In August 2016, Bentley hosted a Bentley Success Factors webinar titled Accuracy, Precision, and Practicality in Structural Analysis. A recording of that webinar can be found at: http://pages.info.bentley.com/video-details/?video=CO_VID_WEB_RAMFRME_08_16&videoDBID=2875ae25-b3b3-498d-a565-e9ed48909388
During that webinar several questions were received. Time did not permit answering all of the questions nor of providing detailed answers. Compiled here are the questions that were received, with more thorough answers.
Q: Is it possible to have a leaning column in concrete construction?
A: Yes, it is. Gravity columns (those designed only for gravity loads) are often smaller than Frame columns, or have less reinforcement and are more prone to cracking in a seismic or wind event. In either case these columns are not as stiff as Frame columns, and in a seismic or wind event they will maintain their stability by ‘leaning’ on the Frame columns.
Q: Regarding the comparison of models with different diaphragm mesh sizes, how did the stresses in the diaphragms compare?
A: In the study comparing models with varying diaphragm mesh sizes only the frame story shears were compared. The diaphragm stresses were not compared.
Q: Do you have to use the same mesh size throughout, or you can specify different size from one area to another?
A: In the RAM Structural System there is currently no way to specify different maximum mesh sizes for different areas. This is a practical approach, since it is generally not necessary to have a refined mesh when analyzing a structure with semirigid diaphragms, when the purpose of such analysis is to determine the impact of the diaphragm on the distribution of story forces to the frames. As was indicated in the webinar, the differences in results between a very coarse mesh and a very fine mesh are very small, so the effort that would be required to refine the mesh in certain areas would not generally be warranted.
Q: In which documentation can I see the list of 188 load cases to which you referred?
A: Consider Dead, Live, and Roof. AISC 360 requires notional loads, in both axis, for a total of six cases. For seismic loads ASCE 7 requires plus- and minus eccentric cases for accidental torsion in both axis (for a total of four cases); see ASCE 7-10 Section 220.127.116.11. For wind load cases ASCE 7 requires twelve load cases (various configurations of X, Y, and rotational wind loads); see ASCE 7-10 Figure 27.4-8. ASCE 7-10 Section 2.3.2 then gives seven basic strength design load combinations by which all of the previously listed load case must be combined. This results in 188 load combinations that need to be investigated.
Q: Are there any efforts being made to combine Response Spectra Analysis and P-delta within the analysis itself other than the non-linear time history analysis as an alternative?
A: As was discussed in the webinar the P-delta analysis based on the Geometric Stiffness method, which is used in RAM Frame and some other software, is compatible with a Response Spectra Analysis, and can be done jointly in the same analysis. However, the iterative method of P-delta is not compatible with Response Spectra Analysis; they can’t be done together in the same analysis. In that case your Response Spectra Analysis does not comply with the requirements of the Code to consider P-delta. I am not aware of any efforts to come up with a methodology in which a RSA and an iterative P-delta analysis can be performed in the same analysis; I don’t think it is possible.
RAM Structural System and STAAD
Q: Which is better, STAAD or RAM?
A: Both programs have their strengths, so it depends on what is being analyzed and designed. The RAM Structural System is specifically for building structures. This allows for faster modeling and more specialized analysis, design, and reporting. Generally the RAM Structural System is preferred for buildings. STAAD has a wider selection of building codes, some of which aren’t available in the RAM Structural System. It is also general purpose, suitable for any structure, building, plant, tank or frame of virtually any configuration. With the Structural Enterprise License, a bundled license of STAAD and the RAM line of products, you can have both:
Q: Can we use STAAD in analyzing and designing multi-story buildings, both steel and concrete structure? What is the limitation of STAAD?
