Simpson Strong-Tie® Strong-Wall® Wood Shearwall – The Latest in Our Prefabricated Shearwall Panel Line Part 1

calebphoto1This week’s post comes from Caleb Knudson, an R&D Engineer at our home office. Since joining Simpson Strong-Tie in 2005, he has been involved with engineered wood products and has more recently focused his efforts on our line of prefabricated Strong-Wall Shearwall panels. Caleb earned both his Bachelor’s and Master’s degrees in Civil Engineering with an emphasis on Structures from Washington State University. Upon completion of his graduate work, which focused on the performance of bolted timber connections, Caleb began his career at Simpson and is a licensed professional engineer in the state of California.

Some contractors and framers have large hands, which can pose a challenge for them when they’re trying to install the holdown nuts used to attach our Strong-Wall® SB (SWSB) Shearwall product to the foundation. Couple that challenge with the fact that anchorage attachment can only be achieved from the edges of the SWSB panel, and variable site-built framing conditions can limit access depending upon the installation sequence. To alleviate anchorage accessibility issues, we’ve required a gap between the existing adjacent framing and SWSB panel equal to the width of a 2x stud to provide access so the holdown nut can be tightened. Even so, try telling a framer an inch and a half is plenty of room in which to install the nut!

SWSB Edge Access
SWSB Edge Access
2x Gap for SWSB Installation
2x Gap for SWSB Installation

 

 

 

 

 

 

 

 

 

While the SWSB is a fantastic product with many great features and benefits from its field adjustability to its versatility with different applications and some of the highest allowable values in the industry, the installation challenges were real.

Back to the Drawing Board

Our goal was to develop a new holdown for the SWSB that would allow for face access of the anchor bolts, making the panel compatible with any framing condition, while maintaining equivalent performance. All we needed to do is cut a large hole in each face of the holdown without compromising strength or stiffness — piece of cake, right? Well, that’s exactly what we did. In the process, we addressed the needs of the architect, the engineer and the builder — and for bonus points, anchorage inspection is now much easier, which should make the building official happy too.

Introducing the Simpson Strong-Tie® Strong-Wall® Wood Shearwall

Simpson Strong-Tie® has just launched the Strong-Wall® Wood Shearwall (WSW) panel, which replaces the SWSB. The new panel provides the same features and benefits, and addresses the same applications as the SWSB; however, now it also features face-access holdowns distinguished by their Simpson Strong-Tie orange color.

Strong-Wall Wood Shearwall
Strong-Wall Wood Shearwall

We’ve also updated the top connection, which now provides two options based on installer preference. The standard installation uses the two shear plates shipped with the panel which are installed on each side of the panel by means of nails. As an alternative, the builder can install a single shear plate from either side of the panel using a combination of Strong-Drive® SD Connector screws and Strong-Drive® SDS Heavy-Duty Connector screws.

woodshear4

Allowable In-Plane Lateral Shear Loads

I mentioned that one of our primary development requirements was to meet the existing allowable design values of the SWSB. Not only did we meet our target values, but we exceeded them by as much as 25% for standard and balloon framing application panels and up to 50% for portal application panels. I’ve included a table below showing the most commonly specified standard and portal application SWSB models and how the allowable wind and seismic shear values compare to those of the corresponding WSW model.

woodshear11

Grade-Beam Anchorage Solutions

I’d be remiss if I didn’t point out the grade-beam anchorage solutions we’ve developed for use with the Strong-Wall Wood Shearwall. The solutions have been calculated to conform to ACI 318-14, and testing at the Simpson Strong-Tie Tyrell Gilb Research Laboratory confirmed the need to comply with ACI 318 requirements to prevent plastic hinging at anchor locations for seismic loading. The testing consisted of 1) control specimens without anchor reinforcement, 2) specimens with closed-tie anchor reinforcement, and 3) specimens with non-closed u-stirrups. Flexural and shear reinforcement were designed to resist amplified anchorage forces and compared to test beams designed for non-amplified strength-level forces.

Significant Findings from Testing

We found that grade-beam flexural and shear capacity is critical to anchor performance and must be designed to exceed the demands created by the attached structure. In wind load applications, this includes the factored demand from the WSW. In seismic applications, testing and analysis have shown that in order to achieve the anchor performance expected by ACI 318 Anchorage design methodologies, the concrete member design strength needs to resist the amplified anchor design demand from ACI 318-14 Section 17.2.3.4. To help Designers achieve this, Simpson Strong-Tie recommends applying the seismic design moment listed below at the WSW location.

woodshear7

We also found that closed-tie anchor reinforcement is critical to maintain the integrity of the reinforced core where the anchor is located. Testing with u-stirrups that did not include complete closed ties showed premature splitting failure of the grade beam. In a previous blog post, we discussed our grade-beam test program in much greater detail as it applies to our Steel Strong-Wall panels.

Strong-Wall® Wood Shearwall

To support the Strong-Wall Wood Shearwall, Simpson Strong-Tie has published a 52-page catalog with design information and installation details. We’ve also received code listing from ICC-ES; the evaluation report may be found here. Now that you’re all familiar with the WSW, be sure to check out next week’s blog post where we’ll cover the basics of prefabricated shear panel testing and evaluation. In addition, to help Designers understand all of the development and testing as well as design examples using prefabricated shearwalls, Simpson Strong-Tie will be offering a Prefabricated Wood Shearwall Webinar on June 21, 2016, covering:

  • The different types of prefabricated shearwalls and why they were developed.
  • The engineering and testing behind prefabricated shearwalls.
  • Best practices and design examples for designing to withstand seismic and wind events.
  • Code reports on shearwall applications.
  • Introduction of the latest Simpson Strong-Tie prefabricated shearwall.

You can register for the webinar here.

Last but not least, we always appreciate hearing from you, whether you’re an engineer specifying our panels or in the field handling the installation. If there are applications that we haven’t addressed or additional resources that would be beneficial, please let us know in the comments below.

Understanding and Meeting the ACI 318 – 11 App. D Ductility Requirements – A Design Example

If you’re one of the many engineers still confused by the ACI 318 – 11 Appendix D design provisions, this blog will help explain what’s required to achieve a ductile performing anchorage. Most building codes currently reference ACI 318 – 11 Appendix D as the required provision for designing a wide variety of anchor types that include expansion, undercut, adhesive and cast-in-place anchors in concrete base materials. This blog post will focus on section D.3.3.4.3(a) for an anchor located in a high seismic region. We’ll go over what these requirements are with a simple design example.

