A New Way to See Whether FRP Is Right for Your Project

This week’s post was written by Griff Shapack, FRP Design Engineer at Simpson Strong-Tie. 

Specifying our Composite Strengthening Systems™ (CSS) is unlike choosing any other product we offer. In light of the unique variables involved with selecting and using fiber-reinforced polymer (FRP) solutions, we encourage you to leverage our expertise to help with your FRP strengthening designs. To get started, we first need to determine whether FRP is right for your project. The fastest way to do that is for you to fill out our Design Questionnaire. Our new Excel-based questionnaire collects your project information and helps you use the existing capacity check to evaluate whether or not FRP is suitable for your project per the requirements of ACI 562-16 Section 5.5.2. After the feasibility study, the questionnaire creates input sheets specifically for your project.

Getting Started

Step 1

Open the FRP Design Questionnaire spreadsheet using Microsoft Excel. If a yellow warning appears at the top of the sheet, click “Enable Content” to ensure that the workbook will function properly. You will start on the worksheet tab named “Main”. “Main” will be the only worksheet tab when you begin, but more worksheet tabs will be created as you use the spreadsheet.

Step 2

Enter the project information and your contact information in Section 1 of the worksheet. The contact information should be for the Designer that you would like Simpson Strong-Tie to work with for this project’s FRP design. See Figure 1.

Step 3

Enter the FRP strengthening information in Section 2 of the worksheet. If the application will require an existing capacity check, an input form requesting the information needed for the check will appear in Section 3 of the worksheet.

Figure 1. Project information and FRP strengthening information.

Step 4                                                                                                                        

For members that support gravity loads, an existing capacity check must be performed to verify that FRP strengthening is suitable before a design can be generated. For these members, the spreadsheet will generate a check table for you in Section 3 of the worksheet. Enter the number of members to be checked and the dead load (D), live load (L) and snow load (S) for each member. Use consistent units for the input. See Figure 2. The spreadsheet will calculate the demand-to-capacity ratio (DCR) for each member. The ratio must be less than or equal to 1.0.

  1. A result of “OK” means the existing capacity check is passed. Proceed to Step 5 below.
  2. A result of “NG” (no good) means the existing capacity check is failed and FRP strengthening is not likely to be suitable. However, consider contacting Simpson Strong-Tie about your design condition to ensure that this is the case.

Figure 2. Existing capacity check.

Step 5

You are now ready to create an element input worksheet for those members that passed the existing capacity check. Click “FRP Questionnaire” from the Excel menu bar. Then click the “Input Sheet” button in the ribbon bar. See Figure 3.

Figure 3. “Input Sheet” button.

This will create an element input worksheet as a new worksheet tab. See Figure 4.

Figure 4. Element input worksheet.

Enter the number of elements to be checked and fill in the design information for each member. The “No. of elements” cell features a drop-down menu with the numbers 1–5, but any number can be typed into the cell. (Each member should have passed the existing capacity check in Step 4.) See Figure 5.   

Figure 5. Element input worksheet.

Step 6

If you would like to add different member types that need to be strengthened, click “Another Type of Strengthening” button in the ribbon bar. See Figure 6. This will create a new “Main” worksheet. Repeat the steps above, until all strengthening types and member data have been entered.

Figure 6. “Another Type of Strengthening” button.

 Step 7

When you have finished inputting all required data, save the spreadsheet file and email it to css@strongtie.com. You should expect confirmation of receipt from us within one business day.

From there, if FRP is a viable option, you can decide to utilize our no-cost, no-obligation design services. Our team will design a unique solution specifying the most cost-effective CSS products that address your particular needs. The design calculations, drawings, notes and specifications are prepared by Simpson Strong-Tie Engineering Services and can then be incorporated into the design documents that you submit to the building official.

Don’t know which FRP solution is the right one for you? We do. Give our new Design Questionnaire a try, and let us be your partner during the project design phase. Learn more at strongtie.com/products/rps/css/frp-engineering-design.

Advanced FRP Design Principles

In this free webinar we will dive into some very important considerations including the latest industry standards, material properties and key governing limits when designing with FRP.


Beat Building Drift with the New DSSCB Drift Strut Slide Connector from Simpson Strong-Tie

This week’s post was written by Clifton MelcherSenior Product Manager at Simpson Strong-Tie.

Structural engineers concerned with building envelopes are always looking for better solutions that help isolate the cladding from the primary structure in conditions where large building drift is a concern. Simpson Strong-Tie has an answer with a unique and innovative solution, the new DSSCB (drift strut sliding clip bypass).

The DSSCB is used to anchor cold-formed steel framing to the primary structure in bypass applications. The DSSCB is a clip that slides inside standard struts that most engineers and contractors are already familiar with. These struts will typically be attached to structural steel. However, there is also a cast-in-place strut option referred to as a strut insert. Many different manufacturers of these struts exist, but three common manufacturers are Unistrut®, PHD and B-line. The strut and strut insert requirements for the DSSCB can be found in the Simpson Strong-Tie DSSCB flier (F-CF-DSSCB17).

The DSSCB has many design features that make it easy to use, cost-effective and designer-friendly.

  • The DSSCB clip has uniquely formed inserts that twist into place easily with minimal friction
  • The clip features squaring flanges that help keep the clip square inside the strut
  • Shoulder screws (included) prevent over-drilling and increase overall capacity
  • Pre-engineered design offers clip, strut and anchorage solutions
  • Pre-punched slots provide a full 1″ of both upward and downward deflection
  • Sight lines facilitate proper screw placement

The DSSCB is also a hybrid clip and accompanies both slide applications as well as fixed applications. In addition to vertical slots, the clip also has round circular holes for fixed-clip conditions. This will make the clip more versatile and limit inventory.

Another great use for this product is for panelized construction. The DSSCB makes it a snap to anchor finished panels to the slab without having to waste time drilling and installing anchors. Locking panels into place is also simple with a DSHS connector clip that can be easily slid into place and attached with only one (1) #10 screw.

