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. 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 or AASHTO FRP Guide Spec Section 1.4.4. After the feasibility study, the questionnaire creates input sheets specifically for your project. For projects in Canada designed per the requirements of CSA S806 or CSA S6, please use our fillable PDF questionnaire to collect your information.

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.


AC398 Now Includes Moment Evaluation of Cast-in-Place Post Bases

This week’s post was written by Jhalak Vasavada, Research & Development Engineer at Simpson Strong-Tie.

When we launched our new, patent-pending MPBZ moment post base earlier this year, the evaluation of the moment capacity of post bases was not covered by AC398 – or by any other code, for that matter. There wasn’t a need – there were no code-accepted connectors available on the market for resisting moment loads.

We proposed adding moment evaluation to the AC398 and presented our research to the ICC-ES committee in June. After a thorough review, which included a public hearing, the provision was approved. Here are some details about the revisions to this acceptance criteria.

What is AC398?

AC398 is the Acceptance Criteria for cast-in-place cold-formed steel connectors in concrete for light-frame construction.

Acceptance criteria are developed to provide guidelines for demonstrating compliance with performance features of the codes referenced in the criteria. ICC-ES develops acceptance criteria for products and systems that are alternatives to what is specified in the code, or that fall under code provisions that are not sufficiently clear for the issuance of an evaluation report.

The criteria are developed through a transparent process involving public hearings of the ICC-ES Evaluation Committee (made up entirely of code officials), and/or online postings where public comments were solicited.

How is the moment load evaluated?

The MPBZ moment post base is a cast-in-place post base designed to resist uplift, download, lateral and moment forces. This blog post in February describes how it works, how it was tested and includes a design example. Since the MPBZ falls under the specialty inserts category of cast-in anchorage, it is not covered by the provisions of chapter 17 of ACI 318-14. Therefore, the MPBZ was evaluated based on AC398 for anchorage to concrete.

Our engineers worked closely with ICC-ES and the American Wood Council to develop evaluation criteria for moment. This revision to the criteria for moment evaluation and testing was posted for public comments on the ICC-ES website, and then presented by our engineers at the ICC-ES committee hearing last June. The presentation included the design, use, testing and load rating of the MPBZ. Following the hearing, and a thorough review, the committee approved the proposed revision to AC398.

What are the revisions to AC398?

With reference to moment evaluation, a few of the key changes to AC398 are:

  1. Moment Anchorage Strength: Similar to tension and shear anchorage strength, the available moment anchorage strength shall be determined using the equation

Where F = applied horizontal test force used to determine moment strength (lbf)

D = vertical distance from top of concrete member to the applied lateral test force F (ft.) (moment arm)

Other terms are as previously defined for tension and shear anchorage strength equations.

  1. Rotation: Testing of moment base connectors subject to an applied moment shall include measurement and reporting of the connector rotation as determined by the relative lateral displacement of gauges positioned 1″ and 5″ above the top of the connector.
  2. Side Bearing: Testing of moment base connectors that rely on bearing of the wood member against the side of the connector to resist moment loads shall address wood shrinkage.

Learn more about the MPBZ in our free upcoming webinar.

Join us live on December 6 for an interactive webinar on the MPBZ moment post base, its evaluation, its testing and its applications. In this webinar, we will discuss MPBZ moment post base product features, product development, design examples and much more. Attendees will also have an opportunity to ask questions during the event. Continuing education units will be offered for completing this webinar. Register today here.

Upcoming free MPBZ webinar.

Join Simpson Strong-Tie R&D engineer Jhalak Vasavada, P.E., and Simpson Strong-Tie product manager Emmet Mielbrecht for a lively and informative discussion of this new product.


Holdown Anchorage Solutions

A couple years ago, I did a post on selecting holdown anchorage solutions. At the time, we had created a couple engineering letters that tabulated SSTB, SB and PAB anchor solutions for each holdown to simplify specifying anchor bolts. About a year later, a salesperson suggested we tabulate SSTB, SB and PAB anchor solutions for each holdown. You know, to simplify specifying anchor bolts…

This conversation reminded me of the difficulty in keeping track of where design information is. In the C-C-2017 Wood Construction Connectors catalog, we have added this material on pages 62-63. Which should make it easier to find. I thought I should update this blog post to correct the links to this information.

