A Critical Element in a Structural Steel Building

What are the structural elements does a steel structure holds?

A common answer would be the beams and columns.

Let us consider an industrial steel building to analyze its structural components.

From the above image, the major structural elements are rafters, columns, mezzanine joist (secondary beams), mezzanine beams, purlins & girts (for cladding support), and staircase stringers.

The interesting part is, we can easily design all these major elements using the STAAD package or similar software package. The only thing we should know is how loads get transferred from one element to another (i.e. what are the loads to be considered while designing each of these elements).

Understanding the load path and basic operation of any structural design software would suffice.

Then what is the most critical part?

“THE CONNECTIONS”

They are the most critical portion of any steel structure. The structural member may have sufficient strength, but if the connection does not meet the requirement, the member has no use at all.

Understanding how a connection behaves, what are the forces contributing to the connection, what are the connection parts to be verified makes it very crucial to design.

Say, for example, if you are designing a structural element, a mezzanine beam.

what are the checks we have to do?

1. The flexural capacity check
2. The shear capacity check
3. Check for Lateral Torsional Buckling
4. Slenderness check
5. Check for deflection

So, roughly 5 checks are enough to design a beam, which can be done easily with a basic understanding of all the above checks, and moreover, we have clear guidelines in the design code (IS 800–2007, if we are designing as per IS code provisions) to work with.

Now let us think about the connection of column and mezzanine beam - "Extended end plate connection" (Something similar to the following image )

What are the checks to be considered in order to design this connection?

There are around 15 checks to be done to properly design each and every component of this connection.

Herewith attached the checklist from “Joints in Steel Connections - Moment Connection”

Without understanding how the components in the connection behave, and the forces that need to be considered to work with this design checks, we cannot reach a proper design solution. This is where most of the designers commit a mistake. If the safety of a connection is not ensured, it may even lead to a major failure of the structure.

This makes the steel connections, the most critical portion in a structural steel building.

Link for a bonus article regarding a structural collapse of a steel catwalk is in the first comment.