Members - Results

When the model is solved, the results are separated into material specific design results and generic results. The generic member results are discussed in this section. The material specific design results are discussed in the following sections of the manual: Hot Rolled Steel - Design, Concrete - Design, Cold Formed Steel - Design, and Wood - Design. For information on Member Detail Reports see the Results section.

Number of Reported Sections

Note that the member results (forces, stresses, code checks) are only reported at the section locations. For example, if you set the Number Of Reported Sections in the Model Settings Dialog to be '2', you will not get any results for the middle of your member, you will only get results for the end points. If you have a point load applied to your member at a location that is not a section location, you will probably not report the maximum moment in the section if it does not occur at an endpoint.

Adjust Number of Sections

To adjust the number of Sections:

1. Go to the Model Settings window.
2. Click on the Solution tab, if it’s not already open.

3. Adjust the No. of Reported Sections as needed.

   Note: Adjusting the number of sections affects the amount of output.

Number of Internal Sections

Internally, the program subdivides the member into equally spaced sections to calculate forces, stresses, code checks, etc. The Number of Internal Sections can be adjusted in the Model Settings Dialog. If this value were set to 100, this would mean that for a member that is 100ft long, RISA-3D will calculate these values at approximately every foot. These values are then used in the member steel, wood, and concrete code checks, the diagrams in the model view, and in the detail reports. The locations of the maximum code checks are reported at a distance from the I-joint.

Adjust Number of Internal Sections

To adjust the number of internal Sections:

1. Go to the Model Settings window.
2. Click on the Solution tab, if it’s not already open.

3. Adjust the No. of Internal Sections as needed.

   All other results are reported at the Number of Reported Sections that you specify in the Model Settings Dialog. This controls how many places you receive reported or printed member force, stress, torsion, and deflection results. These locations are also equally spaced so setting the value to 5 will give you 5 equally spaced sections; at the ends, the middle and the quarter points.

   Note:

   • Adjusting the Number of Internal Sections will not affect the amount of output in the results spreadsheets. 
   • You may want to stick with odd numbers for the Number of Reported Sections. Setting the Number of Reported Sections to an even number will not report forces/stresses at the midpoint of the member, which is often the location of maximum moment.
   • Setting the Number of Reported Sections to '2' will only report end forces which, might be desirable for connection calculation but not when looking for maximum forces along a members length. There is a printing option for end forces that is the equivalent to setting the Number of Reported Sections to '2' but allows you to see more results on screen while printing only the end forces.

Member Force Results

Access the Member Section Forces spreadsheet by going to the Results Menu and then selecting Member Forces then clicking the Sections tab .

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These are the member forces calculated along each active member taking into account any member offsets. The number of sections for which forces are reported is controlled by the Number Of Reported Sections specified in the Model Settings Dialog.

The Maximums Tab shows the maximum force that occurred in the member based on the Number of Internal Sections. Because the Number of Internal Sections is typically much larger than the Number of Reported Sections, this means that the Maximums Tab will always display the highest/lowest force in the member whereas the Sections Tab will miss the highest/lowest force under all but the most simple load diagrams.

The End Reactions Tab shows the member forces at the ends of the member. This may not be useful for continuous members or cantilever members where the i-end and j-end may not be at a support.

The units for the forces are shown at the top of each column. As for the sign convention, the signs of these results correspond to the member's local axes, using the right hand rule. The left side forces at each section location are displayed. There are sixthree force values for each section location.

These are axial, shear parallel to the local y axis (Shear y-y), shear parallel to the local z axis (Shear z-z), torque moment, moment about the member's local y axis (Moment y-y) and moment about the member's local z axis (Moment z-z). Please see the diagram below:

This diagram shows a member section location with all positive section forces. As can be seen, the section forces listed at any given section are the left side forces. For axial forces, compression is positive. For moments, counter-clockwise around the member axis is positive.