A common question we get from specifiers is “What anchor do I use with each holdown?” Prior to the adoption of ACI 318 Appendix D (now Chapter 17 – Anchoring to Concrete), this was somewhat simple to do. We had a very small table in the holdown section of our catalog that listed which SSTB anchor worked with each holdown.

The good old days! (Don’t use this today)

During the good old days, anchor bolts had one capacity and concrete wasn’t cracked. ACI 318 stipulates reduced capacities in many situations, different design loads for seismic or wind, and reductions for cracked concrete. These changes have combined to make anchor bolt design more challenging than it was under the 1997 Uniform Building Code.

This blog has had several posts related to holdowns. So, What’s Behind a Structural Connector’s Allowable Load? (Holdown Edition) explained how holdowns are tested and load rated in accordance with ICC-ES Acceptance Criteria. Damon Ho did a post, Use of Holdowns During Shearwall Assembly, which discussed the performance differences of shearwalls with and without holdowns, and Shane Vilasineekul did a Wood Shearwall Design Example. So I won’t get into how to pick a holdown.

Once you have determined your uplift requirements and selected a post size and holdown, it’s necessary to specify an anchor to the foundation. To help designers select an anchor that works for a given holdown, we have created different tables that provide anchorage solutions for Simpson Strong-Tie holdowns.

Two tables on pages 62-63 in the Wood Construction Connectors catalog summarize holdown anchorage solutions. The tables are separated by wood species (DF/SP and SPF/HF) to give the most economical anchor design for each post material. The preferred anchor solutions are SSTB or SB anchors, as these proprietary anchor bolts are tested and will require the smallest amount of concrete. When SSTB or SB anchors do not have adequate capacity, we have tabulated solutions for the PAB anchors, which are preassembled anchors that are calculated in accordance with ACI 318 Chapter 17.

The solutions in the letters are designed to match the capacity of the holdowns, which allows the contractor to select an anchor bolt if the engineer doesn’t specify one. They are primarily used by engineers who don’t want to design an anchor or select one from our catalog tables. We received some feedback from customers who were frustrated that some of our heavier holdowns required such a large footing for the PAB anchors, whereas a slightly smaller holdown worked with an SB or SSTB anchor in a standard 12″ footing with a 1½” pop-out.

To achieve smaller footings using our SB1x30 anchor bolts, we reviewed our original testing and created finite element (FEA) models to determine what modifications to the slab-on-grade foundation details would meet our target loads. Of course, we ran physical tests to confirm the FEA models. With a 6″ pop-out, we were able to achieve design loads for HD12, HDU14 and HHDQ14.

The revised footing solutions for the heavier holdowns require less excavation and less concrete than the previous Appendix D calculated solutions, achieving desired loads while reducing costs on the installation.

Part of the fun of structural engineering is that there are always new problems to solve. Let us know what holdown anchorage challenges or solutions you have to share!

What Structural Engineers Need to Know About the New OSHA Silica Dust Standards

This week’s post was written by Todd Hamilton, PE. ICI Field Engineer at Simpson Strong-Tie.

In March of 2016, the United States Department of Labor issued new OSHA standards on how crystalline silica dust should be handled in various workplaces including within the construction industry. The changes are intended to limit workers’ exposure to and inhalation of silica dust on the jobsite. These regulations will replace the current standard, which was issued in 1971. Compliance with the new rules will be required on construction jobsites starting September 23, 2017, and will be enforced through OSHA from that time forward.

Crystalline silica is a naturally occurring mineral that is found in sand, sandstone, shale and granite, and since some of these materials can be found on jobsites on their own or as a component of a construction material such as concrete and mortar, changes to how workplaces contain and dispose of silica dust will affect the way our industry operates. Some of the processes performed on a construction jobsite that can expose workers to crystalline silica dust are drilling, grinding and sawing concrete and masonry; jackhammering; and sand blasting. Inhaling crystalline silica can lead to long-term illness and early death. Illnesses caused by inhaling silica dust include silicosis, lung cancer and chronic obstructive pulmonary disease (COPD).

