The known bugs page was formerly hosted here and has since been moved to the MASS software documentation site:

Known Bugs in MASS

For questions about specific bugs, or to report a bug, contact mass@canadamasonrycentre.com

Starting in 2010, Masonry Analysis, Structural Systems (MASS) has been available as a design tool to engineers across Canada. From day one, our mission has been to provide an effective design resource that saves significant time in the engineering design process without compromising the reliability and integrity of your design calculations. We have received a lot of feedback and always make a sincere effort to keep development costs low by only spending on areas that directly improve MASS.

As of May 15th, 2018, the price of all software renewals and purchases can be seen in the table below:

Compared to prices offered starting in 2013, this is equivalent to only a 1.9% annualized increase.

Full pricing can be found on the MASS website. With these new pricing options, there are a number of other items to keep in mind.

License revenue goes straight to improving MASS

Just to list a few examples, a new in-plane lateral load distribution module, Shearline, was created for Version 2.0 to save time on simple, single storey elevations that generally are not allocated much engineering design time. The most recent major update came in Version 3.0 where the entire scope of MASS was shifted to using the updated editions of CSA Standards for designers working in areas where the 2015 National Building Code of Canada has already been adopted. Between these major releases, minor updates have been made and released to add smaller items like fire resistance ratings, more reliable printing, and an improved launch screen. Throughout the entire process, bugs have been diagnosed, tested, and patched within each minor update to ensure that you can be confident when using MASS. The most recent example of this can be seen in Version 2.2.1 which was released after Version 3.0 which you can read more about here.

Currently, work is being done to expand the scope of MASS to include Chapter 16 seismic design requirements added in the 2014 edition of the CSA S304. This will include shear wall deflections, ductility seismic force reduction factors, ductility verification, and plastic hinge requirements. In addition to the seismic work, a new multi-storey shear wall module is under development to save time for many multi-storey structures.

Licensing revenue goes directly to improving MASS and improving it on a continuing basis.

MASS is well supported and maintained

If you have ever had any issues getting MASS running or have had technical questions about the software’s calculations and overall design approach, you have contacted MASS support. Unlike many software packages that operate using a ticketing system and involve waiting periods and escalations, anyone with a MASS license has immediate, direct access to engineering support through the Canada Masonry Design Centre. We take pride in offering excellent customer support that is knowledgeable and available for when you need it.

MASS Licenses include more than just access to the MASS Software

While the biggest part of the decision to renew MASS is based on getting access to the software, once you have a valid license, other benefits are included at no extra cost. While some programs like to nickel and dime for add-ons and features, every MASS user has access to the complete version with no fine print. When updates are released and the software is improved, you don’t have to pay an upgrade fee. Simply maintaining and renewing your MASS license entitles you to the most up to date version that is available.

MASS license holders also get notified first when a new course or seminar has been made available. The most recent iteration of the CMDC’s Engineered Masonry Design Course was announced and filled within 48 hours by MASS users who had the advantage of being the first to know about it.

Discounts are available for everyone

Everyone likes getting a deal and just because individual renewals go for $220 per person doesn’t mean that’s what you have to pay! There are many types of discounts available that you should not hesitate to take advantage of:

Early-bird Renewal Discount

Chances are, you’ve been linked here from one of our email notifications and if that is the case, you will also see that you can save 15% if you don’t put off your renewal to when your next masonry project comes along. This is available to everyone with a MASS license that needs renewing so act quickly to take advantage.

Multi-User Discount

Have more than one engineer working in your office? We have special office packages for groups of 5, 10, or more engineers that make it cheaper and more cost effective compared to purchasing individual licenses. Click here to see all of the available packages along with pricing. Note that these cannot be spread across multiple locations, which leads us to…

Discounts for Companies spread over multiple locations

If you fit this category and have at least four offices with at least one small office package, you have already been proactively contacted with a special discount offer. These are offered to try and help make up for the fact that the larger offices packages cannot be divided between engineers working from different locations.

Creating software is expensive. Period.

Everything in the software creation process takes a lot of time, energy, and money. From specifications and documentation to programming and quality assurance testing, engineering software cannot be done without significant investment both initially and on an ongoing basis. This is all before factoring in support, website maintenance, license management, and distribution.

