This wiki covers the answers to questions asked by attendees during the June 24th webinar Concrete Buildings with RAM: Efficiency Tips and Tricks. Clarifications to some of the material presented are also given. A recording of the webinar can be accessed at the following link:
Q: Please cover how to model sloped concrete floor systems, such as parking garage ramps.
A: This topic, along with others suggested by the audience, will be considered for future seminars. In the meantime, if a wiki or demonstration video on this topic is created on the Structural Analysis and Design wiki site, we will update this response to point you to the content.
Update: A wiki has been posted on this topic:http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/15396.ram-ss-how-to-model-ramps-in-ram-structural-system.aspx
Q: Is there a way to update a floor geometry in RAM Structural System from RAM Concept? Currently you have to create a new level and either use it as a reference and trace it or redraw the loads on the new level.
A: As of now there is no way to transfer geometry modifications made in RAM Concept back into the RAM Structural System model from which the floor originated. Incremental modeling revisions can be transferred only from RAM Structural System to RAM Concept.
Q: When you place one slab over another, does it count your slab thickness in that area as the two slabs combined or just use the higher priority one?
A: In both RAM Structural System and RAM Concept, only the slab with the highest priority is considered in areas where two or more slabs overlap.
Q: When transferring RAM Structural System floor plates to RAM Concept for design, how do you recommend handling snow and snow drift loads, since concept doesn't appear to use snow loads the same way.
A: Unfortunately snow loads are not transferred from RAM Structural System to RAM Concept at this time. A complete listing of the items transferred is available at the link below:
Q: In the RAM Concept auditor, if the sections are collapsed, searching for failures does not work.
A: The word search does not search within collapsed regions, correct. We recommend using the Open All Items/Close All Items toggle at the bottom of the Auditor dialog, in conjunction with the word search, for the best results.
Q: Are there ways to obtain section cut diaphragm forces in RAM frame?
A: Not as it stands, but this is a common request and we are evaluating if we can fit it into this year's development schedule.
Q: Is there a way to copy user defined rebar from one wall to another (concrete shear wall boundary elements)?
A: For a wall panel to which manual reinforcing has been assigned (which would include wall panels with boundaries), the copy command can be used if (and only if) the source and destination wall panels have the same length. This restriction was enforced to eliminate possible ambiguity about the desired boundary lengths for wall panels with drastically different overall lengths.
Q: What slab beam properties did you modify or reduce when using the nomographs to compute K?
A: In RAM Modeler, under PropTable -> Beam Sections, the factors are Axial Factor, Flexural Factor, and Torsion Factor. These factors affect the analytical stiffness of the member, and thus by setting these factors to very small values (0.01), the beams are effectively absent from the analysis. Further, when the Flexural factor is set to 0.01 or less, RAM Concrete uses the full section properties (as if the factor was set to 1.0) when calculating the K factors. As a result, by laying down equivalent beam strips with small stiffness multipliers, we can get RAM Concrete to calculate K factors for the columns supporting a flat slab floor, without double counting the slab from the analytical standpoint. In order to reduce the beam stiffness (e.g., 0.35 factor prescribed by ACI), the elastic modulus can be adjusted.
Q: Is it possible to model a deep trench in a mat foundation?
A: This is best addressed in a separate webinar or paper. We will look into providing guidance on this topic.
Q: Does RAM Structural System release the axial contribution from the slab when collecting load into drags? What would need to be done to mitigate the drag contribution from the slab and let the drags take care of it?
A: This is best addressed in a separate wiki. We will look into providing guidance on this topic.
Q: When walls intersect, is it better to assign them to a common wall group in RAM Concrete Shear Wall, or should they be designed independently? What are the advantages and disadvantages of each approach?
A: We see both approaches used by engineers, so it seems there is no industry consensus. You could argue that considering a "T", "L", or "C" core as a single group is more accurate from the standpoint of the strength calculations, as the flexural properties of the entire section are considered as one. Further, this approach tends to lead to a larger overall calculated strength and therefore more efficient designs.
