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Bracing System - Structural arrangement that ensures stability in Longitudinal Direction

What happens to a building when it is subjected to wind loads? Any building or structures, in general, must ensure stability in two directions (Lateral & Longitudinal) to safely transfer loads from the location of application to the ground. Considering a typical steel warehouse building something similar to the following image, when it is subjected to wind load along the lateral direction, stability is ensured by the portal frame action. Lateral Direction - Along width of the building Longitudinal Direction - Along Length of the building The column and the rafter connected using a rigid joint act as a portal to sustain the lateral loads that act on the building. So, the building is fine in the lateral direction. What if the wind blows in the longitudinal direction?  How longitudinal force gets transferred through the system? In the longitudinal direction, when the force acts on the gable ends of the building, the first component to interact with the load is the cladding materials (

The most CRITICAL structural part in a steel structure..

What are the structural elements does a steel structure holds?

As similar to every other building, the major load-carrying members in a steel structure are columns and beams.

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) 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”[3]

Without understanding how the components in the connection behave, and the force to consider to work with this design checks, we cannot reach a proper design solution. This is where most of the designers commit a mistake.

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

Comments

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