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This page contains a list of TechNotes related to STAAD.Pro

Member Tension And Combination Load Cases [TN]

Pushover Analysis of Steel Structure using STAAD (TN)

Reference Loads An Introduction [CS]

STAAD.Pro Wall Analysis For Dams [TN]

STAAD.Pro EN 1993-1-1:2005 Implementation: Elastic Verification of Cross Sectional Resistance

STAAD.Pro EN 1993-1-1:2005 implementation: Calculation of Torsional Capacities of Cross Sections as per SCI P057

STAAD.Pro EN 1993-1-1:2005 Implementation: Code Check for Torsion

STAAD.Pro EN 1993-1-1:2005 Implementation: Example 2 verification as per SCI P364

STAAD.Pro EN 1993-1-1:2005 Implementation: Example 3 verification as per SCI P364

Discussion on Seismic Detailing Concept of RC Structures (IS:13920-1993)

Limitations of the curved beams in STAAD.Pro ( TN )

“Missing Mass” in Dynamic Analysis

IS:1893 (Part-I)-2002 Response Spectrum Philosophy

Linear static, P-Delta, small P-Delta, stress stiffening, and geometric non-linearity in STAAD.Pro

Direct Analysis per AISC 360-05 and its Implementation In STAAD (TN)

Torsion and Section Analysis

The net torsion moment in a cross section consists of two components.

1. Integrated twisting moment across the cross section
2. Eccentricity of the applied shear to the cross section centroid.

The first component, twisting moment, is associated with the torsional stiffness of the beam and slab elements. It can be essentially eliminated by changing the behavior of the slab and beams to “No-Torsion” (see below). “No-Torsion” behavior factors the element torsional stiffness by 0.001. This results in a very low torsional stiffness, which results in very small twisting moments.

The second component is a function of the loading, shear stress distribution across the section, and the cross section geometry. The simple example below illustrates this component of torsion.

A section cut through a single bay building supported by columns is shown below. A typical design approach is to choose a design section that extends from the slab edge to mid-bay between the column lines.

Ignoring twisting stresses, the shear stress distribution across the section would be similar to what is shown in the graphic below. Because the shear force is ultimately directed into the columns, the resultant shear location is at the column location and not at the centroid of the section. For the section to be in equilibrium there must be a net shear force and a torsion moment at the cross section centroid.

Note that when designing slabs using the equivalent frame approach that variation in the shear stress is ignored and the net shear is assumed to coincide the section centroid. This is equivalent to designing the cross section for a uniform shear stress with the same magnitude resultant. However, it should be clear that a uniform stress distribution does not satisfy equilibrium.

Design strips that include a perimeter beam offset from the column grid line is another common condition that results in torsion due to eccentricity of the resultant shear.

In cases where the torsion due to eccentricity of shear is high, one approach to minimize the torsion is to divide the design strip into narrower full-width strips. This would capture the torsion by designing the narrower strips for a higher resultant shear force rather than a lower resultant shear and torsion at the centroid of a wider section. When using this approach, it is important to always select the “Consider Net Axial Force in Strength Design” option for the span segments and design sections. When narrow strips are used, there may be significant net axial resultants that are associated with flexural equilibrium. Ignoring those axial forces could be very unconservative.

Torsion and Section Design

RAM Concept can consider the net torsion design force on a cross section in four different ways. These four approaches are associated with the Beam, As Shear, As Bending, Wood-Armer, and None options shown below.

A brief discussion of each method follows:

1. Beam. Considers torsion by designing with code beam torsion equations. This method assumes torsion is resisted with a circular shear flow.
2. As Shear. Assumes that torsion is carried entirely by varying shear across the length of the shear core of the cross section. The design shear force is calculated as Vd = V +/- 6*T/L, where V = Shear, T = Torsion, and L = Shear Core Length. This method is appropriate for situations where the torsion is primarily by eccentricity of the resultant shear. “As Shear” assumes torsion is resisted with a vertical shear couple.
3. As Bending. Considers torsion by adding the torsion of the bending moment. The design moment is calculated as Md = M +/- T, where M = Moment and T = Torsion. “As Bending” assumes torsion is resisted with a horizontal shear couple, It is based on the assumption that reinforcement is provided in a perpendicular design strip and that the reinforcement in the two orthogonal design strips work together to resist torsion. This method is not recommended for strips containing beams.
4. Wood-Armer. See Section 53.1.21 in the RAM Concept Manual for more information. The design moment is calculated as Md = M +/- AT, where AT = Absolute Twist. The basis of this method is similar to “As Bending.” This method is not recommended for strips containing beams.
5. None. Torsion is completely ignored in the design even if there is a net torsion from the analysis.
   

Importing DXF Files into RAM SS

General

DXF plans can be imported into RAM Modeler. This process is discussed in Section 3.3 of the RAM Modeler documentation. In order to achieve a successful import, it is imperative that you have a properly formatted DXF file that is precise so that the entities can be mapped properly and subtle framing inaccuracies can be avoided. Here is a link to a sample DXF file that is formatted to match the out-of-the-box RAM Structural System defaults. The only exception is the Grid Label Symbol should be changed to the GRIDLABEL block. It contains the "I" shaped column, rectangular shaped column, and grid label block definitions that are mentioned in this document.

http://communities.bentley.com/products/structural/structural_analysis___design/m/structural_analysis_and_design_gallery/270488

DXF files can only be imported into layout types that contain no information. To import a DXF file, create and select a new layout in RAM Modeler and go to Layout > Type > Import from DXF. Select the DXF file and the following dialog box will appear. The default parameters may be changed in the Defaults Utility in RAM Manager. For simplicity, use the same layers in the DXF as the import defaults so the layer names do not need to be changed in the Import DXF dialog box. When a DXF file is imported, RAM Modeler will only look for information on these layers and other layers will be ignored. In order to prevent inaccuracies, it is recommended that you reduce the drawing to its bare essentials prior to importing. This also speeds up the process of regeneration in very large drawing files. If you intend to import the sample.dxf file, the parameters in the Import DXF dialog box should match those shown below.

