Paul McEntee

About Paul McEntee

A couple of years back we hosted a “Take your daughter or son to work day,” which was a great opportunity for our children to find out what their parents did. We had different activities for the kids to learn about careers and the importance of education in opening up career opportunities. People often ask me what I do for Simpson Strong-Tie and I sometimes laugh about how my son Ryan responded to a questionnaire he filled out that day:

Q.   What is your mom/dad's job?
A.   Goes and gets coffee and sits at his desk

Q.   What does your mom/dad actually do at work?
A.   Walks in the test lab and checks things

When I am not checking things in the lab or sitting at my desk drinking coffee, I manage Engineering Research and Development for Simpson Strong-Tie, focusing on new product development for connectors and lateral systems.

I graduated from the University of California at Berkeley and I am a licensed Civil and Structural Engineer in California. Prior to joining Simpson Strong-Tie, I worked for 10 years as a consulting structural engineer designing commercial, industrial, multi-family, mixed-use and retail projects. I was fortunate in those years to work at a great engineering firm that did a lot of everything. This allowed me to gain experience designing with wood, structural steel, concrete, concrete block and cold-formed steel as well as working on many seismic retrofits of historic unreinforced masonry buildings.

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.

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

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

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

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

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

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

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

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

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

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

Revisiting Stainless-Steel Nail Calculations . . . .

This week’s post was written by Bob Leichti, Manager of Engineering for Fastening Systems.

Those of you who have been following the Simpson Strong-Tie SE Blog for a while may recall our 2013 blog post on the withdrawal resistance of stainless-steel nails. There have been several developments relating to that subject since that blog was posted, and we want to help you catch up.

First, the National Design Specification for Wood Construction (NDS) was revised in 2015. In the 2015-NDS revision, a new chapter 10, Cross-Laminated Timber, was created, moving Dowel-Type Fasteners from Chapter 11 to Chapter 12. Every place in the original blog post where there is a snip of the NDS, you will find the same information in NDS-2015 Chapter 12. Did you know that you can download a free, view-only copy of the NDS from the American Wood Council at awc.org?

Second, after we published our blog post about stainless-steel nail withdrawal, a journal paper was published about withdrawal resistance of stainless-steel nails. This paper has all the nitty-gritty related to withdrawal resistance and bending yield strength for smooth-shank stainless-steel nails: Ramer, D.R. and Zelinka, S.L. (2015). “Withdrawal Strength and Bending Yield Strength of Stainless Steel Nails,” Journal of Structural Engineering, American Society of Civil Engineers, Vol. 141, no. 5, 7 pp. (DOI: 10:1061/ASCE)ST.1943-541X.0001088).

Third, the NDS has been through another revision cycle and will soon have a 2018 copyright date. The chapter on dowel-type fasteners has some significant revisions that we will discuss in a blog post when the NDS-2018 is published later this year. SPOILER ALERT: NDS-2018 has a new withdrawal function for smooth-shank stainless steel nails.

Stay tuned!

The Cold-Formed Steel Construction Catalog is HOT off the press!

The SE Blog is taking some time off for the 4th of July holiday this week. However, we’ve just released the 2017 edition of our Connectors for Cold-Formed Steel Construction catalog – order a hard copy to be mailed to your office or download a PDF copy and start using it today!

Connectors For Cold-Formed Steel Construction

The C-CF-2017 is a 308-page catalog including specifications, load tables and installation illustrations for our cold-formed steel connectors and clips, helping you easily specify and install in commercial curtain-wall, mid-rise and residential construction.


How Heat Treating Helps Concrete Anchoring Products Meet Tougher Load Demands

Joel Houck is a senior R&D engineer for Simpson Strong-Tie’s Infrastructure-Commercial-Industrial (ICI) group based out of the new West Chicago, IL location. He has spent the last 17 years with Simpson developing new mechanical anchors and adhesive anchor components, as well as developing a lot of the lab equipment required to test these products. This experience has given him extensive knowledge and insight into the concrete anchor industry, especially when it comes to the proper function and performance of anchors. Joel is a professionally licensed mechanical engineer in the state of Illinois.

There’s a saying in Chicago, “If you don’t like the weather, just wait fifteen minutes.” That’s especially true in the spring, when temperatures can easily vary by over 50° from one day to the next. As the temperature plunges into the blustery 30s one evening following a sunny high in the 80s, I throw my jacket on over my T-shirt, and I’m reminded that large swings in temperature tend to bring about changes in behavior as well. This isn’t true just with people, but with many materials as well, and it brings to mind a thermal process called heat treating. This is a process that is used on some concrete anchoring products in order to make them stronger and more durable. You may have heard of this process without fully understanding what it is or why it’s useful. In this post, I will try to scratch the surface of the topic with a very basic overview of how heat treating is used to improve the performance of concrete anchors.