A: STAAD can certainly be used for analyzing and designing multi-story structures. STAAD is a general purpose program, permitting the modeling of any type of building, structure, or assembly, in virtually any material. It has extensive implementation of a large number of national and international standards and codes. Because it is a general purpose program it has great versatility in accommodating any configuration of geometry, loading or analysis. RAM Structural System is special purpose software specifically for buildings, so when designing and analyzing building structures it has some advantages over STAAD in speed of modeling and the comprehensiveness in the implementation of building code requirements for buildings. But STAAD is more versatile in the modeling of complex geometries and has a greater selection of international building code and material specifications.
Q: Can we import a model from STAAD to RAM Structural System?
A: Yes, models can be imported and exported between those two programs and between any of Bentley’s structural programs, as well as other popular BIM programs, via the Integrated Structural Model (ISM) technology. Each program can create and update an ISM repository, which can be shared with and opened by the others.
Q: Is there another way of importing STAAD to RAM Structural System other than ISM?
A: No, the mechanism for interoperating with each other is through ISM.
Q: When we import STAAD to RAM Structural System, are we importing model data only or is the load data included?
A: At this time only the model geometry data, including design sizes, is transferred through ISM.
Q: How do we go about validating the analysis results in STAAD.Pro or RAM Structural System?
A: Validation examples are available for both programs. The best way to verify any program is to create a simple model of something that you have already analyzed and designed and compare the program results with those results. It is always good practice with new software or new features to do some simple validation by hand to verify that the program is functioning correctly, and even more so that you are using it correctly.
Q: Can you please make a forum for limitations of RAM Structural System and STAAD?
A: Bentley Communities is an excellent source for information about RAM, STAAD, all of Bentley software. It has wikis, blogs and forums written by Bentley experts as well as Bentley software users. It is a great way to get answers to questions about the software.
RAM Structural System
Q: Does the software comply with the Canadian codes or any other internationally acceptable codes?
A: For steel member design, including composite beams, the requirements of AISC, Canada CAN/CSA S16, BS 5950, Eurocode and Australia AS 4100 have been implemented. For concrete member design the requirements of ACI, CAN/CSA A23.3, BS 8110, Eurocode, AS 3600, China GB50010, and Singapore CP 65 have been implemented. Except for CAN/CSA A23.3 these are also available for the design of concrete shear walls. Seismic design of steel frames is performed per the AISC seismic requirements. Wind forces can be generated per several codes including ASCE 7, NBC of Canada, BS 6399, China GB50011, and AS/NZS 1170.2, plus others. Seismic forces can be generated and response spectra analysis performed per several codes including ASCE 7, NBC of Canada, China GB50011, and AS/NZS 1170.4. Live Loads are reduced as permitted by IBC, NBC of Canada, BS 6399, Eurocode, AS/NZS 1170.1, China GB50009, and Hong Kong Building Code.
Q: Can we use RAM Structural System for high-rise buildings, say 50 stories?
A: Yes, RAM Structural System can be used for buildings of any height. The modeling accommodates tall structures very well with the way that the structure is modeled by floor layouts which can be used on multiple levels (e.g., a typical floor only needs to be modeled once and then used on any number of stories). Each such story is using the same layout, not copies of that layout. The analysis also accommodates tall buildings by utilizing both in-core and out-of-core solvers. It also can make use of multiple CPU’s.
Q: Can RAM Structural System perform response spectrum or time history analysis?
A: Response spectra analysis can be performed, but time history analysis is not currently available.
Q: Can we use RAM Structural System for performance base design?
A: Yes, to a degree. Neither nonlinear analysis nor time history analysis is available in the RAM Structural System.
Q: Can we use RAM Structural System to analyze progressive collapse or disproportionate collapse?
A: While the process of removing columns is not automated, this can be done by going into the RAM Modeler and removing individual columns and then analyzing the structure, repeating the process as necessary.
Q: Are there any plans in future of implementing Indian codes in RAM Structural System?
A: We have been doing extensive investigation of the requirements of the Indian concrete, steel, wind and seismic codes in preparation to implement them in the program.
Q: Is it possible to perform Finite Element Analysis using RAM Structural System?
