RAMSS Gravity Loads [FAQ]
| Applies To | |||
| Product(s): | RAM Structural System | ||
| Version(s): | 9.00.XX - 14.XX.XX | ||
| Environment: | N/A | ||
| Area: | Modeling | ||
| Subarea: | N/A | ||
| Original Author: | Bentley Technical Support Group | ||
Are the applied surface loads cumulative?
No, in RAM Structural System only the top applied surface load counts. The underlying loads are not deleted however, so if you delete the top load you can see the original load underneath. If too many load layers are applied to a model, a polygon error can occur when processing the loads. For this reason it is always best to remove any existing surface loads before modeling new layers.
Also note, this is different than the behavior in RAM Concept. In that program, overlapping surface loads are cumulative. Consequently, when Direct Gravity loads are imported from RAM SS into Concept, they are converted into equivalent separate polygons that do not overlap.
Is the structure self-weight included in the loads?
That depends on the settings under RAM Manager - Criteria - Self-Weight. Here the user can automatically include beam, column, wall or deck self-weight. Note, open web steel joists self-weight is never included.
For composite beam design, the self weight is always considered part of the Construction Dead Load. Hence, if all the self weight options are turned on, and there is no other load present during construction, the user applied CDL might be zero.
On the right hand side of the dialog box are the settings for self-weight as it applies to the building mass which is used for seismic loads, dynamic analysis and for P-Delta calculations.
In order for the steel gravity beam and column self weight mass to be considered in RAM Frame, it is imperative that those modules be run first, using the design-all process. So long as the RAM Manager indicates a green light next to each of those modules, RAM Frame should have the latest member self weight data available.
Note, in RAM Frame, under Loads - Masses, the program calculated diaphragm mass totals can be overridden with User Specified values, normally using calculated masses is advised. There is a similar dialog box for the total Gravity Loads which is used to determine program generated notional loads.
HowistheselfweightofConcreteBeamdetermined?
Theprogramcalculatesrectangularbeamunitself-weightbasedontheareaofthebeamtimesthe"UnitWeightofSelfweight".Theother"UnitWeight"parameterisonlyusedincalculatingtheelasticmodulus,E,ofthemember.
TheConcreteslabcanindependentlybeincludedintheselfweight,soincaseswherethereisaconcreteslabandrectangularconcretebeamstheweightoftheconcretetimesthethicknessoftheslabandthewidthofthebeamisdoublecounted.
Toalleviatethisproblem,"T"shapedbeamsectionsarehandleddifferently.WithTbeams,it'sonlytheareaofthestembelowtheslabthatisappliedasthebeamselfweight.
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Why are my Roof Live loads ignored in the design?
RAM Structural System currently considers Snow OR Roof LL, but not both at the same time. In RAM Manager under Criteria - Members loads there is a toggle to select which the program should consider. Set the toggle to “Consider snow loads, Ignore roof live loads” when snow loads are modeled.
Note: Live Reducible, Unreducible and Storage type loads are always considered, it is only the Live - Roof type loads that are excluded when the option to consider snow loads is turned on.
Are my snow loads automatically added to the building weight for seismic load determination?
No, the program only uses the assigned Mass Dead Loads plus whatever self-mass options are turned on under RAM Manager - criteria - self weight when determining the total building mass or weight used in Seismic load determination (and in P-Delta calculations). The user should increase the Mass DL of applied surface loads to account for the weight of the snow load (or a percentage of the weight as required.
Note, the provided templates for load combinations do correctly consider snow load acting simultaneously with Dead, Live and Seismic loads, however.
This also applied to Storage Live Loads, even if the magnitude entered for the Storage Live load is large (e.g. > 125 psf) no portion of the storage live load is automatically considered in the seismic mass. The user must increase the Mass DL (or manually alter the masses in Ram Frame) when part of a storage live load needs to be added to the seimsic mass.
How can I apply a drift snow load?
Within the snow loads, only the top load counts. Since only the top snow load counts, the drift snow load should typically taper down from the max value to the flat-roof snow load as a minimum. The program gives a warning when any portion of the sloping plane of snow load is 0 or less magnitude.
In general, it’s best to define snow drift loads with M1 and M2 set to the highest value, and M3 set to the flat roof level. Then the loads can be applied in rectangular or trapezoidal areas as required. In the image below, the total snow load on the left is 50 psf tapering down to 30 psf on the right. This would be used in conjunction with a flat roof snow load of 30 psf applied first to the whole roof.
See Also
Structural Product TechNotes And FAQs
External Links
Bentley Technical Support KnowledgeBase
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