Ductility is a benefit in seismic design. A ductile anchor system is one that exhibits a meaningful degree of deformation before failure occurs. However, ductility is distinct from an equally important dimension called strength. Add strength, and a ductile steel element like the one shown in Figure 1 can now exhibit toughness. During a serious earthquake, a structural system with appreciable toughness (i.e., one that possesses both strength and ductility in sufficient degree) can be expected to absorb a tremendous amount of energy as the material plastically deforms and increases the likelihood that an outright failure won’t occur. Any visible deformations could help determine if repair is necessary.

Figure 1 – ½" mild steel threaded rod tensilely loaded to failure (starting stretch length = 8d)
Figure 1 – ½” mild steel threaded rod tensilely loaded to failure (starting stretch length = 8d)

Let’s start off with a simple example that will cover the essential requirements for achieving ductility and applies to any type of structural anchor used in concrete. We’ll arbitrarily choose a post-installed adhesive anchor. This type of anchor is very common in concrete construction and is used for making structural and nonstructural connections that include anchorage of sill plates and holdowns for shear walls, equipment, racks, architectural/mechanical/electrical components and, very frequently, rebar dowels for making section enlargements. We’ll assume the anchor is limited to resisting earthquake loading in tension only and is in seismic design category C – F. Section D.3.3.4.2 requires that if the strength-level earthquake force exceeds 20% of the total factored load, that the anchor be designed in accordance with section D.3.3.4.3 and D.3.3.4.4. We will focus on achieving the ductility option, (a), of D.3.3.4.3.

To understand anchor ductility we need to first identify the possible failure modes of an anchor. Figure 2 shows the three types of failure modes we can expect for an adhesive anchor located away from a free edge. These three failure modes generically apply to virtually any type of anchor (expansion, screw, cast-in-place or undercut). Breakout (Nb) and pullout (Na) are not considered ductile failure modes. Breakout failure (Nb) can occur very suddenly and behaves mostly linear elastic and consequently absorbs a relatively small amount of energy. After pullout failure (Na) has been initiated, the load/displacement behavior of the anchor can be unpredictable, and furthermore, no reliable mechanism exists for plastic deformation to take place. So we’re left with steel (Nsa). To achieve ductility, not only does the steel need to be made of a ductile material but the steel must govern out of the three failure modes. Additionally, the anchor system must be designed so that steel failure governs by a comfortable margin. Breakout and pullout can never control while the steel yields and plastically deforms. This is what is meant by meeting the ductility requirements of Appendix D.

Figure 2 –Three possible failure modes for an adhesive anchor loaded in tension
Figure 2 – Three possible failure modes for an adhesive anchor loaded in tension

Getting back to our design example, we have a single post-installed 5/8” diameter ASTM F1554 Gr. 36 threaded rod that’s embedded 12” deep, in a dry hole, in a concrete element that has a compressive strength of 2,500 psi. The concrete is 18” thick and we assume that the edge distance is large enough to be irrelevant. For this size anchor, the published characteristic bond strength is 743 psi. Anchor software calculations will produce the following information:

ductility4

The governing design strength is compared to a demand or load combination that’s defined elsewhere in the code.

Here’s the question: Before proceeding with the remainder of this blog, judging by the design strength values shown above, should we consider this anchorage ductile? Your intuition might tell you that it’s not ductile. Why? Pullout clearly governs (i.e., steel does not). So it might come as a surprise to learn that this adhesive anchor actually is ductile!

To understand why, we need to look at the nominal strength (not the design strength) of the different anchor failure modes. But first let’s examine the equations used to determine the design strength values above:

ductility5

The above values incorporate the notation φ (“phi”) and a mandatory 0.75 reduction factor for nonductile failure modes (Ncb ,Na) for applications located in high seismic areas (seismic design category C–F). The φ factor is defined in section D.4. However, manufacturers will list factors specific to their adhesive based on anchor testing. The mandatory 0.75 reduction comes from section D.3.3.4.4 and is meant to account for any reduction associated with concrete damage during earthquake loading. The important thing to remember is that the nominal strength provides a better representation of the relative capacity of the different failure modes. Remove these reduction factors and we get the following:

ductility6

Now steel governs since it has the lowest strength. But we’re not done yet. Section D.3.3.4.3.(a).1 of Appendix D requires that the expected steel strength be used in design when checking for ductility. This is done by increasing the specified steel strength by 20%. This is to account for the fact that F1554 Gr. 36 threaded rod, for example, will probably have an ultimate tensile strength greater than the specified 58,000 psi. (Interestingly, the ultimate strength of the ½” threaded rod tested in Figure 1 is roughly 74 ksi, which is about 27% greater than 58,000 psi.) With this in mind, the next step would be to additionally meet section D.3.3.4.3.(a).2 such that the following is met:

ductility7

By increasing the steel strength by 20%, the nominal strength of the nonductile failure modes (Ncb ,Na) must be at least that much greater to help ensure that a ductile anchor system can be achieved. The values to compare finally become:

 

ductility8Now steel governs, but one more thing is required. As shown in Figure 3, Section D.3.3.4.3.(a).3 of Appendix D also requires that the rod be made of ductile steel and have a stretch length of at least eight times the insert diameter (8d). Appendix D defines a ductile steel element as exhibiting an elongation of at least 14% and a reduction in area of at least 30%. ASTM F1554 meets this requirement for all three grades of steel (Grade 36, 55 and 105) with the exception of Grade 55 for anchor nominal sizes greater than 2”. Research has shown that a sufficient stretch length helps ensure that an anchor can experience significant yielding and plastic deformation during tensile loading. The threaded rod shown in Figure 1 was tested using a stretch length of 4” (8d). Lastly, section D.3.3.4.3.(a).4 requires that the anchor be engineered to protect against buckling.

Figure 3 – Stretch length
Figure 3 – Stretch length

Appendix D doesn’t require that an anchor system behave ductilely. Three additional options exist for Designers in section D3.3.4.3. Option (b) allows for the design of an alternate failure mechanism that behaves ductilely. Designing a base plate (or support) that plastically hinges to exhibit ductile performance is one example. Option (c) involves a case where there’s a limit to how much load can be delivered to the anchor. Although option (c) under D.3.3.4.3 falls under the tensile loading section of Appendix D, the best example would apply to anchorage used to secure a wood sill plate or cold-formed steel track. We know from experiments that the wood crushes or the steel yields and locally buckles at a force less than the capacity of the concrete anchorage. Clearly energy is absorbed in the process. The most commonly used option is (d), which amplifies the earthquake load by Ωo. Ωo can be found in ASCE 7 – 10 for both structural and nonstructural components. The value of Ωo is typically taken to be equal to 2.5 (2.0 for storage racks) and is intended to make the anchor system behave linear elastically for the expected design-level earthquake demand.