The sign convention for shear is positive when the free body diagram causes the member to spin clockwise (with I End on the left and J End on the right).

These section forces may also be displayed graphically. Remember that the section forces used for the plot are the left side forces. For an example of what you would see for the graphic plot of the moment diagram for a member, please see below:

RISA-3D uses the right hand rule joint convention and is always consistent with this convention. Since the left side moment is being used, a member under negative Mz moment would have the "holds water" deflected shape, which is contrary to some beam conventions. The opposite is true for My moments which will tend to "hold water" under a positive moment and "shed water" under a negative moment.

The 2nd/1st Moment Ratios Tab shows the ratio of maximum moment with and without secondary P-Delta effect. In general, the larger the ratio is, the more significant the secondary effect is. Notice that some design codes may have a limit on this ratio (e.g., ACI has this limit as 1.4), but this limit is not checked by the program.

For enveloped results, the maximum and minimum value at each location is listed. The load combination producing the maximum or minimum is also listed, in the "LC" column.

The moving load results are enveloped and will display the Load Combinations with maximum and minimum values shown for each section location, for each active member. The governing load combination and step location is shown for each result value under the "LC" column. The first number is the load combination, the second is the step number: (load combination - step number). See Moving Loads to learn more.

Member Stress Results

Access the Member Stresses spreadsheet by going to the Results Menu and then selecting the Member Stresses spreadsheet.

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These are the member stresses calculated along each active member. The number of sections for which stresses are reported is controlled by the Number Of Reported Sections specified in the Model Settings Dialog.

There will be seven stress values listed for each section location along the member taking into account any member offsets. The units for the stresses are shown at the top of each column. As for the sign convention, the signs of these results correspond to the signs of the forces. These line up as positive or negative according to the member local axis directions. Compression is positive and tension is negative.

The axial stress is the ratio P/A, where P is the section axial force. A positive stress is compressive, since the sign of the stress follows the sign of the force.

The shear stresses are calculated as V/A_s, where A_s is the effective shear area. The program obtains A_s by multiplying the total area by the shear stress factor. This factor is calculated automatically for most cross sections, but must be entered for Arbitrary members. Refer to Member Shear Stresses.

The bending stresses are calculated using the familiar equation M * c / I, where "M" is the bending moment, "c" is the distance from the neutral axis to the extreme fiber, and "I" is the moment of inertia. RISA-3D calculates and lists the stress for the section's extreme edge with respect to the positive and negative directions of the local y and/or z axis. A positive stress is compressive and a negative stress is tensile.

Note that two stress values are listed for each bending axis. This is because the stress values for a bending axis will not be the same if the shape isn't symmetric for bending about the axis, as with Tee and Channel shapes. The y-top and y-bot values are the extreme fiber stress for the + or – y-axis locations. The same is true for the z-top and z-bot stresses.

The locations for the calculated stresses are illustrated in this diagram:

So, the y-top location is the extreme fiber of the shape in the positive local y direction, y-bot is the extreme fiber in the negative local y direction, etc. The y-top,bot stresses are calculated using Mz and the z-top,bot stresses are calculated using My.

For enveloped results, the maximum and minimum value at each location is listed. The load combination producing the maximum or minimum is also listed, in the "LC" column.

The moving load results are enveloped and will display the Load Combinations with maximum and minimum values shown for each section location, for each active member. The governing load combination and step location is shown for each result value under the "LC" column. The first number is the load combination, the second is the step number: (load combination - step number). See Moving Loads to learn more.

Single Angle Results

Depending on whether a single angle has been fully restrained against rotation or not, it will either behave about its geometric axes or its principal axes. This behavior can be controlled by correctly specifying the unbraced lengths for the angle. In the diagram below the z and y axes are the geometric axes. The z' and y' are the principal axes. The y' axis is considered to be the weak axis for principal behavior, and the z' is considered to be the strong axis.