Accommodating for building drift and commercial panel construction just got easier with the Simpson Strong-Tie DSSCB!

Design Example

Load required at bypass slide condition attached to steel with ASD reactions of 450 lb. tension (F2) and 422 lb. compression (F3) – based on CFS DesignerTM software or hand calculations

Stud member = 600S162-43 33 ksi at 16″ o.c. – based on CFS Designer software or hand calculations

Per page 4 of the DSSCB flier (F-CF-DSSCB17), allowable F2 = 785 lb. and F3 = 940 lb. for slide-clip connector (shown below)

Per page 7 of the DSSCB flier (F-CF-DSSCB17) allowable loads of F2 = 475 lb. and F3 = 2,540 lb. for strut allowable anchorage with 1″ weld at 12″ o.c. using a 13/16″ strut (shown below)

Note that, at a strut splice (if required), maximum load is not to exceed F2 of 865 lb. per note 6 on page 7 (shown below)

6.  For any connector occuring within 2″ of channel strut splice, load not to exceed — F= 865 lb. and F= 785 lb.

Check connector and strut/anchorage:

F2 (tension):                           Pmax = 450/ minimum of (785,475) = 0.95 < 1 ok

F3 (compression):               Pmax = 422/ minimum of (940,2540) = 0.45 < 1 ok

FAQs:

Q: How are the products sold?

A: The clips are sold in kits of 25. For the DSSCB43 and DSSCB46, one polybag of 83 screws is included. For the DSSCB48, two 55 screw polybags are included. The DSHS will be sold separately from the clips and come in bags of 100. The struts will not be sold by Simpson Strong-Tie.

Q: Can I use the 1 5/8″ x 1 5/8″ strut for the fixed-clip application?

A: No, the fixed-clip application was tested only with the 13/16″ x 1 5/8″ strut. The 1 5/8″ x 1 5/8″ strut would overhang more, which we calculate could reduce capacities.

Q: When should I use the DSHS clip?

A: The DSHS clip should be used where you want to fix the clip in place in the F1 (in-plane) direction. This clip will most likely be used for panelizing, but could be used for stick framing as well when adjustment is required before locking the clip in place.

Q: Why are there two tables that I need to use to determine my connector capacity?

A: One table is for the capacity of the clip, and the other table is for the capacity of the strut/anchorage. Two tables give the designer more flexibility in the design as well as an understanding of what is controlling the failure.

Q: How do I accommodate load requirements at a strut splice?

A: Note 6 to the Strut Channel Allowable Anchorage Loads to Steel table states the capacity of the strut with a clip directly at the splice. The values are based on assembly testing. Refer to page 7 of the flier.

Q: How do I accommodate load requirements at the strut end?

A: Note 10 to the Strut Channel Allowable Anchorage Loads to Steel table states that the connector load is to be located a minimum of 2″ from the end of the strut channel. Note 2 to the Concrete Insert Allowable Load Embedded to Concrete table gives a reduction capacity for end conditions. Reference pages 7 and 8 of the flier.

Q: Why do we show an F1 load on a drift clip?

A: The drift clip without the DSHS does not support any load in F1 direction. F1 load is only supported if a DSHS clip is used in conjunction with the DSSCB clip. This is also noted (note 4) on the DSSCB Allowable Slide-Clip Connector Loads and the DSSCB Allowable Fixed-Clip Connector Loads tables. Refer to pages 4 and 6 of the flier.

Q: How do I accommodate higher concentrated loads at jambs exceeding my typical stud loads?

A: Note 7 to the Strut Channel Allowable Anchorage Load to Steel table gives the capacity of the strut/anchorage if the strut is welded directly at the clip. Refer to page 7 of the  flier.

Q: Can I drive PAFs into my strut?

A: No. The shot pin tool will not fit inside the strut channel.

Q: If I want to attach my strut to the steel edge angle with screws, what brand should I use?

A: Simpson Strong-Tie makes great fasteners, and we would recommend these fasteners (#12-24 Strong-Drive® Self-Drilling X Metal screw). However, you can use any brand fastener provided they meet our Pss and Pts capacities minimum nominal strength values in General Notes for Allowable Connector Load Tables on page 8 of the flier.

Q: At a double-stud condition, is it acceptable to double the capacity if I use two (2) clips?

A: It is acceptable to double the capacity of the DSSCB slide-clip or fixed-clip table loads (pages 4 and 6 in flier). However, the load should not exceed the load listed in the Strut Channel Allowable Anchorage Loads to Steel table (page 7 in flier). If a load is exceeded, please follow note 7 on page 7 of the flier by adding a weld connection directly at the concentrated load. This will allow you to have a wider anchor spacing for your typical studs and only reinforce the higher concentrated loads with connections directly at these locations.

Introducing the New and Improved Simpson Strong-Tie Strong-Wall® Bracing Selector

This week’s post was written by Caleb Knudson, R&D Engineer at Simpson Strong-Tie.

It’s been said that the World Wide Web is the wave of the future. Okay, maybe this is slightly outdated news, as it’s been 25 years since Bill Gates penned his internet tidal-wave memorandum, but it’s a good lead-in to this week’s blog topic – web apps. More specifically, those apps that have been developed to address the wall-bracing requirements defined in the International Residential Code® (IRC). Designers and engineers have no doubt noticed that over the last several code cycles, the wall-bracing provisions in the IRC have become increasingly complex. To help navigate these requirements and calculate the required bracing length for a given wall line, Simpson Strong-Tie introduced the Wall-Bracing-Length Calculator (WBLC) a few years back, as discussed in an earlier blog post. I’ll also mention that the WBLC has since been updated to the 2015 IRC.

Those familiar with the wall-bracing provisions in the IRC know that there are twelve intermittent wall-bracing methods and four continuous-sheathing methods to address wall-bracing requirements. Each of these methods may be used in most applications, and, while some provide advantages over others, the code-based methods provide Designers with quite a bit of flexibility. However, there may be cases where the site-specific conditions are beyond the scope of the IRC, or there just isn’t enough available full-height wall space to accommodate the required wall-bracing length. These cases are most likely to occur at large window openings or at garage fronts.