These same options exist for shear loading cases. However, achieving system ductility through anchor steel is no longer an option for shear loading according to ACI 318 – 11, because the material probably won’t deform appreciably enough to be considered ductile.

While factors such as edge-distance and embedment-depth restrictions make achieving ductility difficult for post-installed anchors, it should come as some consolation that in many cases the Designer can achieve ductile performance for cast-in-place anchors loaded in tension through creative detailing of reinforcing steel (section D.5.2.9) to eliminate breakout as a possible failure mode. This has been explored in some detail in two previous Simpson Strong-Tie blogs titled “Anchor Reinforcement for Concrete Podium Slabs” and “Steel Strong Wall Footings Just Got a Little Slimmer.”

 

Seismic Bracing Requirements for Nonstructural Components

Have you ever been at home during an earthquake and the lights turned off due to a loss of power?  Imagine what it would be like to be in a hospital on an operating table during an earthquake or for a ceiling to fall on you while you are lying on your hospital bed.

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“You Cannot Escape Responsibility Tomorrow by Evading it Today”

While the contents of this blog are certainly not what Abraham Lincoln had in mind when he made the statement that I’m using to title this blog post, it does speak volumes to the pertinence of what will be discussed today. “Design by others” or some variation of this appears in many parts of Simpson Strong-Tie details.

Simpson Strong-Tie receives technical calls from contractors and plans examiners inquiring about information that requires input from the Designer. When these calls occur during construction there can be confusion and frustration in the field because the Designer is needed to evaluate and resolve the issue. Designers and engineers that identify these conditions ahead of time will reduce confusion and delays on their projects.

Strong-Wall® Shearwalls

The Strong-Wall® shearwall product line uses several iterations of “design by others” within its installation details. It is important to note that many details within the installation drawings may require input from the Designer when certain conditions exist.

For example, Detail 7 on SSW2 shows an alternate first-story installation where the Steel Strong-Wall shearwall bypasses the floor framing and bears directly onto concrete. A ledger may be attached to the shearwall to support perpendicular floor framing. The specification of the hanger and attachment is project specific and would require evaluation by the Designer.
framing1

This condition is also on the Strong-Wall SB shearwall installation details as seen in the following detail. The detail is generic and requires attachment information from the Designer.  When these conditions do not exist on the project, it may be beneficial to cross out the detail or delete and state “not used” to lessen confusion during plan check and construction.

framing2

The note “Foundation Dimensions are for Anchorage only. Foundation design (size and reinforcement) by others” can be found in multiple locations on the Wood Strong-Wall,  Steel Strong-Wall and Strong-Wall Shear Brace detail sheets.

framing3

Soil type and loading conditions not related to the product design vary from project to project and cannot be designed into a one-size-fits-all foundation solution. Thus, the information provided by Simpson Strong-Tie in the installation drawings only addresses the concrete anchorage requirements of ACI 318 (Section D5.2.9/ACI 318-11; Section 17.4.2.9/ACI318-14). These details assume no reinforcement in the footing, resulting in rather large foundations. Since design requirements vary with every project, it’s important for Designers to evaluate and verify each condition.

The new Steel Strong-Wall shearwall grade beam solutions reduce the size of the footings required for anchorage. However, the Designer must specify the grade beam reinforcement for proper performance. The details for the grade beam solutions (see SSW1.1 sheet) are based on ACI 318 and testing that was conducted by Simpson Strong-Tie.

For the grade beam solutions, Designers have two options:

(1) Design grade beam to resist the moment induced from amplified forces to the anchor, or

(2) The lesser of the tabulated moment or the amplified LRFD design moment for seismic (ASD Shear / 0.7) x Ω0 x (SSW Height).

Furthermore, the Designer is responsible for specifying the size and number of shear and flexural reinforcement throughout the grade beam beyond the anchor reinforcement depicted in the details.

Delivery of forces to the Strong-Wall shearwall (to the top of wall), including properly sizing the structural members, should be based on project specific requirements.

Strong Frame® Moment Frames

Simpson Strong-Tie Strong Frame® ordinary moment frames and special moment frames contain similar requirements for the Designer. Moment frames have been discussed many times in this blog: Special Moment Frame Installation: What Structural Engineers Should Watch For, Steel Moment Frame Beam Bracing and Breaking News:  Simpson Strong-Tie Strong Frame Special Moment Frame Testing Today.

The notes on SMF2 state “Footing/Grade beam size and reinforcing shall be specified by the Designer as required to resist the imposed loads, such as foundation shear and bending, soil bearing pressure, shear transfer, and frame stability/overturning.”

Moment frame foundation solutions are based on satisfying the minimum concrete anchorage requirements. Detailing can be a crucial area for this product line as it is common to find deeper footings at these locations, which should be reflected on your construction documents.

Like Strong Wall shearwalls, Designers must evaluate the project conditions and detail the load path of the forces to the resisting element (in this case the Strong Frame moment frame). Ensuring proper transfer of forces that are detailed within your construction documents will reduce headaches down the road.

Strong-RodTM Systems

Strong-Rod™ systems are continuous rod tiedown solutions for multi-story, light-frame wood construction. These systems include Anchor Tiedown Systems (ATS) for shearwall overturning restraint and Uplift Restraint Systems (URS) for roofs. Both systems utilize the same components (i.e. bearing plates, rods, couplers and shrinkage compensation devices), however the detailing, design and locations of these two systems differs.

For ATS, the Designer is responsible for the following:

  • Developing the cumulative tension/compression loads,
  • Determining the system displacement requirements as defined in ICC-ES Acceptance Criteria AC316 to satisfy code required drift equations (this specifically addresses the holdown part of the Equation 4.3-1 of the 2015 Special Design Provisions for Wind and Seismic)
  • The location of each holdown/shearwall.

A more elaborate description of the Designer’s responsibilities for ATS can be found on page 23 of our  Strong-Rod Systems design guide (F-L-SRS15). Simpson Strong-Tie incorporates this information into our design of the system and provides calculations and installation drawings to the Designer for review (a sample two-story run is shown below).

framing4

For URS, there are two different approaches to design that have different level of responsibilities. The Designer has fewer responsibilities when specifying a rod with a “system (CRTS)” evaluation report per AC391, but they are still responsible for developing the project’s wind uplift loads, specifying URS details and designing systems for shearwall overturning.

More requirements must be taken into account when designing and specifying a rod system using steel components with a “rod-run only (CRTR)” AC391 evaluation report, or no report at all. (A more elaborate description of the Designer’s responsibilities for URS can be found on page 43 of the  Strong-Rod Systems design guide).

