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Welcome to our Structural Engineering Blog! I’m Paul McEntee, Engineering R&D Manager at Simpson Strong-Tie. We’ll cover a variety of structural engineering topics here that I hope interest you and help with your projects and work. Social media is “uncharted territory” for a lot of us (me included!), but we here at Simpson Strong-Tie think this is a good way to connect and even start useful discussions among our peers in a way that’s easy to use and doesn’t take up too much of your time. Continue reading

Use Strong-Wall® Shearwall Selector to Design Shearwalls

This blog post was written by Travis Anderson.

Strong-Wall Shearwall Selector-Homepage

In time for spring and summer 2017 construction projects, Simpson Strong-Tie has launched the newest version of the Strong-Wall Shearwall Selector for use with engineered design. The latest release is an easy-to-use Web-based application (that’s right, no software to download) that has been updated to comply with the 2015 IBC and now provides solutions for all three Strong-Wall Shearwall types: the Steel Strong-Wall® shearwall (SSW), the Strong-Wall wood shearwall (WSW) and the wood Strong-wall shearwall (SW). If you are familiar with the Strong-Wall Shearwall Selector, you can begin using the web application immediately. For those of you who would like to know more about the web app, please read on.

The Strong-Wall Shearwall Selector was created to help the Designer select the appropriate shearwall solution for a given application in accordance with the latest building code requirements. By performing a technical analysis, the web app provides actual drift and uplift values for a wind or seismic design shear load.

The Strong-Wall analysis also considers simultaneous, vertically applied load. In cases of multiple walls in a line, the program performs a rigidity analysis and determines the actual distributed shear to each wall. When walls are stacked in a two-story configuration, the program evaluates cumulative overturning effects to ensure that the wall, anchor bolt and anchorage to the foundation are not overstressed.

The web app provides two modes for generating an engineered solution: Optimized In-Plane Shear or Manual In-Plane Shear. The Optimized mode lists several possible solutions for the selected criteria in the order of cost. The Manual mode evaluates any number or combination of walls for adequacy based on the selected criteria. The Designer has the option to generate an Anchorage Solution based on foundation type. Once a solution has been selected, the web app will generate a pdf output. Files can be saved and reused for future designs.

Input Variables Within the Two Solution Modes:

Job Name: Enables the Designer to provide a specific job name for a project.

Wall Name: Enables the Designer to provide a name for each wall line in a project.

Wall Type (Manual Only): Solutions are provided for the selected Strong-Wall panel type: SSW, WSW, SW

Application: Defines the proposed application (use) of the wall. The choices are for walls in a garage front, a standard wall on concrete, on a first-story wood-floor system, in a second-floor non-stacked application, in a two-story stacked application, or in a balloon-framed application. For the Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW), garage front may be chosen with or without the portal kit. Higher shear capacities are available when the portal kit is used.

Cold-Formed Steel Construction (CFS): This option appears for “Garage Front,” “Standard Wall on Concrete,” “First-Story, Raised-Floor System” and “Two-Story Stacked” applications. If the check box is enabled, the program will provide the proper Steel Strong-Wall model for use in CFS construction.

1st Story Wall on Wood Floor (SW – Wood Strong-Wall Shearwall only): This check box only appears if a Two-Story Stacked application has been selected. If enabled, the program will then assume the lower story wall, in a stacked application, is installed on a wood floor.

Strong-Wall Shearwall Selector-Input Variables

Design Criteria:

The design criteria may now be selected. Drop-down menus provide options for Applicable Building Code, load type, concrete strength, wall height, wall geometry and floor depth (if applicable). Entry fields may be used to indicate shear- and axial-loading information. The following applies once the appropriate design criteria have been input: If Optimized In-Plane Shear has been selected, the possible solutions are displayed in the Strong-Wall Panel Solutions list. If Manual In-Plane Shear has been selected, a list of available walls will be displayed in the Strong-Wall Panel Solutions list, any of which may then be selected and added to the desired Solution.

Strong-Wall Shearwall Selector-Design Criteria

Code: Wall solutions are provided in accordance with the requirements of the 2015 and 2012 International Building Code (IBC). Code reports may be found here.

