Problem Description

After installing RAM Connection 8.0, the Connection button still fails to appear in the Database ribbon within RAM Elements.

Reason

Starting with RAM Connection 8.0, RAM Connection for RAM Elements is no longer installed automatically with RAM Connection Standalone.

Steps to Resolve

1. Open the RAM Connection installer by running Setup.exe in the following directory:
   C:\BentleyDownloads\rc08000023en
2. Click the link labeled "Install RAM Connection for RAM Elements" as shown in the screenshot below.

A valid license for Ram Connection (or Structural Enterprise) must be available when launching Ram Elements, otherwise the connection toolbars are still hidden.

Finally, go into Ram Elements - e menu - General Configuration - Licenses tab and make sure the box to "Check RAM Connection license” is checked. If it is not, check it and restart. This wiki explains why some users turn that option off intentionally.

See Also

[[Unable to Satisfy All Prerequisites for RAM Connection Release 9.0]]

Structural Product TechNotes And FAQs

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!

***THIS PAGE IS CURRENTLY UNDER CONSTRUCTION***

While hardware locks were previously the means of licensing MStower, this is no longer the case. MStower is now licensed through Bentley CONNECT SELECTservices (BCSS). The fundamental concept in gaining access to software licensed through BCSS is product activation. Activation of a product is required regardless of the type of agreement a customer has with Bentley, the products owned, and the permissions set by a systems administrator. This section describes how to activate MStower and the associated design codes on a computer.

Activating MStower and Design Codes

To configure and activate an MStower license, use the File -> Manage Licensing command. Note that this dialog will appear automatically after the first launch of MStower following installation.

Select the desired design codes in the Enable Design Codes section. Selecting Apply at the bottom of the dialog will enable only the codes that have been selected. Note that at this point the product is not activated, but the design codes chosen will be communicated to SELECT server once activation takes place.

To activate the product, select Product Activation Wizard at the bottom of the dialog. The ensuing screen will list four activation options. To determine which option is appropriate, consult the systems administrator at your organization or contact Bentley technical support. Generally speaking, users new to Bentley will, in most cases, be activating against a hosted SELECTserver.

Detailed instructions for completing the product activation, dependent on which activation method is utilized, are available at the following links:

Activating against a hosted (Bentley) SELECTserver:

https://communities.bentley.com/products/licensing/w/licensing__wiki/4987.aspx

Activating against a deployed (local) SELECTserver:

https://communities.bentley.com/products/licensing/w/licensing__wiki/5277.aspx

Activating as a NON-SELECT or Node Locked User:

https://communities.bentley.com/products/licensing/w/licensing__wiki/5278.aspx

Although a given organization may own a set number of licenses of a specific Bentley product, authorized users may activate and use as many licenses as needed, with no cap enforced on usage. For detailed information on Bentley’s licensing policies and benefits, see the following link:

https://communities.bentley.com/products/licensing/w/licensing__wiki/12388.bentley-connect-selectservices-formerly-selectserver-quick-start-guide.aspx

MStower is offered as a base product plus a number of design codes that can, at the user’s option, be added. The base product consists of the graphical interface, modeling environment, core analysis capabilities, report engines, and interoperability features. The design codes provide member design and load generation to specific code standards. The design codes are categorized by geography and include Australia, United States, Great Britain, and India. The design codes available in each geographic code are listed below.

• Australia: AS 3995, AS 4100
• United States: EIA-222-F, TIA-222-G, ASCE 10-90, ASCE 10-97, ASCE Manual 72
• Great Britain: BS8100 Part 3, BS449, BS 5950, ILE Tech Report 7
• India: IS 802

Note: In versions of MStower prior to V6.2 the monopole and dynamic analysis options were separate add-ons. These options are always included in V6.2 and later.

RAM Concrete is a set of design modules within the RAM Structural System product suite used for the structural analysis and design of mild reinforced concrete beams, joists, columns, and walls. With RAM Concrete, you can efficiently model both gravity and lateral systems, perform complete gravity and lateral load generation and distribution, including live load reduction and skip loading per ACI-318, design and detail reinforcing for beams, columns, and walls per ACI 318, BS8110, EC2, AS3600, CP65 and GB50010, and produce CAD files for framing plans, wall and beam reinforcing elevations, and beam and column schedules.

Error or Warning Message

When opening STAAD.Pro, the following message can occur:

Unable to activate RSS Feed connection

Explanation

This message indicates that STAAD News Feed cannot be activated successfully. In such situation, STAAD News are not shown in the start-up window of STAAD.Pro.

How to Avoid

1. In most cases, it should be enough to install BentleyRSS.msi file, which can be downloaded from here:

   http://communities.bentley.com/products/structural/structural_analysis___design/m/structural_analysis_and_design_gallery/269774.aspx

    

2. If installation of BentleyRSS.msi file does not help, check if you are able to go to the page http://feeds.rapidfeeds.com/8131/ or not. If not, then there is potentially some firewall/security in your network that is blocking the communication when STAAD.Pro is trying to communicate with the RSS feed page.
    
   If you are able to connect to the webpage through Internet Explorer, it means that specifically when STAAD.Pro tries to access information over the internet, that particular communication is being blocked. You may check your firewall settings in your network and add STAAD.Pro (C:\SProV8i\STAAD\Staadpro.exe) to the list of Exceptions. If you have a proxy server in your network then check if that is blocking the communication or not.

See Also

STAAD.Pro TechNotes and FAQs

http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/6380.staad-pro-known-issues-in-the-current-version-20-07-10-41.aspx

This page provides a list of errors and performance-related issues in the current version of STAAD.Pro after it was released. For such issues in prior versions of the program, please see the ReadMe document delivered with the STAAD.Pro installation.

* Prior versions are also affected by this issue 

When will Bentley’s SELECT versions of Microstran, Limcon, and MStower be available?

Our developers are nearing completion of the SELECT versions and we are aiming to post them at the beginning of June.

What is available in the new SELECT versions of the Microstran products?

The most significant enhancement is that the products are now licensed in a far more sophisticated and useful manner: through Bentley Connect SELECTservices. There are many benefits this offers over the hardware locks previously used. Some of the most important are:

• If you need short term access to more licenses that you own, they can be acquired without needing to consult technical support or a sales representative.
• Licenses are pooled across an organization.
• Reports can be generated that show your daily product use, allowing you to make informed business decisions.

The following improvements have also been made:

• Silent deployment of installers, allowing batch installation of the products across an entire organization.
• Signing of installers with Authenticode signatures, preventing Windows 8 from blocking or restricting installations.
• File associations, allowing launching of application by double clicking a file.

I do not have a support agreement in place with Bentley to cover my Microstran products. How do I go about getting them covered under Bentley’s maintenance?

Contact one of our representatives at the email below to cover your products under Bentley’s SELECT program.

sales@microstran.com.au

support@microstran.com.au

Alternatively, if you are new to the Microstran product line and would like more information, please contact:

• Sandra Mora, at Sanrda.Mora@bentley.com in Australia, New Zealand, and Southeast Asia.
• Ingrid Brock, at Ingrid.Brock@bentley.com in all other regions.