Grids

RAM Modeler is capable of creating orthogonal and radial grid systems. For grid lines to be recognized as part of a single grid system, they must be drawn accurately. Orthogonal grid systems must have at least one grid in two orthogonal axes to be recognized. For additional grids to be recognized in the same orthogonal grid system, they must be precisely parallel. If the ‘Split Disconnected Orthogonal Grids' option is selected, any grid lines that do not physically intersect will be treated as separate system. Radial grids must be composed of a circular grid(s) intersected by radial grids lines that pass through the center of the circular grid. Make sure that grid lines are actually lines, not polylines, and not part of a larger block or external reference file. CAD files often have closely spaced grids in which the grid bubbles overlap if they were centered on the grid line. It is common practice to offset the grid bubbles in the drawings using grid extensions. Grid extensions must not exist in the DXF file or they will be erroneously treated as grid lines.

Grid Labels

Grid labels should be drawn on a separate layer than the grid lines. A common problem occurs when users model circles for grid bubbles on the grid lines layer instead of the grid labels layer. The circles will be interpreted as circular grids instead of grid labels. Grid labels should preferably be defined by as a block with a text attribute.
The insertion point should be at the exact center so the grid bubbles are located precisely on the grid lines. Alternatively, draw the grid labels as simple pieces of text that are middle center justified and located at the end of the grid. If desired, grid labels can be added in RAM Modeler so it is not a necessity to have a grid labels in the DXF file.

Columns

Columns should be drawn as blocks. The program will recognize one type of block for "I" sections, Rectangular HS sections, and Round HS sections. You cannot use more than one block type to represent different column sizes within the same drawing and there should not be separate blocks for gravity and lateral columns. When defining the blocks, make sure that the insertion point of the block is in the exact center which is then placed precisely on the grid line. It is required to have all of the gravity columns on a single layer. Likewise, all lateral columns must exist on a single layer.

Beams and Joists

All beams and joists should be lines, not polylines. Use snaps to place lines from column to column as required. The finished beam line should be cut back from the supports just as a beam would typically be drawn on a structural framing plan. The dimension of the offset should be between 6 and 24 inches to maintain accuracy. Joist and infill beams can be drawn in the DXF import file or simply added in the RAM Modeler using the various member generation features available. If they are to be drawn in the DXF import file, remember to use a distinct layer for joists.

Cantilevers

For cantilever beams, draw lines continuous over supports (whether columns or other beams). End the line at the exact endpoint of the cantilever and do not trim it back. Members that frame into the end of the cantilever are then cut back as typical beams. Be sure that the apparent intersection of these beams matches the exact endpoint of the cantilever. Alternatively, cantilevers can be indicated using a block inserted at the end of the beams where the moment connection occurs as shown below. Notice how the cantilever tips extend to the actual location and are not cut back.

Slab Edges and Openings

Slab edges/openings should be lines, not polylines. Slab edges and slab openings are imported as free formed edges/openings with a zero inch offset. Therefore, the slab edges/openings are not tied to the perimeter beams/walls. This is acceptable but can lead to problems building the framing tables when complicated perimeter geometry exists and there are one way slabs. For this reason, it is recommended that slab edges/openings only be imported for two way slabs.

Concrete

The DXF import facility is only for steel members at this time. If you are trying to import concrete columns or beams, first import them as steel members using the procedures above, then use the Modeler Layout - Column (or Beam) - Change Material command to convert the imported members over to Concrete.

Since concrete is not supported, walls are also not imported. It may help to import two columns at the wall CL endpoints so that drawing in walls in Modeler is easier.

Concrete columns, walls and slabs can also be exported from RAM Concept to a new RAM SS layer using RAM Concept - File menu - Sync Ram Structural System - Export Geometry to RAM.

 
Tips and Tricks

If you are working in English units, verify that the drawing units are architectural. If other units are being used it is necessary for one drawing unit to equal 1 inch. If not, the drawing may need to be scaled. For metric or SI drawings, one unit should equal 1 millimeter.

Establish a logical origin point for the drawing that will assure precise locations for grid intersections, and relocate the drawing if necessary. Large coordinates are known to cause problems in RAM Structural System. Typically, the column in the lower left hand corner of the plan should be moved to (0, 0, 0) unless a more logical origin exists. Be sure to reference the World Coordinate system and not a local UCS, since the World coordinates are always referenced in the DXF file.

When saving the drawing as a DXF file in AutoCAD, go to Tools > Options in the Save As dialog box. In the DXF options tab you have the ability to specify the number of decimal places of accuracy. Reducing the decimal places in the DXF file might help eliminate minor framing discrepancies. For example, imagine two grids defined by end points (0, 0, 0) ; (0, 1200, 0) and (240, 0, 0) ; (240.0003, 1200, 0). These two lines are not parallel because of the small inaccuracy in the X coordinates of the second line and would import as separate grid systems. However, if the decimal places where rounded to 3, this inaccuracy would be resolved and the grids would import as a single system as intended. RAM Structural System only displays to three decimal places of an inch but may be stored internally at a higher precision. However, be careful if you have skewed framing or radial grids. Eliminating too many decimal places might cause framing errors in RAM Structural System. In these situations it might be best to save the DXF with 4 decimal places and be certain that the framing is drawn very accurately in CAD. RAM Structural System expects framing locations to be accurate to 3 decimal places of an inch to avoid tolerance related problems.

Once the framing has been imported, try to add a slab edge around the whole perimeter. If there are any other modeling errors they will likely be indicated at this time. If this works fine, then you should add a deck and surface load to the whole floor, assign story data, run the data check, and perform the beam design, all before you make any minor changes to the file. 

