Description

This report presents the results of a computer simulation study to quantify the extent that torsion will increase wall deflections when New Zealand houses with plan irregularity experience earthquakes. Vertical irregularity is not covered in this study.

Houses were modelled in a non-linear computer package and subjected to time history earthquake loading. The floors and ceilings were modelled as rigid diaphragms. The walls were modelled as springs with load/deflection characteristics matched to wall test measurements. The maximum wall in-plane earthquake-induced deflections were plotted against the eccentricity of house mass.

It was found that houses with bracing wall layouts that only just met the minimum requirements of NZS 3604 may twist and deflect excessively. An alternative distribution of bracing elements in houses to limit torsional demand was proposed. This was found to be suitable.

It is recommended that a further study be done to investigate the torsional performance of construction complying with NZS 3604, but with the emphasis on vertical rather than horizontal irregularity. The effect of non-rigid floor diaphragms also needs to be considered.