Existing Bentley customers may also contact their current sales representative.

Is formal training available for these products?

A course entitled Fundamentals of Microstran will soon be available on Bentley Learn.

Are Microstran, Limcon, and MStower included in the Bentley’s Enterprise License Subscription (ELS)?

Yes. The SELECT versions will be part of ELS.

What are the future development plans for Microstran now that a SELECT version is available?

The next release of Microstran coming later in the year will incorporate an export to Bentley’s Integrated Structural Modeling (ISM) format. This will allow reuse of Microstran models in information modeling and structural detailing software such as ProStructures, AECOsim Building Designer, REVIT, and Tekla.

What are the future development plans for Limcon now that a SELECT version is available?

In early 2015, Limcon will be merged with RAM Connection, and the best of each of these products will be offered in one release. Owners of either Limcon or RAM Connection that are covered by a Bentley SELECT contract will pay no upgrade fee for this new version.

What are the future development plans for MStower now that a SELECT version is available?

At the end of 2014, MStower will be merged with STAAD(X).Tower and the best of each of these products will be offered in one release. Owners of either MStower or STAAD(X).Tower that are covered by a Bentley SELECT contract will pay no upgrade fee for this new version.

What floor-to-floor height should I enter in the story data?

Whatever story height you enter into RAM Modeler, that is where the centerline of the frame beams will fall in the finite element model and vertical braces always connect to a work point at the beam and column centerlines. This is done for simplicity in the finite element analysis.

For drift sensitive structures, using a first story height that is equal to the distance from the ground level (or foundation level) up to the top of steel - average frame beam depth / 2 is probably the most accurate modeling (see "Alternate Story El." below). But using a distance from ground level to beam top of steel (a.k.a. deck bearing) is more common practice and is conservative in most aspects (see "Common Story El." below).

The common story approach is also used when the RAM SS 3D model is exported to ISM. In the ISM model the beam locations are established relative to the story datum based on the following rules:

• Non composite deck – top of beam, deck bearing at story datum
• Composite deck – top of beam, deck bearing at story datum
• Concrete slab – top of slab at story datum

Keep in mind, story height can also affect the following calculations:

• Calculated wind exposure (and Kz factors)
• "h" in the vertical distribution of seismic loads calculation (wi*hi/Sum (wi*hi))
• Overturning moment (related to lateral force times story height)
• Unbraced length for columns
• Slope angle and length of braces
• Material takeoff quantities
• And the elevation of the beams shown in the 3D view, or exported out to Revit, ISM, or dxf, which are all artificially adjusted to show all beams with top of steel at the story height.

How can I model a continuous beam?

In Ram Structural System, the framing must all be determinate, so multi-span indeterminate framing is not directly possible. There are two approaches to modeling and designing continuous beams. 

The first is to model each span as a lateral beam. use the same size for each span and be sure to assign the ends to be fixed. The supporting columns also need to be lateral, but they may be pinned (in the plane of the framing). To see the accurate member forces or steel design of the beams, use Ram Frame analysis and the Steel Standard Provisions respectively.

Alternatively, for those that do not have Ram Frame, the system can be approximated using a cantilever and suspended span approach. In other words, model one span normally and add a cantilever extension into the second bay. Then add a suspended span from the end of the cantilever to the third support (or add a cantilever beam in every other bay for continuous beams more then 2 spans long). The length of the cantilever is important here since it dictates the inflection point or point of zero moment.

When using the cantilever approach one side effect is that the supporting columns will assume zero eccentricity in the design.

Can a beam cantilever directly from a support with no back-span?

Yes, the option to create a stub cantilever or beam with a single support was added in version 14.02.  Prior to that version a dummy column of near zero stiffness and a lateral beam with one end fixed was required.

How can I create a sloping floor or roof?

There are some basic limitations to what you can model with RAM Structural System, so it may not be possible to model some structures perfectly, but you can usually get close. The following guidelines should help

• Every beam must have exactly two supports, never 1 or 3, and those supports must be on the same level type. So you can't directly model a bent beam forming a gable unless there is a support at the peak.
• You must be able to model the structure as a flat (wedding cake) type structure first, then create the slopes by changing column (and wall) elevations.
• Any time you have a step (two beams framing into the same support at different elevations), two levels types and two stories are required and the higher beam must be on the higher story.
• You can raise or lower a column (or wall) using the Layout - Column - Modify elevation command and thus slope beams that connect to it. If you want to lower the column more than the story height, then you must also lower the same column on the next lower story. If you want to raise the column more than the story height of the level above, then you must also raise the same column on the level above. Think of the column like a string with beads on it at each story. As you modify the elevation you are lowering the bead, but you cannot cross another bead. In the end, the beads must be at least 0.1’ apart (more separation is preferred).

Other things to note:

• You can have a rigid diaphragm that is sloped, but in RAM Frame this is treated as a horizontal diaphragm. We don't analyze sloped rigid diaphragms. Furthermore, if your structure is subject to trust, diaphragms should be turned off at least while investigating gravity loads. Using a sloped semi-rigid diaphragm is an alternative.
• The gravity steel and concrete beam design will not include any effects of axial forces.

I modeled a roof with multiple slopes, but in the 3D view the deck is a single sloped plane shooting up.  How do I fix this?

Starting in version 14.0, the program will display the surface of the deck in 3D.

For a sloping deck to function correctly in this regard, the deck must be input using a separate polygon for each sloping surface. In other words, for a gable roof, two deck polygons should be defined, one for each side or slope of the roof.  A whole-floor application of the deck is no longer sufficient.

It is suggested to snap to the beam end points when defining these decks, since the beam end points have exact elevations which are derived from the supporting column or wall elevations. Here's a better way to lay out the deck polygons for the model illustrated above:

Even slight imprecision in the support elevations (i.e. warping of the deck) can cause this anomaly in 3D.

The analysis results will only be affected if the warped deck is part of a semirigid diaphragm in RAM Frame or is defined as a two-way deck.

How can I model a 2 story brace, or one that skips a level?

When a brace needs to skip a level use Layout - brace - Add Special and follow the prompts at the bottom left.

For details on how these braces effect frame story shear reporting, please reference [[RAM Frame - Building and Frame Story Shear]].

I have a brace in 3D that does not appear in any elevation view. How can I delete it?

There are two ways to remove rogue braces that are no longer in an elevation view that can be selected.

1. If the braces do not connect to any frame members at either end, then an integrated data check can be performed and the following message will appear: "Some Braces do not attach to Nodes. Do you want them deleted?". Click "Yes" to have them removed. Note – if the brace is connected to a lateral member at one end, but not the other, this message will not appear, so you may need to make some supporting beams or column gravity temporarily.
2. Delete and re-enter the story data for this particular level. This will remove all braces at that level.
    

