For simplicity, I start all of my basic calculations for mild carbon steel at Fb=0.6Fy. Even if I apply 0.75Fy per AISC 9th (F2-1), the conservative 300 lb point supported by a pinned end connection, still exceeds that Fb that a 3/4" dia A36 will provide.
Through the use of the intent of this forum, considering the section props of the side stringers, I have concluded that, with all-around fillets I will consider the end connections as fixed, which, by far, exceeds what is Fb.
Last thoughts; Yes, ladders have long been considered a proven miscellaneous structure. I appreciate that. However, considering previous comments, we tend to be conservative for various reasons. For those who may want to consider wider ladders with longer rung spans, not necessarily wanting to increase the 3/4" bar size, having formerly worked for a fabricator, I have seen ladder rungs inserted into holes in the siderail stringers and then either filleted on the inside or butt welded on the outside. Something to consider ...
Thank you all for you input ...