Impact of seismic demand on construction costs for buildings up to 8 storeys high

The legally binding earthquake performance requirements in New Zealand's Building Act and Building Code emphasise building collapse prevention, allowing for a certain degree of damage to resist the seismic load. However, societal expectations demand that buildings remain operational after an earthquake. This research aims to understand the true cost of up to 8 storeys high building structures that remain operational after an earthquake. Our assumptions are: 1) higher seismic demand is expected to have a limited impact in overall construction costs, and quite minimal impact on total development costs, and 2) the influence of seismic resilience on construction costs is different depending on the structural system. An extensive construction costs database was developed including the most typical structural and foundation systems. The main conclusions are that 1) the effect of location and floor type on construction costs is not critical, 2) the impact of a higher seismic demand on construction costs depends on the structural system, and 3) foundation type has a large influence on construction costs but seismic demand does not. Engineers should prioritise stiff lateral systems because the cost implications of having a stiffer structural system are minimal, especially when considering the development costs. The cost implications of having more resilient buildings that can be readily occupied after an earthquake are negligible, and New Zealand should move towards stiff, damage resisting structures using well understood structural systems like RC walls.  Society expects this from our buildings, our engineers are trained and capable to design them, and the extra cost is minuscule.