According to the ASM Handbook: Heat Treating, heat treatment is a process of heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties.1 In practical terms, metals (usually steel in the case of most concrete anchors) are heat treated in order to improve their properties in some way over their base condition. When steel wire is formed into the complex shapes of anchors during the manufacturing process, the steel needs to be soft and formable; however, it is often beneficial to the performance of the final anchor product to be much harder and stronger than the base steel from which it’s formed. That’s where heat treating comes into play. By heating and cooling soft steel in a controlled manner, changes are made to the crystal structure of the steel in order to improve mechanical properties such as hardness, toughness, strength or wear resistance. Although the steel undergoes very complex microstructural changes during the heat treatment process, the end result is fairly straightforward – the once soft steel becomes harder and stronger as dictated by the heat treating process. As concrete anchors become more and more complex in order to meet the needs of building codes and designers, heat treating is becoming a more common and necessary component of high-strength anchors.

Figure 1. Steel microstructures: (a) soft steel example; (b) heat treated steel example.2

Depending on the desired results, there are many different types of heat treating processes that can be considered. The type of heat treatment and the parameters that are used can be customized for the steel type and the specific anchor application. There are several different types of heat treatments that are typically used for anchors. Two of the most common types are through hardening (also called neutral hardening) and surface hardening (also called case hardening).

Figure 2. Fasteners entering a heat treating furnace.3

Through hardening changes the mechanical properties (hardness, strength, ductility, etc.) of the steel without affecting its chemical composition. In order to alter the microstructure of the steel, it is heated in a furnace to a very high temperature, and then rapidly cooled, usually by submerging it in a liquid quench medium such as water or oil. This process will generally result in a very hard, but brittle material, so a secondary operation, called tempering, is employed after quenching. To temper steel, it is reheated to a lower temperature and then cooled in order to remove the stresses and brittleness created during the original quenching operation. Through hardening is useful where increased strength and toughness are required and surface wear isn’t a big concern, such as in our Crimp Drive® and split-drive anchors, setting tools for drop-in type anchors, high-strength all-thread-rod for adhesive anchors, and gas- or powder actuated fasteners. In order to effectively through harden an anchor, moderate levels of hardening elements must be present in the base steel, usually in the form of carbon. As the carbon content in the steel increases, so does the ability to harden it. The chemical composition of the steel along with the specific heat treating parameters will determine the level of hardness, strength and toughness of the final parts.

Surface hardening changes the hardness of the steel at the surface of the part by modifying the chemical composition of the steel at its surface only. This is done by altering the atmosphere in the heat treating furnace in order to get alloying elements, usually carbon, to diffuse into the surface of the steel. The increased carbon content increases the hardenability of the steel at the surface, but it can’t penetrate deeply into the steel, so a thin case forms around the surface of the steel with higher strength and hardness than the interior of the part. This creates parts that have high ductility throughout most of the interior, but that also have hard, wear-resistant surfaces. This type of heat treatment is useful in heavy-duty anchors where components of the anchors are sliding against each other during the setting process. It’s also useful in screw anchors, where the steel threads need to be very hard and wear resistant in order to cut into the concrete, but the ductility of the anchor must be maintained in order to avoid brittle failures in service. Just as with through hardening, there are many variations of surface hardening used in anchors, depending on the specific application.

Figure 3. Cross-section of surface hardened bar showing different hardness zones at the surface and in the interior.4

By using these two processes along with other heat treating processes, we are able to expand our ability to meet the higher demands placed on anchors in an industry that continues to evolve. As heat treating and steel chemistry continue to innovate, we will continue to use these developments to provide our customers with No-Equal concrete anchors that meet our high standard for performance and safety.

Mechanical Anchors

From complex infrastructure projects to do-it-yourself ventures, Simpson Strong-Tie offers a wide variety of anchoring products to meet virtually any need.


 

1 Lampman et al. (1997). ASM Handbook: Heat Treating. Materials Park, OH: ASM International.

2 “Microstructure of the AISI 4340 Steel.” Digital Image. Research Gate, n.d. Web. 14 June 2017 https://www.researchgate.net.

3 “Heat Treat Furnace.” Digital Image. ThomasNet Web Solutions, n.d. 14 June 2017 http://www.morganohare.com/heat-treating.html.

4 “Macrographs Showing Case Depth of Steels.” Digital Image. Science and Education Publishing Co. Ltd, n.d. 14 June 2017 http://pubs.sciepub.com.