The advantage of treating each face of the core independently as a planar panel is simplicity. Rather than calculating 360 degrees worth of axial-flexural envelope, you are effectively reducing the strength calculation to a single plane. This makes the results easier to interpret and validate.
For ACI codes, there is effectively no difference in the shear strength calculations between the two methods in RAM Concrete, as even when cores are grouped as one wall design group, the program calculates shear strength and demand based on the planar panels within the wall group.
The good thing about RAM Concrete with regard to this issue is that it is easy to perform the design either way. A good approach may be to start simple: design all planar panels as their own wall group, get a sense for the behavior of the design, and then do a final check with all panels in each core grouped together as a single wall group.
Q: When we have a dual frame system, would you recommend running RAM Frame to check drifts and then run RAM Concrete for the wall design?
A: This is a reasonable approach. It's good to make sure drifts are reasonable and thicker or higher strength walls are not needed before spending the time to design the wall reinforcing.
Q: In RAM Concrete Shear Wall, is there a way to design individual panels with a predefined wall flange of say, 12xT (rather than taking the geometry exactly from the model)?
A: As it stands, the module always uses the exact concrete geometry in the model. We recognize though the advantage of being able to trial different flange configurations, and also being able to trim the true flanges to arrive at what ACI defines as an effective flange width. Effective flanges are tricky when integrating wall design into a 3D structural analysis package. What is considered a wall flange or web is a function of the direction of loading, and RAM Concrete doesn't associate different cross sectional geometries with different loading directions. We are still searching for ways to improve this aspect of the wall design.
Q: Is there any way to make RAM Concept design for strength using the load history calculated cracked section? To run a load history the cracked factor has to be set back to 1, which makes the slab too stiff for strength design.
Q: Does RAM Concrete ever account for cracked concrete automatically or do the properties have to always be modified?
A: Whereas RAM Concept can perform a load history analysis that accounts for cracking, creep, shrinkage, and other nonlinear and time-dependent factors, RAM Concrete currently uses a strictly elastic analysis with consideration for the crack factors assigned to the slabs, beams, columns, and walls.
Q: Wall boundary elements are a manual trial and error process now. Are there any plans to get the boundary element design process automated in RAM Concrete Shear Wall?
A: Our primary hurdle in adding more intelligence to the boundary element design is the required run time and selection of the best design from a large number of possible solutions. This is especially true for three-dimensional wall systems (more than just a planar wall). There are some opportunities this year to leverage Bentley's cloud technology, Bentley Connect Scenario Services, within RAM and add more sophistication to both RAM Concrete and RAM Concept. We will keep everyone posted on how this progresses.
Q: Can dynamic loads be exported to RAM Concept for a foundation design?
A: Unfortunately dynamic loads are not transferred from RAM Structural System to RAM Concept at this time (as opposed to seismic loads, which are transferred). A complete listing of the items transferred is available at the link below:
Q: Where is the best place to identify hinge points when designing boundaries in RAM Concrete Shear Wall?
A: The brief answer to this is anywhere you anticipate plastic hinges to form within the wall system when loaded laterally to failure, with consideration for gravity loads as well. The locations in the wall that form the flexural mechanism must be ductile enough ensure the wall system can form the expected mechanism without brittle failures.
Q: Any plans on extending the FEM engine into material nonlinear analysis?
A: While material non-linearity is available in the analysis engine used by RAM Structural System, as of yet there are no plans to expand RAM Frame or RAM Concrete to incorporate material non-linearity. If you are in need of this capability, we would appreciate hearing the specific types of non-linearity you require.
Q: How to address soil-structure interaction in tall buildings with basement?
Q: Is there a way to copy elements (beams/columns) from one floor plate to another, without copying the whole floor?
A: At present there is no such command in RAM Modeler. RAM Data Access can be used to perform this type of manipulation on a RAM Structural System model. RAM Data Access can be built into a spreadsheet macro routine, or can be just a simple executable created for the specific purpose of creating time saving modeling commands that don't exist in RAM Modeler. We will look to add more how-to's and samples on RAM Data Access to solve this type of problem.