Most structural steel failures happen at connections…. where a beam connects to a column, where a joist connects to a beam, where a hanging rod connects to a beam (the Kansas City Hyatt discussed above). The Structural Engineer must design the design the steel members and give guidelines for the connections. Many people in the Construction Industry don’t understand, though, that the Structural Engineer rarely designs the connections. Why is that?
Historically, the Steel Fabricators developed many different ways to make connections. What one Fabricator did in his shop economically might have been quite an expensive way to do it in a competitor’s Fabrication Shop. So the practice developed that the Structural Engineer would size the members, but the Steel Fabricators would design the connections, which the Structural Engineer should then review and approve. If you think that seems like a complicated system prone to error, you’d be correct.
But that is the system we generally have in American construction. So the Construction Supervisor should know something about steel connections and have an idea if they are being installed correctly. A bit of background in Basic Structural Design is helpful, but the main thing to understand is the concept of pin connections versus fixed connections. A beam bolted to a column with clip angles along the beam web likely creates a pin connection.
This means that the beam shouldn’t be able to move up or down, nor in or out, but it can rotate a bit. A steel column bolted to a concrete pier with four anchor bolts also typically creates a pin connection. Again the steel column won’t go up, down or sideways, but it may be able to rotate a bit. The fixed connection must stop that ability to rotate. So for a beam to have a fixed connection to a column, along with clip angles, there may be a plate on the top and bottom flanges of the beam that gets welded to the column.
With all that welding, the beam can no longer rotate. If a steel column is buried four feet deep in a concrete pier, it also would not be rotating at the point that it exits from the concrete. So those are a couple of ways to create fixed (or moment resisting) connections. The Construction Supervisor should be aware if any fixed (or moment resisting) connections are required and understand how they are to be made. Just asking the questions increases the likelihood of a successful project.