The influence of principal axes on dynamic behaviour of irregular structures

Abstract EN

The current seismic codes suggest that dynamic analysis should be performed in the principal directions for irregular structures.

However, they didn’t give any guidance for their determination.

This can lead to relatively weak structural design in one direction.

Therefore, the paper discusses the effect of geometric aspect ratios on the principal axes of L-Shapes irregular structures.

Three basic models, having regular geometric plan, are chosen to conduct this study.

They are five, ten, and fifteen stories.

For each model, the first change is only in the structure plan-configuration to form 15 cases of L-shape building.

Then the later variation takes place in the vertical configuration to form another 15 cases of L-setback buildings for each assumed setback height of 0.2, 0.4, 0.6 and 0.8 of the original height.

The total number of studying cases is 225.

Nonlinear Structural Analysis software and Statistical Software were used during this research.

Four numerical equations were developed to determine the fundamental time period, and the principal axes for both L-Shapes and L-setback irregular structures.

These suggested equations have accuracy not less than 80 %.

It is observed that, there is a significant effect on base shear value and consequently the straining action of the structure members, when performing the dynamic analysis in the principal directions of the building.

Therefore, it is recommended to use these developed equations for helping the structural engineer in performing accurate dynamic analysis.