You may have also noticed that promotion and advertising hasn’t been mentioned. The MASS software is a tool that is growing in popularity thanks to reputation and word-of-mouth alone! None of the revenue from license sales is used for anything that doesn’t go straight back in to the software you are using today.

Putting the “Not” in “Not-for-Profit”

The MASS software represents a joint venture between masonry contractors (through the not-for profit contractor association: CMDC) and masonry block producers (through the not-for-profit industry association: CCMPA). Together, the masonry industry covers over 75% of software related costs, leaving less than 25% which comes from licensing purchase and renewal fees. There is a good reason why there isn’t another masonry design software package for Canadian designers offered by a private company.

Still have questions?

Feel free to reach out to MASS support with any comments, suggestions, or other feedback regarding this change. While we understand that for many designers, masonry is a component that only comes up on projects here and there. We work very hard to make sure MASS is a product that is cost effective and pays for itself after even just one job. MASS licenses are deliberately priced and subsidized in such as way that it can be accessible to any designer in Canada using masonry in their projects.

If you have any questions, please do not hesitate to call or email the Canada Masonry Design Centre. We are here to help!

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

The spots went much more quickly than anticipated but just two days after the course notification was sent out, all of the available seats for the Engineered Masonry Design Course (EMDC) have been filled. There have been quite a few calls that have come in since the last seat was taken and we regretfully cannot accommodate a larger class size. This is a function of our training centre classroom (hosted with OMTC) which can only seat 30 engineers at full capacity.

Classroom ready for the start of the 2018 Mississauga edition of the greatly anticipated EMDC

To be notified when the next course is announced, feel free to contact us and request to be placed on the waiting list. Alternatively, all current MASS users are notified when any new course or seminar is announced. New courses can also be requested on our Course and Seminars pages.

The Shearline module in MASS is a useful tool to quickly and easily determine how lateral, in-plane forces are distributed within a single elevation. While the scope of the shearline module is relatively basic and relies upon a number of simplifying assumptions in the analysis, it doesn’t take much time to gain an understanding of how these loads are distributed around openings and movement joints.

One of the required steps before the loads are distributed is for the user to review the position and geometry of each pier and decide whether it be modeled as “Fixed” or “Cantilever”. More specifically, as an elevation is laterally loaded, whether each element’s deflection would more closely resemble that of a fixed or cantilever shear wall. Below is an illustration of how a shear wall deflects when the top end fixity is left unrestrained, or cantilever (top), compared to a shear wall deflecting with the top end condition fixed, restricting only rotation (bottom).

While the difference has a big effect on the design of the shear wall (fixed top reduces factored moment by 50%, two critical sections instead of one), the important aspect when modelling a shearline is lateral stiffness and rigidity. Cantilever shear walls deflect more than those that are fixed from rotating therefore attracting less load relative to the other shear walls within the elevation. An example I posted online a few years ago is included below and runs through the entire process of designing a shear wall elevation using the Shearline module in MASS.

Looking at the example from the video, consider the two piers highlighted below:

The leftmost pier has nothing above it to restrict lateral rotation so it’s behaviour would more closely resemble that of a cantilever pier. Conversely, the pier on the right has a significant area of masonry which would more likely cause it’s deflected shape to more closely resemble that of a fixed pier.

How to decide of a pier is modeled as a Fixed or Cantilever shear wall

When MASS Version 2.0 was in development, CMDC looked into creating an algorithm that could look at an elevation and automatically designate each element as fixed or cantilever. Unfortunately, development of this functionality did not proceed very far because there was nothing in any building codes, CSA standards, or even consensus within the design community regarding what exactly constitutes fixity at the top of a shear wall. As a result, end fixities were left as direct user inputs, having to be manually assigned by the designer, using their professional engineering judgement, each time a Shearline is created.

Often when there is a difficult engineering judgement, the response it to make the more conservative decision. While there are other design decisions in the development of MASS where choices were made in the interest of remaining conservative, there is no clear-cut “conservative” decision when it comes to lateral load distribution. While a fixed shear wall deflects less (thus attracting a larger shear force due to the increased rigidity) compared to a cantilever shear wall, it is important to remember that lateral, in-plane load distribution is relative. What increases loading for one element will take away from all of the others.

