Around Christmas, the Engineering Department does a white elephant gift exchange. We have no idea who framed this picture and wrapped it up the first time.
Several of our lab technicians (plus a product manager) are posing for the camera, and obviously trying to flex while sucking their bellies in during a concrete pour to test our SSTB(R) anchors. The tradition has it that if you end up with this picture, you hang it on your wall and re-gift it at next year’s gift exchange – so there it is, on the wall in Engineer Dustin’s office. The trick has become wrapping it so that nobody recognizes that it is the picture frame.
Speaking of concrete, between our test labs in Addison, Ill., Stockton and Pleasanton, Calif., we test a lot of concrete. We will certainly be doing a lot more testing to continue to support our new Repair, Protection and Strengthening Systems for Concrete and Masonry product line. But I will ask the lab technicians to keep their shirts on.
I have been following TED Talks for a few years now. Like most websites I have on my “to visit” list, I couldn’t tell you how I found them. It may have been a link on some other website, or a friend on Facebook, or maybe linked on another blog somewhere. What is TED? I’ll steal from their website:
TED is a nonprofit devoted to Ideas Worth Spreading. It started out in 1984 as a conference bringing together people from three worlds: Technology, Entertainment, Design. Since then its scope has become ever broader. Along with two annual conferences — the TED Conference and TEDGlobal — TED includes the award-winning TED Talks video site, the Open Translation Project and TED Conversations, the inspiring TED Fellows and TEDx programs, and the annual TED Prize.
New content is posted on TED every day, so I often miss cool stuff. Thanks to one of our Canadian engineers for pointing out a talk by architect Michael Green, who makes a case for why we should build wooden skyscrapers. I did a previous post about the Timber Tower Research Project that Skidmore, Owings & Merrill LLP did for a 42-story wood framed building. Mr. Green makes the case for taller wood structures from an environmental standpoint and carbon dioxide output of concrete and steel versus wood.
I confess that I listen to a lot of pop music while driving to work, mostly because I forget to change the station after dropping the kids off. It can be slightly embarrassing if I drive with a coworker and I’m tuned into the “all Bieber, all day” station when I start the car.
On Monday, I was without kids and managed to hear several news stories on NPR about Hurricane Sandy. Transcript of one story is here and the NPR blog post about it is here.
The Hurricane Sandy Rebuilding Task Force released a report titled Hurricane Sandy Rebuilding Strategy. The report has 69 recommendations ranging from complex, such as setting minimum flood elevations that account for projected sea level rise, to relatively simple, such as states and localities adopting and enforcing the most current versions of the IBC® and IRC®.
The recommendations cover energy, infrastructure, sanitation, water, fuel supply, internet, transportation, and too many other things to list. But if I had to pick one word to summarize the report, it would be:
Resilience: The ability to prepare for and adapt to changing conditions and withstand and recover rapidly from disruptions.
Regardless of whether the natural disaster is high wind, earthquake, flood or fire, there has been a shift in public policy over the past decade to emphasize resilience. Resilience is a cycle. It begins with mitigation before the disaster. Some examples of mitigation that have appeared in this blog:
Designing new buildings with specific performance targets is a form of mitigation as well. Resilience continues with response after the disaster, and then short and long-term recovery plans to reduce the time between disaster and recovery.
Have recent natural disasters such as Hurricane Sandy changed the way you are designing? Let us know by posting a comment.
One of the first projects I worked on when I got out of school was the Mexican Heritage Plaza in San Jose, California. It was a 200,000 square-foot facility with a theater, classrooms, art gallery and gardens. It was my first time using ETABs and SAFE for the building frame and mat slab designs, and there was no graphical interface. Text file input – those were the days! I learned how to detail bolted and welded steel connections, and then I got to enjoy every junior engineer’s first right of passage – reviewing shop drawings. It was eye-opening to learn that a detailer needed to translate all the dimensions, size call-outs and typical details into exact measurements down to the sixteenth of an inch for every single member, bolt, and hole.
I am sure I spent too much time reviewing them and checking that all the numbers added up. Photocopying E-size drawings was more expensive than a junior engineer’s time back then, so before I hand copied my mark-ups over to five sets of drawings, I reviewed them with my manager. She circled the high-strength anchor rods for the special moment frames and wrote “Too short – recheck.” I pointed out that I had checked the grout pad, base plate and washer thickness to make sure the anchor rods extensions were long enough to fully thread the nuts on (they just worked). She told me that high-strength anchor lengths were always too short. It didn’t make sense to me at the time, but I marked up the drawings and sent them off. More on this later.
Common specifications for steel anchor rods used for concrete anchorage are ASTM A307, A449 and F1554 Grades 36, 55, 105. Some of these anchor rods have specifications appropriate for welding. According to AISC Design Guide 21 on Welded Connections, “unless the supplier of the anchor rod can provide assurance that the compositional limits of ASTM A36 have been achieved, weldability of F1554 Grade 36 should be investigated”. Both ASTM F1554 Grade 55 and ASTM A307 provide supplementary requirements for welding applications in Section S1. The S1 requirements limit the percentage of carbon equivalent permitted for the metal alloy. Where welding is required designers should specify F1554 Grade 36 with the compositional limits of ASTM A36 or F1554 Grade 55 ordered with supplementary requirement S1. ASTM A307 specified with supplementary requirement S1 can be ordered for anchor rods where welding is required.
Threaded Rods
There is a blend of art and science in the manufacturing of high-strength steel anchor rods (ASTM F1554 Grade 105, A325 and A449). Like a pastry chef, creating a perfectly baked soufflé with the correct ingredients and temperature, modern day blacksmiths achieve a balance of strength and ductility characteristics for anchor rods through controlled quenching and tempering treatments. The rapid cooling of metal through quenching increases toughness and strength, but it often increases brittleness. Tempering is a controlled reheating and cooling of the metal which increases ductility after the quenching process. Precise control of time with the application of temperature during the tempering process is critical to achieve an anchor with well-balanced mechanical properties.
Coupler Nuts
AISC does not recommend welding of high-strength anchor rods including, but not limited to, ASTM F1554 Grade 105, A325, and A449. The heat input from welding can alter the physical properties and other elements from the weld metal are introduced altering the metal alloy for high strength anchors. Similarly, quenched and tempered steel used to fabricate high strength nuts or couplers is also not suitable for welding.
Now let’s get back to my first steel project. We asked the steel detailer to recheck the anchor rod lengths, and they added 1” of extension above the top of concrete and shipped the assemblies with 16-gage steel templates attached with double nuts. Several templates were damaged in shipping so the contractor fabricated new ones. Somewhere in the process of swapping out templates and reattaching them with double nuts, the anchor rods were set 1” too low. Since the detailer added 1”, everything fit perfectly. And I understood why high-strength anchor rods could never be too long.
Today the NEES-Soft project has begun testing the steel Simpson Strong-Tie® Strong Frame® Special Moment Frame as a retrofit option for soft-story buildings at the NEES outdoor shake table facility at UC San Diego. The testing is focused on validating the FEMA P-807 design procedure, which attempts to create a least-cost retrofit solution by only retrofitting the garage areas of problem buildings.Continue Reading
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.
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.
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.
Seaside Heights boardwalk rebuild.
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 drives in the first screw.NBC’s Today Show airs live from the reconstructed boardwalk.
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.
Holgate, NJScoured 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
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.
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