See Also

Integrated Structural Modeling Home

Structural Product TechNotes And FAQs

RAMSS Two Way Decks

I have recently purchased a license for Structural Enterprise; what are the products I need to download?

There is no single standalone installer for Structural Enterprise products, though we are working to create a setup tool to help with installing and updating the Structural Enterprise products. The installations for each of the products comprising Structural Enterprise need to be run separately. It is not required to install all of the products, and the order of installation should not matter, other than Ram Elements and Ram Connection which require a base installation and then a second update.

A list of the installers to be run is listed below:

1 ) RAM Structural System V8i (English) x64 (or CONNECT edition)

Comments: This is one installer that installs the entire RAM Structural System suite: RAM Modeler, RAM Steel, RAM Frame, RAM Concrete, and RAM Foundation.

2) RAM Concept V8i (English) x64 (or CONNECT edition)

Comments: This is one installer that installs both RAM Concept and the Post-Tension module.

3) RAM Connection V8i (English) x86 (or CONNECT edition)

Comments: This will install both the standalone version of RAM Connection as well as the version that can be used within RAM.

4) RAM Elements V8i (English) x86

5) STAAD.Pro V8i (English) x86

Comments: This installer includes all design codes, the advanced analysis module, Sectionwizard and STAAD.beava.

6) STAAD Foundation Advanced V8i (English) x86 (or CONNECT edition)

7) Microstran (English) x86

Comments: This installer includes all tiers (basic, Pro, Advanced) and design codes.

8) Limcon (English) x86

Comments: This installer includes all design codes. 

9) Structural Synchronizer V8i (English) x64 (or CONNECT edition)

Comments: This is also known as ISM; it must be installed for ISM interoperability to be available in other products.

Note, make sure to download the dependencies as well. In any case where the dependency has both x86 (32 bit) & x64 (64 bit) architecture for the same file, download the one matching your system architecture. 

The Structural Enterprise license works with either V8i or CONNECT generation products and you can mix and match, but we generally recommend using the latest CONNECT edition where available. 

See Also

Software Download Instructions

Structural Enterprise 3D Analysis and Design Software Suite 

STAAD.Pro was not developed to be executed on Mac OS. However, many successful executions of STAAD.Pro have been installed with Windows emulator running on Mac OS.

Framing Tables Errors

General

There are many instances where modeling errors in Ram Structural System are not caught by a Data Check in Ram Modeler. Data Check looks at general geometric information, but it does not attempt to validate all of the information needed to compile the Ram Gravity Framing Tables.

Many of these errors are slab edge or slab opening related.  When one way decking is modeled, slab edges and slab openings must be associated with adjacent beams/walls.  For this reason, avoid using free formed slab edges/openings with one way decking.  Instead, use Layout - Slab - Slab Edge - Whole Perimeter and Layout - Slab - Slab Opening - In Bay to model the slab edges and slab openings.  Then, revise the slab edges/openings where the offset changes.  To further ensure accuracy, only use beams and walls in your Options - Set Snap Points.  Finally, use a positive, non-zero, slab edge offset.  Zero inch slab edge offsets are permitted, but the program algorithms were originally developed assuming non-zero offsets and some configurations can be problematic.

Below are several common modeling configurations that cause problems for the program but are not caught by Data Check.  The right hand image shows the typical error message produced while building the framing tables.  In the background, the framing tables usually halt at a particular member on a particular floor as shown in the left hand image.  Typically, but not always, the modeling issue occurs in the vicinity of the member where the framing tables halt. 

Illegal Framing Configuration

Most illegal configuration errors are slab edge or slab opening related.  Subtle inaccuracies in member end locations can cause small slab edge segments that are problematic for the framing tables.  Review the member end coordinates using the Layout - Beam - Show command and the slab edge coordinates using Layout - Slab Edge - Show.  Try remodeling the slab edge using the whole perimeter command. 

Starting with version 14.07, this error dialog more often than not references an invalid beam number, "Illegal Framing Configuration Detected on Beam -1.", but the number listed in the background framing tables dialog is still accurate and can guide you to a point near the problem. This error is typically associated with columns under a one-way deck that have no beams framing into them. Adding beams parallel to the deck span from the column to the adjacent framing should prevent the error from occurring.

Missing Slab Edge

Many missing slab edge errors are related to having portions of the structure isolated from the perimeter beam loop under one way decking as shown below.  To resolve the issue, model two beams that connect the isolated structure back to the adjacent framing.  If these beams are modeled parallel to the deck span, they will take no tributary load from decking.

Internal Error in AdvanceNodeList()

Typically, these errors are similar to the missing slab edge error.  The main difference is that there usually is only a single beam/wall connecting the interior structure to the perimeter beam loop as shown below.  Modeling a second beam will resolve the issue.

Beam Loop Intersection not Found

Typically, beam loop intersection errors are related to line loads that are slightly askew from a beam.  Often discrepancies arise when a single line load is added over multiple beams that are not truly collinear.  Review the coordinates of the beam and line load using the Layout - Beam - Show and Layout - Load - Line Load - Show command.  To resolve the issue, delete the line load(s) and remodel them using the Add On Beam command.

This error can also be associated with changes in one way deck orientation or properties.  One way decking should always transition along a beam/wall.  That includes transitions from one way decking to two way decking. 

Furthermore, one way deck angles are normally limited to angles between 0 and 179.99 degrees. If imported models have deck angles larger than 180 degrees, this can also cause a beam loop error.

Failed to Find Slab Edge Loads

These errors are usually related to tolerance problems between the slab edge loop and perimeter beam loop.  Review the slab edge and beam coordinates using the Layout - Slab - Slab Edge - Show and Layout - Beam - Show command.  Try remodeling the slab edge using the whole perimeter command.