The new OSHA standards do the following:

  • Reduce the permissible exposure limit (PEL) for respirable crystalline silica to 50 micrograms per cubic meter of air, averaged over an eight-hour shift. Previous PEL was 250 micrograms per cubic meter of air, averaged over an eight-hour shift.
  • Require employers to use engineering controls (such as water or ventilation) to keep worker silica exposure within the PEL; provide respirators when engineering controls cannot adequately limit exposure; limit worker access to high-exposure areas; develop a written exposure-control plan; offer medical exams to highly exposed workers; and train workers on silica risks and how to limit exposure.
  • Provide medical exams to monitor highly exposed workers and give them information about their lung health.
  • Provide flexibility to help employers – especially small businesses – protect workers from silica exposure.

Beyond that, the OSHA standards offer three methods an employer can use to demonstrate compliance:

  • A list of common jobsite activities and the required engineering control method, plus the additional respiratory protection (if needed) to meet the 50 PEL.
  • For activities/protection methods not included in the preceding list, the use of credible third-party assessment is allowed to show that the exposure level is < 50 PEL. This includes data from universities, trade associations, etc. that can be used provided they are based on conditions similar to, or more inherently hazardous than, the employer’s current conditions.
  • Manufacturers can generate their own data on their workers’ exposure level using an air-monitoring system.

Visit the US Department of Labor’s OSHA website for more in-depth information and useful links.

All these new requirements directly affect contractors onsite, but it’s also important for structural engineers to have an understanding of them. Beyond that, there are some key things that structural engineers should consider when specifying products such as post-installed anchors where the installation process includes drilling concrete, which does generate crystalline silica dust. Back in 2006 when Acceptance Criteria 308 was adopted, it made a lot of changes to how adhesive anchors are tested and qualified, but it also required that the manufacturers’ printed installation instructions (MPII) be published as part of the code report. This tied the published data in the code report to the installation procedures that could be used to achieve those data. And with the adoption of ACI 335.4 in 2015, the requirement for the MPII to be included in the code report continues. Therefore, with MPIIs being a part of the code report, a structural engineer needs to understand the importance of having an installation method that accounts for silica dust generated during the installation process and verify that the MPIIs include an installation process which utilizes a high-efficiency dust-collection system.

To get a better understanding of how these high-efficiency dust-collection systems work, let’s look at the Simpson Strong Tie Speed Clean™ DXS dust extraction system. This system was developed through a partnership with Bosch. Here is a video that clearly explains the system and its method:

So as structural engineers, we should consider what the MPII says when we are specifying a product.  Does it have an installation procedure, such as the Simpson Strong-Tie/Bosch DXS, that properly controls the crystalline silica dust generated? Does the code report lock the contractor into a specific brand of vacuum? Some code reports may only allow the use of a specific brand and model of vacuum and drills that can be used, which in some cases could require the purchase of new tools.

The new OSHA standard is very beneficial to installers because it will protect them from potential long-term health hazards. When it comes to anchor installation, the new regulations, along with compliant technologies such as the Speed Clean DXS, will eliminate the blow-brush-blow installation method that creates a lot of harmful airborne crystalline silica dust and is also often a source of installation error. Even though it will take time and effort for contractors and engineers to come to grips with the full ramifications for their projects, the new regulations are a positive development for the construction industry.

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.


What’s New in the ACI 440.2R-17?

The wait is over. The ACI 440.2R-17 Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures is now available. The following post will highlight some of the major changes represented by this version of the document.

It’s been a long road and countless committee hours to get from the last version of ACI 440.2R-08 to this document. While there are multiple smaller changes throughout the document, the most notable update is the addition of Chapter 13 – Seismic Strengthening.

