RAM Frame - Analysis Tutorial

This section illustrates the analysis and design of the lateral frame elements in an integrated model. This section can only be completed if you have licensed and installed the RAM Frame module. You may begin with the model that you generated in the previous portions of this tutorial, or you may open the model called Tutorial_v14_US_Complete.RSS from the RAM Manager.

RAM Frame Basics

A little background information is needed before beginning work with the RAM Frame program. RAM Frame has three modes of operation, Analysis mode, Steel Post Processing Mode and Drift Control Mode.

In Analysis Mode, the structure is analyzed for individual load cases. Results for the member forces, reactions, drift etc can be obtained for the individual load cases in the Load Cases sub-mode, or the results can be combined in the Load Combinations sub-mode.

In Steel Mode, the previously analyzed load cases are combined and used to determine their design status of steel members. Various design codes can be selected to perform code checks. The steel Mode is sub-divided in to Standard Steel Provisions (e.g. LRFD 3rd edition) and a Special Seismic Provisions (e.g. AISC Seismic Provisions for Structural Buildings).

The third mode, Drift Control allows you to investigate the relative participation of the various members with the structure related to the control of drift. The Steel mode and Drift Control modes are discussed in the following sections of this tutorial.

Concrete members that are designated as Frame Members are analyzed in RAM Frame, but their design is performed in RAM Concrete.

To invoke RAM Frame from the RAM Manager:

• Select Design – RAM Frame or click the 4th square button that depicts part of a braced frame.

When the framing process is complete, a three dimensional wire-frame view of your model will appear on the screen.

The RAM Frame program has a toolbar from which many commands can be issued with just a click of the mouse button. As with the other modules, this tutorial will present the commands as selected through the menus. There are two pull-down lists in the second row of buttons than can be used to switch the program mode and sub-mode. They are also useful for checking the mode you are currently in. The Status Bar at the bottom of the screen also tells you which RAM Frame mode you are currently working in. It also has a light to indicate the status of the current model. If the status indicator light is red, the model has not yet been analyzed. A yellow light is used when the results are available, but may not be absolutely current due to a change in member size for example.

Note: Upon entry into the RAM Frame program, you are always placed in Analysis Mode – Load Cases Sub-Mode. An analysis of the load cases is required before the other modes can be entered.

The View menu has controls for displaying general model information such as finite element node numbers or to modify the rotation of the 3d view. To view the Wall Mesh for example:

• Select View - Meshed Walls.

Notice how the mesh works around the opening in the West wall.

Help is available in any of the following ways:

• Allowing the cursor to rest on top of a toolbar button causes a Tool Tip to appear, as well as a brief explanation of the command in the status bar
• Each dialog box has direct access to its related help topic via a help button.
• The Help index is also accessible from the main menu.

General Analysis Criteria

Before performing the analysis you should always establish your criteria using the Criteria menu. To set the general analysis criteria:

• Select Criteria - General.
  
• Set Rigid End Zones to Include Effects and Type 50 for Reduction %. This means that the beams in the rigid frames will be shorted in the analysis to the face of the column.
• Set Member Force Output to At Face of Joint (when using rigid end zones you have no choice).
• Set P-Delta to Yes and Type 1 for Scale Factor. This means that second-order, P-Delta effects will be calculated for all load cases utilizing the building mass Dead Load as the P in the P-delta calculations. If you wanted to also consider part of the Live Loads in the P-Delta calculations, then you can increase the value somewhat.
• Check the Use Reduced Stiffness for Steel Members checkbox, and click on the τb = 1 radio button.
• For the Wall Mesh set the Max. Distance Allowed between Nodes to 8 (2.5). This means that the program will mesh the walls in such a way that no single element is more than 8' on a side (though they may be smaller due to geometric constraints). More Mesh options are available by clicking the [Advanced] button.
• Check the Store Wall Stresses checkbox for use in the Concrete Shear wall module.
• Click [OK].

Diaphragm Criteria

• Select Criteria - Diaphragm.
  

By default, all floor levels are assumed to be Rigid diaphragms. A rigid diaphragm creates a horizontal constraint for all of the nodes connected to it. For sloped levels, the diaphragm constraint is still horizontal. The size of the diaphragm is dictated by the extent of the slab edge. Since we entered the information for our Semirigid diaphragm in modeler, we will demonstrate now how that information is used.

• Click in the cells for the Roof and both diaphragms on the 2nd floors.
• Select Semirigid from the drop down combo box.
• Enter 1 for the "Hard Node Density Factor"
• Leave the other floors as Rigid.
• Click [Disconnect].
  
