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

It’s real, and it’s spectacular! We are very excited to announce this new release, available immediately and for free to all current, active license holders.

This post originally appeared on the new MASS documentation website. Click here to view the original release notice.

If you are currently using Version 3, you can upgrade to Version 4.0 at any time (download and installation instructions are available at the end of this post).

What’s New in Version 4.0?

A 3 minute preview can be seen below with the longer 11 minute outline available here.

Those videos not enough for you? Click here for the full change log to see what else is new and exciting about the release of Version 4.0.

New Seismic Design Options

MASS has a new seismic design tab for shear walls that allows users to choose between the newer simplified approach added to the 2015 NBCC or the good old equivalent static force procedure. Ductility is now a parameter that can be specified and used for design.

Dealing with a Post-Disaster importance category? You can now specify “moderately ductile” or “ductile” in the seismic tab and let MASS handle the rest – including drift and the ductility verification!

Multi-Storey Shear Walls

Ever found yourself working through a building’s design and asked yourself “What if I could do all this work, but in fewer steps?“. Don’t let your dreams be dreams!

MASS Version 4 adds a new multi-storey module that coordinates the design of several elements to give you a result that matches unit properties and vertically aligns your reinforcement. Worried about your self-weight loads not being up to date as the design changes? Read up on our detailed design strategy and cry tears of joy because we’ve got you covered!

How to Upgrade

Anyone with a current, activated MASS license can upgrade to MASS Version 4.0 at no extra charge. New releases are included as part of keeping an active license, in addition to other benefits such as comprehensive technical support and course notifications.

To begin downloading MASS Version 4.0, click here to visit the upgrades page

Questions about the download, extraction, or installation process? Click here to view the two and a half minute video walk through that will show you how you can install MASS on your computer. There is also a full installation guide available here.

Still have Questions?

Please do not hesitate to contact myself or anyone else in CMDC with any questions or concerns regarding this upgrade.

Canada Masonry Design Centre (CMDC) is the authorized technical service provider for the MASS Software.

Version 4,0 was made possible by the support of our masonry contractor members through CMDC as well as the joint venture partnership through NMDP with CCMPA Canadian Concrete Masonry Producer’s Association – see ccmpa.ca for more information).

When software bugs are found, notifications are posted in the 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 some unrelated testing on Multi-storey walls in MASS Version 4.0. As a result, the fix will be incorporated into the next software release and in the meantime, must be checked for manually by engineers who may encounter this issue.

This post outlines the conditions required to trigger this error, where the design results could have been affected, 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

For shear wall element designs where the web grouting pattern has not been set to “fully grouted” and the flange is fully grouted as a result of vertical reinforcement placed in each cell, the maximum allowable axial load limit is overestimated. The actual envelope curve where axial load is considered to determine moment resistance is plotted correctly and not affected by this bug. As this upper portion of the diagram tends to also correspond to lower factored bending moments, designs with any significant lateral loading would also be unlikely to be affected by this particular item of concern.

The horizontal line represents the maximum axial load, P_r, and in designs affected by the bug, that line’s location is calculated by MASS to be higher than what it should be.

Since this is only triggered for fully grouted walls with the partial grouted selection, there may be other reasons why a bar is being placed in every cell beyond needing the moment resistance. For more information regarding why MASS may be placing so much steel, click here to open this related article (opens in a new tab).

Background Information

The MASS Software has a dedicated design routine for determining Pr,max. The maximum allowable is specified by CSA S304-14: 10.4.1 is 80% of the axial load corresponding to the assemblage in full compression (where ß₁c = l_w).

This upper limit is calculated using a dedicated process which uses a particular formula based on whether the wall is hollow, fully grouted, or somewhere in between. This is done individually for the shear wall web and each flange (or boundary element in the upcoming Version 4.0 release) where the total upper limit is equal to the sum of each of the components added up.

