While you can use social media for personal reasons, it has now become a serious source of professional content that can help make your life as a structural engineer a little easier. Here are some reasons why social media is (still) important for structural engineers:
It Offers Solutions
If you are encountering an issue or problem, there is a strong chance that there are other structural engineers that have faced the same issue. The nice thing is that with social media, you can find those structural engineers a little faster. There are LinkedIn groups for structural engineers, Facebook groups and even blogs that you can turn to if you have a question.
At the Structural Engineering blog, we get questions from structural engineers on a regular basis asking about our calculations or how we have resolved a particular issue. We respond to those questions right away. They also provide us with great insight into the challenges you face day to day.
It Connects You With Other Engineers
We all know that networking is important. Social media just makes it a little easier to start that conversation. Groups on LinkedIn and Facebook are a great way to exchange best practices and ideas. You can also find out about local events with professionals in your area from these groups so that you can network in person.
It Keeps You Informed
Social media is the first place where industry conversations happen now. Whether it is about soft-story retrofit ordinances or truss designer responsibilities, you can find online conversations about structural engineering on a variety of social media platforms.
All in all, social media is a great resource and can supplement the ways that you already enrich your professional career. How has social media helped you with your job? Let us know in the comments below.
I have a special place in my heart for old buildings. Every college design course I took was related to new design. Concrete, steel, or wood design, the design problem was invariably part of a new building. I thought structural engineers designed new buildings. When I showed up for my first day of work wearing dress pants, a button-down shirt and a tie, I was handed a flashlight, tape measure, a clipboard and a Thomas Guide map (no Google maps back then) and sent to do as-built drawings for a concrete tilt-up that we were retrofitting.
When I was designing buildings, I created a lot of as-built drawings. Figuring out how a building was put together, what the structural system was (or wasn’t!) and designing a lateral load path in these old, and often historic buildings, was immensely satisfying. Knowing that history, it should not be surprising I have done a number of blog posts related to seismic retrofits. Soft-Story Retrofits, San Francisco’s Soft-Story Retrofit Ordinance, Remembering Loma Prieta, Resilient Communities, FEMA P-807, and Home Seismic Retrofit (there are probably a couple I forgot).
This week, Los Angeles Mayor Eric Garcetti proposed new seismic safety regulations . The recommendations are to retrofit soft-story wood-framed buildings within five years and older concrete buildings within 30 years. While these are only recommendations, it is encouraging to see politicians supporting policies to promote resiliency and life safety.
In San Francisco, thousands of building owners are already required by law to seismically retrofit multi-unit (at least five) soft-story, wood-frame residential structures that have two or more stories over a “soft” or “weak” story. These buildings typically have parking or commercial space on the ground floor with two or more stories above. As a result, the first floor has far more open areas of the wall than it actually has sheathed areas, making it particularly vulnerable to collapse in an earthquake.
Photo credit: J.K. Nakata and the U.S. Geological Survey
San Francisco’s ordinance affects buildings permitted for construction before Jan. 1, 1978. Mandatory seismic retrofit program notices requiring that buildings be screened were sent out in September, 2013, to more than 6,000 property owners. It is anticipated that approximately 4,000 of those buildings will be required to be retrofitted by 2020.
“When we look at the demographic of these buildings, they house approximately 110,000 San Franciscans. It’s paramount that we have housing for people after a disaster. We know we will see issues in all types of buildings, but this is an opportunity for us to be able to retrofit these buildings while keeping an estimated 1100,000 San Franciscans in their homes and, by the way of retrofit, allowing them to shelter in place after a disaster,” according to Patrick Otellini, San Francisco’s chief resilience officer and director of the city’s Earthquake Safety Implementation Program. “This exponentially kick starts the city’s recovery process.”
One solution to strengthen such buildings is the Simpson Strong-Tie® Strong Frame® special moment frame. Its patented Yield-Link™ structural fuses are designed to bear the brunt of lateral forces during an earthquake, isolating damage within the frame and keeping the structural integrity of the beams and columns intact.
