Author: 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.

Aren’t We Done Testing Yet?

We’ve posted on how we test connectors, holdowns, and screws. Most products have an ASTM standard or Acceptance Criteria that sort of tells you what to test. Yet figuring out how to test a product can be a challenge – in other words, how do we make sure our test simulates installed conditions? Or maybe a product can be used in so many different ways that it is unreasonable to test every possible installation, so what to do?

We have been challenged with these situations over the years, but probably never as much as with our connectors for curtain-wall construction that we introduced about two years ago. In particular, testing our bypass framing connectors to resist in-plane loads (designated as F1 loads) presented testing challenges.

Aren't We Done Testing Yet?

If you’ve been following the Structural Engineering Blog for any length of time, you’ve probably noticed that we like to run a lot of tests around here. Building test setups and breaking them is one of the things we enjoy the most in R&D at Simpson Strong-Tie, but often load rating a product is not as simple as just running a test. At times the process requires significant time and effort, so much so that we start asking ourselves, Aren’t we done testing yet?
We’ve posted on how we test connectors, holdowns, and screws. Most products have an ASTM standard or Acceptance Criteria that sort of tells you what to test. Yet figuring out how to test a product can be a challenge – in other words, how do we make sure our test simulates installed conditions? Or maybe a product can be used in so many different ways that it is unreasonable to test every possible installation, so what to do?
We have been challenged with these situations over the years, but probably never as much as with our connectors for curtain-wall construction that we introduced about two years ago. In particular, testing our bypass framing connectors to resist in-plane loads (designated as F1 loads) presented testing challenges.
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Are the Load Combinations Balanced?

In April’s post about the Omega Factor, one commenter asked of the 1.2 increase allowed by ASCE 12.4.3.3, “Why do they allow a stress increase for allowable combinations? Seems unconservative for steel now that they have essentially balanced the ASD capacity with LRFD.”

To be honest, I have never spent much time analyzing which design methodology was more or less conservative. If I was designing with wood I would use ASD, and if it was with concrete I would use LRFD. Steel was strictly ASD early on in my design career, but LRFD usage grew. The question about balance made me curious. Are the load combinations balanced?

Of course, just comparing the load combinations would be meaningless. We know the LRFD combinations result in higher design forces. But those higher forces are compared to higher design strengths. So we need to normalize things.

Storm Shelters in the Wake of the Oklahoma Tornado

As we continue to learn more about the devastation in Oklahoma from the EF-5 tornado that struck the city of Moore and surrounding areas on Monday, many building professionals and homeowners are questioning the safety of their homes and other structures in tornado-prone areas. Winds of the recent storm reached speeds up to 210 miles per hour and destroyed hundreds of homes, businesses, schools and hospitals. Many structures were leveled to their foundations. The question that is posed after an event like this is – can you build a tornado-resistant home or structure?

A recent article in the Huffington Post asked that question to several design professionals, including our own resident code expert, Randy Shackelford, P.E., a Simpson Strong-Tie engineer based in McKinney, Texas. While designing a tornado-proof home is not practical or economical, properly designed storm shelters can save lives. Take a look at the Huffington Post article here.

Last year, I wrote a post about Building a Storm Shelter to ICC-500 Design Requirements, which presents the most economical solution to resisting the strongest of tornadoes. We’ve also covered this topic from various angles in the blog, from design – a post about Code-Plus Programs that provides some guidelines for building structures that are more resistant to hazards than what the code requires, Designing Light-Frame Wood Structures for Resisting Tornadoes and checking for Building Drift – to addressing specific parts of a structure, such as Preventing Roof Tiles from Becoming Wind-Borne Debris and Roof Deck Design Considerations for High Wind Events. Our Technical Bulletin about how to strengthen dwellings in tornado-prone areas provides further information.

Our thoughts and prayers continue to be with everyone affected by the Oklahoma tornado. We are thankful to report that our local sales reps and families in that area are safe. If you have additional thoughts about the tornado and storm protection, please leave me a comment.

– Paul

What are your thoughts? Visit the blog and leave a comment!

Where Did All These Kids Come From?