 

The new seismic chapter addresses the following FRP strengthening scenarios:

  • Section 13.3 – Confinement with FRP
    • This section includes all of the following: general considerations; plastic hinge region confinement; lap splice clamping; preventative buckling of flexural steel bars.
  • Section 13.4 – Flexural Strengthening
    • The flexural capacity of reinforced concrete beams and columns in expected plastic hinge regions can be enhanced using FRP only in cases where strengthening will transfer inelastic deformations from the strengthened region to other locations in the member or the structure that are able to handle the ensuing ductility demands.
  • Section 13.5 – Shear Strengthening
    • To enhance the seismic behavior of concrete members, FRP can be used to prevent brittle failures and promote the development of plastic hinges.
  • Section 13.6 – Beam-Column Joints
    • This section covers a great deal of recent research on the design and reinforcement of beam-column joints.
  • Section 13.7 – Strengthening Reinforced Concrete Shear Walls
    • This section provides many recommendations for FRP strengthening of R/C shear walls.

Simpson Strong-Tie Can Help

We recognize that specifying Simpson Strong-Tie® Composite Strengthening Systems™ (CSS) is unlike choosing any other product we offer. Leverage our expertise to help with your FRP strengthening designs. Our experienced technical representatives and licensed professional engineers provide complimentary design services and support – serving as your partner throughout the entire project cycle.

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.

Upcoming Free Webinar: Advanced FRP Design Principles

Join us live on July 25 for the second interactive webinar in the Simpson Strong-Tie FRP Best Practices Series: Advanced FRP Design Principles. In this webinar we will highlight some very important considerations during the FRP design processes. This will include topics such as the latest industry standards, proper use of material properties, and key governing limits when designing with FRP. Attendees will also have an opportunity to pose questions to our engineering team during the event. Continuing educations units will be offered for attending this webinar. 

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 You Should Specify Stainless-Steel Screw Anchors When Designing for Corrosive Environments

Figure 1. Spalled concrete below a concrete bridge.

I was driving under a concrete bridge one nice clear day in Chicago, and I happened to look up to see rusted rebar exposed below a concrete bridge. My beautiful wife, who is not a structural engineer, turned to me and asked, “What happened to that bridge?” I explained that there are many reasons why spalling occurs below a bridge. One common reason is the expansion of steel when it rusts or corrodes.

This week’s blog will briefly explain the corrosion process and why concrete spalls when the embedded metals corrode. Corrosion may be defined as the degradation of a material as a reaction to its environment.1. As described in our previous SE Blog post, “Corrosion: The Issues, Code Requirements, Research and Solutions” dated January 3, 2013, corrosion of metallic surfaces is an electrochemical process. Because of moisture evaporation, concrete is a porous material. Water and oxygen molecules enter the pores of the concrete, and an electrochemical process occurs with the carbon-steel bar. The iron in the steel is oxidized, which then produces rust. A buildup of rust products at the surface of the carbon-steel bar exerts an expansive force on the concrete. Based on the amount of oxidation, the rust products of steel can occupy more than six times the volume of the original steel.2 Over time, further rust occurs and surface cracks will form. Eventually spalling will occur, exposing the rusted carbon steel bar. (See figure 1.)

Figure 2. Stages of corrosion.

Just as with reinforcing bars below a concrete bridge, cracking and spalling can occur when a carbon-steel anchor is used adjacent to a concrete edge. Simpson Strong-Tie® has many anchorage products that can be used in these conditions to prevent cracking. One specific product is the new stainless-steel Titen HD® screw anchor. This new innovative screw anchor is made up of Type 316 stainless steel. As seen in Figure 3, Type 316 stainless steel has a high level of resistance. This makes the stainless-steel Titen HD an excellent choice when it comes to an anchorage solution in corrosive environments. These environments include wastewater treatment plants, exterior handrails, exterior ledger attachments, stadium seating, central utility plants, and kitchens just to name a few.

Figure 3. Simpson Strong-Tie level of corrosion by material/coating.