The actual values used in MASS can be found by scrolling down the Detailed Moment Results tab, shown below:

Excerpt from the Results tab showing Pr,max components

The 1039.6 kN value seen in MASS has been incorrectly calculated using the f’_{m,hollow, flange} = 10 PMa instead of the correct f’_m,eff,flange = 7.5 MPa.

Once P_r,max has been calculated, it is can be seen on the P-M diagram (also referred to as the interaction diagram) near the top where a horizontal line is plotted. Values capped by P_r,max as well as those which extend further upward are both shown and can be selected by the user to see more exact values of the individual points.

Pro Tip: When a point is selected, the arrow keys can be used to jump to adjacent points along the envelope curve.

The actual values used along the interaction diagram curve are correctly plotted and are unaffected by this bug. This issue is specifically the height at which the upper limit on axial load has been capped.

What types of designs might be affected?

In order to have a design result that was declared by MASS to be successful when it should not have been, there are two conditions that would have to occur:

Condition 1: The cross section and input selections would need to trigger the bug in the P_r,max calculation.

This means that shear wall flanges with the “partially grouted” selection applied with bars placed in each cell as a result of other user input values are the only types of designs that can have the incorrect P_r,max value calculated. If any one of these conditions is not met, the correct maximum axial load is calculated and even for affected cross sections where the bug is present, the plotted P-M Diagram envelope is still correct, with the exception of the height at which it is capped. Click here to jump to a full description of how to verify this condition

Condition 2: The loading needs to result in an axial factored load that exceeds what would have been the correct P_r,max value.

Load combinations with relatively low factored moments coupled with high axial loads may lie between P_r,max shown in MASS and the correct value. Click here to jump to the full description of how this can be checked in any MASS project file.

Each of these conditions is elaborated upon in the subsequent sections below. If unsure whether a previous design performed in MASS has been affected, MASS technical support is available to manually check the detailed results and confirm whether or not this bug is present in any project file.

How to tell if a design has been affected

Often times, this bug can be seen at a glance by viewing the P-M Diagram for any design. If the horizontal line drawn at P_r,max does not appear to be roughly 80% between the origin and the location where the envelope meets the vertical axis, this project file may be affected. This check is broken down into two conditions, both of which must be satisfied for a design’s results to have been impacted by this bug.

Any use of the software results for design, as well as checks, calculations, and verification described in this section and elsewhere is done at the sole discretion of the user using their own professional judgment. If you have any questions and are not 100% confident in your understanding of the material, please contact MASS support for further assistance.

Manually checking P_r,max (Condition 1)

Confirming whether this bug is present in any MASS project file is a fairly simple procedure. The most thorough approach is to manually calculate the flange contribution to P_r,max seen in the Detailed Moment Results (see example further below for demonstration), however, this can also be done by viewing the P-M Diagram drawing and locating the point of pure compression along the outer envelope curve.

Note: For shear wall designs with flanges, this will correspond to a neutral axis location of the total wall length (including flange thicknesses) divided by 0.8. Also known as the highest point with a corresponding moment resistance of zero.

Visual Inspection Method

In many cases, this issue can be identified by simply eyeballing the general height of the P_r,max limit and comparing it to where roughly 80% or 4/5ths of the height should be capped for the design. The figure below shows an example P-M diagram on the left where the bug is present and from visual inspection alone is clearly not capped at the correct height. The corresponding diagram for the same cross section is shown on the right with the flange grouting pattern changed from “Partially grouted” to “Fully grouted” and as a result, the bug is no longer present and it can be seen that the maximum axial load is capped at the correct height.

Another option is to click on the very top point on the diagram which lies on the P_f axis and multiple that by 0.80. This is less exact than verifying the calculation using the correct inputs (described further below) but can still get a result accurate to within 20kN which will be acceptable for the majority of cases.

Extreme cases like this are relatively easy to spot with a quick glance of the P-M Diagram. The example used in this article is outlined further below, here, and was purposely done using very long flanges and low masonry unit strength to highlight this issue. It is possible that this difference is less pronounced and is less obvious.

