Greetings,
Regarding the new check which was recently added to Limcon Based on Ref.70 (Gusste Plates in Steel Bridges), which resulted in unrealistic and uneconomic gusset plate sizes for both Bracing gusset plates as well as Fin Plates.
We have reviewed AISC Steel construction Manual 13th Edition - Part 9 and the above mentioned paper for Gusset Plates in Steel bridges and we have the following comments:
The used reference is not a solid one, since it is just a paper (report) done by an individual and it is not adopted by any Design Guide or Design code.
The paper is related to Bridges’ design not to Conventional structures.
The Part of the paper talking about von Mises stress section 3.7.d Buckling of Gusset Plates, is investigating gusset plates behavior in the compression Zone, however Limcon is checking von Mises stress using same equation regardless the nature of the applied load (Tension or Compression)
The Paper is investigating von Mises stresses whenever the stresses of any two given diagonal members intersect, i.e. there is an overlap of stresses in the gusset plate, however Limcon is applying in the equation regardless whether the stresses’ zones are intersecting or not.
As per AISC SCM13 Page 9-4, “Thus, what might appear to be a more sophisticated approach to the analysis and design of a connection does not necessarily add any reliability to the resulting design”, accordingly as per AISC this additional sophisticated check does not add any reliability to the connection design.
Moreover, please note that this check is resulting in catastrophic financial impacts on old projects, currently running projects, since some of the projects were already priced based on the old version of Limcon without this check, and currently it is gusset plates sizes is more resulting in financial losses in such cases.
In addition to the complications while getting approval from consultants using updated versions of the software while the design was done by the old versions, which resulted in some of the connections are failing in front of the consultant while it is passing in the companies version.
You are kindly requested to provide more clarification about this newly added check, since it is resulting in a lot of complications in designing and checking of gusset plates, meanwhile kindly remove this check from gusset plates and fin plate design until more investigation is done, or at least make this check optional.
Finally we are sorry to tell you that such approaches of using nonsolid references without studying its financial impact on the companies using the software; might result in losing our confidence in the software, leading us to using other tools other than Limcon in connection design.
Best Regards,
Hassan Elamir
B. Sc. Structural Engineering
Thank you for your prompt reply, we need your support regarding the following points:
We are currently working on several projects using Limcon on daily bases, please advise how to overcome such check, can you release an urgent release of Limcon which does not include this check until the issue is corrected.
Checking the connection based on Ref. 70 to be an optional check not a compulsory one, i.e. the user has the choice whether to apply Ref. 70 for Bridge connections or not, by using check box in “General Configurations” same like the one for checking splice outer bolt row check.
We noticed that Limcon does not check the supporting members in bracing or trusses connection, accordingly we are doing this check manually, kindly advise when can this check be available in Limcon.
Please advise how to download Limcon updates, previously there were a download location and in order to install there were a password, please advise what is the new system after the software was acquired by Bentley.
We are trying to push the updated Limcon release to Software Downloads as soon as possible. It will have a correction to the Whitmore section calculation, but it won't make this check entirely optional.
New enhancements for connection design will all be put into Ram Connection development and that program will be replacing Limcon once it has all the same codes and functionality.
The company I'm currently working for on a big airport project has both Limcon and Ram Connection software. One of the connections we're finding very useful in Limcon is the one described as 'KT gusset plate connection' - gusset welded to top flange of a UB or UC beam - with the brace category as '25: slotted HSS welded to gusset plate'. Used for a large number of truss girders with UC chords and HSS web members.
Can anyone tell me whether Ram Connection has a direct equivalent of this connection - and, if so, what is it called, how do we find it in Ram?