Unlike expansion anchors, screw anchors require the leading threads to cut into predrilled holes. This can be easily achieved with hardened carbon-steel cutting threads. Stainless steel is not hard enough to cut into concrete. The new innovative stainless-steel Titen HD solves the problem by brazing heat-treated carbon-steel cutting threads to the surface of the stainless-steel tips of the screw anchor. (See figure 4.) These carbon-steel threads are hard enough to cut grooves into the surface of a predrilled hole, allowing the anchor to be installed with ease. The volume of the carbon-steel cutting threads is less than 1% of the stainless steel, reducing the buildup of rust that eventually spalls the concrete edge. Other stainless-steel screw anchor manufacturers in the market have a bi-metal product that attaches a full carbon-steel tip. This bi-metal screw anchors contain up to 18% carbon steel. Such a large amount of carbon steel can expand up to six times its volume when it corrodes and can spall the concrete when used adjacent to an edge.

Figure 4. Carbon-steel cutting threads.

Figure 5. Graphic representation of spalling in concrete adjacent to an edge.

When designing an anchorage solution for your next job in a corrosive environment, the stainless-steel Titen HD will provide the best resistance for corrosion, and also give the ability to drive these anchors into the concrete with ease. More information about the product can be obtained by visiting strongtie.com/thdss.

  1. Corrosion Technology Laboratory (https://corrosion.ksc.nasa.gov/corr_fundamentals.htm).
  2. Galvanized Rebar (http://www.concreteconstruction.net/how-to/repair/galvanized-rebar_o).

Stainless-Steel Titen HD®

The Next Era of Stainless-Steel Screw Anchor For Concrete and Masonry.


New Moment-Resisting Post Base

Jhakak Vasavada

Jhalak Vasavada is currently a Research & Development Engineer for Simpson Strong-Tie. She has a bachelor’s degree in civil engineering from Maharaja Sayajirao (M.S.) University of Baroda, Gujarat, India, and a master’s degree in structural engineering from Illinois Institute of Technology, Chicago, IL. After graduation, she worked for an environmental consulting firm called TriHydro Corporation and as a structural engineer with Sargent & Lundy, LLC, based in Chicago, IL. She worked on the design of power plant structures such as chimney foundations, boiler building and turbine building steel design and design of flue gas ductwork. She is a registered Professional Engineer in the State of Michigan.

At Simpson Strong-Tie, we strive to make an engineer’s life easier by developing products that help with design efficiency. Our products are designed and tested to the highest standards, and that gives structural engineers the confidence that they’re using the best product for their application.

Installed MPBZ

Figure 1: Installed MPBZ

Having worked in the design industry for almost a decade, I can attest that having a catalog where you can select a product that solves an engineer’s design dilemma can be a huge time- and money-saving tool. Design engineers are always trying to create efficient designs, although cost and schedule are always constraints. Moment connections can be very efficient — provided they are designed and detailed correctly. With that in mind, we developed a moment post base connector that can resist moment in addition to download, uplift and lateral loads. In this post, I would like to talk about moment-resisting/fixed connections for post bases and also talk about the product design process.

Figure 2. MPB44Z Graphic

Figure 2. MPB44Z Graphic

Lateral forces from wind and seismic loads on a structure are typically resisted by a lateral-force-resisting system. There are three main systems used for ordinary rectangular structures: (a) braced frames, (b) moment frames and (c) shearwalls. Moment frames resist lateral forces through bending in the frame members. Moment frames allow for open frames by eliminating the need for vertical bracing or knee bracing. Moment resistance or fixity at the column base is achieved by providing translational and rotational resistance. The new patent-pending Simpson Strong-Tie® MPBZ moment post base is specifically designed to provide moment resistance for columns and posts. An innovative overlapping sleeve design encapsulates the post, helping to resist rotation at its base.

The allowable loads we publish have what I call “triple backup.” This backup consists of Finite Element Analysis (FEA), code-compliant calculations and test data. Here are descriptions of what I mean by that.

Finite Element Analysis Confirmation

Once a preliminary design for the product is developed, FEA is performed to confirm that the product behaves as we expect it to in different load conditions. Several iterations are run to come up with the most efficient design.

