RAM SS Modeling [FAQ]

	Product(s):	RAM Structural System; Ram Modeler
	Version(s):	Any
	Environment:	Any
	Area:	Modeling

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 structure with alternating typical layout types?

Using repeated typical layout types in the story data is an advantage of the Ram Modeler. You can model a typical layout type just once and repeat that in the story data to create a tall building. The lateral beam sizes can vary even on typical layouts.

Regretfully, in RAM Modeler, typical layout types can only be used on consecutive floor types. Furthermore, any layout that includes a transfer beam can only be used once in the story data. This includes beams that support columns or walls above. Consequently, a building with alternating floor types requires a unique layout type for every story.

An enhancement request has been logged to allow alternating floor types, or other sequences, where a typical layout type could be used on non-consecutive stories, but this requires many changes to the architecture of the program and implementation of the "framing tables" so it won't be possible in the short term.

Models that are synchronized with ISM (iTwin Analytical Synchronizer) also must have a unique layout type for every story. This is necessary to maintain a member unique ID mapping that works with other applications like Revit. When exporting a RAM Modeler with repeated stories to ISM new unique layout types are created automatically, in version 17.

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.

Two cantilever beams still cannot frame tip-to-tip, however. This is not allowed because the force distribution to the two cantilevers is indeterminate. To work around this, one of the cantilevers can be split into two simple spans, or the cantilevers can be shortened to stop just short or each other and then the small gap can be filled with a third short simple span. If the beams (and supports) are lateral members, then you can adjust the end fixity and get the desired indeterminate behavior from the Ram Frame finite element analysis.

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. (Stub cantilever beams which have a single support were added to the program in version 14.02)
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.

If the sloped framing causes anything to look incorrect in 3D, see RAM SS 3D Viewer FAQ.

For more on modeling ramps, see RAM SS - How to Model Ramps in RAM Structural System.

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.

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.

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 can I change a Beam’s material property from Steel to Concrete?

In the RAM Modeler first change the material to “Concrete”. Then go to Layout>Beam>Change Material. This process also applies to columns and braces. The trick here is to set the material to what you want the member to become, not what material it initially is. This is backwards of other commands that only work on members that match the material setting.