When are top surfaces of bearing plates not required to be milled?

The correct answer pertains to the requirement for milling the top surfaces of bearing plates in relation to the type of welds used. When complete joint penetration groove welds are provided, the top surfaces do not need to be milled because the weld creates a continuous and strong connection between the components that is capable of providing adequate bearing and load transfer. The integrity of the joint is maintained through the quality of the weld rather than through the surface flatness that milling would provide, ensuring that the structure's performance is not compromised.

In contrast, the other conditions listed do have situations where milling may still be necessary to ensure proper load distribution and fit. For instance, the presence of bolts implies the need for precise alignment and surface preparation, which typically includes milling. Similarly, while painting or coating can offer protective properties, these finishes do not address the mechanical interlock needed for load-bearing surfaces to function optimally. Therefore, the provision of complete joint penetration groove welds stands out as the specific condition under which milling is not required.