• Make sure the option is checked. This means that any lateral elements that fall outside of the slab edge will automatically be disconnected from that diaphragm. Internal nodes on beams occur in places like our chevron braces where the beam is intersected by another lateral member.
• Set the Semirigid Diaphragm Controls at the bottom of the dialog as shown below.
  
• Click [OK]
  

  Note: For more information on diaphragm types click Help - Manual.

• The Semirigid diaphragm uses a Finite Element Mesh similar to the wall mesh for shear walls. To see the floor mesh, click on View-Meshed Floors or use the menu button on the toolbar as seen here:
  

Ground Level

The Criteria - Ground Level command is used to specify the level at which the ground intersects the structure.

• Select Criteria - Ground Level.
  

The default is for the ground level to be at the base of the model. In this tutorial the default will be accepted and no changes need be made. When a level other than the base is selected as the ground level two things will happen. First, the program generated loads will be adjusted for the new building height and the forces will be applied to the above ground levels only. Second, the ground level and any level below grade will be laterally restrained as if by a vertical roller.

• Click [OK].

Redundancy Factors

Redundancy factors are determined by the program and then used to modify the load factors applied to the seismic load cases in the generated load combinations. It's important to note that the redundancy factors always calculated for every seismic load case, even if your model is in an area of low seismic activity. They only apply to US codes.

• Select Criteria - Redundancy Factors.
  
• For the Code choose IBC 2000/2003 (when code references are separated with a slash, it indicates that the two codes are identical).
• Set the other variable as indicated above and click [OK]. 

Assign Menu Options

In order for the program to perform a Finite Element Analysis, every lateral member must have an assigned size. For our model, that was initially done in the Modeler, but the assign menu in RAM Frame can also be used to assign sizes to lateral members as we will illustrate below for braces we want to make Buckling Restrained Braces.

Buckling Restrained Braces require you to designate a section that is appropriate for the core (yielding section) of the Buckling Restrained Brace. In this model we will assign a solid rod to the bottom braces of the Frame along Grid F and a flat bar to the braces of the level above. This frame will become our Buckling Restrained Brace Frame.

To Assign a Round Bar to the bottom braces:

• Select View-Elevation and click on any beam in the frame along Grid F (the chevron braced frame).
• Select Assign - Braces - Size.
  
• Select the Material, Shape and Size as illustrated.
• Assign [Fence]

The Fence cursor will appear, fence the braces of the lower chevron braces.

Repeat this exercise to assign a flat plate (1/2x6) to the next level of chevron braces to end up with a frame sizes as shown below.

Obviously these braces are small and slender so to appropriately design we designate these as Buckling Restrained Braces.

• If you are not still in elevation mode select View-Elevation and click on any beam in the frame along Grid F (the chevron braced frame).
• Select Assign - Braces - Buckling Restrained.
  
• Select Assign Brace as Buckling Restrained 
• Enter 1.4 for Axial Stiffness Multiplier.
• Click Assign [Fence].
  
  Buckling Restrained Frame
• In the graphics mode, Fence all of the lower two chevron braced frame stories.
  As the assignments are made, a symbol illustrated above will appear in the middle of the Buckling Restrained Brace with the assigned multiplier value shown.

When complete if you want to turn off the labels:

• Select View - Reset Model.

To learn more about buckling restrained braces and their impact on analysis and design refer to the RAM Frame Steel Design Manual.

A variety of information, including the tension-only symbols, the member sizes, end fixity, etc. can all be displayed on screen using the command View - Members similar to the Steel Column module command of the same name.

The assign menu commands can also use used to assign diaphragm connections, frame numbers, wall group numbers and foundations springs.

Mass and Exposure

The load cases for which the structure is to be analyzed and designed must be defined. User defined and program generated load cases can be created. If the program is to automatically generate seismic load cases it requires information on the structure's mass properties, and for the program to generate wind loads, the building's dimensional properties are required. (Mass information is also used any time that second order analysis is performed).

In this model all of the information required by the program to generate seismic and wind forces is already provided. If desired, this data can be overridden. Only the building extents affecting wind generated forces will be modified in this example

• Select Loads - Exposure.
  

The extents that were determined by the program using the slab edges of the model are listed in the Building Extents portion of the window. To change those values:

• Select Use Calculated Values.

The Parapet field is used to indicate the height of the parapet. If a parapet height is specified, additional wind loads will be attributed to that level. If there is another level above the level with a parapet, then the additional wind loads will only get applied to the portion of the lower level that is wider than the level above.

The Exposure column is used to indicate if a particular level does not resist wind loads at all. This might be the case if there is only a partial slab at that level (such as in a mezzanine or stair landing between floors). By changing the exposure flag from Full to None a level is designated as having no exposure, and the wind force is distributed to the adjacent levels instead.

