Computational Simulation of a Full-Scale, Fixed-Base, and Isolated-Base Steel Moment Frame Building Tested at E-Defense

In many finite element platforms, a classical global damping matrix based on the elastic stiffness of the system (including isolators) is usually developed as part of the solution to the equations of motion of base-isolated buildings. The conducted analytical and numerical investigations illustrate that this approach can lead to the introduction of unintended damping to the first and higher vibration modes and the spurious suppression of the respective structural responses. A similar shortcoming might be observed even when a nonclassical damping model (ie, an assembly of the superstructure and isolation system damping sub-matrices) is used. For example, the use of Rayleigh damping approach to develop the superstructure damping sub-matrix can lead to the undesired addition of damping to the isolated mode arising from the massproportional component of the superstructure damping. On the other hand, the improper use of nonclassical stiffness-proportional damping (eg, determining the proportional damping coefficient, β k , based on the first mode) can result in assigning significant damping to the higher-modes and the unintended mitigation of the higher-mode responses. Results show that a nonclassical stiffness-proportional model in which β k is determined based on the second modal period of a base-isolated building can reasonably specify the intended damping to the higher modes without imparting undesirable damping to the first mode. The nonclassical stiffness-proportional damping can be introduced to the numerical model through explicit viscous damper elements attached between adjacent floors. In structural analysis software such as SAP2000®, the desired nonclassical damping can be also modeled through specifying damping solely to the superstructure material.

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confidence: 99%

Effects of the improper modeling of viscous damping on the first‐mode and higher‐mode dominated responses of base‐isolated buildings

Anajafi

Medina²,

Santini‐Bell

2019

“…18,19 This interaction between the horizontal and vertical response of the structure was observed to be strongest in the TPB configuration, yet it was evident in all 3 configurations as the floor accelerations were amplified during 3D excitations compared with 2D. The behavior was replicated by analysis and identified as a horizontal-vertical (H-V) coupling effect between the horizontal and vertical response of the specimen tested, both in the fixed-base and in the isolated configurations.…”

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confidence: 92%

“…The behavior was replicated by analysis and identified as a horizontal-vertical (H-V) coupling effect between the horizontal and vertical response of the specimen tested, both in the fixed-base and in the isolated configurations. 18,19 This interaction between the horizontal and vertical response of the structure was observed to be strongest in the TPB configuration, yet it was evident in all 3 configurations as the floor accelerations were amplified during 3D excitations compared with 2D. In the past, analytical studies have reported an increase of several response parameters of structures isolated with friction bearings subjected to 3D excitation in comparison with 2D.…”

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confidence: 92%

“…Prior analytical studies of the E-Defense building have accurately predicted the floor accelerations and floor spectra, 18,19,22 but none have focused on replicating the vertical response. Prior analytical studies of the E-Defense building have accurately predicted the floor accelerations and floor spectra, 18,19,22 but none have focused on replicating the vertical response.…”

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confidence: 99%

“…Understanding the response of floor systems to vertical excitation and possible coupled response of the structure is necessary to achieve higher performance objectives where damage to NCSs must be avoided to provide continued functionality. Prior analytical studies of the E-Defense building have accurately predicted the floor accelerations and floor spectra, 18,19,22 but none have focused on replicating the vertical response. Higher acceleration amplifications at the roof slab than for the fifth floor slab (dominant slab vibration frequencies of about 7 and 10 Hz, respectively) suggest that individual local vertical modes were activated at each floor level.…”

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confidence: 99%

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Computational simulation of slab vibration and horizontal‐vertical coupling in a full‐scale test bed subjected to 3D shaking at E‐Defense

Pujols

Ryan

2017

Self Cite

Summary This paper focuses on slab vibration and a horizontal‐vertical coupling effect observed in a full‐scale 5‐story moment frame test bed building in 2 configurations: isolated with a hybrid combination of lead‐rubber bearings and cross‐linear (rolling) bearings, and fixed at the base. Median peak slab vibrations were amplified—relative to the peak vertical shake table accelerations—by factors ranging from 2 at the second floor to 7 at the roof, and horizontal floor accelerations were significantly amplified during 3D (combined horizontal and vertical) motions compared with 2D (horizontal only) motions of comparable input intensity. The experimentally observed slab accelerations and the horizontal‐vertical coupling effect were simulated through a 3D model of the specimen using standard software and modeling assumptions. The floor system was modeled with frame elements for beams/girders and shell elements for floor slabs; the insertion point method with end joint offsets was used to represent the floor system composite behavior, and floor mass was finely distributed through element discretization. The coupling behavior was partially attributed to the asymmetry of the building that was intensified by asymmetrically configured supplemental mass at the roof. Horizontal‐vertical coupled modes were identified through modal analysis and verified with evaluation of floor spectral peaks.

Seismic response of sliding equipment and contents in base‐isolated buildings subjected to broadband ground motions

Konstantinidis

Nikfar

2014

Summary Base isolation has been established as the seismic design approach of choice when it comes to protecting nonstructural contents. However, while this protection technology has been widely shown to reduce seismic demands on attached oscillatory equipment and contents (EC), its effectiveness in controlling the response of freestanding EC that are prone to sliding has not been investigated. This study examines the seismic behavior of sliding EC inside base‐isolated buildings subjected to broadband ground motions. The effect of isolation system properties on the response of sliding EC with various friction coefficients is examined. Two widely used isolation models are considered: viscously damped linear elastic and bilinear. The study finds isolation to be generally effective in reducing seismic demands on sliding EC, but it also exposes certain situations where isolation in fact increases demands on EC, most notably for low friction coefficients and high earthquake intensities. Damping at the isolation level is effective in controlling the EC sliding displacements, although damping over about 20% is found to be superfluous. The study identifies a physically motivated dimensionless intensity measure and engineering demand parameter for sliding equipment in base‐isolated buildings subjected to broadband ground motions. Finally, the paper presents easy‐to‐use design fragility curves and an example that illustrates how to use them. Copyright © 2014 John Wiley & Sons, Ltd.