Assessment of ASCE 7–16 Seismic Isolation Bearing Torsional Displacement
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Base isolation provisions in ASCE 7 Standard have been historically shown to be conservative in estimating seismic demands. New torsional bearing base isolation displacement expressions have been proposed recently by the latest ASCE 7–16 Standard. This study compares the accuracy of the new ASCE 7–16 static-based isolation expressions for additional bearing displacement due to plane torsion to the response obtained using simplified structural dynamics’ plane torsion theory expressions. In addition, it conducts a parametric study to assess the effect of accidental eccentricity, damping ratio, and plan aspect ratio on the accuracy of ASCE 7–16 bearing displacement expression. The results showed that the ASCE 7–16 undamped displacement estimations improved compared to the significant conservatism of ASCE 7–10 by 7–33% depending on the eccentricity condition and ratio, which may further promote the use of base isolation in the US as a seismic hazard mitigation solution. However, the study also revealed that a considerable conservatism of the new base isolation bearing displacement provisions of ASCE 7–16 still exists in some cases, which ranged from 52 to 105% in the case of three equal fundamental frequencies and 5–20% in the case of equal lateral frequency and distinct torsional frequency. The study also showed that the ASCE 7–16 conservatism is proportional to the eccentricity and is more pronounced with biaxial eccentricity compared to single eccentricity. Furthermore, the results show that ASCE 7–16 expression accuracy significantly declines with damped systems with a possibility of un-conservative estimation of bearing displacements that can reach 25–40% with larger eccentricities. In addition, the ASCE 7–16 torsional displacement was shown to be inversely proportional to the plan aspect ratio with a discrepancy that can reach ± 20%. The study also exhibited that the ASCE 7–16 torsional displacement conservatism is slightly affected by increasing damping ratio above 4%.
KeywordsASCE 7 Seismic isolation Base isolation Torsion Accidental eccentricity Lead rubber bearing
The revision and insightful feedback and comments of Prof. James Kelly, University of California, Berkeley to enhance this manuscript are greatly appreciated.
- 4.ASCE/SEI 7-16 (2017) Design loads on buildings and other structures. American Society of Civil Engineers, RestonGoogle Scholar
- 5.Matsagar VA, Jangid RS (2008) Base isolation for seismic retrofitting of structures. Practice periodical on structural design and construction. ASCE 13:175–185Google Scholar
- 6.Mansouri I et al (2017) Seismic fragility estimates of LRB base isolated frames using performance-based design. Shock Vib 3:1–20Google Scholar
- 17.Kelly J (2012) Earthquake-resistant design with rubber. Springer Science and Business Media, LondonGoogle Scholar
- 18.Kelly J (2007) Earthquake hazard mitigation. Lecture notes. University of California, BerkeleyGoogle Scholar