In Professional Engineering, Mechanical Engineering and Structural Engineering are different in a few areas:
Structural Engineers primarily focus on engineering systems of structures specifically for site locations to withstand natural and manmade force conditions, such as loads from Dead Loads, Live Loads, Snow, Rain, Ice, Seismic, and Wind.
Mechanical Engineers generally design more explicit systems when components do not repeat as often as Structural Engineers, but span a broader range of mechanical functions and technical fields.

A licensed Professional Engineer in Mechanical Engineering should not engineer significant structures without further becoming licensed as a Structural Engineer. Here at Quanta Engineering LLC, we provide Structural Engineering that falls within the scope of a traditional Mechanical Engineer. These non-significant structures are generally non-repetitive structures.