Masonry Wall - Modeling

The masonry wall panel element allows you to easily model, analyze and design masonry walls for in plane and out of plane loads. Here we explain the masonry specific inputs and procedures for modeling. For general wall panel information, see the Wall Panels topic. For information on masonry design rules, see the Masonry Wall - Design Rules (this is where you can define block thickness and self-weight). For masonry calculation considerations and code references, see the Masonry Wall - Design topic. For masonry wall results interpretation, see the Masonry Wall Results topic.

Note: All code references in this topic refer to the TMS 402-16 specification unless noted otherwise.

Masonry Wall Input

The Wall Panel Editor gives some specific information and options for modeling/analysis of masonry walls.

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Masonry View Controls

Masonry Wall Panels have the following view controls:

View Controls

Icon	Control	Description
	Regions	The Regions icon lets you turn the display of regions on or off.
	Lintel	The Lintel icon lets you turn the display of lintels on or off.
	Out-Plane	The Out-Plane icon lets you turn the display of out of plane reinforcement on or off.
	In-Plane	The In-Plane icon lets you turn the display of in-plane reinforcement on or off, after you have solved the model.

Openings / Lintels

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In the Wall Panel Editor, you have the option of adding rectangular openings to masonry wall panels. To draw an opening, select the Openings icon and then select two nodes or grid intersections which make up the two diagonal corners of your opening. When an opening is drawn a lintel is automatically created above the opening. To view or edit the properties of a masonry lintel, double-click inside the boundary of the drawn opening. This brings up the Editing Properties window for that particular lintel.

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This window shows the design options set in the Wall Design Rules - Lintel spreadsheet to design/analyze your lintel. If you have multiple lintels in a wall and want a specific design that differs from the other lintels, you can double click the lintel then select "Convert to Custom...". When using the custom option, the program uses all of the information set in the Lintel Editor and disregards any information given by the design rule.

The following table includes the different input options available for designing/analyzing lintels.

Lintels Input Options

Control	Description
Depth	Depth is the depth of the lintel.
Bearing Distance	Bearing Distance is the bearing length at either end of the lintel. This is used to calculate the effective length of the lintel.
Bar Size	Bar Size option is the reinforcement size you wish to use for the main reinforcing in the lintel.
Bars Per Layer	Bar Per Layer is the number of bars you wish to have in a given layer of reinforcement. There is also an option to have this value optimized based on geometry of the section, and also the number of layers that you have defined.
Number of Rebar Layers	Number of Rebar Layers lets you have multiple layers of reinforcement in the lintel.
c/c Spacing of Layers	c/c Spacing of Layers is the distance between layers (if there is more than one).
CL Rebar to Lintel Bot	CL Rebar to Lintel Bot is a value used to calculate the “d” value for the lintel.
Stirrup Size	Stirrup Size is the size of stirrup to be added to the lintel if required.

Note: When inputting bar sizes for your lintels, the program will not allow you to place reinforcement that will not actually fit into the lintel because of width constraints. We use the actual dimensions of the block, the face-shell thickness for the given block chosen and use a 1/2" clear cover between reinforcement and the block per section 6.1.3.5.

Regions

Within the Wall Panel Editor, you have the option of creating rectangular regions within the masonry wall panel. Regions are used to define reinforcement in different parts of the wall. Each region will be assigned a uniform reinforcement, which may be different than the reinforcement in other parts of the same wall.

If no regions have been drawn on a wall, then they are automatically generated when a solution is performed.

To automatically generate regions prior to running a solution, click the Automatic Wall Regions icon.

To manually draw regions, select the Manual Wall Regions button and use your cursor to select two nodes or grid intersections which make up the diagonal corners of the region. To exit this tool right-click your mouse.

To view or edit the properties of a masonry region, double-click inside the boundary of the drawn region. This brings up the Review or Change Wall Design Rule window for that particular region.

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You can choose to edit/view the existing wall design rule, or create a new wall design rule. The information is populated from the Wall Design Rules spreadsheet for masonry. For more information see the Masonry Wall - Design Rules spreadsheet on setting this up.