It is no coincidence that the examples shown on the MASS website, in the help files (found by pressing F1 within MASS), in the CMDC Masonry Design Textbook, or shown here highlight cases that are not particularly controversial when it comes to differentiating between fixed and cantilever behaviour. As an example, consider Figure 40 (shown below) from section 6.2 of the MASS Help Files demonstrating a) highlighted piers that would behave as cantilever compared to b) highlighted piers that would behave as fixed shear walls:

The reality is that there are many cases in the middle that can be taken either way with arguments on both sides having valid and rational points. At the end of the day, it is left up to the judgement of the engineer to make the final call.

If you have any questions, please do not hesitate to call or email the Canada Masonry Design Centre.

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

The MASS software is a useful tool for designing the individual structural elements of a masonry building. While there is a shearline module for simple, single-storey elevations, there is no such equivalent when it comes to multi-storey shear wall design (yet). It is left to the designer to model each element of their shear wall within MASS in a way that accurately represents its behaviour. This article will touch on a few of the major aspects that come up when using MASS for multi-storey designs.

To jump straight to a specific aspect, click the heading links below:

• Load Distribution
• Total Height
• Top End Fixity

Click here to jump straight to the summary. 

Load Distribution

Before diving into the multi-storey specifics of shear wall design, it is useful to first recall the scope of the shear wall module in MASS.

Shear wall module scope:

The shear wall module in MASS designs an individual shear wall element for in-plane moment and shear based on the loads that are applied to that individual element.

The shear wall module can be used for multi-storey buildings so long as the designer has taken into account the various ways in which a shear wall element interacts with the structure around it.

This includes:

• The accumulation of axial loads applied above the storey being designed
• The accumulation of lateral loads applied above the storey being designed
• Any overturning moments resulting from lateral loads applied above the top of the storey being designed

Example Exercise

Consider the example below, where the second storey of a four storey shear wall is being designed using MASS. In order to design the second floor shear wall element, all loads must be distributed to the top of the wall from all of the walls above. Each storey is 4m tall and all dead loads include self-weight.

Before expanding the solution, it may be a worthwhile exercise to calculate the solution yourself to test your skills.

Note: All axial loads are assumed to be placed at the centre of the wall and evenly resisted by the full cross section (no load dispersion is considered within the section). In cases where axial loads are applied with some eccentricity, this can be accounted for in MASS using an applied moment with a moment arm equal to the eccentricity of the load.

While distributing loads makes up the majority of the work needed to design multi-storey shear walls in MASS, there are still three other important aspects to consider.

Total Height

It is possible that while the full shear wall is not considered “squat”, an individual storey may have a height to length aspect ratio less than 1. In this case, it is important to change the total height to match the height of the full shear wall so that MASS doesn’t treat the individual storeys as squat shear walls. By default, the total height is set to the same value as the shear wall height so if it is unchanged, there may be an unnecessary reduction in moment resistance.

A full article explaining the difference between “Height” and Total Height” can be found here, including examples showing between 15% to 24% of moment resisting performance losses for not taking the total height into account.

End Fixity

When looking at a shear wall element within a larger shear wall, the objective is to take all aspects of being part of a larger shear wall into account. While there is an option in MASS to fix the top of a shear wall from rotating, the effect on the design can be seen in the difference in bending moment profile below:

Applying a rotational fixity at the top of the wall effectively divides the moment between the top and the bottom of the wall’s supports. While the “Fixed (R)” end condition was added to MASS for the purpose of shear wall designs with significant masonry above which prevent rotation, the scenarios where it is appropriately used would more closely resemble what is pictured below, taken from section 5-7 of the MASS Help files:

As a result, there is no need to change the end fixity of the top of the shear wall, as long as the loads have been properly distributed. Using the cantilever configuration for a multi-storey shear wall , it can be designed element-by-element, accurately designing each storey for the same shear and moment profile as would be used if the full multi-storey shear wall were designed at once.

Only by using the default cantilever fixity selection can an individual storey be adequately modeled without having to apply additional loads to cancel out the effect from a fixed top rotational end condition.