• Click [OK].

It's important to note that the program does not currently calculate wind uplift pressures. The program only calculates horizontal wind forces and applies them to the meshed nodes if the deck is meshed, and the magnitude of the force at the roof level is based on the height of the meshed surface.

NOTE: For Rigid diaphragms the horizontal wind forces are applied at the story height. Modifying the elevations of the columns has no direct impact on the horizontal wind force.

For structures that are partially shielded or structures that have more than one windward and leeward face, the wind loads will have to be entered as User Defined Story Forces (or Nodal Loads), rather than using the code generated lateral loads as done in the next section

Wind Load

This model already includes the gravity load cases created in the Modeler. These loads cannot be modified or deleted within the RAM Frame program. If other load cases are to be considered, such as Wind Loads, Seismic Loads or Dynamic Loads, they must be created in RAM Frame. To define a Wind Load case:

• Select Loads – Load Cases .

• Type Wind in the Label edit box.
• Click the Wind option button under Type.
• Click the down arrow to access the wind load building code selection list and select ASCE 7-05 / IBC 2006 (BS6399: Part 2: 1997)
• Click [Add] .

The Wind dialog box should appear allowing you to define specific characteristics of the wind load:

• Fill out all the fields as indicated in the figure above for US models.

NOTE: In the section marked Natural Frequency, the load is set to use the calculated n. In order to calculate the building frequency for Wind Load (or period for seismic load) the model must have rigid diaphragm levels with masses defined. If diaphragm masses are zero the load case will not run.

• For SI models, select the BS6399: Part 2: 1997 as the building code rather than ASCE 7-05 and set up the load as indicated below.

• Click [OK] .

New load cases are now added to the Load Cases list box, one for each direction selected in the direction box. Some building codes require consideration of winds eccentric to the building. This results in additional wind load cases. Since the wind load here was created with additional tension-only load cases, both the positive and negative direction load cases appear in the list.

Seismic Load

Seismic loads are input similar to wind loads.

• In the Load Cases dialog, type Seismic in the Label edit box.
• Select the Seismic option under Type.
• Click the down arrow to access various building codes and select ASCE 7-05/IBC06 Equivalent Lateral Force option.
• Click [Add] .

• In the dialog that opens, fill in the fields as indicated in the previous figure.

NOTE: Ss and S1 are percentage of gravity values. Also note that the program is set to use the calculated period, but if the calculated period should exceed the upper bound limitation of the code, that maximum period will be used.

• Click [OK] .

8 new load cases are added to the Load Cases list box, this covers the different directions and horizontal eccentricities.

• Without closing the Load Cases dialog, type Modes in the Label edit box.
• Select the Dynamic option under Type.
• Leave the drop down list set to Eigen Solution .
• [Add] .

The Eigen Solution dialog box should appear allowing you to define the number of periods you wish to generate.

NOTE: When Semirigid diaphragms are generated the program has to calculate how many degrees of freedom the structure contains, then determine how many modes are associated with those degrees of freedom. For demonstration purposes use the number of floors times 6 here. A higher number may be needed for the code required participation, but this should be sufficient for this tutorial.

• Click [OK] to select the default number of periods.
• Without closing the Load Cases dialog, type Center in the Label edit box.
• Select the Center of Rigidity option under Type.
• Click [Add] .

NOTE: The center of rigidity load case has no options and does not affect the analysis at all, it simply allows you to review the center of stiffness graphically in the model.

• Without closing the Load Cases dialog, type Notional in the Label box
• Select the AISC 360-05 (BS 8110) Load case in the Notional drop down menu.
• Click [Add] .

• Click [OK] to create Notional Loads with the above defaults.
• Click [OK] to exit the Load Cases Dialog box.

If you need to edit any of the load cases you can select the load case in the Load List at the bottom of the Load cases window and click Change. When a load with multiple cases is selected, like wind load, the full set of loads will be edited together.

Analysis

You have now defined all the load cases for which the frames will be analyzed. To start the analysis and display the Analyze dialog box:

• Select Process – Analyze .

The Analyze dialog box displays all the load cases available for analysis. Those load cases which are preceded by a green dot are available to be analyzed. A red light means that something is preventing that load case from being analyzed (e.g. no diaphragm or diaphragm masses are defined). In this example all load cases should be available.

• Click [Select All] .
• Click [OK] .