Let’s take the following example of a house on Lake Washington – assuming the house is being designed in accordance with the IRC. Presumably, one might prefer to have unobstructed lake views, which of course means lots of large picture windows and not much room left for braced wall panels. Let’s also suppose you’ve got a brand-new Chris Craft that you’d like to protect against the weather when it’s not in the water – this means wide garage doors and, again, not much room for conventional wall bracing.

So what do we do now?

Thankfully, the International Residential Code provides some guidance. Section R301.1.3 states that when a building, or portion thereof, is outside the scope of the IRC, the element(s) may be designed in accordance with accepted engineering practice. The code goes on to state that the extent of the design shall be such that the engineered element(s) are compatible with the performance of conventional methods prescribed in the code. That creates some additional options for our tool box. We could design a site-built shearwall; however, due to aspect-ratio limitations defined in the Special Design Provisions for Wind and Seismic (SDPWS), we still may not be able to get the lake views and wide garage we want. The next option, and one we’ll focus on here, is the code-approved prefabricated Simpson Strong-Tie® Strong-Wall® shearwall.

In an earlier blog post, as previously mentioned, we introduced the Strong-Wall Bracing Selector (SWBS) and defined just how we determine equivalence to conventional bracing methods. We further described the benefit of using the selector in conjunction with the Wall-Bracing-Length Calculator (WBLC). To refresh your memory, when Designers start with the WBLC to determine required wall-bracing-lengths for up to seven parallel wall lines, they can export those bracing lengths as well as project and jobsite information directly to the SWBS with the click of a button. The SWBS will then provide a list of Strong-Wall panels that provide an equivalent bracing length, evaluate their anchorage requirements, and return a list of pre-engineered anchor solutions for a variety of foundation types.

On to the present: We just launched the Strong-Wall Bracing Selector web app version 2.0, and there are a few new features worth noting.

First, I’ll mention that all Strong-Wall solutions have been evaluated according to the 2015 I-Codes. Next, and hopefully this doesn’t come as too much of a surprise, the original wood Strong-Wall shearwall (SW) is being phased out with guaranteed availability through December 31, 2018. In light of this planned obsolescence, we have removed the SW solutions from the latest version of the bracing selector.

Here’s the good news – and this is big: We’ve now added the new Strong-Wall wood shearwall (WSW) to the app and recommend this as a replacement for the SW in all applications. In the interim, while the original wall is still available, version 1.0 of the bracing selector app may be used if an SW bracing solution is required.

Lastly, we’ve provided the Designer with a bit more flexibility and control over the Strong-Wall bracing solutions provided by the app. If you recall, version 1.0 provided a solution using the minimum possible number of Strong-Wall panels to satisfy the bracing length requirement. We’ve changed that in version 2.0; Designers may still select a solution using the minimum number of panels, but they may also select the exact number of Strong-Wall panels to satisfy their wall-bracing-length requirements. Typically, it’s desirable to address the bracing requirement with the minimum number of Strong-Wall shearwall panels possible. Sometimes, however, it may be advantageous to increase the number of panels used, in order to decrease the Strong-Wall panel width used for a solution or to reduce anchorage requirements, i.e., lesser footing dimensions and anchor embedment depths. Stated a little differently, we’re providing the option to find the right balance between the braced wall panel design and the anchorage design – i.e., the Goldilocks zone for prescriptive wall bracing.

So now that we’ve reviewed just why a Designer may need to specify a Strong-Wall shearwall in prescriptive applications and how the Wall-Bracing-Length Calculator and Strong-Wall Bracing Selector web apps help to navigate this process, we’re interested to see what you think. Is there any additional functionality that you’d like to see in the future, or are these apps just right for your design needs? Let us know in the comments below.

Q&A About CFS Designer™ Software

I recently had the pleasure of presenting a webinar with Rob Madsen, PE, of Devco Engineering on our CFS Designer software, “Increase Productivity in Your Cold-Formed Steel Design Projects.” The webinar took place on September 28, and a recording is available online on our training website for anyone who wasn’t able to join us. Viewing the recording (and completing the associated test) qualifies for continuing education units and professional development hours. The webinar covers how to use the CFS Designer software to design complex loading conditions for beams, wall studs, walls with openings, and stacked walls using cold-formed steel studs, tracks, built-up sections, and even custom shapes. We received some excellent questions during the webinar, but due to time constraints were only able to answer a few during the live webinar. Rob and I did get a chance to answer all the questions in a Q&A document from which I’d like to share some excerpts. The complete Q&A webinar list can be accessed here, or through the online recording.

Where can I download the CFS Designer program?

Please visit strongtie.com/cfsdesigner to download a free 14-day trial version of the software or to purchase a license. Webinar attendees should check their email for a special discount code. There are different licensing options based on the number of users.

Is the price for the software an annual subscription fee or is it a one-time purchase price? Is there any maintenance cost?

There’s no annual maintenance fee or subscription fee. You pay only a one-time fee for the license. CFS Designer is based on an update-and-upgrade program. All updates to the program are free to licensed users and occur every few months to correct software bugs and add functionality. Upgrades, which include new design modules and updated code information, will require an additional purchase. Simpson Strong-Tie anticipates releasing upgrades on a two-year cycle, and the next upgrade has a projected release of early 2019. If you elect not to upgrade your version of the software, the current version you have will still work, but will not have the new upgrade features.

Is CFS Designer fully compliant with AISI S100-12?

CFS Designer is compliant with AISI S100-12. You can also access earlier versions of the AISI Specification in CFS Designer by selecting Project Settings/Code and selecting the version.

Are load inputs in ASD or LRFD? Do the load combination factors have to be applied prior to entering loads in the program? Should factored or unfactored loads be input?

The current software is all in ASD (allowable strength design). The next upgrade version will feature up to eight stories of stacked x-bracing and shearwalls, which will be in LRFD. Everything else will be in ASD. The stacked x-brace and shearwalls will be LRFD because of the ACI requirements for concrete. We will also make it much more clear in this version which input is ASD and which is LRFD.