Summary

To quickly summarize, there are three main things to consider when designing a multi-storey shear wall using MASS:

1. Load Distribution: all loads not applied directly to the storey being considered must have their effects included. In particular, the accumulation of axial loads, lateral loads, and overturning moments due to loads applied from storeys above.
2. Total Height: To avoid being penalized for squat shear wall moment arm reductions, be sure to change the total height in order to accurately reflect the full height of the wall.
3. End Fixity: While it may at first seem reasonable to factor in the rotational stiffness from storeys above by changing the top fixity to Fixed (R), it will not result in a moment profile that accurately reflects the moments experienced by the storey in question. The default cantilever selection with properly distributed overturning moments is a more appropriate selection.

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

If you have ever designed a multi-storey shear wall and wondered why the moment resistance is less than expected, the reason is likely CSA S304-14: 10.2.8:

MASS automatically identifies shear walls that have an aspect ratio less than 1 and designates them as squat shear walls. Keeping all calculations and design results in accordance with the CSA Standards, it also correctly reduces the moment arm of all steel in tension when applicable which is why there is a reduction in moment resistance. While it is often the first reaction of many users to assume that this behaviour comes from a bug in the software, MASS is behaving as intended.

Multi-Storey Applications

What if you are designing just one element within a larger shear wall where the element has an aspect ratio less than one but the full shear wall does not? Is it correct to be applying the reductions from clause 10.2.8 to elements such as these? Consider the example below:

This example which was used in the Multi-Storey Shear Wall Design article demonstrates an instance where this clause comes into play. The entire shear wall itself is clearly not squat as it’s aspect ratio is 3.2. As it is loaded, it is behaving as a non-squat shear wall so it is not correct to be applying clause 10.2.8 to the design of an individual storey. In order to design this wall in MASS, only the individual elements can be modeled and designed separately. As you can see, the wall input into MASS on its own is designated as a squat shear wall which is where the Total Height input comes in handy: it allows the user to tell MASS that while an element may be “squat”, it should not be treated as such.

“Height” vs. “Total Height”

The scenario described above is the reason multiple height inputs are available in MASS.

Height refers to the vertical dimension of only the shear wall element being modeled while Total Height refers to the vertical dimension of the full shear wall assemblage, beyond just what is being modeled.

If Storey 2 is modeled in MASS without any consideration of the larger shear wall it is apart of, it is designated as being squat as it’s 4/5 aspect ratio is less than one. When the total height is changed to the full 16m, the aspect ratio used to apply squat reductions from clause 10.2.8 increases to 3.2 and the result is an improved moment resistance.

Impact on Design

How much of a change does this make to a shear wall design? Using the example from earlier, when designing using a 20cm, 15MPa concrete masonry unit, taking the total height into account means the difference between using No. 15 and No. 20 bars placed exactly the same. If using No. 15 bars for both designs, the squat version of the MASS file would need to go all the way from a 15 to 30MPa strength unit to compensate. Furthermore, if the masonry and reinforcement properties were both fixed to the same design, the difference in capacity can be seen on the interaction diagrams below:

Comparison of moment envelope curves for shear wall design both including and neglecting the total height

For the critical load combination (#15: 0.9D + 1.4W), this means that the moment resistance of the wall is reduced from 1333.5kN*m to 1111.5kN*m, or by 222kN*m, simply by not taking the aspect ratio of the full wall into account!

This effect is further demonstrated in the example below where 70% of the vertical reinforcement is concentrated on either end of the wall. This significant reduction in moment is a direct result of a reduced moment arm for the steel that is in tension and furthest away from the compression zone. Note that this design uses the exact same materials simply arranged differently.

Comparison of moment envelope curves for shear wall design both including and neglecting the total height

There is now a 330 – 430kN*m reduction in the moment resistance compared to the 200 – 275kN*m reduction observed when the reinforcement is evenly distributed. One thing to note for all of these comparisons is that the difference in moment resistance diminishes when the applied axial load approaches P_f,max.

For those curious, a comparison of the uniformly distributed reinforcement and concentrated end steel designs can be found by expanding the section below:

If you have any questions, please do not hesitate to call or email the Canada Masonry Design Centre.

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

National Masonry Design Programs is proud to announce the official release of Masonry Analysis Structural Systems (MASS^TM) Version 3.0.

Major Changes in MASS Version 3.0

The major changes are listed below while the full list of changes can be found on the MASS website here as well as in Section 1.6 of the MASS help files.