Failed to Create Slab Edge Load Polygons

This error tends to happen when there is a small level with an incomplete perimeter of framing similar to the one pictured below. Adding the short beam on Gird B between the two concrete columns completes the loop with beams 40, 39 and 41. Adding the other beams would only be required if the deck was intended to load beam 42.

For more information on this issue see Failed to Create Slab Edge load Polygons

Crash with no warning or error message

If a model crashes with no warning or error message then it is harder to diagnose the problem (especially if the Integrity - Data Check offers no clues)

One specific situation that can cause a crash is when a braced frame on an upper level is supported on a two-way deck with no supporting transfer beam. Where it's impractical to add a supporting beam, a work-around for this situation is to model the braces using the Add Standard - Knee brace approach using a vertical offset just a little less than the story height. When the braces intercept the column above the two-way transfer level the framing tables work properly without crashing the analysis and this should have minimal effect on the stiffness matrix.

Two Beams Overlap

Under normal modeling circumstances it should not be possible to model two beams that overlap or cross, but it can happen in some models particularly where the geometry is imported (from dxf, Revit or ISM). 

It's difficult to visually identify where two collinear beams overlap for part or all of the length. Turning on the display of beam numbers can sometimes help.  We have seen cases where one simple span beam and one cantilever beam are in the same location and two numbers will be shown rather than one.

Since the data check does not identify such a problem it only appears when running the framing tables. The error message does not indicate exactly where the problem occurs, but you can usually tell the level with a problem by the status of the framing tables just before the error occurs. 

Finding the beams with the problem usually requires a trial and error process, deleting framing gradually until it works. Then going back and examining those beams that were deleted last in the backup more closely, moving them as required.

We have also seen cases associated with problematic slab opening edges. Deleting and carefully remodeling the slab opening edges at the beam identified where the framing tables stop resolved the problem.

Forcing a "Reframe"

In some cases the beam design module can open and not require a rebuilding of the framing tables, what is commonly referred to as a reframe. A reframe is generally triggered by making any kind of change on a particular level. You can also force a reframe by changing any of the Ram Manager criteria like Self Weight or Live Load Reduction code.

If the design module produces an unexpected error, one simple thing to try is forcing a reframe. You can change one the criteria mentioned above, and click OK. You should get a window like this if previous results are going to be discarded:

Then change the criteria back the way it should be and try the beam design again.

See Also

Failed to Create Slab Edge load Polygons

Effects of Changing Deck Type

Missing or incorrect loads on perimeter beams

RAM Elements - Local versus Principal Axis in Unsymmetrical Shapes

In RAM Elements, analysis and design results are referenced to a local axis system (1, 2, 3) or a principal axis system (1’, 2’, 3’).

The orientation of the local axes is defined as follows:

1. Local axis 1 points from Node J to Node K along the member.
2. Local axis 3 is perpendicular to local axis 1 in the plane of the member.
3. Local axis 2 is perpendicular to the plane formed by the Local 1 and 3 axis.
   

The local axes can be displayed for any member by clicking on the Local Axes button in the View menu - Model Toolbar. See below:

The principal axes represent the axes about which the moment of inertia is maximum and minimum. The orientation of the principal axes is defined as follows:

1. Principal axis 1' points from Node J to Node K along the member. It aligns with the Local 1 axis.
2. Principal axis 3' defines the strong axis of the section. The moment of inertia about this axis is the maximum moment of inertia of the section.
3. Principal axis 2' defines the weak axis of the section. The moment of inertia about this axis is the minimum moment of inertia of the section.

Unlike the local axis system, there is not a way to display the principal axes on screen. However, the angle of rotation of the principal axis can be found in the section properties report under Output-Data-Section Properties;

For symmetrical sections, the local and principal axes will coincide. However, for unsymmetrical sections, such as Z and L shaped sections, the principal axes will be rotated relative to the principal axes.

Analysis Input and Output

Member loads can be defined with respect to the local axes or the global axes only. The tool buttons used to rotate members and create rigid end offsets use the local axes.

Member forces displayed on screen using View – Analysis Toolbar – Member Forces are always displayed with respect to the principal axes. Note reference to 2’ and 3’ (and not 2 and 3) in the menu below.

This can create confusion when the principal axes are rotated 90 degrees relative to the local axes. In this case, the member loads will be displayed relative to the local axes and the member forces associated with them will be displayed relative to the principal axes. In the image below, the M22 moment is a moment about the principal 2 axis, which coincides with the local 3 axis and not the local 2 axis.

Design Input and Output

In the current version of the program, the unbraced length parameters L22 and L33 are associated with the principal axes and not the local axes. This was not always the case. In previous versions of the program, L22 and L33 were associated with the local axes. For sections like a WT 4x15.5 that have a principal axis rotated 90 degrees relative to the principal axis, L33 should be used for the unbraced length for bending about the local 22 axis and L22 should be used for the unbraced length for bending about the local 33 axis. For symmetric sections, like a W18x50, L33 should be used for the unbraced length for bending about the local 33 axis and L22 should be used for the unbraced length for bending about the local 22 axis.

In general, steel and cold-formed sections are designed with respect to the principal axes. Prior to v13.0.3.45, cold-formed section were designed with respect to the local axis only. In AISC 360, single angles are permitted to be designed with respect to either the geometric (local) or principal axis. In RAM Elements, the steel design checks both and uses the worst-case for the design ratio. Some engineers choose to design single, equal leg angles with respect to the geometric axis only. Enhancement #277754 has been filed to do this in a future release.

The list below summarizes program changes that may explain different design results in the current version compared to an earlier version:

1. L22 and L33 are referenced to the principal axes and not the local axes. In earlier versions, these parameters were referenced to the local axes.

2. Cold-formed sections are designed with respect to the principal axes. In earlier versions, these parameters were referenced to the geometric axes.