That being said, just because the bug is present in a project file does not necessarily mean that there are any issues with the design results.

Checking Load Combination Locations on the P-M Diagram (Condition 2)

If there is an issue with the incorrect P_r,max value being used, simply check the P-M Diagram and click on the load combinations with the highest factored axial load, P_f.

Any load combination can be selected in MASS by clicking on the point to reveal the exact factored moment, moment resistance, factored axial load, and neutral axis location.

The factored axial load, or P_f , can be compared to the correct P_r,max value to ensure that even if a shear wall’s envelope has not been capped at the correct location, it is still within the acceptable range.

Quick Calculation Check by Hand

If loads are in the upper region of the diagram and the P_r,max line appears roughly in the correct location, it is a good idea to quickly check the numbers by hand. This situation is covered in the section below. In the Detailed Moment Results section of the software where the P_r,max equations and formulas are found, the results can be quickly verified make sure they are correct.

Note: the f’_m value used in the P_r,max calculation can be found in the Detailed Shear Wall Properties section of the results window, along with all of the other inputs.

If any value of P_f exceeds P_r,max that was calculated manually in the subsection above, MASS has incorrectly passed these designs when they should have failed. If unsure, please do not hesitate to contact MASS support.

Example Design

To illustrate this example, a test case was chosen with many aspects that amplify this error. Consider a basic shear wall design where the web is 2210 mm long (2190 mm plus a 10 mm mortar joint on each end) with a height of 3400 mm and a total height of 24,000 mm. Disable masonry unit selections until only the 15 cm, 15 MPa unit are remaining.

Note: for typical design work, it is generally recommended to first leave several options selected before seeing an initial result and narrowing down the design from there. For purposes of demonstrating this bug, this example involves an already known cross section which is the reason for the other options being disabled.

Once the web design has been specified, click on the flange input tab and add a 2000 mm long flange to each end of the wall. Using the default offset value, specify the distance from the critical section to the top of the web as the total height value used earlier: 24,000 mm. This is a commonly missed step which will ensure that a portion of each flange is included in the cross section used for design. If this value were left at the default 0 mm, only the portions of the flanges directly adjacent to the web (140 mm in this case) would actually be used.

Once the flanges have been specified, click on the loads button and enter basically anything. In this example, a 1kN lateral dead load is applied simply to allow the MASS software to advance to the moment design stage. Since this bug relates to the envelope curve, exact loading is irrelevant as it only impacts where the load combination points will be drawn on the diagram.

Upon running a moment design, there should be successful results displayed with a fairly large spacing of vertical bars. Click on the PM Diagram drawing and note the location of the Pr,max line where axial load is capped.

So far in this example, the bug has not yet presented itself. Proceed by disabling all of the spacings except for 200mm, placing a vertical bar in every cell. It is these designs where you may notice a dramatic shift in Pr,max.

Breaking down the calculation of Pr,max, it is made up of three components: the left flange, the web, and the right flange. Selecting the Detailed Moment Results tab, these values can be seen in the results screen, as well as below:

Manually checking these flange values based on the inputs seen, the following is the expected (and correct) value:

Referring back to the bug summary, this issue presents itself when a shear wall web becomes fully grouted due to a vertical bar placed in every cell at 200mm spacing. The f’_m value used for the flanges is incorrect, referencing the hollow value of 10Mpa instead of the grouted 7.5MPa from Table 4.

As mentioned at the start of this subsection, the example chosen for this demonstration exercise for a few reasons. The first is that a small, low strength masonry unit was chosen because in percentage terms, there is a very large jump (33%) going from the grouted to hollow strength which diminished for higher block strengths. Shear walls with long effective flanges in relation to the web size also experience a higher discrepancy in P_r,max because the flange terms make up a higher portion of the total maximum load.

This bug ended up being very simple to find in the code and fix. It has been added to the known bugs page found here and will no longer be present in Versions 4.0 and newer.

