

Thank you for considering Simpson for your ideas.

 

What You Should Know About the New DGH Fire Wall Hanger Options

Does everyone do year-end performance reviews to discuss how you did on your project objectives and professional development goals? I love meeting with my team to recap all their amazing accomplishments for the past year, discussing long-term career plans and figuring out the steps we will take to implement those plans over the next six months, year, and beyond. I hate, hate, hate, hate doing all the paperwork that HR requires – but I am done with it now, so I’ll get over it.

One of our new product objectives for 2017 was to create a new fire wall hanger that could be installed before the drywall. Creating a joist hanger that can span a gap while still meeting the target loads was a challenging task. We released the DG series of fire wall hangers in July. I discussed the use of fire wall hangers in Why Fire-Rated Hangers Are Required in Type III Wood-Frame Buildings.

Before we finished developing the DG series of hangers, we had already started design and testing for skewed and offset top-flange options. As much as engineers love buildings that look like rectangular boxes, the real world isn’t always square, and framing isn’t always perpendicular.

My colleague, Randy Shackelford, did a series of blog posts about how to specify a hanger, which covered joist hangers, truss hangers and custom hangers. Among the many issues Randy discussed, an important one for engineers is that customized hangers with skews or offset flanges have load reductions. Some reductions are small, and some can be large. One thing the reductions have in common is they are determined through testing.

Like other skewed or offset top-flange hangers, modified DGH hangers have load reductions due to differences in performance when compared to the standard versions. With many of our hanger options, we provide adjustment factors, which Randy covered in his posts mentioned above. Since there are only four loads for the skewed or offset DGH hangers, we tabulated and published the allowable loads in a new flier, F-C-DGHSKEW.

I am still adjusting goals for my team for 2018. Maybe we’ll see about proposing a building-code change to require buildings to be square. Until then, Simpson Strong-Tie will keep your hanger options open.