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For masonry wall panel regions, you can also customize regions which makes it different than the Wall Design Rule. To use a custom design region, select Convert to Custom Design Region. When using the custom option, the program uses all of the information set in the Region Editor and disregards any information given by the design rule for that region.

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Note: For models created with version 9.1.1 or earlier ALL regions will come in set to Custom, bringing over the information exactly as it comes from the existing model. For all newly created models in version 10 or later the regions will default to the wall design rule.

Within this dialog you can specify the properties which will be used for the design of the region. The program can optimize the bar spacing and the boundary zone width based on code checks. The block size, reinforcing strength and the method of self-weight calculation are defined in the Design Rules under the Masonry Wall tab.

Note: The program designs regions separately for out-of-plane and in-plane forces, thus the Region Editor is divided into different parts.

Here we will walk through the different input options available for designing/analyzing regions:

Transfer - This option lets you choose whether or not you want this region to transfer Out of Plane and In Plane Loads. If you check these transfer options, the program dumps those loads above and below an opening into the adjacent regions for design.

Note:

These transfer options are only available when you have defined a region above or below an opening.
If you do not choose to check these transfer options you will see design results for regions above and below openings.

Axial - Lets you to define properties of a region based on axial forces.

Block Grouting - Lets you to define how you want your wall grouted. If you choose "Partially Grouted" the program will optimize the grout spacing with the Bar/Grout Spacing
Reinforced - Gives the option of designing the wall as reinforced or unreinforced.
Bar/Grout Spacing - This Lets you to define the bar/grout spacing. If you have the "Optimize" box checked, the program will optimize the reinforcement spacing based on code checks.
Vert Bar Size - This is the main vertical bar size that will be used in design.
Location - This defines how you want to lay out the reinforcement in your region. Each Face puts reinforcement on both faces of a given cell. Staggered alternates the bars to either face of wall region.

Note: When using the staggered option, you are selecting to space the bars at each face at double the bar/grout spacing defined above. For example, if you have a staggered spacing at 24" oc you have a bar on the outside face at 48" oc and a bar on the inside face at 48" oc. These bars are staggered, thus you have grout filled cores at 24" oc.

In-Plane Reinforcement - Lets you to define properties of a region based on in-plane forces.

Vertical Bar Size - Lets you to define vertical bar size for the boundary zones.
Bars Per Cell - Lets you to define one or two bars per cell.
Boundary Zone Width - You must define a boundary zone width, but RISA optimizes the width if the "Optimize" box is checked.
Note: If you have the optimize checkbox selected, the program optimizes the boundary zone width based on code checks.
Horizontal Bar Size - Lets you define horizontal bar size to be used if horizontal reinforcing is required.
1.5x Shear Increase - This option may be required in high seismic zones. The option is available per section 7.3.2.6.1.2.

Merge Lintels

When an opening is drawn in a masonry wall panel, you will notice that a lintel beam region is automatically created above the opening. If you have multiple openings, you may want to merge the individual lintels into one. To do this, click the Merge Lintels icon.

If you have two lintels you want to merge, then click within each of the openings to merge them into one. If you have multiple lintels that you want to merge, click inside of the two openings that define the ends of the merged lintel that you want. You will see that this merges your multiple openings into one. To exit out of this tool right-click your mouse.

When merging lintels, the top edges of the lintels have to be identical. If, once you have merged lintels, you delete one of the openings the entire lintel will be deleted. At that point, you have to delete any openings left in the wall that don't have a lintel over them.

Optimization / Limitations

Optimization

The program optimizes masonry walls and lintels based on the required demand forces. The program can optimize:

Vertical bar/grout spacing for out of plane design.
Boundary zone widths for in plane flexural design.
Horizontal bar spacing for in plane shear design.
Reinforcement bars for lintel flexural design.

Of these optimizations, the only one that substantially modifies the stiffness of the wall is the vertical bar/grout spacing. To properly adjust the stiffness requires an iterative solution that updates the stiffness of the model. This includes updating the strength properties of the wall as well as the stiffness. This optimization/iteration can be done automatically (by checking the box) or can be done manually (by unchecking the box) in the Model Settings - Solution tab.