Simpson Strong-Tie® Strong Frame® special moment frame
“The structural fuses connect the beams to the columns. These fuses are designed to stretch and yield when the beam twists against the column, rather than the beam itself, and because of this the beams can be designed without bracing. This allows the Strong Frame to become a part of the wood building and perform in the way it’s supposed to,” said Steve Pryor, S.E., International Director of Building Systems at Simpson Strong-Tie. “It’s also the only commercially-available frame that bolts together and has the type of ductile capacity that can work inside of a wood-frame building.”
Installation of the Simpson Strong-Tie® Strong Frame® special moment frame
Another key advantage of the Simpson Strong-Tie special moment frame is no field welding is required, which eliminates the risk of fire in San Francisco’s older wood-framed buildings.
To learn more about San Francisco’s retrofit ordinance, watch a new video posted on strongtie.com/softstory. For more information about the Strong Frame special moment frame, visit strongtie.com/strongframe.
Two weeks ago, I had the chance to present to the Young Members Group of the Structural Engineering Association of Metro Washington on the topic of Multi-Story Light-Frame Shear Wall Design. With all of the large firms in the D.C. area, it wasn’t a big surprise to find out that only about one-third of the group had experience with light-frame shear wall design.
However, while researching civil/structural engineering programs in the Midwest and Northeast last week (for our Structural Engineering/Architecture Student Scholarship program), I was disappointed to find that only about a quarter of the top engineering programs offer a wood design course. So I thought it might be helpful to post a wood shear wall design example this week.
The example is fairly basic but includes an individual full-height and perforated shear wall analysis for the same condition. The design is based on wind loading and SPF framing, both common in the Midwest/Northeast, and is based on the provisions and terms listed in the 2008 Special Design Provisions for Wind and Seismic (SDPWS), available for free download here, along with the recently posted 2015 version.
Multi-Story Shear Wall Example: Wind Loads with SPF Framing
Given:
2012 IBC & 2008 SDPWS
3-Story Wood Framed Shear Wall Line
ASD Diaphragm Shear Forces from Wind as Shown
Wall and Opening Dimensions as Shown
Solution:
Determine total shear force in each shear wall line.
Determine the Induced Unit Shear Force, v, for use with both shear wall types and the Maximum Induced Unit Shear Force, vmax, for the perforated shear wall collectors, shear transfer, and uniform uplift. Note the following:
vmax requires the determination of the Shear Capacity Adjustment Factor, CO, for the perforated shear wall.
The SDPWS provides two methods for determining CO, a tabulated value or a calculated value. This example uses the more precise calculated value.
The perforated method requires the collectors be designed for vmax and the bottom plate to be anchored for a uniform uplift equal to vmax (as illustrated in the following figure).
3. Determine the Tension, T, and Compression, C, forces in the chords (assume no contribution from dead load for this example). Note the following:
Reverse wind loading will require a mirror image of the T & C forces shown in the following figure.
The tension forces, T, shown in the example reflect the cumulative tension forces as they are transferred down from post-to-post, as is typical with traditional holdowns. For continuous rod systems like ATS, the incremental tension forces (resulting from the unit shear, vor vmax, at that level only) must also be determined as shown in the shear wall specification table at the end of this example.
4. Determine sheathing material and fastening pattern based on v calculated in Step 2. The table below is based on 7/16″ wood structural panel sheathing values in SDPWS Table 4.3A.
Individual Full-Height Shear Wall:
i. v3=227 plf: Use 7/16 OSB with a 6:12 nailing pattern which has an allowable load of 336 plf
ii. v2=409 plf: Use 7/16 OSB with a 4:12 nailing pattern which has an allowable load of 490 plf
iii. v1=591 plf: Use 7/16 OSB with a 3:12 nailing pattern which has an allowable load of 630 plf
B. Perforated Shear Wall (apply CO factor to allowable shear capacity):
i. v3=227 plf: Use 7/16 OSB with a 6:12 nailing pattern which has an allowable load of 255 plf
ii. v2=409 plf: Use 7/16 OSB with a 3:12 nailing pattern which has an allowable load of 479 plf
iii. v1=591 plf: Use 7/16 OSB on both sides of the wall with a 4:12 nailing pattern which has an allowable load of 338*2=676 plf
5. Size the posts for compression. Simpson provides some useful tables in the back of the connector catalog with allowable tension and compression loads for a variety of sizes, heights, and species of posts.