Based on the project information provided, the rod manufacturer will design and detail the system and submit calculations and installation drawings to the Designer for review.

Podium Deck Anchorage

The newest details published by Simpson Strong-Tie on podium deck anchorage solutions were developed to reduce the impact of an industry-wide challenge; resolving large tension forces (upwards of 50 kips) from four- to five-story narrow shearwalls into thin (often 10-14 inch thick) concrete podium decks. These solutions (e.g., design tables installation drawings and sample calculations), which are on our website, rely on special anchor reinforcement details using standard construction rebar.

framing5

More information about these solutions can be found this blog post and in the shallow anchor page on our website. It is important to note that the Designer is responsible for selecting the best anchorage detail to satisfy the demand loads based on his/her concrete specification and specific project conditions. The Designer is also responsible for designing and detailing the flexural reinforcement within the slab to achieve the amplified forces.

Summary

Adding standard installation details to your construction documents saves significant design time. However, the responsibility does not end with the copy-and-paste. The installation details by Simpson Strong-Tie contain details of many common applications. Some may not apply to your project, while others may require additional input from you. Of course, the Designer is permitted to use alternate details and is not limited to what is shown on the installation drawings. Providing complete information will save time and frustration during plan check and construction. Simpson Strong-Tie is here to answer questions and help with your next project. Please reach out to us by calling 800-999-5099 or by clicking here.

 

"You Cannot Escape Responsibility Tomorrow by Evading it Today”

While the contents of this blog are certainly not what Abraham Lincoln had in mind when he made the statement that I’m using to title this blog post, it does speak volumes to the pertinence of what will be discussed today. “Design by others” or some variation of this appears in many parts of Simpson Strong-Tie details.
Simpson Strong-Tie receives technical calls from contractors and plans examiners inquiring about information that requires input from the Designer. When these calls occur during construction there can be confusion and frustration in the field because the Designer is needed to evaluate and resolve the issue. Designers and engineers that identify these conditions ahead of time will reduce confusion and delays on their projects.
Strong-Wall® Shearwalls
The Strong-Wall® shearwall product line uses several iterations of “design by others” within its installation details. It is important to note that many details within the installation drawings may require input from the Designer when certain conditions exist.
For example, Detail 7 on SSW2 shows an alternate first-story installation where the Steel Strong-Wall shearwall bypasses the floor framing and bears directly onto concrete. A ledger may be attached to the shearwall to support perpendicular floor framing. The specification of the hanger and attachment is project specific and would require evaluation by the Designer.
framing1
This condition is also on the Strong-Wall SB shearwall installation details as seen in the following detail. The detail is generic and requires attachment information from the Designer.  When these conditions do not exist on the project, it may be beneficial to cross out the detail or delete and state “not used” to lessen confusion during plan check and construction.
framing2
The note “Foundation Dimensions are for Anchorage only. Foundation design (size and reinforcement) by others” can be found in multiple locations on the Wood Strong-Wall,  Steel Strong-Wall and Strong-Wall Shear Brace detail sheets.
framing3
Soil type and loading conditions not related to the product design vary from project to project and cannot be designed into a one-size-fits-all foundation solution. Thus, the information provided by Simpson Strong-Tie in the installation drawings only addresses the concrete anchorage requirements of ACI 318 (Section D5.2.9/ACI 318-11; Section 17.4.2.9/ACI318-14). These details assume no reinforcement in the footing, resulting in rather large foundations. Since design requirements vary with every project, it’s important for Designers to evaluate and verify each condition.
The new Steel Strong-Wall shearwall grade beam solutions reduce the size of the footings required for anchorage. However, the Designer must specify the grade beam reinforcement for proper performance. The details for the grade beam solutions (see SSW1.1 sheet) are based on ACI 318 and testing that was conducted by Simpson Strong-Tie.
For the grade beam solutions, Designers have two options:
(1) Design grade beam to resist the moment induced from amplified forces to the anchor, or
(2) The lesser of the tabulated moment or the amplified LRFD design moment for seismic (ASD Shear / 0.7) x Ω0 x (SSW Height).
Furthermore, the Designer is responsible for specifying the size and number of shear and flexural reinforcement throughout the grade beam beyond the anchor reinforcement depicted in the details.
Delivery of forces to the Strong-Wall shearwall (to the top of wall), including properly sizing the structural members, should be based on project specific requirements.
Strong Frame® Moment Frames
Simpson Strong-Tie Strong Frame® ordinary moment frames and special moment frames contain similar requirements for the Designer. Moment frames have been discussed many times in this blog: Special Moment Frame Installation: What Structural Engineers Should Watch For, Steel Moment Frame Beam Bracing and Breaking News:  Simpson Strong-Tie Strong Frame Special Moment Frame Testing Today.
The notes on SMF2 state “Footing/Grade beam size and reinforcing shall be specified by the Designer as required to resist the imposed loads, such as foundation shear and bending, soil bearing pressure, shear transfer, and frame stability/overturning.”
Moment frame foundation solutions are based on satisfying the minimum concrete anchorage requirements. Detailing can be a crucial area for this product line as it is common to find deeper footings at these locations, which should be reflected on your construction documents.
Like Strong Wall shearwalls, Designers must evaluate the project conditions and detail the load path of the forces to the resisting element (in this case the Strong Frame moment frame). Ensuring proper transfer of forces that are detailed within your construction documents will reduce headaches down the road.
Strong-RodTM Systems
Strong-Rod™ systems are continuous rod tiedown solutions for multi-story, light-frame wood construction. These systems include Anchor Tiedown Systems (ATS) for shearwall overturning restraint and Uplift Restraint Systems (URS) for roofs. Both systems utilize the same components (i.e. bearing plates, rods, couplers and shrinkage compensation devices), however the detailing, design and locations of these two systems differs.
For ATS, the Designer is responsible for the following:

  • Developing the cumulative tension/compression loads,
  • Determining the system displacement requirements as defined in ICC-ES Acceptance Criteria AC316 to satisfy code required drift equations (this specifically addresses the holdown part of the Equation 4.3-1 of the 2015 Special Design Provisions for Wind and Seismic)
  • The location of each holdown/shearwall.