How do I model a transfer girder, or a column setting on a beam?

On the upper story level model the column as a standard column (not a hanger).

On the lower level model the beam passing through the location of the column above. This could also be a beam cantilever.

Use Reference layout types (under the options menu) or construction grids to aid in the alignment of the column and beam below.

I have a column that supports the roof, but does not support anything at the lower level. Do I have to model the column on both layouts in RAM Modeler?

Think of the RAM SS Layout type like a section through the whole structure. Any columns that are cut by the section should be modeled on that layout typically. Don't worry, the program will design the column for the correct, longer unbraced length so long as there are no beams (or optionally decks) at the intermediate story to brace the column.

There is one alternative, however. If the column is only modeled on the Roof, and not modeled on the lower level at all, then you can add a foundation under that column and lower the foundation to stretch the column to the full height. This approach can be helpful in cases where the column is sloped and the story heights are not constant making it hard to determine the exact bottom offset to keep the two-story column in one straight line.

Why am I unable to copy information or import a DXF into a layout?

The Copy and Import from DXF features (RAM Modeler - Layout - Type menu) are only active for layout types that contain no information. These commands are deactivated in RAM Modeler even if the layout contains only grids and no other objects. To use either command, create a new layout and then use the copy or import features before any other information is defined on the layout.

How Do I Model Grade Beams?

Although there is currently no direct way to model grade beams in RAM Structural System, they can be simulated by modeling concrete beams and designed in RAM Concrete. These basic steps produce satisfactory results for most configurations.

1. Model a grade level that contains the concrete grade beams supported by columns. The top of the columns should be pinned and the bottom fixed.
2. Model a slab edge on the grade beam level and assign a noncomposite deck with no selfweight. This is necessary so that there is a diaphragm present on the level in RAM Frame.
3. Add the grade level to your story data.
4. In RAM Frame, set the ground level to the grade level.
5. Run the RAM Frame analysis and RAM Concrete Beam design.

By creating a rigid diaphragm at the grade level with the nodes at the grade beam - column intersections to it, translation is restrained when the ground level is set to the grade level. Therefore, no shear will exist in the column stubs. Since the top of the column stubs are pinned, no moment will be developed in the column stub below the grade beams. Spread footings or pile caps can be modeled at the column stub locations. The foundation loads will only be vertical forces.

There are a couple of important things to note. First, automatic calculation of effective length factors may be inaccurate for this procedure. No boundary condition is assumed at the lower node of the column above the grade beam level. Therefore, the G value for the lower node is a function of the column and grade beam stiffness in the direction being considered. If this is not an accurate assumption, the effective length factor should be explicitly defined. Second, don't specify a story height on the grade beam level that is too small. Using an extremely small story height is not necessary because there will be no translation of the grade beam level and only vertical forces in the stub columns. The only ramification of using a larger story height is an increased selfweight for the stub columns. If you use too small of a story height you might produce a poor mesh if lateral walls are modeled on the grade beam level.

See Also

Product TechNotes and FAQs

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!

How are torsional irregularities considered?

In general, the program automatically accounts for any eccentricity in the stiffness of the structure during the finite element analysis. For each structure, there is a center of rigidity (which you can report if you create a special center of rigidity load case). If the load is applied to the diaphragm eccentric to this center of rigidity location, then torsion in the structure develops.

Accidental torsion is also considered based on the percentage set under loads - masses (default is 5% of the diaphragm dimension). Currently, the application of accidental torsion is limited to rigid diaphragm analysis. A method for incorporating accidental torsion in semi-rigid diaphragm analysis is in development now.

What the program does NOT do, is amplify these torsion effects according to any specific code provisions (e.g. "A_x" from ASCE 7-02 12.8-14) . It is up to the user to account for additional torsion resulting from plan or vertical irregularities. Most people increase the mass eccentricity under loads - masses from 5% to some larger value to account for the extra torsion required by code, though user defined story forces with a modified location also work well.

Are the seismic results ultimate?

For program generated seismic load cases from any modern code (e.g. ASCE 7-05), the force magnitudes are at an ultimate level.

It's important to note, however, that the drift associated with any static seismic load is the elastic deformation (δ_xe from ASCE 7-02 Eq 12.8-15). The user should amplify the program drift results to determine design deflection for comparison against the allowable drift (δ_x  from ASCE 7-05 Eq. 12.8-15)

Also note, the vertical component of the earthquake (Ev) is handled though the generation of load combinations by increasing or decreasing the Dead load factor, it is not part of the individual seismic load cases themselves. Furthermore, increases in the seismic force required by a lack of redundancy (Rho) are only accounted for in the load factors applied to the seismic loads in generated combinations.

What is the difference between seismic loads that use provisions for member forces and provisions for drift?

When creating a seismic load case suing the IBC/ASCE7 equivalent lateral force procedure, there is an option to use provision for member forces or provision for drift (see screenshot below).

The difference between these options is the upper limit of the calculated period used to calculate the seismic loads.  When provisions for member forces are used, an upper limit of T = CuTa is used for the calculated period per ASCE 7-05 12.8.2. When provisions for drift are used, the upper limit on the period is not used per ASCE 7-05 12.8.6.2

Why do I get a warning about mass that's not associated with any diaphragm?

When you have line loads or any members with self weight masses considered (Under Ram Manager Criteria - Self-Weight) that occur outside of the boundary of the diaphragm slab edge you will get the following type of warning:

---------------------------
Some mass has been detected on one or more stories that is not associated with any diaphragms.
It will be ignored in Analysis unless it is combined with one or more diaphragms.
See the Loads - Masses command.

---------------------------

Under Loads - Masses you can evaluate the total diaphragm masses and you can combine these values with some diaphragm, override with User Specified Values or choose to ignore them by doing nothing.

One fairly common modeling mistake is to copy the line loads from another level type, but then modify the framing and slab edge without removing line loads that then fall out in space.

A similar error message also occurs when the Gravity load totals used for Notional loads are uncombined. See [[RAM SS Notional Loads]] for details.

Do I need to divide the Mass DL by the acceleration of gravity?

No, the program is expecting a weight value for the "Mass DL"  despite the name. Enter the same magnitude as the dead load typically (or dead + some portion of the live depending on the live load type and code requirements). In the Ram Frame - Loads - masses dialog we list the total weight and the equivalent mass for clarity.

On the Loads and Applied Forces report, the "Total Building Weight" is reported. This value is the sum of the Mass Dead Loads considered in the seismic analysis which can include member and deck self-weight. This is also a weight term, not a mass.

See Also

[[RAMSS Gravity Loads FAQ]]

[[RAM SS Notional Loads]]

Product TechNotes and FAQs

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!

Are the applied surface loads cumulative?

No, in RAM Structural System only the top applied surface load counts. The underlying loads are not deleted however, so if you delete the top load you can see the original load underneath. If too many load layers are applied to a model, a polygon error can occur when processing the loads. For this reason it is always best to remove any existing surface loads before modeling new layers.

