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Bearing Wall Walk-through

Bearing Wall Walk-through


Summary: This guide walks you through basic use cases of the Bearing Wall (Concrete and Masonry) Module.

Reinforced load bearing walls are used to support gravity loads of elements above, as well as lateral loads such as those resulting from soil pressures, wind, or seismic. These walls differ from in-plane shear walls and are designed as slender walls loaded out-of-plane. For such walls, the in-plane strong axis is braced and out-of-plane weak axis controls the design. Bearing walls are checked for out-of-plane axial compression, flexure, and shear in addition to miscellaneous code checks. Elevated floors are supported vertically on bearing walls and also act to support the wall laterally out of plane. At the foundation level, these walls rest on continuous footings.

TABLE OF CONTENTS

Open a New Module

Select Bearing Wall from the module selection menu at the top left corner next to your Username:

Alternatively, you may use the dropdown menu from Project -> Add Module -> Masonry Wall or Project -> Add Module -> Concrete Wall. You will be prompted to give the new Bearing Wall module a name upon creation. You may edit the name at any time by right clicking the module tab and selecting Rename.

Note: if you do not already have a Project opened, you will be prompted to start a new Project.

Inputs: Defining Material Properties

Under the Properties tab, the following material properties input sections are available for Bearing Walls:

ASD/LRFD

Select between design methods of Allowable Stress Design (ASD) or Load Resistance Factored Design (LRFD) methods. For Concrete Bearing Wall, only LRFD method is supported.

General

Material Type select the material type for bearing wall. Alternatively you may select wall types from new module creation.

Wall Length enter the length of wall for analysis and design. For designs with distributed loads, a 1 foot strip is adequate. If concentrated point axial loads are considered, this length may be modified at discretion of the designer. In these cases, it is recommended that the length to be no more than half the height of the wall for horizontal distribution of axial load.

Material (Masonry)

Nominal Block Dimensions select the width of the block. This module supports common standard CMU block sizes.

Bond Type select the bond type used in Masonry construction. For examples of running vs stack bond, please refer to NCMA TEK 14-06.

Mortar System select the mortar system. Select either Portland cement/lime, mortar cement, masonry cement, or air entrained Portland cement/lime. Note some of these options are grouped.

Mortar Type select from M, S, or N mortar types. Type O is not supported in the module, for more information refer to NCMA TEK 09-01A. 

Grouting select from either fully grouted cells or partially grouted cells. Partially grouted assumes grouting in reinforced cells.

f'm enter specified compressive strength of masonry.

Block Weight enter block weight class for determination of wall self weight. The following unit weights are assumed for the three weight types: Normal Weight = 135 pcf, Medium Weight = 115 pcf, and Lightweight = 103 pcf.

Material (Concrete)

Wall Thickness enter the thickness of wall in the out of plane direction.

f'c enter specified minimum compressive strength of concrete.

Concrete Weight Type select the weight class of concrete mix.

Concrete Unit Weight enter the unit weight of concrete for self weight.

Max Aggregate Diameter enter maximum diameter of aggregate for determination of clear spacing requirements.

Reinforcement

fy enter the specified yield strength of steel reinforcement, i.e. deformed bars.

Vertical Rebar Size select from allowed deformed bar sizes for vertical/longitudinal reinforcing.

Vertical Rebar Spacing select or enter spacing of vertical reinforcing; reinforcement spacing is in multiples of cell spacing for Masonry Walls.

Horizontal Rebar Size (Concrete) select deformed bar size for horizontal/transverse reinforcing.

Horizontal  Rebar Spacing (Concrete) enter spacing of horizontal reinforcing.

(2) Bars Per Cell (Masonry) check this box if design shall have two bars of vertical reinforcing. Vertical reinforcement is NOT assumed to be laterally tied for Masonry bearing walls.

(2) Vertical Reinforcement Curtains (Concrete) check this box if design shall have two curtains of vertical reinforcing. This also assumes two curtains of horizontal reinforcing placed on interior side of vertical reinforcement.

Clear Cover enter clear cover from face of wall to face of vertical reinforcement if (2) Bars Per Cell or (2) Vertical Reinforcement Curtains checkbox is checked. Reinforcement is assumed to be centered otherwise. Designer to verify cover requirements for project conditions.

Laterally Tied Vertical Reinforcement (Concrete) check this box if vertical/longitudinal steel reinforcement is adequately laterally tied per applicable building codes and shall be considered to be engaged in compression in design.

Design Options

Live Load Deflection select the design deflection limit for live, snow, or wind load only relative to span.

Total Load Deflection select the deflection limit for dead plus live load relative to span.

Vert Bar Cut Length enter the maximum fabricated/shipped length of vertical deformed bars  for estimation of total required bar length and weight.

Horiz Bar Cut Length (Concrete) enter the maximum fabricated/shipped length of horizontal deformed bars for estimation of total required bar length and weight.