Load Type: This criterion defines whether the input shear load is due to wind or seismic forces. The Designer must input the controlling load. The appropriate seismic “R” values are provided for the selected code.

Concrete Strength: Concrete strength may be selected based on specific project conditions. Default concrete strengths of 2500 psi, 3000 psi, 3500 psi, 4000 psi and 4500 psi are provided in the drop-down menu. Note that for shearwall selection purposes, concrete strengths are only applicable to Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW). In some cases, lower anchorage forces may be obtained with a higher concrete strength. The concrete strength is also used for determining the anchorage tension capacity.

Wall Height: Select the nominal wall height. Actual wall heights are shown under the “H” column of the Solution(s).

Shear Load: Input the total Allowable Stress Design (ASD) design (demand) shear load along the wall line. Include all appropriate load factors on the shear load prior to input for the load combination under consideration. For Two-Story Stacked applications, input the story shear at each level and the program will evaluate the first-story walls for the total shear.

Floor-Joist Depth: This option appears only with first-story raised-floor systems and two-story

stacked applications. Floor-joist depth affects the capacity of Steel Strong-Wall panels installed on wood floors. Floor-joist depth is also considered in the cumulative overturning evaluation of two-story stacked wood or steel walls.

Header Thickness: This option appears only when “Garage Front” applications and wall heights of 7′ or 8′ with a header on top are selected. This option is used to select the proper Wood Strong-Wall panel model (thickness) based on the nominal header thickness of 4″ or 6″.

Header Type: This option only appears when “Header Thickness” of 4″ is selected. It then provides an option to select a solid or double-ply header. Values for the wood Strong-Wall panels will slightly decrease if the double-ply header option is selected. Steel Strong-Wall panels with multi-ply headers are limited to wind designs and SDC A-C.  .

Maximum Number of Wall Segments per Wall Line (Optimized mode only): Here the maximum number of available wall segments along a particular wall line is specified. The program enables the Designer to select a maximum of four wall segments per wall line (3 segments maximum for garage fronts.) For more wall segments per wall line, use the Manual mode.

Fill Each Segment (Optimized mode only): If this checkbox is disabled, then the minimum number of Strong-Wall shearwalls that can serve as solutions is provided up to the “Max # of Wall Segments” previously specified. If this checkbox is enabled, then the “Max # of Wall Segments” will always be used and filled with Strong-Wall shearwalls.

Segment Number, Maximum Width, Axial (lb.) (Optimized mode only): For each wall segment along a wall line, the maximum desired width of that segment and the axial load on that particular segment may be specified. The axial load is the total vertical upward or downward load assumed to act on the entire panel width. Include all appropriate load factors on the axial load prior to input for the load combination under consideration. A positive axial load reduces the actual uplift of the panel, while a negative axial load increases the actual uplift of the panel. The combined effect of the vertical axial load and overturning force is considered in the Steel Strong-Wall® (SSW) and Strong-Wall wood shearwall (WSW) solutions. The combined effect of the vertical axial load and overturning on the wood Strong-Wall (SW) shall be evaluated by the Designer so as not to exceed the “C4” and “T1” allowable vertical loads. Download an excerpt from our catalog for more information.

Axial Load 1st Story (Manual mode only): See discussion above on axial load. The axial load selected is initially applied on all Available Wall solutions. As walls are selected using the “Add” button, the axial load remains constant. If it is desired that each wall have a different axial load, then input the corresponding axial load value for the first wall and click on “Add Solution” to send it to the Selected Solution. Then enter the new axial load value for the next wall and continue this process until all the product selections are complete.

Maximum Wall Segment Width: This optional input limits the Available Strong-Wall Panels to the maximum width specified.

Available Wall(s) (Manual mode only): Based on the input Design Criteria, all Available Strong-Wall Panels and their allowable loads are listed as an option for selection. The Available Strong-Wall list is independent of the input shear load and instead represents a list whereby any quantity or combination of walls can be selected to resist the shear load.

Solution(s) and Output :

 Possible Solution(s) (Optimized mode only): Up to four possible solutions may be displayed and are designated as Sol # (solution number) in the order of relative cost (lowest to highest material cost).