The analysis will commence and a status message box will keep you informed of the progress. Upon completion of the analysis, click [OK] and notice that the status indicator light on the status bar turns green (if the self weight reactions of beams and columns are not current then he light will be yellow – see the RAM Manager documentation for a complete explanation on status lights). This indicates that the structure has now been analyzed for each of the load cases selected, and analysis results can be viewed for each load case separately.

If there is a stability problem with your model it will result in a warning during the analysis. Adjusting the member fixity can usually correct a stability problem. If there is too little stiffness in your structure, and the analysis is being performed with the P-Delta consideration, that might result in an excess P-Delta warning. You will see a message about the springs taking some of the lateral load. To see the report select Reports-Spring Forces .

The results of the analysis of each load case can now be viewed either on-screen or in printed reports. In either case you can select the load case(s) for which you want results displayed. If you have analyzed many load cases you may find your reports to be quite lengthy. The Reports – Select Cases command acts as an "Output Filter", allowing you to select which load cases will appear in the output.

View/Update

The Process – View/Update command provides information about an individual selected member. While in the Analysis mode for Load Cases, it provides access to the individual member results for each load case analyzed. The View/Update command also allows you to change the member size if desired. To review the results for an individual member:

• Select Process – View/Update .
• Click the cursor on one of the Roof beams in a moment frame.

• Click [View Results] .
• Scroll through the report and get familiar with format of the output.
• Click (X)  to exit the report. Selecting another member size does not immediately affect the member forces, but if the member size is updated, the status light will change to yellow until the analysis is performed again.

It is not necessary to close the dialog box before selecting another member to View. Just click the target cursor on any other lateral member and the dialog box will be updated.

• Click [Close] to close the View/Update dialog box.

Member Forces

The analysis results may also be displayed on-screen. While in Load Cases mode all results, whether on-screen or in reports, are for the individual, unfactored load cases. By switching to the Load Combinations mode and generating load combinations, you can also review the combined values for reactions, member forces and deflections.

• Select Process – Results – Member Forces .

• In the Load Case Member Forces dialog box that opens, select the first Wind Load case.
• Click [OK] .
• In the Load Case Member Forces dialog that opens, select Shear – Major as the Force type.
• Check the box labeled Show Diagrams with a Scale Factor of 1.
• Click [Apply] .
• The 3D graphic will now indicate the member strong axis (Major) shear values diagrammatically.

NOTE: The commands in the View menu, such as Zoom, View – Extents, View – Options – Scale Text and View – Members, can be used to make the output on the screen more readable (see the on-line Help for instructions)

To review forces in Elevation view

• Select View – Elevation and select one of the Moment Frame beams.
• To view the member forces that resulted from a different load case click the [Change Case] button in the Load Case Member Forces dialog box.
• Highlight the Dead Load .
• Click [OK] .
• Set Force Type to Axial .
• Click [Apply] .
• Click [Close] to close the Load Case Member Forces dialog box.

Your last force display remains on the screen. Use the View – Reset Model command to clear the display.

Deflected Shape

The deflected shape which results from applying any of the load cases can be viewed on screen. This is a great way to identify any unusual model behavior.

• Select Process – Results – Deflected Shape .
• In the Load Case Deflected Shape dialog box that opens highlight the first Wind load case, Wind_IBC06_1_X .
• Click [OK] .

• In the Load Case Deflected Shape dialog type 100 for Scale Factor.
• Click [Apply] .

NOTE: If the Include Undeflected Shape box is checked, then both the deflected and undeflected shapes will be displayed.

• Click [Start] .

NOTE: The scale factor and speed can be altered and the animation can be restarted if necessary.

• Click [Stop] .

The deflected shape for other load cases can be displayed by clicking the [Change Case] button and making a new selection from the list box.

• Click [Close] .
• Click View – Reset Model .

Mode Shape

If an Eigen Solution load case has been analyzed, then the Modal Shapes menu choice can be selected:

• Select Process – Results – Mode Shapes .

• In the Mode Shapes dialog box that opens click [Start] .

The on-screen graphic will be animated to show the first principal mode of the structure. In this tutorial, that’s the principal X mode, the period of which will is used in the seismic load calculations.

• When finished, click [Stop] .
• Change the Mode number to 2 and click [Apply] or [Start] .
• When finished, click [Close] .

As with the Member Forces and Deflected Shapes, [Close] removes the dialog box from the screen and the View – Reset Model returns you to the screen display you had prior to issuing this command.

Drift

A drift report for all the load cases can be displayed on screen for any point on the model. The Drift report will only include the load cases selected using the Select Cases button. The drift is only reported for locations within the diaphragm. For points outside the diaphragm or points on levels with no diaphragm, zero drift is always reported. In those cases, the report – Nodal Displacements can be used. To view a Drift Report for a point:

• Select Process – Results – Drift – At a Point.
  

