When designing a shearwall according to the International Building Code (IBC), a holdown connector is used to resist the overturning moment due to lateral loading. From a structural statics point of view, a shearwall without dead load or holdowns would have zero lateral-resisting capacity without any restraint to resist the overturning moment. Since the wall assembly still has the sill plate anchorage providing resistance to overturning, testing can measure the capacity of a wall assembly without holdowns.
Happy Fourth of July
We wish you a happy and safe Fourth of July from all of us here at Simpson Strong-Tie.
Check back next week for our regular blog posts.
Plated Wood Truss Hip End Styles
For many, the first day of summer means it is time to cinch up your favorite hip-hugging bathing suit and enjoy the warm weather. For the truss industry, it’s time to keep those hip-hugging bathing suits in the closet and take advantage of the favorable weather months by bidding and building as many jobs as possible. During the bid and build frenzy, there will be several hip end jobs leaving truss yards across the country, but what exactly is a hip end and what are the different styles?
The Structural Building Components Association website (SBCA) defines a hip roof as a “Roof system in which the slope of the roof at the end walls of the building is perpendicular to the slope of the roof along the sides of the building.” While framing terms differ by region, most trussed hip end systems will include hip trusses, jack trusses (end and side) and a rafter or corner girder truss. Hip end style and setback (distance from side or end walls to the hip girder truss) may also vary by building design and region.
In the western part of the country, a California Hip system is typically seen in many trussed structures. In this hip system, the hip truss flat top chord is dropped by the plumb cut of the jack top chord at the roof pitch. By doing this, the top chords of the end jack trusses can pass over and bear on the dropped flat top chords. As the height of the hip end roof plane increases, the height of the flat top chord also increases, though the interval at which the flat top chord height increases may vary by building design and region.
East of the Rocky Mountains, the California Hip is rare and a Step-Down Hip system is more popular. Differing from the California Hip, a Step-Down Hip system is one where every truss under the hip end plane decreases in height, or “steps down” from the apex until it reaches the hip girder, which is placed at a pre-determined setback.
Less regional and more situational depending on the building design, are the Lay-In Gable, Dutch and Terminal Hip systems. The Lay-In Gable Hip system is one with many regional names and shares similarities with the California and Step Hip systems. Like the Step Hip, every truss steps down moving from the apex to the setback. Like the California, every truss flat top chord has a drop. However, the flat top chord is dropped by the plumb cut of a 1.5” member at the roof pitch, as the gable frame lays flat.
In a Dutch Hip system, the hip end roof plane does not converge with the side planes to form an apex. Instead, the hip end plane pitches directly into the girder truss that is placed at a predetermined setback. Jack trusses then connect to the hip girder truss or to a ledger attached to the hip girder truss. This hip system is also referred to as a Dutch Gable.
Assuming like roof pitches and heel heights, a Terminal Hip system is one where the hip girder truss setback is half of the main truss span or building width. If pitches and heel heights vary, the girder truss is placed at the apex of the three converging roof planes, which could be more or less than half of the main truss span or building width.
While these are some common hip end styles in the truss industry, there are definitely others. Each style has its own advantages and disadvantages, and a discussion of those will be the topic of a future post.
What other types of hip end styles are you familiar with? Let us know in the comment section below.
Resources and Continuing Education for Structural Engineers
I’ll admit that I’m biased, but structural engineers have the best job in the world. We’re needed to create safe sound structures while factoring in the effects of environmental forces using a combination of physics and experience. It takes a really well rounded individual to do all of that.
In my opinion, the key to being a well rounded professional is to never stop learning or seeking out new resources in your industry. I thought I’d share with you some resources that may be helpful to you as a structural engineer, from my own experience:
Continuing Education Webinars
Attending webinars online is a great way to get Continuing Education credits you need. Webinars enable you to stay sharp on topics that are continually changing and that you may need to adapt to in our industry.
Some of the resources engineers at Simpson Strong-Tie go to for webinars and CECs include:
ACI – American Concrete Institute
AISC – American Institute of Steel Construction
ASCE – American Society of Civil Engineers
AWC – American Wood Council
CFSEI – Cold-Formed Steel Engineers Institute
NCSEA – National Council of Structural Engineers Association
SEAOSC – Structural Engineers Association of Southern California
Engineering Associations
Keeping in touch with fellow structural engineers means that you can talk shop and get some great advice about issues you face on the job. Some associations you can look into:
SEAINT- Structural Engineers Association – International
NCSEA- National Council of Structural Engineers Associations
SEAOC- Structural Engineers Association of California
SEAOSC- Structural Engineers Association of Southern California
SEAOCC- Structural Engineers Association of Central California
SEAOSD- Structural Engineers Association of San Diego
SEAU- Structural Engineers Association of Utah
ASCE- American Society Of Civil Engineers
ACI- American Concrete Institute
AISC- American Institute of Steel Construction
PCA- Portland Cement Association
PCI- Precast/Prestressed Concrete Institute
CRSI- Concrete Reinforcing Steel Institute
AISI- American Iron and Steel Institute
Simpson Strong-Tie also offers great software resources for structural engineers and other building industry professionals. What resources do you recommend? Let us know in the comments below.