Selected Solution (Manual mode only):

Add Another Solution: Click on the “Add” button to select wall from Available Wall(s) list, which enters it into the Selected Solution list. You may also double-click on an Available Wall to add it to the Selected Solution.

Clear: Click on the “Clear Selected Solutions” button to entirely remove all previously selected walls in the Selected Solution.

Generate PDF: This button creates a .pdf summary of the wall solution. Under Optimized mode, the output solution is created for the Sol# (solution number) that is highlighted. Under Manual mode, the Output is created for all walls shown in the selected solution list.

Design Anchorage: This option appears at the bottom of the page. If desired, enable the check box next to “Design Anchorage” and select Foundation Type. Anchorage design solutions will then be included in the PDF output.

Notes for Designer: Special notes related to the input variables are displayed in this window during the input process. When the Manual In-Plane Shear tab is selected, the Notes for Designer will indicate whether the Selected Solution is adequate to resist the applied design loads.

Strong-Wall Shearwall Selector-SolutionsStrong-Wall Shearwall Selector-Solution Output

Anchorage Solutions and Output:

 The Designer will have the option to generate an Anchorage Solution appended to the Strong-Wall shearwall solution. If desired, Select Foundation Type, then enable the check box next to Design Anchorage, and the .pdf file will be generated with the anchorage solution on subsequent pages. The designer can choose anchorage solutions based on foundation type for all shearwalls. The two foundation types are slab-on-grade and stemwall and are selected from a drop-down menu. Within each foundation type, the Designer can choose a specific footing type as follows:

Slab-on-Grade Footing Types: Garage curb, slab edge, brick ledge and interior.

Stemwall Footing Types: Garage front and perimeter.

Anchorage solutions are provided based on the shearwall solution(s) selected and the following design criteria: application, load type, actual uplift and concrete strength.

Anchor Bolt: Two anchor bolt solutions are available for the wood Strong-Wall®. They are the PAB7 and the SSTB, both of which are ASTM F1554 Gr. 36 material. The Steel Strong-Wall® uses a single anchor type, SSWAB, which may be either ASTM F1554 Gr. 36 or ASTM A449 (high-strength) material depending on the actual uplift. The Strong-Wall wood shearwall uses a single anchor type, WSW-AB, which may be either ASTM F1554 Gr. 36 or ASTM A449 (high-strength) material depending on the actual anchor tension.

Concrete Service Condition: This criterion refers to whether the concrete is determined to be cracked or uncracked based on analysis at service loads. See ACI 318 for the different reduction factors associated with cracked and uncracked concrete.

Strong-Wall Shearwall Selector-Anchorage Strong-Wall Shearwall Selector-Anchorage Output

The anchorage design .pdf output summarizes all applicable design details including the footing type, minimum footing dimensions, anchor bolt and shear anchorage. The Designer is responsible for foundation design (size and reinforcement) to resist overturning, soil pressure, etc.

Product Information:  Select for more product and application information.

Upload a Saved File: Designer can upload any previously used solution.

Report Applications Issues or Provide Feedback: If you are experiencing issues with the application or simply would like to provide feedback, please use this link. Simpson Strong-Tie values your feedback.

Strong-Wall Shearwall Selector-Info Save Issue

Get started on your next design project with the Strong-Wall® Shearwall Selector web application!

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.

 

Top Three Reasons Why Structural Engineers Should Attend Webinars

We encourage all our employees to always keep learning and seeking out resources that can stimulate new ideas or help improve processes in their jobs. Webinars are a great way for you to stay engaged in your profession and learn new things about the industry. They mix the convenience of online availability with the interactivity of live seminars, and because some are free or offered at a much lower cost than live trainings, they make it even easier to stay up to date on current issues in your field. Our top three reasons why you should attend structural engineering webinars are below:

Close up shot of webinar on a laptop.

Close up shot of webinar on a laptop.

Some Webinars Offer Continuing Education Credits

Webinars for structural engineers can be very useful for staying current with professional development requirements. Look to see if the webinar you are interested in attending offers credits. Simpson Strong-Tie offers a wide range of webinars that allow structural engineers to earn CEU and PDH credits. There are plenty of other professional organizations that offer accredited webinars for structural engineers, also. Paul McEntee shares his list of recommended professional resources (including webinars) for structural engineers here.