Also note, this is different than the behavior in RAM Concept. In that program, overlapping surface loads are cumulative. Consequently, when Direct Gravity loads are imported from RAM SS into Concept, they are converted into equivalent separate polygons that do not overlap.

Is the structure self-weight included in the loads?

That depends on the settings under RAM Manager - Criteria - Self-Weight. Here the user can automatically include beam, column, wall or deck self-weight. Note, open web steel joists self-weight is never included.

For composite beam design, the self weight is always considered part of the Construction Dead Load. Hence, if all the self weight options are turned on, and there is no other load present during construction, the user applied CDL might be zero.

On the right hand side of the dialog box are the settings for self-weight as it applies to the building mass which is used for seismic loads, dynamic analysis and for P-Delta calculations.

In order for the steel gravity beam and column self weight mass to be considered in RAM Frame, it is imperative that those modules be run first, using the design-all process. So long as the RAM Manager indicates a green light next to each of those modules, RAM Frame should have the latest member self weight data available.

Note, in RAM Frame, under Loads - Masses, the program calculated diaphragm mass totals can be overridden with User Specified values, normally using calculated masses is advised. There is a similar dialog box for the total Gravity Loads which is used to determine program generated notional loads.

Is the additional weight of concrete due to beam sag or "ponding" considered?

No, the self-weight of the deck is based on the thickness and weight parameters set in the Modeler - Deck Properties. When beams sag under the weight of the deck it is a common practice for the topping concrete to be leveled off which adds additional weight to the system assuming it's not cambered or shored. This additional weight should be incorporated into the applied construction dead loads (and masses).

How are partition loads handled.

The Partition load is an additional Live Load; it is treated as an unreducible Live Load and will not be reduced. It is in addition to the loads specified as Live Load. Partition loads are defined variously by the Codes, some as Dead Load and some as Live Load. For those codes that define Partition loads as an unreducible Live Load, those should be specified here. For those Codes that define Partition loads as a Dead Load or as part of the regular Live Load, those should be included as part of the Dead Load or Live Load accordingly.

Unlike construction live load, the partition live load is not a portion of the total live load entered. You can apply 0 Live Load and still apply 15 psf Partition Live load, for example.

Partition loads are not automatically included in the seismic mass. The total Mass DL should be increased to account for partition weight as required by the code for seismic loads.

How is the self weight of Concrete Beam determined?

The program calculates rectangular beam unit self-weight based on the area of the beam times the "Unit Weight of Self weight". The other "Unit Weight" parameter is only used in calculating the elastic modulus, E, of the member.
The Concrete slab can independently be included in the self weight, so in cases where there is a concrete slab and rectangular concrete beams the weight of the concrete times the thickness of the slab and the width of the beam is double counted.

 
To alleviate this problem, "T" shaped beam sections are handled differently. With T beams, it's only the area of the stem below the slab that is applied as the beam self weight.

.

Why are my Roof Live loads ignored in the design?

RAM Structural System currently considers Snow OR Roof LL, but not both at the same time. In RAM Manager under Criteria - Members loads there is a toggle to select which the program should consider. Set the toggle to “Consider snow loads, Ignore roof live loads” when snow loads are modeled.

Note: Live Reducible, Unreducible and Storage type loads are always considered, it is only the Live - Roof type loads that are excluded when the option to consider snow loads is turned on.

Are my snow loads automatically added to the building weight for seismic load determination?

No, the program only uses the assigned Mass Dead Loads plus whatever self-mass options are turned on under RAM Manager - criteria - self weight when determining the total building mass or weight used in Seismic load determination (and in P-Delta calculations). The user should increase the Mass DL of applied surface loads to account for the weight of the snow load (or a percentage of the weight as required.

Note, the provided templates for load combinations do correctly consider snow load acting simultaneously with Dead, Live and Seismic loads, however.

This also applied to Storage Live Loads, even if the magnitude entered for the Storage Live load is large (e.g. > 125 psf) no portion of the storage live load is automatically considered in the seismic mass. The user must increase the Mass DL (or manually alter the masses in Ram Frame) when part of a storage live load needs to be added to the seimsic mass.

How can I apply a drift snow load?

Within the snow loads, only the top load counts. Since only the top snow load counts, the drift snow load should typically taper down from the max value to the flat-roof snow load as a minimum. The program gives a warning when any portion of the sloping plane of snow load is 0 or less magnitude.

In general, it’s best to define snow drift loads with M1 and M2 set to the highest value, and M3 set to the flat roof level. Then the loads can be applied in rectangular or trapezoidal areas as required. In the image below, the total snow load on the left is 50 psf tapering down to 30 psf on the right. This would be used in conjunction with a flat roof snow load of 30 psf applied first to the whole roof.

See Also

RAMSS Seismic Loads FAQ

Product TechNotes and FAQs

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!

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. 

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.

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.

Missing or Incorrect Loads on Perimeter beams

Since the advent of free form slab edges, there have been a few framing slab edge configurations that can lead to unexpected loading on the perimeter beams.

In the image below, the slab edge is slightly skewed to the perimeter beam, and crosses it at one point. Consequently beam 8 may be assumed outside of the slab edge and will not receive loads from the one-way deck.

The best way to avoid the problem when using one way decks is to align the slab edge with the perimeter beams and use at least a 1" outboard overhang. Furthermore, make sure the perimeter framing creates a closed loop around the diaphragm. Small gaps in the perimeter framing can also cause problems.

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

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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Overview

This page addresses common issues and questions specific to concrete beams designed and analyzed in the RAM Concrete Module of RAM Structural System

Slab Self-Weight

For rectangular beams, the portion of the slab that intersects the rectangular beam is included in both the slab self-weight andthe beam self-weight. For T-shape beams, this double counting of self-weight does not occur.

Loading Diagrams (RAM Concrete Analysis - Reports - Beam Load Diagram)

The beam loading diagram displays point and line loads that are calculated by the program and applied directly to the member.

The following information is excluded from the reports:

• Magnitudes of supported beam (or column) reactions: These are excluded because the loads are applied as line loads on the supported beams. Force transfer to the supporting beams is completed in the finite element analysis. The analysis does not analyze these beams separately with point loads as is done in RAM Steel Beam. The location of the supported reactions is shown in the report for convenience.The Load Diagram Report in RAM Steel Beam can be used to report find the tributary point load distributed to the beam if one-way decks are used.
• Load from two-way decks: For models containing beams and two-way decks, the surface loads are applied as a series of nodal loads at each finite element node. These load are directed into the framing members and supports based on relative stiffness in the finite element analysis. The program does not perform a yield-line analysis and determine a trapezoidal line load on each beam member. Since a line load is not calculated and placed on a member, the floor load from the two-way deck will not be represented in the Loading Diagram Report. The Beam Load Diagram Report will show the beam self-weight only, since this is the only line load that is calculated by the program and applied directly to the beam.

