California Has Funding for $3,000 Grants for Home Retrofits

Are you an engineer working with California clients whose homes were built before 1979 on a raised foundation?

Evident earthquake damage
Earthquake damage sustained by a two-story building over a cripple wall system after the Mexicali Earthquake (M7.2).

If you are, these clients may be among the 1.2 million California homeowners eligible for a seismic home retrofit. The state of California has approved the continuation of an initiative known as Earthquake Bolt + Brace (EBB). In its second year, this program plans to make as many as 1,600 grants to selected homeowners, nearly three times the number given the previous year. The EBB grant program provides up to $3,000 to homeowners residing in more than 150 California zip codes. Check to see whether your clients live within one of these communities here.

Simpson Strong-Tie has several different resources to assist you in helping your clients understand how to mitigate seismic risks to houses with raised foundations. The Seismic Retrofit Details sheet provides various ways to retrofit the cripple wall system using prescriptive methodologies, which can be adapted for engineered solutions. The picture below highlights the use of the Simpson Strong-Tie universal foundation plate (UFP) to attach the boltless sill plate of the cripple wall to the concrete stemwall. This simple step can help prevent the house from sliding off its foundation. The picture also reveals plywood sheathing used to reinforce the weak cripple wall system. Additional resources for retrofit can be found here.

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Retrofit with UFP foundation plate in Napa, California

To help your clients better understand the impact these simple steps can have in preventing structural damage in an earthquake, click here to watch the story of a Napa business women who had purchased a structure with a raised foundation for her business and retrofitted it just prior to the 2014 M6.0 Napa earthquake, which caused considerable damage to many similar structures.

Let your clients know that the time to apply is very limited if they think they qualify for a retrofit grant. Registration for the 2016 EBB program ends on February 20. To register or learn more about the program, visit www.earthquakebracebolt.com.

When you finish a retrofit for one of your clients, we want to hear how it went. Let us know in the comments below.

Fiber Reinforced Polymer (FRP) Design Example

The following FRP Design example walks the reader through the typical process for designing an FRP strengthening solution for a concrete T-beam per ACI 440.2R Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures.

One of the most important initial checks for an Engineer of Record is to confirm that the unstrengthened structure can support the load combination shown in Equation 5.5.1 in ACI 562 Code Requirements for Evaluation, Repair, and Rehabilitation of Concrete Buildings:

Eq. 5.5.1: (φRn)existing ≥ (1.2SDL + 0.5SLL)new

This check is to prevent a structural failure in case that the strengthening is damaged in an extraordinary event. If the structural element cannot pass this check, then external reinforcement is not recommended.

We have a Design Questionnaire where we ask Engineers of Record for more specific information related to the element to be strengthened:

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For this particular example, the following information was provided for the concrete T-beam.

1.  Structure Type (e.g., building, bridge, pier, garage):

  • 5-story commercial concrete building

2. Element(s) to be Strengthened/Repaired (e.g., beam, column, slab, wall):

  • Reinforced concrete beams

3. Type of Deficiency (e.g., shear, flexural, axial):

  • Flexural

4. Existing Factored Capacity of Section (e.g., kips, kip-ft):

  • 265 kip-ft

5. Ultimate Demand to be Supported (e.g., kips, kip-ft):

  • 320 kip-ft

6. Existing Concrete Compressive Strength:

  • 4,000 psi

7. Existing Rebar Yield Strength:

  • 60 ksi

8. Existing Reinforcement Layout:

  • 3 #7s 2.6875 inches from bottom of web to centroid of steel

9. Existing Dimensions:

  • 36 inches total beam height, 8 inches slab, 24 inches web width, 120 inches effective slab width

10. Relevant Existing Drawing Sheets and/or Pictures:

  • See attached

11. Finish Coating Requirements/Preferences:

  • None

12. For Flexural Strengthening:

  1. Dead Load Moment Applied at Time of Installation
    1. 60 kip-ft
  2. Service Dead Load Moment After Installation
    1. 80 kip-ft
  3. Service Live Load Moment After Installation
    1. 140 kip-ft

We then plug this information into our design program to come up with an FRP solution that meets the needs of the member:

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For a beam that was at 83% of the capacity required for the new loading, we specified a simple, low-impact FRP solution to maintain clearances under the beams. If a traditional fix of adding cross-section to the beam had been specified instead, then additional concrete and rebar would need to be added to the beam, which would impact clearances under the beam and also increase the seismic weight of the building. The additional weight could also translate all the way through the building and even impact footing designs.