Introduction to the Site-Built Shearwall Designer Web Application

Written by Brandon Chi, Engineering Manager, Lateral Systems at Simpson Strong-Tie.

Wood shearwalls are typically used as a lateral-force-resisting system to counter the effects of lateral loads. Wood shearwalls need to be designed for shear forces (using sheathing and nailing), overturning (using holdowns), sliding (using anchorage to concrete) and drift, to list some of the main dangers.  The Simpson Site-Built Shearwall Designer (SBSD) web app is a quick and easy tool to design a wood shearwall based on demand load, wall geometry and design parameters.

The web application provides two options for generating an engineered shearwall solution: (1) Solid Walls; and (2) Walls with Opening using the force-transfer-around opening (FTAO) method. Both options generate solutions that offer different combinations of sheathing, nailing, holdowns, end studs and number/type of shear anchors. The app can generate a PDF output for each of the possible solutions. Design files can be saved and reused for future projects.

App Overview

Design Input: 

Figure 1 shows the input screens for the “Solid Walls” and “Walls with Opening” designs with common wall parameters that are applicable to both design options. The user interface uses quick drop-down menu and input fields for the designer to select the different options and parameters. Unless otherwise noted, all the input loads are to be nominal (un-factored) design loads. The application will apply load combinations to determine the maximum demand forces for the shearwall design.

Figure 1A. Application Design Criteria Input. – Solid Wall

Figure 1B. Application Design Criteria Input. – Walls with Opening

Figure 1C. Application Design Criteria Input. – Common Wall Input Parameters

Figure 2 shows the allowable stress design (ASD) load combinations used for calculating the demand loads for the different components of the wood shearwall (i.e., holdown, compression post, sheathing and nailing design, etc.).

Figure 2. Load Combinations.

In addition to the lateral loads (wind and seismic) applied at the top of the wall and the wall’s own weight, uniform loads on top of the wall and concentrated point loads at the end posts can also be modeled. (See Figure 3.)

Figure 3. Addition Loads on the Wall.

Embedded anchor or embedded strap holdowns can be modeled by the app. (See Figure 4.) For the embedded strap option, additional input parameters are required since they will affect the allowable load of the selected strap holdown.

Figure 4. Holdown Design Options.

The Designer has the option to include additional sources of vertical displacement for drift calculation. (See Figure 5.)

Figure 5. Other Sources of Vertical Displacement Options.

Design Calculations:

For hand-calculated design when the demand forces are determined, the holdown size and shear anchorage can be selected from tabulated values. Design for the sheathing/nailing and compression post is relatively straightforward as well; however, the shearwall drift calculation may take a bit more work. This is where the SBSD app comes in handy. Below are two sections on the shearwall drift and strap force calculations and assumptions used in the SBSD application. If you are interested, please contact Simpson Strong-Tie for other design assumptions used in designing the SBSD app.

Shearwall Deflection Calculations:

Equation 1 shows the shearwall deflection equation from the 2008 Edition of Wind & Seismic Special Design Provisions for Wind and Seismic (SDPWS).

The Δa value from the third term of the equation is the total vertical elongation of the wall holdown system from the applied shear in the shearwall. The third term accounts for the additional displacement from holdown displacement. For holdown deflection, the deflection value depends on the post size used with the holdown size. When hand-calculating shearwall drift, Designers may have to perform a couple of iterations to come to the final post and holdown size. The SBSD app accounts for the holdown displacement and the post size used for overturning force calculation.

For shearwall-with-opening deflection calculation, EQ-2 is used in the SBSD app.

The solid wall, ∆solid wall, term is calculated using EQ-1 above. For the window strip and wall pier deflection terms, the height “h” used in EQ-1 is taken as the height of the window opening. ∆a is the deflection from nail slip in the shearwall. For more information regarding shearwall deflection with opening, please refer to Example 1 in Volume 2 of the 2015 IBC SEAOC Structural/Seismic Design Manual.

Strap Force Calculations:

For the Wall with Opening design option, there are several methods (Drag Strut, Cantilever Beam, SEAOC/Tompson, Diekmann) to calculate the force transfer around the opening. In the SBSD app, the Diekmann technique is used to calculate the pier forces in the shearwall and the strap forces around the opening. When calculating the strap forces, the SBSD app assumes they are the same at the top and bottom of the opening. In addition, contribution of the gravity load only affects the overturning forces in the holdown and post design but not the wall pier forces or strap forces.

Design Output:

Once all design parameters are entered and calculated, a list of possible solutions (where available) will be shown. (See Figure 6.) Common parameters such as sheathing material and type, wood species, minimum lumber grade, etc., are shown first, followed by other design parameters. The user can filter the solutions by seismic drift or wind drift.