What is a web stiffener? How would you use one at a stud, header, or jamb?

A web stiffener is typically a stud or track piece that is used to support the wall stud or joist from crippling at a point load or bearing support. There are different ways to design a stiffener at different locations. Some examples include using a cut piece of stud or track attached to the stud or using a clip attached to the beam. Essentially, a web stiffener is a member that is added to the stud to help stiffen the stud from crippling.

Does this program take into consideration the cold work of forming in the design/analysis?

Yes, per AISI the program’s Project Settings default is to include cold work of forming in the design and analysis.

We generally try to size our cold-formed members to avoid the need for web stiffeners, just to save on construction and material costs. Something that helps quite a bit with the web bending and crippling calc is the bearing length. Are there code requirements for bearing lengths, or is this simply based on how much bearing we anticipate the member to have at its supports?

There are no specific code requirements for calculating bearing length for web crippling; the calculation is usually based on engineering judgment and connection detailing to determine how much bearing there will be at the support. A reasonable bearing length may be the length of the connection clip you are using for the attachment. Since web crippling is a “bearing” phenomenon, where attachments are made through the web, provided the attachment is not isolated near a flange, you may not need to consider web crippling. For stud-to-track types of connections, it’s common to use the track leg length as the bearing length.

Does this software give any stud-to-stud connection calculation like stud tearing and shearing? Checks?

The studs are designed per the AISI code for shear, moment, web crippling, axial load, and the related code-required interactions. Net-section rupture near connections is not checked by the CFS Designer™ software.

What is the difference between flexural bracing and axial bracing?

Flexural bracing is bracing that is used to increase the moment capacity of the stud, and axial bracing is bracing that is used to increase the axial capacity of the stud. These might be the same for your design, but we have given the user the ability to designate different spacings.

Do you have recommendations for how to properly terminate bridging at the end of the wall?

We agree that termination of bracing is often overlooked by engineers and should definitely be considered in design. Accumulation of bridging forces should also be considered. AISI S100-12, D3.3 and AISI S240-15 D3.4 provide methods of estimating brace forces. Simpson Strong-Tie has provided some suggestion in our cold-formed steel typical details sheets that show our SFC clip as one method to properly terminate a line of bridging.

Can the kicker connection be used on the underside of concrete fill over metal deck?

Yes! The SJC kicker connection has been tested and code listed to support diagonal brace loads. Simpson Strong-Tie has also provided a wide range of anchorage solutions for the kicker application that include connecting to the underside of concrete fill over metal deck. Concrete over metal deck may be normal weight or sand-lightweight with f’c of 3,000 psi minimum and 2.5″ minimum slab height above upper flute. Minimum deck flute height is 1.5″ (distance from top flute to bottom flute). Please visit strongtie.com for more information and design tables.

Why do some engineers use steel posts welded to a base plate for low wall applications?

For walls that are not top-supported, some Designers use a welded steel post at a certain spacing and infill with cold-formed steel studs and a top track. Simpson Strong-Tie has developed an innovative moment-capacity connection called the RCKW rigid kneewall kit, which can support many of these same conditions using cold-formed steel studs and eliminate the need for structural steel.

Are there any plans to expand the software capabilities?

We have a long list of enhancements and additions for the software and will continue to make the software more efficient, more user friendly, and with additional design capabilities.

Thanks again to everyone who joined us for the webinar and sent us questions. For complete information regarding specific products suitable to your unique situation or condition, please visit strongtie.com/cfs or call your local Simpson Strong-Tie cold-formed steel specialist at (800) 999-5099.

The Top 5 Helpful Tips for Using CFS Designer™ to Optimize Your Workflows

Back in April of last year, I had the opportunity to show how our new CFS Designer software  could help structural engineers “go lean” in their design process by eliminating repetitive tasks (while still meeting required design standards, of course!). Since then, I’ve had the opportunity to visit with hundreds of engineers in person to teach them about CFS Designer and how it can help them improve and optimize their workflows. As a power user of the software, I want to share my top tips for letting CFS Designer help you save the maximum amount of time.

Tip #1. You need to create only one design file for each project.
CFS Designer has to generate lots of code-compliant designs quickly, but that doesn’t mean you need to end up with dozens of unrecognizable file names on your desktop. The software includes a very handy WorkSpace area in the lower left-hand area of the screen that enables you to save all your wall, jamb, header, and general interaction designs in a single project space. This means that you will be saving only ONE file for each project, a feature that can save you a lot of confusion over time.

Figure 1. The orange box is highlighting the file name (which doubles as the Project Name on the summary reports), which shows up at the top of the WorkSpace area. In this example, I’ve added just one beam/stud model for the sake of simplicity.

Tip #2. Quickly duplicate similar wall sections or design types by right-clicking on the model name in the WorkSpace.
On cold-formed steel projects, there are often very similar wall sections or jambs that you’ll need to design. They may have slightly different parapet heights, different loading or different wall widths. Instead of starting from scratch and creating a new section every time, CFS Designer allows you to right-click on any existing design. The right-click action brings up a “Duplicate” pop-up which lets you create an identical model in your WorkSpace. You then have the ability to change the model name, make slight modifications, and then re-save your project to see it show up as a new model in the WorkSpace area.

Figure 2. Here’s where to right-click in order to get the “Duplicate” pop-up to appear.

Tip #3. Expand the “Member Forces” and “Connection Summary” sub-menus in the Beam Design module to get real-time updates of the reaction loads, member stresses and connection solutions.
A critical area of member design is the reaction points, because it doesn’t really matter whether your cold-formed steel member is adequately designed if the connection points don’t have a solution. Many engineers I met with thought they had to click on the “Summary Report” button every time they wanted to know the reaction forces, waiting anywhere from 10 to 15 seconds for the PDF file to load and then having to scroll through to find the correct section. Thankfully, there’s a much quicker way to view the reactions. CFS Designer instantly updates the reaction values on the design screen, but the onscreen menus that have this useful information need to be opened up first. Within the Beam Design module, click on the small down arrows to the left of “Member Forces” and “Connection Summary,” and that will expand these two useful sections and display the design information without your having to wait and generate the output. On a related note, another useful area to keep an eye on during design is the very bottom of the screen, where green text will let you know when your maximum member stress and web crippling check are compliant, red text will alert you if your member design is insufficient, and the deflection ratio limit is always displayed.