A more elaborate description of the Designer’s responsibilities for ATS can be found on page 23 of our  Strong-Rod Systems design guide (F-L-SRS15). Simpson Strong-Tie incorporates this information into our design of the system and provides calculations and installation drawings to the Designer for review (a sample two-story run is shown below).
framing4
For URS, there are two different approaches to design that have different level of responsibilities. The Designer has fewer responsibilities when specifying a rod with a “system (CRTS)” evaluation report per AC391, but they are still responsible for developing the project’s wind uplift loads, specifying URS details and designing systems for shearwall overturning.
More requirements must be taken into account when designing and specifying a rod system using steel components with a “rod-run only (CRTR)” AC391 evaluation report, or no report at all. (A more elaborate description of the Designer’s responsibilities for URS can be found on page 43 of the  Strong-Rod Systems design guide).
Based on the project information provided, the rod manufacturer will design and detail the system and submit calculations and installation drawings to the Designer for review.
Podium Deck Anchorage
The newest details published by Simpson Strong-Tie on podium deck anchorage solutions were developed to reduce the impact of an industry-wide challenge; resolving large tension forces (upwards of 50 kips) from four- to five-story narrow shearwalls into thin (often 10-14 inch thick) concrete podium decks. These solutions (e.g., design tables installation drawings and sample calculations), which are on our website, rely on special anchor reinforcement details using standard construction rebar.
framing5
More information about these solutions can be found this blog post and in the shallow anchor page on our website. It is important to note that the Designer is responsible for selecting the best anchorage detail to satisfy the demand loads based on his/her concrete specification and specific project conditions. The Designer is also responsible for designing and detailing the flexural reinforcement within the slab to achieve the amplified forces.
Summary
Adding standard installation details to your construction documents saves significant design time. However, the responsibility does not end with the copy-and-paste. The installation details by Simpson Strong-Tie contain details of many common applications. Some may not apply to your project, while others may require additional input from you. Of course, the Designer is permitted to use alternate details and is not limited to what is shown on the installation drawings. Providing complete information will save time and frustration during plan check and construction. Simpson Strong-Tie is here to answer questions and help with your next project. Please reach out to us by calling 800-999-5099 or by clicking here.
 

Report Back from Nepal – Assessing Seismic Damage from April/May Earthquakes

 Dr. H. Kit Miyamoto assessing damage in Nepal.
Dr. H. Kit Miyamoto assessing structural damage in Nepal.

This week’s post comes from Dr. H. Kit Miyamoto, S.E. Kit is CEO of Miyamoto International, a structural engineering firm and president of the nonprofit, Miyamoto Global Disaster Relief. He also is a California Seismic Safety Commissioner.

As soon as news spread that 7.8-magnitude and 7.3-magnitude earthquakes struck Nepal in April and May of this year, earthquake structural engineering experts from our firm, Miyamoto International, hopped on planes from three countries to offer assistance. We do this in hopes that our expertise and technical advice might help stricken communities recover; help them to build better and ultimately help save lives.

0060
Dr. H. Kit Miyamoto on site. Evidence of massive damage is present in the background.

While structural engineers are not first responders, we are well equipped to assess whether it is safe for people to return to homes, businesses, schools and critical-services buildings. We also can help people understand why some buildings stand while others collapse. This information is essential. It is the only way to protect people from future tragedy.

On touch down in Nepal, we found the airport filled with frightened people leaving the country. It is always a bit sobering to see people leaving while you head in.  We struck out for the hotel we could only hope was still standing. Once there, we found the building to be structurally sound, although uneasy guests opted to sleep in the courtyard, leaving us, the structural engineers, the only ones sleeping inside.

I expected the devastation in Kathmandu to be much greater than it was – we all did. Yet because the epicenter was about 50 miles from the capital, the quake’s power was partially dissipated by distance and the Kathmandu Valley’s soft river soil, which likely saved many lives and structures.

Nepal’s Minister of Education asked our team to examine some of the schools in remote areas.  We drove into a village to a horrible find: a large, three-story school reduced to a rubble pile of brick, concrete and broken desks. What we found were columns made of bricks without any reinforcement. This is something I saw in schools in Sichuan, China in 2008, where poor construction practices left tens of thousands of school children vulnerable to disaster. And yet, I have to say that Nepal was lucky. Although more than 7,000 of the country’s schools were severely damaged or destroyed, the quake hit midday on a Saturday when students were not in school. Had the quake hit in the middle of a school day, tens of thousands of students would have died.

IMG_0138
A look inside the collapsed school.

Driving out beyond the city, we found rural areas in the central and western regions particularly devastated, with entire villages destroyed and further isolated by road damage, closures, rugged terrain and the threat of landslides. As is the case in much of the world, unreinforced masonry construction presented the biggest problem. In rural Nepal – where traditional homes are made of stone, mud and wood – we found up to 90 percent of the structures destroyed. Whole villages were gone.

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Absolute devastation of a rural village.

Around the world, the experts involved in construction – from the engineer and contractor to the building inspector – have to invest in constructing safe buildings. No corruption. No excuses. Build as if your children are attending that school or living in those homes and we will begin to have seismically resilient cities.

Many of the newer high-rise buildings in Kathmandu have also exhibited crippling damage and we have assessed more than 30 of these to date. Even when building codes are adhered to, a big gap exists between what code provides and what society expects. Even in places like Los Angeles and San Francisco, people don’t understand that. At one meeting in Kathmandu, luxury condo owners were stunned and angry to learn that the building they bought into met standards, but was still too heavily damaged to occupy. These buildings are not usable now. The financial loss is enormous.

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An aerial view of the earthquake damage. 

We have to understand that people don’t have to die in earthquakes. Earthquakes don’t kill people; buildings kill people. Or more precisely, poorly constructed buildings. This is tragic and avoidable because we know how to design seismically strong buildings. When an earthquake strikes, our disaster response efforts include “knowledge transfer,” during which we train engineers, masons and contractors on simple seismic techniques that save lives and help communities “build back better.” Our profession has disaster-resilient solutions for new construction and retrofits.

At Miyamoto International, our mission is to save lives and positively impact economies through our work. In China, 169,000 lives were lost, including tens of thousands of students in 7,000 classrooms. In 2010 in Haiti, more than 200,000 people died. In Nepal, the earthquake killed more than 8,600 people. It doesn’t have to be this way.  Building seismically resilient cities is possible. It is achievable. We can save lives.

Steel Strong-Wall® Footings Just got a Little Slimmer!

While 54 inches is a good height and will get you on most amusement park rides, what about this dimension for the width of a footing? We did some tests recently — actually a lot of tests — that answered that question.

Steel Strong-Wall® narrow panels are great for resisting high seismic or wind loads, but due to their narrow widths, their resulting anchor uplift forces can be rather hefty, requiring very large pad footings. How large? For Seismic Design Categories C-F, the largest cracked concrete solution per ACI318-11 Appendix D has a width of 54 inches and an effective embedment depth of 18 inches in order to ensure the anchor remains ductile. The overall length of this footing, as seen in Figure 1, can be up to 132 inches. While purely code driven, these solutions have historically presented challenges in the field. Most concrete contractors have to dig footings this size by hand. This often leads to discussions with their engineers about finding a better solution.