• In the Select Plan dialog box that opens, Highlight Roof from the list box.
• Click [OK] .
• This takes you back to the graphics screen. Click the cursor on any point on the floor plan to view drift for that point for all load cases.
• This report starts wi th a listing of the load cases by name. Click the Forward arrow “►” to continue to the next page where the results begin. The report includes the total displacement as well as the inter-story displacement.
• Click (X)  to exit the report.

Upon exiting the drift report, you are returned to the floor plan with the target cursor indicating that you are still in Results – Drift – At a Point mode. You can either continue investigating drift at other points or issue other commands. 

A drift report for up to four predefined points, can also be displayed on screen. To Obtain a Drift Report at Control Points:

• Select Process – Results – Drift – At Control Points .

The Drift at Control Points dialog box will appear on the screen:

• In the row marked 1 type 0 for X and 0 for Y (you can use the arrow or tab keys to move from cell-to-cell..
• In the second row type 125 (40) for X and 60 (18) for Y.
• Click [View Results] to get the drift values at these two corners of the building.
• Click (X)  to exit the report. 

Reports

Many different reports can be generated from the results of the analysis of the structure subject to the various load cases. All reported values are for the unfactored, uncombined load cases while in Load Cases Mode. In the next section you’ll see how to get combined results. Printed output is generated using the Reports menu, but the reports can be viewed on screen as well.

• Select Reports – Screen (if it’s not already checked).
• Select Reports – Reactions.
  

• Click [Unselect All] .
• Highlight 2 from the Frame Number list box.
• Click [OK] . The Frame Reactions report should come up for the support nodes of Frame #2 only.

NOTE: The report can be printed from within the report viewer or it can be printed directly to the printer by selecting Reports – Printer, rather than Reports – Screen.

• Click (X) to exit the report.

Feel free to review other reports. Some of the reports can be quite long and make take some time to generate onto the screen.

Load Combinations

The Load Combinations Mode allows you to manually define or generate a set of custom load combinations. The member forces and other analytical results from those combinations of load cases can then be displayed on screen or reported. If your model is made of steel frames and if you are going to be using the RAM Frame – Steel Mode for the design of those frames, then there will be a separate set of load combinations defined in that mode which are used only in the steel member design. To initiate the Load Combinations Mode:

• Select Mode – Analysis – Load Combinations .

The mode will change and some of the menu options will be affected.

• Select the new menu item Combinations – Custom Combinations .

The program can generate load combinations using templates. The templates are text files stored along with the rest of program tables. The templates are grouped in categories like Concrete combos, Soil Combos, LRFD combos, etc. Those templates are further broken down by building code (at least in the US ).

• In the Custom Load Combinations dialog box that opens select CONCRETE_ACI (CONCRETE_BRITISH) as the template ID.
• In the Code for Combinations select ACI 318-08 (BS8110 1997).

Different codes modify load combinations in various ways and the program doesn’t always know which approach to take. In the case of ACI 318-08 load combinations, the program needs to know if the seismic load was initially defined as a service level load case or an ultimate load case. In our case, the ASCE 7-05 seismic load case we defined was an ultimate level load case.

• Uncheck the first box labeled Seismic is Service. Multiply by 1.4
• Leave the second box checked, this model did utilize the Kd factor in our wind load case (for British code users check the box labeled Use 0.9 Instead of 1.0 for Dead Load Factor).
• Click [Generate] and the program will generate the full set of code combos. This could result in several hundred load combinations. The new load combinations are automatically checked to be Used. You can uncheck any of the boxes in the “Use” column to inactivate a particular load combination without deleting it entirely. 

NOTE: If you generate more load combinations in the Custom Load Combinations dialog box, those additional combos are appended to the end of the list.

Now the analysis results of the selected load combinations can be viewed using the same commands as described in previous sections.

• Select Report – Member Force Envelope – Single .
• Select any lateral member.

The program will generate a report of the minimum and maximum forces in that member for any load combination. The envelope values reports are algebraic. In other words, the minimum mo ment might be a bigger negative number than the maximum, positive moment. Note that the maximum value may occur at the end or at any point along the length of the member. The location of the maximum force, along with the load combination which produces it are both reported.

• Select Mode – Analysis – Load Cases to return to that mode.

You have completed the analysis of the structure for each of the individual load cases. You will now proceed to design your frame members using combinations of those loads.

• Continue to RAM Frame - Shear Wall Analysis Module Tutorial
• Go back to RAM Steel Column Design Tutorial
• Up to the RAM Structural System Tutorial