Deep Beam Design

The ACI code classifies beams with a clear span to depth ratio greater than 4 as deep beams. RAM Concrete Beam can check if beams exceed this ratio. The option to include or exclude this check is found in RAM Concrete Beam – Criteria – Beam Design – Design Checks/Forces tab:

When the option is selected, a design warning is produced when the clear span to depth ratio exceeds the threshold. . RAM Concrete Beam does not design deep beams for flexure and shear;  It is the user’s responsibility to design deep
beams outside the program.

ACI 318 also requires deep beam checks when a concentrated load is located within twice the member depth from the face of the support. RAM Concrete does not check the location of concentrated loads and will not
generate a design warning for this situation.

Torsion Design

RAM Concrete Beam can check the torsion demand to the threshold torsion defined in ACI 318-08 11.5.1. The option to include or exclude this check is found in RAM Concrete Beam – Criteria – Beam Design – Design Checks/Forces tab:

When this option is considered, a design warning will be reported when the beam torsion exceeds the threshold torsion. RAM Concrete Beam does not design the torsion reinforcement;  It is the user’s responsibility to design this outside the program. The Beam Design Report will report the maximum factored torsion at each station and the f_T*T_c.

Effective Depth

The effective depth that is used in the beam design is based on the Assumed Cover to Center of Bars assigned in RAM Concrete Beam – Design Criteria – Assumed Cover to Center of Bars. The program does not automatically determine the effective depth based on the code minimum cover and the longitudinal and transverse bar sizes. If the assumed effective depth is greater than the actual effective depth calculated from the minimum cover and bar sizes, a design warning similar to the following will be displayed:

When this warning occurs, the assumed cover should be increased. This can be done globally for all beams (RAM Concrete Beam – Criteria – Beam Design – Reinforcement tab ) or can be assigned beam by beam (RAM Concrete Beam – Assign – Reinforcement Layout).

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

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What is the relationship of initial deflection and camber?

The Criteria - Camber and Criteria - Deflection criteria together determine if beams will get cambered in the program design. Refer to the Ram Steel Beam manual, section 10.13 for details on exactly how this is done, below is an example for the most common case, Unshored, Composite Construction.

This example uses default camber and deflection criteria:

Which means that beams will be cambered if and only if, the deflection caused from 80% of the applied Construction Dead load is greater than 0.25".

The beam in question is a 20' long girder and the CDL stems from the beam and deck self weight. With 100% of that load considered acting on the pre-composite unshored beam, the deflection is 1.061" downward at mid-span. The deflection due to 80% of the CDL is therefore 0.8 * 1.061 = 0.85". Thus the program cambers 0.75" which is 3 times the 0.25" camber increment.

The Live load deflection is calculated using the composite properties (Ieff) and is therefore a smaller total deflection even though the applied loads may be more than the CDL. This Live load may already be reduced if the beam tributary area is large enough. Construction live loads are used in the Pre-composite strength check of the beam only, not in the initial deflection check.

The Post Composite value is also based on the composite beam effective inertia. The Post Composite load considered is any dead load above and beyond the CDL plus the Live Load. This is often referred to as the superimposed load. 

Thus the Net Total load can be calculated using the formula:

Net Total deflection = Initial defl + Post Composite delf - Camber

In the case above that is 

0.759 = 1.061 + 0.448 - 0.75

It's also worth noting that the initial deflection in this case is large enough to surpass the common L/240 deflection limits for dead loads, but that's OK because there is no limit on initial deflections (using our default deflection criteria). So long as the Live load deflection and Net Total deflection limits are OK, no warning will be given.

It is also worth noting that even with camber, this beam theoretically deflects 1.061 " - 075" = 0.311 inches during construction. The program does not increase the construction dead load to account for the additional topping concrete that might occur from such ponding. The applied loads should manually be increased where this is a concern.

Can I turn off Camber on specific beams?

The Criteria - Camber controls whether to camber or not camber composite beams or non-composite beams for the whole model. In cases where you want no camber on specific beams consider adding a special deflection criteria with an initial deflection limit equal or less than the minimum camber and assign that deflection criteria to the beam in question: 

Are transfer loads from columns or hangers affecting composite beams considered pre-composite or post-composite?

All transfer dead and live loads affecting composite beams are part of the post-composite design. For transfer columns, that typically makes sense since the lower level composite beam should be hardened by the time the upper level is loaded. For hanging columns it's not so clear cut, but the transfer load is still only considered in the post-composite design in Ram Steel.

Transfer loads do not include the column self-weight since column design typically takes place after beam design. A point load for the estimated column self-weight is advised.

See Also

[[structural_analysis_and_design__wiki:RAMSS Design Fy or Py|RAMSS Design Fy or Py]]

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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How can I evaluate an existing composite beam?

Using the Process - View/Update command, select the beam in the model. Change the selected member size, set the stud number to the desired value and click Analyze. Then click Update Database when finished.

If the existing stud count is insufficient to achieve 25% composite action (or the code minimum), go to Criteria - Stud Criteria and for the last option, select to "Use Composite section properties".

Note: the program will never optimize a member with less than 25% composite action (US codes), but you can reduce the number of studs and evaluate this way.

Can I lock or freeze all the beam designs?

Yes, once the designs are correct, use the Process - Freeze Design command to freeze the designs for some or all of the beams. This is often a good idea once construction documents for the project have been released.

The same command can be found in other modules, too.

Why are my composite beams being designed as non-composite members?

Beams that have been defined as composite, may be designed as non-composite for the following reasons:

• Non-composite deck
• Opening or exposed beam 
• Cantilever 
• No load

Non-composite deck: Composite beams will be designed as non-composite if the deck on both sides of the beam is non-composite for any portion of the beam span.

Opening or exposed beam: A beam that spans through an opening or penetration or for which there is a portion supporting no deck, such as an inset beam, will be designed as non-composite. Some times it is desired to design inset beams as composite. In order to do this, you can add a short beam from the column to the perimeter beams at an angle (say 45 degrees). Then define the slab edge so that it follows along these short beams, going out and around the perimeter column. That way, the entire beam is covered by the deck and it can be designed as composite (see below).

Cantilever: If the negative bending moment at the support of a cantilever beam is greater than twice the positive moment of the back span, the beam will be designed as non-composite. When a cantilever beam is designed compositely, the program determined number of studs should all be placed in the back-span. Note, for some codes no negative moment is allowed for composite beam design and in those cases a cantilever will always result in non-composite design.

No Load: If there is no load on the beam it will be designed as non-composite. This is sometimes a result of accidentally orienting the deck in the wrong direction such that the infill beams are not loaded.

Note: once a beam has been designed as a non-composite member, the composite flag for the beam will be set to non-composite. You have to go back to the Modeler and use the layout - beams - change properties command to turn it back into a composite member.

Why is the unbraced length reported less than the maximum unbraced length?

The program evaluates bending for each of the various unbraced segments of a beam along with the maximum moments in that segment. The design might be controlled by a shorter unbraced segment with larger moments, or it might be controlled by a longer unbraced segment with smaller moments.