A: The analysis used by the program to distribute floor loads to the supporting beams and columns, and the tracking of the loads through the gravity members is more sophisticated than Finite Element Analysis, allowing for very complex framing and surface-, line- and point loads. In the analysis of structures with shear walls and/or semirigid diaphragms the program automatically meshes the walls and diaphragms, and performs a Finite Element Analysis of the walls, diaphragms, and frames. If you need to perform a FEA on an object (such as a connection assembly), STAAD.Pro is more suitable for that type of modeling and analysis.
Q: Can RAM Structural System be used for Pre-Engineered Building Structure?
A: The program is often used for such buildings. However, the lack of an ability to analyze and design tapered beams and columns may limit its usefulness in some cases. In that case STAAD.Pro or RAM Elements might be more suitable.
Q: Can it be used for industrial structures like stacks or chimneys?
A: The RAM Structural System was developed for the analysis and design of buildings. While it is possible to use the program for other structures, STAAD.Pro would probably be more suitable for stacks and chimneys.
Q: Can we model hollow concrete column in RAM Structural System?
A: No, not currently. Square, rectangular and round columns can be modeled, analyzed and designed. There has also been some consideration of implementing L- and C-shaped concrete columns.
Q: Can we produce working drawings out of RAM Structural System?
A: An extensive set of drawings can be easily created, including floor plans, column and beam schedules, frame and wall elevations, foundation plans and foundation schedules. Furthermore, interoperability with BIM programs such as AECOsim Building Designer and Revit, and detailing programs such as ProStructure is also available. IFC files and CIS/2 files can also be created.
Q: What is available for the design of concrete floor systems?
A: RAM Concept is for the analysis and design of one-way and two-way flat slabs/flat plates, with or without drop panels, and of one-way slab and beam floor systems. It is also excellent for the analysis and design of mat and raft foundations. More information on RAM Concept can be found here:
RAM Structural System and RAM Concept can directly share information. RAM Structural System can export the slab geometry, material properties and loads to RAM Concept, and after the slab design is completed RAM Concept can export the column loads and moments, including the unbalanced moments, back to RAM Structural System for the design of the columns.
Q: Is post tension design available?
A: RAM Concept is capable of doing both post tensioned slabs and mild reinforced slabs. There are powerful tools to aid in the determination of the ideal tendon layout and in determining the impact and extent of long term deflection and floor vibration.
Q: How do you design connections for truss members using RAM Connection?
RAM Connection can be run in three different modes: launched from STAAD, running a RAM Structural System database, and stand-alone. When run with STAAD or RAM the geometry, member sizes and loads are taken directly from the STAAD or RAM model. When run as stand-alone virtually any configuration of steel members and loads can be specified. Simple framing connections, moment- and braced frame connections, truss connections, and baseplates can be modeled and designed.
Q: Is there a literature source for further learning?
A: For an in-depth discussion on stability analysis (P-delta, member imperfections, out-of-plumbness, etc.) AISC has recently published Design Guide 28: Stability Design of Steel Buildings. Some of this information can also be found in the AISC 14th Edition manual’s Commentary on Chapter C.
An excellent article on the Geometric Stiffness method of P-delta can be found in Chapter 11 of Static and Dynamic Analysis of Structures by Edward Wilson. The text for that chapter can be found by performing a web search on “Geometric Stiffness and P-delta Effects”.
A previous webinar addressed stability analysis in greater detail. The recording of that webinar can be found here:
Q: Is a trial version of the software available?
A: Trial versions of the software are not generally available unless you are already a Bentley client. Bentley clients can download, install and run virtually any other Bentley product, even if they have not purchased licenses for the other software. In that case the program will be run for a trial period of about 10 days, without any charge. Unfortunately there is no mechanism for allowing access to these trial use periods to those that don’t already have a Bentley account.
Q: Where can we access the video presentation for replay purposes?
A: The recording is available here: