Abstract

This investigation examines the effects of nonlinearity in the primary system of the coupled primary-secondary systems on accelerations in the secondary systems during seismic loading. The coupled primary-secondary systems considered in this investigation are those typically found in piers, wharves, and marine oil terminals. This investigation first examines the effects of nonlinearity in the primary system on acceleration at the point of attachment of the secondary system to the primary system and found that:  The acceleration at the point of attachment of the secodnary system to the primary system decreases with increasing level of nonlinearity in the primary system. This occurs because yielding in the primary system limits accelerations that can transmit through it.  The recommendation by Goel (2017a) provides very good estimate of the acceleration at the point of attachment of the secondary system to the primary system in coupled primarysecondary systems when the primary systems remains linear elastic. However, it provides increasingly conservative estimate of the acceleration with increasing nonlinearity in the primary system.  The recommendations in ASCE 7-10 significantly over-predict accelerations at the point of attachment of the secondary system. The level of over-prediction increases with increasing level of nonlinearity in the primary system and period of the primary system. This investigation next examined the effects of nonlinearity in the primary system on amplification of the acceleration in the secondary system due to its flexibility and found that:  The trends in amplification of acceleration in the secondary system due to its flexibility of linear-elastic system no longer apply when the primary system is deformed beyond the linear elastic range. In particular, amplification of acceleration tends to be much larger when period of the secondary system is longer than period of the primary system and this difference increases with increasing level of nonlinearity in the primary system. This occurs because the effective period of the primary system elongates due to its nonlinearity and thereby reduces the effective period ratio, which has the effect of increasing amplification of acceleration in the secondary system.  The nonlinearity in the primary system has minimal effect on amplification of acceleration in the secondary system when period ratio is less than 0.6. For such systems, recommendation by Goel (2017a) may be used to accurately estimate amplification of acceleration in the secondary system when the primary system is expected to be deformed beyond the linear elastic range. Finally, this investigation studied the effects on nonlinearity in the primary system on acceleration in the secondary system and found that:  The recommendation in the ASCE 7-10 document for flexible secondary system generally lead to significant over-prediction of acceleration in the secondary system. The level of over-prediction increases with increasing level of nonlinearity in the primary system and increasing period of the primary system.  The recommendation in the commentary of the ASCE 7-10 document also leads to overprediction, although not as large as that from the recommendation in the main body of the ASCE 7-10 document, of acceleration in the secondary system. The level of over- ii prediction increases with increasing level of nonlinearity in the primary system and increasing period of the primary system.  The recommendation by Goel (2017a) provide a reasonably good estimate of acceleration in the secondary system over the entire range of vibration period of the primary system when the primary system remains in the linear elastic. However, this recommendation provides slight over-prediction when the primary system deforms beyond the linear elastic range.  The recommendation in ASCE 7-10 document and by Goel (2017a) were developed based on studies of linear-elastic systems. The current investigation, which considers nonlinearity in the primary system, indicates that recommendations based on linear-elastic systems lead to conservative estimates of accelerations in secondary system even when the primary system in the coupled primary-secondary system is deformed beyond the linear-elastic range. Based on findings in this investigation, it is recommended not to design coupled primary secondary systems with period ratio between 0.6 and 1.4 and secondary systems weighing less than 20% of the primary system. For such cases, secondary systems may experience excessive accelerations that may equal to or exceed eight times the peak ground accelerations due to strong coupling between primary and secondary systems.

Disciplines

Civil and Environmental Engineering

Number of Pages

118

Publisher statement

Department of Civil & Environmental Engineering, California Polytechnic State University, San Luis Obispo

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URL: http://digitalcommons.calpoly.edu/cenv_fac/323