Figure 1:  Slab-on-Grade Installation (Traditional Solution)
Figure 1: Slab-on-Grade Installation (Traditional Solution)

Simpson Strong-Tie has been studying cast-in-place anchorage extensively in recent years. Our research has been featured in a couple of blog posts: The Anchorage to Concrete Challenge – How Do You Meet It? and Podium Anchorage – Structure Magazine. Concrete podium slab anchorage was a multi-year test program that started with grant funding from the Structural Engineers Associations of Northern California for initial concept testing at Scientific Construction Laboratories Inc. and wrapped up with full-scale detailed testing completed at the Simpson Strong-Tie Tye Gilb Laboratory in Stockton, California. This joint venture studied the performance of anchorage reinforcement into thin podium deck slabs (10-14 inch) to resist the high overturning forces of continuous rod systems on 4-5-story mid-rise construction. The testing confirmed the need to comply with Appendix D requirements to prevent plastic hinging at anchor locations. Be on the lookout for an SE Blog post on that topic in the near future. Armed with what we learned, we decided to develop tested anchor reinforcing solutions for the Steel Strong-Wall.

The newly developed anchor reinforcement solutions for grade beams are calculated in accordance with ACI318 Appendix D and tested to validate performance. Anchor reinforcement isn’t a new concept, as it’s been in ACI318 for some time. Essentially, anchor reinforcements transfer load from the anchor bolt to the reinforcing, which restrains the breakout cone from occurring. For the new grade beam details, the additional ties near the anchor are designed to resist the load from the anchor and are developed into the grade beam. The new details offer solutions with widths as narrow as 18 inches when anchor reinforcement is used.

Two details have been developed: one for the larger panels (SSW18, SSW21, SSW24) as shown in Detail 1/SSW1.1, and one for the smaller panels (SSW12, SSW15) as shown in Detail 2/SSW1.1. The difference between the two is the number of anchor reinforcement ties specified in Detail 3/SSW1.1. For SSW18, SSW21 and SSW24 panels (Detail 1/SSW1.1), the total number of reinforcement per anchor is specified. Due to their smaller sizes, the anchor reinforcement ties specified in Detail 2/SSW1.1 for the SSW12 and SSW15 panels are the total required per panel.

Detail 1/SSW1.1
Detail 1/SSW1.1
Detail 2/SSW1.1
Detail 2/SSW1.1
Detail 3/SSW1.1
Detail 3/SSW1.1

Validation Testing

From the concrete podium deck anchorage test program, we discovered that the flexural and shear capacity of the slab is critical to anchor performance and must be designed to exceed the demands created by the attached structure. For grade beams, this also holds true. In wind-load applications, this demand includes the factored demand from the Steel Strong-Wall. In seismic applications, our testing and analysis showed that achieving the anchor performance expected by Appendix D design methodologies requires the concrete member design strength to resist the amplified anchor design demand from Appendix D Section D.3.3.4.3.

Validation testing was conducted to evaluate this concept. The test program consisted of a number of specimens with different configurations, including:

  • Closed tie anchor reinforcement
  • Non-closed tie u-stirrup anchor reinforcement
  • Control specimen without anchor reinforcement

Flexural and shear reinforcement were designed to resist Appendix D amplified anchorage forces and were compared to test beams designed for non-amplified strength level forces. The results of the testing are shown in Figure 2. In the higher Seismic Design Categories (C-F), the anchor assembly must be designed to satisfy Section D.3.3.4.3 in ACI318-11 Appendix D. In accordance with D.3.3.4.3 (a), the concrete breakout strength needs to be greater than 1.2 times the nominal steel strength of the anchor, 1.2NSA. This requires a concrete breakout strength of 87 kips for a Steel Strong-Wall that uses a 1-inch high-strength anchor.

Figure 2: Steel Strong-Wall Grade Beam Testing
Figure 2: Steel Strong-Wall Grade Beam Testing

Grade beams without the anchor reinforcement detail and with flexural and shear reinforcement designed to the Appendix D amplified anchorage forces performed similar to those with closed-tie anchor reinforcement and flexural and shear reinforcements designed to the non-amplified strength level forces. Both, however, came up short of the necessary forces required by Section D.3.3.4.3 (a). From Test V852, we discovered that even though the flexural and shear reinforcement were designed with the amplified forces, the non-closed tie u-stirrups did not ensure the intended performance. From observation, the u-stirrups do not provide adequate confinement of the concrete and tend to open up under loading conditions, resulting in splitting of the beam at the top as can be seen in the photo.

Test V852: Non-Closed U-Stirrups
Test V852: Non-Closed U-Stirrups

Tests W785 and W841 resulted in the best performance. Both test specimens contained flexural and shear reinforcement designed for the amplified forces, as well as closed-ties. Two configurations were tested to study their performance — two piece closed-tie anchor reinforcement in W785 and a single piece closed-tie anchor reinforcement in Test W841. As seen in Figure 2, their performance was very similar, and met the requirements of Section D.3.3.4.3 (a). The closed-ties helped confine the concrete near the top of the beam, allowing the assembly to reach the expected performance load (See the photo below). It’s important to indicate the following specifics in the New Grade Beam Anchor Reinforcement Details:

  • Anchor Reinforcement is #4 closed-ties
  • SSWAB embedment depth is 16″ +/- ½” (as shown in Detail 3/SSW1.1). This is to ensure there is enough development length of the anchor reinforcement on both sides of the theoretical breakout surface as required by ACI318-11 D.5.2.9.
  • The minimum distances from the anchor bolt plate washer to top and bottom of closed tie reinforcement are 13 inches and 5 inches respectively to ensure proper development above and below the concrete breakout cone (refer to Detail 3/SSW1.1).
  • The spacing between the two vertical legs of the anchor reinforcement tie must be 10 inches apart. While this may differ from your shear reinforcement elsewhere in the grade beam, it ensures the reinforcement is located close enough to the anchor and adequate development length is provided.
  • Flexural reinforcement (top and bottom) and shear reinforcement (ties throughout the grade beam length) are per the designer. Simpson Strong-Tie has provided information in Detail 3/SSW1.1 for the applicable minimum LRFD Applied Design Seismic Moment (See Figure 3) to make sure the grade beam design will at least resist the applied anchor forces. Project design loads not related to the Strong-Wall panel also should be considered and could control the grade beam design.
Closed-Tie Anchor Reinforcement
Closed-Tie Anchor Reinforcement
Figure 3: LRFD Applied Design Seismic Moment
Figure 3: LRFD Applied Design Seismic Moment

Simpson Strong-Tie is interested in hearing your thoughts on the new details. What is your opinion? How have the new details been received on your job sites?

