I had a number of these sets when I was young and spent most of my time converting every bit of space in my bedroom into construction zones.
Kenner Products was a founded in 1947 in Cincinnati, and introduced its popular Girder and Panel building sets in 1957. Kenner was one of the first companies to recognize the potential of TV for advertising their toy products in the USA, the first ads airing in 1958, when these two sets first appeared:
The Kenner Toy Company made many different types of sets from the late 1950's until well into the 70's. The plastic pieces resembled steel girders, window panels, roofs and roadways, and allowed young hands to build large structures in a very short time. Some sets even included water pumps and plastic tanks to make chemical plants, while others featured electric motors and mechanical parts. Later sets featured powered monorail cars. They were great fun for kids and a blessing to parents who could watch the little demons disappear into their rooms and emerge only at mealtimes.
Girder and Panel sets #1, #2, and #3 were the first come on the market beginning in 1958. Set #1 contained the least number of parts, #2 had more, and finally #3 had the most. Early production runs in 1957 contained girders made of styrene plastic which was rather brittle. Soon angry parents and frustrated kids were up in arms about breakage of the small dovetails and pegs. Fortunately, high-density polyethylene (HDPE) plastic was just becoming available and Kenner began using it to manufacture all new parts
The parts in these sets formed the basis for all sets that would follow. Primary to building were the plastic girders, in both the vertical columns and horizontal beams, and the large ugly, green masonite bases. For buildings, window and roof panels covered the outside surfaces (and also added strength). To dress things up, store signs, flags and flag poles were added.
These sets were the early entries that exposed most kids of the time to the world of building. American Bricks and Lincoln Logs did not stick together and Lego would not see entry into the U.S. for nearly another 10 years. Most of us had a least one of these early sets before advancing on.