- Page 43 of 50 - News, Notes and Discussion from the Simpson Strong-Tie Engineering Department

Steel Moment Frame Beam Bracing

In a previous blog post on soft-story retrofits, I briefly discussed beam bracing requirements for moment frames. This week, I wanted to go into more detail on the subject because it’s important to understand that a typical steel moment frame requires lateral beam bracing to develop its full moment capacity. Figure 1 below shows two common methods of beam bracing. While on the surface determining beam bracing requirements may not appear complicated, there are several items that could prove it to be more challenging than you might think, especially when steel moment frames are used in light frame construction.

Figure 1: Steel Beam Bracing

(A) Braced with kicker and metal deck(1)

(B) Braced with kicker and wood joist/beams(2)

Before going into beam bracing in steel moment frames, it is important to discuss the behavior of a simply supported beam under gravity load. Short beams (Lb < Lp)^[3], might not require bracing to achieve the full plastic moment of the beam section. However, when a beam is long (Lb > Lr) and without bracing, the beam can twist or buckle out-of-plane. Figure 2 illustrates these two behaviors along with the case where the beam length is somewhere in between the two (e.g., Inelastic lateral torsional buckling). In addition, if beam sections are non-compact, flange local buckling (FLB) or web local buckling can occur prior to reaching the beams full plastic moment.

Congratulations to our Structural Engineering Blog One-Year Anniversary Winners!

To celebrate the first-year anniversary of the launch of our Structural Engineering Blog, in April we hosted a sweepstakes inviting you to comment on the blog or sign up for blog email updates.

Timber Tower Research Project

In 2009, Simpson Strong-Tie participated in the NEESWood Capstone Test, which was the final experiment in a multi-year study to test and evaluate the seismic performance of various wood-framed buildings. The Capstone Test was a six-story apartment building constructed and tested at the E-Defense test facility, located in Miki, Japan. More information about the Capstone Test is available here.

NEESWood Capstone Test. Photo credit: Simpson Strong-Tie. — NEESWood Capstone Test. Image credit: Simpson Strong-Tie.

I only mention the NEESWood testing because I thought six-stories was pretty tall for wood-framed construction, since U.S. building codes limit us to four or five stories in wood. I recently came across a research project by Skidmore, Owings & Merrill LLP (SOM) for something just a tad taller than that. Looking to minimize the carbon footprint by using timber as the main structural material, SOM published a report for the design a 42-story, 405-ft. tall building. The solution utilizes mass timber for the main structural elements with reinforced concrete at highly stressed areas. The project used the Dewitt-Chestnut Apartments, a 42-story reinforced concrete structure built in 1965, as the benchmark building.

Abstract for the Timber Tower Research Project along with links to the full report and sketches are on SOM’s website.

So, what do you think of a 42-story wood-framed building? Let us know by posting a Comment.

– Paul

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

Rebuilding with Simpson Strong-Tie Products After Hurricane Sandy

Our factory in Gallatin, TN held a Fastener Summit Meeting this past June, which brought together people from all areas of our fastener business. Somewhere, sometime we started calling these meetings “Summits” and the name stuck. The purpose of the Summit is to facilitate candid discussions about what we need to do to better support our customers’ needs through new product development, new application testing, literature, training, or sales distribution.

One of our fastener sales specialists shared a great story about a New Jersey town’s decision to build a better boardwalk following Superstorm Sandy. The town of Seaside Heights decided to design and build a boardwalk to better address future storms. Along with being a local icon, the boardwalk is an integral part of the town’s economy.

Working hand in hand with the town’s borough officials, the project’s engineering firm and contractor, our Columbus, OH branch worked to tirelessly to develop construction solutions to save time and money on this critical project. For Simpson Strong-Tie, this involved testing and ramping up production of stainless steel product to ensure no delays for the project.

A little over two months after Seaside Heights Mayor Bill Akers drove the first deck board screw using our Quik Drive auto-feed screw system, the boardwalk was complete. NBC’s Today Show broadcast live from the boardwalk with New Jersey Governor Chris Christie on May 24. There’s also a cool video on the New York Fox News website showing different time lapse views of the build here.

Seaside Heights Mayor Bill Akers drive in the first screw. — Seaside Heights Mayor Bill Akers drives in the first screw.

The Today Show airs live from the reconstructed boardwalk. — NBC’s Today Show airs live from the reconstructed boardwalk.

You can read the full story in the July issue of our Structural Report newsletter.

– Paul

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

What If You Wrote A Code and Nobody Used It?

Simpson Strong-Tie spends quite a bit of time monitoring the development and adoption of building codes. This effort helps us to have products available to help our customers meet the latest code requirements.

