Reduction of vibration on structural building from train-induced ground motion

Seismic displacement of a geosynthetic-reinforced wall with full-height rigid panel facing (Tanata wall) in the 1995 Hyogo-ken Nambu earthquake is calculated using a pseudo-static method based on a 'multi-wedge' failure mechanism. The calculated value of horizontal displacement of the wall is comparable to the measured one. Based on an investigation into the effect of vertical ground acceleration to the seismic displacement of the wall using vertical and horizontal input ground accelerations in recorded seismograms, it is found that the contribution of vertical ground acceleration to the seismic displacement of the Tanata wall is small, because the peak horizontal and vertical ground accelerations are out of phase. Therefore, the use of peak vertical-to-horizontal ground acceleration ratio obtained in an earthquake event for pseudo-static multi-wedge analysis may overestimate the seismic displacement of a geosynthetic-reinforced wall to some extent. The effect of the embedment of the facing on the seismic displacement of the Tanata is also investigated. It is found that the effect of facing embedment to the seismic stability and/or displacement in the case of the Tanata wall is insignificant.

An analytical method is developed to calculate the statistical properties of the response of hysteretic columns under earthquake excitations, with special emphasis on the effect of the vertical ground acceleration. Both the vertical and horizontal ground accelerations are modeled as amplitude-modulated Gaussian random processes, and the restoring force in a column is assumed to follow a functional relationship proposed by Hata and Shibata. Numerical results are presented for two columns, having two contrasting values of the post-yielding to pre-yielding stiffness ratio of 0.5 and 0.1, respectively. These results indicate that the vertical ground acceleration has an aggravating effect similar to that of the gravitational force in causing greater peak mean-square structural response than one induced by the horizontal ground acceleration alone. The time variation of the mean-square response is found to be extremely sensitive to structural parameters. For softer structures with a small post-yielding to pre-yielding stiffness ratio, large permanent deformations may remain after termination of the earthquake excitations.

A fundamental study of the rocking and overturning response of massive concrete blocks (with relatively high aspect ratio) to simultaneous horizontal and vertical earthquake ground motions is presented. This problem occurs when large concrete blocks are used as radiation shields in particle accelerators or similar nuclear installations. The results of this study also offer insight into the response of the rigid bodies (such as are approximated by some electrical machinery and mechanical equipment) which are not anchored to the ground. The mathematical model used was based on the assumption of a constant coefficient of restitution. A computer program was written to predict the rocking and overturning behavior of rigid rectangular blocks under simultaneously applied horizontal and vertical ground accelerations. Using the computer program, the response of rigid blocks of various aspect ratios and sizes was studied under the accelerograms of various strong motion earthquakes.

SUMMARY The paper presents predictive relationships for horizontal and vertical peak ground accelerations derived from 529 triaxial strong-motion records generated by 219 shallow earthquakes in the European area. If no account is taken of the focal depth, the attenuations of peak horizontal and vertical accelerations, in g, are given by log (ah) = - 1.09 + 0*238M, - log(r) - 0@0050r + 028P and log (a,) = - 1-34 + 0.230Ms - log (r) + 0‘27P where r = (8 + 6*0’)*, d is the source distance in km and M, is the surface-wave magnitude; P is 0 for 50-percentile values, 1 for 84-percentiles. If we allow for tlie effect of the focal depth h, in km, the corresponding equations for ah and a, are found to be lOg(0,) = - 0.87 + 0.217MS - log(r) - 0.00117r + 026P and log (a,) = - 1-10 + 0.200M, - log(r) - 0-OOO15r + 0.26P where r = (d’ + h’)”’. distance, and equal to 0.5. The mean ratio of the peak vertical to horizontal acceleration is found to be almost independent of magnitude and

Vertical effects of near-fault ground motions and the optimal IMs for seismic response of continuous girder bridges with FPB isolators

Based on limit equilibrium principles, this study presents a theoretical derivation of a new analytical formulation for estimating magnitude and lateral earth pressure distribution on a retaining wall subjected to seismic loads. The proposed solution accounts for failure wedge inclination, unit weight and friction angle of backfill soil, wall roughness, and horizontal and vertical seismic ground accelerations. The current analysis predicts a nonlinear lateral earth pressure variation along the wall with and without seismic loads. A parametric study is conducted to examine the influence of various parameters on lateral earth pressure distribution. Findings reveal that lateral earth pressure increases with the increase of horizontal ground acceleration while it decreases with the increase of vertical ground acceleration. Compared to classical theory, the position of resultant lateral earth force is located at a higher distance from wall base which in turn has a direct impact on wall stability and economy. A numerical example is presented to illustrate the computations of lateral earth pressure distribution based on the suggested analytical method.

The measured vertical peak ground acceleration was larger than the horizontal peak ground acceleration. It is essential to consider the vertical seismic effect in seismic fragility evaluation of large‐space underground structures. In this research, an approach is presented to construct fragility curves of large‐space underground structures considering the vertical seismic effect. In seismic capacity, the soil‐underground structure pushover analysis method which considers the vertical seismic loading is used to obtain the capacity curve of central columns. The thresholds of performance levels are quantified through a load‐drift backbone curve model. In seismic demand, it is evaluated through incremental dynamic analysis (IDA) method under the excitation of horizontal and vertical acceleration, and the soil‐structure‐interaction and ground motion characteristics are also considered. The IDA results are compared in terms of peak ground acceleration and peak ground velocity. To construct the fragility curves, the evolutions of performance index versus the increasing earthquake intensity are performed, considering related uncertainties. The result indicates that if we ignore the vertical seismic effect to the fragility assessment of large‐space underground structures, the exceedance probabilities of damage of large‐space underground structures will be underestimated, which will result in an unfavorable assessment result.