Part II: Tensile Performance of Simpson Strong-Tie® SET-XP® Adhesive in Reinforced Brick – Test Results

Guest blogger Jason Oakley, field engineer
Guest blogger Jason Oakley, field engineer

This week’s blog post is written by Jason Oakley. Jason is a California registered professional engineer who graduated from UCSD in 1997 with a degree in Structural Engineering and earned his MBA from Cal State Fullerton in 2013. He is a field engineer for Simpson Strong-Tie who has specialized in anchor systems for more than 12 years. He also covers concrete repair and Fiber-Reinforced Polymer (FRP) systems. His territory includes Southern California, Hawaii and Guam.

This post is the second of a two-part series on the results of research on anchorage in reinforced brick. The research was done to shed light on what tensile values can be expected for adhesive anchors. In last week’s post, we covered the test set-up. This week, we’re taking a look at our results and findings.

To briefly recap the test set up, it was conducted in September 2014, at an office building in Burbank, Calif. Slated for demolition, this building provided an opportunity for Simpson Strong-Tie to install and test 1/2-inch diameter anchors using Simpson Strong-Tie® SET-XP® anchoring adhesive in both the face and end of the 8-1/2 inch wide reinforced brick wall. A 12-ton rated pull rig at the face and end of the wall was used to pull test the anchors to failure.

Table 1 shows the results for both face and end of wall anchors. Each data set was limited to testing three anchors of the same diameter and embedment depth. The coefficient of variation (COV) showed that the spread of the data was fairly narrow (11% maximum) for the face of wall anchors, but much higher for the end of wall anchors (24%). There are a couple of things worth noting here.

Table 1 - Tensile Results of 1/2" Diameter Threaded Rods in Reinforced Brick
Table 1 – Tensile Results of 1/2″ Diameter Threaded Rods in Reinforced Brick

Anchors 4, 5 and 6 showed that reinforced brick is capable of achieving significant capacity for anchors embedded past the grouted portion of the wall to a depth of six inches. The threaded rods were a mix of F1554 Gr. 36 (newer specification) and A307 Gr. C (older specification – likely the anchors that failed at 14,000 lbs.), which might explain the observed variation in capacity for anchors 4, 5 and 6. At what point breakout would have been achieved if higher tensile strength steel had been used is unknown but it can be estimated. What is clear is a significant reduction – probably around 60% (relative to an estimated breakout capacity of around 17,000 lbs. for an anchor embedded six inches deep far away from an edge) – can be expected for near-edge conditions, despite the presence of two #4 bars running along the edge of the wall at the window. A near-edge failure is shown in Figure 6.

Figure 6 – Anchor 13 near edge at window (anchor 14 and 15 similar)
Figure 6 – Anchor 13 near edge at window (anchor 14 and 15 similar)

At a reduced embedment depth of 4-1/2 inches, Table 1 showed that anchor location (anchors 7 through 12) had little effect on performance whether anchors were installed in the middle of the brick or in the head joint mortar. The failure modes were largely a combination of breakout and pullout as shown in Figure 7 and 8.

Figure 7 – Failures of anchors 7 through 12 (white arrows point to anchor center)
Figure 7 – Failures of anchors 7 through 12 (white arrows point to anchor center)
Figure 8 – Anchor 10 failure at face of wall (anchors 7, 8, 9, 11 and 12 similar)
Figure 8 – Anchor 10 failure at face of wall (anchors 7, 8, 9, 11 and 12 similar)

The end of wall anchor results shown in Table 1 revealed a significant reduction in adhesive tensile capacity and greater variation (COV) relative to face of wall results. Two possible contributing factors for such a high COV could be:

1) The bond strength between the grout and surrounding brick wythes is variable, and

2) The size and quantity of the voids present in the grout is probably inconsistent along the height of the wall – some areas are better than others – leading to further variation of the test results.

Figure 9 shows evidence of a slip plane failure for anchors 1, 2 and 3. Looking at the brick top and bottom surface, referred to as the bed, a scored surface can be seen running perpendicular to the length of the brick (and hence the wall surface) as shown in Figure 10. Perhaps the intent of scores is to help improve the bond strength between the brick and mortar. But this assumed benefit is limited to the bed line. The face and side of the brick are smooth. Consequently, the bond strength between the grout and brick is low enough, combined with lack of grout confinement between the two wythes, to have an appreciable effect on the anchor ultimate tensile capacity.

Figure 9 – Anchor 1, 2, and 3 failures at end of wall (1/2 inch x 6” emb.)
Figure 9 – Anchor 1, 2, and 3 failures at end of wall (1/2 inch x 6” emb.)
Figure 10 – Reinforced brick bed profile
Figure 10 – Reinforced brick bed profile

To summarize, this test program discovered that the tensile performance of 1/2-inch adhesive anchors in the face of the wall can be substantial for cases where anchors are located far enough away from a free edge. Performance is similar for anchors placed in the center of the brick or in the mortar joint, suggesting it doesn’t matter where the anchors are placed on the wall (obviously this isn’t true for anchors near a free edge). Special precautions should be taken especially for anchors located near an edge where small intermittent voids may exist in the grout. Anchor installation should ensure that sufficient quantity of adhesive has been injected into the hole. Figure 11 proves that this is possible. However, screen tubes should be considered if large voids are present, although large voids are expected to be rare in reinforced brick. End of wall anchorage applications should be designed carefully especially if significant tensile capacity is a design requirement.

Figure 11 – Anchor 2 end of wall voids filled with SET-XP® adhesive
Figure 11 – Anchor 2 end of wall voids filled with SET-XP® adhesive

Determining what the allowable load should be can be a little tricky. ICC-ES AC 58, the criteria used for adhesive anchors in masonry base material, lists several safety factors depending on whether creep and/or seismic tests have been performed. Conducting creep and seismic tests on an outdated building material like reinforced brick would be difficult because replicating 60- year-old construction accurately in the laboratory will probably be difficult. Reinforced brick has been largely replaced by grout-filled CMU as the preferred masonry building material — at least in Southern California. What safety factor should be used that would permit seismic loading of anchors in a relatively antiquated building material like reinforced brick is debatable.  Perhaps AC 60, the criteria used for assessing adhesive anchor performance in unreinforced masonry elements (URM), would serve as the best guide. It requires a minimum safety factor of five against failure and limits adhesive anchors to resisting earthquake loads only. But AC 60 also requires that the average ultimate load used not exceed an axial displacement of 1/8″ and limits the allowable load to no more than 1,200 lbs.