The design report shows the critical condition and indicates where from the left end the critical case occurs.

Can I turn off the pattern loading on beam cantilevers?

Regretfully, not at this time. Live loads are always consider to act on the cantilever, on the back-span or on the entire beam, whichever condition provides the most conservative design for shear, bending and deflection. This is true even for snow loads which can be overly conservative. Only dead loads are not subject to patterning.

Can I customize the load combinations used in RAM Steel Beam?

Regretfully, not at this time. The load combinations used in RAM Steel are internal to the program and cannot be modified.

See Section 10.3.11 in the RAM Steel Beam Manual for a list of combinations used for each design code.

Note that floor live load and snow or roof live loads are combined and applied as a single live load. Some building codes, such as IBC, permit a reduction (0.75 factor) for combinations including two or more transient loads. RAM Steel uses the combination 1.0 DL + 1.0 LL (effectively, 1.0 DL + 1.0 LL + 1.0 SL). Using the reduction noted above, a load combination of 1.0 DL + 0.75 LL + 0.75 SL is permitted. If the IBC is selected for the code for load combination generation in RAM Frame, 1.0 DL + 0.75 LL + 0.75 SL and not 1.0 DL + 1.0 LL + 1.0 SL. This can cause some design differences for beams designed in RAM Steel Beam versus RAM Frame. 

Can I override the unbraced length of a steel gravity beam?

In cases where you want the unbraced length to be reduced you can add brace points in the Modeler using Layout - Beams - Brace points. Alternatively adding additional short beams framing into the beam in question will brace the top and bottom flange at those locations. Use joists where you want only the top flange braced.

In cases where you want the program to use a longer unbraced length, for example where a beam is set higher than the deck in reality, set the Criteria - Design Criteria - Unbraced length so that neither deck perpendicular nor parallel to the beam braces the top flange. Since it's a global criteria it will affect all beams, however, so you might have to set the criteria this way and check the one beam, freeze the design, and then check the rest using the preferred criteria.

Alternatively, you could add a long penetration (Modeler - Layout - Slab - Slab Penetrations) along the beam covering most of the span.

See Also

[[RAM SS - Steel Beam Deflection and Camber]]

[[structural_analysis_and_design__wiki:RAMSS Design Fy or Py|RAMSS Design Fy or Py]]

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

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Why are the yellow lines for members shortened at the nodes? 

The lines are drawn slightly short of the nodes so that the nodes are clearly visible in line mode.

In the fully rendered view you can see the members full length (or shrunken)

I have a small model and the support icons appear very large, how can I make them smaller?

The size of the nodal support, member hinge and other icons is typically adjusted based on the overall size of the model, but the user can force the icons to appear larger or smaller. 

To control the size of the icons go to the e menu (file menu) and pick General Configuration. On the Display tab, uncheck the box for  Data and Results - Automatic Scale and then enter a number >1 to make the icons larger, <1 to make them smaller.

How can I rotate the view?

In order to rotate the view, click and hold the right mouse button, then drag the mouse to dynamically rotate the view. Note, in RAM Elements, the Y axis typically points upward and this axis is always plumb on the screen.

If you find the rotation is too fast or too slow for your liking, go to the e menu - General Configuration and on the General tab, adjust the Mouse rotation sensitivity slider.

How can I Save a View?

In Ram Elements you can save a particular type of view including the angle of the view, the zoom, perspective settings and display options. To do so, first adjust the graphic as desired, then right click on the view and choose Customized Views - General - Create. Provide a name for the view, check the desired attributes to save and click Create.

These general views work across all files.

The program also allows you to save model-specific views. To do so, again adjust the view the way you like it. Then right click on the view and pick Customized Views - Current Model.

In addition to the attributes mentioned above, Current Model views also store the active selection set and any hidden members for instant recall.

To recall a saved view, simply right click on the graphic and pick the saved view by name from the Customized Views.

How can I make the on screen text easier to read?

At the bottom right corner of the Ram Elements window are the controls for increasing or reducing the text size on screen. Just to the left of that is the control for units.

By not Showing the units more significant digits are shown, filling roughly the same screen area.

Using Larger or Smaller units under Units Configuration can affect the displayed number of digits. For example. if the axial force in a column is -2471.45 pounds, switching to kips changes the display to -2.47 kips which is shorter.

Regretfully, there is no other user control over significant digits displayed.

How can I view the design properties, things like unbraced length?

From the View Ribbon menu, in the Design Toolbar, select Design Properties and one or more of the options:

• Effective length factors (i.e. K22 and K33)
• Axial and torsional unbraced lengths (i.e. L22 and L33)
• Flexural unbraced lengths (i.e. Lbpos and Lbneg)

Note, for unassigned default values (0) nothing will be shown on screen. Only user specified values are plotted.

How do I change the scale of the deflection multiplier?

Click on RAM Element button in the top left corner and click on the button 'General configuration'. Then select tab Display and change the deflection multiplier as shown in the screenshot:

See Also

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

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Steel Unbraced Lengths in RAM Elements

General

The format for steel unbraced lengths (Lb pos, Lb neg, L33, L22, and LTorsion) changed in V11. The help context in the member design parameters worksheet discusses the format. This can be accessed by clicking on a cell in the Members – Steel Design Parameters worksheet and hitting F1 on your keyboard.

Old Implementation

Prior to V11, unbraced lengths were entered as a single value in the steel design parameters. If no value was entered, the unbraced length was assumed to be equal to the physical length of the member (j node to k node). If a non-zero value was entered, that value was used as the unbraced length for every station considered during the design of the beam. However, parameters such as Cb were always calculated using the physical length of the member. This limitation could be unconservative.

V11 Implementation

In V11, unbraced lengths need to be entered such that the sum of the unbraced lengths is equal the physical length of the member. For example, if a beam is 20’ long and the unbraced length is 5’, the unbraced length should be entered as 5;5;5;5. This allows the program to calculate parameters such as Cb for the actual unbraced segment rather than the physical length of the member. A tool button was introduced to rapidly generate the unbraced lengths.

However, this new method introduced some limitations into the program. For example, it is not possible to enter an unbraced length that is longer than the physical length of the member. This might be a necessity if you are modeling a bent or simulating a curved member. In addition, it is not possible to assign multiple Cb values to correspond to the unbraced lengths that were assigned. In other words, only a single Cb value can be entered and it will be used for all segments. If Cb is left blank, it will be calculated for all segments.