Figure 6. Onscreen Output.

The Designer can select the PDF button next to the desired solution to see a PDF design file on a separate screen. (See Figure 7.)  The PDF design file contains the detailed design criteria input by the Designer, calculated demand loads, shearwall material summary, and a design summary for holdown, sheathing, and compression post design. A detail summary for shearwall deflection is also shown, with each term of the shearwall deflection equation (EQ-1) separated. Shear anchorage and design assumption notes follow the design summary section. This PDF file can be saved and printed by the Designer.

Figure 7. Detailed PDF Output.

I hope you find the SBSD web app helpful for your day-to-day wood shearwall design needs. If you have any questions or comments, please leave them in the comments section below.

What Makes a Good Training Facility?

This blog post was written by Charlie Roesset, Director of Training for Simpson Strong-Tie.

When it comes to training, there are many well-researched principles about what makes an environment conducive to improved adult learning.

While we try to hold all training events in facilities that meet most of these principles, (even when traveling to our customers or users means we have to conduct events in hotel meeting rooms) we prefer to host you at our own locations.

To this end, we invest a tremendous amount of time and resources to build and offer dedicated training facilities across the country. These facilities meet all the basic requirements for improved adult learning, but much more as well.

By having our own dedicated training facilities, we can provide learners with a much richer experience and contextually relevant displays.

These displays include partially deconstructed wall segments, foundations and roof systems that give learners a bigger picture of the applications being studied.

Many displays allow for hands-on installations and exercises that allow for improved comprehension of the product use and limitations. Even for the engineering community, who typically are limited to images from a catalog, the hands-on activities add great value. It’s always interesting to see the reaction that engineers have to actually seeing a system approach and having an opportunity to participate in learning that goes way beyond sitting and listening to a lecture.

Sometimes learners just need to see, feel or hold something in order to really understand a concept or product application. We make every effort to bring legitimate educational content to our workshops, supported by products that we hope will furnish solutions to your needs.

Many of our facilities include a plant tour and/or testing-facility tour as well. While these components don’t always align directly with the learning objectives, they do offer a chance for our guests to raise their energy levels and get a better understanding of that scale, capabilities, and commitment to quality that we bring to bear in our endeavor to help people build safer structures.

Additionally, we offer our facilities to customers, associations and industry organizations to use for their own meetings and training events. If you haven’t been to one of our workshops or visited one of our facilities, I highly encourage you to join the 35,000 plus who have over the last four years. You can find a complete list of workshops on our training home page. I expect that you’ll find it an educational and highly engaging experience that helps you build safer structures as well.

Decrypting Cold-Formed Steel Connection Design

As published in STRUCTURE magazine, September 2016. Written by Randy Daudet, P.E., S.E., Product Manager at Simpson Strong-Tie.  Re-posted with permission. 

One of the world’s greatest unsolved mysteries of our time lies in a courtyard outside of the Central Intelligence Agency (CIA) headquarters in Langley, Virginia. It’s a sculpture called Kryptos, and although it’s been partially solved, it contains an inscription that has puzzled the most renowned cryptanalysts since being erected in 1990. Meanwhile, in another part of the DC Beltway about 15 miles to the southeast, another great mystery is being deciphered at the American and Iron Institute (AISI) headquarters. The mystery, structural behavior of cold-formed steel (CFS) clip angles, has puzzled engineers since the great George Winter helped AISI publish its first Specification in 1946. In particular, engineers have struggled with how thin-plate buckling behavior influences CFS clip angle strength under shear and compression loads. Additionally, there has been considerable debate within the AISI Specification Committee concerning anchor pull-over strength of CFS clip angles subject to tension.

cfs-clip-attachment

The primary problem has been the lack of test data to explain clip angle structural behavior. Even with modern Finite Element Analysis (FEA) tools, without test data to help establish initial deformations and boundary conditions, FEA models have proven inaccurate. Fortunately, joint funding provided by AISI, the Steel Framing Industry Association (SFIA), and the Steel Stud Manufactures Association (SSMA) has provided the much-needed testing that has culminated in AISI Research Report RP15-2, Load Bearing Clip Angle Design, that summarizes phase one of a multi-year research study. The report summarizes the structural behavior and preliminary design provisions for CFS load bearing clip angles and is based on testing that was carried out in 2014 and 2015 under the direction of Cheng Yu, Ph.D. at the University of North Texas. Yu’s team performed 33 tests for shear, 36 tests for compression, and 38 tests for pull-over due to tension. Clip angles ranged in thickness from 33 mils (20 ga.) to 97 mils (12 ga.), with leg dimensions that are common to the CFS framing industry. All of the test set-ups were designed so that clip angle failure would preclude fastener failure.

