Using SJI Virtual Joist Girder Tables
A set of tables representing Steel Joist girders is available. Bentley does not warrant the suitability or accuracy of the Virtual Joist Girder tables. The data was provided by the Steel Joist Institute (SJI), and formatted to conform to the table format requirements of the RAM Structural System. The engineer should understand the purpose of the tables, the assumptions made in creating the tables and the limitations of the use of the tables, and should verify the results to his/her satisfaction. Refer to the documentation on the Virtual Joist Girders produced by SJI, currently available on their website at www.steeljoist.org. Technical questions on the Virtual Joist Girder tables or the designs produced should be directed to SJI.
It is the engineer's responsibility to use these tables properly; no warnings are given by the program if they are assigned to the wrong type of members, or to members with unsuitable properties, or with the wrong Criteria selections. It may not be apparent from the designs produced that there was an error in these selections.
To use the Virtual Joist Girder tables in the RAM Structural System, the following is recommended:
In RAM Manager
Select the RAMAISCwithVJG.TAB as the Master Table.
Select RAMVJG.BMS as the Alternate Beam Design Table.
In RAM Modeler
Model the joist girder as a Noncomposite Steel beam, with Fy = 50 ksi. Do not model it as a Steel Joist (that will use the program’s Joist Girder selection routines, not the special Virtual Joist Girder table). Note that if the beam is assigned to be a Composite beam the resulting design will be unconservatively incorrect.
Using the command, assign the girder to Use Alternate Steel Table. Only girders or Frame beams should be assigned to use this table.
For best results assign a maximum depth restriction, otherwise the sizes selected may be excessively deep (the table has joists with depths ranging from 20" to 120"). Setting a Maximum Span/Depth Ratio in RAM Steel Beam may also be helpful, although that Criteria option affects all beams, not just the Virtual Joist Girders. SJI recommends that the depth be no greater than 1/12 of the span and no less than 1/24 of the span (span/depth ratios between 12 and 24, with the most economical between 12 and 18).
SJI recommends that for Gravity members the member be designed assuming an unbraced length of zero. This can be approximated by assigning very close brace points to the girder (if the distance between brace points is less than the value of Lp calculated for the size, the design is the same as if unbraced length is zero).
In RAM Steel Beam
The table is only valid for AISC 360, no other design codes should be specified.
Virtual Joist Girder sizes will be included in the Takeoff, but it should be noted that the weight listed for these sizes does not include the weight of the web members and miscellaneous materials. These add approximately an additional 15% to the total weight.