The rocking response of large flexible structures to earthquakes

The rocking response of structures subjected to strong ground motions is a problem of ‘several scales’. While small structures are sensitive to acceleration pulses acting successively, large structures are more significantly affected by coherent low frequency components of ground motion. As a result, the rocking response of large structures is more stable and orderly, allowing effective isolation from the ground without imminent danger of overturning. This paper aims to characterize and predict the maximum rocking response of large and flexible structures to earthquakes using an idealized structural model. To achieve this, the maximum rocking demand caused by different earthquake records was evaluated using several ground motion intensity measures. Pulse-type records which typically have high peak ground velocity and lower frequency content caused large rocking amplitudes, whereas non-pulse type records caused random rocking motion confined to small rocking amplitudes. Coherent velocity pulses were therefore identified as the primary cause of significant rocking motion. Using a suite of pulse-type ground motions, it was observed that idealized wavelets fitted to velocity pulses can adequately describe the rocking response of large structures. Further, a parametric analysis demonstrates that pulse shape parameters affect the maximum rocking response significantly. Based on these two findings, a probabilistic analysis method is proposed for estimating the maximum rocking demand to pulse-type earthquakes. The dimensionless demand maps, produced using these methods, have predictive power in the near-field provided that pulse period and amplitude can be estimated a priori. Use of this method within a probabilistic seismic demand analysis framework is briefly discussed.

[1]  J. Douglas,et al.  Internet site for European strong-motion data , 2004 .

[2]  Nicos Makris,et al.  Rocking response of rigid blocks under near-source ground motions , 2000 .

[3]  James L. Beck,et al.  The Seismic Response of a Reinforced Concrete Bridge Pier Designed to Step , 1973 .

[4]  N. Abrahamson,et al.  Empirical Response Spectral Attenuation Relations for Shallow Crustal Earthquakes , 1997 .

[5]  George P. Mavroeidis,et al.  A Mathematical Representation of Near-Fault Ground Motions , 2003 .

[6]  C. Allin Cornell,et al.  Explicit Directivity-Pulse Inclusion in Probabilistic Seismic Hazard Analysis , 2007 .

[7]  Anil K. Chopra,et al.  Dynamics of Structures on Two‐Spring Foundation Allowed to Uplift , 1984 .

[8]  Michalis Fragiadakis,et al.  Seismic Reliability Assessment of Classical Columns Subjected to Near Source Ground Motions , 2013 .

[9]  Matthew J. DeJong.  Amplification of Rocking Due to Horizontal Ground Motion , 2012 .

[10]  Nicolas Luco,et al.  Structure-Specific Scalar Intensity Measures for Near-Source and Ordinary Earthquake Ground Motions , 2007 .

[11]  Vitelmo V. Bertero,et al.  Uncertainties in Establishing Design Earthquakes , 1987 .

[12]  A. G. Brady,et al.  A STUDY ON THE DURATION OF STRONG EARTHQUAKE GROUND MOTION , 1975 .

[13]  George Gazetas,et al.  Seismic response of slender rigid structures with foundation uplifting , 2007 .

[14]  Luigi Sorrentino,et al.  Overturning of rocking rigid bodies under transient ground motions , 2006 .

[15]  Anil K. Chopra,et al.  Earthquake response of structures with partial uplift on winkler foundation , 1984 .

[16]  G. Housner.  The behavior of inverted pendulum structures during earthquakes , 1963 .

[17]  Ray W. Clough,et al.  Seismic Response of Uplifting Building Frame , 1978 .

[18]  Mohammad Aslam,et al.  Earthquake Rocking Response of Rigid Bodies , 1980 .

[19]  Michalis Fragiadakis,et al.  Seismic reliability assessment of classical columns subjected to near-fault ground motions: SEISMIC RELIABILITY OF CLASSICAL COLUMNS TO NEAR-FAULT GROUND MOTIONS , 2013 .

[20]  Benedikt Halldorsson,et al.  Near-Fault and Far-Field Strong Ground-Motion Simulation for Earthquake Engineering Applications Using the Specific Barrier Model , 2011 .

[21]  Ioannis N. Psycharis.  Dynamics of flexible systems with partial lift-off , 1983 .

[22]  N. Abrahamson,et al.  Simplified Frequency Content Estimates of Earthquake Ground Motions , 1998 .

[23]  J. Penzien,et al.  Rocking response of rigid blocks to earthquakes , 1980 .

[24]  Anil K. Chopra,et al.  Simplified Earthquake Analysis of Multistory Structures With Foundation Uplift , 1985 .

[25]  Nicos Makris,et al.  Rocking Response of Free-Standing Blocks under Cycloidal Pulses , 2001 .

[26]  J. W. Meek.  Dynamic response of tipping core buildings , 1978 .

[27]  Nick Gregor,et al.  NGA Project Strong-Motion Database , 2008 .

[28]  Reza Sehhati.  Probabilistic seismic demand analysis for the near-fault zone , 2008 .

[29]  Jack W. Baker,et al.  Quantitative Classification of Near-Fault Ground Motions Using Wavelet Analysis , 2007 .

[30]  A. Papageorgiou,et al.  Near‐fault ground motions, and the response of elastic and inelastic single‐degree‐of‐freedom (SDOF) systems , 2004 .

[31]  Sinan Acikgoz,et al.  The interaction of elasticity and rocking in flexible structures allowed to uplift , 2012 .

[32]  J. W. Meek,et al.  Effects of Foundation Tipping on Dynamic Response , 1975 .

[33]  Nicos Makris,et al.  Estimating time scales and length scales in pulselike earthquake acceleration records with wavelet analysis , 2011 .

[34]  R. I. Skinner,et al.  The seismic design of an industrial chimney with rocking base , 1983 .

[35]  J. Bray,et al.  Characterization of forward-directivity ground motions in the near-fault region , 2004 .

[36]  Nicos Makris,et al.  Planar rocking response and stability analysis of an array of free‐standing columns capped with a freely supported rigid beam , 2013 .