The scope of this study is the quantification of vertical peak floor acceleration demands at column lines and along the length of beams of elastic moment-resisting steel frames subjected to recorded ground motions. These demands correlate with the maximum strength demands on rigid nonstructural components attached to a frame structure. Since it is commonly assumed that buildings behave flexibly in the horizontal direction and rigidly in the vertical direction, the assessment of vertical acceleration demands is typically not considered in most cases. The results of this study show that vertical peak floor accelerations can be up to five times larger than the vertical peak ground acceleration, in contrast to horizontal peak floor accelerations that are only up to two times larger than the horizontal peak ground acceleration for the numerical models used in this study. The most significant amplifications estimated in the vertical direction are found at the center of the girders. Further investigations of modified steel frames indicate that the story-wise mass distribution has an influence not only on the vertical acceleration demand, but also on the horizontal component of the response, though to a lesser degree. In contrast, the response in the vertical and horizontal direction is only slightly affected by an increase in the flexural stiffness of the beams. The results of this study strongly indicate that in steel frames it can be considered highly questionable to ignore the amplification of the vertical acceleration component along the height of the structure.

Assessment of RC columns subjected to horizontal and vertical ground motions recorded during the 2009 L’Aquila (Italy) earthquake

Over 700 accelerograms recorded from 12 earthquakes in northeast Taiwan have been analyzed for investigating the behavior of vertical and horizontal peak and spectral ground motion in the near-source region. Peak horizontal and vertical ground acceleration (PGA), velocity (PGV), and displacement (PGD) in the range of engineering interest have been subjected to a two-step nonlinear regression procedure in terms of magnitude and hypocentral distance. In comparison with a number of other studies of global PGA observations, our predictions show lower far-field attenuation, lower near-source amplitudes, higher magnitude saturation for the vertical component, lower magnitude saturation for the horizontal component, and higher magnitude scaling. The 2 / 3 ratio of vertical to horizontal ground motion, commonly used in engineering applications, may be unconservative in the very near-field for high-frequency ground motion. It falls below 1 / 2 at distances greater than 50 km. The same ratio for PGV and PGD tends to increase with distance, the latter at a faster rate. For SMART-1 data the major source of uncertainty appears to be inter-event rather than intra-event randomness. The predominance of the inter-event uncertainty in ground motions near the source is expected to be a characteristic of all dense arrays.

Buckling behavior of the anchored steel tanks under horizontal and vertical ground motions using static pushover and incremental dynamic analyses

Reliability assessment of structure subjected to horizontal-vertical random earthquake excitations

Both horizontal and vertical ground motion can cause damage to vibration-sensitive equipment. However, most mature seismic isolation devices only isolate horizontal ground acceleration; few devices isolate both vertical and horizontal ground acceleration. In this paper, a novel inertia-type bidirectional isolation system (IBIS) is proposed that comprises independent vertical and horizontal seismic isolators. The IBIS’s vertical isolator comprises leverage apparatus with a counterweight, which provides a vertical lifting force in the static state to balance the self-weight of the isolated object, and an additional inertial force in the dynamic state, resulting in higher static but lower dynamic effective vertical stiffness. The horizontal isolator is a conventional sliding-type system comprising a sliding platform and pair of springs. The IBIS’s equations of motion are derived by using Lagrange’s equation, and the theoretical model is verified through shaking-table test results. Numerical simulation and experimental results show that the IBIS has an anti-resonance property in the vertical direction, leading to higher isolation performance under both near-fault and far-field ground acceleration. The conventional sliding-type horizontal isolator component performs well under far-field ground acceleration but may perform unsatisfactorily under near-fault ground acceleration.

Effects of vertical ground acceleration on the seismic moment demand of bridge superstructure connections

The impact of loading from rolling stock on a 25-storey monolithic-frame office building section with a 9-storey parking garage, located near the movement of railway trains in an urban area, was investigated. A two-stage numerical approach was applied to mathematically model the dynamic behavior of multi-storey buildings under loading from rolling stock. At the first stage, a finite element model of the ballast prism and soil was developed in the form of a flat elastic-plastic half-space with a length of 200 m and a depth of 60 m, created using the NASTRAN software package. The loading from the rolling stock was presented as a vertical periodic excitation, concentrated at the center of mass of the system, comprising the bogie frame, wheelsets of a freight train wagon, and the ballast prism. The impact of rolling stock load on the base was studied in a nonlinear static formulation using the Newton-Raphson method. Modal analysis of the base and ballast prism was performed using the Lanczos method. The dynamic behavior of the base was analyzed using the fourth-order Runge-Kutta method. Horizontal and vertical ground accelerations were obtained at various distances and depths of the base model relative to the railway track axis. At the second stage, a 3D model of the building was developed in the SCAD software package. Modal analysis of the structure was conducted using the subspace iteration method. The stress-strain state of the building under the influence of calculated loads and kinematic ground excitation, applied along the height of the building foundation as acceleration vectors, was investigated using the spectral method. The conditions for reliability and structural safety of the building were verified under load combinations, including the influence of base ground vibrations caused by rolling stock.