Figure 3. Here’s where to find the collapsed “Member Forces” and “Connection Summary” menus.

Figure 4. Click on the arrows to the left of the menu titles to see your important design information in detail.

Tip #4. Use the “WorkSpace Report” button for a one-click method of combining ALL the individual summary pages into a single PDF file.
After you’re done generating all your different models and saving them to your WorkSpace, you’re probably going to want to generate the output files you can print and add to your calculation package for submittal. One engineer I met with a couple of years ago told me that this was the most dreaded step because it meant she had to open each model, click on the “Summary Report” button, wait those 10–15 seconds for the PDF file to generate, and then print it out or save it. For large projects, this would need to occur 20–30 times – yikes! Thankfully, a huge part of the development of CFS Designer relies on feedback such as this to help Simpson Strong-Tie continuously improve the program’s functionality. The latest version of CFS Designer introduces a “WorkSpace Report” button, which takes a single click to create all of the summary reports for each model type, saved in a single PDF file.

Figure 5. Be sure to use the “WorkSpace Report” button to save yourself a ton of time generating all your printable output.

Tip #5. Use the onscreen tip pop-ups. Small gray question mark icons are strategically placed throughout CFS Designer to offer helpful tips and tricks for specific input boxes.
Structural engineers are expected to know a lot, but it isn’t always necessary to remember all the details if you know where to look them up. Because the information requested by some of the input boxes may not be completely self-evident, we built in some handy pop-up tips to help out. A small gray circle with a question mark inside makes its appearance next to input boxes. Hovering your mouse over one of these question marks will cause an info box to appear, letting you know what information is required, what code section to reference, or what design methodology is being used. I have found these pop-up tips to be immensely helpful, especially in conjunction with the program’s User’s Manual (located under the Help menu, at the top of the program).

Figure 6. I got this box to pop up by hovering over the question mark next to the “Load Modifiers” section of the Beam Input module. If you search for “Load Modifier” in the User’s Manual, it will direct you to the relevant AISI code section.

I’ve had fun sharing some of my top tips with everyone today, but there is a great opportunity coming up to learn even more about our CFS Designer software from one of the original developers of the software. Join me and Rob Madsen, P.E., Senior Project Engineer from Devco Engineering, for a one-hour live demo of the software and connection solutions. Rob has been described as one of the premier structural engineers in the cold-formed steel design arena, and he will walk you through detailed wall stud, jamb, header and stacked wall design examples using CFS Designer. I’ll be presenting on the innovative, tested and code-listed product solutions that Designers can use to save time in addressing the critical connection points in CFS design. We hope you can join us for the live demo, but if you have other commitments at that time, a recording of the webinar will be made available on our website for your viewing convenience. The course will also earn professional development hours (PDHs) and continuing education units (CEUs) for any folks who need credits to renew their professional licenses.

Bonus Tip: Sign up for our upcoming CFS Designer™ webinar on Thursday, September 28!

Further Reading

For additional information or articles of interest, check out these available resources:

    • AISIStandards – A free download of all the cold-formed steel framing standards adopted by the 2015 International Building Code.

 

    • CFSEI – The Cold-Formed Steel Engineering Institute, an incredibly useful technical and professional resource for Designers of cold-formed steel structures, with a huge library of technical notes.

 

 

 

Q&A About Advanced FRP Strengthening Design Principles

Our thoughts go out to everyone affected by Hurricane Harvey and this disaster in Texas. To help with relief efforts we are donating $50,000 to the American Red Cross Disaster Relief Fund. Employees at our Houston warehouse are safe and the employees from our McKinney branch will be doing as much as they can to help with relief efforts.

This week’s post was written by Griff Shapack, PE. FRP Design Engineer at Simpson Strong-Tie.

On July 25, 2017, Simpson Strong-Tie hosted the second interactive webinar in the Simpson Strong-Tie FRP Best Practices Series, “Advanced FRP Design Principles,” in which Kevin Davenport, P.E. – one of our Field Engineering Managers – and I discussed the best practices for fiber-reinforced polymer (FRP) strengthening design. The webinar examines the latest industry standards, proper use of material properties, and key governing limits when designing with FRP and discusses the assistance and support Simpson Strong-Tie Engineering Services offers from initial project assessment to installation. Watch the on-demand webinar and earn PDH and CEU credits here.

During the live webinar, we had the pleasure of taking questions from attendees during the Q&A session. Here is a curated selection of Q&A from that session:

While I see how you improve the flexural capacity of a beam, how do you increase its shear capacity to match new moment strength?

ACI 440.2R recommends checking the element for shear if FRP is used to increase flexural strength. U-wraps can be used to provide shear strengthening of a beam.

Are there any “pre-check” serviceability checks (deflection, vibration, etc.) similar to the ACI 440 strength check that you recommend when considering the use of FRP?

ACI 440.2R contains a few serviceability checks on the concrete, rebar and FRP that can be performed once you have designed a preliminary strengthening solution.

Are these strengthening limits for gravity loads only? What about for a seismic load combination?

Yes, the strengthening limits are just for gravity loading. Seismic loading does not require an existing capacity check as it is highly unlikely for the FRP to be damaged during a lateral event.

Did Simpson Strong-Tie perform load tests on FRP repaired timber piles?

We are currently testing our FRP products as applied to timber piles at West Virginia University. We have also implemented a full-scale testing program on damaged timber piles at our own lab using our FX-70® fiberglass jacket system.

Will any of your seminars cover FRP and CMU? Seismic applications?

Yes, these are topics we are considering for future webinars.