On the About Paul McEntee page of this blog, I told the story about hosting Take Our Daughters and Sons to Work Day, which was four years ago. My son Ryan then described my job as, “Goes and gets coffee and sits at his desk.” I don’t know what my daughter Kira would have said about my job, as she was too young to attend back then, but ever since I took her brothers she has been asking, “Daddy, when do the kids get to go to your work again?” So, of course, we just had to have this event again this year on April 30.Continue Reading

Why Won’t The Wood Fit? Understanding Lumber Size

Lumber size is often given in “nominal” measurements. This can often lead to confusion when someone is shopping for wood and wood connectors. Paul McEntee, Simpson Strong-Tie Manager of Engineering R&D, addressed lumber sizes and how our company takes them into consideration during product development and testing.

Why Won't The Wood Fit?

Your wood fastening products seem to be built for yesteryear wood sizes. 2x’s are no longer larger than 1½”. Why can’t you manufacture these products with a little closer tolerance?
I received this question from a customer a few days ago via Ask Simpson, a web page where you can submit technical questions to our Engineering Department and we respond by e-mail. We have received similar variations of this question countless times over the years, so I thought it could use some discussion.
The National Design Specification for Wood Construction (NDS) Supplement Table 1A “Nominal and Minimum Dressed Sizes of Sawn Lumber” gives the minimum dry and green dimensions for sawn lumber. This specifies a nominal 2x, for example, as being 1½” dry and 1 9/16” green. NDS Supplement Section 3.1.1 defines dry lumber being seasoned to a moisture content of 19% or less, whereas green lumber is higher than 19%.

So what size do you make the connector?
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The Omega Factor

Section 12.4.3.3 of ASCE 7-05 (or -10) deals with overstrength (Ω_o) load combinations and allows a 1.2 increase in allowable stress when using these combinations. We received a question from a customer last week asking if the 20% increase applies to Simpson Strong-Tie connectors. The simple answer is yes. When demand loads are based on amplified seismic forces, connector allowable loads may be increased by 1.2 per Section 12.4.3.3.

Since the increase may be combined with the duration of load increases permitted in the NDS, you would apply the 1.2 increase to connector allowable loads at a load duration of 1.6, which makes the overstrength factor a little less terrible.

The question got me thinking a little more about overstrength load combinations, so I wanted to discuss what they are used for. It also made me think about a sales meeting several years ago where one of our engineers was addressing a question about an application that required a design using amplified seismic forces. A salesperson asked why the forces needed to be amplified and he said, “Well, there’s this Omega subzero factor…” Never speak in Greek letters to salespeople. They call him Omega Subzero to this day.

So why does the code have amplified forces?

Is Designing with Wood Easy?

In college, I spent some of my free time either attending seminars or reading about high profile structural engineering projects. These projects tend to be noteworthy due to their massive scale or their use of innovative construction technologies (often both). Taipei 101 is 508 meters tall, and used to be the tallest building in the world. The Burj Khalifa has surpassed it as not only the tallest building in the world, but as the tallest manmade structure at 828 meters.

I never thought I would design the world’s tallest buildings, but I did think it would be cool to work on some mid-rises. I never did. My design firm didn’t do that type of work – which looking back, was a good thing for me. We worked on a lot of everything, including commercial, industrial, multi-family and mixed-used projects. The variety of projects meant designing with all the major building materials, including concrete, steel, masonry, and wood. Reviewing my project portfolio and thinking about what was really satisfying to work on, the projects that stand out most were wood-framed.

Code Reports: Uniform Application of Code Intent in a Diverse Environment

Woodworks invited me to do a presentation on Testing and Evaluation of Products for Wood-framed Construction, and I found you can’t really talk about testing without talking about the test standards and criteria used in product evaluations. Usually the goal in testing to these standards is to show compliance with the intent of the building code and have the product listed in a code report.

Why not just follow the code?

Innovative architectural and structural building products not addressed by the building code are in every building. Revisions to the building code are considered on a three-year cycle and some standards are on a five-year cycle. Sometimes it may take several cycles to address a new building product.