Featured Post

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 (

What is so intriguing about Mono-pole Traffic Signboard? - Bi-Axial Bending...

When it comes to structural behaviour, the technical terms might sound a bit complicated, but actual behaviour is NOT.

I am moving forward with the assumption that you know the basic concept of bending.

“Biaxial bending of a member is nothing but the bending of a member in both the axis simultaneously because of the applied load.”

In general, it is same as a beam or column bending which takes place because of the applied transverse load. The only difference is that it occurs in both the principal axis, hence the name “Biaxial Bending”.

This can be easily seen in columns. Especially in the monopole structures. (Monopole is a structure which is composed of only one column. For example, traffic signboard, transmission towers, street lights, etc.)

For our easy understanding, let us discuss this particular behaviour with an example.


The above image shows a traffic signboard with a monopole column. Moving little deeper into the behaviour of the column, lets first fix the principal axis.

For the general convention of the axis, let's take the fog line on the road (continuous white line on the side of the road) as global Z-axis, and the one perpendicular to it is the global X-axis.

Now, let us see how bending would arise in both these directions.


Firstly, bending about global Z-axis would occur because of the cantilever beam which is rigidly connected to the column end. This cantilever beam holds the signboard, that means, those dead load of the signboard will act on the cantilever beam which in turn gets transferred to the column top joint as “vertical load” and “equivalent moment” along Z-axis. This moment induces a bending of the column about that axis (Z-axis).


Moving to the X-axis, as you can visually see, the surface area of the signboard which is likely to subject to the wind load. Assume that, the heavy wind is blowing, the widespread signboard is standing against that. What probably would happen?

The wind that hits the signboard in the direction parallel to Z-axis would result as “horizontal load” and “moment” along X-axis. This is how the bending about X-axis arises in the column.

As it is evident that these two load cases will simultaneously occur in the signboard structure.

What would happen next?

It will bend in both the directions (biaxial bending).


Post a Comment