Laterally Restrained for Torsion Feature

In all versions, there is a way to force the program to align the principal axis with the local axis for a particular section. To do this, edit the properties of the section in the Sections Database and check the box “Laterally Restrained for Torsion.” This change can only be made to user sections. For program installed sections (any section in the United States Group, Europe Group, etc), the section file will need to be copied to a user defined data folder before the laterally restrained for torsion flag can be changed.

What are pseudo-flexible diaphragms?

Pseudo-flexible diaphragms were added to simplify the process of modeling flexible diaphragms, which require manually calculating lateral loads and placing them as nodal loads in Elevation mode of RAM Modeler. They are referred to as “pseudo-flexible” since the behavior of the flexible diaphragm is not directly captured by considering the finite stiffness of the diaphragm, but rather by considering frame portioning of the diaphragm (i.e., by use of independently acting frames with distributed story shears).

What are the steps for modeling a pseudo-flexible diaphragm?

1. Click on RAM Frame – Criteria – Diaphragm and change the diaphragm type to “Pseudo-Flexible."
2. Assign a separate frame number to each braced frame, moment frame, or shear wall. In most cases, the same frame number will be used for the members of a given brace at all levels.
3. Click on RAM Frame – Loads – Pseudo-Flexible Diaphragm Properties and assign a percentage of the story force that will be directed into each frame (listed by frame number) that is connected to the diaphragm at each pseudo-flexible diaphragm level. This should be done for all load cases, including the dynamic load case, which is used to calculate modal periods and frequencies used by program generated seismic and wind load cases. Typically, the percentages are defined according to the tributary area of each frame.

Why are only certain frame numbers listed in the pseudo-flexible diaphragm properties dialog at each level?

In order for the pseudo-flexible diaphragm properties to recognize the frames within the diaphragm boundary, frame numbers must be assigned to a vertical frame member (wall, column, or brace). If all vertical frame members assigned to a given frame number are outside the diaphragm boundary, then that frame number will not appear in the dialog. If only beams are assigned to a given frame number, then that frame number will not appear in the dialog. If no frame numbers have been assigned, then only Frame 0 will appear in the dialog.

How do I assign frame number to a mutual column that is part of two different frames?

In many instances, a single column is part of two different frames. One example is a corner column that is part of a both a x-direction frame and a y-direction frame. RAM Frame permits only a single frame number assignment to each member. When a frame is part of two different frames, consider one of the following approaches:

1. Assign the mutual column the same frame number as one of frames. The total force in the frames will be correct and the overall behavior will be accurate. However, the axial force in the beam will be impacted and might not be correct. This may create an unconservative design and may require you to design the beam by hand for the proper axial force.
2. Assign a unique frame number to mutual column and assign it percentages in both directions. For example, imagine frame 1 is parallel to the X axis and frame 2 is parallel to the Y axis. Each frame takes 50% of the story shear in its respective direction. If they share a mutual column, it could be assigned to frame 100. Then, the percentages in the X direction would be entered as frame 1 and frame 100 each with 25% in the X direction and frame 2 and frame 100 each with 25% in the Y direction.  

Can I use pseudo-flexible diaphragms for frames that are skewed in the XY plane?

Nodal loads that are generated for pseudo-flexible diaphragms are applied in the global x or global y direction only. If a frame is skewed in the XY plane, there will always be a force or mass component that acts in the out-of-plane direction. This out-of-plane component will result in large deflections or instability errors. The following are better options for skewed frames:

1. Use a semirigid diaphragm instead of a pseudo-flexible diaphragm (see RAM Frame - Criteria - Diaphragms and RAM Frame - Semirigid Diaphragms)
2. Model nodal lateral loads in RAM Modeler - View - Elevation View making sure the resultant force is exactly in the plane of the 2D frame. Then, define the diaphragm as Flexible/None in RAM Frame.
3. Assign 0% to the skewed frame and design it in another program. Note that pseudo-flexible diaphragm percentages do not need to add up to 100%.

Why is there an instability error, Eigenvalue error, or large displacements when I run the analysis with pseudo-flexible diaphragms?

The important thing to remember about the pseudo flexible diaphragm in RAM Frame is that it is no diaphragm at all. The behavior is exactly the same as if you set the diaphragm to "Flexible/None." Unless the frames are interconnected with frame members or horizontal braces, they will displace independently.

The following are common issues that lead to errors that prevent the RAM Frame Analysis from running to completion:

1. A frame with a pinned column base is attached to pseudo-flexible diaphragms only and not connected to other frames with frame beams or horizontal braces. Since there is nothing to stabilize the frame in the out-of-plane direction, the frame is free to rotate about the frame axis. To resolve the problem, fix the out-of-plane moment at the base of the column. If the pseudo-flexible diaphragm properties are defined so that the frame is loaded in-plane only, this will not result in a moment reaction at the column base.
2. The base of columns that are part of frames in two directions can remain pinned.A frame wall is attached to pseudo-flexible diaphragms only and is not connected to other frames with frame beams or horizontal braces. Also, out-of-plane wall stiffness but rotational fixity at the base of the wall has been released. This generates an instability error similar to issue 1 above. To resolve the problem, click on RAM Frame – Criteria – General and uncheck the box for releasing rotational fixity at the foundation nodes.
3. Percentages in the Dynamic tab are divided equally among all frames or load one frame in the out-of-plane direction. This will either result in a very long fundamental period or an Eigenvalue error (see RAMSS Eigenvalue Error). To resolve the problem, review the percentages for the Dynamic tab and verify that mass is not attributed to the frame in the out-of-plane direction.
4. For program generated Wind loads or Equivalent Lateral Force Seismic loads, it's probably best to enter estimated frequency and period values rather than have the program perform the eigensolution. These period (and frequncy) values can be obtained by running the model initially using rigid diaphragms.

