Seismic Retrofit of a Heritage Building in Wellington Using Buckling Restrained Braces

Abstract:

A heritage building in Wellington, New Zealand (NZ) was classified as potentially earthquake-prone following an initial seismic assessment (ISA) by the Wellington City Council (WCC). The first four stories of the building were constructed originally in 1908 and an additional lightweight story was added in 1955 and altered in 1993. The building has a rectangular floor plan measuring 24 x 10.5 m. In the longitudinal direction, steel frame with solid unreinforced masonry (URM) infill walls provided resistance to seismic forces. In the transverse direction, perforated URM walls with large openings and nonductile concrete encased steel frames were used for both gravity and seismic load transfer. A detailed seismic assessment (DSA) of the building structure confirmed seismic capacity of the building in excess of 100% of New Building Standards (%NBS) in the longitudinal direction. However, in the transverse direction, the structure, secondary components and non-structural components had a seismic capacity less than 34%NBS, hence the building was confirmed earthquake-prone in its current state under the NZ Building Act. Performance-based engineering was used to devise the seismic retrofit for the principle structure. To retrofit the principle building structure to 100%NBS in the transverse direction, new Buckling Restrained Braced (BRB) frames were designed to carry seismic load. A geotechnical investigation showed that the underlying soil was competent and thus soil-structure interaction (SSI), tie foundation beams and nonlinear analysis were used to obtain realistic demand and capacity for the building after seismic retrofitting. The BRB manufacturer was consulted and the BRB size distribution along the height was optimized. The construction of the seismic retrofit is currently underway.

• Periodical: Key Engineering Materials (Volume 763)
• Pages: 1097-1104
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.763.1097
• Online since: February 2018
• Authors: Amir S.J. Gilani*, Jitendra Bothara, H. Kit Miyamoto
• Keywords: Buckling Restraint Brace, Nonlinear Analysis, Performance Based Engineering, Seismic Retrofit, Soil-Structure-Interaction

References

[1] Wellington City Council (WCC), Earthquake-prone Building Policy, Wellington, New Zealand. www. wellington. govt. nz , (2006).

[2] New Zealand Society for Earthquake Engineering (NZSSEE), NZSEE: Assessment and Improvement of the Structural Performance of Buildings in Earthquake, Welllington, doi: ISBN 978-0-473-30073-9, (2006).

[3] New Zealand Government, The Building Act 2004, Wellington, NZ. (2004).

[4] New Zealand Standards (NZS), NZS1170. 5: Basic Design Loads, Wellington, NZ. (2004).

[5] GeoScience, Geotechnical Investigation for 60 Ghunzee Street, Wellington, NZ, (2015).

[6] JP Singh & Associates, Soil Structure Interaction Report, Richmond, CA, USA, (2016).

[7] Computers and Structures Inc., ETABS: Integrated software package for the structural analysis and design of buildings, Walnut Creek, CA, USA (2017).

[8] American Society of Civil Engineers (ASCE), ASCE/SEI 41/13: Seismic Evaluation and Retrofit of Existing Buildings, American Society of Civil Engineers, Reston, VA, USA, (2014).

DOI: 10.1061/9780784412855

[9] Nippon Steel, Design calculations for unbonded braces for 60 Ghunzee Street, (2017).