(08.28.2012) Bentley-Innovations in Flat Slab Concrete Building Designs eSeminar Attendee Questions

This eSeminar was originally presented on August 28th, 2012.

You can view the recording online at our BeConnected site (Click Here!).

The following are the product-related questions and corresponding answers from the eSeminar.

1. Q: Can you explain a bit more about in-core and out-of-core and the different solver types in RAM Frame?
   
   A:  The direct and direct sparse solvers use different numerical techniques.  The sparse solver is newer and typically faster.  In-core uses RAM memory whereas out-of-core uses hard drive space.  In-core is faster, but you might run into memory issues for large models.  Typically, you should use all available CPU cores.  However, at times this is problematic for some systems, so the single core option is available to work around those issues if they are encountered.
      
2. Q: Will RAM Structural System consider the torsional moment those results from the fact that the center of gravity and center of rigidity do not coincide?
   
   A: The center of mass is typically not located in the same location as the center of rigidity.  This results in inherent torsion for lateral load cases and is considered automatically in the analysis.  In addition, the Loads – Masses dialog allows you to specify an eccentricity percentage to be used for codes that require accidental torsion to be considered.  This is applicable to both semi-rigid and rigid diaphragms in RAM Frame. 
       
3. Q: What maximum distance between nodes should be used to start with in RAM Frame?
   
   A: This is highly dependent on the model, but generally 4 feet is an adequate starting point and that is what is set in the out-of-the-box defaults.  In general, you may want to reduce the mesh size until convergence is achieved for the results that are of concern (lateral load case displacements/forces in Frame).
     
4. Q: Is the EC2 code available for the design of shear walls? 
   
   A: Currently, the EC2 code is available in RAM Concrete Beam and Column, but not RAM Concrete Shear Wall.  We are waiting to see if there is enough demand for the code to implement it.  We will consider this as a request and when there is enough demand, we will implement EC2. 
     
5. Q: Is any module that supports the Canadian concrete code?
   
   A: Currently, RAM Concept supports the Canadian code, but RAM Structural System does not.   Work has already begun on writing the Canadian code component that will be implemented in the RAM Structural System.
     
6. Q: Are similar stress contours and section cuts available for diaphragms as are available for walls?
    
   A: RAM Frame currently does not show diaphragm stresses or have the ability to assign diaphragm section cuts for forces.  Now that we have the new graphical environment in Frame, this has moved up the enhancements list, but a release date for this has not yet been set.
    
7. Q: Do you need RAM Concept to model two way slabs in RAM Structural System?
    
   A: The RAM Frame and RAM Concrete modules in the RAM Structural System do not need RAM Concept installed in order to analyze a two way slab.  However, there is nothing currently in either module that actually designs the two way slab.  That is what RAM Concept is for.  The only features not available in RAM Structural System if RAM Concept is not installed is the ability to integrate the programs in RAM Manager and the ability to use forces from RAM Concept in RAM Concrete Column.
    
8. Q: What is the recommended procedure between RAM components to design flat slab building - e.g. start with Concept and then run Modeler, etc.?
    
   A: This is really user preference.  We typically find that it is advantageous to start in RAM Structural System with the 3D model and then integrate with RAM Concept to finalize slab design and send the column forces back to RAM Concrete.  However, if a Concept model already exists, you can certainly use the Concept model to create the RAM Structural System model.
   
   
9. Q: Will RAM Frame allow use of some diaphragms using composite steel beams and others 2-way concrete slabs?
    
   A: Yes. RAM Frame allows diaphragms consisting of concrete on steel deck (composite floors), noncomposite roof deck, 1-way concrete beam and slab floors, and 2-way concrete slabs. It is permitted to have a mix of diaphragm types in the same model. Each diaphragm can be specified independently as rigid, semi-rigid, flexible (no diaphragm action), or pseudo-flexible (a special designation in RAM Frame that is the same as flexible except the program automatically generates the nodal loads applied to each frame).
   
   
10. Q: How long does it take to become proficient in using all the systems shown today to design a concrete building?
     
    A: The RAM products have a reputation for being quick to learn and easy to use, but it is difficult to provide a timeframe.  If you are already proficient in general purpose finite element programs and slab programs used in structural analysis, RAM Structural System and RAM Concept can be learned fairly quickly because they use the same principles.  Bentley offers training on both products and we have a knowledgeable technical support team to assist with questions not clarified in the manuals or tutorials.
    
