***UNDER CONSTRUCTION***On October 25, 2016, Bentley Product Managers Josh Taylor, P.E., and Francisco Diego, P.E., conducted a Tech Talk titled 'Analysis of Combined Steel and Masonry Buildings for Lateral Loads', which covered recommended practices for designing buildings framed with steel floors and masonry walls using RAM software.
A recording of the tech talk is available at the following link:
This wiki documents the questions that were asked by the audience and provides detailed replies.
1. Can you model a masonry infill panel between the steel framing to take lateral loads only?
2. Did the openings get imported into Elements? How did you model the openings?
A: Yes, wall openings modeled in RAM Structural System are transferred into the RAM Elements model when reading in the *.rss file. This is illustrated in the image below. The left image is an elevation view of the wall in RAM Modeler. The right image is the result after importing the model into RAM Elements and assigning the wall a masonry material.
3. Is the 2nd order analysis being analyzed automatically in the software or the designer have to manually inform the software to do so?
A: The P-Delta analysis is handled by each program (RAM Structural System and RAM Elements) automatically at the user’s choice (it can be considered or ignored).
4. Do you have to import the full model from RAM or can you just import the lateral model when designing shear walls?
A: You have the option of importing either the entire RAM Structural System (*.rss) model into RAM Elements, or just the lateral framing within the *.rss model.
5. Can you design the masonry shear walls with vertical chord reinforcing at each end of the wall, or are you limited to intermittent bar spacing?
A: In RAM Elements you can place vertical reinforcing in a grouted cell anywhere along the extent of wall (including the ends) by adding a column as a rigidity element. The column can be of any dimensions you choose.
6. How do you import RAM SS to RAM elements?
A: First save and close the RAM Structural System model you are working on. If you would like applied forces transferred into RAM Elements, also make sure you have run the analysis in RAM Structural System. Then open RAM Elements and select Import > RAM SS (available from the main RAM Elements button). Note you can choose to import either the entire model or just the lateral framing.
7. If we input them as concrete what do we define them as? Is there a table we can follow that you provide?
8. Is CMU wall analyzed individual?
9. When dealing with unassociated masses to diaphragms, should you always associate them to the topmost diaphragm? For example, would you associate a concrete wall load that's closer to the ground than it is to the roof to the roof?
10. Is the CMU wall reinforcement represents the both in-plane and out of plane reinforcements? Meaning shear wall reinforcement and wind pressure on wall?
11. Can you explain the slide related to defining intermittent stories?
12. How do you define a standard metal roof deck (1-1/2" type B roof deck at 20 gauge is our most common)?
A: RAM Structural System does not have a deck library for metal roof decks as it does for composite floor decks. For a metal roof deck you would explicitly define a steel thickness and weight to be used for the diaphragm properties.
13. How do you address vertical joints in CMU while modelling? Is the wall separated at the joint?
A: For RAM Structural System, the joint needs to be modeled as a gap since there are no built in tools that allow a release within a wall element.
14. Why not use RAM Elements to apply lateral forces in lieu of using Structural Systems?
A: This is certainly a viable approach. We emphasized the reuse of loads from RAM Structural System to maximize the interoperability between RAM Structural System and RAM Elements, but the loading can be handled within RAM Elements also.
15. In previous imports from RAM to Elements, Elements didn't recognize the steel joist sizes and the sizes appeared to have to be manually inputted. Is this correct or is there a way to get the two programs to understand the designed size from the RAM import?
16. Do you model differently if you have walls and steel frames in the same directions?
A: There is no special consideration for the modeling of two different lateral framing systems in the same direction. One special analysis consideration though is setting the appropriate seismic parameters correctly in the model.
17. Like for a stair tower without any diaphragm, enclosed by Block walls, can the walls be designed to span horizontally?
18. Will RAM Elements notify you if the shear wall you are designing requires boundary elements?
19. Is there a table for the roof deck properties?
20. What about the contribution of non-reinforced block walls to the lateral resistance? I believe they have some contribution, and how do you model that?
21. Is the interoperability between the two softwares 2-way? For example, as changes progress within the elements module, are any effects in terms of applied loads applied to the frame module?
A: The interoperability is one-way from RAM Structural System into RAM Elements.
22. Should intersecting 'L' or 'T' walls be modeled integrally or with a gap? In a current project, 6" gap in 'T' walls rotated 90-degrees seem to still act integrally and bear the majority of axial component of lateral loads.
23. What is the best practice for modeling control joints in CMU walls in RAM SS into RAM Elements?
24. Will coefficient Ct be different if we have masonry in one direction and steel frames in another?
A: Yes. You can define different seismic values for each orthogonal direction in RAM Frame within one load case.
25. Is it correct that the lateral loads don't get imported into the "one off" wall module in Elements? What's the best way to get the lateral loads into the one-off module?
26. In the standalone CMU design module, does it consider flange effect for the walls?
27. Are lintels and sill reinforced concrete elements in the spandrel design of RAM Element, especially for seismic cases?
28. As a follow-up to my first question about the full model or just lateral model, if you include all the applicable design combinations that include gravity loads does the lateral model not include any of these gravity loads and therefore not perform any gravity design?
29. For solid walls, there is not a good method to model boundary elements with "column" reinforced at ends, and minimum reinforced at center, for concrete shear walls in RAM Concrete. Is RAM Elements better?
A: The RAM Elements wall design module allows the placement of a column with confined reinforcing at any point along the wall (including the wall ends).
30. What happens to wind load generated when you have a small interior mezzanine? Will the wind force estimated at this intermittent level transfer to walls on other sides or be lost if we lump it to full level above the mezzanine?
31. Will there ever be a wood wall module for Ram Elements? For example, to design shear walls/bearing walls.
32. When you have intermittent levels that do not have a diaphragm, do you need to tell RAM Elements that there is not a level/brace at this height for walls?
33. Can you go into more detail about representing masonry walls with concrete walls in RAM Structure?
A: Walls in RAM Structural System can be modeled using either a Concrete material or a type ‘Other’ material. Users often model masonry walls in RAM Structural System using the type Other material to distinguish them from concrete walls. But, with this being said, walls of either material type are transferred into RAM Elements during the import. One advantage of using Concrete walls to model masonry is that in RAM Structural System, you can adjust the stiffness of the wall element using crack factor settings that are associated with concrete walls. The crack factors not available for walls of material type Other – only for concrete walls.
34. In the UAE, we are using concrete masonry units without steel reinforcement and purely dependent of lintel beams and columns. How does it contribute in the building resistance to lateral loads? Is this condition can be modeled in RAM?
35. At the section in RAM Element it looks like there is a hinge between a wall and diaphragm. Is it possible to model fixed end of the diaphragm that lays on the wall?