Include Wall Self Weight check this box to include self weight of wall as distributed axial compressive load as a linear vertical load.

Inputs: Defining Spans and Adding Loads

For both Masonry and Concrete Bearing Walls, in addition to viewing the different load types as seen in other Vitruvius modules, the interface at the center of the screen allows the designer to:

SECTION CONTENTS

For editing of loads and spans, refer to Edit Inputs: Loads and Edit Inputs: Span.

Add Vertical Load

Select from either linear (i.e. distributed) or point (i.e. concentrated) load in the vertical axis direction. In most cases, it is appropriate to treat gravity loads transferred from a supported floor system as a linear load. For loads resulting from a one-off heavy framing member it is recommended to use a point load. Vertical loads may be applied with eccentricity, this eccentricity is defined as positive and negative per the axes defined in the top left of the interface, eccentricities will induce an additional point moment load to the wall. The load type of this moment will follow the load type for the vertical load. Lastly, define the height (i.e. location) of the acting load along the wall's overall height (i.e. span). 

  • For point loads, refer to Wall Length for distribution of point loads across wall section.
  • Switch between vertical loads by using the load type view icons at the top of the interface. 
  • Tension loading is not allowed in this module.

Add Uniform Load

Enter uniform pressure load in the lateral axis direction. Define load type and start and end locations along the overall height (i.e. span) of the wall. Examples of uniform loads include lateral seismic and wind pressures.

Add Trapezoidal Load

Enter trapezoidal pressure load in the lateral axis direction. Define load type and magnitude at the start and end locations along overall height (i.e. span) of the wall. Examples of trapezoidal loads include lateral earth and varying wind pressures.

Add Moment

Enter point moment about the wall's in plane axis (i.e. bending out of plane), define the load type and location along overall height (i.e. span) of the wall.

Add Span

Adds a span to the top of the wall, enter the length (i.e. height) of new span upon creation. New spans are created with a roller support at top end. This module supports up to three spans.

  • For parapet conditions, with at least two spans, set the topmost support to free while keeping the other supports restrained.

Delete Span

Deletes the topmost span.

Outputs: Shear, Moment, and Deflection Diagrams

After running the calculation (calculator button under the module name tab), for both Masonry and Concrete Bearing Walls:

SECTION CONTENTS

Show Combinations For

Select between showing results load combinations for the design method (refer to LRFD/ASD) or standard deflection load types, namely Dead or Live only.

Shear

Results for out of plane shear demands for the selected load combination along member height (i.e. span).

Moment

Results for flexural bending out of plane (about the in plane axis of wall) for the selected load combination along member height (i.e. span). 

Deflection

Results for deflection out of plane for the selected load combination along member height (i.e. span). 

Outputs: Section View

After running the calculation, for both Masonry and Concrete Bearing Walls:

SECTION CONTENTS

Section View

This is an abbreviated view of a section of the wall along its height. Actual wall thickness is shown along with vertical reinforcement callouts for rebar size, spacing, and estimated lap length. For concrete walls, the horizontal rebar size and spacing callout is also shown. View is not to scale.

Estimated Takeoff Data

Estimated quantities of materials to construct the masonry or concrete wall. Takeoff data is intended for comparison between designs. No contingency factors have been applied unless noted otherwise. 

  • For masonry wall, self weight is from NCMA TEK 14-13B (contingency factors may apply).
  • For masonry wall, grout volume estimation is from NCMA TEK 09-04A (contingency factors may apply).

Outputs: Elevation and Plan View

After running the calculation, for both Masonry and Concrete Bearing Walls:

SECTION CONTENTS

Elevation

Shows an abbreviated view of the elevation with vertical and horizontal (if applicable) reinforcement shown.

Plan

Shows an abbreviated plan view with vertical reinforcement and spacing shown.

Edit Inputs: Loads

After definition of any load, for both Masonry and Concrete Bearing Walls, the designer will be able to view, edit, or delete the loads that have been defined. 

  • Alternatively, the designer may click on the drawn loads and edit via the center interface.
  • For vertical loads, the designer will not be able to switch between linear and point. If desired, please delete the defined load and add a new vertical load.

Edit Inputs: Spans

After definition of any span, for both Masonry and Concrete Bearing Walls, the design will be able to view, edit, or delete the spans that have been defined.

  • Alternatively, the designer may click on the span and edit via the center interface.

Outputs: Adequacies

After running the calculation, for both Masonry and Concrete Bearing Walls:

SECTION CONTENTS

Axial Compression Limit

Maximum demand compression (magnitude) and associated load combination compared to code defined maximum axial compression (strength) and location along member span.

  • Note net axial tension in wall is not allowed.
  • If axial compression limit is exceeded, flexural interaction strength will be displayed as zero.

Flexural Interaction

Maximum combined demand axial compression and flexural interaction and associated load combination displayed in terms of flexural demand (magnitude) and capacity (strength) and location along member span.