6. Select holdowns for the tensions loads and verify post sizes are sufficient. For higher aspect ratio shear walls, the post size and holdown type may significantly reduce the moment arm between center of tension and center of compression, resulting in higher tension and compression forces.
The tables below show the shear wall specification for the walls in the example in a typical format. Note that they do not include some detailing that is required for items such as the uniform uplift force on the bottom plate of all perforated shear walls, or the perforated shear walls with OSB sheathing on both sides.
There are different ways to address the loads, so let us know if you would do anything differently in your designs.
We hope that you and your loved ones have a Happy Thanksgiving. Our U.S. offices are closed Thursday and Friday, November 28-29 for the holiday. Check back next week for a new blog post!
The Greek philosopher Heraclitusis credited with saying “The only thing that is constant is change.”
If that applies to building codes, then it applies doubly to wind design using the 2012 International Building Code® (IBC).
The wind load requirements in Section 1609 of the IBC are based on ASCE 7 and refer to this document for most design information. In the 2012 IBC, the referenced version of ASCE 7 changed from the 2005 edition to the 2010 edition. In ASCE 7-10, the wind design requirements have been completely revised, including a complete design philosophy change.
Wind design has changed from an allowable strength-based philosophy with a load factor of 1 in the ASD load combination to an ultimate strength design philosophy with a load factor of 1 in the strength design load combination. This means wind design has a similar basis as seismic design. So the new load combinations for wind look like this:
Because of the change in load factor and philosophy, the basic wind speed map had to be altered. In the past, one map was provided and the design return period was increased for certain occupancies by multiplying the load by an importance factor. In ASCE 7-10 there are three maps provided so now an importance factor is no longer needed. The return period of the map depends on the risk to human life, health and welfare that would result from the failure of that type of building. This was previously called the Occupancy Category, but it is now called the Risk Category.
Risk Category III and IV buildings use a basic wind speed map based on a 1,700-year return period. Risk Category II buildings use a basic wind speed map based on a 700-year return period. And Risk Category I buildings use a basic wind speed map based on a 300-year return period. Because of the higher return period, the mapped design wind speed will be much higher than when using previous maps. However, with the lower load factors, actual design loads will be the same or in many areas lower due to other changes in the way the map was developed.
Excerpted from the 2015 International Residential Code; Copyright 2014. Washington D.C.: International Code Council. Reproduced with permission. All rights reserved. www.iccsafe.org
Another change to ASCE 7-10 for wind design is that Exposure D is no longer excluded from hurricane prone regions; so buildings exposed to large bodies of water in hurricane prone regions will have to be designed for Exposure D.
Because of the change in wind speeds, there is a change in the definitions of windborne debris regions. Due to the different wind speed design maps, the windborne debris region will be different depending on the Risk Category of the building being built. The windborne debris region is now defined as areas within hurricane-prone regions that are either within 1 mile of the coastal mean high water line where the ultimate design wind speed is 130 mph or greater; or any areas where the ultimate design wind speed is 140 mph or greater; or Hawaii. Risk Category II buildings and structures and Risk Category III buildings and structures (except health care facilities), use the 700-year Risk Category II map to define wind speeds for the purpose of determining windborne debris regions. Risk Category IV buildings and structures and Risk Category III health care facilities use the 1700-year return Category III/IV wind speed map to define wind speeds for the purpose of determining windborne debris regions.
Finally, a new simplified method for determining wind loading on ENCLOSED SIMPLE DIAPHRAGM BUILDINGS WITH h ≤ 160 ft has been added to ASCE 7-10. This is different from the simplified all heights method in the IBC, so it will be interesting to see which method becomes more widely used. Which method do you prefer? Let us know in the comments below.
On Saturday evening, Barclay Simpson passed away peacefully in his sleep, surrounded by his family. He was 93 years old. With Barc’s passing, Simpson Strong-Tie has lost a beloved and inspirational leader. Our country has lost a generous philanthropist, visionary and great American entrepreneur. Those of us who were fortunate enough to know and work with Barc have lost a dear friend, champion and guide.