The 0.6 limit for compressive stress can be very limiting. Can this value be evaluated on a case-by-case basis? The Euro code allows higher limits on compressive stress?

Our designers will report this value, along with the section addressing this check from ACI 440.2R, to the EOR and discuss whether the EOR would like to proceed with the FRP strengthening on his or her project.

Which engineer (EOR or Delegated Engineer) is responsible for specifying the scope of special inspections?

We provide a draft FRP specification to the EOR to use in their final determination of the special inspection requirements for a project. It’s in the owner’s best interest to hire a qualified special inspection agency on an FRP installation project.

For complete information regarding specific products suitable to your unique situation or condition, please visit strongtie.com/css or call your local Simpson Strong-Tie RPS specialist at (800) 999-5099.

Advanced FRP Design Principles

In this free webinar we will dive into some very important considerations including the latest industry standards, material properties and key governing limits when designing with FRP.


Why Fire-Rated Hangers Are Required in Type III Wood-Frame Buildings

One of the first mixed-use designs I worked on as a consulting structural engineer was a four-story wood-frame building over two levels of parking. Designing the main lateral-force-resisting system with plywood shearwalls was a challenge for this project that required new details to meet the high design loads. The high overturning forces were resisted using the Simpson Strong-Tie® Strong-Rod™ anchor tiedown system, which incorporates high-strength rods, bearing plates and shrinkage compensation devices.

At the time, these construction details using Strong-Rod systems and high- load shearwall diaphragms were new, innovative concepts. However, this method of construction rapidly became commonplace as intense demand for housing fueled the trend toward denser, mixed-use developments in downtown areas. I discussed the trend toward taller, denser developments in this post.

A more recent trend in wood-frame construction has been the shift to Type III wood-frame construction, which allows designs up to five stories. To help educate designers on some of the nuances of Type III wood-frame construction and provide guidance on meeting the associated code requirements, we reached out to Bruce Lindsey, the South Atlantic Regional Director for WoodWorks. Bruce wrote a two-part article entitled Fire Protection Considerations with Five-Story Wood-Frame BuildingsPart 1 and Part 2. This post will go into more detail on connecting the floor system to the two-hour fire-rated exterior walls and discuss our new DG series joist hangers that are specially designed for this application.

As a structural engineer, I was aware of fire requirements mostly because I needed to account for the weight of fire sprinklers, added layers of gypsum board, fire-proofing on steel, or concrete slab thickness in my design. While the increased loads can affect the vertical- and lateral-force-resisting systems, I seldom needed to change the details and connections in my designs.

The exterior walls in Type III wood-frame construction require fire-retardant-treated (FRT) lumber with two layers of gypsum board to provide a two-hour fire rating. There are many established fire-rated floor and wall assemblies available. The challenge, as discussed in Part 2 of Mr. Lindsey’s post, is detailing the intersections between the floor and wall systems. Connecting the floor framing to the exterior walls in Type III construction requires careful detailing to transfer the vertical loads without compromising the two-hour fire rating of the wall assembly.

Below is a summary of some of the possible fire wall connections as discussed in Mr. Lindsey’s previous blog posts.

A solid header on top of the wall that has adequate thickness to provide a two-hour rating through its charring capability. The cost and availability of solid rim board material should be considered.

A continuous 2x ledger or blocking to provide one hour of fire resistance. The second hour of resistance is provided by ceiling gypsum board. Some jurisdictions object to this detail over concerns about a fire starting within the floor cavity.

Some jurisdictions interpret the two-hour exterior wall requirement as applying only to the wall and not the floor. In such jurisdictions, designers can sometimes use standard platform framing in Type III construction.

A variation where the ledger can be installed over two layers of gypsum board. Simpson Strong-Tie has tested and published values for ledger connections over gypsum board using our SDWH and SDWC fasteners. The testing of these fasteners was discussed in our Spanning the Gap post from earlier this year.

In this detail, one hour of fire resistance is provided by a single layer of gypsum board running the full height of the wall with a hanger installed over the gypsum board. The second hour of resistance is provided by the ceiling gypsum board.

A variation of this detail is our DU/DHU series of drywall hangers that are installed over two layers of gypsum board. These were addressed in this post.

Designs using hangers or ledgers installed over gypsum board can create construction sequencing challenges. Since the gypsum board needs to be installed before the framing, the contractor will need to coordinate between the trades.

A new solution that eliminates sequencing issues for Type III construction is our series of DG/DGH/DGB fire wall hangers, which are designed to easily install on a two-hour wood stud fire wall. These top-flange hangers feature enough space to allow two layers of 5/8″ gypsum wall board to be slipped into place after the framing is complete.

These new fire wall hangers were tested in accordance with ICC-ES AC13 and ASTM D7147, which I discussed in How We Test – Part I: Wood Connectors. These standards do not explicitly detail how to test a hanger installed on a wood stud wall, so we collaborated closely with ICC Evaluation Services to develop a test setup that meets the intent of the standards.

All three of our new fire wall hangers have been tested according to ASTM E814 and received F (flame) and T (temperature) ratings for use on either or both sides of the fire wall. These ratings verify that the DG/DGH/DGB hangers do not reduce the two-hour fire wall assembly rating.

Our testing and load tables address installation of 2×4 or 2×6 stud walls constructed of Douglas fir (DF), southern pine (SP), spruce-pine-fir (SPF) or hem-fir (HF) lumber.

DG Hanger

DGH Hanger

DGB Hanger

Drywall Notch Detail

If you are working on a Type III wood-frame construction project, check out our Fire Wall Solutions page, which has product profiles with links to further information about the new DG hanger series, as well as our DU/DHU series of drywall hangers and fire wall fastener solutions using Strong-Drive® SDWS Timber screws.

Top 10 Changes to Structural Requirements in the 2018 IBC

This blog post will continue our series on the final results of the 2016 ICC Group B Code Change Hearings, and will focus on 10 major approved changes, of a structural nature, to the International Building Code (IBC).

