New seismic assessment standards and NBS ratings: What property owners need to know
Revision of Section C5 of MBIE Seismic Assessment Guidelines
PROPERTY OWNERS, ENGINEERS AND COUNCILS should be aware Section C5 of the MBIE Guidelines for seismic assessment of existing buildings has been revised and is referred to as the Yellow Book, released in 2018. The initial July 2017 version is known as the Red Book.
Red and yellow book covers
The use of the Yellow Book can lead to very different seismic assessment results compared to the Red Book. The main effects of the change from ‘red’ to ‘yellow’ are summarized as follows:
Using the Red Book, only the vertical lateral force resisting system (e.g. walls and frames) in many existing buildings were previously assessed, but the floor systems were not assessed or rated specifically. Based on the Yellow Book, the overall ratings for these buildings will likely be significantly lower.
Concrete frame buildings (pre-1996) that have precast floors with a very short seating width will likely have lower ratings due to the lateral drift capacity exceeded.
Any concrete buildings (post-1976) that have non-ductile or cold-drawn steel mesh in the floor slabs or walls will likely have significantly lower ratings due to wires that can be stretched further and can break suddenly to cause collapses.
Concrete frame buildings (pre-1976) may have lower ratings due to better assessment of the column shear capacity.
Concrete buildings that can perform in a fully ductile or limited ductile manner will likely have higher ratings. Ductility means the extent to which a structure can undergo large deformations in a stable manner. However, precast floor systems need to be assessed carefully and may limit the overall ratings.
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