Basement joists

This home is dated 1964, small ranch with exposed basement. A tornado came through and wiped out the main floor in 66. Question…just looking at these joists in the basement. A 2x4 with quarter in sides and 1x4 at the bottom. Making a 8x4 joists, but hollow. Anyone come across these before? As im writing this, the electrician steps into the house and says " oh this is a Harnishvager home" walls were made of plywood . Pre built homes. Still dont know how these hold up the house. Learn something new every day.

Harnischfeger also sought more ways to diversify in the 1930s and 1940s, making welding machines, welding electrodes, diesel engines, and even pre-fabricated houses.