See Also

RAM Frame - Criteria - Diaphragms

RAM Frame - Semirigid Diaphragms

RAMSS Eigenvalue Error

The RAM Structural System is powerful and versatile special purpose software for the analysis and design of building structures. It is useful in the design and analysis of commercial, institutional and industrial buildings. The RAM Structural System is composed of the following: RAM Manager, RAM Modeler, RAM Steel (steel gravity design), RAM Frame (lateral analysis), RAM Concrete (concrete design) and RAM Foundation (spread, pile and continuous foundation design).

Browse related content tagged: RAM Structural System

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Files and Interoperability

The RAM Structural System is capable of exchanging data with an Autodesk® Revit® model by either:

• The [[RAM Structural System Revit Link]] - a free Bentley utility used to exchange model data directly between RAM SS and Revit
• Integrated Structural Modeling - a Bentley technology which allows models to exchange data with a wide variety of analysis, design, drafting, and detailing applications using the free Structural Synchronizer applicaiton.

Related Links

[[RAM Concept]], [[RAM Elements]], [[RAM Connection]], RAM Structural System Revit Link, RAM SBeam

How is Mpl and Mstrip Calculated?

The design procedure for base plate design in RAM Connection is based on AISC Design Guide 1. The Design Guide includes some design examples that will clarify how these parameters are calculated.

The equations used to calculate the plate bending moment in the "Flexural Yielding (Bearing Interface)" check are discussed in Section 3.3.2 of the Design Guide.

The strip moment in the "Flexural Yielding (Tension Interface)" check is calculated assuming the tensile loads in the anchors generate one-way bending in the base plate about assumed bending lines. The location of the bending lines depends on whether the anchors are placed inside or outside the column flanges. See Figure 3.1.1(b) and Figure 4.5.2 in the Design Guide. The program assumes a 45 degree load distribution from the anchor to the bending line to determine the width of the bending strip.

See Also

Troubleshooting Errors when Assigning Connections

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

Prevent Truncation of Joint Coordinate values:

Question:

STAAD replaces General format coordinates with scientific format coordinates when the number exceeds 10000 in the format #.###e+00#. Is there a way to stop this truncation of values?

Answer:

Go to the Opening Page of STAAD.Pro.

1.  Go to the File > Configure option.

2. Select the option Input/Output File Format.

    

3. Set the Significant Digit for the Joint Co-ordinates. For example, for a number 10000, the Significant Digit needs to be at least 5.

1. Click “Apply” and “Accept”.

If the specified value of the Significant Digits is set to less than the number of digits the Joint Coordinates have, the value would be reset in the scientific format in the editor.

Please find the screen shot for an illustration.

I am designing a mat foundation supporting multiple columns. How can I check the punching shear at the columns ?

There are two ways to view the punching shear

1. You can go to the Mat analysis/design options > Slab Designer > and click on the Details Report as shown next

2. You can go to the calculation sheet to get the details of the punching shear check as shown next

I am getting excessively high displacements when I analyze my mat in STAAD Foundation Advanced. Any ideas what could be the reason ?

STAAD Foundation Advanced assigns the compression only attribute to the spring supports underneath the mat. So when you analyze the mat, please ensure

1. All load cases that are included as part of the job are real life cases like DL+LL, DL+WL, DL+LL+/-WL, DL+LL+/-EL etc. Refrain from having cases like Wind load ( WL ) acting by itself or earthquake load ( EL ) as part of the job because if you do, the overturning moment due to the lateral loads acting alone, may cause the mat to lose contact with the soil. When that happens, the compression only springs would start getting into tension and would start getting deactivated. The iterative solution may cause more and more springs to get deactivated and subsequently it may cause the mat to just take off leading to absurdly high displacements.

2. Selfweight of the mat is included as part of all the load cases considered for analysis which would help in counteracting any uplift/overturning.

3. The vertical loads are all applied with proper signs ( for example gravity loads are applied with –ve signs )

To ensure that only the real cases get included as part of the job, you should go to Job Setup > Edit Current Job and check that only the appropriate cases appear within the Selected Load Cases window on the right hand side. If you find the component cases like the LL, WL, EL as part of the selected load cases, you should take those out and click on the Edit Current Job to save the change.

I am new to STAAD.Pro and wondering how to get started with some training. Can you please help ?

The best option for new users is to go through one of the many training sessions available at

https://www.bentley.com/en/learn/for-users/training-programs

You can choose the type of training that suits your needs and get started. Here are some additional resources  

You can go to Help > Contents from inside the software and refer to the Getting Started and Tutorials >Tutorials section as shown in the attached screenshot.

Online tutorials/trainings can be accessed from within the software by going to Help > STAAD.Pro Info on Web > Tutorials.

A number of on demand trainings and instructor led trainings can also be accessed from within

http://learn.bentley.com/app/Public/BrowseLearningPaths

You will be taken to the Learn Server page from where you can search for trainings related to STAAD.Pro as shown next

Several online training options will show up from which you can choose a learning path and an appropriate course. For example you can choose STAAD.Pro –General Structural Designer and click on “Courses” to see the related training courses as shown next

Another great resource to learn more about STAAD.Pro and how it is applied to structural analysis is to read a book Principles of Structural Analysis –Static and dynamic loads by Krishnan Sathia. You can find out about this and other books at

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/16421.books-on-staad-from-the-bentley-press

Number of STAAD online seminars are also available at

http://connected.bentley.com/BrowseLive.aspx?keywordSearch=staad

http://pages.info.bentley.com/videos/?Filter=All

Watch out for the ones with Product name STAAD.

How to apply a circular line load to a mat foundation ?

A couple of methods can be used as outlined below

Method 1

In reality a line load would be spread over a certain area for example the base area of a wall. So calculate the pressure based on the line load and the base area over which it acts. Apply a circular pressure load in the downward direction. This loading would load the entire circular area with the value of the pressure load. Add one more circular pressure load of the same magnitude but this time in the upward direction with the appropriate radius such that the net loading represents a downward pressure loading over an annular region. Circular pressure Load option is available within Load & Factors > Add Load For Mat Foundation.