    
11. Q: Is the slab modeled as membrane or shell elements?
     
    A: Two way slabs in RAM Structural System and RAM Concept are represented by shell elements. 
    
    
12. Q: Is RAM Concrete capable of modeling sloped slabs similar to ramps in a parking garage?
     
    A: Sloped slabs can be modeled in RAM Structural System, but there are limitations.  It is difficult to discuss these limitations in this simple Q&A format.  I suggest that you contact technical support for more information.
    
    
13. Q: What is max wind velocity that I can use in the software?
    
     A: RAM Frame generates loads based on the selected code.  The program may not cap the wind speed that is entered, but any entered wind speed should be consistent with the code methodology.  Today’s presentation demonstrated an ASCE 7-10 wind load case.  RAM Frame follows the directional procedure in ASCE 7-10 and assumes an enclosed building.
    
    
14. Q:  Can two story columns that do not intersect a slab at mid height be modeled?  Is slenderness of the tall column considered?
     
    A:   Yes, two story columns can be modeled and designed in RAM Concrete Column.  The unbraced length calculated by the program will automatically reflect the two story condition.  Slenderness can also be considered; it is an option in analysis criteria in RAM Concrete Analysis mode.
    
    
15. Q: Does RAM account for rigid end offsets? 
    
    A: RAM Frame and RAM Concrete have options to include rigid end offsets in their respective criteria.  In addition, you have the ability to reduce the rigid end zone by a percentage.  Please note, rigid end zones are only considered in beam-column joints and are not applicable to slab-column intersections in the current implementation.
    
      
16. Q:  Is there a way to see detailed calculations for the design of concrete shear walls?  Design summaries only show the capacity of the walls.
     
    A: The View Update dialog shows the controlling forces for each load combination and interaction surfaces for number of most critical load combinations defined in the general criteria.  The calculations used to generate the interaction surfaces are currently not available.
    
    
17. Q: I would like to know what the differences are between CAD and RAM. It's the first time that I’ve heard about RAM, and looks more interesting that CAD. 
     
    A:  RAM products are for structural analysis and design whereas most CAD products are strictly drafting tools.  Bentley has products for each step in the structural design process (modeling, designing, construction document production, and detailing).  The Bentley website has more information on the vast number of products we have to support your infrastructure related needs.
    
    
18. Q:  Does RAM Structural System have limitations (i.e. # of members, nodes, etc)?  Can it handle high rise buildings design?
     
    A:  RAM Structural System is geared for building analysis and design.  The vast majority of buildings can be modeled in RAM Structural System quickly and accurately.  Some limitations exist with elaborate framing schemes that are not conducive to a floor/story based approach, but there are no limitations in terms of structure size or height.
    
    
19. Q:  When column layouts are irregular will the program handle it?
     
    A: Absolutely, irregular column layouts can be modeled, analyzed, and designed in RAM Structural System and RAM Concept with nearly as much ease as regular layouts.
    
    
20. Q: Do changes made in RAM Concept transfer back to Ram Structural System?
     
    A: Partially.  Since RAM Structural System generally targets design of different structural components than RAM Concept, it is often desirable to maintain separate slightly different structural models.  This is accommodated in the integrated workflow.  However, the models can be kept in sync by making modeling changes in RAM Structural System which can then be automatically updated in RAM Concept.  Column and wall forces calculated in RAM Concept can be automatically transferred back to RAM Structural System for column and wall design.
    
    
21. Q:  Do the load history deflection calculations include stiffness/restraint from adjacent shear walls? 
    
    A:  The RAM Concept analysis always automatically includes the restraining effects of shear walls and the associated diversion of lateral forces, including post-tensioning.  Restraint to shrinkage strains are not explicitly accounted for, but can be simulated through a setting in RAM Concept designed to account for this.
    
    
22. Q:  Should the 3.35 creep factor in RAM Concept ever be modified?
     
    A: The default creep factor in RAM Concept will provide a good value to use for normal design conditions.  The 3.35 value is taken from a recommendation in ACI 209R, which also defines modifiers to this base value based upon environmental factors.  These factors should be applied where appropriate.
     