Learn About Code Changes and Requirements

Staying up to date on code changes and requirements is one of the reasons why continuing education is so important. The Structural Engineers Association of California (SEAOC) has a helpful lunchtime webinar series that delves into 2015 International Building Code (IBC) changes. Simpson Strong-Tie webinars always review current code requirements for the kinds of structural design under discussion. For example, the Best Practices on Prefabricated Wood Shearwall Design webinar covers code reports on shearwall applications.

Learn About the Latest Products and Technology

 If you can’t make it to a live training session, using webinars to learn about the most recent products and technology is an effective way to stay current in the field. Whether you want to learn about the latest in prefabricated Strong-Wall® Shearwall panels or to gain fuller understanding of Best Practices for FRP Strengthening Design, webinars can help you design using the most advanced technology.

What was the best webinar you’ve attended? Why was it so good, or what was it you learned? Let us know in the comments below.

Q&A: Best Practices for FRP Strengthening Design

frp-design-banner

On December 1, 2016, Simpson Strong-Tie hosted a webinar titled “The Design Fundamentals of FRP Strengthening” in which Justin Streim, P.E. – one of our Field Engineers – and I discussed the best practices for fiber-reinforced polymer (FRP) strengthening design. The webinar examines FRP components, applications and installation. It also features an example of the evaluation that went into a flexural-beam-strengthening design 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 presenting to more than 1,500 engineers who asked nearly 300 questions during the Q&A session. Here is a curated selection of Q&A from that session:

q-a-graphic

Can you discuss the flexural strengthening for reinforced masonry walls?

Out-of-plane flexural strengthening can be provided with FRP on the required face of wall. In-plane (or shear wall type) flexural strengthening can also be provided with vertical FRP strips near the ends of walls.

In general, by what percentage can FRP solutions increase the strength of existing concrete shearwalls?

This really depends on the existing wall, but we have seen strength increases of 22% in our testing of one layer of glass fabric installed on 8″ thick ungrouted CMU shearwall.

How does FRP compete in terms of cost? It seems like a cost-prohibitive solution compared to other remediation techniques in the absence of other limiting factors (space limitations, etc.).

FRP may be expensive on a cost/SF basis. However, if you compare it with the materials and labor involved in section enlargement or demolishing parts of buildings, it becomes cost effective. FRP installations are also not unsightly like bolted steel plates or wide flange members slung under concrete slabs/beams.

Who designs the FRP system: Simpson Strong-Tie or the Structural Designer?

The Simpson Strong-Tie Engineering Services group provides the FRP design on most projects, but we have also worked with the engineer on record (EOR) to check their FRP design on projects.

Are there any deformation compatibility issues between carbon fiber or glass and existing reinforcing bar that need to be accounted for in design? Is long-term creep similar to that seen with reinforcing bar?

CFRP and GFRP have different elastic moduli from each other and from steel. When designing an FRP strengthening solution, these differences must be taken into account. For flexural applications, the FRP should be designed to fail from debonding after the internal rebar begins to yield. Creep is taken into account in design equations through reduction factors and stress checks.

Will ACI 440 be updated to include the use of FRP with post-tensioned beams (i.e., unbonded tendons)? Does Simpson Strong-Tie do all stress checks based on gross section properties when total stress is < 12sqrtf’c?

Yes, there is an ACI 440 committee working on including an unbonded PT section in ACI 440.2R. We will work with the EOR to determine what section properties are most appropriate for the specific member being evaluated.

Can you increase deflection limits with FRP?

While FRP does help to limit deflection in members, members with deflection issues are not typically candidates for FRP repair. Prestressed laminates as used in Europe would be a better solution for a member with deflection issues. We do not currently offer prestressed laminates but may in the future.

Does an aesthetic coating interfere with bridge inspection? What is inspection looking for? Delamination or other defects?

A coating could interfere with a visual inspection of the FRP surface. A visual inspection can reveal changes in color, debonding, peeling, blistering, cracking, crazing, deflections, indications of reinforcing-bar corrosion, and other anomalies. In addition, ultrasonic, acoustic sounding (hammer tap) and thermographic tests may indicate signs of progressive delamination. ACI 440 and AC 178 have extensive special inspection recommendations.

If you would like to view the recorded webinar, you can find it at our website at https://www.strongtie.com/css.

frp-webinar-graphic

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.

 

Three Pieces of Advice for Structural Engineering Grads

If you are a civil engineering student finishing your degree, you are probably starting to explore all the options and opportunities available in the workforce. While structural engineering may be a specialized discipline, there are many paths and backgrounds that can lead someone into an exciting career that is innovatively transforming modern development in cities and towns all over the world.

We recently interviewed three of our engineers to learn what got them interested in the field and how they pursued their first job and built their career as a structural engineer with Simpson Strong-Tie.

Network and Make Contacts

Structural Engineer Griff Shapack headshot

Griff Shapack

Griff Shapack is an Associate FRP Design Engineer for Simpson Strong-Tie. He has bachelors and master’s degrees in civil engineering from North Carolina State University.

“I started looking for employment opportunities six months before graduation. I was working in a structures lab during graduate school, and the lab manager shared a job description for an Associate FRP Design Engineer at Simpson Strong-Tie with a few students. I knew I wanted to work under a P.E., and had experience and interest in FRP design, so I applied.”

“One of the things I love best about my job is that I get to go out and give presentations to structural engineers with our sales reps and field engineers. It’s great to be able to interface directly with our customers.”

“My biggest recommendations for engineering students is to reach out to people you already know in the industry. Classmates and professors can have valuable contacts at firms where you want to work.” 

Persistence Pays Off – Don’t Give Up

Structural Engineer Jhalak Vasavada

Jhalak 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.

“When I was in school for my master’s degree in Chicago, my professor recommended that I apply for a job at a firm called Sargent & Lundy. Unfortunately, at the time I applied, there were no openings at the firm, so I took another job until there was an opening. I interviewed there and got the job. It was a wonderful experience because it was in this role that I had the chance to meet my mentor. Having a female mentor was great in terms of real-life experience and advice. In fact, we still keep in touch.”

“When I moved to California, I wanted to find a job that allowed me to do something different. I applied for a job with Simpson Strong-Tie, and it was the best decision ever because I always get to work on new and exciting projects. My recommendation for students is to be persistent in trying to get a job at the place where you want to work.”

Appreciate and Learn from Every Experience That Comes Your Way

Structural Engineer Neelima Tapata

Neelima Tapata

Neelima Tapata is an R&D engineer for the Fastening Systems product division at Simpson Strong-Tie. She works on the development, testing and code approval of fasteners. She joined Simpson Strong-Tie in 2011, bringing 10 years of design experience in multi- and single-family residential structures in cold-formed steel and wood, curtain-wall framing design, steel structures and concrete design. Neelima earned her bachelor’s degree in civil engineering from J.N.T.U in India and her M.S. in civil engineering with a focus on structural engineering from Lamar University. She is a registered Professional Engineer in the State of California.

“I started searching for a job while I was finishing my master’s program. I started the search about a month before I graduated. My first job was in a consulting firm, and it was a fast-paced environment where you learned a lot on your own. My experience working for different consulting firms gave me a chance to concentrate on designing for a niche market, but my current role helps me see the big picture when it comes to design.”

“One of the things that I love most about my current role is that it allows me to take on multiple projects, so I’m always learning something new. It’s very important to stay curious. I also enjoy interacting with different departments in Simpson Strong-Tie. It gives me an opportunity to take on tasks that structural engineers may not normally get, like writing posts for an interesting publication like our Structural Engineering blog!”

“My advice for young structural engineers is to appreciate every experience that life sends your way. You may not realize it at the time, but it all ends up helping you get where you are now.”

If you are going to receive your degree this year or you know someone who is just starting out or looking to take a different path, Simpson Strong-Tie is hiring! We have several job opportunities in our engineering department. Check out our full list of job openings – then bookmark it! https://www.strongtie.com/about/careers/job-posting/engineerjobs

Snow Loading for Trusses: Why Specifying a Roof Snow Load Isn’t Enough

bill-walton-quoteYou might wonder what a quote about winning basketball games could possibly have to do with snow loading on trusses.  As with basketball, the importance of close teamwork also applies to a project involving metal-plate-connected wood trusses – for the best outcome, the whole team needs to be on the same page. For purposes of this blog post, the team includes the Building Designer, the Truss Designer and the Building Official, and the desired outcome is not a win per se, but rather properly loaded trusses. Snow loading on trusses is one area where things may not always go according to the game plan when everyone isn’t in accord. This post will explain how to avoid some common miscommunications about truss loading.

Which snow load are you specifying?

Which snow load are you specifying?

Like all other design loads that apply to trusses, snow loads are determined by the Building Designer and must be specified in the construction documents for use in the design of the building and the roof trusses. But sometimes the loads that are specified don’t provide enough information to ensure that the design will be correct for the specific circumstances. In the case of designs for snow loads, there needs to be a common understanding among all parties regarding the following:

  • Which snow load value is to be used as the uniform design load for the snow – a ground snow or a factored ground snow?
  • If it is a factored snow load, then how is the ground snow to be factored?
  • What other conditions need to be considered besides uniform load?
Sample Snow Load Specification

Sample Snow Load Specification

For example, say the Building Designer specifies that the trusses are to be designed for a 25 psf roof snow load. At first glance, this may appear to make things easier, since there is no need to convert the ground snow to a roof snow load. So what does the Truss Designer do with this load? There are a few different possibilities:

If unbalanced snow loading isn’t required or specified, the Truss Designer may enter the 25 psf snow load as a top chord live load (TCLL), set the load duration factor to 1.15 for snow, and turn snow loading off completely. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. Provided that no slope reduction factor gets applied to the specified roof snow load, both of these methods result in the same design. However, as discussed in my first blog post on snow loading for trusses, whenever a snow load is run as a roof live load rather than a snow load, it may not be clear to all parties involved what exactly the truss has been designed for, since there will be no notes indicating the snow design criteria on the truss design drawing.

If unbalanced snow loading is required, things get a bit trickier.  There are still two scenarios as to how the truss could be designed, but this time, the design results are different:

  • The truss could be designed based on the assumption that ground snow is being used as the roof design snow load (pg = 25 psf); or
  • The truss could be designed based on the assumption that the 25 psf roof snow load is a factored ground snow load, in which case a ground snow load is back-calculated using ASCE 7 based on the specified roof snow load (pg > 25 psf)

Therein lies the problem with specifying only a roof snow load. The determination of the drift load that is required for unbalanced snow load cases requires the use of the ground snow load, pg, not the roof snow load. If the ground snow load isn’t specified, then a ground snow load needs to be assumed – and the Truss Designer and the Building Designer may not be on the same page as it relates to this design assumption.

ASCE 7 Drift Height Calculation

ASCE 7 Drift Height Calculation

Even when the specification is clear regarding ground snow vs. roof snow load and the applicable snow load reduction factors, there is still the question whether any other conditions need to be considered besides uniform load. This includes not only unbalanced snow loads on standard gable roofs, but also drifting on lower roofs or in valleys, sliding snow, and any other snow-loading and/or snow accumulation considerations. Since trusses are designed as individual planar components, snow-loading conditions that go beyond the simple unbalanced load case on either side of the ridge on gable roof trusses must be detailed by the Building Designer.

Snow accumulation requirements must be detailed by the Building Designer

Snow accumulation requirements must be detailed by the Building Designer

As mentioned in a previous blog post, the truss industry’s Load Guide entitled Guide to Good Practice for Specifying & Applying Loads to Structural Building Components provides a tool to help Building Designers, Building Officials, Truss Designers and others more easily understand, define and specify loads for trusses. Similar to the wind-loading section discussed in that previous blog post, the Load Guide has an entire section on snow loading, how specific snow-loading provisions apply to trusses and how trusses are typically designed for snow loading within the truss design software.

Snow Load Worksheet from the Load Guide

Snow Load Worksheet from the Load Guide

With printable worksheets that can be used to define the snow loads and examples of multiple snow- loading conditions on different roof and truss profiles, the Load Guide is an invaluable tool for getting everyone on the same page. That’s what I would call a win!