Our Response

Bugs of this nature are taken very seriously. It was discovered in-house but not until very late in the Version 4.0 development process. As a result, the bug was investigated and a fix was added to Version 4.0. 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.

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.

In any windows architecture application, there is a limit of 10,000 GDI objects. Internally, there a number of these crated with every design and population of each results screen. Unfortunately, there are a number of these that are not properly “cleaned up” so using the same MASS window for an extended period of time will trigger this crash.

The release of MASS Version 4.0 has mitigated the problem but there are always residual GDI objects between every design. Our recommendation in dealing with this issue is to regularly save your work.

A full video demonstrating this and how to check your GDI object status is shown below:

This issue is most likely to occur when designing a shearline or multi-storey shear wall module as these assemblage options coordinate the creation of several shear wall elements internally, triggering the creation of additional GDI objects.

If you have any questions, please do not hesitate to contact MASS support.

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.

Have you ever saved a MASS file you were working on, only to open it up a few days later to see some values that are orders of magnitude larger? If so, this post explains where the bug comes from, how to tell if a design has been affected, that you are not going crazy, and what has been done to correct it.

Bug Summary

Under some French language localization settings in the Windows operating system, project files created using MASS are reopened with values that are 10 or 100 times larger than the original numbers that had been saved. This is a result of how displayed values are saved internally, with decimals replaced by commas. MASS re-opens a saved project and does not recognize these substituted commas, resulting in values that are orders of magnitudes larger.

If the extra zero’s are manually removed from the input fields, the values will then be correctly saved with the decimal in its intended location. This bug also only applies to values that have been auto-populated by the software (meaning that you did not type them in manually). For example, if a beam length of “3000” mm is entered into MASS, the “3000” will be correctly read and re-opened.

Background Information

Numbers are not written the same way in French as they are in English. One key difference that is relevant to this issue is the French Canadian use of commas in place of decimals. For more information, click here for a summary and explanation from syllabus.com (external link will open in a new tab).

In making Windows more accessible for other languages, it seems that the numbers that show up in input fields such as side cover or yield strength are being automatically translated within MASS. With values “translated” by Windows based on number formatting preferences, the actual values within a saved .masonry14 project file are stored with the commas, shown below using the minimum clearances of a masonry beam for reference. Values that should be saved as 75.00 and 55.00 are “translated” to “75,00″ and 55,00″.

Note that this view is not accessible by the end user (or even myself) and had to be requested from the programmer who was able to see this in the debugger console within Visual Studio.

How to tell if a design is affected

The most obvious sign when encountering this issue is the loss any options of placing rebar within the masonry. After all, it is difficult to fit any steel inside of a unit if the specified side cover is 5.5 m instead of the default 55 mm! Note in the design below how MASS recognizes that it is impossible to place vertical bars so the options have been disabled as a result:

In the case of designing masonry beams, where reinforcement is required, opening these files should raise mental red flags when the yield strength jumps upward to 4000 MPa (!), making it very difficult to yield (with a yield strain that is also 10x larger than the default 0.002). This would be after dismissing all of the pop-ups that the software will prompt on the basis of the specified side cover no longer being satisfied.

What to do if you encounter this error

Before opening MASS, the settings in Windows can be checked to see which punctuation is used to represent the decimal point. To view the instructions on how to open the Customize Format window, click on the heading below to expand the instructions.

Once in the Customize Format window, check the selection to the right of the top drop-down menu item corresponding to Decimal symbol.The screenshot below shows the value that will be correctly recognized by MASS:

If this is anything other than a period, or “.”, MASS will not recognize the decimal in the right place and values can be shifted by orders of magnitude.

If this selection needs to be changed, make the appropriate change and click Apply or OK. The software will need to be restarted to reflect these changes and fortunately, a full machine reboot is not required.

Our Response

Bugs of this nature are taken very seriously. It was discovered in-house but not until very late in the Version 4.0 development process. As a result, the bug was investigated and a fix was added to the eventual release of Version 4.0. 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.

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.

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.