Design Codes and Standards

As mentioned above, Version 3.0 adapts all masonry design procedures from Version 2.2 to using current design standards. Two papers outlining these changes were published and presented by Dr. Drysdale, Dr. Banting, and David Stubbs at the recent 13^th Canadian Masonry Symposium hosted by the Canada Masonry Design Centre (CMDC) and Dalhousie University. These papers can be found here (Part 1: Non-Seismic Changes) and here (Part 2: Seismic Changes). With the exception of seismic minimum reinforcement requirements, all of the changes within the current scope of MASS are considered non-seismic. The next release of MASS which is already in development will increase this scope to include higher levels of ductility performance, as well as the rest of the newly added CSA S304-14 Chapter 16: Special Provisions for Seismic Design.

New Project File Format

In an effort to reduce confusion around which projects have been designed in accordance with which codes and standards, the project file format “.masonry14” was created which designs exclusively to the current standards. MASS Version 3.0 can still open old projects, however upon opening them, you will be prompted to “Save As” a “.masonry14” project as the design results may be affected. An article explaining the difference and compatibility can be found online here.

Additional Bug Fixes

As software issues are discovered, they are posted on our “Known Bugs” page which is linked from the MASS website homepage and kept up to date. There was one bug recently discovered internally at the CMDC what was also present in Version 2.2 which was re-compiled at MASS Version 2.2.1 and included in the Version 3.0 download. An explanation of the bug can be found here and a Version 2.2.1 explanation can be found here.

How to upgrade

Step 1: Open the Notification email and follow the link to the MASS Upgrades page:

Didn’t receive the email? Check with your admin staff or local IT professional who may be in charge of software licensing for your company. Only MASS website account holders or manually assigned users will have been sent the notification email. In the event that you require access to the download but someone else in your office was sent the email, simply using a forwarded copy with the credentials included is enough to access the download (Note that this does not require the account password or other more sensitive information such as address. We do not save or even have access to payment information)

Step 2: On the MASS upgrades page, select the option to download MASS Version 3.0.

Step 3: Copy and Paste your email address and corresponding serial number and clock “DOWNLOAD” to begin the download:

Note: Even a change of one typed character is the difference between the download working and not being found in the database. Please double check your entries or copy and paste from the email notification which has been pulled form the same database.

Step 4: File will begin downloading:

For most web browsers, the keyboard shortcut CTRL + J can be used to open the list of downloaded files.

Step 5: While the package is downloading, it is highly recommended that all existing versions of MASS be uninstalled prior to installing MASS Version 3.0. For assistance on how to uninstall programs, click here.

Step 6: Once the file has finished downloading, the directory can be extracted and opened to show the following files:

After uninstalling all prior versions of MASS (including Version 2.2), run the “setup.exe” file to install MASS Version 3.0.

There is also a video available on the downloads page outlining the same process for MASS Version 2.0 which is essentially unchanged. For assistance, please do not hesitate to contact the authorized MASS technical support provider, Canada Masonry Design Centre.

Back in April of 2016, the release of MASS Version 2.2 marked what was thought at the time to be the final version of MASS which designed using the old 2004 versions of the CSA Standards. In the early development stages of Version 3, before any technical changes were implemented, some user interface items (ie. MASS Welcome Screen) and other common headaches (ie. Printing, activating) were also added to help ease the transition of switching to a new design code in MASS.

The discovery of a new bug prior to the release of MASS Version 3.0 is included on our Known Bugs page as well as having a full explanation available here.

While the bug was investigated and a fix was found and tested, the decision was made to add the fix to Version 2.2 as well in an effort to make it age a little better. While old versions are not supported and there are no plans to release updates to old versions, an exception was made for two reasons.

1. The bug discovery and fix occurred shortly ahead of the Version 3.0 release
2. Version 2.2 is the last version that will design using the old 2004 CSA Standards as well as open the old “.masonry” project files (click here to read more on the new MASS project file format)

What is different in Version 2.2.1?

MASS Version 2.2.1 is identical to Version 2.2 with the exception of a fix to the bug explained here.

How to upgrade Version 2.2 to Version 2.2.1

1. To upgrade Version 2.2 to Version 2.2.1, first uninstall MASS Version 2.2. For assistance on how to do this, click here.
2. Once Version 2.2 is successfully uninstalled, go to the Version 3.0 installation folder and run the file named “MASS221.msi”

The version can be checked within MASS by clicking “Help” on the top toolbar and then select “About MASS“.

