Repairing SLS anomalies in NZ seismic code to reduce earthquake losses

Thomas (Tom) A. Moore
2018 Bulletin of the New Zealand Society for Earthquake Engineering  
The 1992 advent of the Serviceability Limit State (SLS) was for the purpose of eliminating structural and non-structural damage to buildings subjected to small or moderate Earthquakes (EQs). This goal complimented the prior 1976 goal of minimising life-loss due to large Ultimate Limit State (ULS) EQs. However, moderate direct damage and large indirect losses occurred to many medium-rise pre-2004' precast concrete-framed buildings in Christchurch and Wellington CBDs as a result of small or
more » ... t of small or moderate EQ ground motions in 2010 [1-3], 2013 and 2016 [4-6.] A precedence for a proposed SLS level 1 upgrade was set when Christchurch upgraded to a 50 year recurrence SLS following the 2010-2011 earthquakes [7]. Many modern buildings have been engineered with little regard for SLS [8] nor the goal of eliminating disruption from moderate EQs [9, 10]. The proliferation of SLS building damage and large indirect losses [1] have arisen in NZ primarily because of the specification of a too-small SLS demand which corresponds to a ground motion with 25 year return period and because the Structural Performance factor (Sp) is specified in NZ as 0.7 for SLS, which results in a further 30% reduction of the SLS demand. There are also vulnerabilities in 'pre-2004' precast floor-to-beam connection detailing [3]. Cost-benefit analyses show that these building losses may be relieved by first correcting the precast vulnerabilities, then using a SLS limit of 50 year (rather than the current 25 year) return period and/or by specifying Sp = 1. The thus proposed 'maxi-50 year SLS' with a drift limit of 0.25%, has the same elastic seismic demand as the 100 year international SLS event [10, 11] (with Sp = 0.7) and will minimise non-structural and business disruption losses in small to moderate earthquakes.
doi:10.5459/bnzsee.51.1.34-46 fatcat:j7xmgawp2nfh5eijn22mrnnkpi