FRP can be used to increase the flexural strength up to 40% per ACI 440.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.

Add Simpson Strong-Tie to Your Design Team

Simpson Strong-Tie Composite Strengthening Systems™ is unlike choosing any other product we offer.

For your next retrofit project, please contact Simpson Strong-Tie to see if FRP would be an economical choice for strengthening your concrete or masonry element.


Specifying Self-Drilling Screws: “Standard” vs. “Engineered”

In my past life as a Design Engineer, when specifying a screw the size of the screw was the key feature that I considered. In my mind, a #10 screw performed better than #8, and a #12 was better than #10 and all #10 screws were the same. But that is not always true. Just as a shoe size or a dress size may not be exactly the same for all brands, a screw of the same size from different manufacturers may perform differently. The head type, head design, thread design (fine, coarse, thread angle, pitch), thread type (like box threads, buttress threads, unified, square) and drill point type (like #1, #3, #5 drill point) can influence the performance of a screw. When innovatively designed, a #10 engineered screw can meet or exceed the performance of a #12 or #14 screw in loads and drill time and could result in cost savings. You can use fewer screws, which would mean labor savings. For example, our newly designed XU34B1016 screw, which is a #10 screw with 16 threads per inch, a hex washer head and a #1 drill point, that performs better than a #14 standard screw in lighter gauge steels.

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What Are Self-Drilling Tapping Screws?

Self-drilling tapping screws, or self-drilling screws, as the name implies, drill their own hole, eliminating the need for predrilling, and form or cut internal mating threads.  They are  relatively fast to  instal compared to bolts or welds. Unlike pins, they do not require a thick support material to be used. They can be used in very thin steel, such as 26 gauge, up to steel that is ½” thick. Self-drilling screws may be a perfect choice for most applications involving cold-formed steel (CFS). They are most commonly used for CFS connections: either attaching CFS to CFS, wood to CFS or CFS to wood. They are a logical choice when the other side of the connection or material is not accessible.

Most self-drilling screws are made of steel wire that meets the specification of ASTM A510 minimum grade 1018 material as specified in ASTM C1513 standard. Self-drilling screws are heat treated  to case harden then so that they meet the hardness, ductility, torsional strength and drill drive requirements as specified in ASTM C1513 standard.  ASTM C1513 refers to SAE J78 for the dimensional and performance requirements of self-drilling screws.

Screw Selection

While selecting the screw, you need to figure out the head type that works for the application. For example, a flat-head screw would be a good choice for wood-to-steel applications, but for steel-to-steel applications, a hex head or a pan head may be a better choice. Similarly, the length of the screw should be sufficient to fasten  the members of the connection together. According to Section D1.3 of AISI S200, the screw should be at least equal in length to the total thickness of the material including gaps with a minimum of three exposed threads. The length of the drill point is another important feature to consider. It should be long enough to drill through the entire thickness of the material before engaging the threads. This is because thread forming occurs with fewer revolutions than  the drilling process.   if the drill point length is not long enough, the screw threads can engage the connection material and the screw can bind and break.

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Some drill points also have “wings” to  drill a hole in the material that is larger in diameter than the threaded shank. Screws with this kind of point are mainly used for wood-to-steel applications. The blog post by Jeff Ellis titled “Wings or No Wings” provides some useful insights for screws with wings when used in shearwall applications.

The Test Standards and Evaluation Criteria for Standard and Engineered Screws

Per Section D1 of AISI S200, screws used for steel-to-steel connections or sheathing-to-steel connections shall be in compliance with ASTM C1513 or an approved design or design standard.

For ASTM C1513–compliant screws (per AISI S100), Section E4 provides equations to calculate shear, pullout and pullover of screws used in steel-to-steel connections. It also provides safety and resistance factors for calculating allowable strength or design strength. These equations are based on the results of tests done worldwide and the many different types of screws used in the tests. As a result, these equations seem to have a great degree of conservatism.

As discussed earlier, many factors, such as the head type and washer diameter, thread profile, drill point type and length, installation torque and the installation method affect or influence the performance of a screw. In order to qualify the screws as ASTM C1513–compliant or better performing, manufacturers need to have their screws evaluated per Acceptance criteria for Tapping Screw Fasteners AC118 developed by International Code Council – Evaluation Service. The criteria have different requirements depending on whether the intention is to qualify as standard screws or proprietary screws.  For proprietary screws, connection shear, pullout and pullover tests are performed in accordance with the AISI S905 test method. The shear strength and tensile strength of the screw itself are evaluated per test standard AISI S904. The safety and resistance factors are calculated in accordance with Section F of AISI S100. The pictures below are some test set-ups per AISI S905 and AISI S904 test procedures.

screws3 screws4 screws5

Another important consideration is corrosion resistance. AC118 has a requirement for testing the fasteners for corrosion resistance in accordance with ASTM B117 for a minimum of 12 hours. The screws tested shall not show any white rust after 3 hours or any red rust after 12 hours of the test. At the same time, it is important to keep in mind  that  hardened screws are prone to hydrogen embrittlement and are not recommended for exterior or wet condition applications. Also, these screws are  not recommended for use with dissimilar metals.  If self-drilling screws are to be used in exterior environments, the screws need to be selectively heat treated to keep the core and surface hardness in a range that  reduces the susceptibility to hydrogen embrittlement. Other fastener options for exterior environments are stainless-steel screws.

This table shows are some of our screw offerings for CFS applications. Our stainless-screw options can be found in  Fastening Systems Catalog (C-F-14) or at www.strongtie.com.

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What are the screws that you most commonly specify? Share your screw preferences and your ideas on self-drilling screws in your comments below.

Don’t Buckle at the Knees: RCKW Testing

A previous blog post described how Simpson Strong-Tie tests and loadrates connectors used with cold-formed steel structural members per acceptance criteria ICC-ES AC261.

This week, I would like to describe how we test and determine engineering design values for RCKW, Rigid Connector Kneewall, in a CFS wall assembly and how the data can help designers perform engineering calculations accurately and efficiently.Continue Reading

Cold-Formed Steel Connectors

This blog has described how we load rate different products based on test standards, which are covered under various ICC-ES Acceptance Criteria, or ACs. The first was a post on wood connectors (AC13), then holdowns (AC155), threaded fasteners (AC233) and cast-in-place anchors for light-frame construction (AC398 and AC399). I realized today that I have never talked about how we test and load rate connectors for cold-formed steel.

AC261 Joist Test 1

But first, a confession – it has taken me many years to stop calling it “light-gauge steel.” When I started designing with cold-formed steel, I called it “light-gauge” because I had a binder of design information put together by the Light Gauge Steel Engineers Association. Advocates for CFS felt that “light-gauge” may make people think “weak” or “non-structural,” and that perception would limit the use of cold-formed steel in construction. So there was a deliberate effort to banish the word light-gauge and replace it with cold-formed steel, or CFS. I still slip every once in a while.

Connectors for light-gauge, ahem, I mean cold-formed steel members are covered under ICC-ES AC261 – Acceptance Criteria for Connectors Used with Cold-formed Steel Structural Members. The physical testing for cold-formed steel is similar to wood connectors. Build a setup representative of field conditions, apply load till failure and measure the load and deflection data. Both wood-to-wood and CFS connectors have a service limit state of 1/8” deflection.

Strength data for CFS connectors is analyzed much differently, however. Wood connectors generally use a safety factor of 3 on the lowest ultimate load (or average ultimate if six tests are run). We are often asked what the safety factor for CFS connectors is.

AISI S100 Safety Factor

AISI S100 Chapter F details how to determine design strengths for tested CFS products. The design strength is the average test value, Rn, multiplied by an LRFD resistance factor, Φ, or divided by an ASD safety factor, Ω. Determining the resistance factor or corresponding safety factor is based on a statistical analysis dependent on several variables. This is similar in concept to how embedded concrete connectors tested to AC398 or AC399 are evaluated, which I discussed in this post.

