RAM Steel Design Fy or Py

 Applies To 
 Product(s):RAM Structural System; Ram Steel
 Area: Design

Why are my beams being designed per the Canadian (or British) code with a Design Fy (or py) less than the Nominal yield stress assigned in the Modeler?

Please review the Ram Manager manual, section 2.4.7 Canada Parameters, 2.4.8 BS 5950 Parameters and the Ram Steel Beam manual section 10.4 Design Yield Strength.

To summarize, When using either of these codes for design, the steel material type for each type of structural member must be determined from a table. This steel type is combined with the nominal yield strength assigned to each individual member in the model to determine the steel grade and the design yield strength of the section.

For example, a section of type W with a nominal Fy of 350N/mm2 is assigned a steel grade of 350W. But, a nominal Fy of slightly less than 350 will result in a steel grade of 300W. Consequently, assigning a yield stress of exactly 50 ksi while using English / Imperial units, will result in a steel grade of only 300W being used, since 50ksi = 344.7 N/mm^2 which is less than 350.

Specifying a nominal Fy or material type that has no matching steel grade will result in a design yield strength of 0.0 and no grade assignment.

In the Ram Manager under Criteria - Canada Parameters (or BS 5950 Parameters) where the specific grade for various section types can also be specified.

For the example above, if the Material type A572/A992 is selected, then the beam will be designed with a Design Fy=50ksi

The same is also true when using Ram SBeam as explained in the manual for that program. 

For more on treatment of Class 4 sections in RAM Frame, see this article.

Why is the design Fy 0 when using Eurocode

Similar to the points above, in the Eurocode, per SCI Publication 362, there is alimited range of Fy values allowed depending on the nominal thickness of the material.

Ram Structural System conforms to this requirement, assigning a Design fy value of 0 to anything outside the range. 

This also affects steel design within Ram Frame (though the Design fy value is set to a tiny value just greater than zero there).

Why is the composite beam Design py value 355 N/mm2 when the Nominal py is larger?

According to BS 5950 1990 or 2000 codes, the design yield strength will never be larger than the engineer provided nominal yield strength. For composite construction, py is further limited to 355 N/mm2 as required by Clause 3.1.

Base Plate Design

A similar situation affects the Base Plate design in Ram Steel column for CSA S16-01 or S16-09 when using a Base Plate Yield stress (Fy) less than 260 N/mm^2 (38 ksi)

See Also