New Holdown Requirements for the IRC® and IBC® Portal Frame Bracing Method
The IRC® contains several different narrow bracing methods that are made up of portal frames. One method that is useful if you are using intermittent wall bracing is the Method PFH Portal Frame with Holdowns. This method relies on low-deflection holdown anchorage at the bottom, and substantial nailing at the overlap of the sheathing and the header at the top to prevent overturning of the narrow panel. An identical method for use as wall bracing is in the Conventional Construction section in Chapter 23 of the IBC®. These portal frames were first included in the 2006 IBC and IRC.
The method was originally tested with straps clamped to a steel test bed to simulate the embedded holdown straps. The straps were nailed to the wood with enough nails to mimic a 4,200 lb. strap anchor. The original test report is APA T2002-70. At that time, the Simpson Strong-Tie® STHD14 had a published allowable load in excess of 4,200 lbs. based on then-current Acceptance Criteria, so hardware was available to construct this frame throughout the country. However, in 2008, ICC Evaluation Service developed a new acceptance criteria for embedded connectors, AC398, Acceptance Criteria for Cast-in-place Cold-formed Steel Connectors in Concrete for Light-frame Construction. This was in response to the changes in ACI 318 for anchors in concrete. When re-tested and evaluated using the new Acceptance Criteria, the allowable load for STHD14 was reduced below 4,200 lbs. for use in buildings designed for Seismic Design Categories C through F. The same thing happened to other manufacturers’ embedded holdown allowable loads. That made it impossible to properly construct this bracing method in those areas. In response to this, Simpson Strong-Tie worked with APA, the Engineered Wood Association, to design a new test that would determine if a lower capacity holdown could be used with this portal frame method. APA performed the testing at their Tacoma, Washington testing lab. Since the initial testing of the portal frames with the 4,200 lb. holdown was performed using the outdated SEAOSC protocol with an older testing rig that used a stiff beam above the wall, both the old tests with a simulated 4,200 lb. holdown and new tests with a simulated 3,500 lb. holdown were rerun in accordance with the current ASTM E2126 test method using the CUREe protocol. The test was published as Test Report T2012L-24. The tests showed little to no effect of reducing the holdown from 4,200 lbs. to 3,500 lbs. allowable load. Here is one of the graphs of the backbone curves comparing the two assemblies for a 16-inch wide, 10-foot tall portal frame.
With the testing complete, APA prepared and submitted code changes to both the 2012 International Building Code® and 2012 International Residential Code®. The IBC proposal is S291-12, and can be found on page 605 of the 2012 Proposed Changes to the International Building Code – Structural. The IRC proposal is RB311-13, and can be found on page 613 of the 2013 Proposed Changes to the International Residential Code-Building. With support from Simpson Strong-Tie, both of the proposals were approved. So in the 2015 IRC, bracing method PFH will require an embedded strap-type holdown with a minimum capacity of 3,500 lbs. instead of 4,200 lbs. The same will hold true for the Alternate Braced Wall Panel Adjacent to a Door or Window Opening bracing method in the 2015 IBC. APA also re-tested the portal frames with only two sill plates instead of three. This will allow the use of a 5/8” by 8” Titen HD® anchor as a retrofit anchor bolt. What are your thoughts? Let us know in the comments below.
Plated Wood Truss Design Responsibilities
When the opportunity presents itself, glance up at the ceiling. Do you ever wonder who the responsible parties were for the design and construction of the roof above? If you’re involved in the truss industry, there is no doubt you have. If not, it never hurts to be in the know. Since we spend a significant portion of our life under a roof, it helps to know a few facts about what’s over our heads.
Roofs built from prefabricated wood trusses used in light-frame and residential construction will be the focus of this blog post.
The current national design standard for metal plate connected wood truss construction is ANSI/TPI 1-2007, which is the referenced standard in the 2009 and 2012 IBC and IRC. So what are design responsibilities for wood trusses and why are they important? They are a series of responsibilities required by key parties for applications of trusses in the construction of a building. These key parties (Owner, Building Designer, Registered Design Professional, etc.) are important because each is required to produce pertinent information about the truss and truss system from its inception to erection and long in-service life.
As wood trusses have evolved, so have publications about their construction, quality and use. The first standard was published in 1960, with subsequent standards published periodically.