Figure 3. FEA Output of Preliminary MPB Conceptual Design

Figure 3. FEA Output of Preliminary MPB Conceptual Design

Code-Compliance Calculations

Load calculations are prepared in accordance with the latest industry standards. The connector limit states are calculated for the wood-post-to-MPBZ connection and for MPBZ anchorage in concrete. Steel tensile strength is determined in accordance with ICC-ES AC398 and AISI S100-07. Wood connection strength is determined in accordance with ICC-ES AC398 and AC13. Fastener design is analyzed as per NDS. SDS screw values are analyzed using known allowable values per code report ESR-2236. The available moment capacity of the post base fastened to the wood member is calculated in accordance with the applicable bearing capacity of the post and lateral design strength of the fasteners per the NDS or ESR values. Concrete anchorage pull-out strength is determined in accordance with AC398.

Test Data Verification

The moment post base is tested for anchorage in both cracked and uncracked concrete in accordance with ICC-ES AC398.

Figure 4. Uplift Test Setup

Figure 4. Uplift Test Setup

The moment post base assembly is tested for connection strength in accordance with ICC-ES AC13.

Figure 5: Moment (induced by lateral load application) Test Set Up

Figure 5: Moment (induced by lateral load application) Test Set Up

The assembly (post and MPBZ) is tested for various loading conditions: download, uplift and lateral load in both orthographic directions and moment. Applicable factor(s) of safety are applied, and the controlling load for each load condition is published in the Simpson Strong-Tie Wood Construction Connectors Catalog.

Now let’s take a look at a sign post base design example to see how the MPBZ data can be used.

Design Example:

Figure 6: Sign Post Base Design Example

Figure 6: Sign Post Base Design Example

The MPB44Z is used to support a 9ʹ-tall 4×4 post with a 2ʹ x 2ʹ sign mounted at the top. The wind load acting on the surface of the sign is determined to be 100 lb. The MPB44Z is installed into concrete that is assumed to be cracked.

  • The design lateral load due to wind at the MPB44Z is 100 lb.
  • The design moment due to wind at the MPB44Z is (100 lb.) x (8 ft.) = 800 ft.-lb.
  • The Allowable Loads for the MPB44Z are:
    • Lateral (F1) = 1,280 lb.
    • Moment (M) = 985 ft.-lb.
  • Simultaneous Load Check:
    • 800/985 + 100/1,280 = 0.89. This is less than 1.0 and is therefore acceptable.

mpbz-deflection-evaultion

We are very excited about our new MPBZ! We hope that this product will get you excited about your next open-structure design. Let us know your thoughts by providing comments here.

Considerations for Designing Anchorage in Proximity to Abandoned Anchor Holes

danharmon.headshot.finalThis week’s post comes from Dan Harmon, an R&D engineer for Simpson Strong-Tie’s Infrastructure-Commercial-Industrial (ICI) group. Dan specializes in post-installed concrete anchor design and spent a decade managing Simpson’s anchor testing lab, where he developed extensive knowledge of anchor behavior and performance. He has a Bachelor of Science in mechanical engineering from the University of Illinois Urbana-Champaign.

Designers and engineers can spend hundreds of hours on detailed drawings of structures, but there are often conditions and coordination that can change well-planned details and drawings. As we all know, paper and reality don’t always agree. Anchorage locations can move as a result of unforeseen circumstances such as encountering reinforcing bars in an existing concrete slab or interference between different utility trades.

With post-installed anchors, one particular jobsite change may require abandoning a hole that has been drilled, leaving the final anchor location adjacent to the abandoned hole. When a hole for an anchor is drilled but never used, it essentially creates a large void in the concrete. Depending on where this void is located in relation to an installed anchor, there is potential for the capacity of that anchor to be reduced. To give guidance on this situation to specifiers, users and contractors, Simpson Strong-Tie conducted a large series of tests in their ISO 17025–accredited Anchor Systems Test Lab in Addison, Illinois.