Method 2

You can add a series of point loads on the mat to represent a circular line load. The challenge here is that you need to know the coordinates of the load points. The point loads can be applied through Load & Factors > Add Load For Mat Foundation > Add a Point Load

What happens if I don't sign in to Bentley Service through the CONNECTION client?

With most CONNECT Edition or CONNECT Enabled products, the CONNECTION client service is installed automatically and sign in happens at start up. When starting any of the applications, if the user is not signed in the the sign in dialog will appear.

Canceling the dialog using the red x is the same as signing out and the product should perform normally but no Bentley Cloud Services will be available and no project associations can be made. 

What happens if I uninstall the CONNECTION client?

As noted on screen when uninstalling the CONNECTION client, most Bentley CONNECT Edition products require the CONNECTION client in order to function properly. 

We have tested the various structural products behavior when the CONNECTION client is uninstalled and the products all function other than warnings and limitations of the type noted below. Uninstalling the service will result in warnings when starting the software. For example, in RAM Structural System v15, the following message will appear: 

---------------------------
CONNECTION Desktop Client installation not found.
Please visit www.bentley.com to learn more about the benefits of CONNECT Edition.
---------------------------

Those benefits and other questions about Bentley Cloud Services are addressed on the Bentley CONNECT Overview.

A similar message appear with Ram Concept.

---------------------------
CONNECTION Client installation not found.

Run the Concept installer to install CONNECTION Client and utilize Bentley Cloud Services.
---------------------------

I am not planning to use Bentley Cloud Services, how can I access my files without registering a project?

You can always skip the step of assigning any project by canceling the dialog using the Cancel button or the Rec X and still work on your files.

A few users have reported a crash (MFC Application Error) with Ram Manager CONNECT Edition when canceling out of the Assign Project dialog before the list of projects is refreshed. Until we have a solution to this issue we recommend either waiting until the project list is populated and a project can be assigned, or uninstalling the CONNECTION client service as noted above.

I just installed a program, but I'm getting a login error, "User failed to login" 

In case, you have not updated the CONNECTION CLIENT by this date, you will receive the “User failed to login” error. You will need to download the CONNECTION client.

It is available for download from the ‘Software Downloads’ tile at connect.bentley.com. Search for 'CONNECTIONS'.

Further documentation about this problem CONNECTION Client: User Failed to Login.

Note: RAM Elements, STAAD users may get the same login failure error, if the CONNECTION client was not updated before February 6th.

I'm getting the message "Unable to connect to the EULA service. Please try again later."

 When attempting to log into the CONNECTION client, the following error may appear:

And, as a result, applications like Ram Structural System (Ram Manager) CONNECT Edition will report that Bentley Cloud Services are unavailable:

This happens when the date/time on your system is out of sync with our IMS identity server. To resolve the problem right click on the date/time indicator int he system tray and select "Adjust date/time". In the subsequent dialog, reset the time to be accurate (it must be accurate to 5 minutes of global time).

I am trying to install CONNECTION Client as part of the Structural Enterprise, I am getting a message to get a newer version of Windows

CONNECTION Client is tested and certified for Windows 8 (64-bit), Windows 7 (64 bit) and Windows Server 2012 (64-bit). 

You must be using an older operating system like Vista; please update your operating system.

See Also

Bentley CONNECT Overview

This support solution provides steps to disable RAM Connection integration within STAAD.Pro.

Background

STAAD.Pro includes an integrated version of RAM Connection that is accessible to engineers from the RAM Connection tab. Such integration, while useful, also provides a potential source of unintentional use for the RAM Connection license. Fortunately, STAAD.Pro provides a configuration setting for enabling or disabling the integration. Following are steps for disabling it.

Steps to Accomplish

1. Open STAAD.Pro, and locate the Project Tasks sidebar on the main screen.
2. Click the Configuration link.
   
3. In the window that appears, select the Misc. Options tab.
4. Clear the "Use RAM Connection Product License" checkbox if selected.
   
5. Click the Accept button to save changes.

Once disabled, an engineer will encounter an error when attempting to access the RAM Connection tab.

Only very basic functionality that does not require a RAM Connection license will be available.

See Also

Tips for Using RAM Connection within STAAD.Pro [TN].

[[Error getting a RAM Connection License with STAAD.pro SS5]]

Overview

The purpose of this tech note is to outline the implementation of the ACI slenderness methods for the design of frame and gravity columns in RAM Concrete.

Slenderness requirements for concrete columns are addressed in Section 10.10 of ACI 318-08 and ACI 318-11. ACI 318 outlines three methods to account for slenderness effects:

1. Nonlinear second-order analysis (Section 10.10.3)
2. Elastic second-order analysis (Section 10.10.4)
3. Moment magnification procedure (Section 10.10.5)
   

 A nonlinear second order analysis must consider geometric and material nonlinearities. This type of analysis cannot be performed in RAM Structural System.

The P-Delta method in RAM Frame is an elastic second-order analysis. However, the RAM Frame results can only be used to design frame members; these results are not available to design gravity members. There is an option in RAM Frame to include gravity members under two-way decks in the analysis; however, there is not a way to use these forces for design in RAM Concrete. Also, the P-Delta method in RAM Frame does not include P-delta effects (second-order effects associated with deflections along the member length), which are required by ACI 318-11 10.10.2.2.

The moment magnification procedure is used to design gravity members. The forces used to design gravity columns are taken from RAM Concrete, which does not include P-Delta effects. ACI 318-11 10.10.7 outlines a moment magnification procedure for sway members. This procedure is not implemented in RAM Structural System. The program assumes that the forces associated with sway members are from an elastic second-order analysis.