How do you ensure that your design team is all on the same page regarding the loading of trusses? What are the biggest challenges for designing truss loads in your jurisdiction? We’d love to hear your thoughts.

How do you Design Sole-Plate-To-Rim-Board Attachments?

For many years, builders have struggled with the awkward sole-plate-to-rim-board attachment. They often install a few nails and call it good, resulting in a connection with significantly less capacity than needed. This connection is critical to ensure that seismic and wind loads are adequately transferred to the lateral-force-resisting system. With screws becoming much more common in construction, we saw an opportunity to address this problem.

We offer a variety of structural wood screws that have shank diameters ranging from 0.135″ to 0.244″. They form our Strong-Drive® line of structural fasteners. The Simpson Strong-Tie® Strong-Drive SDWC Truss, SDWH Timber-Hex, SDWS Timber, SDWV Sole-to-Rim and SDS Heavy-Duty Connector structural wood screws as shown in Figure 1 can be used to attach sole plates to a rim board as shown in Figure 2. These screws provide structural integrity in the wall-to-floor connection.

The sole-to-rim connection is considered a dry service location. When the sole plate and the rim are both clean wood (not treated), then any of the screws can be used as long as they meet the design loads. However, if one or both members of the connection are treated with fire retardants or preservatives, then you must use the SDWS Timber screw, SDWH Timber-Hex screw or SDS Heavy-Duty Connector screw. The SDWS, SDWH and SDS screws all have corrosion-resistance ratings in their evaluation reports.

Figure 1. Simpson Strong-Tie Strong-Drive screws for fastening the sole-to-rim connection: (a) SDWS Timber screw, (b) SDWV Sole-to-Rim screw, (c) SDWH Timber-Hex screw, (d) SDS Heavy-Duty Connector screw, (e) SDWC Truss screw.

Figure 1. Simpson Strong-Tie Strong-Drive screws for fastening the sole-to-rim connection: (a) SDWS Timber screw, (b) SDWV Sole-to-Rim screw, (c) SDWH Timber-Hex screw, (d) SDS Heavy-Duty Connector screw, (e) SDWC Truss screw.

Figure 2. The load rating for the sole-to-rim connection is for transfer of loads parallel to the sole plate to the rim. This is a dry service condition.

Figure 2. The load rating for the sole-to-rim connection is for transfer of loads parallel to the sole plate to the rim. This is a dry service condition.

The Strong-Drive SDWV structural wood screw has the smallest diameter among these screws. The SDWV is 4″ long and has a 0.135″- diameter shank, and a large 0.400″-diameter ribbed-head with a deep six-lobe recess to provide clean countersinking. It is designed to be fast driving with very low torque. The Strong-Drive SDWS offers one of the larger diameters. It has a 0.220″-diameter shank and is offered in lengths of 4″, 5″ and 6″. It has a large 0.750″-diameter washer head which provides maximum bearing area. Longer screws allow designers to meet the minimum penetration requirement into a rim board, when the sole plate is a 3x or a double 2x member.

We have tested various combinations of sole plates, floor sheathing, and rim boards. Typical test assemblies were built and tested with two (2) Strong-Drive® screws spaced at either 3″ or 6″. Results were analyzed per ICC-ES AC233, “Acceptance Criteria for Alternate Dowel-type Threaded Fasteners.” The allowable loads listed in Table 1 are based on the average ultimate test load of at least 10 tests, divided by a safety factor of 5.0, and are rated per single fastener. The results of these tests can be found in the engineering letter L-F-SOLRMSCRW16.

The evaluated sole plates include southern pine (SP), Douglas fir-larch (DF), hem-fir (HF), and spruce-pine-fir (SPF) in single 2x, 3x or double 2x configurations. Floor sheathing thicknesses are allowed up to 1 1/8″ thick. Rim boards can be LVL or LSL structural composite lumber or DF, SP, HF or SPF sawn lumber. The load rating also assumes that the floor sheathing is fastened separately and per code.

sdwc-load-tables

See strongtie.com for evaluation report information if it is needed.

As a Designer, you can specify any of these Strong-Drive screws that fit your design requirements. Please visit our website and download L-F-SOLRMSCRW16 for more details.

Good luck!