Welcome to the Structural Engineering Blog

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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 →

Storm Shelters in the Wake of the Oklahoma Tornado

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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

Where Did All These Kids Come From?

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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.

While everyone was arriving, we took a little time to have family portraits taken:

Paul with the little McEntees: Kevin, Ryan and Kira

Paul with the little McEntees: Kevin, Kira, and Ryan

After that it was off to our training center where our CEO Karen Colonias introduced herself to the children and talked to them about careers. Our President Terry Kingsfather told them about what we did at Simpson Strong-Tie and followed that up with a great hands-on demonstration to show how weak connections using only nails could be:

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Remember to Enter To Win by Tuesday, 4/30

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Remember to enter to win the Structural Engineering Blog one-year anniversary contest by Tuesday, April 30! April 2013 marks the one-year anniversary of the Simpson Strong-Tie® Structural Engineering Blog. To celebrate, we are holding a contest for our blog readers.

Everyone who posts a comment or subscribes to receive email notifications to the blog (new subscribers only) from now until April 30, 2013 will be entered to win one of five Prize Packs. The Prize Pack consists of:

The contest is open to U.S. and Canadian residents (except Quebec) only. One entry per person. Five entries will be randomly selected to receive a Prize Pack. You can read the Official Rules here.

Good luck!

Why Won’t The Wood Fit?

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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%.

NDS Table 1A

NDS Table 1A

NDS 3.1.1

NDS 3.1.1

So what size do you make the connector?

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The Omega Factor

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Section 12.4.3.3 of ASCE 7-05 (or -10) deals with overstrength (Ωo) 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.

Image credit: ASCE 7-05.

Image credit: ASCE 7-05.

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?

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Seismic Retrofit of Unreinforced Masonry (URM) Buildings

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URM Buildings. Image credit: www.henryturley.com

URM Buildings. Image credit: www.henryturley.com

Unreinforced Masonry buildings in moderate to high seismic areas can be a disaster in waiting. These types of structures have little or no ductility capacity (reference the recent “Building Drift – Do You Check It?” blog post for a discussion on ductility) required for structures to prevent loss of life in a seismic event. Many of these buildings are in densely populated areas, have historical meaning, and can be costly to retrofit. Fortunately, there are tools available for engineers to assess and design the needed retrofits to mitigate the potential loss of life and increase the seismic resiliency of these buildings.

Image credit: International Code Council (ICC).

Image credit: International Code Council (ICC).

ASCE 31-03, Seismic Evaluation of Existing Buildings, and ASCE 41-06, Seismic Rehabilitation of Existing Buildings, are two reference standards that are referenced in the 2012 International Existing Building Code (IEBC). (It should be noted that both of these reference standards are currently being combined into one document – ASCE 41-13.) Although ASCE 31 and 41 provide assistance to engineers in determining minimum seismic retrofits for these brittle structures, it is recommended that design of the retrofits be performed by a qualified engineer with experience in working with these types of brittle structures.

Currently the 2012 IEBC has been adopted in 39 states in the U.S. and several other areas (see reference map below).

2012 IEBC Adoption Map. Image credit: International Code Council (ICC).

2012 IEBC Adoption Map. Image credit: International Code Council (ICC).

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Structural Engineering Blog: One-Year Anniversary

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Photo credit: Thinkstock.

Photo credit: Thinkstock.

This month marks the one-year anniversary of the Simpson Strong-Tie® Structural Engineering Blog! To celebrate, we are holding a contest for our blog readers and sharing a few interesting statistics about the blog, along with our Top 5 Blog Posts from April 2012 to today.

Everyone who posts a comment or subscribes to receive email notifications to the blog (new subscribers only) from now until April 30, 2013 will be entered to win one of five Prize Packs. The Prize Pack consists of:

The contest is open to U.S. and Canadian residents (except Quebec) only. One entry per person. Five entries will be randomly selected to receive a Prize Pack. You can read the Official Rules here.

Continue reading →

Overview of Code-Plus Programs

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Our resident code expert, Branch Engineer Randy Shackelford, P.E., discussed some of the code-plus programs in the October 2012 issue of the Simpson Strong-Tie® Structural Report newsletter (Sign up for newsletters here). Randy has been an engineer for the Simpson Strong-Tie Southeast Region since 1994. He is an active member of several influential committees, including the AISI Committee on Framing Standards, the American Wood Council Wood Design Standards Committee, and the Federal Alliance for Safe Homes Technical Advisory Committee. He is vice-president and member of the Board of Directors of the National Storm Shelter Association. Randy has been a guest speaker at numerous outside seminars and workshops as a connector and high wind expert.

I wanted to share Randy’s informative newsletter article on the blog. Here is his post:

We all know that the purpose of a building code is to provide minimum requirements for the health, safety, and welfare of the occupants of buildings built under that code.  But what if the owner wants a building that will perform better than the absolute minimum allowed by the code?

There are several “code-plus” programs throughout the country that spell out prescriptive requirements for constructing buildings that are more resistant to local hazards than the code-minimum structure.

One of the more well-known code-plus programs is the “FORTIFIED” series from the Insurance Institute for Business & Home Safety (IBHS). The series consists of three basic programs: FORTIFIED Home, FORTIFIED for Safer Living® (new construction), and FORTIFIED for Safer Business®. The FORTIFIED Home program consists of a set of levels, or tiers of reinforcement, that can be applied to either a new or existing home. Each level builds on the previous level, and they are designated as Bronze, Silver, and Gold level.

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Is Designing with Wood Easy?

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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.

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2012 Autodesk University

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Autodesk University is an annual conference focused on keeping the design community up to date on the latest innovations, trends and technologies in design, drafting and visualization. Last year, Autodesk University was held in Las Vegas the week after Thanksgiving. Sadly, events always seem to conspire to prevent me from going to Vegas, but Simpson Strong-Tie was well represented by Frank Ding, our Engineering Analysis & Technical Computing Manager.

Frank received his Bachelors and Masters degrees in Manufacturing Engineering from Beijing University of Aeronautics and Astronautics, and has a Ph.D in Mechanical Engineering from Washington State University. Frank joined Simpson Strong-Tie in 2004 to head up our Finite Element Modeling efforts. Frank now manages all of our technical computing efforts, which includes keeping up with the latest developments that can assist us in our R&D efforts. So with introductions complete, I’ll let Frank tell you about his Autodesk University experience:

It was an exciting time attending my first Autodesk University in 2012. I have been to so many technical conferences during my professional career, but this one was quite different in scale, and the sheer size of it just blew me away. There were more than 8,000 attendees from 102 countries, more than 750 classes offered, and 163 exhibitors. I was impressed by the organization of such a large event, along with the online and mobile apps provided to help attendees manage their conference schedules.

My past impression of Autodesk was only limited to AutoCAD for 2D modeling. Now it has more than 40 SKU’s of different design software for use in the architecture, engineering, construction, manufacturing, media and entertainment industries.

Highlights of the conference, from my perspective, include:

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