Shear

Maximum demand shear (magnitude) and capacity (strength) and location along member span.

Deflection

Maximum service level deflection (magnitude) and limits relative to span set by designer (strength).

Geometry Compliance

Checks related to geometric properties of reinforcement such as cover and spacing per applicable ACI or TMS building code.

Miscellaneous

Any other checks related to applicable ACI or TMS building code such as include limits on reinforcement ratio and limits on member capacities.

Outputs: Print Preview

After running the calculation, for both Masonry and Concrete Bearing Walls:

SECTION CONTENTS

Wall Diagram

Displays number of spans and support conditions of the bearing wall.

Wall Properties

Geometric properties and deflection limits of the bearing wall.

Reinforcement Properties

Properties related to reinforcing steel including number of, grade, cover, and spacing.

Concrete/Masonry Properties

Material specific properties such as specified strengths, modulus of elasticity, weight classes, and others.

Wall Data

Span details including assumed unbraced lengths.

Pass-Fail

Details on adequacy checks, refer to Outputs: Adequacies.

Reactions

Support reactions for unfactored load cases. Reactions for shear (V) displayed in Y-axis and moment (M) about Z-axis.

Plan View

Plan view of segment of bearing wall showing reinforcing and spacing, not drawn to scale.

Load List

List of the loads, including magnitudes, locations, load types, and direction used in analysis of bearing wall.

Additional Diagrams (Optional)

Click the icon on the sidebar to select which diagrams are excluded from or appended onto the end of the print preview. Select from Wall Diagram , Shear/Moment/Deflection Diagrams, and Load Diagram.

User Notes

The following assumptions are assumed by the program, the designer or user of the program shall verify that:

  • Reinforcement clear cover requirements are met based on design specifications and applicable building code requirements. The program will not verify project specific cover requirements.
  • Service load combinations use 0.42 factor for wind load per footnote f. on IBC 2018 Table 1604.3. Wind load deflection is checked with the Live Load Deflection span ratio input.
  • Mortar is applied on top and on the sides of the block for quantity estimation whereas for strength calculations (i.e. net area), it is assumed face shell mortar only for partially grouted conditions with spacing greater than 8 inches on center.

FAQ

Bearing wall frequently asked questions:

    1. How do I model a wall with a parapet condition?

  • Create a multi-span condition with the top support free.Single story concrete wall with parapetTwo story masonry wall with parapet and ledger loads

    2. Why am I getting a tension not allowed error?

  • Bearing walls are design as slender axial compression elements subjected to combined out of plane flexural loading. If a user creates a condition that generates a tension load in the wall, it is recommended to design a more heavily reinforced section to take such loads. The following cases are common ways tension loading may occur:
  • Vertical force direction pointing away from a Y-restrained support.

Force pointing away from Y-restraint

Corrected force direction

  • Member overly restrained in the Y-axis, solution is to release all non-base restraints in the Y-direction.

Over-restrained model

Properly restrained model

    3. What is flexural interaction?

  • The capacity of a bearing wall section is derived from equilibrium of forces and moments about said section using standard engineering assumptions such as plane sections remain plane, code-governed strain limits, and stress-strain relationships. A list of axial/flexural capacity pairs is generated within the calculation engine by iterating the depth to neutral axis. The displayed capacity on the Flexural Interaction adequacy is the flexural capacity interpolated from the internal list of axial/flexural pairs from the demand axial compression.

    4. Does masonry wall consider compression steel?

  • No, doubly reinforced masonry wall sections are designed assuming reinforcing bars do not have any compressive capacity. This is due to the impracticality of adequately confining vertical rebar in masonry bearing wall construction.

    5. How is concrete bearing wall calculating deflections?

  • Modeling concrete deflections with accurate area moment of inertia is an ongoing discussion topic. The current ACI 318 uses effective area moment of inertia from Branson (1965). Bischoff (2005) developed an improved method for calculating effective area moment of inertia for lightly reinforced members for use as single-element idealization that generally produces more conservative results. The engineers of this module have utilized Bischoff's equation as it is a more comprehensive analysis.

    6. What is the appropriate deflection limit for use in masonry walls?

  • The current TMS 402 stipulates that the estimated deflection including second order effects be no more than 0.7% of the height of the wall, this equates to be about a span ratio of L/143. It is therefore recommended that the designer consults the local project building code for applicable deflection limits, particularly with attention on the material being supported by the wall.

    7. Why is there a height to thickness limit for concrete walls?

  • This limit exists to prevent a wall design that would potentially buckle under relatively small axial compression loads due to the inherent instability that accompanies compression members that are too slender (i.e. too tall relative to it's thickness). Currently engineers at Vitruvius are working on alternative methods to address slenderness in concrete walls and limitation may be removed in future updates.


Thank you for reading! If you have any questions please reach out to our customer support at support@thevitruviusproject.com or call 1-800-279-1353.




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