  1. Adoption of ASCE 7-16
    • The IBC wind speed maps and seismic design maps have been updated.
    • A new section has been added to Chapter 16 to address tsunami loads.
    • Table 1607.1 has been revised to change the deck and balcony Live Loads to 1.5 times that of the occupancy served.
  2. New and Updated Reference Standards
    • 2015 IBC Standard ACI 530/ASCE 5/TMS 402-13 will be TMS402-16.
    • ACI 530.1/ASCE 6/TMS 602-13 will be TMS 602-16.
    • AISC 341-10 and 360-10 have both been updated to 2016 editions.
    • AISI S100-12 was updated to the 2016 edition.
    • AISI S220-11 and S230-07 were updated to the 2015 edition.
    • AISI S200, S210, S211, S212 and S214 have been combined into a new single standard, AISI S240-15.
    • AISI S213 was split into the new S240 and AISI S400-15.
    • ASCE 41-13 was updated to the 2017 edition.
    • The ICC 300 and ICC 400 were both updated from 2012 editions to 2017 editions.
    • ANSI/NC1.0-10 and ANSI/RD1.0-10 were all updated to 2017 editions.
  3. Section 1607.14.2 Added for Structural Stability of Fire Walls
    • This new section takes the 5 psf from NFPA 221, so designers will have consistent guidance on how to design fire walls for stability without having to buy another standard.
  4. Modifications of the IBC Special Inspections Approved
    • Section 1704.2.5 on special inspection of fabricated items has been clarified and streamlined.
    • The Exception to 1705.1.1 on special inspection of wood shear walls, shear panels and diaphragms was clarified to say that special inspections are not required when the specified spacing of fasteners at panel edges is more than 4 inches on center.
    • The special inspection requirements for structural steel seismic force-resisting systems and structural steel elements in seismic force-resisting systems were clarified by adding exceptions so that systems or elements not designed in accordance with AISC 341 would not have to be inspected using the requirements of that standard.
  5. Changes Pertaining to Storm Shelters
    • A new Section 1604.11 states that “Loads and load combinations on storm shelters shall be determined in accordance with ICC 500.”
    • An exception was added stating that when a storm shelter is added to a building, “the risk category for the normal occupancy of the building shall apply unless the storm shelter is a designated emergency shelter in accordance with Table 1604.5.”
    • Further clarification in Table 1604.5 states that the type of shelters designated as risk category IV are “Designated emergency shelters including earthquake or community storm shelters for use during and immediately after an event.”
  6. Changes to the IBC Conventional Construction Requirements in Chapter 23
    • The section on anchorage of foundation plates and sills to concrete or masonry foundations reorganized the requirements by Seismic Design Category (SDC) and added a new section on anchoring in SDC E. It also states that the anchor bolt must be in the middle third of the width of the plate and adds language to the sections on higher SDCs saying that if alternate anchor straps are used, they need to be spaced to provide equivalent anchorage to the specified 1/2″- or 5/8″-diameter bolts.
    • The second change permits single-member 2-by headers, to allow more space for insulation in a wall. 
  7. Modification to the Requirements for Nails and Staples in the IBC
    • ASTM F1667 Supplement One was adopted that specifies the method for testing nails for bending-yield strength and identifies a required minimum average bending moment for staples used for framing and sheathing connections.
    • Stainless-steel nails are required to meet ASTM F1667 and use Type 302, 304, 305 or 316 stainless steel, as necessary to achieve the corrosion resistance assumed in the code.
    • Staples used with preservative-treated wood or fire-retardant-treated wood are required to be stainless steel.
    • The new RSRS-01 nail was incorporated into TABLE 2304.10.1, the Fastening Schedule. The RSRS nail is a new roof sheathing ring shank nail designed to achieve higher withdrawal resistances, in order to meet the new higher component and cladding uplift forces of ASCE 7-16.
  8. Truss-Related Code Change
    • The information required on the truss design drawings was changed from “Metal connector plate type” to “Joint connection type” in recognition that not all trusses use metal connector plates.
  9. Code Change to Section 2304.12.2.2
    • A code change clarifies in which cases posts or columns will not be required to consist of naturally durable or preservative-treated wood. This change makes the requirements closer to the earlier ones, while maintaining consistency with the subsequent section on supporting members.
    • If a post or column is not naturally durable or preservative-treated, it will have to be supported by concrete piers or metal pedestals projecting at least 1″ above the slab or deck, such as Simpson Strong-Tie post bases that have a one-inch standoff.
  10. Code Change to IBC Appendix M
    • A code change from FEMA makes IBC Appendix M specific to refuge structures for vertical evacuation from tsunami, and the tsunami hazard mapping and structural design guidelines of ASCE 7-16 would be used rather than those in FEMA P-646.

Once the 2018 IBC is published in the fall, interested parties will have only a few months to develop code changes that will result in the 2021 I-Codes. Similar to this last cycle, code changes will be divided into two groups, Group A and Group B, and Group A code changes are due January 8, 2018. The schedule for the next cycle is already posted here.

What changes would you like to see for the 2021 codes?

The New Way to Connect with Strong Frame®

The April SE blog article, What Makes Strong Frame® Special Moment Frames So Special, explained the features and benefits of the Yield-Link® structural fuse design for the Strong Frame® special moment frame (SMF) connection. In this blog, I will be introducing the Yield-Link end-plate link (EPL) to the Strong Frame connection family.

What is the EPL?
The EPL connection (Figure 1) is the latest addition to the Strong Frame Strong Moment Frame (SMF) solution. The new EPL connection can accommodate a W8X beam which is approximately a 33% reduction in beam depth from a W12X beam. The frame is field bolted without the need for field welding which means a faster installation. The snug-tight bolt installation requirement means no special tools are required. The EPL SMF connection has the same benefit of not requiring any additional beam bracing as the T-Stub connection. The frame can be repaired after a large earthquake by replacing the Yield-Link connection. Since the shear tab bolts will be factory installed, installation time for the frame is reduced by 25% making the EPL connection one of the most straightforward connections to assemble.