In 1995, the Truss Plate Institute (TPI) published ANSI/TPI 1-1995, which served as the first ANSI consensus-based national design standard for metal-plate connected wood truss construction. One of many new chapters established in ANSI/TPI 1-1995 was chapter 2, identifying design responsibilities. While early versions of ANSI/TPI 1 introduced design responsibilities, chapter 2 of ANSI/TPI -2007 has clarified and added areas of responsibility that are vital for today’s component industry. In addition, the 2007 edition defined responsibilities regarding temporary and permanent restraint and bracing, and special inspection requirements to long span trusses (any truss with a span of 60 feet or greater). These are just a few, yet critical additions to the standard.
Without clear definitions of responsibility, how would the industry know who specifies truss connections, or who provides bracing locations necessary to a roof assembly and its duration of service? Additionally, who determines if a project requires a truss submittal package, or the type of information it must provide? While these questions and more are answered in ANSI/TPI 1-2007, any provisions of the TPI 1 Design Responsibilities can be changed in the contract documents for a given project, so long as all parties are made aware of and agree to the revisions.
Ensuring all parties’ know and follow the design standard can help ensure a properly designed, manufactured and erected truss that will lead to a safe roof system. If you’re a component manufacturer, knowing what you’re responsible for and required to produce can get you out of a jam or better yet, help you avoid one altogether. Communication is key to the industry. The Commentary and Appendices of ANSI/TPI 1-2007 is available for web review: http://www.tpinst.org/technical-downloads
Do you know or want to know the answers to the above questions? Or perhaps think there are responsibilities that need to be clarified or added to future publications of ANSI/TPI 1? Let us know in the comment section below.
Wood Design Education Opportunities
Designing wood structures properly requires a broad knowledge base of a variety of materials and how they go together. However, it can often be difficult to find educational opportunities for designers to learn about wood design or keep up with new technologies on wood construction.
Fortunately, there are some unique chances this summer to increase your knowledge about wood as a construction material.
There is a short course titled Advanced Design Topics in Wood Construction Engineering, being held May 21 and 22 at Virginia Tech University in Blacksburg, VA. It is intended for designers, inspection professionals and builders that want to expand their general knowledge of wood as a building material and their knowledge of building design beyond the introductory level. The agenda includes sessions on Decay Processes, Design for Durability, and Insects that Attack Wood; Wood Shrinkage Issues in Construction; Lumber Grading Methods and Design Values; Design of Built-Up Beams and Columns; Glulam Beam Design; Evaluating Structural Capacity of Fire-Exposed Timber Beams and Columns; Multiple-Bolt Wood Connection Design; Basics of Diaphragm and Shear Wall Design; Post-Frame Building Design and Diaphragm/ Shear Wall Tests; Creep of Solid-Sawn Joists, I-Joists, and Floor Trusses; Design Considerations for Preventing Flat Roof Failures from Gravity Loads or Sustained Live Loads; Wood Truss Design Responsibilities; Wood Truss Repair Design Techniques; Permanent Truss Bracing Design Basics; and Lateral Design of Decks.
You can find more information about the Virginia Tech Short Course here. Web registration ended May 14, 2014; you can register by calling the Conference Registrar (540) 231–5182 up to the first day of the course.
If you feel like travelling, the World Conference on Timber Engineering (WCTE) will be held in Quebec City on August 10-14. WCTE is an international biannual event focusing on timber engineering, engineered wood products and design of timber structures. The conference theme is “Renaissance in Timber Construction.” Information on the conference can be found here.
But you don’t have to necessarily travel far to get quality training on wood design.
WoodWorks is a cooperative venture of major North American wood associations, research organizations and government agencies that aim to encourage and assist architects, engineers and others in the use of wood in non-residential and multi-family buildings. WoodWorks deliver knowledge to designers in three main ways: webinars, short 2-3 hour seminars and Wood Solutions Fairs. Upcoming webinars include Mixed Use Podium Design, Changes to Wood Design Standards and Healthy Buildings. Seminars scheduled for June focus on Cross Laminated Timber in California, Pennsylvania, Texas, and Washington. Finally, Wood Solutions Fairs are excellent all-day events where attendees can choose from more than 15 classes in six sessions throughout the day. The Fairs also include exhibits to allow for networking with building product manufacturers. Upcoming Wood Solutions Fairs are May 22 in Chicago, August 27 in Washington, DC, October 23 in Portland, Oregon, and November 12 in Arlington, Texas. Here is a full schedule of WoodWorks events.
If you just can’t get out of the office, or you don’t like to travel, there are still ways to keep up with the wood industry. Several groups offer webinars or self-study classes on various subjects.
