Steel is a very complex object and the physics and knowledge that goes into constructing a building out of steel is amazingly complex. For example, steel literally sways in the wind and is designed to do so! There is a building in China called the Taipei 101 which is designed with a 730 ton ball connected to the steel structure to mitigate any seismic effects when the building sways, like it is designed to do. This will be discussed in depth later down the road but for now the focus is going to be aimed at the simple topics like common terms, load paths, and connections.
Common terms are key when trying to understand what is being discussed. The most common terms used are going to be girder, column, bar joist, live load, dead load, point load, and uniform load. There are many more that will be covered in the “Terms” section, but these are slightly more important. A girder is a large steel beam used to support bar joists and act as a main part of framework. A bar-joist is a smaller beam of steel that acts as a connection between girders to support a floor, roof, etc. A column is a piece of metal (can be large or small) that holds up a girder and rests vertically on the ground. A Live load and dead load are very similar with one key difference, their ability to be taken out of the building. A dead load is the weight of the building itself: the material, the joists, the concrete, everything that is permanently part of the building is a dead load. A live load is anything that can be removed or added, i.e. people, desks, chairs, tables etc. A point load is a load that puts weight in one specific point on a girder or bar joist, and a uniform load is a load that spans a certain distance of a girder or bar joist. The quick, hand drawn picture below can offer a visual to those who are visual learners.
A load path is basically the way a steel structure handles weight, disperses it to the sides/center of the building, and then how the load is transferred into the ground. For example, if there is just a simple structure that looks like a square without the bottom line, then the load path would be simple. The top girder or beam would disperse the weight of the load across to the support columns on the side which are then shot into the ground. As a reference The picture posted below shows how a structure with five columns, and two Girders would handle a five ton load and what the load path would look like. The path travels in a relatively simply manner but when the building is big enough, the load path becomes much more complex.
Connections are definitely the easier of concepts to understand, simply because there is set ways of doing it. The most common practice is to weld connections when fabricating a connection in the shop, and bolting connections while in the field (The actual job site). Bolting is the preferred method for connection while on site. There are two ways to ensure a bolt is done correctly, that is to either snug-tighten them, or have a slip critical bolt. They both act as a high strength connection and differences range between specifications given for the specific connection being made. Another way steel can be connected is through welding, however the costs and labor time required to perform welding keep it from being more popular than bolting. If welding, however, it should be performed on bare metal, and the weld material should have a higher strength than the metals being welded together. Shop welding is much more preferred over field welding though. Shear connections are very prevalent, if not the most prevalent form of connections in steel framing. Shear connections are a webbing that connect any member to another member that will then be subject to shear forces (Forces that try to shift two objects apart). An example of a shear connection is shown below in blue.
If you have any questions, feel free to always ask!