Please do not hesitate to call or email with any questions. Click here for a full outline of the various services offered by CMDC (the authorized technical support provider for MASS)

When software bugs are found, notifications are posted in the MASS website Known Bugs page, on the MASS welcome screen, as well as here on the CMDC website software blog in an effort to be transparent and keep all MASS users informed. This issue was found within our own office as a result of an inquiry from a MASS user that resulted in this post. The bug was found some time after and as a result, the fix was incorporated into MASS Version 3.0, as well as a modified copy of Version 2.2 specifically to address this issue (click here to read more about Version 2.2.1).

This post outlines the conditions required to trigger this error, the designs where this could have affected design results, the details of the bug itself, and how to check to see if this bug is present in any MASS project.

Jump straight to:

• Bug Summary
• Background information
• What types of designs might be affected
• How to check if a design is affected
• Example
• Our Response

Bug Summary

Under a very specific combination of conditions, MASS may calculate the critical axial load for a reinforced wall, P_cr using both (EI)_eff of 0.4E_mI₀ and Φ_er of 0.75, resulting in a P_cr value that incorrectly combines aspects of reinforced and unreinforced analysis.

This bug only affects designs where all of the following conditions are met:

1. vertical reinforcement is not in tension
2. load combinations with steel in compression also govern the design
3. the wall experiences slenderness effects but is not a slender wall (kh/t > 30)

If MASS designs a wall where the vertical steel is in tension, all of the software’s results are correct. The same is true if any of the other conditions listed above is not true. The unlikely combination of circumstances is the reason why most wall designs are not affected and also why this bug has not been discovered until recently. This has been addressed in MASS Version 3.0 as well as in an updated Version 2.2.1.

Background information

If a wall is reinforced, why is it a problem to use the reinforced reduction factor when it comes to slenderness effects?

There is no problem as long as everything else in the calculations is also treating the wall as if it were reinforced. The issue comes from the way in which MASS sometimes treats the wall as if it were unreinforced when the steel is not in tension. This is done intentionally as ignoring the steel allows the software to use CSA S304 chapter 7 clauses governing the analysis of unreinforced walls when it is beneficial. This also assumes that the addition of steel to an unreinforced (but still grouted) wall will not reduce its capacity. For a full explanation on RM/URM analysis for reinforced walls, click here.

Differences between treating the wall as reinforced vs. unreinforced

Reinforced analysis compared to unreinforced differs in two ways when it comes to determining slenderness effects of a wall:

1. Φ_e vs. Φ_er – Resistance factors for member stiffness used for slenderness effects
2. (EI)_eff – Effective stiffness for consideration of slenderness

Resistance Factors – Φ_e vs. Φ_er

There are two different resistance factors that are used in calculating the critical axial compressive load used for determining slenderness effects; Φ_e for unreinforced walls, and Φ_er for reinforced walls. Click the heading below to expand the CSA references from which these resistance factors are based upon.

As stated at the beginning of this post, the bug is that for reinforced walls, the reinforced reduction factor is sometimes incorrectly applied, using Φ_er rather than Φ_e. On its own, this would not be an issue, however, when combined with the reinforcement assumptions used in determining effective stiffness, there can be a “mixing” of assumptions that results in this bug.

Effective stiffness – (EI)_eff

Similar to the resistance factors, the formula used to determine effective stiffness for slenderness effects is a function of whether or not the wall is reinforced. Effective stiffness, or (EI)_eff, for unreinforced walls is 0.4E_mI₀ while (EI)_eff for reinforced walls is 0.25E_mI₀ (where the applied eccentricity is relatively low, below the Kern eccentricity). Click the heading below to expand the CSA references related to effective stiffness.

Reinforced walls with low eccentricities have an effective stiffness capped at 0.25E_mI₀. Compared to 0.4E_mI₀ which is used for unreinforced walls, there is a 37.5% reduction in stiffness simply for using the reinforced equation for the same wall design. Taking advantage of the unreinforced effective stiffness is what also mandates the use of Φ_e rather than the higher Φ_er.

What types of wall designs are affected?

