Open web steel joist

So imagine you have a big metal Lego block that looks like a rectangle, this rectangle is called an open web steel joist. It's used by builders to make floors and roofs for really big buildings - like big warehouses or factories.

The reason why it's called an "open web" is because if you turn it sideways, you'll notice that it looks like a spider web! These little steel lines make the rectangle really strong and sturdy - so it can hold up the weight of the building on top of it.

These open web steel joists come in all different sizes, shapes, and lengths to fit the buildings they are used in. They are also made using special machines that cut and weld the metal together.

So next time you see a big building with a flat roof or floor, you can think about how the open web steel joist helps hold it up!