Effect of vertical ground motion on the response of structures isolated with friction pendulum isolators

This paper presents a study that determines the conditions of testing for determining the bounding properties of seismic isolators for use in analysis and design in a test that is meant to be a replacement of tests Items 2(a) and 3 of ASCE/SEI‐7. Then separately, the study determines the conditions of testing for determining the adequacy of isolators in the maximum considered earthquake in a test is meant to be a replacement of test Item 4 of ASCE/SEI‐7. The test conditions are determined by performing analyses with models that account for the time‐variant properties of the isolators and by computing the resultant isolator displacements. In performing the work, a large number of isolation systems (total of 96 systems, single friction pendulum, triple friction pendulum and lead‐rubber), three different seismic hazards as measured by the spectral acceleration at the period of one second, and a large collection of bi‐directional ground motions with short‐ and long‐duration characteristics (71 pairs of each duration, 96 systems, three seismic hazards) were considered. Fundamental in this methodology is the use of analysis models in which the properties of the isolators (friction or characteristic strength) are dependent on the instantaneous temperature at the sliding interfaces or in the lead core.

Section: Ground Motions Used For Response History Analysismentioning

confidence: 99%

Performance‐based testing specifications for seismic isolators

Kim,

Constantinou

2023

“…12 Additional computational research continued to elaborate on the experimental findings by way of increasingly more comprehensive parametric studies. [13][14][15][16][17] Ongoing work on new isolation devices show the isolator force/base shear amplification effect is generally applicable to any devices that are derivatives of multi-spherical sliding bearings. 18,19 Experimental studies of both reduced and full-scale isolated building models have provided the opportunity to validate modeling techniques used to predict vertical shaking effects in structures with spherical sliding bearings.…”

Section: Noveltymentioning

confidence: 99%

“…Shortly thereafter, effects of vertical shaking were also noted in some of the pioneering experimental programs on structures with multiple pendulum bearings, such as an amplification of base shear 10,11 and horizontal‐vertical coupling 12 . Additional computational research continued to elaborate on the experimental findings by way of increasingly more comprehensive parametric studies 13–17 . Ongoing work on new isolation devices show the isolator force/base shear amplification effect is generally applicable to any devices that are derivatives of multi‐spherical sliding bearings 18,19 …”

Section: Introductionmentioning

confidence: 96%

“…Although many studies have demonstrated the effect of vertical or 3D shaking on increased base shear, no study has developed a general theoretical basis or simplified approach for accounting for such effects that can be implemented for design. Cilsalar and Constantinou 17 developed statistical results for the ratio of base shear with versus without vertical shaking, ranging from 1.06 to 1.22 for far‐field motions and from 1.15 to 1.48 for near‐fault motions. However, these results are not correlated directly to the intensity of vertical acceleration, which is expected to have a sizeable influence on the base shear amplification.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of effect of vertical ground shaking in bridges isolated with spherical sliding bearings

Ryan,

Mojidra

2023

Studies have shown that in structures isolated with spherical sliding bearings, the seismic base shear increases when the vertical component of ground shaking is explicitly considered, since the dynamic variation of bearing axial force is passed on to the base shear due to the friction mechanism. In this paper, the effect of vertical shaking is systematically investigated in multi‐span concrete box‐girder highway bridges isolated with triple pendulum bearings. Grounded in the theory of bearing mechanics, a simplified method to predict the amplification of base shear with vertical ground shaking intensity in such bridges is developed and evaluated. The simplified approach is potentially applicable for bridge design based on equivalent static analysis. At low to moderate vertical intensities, the simplified method can capture the observed variation in the base‐shear coefficient with isolation system parameters. The differences in base‐shear amplification for bridge superstructure parameter variations are insignificant, and thus the method is widely applicable. At high intensity vertical ground shaking, the base shear coefficient can be affected by an uplift and impact phenomenon. Thus, application of the simplified method should be limited to motions with peak vertical acceleration up to 1 g; simulation with 3D motions is recommended for intensities beyond 1 g.

“…Analysis was performed using a rigid structure model with due consideration of bi‐directional ground motion. The vertical ground motion component was not considered because (a) its effects on the isolator displacement are known from analysis and shake table testing to be minor for sliding isolation systems, 23,24 and (b) its effects are known from analysis to be insignificant on the histories of temperature computed for the sliding surfaces of triple FP isolators 3,4 (Note that the vertical ground motion has effects on the peak shear force transmitted through FP isolators, but this was not a topic of this study). The ground motions used for response history analysis consisted of 71 pairs of horizontal orthogonal components with long‐duration characteristics and another 71 pairs of horizontal orthogonal components with short‐duration characteristics that were spectrally equivalent to the 71 pairs of long‐duration motions.…”

Section: Effect Of Finite Plate Depth On Response Of Seismically Isol...mentioning

confidence: 99%

Validity of models for frictional heating in sliding isolators

Kim,

Constantinou

2023

This paper investigates the validity of theories for the prediction of the temperature increase at the sliding interfaces of sliding isolators. The prevailing theory considers the isolator to be indefinite in depth and the heat flux generated at the sliding interface(s) to be infinite in extent. In reality, the depth is finite and small, and bounded by an insulating boundary, whereas the heat flux is bound by the circular area of contact. New theories are presented in which the restrictions of the past theory are relaxed. The resulting solutions have been implemented in program OpenSees for single and for triple friction pendulum isolators but are very complex and time‐consuming to be used in response history analysis with many isolators. Analysis of the response of sliding isolated structures with these models demonstrates that consideration of the finite depth of the isolators and of the limited extent of the heat flux does not have any important effects on the calculated isolator displacement demands in either short‐duration or long‐duration ground motions. It is shown that the finite depth has some effect on the peak temperature at the sliding interface and, more importantly, on the duration of the high temperature in long‐duration ground motions. This is of some importance in the use of these theories for the development of testing specifications for isolators with unusually thin end plates.