To evaluate the effect of abandoned holes located adjacent to post-installed anchors, we performed tension tests meeting the requirements of ASTM E488-15 (see Figure 1). A variety of anchor types with common diameters were tested:

  • Drop-in anchors (1/2″ and 3/4″ diameter)
  • Wedge-type anchors (1/2″ and 3/4″ diameter)
  • Concrete screws (1/2″ diameter)
  • Adhesive anchors with threaded rod (1/2″ diameter)
Figure 1: Common Unconfined Tension Test Set-Up per ASTM E488-15

Figure 1: Common Unconfined Tension Test Set-Up per ASTM E488-15

Each anchor type and diameter was tested under five different conditions:

  • No abandoned hole near the installed anchor. This is considered the reference condition to which other tests are to be compared.
  • One abandoned hole at a distance of two times the hole diameter (2d) away from the installed anchor. See Figure 2.
  • One abandoned hole at a distance of four times the hole diameter (4d) away from the installed anchor.
  • Two abandoned holes, each at a distance of two times the hole diameter (2d) away from the installed anchor. In test conditions with two holes, the holes were located on either side of the installed anchor, approximately 180º from each other. See Figure 3.
  • Two abandoned holes, each at a distance of two times the hole diameter (2d) away from the installed anchor, with the holes refilled with a concrete anchoring adhesive that was allowed to cure fully prior to testing. See Figure 4.
Figure 2: Drop-In Anchor with a Single Hole at a Distance of 2d

Figure 2: Drop-In Anchor with a Single Hole at a Distance of 2d

Figure 3: Drop-In Anchor with Two Holes at a Distance of 2d

Figure 3: Drop-In Anchor with Two Holes at a Distance of 2d

Figure 4: Drop-In Anchor with Two Holes, Filled with Anchoring Adhesive, at a Distance of 2d

Figure 4: Drop-In Anchor with Two Holes, Filled with Anchoring Adhesive, at a Distance of 2d

This test program is summarized in Table 1. In all cases, the abandoned hole was of the same diameter and depth as the hole prescribed for the installed anchor.

Table 1. Summary of Test Program

Table 1. Summary of Test Program

Five tests for each anchor under each condition were tested, and the mean and coefficient of variance of each data set were calculated. These calculated values were used to compare the different conditions.

Across the different anchor types and diameters, the test results showed a number of general rules that held true.

Summary Results

Abandoned holes that are 2” or more away from the anchor have little to no effect on the tension performance of the anchor. Compared to the reference condition with no abandoned hole near the anchor, conditions where the abandoned hole was sufficiently far away were found to be essentially equivalent. This equivalence held true even for anchor types that create expansion forces (drop-in and wedge-type anchors) during their installation.

Two abandoned holes have the same effect on performances as one, regardless of distance from the anchor. This testing showed that adding a second abandoned hole near an installed anchor did not adversely affect tension performance in a significant way. Even within distances of 2 inches, performance did not drop substantially – if at all – in conditions involving two abandoned holes as compared to one.

Filling abandoned holes with an anchoring adhesive prior to installation of the anchor improves performance. In all cases tested, filling abandoned holes with adhesives resulted in increased performance compared to leaving the holes empty. In a majority of cases, performance with filled holes was equivalent to performance in the reference condition regardless of the distance from the anchor.

When the abandoned hole is more than two times the drilled hole diameter but less than 2″from the anchor – and left unfilled – the testing showed a loss in performance. Not surprisingly, the degree of that loss was dependent on the type of anchor. Table 2 shows the capacity reduction compared to the reference condition in testing with expansion anchors. Table 3 shows the same results for concrete screws and adhesive anchors. Conservative suggested performance reductions in these conditions would be 20% for expansion anchors and 10% for concrete screws and adhesive anchors.

Table 2: Performance Reduction for Expansion Anchors

Table 2: Performance Reduction for Expansion Anchors

Table 3: Performance Reduction for Concrete Screws and Adhesive Anchors

Table 3: Performance Reduction for Concrete Screws and Adhesive Anchors

In an ideal world, the engineer’s designs could be followed at all times at the jobsite. But we don’t live in an ideal world. Good engineering judgment is needed in situations where variation is required, and having data to support those decisions is always helpful. In the case of abandoned holes near post-installed anchors, it’s Simpson Strong-Tie’s hope that this testing provides additional guidance for the designer, inspector, and jobsite worker.