23. Q: Will RAM Concept model 2-way waffle slab systems?  
     
    A: Yes, RAM Concept is capable of modeling and designing waffle slab systems.
     
24. Q: Does the RAM Concept vibration analysis cover seismic zone conditions?  Are shock or impact loads considered?  Is vibration induced by machinery or equipment considered?  
    
     A: The vibration analysis in RAM Concept currently only analyzes vibrations caused by walking/dancing on the floor, which can cause disturbance to building occupants or sensitive equipment.  Analysis of other sources of vibration may be added in future versions of RAM Concept. 
     
25. Q: Is it possible to assign uniformly distributed reinforcement in RAM Concept?  
     
    A: Yes, it is quick and easy to assign a uniform mesh of reinforcement over large areas of the slab (or the entire floor).  RAM Concept can then design only reinforcement required in addition to this defined mesh.
      
26. Q: How does RAM Concept handle sloped and stepped decks?  Can RAM Concept handle large vertical steps?
     
    A: RAM Concept models and analyzes vertical slab steps on either the top or bottom of the slab faithfully by allowing input of the surface elevation in addition to the thickness.  Small slopes can be approximated using a series of small steps.  RAM Concept can also handle large vertical steps, such as slabs at two different elevations with a deep connecting beam.  There are a few ways to model such a large step, depending upon the requirements of the designer.  
    
    
27. Q: Does RAM handle wave loads on the concrete foundation?
     
    A: RAM Structural System and RAM Concept do not automatically handle wave loads.  However, there are other Bentley products that may be suited for what you need.
      
28. Q:  Will RAM Concept add unbalanced moment design (ACI 13.5.3) to its analysis capabilities? 
    
    A:  It currently on our backlog, but because this provision can normally be satisfied through detailing of the designed flexural reinforcement and simple hand checks, it is not considered to be a high priority item.  The magnitude of the unbalanced moment is available in the punch check audit to aid in simple hand calculations.
    
    
29. Q: Is it OK for span segments to run along walls? 
     
    A: Yes, it is generally OK for span segment to run along the axis of a wall.  However, since the analytical model is only supported at the wall nodes (unlike the real structure that is continuously supported), watch out for unrealistically large slab forces in the slab interior to the wall.  
    
    
30. Q: Can RAM Concept calculate live load reduction automatically or does a tributary area need to be manually entered? 
     
    A: RAM Concept calculates live load reduction for columns, punch checks, and slabs automatically including the influence and tributary areas.  It is possible to enter a tributary area value manually however, if you wish to override the automatically calculated value.  
    
    
31. Q: For PT design in RAM Concept, is there a way to do individual strip runs to get preliminary PT forces without laying out the PT for the entire floor? 
     
    A: RAM Concept has a strip wizard that allows you to rapidly create an individual strip run.  However, with the available tendon tools you might find it just as fast to generate a 3-D model including PT for preliminary design resulting in far more accurate estimates.
    
    
32. Q: In RAM Concept, can you model two way slabs with beams?  Are beams designed?  
     
    A: Yes, RAM Concept can model a two way slab system with beams, and accomplish the slab design in addition to the beam design, including torsional effects.
     
33. Q: Can RAM Concept model spherical or curved diaphragms like domes in cathedrals? 
     
    A:  No, RAM Concept is not suited for this type of analysis.  Instead consider the STAAD product line for this type of structure.
    
    
34. Q: How do we get the continuing education credits? How can I get a certificate of attendance of CEU's?
     
    A:   Bentley Learning Units (BLU), Bentley Institute’s equivalent to Professional Development Hours (PDH), are granted for the live and recorded eSeminar. Within 2-4 weeks of watching the presentation, Learning Units are added to your transcript. To access your transcript, go to www.bentley.com/mylearninghistory. On the "My Learning History" page, there is a detailed how-to guide related to Learning Units and transcripts, in addition to the link to the user’s online transcript. In most states, users can submit their Bentley transcripts for consideration for continuing education credit toward their registration renewals. 
    
    
35. Q: How do I view this eSeminar again or share it with a colleague? 
     
    A: This event along with the live Q&A were recorded and it is available online at our BeConnected site.