The orientation of the shape is defined using the local y and z axes shown in the above diagram, but for principal axis behavior the bending calculations are done with respect to the y' and z' axes shown (the principal axes). The y' axis is the axis of minimum 'I' and the z' axis is the axis of maximum 'I'. RISA calculates the angle "α" and transposes the moments as shown below:

Mz' = Mz * cos(α) + My * sin(α)

My' = -Mz * sin(α) + My * cos(α)

The My' and Mz' moments are the moments shown as My and Mz respectively in the member forces results. Likewise, the y-top and y-bot bending stresses are relative to the extreme fibers along the y' axis (for the Mz' bending moment). The z-top, z-bot stresses are for My' bending at the extreme fiber locations along the z' axis.

Member Torsion Results

Access the Member Torsions spreadsheet by going to the Results Menu and then selecting Member Torsions. 

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These are the torsional stresses calculated along each member. The number of sections for which torsional stresses are reported is controlled by the Number of Reported Sections option in the Model Settings window.

The units for the torsion stresses are shown at the top of each column. RISA-3D calculates pure torsion shear for any shape type; this value is based on the maximum thickness of any part of the cross section. Closed shapes such as tubes and pipes do not warp, nor do solid rectangular or circular shapes. For these shapes, there are no warping stresses to report. Warping only occurs in open cross sections where the rectangular pieces that make up the cross section do not all intersect at a single point. For example, a Tee shape could be thought of as two rectangular pieces, the flange and the stem. These two pieces intersect at the midpoint of the flange, so there is no warping. A channel, on the other hand, is comprised of three pieces, the two flanges and the web. These three pieces do NOT share a common point, so a Channel will warp. The same is true for a Wide Flange, so warping stresses are calculated only for I shapes (WF,S,H) and Channel shapes with warping restrained.

The shear and bending stresses caused by torsion are integrated into the code check and shear check calculations for the member, so your final code check (and final shear check) values DO include torsional effects. Warping shear is a shear stress acting parallel to the member's local y-and z-axis. Warping bending stress is a triangular stress normal to the cross section acting on the flanges, with the maximum stress at the outer edges of the cross section, the z-top and z-bot locations. As for the sign convention, the signs of these results correspond to the signs of the forces. These line up as positive or negative according to the member local axis directions. Compression is positive and tension is negative. See Torsion for more information on these calculations.

For enveloped results, the maximum and minimum value at each location is listed. The load combination producing the maximum or minimum is also listed, in the "LC" column.

The moving load results are enveloped and will display the Load Combinations with maximum and minimum values shown for each section location, for each active member. The governing load combination and step location is shown for each result value under the "LC" column. The first number is the load combination, the second is the step number: (load combination - step number). See Moving Loads to learn more.

Member Deflection Results

Access the Member Section Deflections spreadsheet by going to the Results Menu and then selecting Member Deflections

Service

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The Service tab will contain deflection results only for load combinations marked as Service in the Load Combinations - Design tab.

Strength

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The Strength tab will contain deflection results only for load combinations NOT marked as Service in the Load Combinations - Design tab.

The Service and Strength tabs are the member deflections calculated along each active member. The number of sections for which deflections are reported is controlled by the Number Of Reported Sections specified on the Model Settings Dialog.

The member section deflections are comprised of 3 translations in the member local axis directions, the rotation (x Rotate) about the local x-axis (the twist), and the relative deflection to length ratios for the y and z deflections. The units for the deflections are shown at the top of each column. As for the sign convention, the signs of these results correspond to the member's local axes, using the right hand rule.

The L/y' and L/z' ratios are the total member length (minus member offsets) divided by the relative deflection. The deflection in this calculation is not the deflection shown in the columns to the left, which are the absolute deflections. The deflection used is relative to the straight line between the deflected positions of the end joints. For cantilevers, the deflection is relative to the original position of the member.