WoodWorks, mentioned above, is a good resource. The American Wood Council (AWC) is the voice of North American traditional and engineered wood products, representing more than 75% of the industry. AWC’s engineers, technologists, scientists, and building code experts develop state-of-the-art engineering data, technology, and standards on structural wood products for use by design professionals, building officials, and wood products manufacturers to assure the safe and efficient design and use of wood structural components. AWC also provides technical, legal, and economic information about wood design, green building and manufacturing environmental regulations advocating for balanced government policies that sustain the wood products industry. AWC has begun offering regular webinars on various subjects with complimentary registration. Upcoming webinars include the AWC Prescriptive Residential Wood Deck Construction Guide on May 22, AWC Web-based Calculators and Other Resources on June 24, and Prescriptive and Engineering Design per the 2012 WFCM will be offered some time in the fall. Also, AWC has a comprehensive library of e-courses on their website as well as a helpdesk via email, info@awc.org.
In addition, the International Code Council offers a variety of online training classes as part of their ICC Campus Online. Most have a nominal fee, but several are available free of charge. They have a Catalog of Classes on their website.
And finally, don’t forget about resources available from Simpson Strong-Tie. These resources range from full and half-day workshops offered at various locations throughout the country to online courses you can take from the comfort of your own office. Many of these courses come with CEU credits and some also offer AIA credits. And if you would like a personal visit, such as a lunch-and-learn, contact your local sales rep, or one of our regional offices and ask to speak with the training manager.
Do you know of any other good events coming up? Keep the conversation going.
Wide Flange Beams in Light Frame Construction
How did that beam get so big? This is what I had to ask myself when I finished sizing and detailing a steel beam that was supposed to fit within the floor joist depth for a flush ceiling. We were removing an unreinforced masonry bearing wall and installing a new wide flange beam to support the existing floor joists as part of a seismic retrofit and remodel. Since the floor joists spliced over the existing bearing wall, it would have been much easier to simply install a new beam below the joists.
The architect did not want the beam installed below the framing, as it would protrude too much. Steel design offers multiple wide flange sections that will work for a given loading. For this particular design, I could use a W24x55, a W16x67 or a W14x90. Each has about the same strength (section modulus, Sxx) and stiffness (moment of inertia, Ixx). Without constraints, you would select the lightest section that works. Space limitations that require a shallower beam result in increased beam weight (and cost).
I proposed two solutions for installing the beam in the floor space and hanging the joists off a nailer. One option allowed the steel beam to extend below the floor joists, while the other used a heavier, shallower beam to fit within the space. The owner wanted a flat ceiling and did not mind the added cost for the beam, which weighed about 60% more than the optimum beam size.
Regardless of space constraints for the design of a steel beam, structural engineers need to specify an appropriate hanger for connecting to the steel beam. Simpson Strong-Tie has many suitable top flange hangers. Most common are hangers that are attached to a wood nailer. Many top flange hangers may also be welded to the beam. Not every nailer solution is rated for uplift, so choose a hanger that meets your requirements. Uplift for welded hangers is addressed in a Simpson Strong-Tie® technical bulletin, T-C-WELDUPLFT2.
Installers may also wish to connect the hangers using powder-actuated fasteners in lieu of welding. Allowable loads for several of our top flange hangers are addressed in current catalog.
Of course, as with all of our hanger loads, we created those loads by running a lot of tests.
What are your thoughts on beam selection and installation? Let us know in the comments below.
How Social Media Can Help Structural Engineers With Their Business
I am pleased to introduce you to one of our newest members of the Simpson Strong-Tie team, Minara El-Rahman. She is our Social Media Manager here at Simpson Strong-Tie. Minara has extensive experience with digital/mobile marketing, social media marketing, engaging with online influencers and blogging. As structural engineers use online resources more and more, she will be contributing to the Structural Engineering blog to help you navigate using them.
The last time we wrote about social media, we gave tips on how structural engineers can use social media to be better at their jobs. But we also believe that you can use social media to grow your business. The more touch points that you can have with your existing and potential clients, the better chance you have at forging a relationship with them. That’s what social media is all about, it is about engaging and fostering a relationship with others: whether it is with an individual, company, brand or your old college buddies.Continue Reading
How Heavy Are Your Calculations?
Designing my first building was truly a learning experience. I remember one event in particular when I determined the required thickness for a steel column base plate. That day I wrote “1.5-inch thk. min.” on my calc pad and months later while out walking the job, I got to see that 1.5-inch thick plate in the flesh. Let me tell you, it was much thicker and heavier in-person than on my calc pad. This eye-opening experience – the realization that what you’re designing isn’t just a word or a number, but rather a physical object with width, height, length and weight – is something every structural engineer goes through early in their career. Designing something on paper doesn’t convey those physical properties very well.Continue Reading