Final answer:
The transport beam under the lift arm assemblies of the MJ-1 series lift truck provides structural support and stability, similar to the function of ships' superstructures or the steel core in overhead power cables.
Step-by-step explanation:
The purpose of the transport beam beneath the lift arm assemblies on the MJ-1 series lift truck is to provide structural support and stability when lifting and moving heavy loads.
Similar to how ships' superstructures provide integrity to the vessel or how container vehicle bodies support the cargo, the transport beam's role is fundamentally about ensuring that the lift truck can perform its tasks without structural failure.
In the realm of engineering, this concept is akin to the use of overhead power cables with a steel core, which are designed to be strong enough to carry heavy electrical loads over long distances without sagging or breaking.