The model codes most commonly used in this country, the International family of codes, are developed by the International Code Council (ICC). ICC lists the following benefits of a uniform, modern set of codes: “Code officials, architects, engineers, designers, and contractors can work with a consistent set of requirements throughout the United States. Manufacturers can put their efforts into research and development rather than designing to different sets of standards and can focus on being more competitive in worldwide markets. Uniform education and certification programs can be used internationally.” ICC offers a statement on why the newest codes should be adopted here.

Nevertheless, for varied reasons, many states do not require adoption of uniform codes statewide. A group composed of national business and consumer organizations, corporations, and emergency management officials is trying to change that. The group is called the BuildStrong Coalition, and they believe that the statewide adoption of building codes will “protect homes and buildings from the devastation of natural disasters.”

The group offers several studies to back this idea. One of the most compelling was a study performed by the Insurance Institute for Business and Home Safety after Hurricane Charley in 2004. The study examined specific houses in the path of the hurricane and compared the damage to the year that the home was built. It showed that in homes built since the adoption of the statewide Florida Building Code, the severity of property losses was reduced by 42 percent, and the frequency of losses was reduced by 60 percent.

The coalition believes that “strong building codes provide our best first line of defense against natural disasters.” It appears that, for whatever reason, the number of disasters has been increasing of late. For example, in the 60’s, there were an average of 19 Major and Emergency Federal Disaster Declarations per year. In the 70’s, the average was 41 per year. In the 80’s, the average was 25 per year. In the 90’s, the average was 52 per year, and since 2000, the average has been 76 Disaster Declarations per year.

The coalition has been working with members of Congress on proposed legislation, the Safe Building Code Incentive Act, which would give states an incentive to adopt and enforce statewide building codes. Rather than mandate state action, the Act would reward states that adopt and enforce nationally recognized model building codes for residential and commercial structures with eligibility for an additional 4% of disaster relief aid after their next disaster strikes.

The Act was recently reintroduced by Senator Menendez and Representative Diaz-Balart. You can read a press release on the reintroduction here.

– Paul

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

New Simpson Strong-Tie Anchor Designer software

Remember back to the days when you used allowable stress design for designing anchorage to concrete? Once you had your design loads, selecting an anchor was quick and easy. The 1997 UBC covered the anchorage to concrete in less than two pages, so the calculation was painless. Post-installed anchors were even easier, since allowable loads were tabulated and you just needed to apply a couple of edge distance and spacing reductions.

Since the introduction of strength design provisions and the adoption of ACI 318 Appendix D, first in the 2000 IBC, designing code-compliant anchorage to concrete has become much more complex. At least once (and probably not more) armed with a pencil, calculator, and an eraser, most of us have set out to design a ‘simple’ anchorage to concrete connection using the Appendix D provisions. Several pages of calculations later (and hopefully with a solution to the problem), most of us, I imagine, came to realize that designing anchorages to concrete by hand required much more time and effort than we anticipated or could allocate time for. As a result, many of us probably created an Excel template to speed up the design process using built-in functions and some Visual Basic programming.

I'm never going for looks on my spreadsheets. — I’m never going for looks on my spreadsheets.

The question is: are you still using the template?

For me, the answer is an emphatic “NO”, mainly because the spreadsheet I created has limited capability given the complexity in adapting the design methodology to complex anchor layouts, changes to the design provisions with each new code edition, and the need to add/modify data each time a new post-installed anchor product is introduced.

What Did Sandy Teach Us?

In the weeks following Hurricane Sandy, I had an opportunity to visit some of the hardest hit communities in the region. At the time, many of New Jersey’s barrier islands were still completely closed off to civilian traffic and all accessible bridges were blocked by military guards. Our local territory manager has great relationships with building departments, so we were able to walk portions of Long Beach Island, NJ with an inspector. The storm surge washed out several sections of the protective sand dunes on the south end of the island in the neighborhood of Holgate and this is where we spent much of the day.

Scoured foundation temporarily shored. Holgate, NJ.

For a structural engineer, there was a lot to observe and many things I could write about here (maybe a future post), but what strikes me the most when looking back is the long- term impact this event will have on the region. The cost of Sandy goes beyond the loss of life and property (72 lives, $50 billion and growing). It would be difficult to estimate a dollar amount that accounts for the displacement of people and disruption to their lives, the hit to local economies that depend heavily on tourism, and the effect on the national economy and taxpayers; but I imagine it would be a staggering sum. So what, if anything, can structural engineers do about it?Continue Reading

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.
Continue Reading

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.

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.