Buckling length – failed so many times!

Buckling length – failed so many times!

In our practice, we quite often check existing buildings. This is to establish whether new loads can be added or whether, for example, a photovoltaic installation can be mounted. Often, we see calculations that were done 20–30 years ago, and often we find that the structure is already damaged.

Many years ago, RM-Win was the main software used in Poland to calculate 2D structures. It is great software, and we used it for many years too. However, there was one default setting in this software that caused many issues: the buckling length was equal to the real length of the bar. This could easily be changed, yet many designers have not done so.

In the pictures, we showed an exaggerated example to demonstrate the difference in results when the buckling length is between braced purlins (the correct approach) and when it is equal to the length between nodes. The ratio was 36% vs 215%!

Can this be repaired on site? Yes, but it will not be a cheap repair.