For shear, it was found that clips with smaller aspect ratios (L/B < 0.8) failed due to local buckling, while clips with larger aspect ratios failed due to lateral-torsional buckling. Shear test results were compared to the AISC Design Manual for coped beam flanges, but no correlation was found. Instead, a solution based on the Direct Strength Method (DSM) was employed that utilized FEA to develop a buckling coefficient for the standard critical elastic plate-buckling equation. Simplified methods were also developed to limit shear deformations to 1/8 inch. For compression, it was found that flexural buckling was the primary failure mode. Test results were compared to the gusset plate design provisions of AISI S214, North American Standard for Cold-Formed Steel Framing – Truss Design, and the axial compression member design provisions and web crippling design provisions of AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, but no good agreement was found. Therefore, an alternate solution was developed that utilized column theory in conjunction with a Whitmore Section approach that yielded good agreement with test results. It was further found that using a buckling coefficient of 0.9 in the critical elastic buckling stress equation will produce conservative results. Finally, for pull-over due to tension, it was found that clip angle specimens exhibited significant deformation before pulling over the fastener heads (essentially the clip turns into a strap before pull-over occurs). However, regardless of this behavior, tested pull-over strength results were essentially half of AISI S100 pull-over equation E4.4.2-1.

Thanks to AISI Research Report RP15-2, there is a clearer understanding of the CFS clip angle structural behavior mysteries that have puzzled engineers for many years. However, just as the CIA’s Kryptos remains only partially solved, some aspects of clip angle behavior remain a mystery. For instance, how are the test results influenced by the fastener pattern? All of the test data to date has used a single line of symmetrically placed screws. This is something that does not occur for many practical CFS framing situations and will need additional research. Another glaring research hole is the load versus deflection behavior of clip angles under tension. As briefly mentioned above, the existing pull-over testing has demonstrated that excessive deflections can be expected before pull-over actually occurs. Obviously, most practical situations will dictate a deflection limit of something like 1/8 inch or 1/4 inch, but today we don’t have the test data to develop a solution. Fortunately, AISI in conjunction with its CFS industry partners continues to fund research on CFS clip angle behavior that will answer these questions, and possibly many more.

Use Strong-Wall® Shearwall Selector to Design Shearwalls

This blog post was written by Travis Anderson.

Strong-Wall Shearwall Selector-Homepage

In time for spring and summer 2017 construction projects, Simpson Strong-Tie has launched the newest version of the Strong-Wall Shearwall Selector for use with engineered design. The latest release is an easy-to-use Web-based application (that’s right, no software to download) that has been updated to comply with the 2015 IBC and now provides solutions for all three Strong-Wall Shearwall types: the Steel Strong-Wall® shearwall (SSW), the Strong-Wall wood shearwall (WSW) and the wood Strong-wall shearwall (SW). If you are familiar with the Strong-Wall Shearwall Selector, you can begin using the web application immediately. For those of you who would like to know more about the web app, please read on.

The Strong-Wall Shearwall Selector was created to help the Designer select the appropriate shearwall solution for a given application in accordance with the latest building code requirements. By performing a technical analysis, the web app provides actual drift and uplift values for a wind or seismic design shear load.

The Strong-Wall analysis also considers simultaneous, vertically applied load. In cases of multiple walls in a line, the program performs a rigidity analysis and determines the actual distributed shear to each wall. When walls are stacked in a two-story configuration, the program evaluates cumulative overturning effects to ensure that the wall, anchor bolt and anchorage to the foundation are not overstressed.

The web app provides two modes for generating an engineered solution: Optimized In-Plane Shear or Manual In-Plane Shear. The Optimized mode lists several possible solutions for the selected criteria in the order of cost. The Manual mode evaluates any number or combination of walls for adequacy based on the selected criteria. The Designer has the option to generate an Anchorage Solution based on foundation type. Once a solution has been selected, the web app will generate a pdf output. Files can be saved and reused for future designs.

Input Variables Within the Two Solution Modes:

Job Name: Enables the Designer to provide a specific job name for a project.

Wall Name: Enables the Designer to provide a name for each wall line in a project.

Wall Type (Manual Only): Solutions are provided for the selected Strong-Wall panel type: SSW, WSW, SW

Application: Defines the proposed application (use) of the wall. The choices are for walls in a garage front, a standard wall on concrete, on a first-story wood-floor system, in a second-floor non-stacked application, in a two-story stacked application, or in a balloon-framed application. For the Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW), garage front may be chosen with or without the portal kit. Higher shear capacities are available when the portal kit is used.