Despite the obvious structural dissimilarity between URM and reinforced brick and additional AC 60 requirements, Table 2 shows what the allowable loads would look like for the results of this test program if a safety factor of five was chosen. These loads are based on a wall of unknown material properties (compressive strength, tensile strength and bond, etc.) for a specific building, and may not apply to other reinforced brick buildings.

Table 2 – Allowable loads of 1/2-inch diameter threaded rods in reinforced brick using AC58
Table 2 – Allowable loads of 1/2-inch diameter threaded rods in reinforced brick using AC58

Many factors were not investigated in this test program, such as shear, creep, the simulated seismic test, just to name a few. While the evidence so far suggests that an adhesive anchor in reinforced brick performs similarly to grout-filled CMU, more testing would be necessary to substantiate this claim fully. What is very clear is the tensile tests performed on the 60-year-old Burbank office building showed that reinforced brick is a material capable of resisting appreciable anchorage forces. Of course, while a major effort is made by manufacturers to provide engineers with lab tested “code values” for design use, it can’t be ignored that the material properties of any structural element can be variable. Additional factors such as material deterioration, workmanship, etc., can all have an effect on anchorage capacity. This means that it’s never a bad idea to assess anchor performance through site-specific pull tests if gauging strength accurately is important to the anchor system design.

What have your experiences been with reinforced brick? Have you called for pull tests in this material? What were the results? Please feel free to share your experiences in the comments below.

 

Part I: Tensile Performance of Simpson Strong-Tie® SET-XP Adhesive in Reinforced Brick: Test Set Up

Guest blogger Jason Oakley, field engineer
Guest blogger Jason Oakley, field engineer

This week’s blog post is written by Jason Oakley. Jason is a California registered professional engineer who graduated from UCSD in 1997 with a degree in Structural Engineering and earned his MBA from Cal State Fullerton in 2013. He is a field engineer for Simpson Strong-Tie who has specialized in anchor systems for more than 12 years. He also covers concrete repair and Fiber-Reinforced Polymer (FRP) systems. His territory includes Southern California, Hawaii and Guam.

 

This post is Part I of a two-part series. In this post, we’ll cover the test set-up and next week in Part II, we’ll take a look at our results and findings.

More than half a century ago, reinforced brick was a fairly common construction material used in buildings located in Southern California and probably elsewhere in the U.S. Reinforced brick can be found in schools, universities, and office buildings that still stand today. This material should not be confused with unreinforced brick masonry (URM) that is also composed of bricks but is structurally inferior to reinforced brick. Engineers are often called to look at existing reinforced brick structures to recommend retrofit schemes that, for example, might strengthen the out-of-plane wall anchorage between the roof (or floor) and wall to improve building performance during an earthquake. Yet, limited or no information exists on the performance of adhesive anchors in this base material. This series of posts shares the results of research on anchorage in reinforced brick in hopes of shedding light on what tensile values can be expected for adhesive anchors, including any important findings encountered during installation and testing.

Reinforced brick sample
Reinforced brick sample

In September 2014, one wall of an office building in Burbank, CA, was slated for demolition. This presented an opportunity for Simpson Strong-Tie to install and test 1/2-inch diameter anchors using Simpson Strong-Tie® SET-XP® anchoring adhesive in both the face and end of the 8-1/2 inch wide reinforced brick wall. The building is shown in Figure 1 and the wall cross section is shown in Figure 2. The bricks measured 3 inches wide by 3-1/2 inches tall by 11-1/2 inches long and the drawings required that the bricks conform to ASTM C62-50, a standard that still exists today. According to the drawings, the walls were reinforced with #4 vertical bars spaced 24 inches on center. Mortar was specified as “1 part plastic cement and 3 parts sand.” The grout used to fill the 2-1/2 inch gap between the two brick wythes is identical to the mortar except “add sufficient water to pour.” The engineer’s drawings specified two #4 bars running parallel to the edge at all wall openings including windows. Although the actual material properties of the mortar, grout, brick, and bond between these components are unknown, the results and findings of this research should serve as a reasonable but rough indicator as to the material quality and workmanship of the wall. Anchor identification numbers and locations are shown in Figures 3 and 4.

Figure 1 – Reinforced brick building
Figure 1 – Reinforced brick building
Figure 2 – Reinforced brick section
Figure 2 – Reinforced brick section
Figure 3 – Anchor identification at inside face of wall (anchor diameter ½”)
Figure 3 – Anchor identification at inside face of wall (anchor diameter ½”)
Figure 4 – Anchor identification at end of wall (anchor diameter ½”)
Figure 4 – Anchor identification at end of wall (anchor diameter ½”)

While the brick base material was mostly solid, in some cases it was necessary to inject more adhesive in the hole due to the presence of small intermittent voids in the grout that were doubtlessly air pockets trapped during the grouting process. To resolve this problem, enough adhesive was injected such that excess adhesive could be observed coming out of the hole during insertion of the ½ inch diameter all-thread rod. This condition was limited to anchors located near the window edge (anchors 13, 14 and 15) and the end of wall (anchors 1, 2 and 3). The base material was solid at all other locations. No screen tubes were used for any holes.

Figure 5 shows a 12-ton rated pull rig at the face and end of the wall used to pull test the anchors to failure. The pull rig reaction bridge has a clearance of 12 inches between supports to allow breakout as a possible failure mode. Using a reaction bridge extension increases the clear span to 18 inches. ASTM 488 requires a free span clearance of four times the embedment depth. This standard was not followed because exceeding the flexural bending capacity of the wall was a concern. In most cases a minimum clear span of at least three times the anchor embedment depth was met.

Figure 5 – Pull rig without (left) and with (right) reaction bridge extension
Figure 5 – Pull rig without (left) and with (right) reaction bridge extension

With the testing parameters in place, next week I’ll share the results of the tests.

What Factors Contribute To A “Resilient” Community?

The world has seen many increasingly catastrophic natural disasters in the past decade, including Hurricane Katrina (Category 3) striking New Orleans in 2005, 2010’s 7.0 magnitude Haiti and 8.8 magnitude Chili earthquakes, the 9.0 magnitude Japan earthquake along with the Christchurch earthquake (6.3 magnitude) in 2011, the tornado outbreak in 2011 which included an EF4 striking Tuscaloosa, AL and a multiple-vortex EF5 striking Joplin, MO. We also saw Category 2 Hurricane Sandy, the largest Atlantic hurricane on record in 2012 and the EF5 tornado striking Moore, Oklahoma in 2013.

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