I am looking at the requirements of the beam at the second story of the chevron BRBF. Why is RAM Frame checking Beam ductility using the Diagonal Brace requirements of AISC 341-16? The output clearly says it does not check the axial demand in the beam, therefore, it should have a h/tw or 59.42 requirement. I am frustrated that this output does not clarify what additional checks need to be done as well. Per AISC 341-16 Table 1-3, the beam I design (W24x62) meets ductility requirements, yet in RAM Frame it pushes my beam size up to W24x131 before it meets the wrong ductility requirement.
It's not that we are assuming no axial force, it's that we just are not calculating Ca for beams. But I take your point. We are taking the conservative assumption from D1.1. I'll check with the developers to see if they have any bright ideas for how to do it more accurately allowing for any configuration of braces and diaphragm types.
Table 1-A is on page 1-31. The RAM Frame output says that it is not calculating any axial forces for this check, hence, a beam with no axial forces would fall under the limit of Ca<0.114 and with Ry=1.1 the limit is 59.42 for the web ductility check. What RAM Frame is giving is the worst case scenario with Ca >0.114. I don't want RAM SS telling me my design fails ductility checks when it is not even including the axial load condition.
Sorry, I posted the wrong part of table D1.1. Here's the part for beams:
As you noted, to do this properly would require this Ca term. Since we don't calculate that accurately we use the lower bounding value of 1.57 (root (E / RyFy)). The report confirms as much:
I don't see any Table 1-A in AISC 341-16.
Please refer to Table 1-A on page 1-31 which clearly delineates the limits by element type.
Sorry, but I disagree with that interpretation. If you read in the second screen shot you sent of Table D1.1 to the very left (Description of Element), it describes those as specifically being Diagonal Braces. If you continue down the table, the correct limits are applied for Beams below. These limits are different based on axial load in the beam, but nonetheless RAM Frame is incorrect in its application.