| Applies To | |||
| Product(s): | RAM Structural System | ||
| Version(s): | 10.0 and later | ||
| Area: | Modeling; Design | ||
Can mat foundations be designed in RAM Foundation?
Mat foundations cannot be designed in RAM Foundation. Mat foundations modeled in RAM Structural System can be exported into RAM Concept for analysis and design using the Ram Manager - Design - Ram Concept option or from within Ram Concept using File - Sync Ram Structural System - New from RAM SS.
The estimated perimeter of the mat must be modeled to encompass all of the supported columns and walls, and some concrete deck also needs to be assigned to the mat in Ram Modeler.
See the following web page for more on importing RAM Structural System models into RAM Concept:
RAM Concept-RAM Structural System Integration
I can't assign base plates or anything else in the Foundation module, what's wrong?
Though foundations are designed in the Foundation module, they must be initially modeled like everything else in the Modeler. Rather than having a whole extra level type for foundations, we expect users to model foundations (using Layout - Foundations...) on the lowest framed level (e.g the second floor framing plan).
How is 1/3 overstress accounted for?
The allowable soil stress assigned to the footing is constant for all combinations. So, there is no good way to accommodate 1/3 allowable overstress in the design if it pertains to some, but not all of the load combinations.
We suggest incorporating the equivalent allowable overstress into the soil combos, by using reduced load factors on the combos with short duration loads.
Alternatively, the model could be designed twice; once with only gravity combos and a lowered allowable soil stress, once using gravity and lateral combos with the higher allowable.
How is uplift and overturning design done for spread footings?
See this blog post for details: Spread Footing Overturning and Uplift Checks in RAM Foundation
Why does the required area of steel increase when I use larger diameter bars?
In small foundations, the longitudinal bars are only partially developed at the critical moment location. When the program reports the area of steel required it is increasing the value reported by dividing by the percentage of full development. This is also true for reinfrocement that is required as a code minimum for temperature and shrinkage. With smaller bars the development length is shorter so less net area of steel is commonly required.
This check can be circumvented by assigning the bars to be hooked (Assign - Geometry command)
The same rule also affects continuous footings in the transverse direction.
How are the foundation loads determined for a column in a wall?
When you have a wall on a continuous footing, and a column (pilaster) on the same centerline, but placed on a separate single column foundation (pile cap or spread footing), the forces in the column at the bottom are attributed to the spread footing and the wall forces are attributed to the continuous footing. The amount of the force that goes through the column vs the wall depends on the relative rigidity of those objects in the Ram Frame (or Ram Concrete) finite element model. See also [[Ram SS Walls FAQ]]
There is not an override to force point loads or upper column reactions through the column pilaster only. You can isolate the column, by shifting the wall to the side for example. It might also be achieved by making the wall very soft relative to the column so that the forces remain in the column. Or you can run a version of the model without the bottom basement wall level and place footings directly under the higher columns.
Why are there two options for the forces from gravity columns only?
The Criteria - Forces dialog has an option for the Gravity load forces to use for gravity column foundations:
But, of all the Analysis Types we do in RAM Structural System, only Ram Frame produces results for lateral loads (Wind, Seismic, etc). To maintain consistency in the stiffness matrix we therefore always use the forces from Ram Frame for lateral column (and wall) foundation design.
Are foundation design live loads reduced?
Yes, the Foundation module uses the same live load reduction values for columns.
For lateral columns, the foundation loads should match Ram Frame analysis results.
For gravity columns, the loads can be taken from either the Ram Steel analysis results or the Ram Concrete analysis results, both of which are subject to Live Load reduction. See RAM SS Analysis Types for reasons why those two results can differ. See RAMSS Two Way Decks for limits on LL reduction for two-way decks.
Why are the continuous foundations so wide for very long walls?
In RAM Foundation, all of the force of a wall segment is applied to the continuous foundation at the center point of the wall. When a wall intersects a footing (i.e. a perpendicular wall), the forces on the walls are resolved into two end reactions considering the wall segments as a simple beam. Having a large reactions from a perpendicular wall near the end of the footing often results in a long continuous footing extension.
To minimize these effects, walls can be further segmented in RAM Modeler. So instead of drawing one 100 foot wall, four 25 foot walls can be drawn in its place. Naturally the smaller the segments, the better distribution of load you will get.
For shorter walls in groups, like an elevator core, we recommend modeling a single mat foundation under the group of walls and designing that with Ram Concept.
In v15.03.00, a change was made so that the load from the intersecting wall are no longer considered in the design of the continuous foundation in the other direction.
Why are spread footings sometimes optimized larger than required when there is uplift and high punching shear?
The size of the spread footings are first optimized for uplift and then their thickness is increased to meet any punching shear requirements. If you assign the footing the thickness needed to meet the punching shear requirement, the optimized size of the footing will be smaller.
How can I model a grade beam?
Refer to Modeling Grade Beams
Is sliding checked in spread footing design?
No, sliding is not considered in the Ram Foundation mode of RAM Structural System. Column shear forces are only considered when the option for additional overturning moment from V * t is checked.