Expressed as an equation, n = L/deflection, where n is what is tabulated in the spreadsheet. The smaller the deflection, the larger the value. If 'NC' is listed, that means the 'n' value is greater than 10000 which is a very small deflection. The minimum value that will be shown is '1'. For example, if the deflection criteria is L/360, check here to make sure no tabulated values are less than 360. Greater than 360 is OK.

For enveloped results the maximum and minimum value at each location is listed. The load combination producing the maximum or minimum is also listed, in the "LC" column.

The moving load results are enveloped and will display the Load Combinations with maximum and minimum values shown for each section location, for each active member. The governing load combination and step location is shown for each result value under the "LC" column. The first number is the load combination, the second is the step number: (load combination - step number). See Moving Loads to learn more.

Note

• For members that have not been designated as a beam, the maximum member deflection ratio from the Service or Strength tab will be reported as the Max Defl Ratio at the end of the member detail report.
• See Spreadsheet Operations to learn how to use Find, Sort, and other options.
• If you wish, you can go to the model view to plot and animate the deflected structure. The amount of deflection shown on the plot is controlled by the magnification factor. The joints are plotted based on the joint displacements, and these member deflections are used to plot the member's curvature between the joints. See Results View Settings - Members to learn how to plot member results.

Beam Deflections

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The Beam Defl spreadsheet shows the strong-axis (y) relative deflections, y', for Beam member types. This spreadsheet will base the L'/y' Ratio on the actual span for multi-span beams. If there are multiple span beams, each span will have it's own entry. The L'/y' Ratio uses the span length of the beam, denoted by L' (as opposed to the full member length, L) compared to the relative deflection, y'.

The program will detect the presence of cantilever spans. If an entire member or the end span(s) of a member are unsupported at one end, the program will consider those spans a cantilever and use 2*Span Length for the L'/y' Ratio calculations.

The location and value for the relative deflection, y', is dependent on the beam being either supported or cantilever. For a member supported on both ends, the maximum relative displacement used in the beam deflection ratio will be the largest straight line distance (in the vertical y direction) between the deflected shape and the original undeflected shape.

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For members with a cantilever end, the location of the maximum relative deflection will be at the free end of the member. The displacement value is equal to the rotation at the supported end multiplied by the length of the member.

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For multi-span members, the program will give span information in the expanded interactive strong-axis absolute deflection diagram. A vertical blue dashed line will be displayed at support locations which will give the proper span information. Note that any vertical reaction boundary conditions along the beam, and any columns (specifically members with their Member Type property set as Column) framing into the beam will be treated as support locations for the sake of determining the deflection ratio.

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The L'/y' Ratio is based on relative deflection and member span length. The relative deflection for each span takes into account the span end deflections and is the maximum vertical deflection component measured from the absolute displacement to a straight line drawn from one end of the span to the other. In the image below, the relative deflection, y', per span is called out as D1, D2, and D3.

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The green line is the actual deflected shape.

The black vertical line (not shown in image) is the cursor marker in the expanded interactive strong-axis absolute deflection diagram.

The blue vertical dotted lines are the support locations.

The dark blue lines are straight line connectors between supports at the deflected location.

The dark red vertical lines are the relative strong-axis (y) deflection used in the L'/y' Ratio.

While the program determines if a member is a cantilever or supported based on member behavior and modeling configuration, there may be cases where the beam is actually considered otherwise. In this case, the Deflection Ratio Options can be used to designate a member end specifically as supported or cantilever. Any members with designated support ends using the Deflection Ratio Options will be denoted by a star suffix on the L'/y' Ratio listed in the Beam Defl spreadsheet.

Beam Check

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The Beam Check spreadsheet shows the local strong-axis (y) deflections for Beam member types for load combinations defined in the Member Design Rules - Deflection tab. If a deflection value exceeds the limit from the design rule then the value will show in RED. This spreadsheet will also base the L/y ratios on the actual span for multi-span beams. If there are multiple span beams each span will have it's own entry.