AC261 Joist Test 2

I don’t want to get too deep into the Greek letters involved in the calculation. The factors that affect the allowable load calculation are type of member tested, variation in the test values, type of manufacturing, and number of samples tested. One factor that has a large impact on the calculation is the target reliability index, βo. In connector testing, this factor is 2.5 if the structural member (joist, stud, track, etc) fails and 3.5 if the connection fails. The net result is a higher safety factor for test values limited by the connection, and lower safety factors if the structural members governed the test load. Typical safety factors for CFS connectors are 1.8 to 2.0 where the failure mode is in the structural members and 2.2 to 2.9 for tests where the connection failed.

Strength Reduction Factor

AC261 has a reduction factor, RS, which is used to adjust test values if your steel strength and/or steel thickness are over the specified minimum. CFS test setups often use different steel in the joist, header and the connector. Reductions are calculated based on the tested and specified strength and thickness for each member. The lowest reduction is used to adjust the test values.

RCKW Kneewall Setup

RCKW Kneewall Failure

One additional complexity in CFS testing is the multiple gauges of steel which must be evaluated. This requires more CFS test setups than a comparable wood connector would require. In the end, we have what we are really after. Design loads that specifiers can be confident in.

RCKW Load Table

Fire Protection Considerations with Five-Story Wood-Frame Buildings: Part 2

Last week’s post reviewed some of the common questions WoodWorks receives from engineers designing five-story, Type III wood-frame buildings—including those related to fire retardant-treated building elements, and fire-rated floor and wall assemblies. This week, we extend that conversation to another common issue—details and fire rating of floor-to-wall intersections.Continue Reading

Fire Protection Considerations with Five-Story Wood-Frame Buildings Part 1

As a regional director for WoodWorks, my job is to provide technical assistance related to the design of nonresidential and multi-family wood buildings. I’ve been with the program since it launched in 2007 and, although we support a full range of building types, I’ve seen a steady increase in the number of design professionals looking for information and support related to mid-rise wood structures in particular.Continue Reading

LinkedIn Best Practices for Structural Engineers

As many of you know, LinkedIn is a social networking website specifically aimed at business professionals and is designed to help you link1connect and network with people you know and trust. You can add colleagues, peers and others as contacts and send them messages. You can create and update your personal profile to let your contacts know about your professional activities, and both recommend or endorse your contacts and get recommended or endorsed by your contacts for your professional skills. In addition, you can join groups to communicate with other professionals within the same sector or industry. You are also able to ask and answer industry-related questions, and to learn about and apply for job openings.

A basic membership on LinkedIn is free, but you can also upgrade your account in order to have access to professionals outside of your network.

To help guide you, here are some best practices for how to set up and optimize your LinkedIn account.

Update and Complete Your Profile

link2Having a complete and updated profile on LinkedIn allows you to put your best face forward. Make sure to summarize your role and responsibilities and current and past work experience, highlighting the details you think will make a prospective customer want to work with you. Include a professional-looking headshot and your current contact information. LinkedIn will even tell you your profile strength on the right-hand rail.

Join Industry Specific Groups

Joining groups that are relevant to our industry will allow you to participate in online industry discussions. Answering questions related to your field of expertise within these discussions is an excellent way to position yourself as an authority and build your professional reputation. Here are some structural engineering groups that you can start with:

Structural Engineer

Structural Engineer USA

SEAOC-Structural Engineers Association of California

Forge Connections

Connect with people you already know using your email contacts. This will help you maintain your existing relationships as well as branch out to connect with industry-related people your contacts may know. Another great feature of LinkedIn is that it will tell you “People You May Know” based on where you work or are already linked to. This feature will help you find meaningful connections.

Follow the Company Page and Share Posts

Simpson Strong-Tie has a company LinkedIn page to connect with customers. Company pages are a way to keep up to date on trends in design and building materials, code changes, product launches and other industry news. Make sure to follow the Simpson Strong-Tie company page so that you can stay informed about our latest news and updates.

Manage Privacy Settingslink3

Make sure to review and manage your privacy settings to help you control how many people can view your activities and personal information. You can do this by hovering your mouse on your thumbnail image on the far right- hand side of your home page.link4You should see an Account & Settings drop-down menu appear with an option that says “Privacy & Settings: Manage.” Click this option. Once you are there, you can manage all of your privacy settings.


How do you use LinkedIn as part of your engineering career? Let us know in the comments below.