This report, which was written by Des Bull of Holmes Consulting Group, indicates that in the light of the damage sustained to stairs and access ramps in the Christchurch earthquakes a review is need of the way in which these items are designed. It is clear that inadequate allowance has been made in the past for the relative movement that occurs between floors in a major earthquake. This report should be of interest to practicing structural engineers.
The report notes that in both previous and current design standards the displacements that stairs must sustain in a major earthquake are under-estimated. A method of determining the required design displacements for stairs in new buildings is outlined and an approach for assessing the required displacements for retrofit of existing stairs on the basis of existing design calculations is given.The report pays great attention to the inadequacy of designs for stairs and ramps. The types of shortcomings and failures that can result are described and illustrated. The conclusion of the report reads:
The methods of calculating inter-storey drifts for structural elements, that span between adjacent floors, given in current and previous new Zealand structural design standards has lead to an underestimate of required displacements that need to be accommodated at supports of stairs and ramps, in major earthquakes. Experience in the Christchurch earthquakes has shown that this has been a major factor in the collapse of a number of stairs and the damage of many others.The report is here.