As mentioned in the summary shown here,

• vertical reinforcement is not in tension
  • c is greater than d for any bar
• load combinations where c exceeds d also govern the design
  • Load combinations with higher axial loads are more likely to have the neutral axis exceed d while load combinations with both low axial load applied with high bending moment are typically closer to a wall’s interaction diagram envelope curve
• the wall experiences slenderness effects but is not a slender wall
  • Slenderness ratio, kh/t, is greater than 10 – 3.5[e₁/e₂] specified in S304-14: 10.7.3.3.1 but less than 30 where axial load is governed by S304-14: 10.7.4.6.4

The only wall designs affected by this bug are those which have axial loads so high that the steel is no longer in tension AND experience slenderness effects without being classified as slender walls (S304-14: 10.7.4.6). Many wall designs that are governed by slenderness effects also require compression forces in masonry coupling with reinforcement in tension and are therefore not affected. For example, single spans with only self-weight and some nominal loads transferred from roof level are often not loaded with enough axial load to move the location of the neutral axis beyond the depth of steel in the wall.

Additionally, in order for a design to be impacted by the presence of this issue, the load combinations where the circumstances above are present must also be critical to the design. Load combinations with the highest axial loads (for example: 1.4D) are most likely to also be governed by load combinations using high lateral loads combined AND lower axial loads (for example: 0.9D + 1.4W).

It might even be easier to rule out the wall designs that are not affected:

• all slender walls are unaffected and correctly handled within MASS
  
• all walls using vertical reinforcement in tension (bars are ignored in compression as they cannot be adequately tied) are unaffected
• all walls that do not have any slenderness effects are not affected
  

Most wall designs fall into one (or more) of these three categories and it takes a special combination of circumstances to trigger a design that results in this bug affecting software result

How to tell if a design is affected

Check to see if the steel is in tension

Look at the location of the neutral axis and compare it to where the vertical bars are placed. If the distance to the neutral axis, c, is less than the depth to the layer of reinforcement, d, then the steel is in tension and your design is not affected.

In this example, a wall constructed using 15cm units (thickness of 140mm) can be checked to see if the steel is in tension by comparing the Neutral axis value in the Simplified Moment Results window to the steel depth, d, which is placed in the middle of the wall (b_w/2).

Steel is in tension (c<d)

Check to see if that load case governs the design result

As mentioned earlier, the load cases resulting in the steel not being in tension tend to differ from the load cases that govern the final design result (1.4D compared to 1.25D or 0.9D + 1.4W). When this is the case, the design is unaffected by the result. The example file highlights this aspect where the load combination resulting in steel being ignored (L.C. #1) is not critical to the design. In this case, load combinations 2 and 3 have total factored moments that are closer to the envelope curve which are based on the correct critical compressive axial load.

Out-of-plane wall designs tend to be governed by load combinations that combine the largest lateral load with the lowest axial load which are more likely to include steel in tension.

Note: To recreate this example for yourself, design a 3m tall, simply supported wall using 15cm, 15MPa units. Apply an unfactored axial dead load of 60kN, turn off self-weight, and apply an unfactored uniformly distributed wind load of 1 kN/m (or 1 kPa when considering a 1m length of wall as is the case for MASS wall modules). When designing for moment and deflection, at the first thing that will happen is that the wall will correctly pass being designed as unreinforced. For the purposes of highlighting this bug, de-select the 0 bars/cell option, effectively forcing reinforcement to be placed in the wall and skipping any iterations that are reinforced.

If the wall design is affected, compare the M_r to the manually adjusted value of M_f,tot

If the bug is present in a MASS project, the total factored moment resistance can be adjusted using the following expression:

M_ftotadjusted represents the adjusted value for the total factored moment taking slenderness effects into account

P_cradjusted represents the adjusted critical axial compressive load

P_crMASS is the critical axial compressive load calculated by MASS for load combinations where the bug is present in the results.

All other terms are defined within the CSA S304-14.

Both a derivation of the P_cradjusted expression as well as an example demonstrating how to use it can be expanded in the two sections below by clicking on each heading:

It is expected that most designs will not meet all of the criteria for the bug to be present as the reinforcement is in tension for most reinforced wall designs. For those designs where the bug is present, it is possible for the the marginal difference in total factored moment to result in a failed design which would have been thought to have passed moment and deflection design. As mentioned earlier, the specific and unlikely combination of circumstances required to trigger this bug within MASS is the likely reason why it has remained undiscovered for so long.