V12 Implementation

The V12 implementation functions as described below.

i. The engineer doesn’t type anything in the spreadsheet cell (either directly or with the tool) and thus the value remains the default “0”:  RE uses the physical length of the member as Lb and Cb will be automatically calculated based on the physical length of the member.

ii. Just one value is entered in the cell

     a. If the value is less than the member’s physical length, RE uses that value for all pertinent code checks (just like before v11.0) and Cb = 1. Besides printing Cb (as 1) in the design report, RE adds a note at the bottom of the report saying “Cb not calculated for the Lb specified. It is conservatively prescribed as 1”. However if there’s a value in the Cb cell other than zero “0”, then that value is used in all segments and the note is not printed.

     b. If the value is equal to the physical length of the member, then it would be exactly the same as i.a above.

     c. If the value is larger than the member’s physical length, RE uses that value for all pertinent code checks and Cb = 1. Besides printing Cb (as 1) in the design report, RE adds a note at the bottom of the report saying “Cb not calculated for the Lb specified. It is conservatively prescribed as 1”. However if there’s a value in the Cb cell other than zero “0”, then that value is used in all segments and the note is not printed.

iii. Multiple values are entered in the cell (either directly and separated with semicolon or using the tool):

     a. If the sum of the values is less or equal to the physical length of the member, RE calculates the difference for the last segment and Cb is automatically calculated for each segment. The sum is validated for unintended, non-summing entries.
 
     b. If the sum of the values is larger than the physical length of the member, RE does NOT allow it. In other words, one single unbraced length for the member, could be larger or smaller than the distance from node to node, but multiple unbraced lengths, must match the member’s physical length.

Note: Old models (prior to v11.0) opened in v12.0 will retain the original unbraced length assignments. These will fall under option ii above. The engineer must keep in mind that the final results may still vary because before, Cb was calculated with the physical length (which now only applies to option i above) and now with Cb = 1.

Similar behavior is applicable to L33, L22 and Ltorsion.

Adjusting the unbraced length of Built-Up members (double angles) to accommodate Intermediate Connectors locations.

In the Steel design criteria for AISC 360 there are two user variables that control this:

1. Intermediate Connectors - This option is used to define the use of two equations in the design of built-up members subjected to compression. The available options are:
   1. Intermediate connectors that are snug-tight bolted, to use the equation E6-1.
   2. Intermediate connectors that are welded or pretensioned bolted, to use the equation E6-2.
   3. Intermediate connectors in shear and bolt values based on bearing values (but pretensioned), to use the equation E6-2..
2. a (Connectors) - The distance between connectors in built-up members. It is used to calculate the modified slenderness of the built-up member following Section E6 specially 2L sections.

See AISC 360 Section E6 for further details.

Does the steel design impose a limit on the slenderness ratio, KL/r?

No, but if the KL/r ratio of a compression member exceeds 200, or if the L/r ratio of a tension member exceeds 300, you will get a warning in the steel design report (and a yellow status color on screen using View - Status). Here's an example from the concise steel report:

Design code: AISC 360-2005 ASD

Member : 3 (BC)
Design status : With warnings

DESIGN WARNINGS

- The slenderness ratio KL/r about major axis of the member in compression should not exceed 200
- The slenderness ratio KL/r about minor axis of the member in compression should not exceed 200
- The slenderness ratio L/r of the member in tension should not exceed 300

See Also

Product TechNotes and FAQs

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!

Effective Length Factors in RAM Elements

General

AISC effective length factors (K33 and K22 factors) can be automatically calculated in V12.  This document discusses the implementation prior to V12 and the changes made in V12.  The value of K Torsion did not change.  It defaults to K=1.0 unless another value is entered in the AISC steel design parameters.

Old Implementation

If the K22 or K33 field was left blank or set to zero in the AISC Steel Design Parameters, the program automatically assumed K = 1.0.  There was tool buttons to calculate K33 and K22. If this tool was selected, the program used the following equations to calculate K.

Members Assigned as Sway
K = SQRT((1.6*GB*GA+4*(GB+GA)+7.5)/(GB+GA+7.5))

Members Assigned as Non-Sway
K = min(min(0.7+0.05*(GB+GA),0.85+0.05*min(GB,GA)),1.0)

GA and GB values depend on member stiffness as described by specification commentary.  Values that were theoretically infinity (pinned) were assumed to be 10.  Values that were theoretically fixed were assumed to be 1.

V12 Implementation

V12 added new Value Type K33 and Value Type K22 parameters.  When the Value Type is set to ‘None’, the program functions as it did in previous versions and K will be assumed to equal 1.0 unless a value is entered for K.  If the Value Type is set to ‘Recommended’, the program will use the recommended approximate values in Table C-C2.2 in the 13th Ed AISC Manual.  If the Value Type is set to ‘Theoretical’, the program will use the theoretical approximate values in Table C-C2.2 in the 13th Ed AISC Manual.

When the tool button in the steel design parameters is used to calculate K, the alignment charts in Chapter C of the commentary in the 13th Ed AISC Manual are used.  This method considers the stiffness of rigidly connected members and uses the equations below.  The tool button cannot be used when the multiple unbraced lengths (L33 and L22) are entered for the member.

Members Assigned as Sway
(GA*GB*(Pi/K)^2-36)/(6*(GA+GB))-(Pi/K)/(tan(Pi/K)))=0

Members Assigned as Non-Sway
(GA*GB/4)*(Pi/K)^2+((GA+GB)/2)*(1-(Pi/K)/(tan(Pi/K)))+(2*tan(Pi/(2*K)))/(PI/K))=0

GA and GB values depend on member stiffness as described by specification commentary.  Values that were theoretically infinity (pinned) were assumed to be 10.  Values that were theoretically fixed were assumed to be 1.

Special Considerations

The automatic calculation of K is based on the physical length of the member.  Therefore, members framing into intermediate nodes along the member have no impact on the calculated effective length.  For this reason, it is best to segment the member so the physical length matches the unbraced length.

When 2D frames are designed, the out-of-plane effective length factor will be calculated for the columns unless a value is entered in the steel design parameters or the out-of-plane value type is set to ‘None’.  Typically, the calculated value would be incorrect and the effective length should be assumed to be 1 for the out-of-plane direction.

There are many instances where the effective length method should not be used and K should equal 1.0.  The program does not attempt to determine these conditions and will always calculate a value based on the parameters and the analytical model.  For example, members with theoretical pinned ends (GA = GB = 10) will always have a calculated effective length of 3.01 for sway frames and 0.96 for non-sway frames.


Practical Example

Consider a simple portal frame with 15’ long W12X96 columns and a 20’ long W21X83 beam.  Assume the bases of the columns are pinned and there are no releases at the top of the column or ends of the beam.  The column is oriented such that the beam frames into the column flange (strong axis bending).

The frame would be classified as sway in the plane of the frame (frame type 2).  In the out-of-plane direction, the K22 value should be assumed to be 1.0 since the frame will lean against the diaphragm or some other support for stability.  Do not simply set frame type 3 to non-sway.  The Value Type K22 should be set to ‘None’.  It is also appropriate to set K33 for the beam to 1.0 or assign Value Type K33 as ‘None’.

If the tool button is used to compute K33 for the columns, the equations below are used.  Looking at the figure C-C2.4 in the 13th Ed AISC manual, K should be around 1.8.  The equation below is nearly zero when K = 1.81.  That matches the value calculated by the program when the tool button is used in the steel design parameters worksheet.