More information on the analysis assumptions in each module can be found here.

There are four possible design categories for concrete columns:

1. Gravity Column, Braced
2. Gravity Column, Sway
3. Frame Column, Braced
4. Frame Column, Sway 

Analysis and design notes for each of these groups are summarized in the following sections.

Gravity Column, Braced

These columns are designed using RAM Concrete Analysis forces. The design forces are calculated using the non-sway moment magnification procedure. The forces reported in the Column Design Report are the magnified forces and not the forces from the analysis.

Gravity Column, Sway

These columns are designed using RAM Concrete Analysis forces. The program assumes that the forces for sway columns are from an elastic second-order analysis. The program does not adjust these using the moment magnification procedure for sway frames. This follows from earlier editions of the ACI code, which allowed for the magnified sway moment to be taken from an elastic second order analysis (see ACI 318-05 10.3.4.1). This is a problem since a P-Delta analysis is not completed in RAM Concrete and RAM Frame results are not available for these columns.

Gravity concrete columns should never be designated as sway columns in RAM Concrete. Instead, these columns should be converted to frame members so that they are included in the RAM Frame Analysis. ACI 318-11 10.10.5.1 permits columns to be assumed non-sway if the increase in column end moment due to second-order effects does not exceed 5%. Gravity, sway column would only occur in structures with significant overturning under gravity load, which would be rare. In future versions of the program, it will not be possible to designate gravity columns as sway columns.

Frame Column, Braced

These columns are designed using lateral forces from the RAM Frame Analysis and gravity forces from either RAM Concrete or RAM Frame (see option in RAM Concrete Column – Criteria – Column Design – Design Checks/Forces tab). The design forces are calculated using the non-sway moment magnification procedure. The forces reported in the Column Design Report are the magnified forces and not the forces from the analysis. Since the moment magnification accounts for both P-Delta and P-delta effects, P-Delta can be turned off in RAM Frame.

Frame Column, Sway

These columns are designed using lateral forces from the RAM Frame Analysis and gravity forces from either RAM Concrete or RAM Frame (see option in RAM Concrete Column – Criteria – Column Design – Design Checks/Forces tab).

The design procedure follows the moment magnification procedure for sway frames in ACI 318-05 10.13. The equation for the magnified end moments is M =  Mns + Delta_Sway*Ms, where

M = total magnified end moment

Mns = non-sway moment

Delta_Sway = sway moment magnifier

Ms = sway moment

In previous versions, ACI 318 permitted magnified sway moments (Delta_Sway*Ms) to be determined from an elastic, second order analysis (see ACI 318-05 10.13.4.1). This is the assumption that is used in RAM Concrete, and a sway moment magnifier of 1 is assumed. Due to this assumption, P-Delta should always be included in the RAM Frame Analysis.

The non-sway moments are the gravity moments, which are taken from RAM Frame or RAM Concrete. In the ACI equation above, the non-sway moments are not magnified. If the option to use gravity forces from RAM Frame is used, the analyzed gravity load cases would include second-order effects from the P-Delta analysis. In most cases, the story displacements associated with the gravity load forces are small, so the increase in forces due to P-Delta effects should also be small. If there is a concern about using an amplified non-sway moment due to P-Delta effects, then gravity forces from the RAM Concrete analysis should be used to design the columns.

For slender columns with high axial loads, the maximum moment may be between the ends of the column and P-delta effects can be important. For this reason, the ACI 318-05 and earlier separated columns for which the slenderness (lu/r) was greater than 35/sqrt(Pu/f’c/Ag). When this threshold was exceeded, the program calculated from the following equation (see ACI 318-05 10.13.5)

M = Delta_NonSway*(Mns + Delta_sway*Ms)

This provision was removed in ACI 318-08.

In ACI 318-08 and later, the sway moments are required to be determined from one of the three slenderness methods (nonlinear second-order, elastic second-order, or moment magnification) for any slenderness ratio. As noted previously, the program is not equipped to run a nonlinear second-order analysis, the elastic second-order analysis does not include P-delta effects, and the sway moment magnification procedure is not implemented. The best the program can do is to combine the elastic second-order analysis with the moment magnification procedure using the same design procedure that is used when the ACI 318-05 is selected.

ACI 318-08 and 318-11 10.10.2.2 requires second-order effects along the length of the member to be considered when the member is slender. Since P-delta effects are not included in RAM Frame, the program should apply 10.10.6 to slender, sway columns. This is not currently done by the program. This is logged as Defect #215527 in our database.

Other Notes

• ACI 318-05 limited kl/r to 100 unless a non-linear, second-order analysis was used. This provision was removed in ACI 318-08 but is still enforced in RAM Concrete when ACI 318-08 or ACI 318-11 is used. Defect #215695 has been filed with the development team.

• RAM Concrete does not check ACI 318-11 10.10.2.1: total moment including second-order effects shall not exceed 1.4 times the moment due to first-order effects. Defect #215527 has been filed with the development team.

• RAM Concrete does not calculate Q ACI 318-11 10.10.5.2 (Eq 10-10). Enhancement #275537 has been filed .with the development team.

• The Column Design Report still references ACI 318-05 10.3.5 when the slenderness ratio is high. This is a reporting error only. This does not affect the design. Defect #215175 has been filed with the development team.

• RAM Concrete does not include an option for using the moment magnification procedure for sway columns. Enhancement #215521 has been filed with the development team.

• ACI 318-05 10.12.3.1 included a lower bound of 0.4 for the parameter Cm. This lower bound was removed in ACI 318-08 but is still enforced in RAM Concrete when ACI 318-08 or 318-11 is used. Deflect #214767 has been filed with the development team.

• Slenderness effects are not included in RAM Concrete Shear Wall.

See Also

Concrete Column Minimum Eccentric Moment

Ram Structural System Support Solutions