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To update the stiffness portion of the wall, the program must re-solve your model with these updated stiffnesses as this will change the distribution of forces through the model. By checking the boxyou are telling the program to re-solve automatically. Thus, the program will start with it's initial stiffness parameters and solve the model. It will then optimize the wall to meet strength criteria. Another solution will then be run with the new stiffnesses and the program will again optimize the wall to meet strength criteria. This procedure will continue to occur until you reach the number of Iterations set or until all wall panel results match those of the previous solution.

By unchecking the box the program will only run the solution once and the results will be based on the original configuration. You can then manually optimize your walls using the Suggested Design spreadsheet.

After the solution is run (with or without optimization) the design results are based on the stiffness used in the last iteration (by unchecking the box a single iteration is run). The program will then compare the design of the last iteration with the stiffness used in that last iteration. If the two are the same, the results shown are the final results. If the two are not the same, the program will then provide these two different results in the Suggested Design spreadsheet.

The program will always present results in the output that coincide with the stiffness used in the final solution.

Note: The updating of the stiffness for the model is only required for the vertical bar/grout. Thus, boundary zone widths, horizontal shear reinforcement and lintel reinforcement are optimized automatically.

Suggested Design

In the Suggested Design spreadsheet you will get a list of wall panels in your model that are not yet fully optimized, showing the vertical bar and/or grout spacing of the last iteration (Current Spacing) and the program optimized spacing (Suggested Spacing). From here you have the ability to Use Suggested? which means that you want to re-run the solution with the Suggested Spacing. You can choose this for each wall panel individually. Once you have these checkboxes checked appropriately, click the icon.

After this, the stiffness matrix is re-formulated and may cause some redistribution of loads through the model. Because of this, the Suggested Spacing may also update and you may need to Use Suggested? multiple times to converge on a solution.

Note:

If the wall does not show up in the Suggested Design spreadsheet, then the current wall panel settings used are the optimal ones.
For more information on wood wall optimization see the Wood Wall - Design topic.
For more information on member optimization see the Design Optimization topic.
Concrete walls do not show up here because the reinforcement optimization does not affect the stiffness of the wall.

Lintels

For masonry lintels you must input the dimensions, bar size and number of layers of bars for the lintel, but are given the option of optimizing how many bars are in a given layer. If you provide a max/min number of bars in the Wall Design Rules - Masonry Lintel tab then the program will optimize the number of bars in a layer. Because this is just a change in reinforcement, this is an automatic optimization that does not require an iterative solution.

Lintel Reinforcement Placement Check

The program will do a check to see that the reinforcement in the lintel will fit properly. The available width for reinforcing in the lintel is based on the width of block, thickness of grout between the block and the reinforcement, and it assumes there will be a double-leg stirrup.

where

t_grout = 0.5 in (per Section 6.1.3.5 of ACI 530-13; the program assumes coarse grout)

dbstirrup = diameter of stirrup (from the Wall Design Rules - Masonry Lintel tab)

Note that we use a minimum bar spacing equal to the minimum of either d_b or 1".

Regions

For masonry regions, there are two options for optimizing. For out of plane design, the program will optimize the spacing of bars for strength (not deflection) considerations of the wall For in-plane design, the boundary zone width will be optimized for strength as well. The spacing of reinforcement/grouting affects the overall stiffness of the wall thus you must iterate your solution to update this spacing. The boundary zone design affects the overall stiffness very little, thus this is an automatic optimization that does not require an iterative solution. If you provide a min/max boundary zone width in the Wall Design Rules - Masonry In tab, then the program will optimize the boundary zone width.

Limitations

Openings and regions must be input only in RISAFloor if you are using RISA-3D and RISAFloor in tandem.
For sloped walls due to sloping floors, openings and regions can not be defined in the upper triangular area of the wall panel. These openings are not supported at this time. This will be addressed in a future version.
For areas of masonry wall panels that are not defined as a region, the stiffness of the wall is assumed to be that of an ungrouted masonry wall and the weight of the wall is assumed to be that of a fully grouted wall.
Masonry has specific requirements regarding the spreading out of concentrated loads at certain angles and for certain depths (Section 5.1.3). These provisions are not considered in RISA, as the finite element mesh stiffness is what determines load path. See the Wall Panels - Load Attribution topic for more information.