Cold-Formed Steel Construction (CFS): This option appears for “Garage Front,” “Standard Wall on Concrete,” “First-Story, Raised-Floor System” and “Two-Story Stacked” applications. If the check box is enabled, the program will provide the proper Steel Strong-Wall model for use in CFS construction.

1st Story Wall on Wood Floor (SW – Wood Strong-Wall Shearwall only): This check box only appears if a Two-Story Stacked application has been selected. If enabled, the program will then assume the lower story wall, in a stacked application, is installed on a wood floor.

Strong-Wall Shearwall Selector-Input Variables

Design Criteria:

The design criteria may now be selected. Drop-down menus provide options for Applicable Building Code, load type, concrete strength, wall height, wall geometry and floor depth (if applicable). Entry fields may be used to indicate shear- and axial-loading information. The following applies once the appropriate design criteria have been input: If Optimized In-Plane Shear has been selected, the possible solutions are displayed in the Strong-Wall Panel Solutions list. If Manual In-Plane Shear has been selected, a list of available walls will be displayed in the Strong-Wall Panel Solutions list, any of which may then be selected and added to the desired Solution.

Strong-Wall Shearwall Selector-Design Criteria

Code: Wall solutions are provided in accordance with the requirements of the 2015 and 2012 International Building Code (IBC). Code reports may be found here.

Load Type: This criterion defines whether the input shear load is due to wind or seismic forces. The Designer must input the controlling load. The appropriate seismic “R” values are provided for the selected code.

Concrete Strength: Concrete strength may be selected based on specific project conditions. Default concrete strengths of 2500 psi, 3000 psi, 3500 psi, 4000 psi and 4500 psi are provided in the drop-down menu. Note that for shearwall selection purposes, concrete strengths are only applicable to Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW). In some cases, lower anchorage forces may be obtained with a higher concrete strength. The concrete strength is also used for determining the anchorage tension capacity.

Wall Height: Select the nominal wall height. Actual wall heights are shown under the “H” column of the Solution(s).

Shear Load: Input the total Allowable Stress Design (ASD) design (demand) shear load along the wall line. Include all appropriate load factors on the shear load prior to input for the load combination under consideration. For Two-Story Stacked applications, input the story shear at each level and the program will evaluate the first-story walls for the total shear.

Floor-Joist Depth: This option appears only with first-story raised-floor systems and two-story

stacked applications. Floor-joist depth affects the capacity of Steel Strong-Wall panels installed on wood floors. Floor-joist depth is also considered in the cumulative overturning evaluation of two-story stacked wood or steel walls.

Header Thickness: This option appears only when “Garage Front” applications and wall heights of 7′ or 8′ with a header on top are selected. This option is used to select the proper Wood Strong-Wall panel model (thickness) based on the nominal header thickness of 4″ or 6″.

Header Type: This option only appears when “Header Thickness” of 4″ is selected. It then provides an option to select a solid or double-ply header. Values for the wood Strong-Wall panels will slightly decrease if the double-ply header option is selected. Steel Strong-Wall panels with multi-ply headers are limited to wind designs and SDC A-C.  .

Maximum Number of Wall Segments per Wall Line (Optimized mode only): Here the maximum number of available wall segments along a particular wall line is specified. The program enables the Designer to select a maximum of four wall segments per wall line (3 segments maximum for garage fronts.) For more wall segments per wall line, use the Manual mode.

Fill Each Segment (Optimized mode only): If this checkbox is disabled, then the minimum number of Strong-Wall shearwalls that can serve as solutions is provided up to the “Max # of Wall Segments” previously specified. If this checkbox is enabled, then the “Max # of Wall Segments” will always be used and filled with Strong-Wall shearwalls.

Segment Number, Maximum Width, Axial (lb.) (Optimized mode only): For each wall segment along a wall line, the maximum desired width of that segment and the axial load on that particular segment may be specified. The axial load is the total vertical upward or downward load assumed to act on the entire panel width. Include all appropriate load factors on the axial load prior to input for the load combination under consideration. A positive axial load reduces the actual uplift of the panel, while a negative axial load increases the actual uplift of the panel. The combined effect of the vertical axial load and overturning force is considered in the Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW) solutions. The combined effect of the vertical axial load and overturning on the wood Strong-Wall (SW) shall be evaluated by the Designer so as not to exceed the “C4” and “T1” allowable vertical loads. Download an excerpt from our catalog for more information.