Barc’s contributions to the construction industry, non-profit community and our employees are immeasurable. He instilled the core values — our “Secret Sauce” — that have made Simpson Strong-Tie a unique and inspiring place to work and have built our reputation as a quality, trusted manufacturer and solid corporate citizen.
The first time I met Barc was less than a week after I started working in the R&D department. I was meeting with a product manager and Barc was walking by, so he stopped in to say hello. We introduced ourselves and chatted for a few minutes. I told him about my work experience, where I went to school, what I was working on, and he even asked where I grew up. He was genuinely interested in getting to know me, which made me feel welcome.
I later noticed that Barc usually parked at the end of the building furthest from his office. He would take a different path through the building – sometimes through engineering, other times he would walk through marketing, accounting, or even the connector test lab. Barc cared deeply for all of his employees, and the intentionally long walk gave him the opportunity to talk with folks.
He firmly believed that everybody in the company is important, and he took every opportunity to remind us. In the video, Barclay Simpson’s Nine Principles of Doing Business, Barc speaks quite passionately about dignifying the contribution of every individual at every level.
In the end of a previous blog post, I mentioned Barc’s 1974 list of Rambling Thoughts on Making One’s Fleeting Moment on This Planet a Pleasant One. In the context of that post, the thoughts of “Attitude Conquers All” and “Keep it light. It really isn’t that important” were appropriate.
Thinking of Barc and his legacy, I prefer this rambling thought from his list:
Strive to have a POSITIVE EFFECT upon those lives touched by your own.
In the past several years, there has been an increase in the use of screws in applications that have traditionally been reserved for bolts and lag screws. Greater innovation in the wood screw market has caused this shift. Proprietary wood screws now offer many more benefits than commodity bolts and lag screws. Today, this post will discuss some of those benefits.
One of the questions I am asked most frequently is “Who is responsible for the truss-to-(fill in the blank) connection? One such example is the truss-to-wall connection. To answer this question, it helps to recognize there are two types of connections: a truss-to-truss connection and a “truss-to-everything-else-except-a-truss” connection. The Truss Designer is responsible for the former, and the Building Designer is responsible for the latter. Pretty simple, right? So why all the questions?
Excerpt from ANSI/TPI 1-2007 Chapter 2 on Design Responsibilities
Some people incorrectly assume the Truss Designer is responsible for connecting the truss to everything the truss touches. Then, when the Truss Designer doesn’t specify a connection to something the truss touches (such as a wall), it prompts the question, “Hey, who is responsible for that connection? I thought the Truss Designer was!” In other cases, the person asking the question is actually challenging the answer, such as “Shouldn’t the Truss Designer be specifying the truss-to-wall connection? Why don’t they?” And finally, the question may be prompted at times when the project doesn’t have a Project Engineer (aka the Building Designer), so the question becomes, “Now who is going to specify that connection? It must be the Truss Designer, right?”
But the Truss Designer isn’t responsible for the truss-to-wall connection – and here’s why. Unless the scope of work has been expanded by contract, the Truss Designer is responsible for designing an individual component. The truss gets designed for a given set of specified loads, environmental conditions, serviceability criteria and support locations, all which are specified by the person responsible for the overall building: the Building Designer. Once designed, the truss will have a maximum download reaction and uplift reaction (if applicable) at each support location. Is that enough information to specify a truss-to-wall connection? No, it is not. First, the Truss Designer may not know what the truss is even sitting on; he or she may only know that the bearing is SPF material and 3 ½” wide. Is it a single top plate or double top plate? Is there a stud below the truss that can be connected to, or is the stud offset? Or, is the truss sitting on a header spanning across a wide window?
Sample Truss Reactions
Second, even if the Truss Designer had all of the information regarding the bearing conditions, there is another problem. The Truss Designer has the reactions resulting from the loads applied to the truss. What about the reaction at the top of the wall (perpendicular to the wall) resulting from the lateral loads applied to that wall? And the shear loads acting parallel to the wall as a result of lateral loads applied to the end wall? These loads also need to be resisted by the truss-to-wall connection (hence, the F1 and F2 allowable loads that are published for hurricane ties), so the Truss Designer cannot select an adequate truss-to-wall connection based on the truss reactions alone.