GA = (EI/L column) / (EI/L beam)
GA =( 29000*833/15) / (29000*1830/20) = 0.607

GB = 10 Assumed at pinned end

(0.607*10*(Pi/1.81)^2-36)/(6*(0.607+10))-(Pi/1.81)/(tan(Pi/1.81)))=0.01

When Value Type K33 is set to ‘Recommended’ for the columns, K33 will be assumed to be 2.1 is indicated in Table C2-2.2(e).

When Value Type K33 is set to ‘Theoretical’ for the columns, K33 will be assumed to be 2.0 is indicated in Table C2-2.2(e).

See Also

Steel Unbraced Lengths in RAM Elements [TN]

Product TechNotes and FAQs

Structural Product TechNotes And FAQs  

External Links

Bentley Technical Support KnowledgeBase

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Use of Two way decks in RAM Structural System

The table below clarifies how One way and Two way decks can be used in RAM SS v14.00 or later:

1. One way deck always requires a complete nodal network, a network of supported beams or walls such that a tributary for every member is defined and encompasses the entire one way deck area.
2. If you have a semi-rigid diaphragm with a one way deck that is not properly supported by a network of beams, RAM Frame or RAM Concrete may run without warning, but loads will be zero.
3. When Two way deck is used, only two modules can give results. RAM Frame with a semi rigid diaphragm option (2-way rigid diaphragms are also allowed starting in v14.03), or RAM Concrete. Furthermore, the user must specify the deck effective E value, thickness and Poisson's ratio for those modules to work. The diaphragm will always be meshed, and out-of-plane stiffness will always be assumed. Hence the beams (if there are any) will resist less force compared to a one way system. Any such beams have a centroid alignment to the center of the slab.
4. No automatic Live Load reduction calculation is performed for members carrying loads from two-way slabs. The reduction to be applied to the Live Load on such members must be assigned to the member in the Modeler (e.g. Layout - Columns - LL Reduction). 
5. RAM Concrete typically considers skip loading for live loads on the beam lines lying under one way decking, if desired. A beam line lying under a two way deck can have skip loading cases only if line and point live loads are applied directly on it. Currently, the surface loading applied to two way decks does not generate any skip loading cases.

Other notable warnings:
RAM Frame, using a Two way deck without using a semi-rigid diaphragm:

RAM Frame: Two-way Deck Found Inside Diaphragm 1 of Story 2.  The Diaphragm Type is not Semirigid.  Gravity Loads on the Diaphragm Disregarded for the Analysis.  Do you want to continue?

RAM Steel - using Two way decks always gives an error of some sort, example:

Warning: Failed to Create Slab Edge Load Polygons for diaphragm 1 on Layout Type Roof. Slab edge loads will not be applied to any beams around the perimeter of that diaphragm. Disregard this warning if the slab edge is Two-way deck.

Hybrid Decks

For Hybrid Deck levels, those that include areas of both one way deck and two way deck, the rules for nodal networks still apply to the one-way decked area. If the network is not complete various framing tables errors can occur.

Furthermore, when the level is meshed in Ram Frame or Ram Concrete you will see that the mesh covers the entire floor so that the diaphragm is continuous. This can cause some unexpected behavior in the one-way regions. Specifically the meshed slab can help in resisting some of the applied loads, effectively holding up the beams.

There is an option in the Concrete Analysis mode, under Criteria - Analysis to alleviate this effect. 

By not checking the option to "Include Out-of-Plane Stiffness for One-Way Decks in Hybrid Slabs" you are telling the program to use a near zero stiffness element in the one-way deck areas so that the beams have to do the work.

For these reasons, mixing one and two way decks in the same diaphragm is not generally recommended.

Concrete Column design with Two-Way Slabs

In Ram Concrete, the column K factor is determined based on the relative stiffness of the beams to the columns. The stiffness of 2-way slabs is not considered in this calculation, so the user should manually assign the proper K factor for columns supporting 2-way slabs.

As noted above, Live Load reduction percentages also need to be manually assigned.

Semi-rigid Diaphragms for Two Way Slabs

Out-of-plane stiffness is assumed when the deck is two way. There are some general concerns in RAM Frame for these diaphragms. The distribution of gravity loads is determined by meshing the diaphragm and then the program calculates the gravity load that is tributary to each node.  Gravity columns/walls are ignored in the Frame finite element analysis. If you have gravity columns and/or walls, the gravity forces on the lateral members will be inaccurate unless you utilize the consider gravity columns/walls as springs options. However, utilizing this option will have an impact on the lateral analysis as well. The following concepts apply to one way decks with out-of-plane stiffness considered, too.

Consider a five story shear wall building with two way 8 inch concrete slabs. Here is the typical plan.

The moments at the base of the walls for a lateral load case in the X direction are 13555 k-ft and the shears are 242 kips.

If you run the same load case and include the gravity columns as springs the moments drop to 11163 k-ft as the gravity column spring form couples that resist much of the overturning moment. The wall major axis shear forces stay the same. You would get similar results if you modeled all of the columns as pinned lateral columns.

As the out-of-plane stiffness of the diaphragm and axial stiffness of the columns increase the moments in the walls decrease. Conversely, when there is negligible out of plane stiffness to the diaphragm, the moments in the walls would not be affected.

In the RAM Concrete Shear Wall Module all of the design forces, including gravity load results, come from the RAM Frame analysis. For the design of shear walls it is important to understand the impact gravity columns have on the forces in the walls.

Transfer Forces

A column or wall may set directly upon a 2-way deck without the need for a beam on the story below (using version 14 or later). The force from the vertical member will transfer through the meshed slab to the supports below. Since this requires a finite element analysis of a meshed two way slab, it has the same limitations in the table above, i.e. it only works using Ram Frame or Ram Concrete analysis.

Generally we recommend that the columns or walls that offset should be modeled as lateral members so that the analysis in RAM Frame will consider those members in the analysis.  That way the program can display or report important information like axial member forces and nodal displacements.

We also recommend modeling a transfer beam in addition to the slab when reasonable to do so.

There are some special considerations when using RAM Structural System in conjunction with Ram Concept for transfer slabs. See these topics for further details:

• RAM Concept-RAM Structural System Integration TN
• Modeling Podium Slabs TN

See Also

RAM SS Analysis Types

RAMSS Common Framing Table Errors

RAM SS Semirigid Diaphragms

Transfer Slabs

Product TechNotes and FAQs

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!

Problem Description

Ram Connection Stand-alone crashes when opening existing files from the file browser or from the Welcome Screen, recent file thumbnails. It may crash right away or only when designing a connection within that file.

Solution

We have not yet identified the root cause of this problem, but a work-around it to turn off the option to "Show the Welcome Screen on Startup". Then close and restart the program and open the file using the upper left file open button instead.

The Welcome Screen can be reactivated using the link under the Help ?.

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server