Axial Load 1st Story (Manual mode only): See discussion above on axial load. The axial load selected is initially applied on all Available Wall solutions. As walls are selected using the “Add” button, the axial load remains constant. If it is desired that each wall have a different axial load, then input the corresponding axial load value for the first wall and click on “Add Solution” to send it to the Selected Solution. Then enter the new axial load value for the next wall and continue this process until all the product selections are complete.

Maximum Wall Segment Width: This optional input limits the Available Strong-Wall Panels to the maximum width specified.

Available Wall(s) (Manual mode only): Based on the input Design Criteria, all Available Strong-Wall Panels and their allowable loads are listed as an option for selection. The Available Strong-Wall list is independent of the input shear load and instead represents a list whereby any quantity or combination of walls can be selected to resist the shear load.

Solution(s) and Output :

 Possible Solution(s) (Optimized mode only): Up to four possible solutions may be displayed and are designated as Sol # (solution number) in the order of relative cost (lowest to highest material cost).

Selected Solution (Manual mode only):

Add Another Solution: Click on the “Add” button to select wall from Available Wall(s) list, which enters it into the Selected Solution list. You may also double-click on an Available Wall to add it to the Selected Solution.

Clear: Click on the “Clear Selected Solutions” button to entirely remove all previously selected walls in the Selected Solution.

Generate PDF: This button creates a .pdf summary of the wall solution. Under Optimized mode, the output solution is created for the Sol# (solution number) that is highlighted. Under Manual mode, the Output is created for all walls shown in the selected solution list.

Design Anchorage: This option appears at the bottom of the page. If desired, enable the check box next to “Design Anchorage” and select Foundation Type. Anchorage design solutions will then be included in the PDF output.

Notes for Designer: Special notes related to the input variables are displayed in this window during the input process. When the Manual In-Plane Shear tab is selected, the Notes for Designer will indicate whether the Selected Solution is adequate to resist the applied design loads.

Strong-Wall Shearwall Selector-SolutionsStrong-Wall Shearwall Selector-Solution Output

Anchorage Solutions and Output:

 The Designer will have the option to generate an Anchorage Solution appended to the Strong-Wall shearwall solution. If desired, Select Foundation Type, then enable the check box next to Design Anchorage, and the .pdf file will be generated with the anchorage solution on subsequent pages. The designer can choose anchorage solutions based on foundation type for all shearwalls. The two foundation types are slab-on-grade and stemwall and are selected from a drop-down menu. Within each foundation type, the Designer can choose a specific footing type as follows:

Slab-on-Grade Footing Types: Garage curb, slab edge, brick ledge and interior.

Stemwall Footing Types: Garage front and perimeter.

Anchorage solutions are provided based on the shearwall solution(s) selected and the following design criteria: application, load type, actual uplift and concrete strength.

Anchor Bolt: Two anchor bolt solutions are available for the wood Strong-Wall®. They are the PAB7 and the SSTB, both of which are ASTM F1554 Gr. 36 material. The Steel Strong-Wall® uses a single anchor type, SSWAB, which may be either ASTM F1554 Gr. 36 or ASTM A449 (high-strength) material depending on the actual uplift. The Strong-Wall wood shearwall uses a single anchor type, WSW-AB, which may be either ASTM F1554 Gr. 36 or ASTM A449 (high-strength) material depending on the actual anchor tension.

Concrete Service Condition: This criterion refers to whether the concrete is determined to be cracked or uncracked based on analysis at service loads. See ACI 318 for the different reduction factors associated with cracked and uncracked concrete.

Strong-Wall Shearwall Selector-Anchorage Strong-Wall Shearwall Selector-Anchorage Output

The anchorage design .pdf output summarizes all applicable design details including the footing type, minimum footing dimensions, anchor bolt and shear anchorage. The Designer is responsible for foundation design (size and reinforcement) to resist overturning, soil pressure, etc.

Product Information:  Select for more product and application information.

Upload a Saved File: Designer can upload any previously used solution.

Report Applications Issues or Provide Feedback: If you are experiencing issues with the application or simply would like to provide feedback, please use this link. Simpson Strong-Tie values your feedback.

Strong-Wall Shearwall Selector-Info Save Issue

Get started on your next design project with the Strong-Wall® Shearwall Selector web application!

New Moment-Resisting Post Base

Jhakak Vasavada

Jhalak Vasavada is currently a Research & Development Engineer for Simpson Strong-Tie. She has a bachelor’s degree in civil engineering from Maharaja Sayajirao (M.S.) University of Baroda, Gujarat, India, and a master’s degree in structural engineering from Illinois Institute of Technology, Chicago, IL. After graduation, she worked for an environmental consulting firm called TriHydro Corporation and as a structural engineer with Sargent & Lundy, LLC, based in Chicago, IL. She worked on the design of power plant structures such as chimney foundations, boiler building and turbine building steel design and design of flue gas ductwork. She is a registered Professional Engineer in the State of Michigan.