Truss-to-Top Plate and Truss-to-Stud Connections
Finally, there’s one more scenario to consider. Say a Building Department requires that truss-to-wall connections must be specified by the Truss Designer on projects that have no Engineer of Record. It wants to ensure trusses are adequately secured to the walls, and the Truss Designer may seem best equipped to determine those connections (this has actually happened in some places). The Truss Designer can find out what exactly the truss is sitting on, and can even calculate some approximate reactions for the top of the wall to conservatively take into account during the selection of the connection. Problem solved? Not entirely. That takes care of the top of the wall, but the load doesn’t stop there. So requiring the Truss Designer to specify the truss-to-wall connection only transfers the problem to the bottom of the wall. Who is going to address those connections?
Continuous Load Path
While most people don’t think of the Truss Designer as being the person responsible for the connections at the bottom of the wall, many do think the Truss Designer should be responsible for the connections at the top of the wall. But because someone – namely, the Building Designer – still needs to ensure that a continuous load path has been satisfied by the connections in the building, does it really help to increase the scope of work of the Truss Designer to specify the truss-to-wall connection?
Imagine that it’s 4:30 a.m. and suddenly you’re awakened by strong shaking in your home. Half asleep, you hang on to your bed hoping that the shaking will stop soon. All of a sudden, the floor gives away and you fall. You think, “What just happened? How could this have possibly occurred? Am I alive?”
These could have been the thoughts of Southern California residents living in one of the many apartment buildings, which collapsed on January 17, 1994, during a 6.7 magnitude earthquake. The Northridge Earthquake brought awareness to buildings in our communities with a structural weakness known as a soft story, a condition that exists where a lower level of a multi-story structure has 20% or less strength than the floor above it. This condition is prevalent in buildings with tuck-under parking and is found in multistory structures throughout San Francisco, Los Angeles and other cities (see Figure 1). These structures are highly susceptible to major damage or collapse during a large seismic event (see Figure 2).
Figure 1: Multi-unit wood-frame building with first weak story.Figure 2: Collapsed soft story tuck under parking building. Image courtesy of LA Times
Soft story retrofits help to strengthen our communities and make them more resilient to major disasters. There are several resources available to structural engineers that need to retrofit weak-story buildings. Some of these resources are mentioned in our September 18 blog post.
During the 2014 SEAOC Convention held in Indian Wells on September 10-13, speakers discussed different methods, analysis and research that address the behavior of various materials and construction types during seismic events along with approaches to retrofit historically poor performing structures. This information can be viewed from the convention’s proceedings available at www.seaoc.org.
On October 20, 2014, the Structural Engineers Association of Southern California (SEAOSC) will be hosting their 4th annual Strengthening Our Cities BAR Summit in downtown Los Angeles. This event brings together many different stakeholders in our built environment, including public officials, building owners and managers, business owners, insurance industry representatives, emergency managers and first responders, and design professionals.
Many prestigious thought leaders, including USGS Seismologist Dr. Lucy Jones will be speaking at the summit, discussing such topics as tools and analysis methods for retrofitting vulnerable buildings and the Building Occupancy Resumption Program (BORP).
Expect a great day full of useful information about ways to strengthen our communities and prepare for major earthquakes as well as opportunities to network with like-minded peers. For additional information and to register, visit www.barsummit.org. We also hope you’ll visit our booth. We look forward to speaking with you there.
We all know that earthquakes physically shape the landscape here in California, but they shape careers as well. Earthquakes I felt while growing up in California’s southern San Joaquin Valley got me thinking about engineering as a career while in high school. When the Loma Prieta earthquake struck on October 17, 1989, like many of you I was watching the World Series live on television and thus got to see the earthquake live as well. I was in my senior year of college at the time, studying Civil Engineering with a structural emphasis. This earthquake cemented the direction I would take in my career. I wanted to be a structural engineer, and I wanted to design buildings that would not fall down in earthquakes.
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