Our Response

Bugs of this nature are taken very seriously. It was discovered in-house but not until very late in the Version 3.0 development process after it had been initially thought to be complete. As a result, the bug was investigated and a fix was added to Version 3.0 as well as to Version 2.2 in the form of MASS Version 2.2.1 (included in the installation directory for Version 3.0 – click here to read more). It has also been posted on our Known Bugs page where it links to this article.

If there is any question regarding the integrity of the results for a specific MASS project file, please feel free to contact CMDC directly. As the authorized MASS technical service provider, CMDC is available to help designers understand the specifics of identifying this issue, as well as any other masonry related technical questions. Click here for more information on technical assistance offered by CMDC.

Length

A beam’s length represents the total length of the entire modeled assemblage including any overhanging length on the outside edges of the supports. This value is typically entered in first and must accommodate the length of the opening above which the beam is spanning as well as the bearing plates on either side. Any additional masonry outside of the primary span is not used when distributing loads and determining the factored moment or shear that must be resisted by the beam. Once specified for a new beam design, a clear span,explained below, is then assumed based on the length needed for bearing on either end.

Clear Span

The clear span refers to the length of the opening above which the beam is spanning. While a beam’s length is typically entered first into MASS, it is also possible to start a MASS design by specifying a clear span and let the software automatically fill in the total beam length based on the length required for bearing on either side, rounded to the nearest modular cell length.

Bearing Length

The bearing length is defined as the length along the beam under which a high concentration of stresses due to concentrated loads is transferred to the supporting structure below. It can be spread over a steel plate or an area of masonry under compression. The default bearing length of 300mm was chosen for MASS because it is the longest allowable bearing length (CSA S304-14: 7.14.1.2) that can use a triangular load distribution and not require additional detailing (ie. using a rocker plate) to ensure a rectangular load distribution. For triangular reaction distributions, the centre of reaction is at one third of the bearing length away from the edge of the clear span and for rectangular distributions, the distance to centre of reaction is at half of the bearing length.

Design Length

Design length is the distance between the centre of reactions between beam supports. It is less than the beam length and greater than the clear span, used to determine the factored moment and shear. For example, checking MASS results by hand and looking to replicate the maximum factored moment at mid-span for a simply supported beam, the design length is used in M_f = wL²/8.

Quick demonstration – From masonry elevation to design using MASS

Starting with an elevation containing an opening with masonry extending above and on either side, a portion must be designated as part of the modeled beam. This example where two courses are assumed for the beam’s height, the full beam length extends one full masonry unit to either side which allows room for the bearing area in addition to the clear span.

For the same elevation, it is also possible to design a single course beam or go all the way up to four courses which can all result in acceptable solutions. Smaller beams have reduced moment capacity mainly from a smaller moment arm between coupling tension and compression forces while taller beams can have intermediate steel requirements (S304-14: 11.2.6.3) and may also have to satisfy additional provisions for deep beams (S304-14: 11.2.7) and deep shear spans (S304-14: 11.3.6). Choosing how a beam is modeled is left to the discretion of the designer.

For all masonry beam designs, a load path for vertical loads must be assumed for transfer to the supporting structure below. The default bearing area with a bearing length of 300mm is shown below resulting in a triangular distribution of the reaction force. Had the bearing length been longer than 300mm, the reaction would have been spread over a rectangular distribution (S304-14: 7.14.1.2).

In order to determine the design length, the centre of each reaction force must be determined. For a triangular reaction distribution, this location is one third of the bearing length away from the edge of the clear span for each support. (Rectangular distributions have a centre of reaction point half way through the bearing area)

The locations of the reaction forces expressed as point loads is then used to determine the design span. They are also where MASS draws the support points underneath the bearing plates in beam drawings.

Note that the difference in unit arrangement between the figures above and MASS has no impact on the design as fully grouted masonry. MASS always starts an assemblage with a full unit however starting with a half unit as was done in the illustrations above is functionally the same design.

As always, feel free to contact us if you have any questions at all. CMDC is the authorized service provider for the MASS software which is a joint effort of between CCMPA and CMDC.