At Simpson Strong-Tie, we strive to make an engineer’s life easier by developing products that help with design efficiency. Our products are designed and tested to the highest standards, and that gives structural engineers the confidence that they’re using the best product for their application.

Installed MPBZ

Figure 1: Installed MPBZ

Having worked in the design industry for almost a decade, I can attest that having a catalog where you can select a product that solves an engineer’s design dilemma can be a huge time- and money-saving tool. Design engineers are always trying to create efficient designs, although cost and schedule are always constraints. Moment connections can be very efficient — provided they are designed and detailed correctly. With that in mind, we developed a moment post base connector that can resist moment in addition to download, uplift and lateral loads. In this post, I would like to talk about moment-resisting/fixed connections for post bases and also talk about the product design process.

Figure 2. MPB44Z Graphic

Figure 2. MPB44Z Graphic

Lateral forces from wind and seismic loads on a structure are typically resisted by a lateral-force-resisting system. There are three main systems used for ordinary rectangular structures: (a) braced frames, (b) moment frames and (c) shearwalls. Moment frames resist lateral forces through bending in the frame members. Moment frames allow for open frames by eliminating the need for vertical bracing or knee bracing. Moment resistance or fixity at the column base is achieved by providing translational and rotational resistance. The new patent-pending Simpson Strong-Tie® MPBZ moment post base is specifically designed to provide moment resistance for columns and posts. An innovative overlapping sleeve design encapsulates the post, helping to resist rotation at its base.

The allowable loads we publish have what I call “triple backup.” This backup consists of Finite Element Analysis (FEA), code-compliant calculations and test data. Here are descriptions of what I mean by that.

Finite Element Analysis Confirmation

Once a preliminary design for the product is developed, FEA is performed to confirm that the product behaves as we expect it to in different load conditions. Several iterations are run to come up with the most efficient design.

Figure 3. FEA Output of Preliminary MPB Conceptual Design

Figure 3. FEA Output of Preliminary MPB Conceptual Design

Code-Compliance Calculations

Load calculations are prepared in accordance with the latest industry standards. The connector limit states are calculated for the wood-post-to-MPBZ connection and for MPBZ anchorage in concrete. Steel tensile strength is determined in accordance with ICC-ES AC398 and AISI S100-07. Wood connection strength is determined in accordance with ICC-ES AC398 and AC13. Fastener design is analyzed as per NDS. SDS screw values are analyzed using known allowable values per code report ESR-2236. The available moment capacity of the post base fastened to the wood member is calculated in accordance with the applicable bearing capacity of the post and lateral design strength of the fasteners per the NDS or ESR values. Concrete anchorage pull-out strength is determined in accordance with AC398.

Test Data Verification

The moment post base is tested for anchorage in both cracked and uncracked concrete in accordance with ICC-ES AC398.

Figure 4. Uplift Test Setup

Figure 4. Uplift Test Setup

The moment post base assembly is tested for connection strength in accordance with ICC-ES AC13.

Figure 5: Moment (induced by lateral load application) Test Set Up

Figure 5: Moment (induced by lateral load application) Test Set Up

The assembly (post and MPBZ) is tested for various loading conditions: download, uplift and lateral load in both orthographic directions and moment. Applicable factor(s) of safety are applied, and the controlling load for each load condition is published in the Simpson Strong-Tie Wood Construction Connectors Catalog.

Now let’s take a look at a sign post base design example to see how the MPBZ data can be used.

Design Example:

Figure 6: Sign Post Base Design Example

Figure 6: Sign Post Base Design Example

The MPB44Z is used to support a 9ʹ-tall 4×4 post with a 2ʹ x 2ʹ sign mounted at the top. The wind load acting on the surface of the sign is determined to be 100 lb. The MPB44Z is installed into concrete that is assumed to be cracked.

  • The design lateral load due to wind at the MPB44Z is 100 lb.
  • The design moment due to wind at the MPB44Z is (100 lb.) x (8 ft.) = 800 ft.-lb.
  • The Allowable Loads for the MPB44Z are:
    • Lateral (F1) = 1,280 lb.
    • Moment (M) = 985 ft.-lb.
  • Simultaneous Load Check:
    • 800/985 + 100/1,280 = 0.89. This is less than 1.0 and is therefore acceptable.

mpbz-deflection-evaultion

We are very excited about our new MPBZ! We hope that this product will get you excited about your next open-structure design. Let us know your thoughts by providing comments here.