Figure 1: New Yield-Link EPL connection

Why Did We Develop the EPL?
The development of the EPL came from strong interest and numerous requests to offer a solution with more head room for clearance of retrofit projects or enhancement for new construction using a shallower beam profile. The original T-stub link design has the shear tab welded to the column flange. The geometry of the shear tab meant that a W12X beam is required to accommodate the Yield-Link Flange. In Figure 2, you can see that a shallower beam profile will bring the Yield-Link flange closer to each other and limit the attachment of the shear tab. A new connection was needed.

Figure 2: Yield-Link flange interference with shear tab

Figure 3: 3 Bolt configuration with notched flange plate. (The 3rd bolt is on opposite side of beam.) The asymmetric layout produced uneven force distribution in the bolts.

How Did We Develop the EPL?
Multiple configurations were studied, including a notched flange plate with 3 bolts (Figure 3) to avoid interference with the shear tab connection to the column. In the end, a compact end plate link combining the shear tab and Yield-Link stem in a single connection was the final design. However, many questions loomed over the prototype. How will the single end plate design perform in a full scale test? Will the new configuration change the limit state? These questions needed to be studied prior to launching an expensive full-scale test program with multiple samples and configurations. Numerous Finite Element Analysis (FEA) models were studied and refined prior to full scale testing of a prototype. Modeling included ensuring the stem performs as a fuse (Figure 4) as discussed in the April blog and the integrity of the shear tab is maintained in the compact design. Figure 5 shows a graph comparing the analytical model to the actual full scale test. The full scale test with a complete beam and column assembly was performed to the requirements under AISC 341 Section K. The full scale test passed the requirements for the SMF classification as can be seen in Figure 6 for the specimen with 6-inch columns and 9-inch beam.

Figure 4: Equivalent Plastic Strain Plot of Yielding-Link Stem

Figure 5: Full Scale Test vs. Analytical model

Figure 6: Moment at Face of Column vs. Story Drift

Where Can I Get More Information?
The EPL is now recognized in the ICC-ES ESR-2802 code report as an SMF. EPL solutions are also offered in the Strong Frame Moment Frame Selector Software. Want to see how the new connection and member sizes can expand your design options? Visit www.strongtie.com to download the new Strong Frame Design Guide or contact your Simpson representative for more information.

Keep Your Roof On

He huffed, and he puffed, and he blew the roof sheathing off! That’s not the way kids’ tale goes, but the dangers high winds pose to roof sheathing are very real. Once the roof sheathing is gone, the structure is open and its contents are exposed to the elements and much more vulnerable to wind or water damage. It is a storyline that we meet all too often in the news.

About two years ago, the ASTM subcommittee on Driven and Other Fasteners (F16.05), addressed fastening for roof sheathing in high-wind areas by adding a special nail to ASTM F1667-17 – Standard Specification for Driven Fasteners: Nails, Spikes and Staples. The Roof Sheathing Ring-Shank Nail was added to the standard as Table 46. Figure 1 illustrates the nail and lists its geometrical specifications. This is a family of five ring-shank nails that can be made from carbon steel or stainless steel (300 series). Specific features of these nails are the ring pitch (number of rings per inch), the ring diameter over the shank, the length of deformed shank and the head diameter. Also, note B specifies that the nails shall comply with the supplementary requirement of Table S1.1, which tabulates bending yield strength. In this diameter class, the minimum bending yield strength allowed is 100 ksi.

Figure 1. Roof Sheathing Ring-Shank Nails (ASTM. 2017. Standard Specification for Driven Fasteners: Nails, Spikes and Staples, F1667-17. ASTM International, West Conshohocken, PA.)

The IBHS (Insurance Institute for Business and Home Safety) discusses roof deck fastening in its Builders Guide that describes the “FORTIFIED for Safer Living” structures. The IBHS FORTIFIED program offers solutions that reduce building vulnerability to severe thunderstorms, hurricanes and tornadoes. Keeping the roof sheathing on the structure is critical to maintaining a safe enclosure and minimizing damage, and roof sheathing ring-shank nails can be part of the solution. As Figure 2 from IBHS (2008) shows, every wood-frame structure has wind vulnerability.

Figure 2. Hurricane, high wind and tornado regions of the US (IBHS. 2008. Builders Guide, Fortified for Safer Living. Tampa, FL. 81 pp.)

More importantly for the wood-frame engineering community, the Roof Sheathing Ring-Shank Nails are being included in the next revision of the AWC National Design Specification for Wood Construction (NDS-2018), which is a reference document to both the International Building Code and the International Residential Code. You will be able to use the same NDS-2018, chapter 12 withdrawal equation to calculate the withdrawal resistance for Roof Sheathing Ring-Shank Nails and Post Frame Ring-Shank nails. The calculated withdrawal will be based on the length of deformed shank embedded in the framing member. Also, Designers need to consider the risk of nail head pull-through when fastening roof sheathing with ring-shank nails. If the pull-through for roof sheathing ring-shank nails is not published, you will be able to use the new pull-through equation in the NDS-2018 to estimate that resistance.
Simpson Strong-Tie has some stainless-steel products that meet the requirements for Roof Sheathing Ring-Shank Nails. These will be especially important to those in coastal high-wind areas. Table 1 shows some of the Simpson Strong-Tie nails that can be used as roof sheathing ring-shank nails. These nails meet the geometry and bending yield strength requirements given in ASTM F1667. See the Fastening Systems catalog C-F-2017 for nails in Type 316 stainless steel that also comply with the standard.

Table 1. Simpson Strong-Tie collated nails made from Type 304 stainless steel that comply with F1667-17 specifications for Roof Sheathing Ring-Shank Nails.

Improve your disaster resilience and withstand extreme winds by fastening the sheathing with roof sheathing ring-shank nails. You can find Roof Sheathing Ring-Shank nails in ASTM F1667, Table 46, and you will see them in the AWC NDS-2018, which will be available at the end of the year. Let us know your preferred fastening practices for roof sheathing.