 

FRP Concrete Strengthening – Five Case Studies

Fiber-reinforced polymer (FRP) composite systems can be used to strengthen walls, slabs and other concrete or masonry members in buildings and other structures. The case studies below show ways in which Composite Strengthening Systems™ (CSS) provide valuable solutions for strengthening buildings and other structures for our customers.

Residential Project in San Francisco

The homeowner for this project wanted to repair some spalling concrete on his concrete piers and also wrap the piers with FRP. We worked with the contractor and homeowner to design a cost-effective solution. This was a successful project for all involved, since the alternative was to jacket the piers with costly and unsightly steel jackets.

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Materials: CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer

School Project in Argentina

The goal of the project was to analyze a standard design of approximately 400 schools in Argentina that were built in the 1980s and to make recommendations to retrofit the structures to meet current seismic code requirements.  On analysis, it was found that columns were in need of shear reinforcement for the schools to meet the new seismic requirements.

Materials: CSS-UCF Carbon Fabric, CSS-CA Carbon FRP Anchors, CSS-ES Epoxy Saturant & Primer

Materials: CSS-UCF Carbon Fabric, CSS-CA Carbon FRP Anchors, CSS-ES Epoxy Saturant & Primer

Hospital Project in Butler, PA

The Engineer of Record on this project wanted to provide continuity across the slab construction joints, something which the existing rebar did not provide. We provided a design of Near-Surface-Mounted (NSM) laminates, which are installed in saw-cut grooves in the top of the concrete slab. This installation allows a flush finished surface, important for allowing the floor finishes to be installed on the slab.

Materials:CSS-CUCL Carbon Precured Laminate, CSS-EP Epoxy Paste & Filler

Materials: CSS-CUCL Carbon Precured Laminate, CSS-EP Epoxy Paste & Filler

Silo Project in Garden City, IA

The concrete silos on this project had spalling at the top portion, which caused a hazard at this site. After repairing the concrete, we provided a ring of carbon fabric to assist in keeping the top concrete of the silos solid for years to come.

Materials:CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer

Materials: CSS-CUCF Carbon Fabric, CSS-ES Epoxy Saturant & Primer

Bridge Project in MN

MNDOT wanted to gain experience working with our CSS products on one of their bridges. We worked with their staff to design several types of strengthening solutions for bridge pier caps and columns. We then provided onsite installation training for the MNDOT maintenance staff to install the FRP products on the bridge.

Materials:CSS-CUCF Carbon Fabric CSS-CUGF E-glass Fabric CSS-ES Epoxy Saturant & Primer CSS-EP Epoxy Paste & Primer frp concrete strengthening

Materials: CSS-CUCF Carbon Fabric, CSS-CUGF E-glass Fabric, CSS-ES Epoxy Saturant & Primer, CSS-EP Epoxy Paste & Primer

We recognize that specifying Simpson Strong-Tie® Composite Strengthening Systems™ is unlike choosing any other product we offer. Leverage our expertise to help with your FRP strengthening designs. Our experienced technical representatives and licensed professional engineers provide complimentary design services and support – serving as your partner throughout the entire project cycle. Since no two buildings are alike, each project is optimally designed to the Designer’s individual specifications. Our pledge is to address your specific condition with a complete strengthening plan tailored to your needs, while minimizing downtime or loss of use, at the lowest possible installed cost.

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Your Partner During the Project Design Phase 

During the Designer’s initial evaluation or preparation of the construction documents, Simpson Strong-Tie can be contacted to help create the most cost-effective customized solution. These plans include detailed design calculations for each strengthening requirement and design drawings with all the necessary details to install the CSS system. Simpson Strong-Tie Engineering Services will work closely with the Design Engineer to provide all the necessary information required to design the system.

Why Use Our Design Services?

  • Assess feasibility studies to ensure suitable solutions to your application
  • Receive customized FRP strengthening solutions
  • Work with our trained contractor partners to provide rough-order-of-magnitude (ROM) budget estimates
  • Collaborate during the project design phase
  • Receive a full set of drawings and calculations to add to your submittal
  • Maintain the flexibility to provide the most cost-effective solution for your project
  • Gain trusted technical expertise in critical FRP design considerations

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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.


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.