Hi everyone,
I have been using RAM Steel Column in the CSA S16 for the design of some WWF sections (required due to limits on column dimensions and our high loading) and are finding the Cr values (Compressive Resistance) calculated using RAM Steel Column for WWF sections to be incorrect. The Cr values for W sections work fine.
I have specified the WWF sections to be Flame Cut Plates in RAM Manager under the Canada Parameters option. According to clause 13.3.1 of CSA S16, for doubly-symmetric welded three-plaet members with flanges oxy-flame-cut , n = 2.24.
Our case is where our section is a WWF350x315, our K = 1, L = 6.6 m (==>KL/ry = 70) and Table 4-30 of the CISC Handbook of Steel Construction (9th ed., 3rd revision) shows the factored axial compressive resitance to be 9880 kN. This is while RAM Column shows it to be 6772 kN!
Another way of checking our calculations would be by using Table 4-5 (page 4-17) of the handbook for KL/ry of 70, the Cr/A = 247, (A = 40200 mm2) ==> Cr = 9929 kN, so RAM seems to be off by 40%!
I wondered if the program incorrectly uses n = 1.34 , but using Table 4-4 (page 4-14) of the handbook, leads to a Cr of 8080 kN.
Does RAM Steel Column design the WWF sections incorrectly here?
Thanks for your help!
Cheers,
Ed
Thanks Seth for looking into this really quick.
Cheers, Ed
Here is some additional information for anyone else interested in WWF Column design per the Canadian design standard.
In the third paragraph of page 2-35 of the Commentary (the commentary for Section 13.3.1) there is some discussion about when a reduced value, n=1.00, should be used. Currently the program always uses n=1.00 for built-up shapes, including WWF’s. So the capacity values Cr that you are seeing in the reports for WWF’s are based on n=1.00. However, WWF’s are fabricated of flame-cut plate rather than mill plate so that restriction should not be getting applied. We will make the correction to the program.
A work around is available upon request from the Technical Support Group by submitting a service ticket online.
We’ll probably need to take a closer look at your model and replicate the program calculations. Please create a service ticket online. Include your model and the original information in this post.
appsnet.bentley.com/.../addcall.aspx
Yes Seth. As I had mentioned in my post, I have the Built-Up control in Canada Parameters set to Flame Cut.
Appreciate your help on this in advance Seth.
In RAM Manager, Criteria – Canada Parameters do you have the Built-Up control set to Flame Cut? Here’s the help topic from that section:
Canada Parameters
Steel Material:
The steel material type (based on Table 6-3 from CSA G40.21) for each type of structural member must be selected. This steel type is combined with the nominal yield strength assigned to each individual member 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. A nominal Fy of slightly less than 350 will result in a steel grade of 300W. Specifying a nominal Fy and material type that has no matching steel grade will result in a design yield strength of 0.0 and no grade assignment. A steel of unknown grade should be designated as a ‘?’ (unknown) steel grade and the program will use the assigned nominal Fy value for the design Fy.
Built-Up:
Flange sections can be designated as being built-up of universal milled plate or of flame-cut plate. The type of plate has an impact on the axial capacity of the section in both RAM Steel Column Design and RAM Frame, as described in CAN/CSA-S16-01 Section 13.3.1. Sections of type WWF are considered to be made with flame-cut flange plates, in accordance with G40.20.